Weds Aug 31 4-6pm Shift

Synopsis

 A ridge of high pressure will slide easterly overnight. A slow moving

 warm front will push across Pennsylvania Thursday and Friday. A cold

 front will approach the State late Saturday and hang overhead through

 Sunday. 

 Short Term (Through Friday Morning):

 A shearing upper trough will begin to cross over the state this 

 afternoon causing varying amounts of mid and high cloud cover. 

 There is a slight chance of precipitation in some locations.   Increasing cloud cover and dew points will result in a milder night 

 across the North West Mountains. Clear skies, light wind and dry air 

 associated with the lingering influence of high pressure along the east

 coast should result in another cool night across the Eastern half 

 of the state. The warm front over Western PA will be the focus 

 for scattered afternoon to night convection on Thursday. High 

 temperatures Thursday will be fairly uniform ranging between

 80-85F, accompanied by increased humidity. 

 Long Term (Through Tuesday)

 A deep south wet flow ahead of the low will transport warm and humid air into the region 

 Saturday and Sunday. Conditions will likely turn more Autumn-like by 

 Labor Day. Friday looks to be mainly rain free as an upper level

 ridge acts to suppress convection. Saturday looks to be the warmest

 day of the weekend as a flow becomes south west behind the warm front. 

 Some locations across Southern PA will likely approach 90F. Sunday looks

 to be a transition day as a cold front approaches. Colder temperatures

 will likely yield an increased chance of cloudiness. Highs will 

 most likely range from the upper 60s to upper 70s in some parts 

such as the lower Susquehanna Valley. 

Forecaster: Meredith Nichols

Wednesday Midday

Overview: High Pressure will dominate one more day before a upper level wave/disturbance moves into the region for Thursday.  Friday will be a transition day as a cold front slowly pushes towards us.  This will effect us for the weekend in terms of showers.

Short-term: Both the GFS and NAM show high pressure for Wednesday then moving off to the coast for Thursday as an upper level disturbance moves into the region.  Then they vary on temperature and when the showers will occur.  Went with a more NAM temp solution, but more of a GFS shower through the day solution.

Long-term: Switching to the GFS, a weak cold font that looks to take its sweet old time as a upper level trough moves into the region will occur this weekend, making for an unsettled Labor Day Weekend.  The GFS has the front moving through late Saturday to Sunday, as it was appear ant on the temperatures.  Basically did not move much from mos at all.

Tuesday Evening Technical Discussion

Tranquil conditions should continue throughout the state on Wednesday with a few low level clouds possible due to afternoon heating. Relative humidity's are over 70% above 850 mb across the Western portion of the state on Wednesday, so expect most cloud cover to exist in Western Pennsylvania. Temperatures will be on the increase Wednesday as winds shift from the south leading to some warm air advection. Expect many areas to reach the upper 70's with some areas reaching the lower 80's. NAM and GFS MOS are both showing that many areas of the state will reach at least 80 on Wednesday. Cloud cover may slow afternoon warming in some of the western regions. Temperatures will fall in to the upper 50's Wednesday night, with cloud cover keeping them from falling back to the lower 50's. Some showers should be expected in the afternoon on Thursday as a weak front moves through the state. Showers should end in the evening as the day time heating is lost, so most shower activity will not reach the eastern portions of the commonwealth. Due to evaporative cooling, showers and cloud cover will keep temperatures in the upper 70's. The 12z GFS does allow the showers to hold together better than the 12z NAM and allows many of the showers to reach the Harrisburg-Lancaster area. Best option is probably the NAM solution as there will likely not be enough energy for the showers to last long into the night. Cloud cover will move through the state Thursday night, which will keep overnight lows in the upper 50's to the lower 60's. Skies will clear for the most part on Friday allowing temperatures to rise back in to the lower 80's. NAM keeps some low level cloud cover in the western portions of the state Friday which may keep temperatures in the upper 70's across the West. Expect cloud cover and dew points to be on the increase Friday night as a front begins to approach the area. This should keep temperatures in the mid to lower 60's overnight Friday. A warm front will move in from the south on Saturday leading to some afternoon showers and thunderstorms across the state. While still in long range, runs of the NAM keep most of the showers in the eastern portions of the state, while the GFS allows showers to form statewide. Expect pre frontal advection to push temperatures well into the mid 80's on Saturday. Showers will die off during the evening as daytime heating is lost. Some cloud cover will remain across the state Saturday night keeping temperatures in the lower 60's. Temperatures on Sunday will reach the lower 80's again as winds shift to the southwest. A cold front will push into the state later in the day on Sunday allowing for more showers statewide Sunday afternoon. Showers may last through part of night before again dying off due to lose of solar heating. Winds will shift from the northwest Sunday night allowing for temperatures to fall back into the mid 50's across the state.

 

Zachary Fasnacht

Tuesday Morning Discussion

Unfortunately the clean, crisp air we are experiencing today and Wednesday will not last throughout the week. Computer models generally agree that a warm front will bring some clouds, humidity, and a chance of summer storms sometime Thursday and Friday. The GFS model shows more storms possible over the weekend as the tail end of a cold front from a Low pressure system up in Canada moves south over the area. It looks like another Low pressure system will develop later to finally push all the unsettled weather out to sea with another cold front passing through sometime on Labor Day. It doesn't look like this Labor Day weekend will be quite as pleasant as we all hope for, but fortunately it won't be ruined by another Hurricane.

Another interesting thing to watch is a possible tropical system developing in the Gulf of Mexico later in the week that could possibly impact Texas and the gulf coast. Both the GFS and the WRF models show a potent system brewing. Also, keep an eye on Tropical Storm Katia out in the Atlantic. It is forecasted to become a Hurricane by Thursday, and it is following a very similar track to Hurricane Irene. Katia could potentially impact the East coast some time next week. Stay tuned...


Josh Aikins

Technical Discussion

Model runs seemed to agree that we'll be clear until Wed/Thurs. We're a bit worried about the presence of a weak warm front that might peak through on Wednesday night and keep nighttime temperatures warm. Other than that, we think most of the rain will keep off until Thursday afternoon where a few storms might fire ahead of a weak disturbance. We decided to focus our precip forecast on Thursday. Friday's temps appear that they will be warmer than model forecasts if we have a partly cloudy sky. Humidity will return on Fri/Sat and more rain is expected Saturday as the front begins to move closer.

[A more detailed discussion will come next week. This is Monday Night's first meeting; we spent most of our time teaching the basics of forecasting.]

Tom Bedard

Technical Discussion

Looking at the new model runs I stayed with consensus for the next few days as a high pressure system moves into the area. Both the GFS and NAM agree. I am worried about the upper level trough/vort max moving through which could produce a few clouds, but with the 700mb showing dry I went with mostly sunny instead of just sunny. The high seems to stick around until Wednesday when an upper level disturbance moves through. Both GFS and NAM have this disturbance and the main threat seems to just be a few more clouds will be around. I wouldn't be surprised with the instability aloft if a few thunderstorms form over the mountains due to high level source heating, but Im keeping it out of the forecast. Both models seem to be heading towards isolated showers and thunderstorms for Thursday as the upper level disturbance moves through. I put showers and thunderstorms in the forecast but I think these will die out as the heating of the day is gone, so I took it out of tomorrow night. Friday and Saturday's temperatures will be probably be higher than mos as we are prefrontal, but I kept showers and thunderstorms out of forecast for Friday as the models are still uncertain. It is something to keep an eye on.


Nick Marguccio

Technical Discussion

Synopsis:

High pressure will build into the region for the first half of the week, allowing for mostly sunny skies and overall fair conditions.  Scattered showers may move into the state on Thursday, associated with a region of low pressure.

Short-Term:

As now-Tropical Storm Irene continues to move up into New England, the 1200 UTC runs of WRF and GFS suggest that a broad area of high pressure will build over the state into the beginning of the week.  The relative humidity projections from the 1200 UTC NAM runs show the corresponding lack of moisture at all levels in the atmosphere.  We accordingly forecasted mostly sunny to sunny skies through at least Wednesday. The latest run of the SREF plumes shows no precipitation falling through Wednesday; after the ascent in precipitation totals due to the outer rainbands from Irene today, the 3-hour precipitation projections completely level off.

Long-Term:

All long-term model guidance (focusing on the 1200 UTC runs of WRF and GFS) suggests that a region of low pressure will approach Pennsylvania on Thursday, bringing a chance for some showers and even thunderstorms.  It is a little too early to be precise on extent and intensity of the precipitation, so we were appropriately vague in our forecasts for precipitation for Thursday