Severe Thunderstorm Warning 55, NWS Pittsburgh, PA

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
702 PM EDT Wed Apr 17 2024

.SYNOPSIS...
Cold front will cross the area this evening bringing
thunderstorms. After a brief dry period Thursday, another cold
front moving through very late Thursday night and Friday will
bring another round of showers before a period of cool and dry
weather moves in for Saturday through Monday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
KEY MESSAGES:

-  Severe thunderstorms with very large hail and damaging winds
   until midnight.

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

For the evening update...refining PoPs with the line of storms
moving through the region. Used a blend of hires and blended
guidance. Timing of latest hires guidance has sped the eastward
movement up just a bit. This lines up well with current radar
speeds. Rapid end to the rain behind the front, so PoPs were
decreased faster later this evening and overnight. Made some
adjustments to late night cloud cover as the threat for stratocu
still remains. Rest of the forecast looks goods.

Previous discussion...

500 mb trough with 50-60 meter height falls rolls through this
evening with associated band of severe thunderstorms along cold
front. A band of supercells has formed ahead of the surface
cold front and will move steadily into eastern OH, western PA,
and northern WV early this evening.

MLCAPE of 1,500 J/kg coupled with 7 to 7.5 C/km lapse rates and
0-6 km shear of 40-50 knots supports large to very large hail.
The 17z KILN had several SARS analogs with 2"+ hail. LCL values
are a bit high for strong tornadoes in the 1,300 m range.
However with 20-30 knots of 0-1km shear tornadoes are possible
especially in Ohio counties before upscale evolution to a solid
squall line focuses threat on wind damage.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
KEY MESSAGES:

- Above normal temperature and dry weather expected for
  transitory day Thursday.
- Another round of showers and low probability thunderstorms
  expected Friday with cold front passage.
----------------------------------------------------------------

Height rises with 500mb ridge move across area Thursday bring
brief period of dry weather with weak surface ridge at the
surface.

A deep upper low then moves across Ontario Thursday night and
Friday with 200 meter height falls into Quebec. Although this is
a glancing blow this far south, it does induce a wave of low
pressure, pushing a cold front through the Upper Ohio River
valley with showers expected starting very late Thursday night
in Ohio and moving through rest of area Friday.

Heights fall about 80 meters Friday night in wake of cold front
and usher in colder air to set up the weekend as 850 mb
temperatures fall to about 0C during the night.

&&

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

- Dry but cooler conditions expected for the weekend.
- Periodic shortwave passages may offer brief precipitation
  windows through the middle of next week.
-------------------------------------------------------------------

Dry and cool westerly flow aloft expected Saturday through
Monday. A large Canadian High settles into the central CONUS
with persistent northwest surface flow and gradually cooling 850
mb temps. By Saturday evening they will drop to -2 to -4C, then
-4 to -6C by early Sunday morning.

While 30s are possible Saturday night, Sunday night appears to
be the coldest with clear skies and light winds creating
favorable conditions for radiational cooling. Even though
boundary layer starts to warm with 850 mb temps warming close to
zero, a sharp inversion is expected with light winds under the
surface ridge. NBM 10th percentile Min Temps are in the upper
20s in the north and lower 30s over much of the central potion
of forecast area. Given the recent warmth and early start to
growing season, we ran the frost tools and widespread frost is
expected Sunday night which may eventually require headlines.

Trough coming out of Midwest Monday night moves into Great Lakes
Tuesday and the northeast states on Wednesday. Showers are
possible Tuesday and may linger on Wednesday as a result of
strong cold advection and possible lake effect showers. 12z
ECMWF even had -10C 850 mb temps reaching into northern PA on
Wednesday.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
Line of showers and thunderstorms will move through the region
until 04z. Will likely be east of ZZV at start of forecast
period. Storms could produce strong winds, hail, and frequent
lightning. Storms will bring a reduction in vis/cig to mainly
MVFR, but iso IFR possible in stronger storms. After line passes
to the east, expect a return to VFR for the overnight period for
most ports, except at FKL and DUJ where MVFR cigs are expected
through most of the forecast period.

A brief lowering of cigs is anticipated around dawn. This is a
low confidence forecast at this point, but most of the model
data is showing this threat. There should be an improvement in
conditions by late morning as a return to VFR is anticipated at
all ports except FKL and DUJ.

.Outlook...
Restrictions remain possible Thursday night into Friday under
another passing upper trough and associated chances for rain.
Prevailing VFR returns over the weekend.

&&

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

&&

SYNOPSIS...Craven
NEAR TERM...Craven/22
SHORT TERM...Craven
LONG TERM...Craven
AVIATION...22

Hazardous Weather Outlook
National Weather Service Pittsburgh PA
220 PM EDT Wed Apr 17 2024

PAZ009-016-074-076>078-WVZ510>514-181830-
Forest-Jefferson PA-Higher Elevations of Westmoreland-
Higher Elevations of Fayette-Indiana-Higher Elevations of Indiana-
Ridges of Eastern Monongalia and Northwestern Preston-Preston-
Eastern Preston-Western Tucker-Eastern Tucker-
220 PM EDT Wed Apr 17 2024

This Hazardous Weather Outlook is for western Pennsylvania and
northern West Virginia.

.DAY ONE...This afternoon and tonight.

There is a marginal risk of severe thunderstorms mainly between 8 and
10 pm this evening with potential for large hail and damaging winds.

Heavy rain associated with thunderstorms could also pose a limited
flash flood risk given saturated grounds across the region.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

A frost or freeze is expected Saturday night and especially Sunday
night.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

OHZ039>041-048>050-057>059-068-069-PAZ007-008-013>015-020>022-029-
031-073-075-WVZ001>004-012-021-509-181830-
Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH-
Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango-Lawrence-
Butler-Clarion-Beaver-Allegheny-Armstrong-Washington-Greene-
Westmoreland-Fayette-Hancock-Brooke-Ohio-Marshall-Wetzel-Marion-
Monongalia-
220 PM EDT Wed Apr 17 2024

This Hazardous Weather Outlook is for east central Ohio, western
Pennsylvania, and northern West Virginia.

.DAY ONE...This afternoon and tonight.

There is a slight risk of severe thunderstorms mainly between 5 and
8 pm this evening with potential for large hail up to golf ball sized
and damaging winds. Isolated tornadoes are possible especially in the
Ohio Counties.

Heavy rain associated with thunderstorms could also pose a limited
flash flood risk given saturated grounds across the region.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Frost and potentially a freeze is expected Saturday night and
especially Sunday night.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

Craven

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