Severe Thunderstorm Warning 77, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1210 PM CDT WED JUL 202005

.AVIATION DISCUSSION FOR 18Z TAFS...

SHORT TERM CONVECTIVE TRENDS MAIN FORECAST ISSUE.

LINEAR MCS MOVING ACROSS FORECAST AREA EARLY THIS AFTERNOON. AIRMASS
ACROSS NRN IL/NW IND BECOMING MODERATELY UNSTABLE...WITH RUC NOWCAST
TOOLS INDICATING 100 MB MLCAPE IN THE 1000-2000 J/KG RANGE AND CIN
ERODING RAPIDLY. THUS EXPECT ORGANIZED LINE OF TSTMS TO CONTINUE TO
ADVANCE ACROSS FCST AREA THIS AFTN...AFFECTING CHI AREA TERMINALS
18-22 UTC. APPEARS THAT BY 00Z CONVECTION SHOULD BE FOCUSED SOUTH
AND EAST OF TERMINALS AS OUTFLOW SPREADS SOUTH/EAST OF CURRENT
STORMS.

SOME CONCERN FOR POTENTIAL MVFR OR EVEN IFR STRATUS/HZ/BR OVRNGT AS
CONVECTIVELY DISTURBED WIND FIELD BECOMES LGT/VRBL. FOR NOW HAVE
GONE WITH AN MVFR VSBY IN HZ.

RATZER

&&

FROM MORNING ZFP/GRIDS...

.DISCUSSION...DECENT PROSPECTS FOR SOME MUCH NEADED IF NOT TOO LATE
RAINFALL FOR PARCHED FIELDS LATER TODAY AND TONIGHT. CLUSTER OF TSRA
OVR SRN MN...NWRN IA...FAR NERN NEB WHERE STG WAA AHEAD OF SHRTWV
TROF MOVG FM NRN PLAINS TWRD UPR MIDWEST. PROFILERS SHOW GODD
BACKING/VEERING SIGNATURE WITH TROF PASSAGE AS WELL AS VERY STG LLVL
FEED OF HOT AIR NNEWRD AHEAD OF TROF WITH 45-55KT SW WNDS AT H8 FRM
TX PNHDL TO ERN NEB ANSD WRN IA. NAM SHOWS THIS ISENT LIFT RATHER
WELL AND TRANSLATES STG UVV E ACROSS MS RIVER INTO SWRN WI AND NWRN
IA BY 18Z AND TO SERM WI AND NERN IL BY 00Z. GFS SUFFERING FEEDBACK
PROBS BY THIS EVE...BUT NAM ALSO BRINGS SIG...ALBEIT LESSER..QPF
ACROSS NRN IL DUR THIS EVE WITH PRECIPITABLE WATER VALUES CLIMBING
TO 2+ INCHES BY 00Z THU. WILL CARRY ONLY HI CHC POPS AS TO NOT HAVE
HOPES DASHED THO AT LEAST DECENT PORTION OF FA HAS GOOD CHC OF
SEEING SOME MEANINGFUL TOTALS LATE TODAY AND TONIGHT. EXPECT OUTFLO
REINFORCED BNDRY ACROSS SRN FA INTO TONIGHT AND THU MORNING WITH
CONT CHC OF TSRA ALONG AND S OF IT. WITH H8 TEMPS WRMING INTO LWR
20C RANGE TODAY AND GOOD SUN BEFORE HIER CLOUDS START ARRIVE TEMPS
SHUD REACH LO AND MID 90S TODAY...WHILE SSE SFC WNDS ADVECT IN ONLY
MODERATELY HI DWPTS SO HEAT INDEX SHUD ONLY FLIRT WITH 100 AT TIME
OF MAX TEMPS. LLVLS COOLED SLIGHTLY ACROSS NRN PORTION OF FA BEHIND
SHRTWV WITH SFC RDG BLDG ACROSS UPR MIDWEST AND NRN GRTLKS THU. SOME
LK COOLING WL KEEP TEMPS IN 80S ALONG SHORE. ANOTHER SHRTWV DROPS
INTO NRN GRTLKS FRI...WITH GOOD SURGE OF HEAT STARTING LATER SAT AS
MORE SIG SHRTWV MOVS OVR UPR RDG ACROSS SRN CANADA. H8 THERMAL RDG
OF 24-27C FCST ACROSS NR IL AT 12Z THO GFS WANTS TO PUSH ANOTHER
CDFNT INTO NRN IL DURG DAY SO COULD PUT DAMPER ON TRIPLE DIGIT TEMPS
FOR NRN IL SUN.

TRS

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
600 AM CDT WED JUL 20 2005

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-202200-
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-
600 AM CDT WED JUL 20 2005

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 CHANCE OF THUNDERSTORMS THIS AFTERNOON AND TONIGHT...WITH
A A SLIGHT CHANCE OF SEVERE THUNDERSTORMS INTO THIS EVENING. THE
MAIN THREAT WOULD BE DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

HEAT INDICES WILL REACH 100 TO 105 ACROSS NORTHERN
ILLINOIS...AND 105 TO 110 FROM THE KANKAKEE AND ILLINOIS VALLEYS
SOUTH ON SUNDAY. THESE LEVELS MAY POSE A HAZARD WITH PROLONGED
EXPOSURE OR EXTENDED PHYSICAL ACTIVITY....ESPECIALLY TO THOSE WITH
SENSITIVITY TO HEAT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NECESSARY LATER TODAY.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)

LMZ740>745-766-202200-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
600 AM CDT WED JUL 20 2005

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

.DAY ONE...TODAY AND TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS THIS AFTERNOON AND TONIGHT...WITH
A A SLIGHT CHANCE OF SEVERE THUNDERSTORMS INTO THIS EVENING. THE
MAIN THREAT WOULD BE DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)