Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 031932
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
332 PM EDT Mon Aug 3 2020

.SYNOPSIS...
A corridor of moderate to heavy rainfall associated with
tropical storm Isaias is expected across eastern Pennsylvania
tonight through Tuesday. The heaviest rainfall will occur early
Tuesday before conditions dry out Tuesday night into Wednesday.
Scattered showers and thunderstorms return to the forecast by
late in the week. Temperatures will dip below average on
Tuesday before trending warmer later in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Near term forecast remains on track into tonight. Latest hires
models continue to show moderate to locally heavy rain showers
spreading northward into south central PA btwn 22-04Z. Another
relative max in shower/t-storm activity will be across the
northwest zones ahead of low pressure and trailing cold front
moving slowly eastward through the Great Lakes and Ohio Valley.

Leading rains ahead of Isaias showing some characteristics  of
a PRE with moisture streaming northward and interacting with
increasing synoptic support ahead of the approaching trough and
the right entrance region of the upper jet. Consensus of hires
models does hit at convection focusing along stationary boundary
which may extend northward into scentral PA from the Blue Ridge
in VA/NC. The bottom line is we will need to monitor this area
for heavy rain potential for localized flooding risk. At the
very least, it would contribute toward more saturated ground and
relatively lower FFGs in advance of heavier rains expected
early Tuesday.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
Main focus will be potential heavy rainfall and flooding impacts
associated with Isaias. The latest blended QPF axis from
WPC/NBM/HREF has trended a tad lower overall with amounts. The
most significant reductions were on the western edge of what
will be a very tight gradient. This reinforces the uncertainty
the how much heavy rain forecast and flooding risk hinges on
where the axis of QPF sets up. Overall, we remain consistent
with 2-4" forecast near and east of I-81. Flash flood watch
remains in effect for this area. Lower Susq tribs to the east of
Harrisburg appear to be most susceptible to minor flooding at
this time. Fortunately, we are going into this event with
relatively dry ground in most places - although the eastern part
of the CWA has been the "wettest" relative to moderate drought
locations in the central and western parts of the CWA.
Antecedent conditions are a big factor when considering
potential flooding impacts.

Increased sustained winds and gusts across the far southeast
zones incorporating guidance from NHC. Peak values are notably
higher than previous fcst but below wind advisory criteria.

The heaviest rain should taper off later Tuesday afternoon into
the early evening with some lingering showers Tuesday night.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The lingering effects of the prior rainfall may be making
flooding over the ern locations on Wed. However, much if not all
of any flooding should be receding by Wed night.

Large picture starts with a slight trough with axis over the OH
Valley. The upper pattern should then turn more zonal for most
of the period but with a couple of small amplitude waves rolling
through. Dry high pressure at the sfc will provide a mainly
dry long range period as it sits overhead or just to our north.

There will be a frontal boundary draped to our south there will
be a small chc of showers over the srn tier on Thurs aftn-Fri.
However, it will be light stuff, and no worries for any renewed
flooding.

The temps should start out very close to normals if not
slightly below normal for the NW plateau. The temps will warm up
a small amount each day into the weekend, and stay very warm
into the beginning of next week. As the temps warm up, there
will also be an increase in diurnal (aftn/eve) convection. A
higher-amplitude trough will near from the west for early next
week, and continue to make the chc of rain rise.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
VFR conditions going into Monday evening with showers/storms
lifting northward into the southcentral PA airspace. Locally
heavy rain may result in some brief IFR visibilities. Cigs
should trend lower into Tuesday morning with rainfall coverage
and intensity ramping up across the eastern 1/3 of the airspace.
Introduced some gusty winds across the southeast airfields as
Isaias tracks north from the Delmarva through far eastern PA/NJ.

Outlook...

Tue...Moderate to heavy rain with MVFR/IFR restrictions likely
across the central and eastern airspace.

Wed-Thu...Trending drier/VFR with just an isolated shower or
t-storm possible.

Fri-Sat...Local impacts from sct showers/tstms.

&&

.CLIMATE...
July 2020 was a remarkably warm and dry month in Central PA.

*Average Temperature*
-Warmest month on record at Harrisburg & State College (82.2F
 at MDT, breaking the old record of 81.8F set in July 1999;
 77.0F at STC, breaking the old record of 76.5F set in 1955).
-T-3rd warmest month at Williamsport (78.2F, tied with July 1921
 and behind 1955 with 79.1F and 1901 with 78.9F)

*Average Maximum Temperature*
-3rd warmest month on record at Harrisburg (92.2F behind 1999
 with 93.5F and 1966 with 93.2).
-5th warmest month on record at Williamsport (90.0F; record of
 93.0F set in 1955 with other warmer Julys in 1988, 1934, and
 1921).

*Average Minimum Temperature*
-Warmest month on record at Harrisburg & State College (72.2F at
 MDT, shattering the old record of 70.7F last year; 67.5F at
 STC, breaking the old record of 66.6F set in 2012)
-2nd warmest month on record at Williamsport (66.4F behind 1901
 with 71.1F)

*90 degree days*
-2nd most on record at Williamsport with 19, behind 1955 with
 25.
-T-2nd most on record at Harrisburg with 22, behind 1966 with 23
 and tied with 1999.

*Precipitation*
-Driest July since 2007 at Williamsport (1.86")
-Driest July since 2002 at Harrisburg (1.35")
-5th driest July at State College (1.38")

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 11 PM EDT this evening through Tuesday
evening for PAZ035-036-056>059-063>066.

&&

$$
SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Dangelo
AVIATION...Steinbugl
CLIMATE...Banghoff


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