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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 230212

Area Forecast Discussion
National Weather Service State College PA
1012 PM EDT Wed May 22 2019

A ridge of high pressure will drift off the Mid Atlantic Coast 
this evening. Low pressure lifting northeast across the Great
Lakes on Thursday will drag a strong cold front across
Pennsylvania late Thursday. Cooler and dry weather will prevail
on Friday. The holiday weekend will bring warmer temperatures,
higher humidity and a renewed chance for showers and storms at


Main weather issue tonight will be a southwesterly low level 
jet and associated plume of anomalous pwats pushing into the 
region from the west. Radar loop at 02Z shows a broken line of 
showers and a few lightning strikes along this feature across 
eastern Ohio into northwest Pa. Latest operational model runs 
and earlier ensemble guidance support a decent chance of showers
tonight, especially over northern Pa, as the low level jet 
presses east. Models do indicate some elevated instability later
tonight, as axis of low level jet arrives, so will maintain a
slight chance of thunder.

Mostly cloudy skies, a light southerly breeze and low level
moisture advection all point toward much a much milder night 
than last night. NBM min temperatures are mostly in the mid to
upper 50s.


Expect a lull in the convection early Thursday, as remnants
over low level jet exit southeast Pa. Focus then shifts toward 
potential severe weather ahead of potent shortwave and cold 
front approaching from the Grt Lks. Partly sunny skies are 
expected to result in moderate instability by afternoon in the 
warm sector over central Pa, while somewhat more stable air 
hangs on east of advancing warm front over eastern Pa. 

The synoptic scale atmospheric signatures are favorable for 
severe weather, including a relatively deep upper trough and 
surface low over the Grt Lks and a strong, moist low level jet 
maximum over Pa. Damaging wind gusts appear the primary threat,
given the 50-60kt 700mb wind fields in the latest model output.
Strong 0-6km shear is supportive of supercells and the 
combination of low LCL and high 0-1km shear is indicative of a 
tornado threat, especially in the vicinity of surface warm front
over the eastern part of the forecast area. 

The latest CAMS indicate the evolving severe weather threat 
could begin as early as midday over the northwest mountains, 
then propagate into the rest of the forecast area during the 


Weighted the fcst to what we had at first with minor 
adjustments to grids, then went across the grids again after 
looking at the 12Z EC. 

Main changes then was to up the POPS Saturday night into Sunday.

I did lower POPS some more for Monday into Tue. Wed is a mix of
the superblend and some minor adjustments. 

Flow pattern remains abnormally fast and active.

Temperatures for the most part will be warmer than normal, but
not that abnormal for the first big holiday weekend of the warm


A ridge of high pressure today will slide off the Mid Atlantic 
Coast this evening.

Widespread VFR can be expected today and much of tonight, with 
scattered restrictions possible with a dying area of showers and
thunderstorms that will traverse the area during the evening and

Winds starting off light and variable will become S-SE 5-10 kt,
eventually gusting into the teens.

Enhanced weather impacts expected on Thursday from mid- 
afternoon through the evening hours as strong to severe 
thunderstorms impact the region. 


Thu...VFR into the afternoon, then strong thunderstorms 
developing mid-afternoon lasting into Thu night.

Fri...Ceiling restrictions poss NW early, then mainly VFR.

Sat...Restrictions in vicinity of showers/thunderstorms. Tstms
more numerous north, scattered south.

Sun...Restrictions possible near scattered tstms, mainly west.

Monday...Still a chance of showers and storms.




SYNOPSIS...La Corte/Martin
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Martin
LONG TERM...Martin