PBZ issues Area Forecast Discussion (AFD) at Jul 2, 7:23 PM EDT131
FXUS61 KPBZ 022323
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
723 PM EDT Tue Jul 2 2024
.SYNOPSIS...
Shower and thunderstorm chances increase Wednesday evening
through Friday with a series of upper level disturbances, with
potential for convective lulls during the overnight periods.
Expect well above normal temperature through the holiday
weekend, with high probability for dry weather returning
Saturday and Sunday.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
KEY MESSAGES:
- High pressure will maintain dry and seasonable weather through
the overnight period.
-------------------------------------------------------------------
Update...
Only minor adjustments to the forecast based on current
observations and near term model trends.
Previous discussion...
Dry and seasonable weather will persist through the rest of the
evening as a 500mb ridge crosses overhead and the surface high
positions along the east coast.
A few cirrus clouds may cross overnight but are unlikely to
alter area temperature much; the main driver of the rising low
temperature is the column warm, moist advection as southwesterly
flow increases.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
KEY MESSAGES:
- Dry weather and seasonable warm weather expected for most of
Wednesday.
- Showers and thunderstorms possible Wednesday night and
Thursday, with low probability threat of severe weather.
-------------------------------------------------------------------
An upper level shortwave and decaying convective complex will
approach the region from the west Wednesday morning as warm,
moist advection persists. Subsidence and the prior dry air mass
should result in dry weather and above normal temperature
through the afternoon. That shortwave will traverse north of the
region during the late afternoon to evening hours and push a
decaying surface boundary east southeast, increasing shower and
thunderstorm probabilities.
The convective focus will be approximately between 20z-01z
(4pm-9pm) across eastern OH where convection is likely to
develop just ahead of the surface boundary. Environmental
conditions supporting the SPC marginal risk for damaging wind
includes mean SBCAPE around 1000-1500 J/kg, around 30kts
effective shear (though potentially decreasing with event time
as shortwave exits), and rapidly rising PWAT values (going above
90th percentiles). The threat remains conditional on a few
factors: 1) the column moisture increase likely coincides with
weaker lapse rates (equating to less intense updrafts); 2)
the decaying front and north-bound shortwave are likely to offer
limited support for initiation and upward growth; 3) there is
potential for convection along the southwest flank of the front
to fire earlier and cut off moist advection to the region
(and/or limit instability with cirrus coverage).
Overnight, isolated to scattered showers remain possible as the
shortwave exits northeast and the front stalls generally along
and south of I-70. Loss of heating should limit severe
potential, with storms relying on elevated instability to
continue through Thursday morning. The rest of the day Thursday
features likely convection along/south of the boundary as
additional weak shortwave cross within the WSW flow aloft.
Localized flash flooding remains a concern given near-record
PWAT values and near parallel upper flow with the surface
boundary; however, marginal instability and weak lapse rates may
limit maximization of rainfall rates. Thursday evening will see
a downward trend in convective activity, with mostly isolated to
scattered storms remain south of I-70.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:
- More widespread storm coverage expected Friday, with non-zero
hazardous weather threat.
- High probability for dry weather and slightly above average
temperature the rest of the weekend.
-------------------------------------------------------------------
A better developed upper level shortwave trough will enter the
lower Ohio River Valley Friday and promote broad jet-aided
ascent for the forecast area. Northward lifting of the
stationary boundary and eventual crossing of a surface cold
front is likely to generate more widespread shower and
thunderstorm coverage Friday afternoon and evening.
Environmental conditions remain variable amongst ensemble
models but mean SBCABE around 1000 J/kg, PWAT above 90th
percentile, and 30-40kts 0-6km shear suggest potential for
hazardous weather in the form of damaging wind and flash
flooding.
Long range patters suggest troughing will persist over the
Central Plains, leaving the Upper Ohio River Valley within weak
southwest flow (and likely within a dry slot). There is fairly
high confidence in dry weather and slightly above normal
temperature occurring Saturday through Monday until the next low
pressure system potentially crosses Tuesday.
&&
.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
VFR is expected through most of Wednesday as an upper ridge
moves east across the region. Wind should veer to the SW after
sunrise, with a few gusts up to 20kt.
A shortwave trough will approach the Upper Ohio Valley region
late Wednesday afternoon and evening. Scattered showers and
thunderstorms are expected to develop in advance of the trough.
The coverage and timing remain in question, with the most
favorable instability for storms expected just to the west of
the area. Included a VCTS mention for now in the tafs with
uncertainty remaining.
.Outlook...
VFR is expected through Wednesday. A slow moving front is
expected to persist across the region Wednesday night through
Friday, bringing showers, thunderstorms and associated
restrictions back to the area through the end of the week. A
cold front will maintain showers, thunderstorms and ocnl
restrictions Friday night/early Saturday.
VFR should return Sunday under high pressure.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Frazier
NEAR TERM...WM/Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...WM
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 2, 7:23 PM EDT---------------
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