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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 200005
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
805 PM EDT Wed Jun 19 2019

.SYNOPSIS...
An unsettled and stormy weather pattern will continue through 
Thursday evening thanks to the close proximity of a slowly 
meandering front. Expect to see several more rounds of showers 
and some will contain heavy downpours that could dump localized
rainfall amounts of 1 to 2 inches within just an hour or so. 
There will be a risk of strong to severe thunderstorms and flash
flooding on Thursday as a potent areas of low pressure moves 
right over the state. a pleasant and dry weekend is in store. 
Temperatures will trend a little cooler than normal for Friday 
and Saturday in the wake of a cold front. A warm up starts next 
week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Quasi-stnry front stretched from near I-80 in Western PA to the
Lower Susq Valley and Philly Metro Area this afternoon and marks
the northern edge of the higher PWAT air and more robust sfc-
based cape that was approaching 2000 j/kg at 18Z.

Recently posted a Flash Flood Watch from 4 pm to Midnight 
tonight across all but the northern tier counties of the CWA. 

Increasing number of showers were developing within small holes
in the otherwise bkn-ovc sky cover, and as a result of subtle 
terrain and weak boundary forcing.

Latest several HRRR runs indicates upscale growth of the showers
into small clusters of TSRA that will drift gradually NE across
the region this afternoon and evening. PWATs range from about
1.25 inches across Northern PA, to between 1.5-1.75 inches 
along and south of the aforementioned front.

Regional model hodographs and MBE vectors points toward new cell
development on the South to SE flank of existing cells which
will create the potential for training and localized very heavy
rainfall. 

FFG over portions of Central PA is as low as ~1"/1hr and 
~1.25"/3hrs, while most of the Southern Tier and Lower Susq 
Valley has FFG 1 hour values of 2-2.5 inches.

Mean, basin-average QPF will be on the order of a few to 
several tenths of an inch this afternoon and evening, and some 
locations will receive less than one-tenth of an inch through 
04Z Thursday. 

Adjusted hour temps and afternoon max temps upward by several 
deg F in some locations today. 

Will continue to carry high PoPs as everyone should get wet at 
some point this afternoon/evening.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Showers will gradually decrease after sunset as forcing remains
weak in the vicinity of the quasi-stnry front, but the
convection may not dissipate completely. 

However, it will only be a brief break in the rain as a wave 
will move across the OH Valley tonight, and a dying MCS should 
enter the Western counties just before sunrise. The rain with 
this initial shot should be generally light to moderate (a few 
to several tenths at most).

A distinct low center will develop and push into wrn PA in the 
morning hours. This low is sub-1000mb and anomalously strong for
the beginning of Summer. It will push its southward trailing  
cold front through during the afternoon and early evening. The 
coincidence of the old west-east front, anomalously high PWATs, 
and this decent long- wave trough + sfc low moving thru around 
peak heating will generate thunderstorms. Some of them will 
produce very heavy rainfall, and severe wind gusts/hail with as
increasing vertical shear and a veering/broad loop hodograph. 

An isolated tornado or two is possible as well due to the 
boundary/shear and low LCLs present - especially from the
KUNV/KIPT vicinity SE to the Lower Susq Valley. 

The heavy rain will probably cause some flooding, but the 
flooding threat area is not highly certain at this point. We may
need a flash flood watch for Thursday, but later shifts can 
take a closer look. It's a little far out to post a watch just 
yet. 

The potent sfc low pressure center (~995 mb) should be over NE 
PA by nightfall, and the cold front dragging down thru MDT. Wrap
around could make some sct SHRA over the W Thurs night, but it 
will be drying out and getting a little gusty by Fri morning.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Breezy and drier/less humid conditions will arrive Thursday
night through Friday on the backside of the departing system. 
Expect a break from the rain for 2-3 days with pleasant
conditions through the weekend before a surge in humidity 
returns showers and storms to the forecast next week.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...

Showers continue to stream through the area. Thunderstorms are
beginning to subside with only isolated TARA now, mainly through
the south and eastern portions of the region. 
 Overall VFR cigs and vsbys though passing showers are bringing
MVFR to brief periods of IFR vsbys in heavy rain. 
 IFR is possible overnight due to the light winds and the
copious amounts of moisture. So look for areas of fog/low 
stratus clouds similar to early this Wednesday morning. 
 Another round of showers and thunderstorms will be possible
late Thursday morning, early Thursday afternoon. 


.Outlook...

Thu...Rain/low cigs possible north. Scattered-numerous PM tsra 
impacts likely Central and Southern PA.

Fri...AM low cigs possible W Mtns.

Sat-Sun...No sig wx expected.

&&

.CLIMATE...
Astronomical summer (solstice) begins Friday, June 21st at
1154AM EDT (1554 UTC).

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until midnight EDT tonight for PAZ012-
017>019-024>028-033>036-041-042-045-046-049>053-056>059-
063>066.

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...Steinbugl
AVIATION...Lambert/Ceru
CLIMATE...