740
FXUS61 KPBZ 171715
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
115 PM EDT Sat Aug 17 2024

.SYNOPSIS...
A slow moving upper level system will promote rounds of showers
and thunderstorms primarily each afternoon through Monday, with
convection peaking Sunday afternoon. There is a low probability
for severe weather this afternoon and evening.

&&

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

- There is a low probability for strong to severe thunderstorms
  this afternoon and evening, favoring a wind and isolated
  flash flooding threat.

-------------------------------------------------------------------

Latest WV imagery shows a slow-moving upper low currently
centered over northern Lake Michigan will slowly shift east
this weekend. By this afternoon, the approach of a pre-frontal
trough and destabilization is likely to aid convective
development along and ahead of a cold frontal boundary. Compared
to Friday, diurnal heating looks to be a bit more robust today
with colder and drier mid-levels. This should allow for MLCAPE
values near 1000-2000 J/kg and more favorable mid-level lapse
rates of 6-6.5 C/km. However, shear remains meager, with bulk
shear values remaining below 30 kts. The primary threat with any
stronger storms will be damaging wind.

Overall confidence in the severe threat remains medium, due
primarily to the potential for lingering cloud cover which could
reduce afternoon destabilization. With weaker upper forcing and
relatively weak shear, this would likely hamper robust storm
organization. SPC has maintained the areawide marginal (1/5)
risk for severe. 90th percentile PWATs (1.5-1.75") will
contribute to an isolated/localized flash flooding threat.

Waning instability after sunset and progression of the trough
eastward will lead to waning precipitation chances after 06z,
though some showers are likely to linger through the night.

&&

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

- Widespread convection is favored Sunday, but poses a more
  limited hazard risk.
- Residual showers with cooler temperatures are likely on
  Monday, diminishing Monday evening.

-------------------------------------------------------------------

By Sunday, the upper low/trough will be centered just to our
north, allowing for lower convective temps and more widespread
thunderstorms development in the afternoon. There is some
uncertainty in favored locations due to slight variations in
trough positioning that may create subsidence holes, but the
overall pattern/environment should support on and off storms
through the evening. The lack of strong instability despite 90th
percentile PWATS and some forward motion of storms should
preclude a flood threat.

The trough continues east on Monday, leaving the area under
cooler, northwest flow. Residual diurnally-driven showers are
possible through the day, eventually diminishing Monday evening.
Area temperatures will drop well below the daily average,
resulting in daily highs in the 60s and lower 70s.

&&

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

- Long range trends favor dry weather and near normal
  temperature.
-------------------------------------------------------------------

The region will remain under northwest flow on Tuesday, but with
dry conditions. Residual cold air advection will lead to
temperature around 10 degrees below the daily average.

Long range analysis favors a continuation of the fairly
amplified pattern of ridging over the Rockies and troughing
along the east coast. This should position the region within the
drier NW flow pattern where precipitation chances will be
heavily reliant on strong shortwave movement over the ridge.
Latest trends don`t favor this and thus suggest a prolonged
period of dry weather and seasonable temperature Wednesday
through the end of the week.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
As a surface trough approaches, more organized showers and
thunderstorms are expected after 19z. Some may be severe with
damaging wind and bring periodic VIS restrictions with heavy
rain. Latest guidance still exhibits differences in overall
coverage, so have introduced a TEMPO group for all sites during
the most likely timeframe for thunder... primarily in the 19z
to 04z timeframe with coverage increasing from west to east. A
few showers may linger overnight with the passage of another
weak surface trough.

With lingering low-level moisture, probabilities increase
overnight tonight after 06z for restrictions to MVFR and
potentially IFR (40-60%), though guidance overdid restrictions a
bit this morning as a whole, so erred slightly on the more
conservative side introducing widespread low-end MVFR across the
board, at least until we get a better idea where rainfall
occurs.

.Outlook...
Periodic restrictions and showers and thunderstorms are possible
through early Monday as low pressure slowly crosses the region.
The greatest coverage of showers/thunderstorms will be in the
afternoon and early evening. VFR returns by Tuesday under high
pressure.

&&

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

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Rackley/88
SHORT TERM...Rackley
LONG TERM...Rackley/Frazier
AVIATION...MLB