Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
659 PM EST Friday Jan 30 2015
high pressure will build in through Saturday. Low pressure will
bring wintry weather Sunday into Monday.
Near term /through Saturday/...
the regional radar mosaic indicates snow shower activity...while
still fairly pervasive...is definitely in a downward trend across
the County Warning Area this evening. Model soundings from both the rap and hrrr
show a scenario whereby inversion heights are falling
simultaneously with boundary layer moisture depth decreasing as
well. Likewise...upstream activity off of Lake Huron is quickly
falling apart...and the trend toward any additional input from the
sliver of Lake Erie that is open will not be particularly helpful
to regeneration of any of the bands. That said...activity will
likely take a few hours to wane with the upslope areas taking the
longest to fully halt their snow shower and flurry action.
However...given the downward trend in activity and minimal
accumulation expectations the rest of the evening...winter weather
advisories for the higher terrain have been allowed to expire as
scheduled at 7 PM.
Northwesterly flow continues through much of the evening hours
before slowly turning west overnight as a surface high builds
generally just to the south of the region. With at the very least
partial clearing...if not full clearing at times...temperatures
should drop rapidly with new snow cover. This combined with
decreasing yet still brisk surface flow will allow for Wind Chill
Advisory criteria wind chill index values by morning over the higher
terrain and northeastern County Warning Area. This is in line with current
headlines...and no additional expansion of these headlines are
anticipated at this time. However...with rapid clearing and new
snow on the ground...all area will likely be very cold by
morning...with many portions of the County Warning Area challenging zero by that
Some warmer air does start to flow northward on Saturday as the
surface high axis moves to the east of the area and southwesterly
flow prevails for a time. Expectations should be
muted...though...as such a cold start and weak vertical mixing
will likely keep most of the area in the 20s. Fries
Short term /Saturday night through Monday/...
high pressure should continue dry weather into Sat evening. A digging upper trough is
prognosticated to advance out of the plains and track across the Great Lakes and
Ohio Valley region sun into Monday. Associated surface low pressure is prognosticated to
deepen as it moves across the Tennessee and Ohio Valley regions also. This will
spread snow into the region lt Sat night through Monday morning with deep
available moisture and Omega.
With a closed 850mb low...a more prolonged precipitation event is expd as
opposed to the open system earlier in the weak. With enough
potential for heavy snow or a snow/ice mix...issued a Winter Storm
Watch for much of the area. Left areas generally S of I 70 out of the
watch...except for the WV/Maryland ridges...as enough warm air is expd to
wrap in ahead of the low to allow for a rain/snow mix or even a period of
all rain. Areas between I 70- and I 80 could see enough warm air
aloft for freezing rain to mix in at times as well. Generally followed a
sref/GFS/ECMWF model blend to work out the details...and used
critical thicknesses/model sounding profiles for precipitation type. Best
potential for greater than 6 inches of snow exists north of pit based
on latest model guidance...though this will be refined over the next
couple of days.
Snow should continue Monday until the upper trough axis shifts east in the afternoon.
Nudged temperatures to the latest colder than seasonal average sref guidance.
Long term /Monday night through Friday/...
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 /00z Saturday through Wednesday/...
MVFR ceilings with IFR visibility in snow showers will continue this afternoon. Genl
improvement can be anticipated thereafter as dry advection and subsidence
increases. Surface wind are expected to continue to gust from the west and northwest
at 15 to 25 knots through the day. Further improvements can be
expected as high pressure builds through Saturday morning.
Outlook.../Saturday night through Wednesday/...
widespread restrictions can be expected with Sunday low pressure and
with a Monday cold front.
Maryland...Winter Storm Watch from late Saturday night through Monday
morning for mdz001.
Wind Chill Advisory until 10 am EST Saturday for mdz001.
Ohio...Winter Storm Watch from late Saturday night through Monday
morning for ohz039>041-048>050-057>059.
PA...Winter Storm Watch from late Saturday night through Monday
morning for paz007>009-013>016-020>023-029-073>076.
Wind Chill Advisory until 10 am EST Saturday for paz008-009-
WV...Winter Storm Watch from late Saturday night through Monday
morning for wvz001>003-023-041.
Wind Chill Advisory until 10 am EST Saturday for wvz023-041.