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July 28-29 Severe Potential


sbnwx85
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If the CAM solutions are right, Madison doesn't need to be in the Enhanced risk. HRRR and 3K NAM still largely agree on a whiff northeast.
Now that I check the WRFs, they give us some storms but not nearly as potent as points north/east.

They’ll be too far northeast.

The biggest question is how quickly the threat fades with southeastward extent. The moderate risk to MKE seems be wishful thinking.


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I'm tending to agree with Purduewx here and thinking the CAMS might be off a bit and too far ne.  As I look at current satellite, radar, and SPC meso values I'm leaning to a more north south orientation as well a bit farther west.  The instability gradient will be all important in its location for what transpires this evening and tonight in the affected areas.

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Interesting curl shape/possible broad cyclonic rotation to the southwest edge of the anvil debris/cirrus clouds currently drifting southeast through central Iowa. Not sure if that has any implications on the scenario for later. The cloud deck in general appears to finally be shrinking/dissipating with heating building back in over MN/IA.

Edit: No change to the southwestern edge of the risk areas at 1630Z, slight/marginal expanded to the northeast.  :huh:

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1 minute ago, CheeselandSkies said:

Interesting curl shape/possible broad cyclonic rotation to the southwest edge of the anvil debris/cirrus clouds currently drifting southeast through central Iowa. Not sure if that has any implications on the scenario for later.

The overnight MCV is being sheared apart due to the strong winds aloft - def can see those remnants aloft w/ the feature over IA. The only implication I can see related to that is the min in instability caused by the warm front being driven S/W by an outflow boundary. Recovery can happen quickly in this setup during the late PM hours, but it's not totally clear where the instability gradient will be as TS ride the ridge SE and then S tonight. The latest HRRR does capture current instability fields relatively well. Hate to say this, but the 12Z GFS actually looks more reasonable than a lot of the CAMs from what I'm seeing so far.

First warning up by Lake of the Woods now. Will be very interesting to see if that's the start of the main show (probably so).

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Update from Grand Rapids.....

 

Area Forecast Discussion
National Weather Service Grand Rapids MI

UPDATE...
Issued at 1225 PM EDT Wed Jul 28 2021

Latest 12Z guidance is continuing the farther north trend of the
most severe convection later tonight, even hinting at the
possibility of a derecho impacting much or parts of wrn Lwr MI.
Since this is a potentially high impact severe weather event
while many folks will be sleeping, communication/messaging the
possibility of high/destructive winds this afternoon/evening will
be critical.

Timing looks to be similar, with potential for a large bow echo
sweeping across Lk MI toward or after midnight. Also some
potential for the warm advection wing ahead of the main line
becoming active a couple hours beforehand. If that does occur, we
could have some tornado potential with discrete cells since the
warm front will be draped over the area. HRRR has 0-1km SRH of
150-200 m2/s2 with LCLs below 1km. A QLCS-type tornado threat may
also develop/exist within the main line.

Also of note, in terms of the straight line wind potential, HRRR
shows 70 kts at 3 km, of potential descending rear inflow into
the back of that line. So some isolated pockets of destructive
80+ mph winds seem plausible later tonight.

As far as heavy rainfall/flooding concerns, some intense rainfall
rates are likely as the strong/svr convection is coming through
tonight, although the progressive nature of the MCS may limit
the overall flooding risk. That said, some urban flooding -
possibly worthy of areal flood advisories/warnings - may also be
needed.
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What even constitutes a good derecho these days for you guys? After Iowa I think it would be hard to get off on more run of the mill events. At least that’s been my experience with tropical stuff. What sort of wind gusts will you need to see to not say meh?

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Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Wed Jul 28 2021

   Valid 282000Z - 291200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS
   WISCONSIN...SOUTHERN HALF OF LAKE MICHIGAN...SOUTHWEST LOWER
   MICHIGAN...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTHEAST
   VIRGINIA...EASTERN NORTH CAROLINA...

   ...SUMMARY...
   Potentially widespread severe thunderstorms are expected late this
   afternoon through tonight along a corridor from northeastern
   Minnesota across Wisconsin into southwest Lower Michigan.  A few
   severe storms are also expected this afternoon over parts of
   Virginia and North Carolina.

   ...Discussion...
   The only change this outlook update is to upgrade severe-wind
   probabilities from the southern half of Lake Michigan southeastward
   into northwest OH.  Recent runs of the HRRR indicate an intense rear
   inflow jet late tonight as a bow moves southeastward across Lake
   Michigan into the Michiana vicinity.  Confidence in a widespread
   severe-gust threat has increased and is depicted in the minor nudges
   upwards in probabilities.

   ..Smith.. 07/28/2021
 
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5 hours ago, Chicago Storm said:


They’ll be too far northeast.

The biggest question is how quickly the threat fades with southeastward extent. The moderate risk to MKE seems be wishful thinking.


.

And then they double down, and bring the mod risk to the IL/WI border and into NW MI/N IN.

Likely overdone.

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Mesoscale Discussion 1378
   NWS Storm Prediction Center Norman OK
   0509 PM CDT Wed Jul 28 2021

   Areas affected...portions of east-central and northeast
   MN...northern WI

   Concerning...Severe potential...Tornado Watch likely 

   Valid 282209Z - 290015Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Rapid development of supercell thunderstorms is
   anticipated in the next few hours, with a risk for very large hail,
   damaging winds, and potentially a few tornadoes.  A Tornado Watch
   will likely be issued prior to 00z.

   DISCUSSION...A warm front extended south/southeast across
   central/southern MN at 22z, and this front will continue to move
   east through this evening as a weak surface low moves east across
   central MN. Latest visible imagery reveals moderate/towering cumulus
   over central MN north of the Twin Cities area, embedded within a
   larger area of clouds over central/northern MN and northern WI.
   Current expectations are for thunderstorms to develop in the next
   few hours near the warm front and move southeast during the evening.
   Northwesterly deep-layer shear of 45-55 kts in the vicinity of the
   front will support intense supercells initially, and
   locally-enhanced 0-3 km SRH will be favorable for low-level rotation
   and potential for tornado development. Steep mid-level lapse rates
   will also support a risk for very large hail, and damaging winds are
   also expected.  Current thinking is that the tornado threat will
   warrant a Tornado Watch for the first few hours after initiation
   given the near-storm environment, with eventual transition into a
   fast-moving MCS with widespread damaging wind potential later this
   evening/overnight.  

   A Tornado Watch will likely be coordinated with affected NWS Weather
   Forecast Offices prior to 00z.

   ..Bunting/Goss.. 07/28/2021

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...DLH...ARX...MPX...
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1 hour ago, StormfanaticInd said:

If a tornado forms in this environment watch out.

The parameters for significant tornadoes and the Violent Tornado Parameter are both very high over the Twin Cities metro area.  These parameters are not everything by themselves, but still, it is not an environment you would want a supercell to form and then go on to produce a significant tornado, especially over a highly populated metropolitan area like MSP.
 

Screen Shot 2021-07-28 at 6.40.02 PM.png

Screen Shot 2021-07-28 at 6.40.21 PM.png

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1 minute ago, CheeselandSkies said:

MD expires in 12 minutes and no watch yet...

That’s what has me scared. I live on the west coast and figured by the time I got home from work I’d have something to track. 

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