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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: PBZ
Regional NWS Weather Office: Pittsburgh, PA

FXUS61 KPBZ 200836

Area Forecast Discussion
National Weather Service Pittsburgh PA
436 AM EDT Tue Oct 20 2020

Periods of rain are expected through Tuesday along a stationary
surface boundary. Well above normal temperature and drier conditions
will develop by Thursday ahead of the next low pressure system this


Surface analysis show the cold front is beginning to enter the PBZ
forecast area as the front is now through the New Philadelphia area,
extending SW to NE. Latest radar trends indicate light rain
gradually overspreading and increasing across the Ohio Valley in
response to another low- amplitude shortwave trough propagating
through broad cyclonic SW flow aloft and favorable right-entrance
divergence of a 120kt jet streak. Additionally, the low-level jet
looks to ramp up from about 30 kts to 45 kts overnight at about
850mb, continuing to bring more than sufficient moisture and warm
advection at that level. HREF members generally agree precipitation
will overspread much of the forecast area within the next few hours
(with the exception of Morgantown and eastward).

Precipitation coverage will peak in the morning and begin gradually
diminishing thereafter as heights build in wake of the shortwave
trough. Additional rainfall of up to a few tenths appears possible
across most of the area north of the Mason-Dixon. Most NWP guidance
progs the model stalling around noon in the vicinity of Allegheny
County, extending to the north side of Wheeling to the West and
northeast towards Brookville PA.

Ample moisture and renewed warm air advection in the low- and mid-
levels will lead to another dreary day for the Upper Ohio Valley and
Allegheny Mtns region. 295-305k isentropic analysis shows quite a bit
of lift again in the lower troposphere, with model soundings
depicting a rather deep saturated layer above the near-surface cold
pool (frontal inversion). This suggests a cloudy day with
intermittent light rain showers or drizzle and perhaps even fog some
areas of fog. A gradually improvement/clearing is likely from south
to north through the day as the front retreats and the boundary-
layer can mix out. However, the PA Laurel Highlands and Allegheny
Mountains of WV/MD may get socked in again Tuesday night with an
upsloping SE wind.

Temps won`t budge much through the day, remaining in the 50s,
especially north of the I-70 corridor. South of that (south of the
front), better insolation and a better-mixed boundary layer may help
raise values to the 60s or even 70.


A deeper shortwave trough and its associated sfc trough will
traverse the northern Great Lakes into southeast Canada Tuesday night
into Wednesday. Due to the more northern track of this trough,
forcing will be much weaker with the frontal boundary remaining hung
up near the northwest portion of the CWA. At the same time, the
southeast U.S. ridge will continue to build, causing pressure heights
over the area to continue rising with warm advection at the sfc. The
result will be isolated/scattered showers near the front Wednesday,
with dry and well above-normal temperature for the rest of the
forecast area.


A deepening central U.S. trough and building southeast U.S. ridge
will further amplify warm advection for the upper Ohio River Valley
Thursday into Friday, with sfc high pressure keeping the region dry.
Almost summer-like temperature is expected Thursday with ample
sunshine while Friday will be slightly cooler given increased cloud
cover, though still well above seasonal average.

The upper trough and associated sfc feature are expected to cross the
region Saturday, though with the upper low core remaining well north
of the region. Expect increased chances of precipitation and cooler
temperature with its passage.

The post-trough passage patterns remains unclear, but general
consensus seems to keep the region in between the longwave trough
axis over the central U.S. and the Atlantic Ridge. The resulting
southwesterly flow will likely hold into early next week, buoying
area temperature near seasonal averages while potential shortwaves
within the flow bring periodic precipitation chances.


Cig and vis restrictions are expected through most of the TAF period
as a pseudo-stationary boundary remains across the area. Much of the
area will start with VFR conditions, but these will deteriorate
quickly as dawn approaches. IFR/LIFR cigs are expected through much
of Tuesday with possibly the exception of MGW and LBE. A second round
of showers will cross the region and continue through much of the
afternoon. By this evening, the boundary should lift northwards as a
warm front with a slow improvement to VFR expected to follow.

Relative improvement is expected during the second half of the work
week before another frontal system crosses this weekend.





Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather