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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 200923

Area Forecast Discussion
National Weather Service State College PA
523 AM EDT Sat Jul 20 2019


----Dangerous heat and humidity expected through Sunday---

We will be dealing with hazy, hot and very humid conditions 
until early next week when a cold front will pass and bring some



Nocturnal convection finally seems to be starting to diminish
over my NWRN zones, even as new storms are forming upstream 
over SRN Ontario and Lake Erie. The NW PA storms formed over 
Lake Erie and propagated east and southeast and have been 
remarkably persistent despite the presence of some very warm air

The potential for future convective developments will be the
biggest forecast challenge today. At this hour we have a
beautiful MCS/MCV moving over Lake Michigan. The outflow around
the system looks almost hurricane-like. Tops have begun to show
signs of warming over the last hour, even while radars show new
convection firing from Cleveland west into NRN IN, and even up 
over southern Ontario. Disturbingly, the latest HRRR doesn't 
see all the current storminess, and has a very dry-optimistic 
forecast as we move into the day today. I have a feeling we may 
be playing catch up in the near term as a result. RAP still 
shows a fair amount of CAPE for the time of night, along with 
respectable mid level lapse rates of 6-8C/KM. Mid level temps in
excess of 10C have done little to dissuade developments so far.

Climatology would suggest that we will yet see a lull in the
convection as the sun comes up. The movement of the upstream 
MCV will have to be watched for developments later in the day. 
SPC confines its Slight Risk to the lower lakes, only bringing 
the Marginal threat into far NWRN PA.

Other than the convection, it will be another hot and very humid
day, making for dangerous heat indices over most of the region.
We kept the alignment of the Heat Advisories and Warnings today
which has the entire CWA in some sort of heat headline.



Heat concerns will continue Sunday. We expanded the Heat Warning
to include the entire SE of the forecast area, as well as
expanding the Advisory west into the CTRL Mountains.

With a cold front sagging into SRN NY/NRN PA, and upper heights
slowly falling, the highest chances for rain will be over the 
NR half of the CWA. CAPEs in excess of 2000J are cooked up by 
all the 00Z guidance as well as the latest GEFS/SREF. The 00Z 
GFS showed surface based CAPEs going nuclear, surging to over 
6000J over the SUSQ Valley! With a very humid airmass in place, 
it seems likely the instability will be enough to overcome the 
warm air aloft making showers possible even over the SE.



Our anomalous ridge and the accompanying heat wave will break
down rapidly early next week, to be replaced by an anomalous
trough and a much welcome break in the heat and humidity.

A cold front will drop into the region later Sunday and Monday.
With a deepening upper trough to the west, models slow the front
and bring a series of waves along it Monday and Monday night.
This will have the potential to bring widespread soaking rains
and possibly flooding to the region to start the new work week,
before we ultimately cool off and dry out for the Tuesday
through Friday timeframe. 


Not a lot of change for the 06Z TAF package.

Main thing was to add some groups.

Still several areas of showers and storms from northwest PA, 
northwest across Lake Erie, to the upper Great Lakes area.

Overall think these areas will slowly weaken, given that the 
dewpoints and temperatures inland from the Lakes not all that
high, compared to the MDT area. The southeast is too warm aloft
for anything prior to late aft. 

For now, only have VCSH in BFD.

Earlier discussion below.

Fair weather and light wind is expected over most of central Pa
overnight associated with a ridge of high pressure. In those 
portions of northern Pa that received rain this evening, patchy 
fog is possible late tonight. High level cloud debris from 
thunderstorms over the Grt Lks may limit radiational cooling and
fog potential for a while, but expect an increasing chance 
toward dawn Saturday. Model soundings also indicate the
possibility for a period of low mvfr cigs over the Laurel
Highlands (KJST) Saturday morning, resulting from a moist,
upsloping west flow. 

Any morning low cigs or fog should lift by late morning, with 
widespread VFR conditions a near certainty later today. An 
isolated afternoon/evening thunderstorm can't be ruled out, but 
the odds are too low to mention in the forecast at this point. 


Sun...AM low cigs possible W Mtns. Scattered PM tsra impacts

Mon...Widespread showers and tsra impacts possible. 

Tue-Wed...No sig wx expected.


Heat Advisory until 8 PM EDT this evening for PAZ004>006-
Excessive Heat Warning until 8 PM EDT this evening for PAZ028-
Excessive Heat Warning from noon to 8 PM EDT Sunday for PAZ036-
Heat Advisory from 8 PM this evening to noon EDT Sunday for 
Excessive Heat Warning from noon today to 8 PM EDT this 
evening for PAZ019-025>027-034-035-045.
Heat Advisory until noon EDT today for PAZ019-025>027-034-035-
Heat Advisory from noon to 8 PM EDT Sunday for PAZ019-025>027-
Heat Advisory from 8 PM this evening to 8 PM EDT Sunday for 
Excessive Heat Warning until 8 PM EDT Sunday for PAZ059-066.


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