The Cap & The Chance Of Overnight Thunderstorms

/The Cap & The Chance Of Overnight Thunderstorms

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.


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.


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.



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.


2018-06-02T08:52:33+00:00June 1st, 2018|General|41 Comments


  1. Stl78(winon,mn) June 1, 2018 at 7:40 am - Reply

    Thx Gary! It’s been extremely hot and humid up this way but we will see a nice break today with temps in the 70s and low humidity. Have a great wknd everyone!

  2. REAL HUMEDUDE June 1, 2018 at 7:58 am - Reply

    Gary, how did you calculate the convective initiation temp of 105F? I know it changes daily based on atmospheric conditions , how is that value determined?

    • Gary June 1, 2018 at 8:26 am - Reply

      You do it by looking and analyzing the soundings, the Skew-T charts. This cap will likely hold strong over Kansas.


  3. Snow Miser June 1, 2018 at 8:01 am - Reply

    NAM seems to think the cap will go away:
    And it’s been showing that for a few days now, too.

  4. Michael Casteel June 1, 2018 at 8:11 am - Reply

    Bring on the Rain! We need it,

  5. Snow Miser June 1, 2018 at 9:28 am - Reply

    “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.”

    It’s only 9:30 and already in the mid-to-upper 80’s, so at this point I wouldn’t be surprised if it made it at least to 100!

    • LYITC41 June 1, 2018 at 9:54 am - Reply

      A higher dewpoint will keep that from happening but it’ll probably feel like 100F!

  6. REAL HUMEDUDE June 1, 2018 at 9:48 am - Reply

    I’m waiting for the HRRR to catch up to the event. HRRR is the truth!! As long as it hits NE KS/ NW MO with widespread rainfall I will happy. I wouldn’t mind a 1/2″-1″ or so myself. Already dusty down at the farm and I’m afraid any one of these rains could be my last for awhile, its that time of year again.

    • Gary June 1, 2018 at 10:05 am - Reply

      The latest HRRR is just now flowing in. It has done a pretty decent job when we get within a few hours of an event. The last HRRR, an hour ago, has an organizing MCS at 2 AM still west of Omaha, so this is still timing out to be around 6 AM if it can turn south.


      • f00dl3 June 1, 2018 at 2:03 pm - Reply

        HRRR now showing it making to KC as broken line of storms, but shifting it more in to KC each run.

  7. DanT June 1, 2018 at 10:16 am - Reply

    Is this a situation where you get a cold pool in Nebraska which drives an outflow boundary into the KC area?

    • LYITC41 June 1, 2018 at 10:57 am - Reply

      Sure, it could even be the whole nine, the storms themselves.

  8. Bill June 1, 2018 at 11:02 am - Reply

    Wait…so no pool day tomorrow??

  9. Richard June 1, 2018 at 11:38 am - Reply

    500 million people are in the path Roker ? Give me a break.
    He might be on NBC, but he is not a meteorologist.
    Why would you be excited to interview the king of hype.

    • REAL HUMEDUDE June 1, 2018 at 2:55 pm - Reply

      He’s just reading what’s on the telepromter Richard. He’s a legend in weather, I always enjoyed him and seems like a classy person too. He’s one of the more entertaining weather persons out there in my opinion, makes me wonder why I can’t be a weather person lol.

  10. Richard June 1, 2018 at 11:46 am - Reply

    That 105 near the surface. Would that be in the sun, or in the shade temp ?
    I know “official” temps are taken in the shade. Add 10-15 in the sun.
    So if we’re talking 96 today, then 105 in the sun would be very feasible.

  11. Mr. Pete June 1, 2018 at 12:13 pm - Reply

    So how is the weather looking tomorrow afternoon? Sunny?


  12. Craig June 1, 2018 at 12:22 pm - Reply

    The latest SPC forecast states they expect the MCS to move “southeastward” overnight and their updated risk area sure seems to point it right at us.

    • DanT June 1, 2018 at 1:40 pm - Reply

      I see they upgraded to a Moderate Risk

  13. f00dl3 June 1, 2018 at 2:01 pm - Reply

    GFS showing 100F here next Sunday.

    • Brittany June 1, 2018 at 2:39 pm - Reply

      Ugh noooo!

  14. jsquibble June 1, 2018 at 2:08 pm - Reply

    there some pretty impressive cape values over central KS. i have never seen cape values over 6000 before

    • LSDoc June 1, 2018 at 11:47 pm - Reply

      Me either. Holy cow!

  15. FDRLincoln June 1, 2018 at 2:58 pm - Reply

    NAM-3K and HRRR have the metro and areas west towards Lawrence/Topeka getting hit by the MCS line Saturday morning. Other models still show it more in NW Missouri and eastward.

  16. Craig June 1, 2018 at 3:11 pm - Reply

    SPC getting ready to get this started:

  17. Emaw June 1, 2018 at 3:19 pm - Reply

    Looks like Jack Squat for most of us south of I-70 especially Ks. side but maybe St. Joe can finally get some decent rainfall. It’s hot out there man.

  18. Matt June 1, 2018 at 4:40 pm - Reply it has Slight Risk almost to 435/50.

  19. Tdogg June 1, 2018 at 8:32 pm - Reply

    Better get some bread and milk for the doozy MCS a comin’

  20. Kstater June 1, 2018 at 8:37 pm - Reply

    If we miss this tonight in Lawrence i will really start to get concerned. No good chances after this for at least a week and everything is dry and getting worse. Corn may all be silage this year here if it doesn’t start raining here soon.

  21. Jason June 1, 2018 at 10:37 pm - Reply

    Slow blog tonight considering

    • LSDoc June 1, 2018 at 11:49 pm - Reply

      Jason, it’s Friday night, and everyone is skeptical of this LRC doing anything for us. LOL

  22. Anonymous June 1, 2018 at 11:03 pm - Reply

    definitely slow….looks like the storms are making the turn.

  23. Turd furgeson June 1, 2018 at 11:41 pm - Reply

    Looks like May be an outflow

  24. Skylar June 2, 2018 at 3:00 am - Reply

    Besides being an enormous MCS, the cap is actually breaking ahead of it with scattered thunderstorms popping up across the area.

  25. Skylar June 2, 2018 at 4:35 am - Reply

    I am shocked Lawrence does not have a severe thunderstorm warning. This was one of the strongest and longest lasting windstorms I’ve ever seen, transformers have been blowing all over the place. The only light is lightning and bright green or red flashes.

    • Kstater June 2, 2018 at 4:48 am - Reply

      Amen skylar! I just lost power here in NW Lawrence. Definitely the strongest wind I have ever experienced not in a severe thunderstorm warning and close to the strongest I have ever seen. I’m not sure how strong it gusted but it definitely was over the 50 they said it would be.

      • Bill in Lawrence June 2, 2018 at 5:24 am - Reply

        Skylar and Kstater:

        That was for sure a wind gust!!!! Im about 10 miles SW of Lawrence between Clinton and Lone Star…..trees bent pretty good LOL!!!

        That said…to me though looking at radar this is a mess of an MCS…it is barely staying together. I am hoping to pick up .25 out here….which would be th biggest rain in 2 weeks for my immediate area. I have had chances….they have just missed.

        Bill in Washington Creek Valley in Lawrence

  26. Anonymous June 2, 2018 at 6:04 am - Reply

    Well this blows not even enough to really get the pavement wet in north olathe

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