
SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0715 AM CDT Sat Mar 15 2025 Valid 151300Z - 161200Z ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ALONG A CORRIDOR FROM CENTRAL MISSISSIPPI INTO NORTHERN/CENTRAL ALABAMA... ...SUMMARY... A tornado outbreak is expected across the central Gulf Coast States and Deep South into the Tennessee Valley. Numerous significant tornadoes, some of which should be long-track and potentially violent, are expected this afternoon and evening. The most dangerous tornado threat should begin across eastern Louisiana and Mississippi during the late morning to afternoon, spread across Alabama late today into the evening, and reach western parts of the Florida Panhandle and Georgia tonight. ...Synopsis... Water-vapor imagery this morning shows an intense mid-level low/trough moving northeast into the Upper Midwest with an upstream trough over the southern Great Plains. A 100+ kt mid-level speed max will move through the base of the trough and into the lower MS and TN Valleys through tonight. A dryline draped from east TX into the lower OH Valley will serve as a western/northwestern delimiter of a moist/unstable warm sector across portions of the South today. An occluded low will migrate northward from the Upper Midwest into Ontario as a secondary low evolves and quickly moves northeast from the Arklatex into the southern Great Lakes through late evening. A seasonably high moisture-rich and unstable airmass will expand across parts of the Deep South and contribute to a dangerous tornado outbreak featuring long-track intense to potentially violent tornadoes (EF3-EF4+). ...Central Gulf States/Tennessee Valley Region... Early morning surface analysis indicates a expanding warm sector across the central Gulf Coast states with upper 60s to 70 deg F dewpoints becoming established over much of LA through the southern 2/3 of MS and into southwest AL. Developing thunderstorms on the northern rim of the richer moisture extend from western/northern MS northeast through northern MS this morning. The 12 UTC raobs from Lake Charles and Slidell, LA and Jackson, MS showed 700-500 mb lapse rates (7-8 deg C) and lowest 100-mb mean mixing ratios 13-15 g/kg---indicative of a potent warm sector. The northeast movement of a 125-kt cyclonically curved 250-mb jet into the lower MS Valley through midday will act to further strengthen wind profiles as a 60-kt southerly LLJ slowly shifts east across the central Gulf Coast during the period. The stronger storms this morning developing within the warm conveyor from LA into northern MS/TN will pose a risk for all hazards, including the possibility for strong tornadoes. To the south and east of this morning thunderstorm activity, strong heating with temperatures warming into the upper 70s will lead to favorable warm sector convective initiation in a few confluence bands beginning in the 17-19z period over MS and adjacent portions of LA. This preferred storm initiation process in conjunction with moderate buoyancy (1500-2500 J/kg MLCAPE) and very large and elongated hodographs, will favor the rapid development of intense supercells. Forecast hodographs show 400-500 0-1km SRH within the Moderate-High Risk area across LA/MS/AL. Numerous tornadoes are forecast with an attendant large-hail risk during afternoon/evening as this activity gradually shifts east. Upper-end parameter space of composite indices (i.e., Significant Tornado Parameter values ranging from 5-10) will support long-track intense to potentially violent tornadoes this afternoon and into evening. Eventually storm consolidation --especially with north extent across northern MS into northern AL/southern Middle TN) will serve as a north delimiter to the forecast stronger tornadoes. Upscale growth with embedded supercells and bowing structures appear increasingly likely this evening over the northern portion of the warm sector. Have made a small northeastward expansion of the Moderate Risk into portions of Middle and southeast TN for a significant wind risk. The risk for strong tornadoes will likely continue tonight as sufficient destabilization occurs immediately ahead of established supercells as one or more clusters of storms track east late this evening into the overnight. ...Southern Appalachians tonight... As the upper trough pivots east into the region late tonight, strong low-level warm/moist-air advection will contribute to a destabilizing airmass. Despite weaker buoyancy with eastward extent over northeast GA into the western Carolinas, very intense low to mid-level flow will aid in maintaining a risk for a few supercells and line segments to survive into a more limited thermodynamic environment and potentially yield a risk for damaging gusts and a tornado threat through early Sunday morning. ...Upper OH Valley/southern Great Lakes... A band of ongoing thunderstorms this morning will continue to move east into weaker instability as drier low-level trajectories from the central/southern Appalachians act to pinch off the northern portion of the warm sector. A hail/wind risk may linger through the morning before weak mid-level shortwave ridging ensues between the departing Upper Great Lakes negatively tilted trough and the amplifying trough over the lower MS Valley. Models maintain a belt of strong 850-mb flow through midday before an intensification (70 kt) of the northern periphery of a LLJ --extending from the central Gulf Coast into the Mid South-- overspreads the region. Primary uncertainty is the magnitude of destabilization and its resultant effects on severe potential. The latest model guidance generally only depicts weak buoyancy (at or below 250-500 MUCAPE) but some airmass recovery in wake of early day storms may occur over Indiana into southern Lower MI. If this scenario occurs, higher severe probabilities may be warranted in subsequent outlooks. ..Smith/Squitieri.. 03/15/2025