SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0245 PM CDT Sun Jul 11 2021 Valid 112000Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHEAST ARIZONA...NEW MEXICO...WEST TEXAS...EAST TEXAS/LOWER MISSISSIPPI VALLEY...UPPER OHIO VALLEY/NORTHEAST... ...SUMMARY... Strong to severe thunderstorms may impact a corridor through tonight from southeast Arizona into New Mexico and west Texas, and also east Texas into the lower Mississippi Valley and parts of the Ohio Valley and Northeast States. ...20Z Update... The primary change to the outlook is a small eastward expansion of the Marginal and Slight Risks across portions of the TX South Plains, where strong thunderstorm development is underway. See MCD 1257 for more information regarding the threat across NM and adjacent west TX. Otherwise, no substantial changes have been made to the outlook. See the previous discussion below for more information. ..Dean.. 07/11/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Jul 11 2021/ ...East Texas to Louisiana/Mississippi... A long-lived but generally decaying linear MCS and its related outflow continues to settle southward across east Texas and central portions of Louisiana and Mississippi. These details are not particularly well-handled by short-term guidance/convection-allowing models, but a general weakening trend is likely to persist. Guidance is likely too aggressive with the northward extent of more appreciable destabilization, although some degree of air mass modification/recovery is expected as far north as near the front across parts of north Texas and the ArkLaTex vicinity. Ample low-level moisture and moderate/locally strong buoyancy in the presence of modest strength west-northwesterly mid-level winds support the redevelopment of severe storms capable of damaging wind gusts late this afternoon into evening, particularly in vicinity of remnant outflow across parts of east Texas into central Louisiana/southern Mississippi. ...Arizona/New Mexico and west Texas... Moderately strong northwesterly winds aloft will reside across much of the region through tonight, with the exception of more off-mountain/higher terrain northeasterly winds across southeast Arizona. Considerable low-level moisture is in place over the mountains and high plains of central/eastern New Mexico, where scattered thunderstorms are expected to form. A combination of very steep low-level lapse rates, sufficient CAPE, and strong northerly flow aloft will promote organized storms capable of gusty/damaging winds and hail. Farther east, scattered thunderstorms are expected to develop over parts of west Texas in vicinity of a weak cold front or remnant outflow boundary from morning convection. These storms will be in a high-CAPE environment with a risk of damaging winds and hail as well for a few hours this afternoon and evening. ...Northeast States including Ohio/West Virginia/Pennsylvania... Have introduced a Slight Risk for portions of the region. To the east of the cyclone centered over the middle Mississippi Valley, a ribbon of moderately strong low/mid-level southwesterly winds will reside across the middle/upper Ohio Valley, with low-level/deep-layer shear expected to be maximized near a northward-shifting warm front across Ohio/northern West Virginia/Pennsylvania later today. While mid-level lapse rates are weak across the region, visible satellite imagery and surface observations at midday imply that the strongest heating/destabilization will continue to occur across West Virginia/far southeast Ohio into Pennsylvania and nearby Maryland/northern Virginia this afternoon. Damaging winds should be the primary risk, but a brief tornado or two and/or marginally severe hail could also occur with the more discrete storms/supercells. ...Northern Montana... A shortwave trough moving eastward along the international border vicinity of the northern Intermountain West/Canadian Rockies will reach southern Saskatchewan and the northern High Plains by late tonight. As a front settles south-southeastward across the region, storms that develop near the Canadian Front Ranges could spread southeastward into portions of northern Montana by late afternoon and evening. Steep lapse rates, modest buoyancy (perhaps up to 1000 J/kg MLCAPE) in the presence of relatively long hodographs (40+ kt effective shear) could support a few supercells/sustained multicells capable of large hail and locally damaging winds. ...Southern Illinois/southeast Missouri and vicinity... Near the vertically stacked cyclone, there is some possibility that the environment near the surface low/nearby triple point could become conducive to a couple of stronger storms pending a thinning of clouds and adequate destabilization. This could include the potential for a few funnels or possibly even a brief tornado. However, the weakening tendency of the cyclone and weak convergence is currently expected to limit this potential. Read more LIVE: spc.noaa.gov
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