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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 210905

Area Forecast Discussion
National Weather Service State College PA
505 AM EDT Sun Jul 21 2019


Another hot and humid day is in store, but a cold front will 
move through the region bringing an end to the recent heat 
wave. Noticeably cooler and less humid air will finally provide 
relief from the sweltering heat by the middle of next week.



Radar shows scattered nocturnal convection moving east over 
the northern tier. The activity is forming in an area of 
moisture convergence associated with a cold front that will
eventually change the weather pattern for us from the recent
heat and humidity to cooler and drier.

The last couple of nights, the HRRR has been of little use
catching onto the scattered convection, and tonight is no
exception with no rain generated in the model in the CWA at this
hour. The RAP is a little better at least depicting some stray 
showers over the northern 1/2 or so of the forecast area through
the morning hours.

Another hot and humid day is in store, though with winds
shifting to the north, our northern counties will begin to see
some measure of relief with highs "only" in the mid 80s. 

We expect more scattered thunderstorms today, starting over the
north this morning, but more area-wide during the afternoon. 
Mid level temps are still progged to be quite warm, but forcing 
associated with the cold front and steep mid level lapse rates 
should be enough to allow showers to pop as the day warms up.

The oppressive humidity will lead to heat indices in excess of
100 deg over much of the region today, from roughly IPT-UNV-AOO
and eastward. Today should be the last day for heat headlines.

The various members of the HREF suggest that the scattered
showers and storms will continue into the evening, and may even
pick up again later at night in response to the frontal system 
becoming influenced by falling heights aloft associated with the
deepening shortwave moving through the Great Lakes.



Monday looks to be an active day. The frontal system will slow 
during its passage and with a deepening upper trough overhead, 
at least one wave is expected to form on the front, 
potentially helping to focus locally heavy rain. 

At this hour I don't have enough confidence to say exactly 
where the best rains will fall, but early indications suggest my
SERN zones where PWATs around 2 inches (2-3 sigma) will pool 
along and ahead of the wavy front. In general, when warm season 
tropical moisture combines with upper forcing more in line with 
a cool season system, we usually see problems develop. We are
leaving it for the day shift to evaluate and possibly issue a 
Flood Watch to start preparation for the potential heavy rain 



The 00Z deterministic NAM and ECMWF are slower in making the
last of the wavy front and the rain exit my SERN zones, with
rain lingering much of Monday night. The GFS and Canadian are 
faster and bring the drier air in sooner.

What is more certain is that by the end of Tuesday we will see
markedly less humid air moving into the forecast area. This 
will be the beginning of a period of pleasant mid summer days 
with temperatures running several degrees cooler than normal, 
and with lower dewpoints and humidity. 

Models agree with keeping the anomalous eastern upper trough the
dominant feature through the end of the week when some
indications of rising heights returning to the NE are depicted. 


06Z TAFS sent.

Unlike last night, not much on the radar. There was some storms
earlier west of Clearfield, could see the lightning on my way in
around 1130 PM last evening.

While there could be some isolated patches of fog later and
lower clouds, not seeing any yet.

Earlier discussion below.

VFR flying are expected over most of the region overnight. 
However, an isolated thunderstorm is possible through around 05Z
at KBFD and KJST.

A plume of higher moisture preceding an approaching cold front,
combined with orographic lift, could possibly result in a 
period of reduced cigs across the western mountains (KBFD/KJST) 
Sunday morning. Otherwise, widespread VFR conditions are 
expected to persist through Sunday. However, scattered 
thunderstorm impacts are possible Sunday PM over primarily 
central and southern Pa. 


Mon...Widespread showers and tsra impacts possible. 

Tue-Thu...No sig wx expected.


Excessive Heat Warning until 8 PM EDT this evening for PAZ028-
Heat Advisory until 8 PM EDT this evening for PAZ019-025>027-


NEAR TERM...La Corte
LONG TERM...La Corte