WSAW - Blogs - Jeremy Tabin

Updated: Risk of Severe Storms 6/3-Failed

Updated 6/4/11 8:45am:

Well the post mortem on the weather conditions on Friday June 3rd didn't feature a whole lot of excitement after all.  Yes, there were record highs in Wausau (90 degrees) and Marshfield (90 degrees), but when it came to any storms, they pretty much never materialized.  As I mentioned below, the #1 reason for this was because the atmosphere was "capped" in North Central Wisconsin.  This means that there was a layer of warm air a few thousand feet up that warmed with height versus getting cooler, thus stabilizing the atmosphere and preventing storms from being able to bubble up.  Good news if you had outdoor plans on Friday afternoon and evening, although I'm sure some folks won't have minded getting a bit of rain after the hot day.  Nevertheless, the cold front did finally push through the region on Saturday morning without much fanfare.

So all in all, the Tornado Watch and severe storm threat was a bust in our area, however summertime weather has settled in for the weekend and much of the week ahead.  Afternoon highs will generally be running in the 80s to at times around 90 through Wednesday.  That air conditioner may be getting a work out at times.  In addition, there will be more chances of showers and storms in the days ahead.  Whether those storms are severe in nature is to be determined.

Original Blog Post 6/2/11:

The timeline for this spring has been littered with severe weather outbreaks in North Central Wisconsin, not to mentioned parts of the Midwest & Southeast U.S.  April 10th featured 15 tornadoes in the Badger State, May 22nd another 11.  Typically June is the target month of severe weather and tornadoes.  Just look back on years past and we have had our fair share.  At this point, it looks promising that this June will make it 3 months in a row with notable storm damage.

Of course, before I get ahead of myself on the risk of storms on Friday, June 3rd, lets lay down the foundation for what could be taking place.

We have had a lot of swings in temperature during the past few days.  Back on Memorial Day, many spots recorded the highest temps so far this year, with the mercury peaking in the mid 80s to low 90s.  In the wake of that cold front, it did get a bit more comfortable and seasonable from Tuesday-Thursday with highs in the low 80s to the low 70s.  A warm front will be sliding through the region Thursday night, bringing a return to the heat and noticeable humidity on Friday.  With some sunshine, afternoon readings should easily climb into the 80s, perhaps low 90s in the far south.  But just like our rise in temps for the end of the holiday weekend, this is going to be a one and done type deal with the arrival of a cold front Friday afternoon & evening.  Of course, this leads to what I'm expecting to be an active storm threat.

First off, there are a variety of severe weather parameters that we look at in the Weather Lab whenever thunderstorms are possible.  The Lifted Index, CAPE, Bulk Richardson Number, wind velocities and shear (change in direction & speed with height), and how temperatures will change from the surface up to let's say 20,000 feet.  Many of these indicators are pointing toward a strong to probable risk of severe storms in the area from mid-afternoon Friday into the evening.

CAPE values ranging from 1500-3000 J/kg
Lifted Index  values from -5 to -9
Directional Wind Change from the surface to 500 mb 50-90 degrees
500 mb temperatures -12 to -18C

You can learn more about these & many other severe weather indicators on the Storm Prediction Center webpage.

What that tells me is that if strong to severe storms develop, the main threats would be storms producing damaging winds, brief heavy downpours of rain and isolated tornadoes.  The 500 mb temps being warmer that -20C would show that large hail could be a lesser threat.  However, anytime a supercell thunderstorm develops, it can easily produce all 3 aspects of wind, large hail and tornadoes.  We've got the ingredients and the cold front working by is the trigger.  Of course, there are a few things that could happen to bust up the stormy weather.

Number 1 on the list is it gets too hot.  Southern Wisconsin, Iowa & Illinois will be sharing in the heat and humid conditions on Friday, but the risk of severe storms is lower for them.  The big reason is their highs will be soaring into the 90s, which in this case creates a lid on the development of thunderstorms.  Not until it cools down back into the lower to mid 80s would conditions be more favorable for them.  In the process, the cold front would already be by most of these areas so only an isolated storm and wind shift would be the most notable aspects.  The other factor that could reduce our chances would be more cloud cover.  Granted on April 10th there wasn't a whole lot of sunshine, but on May 22nd we were basking in the sun from late morning into the early afternoon.  That sun not only heats up the air, but also helps to stir the proverbial pot to allow storms to bubble up.  Last but not least, not everyone in North Central Wisconsin is going to experience strong to severe storms.  Intense storms tend to be scattered about, not necessarily congeal into a squall line.  Each of the last big severe weather days have had storms of a scattered nature.  Where they form & track, you will feel the effects.

So the moral of this forecast is that there is a good chance of thunderstorms on Friday afternoon/evening, some of which could be severe.  So keep an eye to the sky, have a plan in place on where to head of threatening weather approaches your area, and keep it tuned to 24/7 Weather, Newschannel 7 & be sure to check in for updates on wsaw.com, along with the Newschannel 7 facebook page.

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