SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1212 PM CDT Mon Jun 21 2021 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID-ATLANTIC AND SOUTHEAST...MIDWEST AND CENTRAL PLAINS...AND PACIFIC NORTHWEST... ...SUMMARY... Isolated strong to severe storms may occur Tuesday across parts of the Mid-Atlantic and Southeast. Strong to damaging wind gusts should be the main threat. Other isolated severe storms also appear possible across parts of the Midwest into the central Plains, and the Pacific Northwest. ...Mid-Atlantic/Coast Southeast... An upper trough is forecast to cover much of the eastern CONUS early Tuesday morning. Several embedded shortwave troughs are expected to progress through this upper troughing, contributing to some deamplification of the upper trough as well as a general eastward movement. Southernmost embedded shortwave trough, beginning the period over the central and southern Appalachians, will likely have the largest impact on thunderstorm chances. The quick eastward/northeastward progression of this system will help push a cold front through the Mid-Atlantic and coastal Southeast States. Air mass ahead of this cold front will be moist, buoyant, and weakly sheared. This should result in mostly multicellular storm structures, with updrafts/downdrafts that could occasionally become strong enough to produce damaging wind gusts. ...Central Plains/Mid MO Valley.. Across the central CONUS, a weak frontal zone from the western Gulf Coast into south TX will further diminish throughout the day as strong moisture return occurs across the southern/central Plains. A warm front is expected to develop/sharpen near where the leading edge of this moisture return meets the more continental air mass in the wake of upper trough. Strong heating and low-level convergence in the vicinity of this boundary (perhaps aided by a subtle shortwave trough) are expected to result in thunderstorm initiation during the late afternoon. Only modest buoyancy is anticipated, but southerly low-level flow veering to relatively strong northwesterly flow aloft will result in enough vertical shear for organized updrafts capable of large hail. Five percent hail probabilities will be maintained with this outlook, but higher probabilities may be needed in later outlook. Uncertainties at this forecast range, including the extent of moisture return and diurnal heating as well as the location of the strongest low-level convergence, preclude the confidence needed for higher probabilities at this forecast range. ...Pacific Northwest... Low-amplitude shortwave trough is expected to eject northeastward through the far northwestern periphery of the upper ridging Tuesday afternoon. Favorable timing of this shortwave coupled with increasing mid-level moisture and strong diurnal heating should result in afternoon thunderstorm development. Moderate deep-layer vertical shear (i.e. 30-35 kt) should be enough for a few organized, high-based storms capable of producing strong/gusty winds approaching severe limits. ...Southern High Plains... Northwesterly flow aloft will promote afternoon thunderstorms off the high terrain and into the southern High Plains. Environment across the southern High Plains will be well mixed, resulting in the potential for damaging downbursts with any more robust storms. However, overall coverage is too uncertain to introduce any probabilities with this outlook. ..Mosier.. 06/21/2021
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