Area Forecast Discussion
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FXUS61 KPBZ 281201
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
801 AM EDT Fri Apr 28 2017

.SYNOPSIS...
A break in the activity today under high pressure. Unsettled but
warm weather expected for the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Morning update to remove patchy fog and adjust sky grids into
the afternoon. No other changes, and previous discussion
follows.

Dry weather returns today under high pressure. The cool air this
morning, will quickly eject to the north as strong warm air
advection takes over.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
Low confidence forecast through much of the weekend due to
differences in model solutions. Models are having a difficult
time determining the position and timing of a warm front on
Saturday and also the extent and strength of Eastern CONUS
ridge. The upper levels will show a slow increase in 500mb
heights beginning tonight and continuing through most of
Saturday night. This is in response to a large and vigorous
upper level system which will dig into the Southern Plains over
the weekend. Zonal flow this evening will be replace by the
building eastern ridge overnight. As the zonal flow is pushed
northward a series of shortwaves will rush north of the building
ridge, bringing another chance for showers and storms tonight
and Saturday. Models seem to be really suffering from convective
feedback tonight, and late on Saturday, particularly with the
NAM solution. One thing the models do somewhat agree on, most of
the precipitation tonight and Saturday will be over the
northern half of the region, north of the surface warm front.

Discrepancies again arise Saturday night and Sunday. At this
point it seems like the NAM has a better handle on the overall
pattern as rather strong ridge will be in place over the area
and we will be well into the warm sector. This would provide a
more stable atmosphere and limit the prospects for widespread
showers and storms Saturday night and through much of Sunday.

The other question is convective threats with the shortwave
tonight and then on Saturday afternoon. Interestingly enough,
the best lift will ride north of the unstable air, particularly
tonight which will limit storm coverage and intensity. Could see
more bebop type of situation on Saturday under the building
ridge. Again, will lean closer to NAM solution Saturday night
and Sunday as it is showing a better solution to the overall
pattern.

The key for the weekend will be the timing and movement of the
rather well defined warm front. How far north will it push on
Saturday and Sunday and how long will it take for it to move
north of the region.

Warm temperatures are expected through the entire weekend.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Eastern ridge finally begins to break down on Monday, as deep
upper level system spins northward from the plains/Midwest on
Sunday, toward the Great Lakes by Monday night. The 500 low will
eventually move across Southern Canada Tuesday and Wednesday.
The surface reflection will move directly under the 500 low and
swing the occluded front through the Upper Ohio Valley late
Monday/Monday night. This will increase the risk for showers and
storms. A cooler and unsettled pattern will continue through
Midweek.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Patches of IFR fog and MVFR clouds will linger for a few more
hours, with most fog south of the Mason-Dixon line and the low
clouds further north. After 14Z or so, VFR conditions are
expected for the rest of the day under high pressure, with high
clouds and light winds becoming more southerly with time.

Moisture increases after 00Z as a warm front lifts back north.
Clouds will lower with time, with MVFR ceilings showing up
northwest of PIT by sunrise. Showers and a few thunderstorms are
expected as well, with thunder chances too low to include yet,
but brief IFR visibilities are possible late tonight.

.Outlook...
Occasional restrictions are possible this weekend along a
stalled frontal boundary. Better restriction chances arrive with
a strong cold front Sunday night into Monday.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...None.
WV...None.

&&

$$



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