176
FXUS61 KCTP 080203
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1003 PM EDT Sun Jul 7 2024

.SYNOPSIS...
* Dog days of summer continue as heat and humidity persists
* Maximum heat index values >100F likely in parts of south
  central PA again Monday through Wednesday afternoons
* The best chance of rain/t-storms and potential for flooding
  will be later Wednesday as deep, tropical moisture from Beryl
  is funneled north from the Gulf Coast states

&&

.NEAR TERM /THROUGH MONDAY/...
Another mainly clear night expected with patchy to areas of
valley fog across northern PA as the center of high pressure
slides overhead.Minimum temperatures tonight look similar to
those on Sunday morning, bottoming out around 60 in the northern
tier to 70 near the Mason-Dixon line.

Diurnally driven, albeit isolated, showers and thunderstorms
are possible on Monday afternoon with the easterly/southeasterly
flow on the back side of the departing high bringing an
increase of low level moisture/humidity back to central
Pennsylvania. Have changed slight chance wording to isolated to
convey the hit and miss nature of these showers (with most
locations staying dry).

Heat index values are likely to approach or exceed 100F again
on Monday afternoon in south central to southeast PA where a
Heat Advisory has been hoisted. Highs 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 /MONDAY NIGHT THROUGH TUESDAY/...
Increasing clouds are likely Monday night as a result of the
combination of wind flow and positive moisture flux. As a
result, lows on Monday night 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, 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 outflow boundaries, but large scale forcing
looks negligible at this time. Isolated showers/storms seem like
the most likely scenario once again. As with Monday, most
locations will likely stay rain-free.

Notably, 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. A Heat Advisory will likely be
needed on Tuesday again, perhaps with a bigger areal coverage
than Monday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
As we move into the middle of the week, guidance depicts a
pattern of unsettled weather with southwesterly flow bringing a
plume of tropical moisture to much of Central PA.

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 midlatitude trough. 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 2.00-2.50 inches from Wed-Thu afternoon, as per the NBM 90th
percentile.

Not surprisingly, given the tropical nature of the airmass, WPC
has painted a slight risk for excessive rainfall over some of
northern Pennsylvania. 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 likely 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.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Mostly clear skies tonight will provide effective radiational
cooling for much of central PA. Combined with nearly calm winds
overnight, patchy fog is once again possible across the NW
airfields. BFD will likely see visibility restrictions during
the early morning hours on Monday, and vsby restrictions can not
be ruled out at other airfields such as IPT.

After Mon morning fog dissipates, the rest of the day looks VFR
with sct to bkn cu forming between 3500 and 5000 ft.

Outlook...

Tue...Scattered mainly afternoon showers/storms, otherwise VFR

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

Fri...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 Monday for PAZ036-056-057-
059-063>066.

&&

$$

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