Thursday Evening Technical Discussion

Synopsis

Currently, the high pressure system will move off the coast tonight and make way for a cold front located over the Great lakes. As this cold front associated with upper-level trough approaches the area on Friday, there will be the chance for lake-effect snow showers in northwest PA. Behind this front, another area of high pressure will move into area on Saturday. This area of high pressure will dominate the area and provide nice weather through early next week.

Short Term

Clouds have rolled in during the evening and have to put an end to temperatures falling much tonight into Friday morning. As this upper-level trough moves through on Friday, a cold front will pass by and skies will remain partly cloudy. Westerly flow will allow for lake-effect snow bands to set up near Erie and other areas in northwestern PA Friday afternoon into the evening. Once this trough progresses by, 850 mb temperatures will fall to -12 to -14 C. This will result in daytime highs being below normal on Saturday. As high pressure builds in Saturday evening, temperatures will plummet with clear skies and calm winds.

Long Term

This area of high pressure will dominate the weather from Sunday through Tuesday. Daytime highs will be near normal and lows around average due to prime radiating conditions at night. Late in the period, a cold front is possible on Wednesday as an area of low pressure moves through southern Canada.

Wednesday Evening

Synopsis: A low pressure system off the coast will strengthen and move northeast overnight as an accompanying upper level trough pushes eastward across the Mid-Atlantic. All precipitation should cease across the state overnight. High pressure will build into the region creating a dominate westerly flow. A weak shortwave will push across the mid-atlantic Friday Night, followed by a stronger high pressure system. High pressure will then dominate the forecast until the middle of next week.

 

Short-term: Snow and rain showers should end across eastern Pennsylvania overnight as the strengthening low pressure system move's northeast. As a westerly flow sets into place, mostly sunny skies and breezy conditions will impact the region. Westerly winds will blow across Lake Eerie throughout the end of the week producing lake effect snows in the northwestern portions of the state. A weak cold front will push across the Mid-Atlantic, leaving colder temperatures in it's wake on Saturday. Little moisture should be associated with this trough, besides amplified lake effect snow.

 

Long-term: A strong high pressure will build into the Mid-Atlantic bringing clear, calm, and milder conditions into next week. Temperatures will finally be near average next week. The next chance of precipitation comes late next week.

 

Wednesday Midday

Synopsis:  A slow moving cold front has passed through, temperatures have already reached a maximum for Wednesday, as the last part of the "train of moisture" makes its way up the coast today and into tonight.  The very last part should transition to snow as the cold air finally makes its way into the region.  After that high pressure works in for the rest of the forecast, with the chance of morning snow showers in the West Friday Morning.

Short-term:  High temperatures for the state have already occurred with the passing of the front already.  Cold air will slowly creep on in during the day.  As this happens, the heavy rain across much of the state will transition to snow.  The timing on the transition for places across the state will be key on when the cold air comes in.  Pittsburgh looks to transition to snow mid-afternoon, based off of the 12z SKEW-T.  State College looks to transition to snow around 0z based off of the NAM and GFS 0Z forecast SKEW-T.  Scranton transitions later in the evening, around 2z, once again based off of the SKEW-T forecasts.  The question of whether Philly sees snow or not depends on if the cold air reaches the city before the precipitation leaves the region.  Right now the best accumulation of Philly is a coating.  The valleys in SW, Central, and NE PA will see minor accumulations, with higher terrain seeing moderate accumulation.  All snow should be gone by dawn, then we clear out to partly sunny skies for Thursday as a minor high pressure works in for the day.

Long-term:  A deep trough will move through the state late Thursday into Friday, the only system that is on associated this trough is very weak, providing scattered snow showers at best.  Scattered snow showers will be in the forecast for the West and North Central regions of the state Friday Morning, before coming partly cloudy.  High pressure rolls on in from the NW for the weekend.  We remain below the 540dm line and the 0C 850mb temp line, so a cold weekend is on tap.

Kept temperatures near previous shift, with minor changes.

12-6-2011 Technical Discussion

Technical Discussion

Synopsis:

                A series of low pressure systems will develop along a lingering stationary front running across from the Northeast States to Gulf of Mexico. A final low, the strongest, will bring periods of rain and snow to much of the Commonwealth Wednesday night. The low pressure system will slowly intensify as it slides up along the eastern seaboard on Thursday, leaving some colder air behind its passage. The weather will remain calm with some isolated lake-effect snows over the extreme northwestern PA. The next cold front is expected to pass the region over the weekend.

Short-term (Tuesday night-Wednesday night)

                A stationary front that has lingered over the Northeast has produced periods of light to moderate rain showers to the State Pennsylvania. This slow moving front will eventually slide southeastward enough so that the region is located on the colder side of the air masses. A very sharp and squeezed 500-mb trough located over the lower Midwest will gradually become negatively tilted. As it does so, it will accelerate westward toward Tennessee Valley and gain curvature vorticity. The positive vorticity advection ahead of the 500-mb shortwave will create a favorable zone for cyclongenesis. With the lingering stationary front extending into that favorable zone for cyclongensis, a series of low pressure systems will develop and slide northeastward along the front. As the 500-mb shortwave a! pproaches the pre-established stationary front, a weak primary low will form late Tuesday night. The low pressure system will slowly intensify as it moves northeastward due to the continuing negative tilting of the upper-level trough and baroclinic instability. To the south of the warm front, the precipitation type will be all rain. However, to the north of the warm front some snow is expected, especially over higher elevations.  This should by no means be a major winter storm as the surface and mid-level temperature profile will be too warm for any substantial snow accumulations. Most of the models, including the GFS, NAM, and European all indicate a rather warm temperature profiles for the region, therefore, only isolated areas will see snowfall more than 4 inches.  The precipitation should be the heaviest Wednesday night, but the quick moving nature of the system will limit the amount! s. In addition, this is not an ideal synoptic setup for a majo! r Northe ast snowstorm since the evolution of the storm does not involve the phasing of troughs and jet streams.

Mid-term (Thursday-Friday)

                A high pressure system will build into the region on Thursday in the wake of the storm. The skies will clear out, but the temperatures across the Commonwealth will remain cold as cold air advects southward. Locations nearby Lake Erie may see isolated snow showers due to cold air passing over the relatively warm lake water.  Any lake-effect snow should quickly come to an end as the winds shift to coming from the southeast later Thursday. Conditions will remain calm on Friday before the next frontal passage on Saturday.

Long-term (Saturday-Sunday)

                A stronger cold front will sweep through the region on Saturday. The temperatures will drop across the region to below normal values for the first time in a while. With a stronger cold air advection and winds, more substantial lake-effect snow bands should set up, giving regions close to the Great Lakes periods of light to moderate snow showers.

D. Wang

Monday Afternoon 12/5 Technical Discussion

Synopsis:

Rain will work its way into Pennsylvania tonight and will remain in place throughout Tuesday. Wednesday will serve as a day of transition to a colder, more seasonable pattern before we see a system move up from the south and bring in some snow showers early Thursday morning.

Short Term:

As of forecast time, there was a stationary front situated to the west of Pennsylvania. Associated with it is a large swath of rain stretching from Louisiana into southern Quebec. The rain is just beginning to enter Pennsylvania from the NW corner, according to radar imagery. While most of the rainfall at the moment is simply streaming SW to NE along the front, the front will get a push from some upper-level forcing, bringing rain to all of PA by tomorrow morning. Tuesday should be rainy day for nearly all Pennsylvanians. It will also be another very mild day, with temperatures in the high 40s to low 50s. By Tuesday evening, the heaviest rainfall will be ending for most regions.

Long Term:

Wednesday will serve as a day of transition to a colder period with more unsettled weather on the way to end off the week. A westerly wind will limit temperatures during the day, keeping many areas below 40 degrees. While there is still uncertainty in the models as to where exactly a surface low will track later into Wednesday and Wednesday night, it appears nearly certain that southern portions of Pennsylvania especially will see some precipitation from this event, much of it in the form of snow, as temperatures should dive below freezing at the surface. The bulk of this precipitation will make its way through, mostly below the I-80 corridor; it appears, overnight, pushing off to the east by Thursday morning. There will be a slight clearing in the wake of the Thursday system; however, it does look like skies will remain mainly cloudy. We're also monitoring a small slug of moisture which looks poised to work its way towards the state late Friday into Saturday, with some portions of western PA likely to see some light lake-effect snow bands. Temperatures will settle back towards normal values by Thursday and should remain there for several days beyond the end of the forecast period.

~Devin Boyer

Sunday Afternoon Technical Discussion

Synopsis:

High pressure is moving out to sea. A cold front will drop rain Mon. night through Wed. A nor'easter is on tap for Thursday AM.

Models Used: 12Z Runs of NAM (HiRes 4 km), GFS, ECMWF; SREF 15Z Plumes

Short-term:

The front dries out after dumping an inch over Erie. Total Rain across the rest of PA0.05 to 0.25 inches. Temps stay near 50 for highs across the Commonwealth until the front crosses on Wed.

Long-Range:

A nor'easter is coming Thursday morning: light, mixed precip at onset during the early morning; rapidly intensifying and changing to snow during the (noting the 850-mb 0°C isotherm is in NJ, and 540-m 1000-500-mb thickness is in SErn PA). Light snow from the wee hrs. Friday into Saturday. The track and timing is still to be determined. It will leave very cold conditions in its wake.

-Jaron Breen

Thursday Evening Technical Discussion

Synopsis

An area of high pressure currently located over the Ohio River Valley will move into northeast. Behind this, a weak cold front will move through the area on Friday. After the front exits, an area of high pressure will build in for the weekend.  Early next week, a very slow moving cold front will approach the area. It will bring the chance for rain and once it passes; there will be colder temperatures with a chance of snow showers near the end of the period.

 Short Term

With high pressure entrenched over the area, this will promote clear skies and calm winds which will allow low temperatures to fall tonight into Friday morning.  During the day on Friday, a weak cold front will move southeastward and may cause northern zones to flurry. Late Friday into Saturday, a 1036 mb high pressure system will build into the area for Saturday and Sunday. Skies should remain clear with light southerly winds with temperatures a little above normal for Saturday and Sunday.

Long Term

Our attention Sunday into Monday will turn to a system over the Midwest that has a cold front associated with it. Before this cold front moves through, Monday looks to feature mostly cloudy skies and temperatures around normal. This cold front will approach our area Monday night but it will stall there. As a result, we will be sitting right on the stalled frontal boundary. This will result in below normal temperatures and the chance for precipitation on Monday night into Tuesday. As a system develops along this, this will result in some enhanced precipitation during Tuesday night into Wednesday. Behind this front, there is the chance for snow showers.