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June 20-21 and June 24-27 Heavy Rain/Severe Threats


Hoosier

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The sig tor ingredients actually dropped off significantly from the 15z to the 21z run.

They dropped off to a point yes... But i wouldn't say significantly, as in a big decrease. Both STP fixed and cin only dropped by <1.0, and SCP fell by less than 2. And CAPE increased by nearly 300J/KG.

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Regarding tonight in the threat area later today...

MESOSCALE DISCUSSION 1149
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT WED JUN 24 2015

AREAS AFFECTED...CNTRL AND ERN NEB / WRN THROUGH SRN IA / NRN MO /
W-CNTRL IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 240539Z - 240645Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...THE THREAT FOR SEVERE WEATHER IS EXPECTED TO INCREASE
EARLY THIS MORNING WITH TSTMS DEVELOPING OVER THE REGION.
CONVECTIVE TRENDS ARE BEING MONITORED FOR MESOSCALE ORGANIZATION OF
STORMS WHICH COULD NECESSITATE A WATCH.

DISCUSSION...IN RESPONSE TO INCREASING WAA AND ISENTROPIC ASCENT AT
THE TERMINUS OF A NOCTURNALLY STRENGTHENING LLJ...ELEVATED TSTMS
HAVE DEVELOPED FROM E OF SUX TO NEAR AND SW OF DSM AS OF 0520Z.
OTHER STORMS WERE DEVELOPING AT THIS TIME DOWNSTREAM FROM A SMALL
MCS NEAR MCK OVER CNTRL NEB /N OF GRI/. THESE LOW-LEVEL FORCING
MECHANISMS WILL PERSIST /AND LIKELY STRENGTHEN/ OVER THE NEXT COUPLE
OF HOURS...PROMOTING ADDITIONAL STORM DEVELOPMENT ACROSS THE
DISCUSSION AREA.

WHILE THE THERMODYNAMIC CHARACTERISTICS OF THE 00Z OAX AND TOP
SOUNDINGS WERE NOT FAVORABLE FOR VIGOROUS UPDRAFT GROWTH...RICHER
LOW-LEVEL MOISTURE AS SAMPLED BY THE 00Z SGF SOUNDING WILL CONTINUE
TO BE ADVECTED POLEWARD...CONTRIBUTING TO FURTHER DESTABILIZATION
FOR MOST-UNSTABLE PARCELS. AND GIVEN THE STEEP MID-LEVEL LAPSE
RATES AND AMPLE EFFECTIVE BULK SHEAR...THE SETUP WILL BE SUPPORTIVE
OF STRONG TO SEVERE STORMS CAPABLE OF MAINLY LARGE HAIL.

RECENT CONVECTION-ALLOWING MODEL GUIDANCE SUGGESTS THAT THE HIGHEST
PROBABILITY FOR MESOSCALE ORGANIZATION OF STORMS IS OVER CNTRL INTO
ERN NEB WHERE DAMAGING WIND POTENTIAL COULD BECOME A CONCERN IN
ADDITION TO THE HAIL THREAT. AS SUCH...CONVECTIVE TRENDS WILL BE
MONITORED FOR A POSSIBLE WATCH ISSUANCE.

..MEAD.. 06/24/2015

 

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SPC 06Z Thunderstorm outlook highlighted an area from NW'ern/W-Central IA eastward into NW'ern Illinois as having the highest probability of thunderstorms at 40% from 20Z to 00Z... 06Z SPC Severe Outlook should be out soon...

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..THERE IS AN ENH RISK OF SVR TSTMS OVER THE CORNBELT  
 
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE N-CNTRL HIGH PLAINS  
INTO THE MIDWEST...  
 
...THERE IS A MRGL RISK OF SVR TSTMS FROM THE CNTRL AND NRN HIGH  
PLAINS INTO THE OH VALLEY...  
 
...THERE IS A MRGL RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE  
SOUTHEAST U.S....  
   
..SUMMARY
 
 
A SEVERE THREAT IS EXPECTED FROM PARTS OF THE NORTHERN PLAINS EAST  
SOUTHEASTWARD INTO THE MIDWEST MAINLY LATE THIS AFTERNOON AND  
EVENING...THEN FOCUS IN THE CORNBELT REGION LATE TONIGHT. LARGE  
HAIL AND DAMAGING WIND GUSTS ALONG WITH A THREAT FOR A FEW TORNADOES  
WILL BE POSSIBLE DURING THE AFTERNOON AND EVENING. A CONCENTRATED  
AREA OF SEVERE STRAIGHT-LINE WINDS MAY OCCUR ACROSS IOWA INTO  
NORTHERN ILLINOIS TONIGHT.  
   
..SYNOPSIS
 
 
CORRIDOR OF STRONG MID- TO HIGH-LEVEL FLOW WILL PERSIST FROM THE NRN  
ROCKIES ACROSS THE MIDWEST AND INTO THE NORTHEAST. A SERIES OF  
LOW-AMPLITUDE DISTURBANCES EMBEDDED WITHIN THIS FLOW REGIME WILL  
MOVE THROUGH THE NRN PLAINS INTO THE UPPER MIDWEST TO THE N OF A  
MID-LEVEL ANTICYCLONE OVER THE LOWER MS VALLEY. IN THE LOW  
LEVELS...AN EFFECTIVE FRONT WILL EXTEND FROM THE SRN APPALACHIANS  
INTO THE LOWER TO MID MO VALLEY AND ADVANCE NWD INTO IA AS A WARM  
FRONT.  
   
..MID MS VALLEY REGION
 
 
CLUSTER OF ELEVATED STORMS MAY BE ONGOING ACROSS NEB/IA ON THE NOSE  
OF A CNTRL PLAINS LLJ INVOF THE FRONTAL ZONE LOCATED OVER THE LOW TO  
MID MO VALLEY. IT IS POSSIBLE SOME OF THE EARLY-DAY ACTIVITY MAY  
LINGER AS IT MOVES DOWNSTREAM ACROSS IA INTO THE MID MS VALLEY AND  
PERHAPS POSE A LARGE HAIL/WIND RISK. NONETHELESS...CONSIDERABLE  
UNCERTAINTY REMAINS REGARDING THE POTENTIAL IMPACTS OF MORNING  
STORMS ACROSS IA/WRN IL.  
BY MID TO LATE AFTERNOON...CONVERGENCE INVOF THE FRONT AND A  
SHORTWAVE TROUGH --ANALYZED OVER THE NRN HIGH PLAINS TUESDAY NIGHT--  
WILL MOVE TO THE ERN DAKOTAS/MN AND EVENTUALLY INTO THE WRN GREAT  
LAKES BY THURSDAY MORNING. ASCENT ASSOCIATED WITH THIS FEATURE  
COUPLED WITH STRONG HEATING AND AN INCREASINGLY MOISTURE RICH  
BOUNDARY LAYER WILL WEAKEN THE CAP AND ISOLD TO SCTD STORMS SHOULD  
DEVELOP BY LATE IN THE DAY WITHIN A STRONG TO VERY UNSTABLE AIRMASS.  
VEERING WINDS INCREASING WITH HEIGHT WILL LIKELY YIELD A SUPERCELL  
MODE INITIALLY WITH ALL SEVERE HAZARDS POSSIBLE. ENLARGED  
HODOGRAPHS AND VERY MOIST LOW LEVELS DEPICTED BY SOME GUIDANCE WOULD  
SUPPORT AN OTHERWISE GREATER TORNADO THREAT ACROSS IA THAN IS  
CURRENTLY FORECAST. BY MID EVENING...THE INTENSIFICATION AND  
VEERING OF LLJ INTO IA SHOULD PROMOTE UPSCALE GROWTH INTO AN  
ESEWD-MOVING SEVERE MCS OVERNIGHT. A CONCENTRATED SWATH OF SEVERE  
WIND GUSTS WITH A FORWARD PROPAGATING BOW ECHO AND PERHAPS AN  
ACCOMPANYING MESOVORTEX TORNADO RISK MAY RESULT. IT IS POSSIBLE A  
CATEGORICAL UPGRADE TO MODERATE RISK MAY BE NEEDED IF CONFIDENCE  
INCREASES FOR THIS SCENARIO.  
   
..CNTRL/NRN PLAINS.
 
 
ELY LOW-LEVEL FLOW NORTH OF FRONT/SFC LOW WILL MAINTAIN UPPER 50S  
DEWPOINTS BENEATH STEEP LAPSE RATES SUPPORTING A CORRIDOR OF  
MODERATE INSTABILITY. STORMS ARE EXPECTED TO DEVELOP OVER THE HIGHER  
TERRAIN AND SPREAD EWD INTO THE PLAINS WHERE EFFECTIVE SHEAR WILL BE  
SUPPORTIVE OF ORGANIZED STORMS...INCLUDING SUPERCELLS. LARGE HAIL  
AND DAMAGING WIND WILL BE THE MAIN THREATS FROM LATE AFTERNOON INTO  
THE EVENING.  
   
..CNTRL GULF COAST INTO THE SERN U.S
 
 
ISOLD TO SCTD DIURNALLY-DRIVEN STORMS WILL LIKELY DEVELOP INVOF SEA  
BREEZE BOUNDARIES AND LOCALLY WHERE THE CAP IS WEAKEST. A HIGH PW  
ENVIRONMENT AND VERY WEAK FLOW WILL RESULT IN PULSE STORMS. THE  
LARGER AND MORE WATER-LOADED CORES WILL POTENTIALLY YIELD LOCALIZED  
WIND DAMAGE OWING TO 50-60 MPH WIND GUSTS. THE SEVERE RISK WILL  
DIMINISH BY EVENING AS THE BOUNDARY LAYER COOLS.  
 
..SMITH/ROGERS.. 06/24/2015  
 

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Not too sure about the 5% tornado risk... Environment that the "initial supercells" will be in is very impressive as noted by a number of CAM's... Perhaps they're waiting for things to come in to better focus, as far as a more exact location of the WF and therefore an area of generally enhanced tornado/very large hail potential. I'd bet that at the 1630Z update-- if trends continue in models with an impressive environment, and it becomes clear that there will be not much in the way of convection lingering into the afternoon-- that we will see an increase in all 3 probs. To 10% hatched for TOR's, At least 30% hatched for large hail, and 45% hatched (MDT) for damaging winds. But that's just an idea...  

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None of the models I've looked at develop much surface based cape over the northern and northeastern extent of the enhanced portion of the risk area.  Festering morning convection would only further reduce cape further north as well.  In my eyes that's too far northeast, but SPC obviously has fantastic forecasters who are probably seeing some things that I'm not.

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None of the models I've looked at develop much surface based cape over the northern and northeastern extent of the enhanced portion of the risk area.  Festering morning convection would only further reduce cape further north as well.  In my eyes that's too far northeast, but SPC obviously has fantastic forecasters who are probably seeing some things that I'm not.

SBCAPE doesnt make it into the area, since the WF lags to the south... However AT LEAST modest to moderate MUCAPE will likely make it into that area by 03-09Z but maybe not too north of the WI/IL line, and with the impressive forecasted LLJ it makes sense.

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None of the models I've looked at develop much surface based cape over the northern and northeastern extent of the enhanced portion of the risk area.  Festering morning convection would only further reduce cape further north as well.  In my eyes that's too far northeast, but SPC obviously has fantastic forecasters who are probably seeing some things that I'm not.

 

 

It seems like they are hedging toward a well developed linear MCS being able to transport severe winds to the ground, even with a lack of surface based instability in those areas.  Like you, I'm wondering about the northeastward placement, but not having too much extensive daytime activity would be step 1 toward having a better chance.

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06z NAM 4km & 'regular' NAM justify the shift north on the new outlook, it appears. Nasty storms in the northern suburbs by 07z Thursday per the 4km.

Flash flood watch also extended to the northern tier of LOT counties.

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I think the northern metro areas and probably Rockford will end up under the MCS stratiform rain shield. Biggest threat probably will be high winds - like some of you mentioned.

Unfortunately I can see the same areas as Monday night getting the most severe weather tonight.

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seeing the telltale back building across IA (actually back into NE now), should see an adjustment south on the next update

HRRR shows an initial shot favoring south LOT in the evening then a new batch brewing into northern iowa after dark...and would probably get cranking with a noc jet...the frontal area sure looks like its going to see buckets of QPF over the next 24 hours

Edit....sim radar shows numerous discrete cells from Clinton back to Northcentral Iowa at 03Z 25JUNE

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HRRR shows an initial shot favoring south LOT in the evening then a new batch brewing into northern iowa after dark...and would probably get cranking with a noc jet...the frontal area sure looks like its going to see buckets of QPF over the next 24 hours

Edit....sim radar shows numerous discrete cells from Clinton back to Northcentral Iowa at 03Z 25JUNE

 

given the warm front placement (and likely future placement) what we really need is initiation over far S. MN not IA

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Overall trend i am seeing thus far this morning is for a couple distinct rounds in and around N IL...frontal orientation and position differs model to model. I just hope the hardest hit areas a few days ago don't get slammed too hard...looks like things are setting up for another tough night for them though...

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