477
FXUS61 KPBZ 182342
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
742 PM EDT Sat May 18 2024

.SYNOPSIS...
Scattered showers and thunderstorms will dissipate this evening,
with areas of fog overnight. High pressure will provide mainly
dry weather from Sunday into early next week, with a warming
trend in temperature.

&&

.NEAR TERM /THROUGH SUNDAY/...
KEY MESSAGES:

- Isolated showers and storms will end this evening.
- Areas of fog, possibly dense locally, will develop overnight.
  _____________________________________________________________

Evening Update... Showers with the occasional lightning strike
remain isolated this evening, primarily north of Dubois and
farther west in central/eastern Ohio. A few showers have also
been noted in the Ridges. Loss of heating after sunset should
collapse and dissipate any remaining storms, leaving most of the
region clear overnight. This, combined with light wind and
persistent low-level moisture will allow areas of fog to develop
early Sunday morning.

Previous Discussion...
The axis of an upper trough currently lies through western PA
southwestward to the Middle Ohio Valley, with a slowly filling
upper low swirl clearly visible in northern Ohio on water vapor
imagery.

Showers to this point remain quite isolated in most cases, with
the bulk of the activity along the ridges. Latest PIT ACARS
sounding shows 1100 J/kg of CAPE available with no cap,
although moisture drops off significantly above 650mb or so.
With very little flow and forcing in the trough, it appears that
shower and thunderstorm activity west of the ridges will remain
widely scattered/isolated at best, and CAMs continue to
advertise this thinking as well. Also, with precipitable water
slowly dropping off (now 0.93 on that ACARS sounding), any
threat of very localized heavy rain will be driven mainly by the
slow steering flow as opposed to efficient rain processes.
Mesoanalysis plots show the best downdraft CAPE, in the 700-800
J/kg range, across the western CWA. With some dry air aloft,
gusty downburst wind cannot be totally ruled out in a strong
storm.

The trough will continue to slowly sag south and east through
tonight, eventually to be replaced by upper ridging nosing in
from the Ohio Valley. Any showers/storms will collapse during
the evening with the loss of heating. Convective cloud will also
dissipate, leaving most of the region with a mostly clear
overnight period. That, plus the light wind and the lingering
low-level moisture/wet ground, will likely lead to areas of fog
overnight into Sunday morning, and it would not be a surprise if
it was locally dense in spots. Overnight low temperatures,
mainly in the 50s, will remain near to slightly above normal.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
KEY MESSAGES:

- Outside of isolated afternoon showers in the ridges on Sunday, dry
  weather can be expected through Monday night.
- Temperatures will climb some 10 degrees above normal by
  Monday.
  _____________________________________________________________

Upper ridging builds overhead on Sunday, with its axis oriented
from the middle Mississippi Valley northeastward into the Ohio
Valley and lower Great Lakes region. Dry weather is still
forecast for the majority of the region. However, hi-res models
continue to depict isolated showers along the PA/WV ridges,
where subsidence may be a bit weaker and where low-level
easterly flow may aid development. Any such activity should end
with the loss of daytime heating Sunday evening. Higher heights
and increased sunshine should add roughly five degrees to
afternoon highs as compared to today.

The ridge then dominates our weather Sunday night through Monday
night, with the axis passing through during the daylight hours.  Dry
weather and temperatures some 10 degrees above normal can be
expected, with most non-ridge locations reaching the lower to mid
80s on Monday.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
KEY MESSAGES:

- Dry and quite warm Tuesday.
- Rain chances return for Wednesday and Thursday, with some potential
  for strong thunderstorms.
- Seasonable temperatures and lower rain chances are expected Friday
  and Saturday.
____________________________________________________________

Dry weather continues into Tuesday night as the upper ridge slowly
works off of the Atlantic Seaboard. Plenty of sunshine and another
day of drying will help add a degree or two to Monday`s highs,
pushing values further into the 80s.

The models continue to show some differences with the strength and
timing of the next trough crossing the Plains into the Great Lakes,
which will likely have the most impact on the Wednesday and Thursday
forecast. GFS/GEFS seem to prefer a faster/stronger wave, which
could bring precipitation back sooner than the overall grand
ensemble solution, while the ENS leans towards a bit more shallow
trough. In any case, good precipitation chances continue to favor
the Wednesday through Thursday period. We will continue to watch for
the potential for severe weather as the midweek period approaches,
as CIPS/CSU severe guidance showing some potential, particularly on
Wednesday. Well above-normal temperatures Wednesday may be knocked
back closer to climatology by Thursday due to a cold frontal passage.

Model divergence increases further for Friday and Saturday, but
additional, smaller shortwaves may provide lower-end chances for
rain, with temperatures not straying far from climatology.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
A scattered to broken VFR convective type cloud deck has taken
over this afternoon as convective temperatures are achieved.
Very weak boundary layer flow will generally keep wind variable
at 5 knots or less through this evening, perhaps favoring a
northerly direction. Widely scattered showers and thunderstorms
are expected to develop this afternoon after 19z (20-40%
chance... highest to the east), but with no real defined surface
forcing mechanism aside from orographic influence, confidence
is low in impacts to any one terminal at any given time. As
stated, hi res ensemble favors development primarily east of PIT
and potentially affecting at LBE/DUJ with brief restrictions in
TSRA.

Showers and storms will dissipate after 00z and give way to more
widespread restrictions again possible overnight tonight with
lingering low level moisture in place and wind going mostly
calm. Probability for MVFR to IFR VIS returns to 40-70% and with
less cloud coverage and no rain expected, confidence is a bit
higher tonight than Friday night for fog development. FKL/DUJ
have a low to moderate probability of LIFR VIS.

Ridging builds on Sunday and VFR returns with high confidence
after mixing dissipates the fog and erodes any lingering
scattered cloud deck in the morning. Wind will again be light
during the day with a weak pressure gradient in place.

.Outlook...
VFR and dry weather remain high probabilities into Monday and
Tuesday under the influence of high pressure. Precipitation
chances and associated restrictions return Wednesday.

&&

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

&&

$$

SYNOPSIS...CL
NEAR TERM...Rackley/CL
SHORT TERM...CL
LONG TERM...CL
AVIATION...MLB