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Chicago Storm

August 10 Severe Weather

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SEVERE WEATHER STATEMENT  
NATIONAL WEATHER SERVICE DES MOINES IA  
1046 AM CDT MON AUG 10 2020  
  
IAC015-099-125-127-153-169-181-101630-  
/O.CON.KDMX.SV.W.0144.000000T0000Z-200810T1630Z/  
POLK IA-STORY IA-MARSHALL IA-MARION IA-JASPER IA-BOONE IA-WARREN IA-  
1046 AM CDT MON AUG 10 2020  
  
...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1130 AM CDT  
FOR POLK...STORY...WESTERN MARSHALL...NORTHERN MARION...JASPER...  
EASTERN BOONE AND NORTHERN WARREN COUNTIES...  
  
AT 1045 AM CDT, SEVERE THUNDERSTORMS WERE LOCATED ALONG A LINE  
EXTENDING FROM 8 MILES NORTH OF BOONE TO SAYLORVILLE LAKE TO 6 MILES  
SOUTHEAST OF VAN METER, MOVING EAST AT 70 MPH.  
  
THESE ARE VERY DANGEROUS STORMS.  
  
HAZARD...80 MPH WIND GUSTS AND QUARTER SIZE HAIL.  
  
SOURCE...RADAR INDICATED.  
  
IMPACT...FLYING DEBRIS WILL BE DANGEROUS TO THOSE CAUGHT WITHOUT   
         SHELTER. MOBILE HOMES WILL BE HEAVILY DAMAGED. EXPECT   
         CONSIDERABLE DAMAGE TO ROOFS, WINDOWS, AND VEHICLES.   
         EXTENSIVE TREE DAMAGE AND POWER OUTAGES ARE LIKELY.  
  
LOCATIONS IMPACTED INCLUDE...  
DES MOINES, AMES, WEST DES MOINES, ANKENY, URBANDALE, JOHNSTON,  
CLIVE, NEWTON, ALTOONA, PELLA, NORWALK, PLEASANT HILL, GRIMES,  
NEVADA, WINDSOR HEIGHTS, CARLISLE, BON

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9 hours ago, Chicago Storm said:

While most guidance has been tame for today (Monday), the HRRR and HRRRx develop a fast moving MCS/bow that sweeps across IA/IL/IN this morning into this evening.

Digging into things a bit deeper, while the HRRR has been overzealous and alone on an island numerous times this spring and summer, the solution it spits out is actually fairly plausible in this case.

The main trough and wave is currently diving into the Northern Plains from Canada, and along with it is a solid jet streak. This can all be seen very nicely on water vapor and IR satellite currently. There’s also a very nice power-keg environment out across portions of SD/NE/MN/IA currently as well, where initial development is expected within the next several hours. 4k+ cape, PWATS of 1.50”+, DP’s in the 70’s, a great EML with ML lapse rates ~9C, 50kts shear and the main wave and jet streak moving in.

Should likely see development as the HRRR shows in SD and possibly NE within the next several hours, as capping erodes. The environment mentioned above is supportive of MCS formation, and a damaging wind threat.

Now I won’t go as far as saying the derecho the HRRR/HRRRx have is going to occur across IA/IL/IN, but the setup is definitely supportive of something that could be quite good, as long as everything works out. Along the lines of everything working out...One potential caveat is the activity around MSP currently...Does it slowly fade away as it continues to drift east, or does it develop a nice cold pool and drive more SE, which would greatly affect the threat for some downstream areas outlined in this post.


.

success bump

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4 hours ago, A-L-E-K said:

our office building recently power washed the exterior masonry and now my window is filthy, going to be upset if it ruins the view of a nice shelf later

Are your windows facing west?

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Saw something like this coming last night with the steep lapse rates, big CAPE and 50kt jet nosing in. (Tho I saw something like this coming Sunday too and it never did, due to OFBs and poor destabilization). Well this one’s here, it’s not dying any time soon and I’m ready.

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PDS Watch is out. 80-100 MPH gust headline.

 

image.png.306b27ead3323472aa279845e5396b42.png

 

Quote
URGENT - IMMEDIATE BROADCAST REQUESTED
   Severe Thunderstorm Watch Number 426
   NWS Storm Prediction Center Norman OK
   1125 AM CDT Mon Aug 10 2020

   The NWS Storm Prediction Center has issued a

   * Severe Thunderstorm Watch for portions of 
     Eastern Iowa
     Northern Illinois
     Far northwest Indiana
     Far southern Wisconsin
     Lake Michigan

   * Effective this Monday morning and evening from 1125 AM until
     700 PM CDT.

   ...THIS IS A PARTICULARLY DANGEROUS SITUATION...

   * Primary threats include...
     Widespread damaging winds and scattered significant gusts to 100
       mph likely
     Isolated large hail events to 1.5 inches in diameter possible
     A couple tornadoes possible

   SUMMARY...A derecho will rapidly progress across eastern Iowa and
   northern Illinois this afternoon. Widespread severe wind gusts, some
   of which should reach 80-100 mph are anticipated along the track of
   the bow. Brief tornadoes are also possible.

 

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10 minutes ago, cyclone77 said:

Ankeny (KIKV) 78mph.  

Some sort of moisture boundary sitting there through DVN's CWA (upper 70s south, low to mid 70s north) and heating both sides of it. Some serious potential here.

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Probabilities for the watch.

Tornadoes

Probability of 2 or more tornadoes

Mod (40%)

Probability of 1 or more strong (EF2-EF5) tornadoes

Low (20%)

Wind

Probability of 10 or more severe wind events

High (90%)

Probability of 1 or more wind events > 65 knots

High (90%)

Hail

Probability of 10 or more severe hail events

Low (20%)

Probability of 1 or more hailstones > 2 inches

Low (10%)

Combined Severe Hail/Wind

Probability of 6 or more combined severe hail/wind events

High (>95%)

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Don't believe I've been in a PDS SVR watch that mentioned the possibility of 100 MPH gusts before. Although, extrapolating radar the action will miss Madison to the south, unless the northern edge of the MCS expands significantly. Not sure what to make of the convective cells moving NW-SE over northeast Iowa, while an E-W oriented band appears to be filling in and moving NORTH around Waterloo. That's going to crash into the SE moving cluster south of Decorah at some point, not sure what the resulting evolution and motion will be.

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1 minute ago, CheeselandSkies said:

Don't believe I've been in a PDS SVR watch that mentioned the possibility of 100 MPH gusts before. Although, extrapolating radar the action will miss Madison to the south, unless the northern edge of the MCS expands significantly. Not sure what to make of the convective cells moving NW-SE over northeast Iowa, while an E-W oriented band appears to be filling in and moving NORTH around Waterloo. That's going to crash into the SE moving cluster south of Decorah at some point.

There's been six known instances of max wind potential (105 MPH gusts) in any watch, most recent was just last year across Minnesota and Northern Wisconsin 

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Not a whole lot of negatives with this setup.  Really liking the potential, and added bonus for occurring during daylight. 

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