Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 221955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT WED OCT 22 2014

.DISCUSSION...
310 AM CDT

TRANSITION AWAY FROM THE BELOW AVERAGE TEMPS OF LATE TO WARMER THAN
AVERAGE TEMPS BY THIS WEEKEND INTO EARLY NEXT WEEK STILL ON
TRACK...WITH A COUPLE SHOTS OF RAIN POSSIBLE.

ANY LINGERING LAKE CLOUDINESS IN NE IL EARLY THIS MORNING WILL FADE
WITH 100% SUNSHINE LOOKING LIKELY TODAY. TEMPERATURES SHOULD
MODERATE SEVERAL DEGREES OVER YESTERDAY MOST AREAS...THOUGH LAKE
ADJACENT AREAS OF NE IL WILL STILL FACE ONSHORE WINDS AND COOLER
TEMPS THAN THE REMAINDER OF THE CWA. MAINLY CLEAR SKIES AND LIGHT
WINDS SHOULD ALLOW FOR ANOTHER CHILLY NIGHT TONIGHT.

SKIES WILL CLOUD OVER THURSDAY LEAVING OUR PROSPECTS FOR SEEING THE
SOLAR ECLIPSE THURSDAY AFTERNOON DIM. SHARP UPPER TROUGH WILL
APPROACH FROM THE WEST THURSDAY AND DESPITE RELATIVE LACK OF
MOISTURE...FORCING LOOKS TO BE STRONG ENOUGH TO PROVIDE FOR A DECENT
SHOT OF SHOWERS SPREADING FROM WEST TO EAST THURSDAY AND ENDING
EASTERN CWA THURSDAY EVENING. SOUTHERN EXTENT OF THIS SHORTWAVE WILL
BE WEAKENING AS IT RUNS INTO THE NARROW RIDGE BEHIND THE LARGE
EASTERN CONUS UPPER LOW. THE ANTICIPATED GRADUAL WEAKENING OF THE
TROUGH IN OUR NECK OF THE WOODS IS REASONING FOR HIGHEST POPS WEST
AND LOWER POPS EAST...THOUGH GUIDANCE OFTEN WEAKENS THESE SYSTEMS
TOO QUICKLY AND HAVE GENERALLY GONE WITH HIGHER MOS POPS FOR THIS
SYSTEM.

WARM ADVECTION WILL RAMP UP BEHIND THIS SYSTEM AS UPPER RIDGING
BRIEFLY BUILDS INTO THE AREA FRIDAY ALLOWING FOR MODERATING TEMPS.
THE 00Z WRF-NAM DID HAVE A STRONGER TROUGH MOVING THROUGH ON FRIDAY
WITH SOME LIGHT QPF...BUT GIVEN THE GLOBAL MODELS ALL MUCH MORE
MUTED WITH THIS TROUGH WITH NO PRECIP HAVE BUMPED UP SKY COVER A BIT
AND POPS UP TO 10% BUT KEPT FORECAST DRY FOR NOW.

PATTERN WILL REMAIN QUITE AMPLIFIED THROUGH THE WEEKEND WITH DEEP
TROUGH TO OUR NE AND UPPER RIDGE BUILDING INTO THE CENTRAL CONUS.
GUIDANCE HAS TRENDED A BIT FARTHER WEST WITH THE NE CONUS UPPER
TROUGH THIS WEEKEND PLACING OUR CWA A BIT CLOSER TO THE COOLER AIR
MASS...BUT STILL EXPECT HIGHS TO MAKE IT INTO THE 60S. IT NOW
APPEARS THE GFS...ECMWF...AND GEM HAVE MONDAY AS OUR WARMEST DAY
WITH 850MB TEMPS PROGGED TO BE AROUND 1.5 STANDARD DEVIATIONS ABOVE
AVERAGE. GIVEN THE INCREASING SOUTHERLY WINDS THINK MOST OF THE CWA
STANDS A DECENT SHOT TO TAG 70F WITH ENSEMBLE MAX TEMPS AS WARM AS
THE MID TO UPPER 70S. COLD FRONT LOOKS TO END OUR BRIEF STINT OF
INDIAN SUMMER MONDAY NIGHT OR TUESDAY WITH SHOWERS AND POSSIBLY SOME
THUNDERSTORMS ACCOMPANYING THE FRONT.

IZZI

&&

.AVIATION...

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

* -SHRA EXPECTED LATE THURSDAY AFTERNOON AND MVFR CIGS ARE PSBL.

JEE

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

QUIET HIGH PRESSURE IS OVERHEAD LEADING TO CONTINUED VFR
CONDITIONS OVERNIGHT. THE HIGH SHIFTS EAST TOMORROW AS A WEAK
SURFACE LOW OVER MANITOBA APPROACHES. THE MAIN LOW WILL REMAIN
OVER SOUTHERN CANADA AND WEAKEN AS IT MOVES INTO WESTERN ONTARIO.
AN UPPER LEVEL DISTURBANCE ASSOCIATED WITH THE LOWS WARM FRONT
PASSES OVERHEAD TOMORROW AFTERNOON AND THIS WILL BE THE TRIGGER
FOR PRECIP. THE DISTURBANCE AND FRONT WILL BE WEAKENING AS THEY
MOVE OVERHEAD SO HAVE LIMITED CONFIDENCE IN HOW LONG THE BAND OF
PRECIP WILL HOLD TOGETHER. MODELS ARE ALSO SLOWING THE SYSTEM SO
THE ONSET OF PRECIP MAY BE LATER THAN CURRENTLY INDICATED.

AS SUCH ONLY HAVE PRECIP MENTIONED AT ORD. COULD SEE PRECIP
REACHING RFD ARND 18Z...BUT GIVEN THE SLOWING TREND...OPTED TO
KEEP -SHRA OUT OF THE RFD TAF FOR NOW.

GUIDANCE DIFFERS ON CIGS WITH THE PRECIP AS WELL...WITH ONE MODEL
INDICATING MFVR OR LOWER CIGS. GIVEN THE DIFFERENCES AND WEAKENING
TREND...WENT WITH LOW END VFR CIGS WITH A SCT LATER OF MVFR.

LASTLY...WINDS TURN SSW TOMORROW MORNING AND WILL BE ARND 10 KT.

JEE

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

* MEDIUM CONFIDENCE IN TIMING AND COVERAGE OF -SHRA THURSDAY.

* MEDIUM-LOW CONFIDENCE IN TIMING AND OCCURRENCE OF MVFR CIGS
  THURSDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

* THURSDAY NIGHT...CHANCE OF SHRA. MVFR POSSIBLE.
* FRIDAY...DRY/VFR. SOUTHWEST WINDS.
* SATURDAY...DRY/VFR. GUSTY NORTHWEST WINDS.
* SUNDAY...DRY/VFR. SOUTH/SOUTHEAST WINDS.
* MONDAY...SLIGHT CHANCE OF SHRA. GUSTY SOUTH/SOUTHWEST WINDS.
* TUESDAY...CHANCE OF SHRA. STRONG/GUSTY WESTERLY WINDS.

&&

.MARINE...
158 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN GREAT LAKES REGION WILL
REMAIN FAIRLY PROGRESSIVE THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK...WITH SEVERAL FRONTAL PASSAGES ALTERNATING WITH WEAK HIGH
PRESSURE RIDGES.

HIGH PRESSURE WAS SITUATED OVER THE WESTERN LAKES THIS AFTERNOON...
BUT THE RIDGE WILL MOVE SLOWLY EAST TONIGHT WITH SOUTH WINDS
BECOMING STRONGER THURSDAY AS A TROUGH OF LOW PRESSURE MOVES INTO
THE UPPER MIDWEST. PRESSURE FALLS AHEAD OF THIS SYSTEM WILL LIKELY
LEAD TO SOUTH WINDS GUSTING TO 20-25 KT ESPECIALLY ACROSS THE
NORTHERN PART LAKE MICHIGAN THURSDAY AFTERNOON AND EVENING. THE COLD
FRONT ASSOCIATED WITH THIS TROUGH WILL WEAKEN AS IT MOVES THROUGH
THE REGION EARLY FRIDAY...WITH WINDS BACKING SOUTH AGAIN AHEAD OF
ANOTHER DISTURBANCE EMERGING FROM THE NORTHERN PLAINS. THIS NEXT
TROUGH AND COLD FRONT WILL PASS LATE FRIDAY NIGHT...WITH WINDS
VEERING TO THE WEST AND AGAIN GUSTING AS HIGH AS 30 KT INTO SATURDAY
AND SATURDAY NIGHT. A FEW GUSTS NEAR GALE FORCE MAY BE POSSIBLE
SATURDAY NIGHT AS COLDER AIR STEEPENS THE LOW LEVEL LAPSE RATES OVER
THE LAKE AND ALLOWS DEEPER MIXING OF THE HIGHER MOMENTUM AIR FROM
ABOVE. WINDS WILL THEN EASE SUNDAY AS ANOTHER WEAK HIGH PRESSURE
RIDGE MOVES ACROSS THE LAKE LATE IN THE DAY.

A DEEPER LOW PRESSURE SYSTEM IS FORECAST TO DEVELOP OVER THE PLAINS
AND LIFT NORTHEAST ACROSS THE UPPER MIDWEST SUNDAY NIGHT THROUGH
TUESDAY. SURFACE PRESSURE FALLS AND A RESULTING TIGHTENING OF THE
SURFACE PRESSURE GRADIENT WILL RESULT IN WINDS BACK TO THE
SOUTH-SOUTHEAST BY EARLY MONDAY...WITH SPEEDS INCREASING INTO THE
20-30 KT RANGE AGAIN.

RATZER

&&

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

$$

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