Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 020811
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
311 AM CDT SUN AUG 2 2015

.SHORT TERM...
258 AM CDT

THIS MORNING THROUGH THIS EVENING...
REGIONAL IR IMAGERY SHOWS A COUPLE AREAS OF SHOWERS/THUNDERSTORMS
ACROSS THE UPPER MIDWEST...AND A SECOND IN NORTHEAST WISC. CURRENT
EXPECTIONS ARE THAT THIS AREA OF CONVECTION WILL CONTINUE TO
REMAIN NORTH OF NORTHERN IL/NORTHWEST IN. A ROBUST THERMAL RIDGE
AT 925MB EXISTS THIS MORNING...AND STRETCHES ACROSS IOWA NORTHEAST
INTO CENTRAL WISC WHICH HAS MAINTAINED SFC TEMPS IN THE MID 70S
ACROSS THOSE AREAS. MEANWHILE NORTHERN IL REMAINS SOUTH OF THIS
THERMAL RIBBON...WITH SFC TEMPS IN THE UPR 60S FOR THE MOST PART.
THE EXCEPTION IS THE URBAN HEAT ISLAND OF DOWNTOWN CHICAGO...WHERE
TEMPS REMAIN IN THE 70S.

LLVL MOISTURE HAS BEEN SLOW TO REBOUND...WITH MANY AREAS SEEING DEW
POINTS REMAIN IN THE MID 60S. HOWEVER AS THE DAY PROGRESSES MOISTURE
SHOULD POOL NORTH ACROSS THE REGION. MIXING WILL BE STRONG AGAIN
TODAY...WITH MIX-HGTS NEARING 3500FT AGL AND FILTERING TO THE SFC
30KT. EXPECT FREQUENT GUSTS IN THE 30-35MPH RANGE FROM LATE MORNING
THROUGH THIS EVENING...PRIOR TO THE EXPECTED THUNDERSTORMS. HOWEVER
WHAT COULD POSE SOME CHALLENGES TO THE GUSTY WINDS MAY BE SOME
LINGERING CLOUD COVER. THIS MAY LIMIT HOW HIGH THE MIXING MAY OCCUR.

THE 500MB TROUGH WILL BE PIVOTING SOUTH ACROSS THE UPPER
MIDWEST...ALONG WITH A DEEPENING SFC WAVE. THIS WILL ALLOW THE
FRONTAL BOUNDARY THAT WILL BE ACROSS THE CANADIAN BORDER EARLY THIS
MORNING TO DROP SOUTH ACROSS WISC THIS EVENING. THE CHALLENGE FOR
THIS EVENING REMAINS ON TIMING AND COVERAGE OF THUNDERSTORMS FOR
NORTHERN IL/NORTHWEST IN.

CONSIDERABLE DIFFERENCES REMAIN AMONGST THE CONVECTIVE ALLOWING
MODELS...WITH TIMING RANGING FROM LATE THIS AFTERNOON TO THIS
EVENING FOR NORTHERN IL. THE DRIVING CHALLENGE WILL BE WHAT
TRANSPIRES THIS AFTERNOON UPSTREAM ACROSS WISC. GUIDANCE HAS BEEN
KEYING IN ON A COMPLEX OF STORMS DEVELOPING THIS AFTERNOON ACROSS
CENTRAL/EASTERN WISC...WHICH MAY SEND AN OUTFLOW SOUTH TOWARDS
NORTHERN IL. MEANWHILE OTHER GUIDANCE SUGGESTS THE BEST FORCING WILL
BE MORE FOCUSED FURTHER EAST ACROSS LOWER MICHIGAN...WHICH NOW WILL
BE CLOSER TO THE SFC WAVE. THE MOST REALISTIC APPROACH WOULD BE THAT
AS AN OUTFLOW PUSHES SOUTH ACROSS NORTHERN IL THAT THIS WILL SERVE
AS THE TRIGGER FOR A STEADY GROWTH OF CONVECTION ACROSS THE FORECAST
AREA LATE THIS AFTN AND MORE LIKELY JUST AFTER 00Z. HIGHS THIS
AFTERNOON WILL EASILY WARM INTO THE UPR 80S TO ARND 90...AND WITH
THE WARM RIBBON OVERHEAD AND JUST NORTH A FEW LOCATIONS IN THE
NORTHERN CWFA MAY WARM FURTHER TO 91-93 DEG.

THE ATMOSPHERE WILL BE PRIMED WITH CONSIDERABLE INSTABILITY THIS
AFTERNOON/EVENING...ALONG WITH AMPLE DEEP LAYER SHEAR OF AROUND
40KT. SO ONCE CONVECTION DEVELOPS UPSTREAM THIS AFTERNOON...IT SEEMS
FAVORABLE THAT A STEADY GROWTH IN COVERAGE/INTENSITY WILL OCCUR AS
IT ARRIVES ACROSS THE FORECAST AREA. THE CURRENT DAY 1 OUTLOOK FROM
THE SPC HAS MUCH OF NORTHERN IL/NORTHWEST IN OUTLINED FOR AN
ENHANCED RISK OF SEVERE STORMS...WHILE SOUTH OF A ROCKFORD TO
KANKAKEE LINE IN A SLIGHT RISK. THE MAIN HAZARDS FROM
STRONG/SEVERE STORMS FOR OUR AREA WILL BE DAMAGING WIND
GUSTS...AND LARGE HAIL GIVEN THE STEEPENING MID-LVL LAPSE RATES.

TONIGHT THROUGH MONDAY...
BY LATE TONIGHT THE LINE OF STORMS SHOULD BE RELATIVELY
PROGRESSIVE AND SLIDING EAST/SOUTH. CONVECTION WILL BE COMING TO
AN END BY 9Z MON...WITH THE MID-LVL VORT LOBE PIVOTING EAST. WITH
FRONTAL PASSAGE POISED FOR 9-12Z MON...WINDS WILL SHIFT TO
NORTHWEST/NORTH WITH THE MUCH COOLER AIR ARRIVING. MOISTURE
QUICKLY PEELS EAST...AND MAY PROVIDE MOSTLY CLEAR SKIES FOR EARLY
MON. ENOUGH DIFFLUENT FLOW MAY LINGER TO ALLOW SKIES TO REMAIN
MOSTLY SUNNY THRU MON AFTN. TEMPS MON WILL BE MUCH COOLER WITH
HIGHS MAINLY AROUND 80 TO PERHAPS THE LOW 80S.

BEACHLER

&&

.LONG TERM...
310 AM CDT

MONDAY NIGHT THROUGH SATURDAY...

THE PERIOD WILL BEGIN WITH THE TRANSITION TO A MUCH DRIER
AIRMASS MONDAY NIGHT AS A SURFACE RIDGE OF HIGH PRESSURE SETS UP
FROM CENTRAL CANADA...EAST-SOUTHEASTWARD ACROSS MUCH OF THE CENTRAL
CONUS. THIS SHOULD SET UP A DECENTLY COOL NIGHT ACROSS MUCH OF NORTH
CENTRAL ILLINOIS. LIGHT WINDS AND MAINLY CLEAR SKIES LOOK TO ALLOW
TEMPERATURES TO POSSIBLY DROP INTO THE MIDDLE TO UPPER
50S...ESPECIALLY OUTSIDE URBAN AREAS. CONDITIONS DURING THE DAY
TUESDAY LOOK GREAT...WITH HIGHS MAINLY NEAR 80 WITH LOW HUMIDITY.
THE MAIN CORRIDOR FOR ANY SHOWERS AND THUNDERSTORMS LOOKS TO BE
SOUTH AND WEST OF THE AREA...SO DRY CONDITIONS ARE EXPECTED TUESDAY.

HOWEVER...WITH TIME THROUGH THE MID TO LATER PORTION OF THE
WEEK...THE CHANCES FOR A PERIOD OR TWO OF MORE PRECIPITATION LOOK TO
INCREASE. THE MAIN UPPER LOW...CENTERED NEAR THE JAMES BAY...IS
EXPECTED TO SHIFT EAST-NORTHWARD...ESSENTIALLY ALLOWING THE
MID/UPPER LEVEL FLOW OVER THE REGION TO STEER ADDITIONAL SHORT WAVE
DISTURBANCES RIGHT ACROSS THE AREA. OVERALL...IT APPEARS THE BEST
CHANCES FOR MORE RAIN WILL COME INTO THE PICTURE ON WEDNESDAY NIGHT
INTO THURSDAY. AT THIS TIME IT APPEARS THE THREAT FOR THUNDER WILL
BE WITH THIS ACTIVITY OVER NORTHERN ILLINOIS WILL BE LOW...AS THE
AREA LOOKS TO REMAIN IN A FAIRLY STABLE AND COOL EAST-NORTHEASTERLY
LOW LEVEL FLOW PATTERN. TEMPERATURES DURING THE MID TO LATER PORTION
OF THE WEEK LOOK TO MAINLY REMAIN IN THE 70S.


KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SOUTHWEST TO POSSIBLY SOUTH-SOUTHWEST WINDS ON SUNDAY AFTERNOON
  AT SUSTAINED SPEEDS TO 20 KT AND GUSTS TO 30-35 KT.

* POSSIBLE ISOLATED WEAKENING SHRA/TSRA IN THE REGION SUNDAY
  MORNING.

* LIKELY TSRA DURING SUNDAY EVENING...TIMING APPEARS TO BE AFT
  23Z.

BEACHLER

//DISCUSSION...UPDATED 06Z...

MAINLY VFR CONDS WILL START THE DAY...HOWEVER GUSTY WINDS ARE
POISED TO DEVELOP. BY MID-MORNING SOUTHWEST WINDS WILL BE
SUSTAINED BETWEEN 15-18KT AND GUSTS NEARING 30KT. SOME GUIDANCE
MEMBERS INDICATE A FEW ISOLATED SHOWERS/THUNDERSTORMS AROUND THE
AREA EARLY THIS AFTERNOON...HOWEVER THE MORE ORGANIZED
THUNDERSTORMS DOES NOT APPEAR TO ARRIVE AT THE TAF SITES UNTIL
AFTER 22Z.

THUNDERSTORMS ACROSS WISCONSIN MAY PUSH AN OUTFLOW BOUNDARY SOUTH
INTO NORTHERN IL LATE IN THE AFTERNOON...AND THIS MAY SERVE AS THE
DEVELOPMENT TO ADDITIONAL THUNDERSTORMS CLOSER TO 02Z AT THE TAF
SITES. THEN THE WINDS BEGIN TO TURN WEST/NORTHWEST AS A FRONTAL
BOUNDARY SWEEPS SOUTHEAST ACROSS THE REGION. THIS WILL PUSH THE
PRECIP EAST OF THE TAF SITES BY 5Z IF NOT SLIGHTLY EARLIER.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN WIND GUSTS EXCEEDING 30 KT. LOW-MEDIUM IN START
  TIME AND DURATION OF WINDS.

* MEDIUM IN WIND DIRECTION REMAINING 220-230 DURING PEAK WINDS.

* LOW IN ANY SHRA/TSRA DURING MUCH OF THE DAY SUNDAY.

* MEDIUM-HIGH IN TSRA CHANCES DURING THE EVENING. LOW-MEDIUM IN
  TIMING.

BEACHLER

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

MONDAY-TUESDAY...VFR. MAINLY NORTHWEST WINDS.
WEDNESDAY...VFR. NORTHEAST WINDS.
THURSDAY-FRIDAY...CHANCE OF TSRA. NORTHEAST WINDS.

MTF

&&

.MARINE...
248 PM CDT

WESTERLY WINDS IN PLACE TODAY AS LOW PRESSURE REMAINS TO THE
NORTH AND WHILE HIGH PRESSURE IS SITUATED OVER THE SOUTHERN PLAINS
TO THE MID MISSISSIPPI VALLEY. EXPECT WINDS TO BECOME MORE
SOUTHWEST THROUGH THE AFTERNOON AND INTO THE EVENING...WITH SPEEDS
THEN EXPECTED TO INCREASE THROUGH THE NIGHT. SOUTHWEST WINDS WILL
THEN REALLY INCREASE ON SUNDAY WITH THE APPROACH OF A SEPARATE
SYSTEM AND WITH THE HIGHEST WINDS/GUSTS LIKELY FROM LATE SUNDAY
MORNING THROUGH EARLY SUNDAY EVENING. HAVE INCREASED WINDS DURING
THIS TIME FRAME TO 30KT FOR BOTH THE NEARSHORE AND OPEN
WATERS...BUT PRIMARILY FOR THE SOUTHERN HALF. THERE IS SOME
POTENTIAL FOR OCCASIONAL GALE FORCE GUSTS IN THE AFTERNOON...BUT
THIS WILL BE MAINLY FOR THE NEARSHORE WATERS. WINDS WILL DIMINISH
SUNDAY NIGHT INTO MONDAY...WHILE THEY TURN MORE WEST/NORTHWEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...9 AM SUNDAY TO 10 PM SUNDAY.

&&

$$

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