281
FXUS61 KCTP 092026
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
426 PM EDT Thu May 9 2024

.SYNOPSIS...
A nearly stationary frontal boundary at the surface will be
located from far Southwestern PA to Northern VA over the next 24
hours as a few waves of low pressure move east along it.

The front will push southeast to the Delmarva Coast late
Friday.

Several upper level troughs will move across PA Tonight, Friday
and Saturday, bringing periods of light to moderate rain,
followed by a rebound to warmer but still unsettled weather
next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Coupled upper level jetlets over Central PA were responsible for
a trend toward increasing UVVEL via FGEN forcing and an
expanding area of showers/steady light across roughly the SW
half of the CWA.

The timing of the thickening clouds earlier today and the onset
of at least some rain has helped to greatly flatten the diurnal
temp curve, with readings through the rest of the afternoon
staying nearly steady as some of the initial light rain
evaporates in the dry llvls (where sfc dewpoints ranged from the
L40s North to the L50s across the south) and helps cool temps
toward the Wet Bulb.

High temp departures today will range from 5 to 10 deg F below
normal, which equates to readings of 55-60 F from the Central
Mtns and Laurel Highlands to the Northern Mtns. Peak temps in
the mid to upper 60s will be found across the Lower Susq Valley
where dry conditions and some sunshine occurred through thin
spots in the thickening mid and upper level cloud layers.

Followed a blend of NAM and HREF to increase POPS to nearly 100
percent in all locations tonight and 85-95 percent on Friday.
Mid level FGEN max via the NAM has nicely depicted the area of
steadiest light to moderate rain thus far over Nrn Ohio and far
NW PA and there`s no notable reason to deviate from this blend
tonight as additional jet energy arrives from the west and the
center of 1000 MB sfc low slides across Northern WVA and
Central VA.

Enhanced mesoscale lift over the Q-Strny front (just to our
south) via a SSErly 25 KT 850mb jet and the zone of strong, mean
convergence/FGEN in the 850-700 MB layer will boost rainfall
rates to over 0.10 inch per hour at times. Included areas of
1/2SM in fog for later tonight through Fri morning, as typically
occurs with the cool, moist upslope flow from the east.

Min temps tonight will only be about 10-12F lower than daytime
temps due to the higher dewpoints and cloud cover.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
The upper low/trough axis and an inverted sfc trough will
become collocated over the CWA Friday morning. Widespread thick
clouds and frequent showers, if not periods of steadier rain and
drizzle) will be the result.

Wet bulb zero heights from late Thu night through Fri night
will be in the 3000-5000 ft range over the northern half of PA
which should lead to some bright- banding and over-estimates of
radar/MRMS derived rainfall amounts from about 35-45 NM out
from KCCX and KBGM radars over northern PA and a bit further
away across Southern PA and from respective radar sites (KPBZ,
KLWX and KDIX) as Zero Tw levels there will average about 5-7kft
agl.

6 hour FFG values are 2.5 inches or greater across most of the
CWA, and even some pockets of higher end rainfall amounts of
1.5 to 2 inches (within the larger area of basin average rain of
1-1.25 inches) are expected to result in just some ponding in
poor drainage areas and moderate rises on streams/creeks as the
rainfall rates should stay below 0.10 inch per hour for much of
the time and will be spread out fairly evenly over the 24-30
hour period ending Friday evening.

A few breaks in the clouds may develop across the western mtns
later Friday morning and afternoon, and High Res models and
their ensembles indicate a likelihood of a rainfall min or
absence from e Friday evening into Saturday morning across wrn
PA as drier air with a minor ridge in the mid and upper levels
slides across the region. Friday may be the chilliest day for
quite sometime, if not until until this coming Autumn with
cooling aloft mixing down to the surface by the periods of
rain/drizzle.

The unsettled pattern continues into the weekend. Another upper
trough and reinforcement of the cooler/drier air moves in for
Sat. Additional showers are expected for the entire area, esp in
the latter half of the day. Highs stay in the 50s for nearly
everyone Fri (possibly only reaching the upper 40s acrs some of
the higher terrain in Northern PA and the Laurels.

This should be the coolest day for the next 7, and perhaps for
the rest of the warm season. We should rebound ~5F on the maxes
for Sat.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Tendency to have a large scale upper level ridge over the west
this weekend, will result in much below normal 500 mb heights
over the east into next week.

While some milder and drier conditions will be possible Monday
into Tuesday, much of the time it will be cooler than normal
and wet from time to time for much of the upcoming week. Sunday
will be one day that will feature gusty winds and cold temperatures.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
A surface low approaching Central PA will cause
consolidation/expansion of the current, fragmented area of rain
seen on region radar across the state.

A surface boundary is stalled out just south of the PA/MD
border and it won`t move much over the upcoming 18-24 hours.

Latest guidance has the surface low tracking to the south of
Pennsylvania, meaning the heaviest rains and greatest
instability for t-storms will also track to the south.

However, reductions in visibility will develop early tonight
with CIGS lowered into the IFR to LIFR range later tonight and
continue through at least the midday hours on Friday.

Outlook...

Fri...Low cigs/drizzle possible, especially in the morning.

Sat...PM showers/low cigs possible, mainly W Mtns.

Sun...AM low cigs possible W Mtns. Sct afternoon showers/brief
vis reductions possible.

Mon...Still a chance of a shower.

&&

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

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert/Dangelo/NPB
LONG TERM...Martin/Gartner
AVIATION...Lambert