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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 260032
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
832 PM EDT Thu Apr 25 2019

.SYNOPSIS...
Rainy weather is expected in central Pennsylvania tonight 
through Friday evening. Periods of heavy rain and a few strong 
thunderstorms are possible Friday afternoon. Windy and colder 
conditions will arrive for the start of the weekend.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
I did slow down main area of showers by a little here this
evening. 

A few showers across the south now, but the bulk of the showers
will to the west over the midwest and Ohio Valley.

Earlier discussion below.

Occasional light rain will continue across south central PA
mainly south of I-80 into the evening. A blend of hires models
suggests focus for light rain showers will shift into north 
central PA or north of I-80 later this evening into early 
tonight. Continued to trend max temps lower across portions of 
the area where clouds/light rain have persisted for most of the
day. Warm front lifting northeast across the area later tonight
will be a focus for additional rain showers into early Friday 
morning.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Amplifying 500mb trough will send a deepening sfc low from
northern OH through the eastern Great Lakes by 00Z Sat. The
trailing cold/occluded front will be a focus for showers as it
sweeps eastward across central PA during the day on Friday. 

Strong moisture transport/above normal PWs via 40-50kt low 
level jet will bring potential for heavy downpours and 
isolated/localized flooding. Risk for severe storms is also a
concern particularly over the southeast and south central zones
where weak instability overlaps stronger wind fields and shear 
profiles associated with amplifying northern stream shortwave 
trough. SPC D2 places a portion of the lower Susquehanna Valley 
in MRGL risk, but could see this area expand to the north/west 
with some HREF members showing a squall line/QLCS developing 
Friday afternoon. Conditions will turn breezy and colder Friday 
night with a chance of rain/snow showers across the NW mtns into
Saturday morning.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Sat will bring a new shot of cooler air and breezy conditions
with even a few wet snowflakes mixing in with the scattered rain
showers over the highest elevations of NW PA during the morning
hours. This will be followed by another shortwave/surface low 
tracking east from the Ohio Valley and moving right across the 
state on Sunday.

There will be a sharp N/S temp gradient with 850 mb temps around
+10C across the South and near zero C near the NY border. Sfc
low track between Interstate 80 and I-76 looks to be the
consensus track. 

The more southern solutions place the northern mtns under the
gun for at least some mixed precip across the higher elevations
if not a period of wet snow Sometime Sunday morning. Slightly
more northern solutions lessen the snow/mixed rain and wet snow
threat up north but introduce the chance for some gusty
midday/early afternoon TSRA across the SE quadrant of our CWA. 

Will be monitoring changes to the track closely as big
differences in temp, prcip type and the threat for strong
convection varies greatly over a short north/south distance. 

WPC snow graphics do indicate a 1-3 inch snowfall potential
across the higher elevation of the north Sunday morning, but for
now will lean twd slightly lower amounts given the daytime
occurrence of the snow. 

The sfc low will be quick moving and is progged to slowly weaken
as it crosses the state.  

Latest guidance shows the cool shot behind the Sunday storm will
be quite chilly. The growing season has started over the SERN
1/2 of the CWA and we could be dealing with some frost issues
Monday morning - especially since the axis of a 1032MB Sfc high
over the upr St Lawrence Valley extends south through the Susq
Valley. Temperatures will moderate slowly for the rest of the 
week.

After a dry period through most of Monday, the active pattern 
will continue with a new weak wave for Monday night/Tuesday. 
From there, the trailing front could stall near PA keeping the 
mention of showers in the forecast through the end of the week.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
An approaching warm front will bring lowering cigs across
central Pa overnight, along with scattered showers. Upstream
observations and near term model data indicate mvfr cigs will
persist across northwest Pa (KBFD) this evening, with tempo ifr
cigs possible. Elsewhere, vfr conditions should prevail across 
the rest of the area this evening. After midnight, model 
soundings and SREF probability charts support mvfr becoming 
likely across most of the forecast area and possible across the 
southeast (KMDT/KLNS). The high terrain of the Alleghenies from 
KBFD south to KJST could potentially dip to ifr cigs late 
tonight. Another concern will be the possibility of LLWS late 
tonight, as strengthening winds aloft overspread the area. 
Current model soundings indicate marginal LLWS criteria are
likely across all but the southeast airfields late tonight and 
early Friday morning. 

Rising cigs and a diminishing LLWS threat is expected between
12Z-18Z Friday, as a warm front lifts north through the region.
A cold front will sweep east across the region during the
afternoon, accompanied by a round of heavy showers and possible
thunderstorms. A gusty west-northwest winds will develop behind
the front late Friday with a return to VFR conditions in most
places. However, upsloping flow could yield lingering MVFR cigs
in the evening hours over the high terrain from KBFD south 
through KJST.

.Outlook...

Sat...Windy. AM snow showers possible NW Mtns. 
Sun...AM low cigs/rain/snow possible northern Pa. 
Mon...PM rain/low cigs possible, mainly N Mtns. 
Tue...Showers/low cigs possible, mainly N Mtns. 

&&

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

&&

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