Ice Storm in Pennsylvania, December 6, 2016

Area Forecast Discussion
National Weather Service Pittsburgh PA
534 AM EST Tue Dec 6 2016

.SYNOPSIS...
Low pressure is expected to spread precipitation across the
region Tuesday. A Thursday cold front will return snow shower
chances and much colder temperatures for the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
530AM...updated hourly temperatures based on current obs. In most
cases, they were a bit higher than previously forecast, likely due
to increasing clouds and some influence of downsloping. There is
still enough of a spread between temperature and dewpoint to allow
for some wet-bulbing in some areas, but outside of a very brief
period of possible FZRA at onset, most locations outside the
advisory area will see rain during the morning. Rest of forecast
unchanged for now.

Previous discussion...

Weakening low pressure and an associated shortwave will track
across the Ohio Valley today. A new coastal low will form off of
Virginia by 00Z, with the original low opening up over the CWA.

Precipitation is expected areawide as strong isentropic lift
combines with PWAT values approaching one inch and a strong low
level jet. With slightly slower timing, most of the precipitation
outside of the advisory area will be in the form of rain, although
a few brief pockets of freezing rain cannot be totally ruled out
at onset. In the advisory area in the higher terrain, strong
southeast upslope flow will keep colder low level air in place,
while a warm layer aloft allows for sufficient melting to produce
a freezing rain threat. Sleet is also a possibility early due to
evaporative cooling. The freezing rain threat will continue
through the afternoon, ending when low-level flow veers southwest
by the evening. Across the far northeast, temperature profiles
will favor a change to snow this afternoon, and continuing into
tonight, with some accumulation of an inch or so. Sleet and a
little freezing rain are possible here too, but confidence is not
high enough for a headline.

Another concern is wind gusts associated with the low-level jet
this evening. On the ridges, gusts of 30 to 40 MPH are possible.
There are some signs of possible downslope enhancement in
Fayette/Westmoreland counties with reverse wind shear above the
ridgetops, but confidence is low.

Steady precipitation will pull off to the east fairly rapidly
this evening as the coastal low pulls away. Upper level moisture
is lost by midnight across most of the area, meaning that
drizzle or freezing drizzle may be a concern late tonight.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
Dry weather is forecast for Wednesday as surface high pressure
pays a brief visit, although temperatures will remain a touch
below normal. The next cold front is still expected to cross on
Thursday, bringing the coldest air of the season thus far. Kept
the idea of high chance/low likely PoPs for snow showers behind
the front in the developing mid-level trough. Lake enhancement
does not appear likely with generally WSW flow, although some
minor accumulation is possible, especially north of Pittsburgh.
Temperatures will tumble towards values well below normal.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Upper troughing and cold W-WSW flow should persist across the
eastern CONUS through Friday maintaining the chance for lake
enhanced and upslope snow showers. Some accumulation is likely with
a 13+ degree temperature difference between the lake and 850hpa.
But with uncertainty in band placement, have just upped PoPs for
the likely locations through Saturday morning. A less amplified
pattern sets up for the weekend through early next week, with
several crossing shortwaves progged. Differences in the evolution
of these systems prompted the use of the superblend for much of
this timeframe. Much below average temperatures are expected to
moderate by early next week.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
VFR will prevail through the early morning hours before deeper
moisture associated with a northeastward traversing low pressure
approaches.

Most if not all of the model guidance then deteriorates conditions
to MVFR and eventually IFR as moisture spreads across the
terminals. Strong warming aloft should support a mainly rain
event across the TAF sites, save for KFKL and KDUJ where a period
of wintry mix may occur for several hours. There may be some
frozen precipitation at onset further south depending on how
quickly we can saturate, but with low confidence, this was not
mentioned in the TAFs at this time.

An ese wind is expected through much of the day, veering to
southwesterly and westerly as the coastal low becomes the primary
low pressure system. Some low level wind shear may be possible at
KLBE with a strong low level jet in place early this morning,
before we start mixing, but will wait to see if this materializes
as much of the bufkit guidance shows some mixing will occur.

.OUTLOOK...
Improvements look possible on Wednesday before the next cold front
brings the chance for both cig and vsby restrictions in snow
showers.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...Winter Weather Advisory until 10 PM EST this evening FOR
     MDZ001.
OH...None.
PA...Winter Weather Advisory until 10 PM EST this evening FOR
     PAZ074-076.
WV...Winter Weather Advisory until 10 PM EST this evening FOR
     WVZ512>514.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PITTSBURGH PA
413 AM EST TUE DEC 6 2016

OHZ039>041-048>050-057>059-068-069-PAZ007-008-013-014-020>022-029-
031-073-075-WVZ001>004-012-021-509>511-070915-
TUSCARAWAS-CARROLL-COLUMBIANA-COSHOCTON-HARRISON-JEFFERSON-MUSKINGUM-
GUERNSEY-BELMONT-NOBLE-MONROE-MERCER-VENANGO-LAWRENCE-BUTLER-BEAVER-
ALLEGHENY-ARMSTRONG-WASHINGTON-GREENE-WESTMORELAND-FAYETTE-HANCOCK-
BROOKE-OHIO-MARSHALL-WETZEL-MARION-MONONGALIA-
RIDGES OF EASTERN MONONGALIA AND NORTHWESTERN PRESTON-PRESTON-
413 AM EST TUE DEC 6 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL OHIO...NORTHWEST
PENNSYLVANIA...SOUTHWEST PENNSYLVANIA...WEST CENTRAL
PENNSYLVANIA...WESTERN PENNSYLVANIA...NORTHERN WEST VIRGINIA AND
NORTHERN PANHANDLE OF WEST VIRGINIA.

.DAY ONE...TODAY AND TONIGHT.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

MDZ001-PAZ074-076-WVZ512>514-070915-
GARRETT-WESTMORELAND RIDGES-FAYETTE RIDGES-EASTERN PRESTON-
WESTERN TUCKER-EASTERN TUCKER-
413 AM EST TUE DEC 6 2016

...WINTER WEATHER ADVISORY IN EFFECT UNTIL 10 PM EST THIS EVENING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MARYLAND...SOUTHWEST
PENNSYLVANIA AND NORTHERN WEST VIRGINIA.

.DAY ONE...TODAY AND TONIGHT.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE
INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS.

   WINTER WEATHER ADVISORY.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

PAZ009-015-016-023-070915-
FOREST-CLARION-JEFFERSON-INDIANA-
413 AM EST TUE DEC 6 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHWEST PENNSYLVANIA AND
WEST CENTRAL PENNSYLVANIA.

.DAY ONE...TODAY AND TONIGHT.

A WINTRY MIX OF PRECIPITATION IS POSSIBLE TODAY AND TONIGHT...WITH
POCKETS OF SLEET OR FREEZING RAIN IN ADDITION TO SOME LIGHT SNOW.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.