July 28-29 Severe Potential

[sbnwx85]

I haven't started a thread since lake-effect season, so maybe this will bring some luck? I love a good night time squall line. Best severe chances probably wane as the MCS approaches my neck of the woods due to timing, but I'm going to stay up to find out. I don't go to bed until 2 AM most nights anyway. 

KIWX

Timing is also a point of uncertainty as it will depend on
the speed of the MCS. At this point timing on when the MCS could
enter the far NW/N corner of the CWA range from 03z to 09Z.

Convective parameters across the area during that timeframe will
remain conducive to severe weather despite the overnight timing.
MLCAPE is forecast to range 2000-2500 J/kg while 0-6km shear starts
out near 30kt before ramping into the 40-50kt range. While damaging
wind gusts will be the greatest threat from this MCS, hail and an
isolated tornado can`t entirely be ruled out. Given PWAT values
increasing into the +2SD of climatology and a window of MBE
Velocities in the 10-15kt range also keeps the risk of heavy rain
leading to flooding in the mix. Timing on when the MCS will exit the
area ranges from 12Z to 15Z Thursday.

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1228 PM CDT Tue Jul 27 2021

   Valid 281200Z - 291200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS EAST-CENTRAL
   MINNESOTA INTO CENTRAL AND SOUTHERN WISCONSIN...

   ...SUMMARY...
   Thunderstorms associated with severe wind gusts, large hail to very
   large hail, and a couple tornadoes will be possible Wednesday
   afternoon into Wednesday night across parts of the Upper Midwest and
   extending into the southern Great Lakes region.

   ...Upper Midwest into the southern Great Lakes...
   A cluster or two of showers/thunderstorms may be ongoing Wednesday
   morning from northern MN southward into perhaps the IA/WI border
   vicinity within a warm advection regime.  This activity will likely
   dissipate by the late morning.  A subtle mid-level disturbance,
   cresting the mid-level ridge centered over the central Great Plains,
   will move eastward into western MN by late afternoon.  A warm
   frontal zone will become draped from the southwest Great Lakes
   northwestward through WI into northern MN.  Strong heating and a
   very moist boundary layer will lead to a very unstable airmass
   developing by mid afternoon over the Upper Midwest (2500-4000 J/kg
   MLCAPE, locally higher).  Suite of convection-allowing models show
   an initial cluster of supercells will probably develop during the
   late afternoon into the early evening.  Large to very large hail,
   severe gusts, and a couple of tornadoes are possible.  Enlarged
   hodographs near the warm front will favor strong mesocyclones but it
   is unclear how much of a tornado risk will ultimately develop due to
   storm-scale interactions.  Nonetheless, an initial cluster of storms
   will likely grow upscale into a forward-propagating severe MCS over
   the western Great Lakes during the evening with localized intense
   gusts (75+ mph) possible with HP supercell to QLCS transitions or
   with the more pronounced bowing segments.  It seems plausible this
   MCS will move across southern Lake Michigan into the southern Great
   Lakes during the overnight.  The coverage/intensity of gusts will
   probably lessen with time as the squall line encounters weaker
   buoyancy during the pre-dawn hours.  

   ..Smith.. 07/27/2021

[CheeselandSkies]

HRRR is for northern, central and southeastern WI late tomorrow afternoon through the overnight but whiffs me just to the northeast.

[CheeselandSkies]

On 5/29/2021 at 3:54 PM, cyclone77 said:

July will be rockin'

Confirmed. Although I think of this as "proper" July weather for the region, so it doesn't make up for the lame @$$ A/M/J.

[sbnwx85]

Skilling mentions the D-word...https://www.facebook.com/photo?fbid=380591763425773&set=pcb.380591860092430

DERECHO THREAT IN CHICAGO AND THE MIDWEST WEDNESDAY NIGHT

The transition to a cooler pattern may get underway with an atmospheric bang Wednesday night. While a few scattered/isolated, low coverage t-storms are possible during the day Wednesday---IT'S WED NIGHT WHEN A MORE SIGNIFICANT SEVERE WEATHER THREAT APPEARS TO BE TAKING SHAPE.

A classic"northwest flow" situation is taking shape. That's an atmospheric setting which threatens several bowed lines of severe t-storms--even the potential for a "derecho"--a fast, moving damaging line of t-storms which races southeastward beneath a powerful "northwesterly jet stream" and infuses the fast moving storms with wind energy that can produce an extended path of damage.

While many details remain to be firmed up, it would appear the period from midnight Wed night to 4 am Thursday morning appears to be the current focus of concern. That's when a fast moving squall line could sweep out of Wisconsin into northern Illinois and northwest Indiana.

The latest NWS STORM PREDICTION CENTER severe weather risk forecasts for the Wed/Wed night period are posted--as are a series of RPM model hourly panels which track the potential squall line from the North Woods of Wisconsin southward into the Chicago area.

Stay tuned! More to come here and on our WGN weather programs tonight (Tuesday night) and Wednesday. This is an early "head up".

[Avon]

Hmmm.....a notable eastward shift in the placement of the mcs on 0z hrrr run. Would put more of Michigan in play if it were to verify

[Stebo]

3 minutes ago, Avon said:

Hmmm.....a notable eastward shift in the placement of the mcs on 0z hrrr run. Would put more of Michigan in play if it were to verify

18z Euro/21z RAP both shifted east too big.

[Indystorm]

Yeah, Skilling repeated the derecho word on his nine p.m. weathercast as well this evening.

[StormfanaticInd]

Everything is in place for a derecho to happen. Just a question of where?

[Chinook]

06z update- upgrade to Moderate. some highlights here:

Quote

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1249 AM CDT Wed Jul 28 2021

   Valid 281200Z - 291200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM EXTREME
   EAST-CENTRAL MINNESOTA INTO SOUTHEAST WISCONSIN THIS AFTERNOON INTO
   TONIGHT...

   ...SUMMARY...
   Severe thunderstorms, capable of widespread damaging wind gusts,
   very large hail and several tornadoes, are forecast across portions
   of Minnesota and Wisconsin late this afternoon into tonight.
   Isolated strong storms also are possible across parts of the
   Mid-Atlantic and may produce locally damaging wind gusts.

Quote

 Nevertheless,
   strong vertical shear and enlarged low-level hodographs within an
   extremely unstable airmass will support supercell structures (both
   initially and embedded within developing bow echo/derecho). Very
   large hail (greater than 2 inches in diameter) will be possible
   early in convective evolution. As upscale development occurs, a
   transition toward intense, damaging wind gusts is expected, with a
   corridor of 65+ kt wind gusts possible. Tornadoes also are possible
   both early on near the triple point/warm front and once an organized
   bow develops via mesovortex processes. 

highly unstable and sheared forecast sounding in northwest Wisconsin (3km NAM) in advance of the convective line

[CheeselandSkies]

Honestly not looking like a great chase day. Central/northern WI where the chance for discrete supercells is highest is terrible terrain/trees. Of course I will keep tabs on things but the threat doesn't look to get further south until late when it'll be dark and derecho mode in full effect.

[Indystorm]

This morning convection will help to lay down boundaries which will only enhance the main show later tonight.  Gonna be an interesting period.  Shades of Aug. 10, 2020 but this time more from the nw than a west to east progression. Excellent early morning AFD from LOT.

[A-L-E-K]

a nice garden variety+ appetizer this am, hopefully tomorrow morning is a lil more rocking

good luck with the palm crusher derecho up north later

[CheeselandSkies]

"Roared and poured" for about 10 minutes starting right around 2 AM, or 15 minutes before my alarm went off (3AM work start time). I love storms but on this shift every minute of sleep is precious.

[A-L-E-K]

so that mn mcs, gonna survive and go long haul?

[CheeselandSkies]

HRRR is a whiff northeast. So is 3KM NAM, at least with the intense portion of the MCS.

[StormfanaticInd]

WOW!!! You don't see this too often. 6500 cape already!!!

[Scorpion]

Really hope we get some action here, haven’t had a good thunderstorm here since November 

[crossbowftw3]

8 minutes ago, StormfanaticInd said:

WOW!!! You don't see this too often. 6500 cape already!!!

So 7/19/19 levels of instability along with the derecho potential from last August, definitely rather eye-popping 

[hardypalmguy]

2 hours ago, CheeselandSkies said:

Honestly not looking like a great chase day. Central/northern WI where the chance for discrete supercells is highest is terrible terrain/trees. Of course I will keep tabs on things but the threat doesn't look to get further south until late when it'll be dark and derecho mode in full effect.

Leaving from just north of Milwaukee around 3:45 PM, where would you go?  I'm itching to get out.

[Scorpion]

Loving the latest NAM 3k for here. I’ll be on the beach, the pics of this rolling in from the north would be epic.

[TimB]

July 19-20, 2019 immediately popped into my mind. Similar?

[StormfanaticInd]

1 hour ago, crossbowftw3 said:

So 7/19/19 levels of instability along with the derecho potential from last August, definitely rather eye-popping 

Today has explosive potential 

[purduewx80]

Toss most of the overnight CAMs that have little to none of the ongoing WAA activity captured. Orientation of the severe threat looks more N-S oriented than the initial day 1 outlook and may end up father W given the instability axis will have trouble building east as long as the MN TS continue. 

[Malacka11]

8 minutes ago, purduewx80 said:

Toss most of the overnight CAMs that have little to none of the ongoing WAA activity captured. Orientation of the severe threat looks more N-S oriented than the initial day 1 outlook and may end up father W given the instability axis will have trouble building east as long as the MN TS continue. 

If you had to make a guess, where would be the best to chase?

[Chicago Storm]

If you had to make a guess, where would be the best to chase?

I’m not him, but you’d have to be well north in MN/WI, and terrain is terrible.


.

[Harry Perry]

Not really the matter of “if” but more of a “where and when”. One of the more dynamic systems I have seen in recent years (3 jet cores over the area at the same time not to mention up to 70kts of shear)... rather impressive. Looks like the derecho will follow the instability gradient NW to SE with a slight curve (following the warm front) into south central Michigan late tonight/early tomorrow. Anyone between Eau Claire and Kenosha needs to be vigilant this evening. Looking like a once in every 5-10 year event in the making. 
 

Also gotta watch this low pressure meander across the area late tonight too - could add a local tornado threat from Chicago east to  the SBN/KZO/GRR area. 
 

 

[purduewx80]

48 minutes ago, Malacka11 said:

If you had to make a guess, where would be the best to chase?

somewhere inland from duluth will probably have the relatively higher discreet sup potential, but north woods is def not chaser country. don't recommend chasing qlcs tornadoes at night, especially given the terrain and how fast these'll be moving.

[Scorpion]

Up into Moderate Risk now, getting that hurricane anticipation excitement 

[CheeselandSkies]

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.

[Hoosier]

Not too thrilled locally as I currently expect the brunt to remain north, but we'll see how it evolves.  At least it'll be something to watch tonight.