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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 162158
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
558 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. 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/...
As advertised, dewpoints soared with the passage of the warm
front, and with the developing instability we have seen
scattered showers and thunderstorms form. The not-very- 
organized activity seems to align along an axis from the NRN 
Mountains down through State College to southern Bedford and 
Fulton Counties. 

The latest HRRR has not been very helpful thus far, so the near
term POPs are a blend of extrapolation and what the HRW NSSL 
suggests for the remainder of the afternoon.

Convection will tend to diminish after sunset, but given the
ensemble POPs it's hard to forecast a totally dry overnight
anywhere. I basically went with low chance POPs most of the
overnight in most areas, but ramp things up late over the NW
where the ensemble MOS guidance all point to 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 /22Z TUESDAY THROUGH SUNDAY/...
Widespread VFR will be interrupted by some brief MVFR CIGS and
VSBYS in pulse-variety TSRA across the Susq Valley and
north-central mtns through early this evening INVOF of a slowly
eastward moving warm front. A few short lines could exhibit 
bowing structures as water-loaded/rain cores collapse and fan 
out cool outflow air to the east.

Shower activity is most likely to continue across the far 
northwest airspace late tonight into Wednesday morning. 
Elsewhere, some MVFR fog is possible late in areas where it 
rains. Confidence is too low at this time to include in TAFs, 
but conditions will improve rapidly after sunrise.

.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...La Corte
SHORT TERM...La Corte
LONG TERM...Martin/Steinbugl
AVIATION...La Corte/Lambert