Sunday, November 17, 2013

High Risk Issued From Storm Prediction Center

Edited at 2:50 pm MST - Numerous tornadoes have occurred in Illinois this afternoon. Photo above shows destruction in town of Washington, Illinois.

The SPC has issued an outlook for a High Risk of severe thunderstorms today as a strong surface cyclone develops into the northern Great Lakes. The situation is unusual, given how far north the threat has developed. Shown below are this morning's skewT plot and hodograph from Salem, Illinois. Part of the text of the public statement issued by SPC is included at the bottom of this post.

Text from SPC : A potent jet stream disturbance with wind speeds in excess of 120
   knots will sweep east across the central Plains today and across the
   Ohio Valley and northern half of the Appalachians tonight. As this
   occurs, a surface low now over the mid-Mississippi Valley will
   rapidly intensify and accelerate northeastward, reaching northern
   Michigan early tonight and western Quebec Monday morning.

   East of the low, increasingly warm and humid air at the surface will
   spread north across the Tennessee and Ohio Valleys, contributing to
   very unstable conditions over a large part of the east central
   United States. Coupled with daytime heating and ascent provided the
   jet stream impulse, the environment will become very favorable for
   severe thunderstorms --- especially along and ahead of fast-moving
   cold front trailing southward from the low into the mid-Mississippi
   and Ohio Valleys.

   Given the degree of thermodynamic instability, and the strength and
   character of the winds through the depth of the atmosphere, many of
   the storms will become supercells. Some of these will be capable of
   producing strong tornadoes --- in addition to large hail and swaths
   of damaging surface winds.  

   The storms are expected to consolidate into one or two extensive
   lines later today into tonight --- extending the threat for damaging
   winds and isolated tornadoes eastward into the Appalachians by early

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