Scientific Forecaster Discussion
fxus61 kctp 270326
Area forecast discussion
National Weather Service State College PA
1126 PM EDT Wed Jul 26 2017
a cold front will push across the area Thursday night and
Friday morning. The front will likely stall along the Maryland
border for Friday. Heavy rain is possible Friday and Friday
night. A much cooler airmass will overspread the commonwealth
over the weekend and dry and slightly cooler than normal
weather will last into mid-week.
Near term /until 6 am Thursday morning/...
satellite imagery at 02z showing cirrus of varying opacity
covering central PA in region of warm air advection aloft ahead of approaching
trough. Some thin spots noted upstream, but expect a mostly
cloudy night on balance based model rh time sections. Band of
showers associated with dying cold front over southern Ontario
is progged to remain north of the forecast area overnight.
However, stratus and potentially some spotty drizzle is expected
to develop over the higher terrain of northeast PA late tonight
in response to moist southerly flow and associated orographic
lift over the Poconos. Model soundings show a nearly saturated
0-1km layer by dawn over the high terrain of Sullivan County.
Short term /6 am Thursday morning through Thursday night/...
Thursday is likely to dawn gloomy over parts of the region,
especially the northeast portion of the forecast area. However,
model soundings indicate low level cloudiness will mix out to
party sunny skies by midday.
Diurnal heating of marginally unstable air mass, combined with
passage of shortwave during the PM hours, should produce
isolated to scattered thunderstorm coverage during the
afternoon and evening hours. Have placed the highest probability of precipitation
across the eastern counties, where cape the highest, and also in
the vicinity of weak frontal boundary along the New York/PA border.
Despite decent 0-6km shear, lack of much instability is limiting
the severe weather threat to marginal.
As surface high drifts off the East Coast, return southerly flow
will advect much higher humidity into the area Thursday. Model
850 temps support seasonal Max temps in the upper 70s to mid 80s
from north to south.
Long term /Friday through Wednesday/...
main story in the long term is the change from a muggy, stormy,
and wet day on Friday to a very dry and fair pattern for the
rest of the term. A strong short wave trough is slated to push
across the Great Lakes and Ohio Valley Friday. This should help
to deepen at least one ripple of low pressure along an old
front. The front will be over srn PA or Maryland at first and heavy
rain is possible. Wpc Hydro outlook for Fri-night is for a slight
risk of excessive rainfall. Quantitative precipitation forecast from some output is over 3
inches total for the southern third to half of the area. Plumes
from gefs have averages of at least 2 inches there. Lighter
amounts are fcst for the northern half of the area. Convection
and mean westerly flow aloft and light winds at the low levels
seem likely to produce much higher point amounts.
The trough rounds the base of a long-wave trough after it passes
our longitude, and clears things out nicely. This should happen
sometime Sat. Will linger pops in the S for the day Sat, but go
very dry and sunny/clear for the next 2-3 days. Scattered
diurnal convection may then start to pop up - esp in New York state
tues/Wed. But, the risk of a shra/tsra in PA is very low until
at least Wed as the humidity rises back to more-August like
Aviation /04z Thursday through Monday/...
widespread VFR expected for much of the overnight. Some fog
possible late tonight, but clouds may limited fog to the
Some chance of showers and storms on Thu, but nothing
widespread. Used vcsh for now.
More widespread showers and storms on Friday will be
Fri...scattered rain showers north with more numerous and heavier
rain showers/thunderstorms and rain across the south.
Sat-Mon...no sig wx.