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August 22-31 Severe Weather Thread


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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1258 AM CDT WED AUG 24 2011

VALID 241200Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM LOWER MI...LOWER GREAT

LAKES AND UPPER OH VALLEY TO THE MID MS VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF WRN/CENTRAL

OREGON...

...SYNOPSIS...

A SHORTWAVE TROUGH...CURRENTLY MOVING ESEWD ACROSS MANITOBA INTO

ONTARIO PER WATER VAPOR IMAGERY...IS EXPECTED TO AMPLIFY SEWD ACROSS

THE GREAT LAKES AND OH VALLEY REGION THIS FORECAST PERIOD. A

LEAD...MORE COMPACT...SHORTWAVE TROUGH NOW OVER THE CENTRAL GREAT

LAKES IS FORECAST TO DEAMPLIFY AS IT TRACKS NEWD THROUGH THE SAINT

LAWRENCE RIVER VALLEY TODAY. A COLD FRONT ATTENDANT TO THE

AMPLIFYING MANITOBA TROUGH WILL SPREAD E/SEWD ACROSS THE GREAT LAKES

INTO THE OH AND MID MS VALLEYS...WHILE THE WRN EXTENT MOVES SWD FROM

KS INTO OK.

IN THE WEST...A CLOSED LOW/EMBEDDED SHORTWAVE TROUGH...CURRENTLY

MOVING NWD ALONG THE CENTRAL CA COAST...WILL REMAIN PROGRESSIVE

TODAY...BUT DEAMPLIFY AS IT MOVES INTO WRN ORE LATE THIS AFTERNOON

AND EARLY EVENING. AS THIS FEATURE MOVES INLAND...A LOW LEVEL WIND

SHIFT WILL ADVANCE EWD ACROSS OREGON.

...LOWER MI/LOWER GREAT LAKES/OH VALLEY TO MID MS VALLEY...

A WSWLY LLJ ATTENDANT TO THE LEAD SHORTWAVE TROUGH WILL AID IN

SPREADING MOISTURE EWD ACROSS PARTS OF THE OH VALLEY PRIOR TO THE

START OF THIS DAY 1 FORECAST PERIOD. A CONTINUATION OF WSWLY LOW

LEVEL WINDS IN ADVANCE OF THE COLD FRONT WILL MAINTAIN THE ADVECTION

OF A HIGH THETAE AIR MASS EWD ACROSS THE OH VALLEY AND LOWER MI WITH

SURFACE DEWPOINTS ACROSS THE WARM SECTOR RANGING FROM THE UPPER 60S

TO LOWER 70S. A PLUME OF STEEP MIDLEVEL LAPSE RATES /7-7.5 C PER

KM/ WILL ADVANCE EWD ATOP THE MOISTURE CORRIDOR. THESE

THERMODYNAMICS COMBINED WITH DIABATIC WARMING IN THE WAKE OF ANY

ONGOING STORMS EXPECTED TO BE OVER LOWER MI/NRN OH AT 12Z TODAY AND

AHEAD OF THE COLD FRONT SHOULD RESULT IN MODERATE INSTABILITY OVER

LOWER MI TO VERY STRONG INSTABILITY FROM CENTRAL OH TO MO.

HEIGHT FALLS AND FORCING FOR ASCENT ARE EXPECTED TO INITIALLY

PROVIDE SUPPORT FOR TSTMS TO DEVELOP ACROSS MUCH OF LOWER MI THIS

AFTERNOON. WHILE THE AIR MASS SHOULD BE CAPPED WITH SWWD EXTENT

INTO IND/IL...STORMS SHOULD DEVELOP INTO THESE AREAS AS THE COLD

FRONT ADVANCES ESEWD AIDING IN WEAKENING OF THE INHIBITION.

STRENGTHENING OF VERTICALLY VEERING WIND FIELDS AS THE TROUGH

AMPLIFIES SEWD AND EFFECTIVE BULK SHEAR VECTORS ORIENTED MORE NORMAL

TO THE COLD FRONT SUGGEST STORM MODE SHOULD INITIALLY FAVOR

SUPERCELLS...WITH ALL SEVERE THREATS POSSIBLE. GREATEST TORNADO

THREAT SHOULD BE ACROSS SRN LOWER MI INTO NERN IND AND NWRN OH THIS

AFTERNOON ALONG THE AXIS OF THE WSWLY LLJ.

DURING WEDNESDAY EVENING/NIGHT...THE STORM MODE SHOULD EVOLVE INTO A

QUASI-LINEAR SQUALL LINE AS TSTMS CONTINUE TO DEVELOP ALONG THE FULL

EXTENT OF THE COLD FRONT ACROSS THE OH AND MID MS VALLEYS. THIS

SUGGEST THAT DAMAGING WINDS AND HAIL WILL BECOME THE PRIMARY SEVERE

WEATHER HAZARDS. GREATEST 500 MB HEIGHT FALLS /30-60 METERS PER 12

HR/ ARE FORECAST TO SPREAD FROM THE UPPER GREAT LAKES INTO THE UPPER

HALF OF THE OH VALLEY/LOWER GREAT LAKES WEDNESDAY NIGHT. IN

RESPONSE TO THESE FALLS...SWLY LOW LEVEL WINDS WILL INCREASE TO

40-45 KT FROM SRN IND/OH INTO WRN PA...AND UP TO 50 KT ACROSS THE

LOWER GREAT LAKES AND WRN/NRN NY. THE JUXTAPOSITION OF THE

STRENGTHENING WINDS IN THE OH VALLEY AND MODERATE INSTABILITY

SUGGESTS A POTENTIAL INCREASE IN THE COVERAGE OF STRONG DAMAGING

WINDS FROM SRN IND ACROSS MUCH OF OH AND NRN KY.

...PARTS OF WRN AND CENTRAL OREGON...

MODELS SUGGEST THE AIR MASS...ESPECIALLY ACROSS WRN ORE...SHOULD

BECOME MODERATELY UNSTABLE THIS AFTERNOON. FORCING FOR ASCENT

SPREADING INLAND WITH THE MIDLEVEL SYSTEM WILL SUPPORT TSTM

DEVELOPMENT FROM W-E LATE THIS AFTERNOON INTO THE EVENING. GIVEN

THE INSTABILITY AND EFFECTIVE BULK SHEAR UP TO 40 KT...A SLIGHT RISK

HAS BEEN INCLUDED IN THIS OUTLOOK FOR THIS REGION.

...SWRN MO/NRN AR/SERN KS INTO OK...

A DEEPLY MIXED BOUNDARY LAYER IS EXPECTED TO DEVELOP ACROSS THIS

REGION BY PEAK HEATING AS SURFACE TEMPERATURES REACH THE UPPER 90S

TO LOW 100S. 00Z SOUNDINGS SHOWED THE WRN EXTENT OF HIGH MOISTURE

VALUES IS ALREADY IN PLACE WITH PRECIPITABLE WATER VALUES RANGING

FROM 1.5-1.7 INCH. THIS COMBINED WITH STEEPENING LAPSE RATES WILL

RESULT IN MODERATE INSTABILITY. TSTMS SHOULD DEVELOP AS THE COLD

FRONT ADVANCES SWD WITH DAMAGING DOWNBURST WINDS AND HAIL THE

PRIMARY HAZARDS. UNCERTAINTY IN STORM COVERAGE PRECLUDES AN

INCLUSION OF HIGHER PROBABILITIES AND A CATEGORICAL RISK AT THIS

TIME...BUT WILL INTRODUCE LOW SEVERE WIND AND HAIL PROBABILITIES.

..PETERS/SMITH.. 08/24/2011

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Somewhat confused by the SREF sigtors. Last three runs have indicated 20-40% sigtors over southern Ontario today, yet the SPC only has a 5% tornado for the SEMI area. Without accurate Canadian centered outlets to receive advanced severe weather outlooks, what is going on with these parameters? Is the SREF over-performing this potential? It's not every day you see sig tors at 40% on the SREF in this area. Any thoughts? Is there maybe an area of the latest SPC outlook that is out of the US gov'ts reach to forecast for?

(sorry for the IMBY question)

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Eh call me pessimistic but I'm not going to get overly excited about severe wx in SEMI today. The RUC continues to show things not firing up until to late and the HRRR seems to be on board as well now. Not to mention scenarios where we've been capped all day haven't worked out so well this season so far...

I am really liking to looks of southern Ontario though...

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Eh call me pessimistic but I'm not going to get overly excited about severe wx in SEMI today. The RUC continues to show things not firing up until to late and the HRRR seems to be on board as well now. Not to mention scenarios where we've been capped all day haven't worked out so well this season so far...

I am really liking to looks of southern Ontario though...

Interesting that GRR even has the possibility of severe weather just east of grand rapids. We will see.

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696

WWCN11 CWTO 241454

SEVERE WEATHER BULLETIN

ISSUED BY ENVIRONMENT CANADA

AT 10:54 AM EDT WEDNESDAY 24 AUGUST 2011.

---------------------------------------------------------------------

WATCHES/WARNINGS IN EFFECT FOR SOUTHERN ONTARIO...

TORNADO WATCH FOR:

=NEW= WINDSOR - ESSEX COUNTY - CITY OF CHATHAM-KENT

=NEW= SARNIA - LAMBTON COUNTY

=NEW= ELGIN COUNTY

=NEW= LONDON - MIDDLESEX COUNTY

=NEW= HURON COUNTY - PERTH COUNTY

=NEW= WATERLOO REGION - WELLINGTON COUNTY

=NEW= DUFFERIN COUNTY - INNISFIL

=NEW= GREY COUNTY - BRUCE COUNTY

=NEW= BARRIE - ORILLIA - MIDLAND

=NEW= PARRY SOUND DISTRICT - MUSKOKA REGION

=NEW= BURK'S FALLS - BAYFIELD INLET.

RISK OF SEVERE THUNDERSTORMS AND ISOLATED TORNADOES DEVELOPING

THIS AFTERNOON.

THIS IS AN ALERT TO THE POTENTIAL DEVELOPMENT OF SEVERE

THUNDERSTORMS CAPABLE OF PRODUCING TORNADOES..MONITOR WEATHER

CONDITIONS AND LISTEN FOR UPDATED BULLETINS.

---------------------------------------------------------------------

==DISCUSSION==

A LINE OF THUNDERSTORMS IS EXPECTED TO DEVELOP OVER MICHIGAN THIS

AFTERNOON THEN TRACK RAPIDLY EASTWARD INTO SOUTHERN ONTARIO. SOME OF

THESE STORMS ARE EXPECTED TO BE SEVERE WITH LARGE HAIL DAMAGING WINDS

TORRENTIAL DOWNPOURS AND FREQUENT LIGHTNING. THESE STORMS WILL ALSO

BE CAPABLE OF PRODUCING TORNADOES.

THE THREAT FOR SEVERE WEATHER IS EXPECTED TO REACH AREAS NEAR LAKE

HURON NEAR MID AFTERNOON AND THE REMAINDER OF THE REGIONS IN THE LATE

AFTERNOON OR EARLY EVENING.

REFER TO YOUR LOCAL PUBLIC FORECAST FOR FURTHER DETAILS.

END/OSPC

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Eh call me pessimistic but I'm not going to get overly excited about severe wx in SEMI today. The RUC continues to show things not firing up until to late and the HRRR seems to be on board as well now. Not to mention scenarios where we've been capped all day haven't worked out so well this season so far...

I am really liking to looks of southern Ontario though...

It's going to be very close, I think it fires almost right on top of us, which could be bad as this will initially be supercells evolving into a squall line.

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696

WWCN11 CWTO 241454

SEVERE WEATHER BULLETIN

ISSUED BY ENVIRONMENT CANADA

AT 10:54 AM EDT WEDNESDAY 24 AUGUST 2011.

---------------------------------------------------------------------

WATCHES/WARNINGS IN EFFECT FOR SOUTHERN ONTARIO...

TORNADO WATCH FOR:

=NEW= WINDSOR - ESSEX COUNTY - CITY OF CHATHAM-KENT

=NEW= SARNIA - LAMBTON COUNTY

=NEW= ELGIN COUNTY

=NEW= LONDON - MIDDLESEX COUNTY

=NEW= HURON COUNTY - PERTH COUNTY

=NEW= WATERLOO REGION - WELLINGTON COUNTY

=NEW= DUFFERIN COUNTY - INNISFIL

=NEW= GREY COUNTY - BRUCE COUNTY

=NEW= BARRIE - ORILLIA - MIDLAND

=NEW= PARRY SOUND DISTRICT - MUSKOKA REGION

=NEW= BURK'S FALLS - BAYFIELD INLET.

RISK OF SEVERE THUNDERSTORMS AND ISOLATED TORNADOES DEVELOPING

THIS AFTERNOON.

THIS IS AN ALERT TO THE POTENTIAL DEVELOPMENT OF SEVERE

THUNDERSTORMS CAPABLE OF PRODUCING TORNADOES..MONITOR WEATHER

CONDITIONS AND LISTEN FOR UPDATED BULLETINS.

---------------------------------------------------------------------

==DISCUSSION==

A LINE OF THUNDERSTORMS IS EXPECTED TO DEVELOP OVER MICHIGAN THIS

AFTERNOON THEN TRACK RAPIDLY EASTWARD INTO SOUTHERN ONTARIO. SOME OF

THESE STORMS ARE EXPECTED TO BE SEVERE WITH LARGE HAIL DAMAGING WINDS

TORRENTIAL DOWNPOURS AND FREQUENT LIGHTNING. THESE STORMS WILL ALSO

BE CAPABLE OF PRODUCING TORNADOES.

THE THREAT FOR SEVERE WEATHER IS EXPECTED TO REACH AREAS NEAR LAKE

HURON NEAR MID AFTERNOON AND THE REMAINDER OF THE REGIONS IN THE LATE

AFTERNOON OR EARLY EVENING.

REFER TO YOUR LOCAL PUBLIC FORECAST FOR FURTHER DETAILS.

END/OSPC

Wow they "blew their whistle" early....heck up here we don't even issue TORNADO WARNINGS even when pilots call them (picture posted) in as I posted in the Alaska discussion. I would figure that ENVIRONMENT CANADA would have waited to 3pm. I think SPC will issue a meso 1:45 to 3:30pm for Michigan....NE Indiana....and NW Ohio and should issue a TORNADO WATCH for that area by 4:40 to 5:15pm........let's see how good my "guess" is.

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Wow they "blew their whistle" early....heck up here we don't even issue TORNADO WARNINGS even when pilots call them (picture posted) in as I posted in the Alaska discussion. I would figure that ENVIRONMENT CANADA would have waited to 3pm. I think SPC will issue a meso 1:45 to 3:30pm for Michigan....NE Indiana....and NW Ohio and should issue a TORNADO WATCH for that area by 4:40 to 5:15pm........let's see how good my "guess" is.

I think they are being cautious since the Goderich tornado. But, it's not the first time EC has pulled a tornado watch real early.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1124 AM CDT WED AUG 24 2011

VALID 241630Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY

TONIGHT FOR PARTS OF THE GREAT LAKES/OH VALLEY...

..GREAT LAKES/OH VALLEY THIS AFTERNOON/EVENING

AN INITIAL SHORTWAVE TROUGH IS MOVING EWD OVER THE LOWER GREAT LAKES

AND LOSING AMPLITUDE...WHILE A STRONGER UPSTREAM WAVE OVER WI/UPPER

MI PROGRESSES SEWD TOWARD LOWER MI BY EARLY TONIGHT. AN ASSOCIATED

SURFACE COLD FRONT WILL LIKEWISE MOVE SEWD TO NRN MO/NRN IL/NW

INDIANA/SE LOWER MI BY THIS EVENING...PROVIDING A FOCUS FOR SEVERE

THUNDERSTORM DEVELOPMENT.

LOW-LEVEL MOISTURE /BOUNDARY LAYER DEWPOINTS IN THE UPPER 60S TO

LOWER 70S/ IS SPREADING NEWD FROM WI/IL/INDIANA TO LOWER MI IN

ADVANCE OF THE COLD FRONT...ALONG WITH THE EWD EXPANSION OF A STEEP

MIDLEVEL LAPSE RATE PLUME NOTED IN 12Z SOUNDINGS ACROSS MO/IL/WI.

THE INCREASING MOISTURE/LAPSE RATES WILL COMBINE WITH DAYTIME

HEATING TO SUPPORT PRE-FRONTAL MLCAPE VALUES OF 3000-4000 J/KG.

WEAKENING CONVECTIVE INHIBITION WITH DAYTIME HEATING AND ASCENT

ALONG THE FRONT WILL SUPPORT THUNDERSTORM DEVELOPMENT LATE THIS

AFTERNOON/EVENING FROM SE LOWER MI TO CENTRAL IL. EARLIER STORM

DEVELOPMENT WILL OCCUR ACROSS NRN LOWER MI IN THE ZONE OF DEEPER

ASCENT PRECEDING THE MIDLEVEL TROUGH...THOUGH THE MAGNITUDE OF

INSTABILITY WILL BE LIMITED SOMEWHAT BY PERSISTENT LOW CLOUDS.

THE STRONG INSTABILITY AND LARGELY UNIDIRECTIONAL WIND PROFILES

PARALLEL TO THE FRONT WILL FAVOR UPSCALE GROWTH INTO A LINE WITH AN

ATTENDANT RISK OF DAMAGING WINDS AND LARGE HAIL. DEEP-LAYER

VERTICAL SHEAR WILL ALSO BE SUFFICIENT FOR EMBEDDED

SUPERCELLS...WITH THE MORE DISCRETE STORMS EXPECTED THIS AFTERNOON

ACROSS SE LOWER MI. HOWEVER...THE SOMEWHAT STRONGER LOW-LEVEL SHEAR

AND ASSOCIATED TORNADO RISK MAY BE GREATER INTO SW ONTARIO.

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