Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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181 ACUS01 KWNS 170100 SWODY1 SPC AC 170059 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 PM CDT Mon Sep 16 2024 Valid 170100Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS... ...SUMMARY... Thunderstorms capable of severe wind gusts and isolated large hail will be possible this evening across parts of the northern Plains. An isolated tornado threat will continue across parts of eastern North Carolina. A marginal severe threat may continue in parts of the Four Corners region. ...Northern Plains... Southwest mid-level flow is evident on water vapor imagery over the north-central U.S. A shortwave trough appears to be in northern North Dakota, where the RAP is analyzing a distinct vorticity max. At the surface, a low is in southeast Montana with a warm front extending east-northeastward across central and northeast North Dakota. Scattered thunderstorms are ongoing to the north of the front from northern North Dakota into northwest Minnesota. This activity is located along and to the north of an axis of moderate instability, where the RAP has MLCAPE in the 2000 to 3000 J/kg range. Near this convection, regional WSR-88D VWPs have 0-6 km shear around 35 knots, with a substantial amount of directional shear in the low to mid-levels. RAP forecast soundings in the same area have steep 700-500 mb lapse rates. This environment will support a potential for supercells with isolated large hail and severe wind gusts. Organized bowing line segments with a wind-damage threat will also be possible, especially in areas where low-level lapse rates are steep due to warmer surface temperatures. The severe threat will likely continue through much of the evening, as a strong to severe line segment moves east-northeastward across north-central and northeastern North Dakota. ...Eastern North Carolina... A tropical cyclone will move northwestward across northern South Carolina this evening. Rainbands extend from north of the center east-southeastward across central and eastern North Carolina. The latest RAP has moderate instability in place along much of the North Carolina coast, with MLCAPE in the 1000 to 2000 J/kg range. The Moorehead City WSR-88D VWP has a gradually veering wind profile from the surface to about 4 km, with 0-3 km storm-relative helicity around 320 m2/s2. This suggesting the environment will be favorable for rotating storms and possibly tornadoes. The tornado threat will be maximized with cells that remain semi-discrete and are close to the coast where surface dewpoints are higher. The threat is expected to gradually shift northward into the Cape Hatteras area by late evening. ...Four Corners Region... According to water vapor imagery, a mid-level low is located over northern California, with southwest flow from much of the Desert Southwest into the central Rockies. The RAP has a pocket of instability near the Four Corners with another in eastern Arizona. Isolated to scattered thunderstorms are ongoing in these areas. Moderate deep-layer shear and steep lapse rates should be enough for a marginal severe this evening, with isolated severe winds and hail as the primary threats. ..Broyles.. 09/17/2024 $$