Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 311606
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1106 AM CDT SUN MAY 31 2015

.UPDATE...
526 AM CDT

QUICK UPDATE TO LINGER THE DRIZZLE ON THE ILLINOIS SIDE OF LAKE
MICHIGAN A BIT LONGER THIS MORNING. RADAR WOULD INDICATE SOME LAKE
ENHANCEMENT GOING ON COUPLED WITH SOME UPPER FORCING...AND WITH
THE SHALLOW MOISTURE DRIZZLE CONTINUES TO OCCUR. VISIBILITIES
DOWNTOWN CONTINUE TO DETERIORATE WITH DRIZZLE ONGOING AT ORD AND
MDW. WE DO NOT HAVE A GOOD GRASP AS TO HOW LONG THIS WILL
LAST...BUT AT LEAST FOR A FEW MORE HOURS. AREAS IN COOK COUNTY MAY
REMAIN UNDER THE CLOUDS AND DRIZZLE A BIT LONGER GIVEN THE
PERSISTENT NE FLOW OFF THE LAKE TODAY AND WOULD CORRELATE TO LOWER
TEMPS...WHICH ARE ALREADY ONLY FORECAST TO HIT THE UPPER 40S IN
THE CITY TODAY.

KMD

&&

.SHORT TERM...
216 AM CDT

THROUGH MONDAY...

STRONG UPPER LEVEL JET OF 150 KNOT IS PUSHING NE THROUGH SE CANADA
EARLY THIS MORNING. THE SOUTHERN EXTENT OF A POSITIVELY TILTED
TROUGH SOUTH OF JAMES BAY IS SLOWLY DRIFTING EAST ACROSS THE AREA
WITH A SHEARED OUT VORTICITY MAXIMUM. MEANWHILE A SEPARATE AND
STRONG  CIRCULATION IS LIFTING NE THROUGH INDIANA. DECENT SURFACE
LOW ASSOCIATED WITH THIS MORE SOUTHERN STREAM ENERGY HAS INCHED
NORTHEAST INTO CENTRAL INDIANA. A STRONG COLD FRONT HAS CLEARED THE
AREA LEAVING GUSTY WINDS AND MUCH COOLER TEMPERATURES. WIND CHILLS
AT THIS HOUR ARE CURRENTLY IN THE MID 30S TO MID 40S.

WHILE LIGHTNING IS NO LONGER A CONCERN...A MODEST DEFORMATION BAND
HAS SETUP OVER NORTHWEST INDIANA AND EXTENDING BACK INTO
IROQUOIS/KANKAKEE COUNTIES WHERE 700 MB FLOW IS STILL
SOUTHWESTERLY...WHILE 850 FLOW IS COLD ADVECTIVE OUT OF THE
NORTHEAST. PW VALUES ARE STILL SOMEWHAT HIGH...ABOUT 1.4-1.5
INCHES...SO MODERATE RAINS WILL CONTINUE UNTIL THIS AXIS SLOWLY
SHIFTS OFF TO THE EAST THROUGH THE MORNING. RAINFALL TOTALS IN THESE
AREAS HAS TOTALED 1.5-2.5 INCHES THUS FAR WITH RADAR INDICATING SOME
1 INCH PER HOUR RATES. A FLOOD ADVISORY REMAINS IN EFFECT UNTIL
SUNDAY MORNING FOR THESE AREAS FOR ADDITIONAL PRECIP OVERNIGHT THEN
TIME IN THE MORNING TO ACCOUNT FOR ANY RUNOFF AND GIVE THE DAY CREW
A CHANCE TO ASSESS THE SITUATION. RADAR SHOWS THIS DEFORMATION
PRECIPITATION...LARGELY DRIZZLE...EXTENDS BACK INTO PORTIONS OF
COOK...DUPAGE...AND WILL COUNTIES OF ILLINOIS AS WELL...THOUGH THE
BETTER FRONTOGENETICAL/DEFORMATION CIRCULATION IS EAST OF THESE
AREAS. STILL SOME PRECIPITATION REMAINS POSSIBLE THROUGH THE
DAYBREAK IN THESE AREAS AS WELL.

THE NEGATIVELY TILTED CIRCULATION OVER INDIANA WILL CONTINUE EAST
TODAY AND LOSE DEFINITION THROUGH THE MORNING HOURS...ALLOWING THE
PRECIPITATION BAND TO LOSE ORGANIZATION AND MOVE EAST AS WELL. THE
ASSOCIATED SURFACE LOW WILL WEAKEN AS WELL ALLOWING SOME DECREASE IN
THE NE WINDS TODAY...BUT A STRONG HIGH OVER LAKE SUPERIOR WILL BE
MOVING SOUTHWARD AND WILL KEEP A MODEST GRADIENT IN PLACE OVER THE
AREA TODAY SUPPORTING BREEZY AND COOL NE WINDS. EXPECT MORNING
CLOUDS/DRIZZLE TO SLOWLY GIVE WAY TO SOME SUNSHINE...BUT COOL
READINGS FROM THE LOW 50S DOWNTOWN TO THE LOW TO MID 60S FAR WEST.

SUNDAY NIGHT WE WILL BE UNDER SOMEWHAT PROGRESSIVE WNW FLOW
ALOFT...THEN WEAK UPPER RIDGING BEGINS TO INCREASE. WITH THE SURFACE
HIGH ALONG NORTHERN LAKE MICHIGAN...COOL ONSHORE FLOW CONTINUES WITH
HIGHS STILL ONLY IN THE 50S DOWNTOWN...MID 60S FAR OUTLYING AREAS.

KMD

&&

.LONG TERM...
216 AM CDT

MONDAY NIGHT THROUGH SATURDAY...

THE LONG TERM UPPER LEVEL PATTERN WILL CHANGE LITTLE DURING THE
PERIOD...THOUGH SUBTLE EVOLUTION WILL INFLUENCE OUR LOCAL WEATHER. A
QUASI-OMEGA BLOCK TYPE PATTERN WILL EVENTUALLY SETUP LATER IN THE
WEEK AS A WESTERN U.S UPPER RIDGE INCHES ITS WAY INTO OUR AREA A
LITTLE BIT MORE EVERY DAY...BUT BEING SLOWED BY A CUTOFF LOW OVER
NORTHERN MISSISSIPPI THAT WILL REMAINED PARKED OVER THE GULF COAST
STATES THROUGH THE PERIOD.  MEANWHILE AN UPPER LOW WILL EVENTUALLY
CUTOFF OVER SOUTHERN CALIFORNIA. THIS PATTERN WILL ALLOW THE SURFACE
HIGH WAS STEERING WINDS IN OFF THE LAKE IN TO SHIFT EAST AND ALLOW
LOW LEVEL WINDS TO SHIFT MORE SOUTHEAST/SOUTH...BUT NOT FAR ENOUGH
WAY TO PROHIBIT AT LEAST AFTERNOON LAKE BREEZES/LAKE COOLING. THE
LOW LEVEL AIRMASS WILL WARM STEADILY EACH DAY WITH 60S TO LOW 70S AT
THE START OF THE EXTENDED TO EVOLVE INTO MORE WIDESPREAD 80S BY
THE LATTER HALF OF THE WEEK. THE FLY IN THE OINTMENT WILL BE ANY
SHORTWAVES RIDING THE LEANED OVER RIDGE FROM PACIFIC LOW PRESSURE.
THESE SYSTEMS LOOK TO BE IN A DECAYING STATE OVER OUR AREA UNTIL
POSSIBLY LATE IN THE WEEK (FRI/SAT).

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* MVFR THROUGH EARLY AFTERNOON.
* GUSTY NORTHEAST WINDS THRU EARLY EVENING.

CMS/MM

//DISCUSSION...UPDATED 16Z...

PREVAILING MVFR CIGS ARE EXPECTED TO CONTINUE INTO THIS
AFTERNOON...ERODING FROM THE NORTHWEST TO THE SOUTHEAST ACROSS THE
AREA. GYY IS THE ONLY REMAINING SITE WITH DZ AND MOISTURE
STREAMING IN FROM LAKE MICHIGAN. END TIME THERE WILL LIKELY BE
BETWEEN 18-20Z...WITH IFR/LOW MVFR CONTINUING LONGEST.

NORTH/NORTHEAST WINDS WILL REMAIN STRONG/GUSTY THRU MID/LATE
AFTERNOON AND THEN DIMINISH INTO EARLY EVENING WITH SPEEDS LIKELY
DROPPING BELOW 10KTS DURING THE EVENING.

CMS/MM

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH FOR MVFR TIMING.
* HIGH FOR WINDS THRU THE PERIOD.

CMS/MM

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

* MONDAY NIGHT AND TUESDAY...DRY/VFR. NORTHEAST WINDS.
* WEDNESDAY AND THURSDAY...DRY/VFR. EASTERLY WINDS.
* FRIDAY...SLIGHT CHANCE OF TSRA. SOUTHWEST WINDS.
* SATURDAY...SLIGHT CHANCE OF TSRA. NORTH WINDS.

&&

.MARINE...

409 AM...LOW PRESSURE OVER THE OHIO VALLEY WILL MOVE EAST TO THE
MID ATLANTIC REGION BY MONDAY...AS HIGH PRESSURE OVER ONTARIO
MOVES INTO QUEBEC. THE GRADIENT WILL SLOWLY RELAX LATER THIS
AFTERNOON INTO TONIGHT WITH NORTHERLY WINDS TO 30 KT SLOWLY
RELAXING TO 15-25 KT THIS AFTERNOON AND TO 10-20 KT TONIGHT. A
WEAKER RIDGE WILL EXTEND BACK SOUTHWEST ACROSS THE LAKES REGION
THROUGH TUESDAY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014 UNTIL 10 PM SUNDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 10 PM SUNDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM MONDAY.

&&

$$

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