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NWS State College, PA Forecast Discussion


000
FXUS61 KCTP 081133
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
733 AM EDT Wed Jul 8 2020

.SYNOPSIS...
Mid summertime pattern continues through the weekend with isolated
to scattered afternoon and evening thunderstorms.

&&

.NEAR TERM /THROUGH TONIGHT/...
Warm and muggy start today with patchy fog and low clouds
covering much of CPA early this morning. Radar trends show a
slight increase in shower activity over the northeast zones and
made minor adjustments to POPs.

After causing a significant max temperature bust yesterday
(forecast much higher vs. URMA/obs), will the pesky low clouds
put on a repeat performance? The MET (NAM) MOS guidance thinks
so and is much cooler relative to other models. To account for
the uncertainty, utilized a blend of NBM and MAV/MET MOS which
shades the maxT forecast toward the middle of the model spread.
Overall, highs are still running above daily climo averages with
the greatest departures (+10F) forecast across the NW mtns.
Still very warm and humid with dewpoints in the mid 60s to low
70s pushing max HX into the low to mid 90s across most of CPA.

Precip-wise, convection should trigger fairly early around 16z
and eventually become focused along weak/diffuse, southwest-
northeast oriented prefrontal boundary/confluence zone extending
from northern New England back into PA. Model soundings show
1-2k J/KG of SBCAPE, and the combination of ample moisture and
modest instability should be sufficient to support a scattered
storms, peaking before 09/00z. Lack of shear keeps the area out
of the D1 MRGL risk SWO which gets close to Tioga/Sullivan
Counties over the Endless Mtns. The weak flow aloft does support
slower storm motions with short term training and cell mergers
possible. Given the anomalous 1.5-2.0 inch PW air in place,
can`t rule out localized heavy rain rates which could lead to
short duration flooding/runoff issues confined mainly in urban
areas. The WPC D1 MRGL risk ERO covers all but the NW
Alleghenies and will mention/add isolated flooding threat to
HWO.

Isolated-scattered convection fades into tonight with the loss
of heating. Plenty of low level moisture in place and light
winds should lead to more fog and low clouds heading into
Thursday morning. A muggy night with lows in the mid 60s to low
70s.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
Patchy fog and low stratus to start Thursday should give way to
a blend of sun and clouds for the rest of the day. Not much
change to D2 sensible wx with more very warm and humid
summertime conditions and low chance of PM showers/storms.
Relative to prior days, the convective coverage looks more
limited/sparse Thursday afternoon especially across south
central PA; highest POPs 20-30% are located across the northern
tier of CPA.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
10 PM Update...
Little changes if any to the long term with this update. The
weak front passing through on Saturday should enhance the
precip chances. A brief break in the hot/humid wx for the
latter half of the weekend then a reprise of the heat next
week.

Prev...
After the weak trough moves east into the Canadian Maritimes
Wed night, a ridge of high pressure will develop over the
northeast on Thu, bringing drier weather and partly sunny
skies. Meanwhile, an area of low pressure will develop beneath
the ridge near the North Carolina coast. Can`t rule out a few
showers popping up along a weak sfc boundary lingering between
the departing trough and the approaching coastal low.

The coastal low will turn winds out of the SE and E for Fri,
bringing an increase in humidity and clouds over the eastern
half of the CWA. The bulk of the precip associated with the
coastal low looks to fall east of the area, but showers and
storms are possible Fri afternoon-night.

The weekend looks unsettled as an upper trough digs over the
eastern US and interacts with the coastal low. Cooler temps
aloft and plenty of clouds should bring a period of relief to
the heat, with afternoon highs just a couple degrees above
average Fri-Tue. Meanwhile, the 500 mb ridge over the desert
Southwest will continue to build to near 600 dam by Sat. Heat
from this ridge looks to spill back into our area by Wed of next
week after the eastern trough moves offshore.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Visibility issues expected to improve pretty quickly this
morning. MVFR cigs will hang on for a few hours in the eastern
airfields just like they did yesterday, though not expected to
last quite as far into the afternoon.

After clouds dissipate, expect scattered showers and
thunderstorms to develop this afternoon with only brief
reductions in cigs and vis as storms move through. Tonight will
be a repeat of last night with some clouds (still VFR) hanging
out into the overnight hours and then cig/vis reductions after
midnight. Expect widespread MVFR cigs/vis with a few sites
trending IFR for a couple of hours towards sunrise.

Outlook...

Thu...Generally VFR.

Fri...Reductions possible in patchy AM fog/low cigs and
showers/storms (mainly SE).

Sat...Showers and storms with reductions likely.

Sun...Generally VFR.

&&

.CLIMATE...
It looks like the streak of 90-plus days at IPT and MDT is over.
Temps Tuesday only hit 83 at IPT and 84 at MDT.

 ......................
A sustained period of above-average temperatures is expected
to continue through the end of the week. A heat wave is defined
as 3 or more days with temperatures greater than or equal to 90
degrees. Here are some facts about previous heat waves from
Harrisburg (MDT) Williamsport (IPT), and State College (STC),
which have climate periods of record dating back to the late
1800s.

Recent high temperatures:
    7/2 7/3 7/4 7/5 7/6 7/7  90-deg streak
IPT: 95  95  91  93  94  83  5 days (over)
MDT: 93  97  94  96  97  84  5 days (over)
STC: 89  90  88  89  92  80  1 day  (over)

Longest stretch of consecutive 90 degree days:
IPT: 15 (July 4 - July 18, 1988)
MDT: 11 (5 times, most recently July 22 - August 1, 1999)
STC: 15 (July 4 - July 18, 1988)

Annual occurrences of 90 degree days:
 Average Most (Year) Least (Year) 2020 (thru 7/7)
IPT: 16   42(1988)    0 (1979)           6
MDT: 20   60(1966)    3 (2004)           8
STC: 8    35(1988)    0 (11 times)       3

How common are stretches of 5 or more consecutive 90 degree days?
IPT: 15 times since 2000 (12 of 20 years)
MDT: 19 times since 2000 (12 of 20 years)*
STC:  4 times since 2000 ( 4 of 20 years)

*MDT had a stretch of 10 straight 90 degree days from July 3 -
 July 12, 2012. Time will tell if this year`s 90 degree stretch
 that began on July 2 can rival the streak 8 years ago.

&&

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

&&

$$
SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Lambert/Dangelo/Evanego
LONG TERM...Dangelo/Colbert
AVIATION...Banghoff
CLIMATE...Banghoff

NWS CTP Office Area Forecast Discussion

Courtesy of the National Weather Service forecast office State College, Pennsylvania




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