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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 142317
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
617 PM EST Wed Nov 14 2018

.SYNOPSIS...
Low pressure will bring a wintry mix of precipitation area-wide
on Thursday. Temperature will remain below the seasonal averages
through much of the next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
The only alterations needed for the eve update were to hourly
trends of temperature and cloud cover.

Previous...
A closed upper low in the srn Plains will acquire a negative
tilt as a jet rounds its srn periphery. The system will lift
toward the Ohio Valley while downstream upper ridging
strengthens. The net effect will be warm-air advection aloft and
persistent sfc high pressure over the nern CONUS, which will
combine to hazardous effect for the forecast area.

Given the considerable dry air aloft, initial precipitation will
serve to saturate the column. However, wet bulb effect will
yield an initial thermal profile completely below freezing,
leading to likely snow at onset, which should be around 2-4 am
in the srn zones and around rush hour near Pittsburgh.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
A wintry mess is expected area-wide on Thu, with a transition
from snow to sleet/freezing rain and eventual rain anticipated.
There nevertheless remains considerable uncertainty in the
precipitation type, with several possible outcomes still viable.

US models indicate warm air aloft strengthening Thu morning,
leading to classic freezing rain profiles in much of the region.
With sustained sely wind across the Allegheny Mountains, low-
level cold air would be reinforced in the ridge zones and could
lead to considerable ice accrual. Elsewhere, a modest ice
accrual would be expected as all precipitation types are noted.

However, non-US models suggest the cold air reinforced by the
downstream sfc high will dominate, leading to a more-prolonged
tenure of snow instead of transitioning thru varied precip
types.

In either case, potential impacts seem sufficient for headlines,
and all zones previously in a watch have been upgraded to Winter
Storm Warnings, while the remainder of the forecast area is
under a Winter Weather Advisory. It is unsatisfying to say, but
the reality of this event is that the current forecast data
support a range of outcomes from mainly sleet and rain to a
widespread ice event to considerable heavy, wet snow.

The upper-level low will accelerate ewd on Thu as low pressure
develops in the coastal Mid-Atlantic region and the inland sfc
low fills. Cold air will return in its wake Thu night and Fri,
with a return to snow as the upper low vacates.

As cold advection strengthens on Fri and Fri night in the wake
of the upper system, so will low-level instability and moisture,
leading to an increase in lake-enhanced showers downwind of
Lake Erie.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
The wx pattern thru the remainder of the forecast will be
dominated by a wrn-CONUS longwave ridge and ern-CONUS longwave
trough, with precipitation chances dictated by particular
shortwave troughs embedded in the flow.

On the whole, temperature will average below seasonal levels,
with sporadic episodes of lake-enhanced showers as currently-
unresolved disturbances materialize.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
VFR should continue through part of tonight as high pressure
moves east. Deterioration to MVFR, and eventual IFR, is expected
late tonight and Thursday as a wintry mix of precipitation
overspreads the area from S-N as low pressure approaches. PIT
should see snow initially, then a transition to FZRA and PL
before changing to mainly rain for the afternoon. IFR should
continue Thursday night in snow as the low tracks NE and an
upper trough crosses the region.

Outlook...
CIG restrictions should continue through Saturday under broad
upper troughing, with widespread restrictions possible with a
Sunday cold front.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...Winter Storm Warning from 1 AM Thursday to 1 AM EST Friday for
     MDZ001.
OH...Winter Weather Advisory from 3 AM to 7 PM EST Thursday for
     OHZ039>041-048>050-057>059-068-069.
PA...Winter Weather Advisory from 3 AM to 7 PM EST Thursday for
     PAZ013-020-021-029-031-073>076.
     Winter Weather Advisory from 5 AM Thursday to 1 AM EST Friday
     for PAZ007>009-014>016-022-023.
WV...Winter Weather Advisory from 3 AM to 7 PM EST Thursday for
     WVZ001>004-012-021-509>511.
     Winter Storm Warning from 1 AM Thursday to 1 AM EST Friday for
     WVZ512>514.

&&

$$