Valid 291200Z – 301200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS…UPPER MIDWEST AND WESTERN GREAT LAKES…
…SUMMARY…
Thunderstorms associated with a wind damage and hail threat will be
possible this afternoon and evening from parts of the central Plains
east-northeastward into the western Great Lakes.
…Central Plains/Upper Midwest/Western Great Lakes…
An upper-level trough will move from the Upper Mississippi Valley
into the western Great Lakes today with the southern extension of
the trough in the mid Mississippi Valley. At the surface, a cold
front will advance southeastward across Wisconsin, Iowa and
Nebraska. Surface dewpoints in the mid 60s to lower 70s F ahead of
the front will contribute to moderate to strong destabilization by
afternoon. A pronounced increase in low-level convergence along the
front in the mid to late afternoon is forecast to result in
scattered thunderstorm development. Several short line segments
appear likely to develop along the front and move southeastward
across the warm sector. RAP forecast soundings just ahead of the
front from near Omaha to near Chicago at 00Z/Friday generally show
MLCAPE values in the 3500 to 4500 J/kg range. 0-6 km shear values
along this corridor are forecast to range from 35-40 kt at Omaha to
near 50 kt at Chicago. This environment will likely support a severe
threat. Wind damage will be possible with the more organized line
segments. Hail is expected to be the lesser threat mainly due to
warm mid-level temperatures and sub-optimal lapse rates.
Further west into the central High Plains, instability is forecast
to drop off with westward extent. This combined with convective
coverage issues will probably keep any severe threat isolated during
the late afternoon and early evening. Instability is also forecast
to be problematic across lower Michigan. This should help to keep
any severe threat marginal there as well.
..Broyles/Wendt.. 08/29/2019
$$