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September 9th-10th Severe Threat

andyhb

By andyhb,
in Lakes/Ohio Valley

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wxman_ind

wxman_ind

Posted
Posted

Moisture parameters are very impressive with this system, As my colleague pointed out in the AFD,

 

 

NAEFS MEAN INTEGRATED WATER VAPOR TRANSPORT IS SHOWING OVER 4 STANDARD DEVIATIONS COMPARED TO
THIS TIME OF YEAR...AND PRECIPITABLE WATER VALUES IN MOST MODEL SOLUTIONS ARE OVER 2 INCHES AND APPROACHING 2.5 WHICH WOULD BE IN THE TOP 99TH PERCENTILE FOR CLIMATOLOGY.

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Geos

Geos

Posted
Posted

Yeah it's a pretty intense discussion!

Make sure your drains are cleared and your sump pumps are working!

 

 

FOR THE REMAINDER OF THE AFTERNOON AND INTO THE EVENING...CONDITIONS
WILL BE THE RELATIVE CALM BEFORE THE STORM. THE SFC LOW IS
BEGINNING TO DEEPEN OVER THE CNTRL PLAINS WHILE HIGH PRESSURE MOVES
OFF THE EAST COAST. INCREASING SOUTHERLY FLOW IS RAMPING UP OVER
THE LOWER AND MIDDLE MISSISSIPPI VALLEY...SETTING UP VERY STRONG
WARM/MOIST ADVECTION POINTING INTO THE MIDWEST. THIS
AFTERNOON...CONVECTIVE ACTIVITY HAS ALREADY BROKEN OUT ALONG THE
NOSE OF A 50 KT LOW LEVEL JET...EXTENDING FROM WRN IOWA INTO CNTRL
IL. THIS STRONG LOW LEVEL JET WILL CONTINUE TO PUMP MOISTURE INTO
THE REGION WHILE MOISTURE ASSOCIATED WITH THE REMNANTS OF HURRICANE
NORBERT ADVECT OVER THE REGION AT THE MID LEVELS. THE MODELS HAVE
BEEN VERY CONSISTENT ON ADVERTISING A SWATH OF PWATS OF 2.0 TO 2.5
INCHES POOLING AHEAD OF THE FRONT. THE LOW LEVEL WARM ADVECTION
AHEAD OF THE FRONT...CONVERGENCE ALONG THE FRONT...A STRONG MID
LEVEL SHORTWAVE AND A COUPLED JET ALOFT WILL ALL COMBINE TO GENERATE
STRONG AND PERSISTENT THUNDERSTORMS. THERE SHOULD BE ADEQUATE SHEAR
IN THE LOW LEVELS BETWEEN SLY SFC WINDS AND 50 KT SWLY WINDS AT
925-850MB TO SUPPORT AN INITIAL CONVECTIVE MODE SUPPORTING SOME
ISOLATED SUPERCELLS ALONG WITH THE GENERAL THUNDER. SPC HAS
OUTLOOKED THE ENTIRE CWA WITH A SLIGHT RISK OVER SEVERE
THUNDERSTORMS...WITH THE PRIMARY THREATS BEING STRONG DAMAGING WINDS
AND MARGINALLY SEVERE HAIL. THE 12Z SOUNDINGS FROM ILX/DVN INDICATE
THE FREEZING LEVEL AT 13KFT AND WITH PERSISTENT WARM ADVECTION AHEAD
OF THE COLD FRONT...THE FREEZING LEVEL WILL LIKELY RISE SOME UNTIL
THE FROPA. SO...WHILE THE ENVIRONMENT SHOULD SUPPORT SOME STRONG
ROTATING UPDRAFTS SUFFICIENT FOR LARGE HAIL...THE HIGH FREEZING
LEVELS SHOULD GIVE AMPLE TIME FOR SOME MELTING. AS FOR THE WIND
THREAT...WITH THE STRONG LOW LEVEL JET POINTING OVER THE
AREA...STRONG WINDS SHOULD BE ABLE TO MIX DOWN...PARTICULARLY IN THE
WARM SECTOR AHEAD OF THE FRONT WHERE SURFACE BASED CONVECTION SHOULD
BE ABLE TO FORM. SO...STRONG...DAMAGING WINDS WILL BE A CONCERN
DURING THE INITIAL THUNDERSTORM DEVELOPMENT LATE THIS EVENING.

HEAVY RAINFALL...

THROUGH THE NIGHT...CONVECTIVE MODE WILL TRANSITION OVER TO MORE
LINES OR CLUSTERS...AND EVENTUALLY CONGEALING INTO A LARGE AREA OF
THUNDERSTORMS. WITH FLOW ABOVE THE BOUNDARY LEVEL TO ABOUT 700MB
SWLY...AND WLY-WNWLY JET-LEVEL WINDS...CELL MOVEMENT WITHIN THE
OVERALL THUNDERSTORM AREA WILL BE TO THE NORTHEAST WHILE THE LARGER
SCALE PATTERN IS SLOWLY PROGRESSIVE TO THE EAST. SO...ANTICIPATE
THAT THERE SHOULD BE AMPLE OPPORTUNITY FOR REPEATED DEVELOPMENT OR
TRAINING OF STORMS. ALL ELEMENTS ARE COMING TOGETHER FOR A
SIGNIFICANT HEAVY RAIN EVENT. STORMS WILL BE EFFICIENT RAIN
PRODUCERS GIVEN THE DEEP LAYER MOISTURE AND RAINFALL RATES OF 2 TO 3
INCHES PER HOUR FROM SOME STORMS WILL NOT BE OUT OF THE QUESTION.
FORTUNATELY...THE PATTERN WILL BE SLOWLY...BUT STEADILY
PROGRESSIVE...SO RAINFALL WILL BE WIDESPREAD RATHER THAN CONFINED TO
A SMALL AREA. LATEST THINKING IS THAT STORM TOTAL QPF SHOULD BE
ARND 2.0 TO 2.5 INCHES. IN AREAS OF TRAINING OR REPEATED STORM
DEVELOPMENT...LOCALIZED AREAS OF 3 TO 5 INCHES TOTAL RAINFALL WILL
BE POSSIBLE. THE MOST FAVORED TIMING FOR THE STRONGEST STORMS WILL
BE LATE THIS EVENING AND OVERNIGHT. THERE MAY BE A BRIEF LULL IN
ACTIVITY DURG THE MORNING HOURS...HOWEVER...EXPECT ANOTHER UPTICK IN
ACTIVITY DURG THE LATE MORNING/EARLY AFTERNOON AS THE COLD FRONT
PUSHES THROUGH NWRN INDIANA.

 

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RCNYILWX

RCNYILWX

Posted
Posted

I think heavy rain/flash flooding will be the bigger deal with this event, not that there won't be any severe reports. WPC expanded the MDT risk of exceeding flash flood guidance into our NW CWA, with the slight risk east into Chicago.

The moisture transport and pwat anomalies are almost off the charts for this time of year, as alluded to above.

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TimChgo9

TimChgo9

Posted
Posted

5" of rain would absolutely ruin the previously flooded neighborhoods south of me.  Given all of the forecast information there is out there, I would not be surprised at areas of 3", 4" or more around the area. 

 

Making sure floor drains are clear, and, well, we don't have a sump pump, because we don't have over head sewers, but making sure that the storm sewer on the parking area is clear, and no standing water. 

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Kaner88

Kaner88

Posted
Posted

Wow at the WPC map above. I've been focusing on the severe aspect (though I suppose it was marginal to begin with), and ended up missing the heavy rain threat. Got some work to do tonight to make sure the sump pump will hold & the street won't get overwhelmed.

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Gilbertfly

Gilbertfly

Posted
Posted

via DVN....

 

 

TONIGHT...ADDITIONAL RAINFALL OF 1 TO 3 INCHES APPEAR LIKELY. SOME
LOCATIONS MAY RECEIVE 4 TO 6 INCHES...ESPECIALLY IN ANY TRAINING/REPEATING
STORMS. THIS AMOUNT OF RAIN ON VERY SATURATED SOILS WOULD CAUSE SERIOUS
FLASH FLOODING. PRECIPITABLE WATERS WILL BE AT NEAR RECORD VALUES
FOR SEPTEMBER...ABOUT 2.2 INCHES. THIS IS DUE TO RICH GULF MOISTURE
COMBINED WITH MOISTURE FROM THE REMNANTS OF WHAT WAS MAJOR PACIFIC
HURRICANE NORBERT. RAINFALL RATES WILL BE EXTREMELY HIGH SO VERY
TORRENTIAL RAINS WILL ACCOMPANY THESE STORMS. CONFIDENCE IS VERY
HIGH FOR THIS FLASH FLOOD EVENT BUT IS LOWER FOR THE SEVERE THREAT.
THERE IS THE POTENTIAL FOR LOCALIZED WET MICROBURSTS DUE TO THE
VERY SATURATED ATMOSPHERE BUT ANY HAIL SHOULD REMAIN BELOW SEVERE
LEVELS. I AM CONCERNED FOR THE POTENTIAL FOR AN ISOLATED TORNADO
OR TWO ON ANY BOUNDARY AS THE DEEP LAYER SHEAR BECOMES VERY STRONG
EVEN WELL AFTER DARK AS THE SURFACE LOW DEEPENS AND TRACKS TOWARDS
LA CROSSE WI BY 12Z WEDNESDAY. THE HRRR MESO MODEL SUGGESTS ACTIVITY
INCREASING IN OUR SOUTHERN CWA LATE THIS AFTERNOON OR TOWARDS EVENING
THEN SPREADING NORTHEAST AS THE EVENING PROGRESSES...WITH WIDESPREAD
STORMS THEN OCCURRING OVERNIGHT. SOME OF THE STRONGER STORMS WILL
ALSO PRODUCE FREQUENT TO CONTINUOUS DANGEROUS LIGHTNING.

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Gilbertfly

Gilbertfly

Posted
Posted

WPC....

 

post-5865-0-32441100-1410304670_thumb.gi

 

and new disco...

 

 

A SIGNIFICANT HEAVY/EXCESSIVE RAINFALL EVENT IS EXPECTED FROM
PORTIONS OF THE CENTRAL PLAINS/MIDWEST TOWARDS THE LOWER PENINSULA
OF MI -- CONFIDENCE IN THIS FORECAST RATHER HIGH.  A DEEPENING
SURFACE LOW MOVES FROM THE CENTRAL PLAINS THIS EVENING INTO THE
MIDWEST WEDNESDAY MORNING AND THEN INTO THE NORTHERN GREAT LAKES
BY WEDNESDAY EVENING.  AHEAD OF THIS DEEPENING LOW LEVEL CENTER, A
BROAD SOUTH TO SOUTHWESTERLY LOW LEVEL JET WILL INCREASE TO 50+
KTS, WHICH WILL BRING IN PWS IN EXCESS OF 2" INTO AND OVER THE
WARM FRONT LIFTING NORTHEASTWARD AHEAD OF THE LOW.  THE MOISTURE
AVAILABLE SUPPORTS HOURLY RAIN RATES OF 2" AN HOUR WHERE CELLS
TRAIN/BACKBUILD.  THE 18Z TOP SOUNDING HAS THE INGREDIENTS FOR
FORWARD PROPAGATION -- VEERING WINDS WITH HEIGHT, CAPES ABOVE
3000+ J/KG, AND SOME DRY AIR IN THE LOW-LEVELS.  BELIEVE CELL
TRAINING WILL BE THE PRIMARY THREAT AS A LONG BAND OF CONVECTION
APPEARS TO BE FORMING FROM SOUTHEAST NE ACROSS SOUTHERN IA AT THIS
TIME, ALIGNED FROM JUST SOUTH OF DUE WEST TO JUST NORTH OF DUE
EAST -- INCREASED THE RISK FOR FLASH FLOODING/EXCESSIVE RAINFALL
TO HIGH IN THIS REGION.  AN AXIS OF 2-4" AREAL AVERAGE RAINFALL
AMOUNTS ARE EXPECTED, WITH MESOSCALE GUIDANCE INDICATING THAT
LOCAL AMOUNTS OF 6-9" ARE POSSIBLE.  ACROSS PORTIONS OF IA, THE
12Z SSEO NEIGHBORHOOD PROBABILITIES OF EXCEEDING THREE HOURLY
FLASH FLOOD GUIDANCE VALUES ARE >70% DURING THE 01Z-07Z PERIOD,
AND ASSESS THE BULK OF THE EVENT (AS DEFINED BY THE TIME PERIOD OF
>50% PROBABILITIES OF EXCEEDING THE THREE HOUR FFGS) AS BEING OVER
BY 09Z.

FARTHER NORTH, SIGNIFICANT MOISTURE BEING BROUGHT INTO THE THE
SURFACE FRONT DRAPED THRU THE NORTHERN GREAT LAKES ALONG WITH A
FAVORED COUPLED UPPER JET STRUCTURE WILL LEAD TO ANOTHER AREA OF
HEAVY RAINS FROM NORTHERN WI INTO NORTHERN MI.  THE AVAILABLE
MOISTURE SUPPORTS HOURLY RAIN RATES UP TO 1.5" SHOULD ENOUGH
INSTABILITY BE PRESENT.  THE BEST CAPE PARAMETER FROM THE 21Z RAP
RUN INDICATES THAT CAPE VALUES FALL UNDER 500 J/KG BY 07Z --
INDICATING THAT THIS COULD BE A MORE PROLONGED FLOOD THAN A FLASH
FLOOD EVENT.  AREAL AVERAGE AMOUNTS OF 2" ARE FORECAST, WITH LOCAL
AMOUNTS OF 4" POSSIBLE WHERE HEAVY RAIN AREAS TRAIN.
 

 

6 to 9 possible.... :weight_lift:

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Central Illinois

Central Illinois

Posted
Posted

Nope. It's completely right. In fact, I would have removed the 30% altogether. The NAM is too wound up with the low because of convective influences. Tomorrow is not at all an impressive setup for reasons I mentioned earlier. There may be a few severe reports, but I'd be shocked if it were anything beyond that.

+1 flooding is going to be a much bigger issue

Sent from my SM-G900V

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