Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Apr 09 2023 12:54:11 ACUS01 KWNS 091254 SWODY1 SPC AC 091252 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Sun Apr 09 2023 Valid 091300Z - 101200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE SOUTHERN HIGH PLAINS... ....SUMMARY... Isolated severe thunderstorm gusts and large hail are possible across portions of the southern High Plains this afternoon and evening. ....Synopsis... In mid/upper levels, a progressive, somewhat low-amplitude synoptic pattern will gain amplitude through the period, as ridging strengthens over the Great Basin and northern Rockies. East of the ridge, a trough was evident in moisture-channel imagery from MB across the Dakotas, western NE, eastern CO, and central/southern NM. The southern branch of this trough will split eastward through the period, as the poleward portion ejects out of the northern Plains ahead of a separate northern-stream perturbation. By 00Z, the southern segment of the 500-mb trough should be located from central/western OK southwestward to the Permian Basin. This trough should weaken over southern OK and north-central/northeast TX overnight as the trailing northern-stream perturbation strengthens and digs southeastward to the upper Mississippi Valley and central Plains. The 11Z surface analysis showed am elongated area of low pressure along a frontal zone, covering Atlantic waters offshore from SC, GA and northern FL. A cold front extended from that area across central FL to the north-central/west-central Gulf. The continental anticyclone north of that front will move southward from southern ON across the north-central Appalachians through the period, with ridging maintained to its southwest across central/south TX. Lee troughing -- with some influence from mass response to the mid/upper trough -- will move slowly eastward over western KS, the Panhandles and east-central/southeastern NM today. ....Southern High Plains... Isolated to widely scattered, elevated, non-severe thunderstorms already have been occurring this morning from southern NE to the TX Panhandle, in a field of marginal low-level moisture and favorable large-scale lift/DCVA preceding the mid/upper trough. In more- southern parts of the same UVV plume, the addition of boundary-layer theta-e advection and diurnal heating will remove MLCINH and support surface-based development from midday through afternoon, above the Caprock and along/east of the lee trough. Widely scattered, perhaps scattered thunderstorms are possible, continuing into the evening while moving/spreading southeastward. Isolated severe gusts are expected, and marginally severe hail cannot be ruled out. Specific higher concentration(s) of convective coverage within this area are quite possible, but remain uncertain in timing/location, dependent on mesoscale boundary processes yet to evolve. Still, a corridor of greater wind probabilities (in particular) may develop somewhere over about the southern 2/3 of the existing outlook area, if any upscale aggregation occurs to augment the outflow organization. An anticyclonically curved field of weak low-level return flow has set up and will remain around and northwest of the aforementioned surface ridge, permitting meager yet sufficient moisture to support surface-based convection. Dewpoints in the 40s to low 50s F will be maintained amidst counterbalancing processes of deepening vertical boundary-layer mixing and moisture advection, with some temporary late-afternoon moisture deficits as mixing maximizes. Still, forecast soundings show steep low/middle-level lapse rates with forecast max temperatures very near convective temperature, and the potential for differential-heating (and later outflow) boundaries east of the lee trough. Though flow will veer strongly with height, weak winds (10 kt or less) below about 600 mb will limit low-level and deep shear, with effective-shear magnitudes around 25-35 kt being common. Stronger 500-250-mb layer winds will permit robust venting/anvil-level flow, for some help with storm organization. Activity should weaken this evening after moving southeastward across the South Plains/Llano Estacado and Permian Basin regions and atop a nocturnally stabilizing boundary layer farther southeast. The main adjustment for this outlook cycle was to create some extra room for that to occur on the southeast end. ...Edwards/Smith.. 04/09/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .