Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Tue Aug 11 2020 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS... ...SUMMARY... Severe thunderstorms with wind damage and isolated large hail will be possible across parts of the northern Plains on Wednesday afternoon and evening. Marginally severe thunderstorms will be possible in parts of the lower to mid Missouri Valley. ...Northern Plains... An upper-level trough will move across the northwestern U.S. on Wednesday as southwest mid-level flow becomes established across the northern Plains. A 55 to 65 kt mid-level jet will move northeastward from the northern Rockies into southern Saskatchewan. At the surface, a cold front will advance eastward across the northern High Plains. A moist airmass will be in place across much of the Dakotas where moderate to strong instability is forecast by afternoon. Thunderstorms appear most likely to develop across far western North Dakota by late afternoon with this activity moving east-northeastward into west-central North Dakota during the evening. NAM and GFS Forecast soundings in western North Dakota near and to the north of Dickinson for 00Z/Thursday have surface dewpoints in the lower 60s F with MLCAPE around 2000 J/kg. 0-6 km shear values are forecast to be near 30 kt with 700-500 mb lapse rates near 8.5 C/km. This environment would be marginal for supercells. But organized multicells or semi-organized rotating storms will be possible. Isolated large hail and wind damage will be the primary threats. The main problem with this forecast is model inconsistency concerning convective coverage. 700 mb temperatures are forecast to gradually warm during the day across western North Dakota, which would inhibit convective initiation. The time most likely for convective initiation would be during the late afternoon or early evening as low-level flow ramps up across the region. Although the potential for severe thunderstorm development appears conditional, the presence of the mid-level jet to the northwest should help increase convective coverage in the evening. For this reason, have placed a small slight risk far parts of the northern Plains for this outlook. ...Lower to Mid Missouri Valley... A shortwave ridge is forecast to move eastward across the central Plains on Wednesday. A moist and unstable airmass will be in place beneath the ridge from eastern Kansas north-northwestward into southern South Dakota. Due to the upper-level ridge and limited large-scale ascent, convective coverage is expected to remain isolated. In spite of warm air aloft, 0-6 km shear is forecast to be in the 20 to 30 kt range near the upper-level ridge axis. This combined with steep lapse rates may be enough for a marginal wind damage and hail threat late Wednesday afternoon. ..Broyles.. 08/11/2020Read more
from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_0600.html
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