Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KPBZ 220154

Area Forecast Discussion
National Weather Service Pittsburgh PA
854 PM EST Sat Jan 21 2017

Mild weather will continue through the weekend. Rain will move
back over the area on Sunday.


Mid clouds continue to increase over the area as a short wave
traverses nearly overhead at this hour. Radar returns continue to
increase with some indication of convective activity in higher
reflectivity returns around portions of the area. In these areas,
showers aloft will be likely to overcome the relatively deep layer
of dry air below the mid-cloud deck and result in a few isolated
showers. Regardless, the wave will be pushing northeastward rather
quickly, and the window for showers will be fairly brief.

Behind this early evening wave, satellite imagery indicates a
brief period of partial clearing is translating northeastward.
Hi-res guidance has some handle on this with sky cover backing
off centered around 03z-06z. Skies were backed down a bit for all
locations for a period of 2-4 hours from SW to NE as this area of
clearing moves through. With still high surface dewpoints, this
may yield a short period of radiational cooling and thus some
patchy fog development as it does so likewise.

Behind the clearing, mid and high overcast looks to return,
however decent lift really does not enter the picture from the
south again until well into the daytime on Sunday, so the
remainder of the overnight will be dry. Fries


Model depictions of the cutoff low pressure set to dig toward the
Upper Ohio Region have deviated from previous days solutions with
a more westward track of the center. Increasing ascent via deformed
flow and warm advection with increased moisture through the mid
levels all support escalating precip probabilities to categorical
numbers for the period.

With the northern branch of split flow holding colder air north and
west of the region, and with warm advection into the mid levels
of the cutoff, this looks to remain a rain event although the
latest NAM has developed sub-zero air over the region at the 850mb
level despite moist advection and an otherwise warm column.

QPF was progged using a RFC/WPC blend for the period. An inch to
inch and a half is anticipated for the early week with limitations
imposed by low pressure progression and mid level dry slotting.

Relative warmth will continue, although the diurnal temperature
spread will be restricted by clouds and precip.


The trend of the a slow low-pressure-exit on Tuesday continued in
todays deterministic and ensemble depictions. Colder air wrapping
into the western flank of the departing low may thus turn rain to
snow, before ridging ensues in response to plains low pressure.

That system is forecast to interrupt the resulting temperature
moderation via a cold front across the Upper Ohio, which will
drive temperature back to seasonal readings for the latter half of
the week.


VFR conditions are expected most of tonight as a crossing shortwave
maintains mid level clouds across the area, along with a few
light evening showers. Local late night/early morning MVFR fog is
possible in some locations as the temperatures falls near the dew
point, though cloud cover should preclude widespread coverage. VFR
is expected Sunday until the approach of another shortwave later
in the day results in a deterioration to MVFR conditions in rain.

Restrictions are likely through Tuesday with slow moving low
pressure, and again with a Thursday cold front.




$$ is the U.S. government's official web portal to all federal, state and local government web resources and services.