May 20-21 Severe Threat

[Thundersnow12]

3500 j/kg of SBCAPE along the IL/WI border via mesoanalysis.

 

These mid level lapse rates are very impressive too. 8-9 deg C/km from southern IA up to NW IL. 

[Hoosier]

3500 j/kg of SBCAPE along the IL/WI border via mesoanalysis.

 

These mid level lapse rates are very impressive too. 8-9 deg C/km from southern IA up to NW IL. 

 

 

I was hoping somebody would do an 18z sounding but not sure if that's the case.  Models have been indicating really nice mid level lapse rates.

[OceanStWx]

I was hoping somebody would do an 18z sounding but not sure if that's the case.  Models have been indicating really nice mid level lapse rates.

 

I think DVN might be doing one.

 

Edit: They are at 20z

[Hoosier]

I think DVN might be doing one.

 

Edit: They are at 20z

 

 

Good news.  Thanks.

[Thundersnow12]

I think DVN might be doing one.

 

Edit: They are at 20z

 

Awesomeness. 

[tornadotony]

3500 j/kg of SBCAPE along the IL/WI border via mesoanalysis.

 

These mid level lapse rates are very impressive too. 8-9 deg C/km from southern IA up to NW IL. 

Yeah I have zero idea why hatching was removed.  Big hail is a big threat, I would think.

[Thundersnow12]

Yeah I have zero idea why hatching was removed.  Big hail is a big threat, I would think.

 

Exactly what I was thinking. Those are sky high mid level lapse rates. 

[Thundersnow12]

Starting to think eastern IA will have the best tornado threat with discrete supercells early on. Even getting small areas of southerly/backed sfc flow in the near storm environment in model land where sig tor is maxed. 

 

 

[nwohweather]

I would watch central and western Michigan for potential convective initiation anything that forms there would ride the warm front toward southeast MI.

Was thinking the same thing, similar to our last event. Either way looks like the typical NW Ohio Bow Echo event is gonna ride through tonight

[wisconsinwx]

AREA FORECAST DISCUSSION  

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL  

112 PM CDT TUE MAY 20 2014  

   

MESOSCALE DISCUSSION  

 

110 PM CDT  

 

THE MAIN FOCUS THIS AFTERNOON WILL BE TIMING THE INITIATION OF  

CONVECTION LATER THIS AFTERNOON AND EVENING ACROSS THE AREA.  

 

STRONG TO SEVERE THUNDERSTORMS STILL APPEAR TO BE IN THE WORKS FOR  

PORTIONS OF THE AREA LATER TODAY AND ESPECIALLY THIS EVENING WITHIN  

THE VICINITY OF SLOW MOVING COOL FRONTAL BOUNDARY. THIS COOL FRONTAL  

BOUNDARY IS CURRENTLY LOCATED FROM NORTHEASTERN IOWA...WEST  

SOUTHWESTWARD ACROSS KANSAS. THE AIRMASS AHEAD OF THIS BOUNDARY  

FEATURES DEWPOINTS MAINLY IN THE LOWER 60S...WITH TEMPERATURES  

NEARING 80 DEGREES AS OF THE NOON HOUR UNDER SUNNY SKIES.  

 

WATER VAPOR IMAGERY THIS MORNING INDICATES THE PRESENCE OF A  

BROAD MID LEVEL RIDGE ACROSS THE CENTRAL STATES WEDGED BETWEEN  

TWO UPPER LOWS/TROUGHS OVER EAST COAST. THIS IS DRIVING THE MAIN  

BELT OF MID/UPPER WESTERLIES RIGHT ACROSS THE UPPER MIDWEST AND  

GREAT LAKES REGION. THE MORNING RAOBS INDICATED THAT NORTHERN  

ILLINOIS WAS ALONG THE SOUTHERN PERIPHERY OF THIS STRONGER MID/UPPER  

LEVEL FLOW. SEVERAL SMALL SCALE DISTURBANCES...CURRENTLY NOTED IN  

THE WATER VAPOR IMAGERY ACROSS NEBRASKA AND INTO WESTERN IOWA...WILL  

BE OF INTEREST LATER THIS AFTERNOON AS THEY SHIFT EASTWARD TOWARDS  

THE INCREASINGLY UNSTABLE ENVIRONMENT DEVELOPING ACROSS THE AREA.  

 

IT APPEARS THAT STORMS MAY BEGIN TO INITIATE OVER THE NEXT FEW HOURS  

ACROSS PORTIONS OF SOUTHERN IOWA...WHERE BETTER LOWER LEVEL  

CONVERGENCE IS OCCURRING ALONG THE BOUNDARY. THIS ACTIVITY WOULD  

LIKELY SHIFT/DEVELOP EASTWARD ACROSS NORTHERN ILLINOIS BY EARLY THIS  

EVENING. ADDITIONAL STORMS MAY ALSO DEVELOP ACROSS SOUTHEASTERN  

WI...WHERE THE LATEST VIS SAT IMAGERY INDICATES SOME CU FIRING ALONG  

A LAKE BREEZE BOUNDARY. THE RAP SUGGESTS THAT STORM DEVELOPMENT  

HERE COULD DRIVE A BOUNDARY SOUTH ACROSS NORTHEASTERN ILLINOIS...IN  

WHICH STORMS WOULD DEVELOP. EITHER WAY...MUCH OF THE HIRES GUIDANCE  

SUGGESTS THAT THUNDERSTORM ACTIVITY WILL BEGIN TO IMPACT NORTHERN  

ILLINOIS BY THIS EVENING..LIKELY AFTER 5 PM. THE PRESENCE OF VERY  

STEEP MID LEVEL LAPSE RATES...7+C/KM...PER 12 UTC RAOBS...ALONG WITH  

THE POTENTIAL OF SUPERCELLS GIVEN THE DEEP LAYER  

SHEAR...CERTAINLY SUGGESTS THAT VERY LARGE HAIL WILL BE A THREAT  

WITH THESE STORMS TONIGHT. THERE IS ALSO THE THREAT OF STRONG  

DAMAGING WINDS THIS EVENING...ESPECIALLY IF THE CONVECTIVE  

ACTIVITY CONGEALS INTO A FORWARD PROPAGATING MCS.  

 

ALTHOUGH THE ATMOSPHERE IS NOT OVERLY MOIST...PRECIPITABLE WATER  

VALUES ARE PROGGED TO APPROACH 1.5 INCHES BY THIS EVENING.  

IN ADDITION...THE DEEP LAYER WIND FIELDS SUGGEST THAT STORM  

MOTIONS WILL BE MAINLY FROM WEST TO EAST...WHICH COULD RESULT IN SOME  

TRAINING OF CELLS OVER THE SAME AREAS ACROSS NORTHERN ILLINOIS INTO  

THIS EVENING. THIS RAISES SOME CONCERNS FOR SOME HEAVY RAINFALL  

POTENTIAL IN ADDITION TO THE SEVERE THREAT THIS EVENING. AS A RESULT  

OF THIS...THERE IS APPEARS TO BE A CONDITIONAL THREAT FOR SOME  

ISOLATED AREAS EXCEEDING FLASH FLOOD GUIDANCE.  

 

KJB  

 

I think I see the lake breeze they were referring to on UW-Madison's radar that Turtle so kindly brought to our attention a couple years ago.  Looks like it's making its way through Milwaukee and Ozaukee Counties.  I was noticing some cumulus, but nothing that looked like it was about to pop a storm.

[Hoosier]

I think I see the lake breeze they were referring to on UW-Madison's radar that Turtle so kindly brought to our attention a couple years ago.  Looks like it's making its way through Milwaukee and Ozaukee Counties.  I was noticing some cumulus, but nothing that looked like it was about to pop a storm.

 

 

It's visible on MKX also.

[tornadotony]

It's visible on MKX also.

You gotta watch the lake breeze as a focal point for storm intensification of whatever comes out of IA/NW IL also.  This has the feeling of one of those events where the stuff comes out of that area, hits the southern end of the lake, intensifies, and rakes the south side/south suburbs and NWI.

[Thundersnow12]

You gotta watch the lake breeze as a focal point for storm intensification of whatever comes out of IA/NW IL also.  This has the feeling of one of those events where the stuff comes out of that area, hits the southern end of the lake, intensifies, and rakes the south side/south suburbs and NWI.

 

What you think about sup/tor potential in NW IL? Going to probably head to Oregon later as a starting point. 

[tornadotony]

What you think about sup/tor potential in NW IL? Going to probably head to Oregon later as a starting point. 

Honestly, I'm buried neck-deep into studying for my Ph.D. prelim exam in a couple weeks and have only looked at home.  From what little I saw, though, it looks like a good initial play for supercells, and along a warm front, you never know w/r/t a tornado threat.

[hm8]

 

MESOSCALE DISCUSSION 0623
NWS STORM PREDICTION CENTER NORMAN OK
0255 PM CDT TUE MAY 20 2014

AREAS AFFECTED...SRN WI...NERN IL...ERN IA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 201955Z - 202200Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...ISOLATED STORMS CAPABLE OF LARGE HAIL AND LOCALLY GUSTY
WINDS WILL BE POSSIBLE THIS AFTERNOON OVER SERN WI...WITH OTHER
STORMS FORMING TO THE SW INTO IA. TRENDS WILL CONTINUE TO BE
MONITORED FOR POSSIBLE WATCH PLACEMENT.

DISCUSSION...VISIBLE IMAGERY SHOWS AN INCREASING CU FIELD OVER SRN
WI IN THE PLUME OF STEEPER LOWER-LEVEL LAPSE RATES AND WHERE
DEWPOINTS HAVE RISEN INTO THE LOWER 60S F. THIS AREA IS NEAR A LOW
PRESSURE TROUGH...WITH CONVERGENCE BEING ENHANCED BY THE SEA BREEZE.


MODIFIED FORECAST SOUNDINGS SHOW A ROBUST SUPERCELL ENVIRONMENT WITH
STEEP LAPSE RATES ALOFT AND A FAVORABLY LONG HODOGRAPH. ALTHOUGH
LOW-LEVEL WINDS ARE WEAK...THE HODOGRAPH STILL FAVORS A RIGHT MOVING
SUPERCELL CAPABLE OF VERY LARGE HAIL.

SATELLITE ALSO SHOWS CU BEGINNING TO FILL IN SWWD INTO IA WITHIN THE
AXIS OF DILATATION. CONTINUED HEATING IS EXPECTED TO EVENTUALLY
BREAK THE CAP AND RESULT IN SEVERAL STORMS CAPABLE MAINLY OF HAIL.

THE MAIN UNCERTAINTY REGARDING SIG HAIL POTENTIAL IS WHETHER STORMS
WILL DEVELOP INTO SUPERCELLS DESPITE THE RATHER WEAK FORCING AND
WEAK LOW-LEVEL WIND ENVIRONMENT...OR MORE TOWARD MULTICELLS...IN
WHICH CASE THE HAIL COULD STILL BE LARGE BUT NO GREATER THAN ABOUT
GOLF BALL.

..JEWELL/HART.. 05/20/2014

[A-L-E-K]

over under, largest hail size at 1.25" in diameter

[Thundersnow12]

over under, largest hail size at 1.25" in diameter

 

Easy over if that's for IA/WI/IL. 

[SchaumburgStormer]

over under, largest hail size at 1.25" in diameter

 

Over

[tornadotony]

over under, largest hail size at 1.25" in diameter

Over.

[A-L-E-K]

Easy over if that's for IA/WI/IL. 

 

 

let's stick with LOT lsrs

[eureka22]

Correction issued on MCD.

MESOSCALE DISCUSSION 0623  

NWS STORM PREDICTION CENTER NORMAN OK  

0305 PM CDT TUE MAY 20 2014  

 

AREAS AFFECTED...SRN WI...NERN IL...ERN IA  

 

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY  

 

VALID 202005Z - 202200Z  

 

CORRECTED FOR WATCH PROB  

 

PROBABILITY OF WATCH ISSUANCE...80 PERCENT  

[hm8]

New D1 outlook:

 

 

 

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT TUE MAY 20 2014

VALID 202000Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MIDWEST...

...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE CNTRL
HIGH PLAINS...

...SUMMARY...
ISOLATED TO SCATTERED SEVERE STORMS SHOULD DEVELOP BETWEEN 5 AND 8
PM CDT ACROSS PARTS OF IOWA TO THE WISCONSIN/ILLINOIS BORDER. LARGE
HAIL SHOULD BE THE PRIMARY HAZARD...BUT DAMAGING WINDS AND PERHAPS A
TORNADO MAY OCCUR AS WELL. STORMS SHOULD PROGRESS EAST TO SOUTHERN
LOWER MICHIGAN AND NORTHERN OHIO OVERNIGHT...WITH A DIMINISHING
SEVERE RISK.

ISOLATED SEVERE STORMS PRODUCING LARGE HAIL SHOULD OCCUR THROUGH
ABOUT 8 PM MDT ALONG THE CENTRAL HIGH PLAINS.

...IA/WI INTO OH...
DESPITE WEAKLY DIFFLUENT SURFACE WINDS CURRENTLY OVER THE MS VALLEY
AND NEBULOUS FORCING MECHANISMS FOR ASCENT...WIDESPREAD CONSISTENCY
EXISTS IN OPERATIONAL AND CONVECTION-ALLOWING MODEL GUIDANCE IN
DEVELOPING CONVECTION ACROSS IA TO THE WI/IL BORDER THIS EVENING
NEAR A WEAK COLD FRONT. WITH MODERATE BUOYANCY NOW PRESENT WITHIN
LOWER TO MIDDLE 60S SURFACE DEW POINTS AND ON THE SRN PERIPHERY OF
THE MID-LEVEL WLY SPEED MAX OVER THE UPPER MS VALLEY...WEAKLY TO
MODERATELY ROTATING STORMS PRIMARILY PRODUCING LARGE HAIL IS THE
INITIAL EXPECTED THREAT. SOME OF THIS ACTIVITY SHOULD CONSOLIDATE
INTO A CLUSTER WITH SEVERE HAIL/WIND POTENTIAL THAT SPREADS EWD
ACROSS SRN LOWER MI TO NRN OH. BUT WITH THE LLJ FOCUSED FROM THE
OZARK PLATEAU TO THE OH RIVER...WEAK FORCING AND LESSER
DESTABILIZATION WITH ERN EXTENT SUGGEST THAT OVERALL SEVERE RISK
SHOULD WANE OVERNIGHT.

[A-L-E-K]

looks like a line from milwaukee to galena will give it a go

[Stebo]

let's stick with LOT lsrs

Over still.

[Hoosier]

let's stick with LOT lsrs

 

Tough call narrowing it down like that but I'd guess over.  I still wouldn't be surprised to see 2"+ hail reports somewhere even with the removal of the hatching. 

[tornadotony]

Tough call narrowing it down like that but I'd guess over.  I still wouldn't be surprised to see 2"+ hail reports somewhere even with the removal of the hatching. 

Removal of hatching doesn't make sense.  They question supercell vs. multicell mode based off low-level flow, but usually that distinction is predicated by deep-layer or effective-layer shear, both of which are supportive of supercells.  You add in the lake breeze and focused area of low-level vorticity along the lakeshore that shows up on mesoanalysis and I get really confused about the question marks about storm mode.  I'd pretty much guarantee at least a couple supercell structures, and given the thermodynamic environment, I'd go as far to say that 2"+ diameter hail is a guarantee in almost any supercell structure.

[Stebo]

Might be seeing some convective initiation in central Michigan, some showers starting to pop SW along that initial line that went through northeastern Michigan.

[snowlover2]

ILN

 

 

 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
424 PM EDT TUE MAY 20 2014

.SYNOPSIS...
A WARM AND MOIST AIRMASS WILL REMAIN IN PLACE OVER THE REGION
TONIGHT. A COLD FRONT WILL PUSH THROUGH THE REGION TOMORROW AND
TOMORROW NIGHT...WITH DRIER AND SLIGHTLY COOLER AIR MOVING OVER
THE OHIO VALLEY FOR THURSDAY AND FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
WEAK LOW PRESSURE IS LOCATED ACROSS IOWA AND NORTHERN
ILLINOIS...AND THIS LOW WILL GRADUALLY MOVE TO THE NORTHEAST OVER
THE NEXT 24 HOURS. WITH A WARM FRONT LIFTING NORTHEAST THROUGH THE
OHIO VALLEY...THE ILN CWA HAS ENTERED THE WARM SECTOR. THE 12Z
KILN SOUNDING INDICATED A RATHER STRONG MID-LEVEL CAP...WHICH
RECENT NAM/RAP MODEL DATA CONTINUE TO SUPPORT. A PERSISTENT BAND
OF WEAK AND SHALLOW SHOWERS FORMED IN THE SMALL DEPTH OF
INSTABILITY UNDER THE CAP...AT THE NOSE OF A MODEST LOW-LEVEL
JET...BUT THERE IS LITTLE TO NO CHANCE OF ANY LEGITIMATE
CONVECTION BREAKING OUT THIS AFTERNOON. ASIDE FROM THE
SHOWERS...DRY CONDITIONS HAVE BEEN MAINTAINED IN THE FORECAST
THROUGH THE EVENING.

TONIGHT...ALL ATTENTION WILL TURN TO EXPECTED CONVECTIVE
INITIATION IN THE LOT/IWX FORECAST AREAS. SEVERAL RUNS OF THE HRRR
(WHICH SEEMS TO BE A REASONABLE DEPICTION...COMPARED WITH THE
CURRENT-HOUR OVER-CONVECTING OF THE RAP/NAM/GFS) SHOW THAT STORMS
WILL INCREASE IN COVERAGE AND INTENSITY BETWEEN 00Z AND
04Z...EVENTUALLY PROPAGATING INTO THE NORTHWESTER ILN CWA SOME
TIME AFTER MIDNIGHT. THE LIMITING FACTORS FOR SEVERE WEATHER ARE
THAT DIURNAL INSTABILITY WILL BE WANING (AND THE STORMS WILL
EVENTUALLY BE RUNNING INTO THE CAP)...AND 0-3KM SHEAR (IMPORTANT
FOR MAINTENANCE OF STORM COMPLEXES) BACKS FROM NORTHWESTERLY TO
WESTERLY DURING THE OVERNIGHT HOURS...WHICH WILL MAKE IT HARDER
FOR FORWARD-PROPAGATING STORMS TO MAINTAIN INTENSITY WITH
SOUTHWARD EXTENT. WITH THAT SAID...OVERALL SHEAR AND INSTABILITY
PARAMETERS DO STILL SUPPORT SOME LEVEL OF THREAT OF STRONG
STORMS...THOUGH THE HWO MENTION HAS BEEN SCALED BACK TO A SMALL
SELECTION OF NORTHERN ILN CWA COUNTIES. A FEW WARNINGS WOULD NOT
BE OUT OF THE QUESTION...BUT CONVECTION IS EXPECTED TO BE
WEAKENING AS IT MOVES INTO THE FORECAST AREA. OVERALL POPS HAVE
ALSO BEEN TIGHTENED UP AND FOCUSED ON THE NORTHERN CWA THROUGH
MORNING.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
LEFTOVER MORNING CONVECTION AND CLOUD DEBRIS WILL END UP PLAYING A
BIG ROLE IN THUNDERSTORM POTENTIAL FOR WEDNESDAY...WITH AN
OTHERWISE-FAVORABLE SETUP FOR STRONG STORMS.

THE WEAK SURFACE LOW WILL GRADUALLY DRIFT EAST ACROSS THE LOWER
PENINSULA OF MICHIGAN ON WEDNESDAY...WITH A COLD FRONT STRETCHING
TO THE SOUTHWEST INTO THE MIDDLE MISSISSIPPI VALLEY. THOUGH THE
FRONTAL BOUNDARY WILL NOT MAKE IT INTO THE ILN CWA UNTIL LATE
WEDNESDAY NIGHT...THE REGIME AHEAD OF THE FRONT WILL BE MOIST AND
UNSTABLE...AND THIS IS WHERE CONVECTION IS EXPECTED TO DEVELOP.
INSTABILITY WILL BE IMPACTED THE GREATEST BY REMNANTS FROM THE
EARLY WEDNESDAY MORNING ACTIVITY...A NEARLY-IMPOSSIBLE QUESTION
TO ANSWER UNTIL THE SITUATION TONIGHT PLAYS OUT. HOWEVER...THE
MOST LIKELY SCENARIO SEEMS TO FAVOR INSTABILITY GROWING THE MOST
IN THE SOUTHERN AND SOUTHWESTERN PORTIONS OF THE ILN CWA...WITH
THE GREATEST IMPEDING TO INSOLATION IN CENTRAL OHIO. HIGH-RES
MODELS ARE NOT KEYING IN ON MUCH STORM DEVELOPMENT IN THE NORTHERN
PORTIONS OF THE CWA...BUT SHOW A GOOD SIGNAL FOR DIURNALLY-TIMED
CONVECTION FIRING OFF IN THE SOUTHERN HALF OF THE FORECAST
AREA...IN AN AREA WHERE CAPE VALUES OF 2000-2500 J/KG APPEAR
POSSIBLE (AS LONG AS THE SUN CAN HEAT THINGS UP FOR A WHILE). WNW
WIND SHEAR IS COMFORTABLY IN THE MODERATE AREA OF THE
SCALE...WHICH WILL SUPPORT STORM ORGANIZATION. ALTHOUGH THERE IS
A LITTLE BIT OF TURNING (WSW AT THE SURFACE TO WNW AT
6KM)...OVERALL THIS SCENARIO SEEMS TO PRIMARILY SUPPORT A WIND AND
HAIL THREAT (PERHAPS WITH SOME DISCRETE AND ORGANIZED UPDRAFTS).
UNLESS CONVECTION COMPLETELY OVERTURNS THE ATMOSPHERE...A THREAT
FOR THUNDERSTORMS MAY CONTINUE INTO THE OVERNIGHT HOURS...WITH
SOME LINGERING INSTABILITY AHEAD OF THE COLD FRONT.

POPS WERE KEPT IN THE 20-30 PERCENT RANGE THROUGH MUCH OF THE DAY
ON WEDNESDAY...BUT RAMPED UP TO LIKELY IN THE SOUTHERN CWA DURING
THE AFTERNOON AND EVENING. POPS WERE DROPPED TO ZERO AFTER 09Z.

HIGH PRESSURE OVER THE UPPER MIDWEST WILL GRADUALLY SLIDE
EASTWARD...BEGINNING TO INFLUENCE THE OHIO VALLEY ON THURSDAY. THE
AIR MASS MOVING IN WILL BE SIGNIFICANTLY DRIER AND SOMEWHAT
COOLER...WITH HIGHS DROPPING 5-10 DEGREES FROM WEDNESDAY.

[Hoosier]

Removal of hatching doesn't make sense.  They question supercell vs. multicell mode based off low-level flow, but usually that distinction is predicated by deep-layer or effective-layer shear, both of which are supportive of supercells.  You add in the lake breeze and focused area of low-level vorticity along the lakeshore that shows up on mesoanalysis and I get really confused about the question marks about storm mode.  I'd pretty much guarantee at least a couple supercell structures, and given the thermodynamic environment, I'd go as far to say that 2"+ diameter hail is a guarantee in almost any supercell structure.

 

 

The question I've been asking myself regarding the hail threat is what changed since this morning... and it seems like nothing really has.  The instability is being realized and low level flow has been a concern all along, or at least since I've been paying attention to this setup.  The lack of low level flow should be more of a negative factor as far as the tornado threat but of course it can't entirely be ruled out with the boundary and any storm scale interactions that occur.  

[hm8]

DVN 20z sounding