Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Pittsburgh PA
423 PM EST Friday Feb 12 2016

an Arctic front will bring snow showers to the area through
Saturday. Much colder temperatures and dangerous wind chills will
continue into the weekend.


Near term /through Saturday/...
shortwave pivoting along the base of the upper trough will support
increasing snow chances in the ridges ahead of the Arctic front
passage prognosticated for this evening/overnight. Both hi res and longer
range model soundings in BUFKIT suggest a period where deep a layer from about 600mb to 850mb...will be well
within the dendritic growth zone. This should support efficient
snowfall for a period...with additional snow showers anticipated
with and behind the front in upslope snow until the whole boundary
layer falls well below the growth zone. With this in mind...a
Winter Weather Advisory was issued for the ridges of Preston
Tucker and Garrett counties through Saturday morning.

Elsewhere...the model guidance has changed little with the timing
of the snow showers and potential squalls ahead of the front
prognosticated for passage overnight. Expect the line to be into eastern
Ohio and northwestern PA by 00z and Pittsburgh by 03z. Various
runs of the hrrr and to a lesser degree other snow squalls forecasts suggest
that there will be some weakening as the line comes across.
Generally anticipate a half to an inch of snow...with slightly
higher amounts north of Pittsburgh.

Behind the front...strong cold advection will steepen lapse rates
and provide for a period of gusty winds areawide until late
Saturday with maximum wind in the boundary layer approaching 25
to 35kts. This...added to temperatures falling into the single
digits will lead to wind chill values well below zero. This
supports the Wind Chill Advisory that was issued. 40mph wind
gusts overnight in the ridges will allow values to get very close
to warning criteria but at this point...the watch has been
upgraded to an advisory with some -25 values possible in the
highest terrain of Tucker County.

In addition to the Wind...Lake effect snow showers will be
possible in northwest flow with most if not all of the model
guidance suggesting several dual-lake snow bands. The latest
iteration of models has the more prominent band shifted slightly
south from last night so with uncertainty in the actual placement
of snow bands...have opted to upgrade the lake effect snow watch
for Venango County to an advisory for Mercer...Venango...and
Forest counties. Additional lake plumes may support snow beyond
these advisories through Saturday afternoon...but with uncertainty
in their additional headlines were added.


Short term /Saturday night through Sunday/...
Lake effect snow showers will continue to taper off and shift
northward as a surface ridge attempts to build overhead for
Sunday. This should allow for the wind to back off...with wind
chill concerns diminishing in Ohio. However...with the high
pressure and light wind...temperatures will fall close to or below
zero Saturday advisories will remain as is for the rest
of the County Warning Area until Sunday morning. Temperatures will moderate a few
degrees on Sunday with a return of southerly flow and scattering
of the clouds. Temperature forecast was a blend of guidance for
both periods.


Long term /Sunday night through Friday/...
shortwave moving east across the Great Lakes will bring warm
advection along with an increase in deeper moisture Sunday night
into Monday. This will give a period of snow especially south of
Pittsburgh with some accumulation expected. Temperatures look to
rise later Sunday night and will push to near the seasonal average
Monday. By later Monday through Tuesday a strong southern stream
shortwave will induce low pressure along the Gulf Coast which will
quickly move across the Middle Atlantic States. Models still differ
on exact track but system will cross the southern Appalachians and
intensify as it moves toward New England by Tuesday night.
Potential for significant snow...but also potential for a mix with
rain or all rain where better quantitative precipitation forecast is forecast. For now have not
strayed far from previous forecast although even the warmer European model (ecmwf)
wraps cold air back in later Tuesday so have kept mainly snow.

System exits Tuesday night...but will be followed by fast moving
clipper system Wednesday which will deliver another period of snow
showers followed by a quick shot of cold air. Heights aloft then
begin to rise Thursday into Friday with strong warm
advection...especially on Friday.


Aviation /21z Friday through Wednesday/...
light snow has dropped visibility to MVFR or below for a time at kmgw and
klbe as a shortwave shifts east to the middle Atlantic. Snow showers
also will develop ahead of approaching Arctic front...with MVFR to
IFR this evening with and behind the front. Winds will be gusty over
25kts and turning northwest with and behind the front.

Outlook.../Friday night through Wednesday/...

Scattered restrictions in snow showers Saturday. Low pressure
systems will bring widespread restrictions later Sunday night
through Wednesday.


Pbz watches/warnings/advisories...
Maryland...Wind Chill Advisory from midnight tonight to 9 am EST Sunday
for mdz001.
Winter Weather Advisory until 10 am EST Saturday for mdz001.
Ohio...Wind Chill Advisory from midnight tonight to 11 am EST
Saturday for ohz039-048-049-057>059-068-069.
Wind Chill Advisory from midnight tonight to 9 am EST Sunday
for ohz040-041-050.
PA...Wind Chill Advisory from midnight tonight to 9 am EST Sunday
for paz007>009-013>016-020>023-029-031-073>076.
Lake effect Snow Advisory until 7 PM EST Saturday for
WV...Wind Chill Advisory from midnight tonight to 11 am EST
Saturday for wvz003-004-012.
Wind Chill Advisory from midnight tonight to 9 am EST Sunday
for wvz001-002-021-509>514.
Winter Weather Advisory until 10 am EST Saturday for



National Weather Service Glossary of Abbreviations