SPC 0600Z Day 2 Outlook
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
