Dangerous heat builds Sunday, brings back chance for severe storms

So far in 2015 we have really lucked out with very little extreme heat to speak of.  It’s been pretty ordinary with temperatures hovering close to average much of the spring and early summer.  In fact, the metro has managed to record only 1 90°+ day so far.  This is by no means unusual as the majority of our 90° days come in July and August anyway.  But it may seem a little cool just because we have seen so few over the last couple of years with 2014 recording just 2 90°+ days.  Well, we may get that many in the days ahead with Sunday & Monday likely to see some 90s.

But Sunday looks atrocious with temperatures climbing into the 90’s and dewpoints soaring into the 70’s, it will bring back that tropical “Florida-like” feel to Minnesota.  So just how warm will it get?  Well, forecasting models are showing it to be close to the warmest day we have seen since 2013 with the heat index closing in on 110° for some.  Check out potential temperatures and dewpoints for Sunday afternoon…

Remember that these are just a forecast and not a guarantee but if the actual dewpoint and temperatures are anywhere close to these predictions, then it’s going to be one VERY hot day.  When you combine the temperature and the dewpoint, you get what it will actually feel like outside… here is one possible outcome for peak heat index on Sunday…

OUCH! 105° for the metro with areas from New Ulm to Mankato nearing 110°.  While this is a possibility, I think this may be a little overdone with metro heat indices likely closer to 100°.  Regardless, it will be dangerously hot Sunday afternoon.  This heat and humidity will just be adding fuel to the fire… A LOT of it!  Check out the expected CAPE values for Sunday afternoon…

Remember that CAPE is an acronym for Convective Available Potential Energy.  The more you have, the stronger your thunderstorms can be.  In a time of year where 1000 CAPE is more than enough to give you severe weather, the image above is a little frightening.  This shows CAPE values of over 5000… 5 times higher than the typical threshold for severe storm development.  While the rest of the components in the atmosphere to produce severe weather are barely adequate, this is not something you want to see.  Put it this way, when storms fire up Sunday evening, air inside updrafts will be traveling over 100 mph.  To put it another way, air will move upward at roughly 10 thousand feet per minute.  So you could have clear skies one minute, and 5 minutes later have a 50 thousand foot tall angry thunderhead.  Yikes! Stay tuned and stay sky aware!


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