Scientific Forecaster Discussion
fxus61 kpbz 220756
Area forecast discussion
National Weather Service Pittsburgh PA
356 am EDT Mon Jul 22 2019
the approach and passage of a cold front will bring rain throughout
the day. Drier cooler weather can be expected for the remainder of
Near term /until 6 PM this evening/...
surface low pressure will develop along a quasi-stationary boundary
this morning and slide eastward along the front into the afternoon.
The low will be fueled by a shortwave trough, which will work to
drive it, and the stalled front, southeastward. Widespread showers
are expected ahead and along the system, and the rain shield will
drift southeastward throughout the day.
At this point, cannot get a great handle on the amount of convection
possible today. 00z cam models are not showing a great deal of
instability today, in fact they are indicating a steady
stabilization, pushing the real unstable air well to the south of the
region. Forecast soundings are showing marginal shear values which
may be enough to sustain updrafts if they can initialize. The area
will be blanketed by cloud cover all day, reducing atmospheric
buoyancy from daytime heating. Biggest concern would be storms firing
along left over outflow boundaries, which there are plenty of, from
yesterday evenings storms. Surface dewpoints will remain high until
the front exits, so heavy rain will remain a risk with any
convection. Because of the threat for additional heavy rain, have
issued a Flash Flood Watch for a large portion of the area.
Entire surface system will be east of the region by late this
afternoon, and showers/storms will quickly end behind the boundary.
Temperatures will be much cooler today but it will remain humid until
Short term /6 PM this evening through Wednesday/...
impressive shortwave trough will dig into the upper Midwest this
evening and shift eastward overnight. This energy will push the front
southeastward, and it will reach the mid-Atlantic region by early
Tuesday morning. The main area of showers will exit the Southeast Ridge late
this evening. Scattered to isolated showers are possible overnight
as the upper level energy with the main trough axis crosses, and
cold advection takes over.
Cooler and much less humid air will spread across the region tonight.
Cool, comparatively dry air will filter in behind the cold front on
Tuesday. A few lingering showers cannot be ruled out as cool air
moves over a Warm Lake Erie, but otherwise most locales will be dry.
Cloud cover will gradually decrease through the day as high pressure
builds into the region.
Wednesday looks very comfortable with plenty of sunshine.
Long term /Wednesday night through Sunday/...
seasonal or even slightly below seasonal temperatures are expected
across the area through much of next week. Temperatures will rebound
by the weekend as southerly flow returns and high pressure slides off
the Atlantic coast. Ensembles and blended guidance are showing a dry
Aviation /08z Monday through Friday/...
approaching shortwave trough will maintain shower chances, with
increasing coverage today. Expect both ceiling and visibility
restrictions to continue until cold front crosses this evening.
VFR will return behind the cold front passage, with prevailing VFR
expected for much of the week, outside of any morning fog.
Maryland...Flash Flood Watch through this evening for mdz001.
PA...Flash Flood Watch through this evening for paz031-075-076.
Flash Flood Watch until 2 PM EDT this afternoon for paz020-021-029-