Wednesday Night 2/29/2012

Synopsis: A storm system that passed through the region today will scoot off the coast tonight. Breezy conditions will be left in the wake of the storm system during the day tomorrow. An upper level trough will trek through the commonwealth overnight on Friday bringing some intial periods of heavy rain and possible thunder. Snow showers may accompany the tail end of the cold front. Much cooler and calmer conditions will move into place for the beginning of next week.

 

Short-term: Two areas of moisture are currently impacting the commonwealth. The slew of moisture in south should lay down another half inch of moisture throughout the night. In the northern tier of Pennsylvania a line of storms accompanied by a rumble or two of thunder will pass through overnight. Showers will linger in the north, especially in the northeastern corner of the state. A surface rigde will build into the region tomorrow allowing for calm yet breezy conditions to exist. Temperatures will rebound throughout the day tomorrow, reaching just above normal.

 

Long-term: A shortwave will pass north of the state bringing rain showers Friday evening into Saturday. Saturday night and Sunday a cold front will swing through the state potentially causing some thunderstorms to pop up. At the tail end of this front some snow showers may mix in with the rain. A ridge will build into the region early next week allowing for cooler and calmer conditions.

Wednesday Afternoon Technical Disc.

Synopsis:

A potent mid-latitude low is making its way through the Commonwealth and will slide eastward overnight. As it does so, look for thunderstorms near Pittsburgh, Light Snow near Scranton, and rain elsewhere. Behind the front, lake effect snow possible near Erie, but elsewhere, skies will be mainly cloudy. After a brief break in the clouds on Friday, a warm front will move through during the early part of the night. The cold front will move through western PA late Saturday morning and eastern PA late that afternoon. Thunderstorms in the southern portions could accompany the passage, expect rain elsewhere. Once again, rain or snow possible on the back end for Sat. night into Sunday. High pressure builds in for early next week as another system threatens late in the week.

Models Used: 12Z GFS & NAM (slowed down timing); MOS (adjusted down for tomorrow; up for Saturday)

The Rest of the Week:

Southwest PA is in the warm sector of the cyclone, so thunder is likely. Elsewhere, rain will fall. Surface temperatures will remain above freezing for most but it will be chilly. A northwesterly flow sets up behind the front, bringing lake effect precip, mostly confined to places near Erie. The dry air behind the front will continue to funnel in, giving us some sunshine between storm systems, if only short-lived.

The Weekend:

The warm front will reach northern PA and sufficient warm advection is likely ahead of the cold front. With surface temperatures near 60 in the southern third of PA and surface convergence, expect thunderstorms to occur with this system. Once again, a northwesterly flow sets up behind the front. The high pressure area will move into the region on Sunday night, about a day after the cold front moves through.

-Jaron Breen

Tuesday Midday

Synopsis:  High pressure will move to our east today, as a potent storm takes aim at the Commonwealth for Wednesday and Thursday.  We clear out for Friday, but a strong cold front pushes through late Friday into Saturday.

Short-term: It looks like all the models are off with the precipitation field and location of the low for the storm that will be coming to our region Wednesday and Thursday, took that into account in the forecast.  Sunny, clear weather today, no disagreements from the models on that.  The real disagreement comes from what is going on with Wednesday and Thursday.  Because of the differences discussed above, we brought increasing clouds into the forecast tonight with a wintry mix entering by dawn for our Western Zones, then changing over to rain.  The NAM/GFS/EURO all have precipitation coming in AFTER 12z, but currently show very little in the way for precipitation in the Midwest at 15z, while currently there is precipitation (stronger than the models) in that region.  Most of the state looks to be all rain with the exception of NC, NSQ & NE.  NC/NSQ: once the precipitation moves the 850mb temp will be below 0 with the surface below 32, but both will slowly rise during the day, going above freezing early afternoon.  NE:  Both 850mb and surface below freezing, and will struggle to get above freezing for much of the day, and should by evening.  The models have been suggesting that the high NE of Maine will not be as strong, but we are going with that the cold air will be stubborn enough to linger around.  As we progress into Wednesday Night all precipitation should become more scattered in nature.

Long-term:  The clouds will linger on Thursday as the primary low weakens and the secondary low takes over, cannot rule out the chance for a couple of showers.  Clearing conditions overnight into Friday, as high pressure quickly moves in, but will move out as quickly with another storm system knocking on our door steps Friday night.  Cold front pushes through Saturday Morning with showers, in the afternoon might change over to snow.

Kept temperatures near previous shift, with minor changes.

Tech Disco 2-27

Synopsis

As we enter the start of meteorological spring, we will start to see more "typical" seasonal weather as this warm winter begins to conclude. A strong synoptic rain event is projected for this week with some chance of lake effect snow behind the midweek system.  This week, we'll observe the effects of an upper-level cutoff low infused in a strong long wave area of vorticity advection, which will help induce a splitting of an elongated low into two separate systems. In terms of a week summary, high pressure will dominate the days that sandwich this midweek storm.

Short Term (tonight through Tuesday night)

A low pressure system to our northwest will track to our north, leaving us with the remnants from the tail end of a cold front that will cross through the state this evening. As the front pushes through, dowdrafts associated with the frontal passage in conjunction with downsloping winds will keep the western valleys gusty overnight with brisk wind chills in the lower 20s. the idea of lake effect snow overnight is passable, for there is little directional wind shear and a lapse rate supporting adiabatic lift, but the magnitude of the lapse rate isn't strong enough to support the convection necessary for anything significant, just some clouds and a light shower will form at best.  once this front is through, high pressure following the front will slide in Tuesday midday  give us a calm before an approaching storm. Once day turns to night, the pressure gradient will intensify and clouds will move over the state overnight Tuesday. a strong moisture draw within a vast area of warm advection associated with a strong synoptic low from the plains will set the scene for Wednesday's  storm.

Long Term (Wednesday  through Friday night)

Rain along an occluding low pressure cell will begin to fall throughout he state Wednesday morning, and the rain will persist throughout the afternoon. The tricky part occurs where the models begin to disagree with how the storm's end begins. The 12z Nam has the central low placed within a detached area of strong vorticity and PVA aloft, and it's already elliptical shape will help the low split into two. The Nam shows this early, whereas the 12z GFS has it occurring after the system moves out. The Nam's solution splits the low around 21z, and the rear low continues to occlude and show a dryslot ahead of a cold front, while the leading low is dissipating with its rain falling on the bulky part of the comma. The GFS has a synoptic dryslot that clears all precip out by 9z Thursday, while the 15z SREF ensembles have a mean of these two solutions. This setup will probably differ greatly with the newer runs, so for now, we can only conclude lingering showers for Wednesday overnight into Thursday. The vortmax in the cutoff low remains in place throughput Thursday, leaving the possibility for terrain to help induce showers from the clouds overhead. After all this, high pressure builds into the state Friday to clear us out, and it's presence underneath a ridge aloft will help us warm up to weather more typical of this time of year.

CWS Technical Discussions 02/27/12

February 27, 2012 Technical Discussion

Synopsis:

A weak cold front will pass through Monday to start off the week. High pressure will then settle in Tuesday and most of Wednesday. A low pressure system approaches the Commonwealth which will affect the area for the remaining portion of the work week. There will be a good chance of a wintery mix during this time frame as the freezing line fluctuates north and south of Pennsylvania.

Short Term:

As a short wave through moves northeast out of Pennsylvania, a high pressure system will make its way in for the early portion of this week as a system develops to our west.  Furthermore, sunny skies will result Monday and Tuesday from this high pressure with mild temperatures in the upper 50's.

Long Term:

Good lake effect conditions will be present as a low pressure system begins to make its way to the commonwealth. The northwestern portion of the state will receive the hardest hit resulting from lake effect snow and upward sloping snow showers.  As the 540 thickness contour moves north and south through Wednesday night and Thursday, a wintery mix is likely for this time frame. As for the weekend, the same pattern will repeat itself as high pressure comes back over the State as another low develops to the west.

  -Erik Fagerstrom

Sunday Afternoon Technical Discussion

Synopsis:

High pressure in control through Tuesday AM. Weak cold front heads through Monday. Another system hits Wed. and Thursday. High pressure settles to our south on Friday.

Models: 12Z Runs - best to use MOS, note the biases around cyclones for the middle of the work week.

Details:

Monday: Most of the precipitation stays in upstate NY. Some wind is possible.

Wednesday: Mild cold air damming precedes warm front. Initially a mix, the mix changes over to rain rather quickly.

Midnight Wednesday night into Thursday evening: Lake effect snow sets up as the low heads NE.

Other Notes: High pressure usually will settle to the north initially but a weaker high does appear to form to the south of the main highs.

-Jaron Breen

Wednesday Night 2/22/2012

Synopsis: A weak weather system will move by tonight and tomorrow bringing scattered rain showers throughout the commonwealth. Conditions will be mild until Friday when a strong cold front will push through the region. Periods of light and moderate rainfall will accompany the initial warm front. Gusty winds and much cooler conditions will be apparent in the wake of the front. Lake effect and upslope snow will fire across the northern ridges. Another period of moderation is expected earlier next week as a ridge builds into the area.
 
Short Term: Two areas of precipitation will move near the region tonight. A warm front will slide across the northern portions of the commonwealth bringing rain showers with snow showers mixing during the late night hours. Across the entire state, mid and lower levels clouds will be dominant and keep the temperatures generally near or above freezing. This should reduce chances of accumulation in areas that see scattered snow showers. A weak and short-lived ridge will build into the commonwealth tomorrow allowing for some periods of sunshine to break through. Mild conditions will again be widespread and temperatures should range from mid 40s to mid 50s.
 
Long term: On Friday, a strong low pressure system will pass north of Pennsylvania bringing widespread light and moderate rain. The precipitation associated with the initial warm front will bring the heaviest precip accumulations. As the cold front pushes through overnight Friday, scattered rain/snow showers may follow. Gusty winds will also accompany the cold front with gusts near wind advisory criteria. Look for lake effect snows and upslope snow showers to impact the northwestern ridges of the state. Much cooler conditions will follow on Saturday as the clouds clear up and snow showers come to an end. Another ridge will move into the region Sunday and into the beginning of the week. This will allow for another round of moderation early next week. Both the 12Z GFS and 12Z ECMWF have a storm system impacting the eastern half of the country later next week. The ECMWF is currently showing a coastal storm while the GFS hints at a midwest storm. Not much consistency between runs, however it is definitely something to keep on the "radar".

Synopsis: A disturbance will move toward our Northwest tonight into tomorrow morning bringing the threat for rain/snow showers, mainly for the western half of the state. A strong cold front moves through the state on Friday, bringing colder and windy conditions with lake effect snow showers possible for Friday night into Saturday. High pressure returns for Sunday.

Short Term (Tonight through Thursday Midday) :  A vigorous shortwave will move through Lake Erie and into Western New York State between late tonight and tomorrow morning bringing the threat for rain/snow showers, mainly for the western half of the state. Precipitation amounts forecasted by all the models will generally be between the 0.10 and 0.25 inch range. Higher elevations may see an inch or two of wet snow with this disturbance.  Precipitation should end late morning on Thursday as the shortwave pulls away.

Long Term (Thursday evening through Sunday):  A piece of energy diving from the Pacific Northwest will serve to generate a surface low pressure system tomorrow night. This low is expected to intensify as it tracks through the Great Lakes into Northern England. There are some disagreements between the computer models with respect to the intensity of the cyclone. The 12z GFS and NAM have the cyclone intensify into a sub 990mb system as it heads into Northern New England while the 12Z EURO has a weaker cyclone.  Either way, rain will move through the state tomorrow night and last into Friday morning before tapering off Friday afternoon as a sharp cold front moves through the state. Behind the front, a surge of seasonably colder air along with gusty northwesterly winds will filter in as the pressure gradient tightens. With Lake Erie remaining unfrozen, the northwesterly winds will serve to produce lake-effect snow showers for the northwestern parts of the state Friday night and into Saturday.  An area of high pressure will settle in for Sunday bringing fair weather.

Tuesday Midday

Synopsis:  Clouds rolling into the state this morning.  Western PA should see showers before noon.  Several waves move through the area this week limiting the amount of sunshine, but will feel like April.  Cold front should knock us down back to average for the weekend.

Short-term: The models have a good handle on what is to come.  The EURO is the slowest one for the first wave.  We moved the chance of showers entering the state up to this late morning and early afternoon for Western PA.  Rest of the state should see showers in the afternoon and overnight.  The next wave moves through late Wednesday, nothing much expect rain, under warm air advection.

Long-term:  Thursday will start off with those showers from Wednesday night then the third wave moves in with some scattered showers.  All the models have hinted that this.  There will be a brief break before the last wave moves through, and this wave has the biggest spread amongst the models.  The EURO (0z) is the farthest south and more robust, while the GFS (0z) and NAM (12z) have similar solutions.  At the current moment the HPC is going with the models that closely relate to the ensembles, which are the GFS & NAM. For Friday went with morning showers as cold front pushes through, we cold advect back to around average for Friday.  Saturday with NW winds, lake-effect clouds and showers.

Kept temperatures near previous shift, with minor changes.

Monday Morning Technical Discussion 2/20/12 10am -12pm

Synopsis:

High pressure will move into the area overnight and hover over the Commonwealth for the first half of the work week raising temperatures into the mid- 40s through the rest of the week. Cloudy skies will cover much of the State as a Low pressure system moves into the area, bringing the chance for some isolated rain and snow showers Wednesday and into Thursday. Another system will push through the State on Friday, bringing the chance for some interesting weather in the form of rain and snow showers, as temperatures drop from the aforementioned 40s.

Short Term:

Above average temperatures will be the talk of discussion as temperatures rise into the mid to high 40s for this work week. Mild conditions will be prevalent before a low system moves through the area on Tuesday evening/night bring the chance for some isolated rain and snow showers.

Long Term:

A low system will bring isolated rain and snow showers for Wednesday and into Thursday, leaving Thursday with mild and dry conditions. Friday will see moist conditions again as another storm has the possibility to bring some interesting weather in the form of rain and snow showers as temperatures drop back into the seasonable 30s. 

Forecaster: Meredith Nichols

Sunday Afternoon Technical Discussion

Synopsis:

High pressure moving in from the west will keep the state dry through Tuesday afternoon. The nor'easter wannabe affecting the southeast will head due east during the next 24 hours. About two cold fronts will affect PA this week: one for Tuesday into Wednesday and another for Thursday night into Friday. Temperatures will be near average today through Tuesday and then increase from  day to day through Friday before cooling takes place behind the cold front Friday night.

Models used: 12Z NAM & GFS; MOS most of the time

Short-term:

We were at some point watching the low move along the Gulf Coast, wondering how far north the precipitation will get. PA will be dry.

We'll have high pressure in control early this week. Temperatures near 40 for the high and in the mid 20s for lows (into the 30s for Tuesday night). The models showed the clouds rapidly building in for the west from sunrise to around noon on Tuesday. Precipitation is confined to Northern and Western PA and relative humidity (and the chance of rain) drops once you get past the mountains.

Long-range:

Another front will affect PA Wed. and Thursday. I am confident that clouds and precipitation should behave similarly to the clipper system on T! ues. night and Wednesday. The temperatures will be in the mid 40s to low 50s for highs (possibly 60 near Philadelphia on Thursday and Friday); and in the 30s and 40s for lows. I am not sure how far north and west of the Southeast and Capital regions that highs above 50 will get. Adjustments may be needed for the second half of the week once those weak systems move in.

For now, enjoy the nice weather for the next 36-48 hours.

-Jaron Breen

Synopsis: High pressure will provide dry weather and seasonable temperatures for today and into the first part of Saturday. A weak cold front will move through early Saturday evening, bringing a reinforcing shot of cooler air. A potential winter storm could still affect parts of the state for Sunday. Drier weather will return for early next week as a new area of high pressure settles in.

 

Short Term (Today and Saturday)

 

 An area of high pressure will provide for abundant sunshine and temperatures rising into the 40s throughout the State for today. These conditions will continue into the first part of tomorrow. A weak cold front will move through by tomorrow evening bringing a reinforcing shot of cooler air. There can be a brief period of light rain/snow showers across the northern zones.

 

Long Term (Sunday through Tuesday)

 

  An area of low pressure will develop over the Gulf Coast states and move northeast and offshore along the Mid-Atlantic States. The real challenge with this system remains the phasing of the southern branch with the northern branch of the jet stream. The current guidance consensus seems to be that the phasing between these two features occurs late and as a result the low instead of moving north northeast as a typical nor'easter does, it moves east northeast and the northern extent of precipitation shield goes as far north as the southern tier of the state, meaning that the rest of the state sees no precipitation at all from this storm. However, if the phasing occurs earlier than what guidance is predicting, then the low as a better chance of tracking farther north and the precipitation shield moves farther north with accumulating snow likely for most of the state. Regardless of what happens, drier weather will return for early next week as a large dome of high pressure settles in along the Eastern United States. 

Gabriel Lojero

Thursday Midday Short Update

FOR THE WEEKEND USE ONLY:

Based Saturday's forecast off of the new 12z NAM - Northern Branch Shortwave pushes through.  This leaves open Sunday for a potential snowstorm for Sunday.
Sunday went off of the 0z EURO based on the 12z NAM, so a blend with the 12z NAM leading up to the storm entering the East Coast.

The HPC for both events are saying EURO is the way.

Wed Night Discussion

Synopsis: High pressure will scoot off the mid atlantic coast overnight tonight. An area of low pressure to our southeast will move through the area tomorrow, bringing with it some wet weather. High pressure will again move in behind this storm, bringing tranquil conditions into the first half of the weekend. Long term tends to be interesting, with model guidance not converging on a single solution.

 

Short Term: A storm system will approach from the Ohio Valley overnight tonight, with precipitation spreading across the state tomorrow morning. A light wintry mix will fall across the northern half of the state, as 850 mb temperatures will remain below freezing but surface temps rise into the mid 30's. The southern half of the state will likely see rain with this system. Precipitation totals will be on the order of light to moderate. Temperatures will cool off Thursday night, with skies clearing. An area of high pressure will slide east and provide nice weather for Friday. A weak clipper system will scurry to our north on saturday, bringing only the chance of some light snow or flurries to extreme northern portions of the state late on saturday.

 

Long Term: Clouds will increase saturday night, as a complex storm system develops in the southeastern U.S. GFS is the outlier in its solution. It takes the storm northeastward and phases it with the northern jet stream. Ample gulf moisture and phasing with cold air provides a significant winter storm ranging from the Ohio Valley to Maine. NAM and EURO are not on board however. The placement of the high pressure to the north in their solutions surpresses the storm to the south with no phasing. This would only allow for a moderate snowfall for points west of D.C. Will keep a close eye in the coming days for convergence.

Wednesday Afternoon Technical Discussion

Synopsis:

Earlier today, high pressure has moved offshore. A low pressure area, partially fueled by a shortwave trough, is making its way northeastward. It will bring mostly rain to the Commonwealth on Thursday, but mixed precipitation - both at the onset and as the cold front moves through - cannot be ruled out. High pressure will build in during the wee hours Friday and control our weather for Friday and Saturday. We will watch an area of low pressure (currently located in the southwest U.S.)- move along the I-10 corridor throughout the remainder of the week. The 00Z & 12Z GFS trends toward a nor'easter for Sunday, but no other models agree. We have to wait and see.

Models Used: 12Z NAM, GFS, & Euro + 15Z SREF; Navy & CMC models consulted

Short-term (Thursday's Precipitation):

A shortwave is causing the 0°C isotherm and the 540-Dm line to bulge northward right over PA. The precipitation starts around sunrise Thursday -  as rain with some sleet and wet snow mixed in - as the warm front moves north. The cold front zips through after sunset with the chance for a snow shower as it passes. No more than one-half of an inch will fall, with an avg. precip. amount of 0.39".

Long-range (THON weekend forecast, Possible Nor'easter):

High pressure will be in control for Friday and Saturday. It will sit over PA.

A cut-off low is feeding Sunday's potential nor'easter as it sits over the SW US. For the nor'easter scenario to play out, the cut-off low needs to be absorbed back into the flow as it nears TX. While the 00Z and 12Z GFS say it will, the 06Z GFS and all other models say that the cut-off will not interact with the northern branch ! on Saturday AM as it nears TX. The precipitation, if any, will start around sunset Saturday. One thing is clear: the low is likely to interact with the left-exit region of a jet streak (an area favorable for enhanced upper-level divergence), causing the low to rapidly intensify to around 984 mb - IF the scenario plays out. There is the potential for a foot of snow in Philadelphia, but model disagreement and run-to-run inconsistency gives this scenario little chance to play out. It is worth watching closely over the next few days. Our call: a chance of snow showers for the eastern half of PA on Sunday.

-Jaron Breen