853
FXUS61 KPBZ 031832
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
232 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 /THROUGH TONIGHT/...
KEY MESSAGES:

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

Mid-level ridging will continue to very slowly work eastward
tonight before stalling in the northeast CONUS. This will also
result in an approaching surface boundary getting hung up in the
vicinity of the PA/OH border by Saturday morning. Clouds are on
the increase from west to east as warm and moist advection
occurs from the southwest. Showers are currently firing in
eastern Ohio, and with increasing CAPE/ongoing heating
elsewhere, convective temperatures should be breached in more
locations in the next few hours, leading to more widespread
activity as a weak shortwave provides support. Temperatures have
managed to reach the lower and middle 80s in some areas where
cloud cover has been thinnest. The record high at Morgantown may
still be attainable if clouds/rain hold off long enough.

Surface-based CAPE should peak in the 500 to 1500 J/kg range
this afternoon, highest to the south of Pittsburgh. The
instability combined with precipitable water climbing into the
1.3 to 1.4 inch range will support local downpours, although
rates will likely remain below an inch per hour for the most
part according to HREF probabilities. Localized urban high water
issues cannot be totally ruled out, and WPC continues a marginal
excessive rainfall risk. However, larger-scale flooding issues
remain unlikely. Also, the severe threat is correspondingly low
given the lack of deep shear and decreasing levels of mid-level
dryness. Shower/storm coverage will slowly wane through the night as
instability is lost, but scattered activity is likely to
continue. The clouds and high moisture/dewpoints will keep
minimum temperatures well above normal, with some record warm
low temperature standards possibly in jeopardy. See the Climate
section below for details.

&&

.SHORT TERM /SATURDAY 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 THURSDAY/...
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 /18Z FRIDAY THROUGH WEDNESDAY/...
VFR will prevail this afternoon. High clouds will progressively
thicken and high base cumulus fields may develop into the
afternoon as heating continues. Guidance is consistent on
developing shallow updrafts into the day today. Though there has
been no observed lightning so far, the best heating has a chance
of invigorating showers/storms into southwestern Pennsylvania
and northern West Virginia. The current tempo groups highlight
the period of best probability at the sites with the higher
confidence in precipitation.

Into tonight, convection is expected to subside and become
lower coverage before resolving to some morning rain.
Saturation from prior and current rain, with cooling
temperatures may force a MVFR deck by daybreak, with
probabilities of IFR greater than 50% at FKL and DUJ for now.
As the morning continues on, saturated surface conditions near
the surface trough will allow rain and shower chances to
continue into the afternoon in southeast surface flow with
modest improvement in daytime heating.

.Outlook...
Restriction potential continues through Sunday morning, with
additional storm chances Sunday afternoon. Retractions return
early next week as multiple disturbances cross the region.

&&

.CLIMATE...
Some record warm minimum temperatures may be approached on Saturday.
(* denotes current forecast temperature exceeds value)

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


&&

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

&&

$$

SYNOPSIS...CL
NEAR TERM...CL
SHORT TERM...CL
LONG TERM...CL
AVIATION...Milcarek
CLIMATE...MLB/CL