Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sun Apr 23 2017 Valid 231630Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER WESTERN/CENTRAL GEORGIA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTH CAROLINA... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTHERN FLORIDA INTO GEORGIA AND SOUTH CAROLINA... ...SUMMARY... Areas of strong-severe thunderstorms are expected over the Southeast today and overnight. The main threats appear to be damaging gusts over parts of western/central Georgia and central South Carolina this afternoon, followed by potential for a few tornadoes and isolated wind damage overnight in parts of South Carolina. ...Georgia and South Carolina... Satellite imagery indicates an upper low has formed over western Tennessee, and this feature is forecast to move southeastward reaching the Alabama/Georgia border by the end of the period. A band of stronger mid/upper level winds curving cyclonically around the southern periphery of the circulation is expected to spread across parts of Georgia and northern Florida into tonight. At the surface, a low over extreme northwest Georgia will move mainly eastward along a quasi-stationary front extending across east-central Georgia to the central South Carolina coast. The low is forecast to reach east-central Georgia this evening and cross into South Carolina by 24/12Z. A cold front trailing southward from the low will progress eastward to the Atlantic coast from Georgia to northeast Florida by the end of the period. The frontal boundaries are expected to focus the stronger thunderstorm activity through tonight. Initial storm development is expected along the advancing cold front by early afternoon from west central Georgia into the Florida Panhandle as it moves into an axis of slightly greater moisture. Although mid-level lapse rates are generally weak, visible satellite imagery indicates stronger diabatic heating will occur in the warm sector where fewer clouds are present. This will enhance low-level lapse rates and contribute to modest destabilization with MLCAPE of 500-1000 J/kg this afternoon. With some CAM guidance indicating development of QLCS structures along/slightly ahead of the front, stronger cells within the line segments will have potential to produce damaging downbursts as they move through the focused moisture/instability axis. See Mesoscale Discussion 550 for more detailed information. Other storms are expected to develop over parts of central/southern South Carolina this afternoon near the aforementioned east-west front. The lack of clouds south of the boundary is promoting a strong differential heating zone where attendant mesoscale circulations will support storm potential this afternoon. Isolated severe storms will be possible as vertical shear increases over the area, especially along and immediately north of the boundary where backed surface flow will enhance low-level shear. The severe threat over South Carolina is expected to increase somewhat tonight as a south-southeasterly low-level jet strengthens in response to the approaching upper low. This will result in increasing moisture advection from the Atlantic and be associated with stronger low-level shear with an attendant risk for supercells to develop. Low LCL levels and moderate-strong SRH indicate potential for a few tornadoes to occur with any persistent discrete supercells that develop. ...Northern/Central Utah... Isolated weak thunderstorms may develop this afternoon and evening in association with an upper short wave trough that will move eastward across the Great Basin. Column moisture/total precipitable water values are quite minimal /approximately 0.25 inch/ which will limit the coverage and intensity of any convection. However, a dry sub-cloud layer will enhance evaporative cooling and promote transfer of stronger mid-level horizontal momentum to the surface, suggesting potential for convectively-enhanced surface wind gusts. Given the aforementioned limiting factors, we will maintain a sub-severe outlook at this time over the area. ..Weiss/Cook.. 04/23/2017Read more
from SPC Forecast Products http://ift.tt/wWCv9s
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