Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1232 AM CDT Wed Aug 05 2020 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM MONTANA SOUTHWARD INTO THE SOUTHERN PLAINS...AND ACROSS PARTS OF THE MID-ATLANTIC REGION... ...SUMMARY... Isolated severe storms are possible Thursday afternoon and evening from Montana southward through the central High Plains and into portions of the southern Great Plains. Gusty winds and hail will be possible with the strongest storms. Additional strong storms could produce locally damaging winds across parts of the Mid-Atlantic vicinity. ...Montana... An amplified upper ridge will be oriented over the High Plains Thursday morning, shifting slowly eastward over the Great Plains by Friday morning. Meanwhile, a shortwave trough will shift eastward across the Pacific Northwest and northern Rockies during the forecast period. South/southerly low level flow will transport modest boundary-layer moisture westward across MT toward the Continental Divide, with mainly mid 40s to mid 50s F dewpoints forecast. This will tend to limit instability across MT, but diurnally-driven isolated to scattered thunderstorms are expected over higher terrain by mid/late afternoon. As the shortwave trough ejects across the northern Rockies after 00z, deep layer southwesterly flow will increase. This should result in some increase in storm intensity during the evening into early overnight hours as convection shifts off higher terrain toward central MT. Clusters of storms capable of locally damaging gusts and isolated hail could persist across central MT into the overnight hours, though boundary layer inhibition will increase with loss of daytime heating, and overall severe threat could be limited by the ill-timed ejection of the shortwave trough during the overnight hours. ...Central/Southern High Plains vicinity... Further south, convection may be ongoing Thursday morning across parts of southern KS or northern OK. Marginal probabilities have been included as some gusty wind potential could be ongoing with this activity before decaying through the morning hours. Instability will be a bit stronger across the High Plains as dewpoints will generally be higher, from the mid 50s to mid 60s F. Steep midlevel lapse rates will aid in weak to moderate destabilization by peak heating and thunderstorms are expected to develop along higher terrain by mid/late afternoon. Overall, effective shear will remain modest, but adequate for a few semi-organized cells/clusters. Steep low level lapse rates with inverted-v sub-cloud thermodynamic profiles indicated potential for enhancement of outflow winds and gusty winds will be the main concern with this activity, though isolated hail is also possible. Guidance suggests some upward developing cluster could track eastward across the OK/TX Panhandle vicinity during the evening/overnight, potentially along residual outflow from morning convection. If this occurs, some potential could exist for a marginal severe threat persisting eastward into parts of western OK/KS during the nighttime hours. ...Mid-Atlantic vicinity... An upper trough over the upper Great Lakes to the Mid-South area will shift eastward toward the Appalachians through Friday morning. This will result in around 30-35 kt southwesterly mid/upper level flow overspreading parts of the Carolinas into the Chesapeake Bay/Mid-Atlantic vicinity. A very moist airmass will be in place, with dewpoints generally in the upper 60s to low 70s F. Strong heating will result in steepening low level lapse rates, and MLCAPE from 1000-2500 J/kg is forecast across the region. Midlevel lapse rates will be poor, and effective shear around 25-35 kt, limiting updraft organization/longevity. Nevertheless, PW values approaching 2 inches and sufficient instability/shear should result in clusters of strong storms capable of isolated wet microbursts and locally damaging wind gusts. ..Leitman.. 08/05/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
No comments:
Post a Comment