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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 252317

Area Forecast Discussion
National Weather Service State College PA
717 PM EDT Mon Mar 25 2019

Low pressure over southern Indiana will track south of
Pennsylvania late today. Canadian high pressure and associated 
dry air mass will settle south across the area during midweek. A
cold front is then likely to push southeast across the region 
next weekend.


Rain Showers continue to drape across the southern half of
Pennsylvania. Pockets of localized heavy showers are possible
through the Laurels and along the Mason Dixon line this
 The biggest forecast question with this system is the presence
of any snow. The strong dry warm air advection has precluded
precipitation. 850mb temperatures continue to drop to below 0C
and wet bulbs continue to get close. As they do expect light
snowfall to mix with any rain. Accumulations remain probable in
the higher elevations of the Laurels, especially in regions
above 2,000 ft. 
 The system will pivot this afternoon and continue to then move
to the southeast into the early evening hours. 
 Precipitation could linger in the far southeast through the
first half of the overnight period.

 Clearing skies will advance south tonight, as low pressure 
passes off the coast and high pressure builds south from NY 


Canadian high pressure will build into the region Tuesday,
accompanied by abundant sunshine and a light northerly breeze.
Mixing down model 850mb temps yields expected max temps ranging
from the upper 30s over the northern mountains, to the mid 40s
across the Susq Valley.


U.S. and Int'l EFS guidance show a strong consensus on waning NW
flow aloft and a large area of sfc high pressure building SE
from the Glakes and over the NE U.S., with the high amplitude 
upper ridge over the Rockies flattening out as it slides east 
across the Plains states. 

This evolution of the sfc and upper pattern will mean mainly dry
weather with a gradual warmup with above, to well above normal 
temps in the 50s to around 60F on Thursday. Generally light 
wind will become southwesterly thursday ahead of a cold front, 
that will slow or stall and string out nearly east to west 
across PA to close out the week and introduce the chance of 
showers Thursday afternoon into Friday. 

The front will retreat back slightly to the north as a warm 
front later Friday and Saturday as the northern stream trough 
races east across SE Canada, and a southern stream upr wave and 
sfc low approaches from the Central Plains and Mid Miss Valley.
We'll see temps soar in the 60s and perhaps top 70F in some of 
the southern valleys both Friday and Sat. 

The best chance for showers comes over the weekend, when east 
coast ridge breaks down and cold front pushes across the state.

U.S. and Euro models diverge early next week with the timing,
amplification and northern extent of influence with respect to a
southern stream wave. For now, will maintain a dry forecast
unless there is appreciable northern deviation from current 


Wave well to our south is moving rapidly eastward and the 
precip shield over south central PA is drying up as it slides 
south and east. Precip likely over by 01Z at all terminals. Only
JST is at IFR currently (23Z) but should also be clearing out 
shortly. Massive high pressure and strong subsidence will bring 
clear sky tonight with only a small chc of some fog where it has
rained the most today. The near-zero dewpoints will come in 
rapidly, though, on light but steady north wind. Thus, have not 
mentioned fog in the TAFs at this point. Wind picks up just 
slightly late tonight or Tues AM, but stays from the N. Sfc high
will be overhead Tues night and VFR should hold through Friday.


Wed...No sig wx.

Thu...Mainly VFR, but SCT SHRA poss NW along WFRONT.

Fri...SHRA N, mainly VFR elsewhere.

Sat...Mainly VFR, but SCT SHRA poss NW as CFRONT nears.


A weak weather system will move south of the state today through 
tonight producing light precipitation, mainly over the southern 
half of the district. Behind this system, a large area of high 
pressure will build across the eastern third of the country 
through mid week. 

***This area of high pressure contains very dry air, with
 dewpoints in the single digits expected today, Tuesday and
 Wednesday across the northern half of the district. Dewpoints in
 the teens are forecast across the southern half on Tuesday and
 Wednesday. This will result in afternoon relative humidity below
 30 percent all three days. Given sufficient mixing, quick drops
 to below 20 percent are possible in some locations.

Winds are expected to remain on the light side /less than 10mph/ during
this period.




NEAR TERM...Fitzgerald/Ceru
SHORT TERM...Fitzgerald/Ceru
LONG TERM...Lambert