SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0650 AM CST Sun Jan 24 2021 Valid 241300Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF NORTH-CENTRAL/NORTHEAST TEXAS AND SOUTH-CENTRAL/SOUTHEASTERN OKLAHOMA... ...SUMMARY... Large hail and isolated wind damage will be possible this evening and tonight across parts of the southern Plains. ...Synopsis... In mid/upper levels, a pronounced split-flow pattern exists over the western CONUS, with the splitting feature being a cyclone over southern CA and trough extending southwestward from there. Upstream troughing -- extending south-southeastward from a cyclone over the gulf of Alaska -- will dig southeastward toward and across the CONUS Pacific Coast today and tonight. As that occurs, the leading cyclone will pivot eastward and devolve to a strong open shortwave trough over AZ and Sonora by 00Z. The trough will deamplify further -- but remain well-defined -- as it ejects northeastward across NM and the south-central High Plains by 12Z tomorrow. At the surface, 11Z analysis showed a cold front from the upper Mississippi Valley across southeastern KS, through a weak low near PNC, then southwestward over southern NM. A dryline was drawn from southwestern OK/northwest TX through a weak low near FST, then southeastward over northern/central Coahuila. A separate, marine warm-frontal zone was evident across the northern Gulf shelf waters westward over deep south TX. The TX part of this boundary will diffuse as it shifts northward today, with another warm frontal zone developing over north-central/northeast TX this evening, on the southern fringe of a large area of precip and embedded convection. The cold front will overtake the dryline from north-south through the period, as 60s F surface dew points spread northward in the warm sector. The southwest TX surface low should ripple northeastward along the cold front from 00Z onward, approaching the SPS area by 06Z and moving between TUL-FSM around 12Z. By then, the cold front should extend from the low across southeastern OK and northeast through south-central TX. ...Southern Plains to AR... Scattered to locally numerous thunderstorms are possible within two main episodes: 1. A broad area of convection forming along and mostly north of the warm front and surface low this afternoon and evening, spreading/ expanding northeastward across much of north-central/northeast TX, the Red River region, central/eastern OK, and into portions of AR and the Ozarks tonight. 2. Thunderstorms developing initially over parts of northwest TX this evening (probably after 00Z) and moving northeastward, while expanding/backbuilding. The net effect should be a growing area of increasingly organized thunderstorms shifting eastward over north TX and southern OK overnight, ultimately merging with the northwestern part of the first regime over eastern OK or AR. Large hail will be possible in both regimes, with elevated supercells possible in the first. The second may access enough MUCAPE (up to 1000-1500 J/kg) and greater effective-shear magnitudes (55-70 kt) to support both supercell and bowing structures. While a strong and fairly deep stable layer will persist across most of OK, sufficient buoyancy and downdraft intensity may develop above that, in an organized convective complex, to penetrate isolated severe gusts to the surface. An antecedent EML is in place over much of central/south TX, well-sampled by 12Z RAOBs from CRP/BRO/DRT. The EML will spread northward and northeastward, weakening north of the surface warm front, and will remain viable long enough to substantially limit or even prevent development in the free warm sector (south of the warm front). Direct upper-level support from the ejecting trough will be limited as well, at best glancing the northwest fringes of the warm sector. The strongest large-scale ascent (and great majority of substantial convection) should be in a plume of buoyancy elevated over relatively stable surface conditions farther poleward. Nonetheless, strong low-level lift will be associated with the segment of the cold front near and just south of the progressive surface low, as the boundary impinges on the northern part of the warm sector late tonight. This should overcome the basal EML inversion and encourage convective initiation within about 50 kt effective-shear magnitudes, and at least some access to relatively high theta-e in the warm sector, across parts of north-central/ central TX. The DFW Metroplex already was included in the area of largest outlook probabilities for its portion of this regime. However, more room is being given farther south for potential backbuilding of thunderstorms, and at least marginal severe potential therewith. ..Edwards/Gleason.. 01/24/2021
There’s more click here.