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6/19-6/23 Severe Weather Risk


Jim Martin

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Have to wonder if the SPC isn't considering/hedging towards a possible upgrade to high risk across Northeastern Illinois and parts of Northwestern and Northern/Central Indiana.

That's exactly what I was thinking looking at the latest update for the wind probs. We will see in a couple hours.

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Have to wonder if the SPC isn't considering/hedging towards a possible upgrade to high risk across Northeastern Illinois and parts of Northwestern and Northern/Central Indiana. 

Definitely would be a nowcast situation based on the clearing/warm front situation over the next 3/4 hours.

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agree a high risk is possible once mesoscale details become 100% clear. sure is a lot of evidence that the warm front will blast north into chicagoland this afternoon, with all CAMs producing supercells in the area. there may be a corridor north of the true warm front and south of a pseudo-warm front/lake breeze boundary with the lower LCLs and SE winds that can still produce surface-based storms. need sun for a few hours to get temps into the lower 80s with dews in the lower 70s. i think 2" or larger hail is a sure bet for chicago proper, just need to see how the boundaries set up this evening.

 

keep in mind discrete supercells often manipulate the nearby environment/wind field.

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agree a high risk is possible once mesoscale details become 100% clear. sure is a lot of evidence that the warm front will blast north into chicagoland this afternoon, with all CAMs producing supercells in the area. there may be a corridor north of the true warm front and south of a pseudo-warm front/lake breeze boundary with the lower LCLs and SE winds that can still produce surface-based storms. need sun for a few hours to get temps into the lower 80s with dews in the lower 70s. i think 2" or larger hail is a sure bet for chicago proper, just need to see how the boundaries set up this evening.

 

keep in mind discrete supercells often manipulate the nearby environment/wind field.

Another thing to factor in as well with the limited time for heating, temperatures won't be able to blast to 85-93 keeping those LCLs very low over a decently large area.

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Kind of a no brainer... tornado watches.  Could eventually see a transition to severe thunderstorm watches late/farther east but I wouldn't be shocked if that didn't happen.

agreed. tornado watches at the start, but if the derecho threat materializes like we all here think it should, then the 2nd subsequent watches will be Severe thunderstorm, potentially PDS variety depending on how nasty the potential derecho gets.

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AREA FORECAST DISCUSSION...UPDATED  

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  

1152 AM CDT WED JUN 22 2016  

   

UPDATE  

 

1145 AM CDT  

 

A BATCH OF MAINLY JUST SHOWERS IS CURRENTLY SHIFTING OVER THE  

AREA. A REMNANT OUTFLOW BOUNDARY FROM THIS MORNINGS CONVECTION TO  

OUR SOUTHWEST HAS PUSHED THE EFFECTIVE WARM FRONTAL BOUNDARY  

SOUTHWARD WELL DOWNSTATE ILLINOIS. HOWEVER, RECENT OBSERVATIONS  

ACROSS SOUTHERN IOWA AND MISSOURI INDICATE THAT GUSTY SOUTHERLY  

SURFACE WINDS INDICATIVE OF BETTER MIXING OF THE STRONGER FLOW  

ALOFT HAVE DEVELOPED. THIS IS HELPING DRIVE THE WARM FRONTAL  

BOUNDARY MOVE NORTHWARD TO OUR WEST. THUS IT STILL APPEARS THAT  

THIS BOUNDARY WILL HAVE A GOOD CHANCE TO LIFT BACK NORTHWARD  

TOWARDS THE I-80 CORRIDOR BY LATE AFTERNOON AS THE SURFACE LOW  

SHIFTS EASTWARD TOWARDS THE MISSISSIPPI RIVER. THIS WILL BE A  

PARTICULAR FOCUS FOR ENHANCED SEVERE WEATHER.  

 

DESPITE CURRENT CLOUD COVER AND SOME RAIN OVER THE AREA,  

CONDITIONS WILL BE ABLE TO DESTABILIZE LATER THIS AFTERNOON,  

ESPECIALLY CONSIDERING THAT AN ELEVATED MIXED LAYER (CORRIDOR OF  

STEEP MID-LEVEL LAPSE RATES) WILL ADVECT IN AS THE SURFACE WARMS  

AND MOISTENS TO THE SOUTH OF THE APPROACHING FRONT. THIS SHOULD  

ALLOW RENEWED DEVELOPMENT AFTER 4-5 PM THIS AFTERNOON, LIKELY IN  

THE VICINITY OF THE TRIPLE POINT MOST FAVORED OVER NORTHWESTERN  

ILLINOIS/FAR SOUTHWESTERN WI. THIS GENERAL SCENARIO IS SUPPORTED  

BY MANY OF THE CAMS. THESE STORMS WILL LIKELY DEVELOP IN THE FORM  

OF SOUTHEASTWARD-MOVING SUPERCELLS INITIALLY GIVEN THE STRONG  

TURNING MID-LEVEL FLOW. THESE STORMS COULD PRODUCE ALL SEVERE  

HAZARDS, INCLUDING STRONG TORNADOES GIVEN THE ENHANCED HELICITY  

VALUES IN THE VICINITY OF THE SURFACE BOUNDARY. IN ADDITION,  

FORECAST BUNKERS SUPERCELL STORM MOTION IS ORIENTED ALONG THIS  

WARM FRONTAL BOUNDARY, WHICH INDICATES A MAXIMUM RESIDENCE TIME OF  

ANY SUPERCELLS IF THEY WERE TO DEVELOP ALONG THIS BOUNDARY. WHERE  

EXACTLY THIS FRONT WILL BE...THAT IS JUST HOW FAR  

NORTH...CONTINUES TO BE ASSESSED...BUT THE BOUNDARY WILL BE IN OUR  

CWA WITH HIGH CONFIDENCE. THESE STORMS SHOULD THEN BUILD UPSCALE  

INTO WIND-PRODUCING CONGEALED SEGMENTS OR LEWPS AS IT MOVES OVER  

THE CHICAGO AREA AND INTO NORTHWEST INDIANA. THIS WILL MAKE STRONG  

DAMAGING WINDS, POSSIBLY IN EXCESS OF 70 MPH, A THE MAIN THREAT.  

HOWEVER, TORNADOES WILL REMAIN POSSIBLE THAT FAR EAST ESPECIALLY  

IN THE VICINITY OF THE SURFACE BOUNDARY.  

 

THESE STORMS WILL BE FAIRLY PROGRESSIVE AND THIS MAY ULTIMATELY  

LIMIT THE THREAT OF FLASH FLOODING, ESPECIALLY CONSIDERING MUCH OF  

THE HEAVY RAINFALL THIS MORNING STAYED WEST/SOUTHWEST OF THE  

AREA. HOWEVER, DUE TO THE POSSIBILITY OF HEAVY RAINFALL RATES, AND  

THEM POSSIBLY IMPACTING THE URBAN AREAS OF CHICAGO, WE FELT IT  

PRUDENT TO HOLD ONTO THE FLASH FLOOD WATCH.  

 

KJB/MTF  

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Another thing to factor in as well with the limited time for heating, temperatures won't be able to blast to 85-93 keeping those LCLs very low over a decently large area.

exactly...that's what i was trying to hint at. 

 

looking like winds in northeast illinois will stay more s to ssw until that bubble high over central illinois gets out of the way. very strong warm advection under way to its west, as is made evident by 20-30kt se winds over eastern iowa.

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Another thing to factor in as well with the limited time for heating, temperatures won't be able to blast to 85-93 keeping those LCLs very low over a decently large area.

Of course... This goes two ways.. It can also up the inhibition some, it all depends on your overall temperature profile. 

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Of course... This goes two ways.. It can also up the inhibition some, it all depends on your overall temperature profile. 

True but expectations of dew points around 75 is looking pretty likely, that will be enough to overcome inhibition.

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that's rare for him. either he really doesn't like something and is worried it may not be as bad as advertised, or he's more worried than he usually is about the vulnerability and is choosing to play this one as it comes. one other possibility, he's seeing all types of meso-solutions and doesn't want to confuse viewers with the run by run thing.

 

Doubling back on this.  WGN's RPM Model, which was just shown on the 12:30pm update, had storms covering the entire Chicagoland area north to south and moving SE...starting to bow out around 8pm.  This is the first real model detail I have seen regarding the coverage of storms from the WGN/Skilling team.

 

Calling for large hail, 80mph+ winds.  No big mention of tornadoes yet but Demetrius Ivory (local met) is very conservative with his wording.

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LOT AFD just posted; Mentions they believe greatest severe risk is a bit further south along a Rockford - Joliet - Valpo line.

That's an interesting line. RFD -> JOT -> VALPO.

I would trim the JOT buldge, and just connect the line from RFD to VALPO. But I'm being too technical here lol.

I live in western suburbs/Dupage, along i88 about 15mins east of COD in Oak Brook. And I noticed many time where the lake influence reaches out here, but many times it isn't strong enough too.

We'll see, but it's very close.

Meant to post this earlier, but I passed out.

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IWXs new AFD provides nothing new or there thinking

.SHORT TERM...(This Evening through Thursday)

Issued at 200 PM EDT Wed Jun 22 2016

As suspected yda overnight convn and swwd displacement of

composite outflw/wmfnt keeping precip at bay acrs the CWA this

aftn. Decaying upstream stratiform ovr ne IL may hold on long

enough to bring a sprinkle/lt shra to wrn areas yet this aftn hwvr

chcs appear minimal.

Primary focus conts to side w/sewd apch tonight of potent nrn stream

sw trough ovr ne ND this aftn. Sfc reflection back west ovr ern NE

will shift ewd into wrn IN late tonight. Ramping ll waa will aide in

newd mix of wmfnt twd the highway 24 corridor w/commensurate

greatest risk for severe storms btwn 02-07Z generally swwd of a ksbn-

kaoh line. Hwvr most concerning is overlap of extreme shear and mod

cape which point to an enhanced tornado risk alg and sw of the

highway 30 ovr wrn zones mid-lt evening. In addn...nw-se oriented

fntl zone in tandem w/protracted window of mid lvl forcing and

considerable ll mstr flux ewd of sfc cyclone suggest some

substantial rainfall psbl overnight. Hwvr contd dry antecedent conds

and mixed highres signals on where heaviest rainfall may fall lends

no confidence in delineating a potential flood watch and will defer

to oncoming shift.

Otrws besides a lingering shra/isold storm Thu am...general post

fntl drying xpcd to envelope CWA.

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Clearing out rapidly, I really think the WF is going to get further north then some think. That's just my noob eyes though, lol.

I hope you'll be around this evening, SmokeEater.  I always appreciate your EMS updates as well as images.  I think they will be especially needed this evening in highly populated areas, unfortunately.

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I hope you'll be around this evening, SmokeEater. I always appreciate your EMS updates as well as images. I think they will be especially needed this evening in highly populated areas, unfortunately.

Yes sir, be done work hopefully by 330 eastern at the latest, and not a thing to do tonight unless my pager goes off other then track what's out there.
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