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Area forecast discussion 
National Weather Service Pittsburgh PA
142 PM EST Tuesday Mar 3 2015

Synopsis...
low pressure crossing the Great Lakes will spread rain over the
upper Ohio Valley region today. Precipitation may begin as
freezing rain or a wintry mix...and will end by turning back to
snow on Wednesday.

&&

Near term /until 6 PM this evening/...
latest radar imagery showing weak echoes encapsulating the
area...but copious dry air in place is keeping most precipitation
at Bay. 12z sounding showing nearly a 50c dewpoint spread at
850mb. Until we erode this completely...virga will be present. The
dry air looks to hold into the southeast ridges the longest as
925mb flow remains from the southeast. This will keep most areas
south and east of Pittsburgh dry in downsloping flow until the
afternoon when the flow veers to the south.

Have re-configured the winter weather advisories with the largest
changes including cancelling the advisory in the ridges and
speeding up the start time everywhere else. Still...with all the
dry air in place and the lack of upstream radar activity...the
probability of a widespread icing event has dropped.

Once the low-level flow veers to the south much warmer air should
stream in and allow any remaining icing threat to end. This will
happen south to north through the afternoon/evening. Have tailored
the advisories to follow this transition.
Tax

&&

Short term /6 PM this evening through Thursday/...
Winter Storm Watch has been issued for counties across southeast
ridges west to the southern half of the northern WV Panhandle to Noble
County Ohio. This area appears to have best chance for 6 inches or
more of snow late Wednesday PM into Thursday morning based on 12z
models. Previous discussion follows.

With ongoing warm air and moisture advection into the
evening...rain will continue fall area wide and temperatures will
continue to increase until the associated cold front sweeps
across the region starting shortly after midnight. Rain will
remain fairly steady with the greatest amounts focused where middle-
level convergence is greatest...along the I-80 corridor early in
the evening and shifting south of the PA/WV border by Wednesday
morning.
With strong middle-level moisture transport into the area and upper
level divergence associated with the right entrance region of a
+170kt jet...portions of our forecast area could receive 1-1.5" of
liquid through late Wednesday. This...combined with the potential
for snow melt and ice on local creeks and streams...could cause
high water issues for areas mainly south of Pittsburgh. An areal
Flood Watch has been issued.

Colder air will begin to filter in Wednesday as the upper trough approaches
from the west. Expecting temperatures to hold pretty steady through
the day...which keeps the rain/snow line near Pittsburgh through the
afternoon. By late evening temperatures will have fallen enough to
transition rain to snow for all locations. Again there are questions
surrounding how much moisture stays in our forecast area through
Thursday morning as the Gulf of Mexico moisture feed kicks in and the
upper level trough begins to kick the boundary off to our east.
Potential for accumulating snow exists...mainly south and east of
Pittsburgh where the deepest moisture holds. Confidence in snow
totals at this point is fairly low...and will likely change as we
move closer to mid-week.

&&

Long term /Thursday night through Monday/...
overall...the long term period looks quiet with the passage of a
couple of weak fronts Saturday night and then again late Monday.
At this time...models are showing little moisture accompanying
either of these systems. A slow moderation in temperatures is expected
through the entire period.

&&

Aviation /19z Tuesday through Sunday/...
advancing warm front should bring IFR a mix of snow...freezing
rain and rain to kfkl and kduj through 21z or so...with spotty
mixed precipitation to plain rain this afternoon elsewhere. IFR in rain
overnight for all ports...then IFR continues Wednesday as cold
front pushes south with rain mixing over to snow north to south.

Outlook.../Wednesday night through Sunday/...
widespread restrictions are expected into Thursday as low pressure
moves along a cold front. General VFR until a cold front brings
possible restrictions Sunday.

&&

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 begin
Wednesday morning through Thursday afternoon. Uncertainty remains
a factor on the amount of precipitation and where the axis of
heaviest rain will fall.

&&

Pbz watches/warnings/advisories...
Maryland...Flood Watch from 7 PM EST this evening through Wednesday
evening for mdz001.
Winter Storm Watch from Wednesday afternoon through Thursday
afternoon for mdz001.
Ohio...Winter Weather Advisory until 3 PM EST this afternoon for
ohz039>041-048>050-057>059-068.
Flood Watch from 7 PM EST this evening through Wednesday
evening for ohz049-050-057>059-068-069.
Winter Storm Watch from Wednesday afternoon through Thursday
afternoon for ohz068-069.
PA...Winter Weather Advisory until 3 PM EST this afternoon for
paz020-021-029-073-074.
Flood Watch from 7 PM EST this evening through Wednesday
evening for paz014-020>023-029-031-073>076.
Winter Weather Advisory until 7 PM EST this evening for
paz007>009-013>016-022-023.
Winter Storm Watch from Wednesday afternoon through Thursday
afternoon for paz031-075-076.
WV...Winter Weather Advisory until 3 PM EST this afternoon for
wvz001>003.
Flood Watch from 7 PM EST this evening through Wednesday
evening for wvz001>004-012-021>023-041.
Winter Storm Watch from Wednesday afternoon through Thursday
afternoon for wvz004-012-021>023-041.

&&

$$

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