Area Forecast Discussion
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FXUS61 KPBZ 201628 AAC

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
1228 PM EDT Tue Mar 20 2018

A wintry mix of precipitation is expected today with low
pressure. The mix should change to snow tonight before gradually
tapering off Wednesday.


The 12Z RAOB at KPBZ indicated a warm layer present in a sharp
dry layer. However ongoing precipitation will lead to its
erosion via wet-bulb effect and ely cold air advection. As one
might expect from such an evolution, initial freezing rain has
been widely supplanted by sleet, with the ridges changed over to
all snow.

Reports of ice accrual have come in along the nrn fringe of the
current precipitation band, where dry low-level air is helping
wet-bulb temperature to remain below freezing. Given the current
reports of slippery conditions in several locations, ice accrual
in valleys of WV and ice accrual at ASOS sites, a short-duration
Winter Weather Advisory has been issued from far-ern OH to wrn
Preston County through this afternoon, until FZRA threat

Little in the way of warming is expected today as overcast sky
and ely wind will reinforce current sfc temperature in the low-
mid 30s. Temperature may warm slightly N of I-80, where
precipitation is slowest/least likely to arrive.

The morning precipitation will diminish this afternoon as the
associated upper wave weakens ahead of a second wave, which will
strengthen tonight and provide renewed snowfall.


A second low is progged to dig across the OH/TN Valleys tonight
and part of Wed. Cold advection in the wake of the initial
Tue low should result in all snow across the region. Accumulating
snow is expected as temperature drops below freezing at night.

A non-trivial ely H8 wind anomaly will supply increasing
moisture into the ridges, where snow totals were increased over
the previous forecast. Otherwise, very few changes to snow
totals were made. In general, 1-3" in ern OH, 2-5" from near
PHD-LBE, 6-12" in the ridge zones, with localized 16-18" reports
possible in the highest ridges. Less than 1" is expected N of
I-80, where temp today will be highest and the least amount of
precipitation is anticipated.

Headlines generally were kept intact. Only adjustment was to
expand the Winter Storm Warning to the Westmoreland County
Ridges, where snow has already commenced.

The snow should taper off from N-S Wed as lift/upper support
shift off the east coast with a developing coastal low. Dry
weather returns with shortwave ridging Wed night and Thu.
Below-average temperature is expected to persevere.


Surface ridging should maintain dry weather until a srn-stream
low returns rain and snow chances S of I-80 Sat thru early Sun
night. Limited PoPs to chance with a significant model shift
swd with the low in recent solutions. An ern-CONUS ridge should
return dry weather later Sun and part of Mon before a Midwest
trough returns low precip chances late Mon.


Conditions will continue to deteriorate as precipitation
spreads north and low levels. KMGW should remain all rain
however, ports to the north will see a wintry mix eventually
changing over to all snow and IFR restrictions by early
afternoon. Improvement to low MVFR late afternoon through the
evening until snow coverage increases again as a second sfc low
approaches the region.

Restrictions, albeit with gradual improvement, are likely into
Thursday morning.


MD...Winter Storm Warning until 8 PM EDT Wednesday for MDZ001.
OH...Winter Weather Advisory from 8 PM this evening to 8 PM EDT
     Wednesday for OHZ039>041-048>050-057>059-068-069.
     Winter Weather Advisory until 5 PM EDT this afternoon for
PA...Winter Weather Advisory from 8 PM this evening to 8 PM EDT
     Wednesday for PAZ013-014-020>023-029-031-073-075.
     Winter Storm Warning until 8 PM EDT Wednesday for PAZ074-076.
     Winter Weather Advisory until 5 PM EDT this afternoon for
WV...Winter Weather Advisory from 8 PM this evening to 8 PM EDT
     Wednesday for WVZ001>004-012-021-509.
     Winter Storm Warning until 8 PM EDT Wednesday for WVZ512>514.
     Winter Weather Advisory until 5 PM EDT this afternoon for
     Winter Storm Warning from 8 PM this evening to 8 PM EDT
     Wednesday for WVZ510-511.



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