PBZ issues Area Forecast Discussion (AFD) at Oct 12, 11:34 PM EDT588
FXUS61 KPBZ 130334
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
1134 PM EDT Sat Oct 12 2024
.SYNOPSIS...
Mostly dry and relatively warm weather will continue before shower
and thunderstorm chances return late tonight and continue
through Sunday night with crossing low pressure. Much cooler and
unsettled weather is then expected through Wednesday with a
series of crossing disturbances.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
KEY MESSAGES:
- Showers and possibly a thunderstorm possible late tonight
across the north.
-------------------------------------------------------------------
Midnight update...
Made minor adjustments to POPs and temperature based on the
latest observations and near term model data.
Evening update...
The main change for the overnight period was to push the PoPs
further north. Latest model data is showing the track of the
developing midwest low moving further north, which in turn is
pulling the boundary, which is lying across the middle of the
forecast area, further north. Additionally, this track will also
pull the deepest moisture further north as well, so a decrease
in cloud cover, particularly across the south, was installed as
well.
Previous discussion...
A digging shortwave trough is progged to track from the Upper
Midwest tonight, as surface low pressure develops in response
across IL and IN, SE of the trough. This low will pull the
stalled cold front back north as a warm front later tonight into
Sunday morning as it tracks eastward. With increasing moisture
and ascent, enhanced by an approaching low level jet, showers
are likely north of PIT, with lower shower chances to the south,
south of the front. A thunderstorm will also be possible with
the low level jet, and minimal elevated instability (Showalter
indices of 0 to -1 across NW PA through OH.)
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
KEY MESSAGES:
- Showers and possible strong thunderstorms through Sunday
evening
- Much cooler with scattered showers through Sunday night
through Monday night
-------------------------------------------------------------------
The digging shortwave will continue to advance across the
Midwest and Great Lakes region Sunday, as the surface low tracks
across OH through PA. The low will pull a cold front across the
region during the afternoon and early evening hours.
Wind profiles increase through the day Sunday with an
approaching jet. Gusty winds around 30-35mph are possible with
mixing during the afternoon. A narrow band of instability is
progged to develop just ahead of the cold front during the mid
to late afternoon, with mean MU CAPE values around 500 j/kg
generally S-SE of PIT. 0-6km shear is expected to increase to
between 40 and 50kt at the same time. Model soundings indicate
a mid level cap as well, eroding as FROPA occurs. This cap
should help limit thunderstorm development, though a broken
line of showers and embedded thunderstorms are expected along
the front. More convectively enhanced showers or organized
thunderstorms could tap the increased wind field aloft,
resulting in a potential for damaging wind gusts S-SE of PIT.
The Storm Prediction Center has placed this area in a Marginal
Risk (level 1 out of 5) for severe storms Sunday afternoon and
evening. Will highlight this potential in the Hazardous Weather
Outlook.
Showers and thunderstorms will taper off Sunday evening after
FROPA. Showers should increase in coverage again late Sunday
night and Monday as the initial upper trough axis crosses the
region, and cold advection occurs. The trough is progged to
deepen into a closed low across eastern Canada later Monday and
Monday night, as additional shortwaves rotate around it. This,
and cold NW flow off of the Great Lakes, will maintain scattered
to numerous showers across the region through Monday night. A
few snow flakes could also mix in across the higher terrain
areas, as 850mb temperatures drop to around -2 deg C.
Gusty winds are expected through much of the period, generally
ranging from 20-30mph.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
KEY MESSAGES:
- Cooler and unsettled weather through mid week
- Dry and warmer toward late week
-------------------------------------------------------------------
Model ensembles indicate the upper low will remain across the NE
CONUS through midweek, before opening into a trough and exiting
eastward later Wednesday. Continued cold NW flow off of the
Great Lakes, and shortwaves rotating around the low, will
maintain scattered showers across the region. Temperatures at
850mb are progged to range from -2 to -4 deg C through midweek,
and some snow could mix in at times across the higher terrain
areas of the Laurel Highlands and WV.
A ridge, between the exiting trough the the east, and a western
CONUS trough, will build across the region by late week. This
will result in dry and warmer weather returning to the region.
&&
.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
High confidence in VFR at area terminals through 12z Sunday as
the region is positioned within the warm sector of an
approaching surface low. Latest hi-res model trends are bearish
on overnight precipitation chances as they keep shower activity
north of the warm front, with lower (and mentioned) chances at
FKL. A strengthening low level jet will introduce a period of
llws aft 06z that will end as diurnal heating/mixing brings some
of those winds to the sfc while the jet max shifts east.
Latest trends favor dry conditions for the rest of the TAF
period despite a likely passage of an initial surface trough
between 19z and 00z. Confidence is high that this boundary
passage will veer surface wind SW to NW while slowly lowering
cloud decks in its wake. Confidence is low that showers and low
probability thunderstorms develop along the line due to the
lagged positioning of the upper trough axis. Limited mention to
VCSH based on latest hi-res trends, but probability for
showers/thunderstorms could rise with varying upstream
convective evolution.
.Outlook...
Strong cold advection underneath a deepening upper trough axis
will favor widespread cig restrictions and periodic light rain
showers overnight Sunday into Monday. Overall trends will see
only minor variations through midweek under the influence of
upper troughing. A return to VFR under the influence of high
pressure is likely by Thursday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...WM
NEAR TERM...WM/88
SHORT TERM...WM/88
LONG TERM...WM
AVIATION...Frazier
Source:
PBZ issues Area Forecast Discussion (AFD) at Oct 12, 11:34 PM EDT---------------
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