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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 231721
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
121 PM EDT Thu May 23 2019

.SYNOPSIS...

Low pressure lifting northeast across the Great Lakes today 
will drag a relatively strong cold front across Pennsylvania 
late this afternoon and evening. 

Cooler and dry weather will follow for Friday. The holiday 
weekend will bring warmer temperatures, higher humidity and a 
renewed chance for showers and storms at times. Memorial Day 
itself looks to offer up fantastic weather for much of the day 
with near normal temperatures and comfortably lower humidity.

&&

.NEAR TERM /THROUGH TONIGHT/...

A line of fast moving convection has pretty much outrun the
unstable air and so far the storms have underperformed in what
was an enhanced outlook for severe storms. The RAP still wants
to destabilize the SERN zones where a new watch is in effect.
Shear remains impressive with forecast EHIs/STPs about as high
as they get for this part of the world.

The big question is if the Lower Susq can destabilize fast
enough to feed these storms that are racing east at 40-50 mph.
The second biggest question will be if new storms can manage to
form over the western and northern parts of the CWA where the
airmass has not been changed and dewpoints remain in the 60s.
 
Different flavors of the HREF have differing solutions with the
most pessimistic member developing a new line and taking until 
about 10PM to have it drop SE to the Mason-Dixon line. Some HREF
members just develop some scattered activity at worst. I 
suspect that unless we see some upstream activity starting to 
spark off very soon, at worst we will see some late afternoon 
scattered activity and the current line will be the main event.

Afternoon high temps will be several deg above normal or in the
mid 70s north and lower to mid 80s in the southern valleys.

&&

.SHORT TERM /FRIDAY/...
The potentially widespread severe weather event will wind down 
fairly quickly this evening, but storms could linger into the 
late evening near and just in advance of a sfc cold front that 
will sink into southern PA by 02-03Z. This second round of
convection associated with the cold front could be more of a
hail/minor flooding threat this evening across the southern half
of PA.

In the wake of the Cold Front, a pleasant late night tonight, and
Friday is in store for the region with near to slightly above 
normal high temps (mid to upper 60s north and mid to upper 70s 
south), low humidity, and a gusty NW wind of 20-25 mph from the
late morning through Friday afternoon.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The fast, quasi zonal flow and tap of deep moisture/high PWAT
air stretching from the southern Plains to the Ohio Valley and
Great Lakes will support a few bouts of convection (with 
locally moderate amounts of rain) pushing east across the 
Commonwealth over the holiday weekend. 

Memorial Day appears to be trending drier with a decent amount
of sunshine, a light northwest breeze and low humidity. 

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

&&

.AVIATION /17Z THURSDAY THROUGH MONDAY/...
Widespread VFR can be expected this morning with enhanced 
weather impacts early this afternoon through the early evening 
hours. Storms should begin to move through the western TAF 
sites between 16Z to 18Z and continuing west to east through the
afternoon. The main line of convection should be through the 
region between 22Z to 00Z. Have put some timing in the TAFs but 
have left out TSRA due to timing issues. Some of the storms 
could be strong to severe thunderstorms. Gusty Southwesterly 
winds should affect the southwest sites with a brief period of 
LLWS behind the front at JST possible around 22Z. 


.Outlook...

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.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...La Corte/Lambert
NEAR TERM...La Corte/Lambert
SHORT TERM...Fitzgerald/Lambert
LONG TERM...Lambert/Martin
AVIATION...Ceru/Gartner