PBZ issues Area Forecast Discussion (AFD) at May 29, 2:07 PM EDT223
FXUS61 KPBZ 291807
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
207 PM EDT Wed May 29 2024
.SYNOPSIS...
Scattered showers and thunderstorms on Wednesday under an upper
trough. Dry weather returns Thursday through Saturday as high
pressure builds with cooler than average temperatures. An
unsettled but warmer pattern looks to take hold by late weekend
into next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Scattered showers and thunderstorms expected throughout the day
today.
- High temperature around 5 degrees below the daily average.
-------------------------------------------------------------------
An upper low is situated across eastern OH/western PA and vorticity
advection associated with an embedded wave has driven an area of
showers with some rumbles of thunder. Two precip zones have
established with one from Pittsburgh and south having a more
convective look to it resultant of differential heating with thicker
cloud cover north and thinner south. A stratiform area of
precip further north will pivot across the area through the
afternoon hours. The 12z PIT sounding shows PWAT values just
under an inch which isn't much out of the ordinary for today
climatologically. That said, cloud bearing layer flow of less
than 20 knots will support slow moving areas of showers. Colder
air under the core of the upper low will allow for
destabilization of 500-1000 J/kg of mainly skinny CAPE largely
confined to the -10C layer and below which could enhance warm
rain processes thus heavier rates. While widespread flooding
concerns aren't expected, the areas to watch will be typical
urban areas but also the Columbiana-Beaver-Lawrence- Mercer
region where morning rain has sat the longest and CAMs indicate
a probable deformation zone maintaining showers here this
afternoon thus confidence is higher for this area to see the
most rain. Widespread totals will be a quarter to three quarters
of an inch, but amounts locally up to 1.75" under the heavier
showers are not off the table. A Slight Risk (1/5) has been
introduced for Pittsburgh and north while a Marginal (1/5)
remains elsewhere.
Very weak shear should preclude a severe threat today. Small
sub-severe hail may accompany any heavier shower/storm and
brief funnel clouds/cold air funnels are also possible through
the afternoon with cold air aloft and significant low level
CAPE, but instances of contact with the ground will be rare.
Exiting of the upper level trough axis to the east will see surface
high pressure and subsidence build during the evening and overnight
hours. The expectation is for decaying convective activity and
clearing skies after daytime heating is lost. Probability for pockets
of fog, favoring river valley locations, will increase toward
daybreak with hi res ensemble favoring south and east of
Pittsburgh.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
KEY MESSAGES:
- Dry weather expected to close out the week.
- Temperatures remain below average.
-------------------------------------------------------------------
The upper trough will finally begin to make its exit on Thursday.
High pressure will build as one final shortwave traverses the area
in northerly flow aloft, but associated subsidence and increasing
mid-level dry air will keep the area rain-free and mixing will erode
residual cloud cover below a sinking inversion save for the ridges
where low level moisture may be a bit slower to clear. Cool air will
overspread the area with ensemble mean 850 mb temperature ranging
from 3-6C supporting highs in the mid 60s, about 10 degrees below
average, and a northerly gradient breeze through the day as the high
builds in. Lows will bring a bit of a chill to the air with 40s
expected and even a 40% probability of less than 40 mainly for the
higher elevations and north of I-80.
There is slight timing difference with the departure of the trough
lending the chance for slightly cooler highs than forecast on
Friday, but overall dry weather continues to close out the week with
high confidence. Temperature will begin to moderate some with rising
heights and with a dry atmosphere and sunny skies, adjusted NBM dew
points down a bit and highs up a touch to account for mixing bias.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
KEY MESSAGES:
- Shower and thunderstorm chances increase late Saturday into early
next week.
- Temperatures rebound back toward normal by Saturday.
-------------------------------------------------------------------
Upper level clouds increase on Saturday as ensembles eject an upper
wave out of the Plains. Uncertainty comes into play with variations
in strength and timing of the wave with some showing a flatter, more
progressive solution and others a more amplified, slower solution.
Temperatures will rebound Saturday as southerly flow on the backside
of the departing high promotes warm, moist advection.
Thereafter, the overall pattern trends toward weak westerlies aloft
through early next week. Embedded shortwaves may offer periodic
shower/thunderstorm chances but will be much more dependent on
convective evolution to the west to determine
timing/coverage/probability of occurrence for the forecast area.
There is higher confidence that broad height rises should enable
further warming areawide, making low to mid 80 values more likely by
Tuesday.
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
An upper low passing through the region is supporting scattered
to numerous slow-moving showers and thunderstorms across the
area this afternoon. These are bringing periods of heavy rain
and lightning to area terminals as well as restrictions to
cigs/vis. Expect the convection to continue throughout the
remainder of the day, tapering off from west to east after 00Z.
High pressure builds into the area in the wake of the low
overnight into Thursday, bringing VFR conditions and light
north to northwest flow thereafter through the remainder of the
TAF period.
.Outlook...
High pressure remains in place through the end of the week,
resulting in areawide VFR through that time. Some restriction
potential returns Saturday night into Sunday as showers and
thunderstorms return with the next disturbance.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...Frazier/MLB
AVIATION...Cermak/Shallenberger
Source:
PBZ issues Area Forecast Discussion (AFD) at May 29, 2:07 PM EDT---------------
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