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Area forecast discussion 
National Weather Service Pittsburgh PA
1210 am EST Wednesday Mar 4 2015

Synopsis...
low pressure crossing the Great Lakes will continue to spread rain
over the upper Ohio Valley region tonight. Rain will turn to snow
with a Wednesday cold front.

&&

Near term /through today/...
with midnight update...made some minor changes to hourly
temperature and precipitation trends. Some slight downward
adjustments were made across the extreme north with regards to
chances for precipitation and quantitative precipitation forecast as rain shield has generally
stayed south of Mercer and Venango counties so far.

No changes were made for the late evening update...other than to
tweak hourly trends of temperature given the warmth surging across
the region. An updated Winter Storm Watch was issued to update the
time stamp...no other changes at moment.

Otherwise...the Flood Watch has been maintained as snow melt will
aggravate any ongoing poor drainage issues resulting from a general
0.2 to 0.4 inches of rain earlier this evening. However...areas
along and south of a line from Zanesville to Latrobe may want to
pay special attention through the night as a crossing jet streak
is model prognosticated to enhance middle level frontogenesis for better
rainfall focus. Think an additional 0.20 over northern areas to
about an inch over southern counties is a reasonable basin average
prognosis at this time and is based on more conservative European model (ecmwf)
guidance.

A transition to snow will occur with the encroachment of the cold
front on Wednesday. Any snow that falls through the day should be
limited by inefficient snow ratios and little accumulation is
expected into the evening.

&&

Short term /tonight through 6 PM Thursday/...
the Winter Storm Watch for Wednesday night and Thursday has been
continued for areas roughly along and south of a Zanesville to
Indiana line...but the northward extent of deeper moisture and
ascent behind the wave slowed frontal zone is certainly questionable
and an additional set of model runs will be necessary for better
resolution.

At any rate...snow showers will diminish through Thursday afternoon
with Arctic high pressure clearing out skies. With light winds
temperatures expected to crash near or below zero with fresh snow
cover.

Sunshine but continued cold Friday with temperatures 15 to 20
degrees below seasonal averages.

&&

Long term /Thursday night through Tuesday/...
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 /05z Wednesday through Sunday/...
IFR conditions are expected to continue through much of Wednesday
as low pressure crosses the Great Lakes region. A gradual
changeover to snow is expected from north to south during the day
Wednesday...with fkl/duj changing late tonight...pit in the
morning and mgw toward evening. An improvement to low end MVFR is
expected from pit north by afternoon as the associated cold front
pushes south.

Low level wind shear should persist this evening before a low
level jet exits.

Outlook.../Wednesday night through Sunday/...
widespread restrictions are expected into Thursday as a wave of
low pressure moves along a cold front...with snow mainly from pit
south. Restrictions are possible with a Sunday cold front.

&&

Hydrology...
the combination of snow melt and developing rain is expected to
cause significant rises on the cheat... Monongahela and
youghiogheny river basins. These rises will aid in moving ice into
areas where ice jams are known to develop. The rises will most
likely persist through Thursday. Confidence in rain amounts
remains low...but the better chance for more significant
accumulation is expected to be along and south of a Zanesville to
Latrobe line.

&&

Pbz watches/warnings/advisories...
Maryland...Flood Watch through this evening for mdz001.
Winter Storm Watch from this afternoon through Thursday
afternoon for mdz001.
Ohio...Flood Watch through this evening for ohz049-050-057>059-068-
069.
Winter Storm Watch from this afternoon through Thursday
afternoon for ohz057>059-068-069.
PA...Flood Watch through this evening for paz014-020>023-029-031-
073>076.
Winter Storm Watch from this afternoon through Thursday
afternoon for paz021-023-029-031-073>076.
WV...Flood Watch through this evening for wvz001>004-012-021>023-
041.
Winter Storm Watch from this afternoon through Thursday
afternoon for wvz002>004-012-021>023-041.

&&

$$

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