Severe Thunderstorm Warning 134, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
650 AM 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...
REMAINDER OF OVERNIGHT PRECIP HAS MOVED OUT OF IOWA AND INTO
WESTERN PORTION OF FORECAST AREA THIS AM. TAFS COVER THIS ACTIVITY
WITH TEMPO TSRA THROUGH 14Z.

NEXT WX CONCERN WILL BE NEW TSRA DEVELOPMENT THIS AFTERNOON AS H5
WAVE APPORACHES AREA. GIVEN AMOUNT OF INSTABILITY TO BE PRESENT AS
WARM HUMID AIR ADVECTS NORTHWARD INTO TAF AREA EXPECT SOME TSRA
BEECOME SEVERE DURING AFTERNOON. HAVE KEPT PRECIP FROM PREVIOUS
ISSUANCE BUT UPPED CHANCES TO TEMPO GROUP AS AFTERNOON HEATING
COMBINES WITH SHORT WAVE. PRECIP CHANCES SHOULD CONTINUE INTO THE
EVENING HOURS THROUGH COLD FROPA AROUND 03Z. WIND SHIFT OCCURS AT
THAT TIME AND CLOUD COVER WILL BEGIN TO THIN OUT THEN LIFT TO VFR.

&&

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

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO IL
800 AM 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-
800 AM CDT TUE JUL 13 2004

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

.DAY ONE...TODAY AND TONIGHT

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO
EARLY THIS EVENING ACROSS THE ENTIRE OUTLOOK AREA. AN AREA OF
SHOWERS AND THUNDERSTORMS ACROSS EASTERN IOWA AND NORTHWEST ILLINOIS
WILL MOVE INTO NORTH CENTRAL ILLINOIS THIS MORNING BEFORE
DISSIPATING BY AROUND MID MORNING. SEVERE WEATHER IS NOT EXPECTED
WITH ANY THUNDERSTORMS THIS MORNING.

THUNDERSTORMS ARE EXPECTED TO REDEVELOP AFTER 1 PM THIS AFTERNOON AS
A STRONG UPPER LEVEL DISTURBANCE DROPS SOUTHEAST OUT OF CANADA. THIS
DISTURBANCE WILL BRING A GOOD CHANCE OF SEVERE WEATHER TO THE
REGION. THE MAIN THREATS WITH THUNDERSTORMS EARLY THIS AFTERNOON
WILL BE DAMAGING WINDS AND LARGE HAIL. THESE STORMS ARE EXPECTED TO
EVOLVE INTO A SQUALL LINE BY MID AFTERNOON WITH DAMAGING WINDS BEING
THE MAIN THREAT. 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 COME TO AN END.

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...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED THIS AFTERNOON 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-
800 AM CDT TUE JUL 13 2004

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

.DAY ONE...TODAY AND TONIGHT

THE THREAT OF THUNDERSTORMS WILL INCREASE THIS AFTERNOON. THERE IS A
MODERATE RISK OF SEVERE THUNDERSTORMS AFTER 1 PM. THE MAIN THREATS
WITH THE STORMS WILL BE STRONG GUSTY WINDS IN EXCESS OF 45 KNOTS.
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)

RLB