Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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445 ACUS01 KWNS 231259 SWODY1 SPC AC 231257 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Sun Jun 23 2024 Valid 231300Z - 241200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF NEW ENGLAND... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN HIGH PLAINS... ...SUMMARY... Scattered damaging winds and a few tornadoes are likely across parts of the Northeast and New England, with additional severe storms expected across the Ohio Valley, Mid-Atlantic region, as well as the Northern High Plains. ...Northeast/New England... Negligible Outlook changes are warranted, with an active severe-weather day still expected regionally. Rich boundary-layer moisture (dewpoints in the upper 60s to low 70s F) will advect northward, and in the wake of morning convection, filtered solar heating will allow for moderate destabilization over much of New England. Most guidance shows 1500-2000 J/kg of MLCAPE developing by early to mid afternoon despite only modest low and mid-level lapse rates. More than sufficient for strong updrafts, scattered storm development is expected first near the warm front and subsequently along the trailing surface trough. Strong deep-layer shear of 45-60 kt will support both supercells and short line segments. With a favorable parameter space for organized storms, damaging winds, some hail and a few tornadoes are all expected. A corridor of locally greater severe risk remains apparent across portions of southern Maine, VT, NH and west-central Massachusetts. this is were forecast soundings show large curved hodographs with ESRH of 250-350 m2/s2 and STP values of 1.5-3. With the potential for a mix of supercells and line segments, the risk for tornadoes will exist. Eventual upscale growth into a linear cluster may also support a locally greater risk of damaging winds toward the coast later this evening. Additional storms are possible as the cold front moves through later this evening, though multiple rounds of prior convection may limit the severity of any subsequent convection later this evening. ...Mid-Atlantic States... More isolated storm coverage is expected with southward extent. Displaced from the main lobe of ascent from the passing shortwave trough, convection may take longer to organize owing to the warmer mid-level temperatures and weaker synoptic forcing. Still, deep-layer shear and buoyancy are favorable for organized multicell clusters and a few supercells. Damaging winds, and occasional hail are the most likely threats, though a tornado could occur with any sustained supercell. ...Upper Ohio Valley/Tennessee Valley... Ahead of the trailing cold front, scattered thunderstorm development is expected during the afternoon. Rich boundary-layer moisture will support a broad plume of moderate instability. Several bands of thunderstorms should track east southeast along the southern periphery of the enhanced flow aloft. Sufficient for some storm organization, 20-30 kt of effective shear should support a few clusters capable of damaging gusts and isolated hail. ...Northern Plains including eastern Montana to North Dakota... Accompanying the wave over southern Canada and the Northwest, a deepening surface cyclone with a cold front trailing southward into Montana will serve as a focus for isolated storm development this afternoon and evening, with the highest probability for storms closer to the international border where a Slight Risk has been introduced. Low-level southeasterly flow will transport a confined plume of modest low-level moisture into parts of east Montana, resulting in a corridor of MLCAPE from 500-1500 J/kg. Deep-layer shear will be favorable for organized convection capable of isolated damaging winds and hail. ...Central High Plains... Very warm temperatures are expected along a lee trough across the central Plains this afternoon. With temperatures near 100 F, scattered high-based thunderstorms are expected over parts of eastern Colorado, southwest/south-central Nebraska and western Kansas. Deep inverted-v profiles will support a risk for severe gusts with strong downdrafts. Located on the southern periphery of the stronger upper-level flow, these storms may persist through early evening before weakening. ..Guyer/Mosier.. 06/23/2024 $$