Severe Thunderstorm Warning 137, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
1225 PM CDT TUE JUL 13 2004

.DISCUSSION...
FORECAST CONCERN WILL BE CONVECTIVE CHANCES FROM THIS MORNING INTO
THIS EVENING.

REGIONAL PROFILERS INDICATING LLJ BEGINNING TO VEER TO THE WEST
ACROSS EASTERN NEBRASKA/WESTERN IOWA. CONVECTION DEVELOPED IN
ASSOCIATION WITH STRONG MOISTURE CONVERGENCE AT NOSE OF LOW LEVEL
JET ACROSS NWRN IA/SRN MN. WELL PRONOUNCED UPPER LEVEL CYCLONIC
CIRCULATION IS BEGINNING TO ADVANCE EASTWARD INTO SOUTHWEST ONTARIO
WITH KBIS SAMPLING A 50 KNOT 500 HPA WESTERLY WIND IN THE 00Z RAOB
DATA. EVENING RAOB FROM KDVN SHOWING SHALLOW MOIST LAYER BENEATH
VERY DRY WELL MIXED LAYER ABOVE 900 HPA. WEAK SURFACE PRESSURE
GRADIENT LINGERS ACROSS CWA AND WITH SFC DEW POINTS IN MID AND UPPER
60S...FOG HAS ONCE AGAIN THIS EVENING WITH REPORTS OF DENSE FOG
ALONG THE LAKESHORE. COVERAGE DOES NOT SEEM TO WARRANT ANY EARLY
MORNING ADVISORY BUT WILL CONTINUE MENTION OF AREAS OF FOG THROUGH
14Z.

LLJ WILL CONTINUE TO WEAKEN THROUGH MORNING HOURS BUT WILL TRANSPORT
MUCH MOISTER LOW LEVEL AIR INTO CWA. RUC/MESOETA DEPICTING AREA OF
STRONG 850 HPA MOISTURE CONVERGENCE ACROSS EASTERN IOWA BY 12Z
WORKING INTO WESTERN PORTIONS OF CWA IN 15Z-18Z TIME FRAME. WILL
INTRODUCE CHANCE OF MORNING -TSRA GIVEN STRONG MOISTURE CONVG AND
INCREASING INSTABILITY. SOME CONCERN FOR WIND POTENTIAL WITH ANY
MORNING CONVECTION BASED INITIALLY DRY MID LEVELS BUT GREATER SEVERE
RISK WILL EXIST THIS AFTERNOON INTO EARLY THIS EVENING. MID/UPPER
LEVEL JET STREAK SAMPLED ACROSS ND WILL MOVE SOUTHEASTWARD INTO
UPPER MS VALLEY WITH INCREASING UPPER DIFFLUENCE AHEAD OF SOUTHERN
CANADIAN SHORT WAVE. MESOETA HAS BEEN CONSISTENT WITH SB CAPE VALUES
BETWEEN 4000-5000 J/KG THIS AFTERNOON ESPECIALLY ACROSS NW INTO WC
ILLINOIS IN PROXIMITY TO SURFACE LOW WHERE LL DEW POINTS WILL LIKELY
BE MAXIMIZED. ANY DISCRETE AFTERNOON CONVECTION SHOULD QUICKLY
EVOLVE INTO LINEAR MODE BY MID TO LATE AFTERNOON GIVEN FAVORABLE
ORIENTATION OF STRONG MID LEVEL WINDS TO LOW LEVEL BAROCLINIC ZONE.
VERY POTENT UPPER PV ANOMALY ALSO EVIDENT IN ETA/GFS SOLUTIONS WITH
GOOD DRY STRATOSPHERIC INTRUSION ACTING TO ENHANCE WIND POTENTIAL.
SWODY1 UPGRADED TO MODERATE RISK FOR ENTIRE CWA AND WILL KEEP SEVERE
MENTION FOR ALL ZONES THIS AFTERNOON...AND ACROSS SE PORTIONS OF CWA
THIS EVENING.

MUCH DRIER LOW LEVEL AIR ADVECTS INTO NRN IL/NW IND OVERNIGHT BUT
KEPT MINS CLOSE TO GUIDANCE IN MID 60S WITH LACK OF DECOUPLING
OFFSETTING DRIER LOW LEVEL AIR. DECENT SYNOPTIC SCALE SUBSIDENCE FOR
WEDNESDAY BUT WITH COOLER MID LEVEL TEMPS SHOULD SEE JUST A FEW FAIR
WEATHER CU DEVELOP DURING THE AFTERNOON. RATHER UNEVENTFUL NEXT FEW
DAYS WITH NEXT CONCERN FOR FRIDAY. MODELS ALL BRING IN ANOTHER WAVE
IN NORTHERLY UPPER FLOW AND FOLLOWED UKMET/GFS CONSENSUS OF SLOWER
BUT LESS AMPLIFIED SOLUTION BRINGING NEXT CHANCE OF -TSRA TO MAINLY
NRN SECTIONS OF CWA FRI NIGHT. UPPER RIDGE AXIS ACROSS WESTERN CONUS
FLATTENS OUT FOR MON/TUE AS NEXT PAC WAVE CRASHES INTO SW CANADA.
THIS WILL HELP MODERATE TEMPS INTO EARLY NEXT WEEK WITH DRY
CONDITIONS.

NDM

&&

.AVIATION...
FOR 18Z TAFS:
GENERALLY VFR CONDS THROUGH NEXT 24 HOURS...INTERRUPTED BY PERIOD OF
SVR TSTMS THIS AFTN. BOUNDARY MOVING SE THRU LEE COUNTY HEADED SOUTH
OF TERMINALS. MAIN BAND WITH COLD FNT THIS AFTN IS STILL IN WI AND
ERN IA. SHUD BE MOVING TO RFD BY 2 PM...ORD AROUND 3 OR 4 PM AND OUT
OF GYY BY 6 PM. ONLY PUTTING THIS IN FOR A COUPLE HOURS THIS AFTN.
IF TSTMS DO GO THRU...SHUD STABILIZE WITH LTL TIME FOR REHEATING.
WITH FROPA AROUND 8 OR 9 PM...WINDS SHUD SWITCH TO NW WITH SCT CLDS
AROUND 4-8K. WILL MAINTAIN THAT OVERNIGHT TONIGHT...THEN DEVELOP BKN
VFR CU BY 11 AM WITH REMAINING LOW LVL MOISTURE CONVERGING IN
CYCLONIC FLOW.

&&

.LOT...WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LK MI...NONE.

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO IL
1205 PM CDT TUE JUL 13 2004

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-019
-141100-
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DU PAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
1205 PM CDT TUE JUL 13 2004

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL
AND NORTHEAST ILLINOIS...AND NORTHWEST INDIANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO
EARLY THIS EVENING ACROSS THE ENTIRE OUTLOOK AREA. THUNDERSTORMS ARE
EXPECTED TO BECOME MORE NUMEROUS DURING THE AFTERNOON AS A STRONG
UPPER LEVEL DISTURBANCE MOVES  SOUTHEAST ACROSS THE UPPER MIDWEST
AND INTO THE WESTERN GREAT LAKES...PUSHING A COLD FRONT SOUTHEAST
INTO NORTHERN ILLINOIS THIS AFTERNOON...CONTINUING INTO CENTRAL
ILLINOIS AND THROUGH NORTHWEST INDIANA DURING THIS EVENING. THIS
DISTURBANCE WILL BRING A GOOD CHANCE OF SEVERE WEATHER TO THE
REGION. THE MAIN THREATS FROM THE THUNDERSTORMS DURING THE AFTERNOON
AND EARLY EVENING WILL BE DAMAGING WINDS AND LARGE HAIL...WITH ALSO
A THREAT A TORNADO DEVELOPMENT. BY 7 PM...THE THREAT OF SEVERE
WEATHER WILL BE CONFINED MAINLY SOUTH OF INTERSTATE 80 WITH DAMAGING
WINDS CONTINUING AS THE MAIN THREAT THROUGH THE EVENING IN
ASSOCIATION WITH AN EXPECTED SQUALL LINE AS IT TRACKS SOUTHEAST. BY
MIDNIGHT...THE THREAT OF SEVERE WEATHER WILL HAVE COME TO AN END
ACROSS THE OUTLOOK AREA.

HOT AND HUMID CONDITIONS WILL BE WIDESPREAD ACROSS THE REGION TODAY.
HEAT INDICES WILL RISE TO AROUND 100 DEGREES THIS AFTERNOON SOUTH OF
INTERSTATE 80...WITH HEAT INDICES REACHING INTO THE MIDDLE 90S NORTH
OF INTERSTATE 80.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THERE IS ANOTHER CHANCE OF THUNDERSTORMS FRIDAY NIGHT INTO SATURDAY.
THESE STORMS ARE NOT EXPECTED TO BE SEVERE AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS WILL BE NEEDED THIS AFTERNOON...AND LIKELY INTO THIS
EVENING.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WWW.CRH.NOAA.GOV/LOT (LOWER CASE)

LMZ740>746-766-141100-
WINTHROP HARBOR IL TO NEW BUFFALO MI-
LAKE MICHIGAN-
1205 PM CDT TUE JUL 13 2004

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS
AND INDIANA WATERS OF LAKE MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THE THREAT OF THUNDERSTORMS WILL ON THE INCREASING DURING THE
AFTERNOON...WITH A MODERATE RISK OF SEVERE THUNDERSTORMS. THE MAIN
THREAT WITH THE STORMS WILL BE STRONG GUSTY WINDS IN EXCESS OF 45
KNOTS...WITH ALSO A THREAT OF LARGE HAIL AND POSSIBLY TORNADOES.

THE RISK OF SEVERE WEATHER WILL DIMINISH BY AROUND 6 PM THIS EVENING.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THERE IS ANOTHER CHANCE OF THUNDERSTORMS FRIDAY NIGHT INTO SATURDAY.
THESE THUNDERSTORMS ARE NOT EXPECTED TO BE SEVERE AT THIS TIME.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WWW.CRH.NOAA.GOV/LOT (LOWER CASE)

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
1239 PM CDT TUE JUL 13 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

1225 PM     HAIL             AMBOY                   41.72N 89.33W
07/13/2004  1.00 INCH        LEE                IL   TRAINED SPOTTER

            DIME TO QUARTER SIZE HAIL FROM AMBOY TO SUBLETTE

1232 PM     HAIL             SUBLETTE                41.64N 89.23W
07/13/2004  1.25 INCH        LEE                IL   TRAINED SPOTTER

&&

ALLSOPP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
107 PM CDT TUE JUL 13 2004

..TIME...   ...EVENT...     ...CITY LOCATION...      ...LAT.LON...
..DATE...   ....MAG....     ..COUNTY LOCATION...ST.. ...SOURCE....
            ..REMARKS..

1256 PM     HAIL             MENDOTA                 41.55N 89.12W
07/13/2004  1.75 INCH        LA SALLE           IL   TRAINED SPOTTER

1250 PM     HAIL             MENDOTA                 41.55N 89.12W
07/13/2004  1.25 INCH        LA SALLE           IL   TRAINED SPOTTER

1244 PM     HAIL             MENDOTA                 41.55N 89.12W
07/13/2004  1.75 INCH        LA SALLE           IL   TRAINED SPOTTER

1235 PM     TSTM WND DMG     5 SW AMBOY              41.67N 89.40W
07/13/2004                   LEE                IL   EMERGENCY MNGR

            ROOF OFF ADDITION ONTO BARN AND ROWS OF CORN TAKEN OUT AT
            BRYER KNOLL AND ROCKY FORD.

&&

CLK

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