Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
938 am EST Wednesday Feb 10 2016
snow showers will continue today before gradually diminishing
Thursday. Temperatures will continue to fall through the week with
bitter cold to start the weekend.
Near term /through Thursday/...
only cosmetic changes to the previous forecast. Previous
Snow showers should increase late morning ahead of an advancing
shortwave trough. The trough will swing through this
afternoon/evening...further deepening the boundary layer and
giving rise to snow squalls. Near term models all show
favorability for snow squalls from 18-00z in the btv snow squall
parameter. This will have the potential to impact the evening
commute...especially for areas from Pittsburgh north where deeper
lake-enhanced moisture resides.
Lake-enhancement will continue in the wake of the departing upper
trough tonight. Current guidance continuing the trend of showing
multiple lake-to-lake snow bands setting up. Upslope snow will
continue and even strengthen tonight as the colder air pours in
and the dendritic snow growth zone descends through the column.
Expecting snow ratios to maximize this evening through
tonight...which will allow for efficient accumulation.
Temperatures will continue their descent into the well-below
normal range. Many locations will be reaching into the single
digits before sunrise Thursday.
A complicated headline configuration played out this
morning...including an extension of the current long-duration
Winter Weather Advisory in the ridge communities. In
addition...have opted to issue a new advisory for today through
early Thursday for Pittsburgh metropolitan north for the potential impact
to the evening commute and the prolonged efficient lake-effect
snows. Decided to keep areas south of Allegheny County out of the
advisory as snow showers should be more scattered in nature.
Short term /Thursday night through Saturday/...
a bit of a break in the action looks to be in store for Thursday
night into early Friday as low level flow backs to be a bit more
southwesterly. This will cut off the over-lake flow
component...allowing for the boundary layer to dry out and skies
to temporarily scatter out. Inversion heights also falling will
yield a clearing and cold night on Thursday night...however with
flow turning southwest...things high single digits seem a good bet
with new snow cover.
The next system in the northwesterly flow aloft looks to dive
southeastward toward our area for Friday evening or so. Model
timing with this system has been suspect over the past few
runs...and the trend on the 00z cycle was to bring it in a bit
later Friday than in previous cycles. That said...lapse rates look
to rapidly increase through the dendritic layer concurrent with
strong differential positive vorticity advection moving through the area in the left exit
of the upper jet streak. Low level frontogenesis maximizes ahead
of the vorticity maxima and a bout of snow squalls seems likely to move
southeastward through the area. Behind the round of squalls...deep
layer northwesterly flow should allow for lake effect snow showers
to resume with a strong upslope component into the ridges.
Accumulations will be likely most everywhere as this situation
Long term /Saturday night through Tuesday/...
as lake effect winds down and drier air moves over the area by
Saturday night...skies should start to break up. Temperatures at
850 mb on all models drop into the middle -20s celsius by Saturday
night...making this likely the coldest air for this winter to
wander across our area. A multi-model consensus favors Saturday
night as the coldest night of the pattern...with widespread
numbers below 0f at the surface likely overnight.
Shortwave ridging and warm advection follows the brunt of the cold
air going into early next week...however large scale cyclonic flow
will re-establish itself thereafter. This means periodic systems
moving through the area with generally normal or below normal
temperatures and chances of snow showers through the period. Fries
Aviation /15z Wednesday through Sunday/...
restrictions will persist through the remainder of the
week...with mainly IFR through the afternoon...as a large upper
low sits over the area. The best opportunity for improvement to
MVFR looks to be Wednesday morning until winds become better
aligned aloft and more organized as the second...more
potent...push of cold air moves in.
Outlook.../Wednesday night through Sunday/...
restrictions are expected through Saturday under cold upper-
level troughing and occasional snow showers. Sunday is expected to
Maryland...Winter Weather Advisory until 7 PM EST Thursday for mdz001.
Ohio...Winter Weather Advisory until 7 am EST Thursday for ohz041.
PA...Winter Weather Advisory until 7 PM EST Thursday for paz007>009-
Winter Weather Advisory until 7 PM EST Thursday for paz074-076.
Winter Weather Advisory until 7 am EST Thursday for paz013-014-
WV...Winter Weather Advisory until 7 PM EST Thursday for wvz510>514.