Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1256 am EST Thursday Mar 5 2015
low pressure will bring snow mainly south of Interstate 80 through
early Thursday...followed by building high pressure to end the
Near term /through today/...
with 1245am update...made slight changes to hourly precipitation
trends and quantitative precipitation forecast/snowfall totals. Higher totals have been reported
than forecast extending from Allegheny into Armstrong County...but
back edge of snow is already a little farther east than
anticipated with drier air moving into the region. Not sure that
snow will necessarily end more quickly than anticipated...but
think that at a minimum it will keep ratios from becoming any
higher. Measurement at the National Weather Service office yield snow ratios slightly
less than 10 to 1. Did bump up totals through the overnight hours
slightly from Pittsburgh to the south and east...but this does not
impact any headlines. Previous discussion follows.
Snow continues across the region as a surface wave in the
Carolinas moves along a slowly southward moving cold front. A band
of deep moisture continues to stream across the area to the north
of the front. Made very little change for areas in the winter
weather advisories and warnings with northern sections on the
fringe of the precipitation shield should see the least
snowfall...while areas to the south seeing the most with a more
prolonged period of snow with favorable moisture and lift. Did cut
back on snow north of the advisory area with a sharp gradient
Snow should quickly end Thursday as the surface wave exits off the
coast...and high pressure builds in late in the day. Thursdays
highs should be around 25 degrees below average based on the
latest sref numbers.
Short term /tonight through Saturday/...
weather pattern quiets down for the end of the week as a broad
area of high surface pressure pushes in from the west and kicks
out the middle-week system. Lingering light snow showers will
dissipate quickly Thursday night and skies will begin clearing from
the west. Remnant sky cover will play a big role in overnight lows
heading into Friday morning. With calm winds and the presence of a
fresh snow pack...for at least 1/2 of the County Warning Area...all signs point
to decoupling of the lower atmosphere and temperatures beginning
to crater well below average. Met and mav guidance show at least some
clouds holding in during the pre-dawn hours Friday...which would
disrupt efficient radiational cooling. Think this Route is a bit
conservative...and have held lows below those numbers.
Temperatures will warm up quickly heading into the weekend with
drier and clearer conditions expected. Next system poised to
stream north of the forecast area...embedded in the northwest
upper level flow. NAM/European model (ecmwf) seem to have the best handle on this
relatively dry system...and therefore followed this to introduce
light snow Saturday evening.
Long term /Saturday night through Wednesday/...
the long term period looks relatively quiet with a progressive
pattern featuring passage of a couple of shortwave troughs. Probability of precipitation
were forecast generally below chance climatology numbers using GFS
timing...but long term confidence is minimal with doubts about
timing and moisture supply. Seasonally cool temperatures were
forecast via persistence and MOS.
Aviation /06z Thursday through Monday/...
low MVFR and IFR conditions are expected to continue through the
night as moisture continues to flow along a southward sagging
front. The resulting snow area will shift southward and gradual
improvement can be expected on Thursday as high pressure builds in
the wake of the front.
Outlook.../Thursday night through Monday/...
restrictions are possible with a Sunday morning cold front.
Maryland...Winter Storm Warning until 4 PM EST this afternoon for mdz001.
Ohio...Winter Weather Advisory until 4 PM EST this afternoon for
Winter Storm Warning until 4 PM EST this afternoon for ohz069.
PA...Winter Weather Advisory until 4 PM EST this afternoon for
Winter Storm Warning until 4 PM EST this afternoon for paz076.
WV...Winter Weather Advisory until 4 PM EST this afternoon for
Winter Storm Warning until 4 PM EST this afternoon for wvz012-