Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Pittsburgh PA
1131 am EST Monday Feb 8 2016

a cold front will spread rain and snow over the region
today...with snow Tuesday and Wednesday along with colder


Near term /through Tuesday/...
area of rain and snow ahead of first digging shortwave across
eastern Ohio slowly progressing east and northeast. Best lift and
slightly better precipitation rates heading into northeast Ohio through
the afternoon. Band of rain with snow possibly mixed at times will
shift east across region through the afternoon. May be a mix to
Pittsburgh at times with wet bulbing...but precipitation will be light
for the most part and warm lower boundary layer looks to melt most
snow if any. Brief period of light to moderate snow across
eastern Ohio is on the wane as support quickly shifts north. Main
change to afternoon forecast was to add mix up to Pittsburgh. No
other significant changes as temperatures look in line. Previous
discussion for the tonight period follows.

Tonight the front door to the cold air swings open as the low
dives into the area and the upper-level low deepens. Models have
been trending upward in the intensification of the low...and
resultant quantitative precipitation forecast overnight. 00z NAM Omega fields appear to be
overdone...with several bullseyes of quantitative precipitation forecast nearing 1". Still...the
broader operational models of the GFS and European model (ecmwf) show an uptick of
quantitative precipitation forecast with an area of middle-level deformation along the Mason Dixon
line. This trend has resulted in the raising of snow amounts
overnight...and the need for an expansion both in time and area of
the Winter Weather Advisory. Will need to monitor guidance closely
today for any possible northward expansion...or warning upgrades.


Short term /Tuesday night through Thursday night/...
tricky forecast continues into the short term period. Surface low
continues to churn to our north over the eastern Great Lakes
Tuesday. Models generally agree on placement of higher snow
totals across the southern portion of the County Warning Area. A weak trowal
setup/frontogentic forcing are present which will help to enhance
snow totals as compared to areas to the north. There is some very
minor disagreement on northern extent of this more favorable
forcing...but model agreement is relatively good. Continued slow
cold advection will allow cloud microphysical conditions to
improve with time...along with snow ratios. This could lead to
locally higher Tuesday snow totals than currently depicted
depending on where best dynamics ultimately set up. Best forcing
begins to wane later on Tuesday as the colder airmass starts to
settle in. Categorical probability of precipitation were placed from pit on south. To the
north...likely probability of precipitation were maintained...but the lack of significant
forcing...especially as compared to the south...could lead to a
sharper cutoff in snow coverage than currently depicted.

A more typical northwest flow snow pattern begins to set up
Tuesday night into Wednesday as h500 closed low is absorbed into
eastern Continental U.S. Trough. Resulting midlevel trough axis rotates
across the County Warning Area on Wednesday which will help to keep shsn going.
High chance to likely probability of precipitation were maintained for the County Warning Area through
Wednesday. As time wears on...continued cold advection Wednesday
night will push much of the moisture into colder than ideal
dendritic growth conditions. This will act to slow down additional
snow accumulation as ice crystals will not be able to aggregate
efficiently. This process continues into Thursday...with shsn
coverage greatly decreasing by afternoon.

As far as snow totals...currently constructed grids do approach
but do not meet/exceed warning criteria in any given 12 or 24 hour
period in the ridges. This is even more the case in lower
elevation areas to the west. After collaboration with other
offices...elected to go with long-lasting advisories for roughly
the southern half of the County Warning Area...with longer duration in the ridges.
Cannot rule out the need to upgrade to a warning if banding
structures can form and sit over a particular region...but
confidence is too low to place such a warning at this time.


Long term /Friday through Sunday/...
the northwest flow snow shower machine should finally wind down
Thursday night as troughing pattern temporarily relaxes. Arctic cold front will drop down in northwest flow and
cross by the end of the work week. Isolated to scattered snow
showers will accompany it and linger into Saturday...but the
headline may end up being the frigid airmass. Saturday night
looks particularly cold...with some below zero readings possible.
Sunday will be dry and cold. Trough relaxes once again
Monday...allowing for temperature moderation...but another snow
chance may arrive as well. The superblend guidance was used
heavily for this period...with modifications.


Aviation /18z Monday through Saturday/...
VFR conditions will continue into midday for most terminals...until
a cold front swings through. Precipitation currently in central
Ohio will approach zzv this morning with several hours of possible
rain/snow and associated restrictions. As the front moves west to
east...rain will bring brief MVFR further deteriorating to IFR as
it switches over to snow tonight. Expecting IFR and possible LIFR
in snow tonight and Tuesday morning...with southern ports impacted
the most.

Light southerly flow will swing around to the west as the low
moves overhead.

Outlook.../Tuesday through Friday/...
restrictions in snow showers will continue into the middle part
of the week with gradual improvement expected.


Pbz watches/warnings/advisories...
Maryland...Winter Weather Advisory until 7 PM EST Wednesday for mdz001.
Ohio...Winter Weather Advisory from 7 PM this evening to 7 am EST
Wednesday for ohz049-050-057>059-068-069.
PA...Winter Weather Advisory from 7 PM this evening to 7 am EST
Wednesday for paz021-029-031-073-075.
Winter Weather Advisory from 7 PM this evening to 7 PM EST
Wednesday for paz074-076.
WV...Winter Weather Advisory from 7 PM this evening to 7 am EST
Wednesday for wvz001>004-012-021-509.
Winter Weather Advisory from 7 PM this evening to 7 PM EST
Wednesday for wvz510-511-513.
Winter Weather Advisory until 7 PM EST Wednesday for wvz512-



National Weather Service Glossary of Abbreviations