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Severe Storm Outlook Narrative (AC)
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Issued by NWS
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385 ACUS01 KWNS 291957 SWODY1 SPC AC 291956 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Sat Jun 29 2024 Valid 292000Z - 301200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE OHIO VALLEY/MID-ATLANTIC...OZARKS VICINITY...AND THE SOUTHERN/CENTRAL HIGH PLAINS...... ...SUMMARY... Damaging thunderstorm gusts and a few tornadoes appear possible today over parts of the Lower Great Lakes to upper Ohio Valley and Mid-Atlantic. Severe gusts may also be focused this afternoon and evening over the Ozarks vicinity, and the Raton Mesa and adjacent south-central High Plains. ...20Z Update... Extended the Slight Risk westward toward Indiana due to ongoing severe cluster of storms, and an extremely moist air mass ahead of it. GPS PWAT values exceed 2.25" over much of the area, and low-level lapse rates continue to steepen just south, which should support corridors of damaging wind. Farther east, tornado watch 482 remains in effect from eastern OH into PA and toward the NY border. Scattered storms persist, and southwesterly low-level winds will aid theta-e advection into the region. In addition, 0-1 km SRH remains favorable at over 150 m2/s2 from OH to central PA, with stronger values up to 300 m2/s2 into NY where the air mass is less unstable. As such, stronger cells developing this afternoon may acquire rotation with tornado potential. Overnight, the strong shortwave trough will move across southwest Ontario, skirting the Lake Ontario area and into northern NY. Given the strength of the trough, and forecast theta-e advection around 850 mb ahead of the system, additional nocturnal storms producing wind or hail will be possible. ..Jewell.. 06/29/2024 .PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Jun 29 2024/ ...Lower Great Lakes and Upper Ohio Valley into the Mid-Atlantic... A loosely organized band of convection is ongoing across parts of northern/central OH. As an upper trough over the Great Lakes and eastern Canada continues to move eastward through the period, current expectations are for convection to gradually increase in coverage and intensity this afternoon across eastern OH into western PA. Recent visible satellite imagery shows substantial cloudiness across this area, which should hinder diurnal heating to some extent. Still, even modest heating of the rather moist low-level airmass should support at least weak instability by late this afternoon. Low-level and deep-layer shear appear sufficiently strong for a mix of multicells and supercells. Damaging winds will be a concern with any bowing cluster that can form and spread eastward across parts of the Mid-Atlantic through the afternoon/evening. A couple of tornadoes may also occur with any sustained supercell or embedded QLCS circulations. See Mesoscale Discussion 1472 for more details on the short-term severe threat across OH into northern WV and western PA. There also appears to be some chance for additional convection to develop along the cold front across IL/IN this afternoon, perhaps associated with a remnant MCV over eastern MO. Substantial cloudiness is present across much of this region ahead of the front. But, any thunderstorms that can form may be capable of producing isolated hail and/or strong to damaging winds. Considered including this area in a Slight Risk, but confidence remains low in robust convection persisting with eastward extent into the OH Valley in the wake of earlier thunderstorm activity. ...Ozarks... A Slight Risk for damaging winds has been introduced for southern MO, northeast OK, and vicinity. Outflow from earlier convection, along with the slowly sagging cold front, should continue southward across these areas through late afternoon while also providing a focus for additional convection. Moderate to strong instability is forecast to develop this afternoon in a narrow zone along/ahead of the front. While deep-layer shear should remain fairly modest, most 12Z guidance shows a greater concentration of robust convection developing across southern MO and vicinity late this afternoon and early evening. Loosely organized clusters capable of producing mainly damaging winds should spread generally east-southeastward through the evening. Isolated hail may also occur. ...Southern/Central High Plains... No changes have been made to the Slight Risk across the southern/central High Plains. Scattered thunderstorms are expected to develop during the late afternoon and evening in a weak post-frontal, upslope flow regime. Generally upper 50s to low 60s surface dewpoints and steep mid-level lapse rates will support a narrow corridor of moderate instability by late afternoon. While mid-level flow is expected to remain weak, vertically veering wind profiles with height through mid/upper levels will support sufficient deep shear for transient, slow-moving supercells and loosely organized clusters developing off the higher terrain of southern CO and northern NM. Occasional severe gusts appear possible with this activity as low-level lapse rates become steepened through diurnal heating. Some hail may also occur with the strongest cores. ...Michigan... Despite veered low-level winds ahead of the cold front and weak mid-level lapse rates, boundary-layer heating should yield a plume of weak instability, with MLCAPE around 500-1000 J/kg by this afternoon. Strong speed shear will support hodograph elongation. This may yield a supercell or two capable of isolated severe hail and locally strong wind gusts in the eastern U.P. into Lower MI. But, overall coverage of strong/severe thunderstorms is expected to remain rather limited across this area. $$