Severe Weather 4-4-23 and 4-5-23

[Malacka11]

1 minute ago, brianc33710 said:

The SPC didn't mention the possible inhibiting factors they mentioned in previous update. That concerns me. 

Concerns you as in "??" or as in "oh shoot, this might actually be a substantial threat after all"?

[brianc33710]

2 minutes ago, Malacka11 said:

Concerns you as in "??" or as in "oh shoot, this might actually be a substantial threat after all"?

Concerns me that the potential for a more extensive & violent outbreak has returned. I apologize for not making that more clear. 

[Malacka11]

1 minute ago, brianc33710 said:

Concerns me that the potential for a more extensive & violent outbreak has returned. I apologize for not making that more clear. 

I see. You're all good, I figured that's what you meant but feared that I might be jumping the gun due to my own eagerness to chase. Cheers

[hlcater]

Too lazy to repost the pics so enjoy the tweet

[Kaner88]

Really enjoyed LOT's morning AFD, gets into some of the juicy modeling stuff:

 

Quote

Main focus then turns to the potential for severe weather mainly late Tuesday afternoon and evening. As we`ve been noting, this setup appears to be much more "conditional" than last Friday`s for a number of reasons. First is that large scale forcing will be more subtle/weaker as the parent 500 mb low is currently forecast to be well west across western/central Nebraska and South Dakota by early Tuesday evening. Second is that capping will be playing more of a central role as an expansive EML plume characterized by extremely steep mid-level lapse rates and attendant warm nose around 800 mb will likely result in considerably MLCIN through much of the afternoon hours. Whether or not the aforementioned subtle large scale forcing is able to overcome this is one of the main questions yet to be answered and will mean the difference between few to no storms in the local area versus a potential significant severe episode in the region.

 

From a conceptual standpoint, the surface warm front will make slow, but gradual northward progress through the region on Tuesday as more notable pressure falls develop across Wisconsin and Iowa. Seems like the front`s forward progress will probably get held up a bit by the cool lake with it having a harder time making progress north of the Wisconsin state line during the evening. Wide open Gulf trajectories will allow an expansive region of 60s dewpoints to surge northward although forecast soundings continue to indicate the moist layer will be somewhat shallow. Still, seeing signs of higher dewpoints pooling near the warm front, possibly in response to mixing into higher mixing-ratio air just off the surface (with this in mind drizzle and pockets of fog appear possible Tuesday morning and even into the afternoon north of the front). Even the WRF-ARW which utilizes a more aggressive PBL scheme and tends to readily "mix-out" shallow moist layers holds onto low 60s dewpoints up to the I-88 corridor.

 

The big question here is whether the base of the relatively warm EML plume can be lifted and cooled sufficiently by only very modest large scale forcing for ascent with neutral or even positive mid-level height tendencies noted over us in a narrow window during the late-afternoon and early-evening. The ECMWF and GFS both have been consistently saying "yes" to this question as the nose of a 60-70 kt 500 mb jet max pushes across central Illinois during the afternoon hours, but it`s easy to find other guidance which says "no", leaving too much convective inhibition in place for thunderstorm initiation. That said, am somewhat concerned by potential trends noted in hires guidance which seem to be headed more towards the ECMWF/GFS camp in eroding the capping layer just enough to result in explosive thunderstorm development somewhere across eastern Iowa/northeast Missouri/west-central Illinois, and seems like more than half of the EPS members do so as well based on a cursory glance.

 

IF convection develops, it would have access to an highly volatile cocktail of high instability and truly eye-popping kinematic parameters with large, sweeping/looping hodographs driving very high effective SRH and, importantly, significant low-level storm-relative inflows. While a cap bust scenario is still on the table (one where inhibition remains too high and storms struggle to develop or don`t develop at all), it`s hard (and probably foolish) to ignore the consistency of the ECMWF, GFS, and now recent runs of the extended HRRR. Corridor of most focused severe weather potential would seem to be setting across roughly the northwest half of the CWA late Tuesday afternoon into the mid-late evening with all modes of severe weather possible, but contingent on robust convective development materializing in the first place. Given the presence of at least some capping, it`s also possible that only a few storms develop or become severe, but any of these would have the potential to drop sig tors given the parameter space. It`s also conceivable that initial severe thunderstorms start to weaken a bit during the evening as CIN increases with the loss of daytime heating and as they get close to or cross the warm front. We`ll highlight these two scenarios in our graphical messaging today to try to better explain the vast chasm that exists between outcomes.

 

[Malacka11]

8 minutes ago, Kaner88 said:

Really enjoyed LOT's morning AFD, gets into some of the juicy modeling stuff:

 

 

The previous/current severe episodes have prompted me to read the discussions of other offices a little more often and LOT is quite literally on another level. It's just so obvious that they simply hold themselves to a higher standard witht their discussions. They are far more descriptive and easier to understand for a beginner while also being more informative and in-depth overall. 

[sbnwx85]

IWX discussion is solid. I found the bolded section especially interesting.

.SHORT TERM...(This Evening through Tuesday)
Issued at 313 PM EDT Mon Apr 3 2023

The forcing mechanism for rain chances these next 12 hours or so is 
a little murky. As of this writing, a stationary front is bisecting 
the area SW to NE, evident mainly in difference between temperature 
and dew points over the area. Very little to speak of for surface 
wind. Isentropic ascent on the 295K surface seems to line up ok with 
current radar returns hugging the MI-IN line and IL-WI line. Rain 
shower coverage is expected to increase through the evening and 
overnight as lift along this isentropic surface amplifies. 
Additionally, a secondary baroclinic zone at 850-mb lifts in 
overnight. Lapse rates near 7.5C/km offer a slight chance of thunder 
as the previous forecaster stated, so, no change to that piece of 
the forecast.  

Rain chances on Tuesday are expected to decline after sunrise as the 
previously described forcing mechanisms continue to lift north. 
Forcing is generally absent through the daytime hours on Tuesday, 
thus making shower and storm chances uncertain. Therefore, the SPC 
outlook for Tuesday seems to be nocturnal. After sunset, the 850-mb 
jet intensifies according to the NAM and HREF and we're in the right 
exit region which is not ideal for thunderstorm development. Dew 
points will swell to near 60 degrees late Tuesday, indicative of 
ample moisture. MUCAPE and shear will be ample as well. composite 
reflectivity on a suite of CAMs show some discrete supercells 
possible overnight, while others are quiet. I have asked for a 
downgrade to a marginal risk for this uncertainty but was declined 
with no further details. So, we'll continue to message a 
lesser/uncertain threat Tuesday night while focusing more on 
Wednesday.

&&

.LONG TERM...(Tuesday Night through Monday)
Issued at 313 PM EDT Mon Apr 3 2023

The risk of severe weather seems more likely on Wednesday as a 110kt 
500-mb jet moves over Illinois and into Michigan. We'll be in the 
right entrance region late in the day, offering favorable upper-
level support for storms. Forecast soundings show plenty of CAPE and 
shear, and once again a risk for tornadoes via strong SRH (looping 
hodographs). Storm mode is a little murky in the CAMs, with some 
showing discrete storms ahead of the cold front. Others confine the 
severe risk to just the cold front. I'd estimate the severe weather 
risk to begin midday if the discrete storms are able to materialize. 
The cold front looks to sweep from west to east and exit the 
forecast area soon after sunset Wednesday. 

A much welcome break from active weather arrives thereafter with 
high pressure taking shape through at least Saturday. The next upper-
level low moves through the region early next week with significant 
disagreement in guidance at this distance. this low could bring 
cooler and rainy conditions.

[Malacka11]

Still dunno what to think for tomorrow. DVN and the SPC are both fairly optimistic that shit's gonna go down but the fact that we still don't really know when convection might actually occur -combined with the fact that fast storm motions may result in trash chasing conditions- makes me question whether it's worth driving around for half a day straight. Normally I don't really make a decision either way until the morning of an event but I'm supposed to take a couple of friends along and it would be nice to have a plan for them. 

[largetornado]

After looking at 18z, HRRR would have me chasing wednesday. If i went off the nam suite, i would not chase at all but its apparently been having problems this year. At this point, any storms that can become surface based will have a top tier environment to work with. I wish the SPC had a outlook that conveyed spatial coverage as well as potential intensity. Tomorrow would be a slight risk for storm coverage and a moderate risk for intensity IMO. 

[Chicago Storm]

1 minute ago, largetornado said:

After looking at 18z, HRRR would have me chasing wednesday. If i went off the nam suite, i would not chase at all but its apparently been having problems this year. At this point, any storms that can become surface based will have a top tier environment to work with. I wish the SPC had a outlook that conveyed spatial coverage as well as potential intensity. Tomorrow would be a slight risk for storm coverage and a moderate risk for intensity IMO. 

They do. Risk level is coverage based and hatching is for significance. 

Their system is still quite flawed, though.

[sbnwx85]

A rare Day 3 update from SPC: 

Day 3 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0302 PM CDT Mon Apr 03 2023

   Valid 051200Z - 061200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEDNESDAY FROM THE
   GREAT LAKES REGION AND OHIO VALLEY SOUTHWESTWARD INTO THE LOWER
   MISSISSIPPI VALLEY...

   AMENDED FOR SLOWING UPPER TROUGH, WESTWARD EXPANSION OF SEVERE
   THREAT

   ...SUMMARY...
   Severe thunderstorms are possible over a large area from the Great
   Lakes region southwestward to the Lower Mississippi Valley
   Wednesday. This may include cells capable of producing tornadoes and
   extensive wind damage, primarily north of the Ohio River, with other
   severe storms expected into the lower Mississippi Valley.

   This amendment is primary due to the slowing upper trough, and the
   westward expansion of severe probabilities. Severe storms may be
   ongoing as far west as the St. Louis area at 12Z Wednesday, with
   favorable conditions remaining for tornadoes and damaging winds
   expending mainly northeastward. Farther south, lower 70s F dewpoints
   and heating ahead of a cold front is expected to support scattered
   storms during the day into the lower MS Valley, where mainly hail
   and damaging gusts will be possible. This westward demarcation of
   the severe threat will likely be adjusted further incoming updates.

[CheeselandSkies]

7 minutes ago, Chicago Storm said:

They do. Risk level is coverage based and hatching is for significance. 

Their system is still quite flawed, though.

I think the main things that's' not always conveyed is that oftentimes the sparser the storm coverage, the more dangerous the hazards can be from any one storm. Meteorologists & chasers know it, but EMs and the general public usually do not.

[CheeselandSkies]

With the Day 3 update I'm wondering now if Tuesday's initiation (if any) will be too far west for me to chase, even though it should be quite a bit later than last Friday's.

Not really keen on a west of I-35 target after working 3AM-noon. Was one of the things that made Friday a no-brainer go for me.

[largetornado]

6 minutes ago, CheeselandSkies said:

I think the main things that's' not always conveyed is that oftentimes the sparser the storm coverage, the more dangerous the hazards can be from any one storm. Meteorologists & chasers know it, but EMs and the general public usually do not.

Bingo. What makes sense to us can and often times confuses the general public. IE, watch vs warnings. 

[DLMKA]

1 hour ago, Malacka11 said:

The previous/current severe episodes have prompted me to read the discussions of other offices a little more often and LOT is quite literally on another level. It's just so obvious that they simply hold themselves to a higher standard witht their discussions. They are far more descriptive and easier to understand for a beginner while also being more informative and in-depth overall. 

Agree 100%. I enjoy the LOT AFD and learn quite a lot.

[Malacka11]

26 minutes ago, CheeselandSkies said:

Not really keen on a west of I-35 target after working 3AM-noon. Was one of the things that made Friday a no-brainer go for me.

I thought roughly the same area is in play tomorrow? 

[DLMKA]

If anyone wants a co-pilot to chase tomorrow I’d love to ride along. I live just southeast of Galesburg and can meet up wherever. I feel like I’m pretty confident with navigating and understanding where we need to be in relation to a storm and storm tracks. PM me if you’re interested.

[brianc33710]

1 hour ago, sbnwx85 said:

A rare Day 3 update from SPC: 

Day 3 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0302 PM CDT Mon Apr 03 2023

   Valid 051200Z - 061200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEDNESDAY FROM THE
   GREAT LAKES REGION AND OHIO VALLEY SOUTHWESTWARD INTO THE LOWER
   MISSISSIPPI VALLEY...

   AMENDED FOR SLOWING UPPER TROUGH, WESTWARD EXPANSION OF SEVERE
   THREAT

   ...SUMMARY...
   Severe thunderstorms are possible over a large area from the Great
   Lakes region southwestward to the Lower Mississippi Valley
   Wednesday. This may include cells capable of producing tornadoes and
   extensive wind damage, primarily north of the Ohio River, with other
   severe storms expected into the lower Mississippi Valley.

   This amendment is primary due to the slowing upper trough, and the
   westward expansion of severe probabilities. Severe storms may be
   ongoing as far west as the St. Louis area at 12Z Wednesday, with
   favorable conditions remaining for tornadoes and damaging winds
   expending mainly northeastward. Farther south, lower 70s F dewpoints
   and heating ahead of a cold front is expected to support scattered
   storms during the day into the lower MS Valley, where mainly hail
   and damaging gusts will be possible. This westward demarcation of
   the severe threat will likely be adjusted further incoming updates.

The tiniest possible corner of NW AL is in the 2/5 now. Literally, if there's a house on the AL/MS/TN front yard is Slight & the house & back yard are Marginal lol.

[madwx]

1 hour ago, CheeselandSkies said:

With the Day 3 update I'm wondering now if Tuesday's initiation (if any) will be too far west for me to chase, even though it should be quite a bit later than last Friday's.

Not really keen on a west of I-35 target after working 3AM-noon. Was one of the things that made Friday a no-brainer go for me.

Go to RFD and hope for some warm front magic.  Then get up Wednesday morning at home and watch the QLCS roll in

[Malacka11]

FWIW, the RRFS A is up and running again. its 12z run had what discrete cells do fire in Central IA rather than closer to the border. 

[Indystorm]

Am certainly aware of capping EML issues for Tuesday but ever since the Utica IL F3 on April 20, 2004 I am always very leery of warm fronts in the spring, particularly when other parameters are looking like a loaded gun.

[andyhb]

Re: mixing tomorrow and resultant high LFCs and LCLs on the HRRR.

[CheeselandSkies]

2 hours ago, Malacka11 said:

I thought roughly the same area is in play tomorrow? 

That was initial thinking but now looking like the trough is ejecting more slowly.

[Malacka11]

3 minutes ago, CheeselandSkies said:

That was initial thinking but now looking like the trough is ejecting more slowly.

Yeah I'm just starting to catch on to that. Oopsies

[madwx]

53 minutes ago, Malacka11 said:

FWIW, the RRFS A is up and running again. its 12z run had what discrete cells do fire in Central IA rather than closer to the border. 

all the cells it shows are rocketing due northwards.  they are either elevated initially or become elevated pretty quickly after crossing I80

[cyclone77]

Gotta work till 4 but will be out after that.  I'm riding the consistent Euro and FV3 till I go down in flames lol.  Parameters too strong for me to sit this one out.

[CheeselandSkies]

11 minutes ago, cyclone77 said:

Gotta work till 4 but will be out after that.  I'm riding the consistent Euro and FV3 till I go down in flames lol.  Parameters too strong for me to sit this one out.

Yeah, I agree on that.

[Malacka11]

2 minutes ago, CheeselandSkies said:

Yeah, I agree on that.

[CheeselandSkies]

@andyhb What do you make of some of these RAP soundings? Parameters are absolutely off the chains but there's that pesky low-level inversion. Just the other day we were talking about temps in the 80s and mixing issues, but a lot of these seem too cool (uppers 60s/low 70s) almost like we're more used to seeing from the NAM?

[WxSynopsisDavid]

Latest HRRR and RRFS-A showing morning convection going through the warm sector