Today’s Set-Up & The Cap

/Today’s Set-Up & The Cap

Today’s Set-Up & The Cap

Good morning bloggers,

Today will feature “the cap”. There is a capping layer of warm air moving over Kansas and Missouri today. This cap will erode this evening, but how fast?  Here is the HRRR surface forecast valid at 7 PM this evening:

The dry line will become much more apparent later this afternoon and evening as the dew point contrast increased dramatically. The winds ahead of the dry line will likely be out of the south southwest and behind the dry line out of the west. This is not going to provide a lot of convergence. There likely won’t be enough lift from this feature to break through the cap.  This will be changing between 7 PM and midnight as the cold front catches up with the dry line, overtakes it and moves across later tonight. When this happens thunderstorms may finally form.

We can see the capping layer by looking at this mornings soundings. On this sounding you can see the warm layer above the surface where the red temperature line warms dramatically between the 900 and 800 mb level.  This will prevent cumulus clouds from growing or even forming at all for a long while today. The dilemma on days like this is that if the cap does break then where it does a huge thunderstorm may form. This cap appears quite strong and we are leaning heavily into the cap holding strong until sunset of after sunset.

The SPC has placed the slight risk to be located along and ahead of the dry line and it widens a bit near where the surface low will track in Iowa.  The tornado risk is very low today due to the cap likely holding and surface winds not backing enough. Most of the thunderstorms that do form will most likely be elevated, produce a lot of lightning, and the main severe risk type would be hail.

Let’s see how this evolves today. This is yet another reason why near Kansas City is one of the most difficult locations in the world to forecast the weather.  We quite often don’t get to see anything coming our way until it forms.  Here is the latest HRRR model valid at midnight:

This shows thunderstorms clustered south down the state line around midnight tonight. They begin forming just after sunset.  Have a great day!


2017-04-10T08:12:52+00:00 April 9th, 2017|General|14 Comments


  1. stl78 April 9, 2017 at 9:18 am - Reply

    Gary, we have a BIG move this Fri. I see the rain chance is high. Do you foresee this as an all day rain, spotty, ect. I know it’s early but would like your thoughts..thx!

    • Gary April 9, 2017 at 9:34 am - Reply

      The overnight GFS had it mostly dry all day Friday. There is a chance Friday into Saturday, but the flow aloft is very weak. Very low severe risk, but a warm front passes through, so there is a chance of a few thunderstorms.


  2. stl78 April 9, 2017 at 9:49 am - Reply

    Thx for the quick response and thoughts. Have a great day. Not looking fwd to moving a whole house and fam 400 miles…ugh!

    • Richard April 9, 2017 at 12:41 pm - Reply

      Moving to MN ?
      Maybe it was somebody else on here
      At any rate you are moving. Good luck and hope you and family enjoy your new digs and life. Change is good.

      • stl78 April 9, 2017 at 2:01 pm - Reply

        Yes sir Richard. A beautiful little town nestled in the Bluffs in Winona Minnesota

        • Brian April 9, 2017 at 3:20 pm - Reply

          Winona is beautiful. It’s location below the bluffs gives it a completely different climate than up on the flat land. It’s known as the Florida of Minnesota for a reason.

          • stl78 April 9, 2017 at 3:48 pm - Reply

            It is beautiful Brian! I’m lookin forward to slightly cooler summers. Winter may be a different

  3. Mr. Pete April 9, 2017 at 9:51 am - Reply

    The winds have been constant for two days now. Blew all night too.

  4. REAL HUMEDUDE April 9, 2017 at 2:19 pm - Reply

    The winter wheat in my area is about knee high, going bonkers in the sunshine. Bring on some more rain and no hail!

    • Gary April 9, 2017 at 2:38 pm - Reply

      Email me a picture if you get a chance. Wow!


  5. L.B April 9, 2017 at 4:12 pm - Reply

    clouds looking darker here in gardner is cap wearing down?

  6. Mr. Pete April 9, 2017 at 4:22 pm - Reply

    Some precip forming on the radar to the SW.

  7. f00dl3 April 9, 2017 at 4:46 pm - Reply

    HRRR 17z seems to think we’ll get a lone cell ~10 PM and then a line around Midnight:

  8. LSDoc April 9, 2017 at 6:14 pm - Reply

    Thanks for the explanation of the “cap”. Makes total sense now!

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