Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 260521
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
121 AM EDT Fri May 26 2017

.SYNOPSIS...
An upper low directly overhead will slide quickly away today,
leaving northwest flow in it`s wake. Weak ridging will move in
but many chances for showers and a few thunderstorms are seen
through the holiday weekend. The fast flow aloft will keep it
unsettled. A cold front will pass through on Monday.

&&

.NEAR TERM /THROUGH TODAY/...
Upper low is over the eastern zones evidenced by the change in
storm motion which has occurred over the last few hours there.
Short wave dropping SE out of MI/OH will make some light rain in
the SW half of the area overnight. This area of showers will
likely begin to break up into more-cellular showers as the
daylight brings heating under the cyclonic low level flow.
Clouds around this morning call for mild temps and muggy air
in the morning, and a cooler than normal day on Friday. A
slightly confluent flow aloft should keep the showers from
growing too tall. Will keep POPs in the SCT range due to the
expected areal coverage at any time. But, a good forecast will
be that most places may get a little wet. The showers will be
moving along and, again, not tall. Thus, the chances for mod or
hvy rain and for thunder are very low. Maxes are a tough call
due to the clouds and possibility of showers knocking a few degs
off. If there can be more sunny breaks, it may rise above the
current guidance blend. Will stay close to but just a deg below
the locally-produced CTPblend of guidance.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/...
As the sun sets Friday, the showers should dissipate nicely
except perhaps in the NE cos. However, a ridge runner may drop
out of the upper Great Lakes into the state per the GFS. The NAM
has some convection just scooting to the south of the area, and
it is mainly on Saturday. This is also the rough idea of the 12Z
EC. This paints two opposing pictures of Saturday weather. Add
in the HiRes ARW and you get yet another. Too many differences
on timing and placement of possible convective complex(es) to
make a detailed forecast at this point. Will keep continuity
strong with chc POPs over the SW/SC cos and lesser numbers in
the N. Will peak the POPs during the daytime on Sat vs tonight.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
A lower-amplitude but moderately strong westerly (zonal) mid
level flow will set up in the wake of the departing upper trough
with modest height rises/weak will ridging aloft into the
weekend. A warm front is progged to extend east from surface low
in the western Ohio Valley to the mid-Atlantic coast on
Saturday.

Central PA should reside on the north/east fringe of high
instability convective corridor/MCS type pattern expected to
evolve from the central and southern Plains to the southern mid-
Atlantic coast into Saturday night. The greatest risk for
scattered thunderstorms remains over the SW 1/3 of the CWA
which is consistent with previous fcsts. SPC has introduced a
MRGL risk into this area for D3. The remainder of the area
should see a mainly dry start to the holiday weekend but will
maintain slight chance POPs.

The large scale pattern will evolve into a broadly cyclonic
flow regime by Monday with upper trough parked over the Great
Lakes and southeast Canada into midweek. The aforementioned warm
front will lift north across the area on Sunday followed by a
series of weaker cold front associated with shortwave trough
rotating around parent upper low centered to the south of Hudson
Bay. Ensemble blend still supports max POPs on Sunday/Sunday
night into Monday with some additional shower opportunities into
midweek as series of shortwaves rotate around mean upper
trough. Temps should average pretty close to normal/seasonal to
close out the month of May.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Meso anal shows the main surface low just north of PHL as of
11PM. Water vapor loop indicates the axis if the shortwave has
shifted to eastern PA with the remainder of the forecast area
under the main upper low.

Disorganized showers remain, but the overall activity has been
diminishing and the near term CAMS show little more than
scattered showers floating around for the remainder of the
overnight.

The bigger picture is starting to show more variable conditions
as low level moisture from earlier rains helps in the
development of areas of MVFR/IFR. With the upper low continuing
to pivot over the state during the evening and overnight,
reduced conditions will become more widespread.

After some areas of low cigs and fog early in the day Friday,
the afternoon will feature mainly VFR with brief MVFR/IFR in
scattered showers. Moist WNW upslope flow will continue across
the western mountains with the best potential for lingering
reduced conditions.

.OUTLOOK...

Sat...AM fog possible BFD.

Sun...Showers/reduced cigs possible, esp Sun night.

Mon and Tue...AM low cigs poss west. Sct PM tsra impacts poss
east.

&&

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

&&

$$
SYNOPSIS...Dangelo/Gartner
NEAR TERM...Dangelo
SHORT TERM...Steinbugl
LONG TERM...RXR/Steinbugl
AVIATION...La Corte



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