SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0246 PM CDT Mon Jun 05 2023 Valid 052000Z - 061200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER DEEP SOUTH TEXAS... ...SUMMARY... Isolated severe thunderstorms with damaging winds and large hail are possible across several areas of the country this afternoon and evening. The most likely corridor for severe storms appears to be over Deep South Texas through this afternoon into the evening. ...20Z Update... Overall forecast outlined in the previous outlook remains valid. Thunderstorms remain possible across a large portion of the CONUS, with pockets of stronger storms possible over the southern Appalachians and Carolina Piedmont, the Sierra and central valley of CA, western MT, south FL and south TX. Each of these areas is addressed in the discussion appended below. Greatest severe coverage is still expected across south TX, where a few supercells have developed along the outflow boundary moving westward across the region. ..Mosier.. 06/05/2023 .PREV DISCUSSION... /ISSUED 1126 AM CDT Mon Jun 05 2023/ ...Deep South TX... Scattered thunderstorms are ongoing over the northwest Gulf to the Corpus Christi vicinity of the TX Coastal Plain near a minor mid/upper trough. On the backside of this trough, a belt of enhanced mid-level northwesterlies (near 40 kts at 500-mb per 12Z BRO sounding) will slacken through this afternoon. This flow regime should remain sufficient for potential supercell development towards the Lower Rio Grande Valley where low to mid 70s surface dew points and nearly full insolation are prevalent. With minimal MLCIN amid modest mid-level lapse rates, 12Z HREF members (outside of the HRRR) and the RRFS are fairly consistent in backbuilding convection across Deep South TX through late afternoon. A south-moving cluster with embedded supercells may develop with a threat for both severe hail and wind until convection spreads into Tamaulipas by early evening. ...Southern Appalachians/Piedmont... A deep upper low will persist off the New England Coast today. Peripheral influence of this low will maintain a belt of enhanced mid-level north-northwesterlies extending to the southern Appalachians through this evening. This will overlap with the eastern extent of the surface-based instability plume from the TN Valley/Deep South. Pervasive low clouds adjacent to the high terrain should gradually decrease through the day, with convective initiation likely to begin over the high terrain where breaks are already evident. Isolated to scattered thunderstorms will develop and attempt to spread southeast, but may tend to weaken with southeast extent in the Carolinas and backbuild west given the orientation of the instability plume. This should result in a corridor of isolated damaging wind and severe hail during the late afternoon to early evening focused along the lee of the high terrain. ...CA... An upper low spinning off the southern CA Coast should gradually shift inland north of the L.A. Basin by early morning. While its attendant strong mid-level jet will remain confined south of the border over Baja CA, a belt of enhanced south to southeasterlies will curl around the east to northeast semi-circle of the trough. Isolated to scattered thunderstorms are most likely over the Sierra NV towards the higher terrain of northern CA and separately towards the western portion of the Transverse Ranges in southern CA where upslope flow will occur. Steep low to mid-level lapse rates will support an isolated threat for severe wind and hail, mainly during the late afternoon and evening. ...South FL... 30-40 kt mid-level westerlies should persist across the southern third of the peninsula downstream of the minor mid/upper trough over the western Gulf. With generally northeasterly surface winds, weak flow through 3 km, and some backing of winds in the mid to upper levels, mid-level updraft rotation will probably remain relatively transient. Given the strength of the mid-level flow, a few of the stronger cells might produce marginally severe wind and hail during the late afternoon to early evening. ...Western MT... A minor mid-level impulse will continue to drift north from ID into northwest MT. Its attendant cloudiness this morning will slow diabatic heating immediately ahead of it near the ID/MT border, but more robust boundary-layer warming will occur farther downstream in parts of western to north-central MT. With just modest enhancement to mid-level southerlies, effective bulk shear will remain subdued from 20-30 kts. In addition, modest mid-level lapse rates will further temper updraft acceleration. Overall severe threat appears rather marginal, but a few severe wind and hail events may occur.
