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April 8-10 Severe threat


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I'm not too concerned about the uni-flow above H8, as the stretching above that level, combined with incoming vorticity advection, and lowering LCLs with ongoing sups should help to enhance supercell characteristics.  With the crosswise vorticity above the BL it may take a split to kick the dominant right storm into tor mode, but that's splitting hairs at this point lol.  

 

EDIT:  No pun intended lol

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Big shift on the 00z GFS toward a more NAM like solution regarding surface low track and timing and more backing of the surface winds between 21 and 00z (SW to closer to due south) on Thursday over northern IL. 

 

00z GFS at 00z:

gfsCGP_sfc_thetae_072.gif

 

18z GFS at 21z Thursday (frontal passage in progress at 00z Thursday on 18z run):

gfsCGP_sfc_thetae_075.gif

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With things slowing down for Wednesday to the west, things in our subforum are actually looking a bit up for Thursday compared to previous runs. I like Eastern IA/Northern IL a lot actually on the latest runs.

 

My interest is piqued for sure, especially if we can get a surface low track similar to the NAM/GFS/GEM.

 

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As long as all goes well, I think you're underplaying it.

It's not like it'll be coming through at 5AM. It'll be around 0z.

Exactly my thoughts per the 4km and 12km NAM. The next sim ref frame, valid at 00z on the 4km, is still a broken line of discrete supercells headed for the metro. You can see the individual cell tracks on the 3hr precip valid at 00z. Given the strong kinematics with a deepening low, severe/tornado threat will last longer beyond sunset than is typical, and in this case it'll be right after sunset, so the city would certainly be in the game if something like the NAM happened.
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Exactly my thoughts per the 4km and 12km NAM. The next sim ref frame, valid at 00z on the 4km, is still a broken line of discrete supercells headed for the metro. You can see the individual cell tracks on the 3hr precip valid at 00z. Given the strong kinematics with a deepening low, severe/tornado threat will last longer beyond sunset than is typical, and in this case it'll be right after sunset, so the city would certainly be in the game if something like the NAM happened.

Any chance that could be posted?

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Internet running really slow for me for some reason so doing a dprog/dt would take extra time but if anything, it seems like the 12z NAM sped up a little compared to 00z, which would put Chicago proper into a greater risk zone.

 

and also maintained strength of the SLP a little longer too...which could also provide for some longer maintenance if things "work out"

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Internet running really slow for me for some reason so doing a dprog/dt would take extra time but if anything, it seems like the 12z NAM sped up a little compared to 00z, which would put Chicago proper into a greater risk zone.

 

yeah looks like it did speed up to me when comparing sfc low locations at 21z Thursday to previous runs. 

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Any chance for some warm front action in Michigan before the main show with the cold front late?

I think the west side of the state has some chances, though I wouldn't write off the entire warm front. I do think there will be some morning convection as well.

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Internet running really slow for me for some reason so doing a dprog/dt would take extra time but if anything, it seems like the 12z NAM sped up a little compared to 00z, which would put Chicago proper into a greater risk zone.

Yeah the 4km nam is looking pretty stout for west of Chicago and into Chicago between 21z-00z

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Not saying much, but this will probably be Detroit's best shot for severe weather thus far. Timing and placement of the synoptic features is unfavorable as things stand right now, but we're still 2-3 days out.

It will ultimately be the mesoscale features from the previous day's convection that determines how widespread the severe t'storms are and where they develop/track. One thing's for sure, I'd rather not be on the far western and northern edge of the higher risk area this far out.

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GRR's thoughts on Thursday:

 

 

THE PRIMARY FOCUS IS ON THE SEVERE WEATHER POTENTIAL FOR THURSDAY
INCLUDING DAMAGING WINDS AND LARGE HAIL. A TORNADO THREAT LOOKS TO
EXIST AS WELL. CURRENT GUIDANCE INDICATES THAT THE MAIN THREAT IS
LATER IN THE DAY... PARTICULARLY 21Z-03Z. A LOT OF KEY SYNOPTIC
INGREDIENTS FOR SEVERE WEATHER APPEAR TO BE PRESENT LATE THURSDAY
BUT INSTABILITY AND THE FINER DETAILS ARE STILL BIG WILDCARDS.

THERE IS A COUPLED UPPER LEVEL JET STRUCTURE THURSDAY WITH A POTENT
MID LEVEL SHORTWAVE AND DEEPENING SFC LOW LIFTING NORTHEAST THROUGH
THE WESTERN GRTLKS REGION. A 75-90 KT H5 MID LEVEL JET AND A 50 KT
H8 LOW LEVEL JET LEAD TO DEEP LAYER SHEAR IN EXCESS OF 40 KTS.
PLENTY OF SHEAR IS ALSO PROGGED DOWN LOW WITH 0-3KM AND 0-1KM SHEAR
VALUES NEAR OR IN EXCESS OF 30 KTS. IT SHOULD BE NOTED THAT THE
ECMWF IS NOT AS AMPLIFIED WITH THE MID LEVEL SHORTWAVE AND HAS A
MUCH WEAKER AND FARTHER EAST SFC LOW.

IT SEEMS MUCH OF THE SEVERE WX THREAT HINGES ON HOW LONG CLOUDS AND
PRECIP LINGER ON THURSDAY AND HOW QUICKLY THE WARM SECTOR CAN SURGE
NORTH. FREQUENTLY IN THESE TYPE OF SET UPS THE ELEVATED CONVECTION
NORTH OF THE WARM FRONT THROUGH THE DAY CAN HINDER THE NORTHWARD
PROGRESS OF THE SFC WARM FRONT. GUIDANCE CURRENTLY SUGGEST THAT IT
MAY TAKE UNTIL AFTER 21Z THURSDAY TO DEVELOP SUFFICIENT SFC BASED
CAPE IN THE WARM SECTOR... LEAVING A ONLY A RELATIVELY NARROW PERIOD
TO WORK WITH WHEN BOTH THE SHEAR AND INSTABILITY ARE PRESENT
TOGETHER.

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Impressive/ominous AFD out of LOT.

 

.LONG TERM...
327 PM CDT

THURSDAY NIGHT THROUGH TUESDAY...

PRIMARY TROUGH IS STILL PROGGED TO MOVE QUICKLY EASTWARD AND INTO
THE MIDWEST BY THURSDAY AFTERNOON. GUIDANCE VARIES SOME WITH RESPECT
TO TIMING/INTENSITY OF THIS SYSTEM WITH 12Z ECMWF ON THE
FASTER/WEAKER END OF THE GUIDANCE SPECTRUM AND THE NAM/GEM ON THE
SLOWER DEEPER END OF THE SPECTRUM. OFTEN TIMES THE SLOWER GUIDANCE
ENDS UP VERIFYING BETTER WITH THESE STRONGER SYSTEMS...SO TRENDED
THE GRIDS TOWARD THE NAM/GEM SOLUTION. THE GFS SUPPORTS THE IDEA OF
STRONGER SYSTEM BUT SUSPECT IT IS A BIT TOO FAST.

SYNOPTICALLY SPEAKING THE LARGE SCALE PATTERN AND EVOLUTION OF THIS
CYCLONE CONTINUE TO RAISE RED FLAGS FOR THE POTENTIAL OF A
SIGNIFICANT SEVERE WEATHER EPISODE IN THE REGION THURSDAY AFTERNOON
AND EVENING. THE KINEMATIC FIELDS ARE EXTREMELY IMPRESSIVE WITH 90-
100KT UPPER LEVEL JET NOSING INTO THE REGION IN THE AFTERNOON WITH
40KT+ LOW LEVEL JET RESULTING IN VERY FAVORABLE DEEP LAYER SHEAR
PROFILE FOR SEVERE WEATHER. THE MAGNITUDE OF LOW LEVEL SHEAR WHICH
WILL PLAY A ROLE IN THE MAGNITUDE OF A TORNADO THREAT VARIES
DEPENDING ON THE MODEL. THE DEEPER SOLUTIONS HAVE A MORE BACKED
SURFACE FLOW AND LARGER LOW LEVEL HODOGRAPHS AND WOULD BE MUCH MORE
WORRISOME REGARDING TORNADO THREAT.

THE LATEST MODEL RUNS THIS MORNING ALSO SUGGEST AN UNUSUALLY
IMPRESSIVE PLUME OF STEEP MID LEVEL LAPSE RATES FOR SO FAR EASTWARD
BECOME JUXTAPOSED OVER TOP A WARM AND HUMID AIR MASS WITH SURFACE
DEWPOINTS LIKELY IN THE 60S WITHIN THE WARM SECTOR. GIVEN THE
PROGGED INTENSITY OF THE SYSTEM SUSPECT THAT EVEN MORNING CONVECTION
WILL NOT BE ENOUGH TO PREVENT THE WARM FRONT FROM BLASTING NORTH AND
PLACING ENTIRE CWA IN THE HUMID/UNSTABLE WARM SECTOR BY AFTERNOON.

OBVIOUSLY THERE ARE A TON OF MESOSCALE DETAILS THAT CANNOT BE
RESOLVED AT THIS DISTANCE...INCLUDING STORM MODE AND COVERAGE. THERE
IS A LOT THAT CAN CHANGE BETWEEN NOW AND THURSDAY SO A SIGNIFICANT
SEVERE WEATHER EVENT IS FAR FROM A SURE THING...BUT GIVEN THE TRENDS
IN MODEL GUIDANCE AND SYNOPTIC PATTERN THERE IS DEFINITELY REASON
FOR CONCERN ABOUT THE SEVERE WEATHER AND TORNADO POTENTIAL THURSDAY
AFTERNOON AND EVENING.

 

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Thursday is going to be one of those days where I see those low level clouds hauling arse north...typically leads to some decent storm potential in and around the area...

 

18z 12k holds serve with some discrete action into the metro

 

4k brings her down to 991 in SW Wisco at 21Z with discrete action starting to rip

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