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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 181732
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
132 PM EDT Sat May 18 2019

.SYNOPSIS...
A warm front over the Ohio Valley will push into southwest
Pennsylvania today, then north of the entire state on Sunday. 
Low pressure will track north of Pennsylvania Monday, as its 
trailing cold front comes through the state. Pennsylvania will
be on the northern periphery of a building subtropical ridge the
second half of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1015 am update... A narrow band of cloudiness and showers
continues to move eastward into the region from western PA late
this morning, with the showers trending weaker over time. These
showers are mainly tied to warm advection aloft and a northern 
Great Lakes short-wave. As heights aloft build today, the
aforementioned area of showers should continue to lose steam 
with eastward extent during the midday hours. 

Later this afternoon into the early evening, isolated-scattered
convection is still possible, along and just ahead of an
approaching surface warm front. This will mainly occur over the
Allegheny ridges and south-central mountains, where some  
instability will develop, along with low-level convergence near
the aforementioned warm frontal boundary. At this time, we do 
not anticipate any severe storms, as overall forcing is fairly 
weak.

Highs this afternoon are expected to range in the 70s for much 
of central PA, with some of our northern mountainous areas 
staying in the upper 60s, where cloudiness will be more 
prevalent. 

Previous discussion... Regional radar loop early this morning 
shows a band of spotty showers across northern Ohio and 
southwest Pa associated with fgen forcing north of stalled 
frontal boundary. Latest model output supports low POPS this 
morning across the western half of forecast area, as this weak 
fgen forcing lifts north through the eastern Grt Lks. Patchy 
dense valley fog over the northwest counties should dissipate by
around 13Z based climatology and latest NAMNest/LAMP guidance. 

Focus later today will shift toward scattered, diurnally-driven
convection forming south of advancing warm front, which should
lie across the Laurel Highlands and south central mountains by
mid afternoon. Model 0-6km shear of around 20kts suggests
thunderstorms will be of the pulse variety with little chance of
organized severe weather. 

Upstream satellite imagery supports a mostly cloudy morning
across the southwest half of the forecast area associated with 
aforementioned fgen forcing, while mostly sunny skies are
expected over the northeast counties. By afternoon, model rh 
profiles support partly sunny skies area-wide.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Upper level ridging and associated lack of forcing would support
dwindling convection after sunset, so have undercut NBM/Superblend
POPS tonight. A southerly breeze and advection of higher 
dewpoints will result in a mild night with lows fairly close to 
60F.

The surface warm front is progged to lift north of the entire 
region Sunday, with scattered strong, to potentially severe, 
thunderstorms erupting during the heating of the day. Mid level
wind fields and deep layer shear are not looking that 
impressive. However, HREFV2 surface based capes surge to near 
2000 j/kg by afternoon and the presence of dry mid level air and
associated downdraft capes support the possibility of strong 
downbursts.

Sunday should be the first summerlike day of the season with
dewpoints well into the 60s and highs well into the 80s based on
latest 850mb temps.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Surface low is progged to track north of the area Monday, as 
its trailing cold front comes through central Pa. Latest model 
guidance indicates the best chance of showers/tstorms will come
with passage of low level jet and associated plume of highest 
pwats Sunday night and early Monday. However, can't rule out a 
few strong thunderstorms as the surface cold front moves through
eastern Pa Monday afternoon. 

Medium range guidance lends increasing confidence in a period 
of dry/cooler weather Tuesday, as high pressure and low pwat air
mass builds southeast into the area. 00Z NAEFS indicates 
Pennsylvania will be on the northern periphery of a building 
subtropical ridge the second half of next week. Shortwaves 
riding over the top of the ridge will bring back the daily chance
of convection Wednesday-Friday.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
18z update... Primarily VFR/unrestricted conditions are expected
for the central PA terminal sites over the next 24 hours. 

That being said, there are a few concerns. First, a few isolated
showers/thunderstorms are possible late this afternoon into the
early evening period. However, coverage looks sparse enough to
preclude mention in the terminal forecasts at this time. Second,
lower ceilings/light fog seem probable late tonight into the 
early morning hours Sunday for a good portion of the area 
(roughly a 6-hour period). At this juncture, MVFR-fuel 
alternate restrictions are foreseen. Lastly, thunderstorms are 
expected to fire up Sunday afternoon. However, most of this
should occur after 18z Sunday. 

Surface winds should generally average 5 kt or less through
early Sunday. Winds should pick up a bit from the S at 8-10 kt
by midday Sunday. 

.Outlook...

Mon...Restrictions possible from early morning lower ceilings
and midday-afternoon showers and thunderstorms. 

Tue-Wed...Mainly VFR.

Thu...Restrictions possible from lower ceilings, as well as
potential showers and thunderstorms.

&&

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

&&

$$
SYNOPSIS...Fitzgerald
NEAR TERM...Jurewicz/Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald
AVIATION...Jurewicz/RXR/Evanego