SPC Mar 14, 2025 2000 UTC Day 1 Convective Outlook
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Fri Mar 14 2025 Valid 142000Z - 151200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THE LOWER/MID MISSISSIPPI VALLEY INTO THE LOWER OHIO VALLEY... ...SUMMARY... A regional outbreak of severe thunderstorms is likely this afternoon through tonight across parts of the Lower/Mid Mississippi Valley and portions of the Lower Ohio Valley and Mid-South. Numerous tornadoes, several of which could be strong to intense, widespread severe gusts ranging from 60 to 100 mph, and scattered large hail up to baseball size all appear likely. ...20z Update... Widespread significant severe weather remains likely this afternoon through tonight over much of the MS Valley and parts of the Southeast. An intense, negative-tilt upper trough and 120 kt mid-level jet will rapidly eject northeastward over the central Plains through the day. An associated deep surface low over western KS will continue to intensify as it lifts east/northeast tonight. Initial updrafts along a bent back dryline from northeastern KS, far eastern OK, and western MO will spread northeastward into a warm and rapidly moistening air mass over the MO Valley. While initial dewpoints are quite limited, (40s F) very steep low and mid-level lapse rates and a rapid surge of low-level moisture is likely later this afternoon/evening. A broken line of initially high-based storms will quickly spread eastward within very strong tropospheric flow. Efficient downward momentum transport will support widespread damaging gusts, potentially as high as 80-100 mph. Ahead of these storms, low-level dewpoints should rapidly surge into the 50s and low 60s F. Lowering cloud bases, and very strong mid and low-level shear will allow for a few semi-discrete/embedded supercells to form/mature over eastern MO, southern IA, western IL and northern AR. A tornado threat (some strong to intense), is likely to develop with these storms through the late afternoon and evening hours, along with a continued risk for damaging winds and large hail. Farther south over parts of the ArkLaMiss and southwest TN, scattered storms are expected to evolve within a strong low-level warm air advection regime and ahead of the Pacific front. Dewpoints in the mid 60s F will quickly lift northward over northern LA, southern AR, into central MS. While forcing for ascent is likely to be more nebulous, strong low-level flow within a 45-60 kt low-level jet will support significant hodograph enlargement and sufficient moisture/buoyancy for strong supercells. Recent CAM guidance has come into better agreement on the positioning/timing of a cluster of likely supercells evolving across northern LA and west-central MS later this evening. Given the intensifying wind fields, and STP environment of 3-4, strong tornadoes appear more likely through the evening and into the overnight hours. Given increased confidence in the development of intense supercells, have adjusted the Moderate area farther south and west over MS/LA/AR. ..Lyons.. 03/14/2025 .PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Mar 14 2025/ ...Synopsis... Water-vapor imagery late this morning indicates a powerful and negatively tilted mid/upper-level shortwave trough over the southern High Plains. An intense mid-level jet (with winds of 100-115+ kt at 500 mb) will continue to round the base of the trough, and quickly eject northeastward across OK and eastern KS this afternoon. This mid-level jet will move over parts of the mid MS Valley and Midwest this evening and tonight in tandem with the northeastward-advancing shortwave trough. Strong ascent aloft associated with both of these features will overspread portions of the central CONUS as a deep surface cyclone develops northeastward from the central High Plains into the Upper Midwest this afternoon through tonight. In the low levels, a dryline will surge eastward across the southern/central Plains through the day, eventually arcing from the low southeastward into the Ozarks. A large area of significant severe potential remains evident across parts of the lower/mid MS Valley into the Midwest and Mid-South. ...Mid Mississippi Valley into the Midwest and Mid-South... Ample diurnal heating is expected through this afternoon ahead of the cyclone, with elevated convection already occurring across parts of eastern OK into southeast KS and southwest MO. More robust, surface-based thunderstorms will likely develop by early/mid afternoon (18-21z) along/east of the dryline from parts of eastern NE southward into eastern KS/western MO, as a southerly low-level jet attempts to bring shallow boundary-layer moisture northward into the mid MS Valley and vicinity. The northern portion of this convection will be oriented more orthogonal to the ejecting mid-level jet, and current expectations are for quick upscale growth into a fast northeastward-moving band, posing a risk for widespread severe/damaging winds as this activity moves into IA and towards the MO/IA/IL border region. Given the strength of the low/mid-level flow and presence of steep lapse rates aloft, along with a well-mixed boundary layer, intense thunderstorm straight-line gusts peaking locally in the 80-100 mph range are possible with the stronger cores/inflections in the band as it matures and moves across parts of the mid MS Valley, and eventually into the southwestern Great Lakes this evening through tonight. Additional, potentially more discrete, severe thunderstorms will develop this afternoon farther southeast along the wind shift into central/eastern MO, generally on the northern periphery of somewhat better low-level moisture from southeast MO southward into the Mid-South. Stronger high-level flow and ample deep-layer shear over these will likely promote at least semi-discrete supercells. Latest model guidance, including various convection-allowing HREF members, suggest scattered supercells developing late this afternoon and evening as far south as the MS/AR/TN border region. Have nudged severe probabilities and the corresponding SLGT/ENH/MDT westward a little in western/central MO to account for a slightly earlier initiation. Various NAM/RAP forecast soundings strongly favor intense supercells capable of large to very large hail (up to 2-3 inches in diameter), and potentially multiple strong to intense tornadoes this evening as effective SRH rapidly increases in tandem with a southerly low-level jet strengthening to 50-65+ kt. This substantial severe threat is expected to continue eastward overnight into parts of the lower OH Valley/Midwest, before convection eventually outpaces the low-level moisture return and weakens. ...Lower Mississippi Valley... Large-scale forcing for ascent appears a bit more nebulous/weak farther south into the lower MS Valley. Still, the 12Z suite of guidance shows some potential for surface-based thunderstorms developing by late this afternoon across the ArkLaMiss region. While the stronger low/mid-level flow and forcing are expected to remain to the north of this region, greater low-level moisture and related instability will be present. This favorable thermodynamic and kinematic environment will support supercells, with associated threat for large to very large hail, damaging winds, and tornadoes. Some of tornadoes could be strong this evening with any sustained supercells, especially across central MS and vicinity. Have expanded the ENH to account for this potential, and consideration was given to expanding the MDT southward into central MS as well. But, there is still some uncertainty with overall thunderstorm coverage.
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