Day 1 Convective Outlook
American Severe Weather Forecast Center
12:30 AM CDT, October 13, 2009
Valid: 13/12:00 UTC - 14/12:00 UTC
...No Organized Severe Thunderstorms Expected...
National Synopsis
Evening analysis and water vapor imagery depict a large upper trough moving onto the West Coast of the U.S. ahead of a mainly zonal flow and flat ridging in the East. A smaller shortwave was evident in the flow across the Western Great Lakes. At the surface, a stalled frontal boundary was located across the Gulf Coast states, with a secondary front over the Ohio Valley, in conjunction with a surface low pressure area. Behind the front, a large surface high is located over the central and northern Plains.
Southern Plains/Lower Mississippi Valley
West-southwesterly flow will be in place across the Plains and Lower MS Valley today as a warm front advances northward across east TX and LA. A subtle shortwave trough evident on water vapor imagery over northern Mexico and western TX will move across the Arklatex region late this morning and early this afternoon. Ahead of this feature, thunderstorm activity should increase in coverage along the warm front with a cluster of storms moving eastward into the Lower MS Valley by afternoon. Although forecast soundings along this corridor increase MLCAPE into the 1000 to 1500 j/kg range by early afternoon, the stronger vertical shear profiles are forecast further north in the Ozarks beneath the belt of prevailing westerlies. If more vertical shear and low-level flow can be realized than is currently forecast, a marginal wind damage threat would be possible across the region mainly this afternoon. At this point, the scenario is conditional upon moisture return and the strength of the low-level flow.
California Coast
A well-developed mid-level jet associated with an upper-level trough off the West Coast will move eastward into central and northern California today. Diffluence in the exit region of the jet and moisture ahead of the upper-level trough should result in some thunderstorm activity in coastal areas of California. Although vertical shear will be quite strong, a weakness in lapse rates and instability should prevent severe storm potential.
GOSSAGE