Severe Thunderstorm Warning 131, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO IL
625 PM CDT TUE JUL 6 2004

.DISCUSSION FOR AFTERNOON ZONES/GRIDS:

BIG QUESTION THIS EVENING IS WHETHER OR NOT CONVECTION WILL GET GOING
OVER SRN/ERN PORTION OF FA.  WILL GO WITH LIKELY POPS SRN PORTION OF
AREA AND CHC POPS THIS EVENING ELSEWHERE.  ETA APPEARED TO
INITIALIZE BETTER TDY ESPECIALLY IN HANDLING STG S/W NOW MOVG THRU
MO VLY INVOF FSD.  THIS FEATURE WILL FOLLOW ITS PREDECESSOR ACROSS
UPR MIDWEST TNGT AND WED.  AMS MODERATELY UNSTABLE AS STRENGTHENING
MID LVL WINDS APCH THIS EVENING.  BLUE RIVER AND WINCHESTER
PROFILERS SHOW MID LVL WINDS HAVE BACKED SIGNIFICANTLY SINCE NOON
AND INCREASED TO ABV 50 KTS.  GIVEN THESE DYNAMICS...WILL GO WITH
MOS POPS IN RGN WHERE ETA/MESOETA SUGGESTS LINEAR CONVECTIVE GROWTH
IN OMEGA FIELD...FROM RUFLY PONTIAC AREA...TO KANKAKEE TO GARY AND
POINTS S AND EWD.  AS OF NOW...VIS SATLT IMAGERY SHOWS SOME MDT CU
DVLPG IN THIS AREA...BUT DVLPMT IS QUITE SLOW TO OCCUR DUE TO
MARGINAL INSTABILITY AND DEEP CONVECTION OVER LWR OH VLY. AM
ANTICIPATING MORE TSTM DVLPMT AS MID LVL FORCING IS EXPECTED TO
OVERCOME WEAK INSTABILITY...ESPECIALLY OVER SRN AND ERN FA THIS
EVENING.

LTL CHG TO RMNDR OF FCST.  DEEP UPR LOW TO MOVE THRU UPR MIDWEST ON
WED...LEADING TO SIG LO LVL INSTABILITY...SO EXPECT MORE CLOUDS THAN
SUN BY AFTN DUE TO CU DVLPMT.  THIS CONVECTION SHOULD BE RATHER
SHALLOW...BUT WOULD NOT BE SURPRISED TO SEE A FEW SHWRS POP UP DURG
AFTN AS FAR S AS CWA/S NRN TIER OF COUNTIES. SKIES TO CLR WED NGT AS
SFC HI PRES BLDS IN AND COLD AVDECTION ABATES. THUR LOOKS LIKE BEST
DAY IN FCST PERIOD.   LGT WINDS...LO HUMIDITY AND TEMPS STILL
COMFORTABLE.  AS H5 RIDGE BUILDS OVR SRN PLAINS BY FRI...AND
FLATTENS EWD ACRS SRN U.S. OVR WEEKEND...TRUE SUMMERLIKE CONDS ARE
EXPECTED TO OVERSPREAD THE MIDWEST.  H85 TEMPS FCST TO BE ARND
20 C  BY SAT SO WILL GO WITH HI TEMPS AOA THE BIG 9-0 OVER THE
WEEKEND.  WEAK COLD FRONT TO PASS THRU ABOUT SUN NGT SO WILL
CONFINE TSTM MENTION TO SUN/SUN NGT AND AVOID A LITANY OF 30 PCT
POPS.

MERZLOCK

&&

.AVIATION FOR 00Z TAFS...
CONVECTION BEGINNING TO INCREASE IN COVERAGE ALONG SURFACE TROUGH
POSITIONED FROM FAR NE IL/NW IN SOUTHWARD INTO EAST CENTRAL
ILLINOIS. NOSE OF STRONGEST INSTABILITY AXIS IS POSITIONED FROM
ACROSS NRN INDIANA AND EXPECT INCREASING CONVECTIVE TREND TO
CONTINUE THROUGH 03Z. SCATTERED RAIN SHOWERS ALSO EXTEND ACROSS
EASTERN IOWA IN DPVA REGION ASSOCIATED WITH RATHER AMPLIFIED UPPER
TROUGH AXIS EXTENDING FROM CENTRAL MINNESOTA INTO WESTERN IOWA.
PRECIPITATION WISE...WILL CARRY THUNDER MENTION FOR GYY/MDW IN
CLOSER PROMIXITY TO PRIMARY INSTABILITY AXIS AND JUST MENTION TS
VICINITY MENTION FOR ORD/DPA. FURTHER BACK TO THE WEST ACROSS
RFD...WILL ALSO INCLUDE JUST SOME RAIN SHOWERS THROUGH 04Z WITH
APPROACH OF UPPER LEVEL TROUGH AXIS BUT INSTABILITY MUCH WEAKER BACK
TO THE WEST. WILL NEED TO MONITOR RADAR TRENDS IF PRECIP ASSOCIATED
WITH THIS UPPER WAVE REACHES AS FAR EAST AS EASTERN TERMINALS BUT
FOR NOW WILL TREND TOWARD DRY CONDITIONS AFTER 03Z. MAINTAINED TREND
TO MVFR CIGS LATER THIS EVENING CONTINUING THROUGH FORECAST PERIOD
WITH BROAD 1000-500 HPA THICKNESS TROUGH MOVING INTO NRN IL
ASSOCIATED WITH UPPER TROUGH.

NDM

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO IL
437 PM CDT TUE JUL 6 2004

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-019
-071100-
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-
437 PM CDT TUE JUL 6 2004

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

.DAY ONE...TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS ACROSS THE OUTLOOK AREA LATE THIS
AFTERNOON AND THIS EVENING. THERE IS A SLIGHT RISK OF SEVERE
THUNDERSTORMS GENERALLY ALONG AND SOUTH OF A LINE FROM LASALLE TO
WAUKEGAN ILLINOIS...HOWEVER THE GREATEST RISK APPEARS TO BE ALONG
AND SOUTH OF A LINE FROM GALESBURG...TO JOLIET...TO THE SOUTH SIDE
OF CHICAGO. DAMAGING THUNDERSTORM WIND GUSTS OF 60 MPH OR HIGHER AND
LARGE HAIL ARE THE MAIN THREATS FROM THESE STORMS. IN
ADDITION...BRIEF HEAVY DOWNPOURS COULD LEAD TO LOCALIZED MINOR
FLOODING.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH TUESDAY

HIGH TEMPERATURES MAY REACH THE LOWER 90S ON SATURDAY WITH HEAT
INDICES IN THE UPPER 90S POSSIBLE.

THERE IS A CHANCE OF THUNDERSTORMS SUNDAY AND SUNDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS MAY BE NEEDED THIS EVENING.

&&

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

LMZ740>746-766-071100-
WINTHROP HARBOR IL TO NEW BUFFALO MI-
LAKE MICHIGAN-
437 PM CDT TUE JUL 6 2004

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

.DAY ONE...TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN
THIS EVENING. THERE IS A SLIGHT RISK FOR SEVERE STORMS. THE MAIN
SEVERE WEATHER THREAT WILL BE DAMAGING WINDS OF 60 MPH OR GREATER.

DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH TUESDAY

THERE IS A CHANCE OF THUNDERSTORMS SUNDAY AND SUNDAY NIGHT.

&&

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

RATZER