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The Cap & The Chance Of Overnight Thunderstorms

Good morning bloggers,

Get ready for a hot Friday afternoon in Kansas City. Today may be a rather exciting day for me, as I will likely be interviewing Al Roker this afternoon on our 4 PM newscast.  What should I ask him?  There is a risk of severe weather to our north tonight.  There is also a capping layer of warm air around 6,000 to 10,000 feet above us that may prevent thunderstorms from turning southeast over KC.

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Here is todays severe weather risk:

There is a strong, a very strong cap developing today. The “cap” is a layer of warm air aloft that is so warm, that it prevents the hot air near the surface from bubbling up and breaking through this warmer air.  To break the cap one of a few things must happen. A strong front that would cause enough lifting to help break through the cap with explosive development is one way, and there is not a strong enough front in this situation developing until sometime early Saturday morning.  A second way would be for it to become hot enough near the surface, but it would take 105° or hotter and this is likely not going to happen.  A third way could be a strong enough complex of thunderstorms that creates its own disturbance that would help break through the cap and force it south around this disturbance. This is a possibility.  From the SPC:  “Most of the day will be void of any thunderstorm activity, but conditions are expected to change rapidly from late afternoon through the evening.  Strong heating and northward advection of moisture will lead to an extremely unstable air mass with MUCAPE forecast to be in excess of 4,000 J/kg across Nebraska into southern South Dakota. Veering wind profiles will support initial supercell development near the surface trough with very large hail and perhaps a tornado or two.  With time, there is a strong likelihood of a severe MCS which may be capable of significant wind damage as it evolves out of merging supercells.

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Here is a look at one of the early morning HRRR models:

The red line shows where the cap is powerfully strong.  I have seen caps like this break in the past, but rarely does this happen.  The initial thunderstorms will likely form way up to the north, and on this model you can see that they are north and west of Omaha, NE at 11 PM.

hrrr_ref_frzn_ncus_18

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By early morning, a stronger cold front will be developing.  The complex of thunderstorms that forms may turn south southeast. If that happens, then Kansas City will have a chance of the cap being obliterated just in time to have some rather strong to severe thunderstorms heading our way. This would happen around 3 to 6 AM, but this is about the time the thunderstorms will begin weakening.  We will have to monitor the models closely.

Kansas City Weather Timeline:

  • Today:  Mostly sunny and hot. A light south breeze. High:  96°
  • Before 3 AM tonight:  Dry with south winds increasing at 10-20 mph.  Temperatures in the 80s dropping into the 70s
  • 3 AM – 9 AM Saturday:  There is a 20% chance of thunderstorms south of a Lawrence to Harrisonville line. The chance increases to 60% north of a Leavenworth, KS to Sedalia, MO line.  In between there is a 40% chance of thunderstorms turning over Kansas City.  There is a slight risk of severe weather with wind damage being the main risk type.

Thank you for spending a few minutes of your day reading the Action Weather Blog featuring Weather2020 and the LRC.  Click on the Weather2020 blog to join in the conversation as we track this potential complex of thunderstorms late tonight.  Here is the link to the blog:  Todays Blog  Have a great day. It will be a hot one!

Gary

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