SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0151 PM CST Tue Nov 24 2020 Valid 242000Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHEAST TX PANHANDLE INTO NORTHEAST OK... ...SUMMARY... Severe thunderstorms are expected from the Texas Panhandle into Oklahoma through this evening. More isolated severe storms are possible overnight from northeast Texas into Arkansas. Large hail and damaging winds will be the main threats, along with a couple of tornadoes. ...20z Update - Southern Plains/Ark-La-Tex... Only minor adjustment have been made to the 10% general thunderstorm line across parts of the Plains based on latest trends and CAMs guidance. Otherwise, the ongoing outlook is on track. Strong thunderstorms have developed across parts of the OK/TX Panhandles this afternoon where temperatures have warmed into the 60s and MLCAPE has increased to around 500 J/kg near and east of current convection. Additional storms are expected to develop with time as the surface low and cold front develop eastward toward western OK over the next couple of hours. Large hail, damaging gusts, and a tornado or two still appear possible through this evening across the Slight risk area. Most recently, 1 inch hail has been reported with storms in Beaver County, OK. For more details, reference MCD 1807. ..Leitman.. 11/24/2020 .PREV DISCUSSION... /ISSUED 1027 AM CST Tue Nov 24 2020/ ...Parts of the southern Plains to the Ark-La-Tex through tonight... A midlevel shortwave trough over NM this morning will progress eastward to northwest TX and western OK by late evening, and then continue northeastward to MO/AR by the end of the period. The midlevel trough will be preceded by a surface cyclone that will develop eastward from the TX Panhandle this afternoon to western OK this evening, and then northeastward to MO overnight. A narrow corridor of mid-upper 50s boundary-layer dewpoints will return northward to the east of a dryline, where a few cloud breaks could allow pockets of surface heating as far north as west central or northwest OK by mid-late afternoon. Storm development appears probable by mid afternoon in the TX Panhandle near the triple point, and storms will subsequently spread eastward into west central and northwest OK late this afternoon/evening, generally along and north of I-40. Deep-layer shear will support supercells, but rather modest low-level shear and substantial forcing for ascent in the left-exit region of the mid-upper jet suggest that some upscale growth into clusters or line segments is also probable. Thus, there will be some threat for a tornado or two relatively early in the convective evolution across northwest OK, in proximity to the surface boundaries and where low-level lapse rates/CAPE will be largest. Isolated very large hail will be a threat with supercells given steep lapse rates and 500 mb temperatures colder than -17 C, and damaging winds will become more of a concern this evening as convection grows upscale. A separate zone of convection is expected overnight from northeast TX into southeast OK and western AR, both in pre-frontal warm advection and along the cold front as it encounters richer low-level moisture and weakening convective inhibition. Convection will likely remain elevated near and north of I-40, with more surface-based convection closer to northeast TX. Vertical shear will be strong in this corridor, but there will be a tendency for the stronger forcing for ascent to begin passing north of the more unstable warm sector late in the period. Overall, isolated severe storms may occur overnight from northeast TX into AR, but it is still not clear that a more concentrated severe threat will evolve in this corridor, so low severe probabilities will be maintained in this update.
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