Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 211128
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
728 AM EDT Mon Oct 21 2019

.SYNOPSIS...
This week will feature more dry days than wet days with rain
expected on Tuesday. Seasonably mild temperatures on Monday
will trend modestly cooler through midweek and remain near
average through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Low clouds and fog this morning should give way to a partly to
mostly sunny afternoon. Sfc obs and RWIS data indicate areas of
dense fog/lowest visby AOB 1/4SM being observed over the higher
terrain from the Laurel Highlands into the Endless Mountains. An
SPS may be issued through the morning commute. Lower elevations
to the east of the Allegheny Plateau are primarily dealing with
low clouds with some patchy fog in spots.

The main forecast issue today will be timing low cloud
dissipation. HREF data indicates the south central ridge and
valley region will take the longest to erode and not fully
break out until after 16-18Z. The earlier an area breaks out of
the clouds, the more upside they will have in terms of maxT.
Overall, expect the mildest readings in the mid to upper 60s on
the northwest and southeast fringes of the CWA with the coolest
temps (around 60F) over the interior high elevations along the
Allegheny Front.

Fcst soundings suggest the potential for a few sharp dewpoint
drops given mixing of very dry air just above the inversion
layer. This is mostly likely to occur over the northwest mtns
where skies will be mostly sunny.

Clouds will increase into tonight with an increasing south
southeast flow ensuring very mild minimum temps running +10 to
+15 degrees above average for late October. 00Z HREF shows the
leading edge of frontal rains reaching the far western zones by
12Z Tuesday.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Confidence remains very high in a band of rain moving west to
east across CPA on Tuesday. The strong south-southeast flow will
transport 1-1.5 inch PWAT air (+2-3 standard deviations above
the mean) into the region and support widespread soaking rain.
Instability (MUCAPE) appears to be negligible (so no mention of
thunder) but the deep moisture available should allow for
locally heavy downpours. NBM/WPC blended QPF amounts are still
in the 0.50 to 1.00 inch range with the highest totals most
likely over the favored southeast flow/upslope areas across
east-central PA. A secondary low developing over the Delmarva
and tracking to LI may enhance rain should bring the last round
of rain to far eastern/northeastern zones btwn 00-06Z Wed before
pcpn shuts off west to east across the CWA by the predawn hours
Wednesday. Flash flooding is not expected given the recent
dryness (3hr FFGs 2-4+ inches) and limited rain rates in the
absence of deeper convection. However, can`t rule out some very
minor nuisance type street flooding or ponding in urban areas
due to leaves clogging storm drains.

It will turn mostly sunny, breezy and cooler on Wednesday behind
the departing frontal system. High pressure will provide dry wx
through Wednesday night with some potential frost/freeze risk
for southeast zones still active in the extended growing
season.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
There is reasonable consensus among the guidance in showing some
light rain/showers skirting across the eastern Great Lakes and
possibly clipping the northern tier of CPA on Thursday. However,
pattern evolution uncertainty grows quickly heading into the
weekend with very low confidence in the forecast at this time.

The global model guidance continues to offer 2 possible
solutions by this weekend: 1) a less amplified GFS with weaker,
faster system with little to no rain; or 2) a stronger and
slower system with a much higher probability of rain (later
Sunday into Sunday night) advertised by the ECMWF/UKMET/CMC.

Until there is a convergence/trend toward a common solution, the
wide range of outcomes results in a very low confidence forecast
which leans on gridded data from the National Blend of Models.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
IFR conds in low clouds and areas of fog, especially along the
hier elevation taf sites across the north and west, will give
way to improved conds by mid morning. Elsewhere VFR conds will
continue through the day.

A return to wet conditions on Tuesday as a cold front crosses
the airspace from west to east. Then improving conditions after
Tuesday, as weak high pressure builds into the region.

.Outlook...

Tue...Rain/low cigs possible.

Wed and Thu...No sig wx expected.

Fri...Some showers possible, especially west late.

&&

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

&&

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


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