Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 171806
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
106 PM CDT WED SEP 17 2014

.DISCUSSION...
231 AM CDT

OVERARCHING THEME OF THE FORECAST FOR THE NEXT SEVEN DAYS IS FAIRLY
NICE EARLY FALL WEATHER WITH A DASH OF UNSEASONABLE WARMTH AND
SPLASH OF THUNDERSTORMS.

TODAY LOOKS TO BE ANOTHER GLORIOUS DAY...LIKELY A COUPLE/FEW DEGREES
WARMER THAN TUESDAY. GUIDANCE WAS A COUPLE DEGREES TOO COOL WITH
HIGHS TUESDAY AND WITH 925MB AND 850MB TEMPS PROGGED TO BE 2-3C
WARMER THAN YESTERDAY HAVE OPTED TO GO A COUPLE DEGREES ABOVE
GUIDANCE WITH HIGHS NEAR OR INTO THE LOWER 70S MOST AREAS. SOME
ACCAS AND MID LEVEL CLOUDINESS UPSTREAM ASSOCIATED WITH MID-LEVEL
WARM AIR ADVECTION COULD LEAD TO A BIT MORE CLOUDINESS THAN THE
NEARLY CLOUD FREE SKIES TUESDAY BUT STILL LOOK FOR PLENTY OF
SUNSHINE TODAY.

WEAKENING BACKDOOR COLD FRONT MOVES IN OFF THE LAKE EARLY THURSDAY
MORNING RESULTING IN SOME SLIGHTLY COOLER TEMPS THURS...ESPECIALLY
DOWNWIND OF THE LAKE WHERE NORTHEAST WINDS WILL HAVE A BETTER UMPH
BEHIND THE FRONT AND RESULT IN A GREATER LAKE INFLUENCE TO TEMPS.
WINDS BEGIN TO VEER AND SHOULD BECOMING SOUTHEASTERLY THURSDAY NIGHT
WITH WARM AIR ADVECTION GETTING UNDERWAY. WARM AIR ADVECTION GETS
GOING INTO FULL GEAR BY LATE FRIDAY AND GIVEN THE LATER ARRIVAL OF
THE TOASTIER TEMPS ITS UNCLEAR HOW MUCH WARMING WILL BE REALIZED
WITH HIGHS FRIDAY. HAVE CONSERVATIVELY BUMPED TEMPS UP INTO THE 70S
AREA WIDE...BUT PROGGED 00Z 850MB/925MB TEMPS WOULD ACTUALLY SUPPORT
TEMPS AROUND 80F. FRIDAY NIGHT LOOKS TO BE FAIRLY WARM WITH
SOUTHERLY WINDS CONTINUING...IN FACT MANY AREAS WILL SEE LOW TEMPS
FRI NIGHT WARMER THAN HIGH TEMPS WERE LAST WEEK! GUIDANCE CONTINUES
TO ADVERTISE 850MB TEMPS IN THE MID-UPPER TEENS WITH 925MB TEMPS
AROUND 20C...WHICH CLIMO SUGGESTS HIGHS WELL INTO THE 80S. HAVE
TRENDED TEMPS UPWARD SOME INTO THE LOW TO MID 80S AND WITH ENOUGH
SUNSHINE EVEN THOSE FORECAST HIGHS COULD END UP BEING A BIT TOO LOW!

COLD FRONT STILL LOOKS SLATED TO ARRIVE LATE SATURDAY WITH SHOWERS
AND THUNDERSTORMS CERTAINLY LOOKING LIKE A DECENT BET ALONG THE
FRONT. MEDIUM RANGE GUIDANCE HAS TRENDED TOWARD LESS PHASING WITH
THE NORTHERN STREAM TROUGH AND THE REMNANTS OF ODILE...SO NOT
LOOKING LIKE QUITE AS BIG OF A RAIN PRODUCER AS PREVIOUS RUNS
SUGGESTED. THE PUSH OF COLDER AIR BEHIND THE FRONT SATURDAY LOOKS TO
COME IN PHASES...WITH THE FIRST PHASE INITIALLY LOOKING LIKE MORE OF
A PUSH OF PACIFIC AIR SUNDAY BEFORE SECONDARY PUSH OF MORE
SUBSTANTIAL COLD AIR ARRIVES EARLY NEXT WEEK SENDING TEMPS DROPPING
BELOW AVERAGE AGAIN.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON.

* COLD FRONT PASSAGE EARLY THURSDAY WITH CHANCE OF LOWER STRATUS
  BEHIND.

* NELY WINDS TO 10KT THURSDAY AFTERNOON.

KREIN

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

A LARGE AREA OF HIGH PRESSURE COVERS THE REGION. THE WEAK PRESSURE
GRADIENT SHOULD ALLOW FOR A LAKE BREEZE TO DEVELOP LATE THIS
AFTERNOON. WITH LAND AND WATER TEMPERATURES SOMEWHAT
SIMILAR...THERE WILL NOT BE MUCH PUSH BEHIND THE BOUNDARY...SO
EXPECT THAT EXPECTED ELY WINDS SHOULD ONLY BE 5-7 KT.

WITH SUNSET...THE LAKE BREEZE SHOULD WASH OUT AND WINDS WILL
BECOME LGT/VRBL. THE LIGHT WINDS AND MOSTLY CLEAR SKIES SHOULD
ALLOW SOME PATCHY SHALLOW GROUND FOG TO DEVELOP...MAINLY IN RURAL
AREAS.

A COLD FRONT IS EXPECTED TO DROP SOUTH OUT OF WISCONSIN AND DOWN
THE LENGTH OF LAKE MICHIGAN...SETTING UP NELY WINDS BY THE LATE
MORNING HOURS. WITH A STRONGER COLD PUSH BEHIND THIS
BOUNDARY...ANTICIPATE THAT THE NELY WINDS SHOULD APPROACH 10KT
DURG THE AFTERNOON HOURS. THERE IS A CHANCE OF SOME LOWER STRATUS
BEHIND THE COLD FRONT...ESPECIALLY CLOSER TO THE LAKE FRONT...BUT
THE MODEL GUIDANCE IS STILL SHOWING A FAIR AMOUNT OF VARIABILITY
TO THE LOW LEVEL MOISTURE PROFILES...SO WILL KEEP THE GOING
FORECAST FOR VFR SKIES AND MONITOR CONDITIONS AS THE COLD FRONT
WORKS DOWN THE LAKE LATER THIS EVENING AND TONIGHT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH CONFIDENCE IN LAKE BREEZE TIMING TO WITHIN AN HOUR
  OR TWO.

* LOW CONFIDENCE IN CIGS THURSDAY MORNING.

* HIGH CONFIDENCE IN VFR CONDITIONS TODAY AND MOST OF TONIGHT.

* MEDIUM CONFIDENCE THAT WINDS COULD REACH OR SLIGHTLY EXCEED 10
  KT TOMORROW AFTERNOON.

KREIN

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

THURSDAY NIGHT THROUGH FRIDAY...VFR
SATURDAY...CHANCE OF THUNDERSTORMS.
SUNDAY THROUGH TUESDAY...VFR.

BMD

&&

.MARINE...
222 AM CDT

AREAS OF HIGH PRESSURE LIE ACROSS THE OHIO VALLEY AND THE CANADIAN
PRAIRIES EARLY THIS MORNING WITH COLD FRONT IN BETWEEN THESE TWO
FEATURES JUST NORTH OF LAKE MICHIGAN. THIS FRONT WILL MOVE SOUTH
ACROSS THE LAKE THIS EVENING AND TONIGHT WITH WINDS TURNING
NORTHEAST AND INCREASING SHARPLY INTO THE 20-25 KT RANGE
PARTICULARLY OVER THE NORTH HALF OF THE LAKE. WINDS DIMINISH
THURSDAY..THEN TURN BACK TO THE SOUTHEAST AND INCREASE AGAIN
THURSDAY NIGHT INTO FRIDAY. BY FRIDAY...SOUTH WINDS TO 30 KT ARE
EXPECTED OVER THE NORTH HALF OF THE LAKE AND A BRIEF PERIOD OF SOUTH
GALES IS NOT OUT OF THE QUESTION. WINDS WILL REMAIN FRESH THROUGH
THE WEEKEND...TURNING NORTHWEST ON SUNDAY AS ANOTHER COLD FRONT
MOVES ACROSS THE LAKE.

BMD

&&

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

$$

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