PBZ issues Area Forecast Discussion (AFD) at Apr 5, 2:48 PM EDT076
FXUS61 KPBZ 051848
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
248 PM EDT Sat Apr 5 2025
.SYNOPSIS...
Rounds of showers and thunderstorms will continue into Sunday
with the approach and passage of a slow-moving cold front. Heavy
rainfall totals remain possible, and a severe storm or two is
possible this afternoon and evening. Much colder air arrives
behind the front for early next week, with a bit of wintry
precipitation expected.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
KEY MESSAGES:
- Flood Watch remains in effect for much of the region; heavy
rain threat continues into Sunday.
- Marginal risk of severe storms this afternoon/evening.
- Cold front arrives later tonight and slowly crosses through
Sunday, bringing much cooler air.
-------------------------------------------------------------------
The lingering boundary has pushed north as a warm front, and has
largely cleared the CWA, save for perhaps the far northeastern
corner (DUJ still showing a SE wind). This has placed most of the
region in the warm sector, with only scattered showers at present.
Some breaks in the clouds have developed as well, and along with
dewpoints increasing to around 60, this has allowed for some modest
surface-based CAPE of 500 J/kg or less to develop, highest south
of I-70.
As a shortwave trough rotates across the northern Great Lakes, the
western portion of the wavy boundary approaches and enters the
region tonight as a cold front. With time ahead of the front, the
500 J/kg line may creep northwestward to near PIT by 21Z according
to RAP mesoanalysis. Combined with sufficient levels of effective
shear, the SPC marginal risk of severe thunderstorms during the late
afternoon/evening appears justified. Poor lapse rates and the lack
of dry air aloft may temper the hail threat, but damaging wind gusts
and perhaps a tornado cannot be ruled out.
We also will continue with a heavy rain threat overnight into early
Sunday. Increasing convergence along the boundary will ramp up low-
level frontogenesis along it. Precipitable water values approaching
1.5 inches will pool just ahead, above the top end of climatology.
Saturated lower levels and decent warm cloud depths also point to
efficient rainfall production. NBM Probabilities of an inch or
more of rainfall through 8 PM Sunday are 40-60% generally south
of US- 422. However, locally higher totals are certainly
possible in any convective banding that sets up - 2 inches or
more doesn't seem to be out of the question. Thus, the Flood
Watch will continue, and in fact may have to be extended past 8
AM Sunday if the heavy rain threat lingers past then.
Rain coverage peaks overnight and then slowly fades from north to
south on Sunday as the cold front slowly settles through the region.
Cold advection commences overnight, dropping temperatures into the
30s generally north and west of Pittsburgh by 12Z Sunday.
Temperatures will not rise much on Sunday, reaching/remaining in the
40s in most cases. Temperature profiles suggests snow and/or
sleet may mix in with rain north of I-80 Sunday morning, and
perhaps as far south as Pittsburgh by evening. No snow
accumulation is foreseen.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
KEY MESSAGES:
- Widespread precipitation ends by Monday morning with the
departure of the front.
- Below-normal temperatures continue with late day/Monday night
rain and snow showers.
-------------------------------------------------------------------
A low pressure wave along the front, which will lie in or near
the ridges by 00Z Monday, may reinvigorate precipitation
coverage Sunday evening, mainly east of Pittsburgh. The front
finally gets a good kick east by later Sunday night/early Monday
morning as troughing deepens over the Ohio Valley, bringing
widespread precipitation to an end. The snow/sleet possibilities
expand to most of the region Sunday night into Monday morning.
Any accumulation will likely be limited to less than an inch,
generally north of US-422 and on the higher ridges, as the warm
and wet ground is a hindrance.
Precipitation coverage may briefly drop off for part of Monday,
however another cold front dropping southeast from the Great
Lakes may bring scattered showers to the region later Monday
afternoon and night. Precipitation would start as rain with
daytime temperatures mainly in the upper 40s/lower 50s, but a
mix with and change to snow is likely Monday night, with a minor
accumulation of less than an inch possible during the nighttime
hours. Widespread low temperatures in the 20s are forecast,
representing well-below normal values.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
KEY MESSAGES:
- Cold air mass peaks on Tuesday.
- Dry weather briefly returns midweek before additional
precipitation chances by late week.
-------------------------------------------------------------------
850mb temperatures reach their minimum values of -11C to -13C on
Tuesday as the 500mb trough axis reaches the Atlantic Seaboard. By
this point, most snow showers should be confined to areas north of
Pittsburgh, and these will end during the day as low-level ridging
arrives. High temperatures some 15 to 20 degrees below normal can
be expected. Dry weather continues through Wednesday as the surface
high crosses, with a brief bout of quasi-zonal mid-level flow
pointing to some temperature moderation back to around 10 degrees
below normal Wednesday.
By Thursday, it appears likely that the upper trough will be
reinforced by a potent shortwave dropping across the Upper Midwest.
Ensembles differ on the exact details, but rain chances do ramp up
for Thursday and Friday as an associated surface low and maturing
frontal system may cross the Upper Ohio Valley. How quickly the
500mb trough axis crosses the region is in question, as some model
solution close off an upper low in the base of the trough, slowing
system progression. That could keep some threat of precipitation in
the forecast into Saturday.
&&
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Showers and isolated thunderstorms will continue today with a
lingering stationary boundary. Areas north of the warm sector
(BVI, FKL, DUJ, and at times ZZV) have seen cigs drop to
IFR/LIFR. Areas within the warm sector (PIT, AGC, LBE, MGW, HLG)
continue to bounce between VFR to MVFR.
This afternoon, with strong southwest flow, cigs north of PIT
are expected to improve to at least MVFR and potentially VFR.
However, the threat for thunderstorms increases with an uptick
in instability. Probabilities for strong thunderstorms are
slightly higher south of PIT.
A shift in the frontal boundary is expected between 23Z to 01Z,
to the south. With this change, expect widespread IFR to LIFR
conditions as cold air resides at the surface and warm air
continues to advance aloft.
Advancing low-level dry air with a cold front is expected to mix
the boundary layer late morning Sunday and increase cigs from
north to south.
Outlook...
Heavy rain is likely to break Sunday into Monday as an upper-level
trough impinges upon the area, switching us over to a cooler pattern
featuring periodic rain/snow chances. This pattern switch likely
means a continued period of restrictions through mid-week.
&&
.HYDROLOGY...
Heavy rainfall potential continues through Sunday. An
additional 0.75 to 1.50 inches is expected through Sunday
evening, with heavier rain tapering off behind a cold front.
Localized higher amounts with thunderstorms can't be ruled out-
totals above 2 inches could be seen in localized cases. The
Flood Watch currently continues through 8 AM Sunday, and may
need to be extended depending on where the heavy rainfall threat
is likely to linger.
Precipitable water is expected to remain elevated through
Sunday, with some periodic jet enhanced ascent. Even after the
heavy rain potential ends, river levels will likely remain
elevated for a few days. Several River Flood Warnings are
already in effect for expectations of minor flooding, and many
other river forecast points will reach action stage.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through Sunday morning for PAZ013-014-020>022-029-
031-073>078.
OH...Flood Watch through Sunday morning for OHZ039>041-048>050-
057>059-068-069.
WV...Flood Watch through Sunday morning for WVZ001>004-012-021-509-
510.
&&
$$
SYNOPSIS...CL
NEAR TERM...CL
SHORT TERM...CL
LONG TERM...CL
AVIATION...Hefferan
HYDROLOGY...CL
Source:
PBZ issues Area Forecast Discussion (AFD) at Apr 5, 2:48 PM EDT---------------
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