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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 170057
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
857 PM EDT Tue Jul 16 2019

.SYNOPSIS...
---Mid Summer heat and humidity to stick around through the
 weekend---

The remnants of once Hurricane Barry will move through the area
Wednesday through early Thursday with scattered thunderstorms
and localized heavy downpours. Otherwise we will be dealing 
with hazy hot and very humid conditions until early next week 
when some relief is in sight.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Dewpoint and humidity increased with the passage of the warm 
front Tuesday afternoon. This helped trigger scattered showers
and and thunderstorms. Most of the storms have moved into 
Lancaster and Eastern PA. Thunderstorms should continue to 
diminish after sunset, but a few small showers remain possible. 
Pops ramp up late over the NW Counties in advance of the main
trof associated with the remnants of Barry increasing chances 
for late night showers and thunderstorms. It will be a very 
mild to steamy night with lows ranging from the mid and upper 
60s north to the lower to mid 70s south.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
*Heavy downpours possible Wed with remnants of TC Barry. 

The airmass will be very juicy with PWATs in the 1.75-2" range,
or some 2-3 sigma. The threat for local downpours cannot be
ignored, but the diffuse nature of the unwinding tropical
system makes it hard to pinpoint a best area for potential heavy
rain/flooding. The SREF and GEFS show the best chance for inch 
or more rains being over the NRN 1/3 or so of the forecast area,
which matches pretty well with the SPC HREF through the day 
Wednesday.

Models are consistent in keeping highs very warm to hot, 
suggesting there will be at least some sunshine and the rain 
will be very convective. With that in mind I favored the 
afternoon with the highest chances for rain/thunder.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
*Excessive heat risk Fri-Sat 

Model guidance continues to signal the potential for excessive
heat around the end of the week and into the weekend. Maximum
heat index values peak in the 100-105 range Friday and Saturday.
Heat headlines appear likely during this time and will continue
to highlight heat risk via HWO, social media and DSS briefings.

Very warm mid-level temperatures may act 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. 

New part of discussion below.

I did look over temperatures and dewpoints several times this
shift. Made a few minor adjustments to the temperatures and 
dewpoints. 

I did cut pops back some after early Thursday, and prior to
later Sunday, based on mew model data and a very warm airmass.

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 Tuesday, as the mean upper level
trough is nearby.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
VFR will dominate through most or all of the overnight hours
with a mainly BKN mid level Altocu cloud layer based between
090-120 KFT AGL. 

Scattered VSBYS in the 4-6SM range are possible between 06-12Z
but confidence in the location and duration is low enough to
keep it out of the 00Z TAF forecast. 

The leading edge of the moisture plume from the remnants from
what was once Hurricane Barry will push into the NW part of our
CWA INVOF KBFD after 03Z and stay confined mainly to the NW Mtns
of PA through the mid morning hours of Wed bringing at least ocnl
MVFR VSBYS and CIGS.

Best flying conditions Wed will be in the 12Z-18Z period. 

The plume of greatest moisture spreads east across Central PA
and Susquehanna Valley airfields Wednesday afternoon and
evening, supporting the quick development and expansion of heavy
showers and ocnl TSRA with brief gusty winds and FQT lightning
leading to brief impacts to takeoff and FAP. 

Winds will be mainly light and from the south to southwest late
tonight through the mid morning hours Wed, then veer more to 
the 220-240 deg direction and increase to 8-10KTS with gusts 
into the teens for the late morning and afternoon hours.

.Outlook...

Wed...Scattered to numerous showers/thunderstorms with heavy
downpours probable.

Thu-Sun...Mainly VFR with isolated PM thunderstorms possible.

&&

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

&&

$$
SYNOPSIS...La Corte
NEAR TERM...Watson/La Corte
SHORT TERM...La Corte
LONG TERM...Martin/Steinbugl
AVIATION...Lambert