Tuesday Night Technical Discussion 1/31/12

Synopsis...

The unseasonably mild temperatures seen on Tuesday will last for one more day Wednesday. A broad area of high pressure will build in for Friday and allow for a beautiful weekend.

Short Term...

Clouds will steadily increase throughout the day on Wednesday as a passing low pressure system to the north and a weak low pressure system to the south make their way through the commonwealth. Areas in the northern tier of the state can expect a few rain showers overnight into Wednesday morning, while some light precipitation is possible in the extreme southern areas. The GFS shows a ridge building in with dry air packed into it, which will bring abundant sunshine to the commonwealth Friday and early Saturday.

Long Term...

The high pressure system will begin receding by Saturday morning. All models are in good agreement that a developing positive-sloped 500mb trough will push this high along and allow for cloud cover to build in over the commonwealth. An approaching low pressure system associated with this trough will likely bring snow showers to the lower half of the state. The low pressure system at this time does not look to be all that strong when it passes through, though as the trough moves east, this system will develop faster once it reaches the eastern seaboard. SE Pennsylvania should keep an eye on this because any veering of this system to the north could help bring a more considerable snow event.


Andrew Dzambo

We Are... Penn State Meteorology

Tuesday Midday

Synopsis:  A warm front is pushing through the state this morning.  Western PA as of 10am is already in the upper 40's to around 50, while Eastern PA is in the 30's.  Warm air advection will occur today and tomorrow before a cold front loses its strength as it crosses the state.  A potential storm will try to take aim at us for Thursday, but will be suppressed to the south.  Places south of the Turnpike might see a sprinkle or two on Thursday.  A brief cool down for the rest of the week will occur as high pressure moves through the region. 

Short-term:  A warm front moves through the state by noon today, warm air advection will occur for the rest of the day, and into Wednesday ahead of a cold front that seems to lose strength as it moves across the state.  This means scattered showers in the morning and early afternoon for the state, with clearing conditions.

Long-term:  The models have been inconsistent from Thursday to the end of the weekend, so the forecast could change.  Right now the models try to have a storm like 2 weeks ago make a run at us, problem is it will be short of the goal line for Thursday.  We cannot rule out a chance of a sprinkle on Thursday for anyone south of the PA Turnpike.  Everyone else should be partly sunny for the day.  For the past week, the models have tried to bring another storm up for the weekend, this time a snowier one.  The models have once again been inconsistent with having a storm moving through.  So at this time, the period from Friday-Saturday we are going with a no-storm approach until the models resolve their issues.  High pressure is in charge for Friday and Saturday continuing our brief winter blast (not really blast, with temps projected to be above 32F).

Kept temperatures near previous shift, with minor changes.

Technical Discussion Monday Morning, January 30th, 2012

Synopsis:

Today brings partly sunny skies and temperatures in the high 30s before a high will sit above the Commonwealth tomorrow. Temperatures will be on the rise as Tuesday approaches, temperatures will reach the unseasonably low 50s with sunny skies. A small system will quickly pass across the Commonwealth on Wednesday leaving most of the state with the possibility of some showers, but temperatures will continue to stay in the low 50s. Temperatures drop to the low to mid 40s during the day on Thursday and Friday as a low pressure system shifts out to sea on our north from the Great Lakes. The weekend seems to be highly uncertain with the possibility of storm in the mix.  

Short Term:

Today marks the last of the cooler weather from the low passing across the State over the weekend. A high will sit above the Commonwealth for the middle of the workweek leaving us with unseasonably warm temperatures reaching the mid 50s in some locations. The possibility for a few showers Thursday is in the forecast as a small front sweeps across the state.

Long Term:

Temperatures begin their decline Friday as the 540mb line drops below the commonwealth again. Skies should be partly cloudy as the possibility of a storm is debated by the models for Friday night into Saturday.

Forecaster: Meredith Nichols 

Sunday Afternoon Technical Discussion

Synopsis:

A cold front is making its way across eastern Ohio and will produce periods of snow between sunset tonight and the wee hours Monday morning. High pressure will settle to the south while we wait for a weak mid-latitude system to affect our weather (mainly clouds but snow cannot be ruled out) on Monday night through Wednesday night. For the end of the work week, a weak high will settle over the PA-NY border while a weak "nor'easter" affects extreme southern PA - something to watch later.

Models Used: 12Z GFS & NAM, Raw outputs used for temperature - SREF + PA NAM (15-prog. panel)

Tonight:

An extreme vorticity gradient (40 s^(-1) from Franklin, PA to Bradford, PA - 110 km) and a peak Omega value of -8 x 10^(-6) bar/ sec exists in West-Central PA. This indicates extreme vertical motion, leading to thunder-snow, which accompanies extreme snowfall events. This is likely this evening, especially when considering the METARS in Youngstown, Cleveland, & Akron were (or currently are) reporting thunder-snow.

Monday and Tuesday:

The high to the south sets up a track for the warm front as the low will then encounter a westerly flow aloft as it heads NE. Northern PA gets rain, mostly near the NY border. The cold front moves through from west to east. The rain builds along it but dries out as it hits the Appalachians. High pressure builds in behind it for Thursday. Extreme warmth will be noticeable after the warm front.

Long-range:

We'll be watching a nor'easter head eastward south of the Mason-Dixon line, blocked by the high pressure system building in behind the front. A cool down is likely. after the cold front moves through.

-Jaron Breen

Friday Morning Technical Discussion

Friday Morning Technical Discussion

 

Synopsis:

 

      The storm system that brought the showers and rain yesterday will continue to lift north and east today. Behind it we will find mostly cloudy skies and significant cold air advection behind the storm. Without the help of much solar heating, the temperature will fall throughout the day. Things should settle down for the start of the weekend. The biggest story in the next few day will be two relatively weak fronts that will move through. The first one will come in Saturday evening bringing with it some rain or snow showers and the second front will blast through Sunday night, bringing with it wind and a much greater chance of light snow and/or snow showers to much of the state. Temperatures will bottom out on Monday behind the front, but quickly rebound to well above normal values by Tuesday with a strong south to south westerly return flow around a high pressure system situated to our southeast.

 

Short Term:

 

       The storm that brought the rain over the last 36 hours is currently located over the Adirondacks and making its way northeast. The weather we see today will be a result of a rather strong frontal boundary extended south to north from the center of the low. Ahead of the front temperatures have been near 60° in Philadelphia. On the other hand, behind it things are rather chilly though not unseasonably so. Temperatures in the western part of the commonwealth are falling through the low and middle 30's. The temperatures will continue to fall through today with a strong westerly flow through the lower 200 mb of the atmosphere. The wind we experience today will calm down into the overnight. Saturday temperatures will rebound a bit, ahead of the next weak front. The front will move through Saturday night bringing with it rain showers to low elevations and snow showers to higher elevations. Sunday will feature the rapid approach of a more potent frontal boundary. This one will come with strong wind, light snow and snow showers, and a significantly more chilly air mass.

 

Long Term:

 

Sunday night's front will bring but a glancing blow of cold air. With some sun out on Monday, ttemperatureswill like climb into the 30's in the southern two thirds of the state. A significant amount of cloud cover will occur as the cold air rapidly retreats Monday night, giving way to a much warmer day on Tuesday. The pattern on Tuesday almost looks like a summer pattern with a Bermuda type high parked out over the Atlantic. The flow will blast in from the South driving the temperatures into the 50's across much of the commonwealth. Temperatures might even approach 60 if the sun comes out in the warmer parts of the state. With a storm system making its way well to our north, things will stay warm into the middle of next week, though there might again, be a bout of showers and rain.

 by Joshua Glazer

Wed Night Discussion

Synopsis: A Storm system developing in the lower mississippi valley will move northeastward overnight tonigh and provide the states weather for the next couple of days. As the low pressure departs from the finger lakes of New York on friday, much colder, but nicer conditions can be expected for the weekend and beyond.

 

Short Term: A light wintry mix will spread across the state tonight, as moisture continues to extend out in front of the developing system in the mississippi valley. As the low approaches tomorrow, a steady light-to-moderate rainfall will occur statewide. Rainfall of approxiamately a half of an inch to three quarters of an inch are expected into friday. The low will make a line for the finger lakes of new york, and then scurry off towards the coast. As it does so, it will pass a cold front through the region.

 

Long Term: Much cooler conditions are expected for the weekend in the wake of the previous storm. A short wave will carve out a deep trough on Saturday, allowing for snow showers to spread across the region. Accumulation is possible in the lake effect prone areas. Temperatures will decrease to below normal for the second half of the weekend and beyond.

Wednesday Afternoon Technical Discussion

Synopsis:

High pressure exits tonight as a warm front moves through the State from SW to NE overnight, resulting in a mixed bag of precipitation (light in intensity overall) changing to all rain early tomorrow morning. The cold front moves through the Commonwealth tomorrow night into Friday, with temperatures dropping during the day. Isolated rain or snow showers are possible early as the system exits. High pressure builds in behind it; then, the high heads offshore to the south and east keeping that part of the state dry while lake effect snow and a clipper system affect the northern and western portions of PA on Saturday and Sunday respectively.

Models Used: 12Z NAM & GFS; 15Z SREF Plumes and Prob. Charts; Raw temp. outputs and MOS

Short-term:

Over the past six hours, a stationary front has formed in an inverted trough - stretching from the same low pressure system that is affecting TX and LA to southern PA. A vort. max is located over Cape Girardeau, MO and the divergence aloft ahead of it will lead to cyclogenesis above Bowling Green, KY... right along the stationary front. The wave will propagate north-northeastward from there thanks to advection, with the warm front to the east and the cold front to the south. As for PA, the 540 line and 850-mb 0-deg.-C isotherm will be located near I-80, allowing a mixed bag to fall as the warm front heads north. he cold front follows on Thursday evening.

Long-range:

SREFs and GFS Model showed two systems affecting northern and western PA during the weekend. Timing will be an issue but precipitation type is all snow.

Temperatures: RAW Data recommended for highs and lows on Thursday and Friday. Use MOS for the rest of the period.

-Jaron Breen

Monday Night Technical Discussion

Synopsis:

 

    The storm system that brought the showers to much of the state of Pennsylvania on Monday is on its way out. Behind it will be a seasonably chilly air mass, cold enough to produce lake effect and lake enhances snow showers on Tuesday. A relatively small and week area of high pressure will move across the state mid-week and as it moves out, warm air will gently begin to ascend over the the cool air mass in place producing clouds and a few showers. As a system passes to our south and a front moves through on Thursday, we'll see a greater chance of showers and rain. How close the storm comes to us is still a matter of some uncertainty, though more recent runs of the models are bring the storm further north with more significant precipitation for the state. By Friday and Saturday thing calm down a bit, though by late Saturday clouds might begin to increase with the approach of a more significant front; one which could spell bigger changes in temperatures for early next week.

 

Short Term:

 

       The temperature today really struggled to get into the 40's in many locations despite the strong southerly flow through a good portion of the lower levels. A part of this could have been due to snow cover on the ground. Presently, a fairly significant inversion across much of the state exists. By Tuesday things should clear out quite a bit with some sunshine, especially further south in the Commonwealth. The only precipitation possible would be relatively light lake effect and lake enhanced showers in the Northwest section and the Laurel Highlands. Wednesday morning might start out quite clear and cold, as high pressure will be moving overhead. However, an overrunning pattern will likely kick in by later in the day on Wednesday, bringing in greater cloudiness and even rain or snow showers.

 

Long Term:

 

     The models have wavered a bit on Thursday's storm. The latest run of the GFS rides a fairly significant, rain making storm system along a north-south oriented frontal boundary. This situation would mean a washout for Thursday afternoon and night, and perhaps even Friday morning in eastern sections. There seems little doubt that things will improve on Friday behind the front with some sunshine and seasonable temperatures. With a westerly flow for the start of the weekend, the arctic air will stay at bay. However, clouds will again increase late Saturday with the approach of the next frontal boundary. the front which moves through late Saturday, into early Sunday will shift the flow to a more northwesterly direction bringing in much colder air for early next week.

by Joshua Glazer

Monday Afternoon Technical Discussion

Synopsis:

A cold front will move through during the wee hours tonight with rain (thundershowers N+W) ending around midnight. High pressure will work its way in for Tuesday night, producing lake-effect snow  as it enters. The high will exit Wednesday evening and a warm front will approach from the south and west bringing rain to the region on Thursday AM. The rain continues on Thursday with an overnight changeover - as the upper-level portion of the cold front moves over PA. The precip. will end from west to east early Friday.

Models used: 15Z SREF Plumes, 12Z NAM & GFS

Short-term:

See SPC Mesoscale Discussion 62 for he convection. Clearing ahead has resulted in marginal istability leading to convective showers producing gusty winds and small hail.

The front moves through from west to east overnight... the clouds dissipating will be the sign that the cold front is moving through. Little change in temps. but its passage causes a drop to the 30s on Wed.

Long-range:

High builds in for Tues and Wed; the front moves through Thursday and Fridau. Ahead of warm front is clouds then rain (sleet mixing in cannot be ruled out during the early AM.). The front will move N&E. the cold front will move through - upper levels will cool below freezing in the western half of PA.

-Jaron Breen

Sunday Afternoon Technical Discussion

Synopsis:

Precip ahead of a warm front tonight: freezing rain. Cold front changes the freezing rain to plain rain on Monday. For Tuesday, AM rain, PM lake effect snow. The lake effect confines itself to Erie after sunset. We then wait under high pressure until a front approaches on Thursday, which could bring rain or snow during the later  part of the week.

Models Used: 15Z SREF, 12Z NAM & GFS

Short term:

NWS Alert: Freezing rain advisory in effect from now until 8 AM tomorrow.

The warm front ahead of the system is upon us.. we're seeing the clouds now. A huge ridge will form from the warm front but the temp. & thickness gradients are small. The cold front will bring those values back to where they currently are, which is 5 PM on the 22nd. Earlier models showed the cold front to be much more powerful but the trend continues to favor the above scenario.

The front exits and lake effect snows form on Tuesday. Normally, the lake effect snow machine is off due to frozen lakes, but until a few weeks ago, temperatures this winter were above average and thus the Lakes haven't frozen over yet.

Long range:

High pressure will quickly build in behind the front then exit on Thursday AM as a mid-latitude cyclone approaches from the west. Precipitation could fall as rain, snow or a mix (Source: NWS's Hazardous Weather Outlook) but it is too early to tell and should be monitored this week.

-Jaron Breen

Friday Morning Technical Discussion

Friday Morning Technical Discussion

 

Synopsis:

                The fast moving clipper system last night dropped an inch or two of snow on parts of the state made its way out fairly quickly last night and in its wake high pressure is moving in, setting up our next storm system tonight. Tonight's storm will bring widespread wintry mix to and snow across the state, but will move through relatively quickly. Things will clear out behind it for the start of the weekend, but warmer air, showers and rain will begin to make their way in Sunday into Monday as a relatively strong cold front approaches from the West. The front will move through the state quickly on Monday, bringing a bout of heavy rain and perhaps even a rumble of thunder in spots. By Tuesday, things will become mellow as a chilly high pressure system scoot to our North.  No significant weather appears until late next week when a storm system f! rom the gulf region might makes its way north.

Short Term:

                The clipper system that moved through last night, might be most significant not in its actual initial impacts, but in how it has set up tonight's storm. The clipper was essentially an elongated frontal boundary with waves of energy along it. Behind the clipper a relatively small, but very chilly high pressure system has made its way in. As the surface high drifts to the east, it will maintain a cold north and northeasterly flow on the surface across much of the state. Tonight, as a relatively weak area of low pressure makes its way east and north, snow will break out in the cold air dammed up against and in-between the mountain ridges of Pennsylvania.  A relatively strong low level jet stream out of the south tonight will have two signif! icant impacts. First of all, it will produce a heavy pocket of precipitation northeast of the storm center. Second, it will bring in enough warm air aloft to change the precipitation to sleet and freezing rain across a good portion of the southern half of the state. Snow accumulations will likely surpass 6 inches in a swath through the center of the state and decrease north and south due to either mixed precipitation or changes in proximity to the storm. The precipitation will exit the state entirely by tomorrow afternoon and by Sunday morning, with snow and ice covering a good portion of Pennsylvania, temperatures will plunge into the teens and perhaps single digits in colder spots by Sunday morning.  Temperatures will begin their rebound on Sunday with considerable cloudiness and rain or snow showers, as a storm system begins to make its way toward the great lakes.

Long term:

              The start of the work week will feature a considerable warm up as a strong southerly flow sets up ahead of the next cold front. As the front passes on Monday, there will likely be a period of considerably heavy rain.  Though CAPE values will remain relatively low, it's not inconceivable that the front comes with a rumble of thunder or two as temperatures will be fairly warm ahead of it (perhaps approaching 50°). With the passage of the front and storm system on Monday things will become breezy on Monday night, but not tremendously cold, by any mean. Behind the front will be seasonable conditions for the early and middle part of next week as the core of the arctic air will remain locked over Eastern Canada. The middle of next week also features the! potential for a weak easterly flow to set up. While it might not produce a whole lot of rain or snow, it could bring cloudier condition than one might initially expect.

 byJoshua Glazer

Thursday Evening Technical Discussion

Synopsis:

Behind this clipper system, a cold front will move through the region tonight. An area of high pressure will make a return to the area during the day on Friday before another area of low pressure brings mixed precipitation to start the weekend.  Following this low pressure system, ridging will build in on Sunday into Monday before another disturbance approaches the area on Tuesday bringing the chance of precipitation.

Short-term:

Snow has begun to taper off over most of the forecast area. Some light snow will linger on over the eastern parts of PA. With clear skies, light winds, and surface snow cover, temperatures tonight will likely fall below MOS values. On Friday, clouds will be on the increase as a low pressure system approaches the area. Snow will begin across the area in evening and steadily increase through the overnight hours. Most of the SREF plumes agree that this storm will be relatively fast which should keep snow amounts done. There seems to be a model consensus of a2-4 inches across most of the northern half of PA. There is also the chance for some sleet to mix in over some places further south.

Long-term:

Once this low pressure moves out, there is the chance for scattered rain/snow showers during Sunday night. These showers will dissipate on Monday and some ridging could build in before another low pressure system approaches the area on Tuesday. This is far out so will just include a chance of precipitation late in the forecast period.

Technical Discussion

Synopsis:

Three disturbances will move through the region during the forecast period.

Short-term:

Radar reflectivities are preceding surface snowfall reports this evening. Sporadic reports of moderate snow have appeared in OH and IN from earlier today. We are maintaining the view of generally light accumulations and for only a several hour event.

For especially northern and central PA, low temperatures tonight will likely fall below MOS values, with clear skies, abnormally light winds, and surface snow cover are expected after the fro-pa. The behavior of the SREF plumes helps confirm this possibility as several members drop well below the consensus. There is a similar setup for bottoming-out temps on Saturday night.

Long-term:

Both the WRF and GFS have scattered rain/snow showers appearing Sunday night well ahead of the approaching storm from the west. The 18Z WRF has a weak closed low near the Delmarva peninsula. Would recommend weak language towards this possibility until a more coherent structure appears in later model runs, or at least until the forecast lead time diminishes.

Wed Night Shift

Synopsis: A weakening clipper system will approach the area tomorrow, spreading snow showers across much of the state. That will depart quickly tomorrow night, giving way to high pressure for Friday. The next chance at precipitation will come on Saturday, with an approaching system from the west. This storm will be warmer and will have more moisture to work with.

 

Short Term: Mid to upper level clouds will continue to increase overnight tonight and into tomorrow morning. A cold front associated with a surface low pressure in Canada will swiftly sweep through the region, west to east, through the day. It will be moisture starved however. Western zones may see upwards of 4 inches due to a very cold layer of air at the 850mb level, giving high water to snow ratios. It should also be noted that northern zones may see some breezy conditions. As the clipper moves south and west totals will likely decrease to a dusting or less from State College to points south and east. Clearing will occur through Thursday night as an area of high pressure approaches on Friday, keeping conditions dry and tranquil.

 

Long Term: A larger and more complex system will approach the area late Friday night into Saturday. Model guidance agrees on the timing and the amount of moisture associated with this system, but the precipitation type remains in question. 00z NAM shows a region of light snow develop across the state with a passing warm front from a system developing in the Ohio Valley. This snow would then change to a sleet and freezing rain mix as temperatures remain well below freezing at the surface, but a layer of warm air slides in at 850mb. 00 GFS wants to keep it a mainly snow event in all points north of Altoona. If this solution is correct, there could be some minor to major accumulations. In either case, this system will bring some wintry precipitation, and will move out for Sunday.

--
Paul Svenson

Wednesday Afternoon Technical Discussion

Synopsis:

High pressure will be in control until Thursday evening. A clipper system (currently located in the Dakotas moving to the ENE) will move through on Thursday night producing snow. High pressure will move through on Friday while a Low approaches from the Southwest. The low will affect our area on Friday night and exit within a day. Snow will fall on the entire State at first, but for areas south of I-80 (especially along and S of the Turnpike), the snow won't last long. After the system exits on Sunday, skies look to remain mostly cloudy as we wait for a cold front to move through.

Models Used: 15Z SREF; 12Z NAM, GFS & European

Short-term (Wed. Night through Friday AM):

The GFS and NAM are consistent: A mix of clouds and sun for Thursday; PA gets about an inch of snow overnight Thursday into Friday; and skies are mostly cloudy between the clipper system & Saturday's snow.

Possible differences in amounts: (1) the high-res. NAM shows a snow squall affecting central PA and (2) the low's track is to the north.

Mid-range (Friday evening through Saturday afternoon):

The positions of the 540-line & 850-mb 0°C isotherm coincide but each model places those lines differently. The European model and half the SREFs place the line in Nrn PA while the GFS, NAM and the other half of the SREFs place it in Srn PA.

Here are the consistencies: (1) Large temperature gradient; (2) temperature affected by positions of High pressure over the Western Lakes & Low pressure S of the Mason-Dixon line; (3) All snow to start; (4) Northern PA and the mountains remain snowy; (5) Central PA's valleys see a changeover to sleet/ freezing rain Sat. AM; (6) Southern PA (especially near Pittsburgh and Philadelphia) see a changeover to rain during the wee hours Saturday; AND (7) wintry precipitation that occasionally mixes in cannot be ruled out. This is subject to extreme changes at times.

Long-range (2^nd half of the weekend into early next week):

A cold front will affect PA during this period.

---------------------------------

GOOD LUCK forecasting Friday night's storm.

-Jaron Breen

Tuesday Midday

Synopsis:  A storm system running NW and parallel to the Ohio River Valley will be passing to our NW today.  Southwest/South air flow will be flowing up into the state, making it possibly the warmest day of the week.  The associated cold front will push through, bringing the state back to winter for the rest of the week.  Wednesday will be a calm day, before a clipper system runs through the state Thursday Evening.  Friday will be a transitional day as we await a possible storm system that looks to run parallel with I76, meaning a wintry mix for much of the state Friday night into Saturday.

Short-term:  Everyone in the state is at or above freezing and should warm up into the upper 30's, lower to mid-40's today, before the current cold front pushes through.  Breezy conditions will pick up across the state as the storm system leaves the states and enters into Canada, with the NW wind behind the front, lake effect is also a concern for the Erie area.  They are currently under a Lake Effect Snow Watch until Wednesday Afternoon.  Wednesday for the rest of the state should be periods of clouds and sun as we have lake-effect clouds push their way southeast.

Long-term:  Clouds will increase on Thursday as a clipper system makes its way towards us.  This time, we have cold air in place, hence this clipper system will be mainly an all snow event for the state.  The problem becomes, does the clipper system loose energy crossing the state, as the NAM & GFS suggest?  Even the SREF losses some of the clipper's energy.  Either way, we went with a period of light snow with minor accumulations at best for Thursday overnight into Friday for the state.  Friday we clear out some, before the clouds work back in as a shortwave rumbles through the area Friday night into Saturday.  At the current time the Low looks to travel along I76, which would leave rest of the state under a wintry mix, as we will have the 850mb 0c and 540mb markers within the state at this time.  Also the gradient between the 540 and 570mb is very small, compared to the 540 and 510mb.

Kept temperatures near previous shift, with minor changes.

--
Tyler B. Roys

The Pennsylvania State University

Meteorology Class of 2012

tech disco 1-16-2012

Afternoon Technical Discussion 1-16-2012

Synopsis             

This week will mainly feature just a single threat for messy, wintry weather as a low pressure cell starts to trudge across the nation. Tuesday will be the wet day of the week with the bulk of the state seeing rain for the bulk of the afternoon with clearing starting to occur overnight. Afterwards, the will be a calmer scene Wednesday with just some hinting at snow for Thursday, but the main concentration of our forecast will be settled on rain for Tuesday, a cold yet pretty Wednesday, and a less worryful threat of snow for Thursday with a cold start to the weekend.

Short Term (Tonight through Wednesday night)

With showers already crossing through the western half of the state, there will be scattered showers across the central and eastern thirds of PA this evening and overnight tonight. The 12 and 18z NAM runs have precip falling within the areas where rain already exists, whereas the GFS has nothing anywhere. This gives me better confidence in the NAM's solution to the events occurring within the next 48 hours. With a low pressure cell beginning to strengthen and progress our way, it will bring some scattered rain showers for the morning and afternoon hours on Tuesday, and with warm advection occurring within the region with precipitation. Tomorrow will be a rain event, with the only chances of a wintry mix occurring along the ridges and plateaus. The rain event will be brief through this period however, for the low will quickly occlude and form a dryslot, which will help break the "comma" down into a northern sector, which will send the longer-lasting showers along the northern half of PA, and a southern portionwill dissipate into the southeastern U.S. This dryslot will quickly clear out the state overnight Tuesday, bringing with it post-frontal cold advection and frigid nighttime wind chills. With a tight pressure gradient prevalent throughout Tuesday and early Wednesday, there will be plenty of wind blowing accompanied by some bitter wind chills. The GFS also hints at lingering lake effect snow for overnight Tuesday, but anything that falls will be light and nothing to really worry about. The dryslot's main role will be opening up an area for high pressure to filter in, helping to calm the winds down and clear the sky for sunshine to dominate. This high will remain settled in the night, causing frigid overnight lows in the lower 20s statewide, with spots in the northeast and mountain valleys dipping into the teens.

Long Term (Thursday and Friday)

With the high beginning to make a quick exit, warm advection ahead of a weak cold front will make Thursday a cool, cloudy day. The NAM and GFS have pretty much the same idea of afternoon clouds billowing overhead, and both show a small section of flurries over the northwestern area of the state.  This will generally be the result of weak convergence and thermal lift over the Great Lakes, and both models have the system too far north, leaving Erie and cities along the northern border too see any snow from this system. A weak cold front will also come into play overnight Thursday, leaving the state with another frigid night and a cold start to the weekend. Highs for these days will not depart too far from the freezing mark, with the warmest spots in the southern half seeing highs in the mid 30s for Thursday and Friday, and lows dipping into the teens.

Written by Steve Engblom