Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1253 am EST Friday Jan 30 2015
colder temperatures and snow showers today. High pressure will
build in from the west late this afternoon...diminishing the risk
for snow showers. A dry Saturday with another storm for Sunday.
Near term /through today/...
widespread snow showers with embedded squalls will cross the area
late tonight ahead of a strong shortwave...which will also usher
in the next blast of Arctic air. This shortwave is rushing
eastward and would expect the snow showers to dissipate once it
exits. Upstream observation agree with this assessment as most sites are
now snow free. Will need to keep an eye on the possibility for
patchy freezing drizzle behind the snow as moisture aloft will
exit...preventing the infusion of ice crystals into the lower cloud
deck. However...with such strong cold air advection behind the aforementioned
shortwave...snow growth zones drop quickly as well. If forecast
soundings are correct...the atmosphere should be cold enough to
support scattered snow showers or flurries.
Another shortwave trough will cross the area this morning...
providing another push of Arctic air. This will sustain the risk
for snow showers throughout the morning with the best chance
across the north and especially the ridges. Upslope snow showers
in the ridges will be cranking through the morning hours and this
will be the locations were snow accumulations will be optimal.
Will keep the advisory as is.
Steering winds begin to show a more northerly component this
afternoon behind the exiting trough. These strong winds will drive
the Arctic air southward across my entire County Warning Area. The snow shower
threat will wane throughout the afternoon due to the veering and
shear in the winds and also the lowering of inversions. The ridges
will hold onto snow showers the longest thanks to the always
persistent orographic effects.
Highs will be reached in the morning...with temperatures slowly falling
throughout the day.
Short term /tonight through Sunday/...
snow showers will end in the ridges this evening as high pressure
spreads across the region. The Arctic air mass will quickly shift
toward the northeast in response to the middle-level ridge that
builds into the upper Midwest.
High pressure will keep the area dry Saturday.
Models are beginning to come into agreement for another snow
producing storm Sunday. Still lots of uncertainty on the exact
track of the system...but it does appear that most if not all of
the area will be on the cold side of the surface low. Model
depictions of this system have varied greatly over the past few
days...so there still is a lot of uncertainty of what will be the
final solution. For now will lean close to the 21z sref solution
as it seems to be a nice mix of the 00z NAM and GFS. If this
system and its track comes to fruition...headlines will be needed.
Long term /Sunday night through Thursday/...
a cold...winter pattern will continue for the rest of the long
term. The next best chance for snow showers will arrive late in
Aviation /06z Friday through Tuesday/...
MVFR conditions will persist through much of the day today. IFR
and even spotty LIFR are possible over the next few hours as
initial batch of -shsn moves through. Upslope conditions will be
setting up thereafter with gusty west-northwest winds...with duj and lbe
seeing the most activity. After 18z...slow improvement begins as
ceilings gradually begin to lift. Some of the western terminals may
scatter out towards the end of the taf period.
Outlook.../Friday night through Tuesday/...
improvements can be expected as high pressure builds on Saturday.
However...snow and restrictions are likely with Sunday low pressure.
Maryland...Winter Weather Advisory until 7 PM EST this evening for mdz001.
PA...Winter Weather Advisory until 10 am EST this morning for
Winter Weather Advisory until 7 PM EST this evening for paz074-
WV...Winter Weather Advisory until 7 PM EST this evening for wvz023-