Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
197 ACUS02 KWNS 200557 SWODY2 SPC AC 200556 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1256 AM CDT Wed Aug 20 2025 Valid 211200Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE CENTRAL/EASTERN DAKOTAS INTO PARTS OF MINNESOTA... ...SUMMARY... An isolated severe threat is expected to develop Thursday into Thursday night over parts of the Dakotas into Minnesota, with severe gusts and hail possible. ...Northern Plains into parts of MN... A mid/upper-level shortwave trough is forecast to evolve into a deep-layer cyclone as it moves eastward across parts of the Canadian Prairies on Thursday. A trailing cold front will move through the Dakotas and northwest MN, with a weak frontal wave potentially developing across SD. Diurnal heating of a relatively moist airmass will result in moderate to locally strong destabilization by late afternoon. An embedded mid/upper-level shortwave trough and associated remnant convection is expected to move across MB/ND and northern MN early in the day. In the wake of this shortwave, large-scale ascent is expected to be generally weak until later Thursday night, resulting in uncertainty regarding afternoon/evening storm development. Isolated storm development cannot be ruled out near the front, and potentially near the weak surface low across SD. An increase in storm coverage is expected late Thursday night, as somewhat stronger midlevel height falls and upper-level difluence overspread the region. The strongest mid/upper-level flow will tend to lag behind the front, but deep-layer shear will still be sufficient for some storm organization, including conditional supercell potential. The Marginal Risk has been maintained with this outlook, but greater severe probabilities may eventually be needed, depending on trends regarding storm coverage and timing from parts of the Dakotas into northwest MN. Other strong storms may develop Thursday night across parts of the northern High Plains, within a favorably sheared post-frontal regime. Severe probabilities may eventually need to be expanded westward, if confidence increases in a favored post-frontal corridor. ...Coastal NC... The center of Hurricane Erin is forecast by NHC to remain well offshore of coastal NC on Thursday as it begins moving northeastward. However, the western periphery of Erin`s large wind field will result in rather strong deep-layer northerly flow across the Outer Banks and vicinity. If modest diurnal heating can occur, then showers and possibly a few weak storms may develop during the afternoon, though it is uncertain if any such development would be sufficiently vigorous to support convectively augmented gusts. ...Parts of the Southeast/southern Appalachians... Scattered thunderstorms are forecast to develop across parts of the Southeast and southern Appalachians vicinity Thursday afternoon. Deep-layer shear will remain quite weak, but northerly low-midlevel flow may support one or more southward-moving clusters. Poor midlevel lapse rates will tend to limit updraft intensity, and the organized severe threat appears low, but localized tree damage could accompany these storms during the afternoon and early evening. ...Arizona... Thunderstorms are expected to develop Thursday afternoon and evening across parts of AZ, initially near the higher terrain. Isolated strong gusts could accompany these storms. With an amplified upper-level ridge anchored near the Four Corners, midlevel flow will generally be easterly across central/southern AZ. The easterly steering flow and a very hot and well-mixed environment could support a threat of strong outflow gusts into the lower elevations, though it is uncertain if storm coverage will be sufficient for larger-scale outflow development and more than very isolated damaging-wind potential. ..Dean.. 08/20/2025 $$