####018008352#### ACUS01 KWNS 061604 SWODY1 SPC AC 061602 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1102 AM CDT Mon May 06 2024 Valid 061630Z - 071200Z ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS FROM CENTRAL AND NORTHERN OKLAHOMA INTO SOUTH-CENTRAL KANSAS... ...SUMMARY... A regional outbreak of severe weather with multiple intense (EF3+), long-tracked tornadoes, as well as very large hail and severe thunderstorm gusts, is expected over parts of the south-central Plains from this afternoon through evening. ...NE/KS/OK to north TX... Water-vapor imagery late this morning shows a potent mid- to upper-level trough/low over the central Rockies with a speed max moving through the base of the trough and into the southern and central High Plains. This negatively tilted mid level trough will continue northeast to near the Black Hills by this evening while its southern portion overspreads the KS/OK corridor. The 12z Amarillo, TX raob showed the leading edge of stronger 700-600 mb southwesterly flow nosing eastward into the High Plains. A cyclone near the NE Panhandle this morning will deepen as it moves north-northeast to the SD/ND border early Tuesday morning. An associated Pacific front will push east into the High Plains and overtake the northern portion of the dryline across parts of the central High Plains this afternoon into this evening. Farther south, a dryline will mix east into western OK by late this afternoon with a broad moist/unstable warm sector across the southern Great Plains and becoming increasingly pinched in spatial width farther north into the north-central Great Plains. An attendant warm front will advance northward from OK into the lower MO Valley by early evening and later into the mid MS Valley. Visible satellite imagery shows considerable low stratus and stratocumulus from north TX into the central Great Plains. The 12z Fort Worth, TX raob sampled the richer low-level moisture (15 g/kg lowest 100mb mean mixing ratio) compared to areas farther north. Surface analysis late this morning shows rapid northward transport of moisture into OK with 65-70 deg F dewpoints advecting northward through OK to the KS border. This plume of richer moisture will continue northward today beneath an EML and lead to moderate destabilization over NE with a very to extremely unstable airmass forecast to develop farther south over the southern half of KS into OK and adjacent north TX. Initial thunderstorm development is likely as the upper forcing impinges on the northwestern periphery of the moist/unstable sector across the central High Plains (western KS/NE) and northward into SD with time. Steep 700-500 mb lapse rates and strengthening flow becoming more meridional with time will favor organized storms, including supercells and bands of storms with an associated isolated to scattered risk for hail/wind and perhaps a few tornadoes. Farther south, the erosion of the cap is expected initially over the KS portion of the dryline and perhaps into northwest OK by the mid afternoon. Strengthening flow through the column combined with strong to extreme buoyancy (2500-4500 J/kg MLCAPE) --from I-70 in central KS to I-40 in central OK-- will strongly favor supercell development. Strong upper-level diffluence across the central Great Plains and intensifying southwesterly to westerly 250-mb flow, which will result in very long hodographs, will strongly favor discrete storm modes, at least initially. Large to giant hail (3-4 inches in diameter) is possible with the more robust supercells. The LLJ is forecast to be strongest over KS northward into the north-central Plains through 21z. During the 21-00z timeframe, the flow associated with the LLJ will strengthen over OK acting to enlarge hodographs. Climatologically large combinations of deep-layer shear, buoyancy, and SRH will result in extreme values of composite indices (STP 6-12) during the 22z-06z timeframe across the Moderate to High Risks. Several discrete supercells are expected to traverse across a large portion of the Moderate and High-Risk equivalent tornado probabilities. Tornadoes, some of which can be intense (EF3+), are forecast late this afternoon and well into the evening. Some model guidance shows regenerative supercell development across central OK this evening. Have extended the High Risk slightly farther south to account for this possibility. ...Lower MO Valley/Ozarks/mid MS Valley late... As greater storm coverage and merging occurs this evening across KS into northern OK, large-scale ascent will further promote upscale growth into a severe squall line across eastern KS and moving into the lower MO Valley and western part of the Ozarks. Have upgraded severe-wind probabilities and this resulted in a slight spatial extension of the Moderate Risk to the east across southeast KS/northeast OK. A severe risk will probably continue east to the MS River overnight with an attendant wind risk and perhaps an isolated risk for a tornado. ...Northern Plains... No appreciable change from previous forecast thinking for severe potential across the northern Plains. A prefrontal corridor of favorable moisture and diurnal destabilization will become quite narrow with north and northwestward extent. Nonetheless, it should support scattered thunderstorms in northward-shifting plume, curving from the western Dakotas (and perhaps parts of extreme northeastern WY and southeastern MT) southeastward to central NE, and connecting to the northern part of the central Plains severe threat. With strong large-scale lift, cooling aloft, rapidly weakening MLCINH, and robust low-level mass response/shear expected ahead of the ejecting shortwave trough, confidence is growing that an arc of strong-severe thunderstorms will develop, offering large hail, severe gusts and at least marginal tornado potential. Even with 50s to low 60s F surface dewpoints and limited time for substantial diabatic heating, the net steepening of low/middle level lapse rates should support peak MLCAPE near or slightly above 1000 J/kg. Deep shear may not be particularly intense in a regime of strongly difluent flow aloft, but still should be adequate for supercell potential given large lowest-km hodographs possible, and effective SRH in the 150-300 J/kg range. Severe potential should diminish after about 00Z. ...West-central/southwest TX... Model guidance continues to indicate isolated thunderstorms are possible in mid/late afternoon along/ ahead of the dryline over northwest to southwest TX. Although large-scale/mid-upper forcing will be negligible (displaced to the north), any pockets of relatively persistent/maximized low-level lift may aid in local erosion of the cap and convective initiation. Mid/upper 60s to low 70s F surface dewpoints and steep low/middle-level lapse rates will contribute to 3000-4000 J/kg MLCAPE amidst enough deep shear for supercells. A conditional significant-hail and marginal tornado threat exists with sustained supercell(s) -- if any can form. Coverage concerns preclude more than marginal categorical outlook at this time. ...Mid South/TN Valley into the southern Appalachians... A mid-level shortwave trough over TN this morning will continue to move east into the southern Appalachians today. An enhanced belt of westerly mid-level flow accompanying this impulse will overspread this general region. In wake of decaying morning convection over the southern Appalachians, ample heating of a moist boundary layer will result in moderate destabilization by early-mid afternoon. Storm redevelopment is forecast this afternoon along and north of a trailing/diffuse convective boundary over the TN Valley. Scattered thunderstorms will probably develop by early to mid afternoon. Effective shear magnitudes 25-30 kt will support some organization in the form of clusters and perhaps transient supercells. Marginal Risk equivalent severe probabilities have been added to highlight this isolated severe threat. ..Smith/Moore.. 05/06/2024 $$