Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
545 am EDT sun Jul 31 2016
the plume of deep moisture that brought numerous heavy showers
and scattered thunderstorms to the region on Saturday, will slide
into extreme Pennsylvania late this morning as a weak trough
drifts across the state. Behind this first trough, another
disturbance aloft and weak area of low pressure at the surface
will drift northeast from the Ohio Valley...bringing scattered
mainly afternoon showers and isolated thunderstorms.
A slight chance of showers and isolated afternoon thunderstorms
will continue on Monday as a pool of cooler air aloft moves over
the warm and still rather humid air at the surface. Warm and dry
conditions are expected for Tuesday and Wednesday.
Near term /until 6 PM this evening/...
slowly northeastward drifting showers will be confined to mainly
the northeastern one-third to one-half of the County Warning Area for the rest of
this morning as the axis of high...2 inch precipitable water air and meso jet of
30-40kt southerly 850 mb winds drifts into far nepa and sern New York.
A quasi-stationary sfc front was draped east-west along the entire
length of Interstate 80 in PA at 0830z.
A 60-70kt upper level jetlet over the middle Ohio Valley will
move northeast...dragging its thermally direct right entrance
region over the frontal boundary (and plume of higher precipitable water air
across eastern pa) this afternoon. This mesoscale area of lift
and favorable convective parameters will help to spark scattered
showers and isolated afternoon thunderstorms and rain. Though basin average rainfl
amounts are expected to be 0.20 or less today...highly localized
one-inch amounts are still possible across the susq valley and
points east by dusk.
Areas of fog (and highly localized dense fog) will persist through
13z before dissipating to just some areas of 5-6sm haze later this
morning...then 7-10sm this afternoon.
Max temps this afternoon will be a few to several deg f warmer
than Saturday in many locations...ranging from the u70s to around
80f across the northern and western mountains...to the mid 80s in
the susq valley.
Short term /6 PM this evening through 6 am Monday/...
sfc frontal boundary sags se across the state tonight. Any sctd
evening showers (and a few isolated thunderstorms and rain prior to 02z) will end
around or by after midnight across all but perhaps the far
eastern part of our County Warning Area.
Areas of partial clearing...combined with light wind and still
moderately high sfc dewpoints in the 60s will lead to areas of
1/2sm fog forming late.
Min temps early Monday will vary from the u50s in the perennial
cold spots of the north...to the u60s in the southeast valleys.
Long term /Monday through Saturday/...
main upper level trough axis and pool of cool mid/upper level air
drifts across the County Warning Area Monday. Low-mid level lapse rates will
increase to 6-6.5c/km Monday afternoon...causing one final round
of scattered showers and isolated thunderstorms and rain (especially across the
eastern half of the state)...before high pressure builds in from
the west at the sfc and aloft for Tuesday and Wednesday with dry
conditions and near to slightly above normal high temps.
Short-wave energy over the upper Great Lakes Wednesday weakens and
drops to the southeast as large scale height rises push northeast and
sharpen across that region. A second/minor upper ridge axis
builds into western PA by 12z Thursday.
Any upstream convection from this aforementioned shortwave should
dive mainly south-southeast toward the mid Ohio Valley Wed night (with the
eastern edge of the rain showers/thunderstorms and rain possibly brushing the Laurel
Highlands during that period. 30/12z nbm pops are in the 25-30
percent range across our western zones Wed night...while gmos and
official ndfd grids are closer to 10 percent.
European model (ecmwf) takes the bulk of any convection south across Ohio into wva
leaving PA dry for late Wed night through Thursday night. 31/00z
GFS/gefs is weaker and further north with some convection over the
southern and wrn mtns of PA. Stayed closer to the European model (ecmwf) solution
with no pops at this point. Both models agree on a more rigorous
cold front dropping southeast toward PA on Friday. This will help
surge the temperatures and humidity up ahead of it over central PA
Friday. Right now the timing is such that late day convective
storms will feed off the days heat and humidity and roll through
late in the day into the overnight. Models bring the cold front
southeast across PA overnight and then stall it near the Mason-
Dixon line for Saturday.
Aviation /09z Sunday through Thursday/...
been updating tafs quite a bit this shift. While most places
have some fog, there is a lot variation in conditions.
Expect things to improve some this afternoon. However there
will be still a chance for a few showers and storms.
Some fog is possible late tonight again.
Conditions should improve for Tuesday into Wednesday, as weak
high pressure builds southward from eastern Canada.
Monday...am fog possible, then isold PM tsra impacts possible.
Tuesday...am fog possible.
Wednesday...no sig wx expected.
Thursday...isold PM tsra impacts possible western PA.