Active Weather is Back for Wednesday June 12, 2013

An incoming warm front ahead of a deep area of low pressure will set the stage for rounds of showers and thunderstorms Wednesday afternoon into Thursday. Below is the convective outlook for Wednesday issued by the storm prediction center out of Norman, OK.

Photo 1. Convective Outlook for Wed. June 12th, 1013

All of Michiana is under a SLIGHT RISK for severe weather. An area of low pressure moving in from the west will have plenty of moisture from Monday's rain (some areas received over an inch) to develop numerous showers and storms heading into Wednesday evening. There will be a chance for strong storms developing hail, isolated tornadoes (but not as likely) but there will mainly be a threat for damaging winds from outflow diving out of mature storms.

The ingredients needed for strong to even severe storms will all be in place for for tomorrow. You need three things for a thunderstorm to develop: (1) Moisture, (2) Lift and (3) Instability. But for severe storms, you need something extra to get the storm to strengthen and even rotate to the point of potentially developing a tornado. That thing is (4) Wind Shear - which is rotating winds withing the atmospheric column.

For moisture, dewpoint is the best way to go to find the true amount of moisture over an area. Below shows the dewpoints across the nation at 2 PM Wednesday.

Photo 2. NAM of dewpoint values at 2 PM June 12th

Dewpoints are well into the 60s with this model showing levels getting into the mid to even upper 60s. That air is almost tropical. So there will be plenty of water to fuel thunderstorm development.

For lift, a warm front ahead of an area of low pressure with a trailing cold front with do a great job of vertically developing copious amounts of moisture into t-storms. Below shows an image of the approximate location of the low and fronts tomorrow evening.

Photo 3. Front and Low Locations at 8 PM June 12th.

Instability will be well in place with the highest levels of CAPE making its way to Michiana tomorrow. CAPE - Convective Available Potential Energy is a way to see how efficiently thunderstorms grow vertically. The higher the value the more unstable the environment and sometimes leads to a higher likelihood of strong storms. Below shows CAPE levels over 3000 J/kg already in place at 2 PM before the low pressure center arrives. This is the highest I've seen our instability values get so far this season.

Wind shear is very important for severe storm development. It will be present through multiple levels of Michiana's stretch of atmosphere. It is required for both storm strength and it can stretch rotating air into the vertical...possibly developing tornadoes. Below is an image of low level helicity (rotation in lower atmosphere).

Values over 100 m^2/s^2 show up over Michiana along the warm front. That suggests there will be a lower-end strength of rotation present within developed storms. This suggests a possibility of isolated tornadoes.

There will also be a risk for heavy rain from the passing storms as the low lingers into Thursday morning. Below is an image for the Hyometeorological Prediction Center forecast for rainfall from Wednesday through Thursday morning.

Numerous strong storms developing over the region may bring rainfall totals anywhere from the 1" to even 3" range from Wednesday through Thursday. Local areas of flash flooding may be possible. So be mindful of spots you know of or live near that floods from even a quick inch of rain.