Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
384 ACUS02 KWNS 041721 SWODY2 SPC AC 041720 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1220 PM CDT Thu Jul 04 2024 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM LOWER MICHIGAN INTO THE OHIO VALLEY...CENTRAL APPALACHIANS AND WESTERN/CENTRAL NEW YORK...AS WELL AS NORTHEAST NEW MEXICO... ...SUMMARY... Strong to severe thunderstorms are possible from Lower Michigan into the Ohio Valley, Central Appalachians and western/central New York. Additional isolated strong storms are possible across northeast New Mexico. ...Synopsis... An upper trough will be centered over the upper Great Lakes/central U.S. Friday morning. This feature will slowly pivot east through the period, with a couple of embedded convectively enhanced vorticity maxima/lead shortwave impulse migrates through southwesterly flow over parts of the Upper OH Valley/Central Appalachians into western/central NY. At the surface, a very moist airmass will be in place ahead of an eastward-advancing cold front. The front is forecast to extend from Lake Michigan south/southwest into central/southern AR/OK and northwest TX/eastern NM during the morning. Some showers and thunderstorms may be ongoing across parts of the OH Valley in a modest warm advection regime and as a continuation of convection expected in the Day 1/Thu overnight period. Some guidance suggests an MCV related to this activity may float east across parts of the adjacent Appalachians through the afternoon. This general pattern should support at least isolated/sporadic organized thunderstorms capable of mainly strong/locally damaging gusts. Further west, thunderstorms also will be possible across eastern NM in a post-frontal upslope flow regime and eastward into portions of central TX along the southward sagging cold front. ...Lower MI... Isolated to scattered thunderstorms are expected during the afternoon as a seasonally moist airmass destabilizes in the vicinity of a surface low/triple point and within the cold core of the upper trough. While instability will remain modest (less than 1000 J/kg MLCAPE), vertical shear will support transient organized cells/small line segments. Cool temperatures aloft and elongated forecast hodographs suggest marginal hail to near 1 inch diameter will be possible with any more intense/organized updrafts. Occasional strong gusts also are possible. ...OH Valley/Central Appalachians into western/central NY... Areas of ongoing convection and general cloudiness are expected across the region. However, a very moist airmass will be in place and even modest heating will allow for moderate destabilization (MLCAPE 1500-2000 J/kg). Vertical shear will be strongest with northward extent closer to the midlevel jet max oriented from OH into NY. However, forecast guidance suggest a convectively enhanced vorticity max over KY may drift east across the central Appalachians, providing some enhancement to shear across this area. Shear should be sufficient for at least transient organized cells/clusters amid a high PW environment. Thunderstorms across the region will mainly pose a risk for strong/locally damaging gusts during the afternoon/evening. Some uncertainty exists regarding eastward extent of damaging wind potential as vertical shear weakens into the VA Piedmont/Chesapeake Bay vicinity. Severe probabilities may need to be adjusted eastward in subsequent outlooks if confidence increases in storm coverage or maintenance of an eastward propagating cluster east of the mountains. ...Northeast NM... Modest boundary-layer moisture will be maintained in a post-frontal upslope flow regime Friday afternoon. Isolated thunderstorms will develop over the higher terrain near the Raton Mesa vicinity. Cool temperatures aloft and midlevel lapse rates near 7.5-8 C/km will support modest instability, while vertically veering wind profiles will be sufficient for around 30-35 kt effective shear magnitudes. A couple of strong/severe storms producing hail and strong gusts will be possible during the afternoon/early evening. ...OK/TX into the Southeast... Thunderstorm clusters are expected along the southward sagging cold front across portions of OK/TX eastward into TN Valley vicinity. Vertical shear will be weak and lapse rates poor. However, a very moist/high PW airmass will be in place amid 1000-2000 J/kg MLCAPE. Locally gusty winds may accompany thunderstorms, but organized severe potential appears low. ..Leitman.. 07/04/2024 $$