SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Sun Apr 14 2024
Valid 141200Z - 151200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING ACROSS PARTS OF EAST CENTRAL OHIO...WESTERN
AND NORTHERN PENNSYLVANIA...
...SUMMARY...
Severe thunderstorms are likely to develop late this afternoon in a
corridor across the upper Ohio Valley and Allegheny Plateau, into
the Poconos and Catskills vicinity. Damaging wind gusts, some hail
and perhaps a couple of tornadoes are possible as this activity
spreads slowly southward into this evening.
...Synopsis...
It appears that large-scale mid-level troughing will maintain
considerable amplitude offshore of the Atlantic Seaboard into at
least this afternoon. Thereafter, models suggest that flow will
trend a bit more zonal east of the lower Great Lakes into the
Canadian Maritimes, to the south of a deepening mid-level low
becoming centered southeast of Hudson Bay. A low amplitude short
wave perturbation embedded within this regime will turn east of the
upper Great Lakes, and generally pass north of the lower Great Lakes
through Canadian Maritimes by 12Z Monday. A modest surface frontal
low accompanying this feature probably will not deepen much further
while migrating east-southeast of the lower Great Lakes through
southern New England. However, a notable trailing cold front may
advance southward through much of the upper Ohio Valley and northern
Mid Atlantic coast vicinity by the end of the period.
Upstream, models indicate that a number of amplified perturbations
will remain at least slowly progressive within the westerlies across
the mid- and subtropical latitudes of the Pacific into western North
America. This includes one significant short wave trough and
embedded cyclonic circulation which are forecast to migrate inland
of the California coast through much of the Southwest, as another
perturbation progresses inland across the British Columbia coast.
Downstream of these features, surface troughing will deepen to the
lee of the Rockies by late this afternoon. Modest low-level
moistening is already underway on southerly return flow off the Gulf
of Mexico. While this will likely continue to gradually improve,
relatively warm and capping elevated mixed-layer air is forecast to
continue overspreading much of the Great Plains, Mississippi and
Ohio Valleys.
...Upper Ohio Valley into lower Hudson Valley...
In the wake of the initially amplified offshore mid-level troughing,
low-level moisture will initially be quite limited across and east
of the Mississippi Valley. However, a plume of rather steep lapse
rates, associated with warm elevated mixed-layer air, is currently
in the process of overspreading the Great Lakes region. As strong
lower/mid-tropospheric flow (including speeds of 40-70+ kt in the
850-700 mb layer) takes on an increasing westerly and southwesterly
component to the east-southeast of the lower Great Lakes through the
northern Mid Atlantic, this air will tend to advect eastward through
the day.
Beneath this regime, moistening within a narrow pre-cold frontal
corridor is forecast to contribute to conditionally and convectively
unstable thermodynamic profiles across the upper Ohio Valley into at
least western portions of the Allegheny Plateau. Mixed-layer CAPE
on the order of 500 to 1000 J/kg appears probable across north
central Ohio into western Pennsylvania by late afternoon, with more
uncertainty across the higher terrain of north central Pennsylvania
into the Poconos and Catskills.
Although stronger mid-level height falls are forecast to pass to the
north of this corridor, mid-level cooling, coupled with low-level
forcing for ascent, probably will support increasing thunderstorm
development ahead of the southward advancing front by around 21Z.
Activity may tend to quickly grow upscale into an organizing narrow
squall line, though with perhaps more discrete development
persisting near pre-frontal surface troughing trailing southwestward
across western Pennsylvania into Ohio through this evening.
Damaging wind gusts appear the primary potential hazard with the
evolving line, but severe hail and perhaps a couple of tornadoes
will be possible in the more discrete initial storm development (and
somewhat better boundary-layer moisture) across the upper Ohio
Valley, aided by large and clockwise-curved low-level hodographs.
..Kerr/Lyons.. 04/14/2024
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