May 22-? Severe weather

[thewxmann]

I am just worried about dews. GFS/NAM has been worthless as of lately with respect to boundary layer moisture. RAP superior minus a slight dry bias. Seems like a narrow window across NW WI tomorrow.

I'm also a little concerned about storm mode if it's tornadoes we're talking about. It's probably the best setup this May thus far (which is not saying much), but I can't see this being 'historic' in magnitude.

[baroclinic_instability]

00 ECMWF progging a 996 hpa low tomorrow at 00z, GFS 985. Been a while since I have seen such sensitivity issues in the global guidance. Convective depiction tonite playing a major role in how models handle large scale synoptics...mainly through advection patterns and the related coupled upper jet across the northern plains.

[baroclinic_instability]

I think the worst that will happen is we won't see much. I'm not really worried about a tornado running us over or something. Jason and Mark chased the high risk in NC last yr which probably had slower motions but was a pretty complex chase. It's not necessarily what Id be looking for and maybe not worth it if it was not 'on the way' and with how this yr has gone you take what you can get... Tho I do have reasonable hope in the next week, pessimism by those who can pick and choose aside.

I think NW Kansas has potential on Sunday...Brett disagrees...Brett is prolly right.

[Hoosier]

Historic is an attention grabbing headline for sure. I'd guess this is probably in the early part of peak season for that area, so depending how it goes one might be able to get away with calling it the h word.

[tornadotony]

I'm also a little concerned about storm mode if it's tornadoes we're talking about. It's probably the best setup this May thus far (which is not saying much), but I can't see this being 'historic' in magnitude.

I could definitely see a solid number of weak tornado spinups, along with likely a few more substantial tornadoes tomorrow. With the insane shear values you're going to have, it would be a battle for a mature updraft not to intensely rotate. If I had to throw numbers out, I'd say 13-18 tornadoes tomorrow, 3-4 strong (EF2, maybe an EF3). That is my current expectation. And up there (N WI/UP of MI), that would be a pretty historic day tornado-wise.

[MnWeatherman]

Chanhassen will be busy!

[tornadotony]

I think NW Kansas has potential on Sunday...Brett disagrees...Brett is prolly right.

I would certainly think some potential. Would have to watch moisture and storm mode, given the NE-SW oriented boundary which will likely cause things to grow upscale, especially from along the state-line nwd, but tail-end might provide something nice.

[Ian]

I think NW Kansas has potential on Sunday...Brett disagrees...Brett is prolly right.

Who know how much but it has some for sure.

[baroclinic_instability]

The meat of the SPC day 1 disco...much of which has been discussed to some degree here.

..UPPER MS RIVER VALLEY...

AS HAS BEEN THE CASE WITH SOME OF THE MORE RECENT SEVERE STORM

EPISODES...LIMITED LOW LEVEL MOISTURE AND STRONG CAPPING WILL AGAIN

PLAY A ROLE IN THE EVOLUTION OF SEVERE WEATHER POTENTIAL FROM IA AND

IL NORTH ACROSS ERN WI AND MUCH OF WI TODAY. DESPITE THESE

LIMITATIONS...THERE IS CONSIDERABLE AGREEMENT AMONGST THE LATEST

GUIDANCE THAT SUBSTANTIAL SHEAR AND FORCING WILL ACCOMPANY THE

DEVELOPING LOW PRESSURE SYSTEM FROM IA NNEWD ACROSS WRN WI LATER

THIS AFTERNOON. GREATEST CONCENTRATION OF TSTMS WILL LIKELY BE ALONG

THE COOLER SIDE OF THE SURFACE BOUNDARY...AT LEAST INITIALLY...WHERE

PARCELS WILL BE FORCED TO ACHIEVE AN LFC ELEVATED ABOVE A STABLE

SURFACE LAYER. EVEN IN THIS REGIME...SOME HAIL AND EVENING

OCCASIONAL STRONGER WIND GUSTS MAY OCCUR WITH CELLS OR LINE SEGMENTS

RACING NEWD AT 40-50KT.

WARM SECTOR TO THE EAST OF THE SURFACE LOW IS LIKELY TO REMAIN

CAPPED GIVEN PLUME OF VERY WARM AIR AT MID LEVELS STREAMING NEWD

AHEAD OF THE EJECTING UPPER TROUGH. HOWEVER...OVERNIGHT RAIN AND

CONTINUED SLY FLOW SHOULD ALLOW SURFACE DEWPOINTS TO CLIMB INTO THE

LOW 60S F AS FAR WRN WI. MLCAPE COINCIDENT WITH THE DEEPENING

SURFACE LOW MAY REACH INTO THE 500-1000 J PER KG RANGE AND...GIVEN

MAGNITUDE OF FORCED ASCENT ACCOMPANYING THE INTENSIFYING LOW

PRESSURE /DEEPENING AROUND 1MB/HR BETWEEN 18 AND 21Z PER LATEST

PROGS/...EXPECT POTENTIALLY DANGEROUS AND FAST-MOVING STORMS TO

DEVELOP. THE WINDOW OF OPPORTUNITY FOR THIS DEVELOPMENT WILL BE

RATHER SMALL...FROM ABOUT 19-23Z AND OVER A RELATIVELY CONFINED

REGION FROM EXTREME ERN MN INTO WRN/NWRN WI. FORECAST CONDITIONS IN

THIS TIME AND AREA APPEAR SUPPORTIVE OF A COUPLE OF POSSIBLY STRONG

TORNADOES AND/OR FAST-MOVING LINE SEGMENTS CAPABLE OF DAMAGING

WINDS. SHEAR AND INSTABILITY VALUES NEAR THE LOW SUPPORT THE CURRENT

CORRIDOR OF HIGH TORNADO PROBABILITIES AND AN UPGRADE TO GREATER

PROBABILITIES/CONFIDENCE IS POSSIBLE WITH THE LIGHT OF DAY AND A

CLOSE INSPECTION OF OVERNIGHT STORM-SCALE GUIDANCE.

ADDITIONAL SURFACE-BASED STORM DEVELOPMENT IN THE FORM OF LINES OR

BOWS MAY OCCUR THROUGH THE LATE AFTERNOON ALONG THE ADVANCING COLD

FRONT. MAGNITUDE OF MID LEVEL FLOW DIRECTED INTO THE DEVELOPING

CONVECTION SUGGESTS THAT THESE STORMS MAY POSE A THREAT OF DAMAGING

WINDS AS THEY MOVE EAST FROM NERN IA INTO SRN WI AND PORTIONS OF NRN

IL.

[baroclinic_instability]

I could definitely see a solid number of weak tornado spinups, along with likely a few more substantial tornadoes tomorrow. With the insane shear values you're going to have, it would be a battle for a mature updraft not to intensely rotate. If I had to throw numbers out, I'd say 13-18 tornadoes tomorrow, 3-4 strong (EF2, maybe an EF3). That is my current expectation. And up there (N WI/UP of MI), that would be a pretty historic day tornado-wise.

In that case, I can see the historic wording being tossed around.

Given the deeper layer moisture return, I can see NW WI tomorrow...but worried about cloud cover and ongoing DMC ruining afternoon insolation. That said, should insolation occur...dews there will not mix out like they have as of late given progged low level flow/moisture streaming over NW WI.

[brettjrob]

I think NW Kansas has potential on Sunday...Brett disagrees...Brett is prolly right.

No, there's certainly potential... hard to rule anything out from this range, after all.

I'll freely admit to becoming disillusioned as we've watched peak season for OK/KS come and go nearly empty-handed, and it's affecting my judgment. In that sense, Ian is more than justified in taking a different perspective on this upcoming string of days than mine. After somewhere in the neighborhood of a dozen busts for me so far this year, my hopes for this trough to somehow "redeem" everything were hardly realistic. There are years to envy those of us chasing based out of the Alley year-round... and this is not one of them. I'd much rather be going into the next couple weeks with a clean slate, instead of utterly drained, burned out, and hesitant to gamble on anything shaky...

FWIW, 00z ECMWF popping a 997 mb secondary low in W KS for Sunday's setup with a 40+ kt southerly LLJ. Really looks more solid than I gave it credit for earlier... think I was too wrapped up in disgust over Saturday's hopes circling the drain. Should probably just pink-tag me until the next overperforming event snaps me into shape.

[Ian]

No, there's certainly potential... hard to rule anything out from this range, after all.

I'll freely admit to becoming disillusioned as we've watched peak season for OK/KS come and go nearly empty-handed, and it's affecting my judgment. In that sense, Ian is more than justified in taking a different perspective on this upcoming string of days than mine. After somewhere in the neighborhood of a dozen busts for me so far this year, my hopes for this trough to somehow "redeem" everything were hardly realistic. There are years to envy those of us chasing based out of the Alley year-round... and this is not one of them. I'd much rather be going into the next couple weeks with a clean slate, instead of utterly drained, burned out, and hesitant to gamble on anything shaky...

FWIW, 00z ECMWF popping a 997 mb secondary low in W KS for Sunday's setup with a 40+ kt southerly LLJ. Really looks more solid than I gave it credit for earlier... think I was too wrapped up in disgust over Saturday's hopes circling the drain. Should probably just pink-tag me until the next overperforming event snaps me into shape.

Trust me, I'd rather see you be bullish. However, I think the series of troughs -- including the one after the weekend one should keep us moving at least through much of the first 7-10 days. It's not necessarily a dream pattern by any stretch but as you know by this time of year it's much easier to squeeze all of the potential out of something even if it only means a few tornadoes. I'm pretty flabbergasted with the continual east coast troughing that's been screwing with moisture return myself. But... gotta hope for the best since we pulled the trigger to come out. Not to mention we are able to be much more mobile than those who have other things in life over the coming period.

[tornadotony]

One thing important to note is that tomorrow's overall synoptic setup is a classic, with the strong embedded shortwave and the deepening sfc low. Sometimes we tend to overthink severe wx forecasting (myself included) by focusing too much on specifics (how much 0-1km SRH is progged or CAPE) and fail to step back and analyze an overall synoptic setup. It works both ways. For instance, I went back and did an exercise where I forecasted for a few select setups to compare to verification. One of the setups I was given was 4/15 of this year, the moderate risk bust in IA/MN. All I had to work with was 12z observed data and I was able to identify it as a likely bust case, even though I wasn't totally aware of what day it was until a few hours of looking it over. The day-of, however, I was all gung-ho about a wind damage and tornado threat.

Same goes for tomorrow, IMO, but in reverse. This is a very classic pattern for significant severe wx, and more often than not, with a pattern this classic, something has to give. The pattern makes it easier for the smaller-scale pieces to fall into place. Moisture will likely be a bit of a limiting factor, but with the deepening low and insane wind fields that will accompany it, moisture should be sufficient for some significant severe wx. With the deepening low, strengthening front, and associated frotogenetic forcing, you're gonna get DMC tomorrow. And with the shear that will be in place, cells are going to have the proclivity to rotate.

[tornadotony]

In that case, I can see the historic wording being tossed around.

Given the deeper layer moisture return, I can see NW WI tomorrow...but worried about cloud cover and ongoing DMC ruining afternoon insolation. That said, should insolation occur...dews there will not mix out like they have as of late given progged low level flow/moisture streaming over NW WI.

It's a fine line, but I'd almost rather see limited insolation tomorrow for a better tornado threat, given the moisture profiles. Stuff is going to spin in that environment pretty much no matter what.

[baroclinic_instability]

One thing important to note is that tomorrow's overall synoptic setup is a classic, with the strong embedded shortwave and the deepening sfc low. Sometimes we tend to overthink severe wx forecasting (myself included) by focusing too much on specifics (how much 0-1km SRH is progged or CAPE) and fail to step back and analyze an overall synoptic setup. It works both ways. For instance, I went back and did an exercise where I forecasted for a few select setups to compare to verification. One of the setups I was given was 4/15 of this year, the moderate risk bust in IA/MN. All I had to work with was 12z observed data and I was able to identify it as a likely bust case, even though I wasn't totally aware of what day it was until a few hours of looking it over. The day-of, however, I was all gung-ho about a wind damage and tornado threat.

Same goes for tomorrow, IMO, but in reverse. This is a very classic pattern for significant severe wx, and more often than not, with a pattern this classic, something has to give. The pattern makes it easier for the smaller-scale pieces to fall into place. Moisture will likely be a bit of a limiting factor, but with the deepening low and insane wind fields that will accompany it, moisture should be sufficient for some significant severe wx. With the deepening low, strengthening front, and associated frotogenetic forcing, you're gonna get DMC tomorrow. And with the shear that will be in place, cells are going to have the proclivity to rotate.

I hate comparing...but this has some MINOR similarities to March 2nd with respect to the way this system is progged to rapidly deepen (through 24 hrs), the track, the somewhat subcompact surface low, and the low level wind fields. Hence why I brought up the rather disparate differences between ECMWF/GFS with respect to deepening and the associated wind fields. Going to be an interesting day should everything come together.

I know NW WI is not Brettjrob territory....but would love to hear what he thinks.

[Ian]

One thing important to note is that tomorrow's overall synoptic setup is a classic, with the strong embedded shortwave and the deepening sfc low. Sometimes we tend to overthink severe wx forecasting (myself included) by focusing too much on specifics (how much 0-1km SRH is progged or CAPE) and fail to step back and analyze an overall synoptic setup. It works both ways. For instance, I went back and did an exercise where I forecasted for a few select setups to compare to verification. One of the setups I was given was 4/15 of this year, the moderate risk bust in IA/MN. All I had to work with was 12z observed data and I was able to identify it as a likely bust case, even though I wasn't totally aware of what day it was until a few hours of looking it over. The day-of, however, I was all gung-ho about a wind damage and tornado threat.

Same goes for tomorrow, IMO, but in reverse. This is a very classic pattern for significant severe wx, and more often than not, with a pattern this classic, something has to give. The pattern makes it easier for the smaller-scale pieces to fall into place. Moisture will likely be a bit of a limiting factor, but with the deepening low and insane wind fields that will accompany it, moisture should be sufficient for some significant severe wx. With the deepening low, strengthening front, and associated frotogenetic forcing, you're gonna get DMC tomorrow. And with the shear that will be in place, cells are going to have the proclivity to rotate.

I agree with this. I'm much more of a pattern recognition forecaster than the specifics. This one has looked pretty solid off and on for a while with how it sets up.

[tornadotony]

I agree with this. I'm much more of a pattern recognition forecaster than the specifics. This one has looked pretty solid off and on for a while with how it sets up.

The more I look at it, the more impressed I am. The forcing is most certainly going to be there, between strong dCVA, frontogenetic forcing, and a coupled jet structure. Convection is gonna happen. And with the insane progged hodos, it's gonna spin. All you need is enough low-level instability to stretch the vorticity to the sfc and boom you have tornadoes. And I think we'll have that tomorrow.

[Ian]

DMC is deep moisture convergence?

[baroclinic_instability]

Deep Moist Convection. I will admit I am not sure who coined it, but CD3 (Chuck Doswell) made it popular back in the day (at least I think). I am sure someone can correct me on the details there.

[tornadotony]

DMC is deep moisture convergence?

Deep moist convection.

Oh, and 200J/kg 0-3km CAPE will do the trick...

[andyhb]

Deep moist convection I believe, and that is a great and descriptive Day 1 from the SPC, btw...

[Ian]

Deep moist convection.

Oh, and 200J/kg 0-3km CAPE will do the trick...

thx. one thing seems a sure bet is that we will need to place ourselves extremely well to have a chance. we were going to hit madison and go from there but now thinking eau claire and going from there.. guess we'll figure it out as the sun rises.

[andyhb]

Deep moist convection.

Oh, and 200J/kg 0-3km CAPE will do the trick...

That sent my alarm bell ringing...

[tornadotony]

Part of me wonders, and I'm posting this in near-stream-of-consciousness, if, with all the parameters really coming together right near the sfc low tomorrow, if we're not gonna see some sort of "sweet-spot" scenario, where you get a very long-tracked tornado near/just SE of the sfc low with a long-lived, steady-state supercell (AR 2008, you can fill in the other blank). NSSL-WRF almost has something like this depicted in updraft helicity.

[andyhb]

Well, with the 60-70+ kt H85 jet shown on the GFS/NAM, any storm in that vicinity would certainly have access to some incredible low level wind profiles and would be right in that zone of high 0-3 km CAPE.

[mnchaser]

I'm not too sure on this one! Anything east of the Mississippi is forbidden territory "IF" this pans out with these storm motions and the cluster of chasers I've been seeing lately it could be a very dangerous situation

[thewxmann]

One thing important to note is that tomorrow's overall synoptic setup is a classic, with the strong embedded shortwave and the deepening sfc low. Sometimes we tend to overthink severe wx forecasting (myself included) by focusing too much on specifics (how much 0-1km SRH is progged or CAPE) and fail to step back and analyze an overall synoptic setup. It works both ways. For instance, I went back and did an exercise where I forecasted for a few select setups to compare to verification. One of the setups I was given was 4/15 of this year, the moderate risk bust in IA/MN. All I had to work with was 12z observed data and I was able to identify it as a likely bust case, even though I wasn't totally aware of what day it was until a few hours of looking it over. The day-of, however, I was all gung-ho about a wind damage and tornado threat.

Same goes for tomorrow, IMO, but in reverse. This is a very classic pattern for significant severe wx, and more often than not, with a pattern this classic, something has to give. The pattern makes it easier for the smaller-scale pieces to fall into place. Moisture will likely be a bit of a limiting factor, but with the deepening low and insane wind fields that will accompany it, moisture should be sufficient for some significant severe wx. With the deepening low, strengthening front, and associated frotogenetic forcing, you're gonna get DMC tomorrow. And with the shear that will be in place, cells are going to have the proclivity to rotate.

As much as I post about details WRT failure modes, I have to say I agree with the bolded part, which in fact led me to believe the Leap Day event was going to be more significant than the consensus forecast. Sometimes the synoptics override details, which we (by that, myself included) often forget.

But I am completely stumped about tomorrow. I just dont think there is enough turning between H5-H85 to call this "classic". And I'm guessing Timmer's "historic" doesn't mean "historic by nrn WI standards".

[Ian]

East of the dewpoint tongue it feels like fall.

[Chris G]

Hi all... been a long time since I posted. A few of my meteorology friends will be chasing in WI...who else will be there?

[jpeters3]

Hi all... been a long time since I posted. A few of my meteorology friends will be chasing in WI...who else will be there?

I'll be chasing with a group of people. We are in Sioux City, IA (from last night's chase) right now, probably leaving and driving toward somewhere in NW WI (to be decided, will probably drive up 29 to 90 and then east on 90).