March 26-28 Severe Threat

[crossbowftw3]

If they go high risk if not by 0600 then almost certainly by 1630, multiple precluding factors still at hand 

[Hoosier]

31 minutes ago, StormChaser4Life said:

0z hrrr is verbatim high risk worthy. Those helicity tracks are mind boggling. I think cape/dews may be overdone a bit but regardless still looks to be a big day

Yeah, I will eat my hat without anything to drink if we get 70 degree dews in central IL.  Mid-upper 60s dews definitely look doable though, considering current dews to the south.

[bdgwx]

I don't know about the high risk. HRRR looks potent now, but what will things look like tomorrow? We've seen this type of over-reaction by CAMs only to curtail their outputs a few runs later or the day-of ends up being a bust. Nah...I see < 50% of a high risk tomorrow. I'll accept a good ribbing if I'm wrong though. We'll see.

[Quincy]

4 minutes ago, bdgwx said:

I don't know about the high risk. HRRR looks potent now, but what will things look like tomorrow? We've seen this type of over-reaction by CAMs only to curtail their outputs a few runs later or the day-of ends up being a bust. Nah...I see < 50% of a high risk tomorrow. I'll accept a good ribbing if I'm wrong though. We'll see.

The synoptic signal is strong. Mesoscale and global models more or less in agreement that there’s at least modest destabilization ahead of the cold front. Even with the HRRR being a bit overdone with dewpoints, it still yields an eerily volatile setup.

With low LCLs, fast storm motions and large low-level instability, expect multiple long track tornadic supercells.

It’s hard to imagine this not going high risk, in my opinion. 

[Radtechwxman]

3km nam at other end of spectrum of hrrr. Multiple rounds of convection lasting into the afternoon. Would definitely temper the threat and likely shift it west and south

[Jim Marusak]

quick question here, i know maybe something really small in the big scale of things. But given the much lower air traffic compared to normal, we have less cirrus cover than normal, which may allow for a few more w/m2 of solar incoming radiation to come through during the times when it clears out between any convection bands during the daytime hours. Will that little bit more solar input maybe help to break caps a bit earlier than expected before sunset?

[Indystorm]

Hard to believe the 70 dew points that HRRR is pooling along the front tomorrow, even though St. Louis is currently 74/64 this evening, but other HRRR parameters are downright scary.

[Quincy]

7 minutes ago, StormChaser4Life said:

3km nam at other end of spectrum of hrrr. Multiple rounds of convection lasting into the afternoon. Would definitely temper the threat and likely shift it west and south

Verbatim, it keeps the warm front down around US-136 through about 19-20z. A lot of that early convection quickly advances over the warm front. Elevated convection/hail threat. 

Dew points are about 3F lower than the HRRR, but the parameter space around the NE MO/SE IA/NW IL area is still highly supportive for tornadoes. 

[jpeters3]

Just now, Quincy said:

Verbatim, it keeps the warm front down around US-136 through about 19-20z. A lot of that early convection quickly advances over the warm front. Elevated convection/hail threat. 

Dew points are about 3F lower than the HRRR, but the parameter space around the NE MO/SE IA/NW IL area is still highly supportive for tornadoes. 

After a bit of staring at the NAM and RAP, i think I see what the difference is.  The NAM (and consequently NAM NEST) develops more early morning convection/precip over AR/MO, which creates a subtle shortwave vort max in the jet.  As this feature passes over the warm sector, there is a bunch of junkvection that forms.  In contrast, the RAP (and consequently HRRR) seems to keep AR/MO comparatively clear of convection and has no commensurate shortwave feature.  This leads to a less junkvectiony warm sector.

[Hoosier]

3 minutes ago, Indystorm said:

Hard to believe the 70 dew points that HRRR is pooling along the front tomorrow, even though St. Louis is currently 74/64 this evening, but other HRRR parameters are downright scary.

We do have upper 60s dewpoints farther south right now, so it shouldn't be hard to get mid-upper 60s dews farther north in IL tomorrow.  

[Sydney Claridge]

SPC Mesoanalysis is showing an area of upper-60s dewpoints just east of St. Louis right now.  If these high dewpoints are already in place, I do not want to discount the possibility of dewpoints around 70 in Illinois tomorrow.

[SchaumburgStormer]

Even tossing the incredible HRRR, this is the beat severe setup N Central IL has seen in years. Would absolutely be locally chasing, but forward speed and some of these model runs have me hedging towards staying home with the wife and kids and watching them roll on in. 

[Quincy]

1 minute ago, Hoosier said:

We do have upper 60s dewpoints farther south right now, so it shouldn't be hard to get mid-upper 60s dews farther north in IL tomorrow.  

I didn’t realize there are already fairly widespread 66-68F dews across southern IL. Sure, the warm front may have trouble making much northward progress prior to midday, but dews in the mid to upper 60s in the warm sector look quite likely, barring some unforeseen massive junkvection in the morning. 

[Radtechwxman]

Current dew points 

[CheeselandSkies]

23 minutes ago, StormChaser4Life said:

3km nam at other end of spectrum of hrrr. Multiple rounds of convection lasting into the afternoon. Would definitely temper the threat and likely shift it west and south

Very odd, I remember the two models' solutions being the reverse of that on 4/9/15. Hi-res NAM was gangbusters while HRRR was more subdued with the UH (at least on the last run I looked at before leaving the house ). Of course the models were somewhat different then (3KM NAM was the 4KM NAM, for one).

[Jim Marusak]

how coupled are the HRRR, 3km NAM, and other models to the current soil moisture in the region?

is that maybe skewing the potential dew points high or low for tomorrow?

https://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Soilmst/Soilmst.shtml#

[SchaumburgStormer]

Just now, StormChaser4Life said:

Current dew points 

Jesus. Mid-60’s to a SPI-DEC-CMI line. Definitely snuck up, as I wasn’t paying that much attention to current conditions down there quite yet 

[Quincy]

Local obs:

[Radtechwxman]

Just now, SchaumburgStormer said:

Jesus. Mid-60’s to a SPI-DEC-CMI line. Definitely snuck up, as I wasn’t paying that much attention to current conditions down there quite yet 

Don't think there will be any issue seeing mid to upper 60 dews in moderate risk area. 3km nam definitely highlights a potential fly in the ointment with convection persisting into the afternoon instead of clearing mid to late morning like HRRR

[Quincy]

FWIW, NSSL WRF has some of that early day, elevated junk, then initiates across south-central/southeastern IA by 21z. To the east, it barely convects at all in NW IL until around sunset. 

A key difference with the HRRR is that it shows a trough-like feature ahead of the cold front, that initiates convection earlier and slightly farther NE. 

[Hoosier]

I took a cursory look at some past significant severe events in the region from mid March-Mid April, and having mid-upper 60s dews as far north as is being progged tomorrow is elite level territory.  There is more to a severe weather setup than dewpoints of course, but that aspect is very impressive for the time of year.  

[Quincy]

5 minutes ago, Hoosier said:

I took a cursory look at some past significant severe events in the region from mid March-Mid April, and having mid-upper 60s dews as far north as is being progged tomorrow is elite level territory.  There is more to a severe weather setup than dewpoints of course, but that aspect is very impressive for the time of year.  

Oof. Granted it’s mainly 12z/00z data, but SPC climo doesn’t show any >63F RAOB dews at ILX until early April. For DVN, there are none until May. 
 https://www.spc.noaa.gov/exper/soundingclimo/

[Hoosier]

2 minutes ago, Quincy said:

Oof. Granted it’s mainly 12z/00z data, but SPC climo doesn’t show any >63F RAOB dews at ILX until early April. For DVN, there are none until May. 
 https://www.spc.noaa.gov/exper/soundingclimo/

This is what I was using.  He has surface maps from afternoon hours

http://bangladeshtornadoes.org/UScases.html

[CoalCityWxMan]

Incase anyone is interested, NIU met professor Victor Gensini did an analysis of 0z models, pretty interesting. https://www.facebook.com/vgensini/videos/10107425952369029/

[Sydney Claridge]

SPC MD says the storms in central MO are elevated, but I am starting to wonder about that cell approaching Jefferson City.  SPC Mesoanalysis shows 1000+ J/kg SBCAPE, 0-3km EHI between 2 and 3, and little CIN in that area.

This looks to be a major hail producer nevertheless.

[Indystorm]

I can remember just by anecdote some svr wx events that had storms early in the day to prime the atmosphere and put down boundaries, then had clearing and insolation, and powerful storms later in the day.  The classic extensive example of course is 4/27/11 but am not saying this will be anything like that.  Much smaller regional outbreaks have also had a similar pattern.

[WeatherMonger]

Under a watch here, no watchbox by SPC available

 

[WeatherMonger]

 

URGENT - IMMEDIATE BROADCAST REQUESTED
   Severe Thunderstorm Watch Number 66
   NWS Storm Prediction Center Norman OK
   1015 PM CDT Fri Mar 27 2020

   The NWS Storm Prediction Center has issued a

   * Severe Thunderstorm Watch for portions of 
     West-central Illinois
     East-central Missouri

   * Effective this Friday night and Saturday morning from 1015 PM
     until 400 AM CDT.

   * Primary threats include...
     Scattered large hail and isolated very large hail events to 2.5
       inches in diameter possible
     Isolated damaging wind gusts to 60 mph possible

   SUMMARY...Initially elevated supercell across central Missouri
   should progress near the I-70 corridor with additional development
   possible to the east-northeast into the early morning. Large hail
   will be the primary hazard.

   The severe thunderstorm watch area is approximately along and 45
   statute miles north and south of a line from 15 miles west southwest
   of Columbia MO to 30 miles south of Decatur IL. For a complete
   depiction of the watch see the associated watch outline update
   (WOUS64 KWNS WOU6).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A Severe Thunderstorm Watch means conditions are
   favorable for severe thunderstorms in and close to the watch area.
   Persons in these areas should be on the lookout for threatening
   weather conditions and listen for later statements and possible
   warnings. Severe thunderstorms can and occasionally do produce
   tornadoes.

   &&

   AVIATION...A few severe thunderstorms with hail surface and aloft to
   2.5 inches. Extreme turbulence and surface wind gusts to 50 knots. A
   few cumulonimbi with maximum tops to 500. Mean storm motion vector
   25050.

   ...Grams

[Radtechwxman]

43 minutes ago, Quincy said:

FWIW, NSSL WRF has some of that early day, elevated junk, then initiates across south-central/southeastern IA by 21z. To the east, it barely convects at all in NW IL until around sunset. 

A key difference with the HRRR is that it shows a trough-like feature ahead of the cold front, that initiates convection earlier and slightly farther NE. 

A prefrontal trough would certainly increase the tornado potential for this. Prevent a more linear storm mode near pacific front

[StormySquares]

2 inch hail in Jeff City MO