266
FXUS61 KPBZ 040002
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
802 PM EDT Fri May 3 2024

.SYNOPSIS...
Precipitation chances increase this afternoon and evening and
continue through the weekend. Cooler, but still above average,
temperatures prevail Saturday and Sunday with warm and unsettled
weather continuing into next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
KEY MESSAGES:

- Showers and thunderstorms expected this evening, with
  decreasing coverage overnight.
- Temperatures well above average tonight, with record warm
  minimum standards being approached.
-------------------------------------------------------------------

Weak but noted 700mb shortwave movement amid a warm, moist
environment with limited elevated instability will continue to
push a wave of showers with embedded lightning through the Upper
Ohio River Valley this evening. Precipitation chances are likely
to dwindle beyond midnight as the shortwave wave exits, surface
lift/heating is nonexistent, and elevated instability wanes. The
higher terrain of WV and the Laurel Highlands figure to have the
highest chances for residual showers through 6am Saturday given
weak surface convergence between NW flow to the west and SE to
the east.

Limited air mass change at the surface combined with excessive
cloud cover will buoy overnight temperature, putting a few
record high minimum temperature at area climate sites at risk
(see more details below). The likely limiting factor will be the
effects of precipitation cooling that will bring area
temperature closer to current upper 50s to lower 60s regional
dew point values.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Unsettled pattern remains with rain chances continuing
  through Sunday. Thunder possible on Sunday.
- Temperatures drop, but still remain above normal.
-------------------------------------------------------------------

Eastward progression of the 500mb ridge axis slows considerably over
the northeast CONUS on Saturday, with the quasi-stationary
surface boundary lingering near the PA/OH border. Shortwave
energy riding up the Ohio River will spread rain over the entire
forecast area during the day. Areas near and to the west of the
stalled boundary will have the bulk of the modest instability
during the afternoon, leading to better chances of thunderstorms
and notable rainfall. NBM probabilities of greater than 0.25"
of rain are highest in far western PA and eastern Ohio, as
expected given the above. The clouds and rain will keep
temperatures suppressed as compared to recent days. In fact,
easterly flow into the ridges may keep daytime highs some 15-20
degrees cooler in that region as compared to today.

The upper pattern shows better movement on Sunday, as increased
troughing over the northern Great Lakes shunts the larger trough
axis eastward, with the northeast CONUS ridge crossing into the
Atlantic. Shower coverage should be reinforced by the approaching
trough and a secondary frontal boundary. Instability of greater than
500 J/kg has 50% or greater probability across most of the forecast
area according to the NBM, thus thunderstorms are a higher
probability. Severe chances remain quite low as overall instability
remains marginal and flow is relatively weak in the lower and mid
levels. Temperatures will recover a bit in south/southwest flow,
with most non-ridge areas reaching the 70s once again.

Most-likely rainfall totals across the region roughly in the 1.0 to
1.25 inch range through Sunday, with isolated higher totals likely.
Large-scale flooding concerns remain small given the relatively dry
antecedent conditions, but slow storm motions could lead to isolated
issues if any one location gets hit multiple times with
thunderstorms.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:

- Rain chances continue into early next week but more uncertainty
  lends lower confidence.
- Temperatures favored to remain above normal.
-------------------------------------------------------------------

Ensembles have been consistent in showing a shortwave trough over
the Middle Ohio Valley approaching, but weakening, on Monday as it
interacts with flat ridging over our region. A south-to-north
gradient in PoP values still seems appropriate for the Monday/Monday
night period.

Uncertainty still reigns after Monday.  Most guidance depicts a
ridge centered over the Great Lakes at 12Z Tuesday, along with a
deep closed upper low in or near the Dakotas. The upper low appears
likely to fill during the midweek period, and as it does so,
shortwaves rotating around it appear to flatten out the ridge as it
moves across the Upper Ohio Valley, finally eroding it almost
completely in the northeast CONUS. Some strength and timing issues
remain with the details of this process, which in turn could impact
precipitation amounts and timing.

Nevertheless, a warm front is likely to cross on Tuesday as the
ridge progresses eastward. This will lead to the persistence of a
warm and moist airmass, with precipitable water values at or above
the 90th percentile in the climatology. Along with the previously
mentioned shortwave activity, this will keep an active weather
pattern in place for our region, with decent daily precipitation
chances through Friday. Deep-layer shear will increase as well
behind the departing ridge, so severe weather chances will need to
be monitored as well.  According to CSU machine-learning guidance
and NBM CWASP probabilities, Wednesday and Thursday may be the
days to watch.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
VFR ceilings and scattered light showers are ongoing across the
area this evening. Removed the mention of thunder from 00Z TAFs
as instability is waning and any lingering occurrences of
lightning would be brief and isolated, with little impact to
area terminals. Into tonight, convection is expected to subside
in coverage, with only some light lingering showers possible
primarily southeast of a ZZV-PIT-DUJ line. Meanwhile, saturation
from the rain and cooling temperatures may allow an MVFR cloud
deck to settle in by daybreak as winds shift to southeasterly.
The highest probabilities for ceiling restrictions, per the
latest hi-res ensemble guidance, exist north and west of
Pittsburgh, across portions of eastern Ohio and northwestern
PA. East of PIT, it appears downsloping southeasterly winds may
help keep low-level moisture profiles slightly less saturated
and thus, mitigate the formation of widespread MVFR/IFR ceilings.

Widespread rain chances increase again after 18Z Saturday.
Locally lower ceilings and visibilities can be expected in the
heavier showers. Continued to leave thunder out of the TAFs
during that period given uncertainty surrounding how much
instability will develop. If lightning does occur, the best
chances according to hi-res ensembles would be southwest of
PIT, so a mention of thunder at ZZV and HLG may be needed in
future updates.


.Outlook...
Restriction potential continues through Sunday morning, with
additional storm chances Sunday afternoon. Periodic restrictions
may continue through early next week as multiple disturbances
pass through the region.

&&

.CLIMATE...
Some record warm minimum temperatures may be approached on Saturday.
Below is a table showing the latest forecasted low temperature for
each climate site, their respective record value, and the year it
was set.

                  Forecast    Record     Year
Pittsburgh          60          65       1938
Wheeling            62          63       1931, 1939, 1941
Morgantown          61          63       2021
New Philadelphia    60          60       2012
Zanesville          63          65       1902

&&

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

&&

$$

SYNOPSIS...CL
NEAR TERM...Frazier
SHORT TERM...CL
LONG TERM...CL
AVIATION...Cermak/Milcarek
CLIMATE...Frazier