798
FXUS61 KCTP 191957
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
357 PM EDT Fri Jul 19 2024

.SYNOPSIS...
* High pressure over the region will maintain dry weather and
  lower humidity into early Saturday.
* Southerly winds usher in an uptick in humidity on Saturday
  with scattered afternoon showers and thunderstorms.
* Dry conditions on Sunday into Monday precede a more unsettled
  pattern next week with seasonable temperatures.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A ridge of high pressure extending from Indiana into PA was
linked to/supported by broad subsidence beneath the thermally
direct left entrance region of a 60-70 kt zonal jet core
extending from the Ohio River Valley to the Southern New England
Coast.

PWATS averaged around 7 tenths of an inch across the CWA this
afternoon - a refreshing chance from the extended heat and
humidity earlier this week.

The sharp gradient in PWAT seen across Central and Southern VA
at 18Z today - with the main gradient of Theta-E air in the
850-700 mb layer seen further north about 50 NM either side of
the Mason/Dixon line, will both lift north as the two favorable
quadrants for ascent in association with second, slightly
anticyclonically curved upper jetlet lift north across PA late
tonight into Saturday, with the jet strengthening slightly.

Patchy fog could again develop again tonight into Saturday
morning across the NW mtns given the increasing moisture and
scattered cloud cover expected, though coverage is not expected
to be as extensive as this morning. Morning lows on Saturday
will trend a few degrees warmer than this morning - from the
middle 50s in the northwest to upper 60s southeast.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
As the aforementioned sfc high slides east and off the Mid
Atlantic Coast developing SE-southerly sfc flow and south-
southwesterly flow through about 7-8 KFT AGL will advect
increasing clouds north into the state very late tonight/early
Sat.

Trimmed POPS to under 10 percent through the early morning
hours Sat, and made just slight upward adjustments to cloud
cover while maintaining the overall SCHC to CHC pops for
SHRA/SCTD PM TSRA as PWATs increase to between 1-1.5 inches from
NW PA to SE PA respectively.

There appears to be a fairly significant, 7-8 kft thick layer
of dry air between the low clouds and a thickening layer of
cirrus/high altostratus, which should prevent much opportunity
for significant drop formation/ QPF amounts.

Min temps tonight will be about 6-8 deg F warmer that last night
as moisture and clouds gradually increase from the south late.
Lows will be in the mid to upper 50s across the north and mainly
mid to upper the southern valleys.

Pertinent/still valid points of the previous disc...

A short wave disturbance will bring increased rain chances for
the afternoon on Saturday when isolated to scattered coverage of
showers and storms develops over parts of the Laurels, SC
Mountains and Central Mountains. Best chance for rain appears to
be along the spine of the Appalachians with current rainfall
amounts generally less than a tenth of an inch, with isolated
pockets exceeding 0.5 inches possible.

Generally weak forcing, shear and instability will almost
certainly preclude any severe TSRA or flooding potential as the
SREF probability of CAPE exceeding 1000 J/KG is 20 percent or
less from KELM to KBFD and SW to KJST and KPIT. In fact, with
expanding drought conditions across the region, rainfall will be
beneficial for all recipients.

There will be a noticeable uptick in humidity on Saturday from
the 24 hours prior for everywhere except the northwest
mountains with temperatures staying pretty steady relative to
Friday. If anything, we could be several degrees too bullish on
temps based on the increasing cloud cover after the largely
clear to partly cloudy first half of tonight with decent
radiational cooling.

High pressure will regain control of our weather Saturday night
with clearing skies expected and patchy fog in locations that
received rain earlier in the day. Dry conditions prevail on
Sunday with increasing clouds but still partly cloudy skies.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Temperatures will trend a few degrees above normal Sunday
afternoon as high temps across the south approach 90 once again.
Dry weather continues Sunday night as clouds continue to stream
in and humidity increases. The uptick and clouds and humidity
will help overnight lows continue to moderate each day into next
week.

Near to below normal pwats beneath a weak area of high pressure
will provide a rain-free and less humid end to second-to-last
weekend of July. There should also be good viewing at night for
the full Thunder or Buck moon with patchy fog developing in the
northern river/stream valleys into early Monday morning.

Latest model and ensemble guidance shows an amplified pattern
that will be fairly slow to evolve next week. The key synoptic
features will be a wavy front on the leading edge of a Great
Lakes to southern Plains mean trough that will promote multiple
days of diurnally enhanced thunderstorms and potential heavy
rainfall across the region. The southern tier of central PA
could really use some rain to lessen the impacts of moderate to
severe drought conditions (D1-D2 drought monitor).

Max/min temperatures (80-90/60-70F) will remain above the
historical average with for late July with humidity/dewpoints
returning to elevated levels; however the heat and humidity
combination is not expected to be excessive.

WPC introduced a marginal risk ERO for day 5/Tuesday with
guidance ramping pwats to 1.5-2.0 inches or +1-2SD. The Tuesday
into Wednesday timeframe appears to have the best odds for
heavy rainfall (max POPs) before pwats trend lower from NW to
SE as the frontal zone slowly presses to the southeast with
time by late week.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
There remains high (> 95%) confidence in VFR conditions through
at least 06Z Saturday with light and variable wind and excellent
VSBY. SCT fair weather cu will gradually dissipate as we head
toward the early evening.

Patchy fog is expected to be slightly more widespread than last
night with slightly higher confidence in fuel-alternate
restrictions at BFD after 08Z Saturday. LAMP guidance outlines
some potential for IFR conds as early as 06Z; however, have
hedged closer to persistence for this forecast cycle. There is a
bit of uncertainty on how far south fog mentions will be needed
with lower potential and confidence (20%) of restrictions at
UNV/IPT so have opted to show some gradual lowering of cigs/vsby
in the 12Z TAF cycle.

Outlook...

Sat-Mon...Primarily VFR/unrestricted conditions. Patchy late
night/early morning fog and low ceilings are possible.

Tue...More widespread PM showers and thunderstorms could lead
to at least brief restrictions.

&&

.CLIMATE...
The average temperature from July 1 to July 18 at Harrisburg is
81.6F which is the warmest July month-to-date.

&&

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

&&

$$

SYNOPSIS...Lambert/Banghoff
NEAR TERM...Lambert/Banghoff
SHORT TERM...Lambert/Banghoff
LONG TERM...Steinbugl
AVIATION...Lambert
CLIMATE...Steinbugl