Saturday, April 9, 2011

Severe Weather Update...Plains & Midwest

Thunderstorm development appears likely during the next 2 hours across portions of the Missouri River Valley.  Once thunderstorms develop, they are likely to become severe rapidly...
The latest water vapor satellite image (shown below), indicates the first in a series of upper-level weather disturbances is lifting Northeast across portions of Nebraska and South Dakota at this time.  A stronger band of jet stream winds also accompanies this feature (as shown by the red arrow).

The low levels of the atmosphere are becoming more unstable along and ahead of a surface dryline / cold front over portions of eastern Nebraska, southeast South Daklota and adjacent portions of Minnesota and Iowa.   Thunderstorms are expected to develop in this region during the next couple of hours, as the upper-level energy overruns the increasingly unstable low level airmass and convergence along the dryline / cold front increases.

The latest visible satellite image (shown below) indicates towering cumulus clouds are increasing across central and eastern Nebraska, as well as along the Nebraska/Iowa border ahead of these features:
Thus far, a strong capping inversion in place across the region has prevented thunderstorm development.  This is expected to change, however, as the upper level energy overspreads the region during the next few hours.  Large hail, damaging winds and tornadoes will be possible with activity as it forms in this region and moves / develops Eastward into the evening hours.

A Moderate Risk of severe thunderstorms, including tornadoes, continues to be forecast by the SPC across much of the region through tonight:

You can also see cumulus towers increasing further southward along the dryline into portions of central Kansas and northwest Oklahoma (as noted by the yellow circle on the image below):

There is still a very strong capping inversion present across this portion of the dryline, and it will be hard for thunderstorms to develop on a widespread basis.  Any thunderstorm that does develop, however, is likely to become severe rapidly, with large hail and isolated tornadoes possible.

The most likely time for any isolated development this far south on the dryline will be between 5 and 7pm, as daytime heating and instability are maximized.

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