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July 17th-21st Severe Thread


andyhb

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Noticed this in the 01z outlook:

CONSIDERABLE VEERING AND WEAK LOW LEVEL CONVERGENCE APPEAR TO BE PARTLY RESPONSIBLE FOR LACK OF STRONG CONVECTION ACROSS THE UPPER MS VALLEY THIS EVENING.

We're going to have this same issue tomorrow at least in part of the warm sector.

 

 

yep

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Hrrr keeps it clear till the main FROPA but struggles to build instability over SEMI for some reason.

Sent from my HTCONE 4 Beta

 

It mixes the dew point down to under 60 in pockets, I give that a 0.00000000001% of happening, and if it were to happen we would be 100-105 today, which is equally as unlikely.

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Hrrr keeps it clear till the main FROPA but struggles to build instability over SEMI for some reason.

Sent from my HTCONE 4 Beta

 

It mixes the dew point down to under 60 in pockets, I give that a 0.00000000001% of happening, and if it were to happen we would be 100-105 today, which is equally as unlikely.

Yup I see that now. IIRC it's had similar problems in the past so I'm not concerned.

Sent from my HTCONE using Tapatalk 4 Beta

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So far all I have heard this morning, regarding storms: 

 

"Isolated"

"Widely scattered"

"Best chance is the afternoon, but those storms will be isolated"

 

"MicroCast" according Mr. Schwartz at ABC7 gives us about .03"-.10" this afternoon.

 

Looks like the storm action will be east of us.

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87/74 at the 11:30 obs  :icecream:. At least there's a breeze today, blowing according to the station 20 with 30 MPH gusts. SBCAPE currently is at 3500-4000 j/kg and with time left in the day we could approach 5000+. With a solid LLJ and that kind of instability, we could really have some serious damaging winds today

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LOT currently in anti-punt mode...

 

 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1141 AM CDT FRI JUL 19 2013

.DISCUSSION...
1138 AM CDT

THE MORNING CONVECTION AND THE ASSOCIATED CLOUD COVER HAVE
DISSIPATED OVER THE PAST COUPLE HOURS ACROSS SOUTHERN WISCONSIN. IT
APPEARS AN OUTFLOW BOUNDARY...LIKELY ELEVATED IS PUSHING ACROSS
NORTHERN ILLINOIS AT THIS TIME. WITH SKIES REMAINING CLEAR ACROSS THE
REGION...TEMPERATURES ARE QUICKLY WARMING INTO THE LOW 90S EARLY
THIS MORNING. WITH EVEN WARM 925 MB TEMPERATURES TODAY NEAR 27
DEGREES C...PER 12 UTC DVN RAOB...I SEE NO REASON WHY TEMPERATURES
WILL NOT WARM INTO THE MIDDLE 90S BY EARLY AFTERNOON. THEREFORE...I
WARMED TEMPERATURES A FEW DEGREES. THE INCREASING SOUTHWESTERLY
WINDS SHOULD HELP MIX OUT DEW POINTS SOME...RESULTING IN SOME
SLIGHTLY LOWER DEW POINTS IN THE UPPER 60S TO THE LOW 70S.
THEREFORE...HEAT INDEX VALUES STILL APPEAR TO PEAK NEAR 105 THIS
AFTERNOON.

IT APPEARS CONVECTION WILL FIRE UP ACROSS NORTHERN ILLINOIS AFTER 19
UTC. MODIFYING DVN 12 UTC RAOB FOR CURRENT CONDITIONS INDICATE VERY
LITTLE CAP REMAINING ACROSS THE AREA WITH SB CAPE AROUND 2800 J/KG.
THEREFORE...IT IS NOT SURPRISING THAT THE REGIONAL SATELLITE IMAGERY
SHOWS AN AREA OF CLOUD COVER WITH INCREASING AGITATION ACROSS
PORTIONS OF IOWA. THIS AREA ALSO COINCIDES WITH SOME ENHANCED
BOUNDARY LAYER CONVERGENCE JUST AHEAD OF THE SURFACE COLD FRONT.
THIS ACTIVITY SHOULD CONTINUE TO DEVELOP AND MOVE TOWARDS MY
NORTHERN COUNTIES AFTER 19 OR 20 UTC AS THE SURFACE FRONT CONTINUES
TO DROP SOUTHWARD. ADDITIONAL ISOLATED TO SCATTERED CONVECTION COULD
ALSO DEVELOP FARTHER SOUTH AND EAST ACROSS THE SOUTHERN SUBURBS OF
CHICAGO AND INTO NORTHWESTERN INDIANA THIS AFTERNOON...IN
ASSOCIATION WITH INCREASING BOUNDARY LAYER CONVERGENCE ALONG A
PREFRONTAL TROUGH.

IT APPEARS THE MAIN SEVERE THREAT FROM THIS ACTIVITY WILL BE
DAMAGING WIND GUSTS. DEEP LAYER SHEAR REMAINS RELATIVELY WEAK...20
TO 25 KT...MAINLY DUE TO THE STRONGER MID LEVEL FLOW REMAINING TO
THE NORTH BEHIND THE FRONT. HOWEVER...WET OR EVEN HYBRID
MICROBURSTS ARE LIKELY WITH THIS ACTIVITY WITH LAYER THETA-E
DIFFERENCES IN EXCESS OF 20 DEGREES C.

THE OTHER THREAT WILL BE THAT OF TORRENTIAL DOWNPOURS WITH THIS
ACTIVITY. PWATS ARE PROGGED TO BY AROUND 2 INCHES...THEREFORE THESE
STORMS WILL HAVE PLENTY OF HIGH THETA-E AIR TO WORK WITH. RAINFALL
RATES IN SOME OF THESE STORMS COULD EASILY EXCEED AN INCH OR TWO AN
HOUR...WHICH COULD RESULT IN SOME LOCALIZED HYDRO
ISSUES...ESPECIALLY IF THIS OCCURS OVER THE URBAN AREAS. I DECIDED
TO ADD HEAVY RAINFALL TO THE GRIDS EARLY THIS EVENING...BUT I KEPT
IT SOUTH OF CHICAGO...MAINLY ACROSS EAST CENTRAL ILLINOIS AND
NORTHWESTERN INDIANA WHERE THE CONVECTIVE ACTIVITY COULD LINGER
THIS EVENING. STORM MOTIONS SHOULD BE TO THE EAST AROUND 25
KT...SO THE POTENTIAL FOR SOME TRAINING CELLS COULD RESULT IN
LOCAL HEAVY RAINFALL AMOUNTS.

KJB
 

 

 

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