Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
756 PM EDT Friday Jul 31 2015
High pressure over the central U.S. Will nose into the region this
weekend. A persistent upper level trough will sit over the Great
Lakes and northeast states this weekend...and send a series of
weakening cold fronts southeast across Pennsylvania...bringing
the possibility of some scattered showers and isolated
Near term /until 6 am Saturday morning/...
A weak shortwave and cold front moving into the eastern Great
Lakes is acting on a narrow ribbon of instability and triggering
scattered convection from central Ohio up over Lake Erie up into
southern Canada. High res short range guidance suggests the best
chance for a stray shower or thunderstorm will be over my far northwestern
areas this evening and overnight.
Lows tonight will vary from the middle 50s across the northwest mountains...to
the lower and middle 60s throughout the southern valleys.
Short term /6 am Saturday morning through 6 PM Saturday/...
The weak cold front will exit our eastern zones during the middle to
late morning hours with isolated-scattered showers.
Afterward /and very similar to Friday/...surface high pressure ridge
will build back into the region from the Ohio River valley.
Surface dewpoints should edge down by 3-5 degree f compared to Friday/S
values. This will lead to mainly scattered fair weather cumulus...with
little if any chance for afternoon showers to the south of I-80.
Slightly steeper middle-level lapse rates /around 6c per km/ across
the northern mountains will lead to areas of MDT to towering cumulus with a few showers
dotting the radar scope after 17z.
Maximum temperatures will be near normal over the central and southeast
valleys...but a few degree cooler than normal across the northern and western
Long term /Saturday night through Friday/...
Little change is anticipated in large scale flow pattern across
the Continental U.S. Through the extended period. A broad upper trough
extends southward from eastern Canada across the eastern U.S.
Temperatures should average near normal into early next week before
trending cooler later in the week. Several short waves will rotate
around the upper low in a fashion reminiscent of winter. As is the
case with most upper low vs. Short wave spokes...confidence is
low on timing of precipitation chances.
Aviation /00z Saturday through Wednesday/...
Nice middle Summer evening outside. VFR conditions prevail across
the area. Some showers and storms near the lower lakes...but most
of these should stay north of our area.
Did keep vcsh in at bfd.
Main change at 00z was to add vcsh in at jst. A few showers
The other change was to adjust winds on the tafs during the
day on Sat. Cooler air aloft should result in some mixing
after middle morning.
Earlier discussion below.
Surface high pressure ridging NE into the region from the Ohio River
valley...will sag southeast late today and tonight...allowing a weak surface
trough...then moisture challenged cfront to slide southeast overnight.
Isolated to scattered showers and thunderstorms and rain are possible late this afternoon
and tonight...mainly at taf sites to the north of Interstate 80.
Otherwise...widespread VFR will continue through this weekend.
Mon-Wed...VFR...except for brief MVFR in isolated-scattered
mainly afternoon and evening showers/thunderstorms.
The Williamsport ASOS high of over 100 degrees today was the
result of a faulty sensor. Technicians are working on the
problem and should have it fixed later this evening.
near term...la corte