ASTORP is pretty bullish for 21z-00z tonight. Stormnet is also showing a 20% chance in the same area for the same timeframe
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Severe Weather Thread - 7/18 - 7/21/2026
- Thread starter WeathermanLeprechaun
- Start date
jiharris0220
Member
This is similar to the June 17 set up synoptically, instead this time around, far more thermodynamically favorable with the sacrifice of extreme shear, but still plenty enough, and the leading MCS will be out of the area of initiation for a grand total of 7 hours.
By the time the cold front (which is extremely diffuse, combined with orthogonal jet streak orientation over the PBL winds, guarantees a discrete storm mode) convects, the parameter space will be completely untapped.
By the time the cold front (which is extremely diffuse, combined with orthogonal jet streak orientation over the PBL winds, guarantees a discrete storm mode) convects, the parameter space will be completely untapped.
- Thread starter
- #63
WeathermanLeprechaun
Member
I have questions about low level stability and etc, but a intense tornado isn't completely ruled out today. Strong vertical instability aloft may compensate for this. Extremely interesting day coming up.
jiharris0220
Member
Low level stability will be non existent today.
Honestly the only failure mode I see are storm motion vectors. Supercells need to deviate hard right wind when your PBL winds are southwest to northeast orientated to fully take in streamwise vorticity.
If they stay on an east south east trajectory instead of straight southeast, especially since storm motions will be up to 30-40+knots, and the LLJ speed will be 30-40+knots too (coming from west to east), then expect to see an outflow dominated congo line. The relatively dry mid levels also exacerbates this issue as well.
- Thread starter
- #65
WeathermanLeprechaun
Member
Understandable but this sounding seems to reveal some remnant stability of sorts, from SW WI in the vicinity of one of your supercells. SE storm mode is finicky, but i think it can work out. I'm paying lots of attention to how cells orient themselves in the warm sector with these type of decent ceiling events, and i think this is one of those events where it'll manage given your comments regarding the orthogonal jet streak over PBL winds and etc which is found to have produced some of your more potent events. I'm still questioning low level thermodynamics, but shear in this sounding can absolutely compensate for those lower levels.
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jiharris0220
Member
That vertical profile is actually exactly what you want in terms of thermos.
Thanks to the left over MCS cold pool, over mixing would’ve been a likely death sentence to any sort of tornadogenesis potential. The LLLR take a hit but is astronomically a better solution (for tornado potential) than what could’ve been a 20+ degree dew point spread.
But even with that, as you see with that vertical profile, from the surface to the mid levels, the air is quite dry, and it’s being strongly advected from the west, that could keep updrafts anemic, especially with how diffuse the cold front is. At the same time, it’s those reasons as to why the storm mode will be discrete, so a double edged sword there.
I suspect that the strong forcing mechanism will easily sustain strong updrafts, as every cam models suggests this.
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- Thread starter
- #67
WeathermanLeprechaun
Member
Yeah that's a good point. You don't want overmixing but I would rather prefer a more steady low level profile if that makes sense. Moisture quality and spreads are fine but how we distribute those low levels is a bit finicky. We'll see. Double edged sword is a good way to put it. It could help or it could ruin. I am aware that I picked a slightly contaminated sounding but it's better than cherrypicking STP like most do. Let me see if I can find a sounding that has a different vertical profile of sorts.
Editing this because I don't want to spam you up with replies, but i appreciate the insight on these soundings. I found this one and it's a lot different. Not as dry but moreso has a subtle surface inversion and a warm nose there around 850/700.
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Kds86z
Member
Kds86z
Member
New day 1:
ALSO BE SUBSTANTIAL, WHICH COMBINED WITH THE MOIST
BOUNDARY LAYER, STEEP LAPSE RATES AND LARGE BUOYANCY WILL SUPPORT
THE POTENTIAL FOR A FEW STRONG-INTENSE TORNADOES. VERY LARGE HAIL
WILL BE POSSIBLE WITH THE MORE DISCRETE SUPERCELLS, WHILE
SIGNIFICANT SEVERE OUTFLOW GUSTS WILL BE POSSIBLE WITH ANY
CLUSTERING OF STORMS LATER THIS AFTERNOON/EVENING.
ALSO BE SUBSTANTIAL, WHICH COMBINED WITH THE MOIST
BOUNDARY LAYER, STEEP LAPSE RATES AND LARGE BUOYANCY WILL SUPPORT
THE POTENTIAL FOR A FEW STRONG-INTENSE TORNADOES. VERY LARGE HAIL
WILL BE POSSIBLE WITH THE MORE DISCRETE SUPERCELLS, WHILE
SIGNIFICANT SEVERE OUTFLOW GUSTS WILL BE POSSIBLE WITH ANY
CLUSTERING OF STORMS LATER THIS AFTERNOON/EVENING.
- Thread starter
- #70
WeathermanLeprechaun
Member
SPC upgraded to 10 hatch via IEMbot
Storm Prediction Center Jul 20, 2026 1630 UTC Day 1 Convective Outlook
Severe weather, tornado, thunderstorm, fire weather, storm report, tornado watch, severe thunderstorm watch, mesoscale discussion, convective outlook products from the Storm Prediction Center.
www.spc.noaa.gov
Kds86z
Member
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- Thread starter
- #73
WeathermanLeprechaun
Member
I have stronger confidence in a intense tornado ie two due to this video by meteorologist Chris Jakob which finds that when 200mb flow is orthogonal to your main initiating boundary between 210-270 degrees like today has, outbreaks tend to perform better. Wanna watch this video? IMHO, this is more groundbreaking than the OMEGA project. This is something to consider in the future with events. This is a extremely brilliant discussion.
Touches on 5/20/19 and 3/15/25 as underperforming cases
Touches on 5/20/19 and 3/15/25 as underperforming cases
CheeselandSkies
Member
That's interesting. I tend to overlook 200mb flow when forecasting; focusing on 500mb and below as important to tornadoes. I suspect I'm not alone in that. I will have to reconsider that approach.
- Thread starter
- #75
WeathermanLeprechaun
Member
I didn't mean to call 3/15 a underperformance, first correction there on my comment. Moreso i think that in cases where your flow is not orthogonal and parallel, you rely on confluence bands instead of your main initiating boundary. Case in hand, 3/15/25. Didn't verify on the main initiating boundaries and needed confluence bands to get your tornado threat going. I trying to find a email for Chris because I want to contact him regarding the 5/6/24 200mb. It doesn't feature a 100+ kt 200mb jet and has 70+ kt flow, albeit orthogonal but it is also parallel as it centers off into C OK/S KS. I wonder if flow being orthogonal initially helped the discrete mode but as this parallel feature of sorts became prominent towards 00z, storms clustered significantly. Or simply, weaker 200mb flow couldn't verify a significant event. I might contact our other Chris about this too.
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Timbo64
Member
I'm pretty busy and I haven't had much time to look, so can anyone tell me how this storm system is going to look later on this afternoon and evening in the Oshkosh, Wisconsin area?
EAA's AirVenture 2026 officially started today at Wittman Regional Airport.
This screen-capture shows only a small portion of the total aircraft on the field and more keep flying in.
At peak times, there can be several thousand aircraft parked on the field.
I wish I was there!
This is a link to all of the EAA's AirVenture 2026 live streams.
EAA's AirVenture 2026 officially started today at Wittman Regional Airport.
This screen-capture shows only a small portion of the total aircraft on the field and more keep flying in.
At peak times, there can be several thousand aircraft parked on the field.
I wish I was there!
This is a link to all of the EAA's AirVenture 2026 live streams.
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KakashiHatake2000
Member
New MD with 95% tor watch probs:
Areas affected...Northeast Iowa into northwest/north-central
Wisconsin
Concerning...Severe potential...Tornado Watch likely
Valid 201853Z - 202100Z
Probability of Watch Issuance...95 percent
SUMMARY...All severe hazards, including some significant, are
possible as supercells develop by late afternoon. Timing and
location of initiation are the main uncertainties. A tornado watch
is likely.
DISCUSSION...A very moist airmass is evident ahead of a cold front
in the Upper Mississippi Valley. A capping inversion was present on
the 12Z MPX observed sounding. Cumulus along the front have yet to
become vertically developed as a result. Mid-level convection has
been ongoing in southern Minnesota. This activity is now moving into
modifying outflow from an earlier MCS in the La Crosse/Davenport
vicinity. Lift from a shortwave trough in northern Minnesota will
continue to overspread the area this afternoon. With time, continued
heating and moistening ahead of the cold front and near the outflow
front intersection should allow storms to develop, most likely by
late afternoon. Given strong shear (50-60 kt effective) across the
cold front, supercell structures will be favored. Steep mid-level
lapse rates will support the threat for large to very-large hail. A
tornado threat, some possibly strong, will also be present with
supercells. Severe winds will also be possible. Wind gusts of 75+
mph are possible, particularly where activity grows upscale. The
exact timing/location of storm initiation is not clear though a
tornado watch is likely.
..Wendt/Thompson.. 07/20/2026
Areas affected...Northeast Iowa into northwest/north-central
Wisconsin
Concerning...Severe potential...Tornado Watch likely
Valid 201853Z - 202100Z
Probability of Watch Issuance...95 percent
SUMMARY...All severe hazards, including some significant, are
possible as supercells develop by late afternoon. Timing and
location of initiation are the main uncertainties. A tornado watch
is likely.
DISCUSSION...A very moist airmass is evident ahead of a cold front
in the Upper Mississippi Valley. A capping inversion was present on
the 12Z MPX observed sounding. Cumulus along the front have yet to
become vertically developed as a result. Mid-level convection has
been ongoing in southern Minnesota. This activity is now moving into
modifying outflow from an earlier MCS in the La Crosse/Davenport
vicinity. Lift from a shortwave trough in northern Minnesota will
continue to overspread the area this afternoon. With time, continued
heating and moistening ahead of the cold front and near the outflow
front intersection should allow storms to develop, most likely by
late afternoon. Given strong shear (50-60 kt effective) across the
cold front, supercell structures will be favored. Steep mid-level
lapse rates will support the threat for large to very-large hail. A
tornado threat, some possibly strong, will also be present with
supercells. Severe winds will also be possible. Wind gusts of 75+
mph are possible, particularly where activity grows upscale. The
exact timing/location of storm initiation is not clear though a
tornado watch is likely.
..Wendt/Thompson.. 07/20/2026
Conditions are already favorable for these storms in Northern Iowa to produce tornadoes. There's still a moderate cap in place though, so it'll be interesting to see if they can maintain or grow.