Hail and Damaging Winds in Illinois, May 27, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
215 PM CDT SAT MAY 27 2006

.DISCUSSION FOR AFTERNOON GRIDS/ZONES...
215 PM CDT

MODELS NOT DOING WELL WITH CONVECTION IN IA TODAY. SPC ANALYSIS
SHOWING MSTR AND THETA E CONVERGENCE AXES UP MS RVR VLY AND INTO
SWRN WI. TREND APPEARS FOR CONVECTION TO CONT NE INTO WI THIS
EVENING. CAN SEE NEW CONVECTION FORMING N OF MLI IN TRAJECTORY FOR
FREEPORT. THIS TOO CLOSE TO WRN EDGE OF CWA TO TAKE OUT CHC OF PCPN
SO AM CONTINUING A THREAT FOR 1ST 2 TIERS OF NRN COUNTIES AT LEAST
UNTIL MIDNGT. HIER POP AT RFD AND TAPERING LOWER SOUTH AND EAST.
ACARS HOWEVER SHOWING SOME DECENT LOW LVL CAPPING EVEN AT RFD SO
DONT THINK CONFIDENCE CALLS FOR MORE THAN CHC CATEGORY. HOWEVER
WILL MONITOR SITUATION FOR NEXT HOUR AND SEE HOW TSTMS BREWING N OF
MLI REACT. MODELS SHOWING RISING HTS AND THICKNESS OVER IL TNGT AND
SUNDAY...SO EXPECT THREAT NOT TO EXPAND BEYOND THIS EVENING.

WITH STRONG SW FLOW FEEDING OVER AREA ON SUNDAY AND HIGHS RISING TO
AROUND 90...CAPPING SHUD KEEP CONVECTION AT BAY THIS FAR EAST.
CONVECTIVE TEMP FCST NEAR 97 ALTHO LI VALUES -6 AND CAPES OVER 2K.
YET WAVES CONT TO FEED NE ACROSS IA INTO WI...WITH WIDE OPEN GULF
MSTR SUPPLYING TSTM GROWTH. THESE WAVES SLIP EASTWARD MON NGT AND
HAVE MOVED UP CHC OF TSTMS TO MON EVENING. THIS PATTERN TO CONT THRU
MUCH OF WEDNESDAY AND ENDING WITH FROPA WED AFTN.

COOLER AND DRIER POST-FRONTAL FLOW THURSDAY AND FRIDAY SHUD PRECEDE
HIGH PRESSURE BLDG OVER THE REGION FOR THE WEEKEND.

RLB

&&

.AVIATION DISCUSSION FOR 18Z TAFS...
105 PM CDT

MAIN FORECAST ISSUES WILL CENTER AROUND WINDS AND CHANCES FOR ANY
PRECIP THIS AFTERNOON/EVENING.

REMNANT MCVS FROM LAST NIGHTS CONVECTION WILL BE THE MAIN FORCING
MECHANISMS THROUGH THIS EVENING. VISIBLE SATELLITE IMAGERY
EARLIER THIS MORNING WAS SUGGESTING MCV ACROSS NORTHEAST IOWA WITH
ANOTHER ACROSS SOUTHWEST IOWA. SOUTHWESTERLY MID LEVEL FLOW SHOULD
TAKE LEADING MCV INTO SOUTHERN WISCONSIN THROUGH THE REMAINDER OF
THE AFTERNOON HOURS...WITH TRAILING MCV LIKELY TO SKIRT ACROSS SWRN
WISCONSIN/NWRN ILLINOIS THIS EVENING. THIS SECONDARY VORT MAX WILL
LIKELY BE THE FEATURE TO FOCUS ON FOR CONVECTIVE POTENTIAL ACROSS
NORTH CENTRAL ILLINOIS LATE THIS AFTERNOON/EARLY THIS EVENING.
17-18Z ACARS SOUNDINGS ACROSS THE AREA STILL INDICATING NEARLY
ISOTHERMAL LAYER FROM 800-750 HPA WHICH WILL LIKELY CAP THINGS UNTIL
LATE AFTERNOON. BY THIS TIME...THE SECONDARY MCV WILL LIKELY BE
ENTERING NE IOWA WITH A LITTLE BETTER FORCING FOR ASCENT ACROSS NWRN
IL BY THIS EVENING. MAGNITUDE OF INSTABILITY IS RATHER
IMPRESSIVE...WITH MLCAPES ON THE ORDER OF 1500 J/KG. WITH
INSTABILITY AND MOISTURE IN PLACE...FORCING IS THE MAIN QUESTION AND
SOME CONCERN THAT BETTER FORCING WITH THESE MCVS MAY REMAIN JUST TO
THE NORTH AND WEST OF THE TERMINALS. GIVEN UNCERTAINTY...WILL CARRY
VCTS MENTION AT RFD FROM 22Z-02Z. BY THIS EVENING...MID LEVEL
THERMAL RIDGE WILL ADVECT INTO NORTHERN ILLINOIS WHICH SHOULD ALLOW
MOST OF THUNDERSTORM ACTIVITY TONIGHT TO REMAIN TO THE NORTH.

LAKE ENHANCED BOUNDARY STRETCHING FROM APPROXIMATELY ORD-MDW-GYY
WILL PROBABLY NOT ADVANCE MUCH FURTHER WEST AND EVENTUALLY WASH OUT
AS LOW LEVEL FLOW CONTINUES TO STRENGTHEN THIS AFTERNOON. WITH THIS
INCREASING SYNOPTIC GRADIENT...WILL MAINTAIN SOUTHEAST WINDS IN THE
10-15 KNOT RANGE FOR THIS AFTERNOON...WITH WINDS VEERING TO THE
SOUTH 10 KNOTS OR LESS DURING THE EVENING. WINDS WILL THEN VEER S-SW
TOMORROW MORNING WITH BETTER GUST POTENTIAL SETTING UP IN THE
AFTERNOON TOMORROW WITH GUSTS UP AROUND 20 KNOTS POSSIBLE. TIGHTER
GRADIENT TONIGHT SHOULD HELP PREVENT SIGNIFICANT FOG...AND WILL
CARRY GENERALLY 5SM VSBYS OVERNIGHT.

NDM

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...NONE.
.IN...NONE.
.LM...NONE.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
430 AM CDT SAT MAY 27 2006

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-280930-
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-
430 AM CDT SAT MAY 27 2006

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 TONIGHT...GENERALLY NORTH OF
INTERSTATE 80.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

THERE IS A CHANCE OF THUNDERSTORMS TUESDAY AND WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NECESSARY.

&&

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

LMZ740>745-766-280930-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
430 AM CDT SAT MAY 27 2006

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 TONIGHT.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

THERE IS A CHANCE OF THUNDERSTORMS TUESDAY AND WEDNESDAY.

&&

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