Wed Night Technical

Synopsis: Area of high pressure moving eastward from the Ohio valley will dictate the weather for Thursday, bringing mild and dry conditions. A weak cold front will pass through on Friday; however, there is not that much moisture to work with. Another area of high pressure will bring nice conditions for the weekend with the next chance of precipitation coming early next week.

 

Short Term: High pressure will slide eastward from the Ohio valley overnight tonight and last through Thursday. Tomorrow will see dry conditions with seasonable temperatures due to this high pressure. A week cold front will move southeastward during the day on Friday. There seems to be little, if any, moisture to work with though. For this reason, only northern zones may see a sprinkle or a flurry. Otherwise, the rest of the state will remain dry with clouds from time to time on Friday. The front will bring cooler temperatures. Very cold conditions can be expected Friday night, statewide.

 

Long Term: Another high pressure will enter the region, bringing sun and dry conditons for the weekend. Another system will take shape next week and will begin to affect the state by Monday. New models show a system forming along a stalled frontal boundary, possibly becoming cut-off like the system that just passed. It is still too far out to converge on a solution though.

Wednesday Afternoon November 30th, 2011

Synopsis

The cut-off low will finally move over the Commonwealth as we head into Thursday. Winds will pick up as the system departs and a high pressure moves into the area from the south for Thursday, looking to bring drier conditions. A weak low will move in Friday afternoon, bringing lower temperatures and the chance for some light snow showers in Northern PA. As we move into the weekend, another high will take over leaving us with sunshine and calm conditions for Saturday, but quickly departs for a cold front to bring a few rain showers across Western PA, and moving across the Commonwealth heading into Monday.

Short Term

The cut-off low will move across the Commonwealth as Thursday approaches. Winds will pick up as the system exits and a high pressure moves into the area. A weak low will move in bringing lower temperatures in the mid-40s for Thursday and Friday. This leaves the chance for a possibility of some light snow showers in Northern PA Friday night as temperatures drop into the low 30s and high 20s in some places.

Long Term

As the weak low exits the area Friday night, high pressure will take over for Saturday, leaving us with mostly sunny skies. Clouds will enter the Commonwealth Saturday night as a cold front moves in, leaving us with the chance for a few rain showers across Western PA. Showers should move across the Commonwealth as we head into Monday, leaving us with the possibility to see some snow showers as the 540mb line hovers close to the commonwealth. 

Forecaster: Meredith Nichols

Tuesday Night Technical Discussion

The cutoff low moving through the Great Lakes will continue to move north on Thursday into northern New England with only a few rain or snow showers possibly lingering in western Pennsylvania early on Thursday. Winds will shift WNW to NW Wednesday afternoon and become breezy with some ridge tops in western Pennsylvania possibly reaching 30kts. High pressure will move in from the south later in the day on Thursday bringing drier conditions through Friday. A weak cold front will try to push through late in the day on Friday only bringing a slight chance for a snow shower or two in northern Pennsylvania Friday night. The front will quickly exit Friday night with high pressure taking over for the first half of the weekend. Another cold front will approach the state from the west on Sunday bring cloudy skies later in the day and the chance for a few rain showers overnight across extreme western Pennsylvania. The showers will move across the commonwealth on Monday and possibly change over to a few snow showers by Tuesday across western Pennsylvania as the 540 line pushes west to east.  

Zachary Fasnacht

Technical discussion for 11/29/2011

Short- term

 

The occluding low pressure system that has been over the region today will slowly shift northeastward tonight into Wednesday. Precipitation associated with system will be limited through the short term as much the region becomes positioned in the dry slot behind the cold front moving north.  Behind the front, nam mos has been predicting temperatures relatively well with a slight biased to the high side. Wednesday into Thursday, much drier air will be advected over the state, leading to clearing of skies on Thursday.  Temperatures will reach into the low 30s to mid 20s for most of the state as radiative cooling allow for larger diurnal ranges.

 

Long term

 

In the long term, a high pressure system will settle over the region bringing clear skies and warmer temperatures to the area.  There will be a slight chance for lake effect snow as a low pressure system moves over the northeast with a high pressure moving in from the west.

Sunday Afternoon Technical Discussion

Synopsis: Light rain tonight resulting from a weak short-wave trough. A break on Monday. An unusually fast-moving, upper-level cut-off low brings rain for Tuesday and Wednesday. High pressure moves in on Thursday and moves out Friday night.

Models Used: 15Z SREF Probability Charts & Precip. Plumes, 12Z GFS & NAM Models and MOS

Short-term: Warm start. Light rain stays in northern and western PA tonight and ends (~0.1" accumulation)

Cut-off Low info: The low gets cut-off during the period and is absorbed by the flow again as it moves off the coast. It is fast-moving due to (1) the short duration it is isol'd from the flow and (2) it being pushed by a short-wave upper-level ridge behind it. SREF Plumes (PSU area) showed 0.55 to 0.9 inches falling

Temperatures: MOS was giving me trouble with cloud-cover vs. my forecast, so the forecast requires a closer look. Also, the durnal range from Tues. night into Wed. is very small and requires the use of the  "SREF 2m Temp" (raw output).

Notes: SREF plumes picked up snow on Wed. and Thurs. Something to keep an eye on.

-Jaron Breen

Thursday Evening Technical Discussion

Synopsis

The strong westerly winds will continue to bring lake effect snows to northwestern area of Pennsylvania tonight. On Friday, an area of high pressure will build and it will set up along the East Coast for this weekend. Later on Sunday, a cold front will move south into the area. Late Tuesday and Wednesday, a storm system will approach PA bring the chance of rain.

 

Short Term

Strong westerly winds will continue through the morning hours on Friday.  There is the possibility for snow showers in the northwestern area of PA.  Most areas lows tonight will be in the 20's as 850 mb temps range from -8 to -10 C. However, temperatures will begin to moderate Friday as the westerly winds begin to die down and 850 mb temperatures begin to rise to -4 to -6 C. This should allow temperatures to rise into the low to mid 40's on Friday.  Later on Friday, a ridge of high pressure will build into the area. This ridge of high pressure will bring clear skies and dry conditions as well as a southwesterly flow on Saturday.

 

Long Term

 

The ridge of high remains over the area until Sunday when another cold front will move into the commonwealth. Scattered showers will affect the central and southern parts of the state. This front will stall out over the area and will bring the chance for more showers on Monday into Tuesday. Later in the week, there is the chance for more precipitation as an area low pressure approaches the area from the southwest.

Thursday Afternoon Technical Discussion

Synopsis: A cold front moved through last night, bringing cold air into the region. Cool conditions should persist until later and through this weekend when high pressure will set into place. Clear and warmer conditions should persist during this time period. High pressure should remain in place until Sunday when another cold front will move through the region. More storm systems aim to impact the region over the course of next week.

Short term: Chilly, breezy, and cloudy conditions will be present as a northwesterly flow dominates the weather pattern. Lake effect snows will continue to impact the Pennsylvania region throughout the remainder of today and tonight. Winds should calm down on Friday allowing the skies to clear up and the snow to generally end in the northwestern parts of the state.

 
Long term: A ridge will build into the region over the weekend. Clear and mild conditions will set into place during this time period. These conditions will persist until Sunday when another cold front will move into the commonwealth. Scattered showers will affect the central and southern parts of the state, whereas northern parts of the state may see a flake or two. Additional precipitation may come after this cold front as several waves of low pressure may impact the region next week.

 

Wednesday Night

Synopsis: Cold air will rush into the region overnight as a coldfront clears the commonwealth and slides off the East Coast. Cool conditions should persist until later this weekend when high pressure will set into place. Clear and warmer conditions should persist during this time period. High pressure should remain in place until Sunday when another cold front will move through the region. More storm systems aim to impact the region over the course of next week.

Short term: Rainy conditions will cease across the area during the late hours tonight as the backend of the coldfront exits the region. Chilly, breezy, and cloudy conditions will be present as a northwesterly flow dominates the weather pattern. Lake effect snows will also begin to impact the Pennsylvania snowbelt Thursday and Thursday night. Winds should calm down on Friday allowing the skies to clear up and the snow to generally end in the northwestern parts of the state.

 
Long term: A ridge will build into the region over the weekend. Clear and mild conditions will set into place during this time period. These conditions will persist until Sunday when another cold front will move into the commonwealth. Scattered showers will affect the central and southern parts of the state, whereas northern parts of the state may see a flake or two. Additional precipitation may come after this cold front as several waves of low pressure may impact the region next week.

Wednesday November 16th, 2011 Afternoon

Synopsis:

The rain will continue overnight as the low pressure remains stalled for a few more hours before exiting the commonwealth. Skies should begin to clear by Thursday morning as cooler temperatures set in as the 540mb line drops below the Commonwealth. The cooler temperatures may create some lake effect snow showers late Thursday and early Friday in the northwestern part of the state. Friday looks to be sunny with temperatures beginning to rise as a high pressure enters the state leaving us with dry and sunny skies. The weekend looks even brighter with above average temperatures and mostly sunny skies before a possible cold front moves in late Sunday and into Monday morning.

Short Term:

Showers will continue across the Commonwealth as a stalled low pressure system travels across the state, tapering off by Thursday morning. Temperatures across the region Thursday should be in the mid to high 40s, while at night look to be in the high 20s. With cooler temperatures in the Northwest, lake effect snow showers are possible late Thursday and early Friday morning. Friday looks to be drier as a high pressure moves into the area with overnight temperatures closer to the low 30s.

Long Term:

Mostly sunny skies with milder temperatures will take over on Saturday with the high in the low 50s. Sunday should also be very sunny with temperatures in the mid-50s. The high pressure will dominate the region keeping skies mostly clear with above average temperatures to look forward to. A possible cold front looks to move into the area late Sunday and into Monday morning.

Forecaster: Meredith Nichols 

Wednesday Midday

Synopsis:  Cloudy conditions have over taken the state, as balloon of moisture makes its way up the Appalachian Mountains towards the state.  Wednesday looks to be the wet day of the week, with cooler conditions as high pressure works in for Thursday and Friday.  Next shot of rain… Sunday.  On a side note, we do need the rain.  On average for the 1^st 14 days of November, Altoona should have about 1", so far this year: 0.04".  A very dry start to November in deed.

Short-term:  Looking just at current conditions and radar, we can predict that most if not all the state will see rain late morning and all afternoon and into the evening today.  Rain will be heavy at times.  The cold front that is associated with the precipitation will push through the state on Wednesday.  At the time of the forecast, one can argue that the front has already moved into the western parts of the state.  Thursday we will cold advect, with winds out of the Northwest, and a building high pressure from the south.  This will likely inhibit/slow down the lake-effect process for the lake-effect areas, but still cannot rule out any lake-effect shower or snow shower.  The Southeast will continue to see precipitation during the day, with it drying out later in the afternoon and evening hours.

Long-term:  Friday and Saturday, high pressure will dominate the region, leading to mostly sunny conditions and temperatures climbing slightly above average.  The real challenge comes on Sunday.  Another frontal system looks to make its way towards the state for Sunday, with it precipitation 1^st in western parts of the state, with increasing clouds for the afternoon and showers for the rest of the state overnight.  The front from this looks to pass through the state late on Sunday.  This is something to keep looking at, as this could change with future shifts.

Kept temperatures near previous shift.

Technical Discussion 11/15/11

Synopsis...

Showers will move through the commonwealth early in the day Wednesday. High pressure will build in Thursday and persist through the end of the weekend.

Short Term...

A very broad cold front will move its way through the commonwealth during the day Wednesday, bringing consistent showers. As indicated by the 18Z GFS MOS, strong cold advection will occur behind this front. This will create a windy evening Wednesday night, and significantly drop temperatures for Thursday and Friday. The high pressure system mentioned will begin building in during the day Thursday, however, it will likely remain breezy and cold during the day Thursday as a deep upper-level trough pushes northeast. By Friday, both the GFS and the NAM push the high pressure system eastward, creating conditions favorable for moderate warm air advection to occur from the southwest - evidenced by the numerous solenoids present at 18Z Friday. High temperatures will rebound back into the high 40s / low 50s by Friday and rebound into the 50s by Saturday.

Long Term...

The high pressure system will hold in place through later in the day Sunday as another front pushes its way from the northwest. However, I am not sold on this front being a huge rain producer as the bulk of the PVA will still be well off to the NW of Erie, and an upper-level jet streak at this location indicates the commonwealth would be under the right exit region - all of this favoring little to no precipitation by the end of the day Sunday. As this front pushes closer though, and the jet streak moves along, a more significant rain event is possible early next week. This will be something to keep an eye on.


Andrew Dzambo

We Are... Penn State Meteorology

11-15 Technical Forecast Discussion

Nov. 15. 2011 Technical Forecast Discussion

Synopsis:

A slow moving front will bring on and off showers for the rest of the day on Tuesday with a steadier rain arriving later Tuesday night. The rain will be moderate in intensity for the morning hours on Wednesday and tapering off to light rain showers by Wednesday afternoon. The clouds will linger into Thursday with some showers possible for southeastern portion of the state. The clouds will gradually clear up on Friday with mostly sunny skies to start the weekend.

Short-term (Tuesday evening-Wednesday evening)

A cold front accompanied with a strong jet stream and vigorous upper-level shear that brought lines of thunderstorm squalls through the Ohio Valley and Pennsylvania will stall just south of the region Tuesday evening. Moisture riding along this stationary front will create periods of rain showers to the region. As the broad 500-mb upper-level trough situated over the upper Midwest continues to swing packets of vorticity maximums south-eastward, a series of low pressures will form over the Tennessee Valley and slide north-eastward.  As result, overrunning events will occur and bring some rain later Tuesday night and into Wednesday morning. This overrunning event is going to be a rain event because the temperature is just simply too warm for any frozen precipitation. The rain will continue throughout Wednesday and taper off to showers later in the afternoon. We can't rule out the possibility of seeing more rains falling Wednesday night, as GFS suggests.

However, this synoptic setup is a close call for a northeast snowstorm: a strong upper-level trough advecting positive vorticity southward, a vigorous cut-off upper low swinging through the southern states, a weak ridge attempting to form over the Rockies to amplify the upper-level trough. The only ingredients that are missing are the phasing of the northern and southern upper-level trough and the amplification by the west coast ridge. These can all be attributed to the unfavorable locale of the polar vortex situating over Alaska, bring waves after waves of troughs to the west coast and keeps the heights over the southeastern U.S abnormally high; allowing for a rather zonal flow across the country. In the case with the recent October snowstorm, the trough dipping down from the upper Midwest was just marginally deep enough to phase with a southern branch of the jet stream to cause a robust coastal storm. If anyone reading this has attended Dr. Uccellini's, the Director of NCEP, presentation featured by PSUBAMS, he or she should pay close attention to rapidly changing forecasts this winter. As Dr. Uccellini theorized, the phasing of the troughs tends to be harder to predict during La Nina ENSO conditions. Last winter we had a moderate La Nina and the post-Christmas snowstorm occurred. The ENSO is again forecast to be a moderate La Nina and we already have seen its possible effects on cyclongenesis prediction in the recent October snowstorm, where models failed to converge.

Mid-term (Thursday-Friday):

That was just some side notes, now back to forecasting. The rain showers should have moved out of the region by Friday morning except for extreme southeastern Pennsylvania might still see some lingering showers. The clouds will linger for most of the state and the temperatures will be cooler comparing to what the region will see on Wednesday. The winds might also be quiet strong behind the cold front, so please bundle up. The clouds will gradually clear out Thursday night if the forecast goes as planned. We should mostly sunny skies on Friday as a ridge of high pressure builds in over the region.

Long-term (Saturday-Sunday):

                Calm weather conditions will persist into the upcoming weekend as the overall weather pattern favors a dominant southeast ridge. The temperature will warm up to above normal as warm air is being advected from the south by the large area of high pressure. The next chance for some precipitation will be later on Sunday as another cold front approaches from the west.

Written by David Wang

Monday Afternoon Technical Discussion

Synopsis:
Strong storms likely in Western PA tonight ahead of a frontal passage. Most areas will see rain tonight and again on Wednesday, before skies will clear for the latter half of the week. Temperatures remain mild on Tuesday, begin their slide on Wednesday and spend the rest of the week recovering back to near-normal levels.

Short-Term:

A tornado watch was issued for the northwest corner of the state earlier this afternoon. It is in effect until 11PM EST. Some strong to severe storms will roll through the western part of the state as we go through the evening hours, fueled along by an upper-level jet streak. They should begin to die out later in the evening. Most areas of the state will likely see some rainfall during the overnight hours as the front passes to our south diagonally across the state. Drier conditions will prevail on Tuesday, though partly cloudy skies should remain throughout the day. Temperatures will remain mild on Tuesday, with most locations across PA remaining about 10 degrees above average.

Long-Term:

Our next piece of energy, will work its way across the country and be just to our south by Wednesday morning, ushering more rain into the area. The precipitation should fall entirely as rain, as temperatures will not be cold enough for snowfall likely anywhere. Temperatures begin their downward tumble on Wednesday, falling back near normal levels. As the low slides off to our east Wednesday night, clearing skies should prevail. A strong surface high will position itself just to our south beginning on Thursday, where it will remain for the next several days. Expect cold temperatures through the end of the work week, continuing to moderate back towards average each day. Guidance from the 12z GFS suggests our next weather-maker past Wednesday does not approach the area until Sunday. This system could usher in some lingering lake-effect snow showers in its wake, though exact details on this are still several days away.

~Devin Boyer

Technical Discussion

Synopsis:

A trough of low pressure will hover over the state through the mid-week, allowing for unsettled conditions.  The passage of a cold front Monday into Tuesday will bring precipitation off and on from late tonight through late Wednesday.  Later in the week, high pressure will manage to gain control, so expect drier and sunnier conditions.

Short-Term:

The 1200 UTC runs of both GFS and WRF are projecting a trough anchored over much of the United States to dominate the weather through Wednesday.  A surface low pressure system is forecasted to pass through Pennsylvania, dropping a cold front through the state late Monday into Tuesday.  All models are projecting precipitation in association with this front.  The 1500 UTC run of the SREF plumes suggests a round of precipitation starting late tonight and lasting through Wednesday, with perhaps a small respite on Tuesday.  For State College, the bulk of the ensemble members are forecasting below .4 inch total precipitation.  For Philadelphia, the bulk of the ensemble members are projecting even lower amounts.  This does not seem like a significant precipitation event for the bulk of the state through Tuesday, although northwestern and western portions of the state could see up to 1.6 inches of precipitation when all is said and done, according to the SREF runs. 

Long-Term:

The 1200 UTC runs of SREF precipitation type probabilities and the 850 mb temperature projections in general all suggest the precipitation to be purely rain through Tuesday.  However, with the cold air advection building in after the passage of the cold front by Wednesday, snow showers and mixed precipitation could be likely in higher elevations and northwestern portions of the state.  We forecasted accordingly and carefully.  The 1200 UTC runs of MOS temperature projections show the low temperatures Wednesdaynight barely breaking freezing as well. The 1200 UTC runs of both WRF and GFS show a ridge of high pressure dominating by Thursday, allowing for mostly sunny skies, as dry conditions are projected for all levels of the atmosphere.

Thursday Eveing Techincal Discussion

Synopsis

As the 500-mb trough approaches the area, there is the chance for snow showers in the northwest areas overnight. As this upper level trough moves through on Friday, conditions will remain cold and blustery. Behind this trough, an area of high pressure will build in this weekend.  There is a chance that a cold front will move southward into Pennsylvania around next Tuesday.

Short Term

The cold front that went through the area this afternoon has caused temperatures to drop. Temperatures will fall slowly tonight as there should be winds and clouds. Expect northern zones to have lows in the upper 20's and in southern zones in the lower 30's Friday morning. Skies will remain cloudy on Friday and temperatures should not go very far as the 850 mb temperatures are -4 to -6 C and there is strong cold air advection. High pressure will build on Saturday which will promote dry and clear conditions. This will allow temperatures to moderate some into the 50's.

 

Long Term

Skies look to be remain dry and sunny for the weekend as the ridge continues to build in. Temperatures should stay in the 50's Sunday. Some clouds will work their way back into the area Monday as a cold front approaches the area. During the day on Tuesday, a cold front should move through the area and bring a chance of showers. This will bring some cooler temperatures for Wednesday.

-Matt Mehallow