Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 210802
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
302 AM CDT TUE APR 21 2015

.SHORT TERM...
256 AM CDT

THROUGH WEDNESDAY...

MAIN CONCERNS FOR TODAY WILL RESIDE ON THE GUSTY WINDS...WHICH COULD
GUST TO 45 MPH THIS AFTN. THE SECOND CONCERN FOR TODAY WILL BE ON
STRONG MIXING...WHICH WILL PRODUCE CONSIDERABLE SUBSIDENCE WITH DEW
POINTS BEING PUSHED INTO THE LOW/MID 20S...LEADING TO MIN RH VALUES
NEARING RED FLAG CONDITIONS.

THE BULK OF THE CLOUDS EARLY THIS MORNING HAVE BEEN CONFINED TO THE
NORTH IN WISC/MICH. WINDS HAVE BECOME SOUTHWESTERLY WITH THE 500MB
TROUGH AXIS PIVOTING OVERHEAD...HOWEVER WINDS WILL BECOME WESTERLY
AFT DAYBREAK. WITH MINIMAL CLOUD COVER TO START THE DAY...EXPECT
MIXING TO QUICKLY INCREASE AND BEGIN PRODUCING GUSTS TO 35 MPH BY
LATE THIS MORNING. THERE CONTINUES TO BE SOME MODEL DIFFERENCES WITH
RESPECT TO AFTN/EVE CLOUDS ROTATING SOUTHEAST ACROSS WISC INTO
NORTHERN IL/NORTHWEST IN. SOME OF THE HI-RES GUIDANCE HOLD CLOUDS
NORTH UNTIL AFT 00Z. IF CLOUDS CAN PUSH IN EARLIER IN THE
AFTN...THIS MAY HELP TO LIMIT WIND GUSTS BELOW 40MPH. HOWEVER
CONFIDENCE REMAINS RELATIVELY HIGH THAT THE FREQUENCY OF GUSTS WILL
REMAIN TO WARRANT HOISTING A WIND ADVISORY FROM 16Z-00Z.

TEMPS WILL SLOWLY WARM TODAY...WITH HIGHS GENERALLY IN THE LOW/MID
50S. WITH CLOUDS PIVOTING SOUTHEAST LATE THIS AFTN...THERE IS THE
POSSIBILITY THAT LGT SHRA MAY DEVELOP BUT SHUD REMAIN CONFINED TO
AREAS NORTH OF I-80.

STRONG ANTI-CYCLONIC FLOW WILL CONTINUE TO SLIDE SOUTH FROM CENTRAL
CANADA TO THE CENTRAL PLAINS TONIGHT. THIS COUPLED WITH THE SFC LOW
OVER ONTARIO WILL RESULT IN CONTINUED TIGHT GRADIENT ACROSS THE
WESTERN GREAT LAKES AND BREEZY CONDS TONIGHT. COLD AIR WILL CONTINUE
TO ADVECT OVER THE FORECAST AREA TONIGHT...WITH LOWS IN THE LOW/MID
30S. A FEW SPOTS COULD DIP TO FREEZING LATE TONIGHT ACROSS THE
NORTHWEST CWFA. WINDS AND LOW DEW PTS WILL HELP TO PREVENT ANY FROST
FORMATION TONIGHT.

DRY AIR WILL RETURN FOR WED...WITH LESS CLOUD COVER AND ANOTHER
BREEZY DAY. WINDS WILL BE LESS ROBUST...HOWEVER COLD AIR WILL
CONTINUE TO ADVECT SOUTHEAST AND LIMIT AFTN HIGHS FROM WARMING
BEYOND 49-53. WED NGT WINDS DIMINISH WITH DRY CONDS AND LOWS DIPPING
INTO THE LOW 30S. A PORTION OF THE CWFA COULD SEE TEMPS DIP BELOW
FREEZING WED NGT.

BEACHLER

&&

.LONG TERM...
256 AM CDT

THURSDAY THROUGH MONDAY...
ENSEMBLES CONTINUE TO SHOW MINIMAL SPREAD AMONGST MEMBERS IN THE
MEDIUM TERM...KEEPING THE GREAT LAKES REGION IN A TROUGHING
PATTERN WITH BLOCKING OVER THE NORTH ATLANTIC SLOWING THE EASTERN
PROGRESSION TO THE TROUGH. THIS WILL KEEP UNSEASONABLY COOL CONDS
THRU AT LEAST THUR/FRI FOR THE REGION. OPER SOLUTIONS SLIDE A SFC
RIDGE OVER THE FORECAST AREA THUR NGT...ALLOWING LGT WINDS TO
DEVELOP. WITH CONTINUED DRY WEATHER FROM THE PRIOR COUPLE OF
DAYS...LOWS COULD EASILY DIP TO THE LOW/MID 30S WITH POSSIBLE
FROST FORMATION.

OPER SOLUTIONS DIVERGE ON HOW TO RESOLVE THE SOUTHERN STREAM LATE IN
THE WEEK INTO THE FIRST PORTION OF THE WEEKEND. IT APPEARS SFC
RIDGING SHUD LINGER THRU MUCH OF FRI...THEN A BRIEF PERIOD LGT
SHOWERS FRI NGT BEFORE THE SOUTHERN STREAM PUSHES BACK SOUTH FROM
ANOTHER SFC RIDGE SAT NGT. THEN THE REMAINDER OF THE WEEKEND LOOKS
TO REMAIN DRY...WITH TEMPS TRYING TO RETURN TO SEASONAL CONDS IN THE
UPR 50S TO NEAR 60 SUN/MON.

BEACHLER

&&

.FIRE WEATHER...
STRONG WINDS WILL DEVELOP TODAY...WITH GUSTS BETWEEN 40 AND 45
MPH. DEEP MIXING FROM A DRY AIRMASS WILL LIKELY LEAD TO STEADY
DRYING AND DEW POINTS FALLING INTO THE LOWER TO MIDDLE 20S.
CURRENT PROJECTIONS ARE FOR AFTERNOON MINIMUM RH VALUES TO FALL
INTO THE 25 TO 35 PERCENT RANGE...HOWEVER SEVERAL MODELS HINT THAT
WE MAY TRIM AN ADDITIONAL FEW DEGREES OFF OF DEW POINTS RESULTING
IN RH VALUES CLOSER TO 20 PERCENT.

MIN RH VALUES WILL BE NEARING RED FLAG WARNING CRITERIA...HOWEVER
GIVEN THE RECENT RAINFALL FROM SUNDAY NIGHT BETWEEN A HALF TO
THREE QUARTERS OF AN INCH OF RAIN...10 HOUR FUEL MOISTURE MAY NOT
REACH RED FLAG CRITERIA. FASTER DRYING FUELS HOWEVER WILL LIKELY
DRY OUT QUICKLY GIVEN THE CONDITIONS TODAY RESULTING IN AN
ELEVATED FIRE DANGER.

BMD/BEACHLER

&&

.AVIATION...

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

* STRONG WEST WINDS...POTENTIALLY GUSTING TO OR JUST OVER 40KT
  AT TIMES LATE TUES MORNING THROUGH THE AFTERNOON

KMD

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

NO REAL CHANGE IN THIS SET OF TAFS. EXPECT WINDS TO RAPIDLY
INCREASE DURING THE DAY TUESDAY...ESPECIALLY MID TO LATE MORNING.
CURRENT TAFS REFLECT WHAT WOULD GENERALLY BE THE EXPECTED STEADY
STATE CONDITIONS WITH GUSTS 35 KT (HIGHER AT GYY)...BUT GUSTS AT
MOST TERMINALS COULD REACH 40 KT AT TIMES. EXPECT A RAPID DECLINE
AT SUNSET WITH A SLOW SHIFT FROM A 270 DIRECTION TO MORE OF A NW
WIND BY DAYBREAK WEDNESDAY. VFR CIGS EXPECTED TUESDAY AFTERNOON
WITH MAYBE A PASSING AND SHORT LIVED SPRINKLE OR SHOWER. A MORE
A QUICK MOVING AND MORE ORGANIZED BAND OF RAIN WILL PASS SOUTH OF
THE MAIN TERMINAL AREAS TUESDAY LATE EVENING AND OVERNIGHT.

KMD

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS...EXCEPT MEDIUM-HIGH
  CONFIDENCE ON STRENGTH OF FORECAST GUSTS WHICH COULD
  OCCASIONALLY BE SLIGHTLY HIGHER.

KMD

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

WEDNESDAY THROUGH SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
228 AM CDT

WINDS OVER THE LAKE WILL BE PREDOMINANTLY WNW FOR A FEW DAYS AS LOW
PRESSURE WORKS ITS WAY TOWARD THE ATLANTIC COAST...WHILE A HIGH
PRESSURE RIDGE BUILDS ACROSS THE CANADIAN PRAIRIES AND THEN
SOUTHEAST INTO THE PLAINS. STRONG MIXING TODAY OVER LAND WILL BE
REALIZED CLOSE TO SHORE ALONG THE NEARSHORE WATERS GIVEN THE
OFFSHORE WIND COMPONENT...AND THEREFORE THE GALE WATCH WILL BE
UPGRADED TO A GALE WARNING. PRIME PERIOD WILL BE MID MORNING THROUGH
LATE AFTERNOON. STILL FEEL THAT THE OPEN WATERS ARE TOO STABLE TO
SUPPORT STRONG MIXING TODAY NEEDED FOR GALE FORCE WIND GUSTS. GUSTY
WNW WINDS ARE EXPECTED AGAIN IN THIS PATTERN ON WEDNESDAY...THOUGH
THE WIND FIELD ALOFT IS WEAKER...SO NOT EXPECTING GALES WEDNESDAY.
WINDS WILL GRADUALLY SHIFT MORE NORTHERLY AS HIGH PRESSURE SHIFTS EAST
AND SEVERAL LOWS PASS BY WELL TO THE SOUTH OF THE LAKE.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
     ILZ032-ILZ033-ILZ039...11 AM TUESDAY TO 7 PM TUESDAY.

IN...WIND ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019...11 AM
     TUESDAY TO 7 PM TUESDAY.

LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...9 AM
     TUESDAY TO 9 PM TUESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 9 AM TUESDAY.

&&

$$

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