Area Forecast Discussion
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FXUS61 KPBZ 201254

Area Forecast Discussion
National Weather Service Pittsburgh PA
754 AM EST Sat Jan 20 2018

High pressure will maintain dry and warmer weather through
today. Light rain chances return with the new week.


Only minor adjustments were needed to the immediate near term
to reflect current satellite observations and hi res model
trends. Otherwise high pressure will keep the region dry today.

SE CONUS surface high pressure and Nrn Great Lakes
low under zonal flow aloft will maintain dry weather, warm
advection, and moderating temperature through tonight. That
temperature moderation will not be compromised by increasing
cloud cover as per escalating boundary layer moisture; on the
contrary, the increase in surface dewpoints will hasten the snow
melt later in the day and into eve.

Much of the area has the water equivalent of an inch (up to 2
inches over I 80 zones) of snow still on the ground. Weekend
weather will thus provide ideal conditions for a gradual snow melt
and ice rot, without the complications of heavy rainfall. Ice
jam and backwater flooding will remain a localized hydrologic
possibility; hence, no headlines are anticipated.


Intensifying warm advection under building upper high pressure
in advance of a Cntrl Rockies-to-Plains low will drive Upper
Ohio temperature well above the averages for the start of the
new week. Rain chances will be initially be limited to light
precip with the low level warm frontal moisture surge on Sunday
and Monday.

The continued advance of that low toward, and across the Great
Lakes on Monday and early Tuesday will provide the next likely
chance for measurable rain as that system pulls a cold front
across the region. Low pressure track, rapid progression, and
projections of a narrow moisture plume should preclude
widespread flood issues as per QPF expectations of a half inch
or less, especially as snow melt will be complete.

That cold front will also interrupt the January flaw by heralding
more seasonal temperature for mid week.


Late week weather is expected to feature another temperature
moderation and generally dry weather as another trough digs over
the Wrn U.S., with warm advection for points east. Rain chances
will increase again as that trough emerges from the Cntrl U.S.


VFR will be marred for the first half of the TAF period by llvl
wind shear and eventual gusts of 20 to 25 kts due to the tight
pressure gradient between SE CONUS high pressure and Nrn Great
Lakes low.

Otherwise, VFR conditions are expected to deteriorate this
afternoon and evening as primarily MVFR stratus develops in the
intensifying warm, relatively moist advection regime.

Restriction potential continues for the first half of the week
with the approach and passage of a frontal system.




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