More heavy rain overnight and why severe storms did not develop

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HEAVY RAIN

A channel of  heavy rain continued to flow into the state late Thursday night with some very impressive rainfall totals.  Through 10pm, moderate to heavy rain was still falling with over 1″ down over the past 24 hours.  The 3 day rainfall total is now over 3.5″ for the city.  Frankfort in Clinton county reported 4″ down so far this week.  3 days of heavy rain will keep area creeks and streams in flood for several days. 

A flash flood watch is in effect for all of central Indiana through Friday morning.

Estimated Rainfall

Radar Estimated rainfall

SEVERE OUTBREAK A NO SHOW?

Unseasonably warm, moist air.  Strong winds at the surface and aloft.  Deep low pressure and an approaching cold front.  All the ingredients for a Spring severe weather outbreak.  Conditions so favorable that the Storm Prediction Center issued a rare PDS tornado watch for most of Indiana – at 10AM in the morning!  On high alert all day and not one severe storm crossed the state.  The best laid plans.  So why did the severe weather fail to ignite?  Left-overs.  Yes left-overs.  The remnants of thunderstorms that dumped heavy rain over northern Illinois during the overnight hours.

Early morning storms were feared to exhaust when reaching Indiana early.  They did indeed, stalled leaving a pool of cooler and more stable air.

Afternoon heating slowed or was limited by clouds and cool air from the collapsed thunderstorms.  Warmer air is more buoyant rises quickly.  A key to explosive thunderstorm development.

Upper Level Winds a key to rotating storms arrived on the scene as expected – but the timing of thunderstorm build up was now off.  As the storms started to build and move into a recovering (warming/moist environment) these winds will now bring the demise of the blooming storms.  Strong winds shear off the tops of these storms and prevent the towering cumulonimbus storms to form.  These winds are now tearing the storms apart.

It’s very rare to see a PDS tornado watch not verify but also shows how complex severe storm forecasting can be.  “Conditions are Favorable” under a watch situation but it is not carved in stone that these storms will materialize.

Split Screen

A date with severe storms – no show

Shelf Cloud 4-16-2013 Geist

Ominous Shlf Cloud over Geist Thursday afternoon

BIG COOL OFF

A cold front passes in the pre dawn hours bring an end to the heavy rainfall.  Grab the winter coats!  Temps tank into the lower 40’s earl;y Friday morning.  The wind chill may dip into the upper 20’s!  Dry weather expected Saturday through Sunday with cool afternoons this weekend.