Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1227 am EST Thursday Nov 26 2015
strong high pressure will drift east over Nova Scotia tonight.
This weather feature will maintain dry weather with moderating
temperatures into Friday. A cold front will move across the state
Friday night into Saturday bringing the next chance of rain
Near term /until 7 am this morning/...
clear skies covering most of the region at 03z will give way to
variable amounts of high clouds after midnight. Light southeast surface wind
over the middle and lower Susquehanna valley allowed the blyr to
quickly decouple early in the evening...and temperatures have dipped into
the middle and upper 30s. A general 5-10 knots sserly flow over the northern
and western high terrain helped to keep the boundary layer fairly
mixed...leading to slightly higher temperatures this hour - in the upper
30s to middle 40s.
The main forecast challenge very late tonight/Thursday morning
centers around the potential for a stratus or strato cumulus layer to
develop/advect in from the south/southeast.
Relative humidity forecasts from the 21z sref and most 00z model sources indicate
increasing relative humidity at or below the 925mb level...thanks to the development of
a moderately strong south-south-southwest lljet of 35-45kt after 06z. This
wind maximum /at the top of the strong subsidence inversion/ weakens
by 10-15kt and veers to the SW Thanksgiving morning...but could
still help to trap moisture /especially across the susq valley and
points east/. This will complicate the temperature forecast and could hold
afternoon maxes 4-6 degree f lower /in the middle to upper 40s/ across
the middle susq valley and western Poconos...compared to other
locations which will see the Mercury climb into the l-M 50s.
Will maintain the increase in clouds across the central mountains
after midnight...and in the east just before sunrise. Temperatures will
then follow an odd trend by rising a few degree f leading up to
Short term /7 am this morning through 6 PM Friday/...
very strong high pressure /1048 mb/ near Nova Scotia will extend
its ridge into the deep south...keeping our weather high and dry
here in central Penn. However...there still is the potential for
some areas of low clouds over the central and east in the
morning. Relative humidity forecasts are very high for the low layers in the
morning...but this slides to the east as the lljet decreases and
some mixing takes place. It could take quite a bit of the daylight
for the clouds to decrease in the east...and have nudged temperatures
down slightly in the east for this reason - with the coolest
numbers/biggest deviations from guidance in the Poconos/middle susq. Some
middle clouds come in from the west but these should not be of much
worry...and MO sunny will hold there. Some clouds may form in the
east again Thursday night. So...have painted a general pt cloudy 60 percent
cover for the night. Mins will keep about 5-8f above Thursday morning
due to the south wind and perhaps some clouds.
Long term /Friday night through Wednesday/...
broad southwesterly flow aloft will continue into late week across
the eastern half of the Continental U.S. Between upper an ridge extends northeastward
from the deep south into the Carolinas and a strong...digging upper
trough currently spinning over Nevada. A northern stream trough is forecast
to swing through the northestern Continental U.S. Over the weekend. Energy from the
western trough is forecast to eject eastward next week leading to a more
unsettled pattern across the east.
Mild and dry weather will persist into most of Friday as the southern
end of strong surface high pressure remains over the Middle Atlantic
States. The northern steam trough will bring a cold front across the
region late Friday into Sat with the chance of showers...but
significant rainfall amounts are not likely. What is likely is
a return to more late November-like weather.
Latest mdm rain guidance continues to show that the front will
stall to the south of the region late in the weekend and slowly
works its way northward early next week as energy moves east from the
upper low. This type of pattern change is generally fraught with
increased forecast uncertainty...and this time is no exception.
At this time range have painted increased chance probability of precipitation for Monday
into Wednesday across the region. This includes the possibility of
a snow rain mix...mainly across northern sections. But at this
time...the possibility of significant storm development in the
long term period appears low.
Aviation /06z Thursday through Monday/...
as of midnight...clear skies prevail.
Main concern is low level wind shear.
06z tafs sent.
Earlier discussion below.
VFR conditions in place this evening with few clouds to speak
of...at least for the next several hours. An increasing
southwesterly lljet will peak around 40 kts over western and
central areas overnight...with surface winds remaining around
10 kts at kbfd-kjst with some gusts to 20 kts this evening.
There is potential for a strong subsidence inversion to trap
moisture and produce clouds in parts of the central mountains
after 08z. Didn/T go quite as aggressive with very low ceilings as
previous forecast...but srefs/BUFKIT still hinting that an MVFR deck
could form over the susq valley from kipt-kmdt-klns. This deck if
it forms could linger into Thursday...while VFR conditions continue in
Cold front drops northwest-southeast through the area Friday night and
Sat...bringing widespread light showers.
Thursday PM-Friday am...fog/low ceilings possible central-east. VFR elsewhere.
Friday PM-Sat...VFR/MVFR with rain showers.
Sun-Mon...mainly VFR - rain possible south.