Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 042003
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 PM CDT SAT JUL 4 2015

.SHORT TERM...
203 PM CDT

THROUGH SUNDAY AFTERNOON...

THE LAKE BREEZE BOUNDARY CONTINUES TO MOVE INLAND TOWARDS ORD/MDW
AND INTO NORTHERN LAKE AND PORTER COUNTIES IN INDIANA. STILL AN OFF
CHANCE FOR A ROGUE SHORT LIVED SHOWER OR STORM POPPING ON THE LAKE
BREEZE BOUNDARY YET THIS AFTERNOON BEFORE THE BOUNDARY WASHES OUT
EARLY THIS EVENING. CU IS MOST EXTENSIVE SOUTH OF A MDW-JOT LINE
WITH ANOTHER AREA TOWARD THE WI BORDER AT MID AFTERNOON WHICH IS
COINCIDENT WITH THE SMALL AMOUNT OF INSTABILITY THAT HAS BEEN
DEVELOPING...WITH A FEW CU IN BETWEEN THESE AREAS. OTHERWISE TEMPS
WILL BE A LITTLE SLOWER TO COOL THAN PREVIOUS EVENINGS AND LEVEL OFF
IN THE LOWER 60S FOR MOST AREAS OVERNIGHT BUT WITH MID 60S IN THE
CHICAGO METRO AREA. AN UPPER LEVEL RIDGE WILL CREST THE AREA TONIGHT
WHILE A SHORTWAVE TROUGH MOVING ACROSS THE EASTERN DAKOTAS AND
NEBRASKA THIS AFTERNOON DAMPENS OUT. DRY CONDITIONS WILL PERSIST AND
THE AIRMASS WILL MODIFY WITH H85 TEMPS WARMING SLIGHTLY TO 15-16C
AND H92 TEMPS WARMING TO 21-22C. LOCAL H85/H92 CLIMATOLOGY SUPPORTS
HIGHS IN THE MID/UPPER 80S. SOUTHERLY WINDS WILL STEADILY INCREASE
THROUGH THE AFTERNOON SO THE INCREASED MIXING MAY ALLOW A FEW SITES
TO REACH 90. THE LAKE BREEZE DETAILS WILL BE SOMEWHAT TROUBLESOME TO
PIN DOWN. FLOW WILL BE VERY LIGHT THROUGH THE MORNING WHICH WOULD
SUPPORT AN INLAND MOVING BOUNDARY ALLOWING AREAS WITHIN A FEW MILES
OF THE LAKE TO COOL INTO THE LOWER 70S AFTER AN INITIAL WARM UP IN
THE MORNING BUT THE STEADILY INCREASING WIND MAY HELP PUSH THE
BOUNDARY BACK TOWARDS THE LAKE ALLOWING MANY OF THESE SAME AREAS TO
WARM UP LATE IN THE DAY. IF THAT OCCURS AS EXPECTED LAKEFRONT AREAS
OF ILLINOIS WOULD LIKELY BE HELD TO AROUND 80 FOR HIGHS WITH
NORTHEAST LAKE COUNTY IL BEING A BIT COOLER WITH A SOUTHEAST WIND
OF THE LAKE SETTING UP THERE. NORTHWEST INDIANA LAKESHORE AREAS
SHOULD WARM TO THE MID/UPPER 80S WITH OFFSHORE FLOW TAKING OVER
DURING THE AFTERNOON.

MDB

&&

.LONG TERM...
302 PM CDT

SUNDAY NIGHT THROUGH SATURDAY...

A LOW PRESSURE SYSTEM IS CURRENTLY OVER MANITOBA AND A SECONDARY LOW
WILL FORM ALONG THE PRIMARY LOW/S COLD FRONT SUNDAY EVENING OVER THE
CENTRAL PLAINS. THE SECONDARY LOW WILL DEEPEN AS IT MOVES OVER THE
UPPER MIDWEST MONDAY. THE MAJORITY OF THE WARNING AREA WILL BE DRY
MONDAY WITH ONLY A CHANCE OF THUNDERSTORMS WEST OF A WOODSTOCK TO
PERU IL LINE MONDAY AFTERNOON.  EXPECTING AMPLE WAA WITH HIGH
TEMPERATURES GETTING NEAR 90 ACROSS NORTHERN IL AND NW INDIANA.
WINDS WILL BE GUSTING UP TO 30 MPH ESPECIALLY ALONG THE IL/WI STATE
LINE MONDAY AFTERNOON.

SHOWERS AND THUNDERSTORMS SPREAD ACROSS THE REGION MONDAY NIGHT AND
HAVE MEDIUM CONFIDENCE IN HOW QUICKLY THE PRECIP SHIFTS EAST. MODEL
SOUNDINGS ARE DRY SO PRECIP COULD TAKE A BIT LONGER AS THE SHOWERS
MOISTEN THE ENVIRONMENT. MODEL SOUNDINGS ALSO FEATURE CAPE OF
VARYING AMOUNTS. THE USUALLY TOO MOIST NAM HAS VALUES OVER 2000 J/KG
WHILE THE GFS HAS LESS THAN 1000 J/KG. THEREFORE COULD SEE SOME
STRONGER STORMS BUT CONFIDENCE IS LOW.

THE LOWS COLD FRONT STALLS JUST SOUTH OF THE WARNING AREA ACROSS
CENTRAL IL AND INDIANA TUESDAY.  SO SHOWERS AND THUNDERSTORMS WILL
SLOWLY SHIFT TO THE SOUTHEAST AND MAY SEE LINGERING SHOWERS AND
STORMS SOUTH OF A VALPO TO PONTIAC LINE TUESDAY AFTERNOON AND THEN
SOUTH OF A FAIRBURY IL TO FOWLER INDIANA LINE TUESDAY NIGHT INTO
WEDNESDAY. ONLY HAVE MEDIUM CONFIDENCE IN HOW LONG SHOWERS AND
STORMS WILL LINGER OVER THE FAR SOUTHERN WARNING AREA. TEMPS ON
TUESDAY WILL BE MUCH COOLER WITH HIGHS IN THE 70S AND ONLY RIGHT
AROUND 60 ALONG THE LAKE.

OUTSIDE OF THE LINGERING COLD FRONT...HIGH PRESSURE BUILDS OVER THE
REGION WEDNESDAY AND A LOW PASSES JUST TO OUR SOUTH ACROSS CENTRAL
IL AND INDIANA WEDNESDAY NIGHT INTO THURSDAY.  INHERITED A SLIGHT
CHANCE OF SHOWERS AND STORMS ACROSS THE ENTIRE WARNING AREA THURSDAY
AND KEPT THEM IN CASE THE LOW SHIFTS NORTH OR THE WEAK SHORTWAVE
THAT SWINGS THROUGH AT THE SAME TIME FORCES SOME PRECIP.

WE WARM BACK INTO THE LOW 80S LATE NEXT WEEK WITH A CHANCE OF
PERIODIC SHOWERS AND STORMS. HAVE LOW CONFIDENCE IN OCCURRENCE AND
COVERAGE OF STORMS AS THE LONG TERM MODELS DIFFER ON THE PATTERN AND
HOW FEATURES WILL EVOLVE. THEREFORE LEFT THE CHANCE OF PRECIP IN THE
FORECAST.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LAKE BREEZE WIND SHIFT TO EAST ARRIVING SHORTLY.

* SMALL CHANCE FOR LAKE BREEZE SHIFT ON SUNDAY.

RC

//DISCUSSION...UPDATED 20Z...

LAKE BREEZE HAD BEEN MAKING STEADY PROGRESSION TOWARD MDW
SUPPORTING EARLIER TIMING BUT SINCE HAS SLOWED. BOUNDARY SHOULD
PUSH THROUGH BOTH ORD AND MDW SHORTLY PER RADAR AND OBSERVATIONAL
TRENDS....WITH FIELD SENSORS ON EAST SIDE OF ORD POSSIBLY ALREADY
BEING INFLUENCED BY LAKE BREEZE WINDS. STILL EXPECTING SPEEDS TO
REMAIN PRIMARILY BELOW 10 KT BEHIND SHIFT...THOUGH COULD BE AROUND
10 KT FOR A BRIEF PERIOD.

RC

FROM 18Z...

WEAK HIGH PRESSURE OVER THE AREA AND LIGHT WINDS DUE TO IT
ARE SUPPORTING STEADY INLAND PROGRESSION OF LAKE BREEZE. HAVE
MOVED UP TIMING OF EAST WINDS AT MDW TO 1830Z...BUT KEPT ORD AT
20Z FOR NOW. WILL CONTINUE TO TRACK LAKE BREEZE VIA RADAR FOR ANY
TIMING CHANGES. SPEEDS APPEAR THEY WILL REMAIN MOSTLY BELOW 10 KT
GIVEN OBS BEHIND THE LAKE BREEZE...BUT CANNOT RULE OUT A BRIEF
PERIOD OF SPEEDS AROUND 10 KT. LIGHT SOUTHERLY WINDS TONIGHT WILL
PICK UP SOME ON SUNDAY AS HIGH PRESSURE SLIDES EAST. LAKE BREEZE
SHOULD STILL PUSH INLAND INTO ILLINOIS...BUT EXPECTING DEEPER
MIXING TO TAP INTO SOUTH TO SSW WINDS CLOSE TO 10 KT SUNDAY
AFTERNOON AND PREVENT IT FROM REACHING ORD AND MDW. PREDOMINANTLY
VFR CONDITIONS ARE IN STORE THROUGH THE PERIOD...WITH POSSIBLE
MINOR EXCEPTION OF PATCHY MVFR BR IN OUTLYING AREAS LATE TONIGHT
INTO EARLY SUNDAY.

RC

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH IN LAKE BREEZE SHIFT TO EAST WINDS...MEDIUM-HIGH IN TIMING
  AND SPEEDS REMAINING PRIMARILY BELOW 10 KT.

* MEDIUM-HIGH THAT LAKE BREEZE WILL NOT PUSH THROUGH ORD AND MDW
  ON SUNDAY.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...TSRA LIKELY MONDAY NIGHT. BREEZY SOUTH WINDS.

TUESDAY...CHANCE OF MORNING TSRA.

WEDNESDAY...VFR...CHANCE SHRA/TSRA WED NIGHT.

THURSDAY...SLIGHT CHANCE TSRA.

FRIDAY...SLIGHT CHANCE TSRA.

RODRIGUEZ

&&

.MARINE...
302 PM CDT

HIGH PRESSURE IS OVER THE REGION AND IT WILL SLIDE EAST THROUGH
SUNDAY WITH WINDS BECOMING SOUTH LATE TONIGHT INTO SUNDAY. A SFC LOW
WILL FORM OVER THE CENTRAL PLAINS SUNDAY AFTERNOON AND DEEPEN AS IT
MOVES OVER LAKE SUPERIOR MONDAY EVENING. AS SUCH...WINDS INCREASE IN
SPEED WITH 30KT GUSTS PSBL OVER THE NORTH HALF OF THE LAKE MONDAY
AFTN. WIND SPEEDS WILL BE IN EXCESS OF 40KT AROUND 1500 FT ABOVE THE
SURFACE...BUT A STOUT STABLE LAYER SHOULD KEEP THOSE GUSTS FROM
MIXING DOWN TO THE SFC.  A SMALL CRAFT ADVISORY WILL LIKELY BE
NEEDED MONDAY AS WIND GUSTS WILL BE HAZARDOUS TO SMALL CRAFT. THE
LOWS COLD FRONT SWEEPS OVER THE LAKE MONDAY NIGHT WITH WINDS
BECOMING NORTHWEST BEHIND THE FRONT.  WINDS DIMINISH AND BECOME
VARIABLE IN DIRECTION AS HIGH PRESSURE BUILDS IN BEHIND THE COLD
FRONT TUESDAY NIGHT.  WINDS BECOME MORE ORGANIZED OUT OF THE SOUTH
THURSDAY AS THE HIGH MOVES OVER THE EASTERN U.S.

JEE

&&

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

$$

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