3-1-2011 Technical Discussion

Technical Discussion

Synopsis

The storm system that brought us periods of heavy rain and thunderstorms is currently racing towards the northeast away from the Commonwealth. Expect gradually decreasing clouds Monday night. Tuesday will feature abundant sunshine for majority of the state. The temperatures will be near the seasonal values. Expect more sunshine on Wednesday, though a few clouds may mix in as a weak cold front passes late Wednesday afternoon. We could see some warmer temperatures creeping back into the region on Friday. Expect increasing clouds throughout the first half of the weekend and rain showers for the later half.

Short-term (Tuesday – Wednesday evening) 

A ridge of high pressure building in behind the departing storm will bring calmer weather conditions on Tuesday. Ahead of it, the winds will be coming from the north, which will bring cooler air down south from Canada. The good new is that this fresh shot of cooler air does not look terribly cold. The high temperature for Tuesday will only fall slightly to near seasonal values. Once the high pressure slides off to our east later Tuesday evening, the winds should shift from northerly to westerly; which will allow some warmer air to enter the region. Thus, do not expect a significant drop in temperature Tuesday night. A cold front will sweep through the region Wednesday afternoon. However, this cold front will be moisture starved and will only bring a few passing clouds across the state, especially for the northern portions.

Mid-term (Thursday – Friday night)

Another high pressure will build into the region behind the cold front, bringing another shot of cooler air. The models do not suggest a large temperature gradient to follow behind the cold front. Thus, the temperatures will only fall slightly to near seasonal or just below seasonal on Thursday. Any lingering clouds associated with the cold front will clear out early in the day; give way to mostly sunny skies. However, the clouds will once be on the increase Thursday night as the high pressure loses its footing and slides offshore. Warm air advection occurring on the western side of the high pressure will help to build some high clouds in the upper level of the troposphere. A short wave passing through the Great Lakes will drag a stationary front stretching across the Midwest. We may see a brief period of shower on Friday if enough moisture is present along the stationary front. However, the main story will be the low pressure that is forecast to develop along this stationary front as we enter the weekend.

Long-term (Saturday – Sunday)

Once again, the long-term forecast looks to be highly uncertain. A region of positive vorticity advection coming off the Rockies will generate a low pressure system along the stationary front. The 500-mb trough will gradually become more amplified as cold air advection on the backside of the storm really cranks up the system. The question remains on how much this 500-mb trough will amplify. The GFS has really backed off from its original idea showing a much less amplified 500-mb trough. The latest GFS run depicts a shallower 500-mb shortwave swing around the base of a long wave over Central Canada and the surface low remains intact throughout the period. As result, a long-duration rain event that may possibly end with some snow now looks unlikely according to the GFS. If the GFS is true, then expect a mainly rain event for Saturday as the majority of precipitation will fall while the warm air is still in place. However, some of the foreign models including the Euro and Canadian are still showing the development of a rather amplified 500-mb trough. The Canadian model is on the extreme side of this spread as it amplifies the trough so much that it eventually cuts it off over the Gulf states. As result, a series of slow progressing surface lows will ride along the aforementioned stationary front, feeding in copious amount of moisture from the GOM and the Atlantic as it does so. If this solution is correct, we could see a long-duration rain event, possibly heavy at times on Saturday. As that stationary front slowly progresses eastward, the cold air on the east side of the front has the potential to change the rain to periods of snow Saturday night, especially for northwestern PA. The Euro model is less extreme on this, however, with a similar idea.

David Wang

Technical Discussion

Technical Discussion

…Synopsis…

A cold front will be passing through late this night in most regions of Pennsylvania. A high pressure system should be making its way in for the next couple of days bringing relatively fair weather with mostly sunny skies.

….Short Term…

Most places within Pennsylvania should be experiencing relatively fair weather for most of the upcoming week. The GFS 12Z run shows a few high pressure systems moving in producing sunny skies for the next couple of days. Around Wednesday into early Thursday, the GFS also shows a low pressure system that is staying mostly within the bounds of Canada. This in turn could produce some spotty showers in the northern parts of Pennsylvania but little accumulation is expected. The 540 line seems to be hovering around most of Pennsylvania during this week, so temperatures should not be departing to far from the current normal temperatures.

….Long Term…

The main concern is for the later part of this week. Most models, including the GFS,  show a large low pressure system coming in on Friday. This in turn will produce a lot of rain and with temperatures hovering in the cooler temperatures, there is a chance for snow and mixed precipitation. The most ideal scenario at this point is rain in most regions of the state however.

-Stephen Quinn

Technical Discussion 2-28-11

Synopsis...

A strong storm system with thunderstorms and heavy rain is passing through the state currently, which may end as a few rain/snow showers tonight. High pressure will dominate much of the rest of the week until Friday. A trough will push south into the state on wednesday and thursday to bring a brief shot of cold air with little or no precipitation associated with it. The next storm will affect the state over the weekend.

 

Short Term...

The storm system today has a strong warm front associated with it, which is allowing thunderstorms to build due to increased instability with lower-level warm advection ahead of the cold front. Some storms could have strong wind gusts associated with them as winds are fairly strong just above the surface. Temperatures will drop fast behind the cold front and may allow some rain/snow showers to mix for some areas of the state tonight. Skies will clear for the day on tuesday with temperatures near the 30 year normal.

 

Long Term...
A short wave trough will move into the state during the day on wednesday from the north. Little or no precipitation will be associated with this cold front as mainly cold, dry air will infiltrate the state wednesday and thursday before a moderation in temperatures for friday. The next storm system will be on our heels on friday with some rain/snow showers isolated to the western part of the state. Central and eastern parts of the state won't get in on the action until saturday and sunday as a fairly potent storm could move into the region. Timing, track, and intensity of this storm is still variable within the forecast models, so this is another storm to keep an eye on.

Josh Aikins

Sunday Afternoon Technical Discussion

Synopsis:

Clouds are moving in ahead of a system currently over the Southern Plains. These clouds will thicken and bring rain to the state beginning after dark. The rain will move in from southwest to northeast, with all areas seeing precipitation by tomorrow morning.  Rain may be heavy at times, with a chance of thunderstorms as well. A cold front will sweep through tomorrow afternoon, possible changing precipitation over to snow briefly before ending. High pressure will begin to build into the region beginning on Tuesday, bringing with it sunny skies and seasonable temperatures through at least Thursday.

Short-term:

A fast-moving storm system will spread precipitation into the state overnight. Temperatures are currently above freezing state-wide and with a strong southerly flow they shouldn't fall much at all tonight, so expect all precipitation to fall as rain. A warm front will cross the region by tomorrow morning, putting the state into the warm sector, where heavy rain and thunderstorms are possible. Between the heavy rain and some snow melt, minor flooding is possible. The cold front will cross the state tomorrow afternoon, bringing cooler temperatures and an end to precipitation. Some areas, especially across the northwest portion of the state, may briefly change over to snow before ending. Skies will begin to clear tomorrow night, giving way to sunshine and seasonable temperatures on Tuesday.

Long-term:

High pressure should dominate our weather for most of the week, bringing nice conditions through at least Thursday. There may be a scattered snow shower moving through on Wednesday across the extreme northern portions of the state, but expect little to no accumulation. Our next system of interest will move in over the weekend, but it appears as though we will again be on the warm side of the system with mostly rain falling.

Sunday Technical Discussion

Synopsis:

Clouds will increase throughout the day today as another storm system pushes into the area. Rain should begin overnight pushing east by daybreak. It will be raining across the state by daybreak on Monday. The warm front associated with the storm will push through on Monday allowing temperatures to increase. Some of these storms could produce heavy rain and even thunder. It will be windy throughout the day Monday. The storm system will push east Monday night bringing with it cooler temperatures and clearing skies. Clearing will continue on Tuesday as high pressure builds into the area bringing with it sunny skies. For the remainder of the week, we will see mostly sunny skies during the day with temperatures in the low to mid 40s.

Short-term:

A complex system with a warm front ahead of it and a cold front behind will push in to the area today and overnight. Clouds will increase ahead of the system making for a cloudy day today. Rain should begin from west to east overnight with everyone seeing rain by daybreak tomorrow. Because the 540 will be to our north, we will see all rain from the system on Monday. There will be some severe storms associated with the system and we could not rule out the possibility of some localized thunder with these severe storms. Expect windy conditions during and after the storm on Monday and into Tuesday. All models are showing that the storm will push east on Monday night and should be out of the area by daybreak on Tuesday. Behind the storm, we will see cooler temperatures on Tuesday as sunny skies return to the area.

Long-term:

Sunny skies and cooler temperatures will prevail after once the storm system moves to our east. For the rest of the week we should see pretty nice conditions with sunny skies for both Wednesday and Thursday. It will be cooler on Thursday as some cool air from Canada will try to work its way in. We could see our next system try to push in on Friday.

Saturday morning technical forecast

Synopsis:

 

We are leaving behind the moderate to heavy rain associated with yesterday's cold front passage. In the wake of it, we will see chillier weather (although not really cold) and, up north, the chance of a few snow showers for today. This will move out of the area tonight, and we will see a brief break from precipitation for tomorrow. It will start to get milder tomorrow, as we see winds ahead of a warm front. The warm front will move through early on Monday, giving most areas of PA a period of moderate to heavy rain. Then, later on Monday, a cold front will sweep through the state, enabling another period of moderate to heavy rain. An isolated thunderstorm or two could also be embedded in this rain. Once the frontal passage occurs, expect blustery conditions, and noticeably colder temperatures (although again, it won't be really cold). Through much of the rest of the week, we will see clouds and sun, and temperatures in the 40s, for the most part.

 

Short-term:

 

An area of low pressure will pass to the north of the state today, giving northern areas a little bit of snow later this afternoon and tonight. Otherwise, most areas will be dry, seeing some sun, but more clouds further north. Tomorrow, expect a warming trend to begin, as the 540 height line moves northward, and winds start coming from the south. A pretty complex storm system, with a warm front ahead of it, and a cold front behind it, will make its' presence known across Pennsylvania starting late Sunday night and into Monday. There will be some rain as a result of the warm front, but heavier rain (as well as the possibility of a few isolated thunderstorms) are more likely ahead of the cold front. Both the 12Z GFS and WRF have the cold front passing through Pennsylvania Monday night, but the WRF has it swinging across at about 9Z (4 AM), whereas the GFS has it moving through at about 3Z (10 PM). In any case, expect winds to be turning from a southerly direction to a northwesterly direction pretty quickly once the cold front passes. Also, expect (before the front passes) some pretty heavy precipitation amounts. According to the 12Z WRF, areas of northwestern PA could see up to 3.5" of precipitation from this storm, as the low tracks across that part of the Commonwealth. The 12Z GFS keeps precipitation amounts down, but does show heavy amounts south of Pittsburgh (up to 2"). It all depends on how the low associated with the cold front treks. Beyond that, we will see more tranquil conditions for the rest of the week.

 

Long-term:

 

Expect colder temperatures once the cold front moves through, as well as blustery conditions. The winds will calm down Tuesday evening, and beyond that, we will see pretty nice weather until Friday, when our next front is expected to move across the area. There will be some clouds in the northern areas Wednesday, and possibly a flurry or two Wednesday night, but nothing more than that. It will be colder come Thursday, as some Canadian air tries to move in, but it will not be anything major.

Technical Discussion

Synopsis:

A low-pressure system will move through the state today, bringing rain showers changing into snow showers later in the day. The passage of an associated cold front will drop temperatures somewhat significantly as the day progresses. Expect mostly cloudy skies on Saturday and Sunday with lingering snow showers possible, especially in northern regions of the state.  Another disturbance will approach the state by Monday, creating an opportunity for windy conditions, rain showers, and even a possible thunderstorm.

Short-Term:

The 0000 UTC runs for the WRF and GFS models both indicate a deepening low pressure system approaching the state from the southwest. The surface low will pass through the state by this afternoon, off to the northeast.  All model runs show a nice swath of precipitation associated with the low pressure system.  The 18Z run of the GEFS plumes shows strong consistency in the timing and extent of the precipitation, as is to be expected in such a short-term forecast.  By tomorrow morning, the accumulated precipitation (liquid equivalent) is projected to be between 1 inch and 1.5 inches, with the majority of the ensemble members supporting precipitation amounts on the higher end of the range.  The plumes also indicate mainly rain for the first part of the day today, changing over to snow by evening.  Some ensemble members even have a little bit of freezing rain into Sunday.  The SREF probability fields for NE PA, initialized at 1500 UTC, indicate a very high probability for rain showers throughout the day today, switching over to a high probability for snow, especially in more northern regions and the mountains.

Long-Term:

Another low pressure system is projected to evolve over the Midwest over the weekend and affect the state on Monday.  It's too early predict with any strong certainty if the passage of the system will spark thunderstorms, but early guidance suggests that it is a possibility, along with strong winds and rain showers.

Technical Discussion

Synopsis:

Low pressure over the southern plains will push into our region over the next 24-36 hours. This storm will bring moderate to heavy rain across the state, with some snow showers and wintry precipitation mixing in across the northern counties. High pressure will build in behind this departing system for the early part of the weekend.  A weak disturbance looks to skirt across the northern tier of the state during the overnight hours Saturday into Sunday, leaving a light snowfall across northern counties. Clearing skies late Monday will only give way to another storm set to move into the region early Monday morning.

Short Term:

A large slug of moisture associated with a low pressure system currently centered over the southern plains will continue to move north and east into our region over the next 24-36 hours. Precipitation will start out as rain across the state, eventually transitioning to snow/wintry mix. Cold FROPA during early afternoon hours on Friday will lead to a changeover in most zones. Upcoming shifts should look to fine tune the timing of this changeover. Total QPF from this storm look to be on the order of 1-1.5" across much of the state with locally higher amounts in the northern and western zones. Winds will ramp up Friday evening in the wake of this departing system, gradually subsiding during the overnight hours and into Saturday. High pressure builds in across the region for Saturday with temps remaining close to climatological means for the weekend. A week disturbance moves in overnight Saturday and into Sunday bringing a light snow across the northern tier of the state. The WRF appears to be the outlier at the moment, currently showing a light swath of precipitation moving SE across the state. SREF guidance along with the GFS, CMC show a more northern track to this system, likely moving across the NY-PA border. Nonetheless, precipitation totals from this disturbance will be light.

Long Term:

Strong WAA ahead of a developing system over the Central Plains will allow temps across the state to climb much above average for late February, with most locals approaching 50 on Monday. The ECMWF has this storm moving through the region Monday into Tuesday. We made sure to include rain showers in the forecast for Monday. Although appearing unlikely at the moment, a convective outlook from the SPC for Monday shows a slight chance of a stray thunderstorm across southern counties.

Christopher Cornwell

Discussion - 2/24

The WRF is showing a strong low pressure make its way in from the southwest.  This system is expected to bring heavy precipitation across the state for this evening and for tomorrow.   The center of the low appears to be setting up over the Pittsburgh Metro/Laurel Highlands region and quickly stretch to the Northeast region of PA.  The low appears to be following a warm front - so, this system will bring warm air advection as it passes through our region.  Therefore, southern regions of the state (including LH, CR, and SE) will see rain over the next 48 hours, while areas to the north including NC, NS, Centre, and NE will see mix precip during the daytime hours of Friday and the possibly of snow.   Once this system is all said and done, it will bring warm air to the region and we can expect temperatures back into the lower to mid-50's across the state as we begin the new week.

Patrick J. Ritsko

The Pennsylvania State University
College of Earth & Mineral Sciences
Undergraduate of Meteorology, Class of 2013

Tech Discussion 2-23-2011

SYNOPSIS

The sunny conditions experienced today will soon be a thing of the past as a powerful storm system approaches Pennsylvania. The storm, which is currently developing over the southern plains, will intensify overnight tonight. This system will then swing up the Appalachian Mountains tomorrow morning bringing precipitation to the state by tomorrow afternoon. A cold soaking rain will be the signature of this storm with much of the mountainous areas seeing over an inch of rainfall. Although most of the precipitation associated with this storm will fall as rain, a wintry mix is possible north of the Interstate 80 corridor Thursday night. The low pressure system will vacate the region by Friday night leaving a weak area of high pressure in its wake. This high pressure system will allow for clouds to decrease on Saturday before our next system moves into the area on Sunday, bringing precipitation back to the commonwealth for the beginning of the next work week.

Short Term (Now until Thursday night)

The sunshine that we saw today will be the laat we see for a short while. This evening, the 500mb ridge keeps the state relatively dry for the night, but that will chance as positive vorticity aadvection begins to occur with the presence of an incoming low. The PVA helps develop the system we see later in the week, but it is starting to develop now. A low pressure system hanging near the southern plains will begin to move in tomorrow, showing as an increase in clouds for the better part of Thursday. The PVA feeding the low will help create a warm front that helps force the precipitation that we will see Thursday night going into Friday. As the precipitation moves in, the 540 dam line bends northward into NY, showing that rain will be the most likely precip type that will fall. Temperatures will remain in the upper 30s to low 40s  for the most part on Thursday, with some areas  with the clouds and moisture helping to keep the state above freezing as the storm progresses overnight.

 

Long Term (Friday into Sunday Night)

With the rain falling in the morning comes a bit of a warmup. The warm front associated with the  low will move through early morning Friday, and that rain lingers for most of the afternoon, and as a cold front pushes through Friday evening, high pressure behind the front quickly builds in to dry out the state for Saturday morning.Friday afternoon's rain will be blown by some decent winds due to the tight pressure gradient behind the front. The 18z WRF has the low moving straight out of the central plains while the 12z GFS gives it a more coastal track, and it hints at sending the center of the low right through the state. Another low is under development in the southern plains, and a band of clouds from that long stretches over the state throughout the day Saturday into Sunday morning. Cloudiness will be the story for Sunday morning as clouds begin to move out during the day. Temperatures will recede into normal late February conditions beyond the rain and cold front as we wait for Spring to come again.

Steven C. Engblom Jr.
Department of Meteorology
College of Earth and Mineral Sciences
Class of 2013

Technical Discussion

Synopsis:

A large area of high pressure centered over southern Ontario will settle into the commonwealth on Wednesday. This will bring another chilly, but delightful day across the state. Moist southerly flow will develop on Thursday ahead of our next storm system. The area of low pressure will bring rain showers with it Thursday afternoon before changing over to a wintry mix Thursday night and early Friday.

Short-Term:

Not much to talk about in the short-term forecast. The area of high pressure which was situated to our north on Tuesday will continue to slide to the south on Wednesday. This will provide brilliant weather across the entire commonwealth under mostly sunny skies. Temperatures will be close to normal across much of the state with highs in the middle to upper 30s. Some locations in the southwest corner of the state could approach 40. Winds will become southerly ahead of our next system on Wednesday night. These southerly winds will keep temperatures into the 20s Wednesday night. There will also be an increase in cloud cover late Wednesday night in the wake of the next storm system.

Long-Term:

Boy do things get interesting with this next storm system. There is still a lot of uncertainty with the precipitation type(s) Thursday evening into Friday making the forecast quite complex. The area of low pressure will make its way out of the southern plains Thursday and begin to move into the western parts of the state late Thursday afternoon and evening. Currently, the SREF plumes show the precipitation being all rain during the onset. Both the WRF and GFS support the a rainy solution to begin, but then slightly diverge from there. Both the soundings of the WRF and GFS support rain throughout much of the event. The 0 degree isotherm at 850mb on the 0Z WRF is pushed into the southern tier of New York Thursday night. The lower levels near the surface will be below freezing which supports a wintry mix during the overnight period. As Friday morning approaches, the wintry mix will change over to completely snow as the winds shift from southwest to northwest. The storm will also quickly make its way out on Friday with decreasing cloudiness during the evening hours and into Friday night. Therefore here is how I see it going down: the onset of the precipitation will be rain. It will then switch over to a wintry mix during the overnight hours and early part of the morning on Friday. As the residual precipitation is making its way stage east, it will switch over the snow.

Saturday looks to remain dry with partly cloudy skies across much of the commonwealth. There will be a chance of some light snow on Sunday as a week system moves just to our north. Early next week look pretty interesting...stay tuned!

~ Matt Alto