349
FXUS61 KCTP 081851
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
251 PM EDT Mon Jul 8 2024

.SYNOPSIS...
* Dog days of summer continue as heat and humidity persists
* Maximum heat index values >100F are likely in parts of south Central
  PA and the Susquehanna Valley again today through Wednesday
  afternoons
* The best chance of showers and thunderstorms will be later
  Wednesday as deep, tropical moisture gets funneled north between
  the remnants of Beryl to the west and a strengthening Bermuda
  High to the east.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A Heat Advisory remains in effect for the Lower Susq Valley
today through Tuesday evening, where afternoon heat index
values are expected to exceed 100F today and tomorrow.

Diurnally driven, isolated to scattered showers and
thunderstorms are possible this afternoon into early this
evening as weak troughing develops after the departure of the
ridge of high pressure that`s been over the region the past 24
hours.

The easterly/southeasterly flow on the back side of the
departing high will bring an increase of low level
moisture/humidity back to Central Pennsylvania.

A compact, moderately strong mid/upper level swrly wind max
(and weak 700 mb thermal trough) crossing NW PA and Southern New
York later today should increase the chc for at least SCT
showers/TSRA as much of the CWA will experience a several hour
period of MESO-B scale UVVEL associated with the passage of the
thermally direct, right entrance region at the time of (and just
after) max heating.

Highs today will range from the mid 80s in the northern tier to
middle or upper 90s in the south. Dewpoints in the mid to upper
60s will make it feel a bit muggy, but will remain tolerable
relative to building humidity later in the week.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
Increasing clouds are likely tonight as a result of the
combination of wind flow and positive moisture flux. As a
result, lows on at daybreak Tuesday  will be a bit milder in
the 65-75F range (+10-15F above climo), making it feel quite
muggy once again as dewpoints remain in the same range. Fog will
be possible in locations that get rain Monday afternoon and
evening, but clouds and southeast flow should limit radiational
cooling and the extent/thickness of the fog.

Lowered shower/storm chances for Tuesday given neutral to
positive height tendencies as the remnants of Beryl and a mid-
latitude trough slowly phase in the Mississippi Valley. Will
still see some terrain-induced storms pop along with additional
convection along any remaining/subtle outflow boundaries, but
large scale forcing looks negligible (compared to Monday
afternoon) at this time. Isolated showers/storms seem like the
most likely scenario.

Most of the area south/east of the I-80/I-99 corridor will join
the Heat Advisory on Tuesday. Tuesday looks like the hottest
day of the week for most of Central PA as temperatures approach
the century mark in parts of south central PA. Dewpoints again
in the 60s will combine with these hot temperatures to push heat
index values near or above 100F Tuesday afternoon.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
There is a MRGL risk for severe weather and a SLGT risk for
excessive rainfall on Wed as the remnants of Tropical Cyclone
Beryl pass to our west. The risk for river flooding is low,
given favorably low antecedent streamflows and expected rainfall
amounts of less than 2 inches on average.

The latest forecast cone from NHC brings the center of Beryl
through the Ohio Valley as it weakens to a post-tropical
depression and gets absorbed by a mid-latitude trough. The
eastern edge of the forecast cone does clip Warren and McKean
counties as the circulation makes its closest approach late Wed.

Even if the remnant circulation passes well to our west, the
gradient between the low pressure system and strengthening high
pressure over Bermuda will result in a conveyor belt of deep
tropical moisture with PWAT progged to exceed 2.00 inches over
much of central PA between Wed afternoon and Thursday. Also of
note, the GFS is showing the freezing level between 13-15kft
Wed-Thu, suggesting efficient warm rain processes.

The highest PoPs look to be Wednesday afternoon into Wed night,
although we will likely see continued chc/slight chc PoPs right
into next weekend (peaking with the daytime heating each
aftn/eve). A reasonable worst case scenario for 24 hr rainfall
is 2 to 3 inches from Wed-Thu afternoon, as per the NBM 90th
percentile. The most likely scenario brings 0.75-1.25 inch of
rain across much of central PA, with locally higher amounts
possible in training convection.

SPC mentions a risk of both damaging winds and isolated
tornadoes in their discussion for Wed. The combination of 30 kts
of 0-3km shear, MLCAPE > 1000 K/kg, and LCLs between 500-1000m
is favorable for severe weather. The amount of low level SRH, or
veering of the flow in low levels of the atmosphere, will
depend on the exact track of Beryl`s remnants.

WPC has expanded the SLGT risk of excessive rainfall to cover
the northern 2/3 of PA. Farther south, where conditions over
the past few months have been much drier, any rainfall coming
this week will largely be beneficial.

In terms of heat and humidity, the extended period looks to
feature a continuation of the warm and humid weather we`ve been
seeing recently. Heat index values will have a shot at the low
100s again Wednesday in the lower Susq valley, especially if
clouds/precip hold off until later Wed afternoon or Wed night.
Although Wednesday will not get quite as hot as earlier in the
week, dewpoints surging into the low to middle 70s will make for
a sultry afternoon. This humidity will also help keep low
temperatures extremely mild during the overnight hours through
the end of the week. See the climate section for more details
about potential record overnight warmth (and a notable streak of
temperatures at or above 70F at Harrisburg).

A shot of somewhat less humid air (upper 50s to low 60s
dewpoints) appears possible behind the remnants of Beryl late
Thursday into Friday across western zones, but the tropical
moisture will be slow to move out of the east. A chance of at
least scattered diurnal convection will continue through at
least Saturday, maximized over the eastern half of PA, with PoPs
decreasing to just a slight chance for most of the CWA Sun-Mon.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
The rest of today looks VFR with sct to bkn cu forming with
bases at or above 5000 ft. There is a slight chance for a pop
up thunderstorm or two later this afternoon into this evening,
but coverage of these storms will remain limited.

Tonight will look very similar to last night with patchy valley
fog developing across portions of Pennsylvania, mainly in the
north. A few early morning visibility restrictions are possible
for Tuesday morning with this fog.

Much of Tue will remain VFR, with scattered showers/storms in
the afternoon and evening.

Outlook...

Wed-Thu...More numerous SHRA/TSRA causing restrictions

Fri-Sat...Scattered mainly afternoon showers/storms, otherwise
VFR

&&

.CLIMATE...
A prolonged stretch of very mild nights is in store thanks to
anomalous moisture in Central PA. The following minimum
temperatures records are in jeopardy of being tied or broken at
Harrisburg and Williamsport this week.

                 HARRISBURG                WILLIAMSPORT
DATE      HIGHEST MIN T    YEAR       HIGHEST MIN T    YEAR
July 9         76          1994
July 10        77          1993            74          1925
July 11        76          1989            72       1910, 1921
July 12        75       1911, 2011

The duration of warmth may also end up being notable. Harrisburg has
not dropped below 70 degrees since July 3rd. Here are the longest
stretches with temperatures at or above 70 on record at Harrisburg.

# OF DAYS   DATES      YEAR
17        7/19-8/04    2020
13        8/16-8/28    2021
13        7/13-7/25    2010
12        7/18-7/29    2022
12        7/17-7/28    1999
12        7/20-7/31    1940
11        8/04-8/14    1977
10        8/10-8/19    2016
10        7/14-7/23    2013
10        7/21-7/30    1898
9   12 times, most recently 7/7-7/11/2020

     .................................................

4+        7/04-??      2024

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon to 8 PM EDT Tuesday for PAZ026>028-035-
046-049>053-058.
Heat Advisory until 8 PM EDT Tuesday for PAZ036-056-057-059-
063>066.

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Lambert/Banghoff
SHORT TERM...Guseman/Lambert/Banghoff
LONG TERM...Evanego/Colbert
AVIATION...Colbert/Bowen
CLIMATE...Banghoff