Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 171941
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
241 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 20Z...

* LAKE BREEZE THIS AFTERNOON...MOVED TIMING OF BOUNDARY PASSAGE
  AND WIND SHIFT TO ELY UP TO 22Z AND BUMPED UP WINDS TO 8KT.

* COLD FRONT PASSAGE EARLY THURSDAY MORNING WITH MVFR STRATUS
  BEHIND...CHANCE THAT CIGS COULD BRIEFLY DROP TO IFR FOR AN HOUR
  OR SO.

* 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 20Z...

* MEDIUM-HIGH CONFIDENCE IN LAKE BREEZE TIMING.

* MEDIUM TO HIGH CONFIDENCE IN MVFR CIGS THURSDAY MORNING...LOWER
  CONFIDENCE IN CHANCES FOR IFR CIGS.

* 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...
128 PM CDT

AN AREA OF LOW PRESSURE OVER THE EASTERN UPPER PENINSULA OF MICHIGAN
EARLY THIS AFTERNOON WILL CONTINUE TO MOVE EAST TONIGHT...TRAILING A
COLD FRONT WHICH WILL PUSH SOUTH DOWN THE LENGTH OF LAKE MICHIGAN
THROUGH TONIGHT AND EARLY THURSDAY MORNING. AS THE FRONT BEGINS TO
DROP SOUTH OVER THE NORTHERN END OF LAKE MICHIGAN BY EARLY THIS
EVENING...WINDS WILL VEER TO THE NORTH IN THE 20-25 KT RANGE. WINDS
WILL DIMINISH LATE TONIGHT AND THURSDAY AS THE FRONT PUSHES FARTHER
DOWN THE LAKE...AND LOSES SOME OF ITS PUNCH. HIGH PRESSURE WILL THEN
BUILD SOUTHEAST ACROSS THE NORTHERN LAKES AND EVENTUALLY ACROSS NEW
ENGLAND BY FRIDAY...WITH WINDS ON LAKE MICHIGAN SHIFTING BACK TO THE
SOUTH AND INCREASING LATE THURSDAY NIGHT. SOUTH WINDS TO 30 KT ARE
ANTICIPATED ACROSS THE LAKE FRIDAY AS THE GRADIENT TIGHTENS IN
RESPONSE TO LOW PRESSURE MOVING NORTH OF THE LAKES...AND A PERIOD OF
GALES OR AT LEAST SOME GALE FORCE GUSTS ARE POSSIBLE ESPECIALLY
ACROSS NORTHERN LAKE MICHIGAN LATE FRIDAY INTO EARLY SATURDAY.
FORECAST SOUNDINGS DEPICT 35-40 KT ABOVE THE SHALLOW MARINE BOUNDARY
LAYER DURING THIS TIME...WITH THE DRIVING FACTOR BEING THE DEPTH OF
MIXING IN THE SOUTHERLY WARM ADVECTION FLOW. THE LOW WILL PASS NORTH
OF THE LAKE LATE SATURDAY INTO SUNDAY...WITH A COLD FRONT PUSHING
SOUTHEAST SATURDAY NIGHT RESULTING IN A SHIFT TO NORTHWEST WINDS FOR
SUNDAY AND MONDAY.

RATZER

&&

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

$$

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