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June 21-27 Severe Weather


Chicago Storm

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Can see the outline of the sun already shining through the clouds. Temp on the way up.

Hearing several more MCS's are possible before the break at the end of the week for our subforum.

 

Edit: Flash flood watch extended east.

 

Still a lot of outages after yesterday's bow line.

 

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New day 2 dropped the hatched area.

 

  DAY 2 CONVECTIVE OUTLOOK 
   NWS STORM PREDICTION CENTER NORMAN OK
   1225 PM CDT TUE JUN 25 2013

   VALID 261200Z - 271200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID/UPPER-MS VALLEY TO
   THE NORTHEAST...

   ...SYNOPSIS...
   AN UPPER-LEVEL RIDGE WILL BUILD ACROSS THE WEST AS AN ANTICYCLONE
   STRENGTHENS NEAR THE FOUR CORNERS. IN RESPONSE...A WEAK SHORTWAVE
   TROUGH OVER THE NRN HIGH PLAINS WILL SHIFT EWD AND EVENTUALLY SEWD.
   A SHORTWAVE IMPULSE OVER NWRN ONTARIO WILL PROGRESS INTO SRN QUEBEC.
   A SERIES OF CONVECTIVELY-INDUCED IMPULSES SHOULD MOVE EWD FROM PARTS
   OF THE MS VALLEY TO THE NORTHEAST.

   ...MID/UPPER-MS VALLEY TO THE NORTHEAST...
   A BROAD AREA OF AT LEAST SEMI-ORGANIZED SEVERE RISK IS
   EVIDENT...WITH CONCENTRATED REPORT SWATHS LIKELY MODULATED BY THE
   IMPACT OF D1 CONVECTION AND SUBSEQUENT INFLUENCE OF REMNANT MCV/S ON
   BOTH THE THERMODYNAMIC AND KINEMATIC ENVIRONMENT. ON THE
   LARGE-SCALE...WITH A VEERED LLJ RELATIVE TO RECENT DAYS FROM THE SRN
   PLAINS ACROSS THE MIDWEST...A CONSIDERABLE AMOUNT OF CONVECTION
   SHOULD BE ONGOING AT 12Z/WED WITHIN A WAA REGIME. POCKETS OF STRONG
   DOWNSTREAM INSOLATION SHOULD RESULT IN SOME OF THIS ACTIVITY
   INTENSIFYING WITH AT LEAST SUFFICIENT DEEP-LAYER SHEAR FOR MULTICELL
   CLUSTERS...YIELDING RISKS OF DAMAGING WINDS AND SEVERE HAIL.

   THE MOST VOLATILE THERMODYNAMIC/KINEMATIC ENVIRONMENT WILL PROBABLY
   BE CENTERED FROM THE MID-MS TO LOWER OH VALLEY. WITH A BELT OF
   ENHANCED MID-LEVEL FLOW /BECOMING NWLY/ AND SUSTENANCE OF THE
   LLJ...DEEP-LAYER SHEAR WILL BE FAVORABLE FOR SUPERCELLS. WARMING
   MID-LEVEL TEMPERATURES WILL WEAKEN LAPSE RATES...BUT VERY WARM/MOIST
   MIXED-LAYER PARCELS SHOULD STILL BE SUFFICIENT FOR A STRONGLY
   UNSTABLE AIR MASS. INITIAL SUPERCELLS WOULD BE CAPABLE OF ALL SEVERE
   HAZARDS. HOWEVER...GIVEN WINDS LARGELY SLACKENING WITH HEIGHT FROM
   THE MID TO UPPER-LEVELS...SETUP SHOULD YIELD UPSCALE GROWTH INTO AN
   MCS BY LATE AFTERNOON/EVENING. POTENTIAL DOES EXIST FOR BOWING LINE
   SEGMENTS RESULTING IN A PREDOMINANT SEVERE WIND THREAT. ACTIVITY
   SHOULD PERSIST E/SEWD TOWARDS PARTS OF THE CNTRL/SRN APPALACHIANS
   AND TN VALLEY WITH DIMINISHING DAMAGING WIND RISK OVERNIGHT.

   ..GRAMS.. 06/25/2013

 

 

post-4544-0-42462900-1372181545_thumb.gi

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12z 4km NAM really backbuilds convection over the area for a large portion of the night.

 

Especially for LakeCook Rd. on southward. Don't need 2-3" though up here like it's showing!

 

RPM depicts a line of storms moving into Chicago just in time for rush hour.

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MESOSCALE DISCUSSION 1219
   NWS STORM PREDICTION CENTER NORMAN OK
   1243 PM CDT TUE JUN 25 2013

   AREAS AFFECTED...E-CNTRL/NERN MO...A LARGE PART OF IL...PARTS OF FAR
   ERN IA...PARTS OF FAR WRN INDIANA

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

   VALID 251743Z - 252015Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...THUNDERSTORMS WILL LIKELY INCREASE IN COVERAGE AND
   INTENSITY THROUGH THE AFTERNOON HOURS...AND MAY PRODUCE SVR WIND
   GUSTS AND HAIL. THE AREA IS BEING MONITORED FOR POSSIBLE SVR TSTM
   WATCH ISSUANCE.

   DISCUSSION...EARLY AFTERNOON SFC MESOANALYSIS HIGHLIGHTS A COUPLE OF
   SFC FEATURES THAT WILL POTENTIALLY SERVE AS FOCI FOR INITIAL
   THUNDERSTORM DEVELOPMENT THIS AFTERNOON:
   /1/ AN OUTFLOW BOUNDARY ARCING FROM NRN IL INTO E-CNTRL IA DEPOSITED
   BY A CONVECTIVE CLUSTER WHICH MOVED ACROSS THAT GENERAL AREA EARLIER
   TODAY...AND
   /2/ A DIFFERENTIAL HEATING ZONE OVER THE FRINGES OF MULTI-LAYERED
   CONVECTIVE CLOUD DEBRIS EXTENDING APPROXIMATELY W/E THROUGH CNTRL IL
   AND NE/SW IN NERN/CNTRL MO. INITIAL CELL DEVELOPMENT HAS ALREADY
   BEEN NOTED IN LOGAN COUNTY IL INVOF THE DIFFERENTIAL HEATING ZONE.

   MODIFICATIONS TO THE ILX 12Z RAOB FOR SFC CONDITIONS S OF THE
   OUTFLOW BOUNDARY SUGGEST MLCAPE HAS INCREASED TO AROUND 3000-3500
   J/KG WITH VERY LITTLE MLCINH. CONTINUED DIABATIC SFC HEATING AMIDST
   RICH LOW-LEVEL MOISTURE -- E.G. LOWEST 100-MB MEAN MIXING RATIO
   AROUND 16.5 G/KG PER 12Z ILX RAOB -- BENEATH THE NEWD EXTENT OF AN
   EML FEATURING 7-8-C/KM MID-LEVEL LAPSE RATES SHOULD YIELD A VERY
   UNSTABLE AIR MASS THROUGH THE AFTERNOON.

   PRESENT INDICATIONS ARE THAT CONVECTION WILL INCREASE IN
   COVERAGE/INTENSITY THROUGH THE AFTERNOON...WHILE WEAK WAA
   ACCOMPANYING A 20-30-KT LOW-LEVEL JET MAX PERSISTS. THE
   AFOREMENTIONED DEGREE OF BUOYANCY SHOULD SUPPORT VIGOROUS
   UPDRAFTS/DOWNDRAFTS...CAPABLE OF DMGG WINDS GUSTS AND SVR HAIL. WITH
   25-35 KT OF EFFECTIVE BULK SHEAR -- HIGHEST N OF INTERSTATE 70 -- A
   FEW ORGANIZED STORM STRUCTURES/SMALL CONVECTIVE CLUSTERS MAY ENSUE.
   THERE IS SOME QUESTION REGARDING THE ANTICIPATED COVERAGE OF SVR
   CONVECTION...HOWEVER...AS DEEP-LAYER FORCING FOR ASCENT SHOULD BE
   LIMITED. REGARDLESS...THE AREA WILL BE MONITORED FOR THE POSSIBLE
   ISSUANCE OF A SVR TSTM WATCH THROUGH THE AFTERNOON.

 

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MDW managed to fight up to 82/71 despite at best filtered sun. 

 

Prominent boundary still well south of the area but trying to wash/lift north.  If things go as quick as some guidance is suggesting, heavy rain threat could be shifted further south.

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IZZI...

 

 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1259 PM CDT TUE JUN 25 2013

.MESOSCALE DISCUSSION...
100 PM CDT

COMPLEX CONVECTIVE SCENARIO THIS AFTERNOON INTO THIS EVENING...WITH
POTENTIAL FOR SEVERE THUNDERSTORMS WITH PRIMARY THREAT BEING
TRANSITION TO DAMAGING WINDS.

REMNANT OUTFLOW BOUNDARY FROM OVERNIGHT AND THEN RE-ENFORCED BY
MORNING CONVECTION LIES FROM ROUGHLY ALONG I-80 EARLY THIS
AFTERNOON. THIS BOUNDARY IS MOST EVIDENT IN VISIBLE SATELLITE
IMAGERY AS AN AREA OF FESTERING AND MORE PROMINENT CUMULUS BUBBLING
UP...EVEN BENEATH PRETTY EXTENSIVE (BUT FADING) CIRRUS SHIELD.
DEVELOPING. SFC OBS INDICATE THAT AIR MASS NORTH OF THE OUTFLOW
BOUNDARY IS RECOVERING VERY QUICKLY WITH TEMPS/DEWPOINTS RAPIDLY
RISING AND WINDS VEERING AROUND TO S/SW AND BEGINNING TO GUST.

SHORTWAVE TROUGH WE`RE WATCHING CLOSELY AS A POTENTIAL IMPETUS FOR
STORMS THIS AFTERNOON IS OVER EASTERN IA/MO AND PUSHING EASTWARD.
WHILE NOT SEEING MUCH INDICATION OF CONVECTION DEVELOPING OVER
EASTERN IA ON VSBL IMAGERY WITHIN THE MASS OF MID LEVEL CLOUDINESS
AT THIS TIME...THE ASCENT NEAR AND DOWNSTREAM FROM THIS SHORTWAVE
LOOKS LIKELY TO ASSIST IN CONVECTIVE DEVELOPMENT THIS AFTERNOON OVER
NORTHERN OR CENTRAL ILLINOIS. CURRENT SATELLITE TRENDS SUGGEST THAT
THE OUTFLOW BOUNDARY WASHING OUT NEAR I-80 COULD SERVE AS A FOCAL
POINT FOR DEVELOPMENT...MOST LIKELY FROM I-80 OR I-88 SOUTHWARD.
FARTHER NORTH...WHILE BOUNDARY LAYER AIR MASS IS RECOVERING
QUICKLY...LACK OF OBVIOUS FOCUS FOR DEVELOPMENT ALONG WITH WEAKER
MID LEVEL LAPSE RATES IN WAKE OF EARLIER STORMS RAISES DOUBTS ABOUT
THE LIKELIHOOD OF INITIATION THIS AFTERNOON.

STRONGLY UNSTABLE AIR MASS (MLCAPES >3000 J/KG) ALONG WITH FAIRLY
STRONG MID LEVEL FLOW (40-50KT @ 6KM) AHEAD OF THE EASTERN IOWA
SHORT WAVE SHOULD ALLOW FOR SUSTAINED CONVECTION TO POTENTIALLY
BECOME SEVERE WITH BOTH LARGE HAIL AND DAMAGING WINDS. UNCERTAINTIES
REMAIN ON COVERAGE...BUT SHOULD STORMS CONGEAL INTO A LINE THEN
DAMAGING WINDS WOULD POSE A BIGGER THREAT...PARTICULARLY
SOUTHEASTERN CWA INTO NORTHWEST INDIANA.

WILL CONTINUE TO MONITOR SATELLITE/RADAR TRENDS FOR MORE IMMINENT
SIGNS OF ROBUST CONVECTIVE INITIATION.
 

 

 

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