Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 24 2023 12:38:48 ACUS01 KWNS 241238 SWODY1 SPC AC 241237 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0737 AM CDT Sun Sep 24 2023 Valid 241300Z - 251200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF SOUTHERN OKLAHOMA AND THE ARKLATEX VICINITY INTO CENTRAL TEXAS... ....SUMMARY... Severe hail and damaging gusts are possible today into this evening from parts of southern Oklahoma and the Arklatex vicinity into central Texas. ....Synopsis... Substantial, mean troughing in mid/upper levels will amplify this period over the northeastern Pacific, as an embedded synoptic cyclone deepens west of Vancouver Island. This will contribute to amplifying ridging over the Rockies and northern High Plains, with a blocky, split-flow pattern downstream. The split will be related to a long-lived cyclone -- now centered over northeastern SD and forecast to both occlude more deeply and cut off from the prevailing northern-stream southwesterlies. The associated 500-mb low will move little through 12Z tomorrow, perhaps drifting erratically into western MN. Meanwhile, a downstream trough -- containing the remnants of former Tropical Storm Ophelia -- will move northeastward off the Mid-Atlantic Coast and weaken, leaving behind a large area of broadly cyclonic flow -- weak in the midtroposphere, but with a 70-85-kt 250-mb jet developing over the Tennessee Valley to central/ southern Appalachians. Ridging will persist over northern MX. Given those surrounding processes, strongly difluent, westerly to northwesterly flow aloft will prevail across the southern Plains. An embedded shortwave trough -- evident in moisture-channel imagery over scentral/southern CO and northern/central NM -- will shift eastward to northern OK and the TX Panhandle/northwest TX region by 00Z, then weaken somewhat while turing southeastward toward AR and the Red River by the end of the period. At the surface, 11Z analysis showed a primary low over the eastern Dakotas between ABR-JMS, near the mid/upper cyclone center. The associated occluded/cold front arched from there over northwestern/ central IA, western MO, and northeastern OK, to a secondary/frontal- wave low over the Red Rover between SPS-ADM, then southwestward across the Permian Basin. Given the stacking and quasistationary character of the deep-layer/northern low today, the northern segment of the occluded/cold front over the mid/upper Mississippi Valley region should move little today, with mainly a northeastward to eastward drift. The southern low and front should settle slowly southeastward through the period. By 00Z this low should be near the Red River north or northeast of DFW, with the front eastward over southeastern OK and southwestward over north-central, west- central and southwest TX near SEP, SJT and the Big Bend region. By 12Z, the front should be over the Arklatex region and central TX, but with more strongly baroclinic outflow boundaries probable to its south. ....Central TX to Red River/Arklatex regions... Multiple episodes of strong-severe thunderstorms are possible across the outlook area through the period, beginning with a small cluster of convection now located over the Arklatex region. Its longevity past the SHV area is uncertain, given the increasingly hostile (larger MLCINH, smaller MLCAPE) environment it will continue to penetrate in the short term, over the next couple hours. However, if the convection can persist into the diurnal destabilization cycle, or redevelop along an associated pressure/theta-e perturbation in the low levels, then a conditional wind threat may extend or redevelop south-southwestward into east TX later this morning. The morning convection should leave behind an outflow/ differential-heating boundary across portions of east-central through north-central TX, perhaps further south depending on longevity of the initial complex and its cloud shield. This boundary, and more likely the front and a weak prefrontal trough/ convergence zone, may focus afternoon into overnight development. The environment of the unmodified warm sector between the front and outflow boundary should be characterized this afternoon by strong surface heating, with more intense/deeper mixing westward onto higher elevations. This, amid mid-60s to near 70 F surface dewpoints, should erode MLCINH enough for widely scattered to scattered multicellular to occasionally supercellular thunderstorms late this afternoon into evening in a roughly southwest-northeast configuration. Well-mixed subcloud layers with strong low-level lapse rates -- beneath 2500-3500 J/kg MLCAPE -- will support maintenance of strong-severe downdrafts and hail to the surface. Some of the hail may reach at least 2 inches in diameter. Low/ middle-level winds will veer with height, but should be weak in magnitude, rendering small boundary-layer hodographs but around 25-40-kt effective-shear magnitudes. Nocturnal development may include: 1. At least short-lived (2-4-hour) clustering of evening convection in central TX moving into the warm sector, offering damaging gusts and/or large hail, and/or 2. Initiation over portions of the surface-850-mb front located northeast of the prefrontal boundary and east to northeast of the surface low, where nocturnal warm advection/LLJ processes can moisten/destabilize the low levels along or even slightly north of the surface front in the southern OK/north TX region. Several progs depict this second process leading to an MCS with at least isolated severe-wind/hail potential across northeast/east TX, and perhaps parts of the Arklatex region, over and west of the prior morning convection's track. ...Edwards/Kerr.. 09/24/2023 $$ = = = 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) .