Area Forecast Discussion
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FXUS61 KPBZ 191154
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
754 AM EDT Fri Apr 19 2019

.SYNOPSIS...
Rain will spread across the region on Friday with the passage of a
slow moving cold front. Occasional rain showers can be expected until
Sunday until the low pressure system exits the area.

&&

.NEAR TERM /THROUGH TONIGHT/...
Regional radars show precipitation extending along a cold front from
north-central Ohio southward. The progression of both the rain and
cold front has been rather slow to make it into PBZ CWA since an
upstream low over the lower Ohio River Valley has begun to deepen in
response to an amplifying southern stream upper trough. This will
essentially "hold back" the frontal passage until later today as the
surface low progresses eastward. Until then, poleward movement of
warm, moist flow ahead of this deepening low will act to enhance
frontogenetical forcing across Ohio. Low-to-mid level transport of
this air over the low level cold front will maintain showers through
much of the morning as this front crawls eastward into eastern Ohio,
the northern WV Panhandle, and eventually western PA. Model consensus
shows forecast lapse rates to be rather poor... as such, have removed
thunder out of the much of the forecast area.

The exception to this would be from some area of approximately
Latrobe southward towards Morgantown, WV and eastward into Garrett
County MD. Hi-res models all suggest a mid-afternoon surge of warm,
moist low level air which would attribute to SB-CAPE in excess of
1000 J/kg. If this were to be realized, showers (or tstorms)
initiating along or ahead of the front would have the potential to be
severe, especially given strong low/mid level shear. However, I`m
rather skeptical of this solution as a whole given that insolation
through the day will be minimal. Will have to keep a close eye later
today to see how this instability materializes.

By Friday night, the deep southern stream cut-off low will move up
the Ohio River Valley. Isentropic ascent ahead of the low center, along
with DPVA, will maintain the chance for precipitation through much
of Friday night. Precipitation totals by dawn Saturday will be modest
at best, with much of the area receiving less than 0.75 of an inch.
The highest rainfall totals are expected to be on the edges of the
CWA... or across 1) eastern Ohio, where frontogenetical lift will
sustain showers through much of Friday and 2) along the Allegheny
Mountains where instability will be highest through the event.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
By dawn Saturday, the southern stream cut-off low will be centered
across the Mid-Ohio River Valley and gradually moving northeastward.
Cloud cover with a few rounds of light showers will be possible as
this system moves northeastward through the day Saturday into
Saturday night.

The cold air reservoir associated with the closed low may actually
lead to some light, wet snow across the crests of the Alleghenies
Saturday night into Sunday morning. Models soundings support
dendritic snow growth in the cloud layer, however, the low level
temperatures may be too marginal to support snow. For now, I`ve kept
accumulating snow out of the forecast package... but may have to
amend if surface temperatures look to get any colder.

As the low exits to our east over the course of the day Sunday,
somewhat pleasant weather may be in store. Cloud cover will
gradually erode through the day as low level moisture departs east
and a shortwave ridge approaches the area. Given cool northwest
flow, expect highs a little cooler than the climatological mean,
with values in the 50s to around 60 on Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Looking ahead... upper level flow will substantially "flatten" out
next week. Monday will be rather tranquil in terms of weather as the
area will remain under influence from a ridge. Temperatures should
get into the upper 60s and 70s for most places, with no rain
expected. Hooray!

Unfortunately the rain-free day count (of 1) ends Tuesday as a quick
moving shortwave swings through the area. A low will move across the
Great Lakes into Southern Ontario with a cold front extending
southward through the Ohio Valley. Precipitation will be mainly
along the front itself, as it moves southward over the course of
Tuesday.

Global models have converged a bit on the long term picture- that of
one with fairly tranquil weather over the CWA late in the week.
Quasi-zonal flow looks to develop overhead with the strong upper
dynamics now retreated far into Canada (thanks Spring!). A gradual
warming trend late in the week can be expected as a deepening west
coast troughing looks probable.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...

Scattered showers expected today ahead of slow moving frontal system.
Based off latest forecast soundings...restrictions should be limited
to MVFR cigs. Gusty sfc winds will develop by late morning with
increased mixing.

.Outlook...
Restrictions and showers are likely through the weekend as strong
low pres traverses the region.

&&

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

&&

$$


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