Day 1 Convective Outlook
American Severe Weather Forecast Center
12:30 AM CDT, Sunday, May 4, 2003
Valid: 04/12:00 UTC - 05/12:00 UTC
There is a High Risk of severe thunderstorms today and tonight across Far Southeastern Nebraska, Eastern Kansas, Western and Central Missouri, Eastern Oklahoma, and Western and North Central Arkansas.
Surrounding the High Risk, there is a Moderate Risk of severe thunderstorms today and tonight from Southeastern Nebraska to Western Illinois, southward to Northeastern Texas and Northwestern Mississippi.
There is a Slight Risk of severe thunderstorms today and tonight from the Central and Southern Plains into the Ohio and Tennessee Valleys.
***Major Severe Weather Outbreak expected from portions of the Lower MO and Mid MS Valleys into the Arklatex***
***Major metropolitan areas in the High Risk area include: Topeka, KS; Kansas City, MO; Springfield, MO; Tulsa, OK; McAlester, Ft. Smith, AR; and Little Rock, AR***
National Synopsis
Progressive mid-upper level pattern continues today with main large-scale feature being western CONUS trough. Associated cyclone, now evident on moisture channel imagery over eastern portions of Wyoming and Montana, is expected to drift eastward into the western Dakotas, while strong speed max and shortwave trough now evident over western Colorado move eastward across Kansas and Nebraska. Upstream, strong shortwave trough now moving ashore across Washington and Oregon should shift east-southeastward through the afternoon.
At the surface, large outflow pool from Nebraska MCS has effectively bifurcated surface cyclone, but low should consolidate again over southern Nebraska and northern Kansas during the day and move eastward, then northeastward, into western Iowa by 00z. Dryline, now analyzed from west central Kansas, southward across eastern portions of the Oklahoma/Texas panhandles then southwestward to the Permian Basin, should advect and mix eastward throughout the remainder of the morning/afternoon, reaching eastern portions of Kansas and Oklahoma by late afternoon when initiation of most intense convection is forecast. Warm front, now analyzed from central Kansas/Nebraska border region southeastward across south central Arkansas to the western Florida panhandle, should lift rapidly northward across northeastern Kansas, remainder of Arkansas, and much of Missouri by this afternoon, and into western Illinois by tonight.
Lower Missouri/Mid MS Valley Region to Arklatex
Significant severe thunderstorm event likely, with outbreak of tornadoes, large hail, and damaging wind anticipated today from eastern KS/OK, far southeastern NE, eastward across much of Missouri and Arkansas, and possibly southward into northeastern Texas and eastward toward the Mississippi River area of IL/KY/TN/MS with time. Potential exists for long-track and violent tornadoes with a few supercells in High Risk area, and several cyclic/multiple tornado producing supercell thunderstorms should occur. Numerous events of damaging wind gusts/large hail are possible from these storms, as well as later bow echoes and LEWPs that may evolve from earlier supercells or along late evening squall line ahead of cold front/dryline structure.
Sporadic and mainly marginally severe hail is possible this morning from band of thunderstorms, in strong WAA isentropic ascent regime now maximized from southeastern Missouri to southwestern South Dakota and forecast to weaken as it moves eastward/northeastward. Subsequently, main severe threat will be from this afternoon through at least 6Z over east central Plains, Lower Missouri Valley, and into Arklatex area. Cap should break along dryline throughout afternoon in discrete cells, allowing for rapid development of thunderstorms in a sweeping arc over western portions of SLGT/MDT categorical risk areas. Unusually intense updraft accelerations and rapid evolution to supercells is anticipated given strength of both instability and environmental kinematic fields.
By early afternoon, air mass over that portion of this region north of the Missouri River will have had sufficient time to heat/destabilize after morning convection, through both warm air advection and surface insolation. Further south across portions of eastern and southeastern Kansas, eastern Oklahoma, and western Missouri/Arkansas, low level air mass is uncontaminated by prior convective stabilization and should become very unstable by this afternoon behind warm FROPA. Modified RAOBs and RUC soundings suggest MLCAPE ranging from almost 4000 j/kg in the Arklatex region to 2500 j/kg in the Nebraska/Missouri border region. Strong vertical shear forecast throughout region, e.g., 60-80 kt of 0-6 km deep layer vector shear and 90-120 kt BRN shear. Large hodographs forecast with 0-1 km SRH of 200-400 m2/s2 and 0-3 km SRH of 300-600 m2/s2 near and south of warm front across MDT/HIGH risk areas. Activity may backbuild further southward into portions of northeastern Texas during the late afternoon and early evening, with outlook being more conditional in this area because of capping. Still, threat of very large hail, damaging winds, and an isolated strong or even violent tornado will exist with any sustained supercell thunderstorm along and ahead of the dryline in this region.
Southeastern CONUS
Scattered to widely scattered thunderstorms should develop in clusters today in vicinity of northward moving warm front over Lower MS/TN Valley regions. Large hail and damaging winds each should occur with most persistent/intense cells, and tornadoes will also be possible (even an isolated strong tornado possible in western portions of this area closer to stronger low-level shear. Throughout entire area, vertical shear should support at least isolated supercell structures with 45-60 kt 0-6 km shear vectors and 0-3 km SRH of 150-250 m2/s2, with supercell structures most likely in conjunction with meso-beta to storm scale boundary interactions.
GOSSAGE