Thursday, July 18, 2019, 9:55 AM EDT
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Area Forecast Discussion
Valid At
Wed, Dec 31, 7:00pm EST
FXUS61 KCTP 181140

Area Forecast Discussion
National Weather Service State College PA
740 AM EDT Thu Jul 18 2019

----Dangerous heat and humidity possible this weekend---

We will be dealing with hazy, hot and very humid conditions 
until early next week when some relief is in sight. Dangerous 
heat will build Friday and Saturday, with heat indices peaking 
on Saturday afternoon, easily exceeding 100 over southern and 
especially southeastern areas.


Isolated showers still petering out across the southern half of
central PA early this morning. Air mass is still quite humid,
but ever so slightly drier air is filtering southward into the
Northwest Mountains. Isolated pockets of dense fog starting to
show up over portions of the Alleghenies and may need a Dense
Fog Advisory before the morning is through.

Patchy dense fog to start the day will be slowest to leave the 
southeast and along the MD border where isolated to scattered 
showers and thunderstorms cannot be ruled out into Thurs 
evening. Elsewhere, it will be a drier day with a slight
downtick in humidity from Wednesday, but it is still quite warm
throughout. Highs to range from the mid 80s north to the lower 
90s south. This keeps Heat Index below advy numbers in the SE.\

Fair, warm and muggy conditions to prevail tonight with areas of
valley fog expected. Lows won't be very low, ranging from the
mid to upper 60s north to the lower 70s southeast.


*Excessive Heat Watch in effect noon Friday through Sunday 
 evening for eastern quarter of CWA

Main story heading into the weekend is for dangerous heat to
build across the area, with maximum heat index values peaking 
in the 100-105 range Friday, and even higher on Saturday. Can't
rule out an isolated afternoon or evening shower, but most areas
will remain dry. Highs range from upper 80s north and along the
spine of the Alleghenies to the mid to upper 90s south.


Excessive heat continues this weekend. Maximum heat index 
values peak in the 105 to 110 range Saturday before lowering
slightly again for Sunday. Excessive Heat Watch remains in
effect from noon Friday through 8 pm Sunday for areas from 
Harrisburg to Williamsport and east. Area in watch may need to 
be expanded later if confidence increases. Will also continue to
highlight heat risk via HWO, social media and DSS briefings in 
addition to the watch.

Very warm mid-level temperatures look to limit/cap t-storms 
Fri- Sun. That said, models hint at the potential for MCS 
activity propagating along wavy frontal zone on the northern 
periphery of summertime upper ridge/heat dome. 

Flow is fast and strong across the US and Canada border overall 
for mid July, but we are south of the main westerlies. The
airmass is warmer than what we have seen lately. 1991 and 1995
featured such warm air. In this case, the warmest air is
advected toward BUF late Friday. Warmest air for central PA is
Friday into Saturday. 850 mb temperatures fcst to be near plus
24 degrees at 850 mb late Friday across Lake Erie. Will be
interesting to see how fast water temperatures come up on Lake
Erie by next week. 

A cool down is expected by next Monday, as the mean upper level
trough is nearby.


12Z TAFS sent.

Several more hours of low clouds and fog.

The main issue later this afternoon and early evening
is showers and storms. Most likely area to get activity
is MDT and LNS, as the remains of the low pressure system
drifts southeast away from our area, similar to the low
we saw on Monday, July 8th.

Most of the rest of the week will be dry, very warm aloft
should make it hard for storms to develop. 

Models are a tad cooler at 850 mb by 00Z Saturday at the east
end of Lake Erie, but plus 22 degree air at 850 mb is still 
hot, but not as hot as plus 24 degree air. Time will tell how
much the warm air holds down the shower and storm formation.


Fri-Sun...Mainly VFR with isolated to widely scattered PM 
thunderstorms possible. Heat/humidity will make the density 
altitude much higher - takeoffs/landings will take more 

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


Excessive Heat Watch from Friday afternoon through Sunday 
evening for PAZ028-036-041-042-046-049>053-056>059-063>066.


LONG TERM...DeVoir/Gartner/Steinbugl

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