12/10 Technical Discussion

Synopsis:

Warm temperatures today and tomorrow precede the next big system. Pennsylvania will see just about every type of precipitation from this storm, which will affect the Commonwealth from Sunday through the end of the forecast period. Expect the lake effect snow machine to gear up once more for the beginning of next week along with bitterly cold temperatures and high winds.

Short-Term:

A smattering of snow showers is currently stretching across Pennsylvania. We expect these to clear out by this afternoon and see temperatures warm tomorrow. This warming comes right before the next major storm system. The GFS and the WRF both show the system moving into the state Sunday morning and persistent precipitation through the day. Temperatures in the afternoon will likely be warm enough that most precipitation will be rain (as predicted by the SREF. The SREF also shows a slight possibility of freezing rain Sunday morning for the Laurel Highlands. Timing of the passage of the cold front is still up in the air, though the window looks to be closing on sometime Sunday night.

Long-Term:

Monday and Tuesday will be bitterly cold, with high winds across much of the state. A lake effect scenario will definitely be occurring, as current Lake Erie surface water temperatures range between 35-45 degrees Fahrenheit. These snow showers will reach far across the state as winds are expected to be in the range of 15-20mph in the wake of this storm. Some areas could see blizzard-like conditions if the snow is heavy enough.

-Burkely Twiest

Technical Discussion

Synopsis:

A clipper system looks like it will bring some snow showers to western and northern Pennsylvania.  The track of the big system is still in question, but a westerly solution looks to be in great favor.  Another perfect lake-effect snow setup for next week.

Short-term:
Radar images from this evening have shown numerous light snow showers far east of where the snow begins at the surface.  SREF precip type indicates snow down to Pittsburgh and out to Johnstown and State College, as well as Erie and Bradford.

Long-term:

The GFS is quicker and more defined with the FroPa through western Pennsylvania, while the WRF seems to get caught-up in the merger of the Lakes low and the Coastal low.  The timing of the cold front is the timing of the snow, as temperatures ahead of the cold front appear to be just above freezing except at higher elevations.  We generally favored the GFS because its solution looks more natural.

Deep low-level moisture can be seen with the lake-effect snow on the east-west border between Erie and Bradford, almost like there is a mixing layer that extends to 700mb.  This to me is unusual, so I thought the best assumption was that this means heavy snow.

22z Technical Discussion - 12/9

Synopsis…

All eyes are already shifting to the large storm expected to move into the region for Sunday, but until then, we'll have to deal with continued cold and snow showers. After what may be the coldest night of the season so far, a weak clipper system will drop down from the Great Lakes and bring scattered snow showers to the area. In the wake of this system, the flow turns more southerly ahead of a strengthening low that may strengthen rapidly as it reaches the coast. There is still very little agreement in guidance for this system, but some type of frozen precip will reach PA at some point by Monday morning. We can definitely say the coldest air of the season will settle in for the early part of the week.

 

Short Term…

Lake effect snow is slowly giving way to high pressure located to our NE, which will hang around just long enough to keep conditions right for a cold night; MOS is in the teens for the CTP area. The weak clipper is running into lots of dry air, GFS-MOS-indicated dew points in the single digits. Right now we think any measureable snow will be north of I-80. Models agree on general southerly flow, pumping milder air upward for Saturday…temps reaching into the 30s for many areas for the first time in a while.

 

Long Term…

Models are confuzzled on the weekend…run-to-run and model-to-model inconsistencies abound. 0z GFS runs looked a little more promising for snow, but new 18z runs show a more westerly track…Even more interesting, any discernable trends suggest it's more likely the western low will not even merge with weak coastal low until after they pass PA; this would result in a busted storm for us, with light precip. Going with an ensemble mean, it looks like the rain-snow line is trying to set up right thru the CTP CWA. In depth looks show a mix for UNV, all snow for DUJ, and all rain for PHL. It seems like no one has been able to pin this storm down yet, so we're generally going with means…Our consensus says things are far too uncertainty for anything else. Expect some accumulating snow in the NW and maybe PIT, and periods of mdt to hvy rain in the SE, but in between a mix is most likely, transitioning to rain, especially with indications of upper-level warmth sneaking into some forecasted profiles…meaning FZRA may be a problem. But 18z WRF keeps storms apart, giving UNV region light rain with some light snow on the backside. Still, HPC has >40% chc of 4+" of snow in western PA. Timing of storm is at least looking more certain, with precip moving in Sun night and lasting into Mon. Lake effect looks likely again afterward, with Arctic air moving in. High temps may struggle to top 10 F in BFD Tues...May need to closely monitor potential for dangerous wind chills during PSU finals week.

 

Forecaster: Matt Mahalik

Technical Discussion

Synopsis:

 

A halt in the lake effect snow for today will give way to partly sunny skies in the western portion of the state and clearer conditions in the eastern portion of the state.  A clipper system will move to our north tomorrow...with minimal precipitation possible in the northern section of the state.  Saturday looks to be mostly cloudy, but dry.  Things get interesting Sunday into Monday as a warm front associated with a low pressure system combined with a secondary low off the coast will impact the area.

 

Short Term:

 

After that dosing of snow we had last night, things appear to be calming down throughout PA as far as lake effect snow goes.  High pressure will be moving in from the west, which will halt the lake effect snow that we've been seeing the past few days.  Some lingering snow showers are still present in northwestern PA today as low level convergence is still present, however, they should decrease in intensity by the afternoon today.  So, any accumulations today would most likely be in the northwest section of the state.  700 mb relative humidity moisture values overall are forecasted to be low throughout the day today and overnight.  Overall, most of the western half of the state, including most of central PA will see Partly Sunny skies today, with the eastern half of the state having more broken clouds and clearer conditions.  A clipper system will be the next weather maker on Friday.  However, the clipper should move to the north of the region, meaning that there will be minimal precipitation.  Northern parts of the state may receive a dusting to an inch.  The clipper will allow for temperatures to climb above the freezing mark for most areas.  Saturday is looking like a dry day.  700mb moisture is low, but clouds seem to stick around for most areas.

 

Long Term:

 

Things start to get interesting on Sunday into Monday morning as a warm front associated with a low pressure system will develop and strengthen to the west of us.  This is a tricky situation because it seems as if the low pressure system to our west is transitioning its energy to a secondary low pressure system off the North Carolina/Virginia coastline.  The 12Z WRF has the rain/snow line moving from west to east with areas in the western and central portion of the state receiving rain to snow and areas in the eastern portion of the state getting mainly rain.  When the system finally moves out on Monday, a Northwesterly flow will take place.  Lake effect snow showers could potentially return, creating a situation similar to what we've had the last few days.

 

 

Forecaster:  Frank Vecchio

Forecast Discussion

Synopsis...

A clipper system and a strengthening low pressure system in the southern United States outline the big events for this forecast period. Neither system will bring a ton of snow, and the bitter cold weather will disappear until Monday.

Short Term...

Thursday looks to be a carbon copy of Wednesday: overcast skies for the commonwealth with temperatures below freezing and no bitter wind chill. An upper level shortwave picked up by the 18Z GFS model indicates a good old fasioned "Alberta Clipper" in store for the commonwealth on Friday. The low pressure associated with this system should pass by far north (in Southern Canada). For this reason, I would not expect very much precipitation out of this system, which the MOS precipitation outputs indicate. Many areas, especially in the northern regions, will not receive more than a dusting to an inch of snow (with higher amounts in the higher elevations). The approach of the clipper later in the day Friday will allow for temperatures to climb above the freezing mark for the first time on Friday for most areas.

Long Term...

Temperatures throughout the state will remain above the freezing mark through the weekend. An approaching warm front associated with a strengthening low pressure system at this time may allow for temperatures to reach the upper 30s/low 40s in the southwestern regions. The WRF, however, indicates a transition in the location of the low pressure system - the center of the low pressure system will redevelop off the Atlantic Seaboard near Virginia. Most of the moisture associated with this system will funnel well off the coast, so any precipitation associated with this system will be light. Most areas can expect a mix of rain and snow, especially in the southern regions, with a better chance of snow in the northern regions. Once this system moves up the Atlantic Seaboard, a few "backdoor" snow showers will move through the western part of the state. On Monday, this low pressure system will be far enough into Canada to induce a NW flow, meaning lake-effect snow and bitterly cold temperatures will return (just in time for finals week). Most MOS runs show high temperatures staying below the 20 degree mark for the commonwealth, with very breezy winds.


Andrew Dzambo


We Are... Penn State Meteorology

                                                                                                             Technical Discussion

Synopsis:

The low pressure that brought all the lake effect snow and windy conditions will move out of the area and a high pressure will take its place for the beginning part of the weekend. A low pressure system will move of the coast for Sunday and bring a mix bag of precipitation to the region. Behind this, bitterly cold air will filter into the state with temperatures not even reaching into the 20s.

Short-term (Thurs-Fri)

A low pressure system to our north will continue to pump in lake-effect snow to the area, esp the northwest portions. A high pressure system will move in  late Thursday and should bring sunshine for the beginning part of the weekend, which will help the temperatures rise into the 30s, even lower 40s.

Long-term (Fri-Sat)

A low pressure system will move up the coast and as of the last few GFS runs looks like it will bring a mixture of precipitation. The biggest danger right now is the threat of freezing rain. This should move out by Sunday night and an artic air mass will bring very cold temperatures for the beginning part of the week.

Technical Discussion

Synopsis

Lake effect snow showers will continue across the Northwestern portions of the state Wednesday before coming to an end early Thursday due to the approach of a high pressure system. Expect dry conditions on Thursday before a clipper system moves in from the west on Friday, providing some light snow later Friday evening and overnight. Expect temperatures to warm up a few degrees Friday and Saturday as the high pressure slides to our east. Skies will clear Saturday before a larger storm approaches the region early on Sunday.

Short Term (Wed-Early Thursday)   

The retrograding low pressure providing the northwest winds over the past few days, will lift into northern Canada tomorrow switching our winds more WNW and leading to weaker lake effect snow showers on Wednesday. Temperatures remaining well below average Wednesday across the state with the winds from the northwest advecting in cold air. As the low pressure moves away a high pressure system will begin to push into the region from the south later on Wednesday. The high pressure will lead to weaker winds on Thursday ending any lake effect snow showers by midday Thursday.

Mid Term (Thur-Sat)

High pressure will lead to dry conditions on Thursday and Thursday night. The high pressure slides east on Friday providing some warm air advection early Friday before a clipper system moves in later Friday leading to light snows across northern Pennsylvania Friday evening. Skies will clear behind the clipper on Saturday as high pressure remains just east of the region. A southerly flow on Saturday will provide more warm air advection on Saturday bringing temperatures closer to average. Saturday will be "the calm before the storm".

Long Term (Sat Night-Sun)

A low pressure system will move up from the Mississippi Valley later Saturday increasing cloud cover overnight Saturday. This storm will move into the region on Sunday but the models are conflicting on whether the storm will move to our west or east. A more westerly track would lead to mainly rain with some mixing with snow possibly across western Pennsylvania, while an eastern track would lead to rain in eastern portions of the state and snow from Central Pennsylvania west. At this point leaning with a western track, but future model runs will hopefully lead to more confidence. Cold air advection will reestablish itself behind the storm leading to cooler conditions and some more lake effect snow early next week.

Zach Fasnacht

Technical Discussion

Synopsis...

Lake effect snow will diminish throughout the day and tonight as pressure gradient relaxes and winds go more westerly.  Temperatures will remain very cold and below average as large dome of high pressure builds in from Midwest.  Temperatures in single digits this morning in IA/IL.  This airmass will moderate as it moves eastward but bring the chilliest air of the season the Commonwealth tomorrow and Thursday.  Weak clipper system to affect portions of region Friday night before large amplification of E-CONUS trough on Sunday/Monday which will spawn strong SFC low and bring us an eventful end to the weekend.

Near Term (Tues-Tues Night)...

Snow showers ongoing this morning across western portions of the state.  Expect this activity to persist throughout the day with isolated locations picking up an additional few inches of snow.  Winds will remain gusty and temperatures in the 20s and 30s.  Eastern portions of the state should see some more sun today and no snow making it a bit more bearable to walk around outside.  Temperatures drop off tonight and could fall nicely in areas with fresh snowpack.  Limiting factors to radiational cooling will be persistent cloud cover and winds.  It seems as if the places with the most snow pack will have the most clouds and places with least snow pack will be clear, allowing low temperatures to be fairly uniform across the state tonight in the teens to near 20 in the Southeast.

Short Term (Wed-Thurs)...

High pressure begins to take control on Wednesday as winds slacken and become westerly.  Temperatures will remain well below average even though eastern areas of the state will see a decent amount of sunshine (especially on Thursday).  Snow showers will be confined to the usual NW/NC zones on Wed allowing for a reprieve across central and southern areas.

Long Term (Fri-Sat)...

Clouds will increase on Friday ahead of weak clipper passing north of the region.  Some warm advection snow is possible on Friday night and looks to be mainly in the northern half of the state where some places could pick up a few inches.  Temperatures will moderate on Friday and Saturday as 850mb temps warm to -5C and 500mb ridge slides over the region.  Definitely not warm by any means but much closer to normal.  Weather pattern becomes very active again late in the weekend as shortwave dives out of the Rockies into the Plains.  Large discrepancies between the models at this point with eventual track of system and this has a drastic impact on p-type for our region.  GFS is the furthest east of the models with the low going from Nashville, up the Appalachians. This would be the more wintry scenario while the ECMWF argues for all rain as the low goes over Chicago.  The key for the track is when do the arctic and polar jets phase (farther east would be better for snow) and how amplified the ridge is in the West (flatter means snow more likely for us).  Storm is still 6 days away so refrained from mentioning any precip in the forecast although did mention storm possibility in discussion.  Whatever scenario pans out, next will will be bitterly cold (thicknesses near 510 with -20 C 850 temps) with lake effect snow showers.

-ddpdtdt

Technical Discussion

Synopsis...

Cold and blustery weather continues through the next few days... The lake-effect snow machine will continue to bring a steady light snow to the northeastern regions, and a clipper system is on the way for Thursday. A potent low pressure system will likely bring rain to the commonwealth late on Saturday into Sunday, but the track of this system is very uncertain and the type of precipitation will be determined depending on how far this system veers to the east.

Short Term...

The GFS shows a strong and steady northwesterly wind that will continue through Wednesday. This, combined with temperatures in the mid- to upper- 20s for most regions, will bring really bitter wind chills until then. Lake-effect snow will continue to fall in the northwestern regions of the state through early Thursday according to the WRF - the snow will shut off once the blocked off low pressure system sitting in the Canadian maritime finally moves away. This will, however, allow for a clipper system to move through the commonwealth unimpeded on Thursday. Many areas from this system, based on the current model runs, should expect anywhere from a dusting to an inch or two of snow (more likely in the higher elevations). The windy conditions, regardless, will subside by this time.

Long Term...

Though the skies will still be cloudy by Friday, temperatures will finally rise a bit. According to MOS, most regions by Friday should make it to the low 30s. This is due in part to an approaching frontal system associated with what will be a strengthening low pressure system in the southern United States. This system, according to the 18Z GFS, appears to arrive Saturday evening from the west. Because the track of this system has shifted to the west, the precipitation expected from this system will likely be rain. There is, however, a lot of time to watch this system and come to a final conclusion as to the exact track and strength of this system. For now though, this will be the big thing to watch, and if the track of this system shifts far enough east, this could be our first large snowfall of the season.


Andrew Dzambo


We Are... Penn State Meteorology

Technical Discussion (Monday Afternoon Shift)

Synopsis:

A large upper level low pressure system in Canada will slowly retrograde westward over the next couple of days bumping into a high pressure system located over the central plains. This has created an extreme pressure gradient force which has caused a robust northern wind to develop. This northerly flow over the great lakes has activated the lake effect snow machine. This pattern will remain in place through Wednesday before high pressure retakes the state. This will cause for quite weather Wednesday evening and Thursday before a clipper system moves into the region causing more snow showers Friday and into Friday night.

Short Tem (Now through Wednesday morning):

The aforementioned low pressure system in Canada currently has a pressure of 967mb and it is bumping into a 1034mb high. You do the math people! That's an extreme pressure gradient and with great PGF comes great responsibility. Haha just kidding, but what it does mean is that a robust, sturdy, or whatever other synonym for strong northerly wind has developed which is just funneling cold air down from Canada and across the north east.  This has also created lake effect snow bands that will persist until the PGF decreases and this storm system lifts off to sea.

Mid-term (Wednesday night through Thursday):

High pressure will slowly move back over the region on Wednesday causing decreasing clouds from the southwest to the northeastern portions of the state. Models show that skies should remain partly cloudy Through Thursday before a clipper system approaches the region. Look for very cold temperatures Wednesday and Thursday night.

Long-term (Friday):

The clipper system will swing through the state on Friday with up sloping regions picking up a few extra inches of snow before the system vacates the region on Saturday.

RJ Patrizio

12-06-2010 Forecast Discussion

Technical Discussion

Synopsis:

An area of low pressure will continue to spin over Eastern Canadian seaboard as a blocking high over Greenland prevents any eastward progression. As result, the winds will continue to flow from the northwest off from the Great Lakes, creating bands of heavy snow showers, especially in the northwestern portion of the state. This kind of weather setup will stay until Wednesday; some parts of northwestern PA may see up to a foot of snow before the snow ends on Thursday. A small ridge of high pressure will build into the region after the Canadian low finally lifts northward. The snow showers will gradually end on Thursday. An Alberta clipper system is going to pass by to the north and only brining as a chance of light snow showers on Friday.

Short-term (Monday-Wednesday):

A highly amplified ridge will continue to form a blocking high over Greenland on Monday. As result, a large area of 500-mb trough will sit above the northeastern United States and keep the heights on the end throughout the forecasting period. With pieces of upper-level energy swinging around the base of the 500-mb trough, multiple low pressures will develop along the Eastern Canadian seaboard and retrograde westward back to continental Canada.  The developing storms will keep the winds predominately from the northwest off the Great Lakes. Cold air flow over warmer lake waters will allow bands of snow showers to form and travel down toward Pennsylvania.  If the conditions are favorable enough ( i.e strong northwesterly flow and good dendrite forming mechanism), some of these snow bands will pack a lot of moisture as they stretch across both Lake Superior and Lake Erie. Some parts of the western PA will see up to a foot of snow before Wednesday.

Mid-term (Thursday – Friday night):

The lake-effect snow will gradually become less favorable throughout the day on Thursday as the 500-mb trough finally gets a chance to lift northward. The northwesterly flow will weaken along with the trough's departure and with the absence of strong northwesterly flow, the snow showers will gradually end on Thursday. A ridge of high pressure will building over the region Thursday night between the departing trough and the next incoming trough over Upper-Midwest.  Partly cloudy skies will prevail on Friday before an Alberta clipper system associated with the Midwest trough approaches. Clouds will once again thicken Friday evening and some snow showers might breakout, but only with light accumulations as the clipper system will be relatively moisture starved.

Long-term (The weekend)

The guidance models continue to agree on the presence of a storm somewhere on the eastern 1/3 of the United States.  However, the timing, strength, and track of this potential storm are still largely up in the air as of now. Most of the models have their own preference on where this low is going to go, how strong this storm is going to be, and when the storm is going to form. The 12z GFS this morning brings a decent strength inland low over the Northeast. If this solution is true, then the prospect of snow chances does not look too good for Pennsylvania as the majority of the state will be under the warm sector of the storm. The ECWMF model is on the inland-end of the extreme, bringing a primary low across the Upper-Midwest and into South-Central Canada and possibly a secondary low developing along its cold front over the Northeast. The precipitation type will also be rain if this solution holds true. The Canadian model, however, is on the offshore end of the extreme. If the Canadian model is true, then majority of the Northeastern U.S will see a major snow storm Sunday night and into Monday next week.

-by David Wang

Technical Discussion

Synopsis…. 

A storm system will stall over parts of New England and eastern Canada, allowing for slightly unsettled conditions to prevail over most of the state for the first half of the week.  Expect a chance of snow showers every day and continued cold conditions.  The Laurel Highlands and northwestern regions of the state will have the greatest opportunity for significant snowfall accumulations, due to the high elevation and lake-effect snow occurrences.

Short-Term…. 

The models all show the moderately strong low-pressure system that will remain over New England and eastern Canada through Tuesday and associated swath of moisture that dips down nearly into Pennsylvania.  The disturbance will help create and maintain a deep northwesterly flow over western portions of the state.  The winds are aligned appropriately to initiate convection over some of the Great Lakes, which will result in significant lake-effect snow events that will affect northwestern regions of the state.  Additionally, orographically-driven snow showers will affect much of the Laurel Highlands into Tuesday.  The 1200 UTC run of the GFS shows snow showers beginning to affect western portions of the state later this evening and affecting regions towards central Pennsylvania as Monday progresses.  The GFS has the snow showers tapering off by late Tuesday, with only a few lingering bands of showers in the western regions after that.  The 1200 UTC run of the WRF shows similar, except that it is projecting heavier bands of snow on Monday in extreme northwestern regions.  The1500 UTC run of the SREF precipitation ensemble shows similar distributions of snow showers, but has them significantly lingering around the state until late Wednesday night.  We forecasted accordingly.

Long-Term…. 

The models all project high pressure building into the state on Wednesday and Thursday, halting the lake effect snow and other snow shower activity briefly.  It looks like the state will stay relatively precipitation free, especially on Thursday, but there will be still be some low-level moisture remaining that will allow for some clouds over portions of the state intermixed with a bit of sun here and there.