Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
615 am EST sun Feb 1 2015
low pressure will bring wintry weather Sunday into Monday with
cold temperatures for Tuesday morning. Another cold front for the
Wednesday night will reinforce cold air for the latter part of
Near term /through Monday/...
warmer trend in the models continues. Surface low tracks into the
Ohio Valley later today...and then east-northeast into the County Warning Area by 12z Monday.
Initial light band of precipitation this morning will mainly be in the form
of snow. Best accumulation of an inch or two will be seen across
the western County Warning Area. This band lifts out by this afternoon...with a dry
slot then entering the County Warning Area from the southwest. This may reduce
precipitation to drizzle for a time as it rotates across through the early
evening. First of two low level warm punches also arrives...with
areas south of I-70 turning to liquid by 00z.
Second warm punch accompanies approach of h850 low tonight...which
will track across Northern Ohio to Erie by 12z Monday. Increasing
SW flow will bring a renewed feed of moisture...and also the h850
zero line to just south of I-80. Thus...snow will mix with rain and
freezing rain...before turning to all rain for the majority of the
County Warning Area by 06z Monday. Surface low passes near or just south of pit late
tonight...which will turn winds to more of a westerly component and
start to bring colder air back in. Expect most of Ohio to turn back
to snow by 12z Monday...with rest of County Warning Area following in quick order
later Monday morning. Probability of precipitation decrease as well with deeper moisture
being shunted off to the east.
After collaboration...elected to downgrade Columbiana and Beaver
counties to an advisory...and left all other headlines intact for
now. Will not be surprised if a further northward movement of
warnings/advisories is needed later today depending on eventual
strength of warm surge. Forest/Venango/Mercer still pictured as
remaining mostly snow...although a brief mix will still be possible
tonight. Wintry mix and rain will hold back accumulations south of
Short term /Monday night through Tuesday/...
dry slot will begin pushing east of the County Warning Area line by Monday morning as
we transition to cold advection in the wake of the low. 12z Monday
Marks a good transition point in the system as most precipitation will have
fully changed over to snow as the surface low moves east through PA.
Stratiform snow will still be present through middle-morning as the
middle-level deformation band evident on the latest NAM swings
through...despite a Stout 500mb jet that will inject dry air into
axis of the upper low. Copious moisture still exists from the surface to
700mb and remains through the early evening as the bottom drops out
on the middle-level temperatures.
Very strong cold air advection will bring 850mb temperatures down nearly 20c in the matter
of 12hrs. The dendritic growth zone will drop like an anchor to the
surface allowing every bit of moisture to precipitate out in the form of
snow. Rapid cooling of the middle-levels will translate to the surface
causing additional problems as surface temperatures are expected to decrease
through the day. This will mean that untreated pavement surfaces
could see flash freezing...and that slick spots could exist even in
the absence of earlier heavy snow or mixed precipitation.
Snow showers in cold air behind the upper low could produce around
an inch of fluffy accumulation across much of the lowland
counties...with a little more in the ridges of PA/MD/WV and up
north. Expecting fluffy snow showers to finally taper down to
flurries and then fully cease by midnight Monday as the moisture dries
up. Temperature forecast Tuesday morning is tricky...as soon as the
cold air arrives...its gone and warm air advection begins to kick in by day break
Tuesday. Will remain below guidance Tuesday morning as we decouple under
high pressure with clearing skies and a lingering snowpack. Calm
surface winds may preclude the need for a Wind Chill Advisory along the
north Tuesday morning...but it will be downright cold regardless.
Long term /Tuesday night through Saturday/...
the temporary exodus of high pressure Marks the beginning of the
extended as a weak low moves through the southern Great Lakes by
mid-week. This relatively dry system should produce light snow along
the northern periphery of the County Warning Area Wednesday into Thursday...but just as
important...the trailing cold front will reinforce the upper level
trough as cold air pours in towards the end of the week. High pressure
will ensure a dry start to the weekend...but another low is poised
to impact the area by next sun.
Aviation /11z Sunday through Thursday/...
initial band of light snow in place...with mostly MVFR ceiling and
IFR visibility. Fkl/duj will begin to snow soon. Expect this band to
lift out by midday. A dry slot may impact the area this
afternoon...leading to several hours of VFR condtions for many
terminals. Fkl/duj should remain in the snow for the most party
with low MVFR/IFR. Low confidence forecast for the afternoon.
Renewed moisture push tonight as surface low approaches...with all
sites expected to drop down to IFR and perhaps LIFR. Fkl/duj will
continue with snow...while other sites change to rain or have a
period of wintry mix. Did not include icy precipitation types
yet...hoping for more clarity in future forecasts. Colder air
returns to zzv just before the end of the taf period...with rain
changing back to snow. Cl
Outlook.../Monday through Thursday/...
widespread restrictions can be expected into Monday as a low
pressure system crosses the region. Next chance for widespread
restrictions will be with a Wednesday cold front.
Ohio...Winter Weather Advisory until noon EST Monday for ohz039>041-
PA...Winter Weather Advisory until noon EST Monday for paz020-021-
Winter Storm Warning until noon EST Monday for paz007>009-
WV...Winter Weather Advisory until noon EST Monday for wvz001>003.