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September 9th-10th Severe Threat


andyhb

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looking forward to my heavy rain MCS

 

Feeling about the same for here.  Timing for severe isn't the best this far west the way it's looking.  Still looks like some decent rains though with the tropical connection the other peeps mentioned.  Gonna be fun to watch how the whole thing evolves over the coming days.

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I couldn't help myself. I was unimpressed with the CAPE values on the GFS run so I just had to see what the DGEX was showing. It's like a black hole...it sucks you in sometimes :)

 

 

I thought the GFS was decent with SBCAPE.  This is the 18z run valid 21z Wed.  Struggles to get much instability into Michigan but pretty good farther south/west given the available shear.

 

 

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The 18Z DGEX run looks interesting for southern MI and northern IN. 344+ theta-e is widespread with a backed surface flow and 925mb winds ripping at 40 kts.

 

High theta-e at the surface might not mean much if the mid level lapse rates are near saturated adiabatic.

 

00z GFS appears to have come in significantly faster/less amplified than the 12z run.

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High theta-e at the surface might not mean much if the mid level lapse rates are near saturated adiabatic.

 

00z GFS appears to have come in significantly faster/less amplified than the 12z run.

 

 

I thought that Halloween 2013 case that you mentioned earlier was worth talking about for a minute as it serves as an example of unimpressive mid level lapse rates being overcome and resulting in a fairly prolific severe weather episode.  Per mesoanalysis archive, mid level lapse rates for that event are roughly on par with what's being shown for this one and CAPE was even less.  However, that system was more impressive dynamically and had a surface low that was more or less bombing out.  Not sure we will have that kind of deepening in this case.  

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I thought that Halloween 2013 case that you mentioned earlier was worth talking about for a minute as it serves as an example of unimpressive mid level lapse rates being overcome and resulting in a fairly prolific severe weather episode.  Per mesoanalysis archive, mid level lapse rates for that event are roughly on par with what's being shown for this one and CAPE was even less.  However, that system was more impressive dynamically and had a surface low that was more or less bombing out.  Not sure we will have that kind of deepening in this case.  

 

That trough was nearly as strong as the 11/17 one, although the surface low didn't deepen as much as that one on the day of the event. It was really maturing when it moved north of the border on 11/1 deepening below 976 mb. There was E Pacific tropical activity affecting that one as well (Sonia/Raymond).

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It is the NAM of course, but it generates about 1000 to 2000 J/KG of SBCAPE in the warm sector of this system Wednesday...

 

 

Was just going to post that.  Generally don't trust the NAM in the 72-84 hour range but I was interested to see what kind of instability values it was generating.  It's doing that with temps that aren't extraordinarily high and dews generally under 75.  

 

Day 3 outlook hinted at higher probs and a possible upgrade to moderate risk.  Day 4 risk area is unchanged.

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Potential is there, but key instability ingredients will probably be lacking, especially on Wednesday. (as mentioned, mid-level lapse rates are lousy looking)

While it may be on the western fringe of (mostly west of) this sub-forum, Tuesday seems to have the higher ceiling at this point. Even there it's not a lock yet, especially if convective debris wins out and further mitigates the threat.

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Plenty of questions with this setup and certainly will be interesting/educational to watch it play out.  A bit tough to pin down the best area for Wednesday but at this point it seems to me like the best ingredients may line up over Indiana (trying not to be a homer lol).  I'm skeptical about the threat once you get north of southern Michigan. 

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I think I'm going to have to agree with the central Indiana area as well. The NAM is still a bit more bullish with the theta-e advection into Michigan, but I'm not convinced that'll verify. Plus, like andyhb said the lapse rates are very unimpressive up there so it might not matter anyway. The shear/instability alignment from the 00Z GFS valid at 21Z on Wednesday was about 40 kts 0-6km and 1800 j/kg of SBCAPE near Indianapolis so that's respectable. The NE/IA border area seems to be in the hotzone for nearly every outbreak this summer it seems.

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New day 2

 

 

DAY 2 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1232 AM CDT MON SEP 08 2014  
 
VALID 091200Z - 101200Z  

 
...THERE IS A SLGT RISK OF SVR TSTMS LATE TUESDAY AFTERNOON INTO  
TUESDAY NIGHT ACROSS PARTS OF THE CENTRAL PLAINS/MID MISSOURI VALLEY  
REGION INTO THE UPPER MIDWEST...  
   
..SUMMARY
 
 
SEVERE STORMS ARE EXPECTED LATE TUESDAY AFTERNOON INTO TUESDAY NIGHT  
ACROSS PARTS OF THE CENTRAL PLAINS AND MID MISSOURI VALLEY  
REGION...NORTHEASTWARD INTO THE UPPER MIDWEST. THESE STORMS WILL BE  
ACCOMPANIED BY THE RISK FOR SWATHS OF DAMAGING WIND GUSTS...A FEW  
TORNADOES...AND PERHAPS LARGE HAIL.  
   
..SYNOPSIS
 
 
IT STILL APPEARS THAT THE STRONGER POLAR WESTERLIES WILL REMAIN NEAR  
OR NORTH OF THE CANADIAN/U.S. BORDER AREA THROUGH MUCH OF THIS  
FORECAST PERIOD. HOWEVER...AS ONE SIGNIFICANT EMBEDDED CYCLONIC  
CIRCULATION ACCELERATES EAST OF HUDSON BAY...MODELS INDICATE THAT  
ANOTHER WILL BEGIN TO EVOLVE WITHIN BROADER-SCALE UPPER TROUGHING  
DIGGING SLOWLY ACROSS THE WESTERN CANADIAN PROVINCES AND  
INTERNATIONAL BORDER AREA. AT THE SAME TIME...TO THE SOUTHEAST OF  
THIS LATTER FEATURE...A SIGNIFICANT UPPER JET... EMERGING FROM THE  
PACIFIC...IS FORECAST TO CONTINUE PROPAGATING EAST NORTHEASTWARD  
AROUND THE NORTHERN PERIPHERY OF REMNANT SUBTROPICAL RIDGING  
CENTERED OVER THE SOUTHERN TIER STATES.  
 
WITHIN THE STRONGER SUBTROPICAL STREAM...ONE SIGNIFICANT IMPULSE IS  
EXPECTED TO PROGRESS ACROSS THE NORTH CENTRAL PLAINS AND MIDDLE  
MISSOURI VALLEY BY EARLY TUESDAY EVENING...THEN INTO THE UPPER  
MIDWEST OVERNIGHT...AS AN UPSTREAM IMPULSE SHIFTS ACROSS THE GREAT  
BASIN AND CENTRAL ROCKIES. AT LEAST PARTLY IN RESPONSE TO FORCING  
ASSOCIATED WITH THESE PERTURBATIONS...MODELS CONTINUE TO SUGGEST  
THAT SIGNIFICANT CYCLOGENESIS WILL OCCUR ALONG A SOUTHWARD ADVANCING  
COLD FRONT. AT THE SURFACE...IT STILL APPEARS MOST PROBABLE THAT  
THIS WILL COMMENCE IN THE VICINITY OF THE MID MISSOURI VALLEY DURING  
THE EVENING...BEFORE PROCEEDING NORTHEASTWARD TOWARD THE UPPER GREAT  
LAKES REGION OVERNIGHT. THIS SHOULD BE ACCOMPANIED BY CONSIDERABLE  
STRENGTHENING OF LOWER/MID TROPOSPHERIC WIND FIELDS AND VERTICAL  
SHEAR WITHIN THE WARM SECTOR OF THE LOW...WHERE MOISTURE CONTENT IS  
ALSO EXPECTED TO INCREASE TO SEASONABLY HIGH VALUES.  
 
GIVEN THE INCREASING LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION  
AND DESTABILIZATION...A SUBSTANTIAL INCREASE IN CONVECTIVE POTENTIAL  
IS EXPECTED ACROSS THE MID MISSOURI VALLEY THROUGH THE UPPER MIDWEST  
TUESDAY INTO TUESDAY NIGHT...INCLUDING THE RISK FOR SEVERE STORMS.  
OTHERWISE...THE RISK FOR THUNDERSTORM ACTIVITY WILL BEGIN TO LOWER  
ACROSS SOUTHWESTERN DESERTS INTO THE CENTRAL AND SOUTHERN  
ROCKIES...THOUGH WIDELY SCATTERED DIURNAL THUNDERSTORM ACTIVITY  
REMAINS POSSIBLE. THE RISK FOR THUNDERSTORM ACTIVITY MAY ALSO  
LINGER ACROSS PARTS OF THE SOUTHEAST...MAINLY NEAR OR JUST EAST OF  
SOUTHERN MID ATLANTIC COASTAL AREAS.  
   
..CNTRL PLAINS/MID MO VALLEY INTO THE UPPER MIDWEST
 
 
WHILE CONFIDENCE IN THE DEVELOPMENT OF SEVERE THUNDERSTORM ACTIVITY  
IS INCREASING FOR LATE TUESDAY INTO TUESDAY NIGHT...A NUMBER OF  
UNCERTAINTIES LINGER WHICH WILL TEMPER THE PROBABILISTIC  
FORECAST...AND PRECLUDE A HIGHER CATEGORICAL OUTLOOK AND THE  
INCLUSION OF 10 PERCENT SIGNIFICANT SEVERE PROBABILITIES...AT LEAST  
FOR NOW. DIFFERENCES AMONG THE MODELS CONTINUE CONCERNING THE  
TIMING OF MORE RAPID DEEPENING OF THE SURFACE LOW AND ITS  
TRACK...WHICH COULD HAVE AN APPRECIABLE IMPACT ON THE SEVERE WEATHER  
POTENTIAL. FURTHERMORE...MODELS CONTINUE TO SUGGEST THAT  
CONSIDERABLE HIGH-LEVEL CLOUD COVER/CONVECTION ASSOCIATED WITH THE  
LEAD UPPER IMPULSE WILL OVERSPREAD MUCH OF THE REGION DURING THE  
DAY. WHILE LOWER/MID TROPOSPHERIC LAPSE RATES MAY BE INITIALLY  
FAIRLY STEEP ACROSS THE DEVELOPING WARM SECTOR...MODEL FORECAST  
SOUNDINGS INDICATE MOISTENING AND SATURATION FROM UPPER INTO  
MID-LEVELS PRIOR TO THE ONSET OF EXPECTED VIGOROUS STORM  
DEVELOPMENT. AND IT REMAINS UNCLEAR WHAT...IF ANY...IMPACT THIS  
WILL HAVE.  
 
STILL...WITH SURFACE DEW POINTS LIKELY TO INCREASE TO AROUND 70F  
/ALONG WITH PRECIPITABLE WATER INCREASING UP TO AROUND 2  
INCHES/...BENEATH REMNANT STEEP LOWER/MID TROPOSPHERIC LAPSE  
RATES...SIZABLE MIXED-LAYER CAPE ON THE ORDER OF 2000-3000 J/KG IS  
FORECAST TO DEVELOP BY TUESDAY AFTERNOON. AS THIS OCCURS AND  
LARGE-SCALE ASCENT BEGINS TO INCREASE ACROSS THE MID MISSOURI  
VALLEY...TOWARD THE UPPER MIDWEST...BOUNDARY LAYER BASED STORM  
DEVELOPMENT MAY BEGIN AS EARLY AS THE 20-22Z TIME FRAME.  
 
VERTICAL SHEAR IS EXPECTED TO ALREADY BE CONDUCIVE TO THE  
DEVELOPMENT OF SUPERCELLS BY THE TIME THIS OCCURS...BEFORE SOUTHERLY  
LOW-LEVEL JET STRENGTHENING /TO AT LEAST 40-50 KT AT 850 MB/  
CONTRIBUTES TO THE EVOLUTION OF SIZABLE CLOCKWISE CURVED LOW-LEVEL  
HODOGRAPHS SOMETIME LATE TUESDAY AFTERNOON OR EVENING. AT THE SAME  
TIME...LIFT ASSOCIATED WITH STRENGTHENING LOW-LEVEL WARM ADVECTION  
PROBABLY WILL SUPPORT A CONSIDERABLE INCREASE IN STORMS...AND THE  
UPSCALE CONVECTIVE GROWTH OF AN ORGANIZING CONVECTIVE  
SYSTEM...INITIALLY ACROSS PARTS OF EASTERN NEBRASKA INTO  
IOWA...BEFORE SPREADING NORTHEASTWARD. HOW QUICKLY THIS OCCURS MAY  
IMPACT THE TORNADO POTENTIAL...WHICH SHOULD BE PRESENT GIVEN THE  
SIZE OF THE LOW-LEVEL HODOGRAPHS IN THE PRESENT OF HIGH  
BOUNDARY-LAYER MOISTURE CONTENT/HUMIDITY.  
 
A STRONG TORNADO OR TWO MAY NOT BE OUT OF THE  
QUESTION...PARTICULARLY WITH ANY LINGERING DISCRETE STORMS EARLY  
TUESDAY EVENING. HOWEVER...IT SEEMS THAT POTENTIALLY DAMAGING WIND  
GUSTS WILL BECOME THE MORE PREDOMINANT SEVERE THREAT...AS HEAVY  
PRECIPITATION LOADING AND THE DOWNWARD TRANSPORT OF MOMENTUM  
INCREASE WITH THE DEVELOPING MESOSCALE CONVECTIVE SYSTEM.  
 
..KERR.. 09/08/2014 

 

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New day 3

 

 

DAY 3 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0230 AM CDT MON SEP 08 2014  
 
VALID 101200Z - 111200Z  

 
...THERE IS A SLGT RISK OF SVR TSTMS WEDNESDAY AFTERNOON AND EVENING  
ACROSS SOUTHERN PORTIONS OF THE GREAT LAKES REGION INTO THE MIDDLE  
MISSISSIPPI AND LOWER OHIO VALLEYS...  
   
..SUMMARY
 
 
SEVERE STORMS ARE POSSIBLE WEDNESDAY ACROSS SOUTHERN PORTIONS OF THE  
GREAT LAKES REGION INTO PARTS OF THE MIDDLE MISSISSIPPI AND LOWER  
OHIO VALLEYS. THIS WILL BE ACCOMPANIED BY THE RISK FOR DAMAGING  
WIND GUSTS...POSSIBLY A COUPLE OF TORNADOES...AND COULD IMPACT THE  
CHICAGO...DETROIT...INDIANAPOLIS AND CLEVELAND METROPOLITAN AREAS.  
   
..SYNOPSIS
 
 
MODELS CONTINUE TO INDICATE A SOUTHWARD SHIFT OF THE POLAR  
WESTERLIES THROUGH THIS FORECAST PERIOD. STRENGTHENING OF CYCLONIC  
MID/UPPER FLOW IS EXPECTED ACROSS THE NORTHERN ROCKIES AND NORTHERN  
PLAINS...AROUND THE SOUTHERN PERIPHERY OF AN ELONGATED CLOSED  
LOW/POSITIVELY TILTED TROUGH ADVANCING ACROSS THE INTERNATIONAL  
BORDER AREA. THIS WILL BE PRECEDED BY A SOUTHWESTERLY SUBTROPICAL  
JET...WHICH IS FORECAST TO CONTINUE PROPAGATING NORTHEASTWARD  
THROUGH THE GREAT LAKES REGION WEDNESDAY AND WEDNESDAY NIGHT.  
 
ASSOCIATED WITH THESE DEVELOPMENTS...A FAIRLY DEEP SURFACE CYCLONE  
SHOULD CONTINUE TO MIGRATE NORTHEAST OF THE UPPER MISSISSIPPI  
VALLEY...THROUGH PORTIONS OF EASTERN ONTARIO/WESTERN QUEBEC BY THE  
END OF THE PERIOD. IN ITS WAKE...A SIGNIFICANT COLD FRONT WILL  
CONTINUE TO SURGE SOUTHEASTWARD...REACHING THE LOWER OHIO  
VALLEY/OZARK PLATEAU AND SOUTHERN PLAINS BY 12Z THURSDAY. THESE  
FEATURES ARE EXPECTED TO PROVIDE THE FOCUS FOR THE HIGHEST  
THUNDERSTORM PROBABILITIES ON WEDNESDAY...INCLUDING THE RISK FOR  
SEVERE STORMS ACROSS SOUTHERN PORTIONS OF THE GREAT LAKES REGION  
SOUTHWESTWARD AT LEAST THROUGH THE MID MISSISSIPPI VALLEY.  
   
..SRN GREAT LAKES REGION INTO MID MS/LOWER OHIO VALLEYS
 
 
SIMILAR POINTS OF UNCERTAINTY CONCERNING THE SEVERE WEATHER  
POTENTIAL ON TUESDAY CONTINUE INTO WEDNESDAY WITH THE EVOLVING  
SYSTEM OVER THE UPPER MIDWEST/GREAT LAKES REGION. IT CURRENTLY  
SEEMS MOST PROBABLE THAT A WEAKENING AREA OF CONVECTION ASSOCIATED  
WITH THE STRONGEST FORCING FOR UPWARD VERTICAL MOTION...AND THE CORE  
OF THE STRONGER DEEP-LAYER WIND FIELDS...WILL SPREAD AHEAD OF THE  
CYCLONE...ACROSS PARTS OF LOWER MICHIGAN AND ADJACENT PORTIONS OF  
THE GREAT LAKES EARLY WEDNESDAY. HOWEVER...ON THE TRAILING SOUTHERN  
FLANK OF AN ASSOCIATED OUTFLOW BOUNDARY...WARM ADVECTION MAY SUPPORT  
ANOTHER DEVELOPING CLUSTER OF STORMS ACROSS PARTS OF NORTHERN  
ILLINOIS AND INDIANA BY MID DAY. IT APPEARS THAT THIS WILL COINCIDE  
WITH THE EASTWARD/NORTHWARD ADVECTION OF SEASONABLY HIGH MOISTURE  
CONTENT...WITH SURFACE DEW POINTS INCREASING TO NEAR 70F EXPECTED AS  
FAR NORTH AS SOUTHERN LOWER MICHIGAN /AND PRECIPITABLE WATER  
INCREASING TO 1.75 TO 2 INCHES/. AND IT APPEARS THAT THIS WILL  
OCCUR IN THE PRESENCE OF AT LEAST 40-50 KT MEAN WEST SOUTHWESTERLY  
LOWER/MID TROPOSPHERIC FLOW.  
 
WITHIN THIS ENVIRONMENT...INCREASING INFLOW OF WEAK TO MODERATE  
MIXED-LAYER CAPE SHOULD SUPPORT FURTHER CONVECTIVE  
INTENSIFICATION...WITH THE UPSCALE GROWTH INTO AN ORGANIZING  
CONVECTIVE SYSTEM POSSIBLE. AS THIS OCCURS...HEAVY PRECIPITATION  
LOADING AND THE DOWNWARD TRANSPORT OF MOMENTUM ARE EXPECTED TO  
CONTRIBUTE TO SWATHS OF DAMAGING WIND GUSTS AS CONVECTION SPREADS  
TOWARD THE LOWER GREAT LAKES REGION THROUGH EARLY EVENING.  
 
ADDITIONAL STORM DEVELOPMENT IS EXPECTED ALONG AND AHEAD OF THE  
SOUTHWARD ADVANCING FRONT...INTO A PROGRESSIVELY WEAKER FLOW REGIME  
ACROSS THE SOUTHERN PLAINS.  
 
..KERR.. 09/08/2014  

 

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I know that I'm not trusting the NAM...yet. It's been kinda on it's own so far.

 

 

We're going to need as much surface heating as possible, especially with the very poor mid level lapse rates.  If lapse rates aloft were steep then it would be easier to get away with less than ideal heating, but it gets harder in a case like this.  NAM is suggesting temps AOA 80 for about the southern 2/3 of the state.   With 850 mb temps around 18-20C, any short period/breaks of sun should allow that to occur.

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