Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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627 ACUS01 KWNS 251638 SWODY1 SPC AC 251636 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1136 AM CDT Wed Sep 25 2024 Valid 251630Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE GULF COAST INTO THE SOUTHERN/CENTRAL APPALACHIANS AND FLORIDA PENINSULA... ...SUMMARY... Isolated severe storms are possible this afternoon from parts of the Southeast and central/southern Appalachians to the Texas/Louisiana Gulf Coast. Some tornado threat may develop across the Florida Peninsula by this evening, in association with Tropical Cyclone Helene. ..Southeast and southern Appalachians... The influence of the upstream mid/upper-level trough and moisture streaming north from the Gulf of Mexico and Helene will lead to widespread precipitation across parts of the Southeast and southern Appalachians. This will tend to limit available buoyancy in some areas, but strong to locally severe storms may occur. Favorable deep-layer winds/shear exist, especially across the southern Appalachians vicinity where a few semi-discrete supercells could occur aside from more prevalent quasi-linear convective bands. Locally damaging wind gusts and perhaps a tornado could accompany the strongest storms, before low/mid-level lapse rates and buoyancy become increasingly weak with time, and an outflow-reinforced effective front sags southward across the region. ...Texas Gulf Coast/Middle Gulf Coast... Somewhat stronger diurnal destabilization will be possible from parts of central/east Texas into Louisiana, and perhaps into Mississippi, with MLCAPE potentially increasing above 1500 J/kg. Isolated to widely scattered thunderstorm development will be possible near a southward-moving cold front. Effective shear will generally range from 25-35 kt, and a few modestly organized storms are possible. Isolated damaging gusts could accompany the strongest storms within this regime. ...Florida Peninsula and Keys... Hurricane Helene`s wind field is forecast to be rather large, especially on the east side of the circulation, associated with a strengthening Helene through the afternoon and tonight. Reference the National Hurricane Center for the latest Helene details. This scenario will result in modestly strengthening low-level shear/SRH across the Florida Peninsula during the day, but more so into the evening and overnight after the peak diurnal instability cycle. Instability will likely remain rather weak overall, and details regarding the intensity of any outer rain bands remain uncertain. However, some tropical-cyclone tornado threat could evolve across parts of the Florida Peninsula and Keys, mainly into tonight. ...Eastern Washington/northern Idaho/northwest Montana... While buoyancy is expected to remain quite weak, relatively steep mid-level lapse rates will support thunderstorm potential late this afternoon through early evening from eastern Washington into northern Idaho and northwest Montana, in advance of the approaching shortwave trough. Strong deep-layer flow/shear could support a locally severe storm or two with gusty winds and possibly some hail. ..Guyer/Lyons.. 09/25/2024 $$