Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 182001
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
301 PM CDT SAT OCT 18 2014

.DISCUSSION...
300 PM CDT

FORECAST CONCERNS LIE AROUND FROSTY CONDITIONS FOR TONIGHT...ANOTHER
CHANCE FOR LIGHT RAIN SHOWERS LATE SUNDAY INTO MONDAY...AND POSSIBLY
SOME LAKE EFFECT SHOWERS INTO EARLY TUESDAY...FOLLOWED BY A GRADUAL
WARMUP.

THE SHARP UPPER TROUGH RESPONSIBLE FOR THIS MORNINGS LIGHT RAIN IS
CONTINUING ITS NOSE-DIVE OFF TO THE SOUTHEAST THIS AFTERNOON. THERE
IS STILL PLENTY OF CLOUD COVER OVER THE LAKE. WE ARE STARTING TO SEE
SOME CLOUD BREAKS FROM NORTH TO SOUTH AS DRIER AIR FILTERS IN AND A
CORRESPONDING SUBSIDENCE INVERSION/RAPID HEIGHT RISES CONTINUE TO
SQUASH THE DEEPER MOISTURE. THE UPPER RIDGE IN THE PLAINS WILL
DAMPEN AS IT SPREADS EAST TONIGHT...BUT WITH SPRAWLING SURFACE HIGH
PRESSURE TRANSITING THE REGION TONIGHT...EXPECT BETTER CLEARING GOOD
RADIATIONAL COOLING CONDITIONS TO ALLOW FOR CLEARING TO CONTINUE FOR
TEMPERATURES TO DROP RATHER QUICKLY. OUR NEXT SYSTEM IS ALREADY
SPREADING EAST THROUGH THE NORTHERN ROCKIES AND SOUTH CENTRAL CANADA
THIS AFTERNOON...AND WE WILL LIKELY SEE SOME OF THE HIGH CLOUDINESS
ASSOCIATED WITH IT SPREADING INTO OUR AREA LATER TONIGHT WHICH
SHOULDN`T DO TOO MUCH TO SLOW THE COOLING TONIGHT. DO NOT SEE ANY
GUIDANCE TO SUGGEST A WIDESPREAD FREEZE IN SPITE OF A FEW OUTLYING
LOCATIONS POSSIBLY TAGGING THE FREEZING MARK THIS EVENING AS
COLDER DEWPOINTS SPREAD SOUTH...SO WILL MAKE LITTLE CHANGE TO THE
TEMPS TONIGHT OR THE FROST ADVISORY. MODEL SOUNDINGS SUGGEST
CLOUDS WILL HANG ON IN NW INDIANA THROUGH AT LEAST MIDNIGHT BEFORE
BEGINNING TO CLEAR WHICH WILL SLOW THE COOL DOWN AND LIMIT FROST
POTENTIAL...ESPECIALLY CLOSER TO THE LAKE. BUT WE ARE SEEING
PRETTY GOOD CLEARING OF THE LAKE CLOUDS FARTHER UPSTREAM...AND
GIVEN THE LOW STARTING POINT AND AT LEAST GAPS IN THE CLOUDS
EXPECTED THAT OUTLYING AREAS IN NW INDY ALSO WILL BE SUSCEPTIBLE
TO SOME FROST...THOUGH WITH A BIT LOWER CONFIDENCE THEN IN
ILLNOIS. ADDITIONALLY...THERE MAY BE SOME PATCHY FOG IN RIVER
VALLEYS LATE TONIGHT AS WELL.

SUNDAY...THE AFOREMENTIONED SYSTEM IN THE NORTHERN ROCKIES WILL
BEGIN TO TAKE AIM AT THE REGION. IT WILL BE A COOL START TO THE DAY
AND EXPECT INCREASING CLOUD COVER AS THE DAY GOES ON WHICH WILL KEEP
TEMPERATURES IN THE MID TO UPPER 50S AT BEST. FOR SUNDAY NIGHT...THE
SYSTEM WILL BE TAKING A SOMEWHAT SIMILAR TRACK TO TODAY`S THOUGH IT
IS NOT QUITE AS SHARP. BY EARLY MONDAY MORNING THE SURFACE COLD
FRONT NEARS BRINGING A ANOTHER SHOT OF LIGHT RAIN SHOWERS.
GUIDANCE IS MIXED AS TO THE DEGREE AT WHICH THE LOW LEVEL FLOW
TURNS NORTH-NORTHEASTERLY...BUT THERE LOOKS TO BE SOME LAKE EFFECT
CLOUDS AND SHOWERS LINGERING INTO EARLY TUESDAY...POSSIBLY BACK TO
THE ILLINOIS SIDE OF LAKE MICHIGAN.

THE LATTER HALF OF THE WEEK IS STILL LOOKING FAIRLY NICE WITH MILD
AND DRY CONDITIONS THERE IS A PACIFIC SYSTEM THAT WILL ATTEMPT TO
PROGRESS THROUGH THE RIDGE BUT MODELS ARE SPLITTY WITH THIS ONE
GENERALLY JUST BRINGING SOME CLOUDS WITH IT AT THIS POINT.

KMD

&&

.AVIATION...

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

* MVFR CIGS WILL CONTINUE THRU 22Z...THEN STEADILY LIFT TOWARDS
  VFR CONDS ARND SUNSET.

* NORTH WINDS UP TO 10KT...THEN FURTHER DIMINISHING TO NEAR CALM
  CONDS OVERNIGHT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY CONTINUES TO SHOW CONSIDERABLE CLOUD COVER ACROSS
THE REGION...WITH MOST CIGS ARND 2300-2800FT AGL. SOME DRY AIR IS
BEGINNING TO WORK INTO SOUTHERN WISC AND WILL EVENTUALLY ARRIVE
ACROSS NORTHERN IL AND HELP TO START BREAKING UP THE OVC CONDS
INTO A BKN DECK ARND 22Z AND ALSO LIFT CIG BASES UP TO ARND
3500-4000FT AGL. THE GRADIENT WILL CONTINUE TO SLACKEN LATER THIS
EVENING...AS ADDTL DRY AIR FURTHER SCOURS THE CLOUDS. EXPECT NEAR
CALM CONDS TO DEVELOP BY 8Z SUN AND MINIMAL CLOUD COVER. WINDS
ARND DAYBREAK SUN BEGIN TO TURN SOUTHWEST WITH SOME GUSTS
DEVELOPING BY MIDDAY SUN TO ARND 16KT.

BEACHLER

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

* HIGH CONFIDENCE IN WIND DIR/SPEED.

* HIGH CONFIDENCE IN MVFR CIGS STEADILY IMPROVING TO VFR CONDS
  LATER THIS EVE. MEDIUM CONFIDENCE IN PRECISE TIMING OF CIGS
  LIFTING TO VFR.

BEACHLER

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

* SUNDAY NIGHT...CHANCE OF SHRA.
* MONDAY...CHANCE OF SHRA. WEST WINDS BECOMING NORTH.
* TUESDAY...DRY/VFR. NORTHEAST WINDS.
* WEDNESDAY...DRY/VFR. EAST WINDS.
* THURSDAY AND FRIDAY...DRY/VFR. SOUTHWEST WINDS.

&&

.MARINE...
111 PM CDT

IN THE NEAR TERM...HAVE ALLOWED GALE WARNING FOR THE LAKE MICHIGAN
OPEN WATERS TO EXPIRE AT 1 PM CDT...AS ISALLOBARIC (PRESSURE CHANGE)
GRADIENT HAS WEAKENED AND OBSERVED GUSTS HAVE EASED INTO THE 25-30
KT RANGE OVER THE PAST COUPLE OF HOURS.

THE SURFACE PRESSURE GRADIENT WILL CONTINUE TO WEAKEN THIS AFTERNOON
AND THEN MORE QUICKLY THIS EVENING/TONIGHT AS HIGH PRESSURE FROM
WESTERN ONTARIO TO THE CENTRAL PLAINS MOVES STEADILY EAST-SOUTHEAST
TO THE WESTERN LAKES AND LOWER OHIO VALLEY THROUGH TONIGHT. THIS
WILL RESULT IN 30 KT NORTH WINDS DIMINISHING QUICKLY THIS EVENING...
AND BACKING TO THE WEST-SOUTHWEST BY MORNING AS THE SURFACE RIDGE
AXIS PASSES. CURRENT SMALL CRAFT ADVISORY HEADLINES FOR THE IL
NEARSHORE WATERS WILL REMAIN IN EFFECT THROUGH 4 AM CDT...WITH THE
IN WATERS CONTINUING THROUGH 10 AM CDT SUNDAY MORNING AS WAVES
SLOWLY SUBSIDE AFTER THIS PERIOD OF STRONG NORTHERLY FETCH.

LIGHT WINDS ASSOCIATED WITH THE HIGH PRESSURE RIDGE WILL BE SHORT
LIVED HOWEVER...AS THE PROGRESSIVE NATURE OF THE CURRENT WEATHER
PATTERN CONTINUES WITH ANOTHER LOW DEVELOPING OVER CANADA AND MOVING
SOUTHEAST ACROSS THE NORTHERN LAKES SUNDAY AND SUNDAY NIGHT.
SOUTHWEST WINDS WILL PICK UP INTO THE 20-25 KT RANGE PERHAPS WITH A
FEW GUSTS TO 30 KT AGAIN SUNDAY IN ADVANCE OF THIS LOW AND TRAILING
COLD FRONT WHICH WILL MOVE ACROSS THE LAKE THROUGH MONDAY MORNING.
WINDS SHIFT NORTH BEHIND THE FRONT...WITH A PERIOD OF 25 KTS LATE
MONDAY INTO TUESDAY AS ANOTHER HIGH SPREADS ACROSS ONTARIO AND
EVENTUALLY OVER THE GREAT LAKES WEDNESDAY AND THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...3 AM SUNDAY TO 8 AM SUNDAY.

IN...FROST ADVISORY...INZ019...3 AM SUNDAY TO 8 AM SUNDAY.

LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 AM SUNDAY.

&&

$$

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