Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service State College PA
520 am EDT Monday Jul 25 2016

Synopsis...
a cold front will push southeast across Pennsylvania late today
and tonight...accompanied by a likelihood of showers and scattered
thunderstorms and rain. High pressure will return for mid week with continued warm
temperatures. Temperatures may trend back to near or slightly
below normal over the weekend.

&&

Near term /until 6 PM this evening/...
a hot and humid airmass will be in place across the region
today...ahead of a cold front currently extending from Southern
Lower Michigan...sswd to the Chicago area.

Significant breaks in the high based strato cu and Alto cu cloud
decks will allow instability/ml cape to ramp up significantly this
afternoon bringing the threat for a few clusters of potent
thunderstorms to move quickly east across the region.

The southern two thirds of the County Warning Area is under a slight risk for svr
tsra today with the primary triggering mechanisms being the
aforementioned cold front...and well-defined entrance region of an
80 kt upper jet that will be sliding over southern New York state
and northwestern PA.

By 18z, 2 or 3 areas of quite high...0-1 km ehi of 2-3m2/s2
develops across the alleghenies of nrn and wrn Penn, then shifts
southeast to the lower and mid susq valley and increases even a little
more to pockets of 2.5 to 3.5 m2/s2.

A couple of short-lived hp supercells...transient mini Bow echoes
and a few compact mesoscale convective vortex are possible across much of the region today
with localizedstrong/damaging wind gusts, and some instances of
large hail.

Lagging upper trough and sfc cold front (briefly elongating to a
more west/east direction this evening into the first half of the
overnight hours) will combine with the very high...2+ inch precipitable water
values to bring the threat of some training thunderstorms and rain with highly
localized very heavy rainfall of 2 inches plus within just an
hour.

Headwater flash flood guidance values are extremely high and
4 inches plus for the 1-3 hour period, so at this point there
isn't a big concern for flash flooding. However, pwats are just
about as they head around this part of the country.

Timing for the larger scale - bkn line of significant shra/tsra
will be across the NW mtns between 15-18z...then bisecting the
state from NE to SW around 19z...before impacting the lower susq
valley mainly after 20z.

Patchy fog will occur through about 13z in some of the valleys in
central and southern PA where the more widespread light to
moderate rainfall occurred Sunday evening.

Temps to start the day will range from he u60s across the mtns of
northern and western PA, to between 70 and 75 degrees across the
ridge and valley region of central PA.

Ens mean 8h temps support Max temps today from the u80s across
the Allegheny plateau, to the m90s across the susq valley. The
combination of heat and humidity warrants continuation and slight
northward expansion of the heat advisory across roughly the southeast
half of the fcst area.



&&

Short term /6 PM this evening through 6 am Tuesday/...
the relatively weak sfc cold front will slide southeast across the southeast
half of the state late today and tonight, accompanied by
scattered showers and perhaps a few tsra early tonight.

Clearing skies lower precipitable water air, and a rather light west-northwest breeze of 5
kts or less could lead to some patchy dense stream/River Valley
fog...esp north late tonight and early Tuesday morning.

Low temps early Tuesday will vary from the l60s across the
north...to the lower 70s across the southeast zones.

&&

Long term /Tuesday through Sunday/...
big story in the extended fcst is the likelihood for modest
cooling by Tue/Wed behind the weak cold front. However, temps
still likely to remain somewhat abv normal within a generally
zonal flow.

Midweek weather looks dry again, with just low pops for isolated
tstms. Fri looks to be the next higher chance for tstm impacts
areawide as another cool front progged to move through.

&&

Aviation /08z Monday through Friday/...
fog starting to form in the places it rained in the last 24 hours.
However, the thickest fog and lowest cigs are up in bfd where it did
not rain. Model soundings and llvl moisture progs for the northwest
mountains keep the low crud in there until 8 or 9 am - when showers
will start to form/move in from the west. There is a short wave
trough moving through tol/DTX at this time and it will touch off
most of the sh/thunderstorms and rain today. Timing from most sources would take most
of the storms to our south by 00z. There could be some
stronger/gusty storms over the southern terminals this aftn/eve, as
heating and the approach of a longer-wave upper trough slides in
right behind the first trough. Dewpoints do not dip all that much
tonight, so fog is almost likely with some clearing and residual
llvl moisture from the rain earlier. However, if there is enough
time to dry it up before nightfall/clearing, we may not fog up.

Other than some lingering showers in the evening/early night, it
dries up for later tonight and right through Thursday. Don't even
expect much fog in the mornings of the mid-week.

Outlook...

Tue-Wed...VFR.

Thu-Fri...mainly VFR. Scattered PM shra/tsra.

&&

Climate...
record high for Harrisburg today is 99 degrees set in 1940.

Record high for Williamsport is 100 set in 1934.

&&

Ctp watches/warnings/advisories...
heat advisory from 3 PM this afternoon to 8 PM EDT this
evening for paz027-028-035-036-049>053-056>059-063>066.

&&

$$
Synopsis...Lambert
near term...Lambert
short term...Lambert
long term...Lambert/gartner
aviation...Martin
climate...Lambert

National Weather Service Glossary of Abbreviations