Thursday Afternoon Discussion

Synopsis:  Low pressure continues to linger in the northeastern CONUS but over the course of the next few days it will gradually move out to sea.  Until then, scattered snow showers are likely across the central and western half of the state as a northerly flow advects lake effect snow showers into the commonwealth.  A gradual drying will occur as the weekend approaches and into early next week as high pressure settles in.

Short Term:  Light snow showers will continue through the next couple of days across much of the northern and western portion of the state.  A northwesterly and northerly flow will allow lake effect snow showers and clouds to filter in impacting the favorable snow belt regions of the northwest.  Light accumulations are possible.  The rest of the state will remain dry with a slight chance of a few flurries here and there. Not much change for temperatures over the course of the next few days as a northerly flow will keep them below average.  However, no cold spells are expected. 

Long Term:  The lingering low will be gone by next week and the state will dry out for a few days.  High pressure will settle in and will allow for some clearing across the state, allowing for sunshine on starting on Monday and lasting through the majority of next week.  Temperatures will begin to rise through mid week as a ridge develops over the eastern CONUS advecting warmer air into the area.

Thursday Morning Discussion

Thurdays Morning Discussion

Synopsis:  We are currently experience a bit of of unsettled weather in the form of scattered snow showers across the commonwealth.  We should expect this unsettled weather to continue until early Saturday.  After Saturday, it appears that skies will remain cloudy for the rest of the forecast period.  We can also expect temperatures to remain at of above normal for the next week or so with no major storms in sight.

Short Term:  The scattered snow showers that we are experiencing this morning are due to an upper level low associated with the storm system that came across the region yesterday.  Temperatures will be seasonal to a little below average, in the upper 30s for the next couple of days.  Snow and/or rain showers will also be possible at anytime over the course of the next couple days.  The snow and/pr rain showers will become less numerous as we head into tomorrow.

Long Term:  In the long range it seems as though the weather will remain fairly quiet.  From Saturday onward temperatures will remain fairly steady with highs around 40 and lows in the upper 20s to around 30.  The only possible threat of storm system exists around the fifth or sixth of March.  This is still very far out but definitely something for us to keep an eye on.

Monday Night Technical Discussion

Synopsis

 

As high pressure exits the state to the northeast tonight, a low pressure system will begin to approach the state Tuesday morning.  Southeasterly flow ahead of the precipitation will bring warmer air into the region and result in rain showers across western Pennsylvania while precipitation begins as a wintry mix across the rest of the state. Expect it to quickly change to rain across eastern Pennsylvania Tuesday afternoon while cold air damming keeps enough cold air across central & northern Pennsylvania to remain a mix of snow, sleet, and freezing rain. Higher elevations of the Laurel Highland should also remain a mix of snow and freezing rain. Precipitation will change over to scattered snow and rain showers Wednesday morning as precipitation moves off to the northeast Wednesday afternoon. Scattered snow showers will spread across the state late Wednesday night through Friday morning, as the low pressure system slowly crosses the state. Arctic air will then make its way into the state behind the exiting system as a mean northerly flow will persist for the weekend producing scattered lake effect snow showers.

 

Short Term (Monday Night thru Wednesday Afternoon)  

 

High pressure currently sitting over the region will move toward Maine tonight. Clouds will slowly make their way into the state as a strong low pressure system to the southwest approaches. A southeasterly flow will escort warmer air into the area as rain begins to fall in extreme southwestern counties by about 16Z Tuesday according to both 18Z NAM and GFS. Precipitation could start out as snow Tuesday afternoon for central and northern portions of the state, but then change to a mix of snow, sleet, and freezing rain to the north and for higher elevations, and rain mixed with some snow elsewhere. Precipitation will be falling statewide by 00Z Wednesday. The majority of the precipitation will fall ahead of the warm front. The models split the low pressure system into two separate centers of low pressure due to cold air damming. One center of low pressure appears to develop off the coast and produce heavy rain for southeastern PA late Tuesday night. The other low pressure remains stationary over western Ohio during the day Wednesday. The inland low pressure should remain dominate through Wednesday as it pushes east through northern Pennsylvania and eventually off the New England coast.

 

Long Term (Wednesday Night into the Weekend)

 

Wednesday night will bring colder air as the cold front continues to make its way east. The inland low pressure will slowly make its way across the state from west to east along with scattered snow showers Wednesday night through Friday morning. The heaviest snowfalls will occur in western portions of the state due to lake effect snow persisting through Friday night due to a mean northerly wind from the wraparound of the low pressure sitting off the coast according to the 18Z GFS.  A deep trough will develop for the weekend bringing cold air and a northerly flow allowing for a chance for scattered lake effect snow showers for the weekend, especially across the western half of the state. 

~AJ Herbert

Monday PM Disco- Wednesday Nighrt Washout!

Synopsis

High pressure sitting atop the state will slide out tomorrow as an intensifying cyclone approaches. Gusty warming winds will lead the precipitation, which will hit as rain overnight Tuesday, and will persist as the upper level low remains stagnant over the Northeast.  Rain will turn to light snow after a brief break Wednesday afternoon, and then light snow will persist into Friday, leaving for a rather damp and dreary week. Beyond this, a strong trough aloft will help escort a rush of cold Canadian air for the weekend.  

Short Term (Monday Night Into Wednesday Afternoon)

High pressure sitting atop the Northeast will progressively slide toward Nova Scotia as overnight tonight, leaving for partial cloud cover in the late night to Tuesday morning hours. A strong cyclone (TWC's  Rocky) over the south central Pains will continue to intensify as the upper level cutoff makes a beeline toward the Northeast. A strong pressure gradient will develop over the state by 21z Tuesday, and rain will begin to fall in SW PA shortly before 18z Tuesday (with surprisingly a strong consensus from the 12z NAM, GFS, and Euro), then will completely engulf the state by 0z Wednesday.  The bulk of the rain will fall primarily ahead of the occluded front that the models are trying to develop , and by 12z Wednesday, the models all show the upper level low sitting atop the surface low, hinting at a decay of the surface low. The issue here is the models split the surface low into two, with the Appalachian axis serving as the bisector.  The east low appears to develop newly out of the west low, and it rapidly strengthens to precipitate heavily over SE PA, leaving room for flooding of local streams and creeks. The 540-dam line doesn't  move too much during the day, leaving the bulk of the heavy precip ahead of the surface low as rain.  

Long Term (Wednesday Night into the Weekend)

Upon nightfall, Wednesday will begin to feel the transition to a colder pattern as the weakened west low slowly moves northeast. The upper level low will remain stagnant for Wednesday and Thursday, sporadically developing isolated snow showers in and around the state. The heaviest of the snow showers will stay off to the west, but the 12z NAM spits out a stronger isolated snow cell over Harrisburg and Philly, which could lead to a burst of 3 to 4 inches of snow around these parts around 6z Thursday in a few hours (check the 4km NAM when made available) beyond this, the GFS and Euro decay the upper level low, but hint at north wind induced lake effect snow for western areas Thursday into overnight Friday, which could also be linked to a strengthening shortwave over these parts. Looking toward the weekend, the 12z Euro and GFS develop a very deep trough, and despite the GFSX MOS only dipping high temp locally into a 3 to 5 day below normal zone,  but with such low anomalous 500mb heights, look to see those MOS values drop as the week rolls along, for as of right now, the GFS implies light snow showers falling in north central Florida.

Sun. Eve - Rain & Snow Mix

Synopsis:

High pressure heads east Monday as a mid-latitude cyclone organizing in the Southern Plains, will arrive on Tuesday into Wednesday. The upper-level low will stall over the Commonwealth for the end of the week into the weekend.

Models Used: 12z ECMWF, 18z GFS, 18z & 00z NAM, 00z Hi-Res NAM

Short-Term:

According to the HPC Model Diagnostic Discussion, the Euro & GFS were handling the timing and track of the low pressure system well, with the NAM also doing reasonably well. With highs expected to be in the upper 30s and lower 40s, most of the precipitation will be rain with wet snow mixing in. For the Laurel Highlands, according to the NWS discussion, with morning surface temperatures struggling to pass the freezing mark, a period of freezing rain cannot be ruled out.

Based on Hi-Res NAM guidance, there will be a period of windy conditions as the precipitation winds down on Wed. night into Thursday. Given its short duration, we did not include it in the General Discussion but did put it in the zone forecasts.

Long-Term:

The upper-level low will likely stall over the Commonwealth, bringing rain and wet snow to the western half of the state for the end of the week into the weekend.

-Jaron Breen

Synopsis:

A disturbance will move through starting tomorrow and will bring a wintry mix across much of the state.  Freezing rain, sleet, and a rain/snow mix is likely through Saturday afternoon before changing to all rain and departing in the evening.  A brief lull in the action will occur Sunday and into Monday before another disturbance moves through Tuesday with more wintry mix conditions.

Short Term:

A ridge of high pressure is beginning to move into the region.  Much of the state has cleared out with only a few lake enhanced clouds in the northwestern portion of the commonwealth.  Those will dissipate as the evening progresses.  Clouds will increase overnight out ahead of our next disturbance.  Precipitation is expected to move into the western portion of the state late morning tomorrow and early afternoon elsewhere.  Snow will likely fall first before a transition to sleet and freezing rain occurs.  Many surfaces will likely stay below freezing for much of the morning and afternoon.  A warm layer above 850mb seems likely for much of the western and central states which will allow for precipitation to melt and force freezing rain to occur. This icy mixed precipitation will likely last through Saturday morning before the system departs.  

Long Term:

A few flurries are expected for Sunday in the NW PA, but the rest of the state should remain dry.  Some sun is likely as well and it should be a decent day.  Monday is also looking nice with plenty of sun across the commonwealth and WAA out ahead of our next system will allow temperatures to hit the 40s.  That system moves in Tuesday, although the Euro and GFS are in disagreement with timing.  The GFS is much faster and has it moving in overnight Monday while the Euro has it Tuesday night.  Leaning towards the Euro solution at this time but we'll see. Either way, more wintry mix is likely at some point in the middle of the week. Temperatures remain consistent through the week with no large cold spells in view. 

Thursday Morning Forecast

Synopsis:

We should expect below average temperatures across the commonwealth this morning with scattered flurries this morning. The weather will then become very unsettled after today. Tomorrow will feature a mix of rain, snow, sleet, and freezing rain moving in after noon and continuing throughout day. Another impulse and rain and or snow may come through on Sunday, although there remains a lot of uncertainty with this storm system. In the longer range, temperatures look to remain at or just below normal with a storm system coming through every few days.

Short Term:

A strong ridge over the region will keep our skies partly clear through the rest of Thursday. This ridge will begin to break down, though, as the remnants of the storm that blasted the Plains moves into our region. Current NAM runs show QPF totals no higher than half an inch across the commonwealth with precipitation moving into the region around 15Z Friday morning. 

Long Term:

GFS, NAM, and ECMWF are in strong agreement with the formation of a decent New England snowstorm on Saturday. The remnants of the Plains storm that affected our region is forecast to merge with a disturbance swinging up from the Gulf. These two systems will combine early Sunday morning off of Cape Cod and may dump a foot of snow in eastern MA and southern NH. Thankfully, though, other than a few snow showers in eastern PA (with 2-3 inches of accumulations), the commonwealth won't see much of the combined system. Expect a cold, cloudy weekend across PA and some scattered lake-effect snow showers on Monday once the storm scoots out to sea.

Monday Night Technical Discussion

Synopsis

 

A mean southerly flow will dominate tonight, allowing temperatures to warm up near the surface ahead of the cold front Tuesday morning. Rain and snow showers ahead of a cold front will affect the state Tuesday. The cold front will cause temperatures to plummet and set up conditions favorable for significant lake effect snow for northwestern Pennsylvania. A stronger system could bring some wintry precipitation later in the week as a storm moves across the nation and strengthens along the southeast coast Friday night.  

 

Short Term (Monday Night thru Tuesday Night)

 

The state will experience warm conditions, as southerly flow ahead of the cold front will produce a warm surface layer Tuesday Morning. Areas of central Pennsylvania will see warming aloft but cold air damming will cause surface temperatures to remain cold for several hours. The cold front should enter the state close to 09Z and make its way east, as mixed precipitation at the leading edge of the front will fall statewide.  The 18Z GFS and NAM agree with precipitation beginning to fall for western PA around 09Z. The 18Z GFS has the precipitation associated with the cold front exiting eastern portions of the state by 01Z, but the 18Z NAM has the precipitation lingering in the east until 04Z. The precipitation will begin to fall as rain in the west and quickly mix and transition to snow within the first two hours of precipitation. This mix should spread across the state through the morning before changing to rain during the afternoon, especially across southern Pennsylvania. Portions of central and northern Pennsylvania could see light snow and ice accumulations before the changeover Tuesday afternoon. Later Tuesday evening, the cold front will wrap in much colder air changing any remaining rain showers to snow showers. As the snow showers exit the state to the east, a westerly flow and cold air advection will begin to produce lake effect snow showers for northwestern counties late Tuesday night.

 

Long Term (Wednesday thru the weekend)

 

Westerly flow will slowly change to northwesterly flow, creating a large fetch over Lake Erie. The large fetch and cold air advection will help produce significant lake effect snow throughout the day Wednesday and Thursday morning for northwestern PA. Extreme northwestern counties could see as much as 3" of additional snow, with light accumulations possible as far southeast as Centre County. A strong mean northerly flow will persist through Thursday keeping temperatures cold, but warm air associated with a weak system approaching from the south will move in with a chance for a few rain or snow showers across the state Friday night according to the 18Z GFS. As the showers associated with the weak system dissipate early Saturday morning, the 18Z GFS indicates a Miller Type B storm situation may form and produce a coastal low that could bring mixed precipitation across the sate Saturday.

~Aaron Herbert 

Monday Afternoon Disco Dango 2-18-2013

Synopsis

With mild air approaching, tonight will not be as much as a deep freeze as last night, but a freeze is in store for us overnight tonight. Tomorrow, things will get messy as rain showers will lead snow showers in their west to east progression. A cold front will begin to wreak havoc, producing single digit wind chills in parts across the state, and another potent lake-effect setup will occur Tuesday through Thursday across the northwestern counties. Beyond this, another system looks to bring some light rain into the southern border areas, yet it looks to far south to be impactful as the weekend fun begins!

Short Term (Monday Afternoon through Tuesday)

Looking at the surface, a dominant warm conveyor belt will be in action as day turns to night over PA. This will not prevent temps from dropping into the 20s, yet it will be warm enough to setup a warm surface layer ahead of the cold front looking to pass through starting Tuesday morning. Starting around 9 to 10z tonight (early Tue morning), mixed precip showers will progress around Pittsburgh, with a quick progression through the state, reaching State College by 15 to 16z, then hitting Philly by 19 to 20z, and completely exiting by about 4z Wednesday(for lingering showers in Scranton, out of Philly by 0z) The entrainment of warm air at the surface layer should allow for rain to fall for an hour or two before mixing with and turning to snow. Most places will see persistent precip for about 4 to 6 hours. The swift movement of the front is attributed to strong winds along the frontal boundary as well as the distance from its central low.  All this was derived from the 12z NAM, but the 12z GFS and 15z SREF do not differ much from this solution. Strong winds within the system will work with the rapic cold advection to produce single-digit/near-zero wind chills statewide, yet it will be more bitter with the wind chills Wednesday, but Tuesday, the wind will indeed be noticed.

Long Term (Wednesday to Friday)

A west-northwest wind stacked throughout the 1000mb to 700mb layer will provide a juicy fetch across Lake Erie. This fetch will setup lake effect snow for the bulk of the Tuesday to Thursday period. The northwest counties will get hit the hardest, with 15z SREF means around 5 inches at the end of the week, yet snowfall rates will remain consistent at about 1" per 12 hours, at least at the Erie station.  Areas further away will see at most 3" from this event, yet the strong winds in the layer will attempt to oscillate over the ridges to carry snow showers all the way to Centre and Huntingdon counties. Strong winds with this system overall will produce teen-regime wind chills, especially when the ridge for Thursday creeps in. Northwesterly flow will remain in control Thursday, keeping things cold with colder wind chills, but Friday starts a mild boost where light rain showers could fall along the southern counties, as implied by the 12z GFS. Keep an eye on this, forit appears that the shortwave aloft controlling the development of this cell will retract north, giving us potential for a little more than just showers going into the weekend.

Sun. Eve - A Wild Week

Synopsis

High pressure to our south slides eastward as a fast-moving yet strengthening Mid-Latitude cyclone now over the Rockies threatens on Tuesday. Arriving in western PA around daybreak and leaving eastern PA around midnight, precipitation type is a tough question since the rain-snow-and-mix lines converge over the state. Behind the front, the winds will pick up and lake effect snows will bombard the western parts of the Commonwealth on Wednesday. For Thursday, the sun will come out, but the high pressure system that will provide the sinking air is in west-central Canada. Another system will clip the state from the south, heading east/ east-northeast for the weekend with wintry precipitation possible, heaviest near the PA-MD border.

Models Used: 00z & 18Z NAM, GFS, & Hi-RES NAM, 12Z ECMWF, 21Z SREF

Early Week

Models over the weekend have been consistent between each other and between runs. The question is where exactly to place the precipitation type. Forecast soundings showed that the layer between the surface and 900 mb are isothermal very close to the 0°C line with colder air above the 850-mb level. Southern PA and the northeast zone will see rain and wet snow with some freezing drizzle. Central PA will see snow, sleet and freezing drizzle and the rest of the state sees all snow. The Hi-Res model has been the most helpful, but the hour-by-hour guidance for the entire storm won't be available on the eWall until Monday's 12Z or 18Z runs. The winds pick up overnight.

Mid-Week

Wednesday – The Hi-Res NAM & 12-km NAM have been the most helpful with both wind and lake-effect snows. As for wind shear, it won't become favorable for lake-effect snows until the morning hours. The fetch will be long (some energy from Lake Michigan) but short-lived. The fetch off Lake Erie will be enough to sustain long bands of heavy snow in the northwest and north-central zones. With the winds, getting snow to accumulate to a dusting in State College and Altoona (two cities past the Allegheny Ridge) is not too tough a task. With the fetch off of Lake Michigan, accumulations near Johnstown are not out of the question. The instability is enhanced by the long-wave trough expected to pass over the Lakes around the same time.

Thursday – The high pressure over Central Canada I alluded to in my synopsis will become elongated.

End of Week

The 850-mb 0°C isotherm will be just north of the Mason-Dixon Line. The GFS places the heavier precipitation in extreme southern PA.

-Jaron Breen