Technical Discussion

Technical Discussion

Synopsis...

An intense winter storm system will be making its way into Pennsylvania late this evening into Wednesday Evening. Most areas will experience snow this evening with mixed precipitation following adding for potentially hazardous conditions in most places. Ice accumulations will be evident in most places with northern Pennsylvania experiencing more Snow.

 

SHORT TERM NOW THROUGH 6 PM TUESDAY/...

Temperatures will be cold over all of Pennsylvania. Over midnight, snow is expected in northern to central Pennsylvania. Central to southern PA will be experiencing more of a mixed precipitation due to places hovering around the freezing point. This in turn will add to the impact of the total precipitation since ice accumulation will be evident in most places of Pennsylvania. So for the short term, cloudy conditions will be evident from Now through Tuesday with temperatures mostly in the 20s. Temperatures could rise to the melting point of snow during the day and drop into the teens during the evening. Intense precipitation will be the major factor during this time period.

 

 LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...

Tuesday evening will be in the middle of the winter storm, so most places in PA will be experiencing their share of mixed precipitation. This mixed precipitation will add on to the already present snow, sleet, and freezing rain making way for hazardous road conditions. By Wednesday evening, the storm should be making its way out, so little precipitation is expected on Wednesday evening. After the storm leaves, cloudy conditions and cold temperatures are expected. A high pressure system should be making its way in on Friday making way for cold temperatures that could dip well into the teens for most places. A storm will be making its way up the east coast this weekend, so cities in PA that are east of State College may experience some snow showers at times.

 

Stephen Quinn

Technical Discussion

Technical Discussion 1-31-11

Synopsis:

 

A potent winter storm will begin to take shape over the next couple days that will impact just about everyone across the state. A mixture of wintry precipitation is possible for many across the state as the storm moves through tuesday and wednesday. Cold air will again infiltrate following the storm for thursday and friday.

 

Short Term (Mon. - Wed.):

 

Partly cloudy skies will remain for much of the state today, but clouds will build after nightfall with snow showers developing for the western and central parts of the state. This first wave of precipitation will move eastward bringing snow to the northern half of the state and a mix of precipitation to the southern half during the day on tuesday. The models are showing a general uniform total of up to a half inch of liquid water equivalent of precipitation with this first wave, which could be 3-5 inches of snow for the northern half of the state with smaller amounts in the south where sleet and freezing rain may mix in. The precip. will die off for a short time tuesday evening and overnight before the next slug of moisture moves in with the main center of low pressure overnight and into wednesday morning. The models are showing the critical 540 line moving up into southern New York state tuesday night and wednesday morning, which means much of central and northern PA will see freezing rain and sleet with areas to the south getting plain rain during the day on wednesday. The 09Z SREF shows this as well. A major threat for significant icing is possible with this second wave of moisture, so be prepared for some hazardous conditions. The storm will move out of PA overnight on wednesday ending with some snow showers for the western mountains as cold arctic air works its way in.

 

Long Term (Thurs. - Fri.)

 

The skies should clear for the end of the week, but cold arctic air will infiltrate much of the state as high pressure moves in for thursday and friday. Single digit low temperatures for thursday night are possible for much of the state with temperatures in the teens and 20's for the daily high on thursday and friday.

 

Josh Aikins

Technical Discussion

Synopsis...

Strong high pressure over S. Canada will slide eastward tonight and tomorrow reinforcing the chilly air which will set the stage for a major winter storm on Tuesday and Wednesday.  This prolonged event has the potential to bring all wintry precip types to the state with icing being a major threat.  The typical northwesterly flow and mountain snow showers will follow in the wake of the storm for Thursday.

Near Term (Sun Night-Mon)...

Partly cloudy skies will persist overnight as high pressure moves in the region.  Temperatures will be able to drop a lot tonight in most places due to the lack of cloud cover.  Expect lows in the teens across much of the state with 20s S and E.  Monday will begin fairly pleasant but cold as high pressure dominates.  High clouds will overspread the region throughout the day and lower/thicken by evening as the first impulse from the approaching storm system nears the region.  High temperatures on Monday will struggle to make it to freezing across the state.

Short Term (Mon Night-Wed AM)...

Lots to discuss with the upcoming storm system.  First waves moves in on Monday night.  Timing looks to be a bit after midnight in the west and near dawn in the east.  Most areas should see at least a period of snow with this WAA precip but SE/CR/PM have the best chance of mixing with pl/zr by dawn on Tuesday.  Total liquid is 0.3-0.6 for most of the state with this first wave and should lead to 3-5" of fresh snow across northern and central regions.  Fairly good model agreement with this first wave although precip types/amounts still have to be refined for the zones.  Will leave it to future shifts to fine tune the forecast :)  Wintry precip will taper off to zr dz/flurries Tuesday afternoon.  This respite would be a key time for road crews to clear roads because of much heavier precip coming at night.  The next wave will start after dark across the west and move eastward quickly overnight.  Total QPF is 0.6"+ with this system leading to a total of 1-1.5" total across much of the state total with the whole system.  SREF means show this as well.  Bottom line is that there is lots of consensus on generalities of this storm as well as the total precip.  Hard part is nailing down the precip types/times of changeover.  At this point our thinking is that LH/Centre Region/NE/NSQ have the best chance of significant icing with more sleet/snow in NC.  SE/RV/CR/NW/PM should change to plain rain for a time on Tuesday night/ Wed morning as sfc temps rise above freezing.  Strength of high pressure over Canada will be key to see how strong the CAD is during the course of the event.  Still time to fine tune this forecast so did not get into specifics in the zone forecasts.

Long Term (Wed PM-Thurs)...

Storm departs quickly on wed afternoon and winds turn westerly, ushering in chilly temps and changing any leftover precip to snow showers and 850s crash to -10C by evening.  The usual mtn snow showers will continue overnight and Thursday but winds will die down by Thurs as high pressure again takes control.

--
Dan DePodwin

Pennsylvania State University
College of Earth & Mineral Sciences
Undergraduate of Meteorology
General Option; Forecasting Focus
Geographic Information Sciences Focus

Sunday Morning Technical Discussion

Synopsis:  A very weak short wave is bringing light snow to Pitt Metro, Laurel Highland, and into Ridge and Valley.  Everyone else is under mostly cloudy skies.   Clearing will occur on Sunday to mostly clear skies.  Monday looks to be cold and clear, but clouds will increase Monday night for what will be the show down of the week.  A two punch storm that will bring everything and maybe the kitchen sink for Tuesday and Wednesday.  The storm moves out Wednesday Night, bring colder and clearer conditions for Thursday.

Short-term:  Neither the WRF or GFS show the light snow that is falling over PM/LH/RV this morning.  But they do have the clouds associated with it.  They both show clearing conditions for the state Sunday afternoon and into Sunday night.  Monday will be cold after this short wave passes through but clear.  Relative Humidity at 700mb and 850mb levels start to increase Monday night as our two punch storm system purges from the southeast.  Overrunning snow will start as our first punch after Midnight on Tuesday.

Long-term:  The WRF is the warmer of the three models looked at (WRF, GFS, & EURO) for this storm.  The 850 0C temp line during the height of the storm looks to be positioned just above the state.  This brings an interesting wintry precipitation.  Based on very cold stubborn air prior to the storm, warm air will have a hard time trying to reach the ground.  The first batch of snow will end mid day for most of the state.  A break in the action around dinner will occur before the more propionate second punch comes in for Tuesday night and Wednesday morning.   Along the PA Turnpike and points south they will start off as snow then change over to rain before changing back over to wintry mix Wednesday Morning.  North of the PA Turnpike they will see snow before changing over to wintry mix then back to snow for Wednesday Morning.  The storm clears out for Wednesday afternoon and night, bringing in colder air.  Thursday looks to be cold and clear.

Technical Forecast

Synopsis:

 

Short-term, it looks like our second clipper system will make its' way through the Commonwealth for today, giving many areas a couple more inches of snow. That system should move out by tonight. Another low-pressure system moves to our north tomorrow, but will probably only give the north-central region a few flurries - everybody else should be dry. On Monday, high pressure in Ontario will give us partly to mostly cloudy skies and a temporary break from the snow. By Tuesday, however, another area of low pressure - this time coming up from the southern Great Plains - will move towards the Northeast, and this one looks like it could be pretty impressive. Once it moves offshore by Wednesday, areas of southeastern Pennsylvania could receive quite a lot of snow, which may mix with rain. Other parts of Pennsylvania will likely receive a good amount of snow from this area of low pressure as well, as it looks to be a pretty potent storm.

 

Short-term:

 

Today, the clipper is moving through Pennsylvania, which will give many areas of Pennsylvania a couple of inches of fresh snow for today. That system will move out by tonight, and another area of maximum vorticity will move through to the north of us for tomorrow, possibly producing a few snow flurries in north-central Pennsylvania. Tomorrow night into Monday, however, we will see an area of high pressure dry things out over the state. Winds will be from the north to northwest, since this high pressure will be up in Ontario. Thus, the temperatures will stay cold, and the 540 line will stay south of our area. However, this dry weather will not last long ...

 

Long-term:

 

An impressive area of low pressure looks to move up from the southwest, and it will be a potent one. The pressures don't look to be too low at this point (1004 mb. when it moves out over the Atlantic); however, it does have a lot of moisture drawn up with it. This will be due to the southerly influence of warm air from the Gulf of Mexico. Also, there is a huge area of high pressure that is set to move in over the northern Great Plains. One model has this high pressure getting as strong as 1050 mb! This is definitely an Arctic high that will be setting in, and the contrast between it and the warmer air down south will set up an impressive line of precipitation all the way from Texas through Pennsylvania. Once this low moves through, the Arctic high will be moving east, and giving us our turn of very cold temperatures (although it will not be as cold as in the Midwest). It is hard to say when the snow will begin, and also how exactly this low will track. The WRF has the low tracking a bit more to the north, which might mean a mix of snow, sleet, freezing rain, or rain for some parts of PA, but the GFS keeps the low a little bit more to the south. This seems more accurate, considering the general blocking pattern that has kept the eastern half of the country below average this winter, and the western half above average. All in all, a potentially very dicey situation this upcoming week!

Forecast Discussion

Synopsis:

Yesterday's storm continues to push off to our north and east. Snow showers in the western mountains will gradually diminish throughout the remainder of the day. A series of clipper systems will move in Friday and during the early part of the weekend, bringing light to moderate snow accumulations across much of the state. A weak ridge of high pressure will build in across the Northeast come late Sunday and into early Monday.

Short Term:

Snow showers across the northern and western mountains will continue to diminish throughout the late afternoon and early evening hours as the general flow shifts to be more out of the West and SW ahead of the first clipper system entering the region. There is general agreement for the setup of these clippers but the timing of each varies slightly. We went with the SREF's as the best guidance for the short term forecast. The 15z run indicates that a wide swath of light snow will begin moving into Western counties close to midnight and continue to spread across the state during the day Friday. The next clipper looks to move into the state early Saturday morning. Total accumulations from these two clippers may be on the order of 1"-3" across much of the state with some locals in the Northern and Western mountains likely seeing more. As far as temps are concerned, we erred slightly on the cooler side of MOS guidance due to the snow pack across the state. Temps look to be at or slightly below average.

Long Term:

We will see a slight cool down in temps early next week in the wake of this string of clippers as they move eastward and out to sea. A weak ridge builds in across our region late Sunday and into early Monday. The next round of snow showers look to move into NW zones come late Monday and into Tuesday. Upcoming shifts should keep an eye out for an interesting storm that is looking to develop in the lower Mississippi Valley and move into the NE come mid-late week.

 

Christopher Cornwell

Forecast Discussion

Synopsis...

A series of weak clipper systems will move through the commonwealth over the next 5 days. None of them appear to be that strong, but could add a couple of inches of snow to the current snow pack. Temperatures will hover near and slightly below average throughout the week.

Short Term...

The European and 18Z GFS models agree that a weak disturbance will move into the western part of the state late in the day on Thursday going into early Friday morning. Both models indicate a relative lack of moisture, so snow accumulations from this system will range from a dusting to an inch or so of snow. A secondary clipper system will follow this system late in the day on Friday. All models agree that this system will be stronger than the previous one, and will cause accumulations to range from 1-3 inches statewide. This system will also dive into the central and eastern parts of the state in addition to the western part. Temperatures over these three days will be persistent as geostrophic flow, wind and cloud cover maintain similarly over these couple days.

Long Term...

Sunday should remain mostly dry and cooler compared to the previous days as cold Canadian air builds in behind the passing clipper systems. The next real area of concern will come later in the day on Monday as another broad but weaker clipper system descends its way through the commonwealth. The timing and strength will be keys to watch as the week progresses.


Andrew Dzambo


We Are... Penn State Meteorology

Synopsis:

A low pressure system will make its way NE along the Eastern Seaboard over the next 36 hours. The event will bring significant snow accumulation to southeast Pennsylvania, the Mid-Atlantic States, and the Tri-State area before making through southern New England on Thursday afternoon. After the system exits on Thursday afternoon, another disturbance will make its way through the Commonwealth on Friday and lasting into Saturday. Moderate to heavy snowfall can be expected across the state.

 

Short Term (Through Thursday Afternoon):

The low pressure system can be expected to affect Pennsylvania between Wednesday (0z) and Thursday (700z). Warm air advection can be expected prior to the arrival of the storm. This will allow for temperatures in the southeastern and south central areas of the state to rise slightly above 0®C for a short period of time. This will bring in the possibility of a wintry mix ahead of the warm front. However the temperature will quickly drop below zero. Moderate snowfall can be expected across the state. Heavier snowfall amounts are expected in the southeast and southwest sectors. We chose to utilize the WRF model due to its accuracy over the past season. The conditions at t=0 were similar to the current conditions throughout the state as well. The HRRR and WRF simulated radars were also utilized to gain a better perspective on the amount and location of precipitation. The center of the system will take a more northeastern vector path than had been previously predicted. This will carry the bulk of the precipitation through Pennsylvania, which is contrary to model predictions late last week. The storm will make its way off the US coast come Thursday afternoon, leaving significant snowfall and breezy winds.

 

Long Term (Thursday Afternoon to Sunday)

Although it goes against the hopes of most Pennsylvanians, more snow lies in the long term forecast. After the passing of the low pressure system on Thursday morning, it appears that two additional (but smaller) disturbances will pass through the state before the weekend is over. The first disturbance will move into the state on Friday morning, bringing mostly light snowfall with it. Behind the disturbance, a brief period of lake effect snow can be expected in the Northwest sector. The next disturbance will
"clip" through the Commonwealth on Saturday, exiting Sunday morning. It will bring light snowfall to most of the state, but areas of moderate snowfall can be expected in the Northwestern and North central areas of the state. Cold air advection and a wind from the Northwest following the disturbance will bring isolated lake effect snow showers to the Laurel Highlands and the Northwest sector. The WRF and GFS models were used in combination for this forecast. The WRF has provided very accurate precipitation predictions, but is often too overzealous when forecasting for larger, weaker systems.

Forecaster: Tom Bedard

Re:

Synopsis:

A low pressure system will make its way NE along the Eastern Seaboard over the next 36 hours. The event will bring significant snow accumulation to southeast Pennsylvania, the Mid-Atlantic States, and the Tri-State area before making through southern New England on Thursday afternoon. After the system exits on Thursday afternoon, another disturbance will make its way through the Commonwealth on Friday and lasting into Saturday. Moderate to heavy snowfall can be expected across the state.

 

Short Term (Through Thursday Afternoon):

The low pressure system can be expected to affect Pennsylvania between Wednesday (0z) and Thursday (700z). Warm air advection can be expected prior to the arrival of the storm. This will allow for temperatures in the southeastern and south central areas of the state to rise slightly above 0®C for a short period of time. This will bring in the possibility of a wintry mix ahead of the warm front. However the temperature will quickly drop below zero. Moderate snowfall can be expected across the state. Heavier snowfall amounts are expected in the southeast and southwest sectors. We chose to utilize the WRF model due to its accuracy over the past season. The conditions at t=0 were similar to the current conditions throughout the state as well. The HRRR and WRF simulated radars were also utilized to gain a better perspective on the amount and location of precipitation. The center of the system will take a more northeastern vector path than had been previously predicted. This will carry the bulk of the precipitation through Pennsylvania, which is contrary to model predictions late last week. The storm will make its way off the US coast come Thursday afternoon, leaving significant snowfall and breezy winds.

 

Long Term (Thursday Afternoon to Sunday)

Although it goes against the hopes of most Pennsylvanians, more snow lies in the long term forecast. After the passing of the low pressure system on Thursday morning, it appears that two additional (but smaller) disturbances will pass through the state before the weekend is over. The first disturbance will move into the state on Friday morning, bringing mostly light snowfall with it. Behind the disturbance, a brief period of lake effect snow can be expected in the Northwest sector. The next disturbance will
"clip" through the Commonwealth on Saturday, exiting Sunday morning. It will bring light snowfall to most of the state, but areas of moderate snowfall can be expected in the Northwestern and North central areas of the state. Cold air advection and a wind from the Northwest following the disturbance will bring isolated lake effect snow showers to the Laurel Highlands and the Northwest sector. The WRF and GFS models were used in combination for this forecast. The WRF has provided very accurate precipitation predictions, but is often too overzealous when forecasting for larger, weaker systems.

Synopsis:

A low pressure system will make its way NE along the Eastern Seaboard over the next 36 hours. The event will bring significant snow accumulation to southeast Pennsylvania, the Mid-Atlantic States, and the Tri-State area before making through southern New England on Thursday afternoon. After the system exits on Thursday afternoon, another disturbance will make its way through the Commonwealth on Friday and lasting into Saturday. Moderate to heavy snowfall can be expected across the state.

 

Short Term (Through Thursday Afternoon):

The low pressure system can be expected to affect Pennsylvania between Wednesday (0z) and Thursday (700z). Warm air advection can be expected prior to the arrival of the storm. This will allow for temperatures in the southeastern and south central areas of the state to rise slightly above 0®C for a short period of time. This will bring in the possibility of a wintry mix ahead of the warm front. However the temperature will quickly drop below zero. Moderate snowfall can be expected across the state. Heavier snowfall amounts are expected in the southeast and southwest sectors. We chose to utilize the WRF model due to its accuracy over the past season. The conditions at t=0 were similar to the current conditions throughout the state as well. The HRRR and WRF simulated radars were also utilized to gain a better perspective on the amount and location of precipitation. The center of the system will take a more northeastern vector path than had been previously predicted. This will carry the bulk of the precipitation through Pennsylvania, which is contrary to model predictions late last week. The storm will make its way off the US coast come Thursday afternoon, leaving significant snowfall and breezy winds.

 

Long Term (Thursday Afternoon to Sunday)

Although it goes against the hopes of most Pennsylvanians, more snow lies in the long term forecast. After the passing of the low pressure system on Thursday morning, it appears that two additional (but smaller) disturbances will pass through the state before the weekend is over. The first disturbance will move into the state on Friday morning, bringing mostly light snowfall with it. Behind the disturbance, a brief period of lake effect snow can be expected in the Northwest sector. The next disturbance will
"clip" through the Commonwealth on Saturday, exiting Sunday morning. It will bring light snowfall to most of the state, but areas of moderate snowfall can be expected in the Northwestern and North central areas of the state. Cold air advection and a wind from the Northwest following the disturbance will bring isolated lake effect snow showers to the Laurel Highlands and the Northwest sector. The WRF and GFS models were used in combination for this forecast. The WRF has provided very accurate precipitation predictions, but is often too overzealous when forecasting for larger, weaker systems.

--
Thomas Bedard

Pennsylvania State University
Undergrad of Meteorology
Fundraising Chairman, Earth and Mineral Sciences Student Council
Advertising Chairman, Campus Weather Service

Technical Discussion

Synopsis

 A storm system will approach from the gulf coast region and affect the commonwealth tomorrow morning into early Thursday morning.  The heaviest precipitation will be confined to the southeastern portion of the state with the rest of the state seeing scattered snow showers. Behind the storm, skies will remain mostly cloudy and breezy with colder temperatures lasting into the weekend. A clipper system will approach on Saturday, bringing the threat of some snow showers.

Short term (Tonight through Thursday Morning)

Clouds will continue to thicken up ahead of an approaching storm from the south. Most of the computer models have come to a general consensus that the low will track off the North Carolina coast and move up the coast, deepening as it does so. With this general track, the heaviest precipitation will be confined into southeastern PA. Precipitation will overspread the area by tomorrow morning and enough warm air will be in place that a mix of rain, sleet, and snow is likely. As the storm continues to deepen, it will draw in colder air from the north and the changeover to all snow is likely by evening. There will be several hours of snow that it has prompted the National Weather Service to issue Winter Storm Watches for the entire southeast area for significant accumulations. When all is set and done, a general 3-6 inches will fall with locally higher amounts. Snow will taper off by dawn on Thursday.

 

Long term (Thursday into Saturday)

Behind the storm system, winds will increase from the northwest, causing colder air to funnel down from Canada. A clipper system will approach from Canada on Saturday, bringing the chance of some snow showers.

1-25-2011 Technical Discussion

Technical Discussion

Synopsis

A weak disturbance will pass over the region Monday night, giving as a chance of snow showers. Tuesday will feature partly to mostly cloudy skies and warmer temperatures ahead of an approaching storm from the Gulf of Mexico. Clouds will build throughout Wednesday and some snow might be breaking out later in the day. Snow should peak around midnight hours Wednesday night and gradually end on Thursday. Some breaks in clouds are possible Thursday afternoon, however, the skies will remain mostly cloudy. Friday will see cooler temperatures as colder air funnels in from Canada behind the storm system.

Short-term (Tuesday – Wednesday)

A weak cold frontal passage Monday night will not cool the temperature too much as warmer air starts to advect northward on Tuesday as high pressure slides offshore. The skies will likely to be cloudy as some moisture lingers in the atmosphere. The temperature is not going to be as cold Tuesday night as warmer air continuous to flow in from the south ahead of a developing storm in the Gulf Mexico. Wednesday should be an interesting day to forecast as the storm system travels northeastward toward the Mid-Atlantic. In general, Wednesday will feature increasing cloudiness with possible snow showers later in the day.

Mid-term (Wednesday night – Thursday)

The latest models have come into a better agreement on where to put the surface low along the east coast. The earlier runs of WRF seemed invalid as they put the surface low a few hundred miles east of the 500-mb low. However, the WRF has trended westward with this system throughout the day and is now closer to the other model outputs such as the GFS and Euro. In contrast with the original forecast, this system now looks to be more of a Miller-Type B storm instead of Miller-Type A. As the models suggest, the primary low is going to form in the Gulf of Mexico and travel northeastward. However, as it does so, it is going to encounter a wedge of cold air sitting over the Appalachians and might weaken a bit because of that. If this scenario is true, a secondary low is likely to develop somewhere along the South Carolina coast and move northeastward. Whether or not this happens will be the deciding factor on how much snow the Northeast will see Wednesday night. If a secondary low develops, the bulk of precipitation will likely to be confined near the immediate coastline with a sharp precipitation cutoff along the Harrisburg – Scranton line. Another possible scenario is that the primary low stays strong as it moves directly over the Appalachians and New Tri-state area. If this happens, the axis of heaviest snow will be over Central – Western Pennsylvania with the I-95 corridor seeing mostly rain. Which solution is going to pan out is still hard to predict as of now, but leaning toward the former scenario described above.

Long-term (Friday – Saturday)

The skies will remain mostly cloudy in the wake of the storm. Colder air will funnel in behind the storm on Friday. However, the temperatures will be on the rise again on Saturday as a clipper system swings across Southwestern Canada. Some snow showers are also possible during the weekend.

 

David Wang

Sunday Morning Technical Discussion

Synopsis:

Scattered lake effect in the central portions of the state will die down during the day.  Monday is a clear day, but a clipper system from the north moves through the region with light snow.  Tuesday we clear out again only to have clouds roll back in from a potential major storm to our south.  Wednesday the storm provides snow for the state, and departs by Wednesday night.  Lake effect snow begins again out west for Thursday.

Short-term:

Both the NAM and GFS show lake effect snow for Sunday, and radar confirms at 13z of that lake effect snow.  Both models show the clearing that will occur Sunday night into Monday.  Monday looks to be a nice clear cold day with temperatures around 20.  Both models show a clipper system moving into the Great Lakes.  The NAM is faster than the GFS so we did a compromise.  Snow will develop 1^st in the west and last in the east, and will clear out the same way.  By the end of morning rush hour the snow should be out of the eastern half of the state.

Long-term:

Clearing from the clipper system will occur on Tuesday with mostly sunny skies.  But it will not last.  A storm system from the south is taking aim at us.  The NAM is quicker than the GFS, and the EURO model appears to be on the same track as timing with the NAM and might even be a little faster.  So a compromise was made between the NAM and GFS for Tuesday night with increasing clouds for the state.  For Wednesday, the 500mb height low will be over the surface low as the low tracks to the west of us.  A compromise was made between the GFS and EURO.  Snow will overspread the state with the moderate-heavy in the eastern & central portions and lighter snow in the western sections.  After the storm departs the area Wednesday night, lake effect snow will being out west for Thursday.

The GFS MOS got to warm for our forecast period from Tuesday night to Thursday, so we are off by at most 3-4 degrees.

Saturday morning forecast

Synopsis:

Westerly to northwesterly winds will continue through the weekend across much of the Commonwealth, ahead of high pressure to the west. The 540 mb. height line will stay in the southern part of the country through the weekend and into early next week, ensuring very cold temperatures across the eastern part of the United States, including here in Pennsylvania. Temperatures will stay in the teens and 20s for highs through Monday, with lows likely going below zero Sunday night into Monday for the northern and central parts of the state. A couple of low pressure systems will skirt across the Great Lakes over the next few days, giving areas around Erie and Bradford a chance of a bit of snow tonight into the first part of tomorrow. Otherwise, expect pleasant and dry conditions until Monday. At that point, a more interesting area of low pressure will swing down from the northern Great Plains, move eastward, and develop out over the Atlantic. There could be some snow for the southern and eastern areas of PA later Tuesday into Wednesday from this one, but it will probably not be a significant snow event. However, do keep your eyes out for this feature.

Short-term:

All the model runs (ETA-3z, WRF, GFS) are consistent on the westerly to northwesterly winds through this weekend - again, keeping that cold air entrenched across the state. GFS model has the low skirting to the north tonight and early tomorrow bringing in a bit of lake-effect snow up north, but even it keeps totals down (probably no more than an inch or so). Otherwise, the models are pretty consistent with keeping things dry. Some 850 mb moisture will move through the state tomorrow (as a result of that weak trough moving through up north), but at 700 mb, things are quite dry. So, for most areas Sunday, it will stay dry, albeit cloudier than today. Monday, the next low pushes a bit to the south of PA (which will strength over the Atlantic long-term), possibly giving the mountains a little snow Monday night into Tuesday. More snow will occur towards the middle of the week ...

Long-term:

The models seem to be somewhat inconsistent with the timing of the development of this area of low pressure. WRF shows the same low still just away from the Florida coast come Tuesday. However, the ETA-3z and GFS models show that same low pressure system just off the Virginia coast, which seems more favorable, considering the upper-level winds and where this low is coming from. Again, it seems like the low will be too far off the coast for this to be a big snow event, but if the pattern of the jet stream changes at all (putting the low-pressure system closer to the coast), then it could be a potentially bigger snow event. Winds from the SE (from this low-pressure system) will try to bring a little bit milder air towards PA, possibly resulting in a rain-snow mix during the day across extreme SE PA (Philadelphia area) Wednesday. However, with the general meridional pattern across the country (big ridge out in the western half of the nation, big trough here in the eastern half), it looks like we will not get much above freezing anywhere for the next week or so.

23z Forecast Discussion

Light snow has moved into the region and will continue throughout the night, giving the entire forecast area a steady, accumulating snow for the entire area. An Arctic high will fill in behind the departing storm, leading to some of the coldest conditions we will see this year. Conditions will remain calm but cool into the first part of next week.

Short Term…

Clipper-esque system coming out of the MW is poised to deliver a LT to MDT snowfall. 18z WRF is going with 0.25-0.5 QPF for most of PA, but ensembles show a slightly lower total. NWS seems on the ball with a general 2-5" snow, with heavier totals in the hilltops and NEPA. I could see this being a little too low given low temps aloft, indicating high snow ratios. Pretty good agreement with exit timing…expect only lingering SNSH, esp in the Laurels and NE. Tight press gradient will lead to breezy conditions and blowing snow. Arctic chill sets in following the storm, with some lingering lake-effect and upslope SNSH in the west.

Long Term…

Big story Fri-Sun will be frigid conditions. Temps will struggle to reach 20 across much of PA during the wknd, with subzero temps widespread during the night. New indications show that normally colder locations may go below -10 or -15F. Mcldy to Pcldy cndtns dominate the rest of the period before the next system works its way in for midweek. Still a long way out, but it looks like an interesting pattern shaping up (keep an eye on Euro).

"Jamba Enjoys Terrific Storms"

MCM

Forecast Discussion

Synopsis...

Snow on the way for Thursday. Frigid temperatures to follow. Both events will be fairly significant as we close out the week.

Short Term...

The 18Z GFS model has the next round of snow showers breaking in to the commonwealth by Thursday early evening. This system has a fairly healthy looking flow of moisture coming into it, and a strengthening high pressure area behind it will help to pad final snow totals. A light to moderate snow should occur over much of the commonwealth through Friday afternoon. Friday looks to be a breezy day as the trailing high pressure system situates itself in the northeast. The biggest story Friday night will be the cold... 850mb heights will drop to almost -20 degrees, based on a mix of WRF and GFS data. This means low temperatures, especially in higher elevations, could approach zero degrees.

Long Term...

Saturday and Sunday will be dominated by cloudy skies with a chance of an isolated snow shower... Weak disturbances from the central US and southern Canada will contribute to this extensive cloud cover. The moisture backing in either of these systems, however, seems to be lacking initially. The long term GFS keeps the state out of the woods for more snow, and in fact shows possible warming as a steady SW flow and high pressure builds in. The next system appears to be in the works for mid to late next week.


Andrew Dzambo


We Are... Penn State Meteorology

Wednesday Afternoon Technical Discussion

Overview:
The storm system that brought the icy conditions to Pennsylvania this morning will lift off to the Northwest this evening.  A weak ridge of high pressure will move over the region late tonight and into tomorrow attempting to dry out the state. However, lingering low level moisture will only allow for the sun to occasionally peak out tomorrow before out next system moves into the area. This system will bring a quick burst of light snow across the commonwealth with the western mountainous regions seeing the heaviest accumulation Friday and into Friday night. Behind this system conditions will get very cold as a strong northerly flow will cause the temperatures to struggle to get out of the teens on Saturday.

Short Term:
The system that brought the precipitation to the state today will move out to see tonight allowing for a weak area of high pressure to develop in its wake. However, this high pressure system is more a result of a lull between two storm systems rather than a true winter high. This means that although the models are trying to bring in dry air at the 700mb level for Thursday, low level moisture will keep most of the state cloudy during the day with only partial clearing Thursday evening. The next system will approach the region Thursday night causing clouds to be on the increase towards Friday morning. Temperatures will also be on a downward trend over the next few days.

Long Term:

The snow will move into the state sometime late Thursday night or early Friday morning. All of the critical temperatures are to the south of PA so this will be an all snow event. The WRF model has been fairly consistent about when the snow will move into the state however, the 18z run has a bit less precipitation falling. Therefore, I would tend to be a bit conservative on my snowfall totals, especially in the central mountains of Pennsylvania.  The GFS has had a lot more variability from run to run, however, the 18z run is quite similar to the 18z WRF.

Longer Term:

Behind this system, a stiff northerly flow will cause temperatures to plummet for the beginning of the weekend with temperatures in the single digits Friday and Saturday night and daytime highs struggling to get out of the teens on Saturday.

RJ Patrizio