Southern Great Lakes derecho - August 4-5

[CrazyC83]

MESOSCALE DISCUSSION 2028
NWS STORM PREDICTION CENTER NORMAN OK
0645 PM CDT MON AUG 04 2008

AREAS AFFECTED...PORTIONS NRN IL...SERN IA...NRN INDIANA...EXTREME
SWRN LOWER MI.

CONCERNING...SEVERE THUNDERSTORM WATCH 806...

VALID 042345Z - 050115Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 806
CONTINUES.

NEW OR REPLACEMENT WW LIKELY WILL BE REQUIRED FARTHER ESEWD TO
INCLUDE MORE OF NERN IL AND NRN INDIANA...FOR HIGH-END DAMAGING WIND
THREAT. CATEGORICAL SVR OUTLOOK IS BEING UPGRADED TO MDT RISK FOR
PROJECTED WIND EVENT CORRIDOR AS WELL.

DERECHO WITH HIGH-END DAMAGING WIND THREAT COULD AFFECT CHICAGO AND
SURROUNDING AREAS...THEN INTO NWRN INDIANA. SVR MCS -- NOW OVER
NWRN IL AND EXTREME ERN IA -- SHOULD BECOME EVEN BETTER ORGANIZED
AND MOVE ESEWD. 56 KT SVR GUST AND DAMAGE WERE REPORTED IN
STEPHENSON COUNTY IL...AND CONVECTION APPEARS TO HAVE INTENSIFIED
SINCE. MAIN THREAT WILL REMAIN DAMAGING WIND...BUT WITH
BRIEF/QLCS-TYPE TORNADIC CIRCULATIONS ALSO POSSIBLE.

BOW ECHO DEVELOPMENT IS OCCURRING WITH TSTM COMPLEX AS BASE VELOCITY
LOOPS INDICATE DEVELOPING REAR-INFLOW JET. COMPLEX CURRENTLY MOVING
ESEWD APPROXIMATELY 45 KT ACROSS NWRN IL INTO ANALYZED PRESSURE FALL
REGION...AND IS EXPECTED TO ACCELERATE. TSTMS SHOULD MOVE ALONG
NWD-MOVING...WNW-ESE ALIGNED BAROCLINIC ZONE ASSOCIATED WITH OUTFLOW
FROM MORNING CONVECTION. THIS BOUNDARY IS MOVING NWD 10-15 KT INTO
SRN PORTIONS CHI AREA...AND EXTENDS WNWWD INTO OGLE/LEE COUNTIES IL.
VERY STG STORM-TOP DIVERGENCE IS INDICATED IN VIS ANVIL
TRENDS...AND LOW LEVEL CONDITIONS WILL REMAIN FAVORABLE. BOUNDARY
LAYER VORTICITY AND CONVERGENCE EACH SHOULD REMAIN MAXIMIZED ALONG
OLD OUTFLOW BOUNDARY...WHICH WILL BE PREFERRED FORWARD-PROPAGATIONAL
PATH FOR MCS. STORM-RELATIVE INFLOW WILL REMAIN FAVORABLE AS FORCED
ASCENT CONTINUES ALONG LEADING EDGE OF COLD POOL. PROSPECTIVE
INFLOW AIR MASS INTO CENTRAL/NRN INDIANA WILL REMAIN FAVORABLE WITH
SFC DEW POINTS COMMONLY 70S F...LEADING TO MLCAPES APCHG 6000 J/KG S
OF BOUNDARY PER MODIFIED RUC SOUNDINGS. DEEP-LAYER MEAN WIND AND
BULK SHEAR VECTORS ARE ALIGNED FAVORABLY PARALLEL WITH INSTABILITY
GRADIENT ACCOMPANYING BOUNDARY...WITH EFFECTIVE SHEAR MAGNITUDES
40-45 KT.

..EDWARDS.. 08/04/2008


ATTN...WFO...IWX...IND...LOT...ILX...MKX...DVN...

41739087 41869010 42088952 42358934 42598911 42538810
41838606 41268498 40108522 39918605 41439057

[CrazyC83]

Guessing there will be a PDS Severe Thunderstorm Watch shortly. Moderate Risk expected at 0100Z. This is all caught in the tropical activity, but much more dangerous...

[CrazyC83]

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
702 PM CDT MON AUG 4 2008

ILC037-089-093-103-141-050045-
/O.CON.KLOT.SV.W.0162.000000T0000Z-080805T0045Z/
OGLE IL-KANE IL-DEKALB IL-LEE IL-KENDALL IL-
702 PM CDT MON AUG 4 2008

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 745 PM CDT
FOR NORTHERN KENDALL...EASTERN LEE...DEKALB...KANE AND EXTREME
SOUTHEASTERN OGLE COUNTIES...

AT 702 PM...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
INDICATE A LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING NICKEL
SIZE HAIL...AND DESTRUCTIVE WINDS IN EXCESS OF 80 MPH. THESE STORMS
WERE LOCATED ALONG A LINE EXTENDING FROM 7 MILES NORTH OF KIRKLAND TO
MALTA TO COMPTON...MOVING EAST AT 63 MPH.

SEVERE THUNDERSTORMS WILL BE NEAR...
SYCAMORE...HINCKLEY...GENOA...AND CORTLAND BY 710 PM...
LITTLE ROCK...SANDWICH...MAPLE PARK...AND BURLINGTON BY 715 PM...
SUGAR GROVE...AND PLANO BY 720 PM...
AURORA BY 725 PM...

THIS IS A DANGEROUS LINE OF STORMS. IF YOU ARE IN ITS PATH...PREPARE
IMMEDIATELY FOR DAMAGING WINDS...DESTRUCTIVE HAIL...AND DEADLY CLOUD
TO GROUND LIGHTNING. PEOPLE OUTSIDE SHOULD MOVE TO A SHELTER...
PREFERABLY INSIDE A STRONG BUILDING BUT AWAY FROM WINDOWS.

WIDESPREAD SIGNIFICANT WIND DAMAGE HAS BEEN REPORTED WITH THIS LINE
OF STORMS.

VERY HEAVY RAINFALL MAY CAUSE LOCALIZED FLOODING.

LAT...LON 4214 8827 4164 8828 4164 8872 4163 8919
4192 8898 4215 8895
TIME...MOT...LOC 0002Z 287DEG 55KT 4218 8885 4185 8882
4162 8900

$$

MARSILI

[CrazyC83]

SEL7

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 807
NWS STORM PREDICTION CENTER NORMAN OK
715 PM CDT MON AUG 4 2008

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

NORTHEAST ILLINOIS
NORTHWEST INDIANA
EXTREME SOUTHWEST LOWER MICHIGAN
LAKE MICHIGAN

EFFECTIVE THIS MONDAY NIGHT AND TUESDAY MORNING FROM 715 PM UNTIL
200 AM CDT.

...THIS IS A PARTICULARLY DANGEROUS SITUATION...

EXTREMELY DAMAGING THUNDERSTORM WIND GUSTS TO 90 MPH...LARGE HAIL
TO 2 INCHES IN DIAMETER...AND DANGEROUS LIGHTNING ARE POSSIBLE IN
THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 50
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 55 MILES WEST
SOUTHWEST OF MEIGS FIELD ILLINOIS TO 30 MILES SOUTHEAST OF SOUTH
BEND INDIANA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...CONTINUE...WW 806...

DISCUSSION...DEVELOPING INTENSE BOW ECHO IN NRN IL WILL LIKELY MOVE
THROUGH THE CHICAGO AREA INTO NW INDIANA DURING THE NEXT FEW HOURS.
THE MCS SHOULD MAINTAIN INTENSITY MOVING ALONG A GRADIENT OF EXTREME
INSTABILITY ACROSS NE IL INTO NW INDIANA. VERY DAMAGING WINDS WILL
BE POSSIBLE IN A NARROW SWATH INCLUDING CHICAGO...ALONG WITH AN
ISOLATED/BRIEF TORNADO AND LARGE HAIL.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 80
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 600. MEAN STORM
MOTION VECTOR 28050.


...THOMPSON

[CrazyC83]

Tornadoes
Probability of 2 or more tornadoes
Low (20%)


Probability of 1 or more strong (F2-F5) tornadoes
Low (5%)


Wind
Probability of 10 or more severe wind events
High (90%)


Probability of 1 or more wind events > 65 knots
High (80%)


Hail
Probability of 10 or more severe hail events
Mod (40%)


Probability of 1 or more hailstones > 2 inches
Low (20%)


Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind events
High (>95%)

[RL3AO]

Wowzer.

[RL3AO]

BV on right.

[CrazyC83]

SEVERE THUNDERSTORM WARNING
ILC007-031-043-063-093-097-099-111-197-201-050130-
/O.NEW.KLOT.SV.W.0163.080805T0018Z-080805T0130Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
718 PM CDT MON AUG 4 2008

THE NATIONAL WEATHER SERVICE IN CHICAGO HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
SOUTHERN BOONE COUNTY IN NORTH CENTRAL ILLINOIS...
NORTHEASTERN LA SALLE COUNTY IN NORTH CENTRAL ILLINOIS...
EXTREME EAST CENTRAL WINNEBAGO COUNTY IN NORTH CENTRAL ILLINOIS...
COOK COUNTY IN NORTHEAST ILLINOIS...
DUPAGE COUNTY IN NORTHEAST ILLINOIS...
NORTHERN GRUNDY COUNTY IN NORTHEAST ILLINOIS...
KENDALL COUNTY IN NORTHEAST ILLINOIS...
SOUTHERN LAKE COUNTY IN NORTHEAST ILLINOIS...
SOUTHERN MCHENRY COUNTY IN NORTHEAST ILLINOIS...
NORTHERN WILL COUNTY IN NORTHEAST ILLINOIS...

* UNTIL 830 PM CDT...

* AT 711 PM CDT...NATIONAL WEATHER SERVICE RADAR INDICATED A LINE OF
SEVERE THUNDERSTORMS LOCATED ALONG A LINE EXTENDING FROM BELVIDERE
TO 19 MILES WEST OF DUPAGE AIRPORT TO SOMONAUK TO EARLVILLE...AND
MOVING EAST AT 65 MPH. THESE STORMS ARE CAPABLE OF PRODUCING NICKEL
SIZE HAIL...AND DESTRUCTIVE WINDS IN EXCESS OF 80 MPH.

* SEVERE THUNDERSTORMS WILL BE NEAR...
NEWARK...AND MARENGO BY 725 PM...
WOODSTOCK...WEST CHICAGO...WARRENVILLE...AND HUNTLEY BY 730 PM...
WESTERN SUBURBS OF CHICAGO IN DUPAGE COUNTY BY 730 PM...
WINFIELD...WHEATON...PLAINFIELD...AND NAPERVILLE BY 735 PM...
DOWNTOWN CHICAGO BY 750 PM...

THIS SEVERE THUNDERSTORM WARNING INCLUDES THE CITY OF CHICAGO.

THIS IS AN EXTREMELY DANGEROUS AND POTENTIALLY LIFE THREATENING
SITUATION. SEEK SHELTER IN A BASEMENT OR INTERIOR ROOM OF A STURDY
BUILDING. STAY AWAY FROM WINDOWS.

VERY HEAVY RAINFALL MAY CAUSE LOCALIZED FLOODING.

LAT...LON 4140 8755 4139 8892 4163 8897 4163 8826
4215 8824 4217 8894 4232 8895 4231 8781
4214 8774 4207 8765 4191 8762 4189 8758
4171 8754
TIME...MOT...LOC 0016Z 279DEG 57KT 4228 8878 4188 8851
4168 8859 4153 8881

$$

MARSILI

[Category 5]

On the current track, Chicago takes a direct hit.

[RL3AO]

SRV on the right. Rotation clear with cell under TOR.

[CrazyC83]

Seems to be a large area of winds >70 kt on the radar (80 mph).

[Category 5]

The Cubs are playing at home right now on ESPN, I hope the stadium workers know whats going on here.

[CrazyC83]

Edouard, you have NOTHING on this bow echo...

[Category 5]

This is bad

SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
744 PM CDT MON AUG 4 2008

ILC031-043-063-093-097-099-111-197-050130-
/O.CON.KLOT.SV.W.0163.000000T0000Z-080805T0130Z/
MCHENRY IL-LAKE IL-COOK IL-DUPAGE IL-GRUNDY IL-KENDALL IL-WILL IL-
LA SALLE IL-
742 PM CDT MON AUG 4 2008

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 830 PM CDT
FOR NORTHEASTERN LA SALLE...NORTHERN WILL...SOUTHERN KENDALL...
EXTREME NORTHERN GRUNDY...DUPAGE...COOK...SOUTHERN LAKE AND
SOUTHEASTERN MCHENRY COUNTIES...

AT 742 PM...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
INDICATE A LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING NICKEL
SIZE HAIL...AND DESTRUCTIVE WINDS IN EXCESS OF 80 MPH. THESE STORMS
WERE LOCATED ALONG A LINE EXTENDING FROM CRYSTAL LAKE TO LISLE TO
CRYSTAL LAWNS TO LISBON...MOVING EAST AT 62 MPH.

SEVERE THUNDERSTORMS WILL BE NEAR...
WAUCONDA...ISLAND LAKE...WOOD DALE...AND WILLOWBROOK BY 750 PM...
BURBANK...WORTH...WESTCHESTER...AND SUMMIT BY 755 PM...
INDIAN CREEK...AND VERNON HILLS BY 800 PM...
DOWNTOWN CHICAGO BY 810 PM...
THIS SEVERE THUNDERSTORM WARNING INCLUDES THE CITY OF CHICAGO.

THIS IS AN EXTREMELY DANGEROUS AND POTENTIALLY LIFE THREATENING
SITUATION. SEEK SHELTER IN A BASEMENT OR INTERIOR ROOM OF A STURDY
BUILDING. STAY AWAY FROM WINDOWS.
VERY HEAVY RAINFALL MAY CAUSE LOCALIZED FLOODING.

LAT...LON 4140 8755 4143 8862 4161 8880 4163 8826
4215 8824 4216 8858 4231 8858 4231 8782
4214 8774 4207 8765 4191 8762 4182 8756
4171 8754
TIME...MOT...LOC 0042Z 283DEG 54KT 4228 8833 4180 8806
4160 8812 4141 8850

$$

MARSILI/CMS

[Praxus]

Never heard the term 'derecho', expect in spanish! I guess it means a severe thunderstorm?

[CrazyC83]

Coverage found: http://media.myfoxchicago.com/live

[RL3AO]

Red dot north of Chicago is Wrigley Field.

[Praxus]

Incredible convection

[Bunkertor]

Cups game just interrupted for emergency break

[LSU2001]

A derecho (from Spanish: "derecho" meaning "straight") is a widespread and long-lived, violent convectively induced straight-line windstorm that is associated with a fast-moving band of severe thunderstorms usually taking the form of a bow echo. Derechos blow in the direction of movement of their associated storms, similar to a gust front, except that the wind is sustained and generally increases in strength behind the "gust" front. A warm weather phenomenon, derechos occur mostly in summer, especially July in the northern hemisphere. They can occur at any time of the year and occur as frequently at night as in the daylight hours.

The traditional criteria that distinguish a derecho from a severe thunderstorm are sustained winds of 58 mph/92 km/h during the storm as opposed to gusts, high and/or rapidly increasing forward speed, and geographic extent (typically 250 nautical miles (460 km) in length. [1]) In addition, they have a distinctive appearance on radar (bow echo); several unique features, such as the rear inflow notch and bookend vortex, and usually manifest two or more downbursts.

Although these storms most commonly occur in North America, derechos may infrequently occur elsewhere in the world. Outside North America they may be called by different names. For example, in Bangladesh and adjacent portions of India, a type of storm known as a "Nor'wester" may be a progressive derecho.

Source: http://en.wikipedia.org/wiki/Derecho