ACUS02 KWNS 130545
SWODY2
SPC AC 130543

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1243 AM CDT Sun Apr 13 2025

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN THE UPPER OH
VALLEY AND CENTRAL APPALACHIANS...

...SUMMARY...
A couple tornadoes along with scattered damaging winds and large
hail are possible from mid-afternoon to mid-evening across parts of
the Upper Ohio Valley and central Appalachians.

...Synopsis...
A shortwave trough will further amplify over the Upper Great Lakes
towards the ON/QC border, supporting gradual deepening of a surface
cyclone from 995 to 990 mb. In its wake, a separate shortwave
impulse and intense mid-level jetlet will dive southeast across the
northern Great Plains towards the Lower OH Valley. A surface cold
front will arc south across the Lower Great Lakes and then
southwestward through the Mid-South by late afternoon Monday.

...OH Valley to the Mid-Atlantic States...
While guidance has largely been consistent with synoptic-scale
pattern over the past several days, large spread exists in the
degree of boundary-layer heating on Monday afternoon ahead of the
surface cold front. For example, the 00Z NSSL-ARW and HRW-FV3 are
10-15 F colder with warm-moist sector surface temps compared to the
00Z HRRR and HRW-ARW. These latter models simulate multiple
long-track supercells. This heating discrepancy, along with low
confidence in the aggressive low-level moistening indicated by most
guidance beneath an expansive EML, mitigates a categorical upgrade
this cycle. But all three hazards have been highlighted with level
2-SLGT risk probabilities.

Overall expectation is for a ribbon of mid to upper 50s surface dew
points to advect as far northeast as the Upper OH Valley. If robust boundary-layer heating indeed occurs, this would support MLCAPE near
1000 J/kg. The initial presence of the EML may delay storm
development along the front until mid afternoon. But guidance
consensus suggests at least scattered thunderstorms should form in
the Central to Upper OH Valley vicinity as mid-level height falls
increase atop the modestly convergent surface front. The approach of
an intense mid-level jet will support fast-moving convection, along
with effective bulk shear above 60 kts. Despite veered surface
winds, low-level hodograph curvature should be moderately enlarged.

A few supercells seem plausible in this setup, a couple of which may
become long-tracked. These appear most probable across the southeast
OH to northern WV vicinity, where tornado potential should be
maximized during the early evening. Otherwise, a mix of large hail
and damaging wind swaths are expected. East of the higher terrain in MD/northern VA, remnant steep low-level lapse rates may support
isolated damaging gusts and marginal hail, before convection
wanes/becomes increasingly elevated Monday night.

..Grams.. 04/13/2025

$$
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