Tornado and Flash Flooding in Illinois, April 17 to 18, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
647 AM CDT WED APR 17 2013

.DISCUSSION...
338 AM CDT

TODAY THROUGH TONIGHT...
IR IMAGERY EARLY THIS MORNING SHOWS A DEVELOPING RIBBON OF CLOUDS
ALONG A LLVL BOUNDARY STRETCHING FROM CENTRAL NEBRASKA EAST THROUGH
CENTRAL IL INTO SOUTHCENTRAL IN. CLOUD TOPS HAVE BEEN RAPIDLY
COOLING...AS IT APPEARS THE ATMOSPHERIC RIVER IS BEGINNING TO
DEVELOP FROM THE CENTRAL PLAINS STRETCHING NORTHEAST THROUGH THE
WESTERN GREAT LAKES. SOUTH OF THIS BOUNDARY TEMPS ARE MAINLY IN THE
UPR 40S WITH DEW POINTS IN THE MID 40S. TO THE NORTH...WHICH
INCLUDES MUCH OF THE CWFA...TEMPS HAVE ONLY COOLED INTO THE LOW 40S
WITH DEW POINTS SLIGHTLY DRIER IN THE LOW/MID 30S. REGIONAL RADAR
MOSAIC WAS ALSO INDICATING SPOTTY SHOWERS/THUNDERSTORMS BEGINNING TO
BLOSSOM ALONG THIS BOUNDARY. A COUPLE AREAS OF STRONGER JETS WERE
NOTED ACROSS THE FRONT-RANGE OF THE ROCKIES...WITH THE MORE POTENT
SPEED MAX ALONG THE TROUGH AXIS SOUTH OF THE FOUR-CORNERS REGION OF
THE CONUS. WITH ANTI-CYCLONIC FLOW POSITIONED NORTH OF THE
CWFA...THE EASTERLY WIND COMPONENT HAS BEEN ABLE TO KEEP A BULK OF
THE PRECIP SOUTH OF THE CWFA OVERNIGHT. ALTHOUGH THIS FEATURE WAS
SLIDING NORTHEAST INTO QUEBEC EARLY THIS MORNING.

AS THE ELEVATED FRONTAL BOUNDARY STEADILY ADVECTS NORTH...PRECIP
CHANCES WILL STEADILY INCREASE FROM SOUTHWEST TO NORTHEAST. HI-RES
LCL ARW INDICATES PRECIP WILL PUSH INTO WESTERN IL ARND 12Z OR
SHORTLY AFT DAYBREAK. THIS MATCHES UP RELATIVELY WELL WITH THE
SHRA/TSRA THAT IS LIFTING NORTHEAST CURRENTLY ACROSS SOUTHWEST IA.

THE CONVECTION THAT IS DEVELOPING OVER THE CENTRAL PLAINS IS IN A
FAVORABLE REGION FOR FURTHER GROWTH...WITH MODERATE MID/LOW LEVEL
MOISTURE CONVERGENCE. AS THE BOUNDARY LIFTS NORTH...PWAT VALUES WILL
STEADILY INCREASE. GUIDANCE HAS CONTINUED TO SUGGEST PRECIPITABLE
VALUES AROUND 1" BY MID-MORNING. THE LARGEST CHALLENGE WILL BE ON
HOW FAR NORTH THE BOUNDARY CAN LIFT THIS AFTN...AS GUIDANCE
CONTINUES TO INDICATE THE I-80 CORRIDOR. IT APPEARS A COMPLEX OF
SHRA/TSRA WILL LIFT NE ACROSS CENTRAL IA INTO WESTERN IL/SOUTHERN
WISC THIS AFTN. BULK SHEAR VALUES RAMP-UP THROUGHOUT THE
AFTN/EVE...WITH GUIDANCE SUGGESTING THE 0-3KM VALUES TO HOVER ARND
40KTS FROM THE SOUTH. THE LARGEST CONCERN FOR TODAY AND ANY STRONG
STORMS THAT DEVELOP WILL BE ON THE POTENTIAL FOR ROTATING
UPDRAFTS...GIVEN THE BACKED WINDS NORTH OF THE BOUNDARY AND HELICITY
VALUES PROGGED IN THE REGION OF THE BOUNDARY.

AS NOTED ABOVE...PWAT VALUES WILL BE ON THE INCREASE. WITH
ADDITIONAL MOISTURE POOLING INTO THE CWFA AND CONTINUES TO ADVECT
NORTH FROM THE WESTERN GULF OVERNIGHT...SOME OF THE THUNDERSTORMS
COULD EASILY PRODUCE HEAVY DOWNPOURS. IN ADDITION PWAT VALUES MAY
TOUCH 1.5-1.75" IN A FEW PORTIONS OF IA/IL OVERNIGHT...WITH
THUNDERSTORMS PERSISTING ALONG THE MOIST BOUNDARY. BASED ON THIS
HAVE MAINTAINED THE FLOOD WATCH AS WELL AS THE MENTION OF HEAVY RAIN
WITHIN THE FORECAST.

GUIDANCE OVERNIGHT INDICATES THE WARM/MOIST BOUNDARY WILL LIFT
OVERHEAD INTO SOUTHERN WISC...PLACING THE ENTIRE CWFA WITHIN THE
WARM SECTOR. THIS WILL PROVIDE A MILD OVERNIGHT...WITH DEW PTS
HOVERING THE LOW 50S. GUIDANCE IS BEGINNING TO INDICATE A LULL IN
THE CONVECTIVE CHANCES OVERNIGHT...MAINLY IN THE 06-12Z THUR WINDOW.
HAVE REFLECTED THIS IN THE FORECAST WITH SLIGHTLY LOWER POPS.

CONFIDENCE IN TEMPERATURES...HIGH.
CONFIDENCE IN PRECIPITATION/HEAVY RAIN...HIGH.

THURSDAY...POSITIVE TILTED DEEP TROUGH CONTINUES TO SLOWLY PUSH EAST
OF THE ROCKIES. WARM/MOIST ENVIRONMENT IS POISED TO CONTINUE THRU
THUR...WITH THE GREATEST FOCUS BEING ON POTENTIAL FOR SEVERE
WEATHER. 850MB THERMAL RIDGE OF 13-15 DEG C WITH SFC TEMPS WARMING
WELL INTO THE UPR 60S TO LOW 70S AHEAD OF THE COLD FRONTAL PASSAGE.
SFC LOW HAS SLOWED IN THE ARRIVAL WITH LATEST GUIDANCE...AND
INDICATING SOME STRENGTHENING PRIOR TO ARRIVAL. THE DYNAMICS REMAIN
VERY IMPRESSIVE...WITH EFFECTIVE SHEAR PROGGED TO BE ARND 50KTS. LCL
WRF-ARW IS INDICATING LLVL FLOW MAY BEGIN TO BACK JUST AHEAD OF THE
SHORTWAVE THUR. WHICH MAY PROVIDE SOME ENHANCEMENT TO THE HELICITY
AND POTENTIAL OF ROTATING UPDRAFTS AND AN ISOLATED TORNADO. AT THIS
TIME THE THINKING IS THAT AS HEATING OCCURS AND THE BOUNDARY
APPROACHES FROM THE WEST...CONVECTION WILL QUICKLY DEVELOP AND PUSH
EAST. AT THE ONSET A FEW ISOLATED STRONG STORMS WILL MOST LIKELY
EVOLVE INTO A LINEAR SEGMENT. GIVEN THE SHEAR PROGGED FOR
THUR...THESE STORMS COULD EASILY TAKE ON A BOW-LIKE FEATURE AS THEY
PUSH EAST.

HEAVY RAINFALL REMAINS POSSIBLE AGAIN THUR WITH THE CONVECTION THAT
IS EXPECTED...AND HAVE MAINTAINED MENTION OF THIS WITHIN THE
FORECAST. GUIDANCE CONTINUES TO SUGGEST PRECIP TOTALS WED/THUR IN
EXCESS OF 3" FOR PORTIONS OF NORTHERN IL.

CONFIDENCE IN TEMPERATURES...HIGH.
CONFIDENCE IN PRECIPITATION/HEAVY RAIN...MEDIUM.

FRIDAY THROUGH TUESDAY...
EXTENDED PERIODS THROUGH SUN CONTINUE TO DEPICT MINIMAL SPREAD
AMONGST ENSEMBLE MEMBERS...WITH GROWING DIVERGENCE FOR EARLY NEXT
WEEK. THE 500MB TROUGH AXIS WILL ARRIVE FRI ACROSS THE GREAT
LAKES/OHIO VALLEY...HOWEVER IT DOES APPEAR THAT THE TROUGH WILL
BEGIN TO SLOW IN ANY FORWARD PROGRESSION. A DOWNSTREAM
RIDGE...PLACED ACROSS THE WESTERN ATLANTIC...WILL SLOW THE
PROGRESSION OF THE TROUGH. THIS DOWNSTREAM RIDGE HAS SHOWN SOME
STRENGTHENING OVER THE PAST COUPLE OF DAYS...INDICATING THAT THE
COOLER AIR EXPECTED TO PUSH OVER THE CWFA LATER THIS WEEK/EARLY
WEEKEND MAY LINGER. WELL UPSTREAM ACROSS THE PAC-NW IS ANOTHER HIGH
AMPLITUDE RIDGE THAT DOESN'T APPEAR TO MAKE ANY PUSH EAST OVER THE
BULK OF THE EXTENDED. WITH THE PLACEMENT OF THE TWO MID-LVL
RIDGES...THIS SETUP SUGGESTS THAT THE EXTENDED PERIODS MAY CONTINUE
TO SEE UNSEASONABLY COOL WEATHER FOR THE CWFA. THE CAVEAT COULD BE
THE ANTI-CYCLONIC FLOW THAT WILL ARRIVE FRI NGT/SAT BEGINS TO DRIFT
EAST SUN. THIS MAY ALLOW A BRIEF SOUTHERLY FLOW AND ADVECT WARMER
AIR BACK INTO THE REGION SUN/MON. HOWEVER...IT DOES APPEAR PRECIP
CHANCES RETURN IN THIS SAME TIMEFRAME.

CONFIDENCE IN TEMPERATURES...HIGH.
CONFIDENCE IN PRECIPITATION...MEDIUM.

BEACHLER

&&

.HYDROLOGY...
350 PM CDT

WITH SEVERAL AREA RIVERS ALREADY NEAR OR ABOVE FLOOD STAGE...CONCERN
IS INCREASING FOR SIGNIFICANT ADDITIONAL RIVER RISES MID TO LATE
WEEK. PERIOD SHOWERS AND THUNDERSTORMS BEGINNING OVER THE
SOUTHERN PORTIONS OF THE CWA LATE TONIGHT WILL BRING SOME
RAINFALL... AGGRAVATING THE SITUATION AS IN ADDITION TO THE AREA
RIVERS THAT ARE ALREADY AT OR NEAR FLOOD FLOOD STAGE...THERE HAVE
BEEN REPORTS OF MANY DRAINAGE PONDS AND SMALLER STREAMS AT
CAPACITY. WHILE THE INITIAL THUNDERSTORM ACTIVITY EXPECTED THROUGH
THE DAY TOMORROW WILL BRING SOME LOCALLY HEAVY RAINFALL...THE
PRIMARY FLOODING CONCERN WILL INCREASE THROUGH WEDNESDAY NIGHT
WITH HEAVY RAIN LIKELY TO PERSIST INTO FRIDAY MORNING.

WITH THE DEEP UPPER TROUGH AND DEVELOPING LOW PRESSURE SYSTEM OVER
THE PLAINS...COPIOUS AMOUNTS OF GULF MOISTURE WILL STREAM
NORTHWARD INTO THE MIDWEST. FORECAST PRECIPITABLE WATER VALUES
ARE EXPECTED TO BE VERY HIGH...IN EXCESS OF 1.5 INCHES...WHICH IS
2 TO 3 STANDARD DEVIATIONS ABOVE NORMAL BY WEDNESDAY AND MAY GET
CLOSE TO 2 INCHES BY THURSDAY...WHICH WOULD BE 3 TO 4 STANDARD
DEVIATIONS ABOVE NORMAL. IN OTHER WORDS...THE POTENTIAL FOR
HEAVY/EXCESSIVE RAINFALL IS HIGH. THE LATEST FORECAST UPDATE IS FOR
NEARLY 4 INCHES OF STORM TOTAL PCPN...WHICH INCLUDES THE INITIAL
CONVECTIVE ACTIVITY EARLY WEDNESDAY...THROUGH THE PERIOD OF
GREATEST HEAVY RAIN POTENTIAL ON THURSDAY AND THE WRAPAROUND
LIGHTER PCPN FOLLOWING THE FROPA ON FRIDAY.

CONFIDENCE IS INCREASING FOR A HEAVY PRECIPITATION EVENT FOR
NORTHERN ILLINOIS AND NORTHWEST INDIANA. THE POTENTIAL EXISTS FOR
UP TO 4 INCHES OF RAINFALL WEDNESDAY INTO FRIDAY...WHICH WOULD SEND
RIVERS NEAR OR ABOVE FLOOD STAGE MODERATE OR MAJOR FLOOD
LEVEL...WHILE RIVERS CURRENTLY WELL BELOW FLOOD OR BANK FULL STAGE
LIKELY REACH OR EXCEED FLOOD STAGE. ALSO...WIDESPREAD HEAVY
RAINFALL MAY LEAD TO URBAN FLOODING ISSUES FOR VIADUCTS AND LOW.
ALSO...STORM DRAINS AND DRAINAGE DITCHES AND PONDS MAY NOT HAVE
THE CAPACITY TO HANDLE SOME PERIODS OF THE HEAVIEST RAINFALL...
LEADING TO FURTHER FLOODING ISSUES FOR ROADWAYS AND SUBURBAN AREAS
AS WELL.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* SCT SHOWERS AND THUNDERSTORMS THIS MORNING.
* GUSTY EASTERLY WINDS TODAY...BECOMING SOUTHERLY WEDNESDAY
  NIGHT.
* THUNDERSTORM CHANCES AGAIN THIS AFTERNOON AND TONIGHT.
* LOWERING CIGS THROUGH THE DAY. WITH VERY LOW MVFR TO IFR CIGS
  LIKELY BY LATE THIS AFTERNOON.

KJB

//DISCUSSION...UPDATED 12Z...

SCATTERED SHOWERS AND SOME THUNDERSTORMS CONTINUE TO DEVELOP WITHIN
A STRENGTHENING WARM AIR ADVECTION REGIME ACROSS PORTIONS OF
NORTHERN ILLINOIS THIS MORNING. THE MORE WIDESPREAD ACTIVITY HAS
REMAINED FARTHER WEST ACROSS IOWA AND FAR NORTHWESTERN ILLINOIS
CLOSER TO THE BEST MOISTURE CONVERGENCE ALONG THE NOSE OF A 40 KT
LOW LEVEL JET. THIS ACTIVITY WILL BEGIN TO AFFECT THE RFD AREA
BETWEEN 12 AND 13 UTC THIS MORNING. IT APPEARS MORE WIDELY SCATTERED
SHOWERS AND A FEW THUNDERSTORMS LOOK TO AFFECT THE EASTERN TERMINALS
THROUGH THIS MORNING AFTER 13 UTC.

ADDITIONAL CONVECTIVE ACTIVITY STILL LOOKS TO BE A DECENT BET THIS
AFTERNOON AS WELL...AS THE ACTIVITY CURRENTLY ACROSS EASTERN NEBRASKA
...KANSAS AND NORTHWESTERN MISSOURI LIFTS EAST-NORTHEASTWARD ALONG
THE 850 MB WARM FRONT THROUGH THE DAY. THE OVERALL TIMING APPEARS TO
BE BY MID TO LATE AFTERNOON. HOWEVER...CONFIDENCE ON THE EXACT
TIMING IS FAIRLY LOW AT THIS TIME.

ONCE THIS INITIAL COMPLEX OF ACTIVITY MOVES ACROSS THE AREA THIS
AFTERNOON AND EARLY THIS EVENING...THERE COULD BE A TEMPORALLY LULL
IN THE CONVECTIVE ACTIVITY. HOWEVER...SOME LOWER VISIBILITIES MAY
REMAIN IN PLACE INTO THE EVENING WITH VERY LOW CLOUDS AND FOG AHEAD
OF THE APPROACHING SURFACE WARM FRONT. WINDS WILL REMAIN EASTERLY
THROUGH EARLY THIS EVENING...AND COULD BECOME A BIT GUSTY.
HOWEVER...LATER THIS EVENING AND OVERNIGHT THE SURFACE WARM FRONT
SHOULD SURGE NORTHWARD ACROSS THE AREA. SOME STRONGER SOUTHERLY
WINDS WILL SET UP LATE TONIGHT AND INTO THURSDAY.

THE NEXT SHOT AT MORE WIDESPREAD CONVECTIVE ACTIVITY LOOKS TO BE
THURSDAY MORNING. THIS SECOND BATCH OF THUNDERSTORMS WILL LIKELY
CONTAIN VERY HEAVY RAINFALL WITH LOW VIS AND CIGS...AND THIS
ACTIVITY WILL EXTEND BEYOND THE CURRENT 30 HOUR ORD TAF PERIOD INTO
THURSDAY AFTERNOON. SOME STRONG STORMS ARE ALSO POSSIBLE ACROSS THE
AREA.

I HAVE ALSO ADDED SOME LOW LEVEL WIND SHEAR TO THE TAFS FOR THIS
EVENING AND INTO THE OVERNIGHT. A STRONG 50 KT LOW LEVEL JET IS
EXPECTED TO DEVELOP AROUND 2000 FEET AGL AND UNTIL SURFACE WINDS
BEGIN TO GUST IN THE WAKE OF THE WARM FRONT...IT APPEARS THAT LOW
LEVEL WIND SHEER WILL BE FAIRLY HIGH.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MODERATE TO HIGH CONFIDENCE IN SCT SHOWERS AND A FEW
  THUNDERSTORMS THIS MORNING AFTER 13 UTC.
* HIGH CONFIDENCE IN WIND FORECAST.
* MODERATE CONFIDENCE IN TIMING OF CONVECTION THIS AFTERNOON.
* MODERATE CONFIDENCE IN TIMING OF LOWER CIGS LATER TODAY INTO
  TONIGHT.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...TSRA LIKELY MAINLY IN THE EVENING. PERIODS OF IFR.

FRIDAY...CHANCE SHRA. PERIODS OF MVFR.

SATURDAY...VFR.

SUNDAY...VFR.

MONDAY AND TUESDAY...VFR. CHANCE SHRA.

KJB

&&

.MARINE...
318 AM CDT

A STRONG STORM SYSTEM WILL TAKE SHAPE ACROSS THE CENTRAL AND
SOUTHERN PLAINS TODAY. EASTERLY WINDS ARE EXPECTED TO SLOWLY
INCREASE IN INTENSITY TODAY AND TONIGHT AS THE LOW CONTINUES TO
STRENGTHEN. EASTERLY WINDS UP AROUND 20 TO 25 KT ARE EXPECTED...AND
THIS WILL RESULT IN SOME HIGHER WAVES OF 3 TO 5 FT INTO THE
NORTHEASTERN ILLINOIS NEAR SHORE WATERS TODAY AND TONIGHT. I WILL
HOLD OFF ON A SMALL CRAFT ADVISORY...BUT CONDITIONS WILL BE CLOSE.

A SURFACE WAVE AND WARM FRONT WILL SURGE NORTHWARD ACROSS THE
SOUTHERN HALF OF THE LAKE LATER TONIGHT AND INTO THURSDAY. THIS
FRONT WILL MARK THE DIVIDING LINE BETWEEN EAST NORTHEASTERLY WINDS
ACROSS THE NORTH END OF THE LAKE...TO SOUTHERLY WINDS SOUTH DURING
THE DAY ON THURSDAY. STRONG SOUTHERLY WINDS LOOK TO DEVELOP SOUTH OF
THE WARM FRONT. SOUTHERLY WINDS OF 30 KT...WITH SOME GALE FORCE
GUSTS ARE EXPECTED OVER THE OPEN WATERS OF SOUTHERN LAKE MICHIGAN.
MUCH WARMER AIR MOVING OVER THE LAKE WILL LIKELY KEEP EVEN STRONGER
WINDS ALOFT FROM REACHING THE WATER SURFACE. HOWEVER...THIS WILL NOT
NECESSARILY BE THE CASE FOR THE NEAR SHORE WATERS FROM CHICAGO
EASTWARD INTO NORTHERN INDIANA. THE OFFSHORE COMPONENT WILL LIKELY
ALLOW SOUTHERLY GALES OF 35 TO 40 KT TO AFFECT THE NEAR SHORES.
BECAUSE OF THIS...I WILL ISSUE A GALE WATCH FOR THE NEAR SHORES FROM
CHICAGO TO MICHIGAN CITY FOR THE DAY ON THURSDAY.

A SECOND LOW IS EXPECTED TO TRACK NORTHEASTWARD ALONG THE SURFACE
BOUNDARY...WHICH LOOKS TO SET UP SOMEWHERE ACROSS THE MID SECTION OF
LAKE MICHIGAN. ONCE THIS SECOND LOW PASSES OVER THE LAKE LATER
THURSDAY NIGHT...THE WINDS WILL BECOME MORE WESTERLY. STRONG WEST TO
NORTHWEST WINDS WILL LIKELY SETUP LAKE-WIDE DURING THE DAY ON
FRIDAY...AND THEN CONTINUE INTO FRIDAY NIGHT. THIS WILL BE THE TIME
WHEN GALES ARE FAVORED OVER THE OPEN WATERS.

IN ADDITION TO THE WINDS...THERE WILL LIKELY BE SEVERAL WAVES OF
SHOWERS AND THUNDERSTORMS LATER TODAY THROUGH THURSDAY EVENING.
SOME OF THESE STORMS COULD PRODUCE SEVERE WEATHER OVER SOUTHERN LAKE
MICHIGAN...ESPECIALLY TONIGHT AND ON THURSDAY.

THINGS FINALLY SETTLE DOWN FOR A PERIOD THIS WEEKEND AND A SURFACE
RIDGE OF HIGH PRESSURE BUILDS OVER THE GREAT LAKES REGION.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FLOOD WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
     ILZ032-ILZ033-ILZ039...1 PM WEDNESDAY TO 7 AM FRIDAY.

IN...FLOOD WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...1 PM
     WEDNESDAY TO 7 AM FRIDAY.

LM...GALE WATCH...LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...5 AM THURSDAY
     TO 10 PM THURSDAY.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
458 AM CDT WED APR 17 2013

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
181000-
WINNEBAGO-BOONE-MCHENRY-LAKE ILLINOIS-OGLE-LEE-DE KALB-KANE-
DUPAGE-COOK-LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-
IROQUOIS-FORD-LAKE INDIANA-PORTER-NEWTON-JASPER-BENTON-
458 AM CDT WED APR 17 2013 /558 AM EDT WED APR 17 2013/

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

.DAY ONE...TODAY AND TONIGHT.

  WEATHER HAZARDS EXPECTED:

  THUNDERSTORMS...A FEW MAY PRODUCE:
  HAIL TO ONE INCH.
  STRONG DAMAGING WIND GUSTS IN EXCESS OF 60 MPH.
  HEAVY RAINFALL.
  ISOLATED TORNADOES.

  AREAS AFFECTED AND TIMING:

  THUNDERSTORMS ARE EXPECTED TO STEADILY DEVELOP ACROSS EASTERN IOWA
  THIS MORNING AND SPREAD EAST ACROSS NORTHERN ILLINOIS AND
  NORTHWEST INDIANA...AS COVERAGE OF THUNDERSTORMS INCREASES.
  THUNDERSTORMS ARE EXPECTED TO CONTINUE THROUGH TONIGHT. THE
  POTENTIAL FOR SEVERE THUNDERSTORMS WILL BE ACROSS ALL OF THE
  OUTLOOK AREA OF NORTHERN ILLINOIS AND NORTHWEST INDIANA THROUGH
  TONIGHT.

  DISCUSSION:

  A WARM FRONTAL BOUNDARY IS EXPECTED TO LIFT NORTH ACROSS THE
  AREA THIS AFTERNOON...WITH AN ANOMALOUSLY WARM AND MOIST AIRMASS
  TO THE SOUTH OF THIS BOUNDARY. THUNDERSTORMS ARE EXPECTED TO DEVELOP
  ALONG THIS WARM FRONT AND CONTINUE TO RIDE ALONG THIS BOUNDARY
  THROUGH TONIGHT. THUNDERSTORMS MAY BECOME SEVERE THIS AFTERNOON
  THROUGH TONIGHT AS THE INSTABILITY CONTINUES TO INCREASE THROUGHOUT
  THE DAY...MAINLY FOR AREAS ALONG AND SOUTH OF INTERSTATE 80.
  AT THIS TIME THE GREATEST HAZARDS FROM THUNDERSTORMS
  WILL BE DAMAGING WIND GUSTS AND HAIL TO ONE INCH IN DIAMETER...ALONG
  WITH HEAVY RAINFALL. IN ADDITION...SOME OF THE STRONGER THUNDERSTORMS
  MAY BEGIN TO ROTATE ALONG OR JUST NORTH OF THE WARM FRONTAL BOUNDARY.
  THUS THE POTENTIAL FOR AN ISOLATED TORNADO MAY OCCUR THIS AFTERNOON
  INTO TONIGHT.

  THUNDERSTORMS ARE EXPECTED TO TRAIN ACROSS THE SAME LOCATIONS
  THIS EVENING INTO THE OVERNIGHT...WHICH MAY LEAD TO FLOODING. WITH
  SATURATED SOILS ALREADY...ANY HEAVY RAINFALL WILL FURTHER EXACERBATE
  THE CURRENT FLOODING CONDITIONS.

PORTIONS OF MANY AREA RIVERS AND STREAMS WILL REMAIN NEAR OR
ABOVE FLOOD STAGE DUE TO RECENT RAINFALL.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

SEVERAL ROUNDS OF HEAVY RAIN PRODUCING THUNDERSTORMS WILL CONTINUE
THROUGH THURSDAY. THIS MAY LEAD TO SIGNIFICANT FLOODING
ON AREA RIVERS...SOME OF WHICH ARE ALREADY NEAR OR ABOVE FLOOD
STAGE FROM PREVIOUS RAINFALL. LOCALLY HEAVY RAINFALL MAY ALSO
LIKELY RESULT IN FLOODING OF LOW LYING AND URBAN AREAS.

PORTIONS OF MANY AREA RIVERS AND STREAMS WILL REMAIN NEAR OR
ABOVE FLOOD STAGE DUE TO RECENT RAINFALL.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS MAY BE NEEDED THIS AFTERNOON THROUGH TONIGHT.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO
WEBPAGE: WEATHER.GOV/CHICAGO

LMZ740>745-181000-
WINTHROP HARBOR TO WILMETTE HARBOR-
WILMETTE HARBOR TO NORTHERLY ISLAND-
NORTHERLY ISLAND TO CALUMET HARBOR-CALUMET HARBOR TO GARY-
GARY TO BURNS HARBOR-BURNS HARBOR TO MICHIGAN CITY-
458 AM CDT WED APR 17 2013

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

.DAY ONE...TODAY AND TONIGHT.

PERIODIC THUNDERSTORMS ARE LIKELY THIS AFTERNOON THROUGH TONIGHT.
A FEW THUNDERSTORMS COULD BE STRONG AND PRODUCE GUSTY WINDS.

GALE FORCE WINDS ARE POSSIBLE LATE TONIGHT THROUGH THE
OVERNIGHT FROM CHICAGO TO MICHIGAN CITY.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

PERIODIC THUNDERSTORMS ARE LIKELY THURSDAY.

GALE FORCE WINDS ARE POSSIBLE FRIDAY THROUGH FRIDAY NIGHT FOR THE
ENTIRE NEARSHORE WATERS OF ILLINOIS AND NORTHWEST INDIANA.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO
WEBPAGE: WEATHER.GOV/CHICAGO

LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-181000-
LAKE MICHIGAN FROM MICHIGAN CITY IN TO ST. JOSEPH MI 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM SEUL CHOIX POINT TO ROCK ISLAND PASSAGE 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN SOUTH OF A LINE FROM SEUL CHOIX POINT TO THE
MACKINAC BRIDGE AND NORTH OF A LINE FROM CHARLEVOIX MI TO SOUTH
FOX ISLAND 5 NM OFFSHORE-
LAKE MICHIGAN FROM CHARLEVOIX TO POINT BETSIE MI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM POINT BETSIE TO MANISTEE MI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM ROCK ISLAND PASSAGE TO STURGEON BAY WI-
LAKE MICHIGAN FROM STURGEON BAY TO TWO RIVERS WI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM TWO RIVERS TO SHEBOYGAN WI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM SHEBOYGAN TO PORT WASHINGTON WI 5 NM OFFSHORE
TO MID LAKE-
LAKE MICHIGAN FROM PORT WASHINGTON TO NORTH POINT LIGHT WI 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM NORTH POINT LIGHT TO WIND POINT WI 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM WIND POINT WI TO WINTHROP HARBOR IL 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM WINTHROP HARBOR TO WILMETTE HARBOR IL 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM WILMETTE HARBOR IL TO MICHIGAN CITY IN 5 NM
OFFSHORE TO MID LAKE-
LAKE MICHIGAN FROM PENTWATER TO MANISTEE MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM WHITEHALL TO PENTWATER MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM GRAND HAVEN TO WHITEHALL MI 5 NM OFFSHORE TO
MID LAKE-
LAKE MICHIGAN FROM HOLLAND TO GRAND HAVEN MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM SOUTH HAVEN TO HOLLAND MI 5 NM OFFSHORE TO MID
LAKE-
LAKE MICHIGAN FROM ST. JOSEPH TO SOUTH HAVEN MI 5 NM OFFSHORE TO
MID LAKE-
458 AM CDT WED APR 17 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE OPEN WATERS OF LAKE
MICHIGAN.

.DAY ONE...TODAY AND TONIGHT.

PERIODIC THUNDERSTORMS ARE LIKELY THIS AFTERNOON THROUGH TONIGHT
FOR THE SOUTHERN HALF OF LAKE MICHIGAN. A FEW THUNDERSTORMS
COULD BE STRONG AND PRODUCE GUSTY WINDS.

OCCASIONAL GALE FORCE GUSTS MAY OCCUR THIS EVENING THROUGH TONIGHT
MAINLY FOR THE SOUTHERN TIP OF LAKE MICHIGAN.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

PERIODIC THUNDERSTORMS ARE LIKELY THURSDAY.

GALE FORCE WINDS ARE POSSIBLE FRIDAY THROUGH FRIDAY NIGHT.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO
WEBPAGE: WEATHER.GOV/CHICAGO

BEACHLER

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
724 AM CDT WED APR 17 2013

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

0723 AM     HAIL             SYCAMORE                41.98N 88.70W
04/17/2013  E0.25 INCH       DEKALB             IL   TRAINED SPOTTER

&&

C

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
748 AM CDT WED APR 17 2013

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

0747 AM     HAIL             AMBOY                   41.72N 89.33W
04/17/2013  M0.25 INCH       LEE                IL   TRAINED SPOTTER

&&

C

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
819 AM CDT WED APR 17 2013

ILZ008-010>012-019-020-171415-
DE KALB IL-KANE IL-KENDALL IL-LA SALLE IL-LEE IL-OGLE IL-
819 AM CDT WED APR 17 2013

...SPECIAL WEATHER STATEMENT...

AT 819 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR MENDOTA...MOVING NORTHEAST AT 40 MPH.

NICKEL SIZE HAIL...WINDS GREATER THAN 40 MPH...OCCASIONAL CLOUD TO
GROUND LIGHTNING...BRIEF HEAVY DOWNPOURS...ARE POSSIBLE WITH THIS
STORM.

CITIES AND TOWNS AFFECTED...
  MENDOTA...            PAW PAW...            EARLVILLE...
  SHABBONA...           LELAND...             WATERMAN...
  SOMONAUK...           SANDWICH...           MALTA...

OTHER LOCATIONS AFFECTED...
NORTHERN ILLINOIS UNIVERSITY...SANDWICH FAIRGROUNDS...TRI-COUNTY
FAIRGROUNDS...WAUBONSEE COMMUNITY COLLEGE...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

GUSTY WINDS MAY CAUSE SMALL OBJECTS SUCH AS TRASH BINS TO BLOW
AROUND. STAY AWAY FROM HIGH OBJECTS OUTDOORS SUCH AS TREES. HEAVY
RAINFALL COULD LEAD TO STANDING WATER ON ROADWAYS AND POOR
VISIBILITY. SEEK SHELTER IN A STURDY STRUCTURE UNTIL THIS STORM HAS
PASSED.

&&

LAT...LON 4208 8867 4166 8834 4146 8917 4158 8917
      4158 8926 4168 8932
TIME...MOT...LOC 1319Z 242DEG 34KT 4164 8908

RODRIGUEZ