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ACUS01 KWNS 140553

SWODY1

SPC AC 140552



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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