Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 250745
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
245 AM CDT SAT OCT 25 2014

.DISCUSSION...
947 PM CDT

ISOLATED SHOWERS ARE MOVING THROUGH THIS EVENING. MOST AREAS WILL
REMAIN DRY...AND EXPECT SHOWERS TO BE INTO NW INDIANA AFTER
MIDNIGHT...AND EAST OF THE AREA SHORTLY THEREAFTER.
OTHERWISE...EXPECT SOME FOG TO REFORM AGAIN TONIGHT...WITH WESTERN
AREAS FAVORED DUE TO A THINNING AND LOWERING OF CLOUDS.

KMD

//PREV DISCUSSION...
304 PM CDT

THIS EVENING AND TONIGHT...
BROAD SURFACE HIGH STRETCHES FROM THE LOWER MISSISSIPPI VALLEY INTO
THE UPPER OHIO VALLEY AND EASTERN GREAT LAKES THIS AFTERNOON WHILE
LOW PRESSURE LIES OVER ONTARIO WITH A COLD FRONT STRETCHING INTO THE
CENTRAL PLAINS. A NARROW RIBBON OF MOISTURE IS ANALYZED OUT AHEAD OF
THE COLD FRONT WITH 60 DEGREE DEWPOINTS STRETCHING NORTH INTO
NORTHERN IOWA THIS AFTERNOON...AND JUST OFF THE DECK A CORRIDOR OF
LOW/MID LEVEL THETA-E ADVECTION IS DRIVING AT LEAST A FEW VERY WEAK
RADAR RETURNS OVER FAR SE MN AND NE IA. RAP/HRRR GUIDANCE SHOWS THIS
AREA PERSISTING ACROSS NORTHERN ILLINOIS THIS EVENING WITH THE
CHANCE FOR A FEW SHOWERS. GIVEN THE VERY SPARSE COVERAGE SO FAR
UPSTREAM AND THE DRY SOUNDINGS/LIMITED DURATION OF FORCING...NOT
BITING OFF ON PRECIP MOVING ACROSS THE FORECAST AREA...BUT WILL
MAINTAIN SOME LOW END SLIGHT CHANCE POPS SINCE THERE ARE SOME
INGREDIENTS IN PLACE.

SATURDAY THROUGH SUNDAY...
WEAK FRONT WILL PASS ACROSS THE AREA EARLY ON SATURDAY WITH DRY AIR
FILTERING BACK INTO THE REGION AS AN UPPER RIDGE BUILDS OVER THE
AREA AND SUBSIDENCE SETS IN OVERHEAD. EXPECT DEW POINTS TO MIX OUT
NICELY TOMORROW AFTERNOON...ESPECIALLY IN NORTH CENTRAL ILLINOIS
WHERE DEW POINTS MAY DROP INTO THE LOW TO MID 30S. THE DRY
CONDITIONS SHOULD ALLOW FOR A NICE RESPONSE FROM DIABATIC HEATING
WHICH WILL RESULT IN TEMPS A FEW DEGREES WARMER TOMORROW.
MEANWHILE...SURFACE HIGH WILL BUILD FROM THE NORTHERN PLAINS
SATURDAY DIRECTLY OVERHEAD EARLY TUESDAY MORNING WHICH WILL ALLOW
FAVORABLE RADIATIONAL COOLING SUNDAY MORNING WITH LOWS DIPPING INTO
THE 30S IN OUTLYING AREAS AND SOME OF THE TYPICAL COLD SPOTS.
ELSEWHERE EXPECT LOW 40S WITH DOWNTOWN CHICAGO STAYING PROPPED UP IN
THE MID 40S. TEMPERATURES MAY BE A BIT TRICKY SUNDAY WITH WARM
ADVECTION ALOFT INCREASING THROUGH THE DAY ON THE BACKSIDE OF THE
SURFACE HIGH. A COOL STARTING POINT AND INCREASING CLOUD COVER
THROUGH THE DAY WILL KEEP HIGHS ONLY INTO THE 60S SUNDAY AFTERNOON.

SUNDAY NIGHT THROUGH MONDAY...
UPPER RIDGE BEGINS TO BUCKLE SUNDAY NIGHT INTO MONDAY AS SHORTWAVE
TROUGH DIGS FROM THE PAC NW INTO THE CENTRAL PLAINS. BROAD SURFACE
LOW PRESSURE OVER THE PLAINS WILL SHIFT EAST TOWARDS THE MIDWEST
EARLY MONDAY WITH SOUTHWEST FLOW INCREASING OUT AHEAD AND A CORRIDOR
OF MODERATE TO STRONG MID LEVEL THETA-E ADVECTION LIFTING ACROSS THE
LOCAL FORECAST AREA ON THE NOSE OF A 40KT OR SO LOW LEVEL JET.
COLUMN IS FAIRLY DRY OUT AHEAD OF THE BAROCLINIC ZONE BUT A NARROW
LAYER OF SATURATION COULD TAP INTO SOME MODEST INSTABILITY ROOTED
BETWEEN H7-H9. THIS DOES POINT TO SOME CHANCES FOR THUNDERSTORMS
THOUGH CHANCES ARE BETTER TO OUR NORTH WHERE THE MUCAPE ALIGNS
BETTER WITH THE FORCING FROM THE LOW LEVEL JET. EXPECT LOWERING
CLOUDS IN THE PREDAWN HOURS AS THE SURFACE WARM FRONT APPROACHES.
THE MID LEVELS DRY OUT AGAIN AND THE MOISTURE IS FAIRLY SHALLOW SO
ANY ADDITIONAL PRECIP EARLY ON MONDAY MAY JUST BE DRIZZLE. SURFACE
WARM FRONT LIFTS ACROSS THE AREA MID MORNING MONDAY AND EXPECT DRY
CONDITIONS ONCE IN THE WARM SECTOR WITH LOW CLOUD COVER EVENTUALLY
SCATTERING. H85 TEMPS WARM TO 15-16C WITH 17C BEING THE 99TH
PERCENTILE OF UPPER AIR CLIMO FOR THE END OF OCTOBER. SURFACE HIGHS
WILL BE WELL ABOVE NORMAL...POSSIBLY PUSHING 20F ABOVE
NORMAL...THOUGH THE RECORD HIGH SHOULD BE SAFE. LEANED HEAVILY ON
EC/ECBC FOR AFTERNOON HIGHS MONDAY FORECASTING MID 70S...WITH UPPER
70S SOUTH OF I-80. THE WARMER CONDITIONS WILL BE ACCOMPANIED BY
STRONGER WINDS HOWEVER WITH SOUTHWEST WINDS GUSTING 20 TO 25 MPH AND
POSSIBLY 30 MPH AT TIMES.

TUESDAY THROUGH FRIDAY...
MODELS ARE INDICATING A STRONG LOW PRESSURE SYSTEM WILL BEGIN TO
DEVELOP OVER THE REGION EARLY NEXT WEEK WITH A COLD FRONT SWEEPING
ACROSS THE ARE MONDAY NIGHT INTO EARLY TUESDAY BRINGING CHANCES FOR
SHOWER AND THUNDERSTORMS. THE LOW REALLY BEGINS TO DEEPEN IN EARNEST
AS IT LIFTS ACROSS THE GREAT LAKES INTO CANADA TUESDAY INTO
WEDNESDAY WITH DRIVING POLAR AIR SOUTH INTO THE CANADIAN PRAIRIES
AND A COLD POLAR HIGH GRAZING THE LOCAL AREA LATE NEXT WEEK. DETAILS
STILL MURKY THIS FAR OUT BUT DOES APPEAR WE COULD BE IN FOR A BIG
COOL DOWN LATE NEXT WEEK IN TIME FOR HALLOWEEN IF CURRENT GFS/ECMWF
RUNS PAN OUT.

DEUBELBEISS

&&

.AVIATION...

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

* MVFR CIGS LIKELY OVERNIGHT...IFR CIGS A POSSIBILITY.

* MVFR VSBY POSSIBLE OVERNIGHT.

* IMPROVING CIG/VIS SATURDAY MORNING.

* BREEZY WEST-NORTHWEST WINDS...WITH GUSTS TO ARND 20KT.

KREIN

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

A WEAK SFC TROUGH AND MID LEVEL IMPULSE WILL CROSS THE REGION
OVERNIGHT. LATEST SATELLITE IMAGERY INDICATES JET CIRRUS AND SOME
MID LEVEL CLOUDINESS OVER THE AREA...BUT THE HIGHER LEVEL CLOUD IS
PUSHING EAST OF THE REGION...AND LOCATIONS THAT HAVE LOST THE
HIGHER LEVEL CLOUD COVER ARE ALREADY SEEING LOWERING STRATUS AND
FOG. ANTICIPATE THAT CIGS WILL GRADUALLY LOWER WITH THE WRN
TERMINALS...RFD/DPA LOWERING FIRST AND THEN ORD/MDW/GYY A LITTLE
LATER. STILL HAVE SOME CONCERNS FOR IFR CIGS DEVELOPING...WITH
HIGHER CONFIDENCE IN IFR CONDITIONS AT RFD/DPA...BUT HAVE ENOUGH
CONFIDENCE IN IFR CIGS AT ORD/MDW/GYY TO AT LEAST INCLUDE IN A
TEMPO GROUP. THERE IS SOME CONCERN FOR LIFR CIGS/VIS...ESPECIALLY
AT RFD...WHICH WILL HAVE THE LONGEST PERIOD OF TIME WITHOUT THE
HIGHER LEVEL CLOUD. ALSO...AS THE WEAK SFC TROUGH AXIS CROSSES THE
AREA...WINDS DECREASING TO BLW 5KT COULD ALSO HELP WITH DENSER FOG
DEVELOPMENT AWAY FROM THE CHICAGO AREA URBAN HEAT ISLAND.

WITH AMPLE SUNSHINE EXPECTED...CONDITIONS SHOULD QUICKLY IMPROVE
AFTER SUNRISE AND THE REMAINDER OF THE DAY SHOULD SEE VFR
CONDITIONS. THE MAIN ISSUE FOR THE REMAINDER OF THE DAY WILL BE
WINDS. FOLLOWING THE PASSAGE OF THE WEAK SFC TROUGH...HIGH
PRESSURE BUILDING OVER THE NRN PLAINS WILL SET UP A STRENGTHENING
WNWLY-NWLY GRADIENT OVER THE AREA. WITH AMPLE MIXING THROUGH THE
AFTERNOON...WINDS SHOULD BECOME MORE GUSTY...WITH GUSTS TO ARND
20KT THROUGH SUNSET.

KREIN

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

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR OVERNIGHT. MEDIUM
  CONFIDENCE IN IFR CIGS DEVELOPING.

* MEDIUM CONFIDENCE IN MVFR VIS OVERNIGHT.

* HIGH CONFIDENCE IN IMPROVEMENT TO VFR AND WNWLY-NWLY WINDS
  SATURDAY...WITH GUSTS TO ARND 20KT IN THE AFTERNOON.

KREIN

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

SUNDAY...VFR. SLGT CHC SHRA/TSRA SUNDAY NIGHT. SE WINDS.

MONDAY...VFR BY DAY...SHRA/TSRA LIKELY MONDAY NIGHT. BREEZY
SOUTH WINDS.

TUESDAY...CHC SHRA/TSRA. MVFR POSSIBLE. SOUTHWEST-WEST WINDS.

WEDNESDAY AND THURSDAY...VFR. WEST-SOUTHWEST WINDS.

RATZER

&&

.MARINE...
229 AM CDT

LOW PRESSURE OVER JAMES BAY ALONG WITH A SFC RIDGE CENTERED OVER
THE NORTHERN PLAINS HAS CREATED A TIGHT PRESSURE GRADIENT BETWEEN
THE TWO SYSTEMS...WHICH IS POSITIONED OVER THE LAKE. THIS HAS
RESULTED IN BREEZY SOUTHWEST WINDS OVER THE LAKE WITH SPEEDS
GENERALLY BETWEEN 20-25KT. ACROSS THE NORTHERN HALF OF THE LAKE
THE GUSTS MAY NEAR 30 KT THIS MORNING. AS HIGH PRESSURE SLOWLY
BUILDS IN FROM THE WEST ACROSS THE LAKE...WIND WILL TURN
WEST/NORTHWEST AND GRADUALLY DIMINISH LATE TONIGHT/EARLY SUN. HIGH
PRESSURE WILL BECOME CENTERED OVER THE LAKE SUN...THEN CONTINUE TO
SLIDE EAST BY LATE SUN NIGHT. THIS WILL ALLOW ONLY A TEMPORARY
LULL IN THE WINDS...BEFORE WINDS TURN SOUTH/SOUTHWEST AND BEGIN TO
INCREASE. ANOTHER LOW PRESSURE IS POISED TO DEVELOP ACROSS THE
CENTRAL PLAINS MONDAY AFTERNOON...AND SLOWLY LIFT NORTHEAST
TOWARDS LAKE MICHIGAN MONDAY NIGHT/EARLY TUE. THIS LOW WILL THEN
DEEPEN TUE AFTERNOON AS IT LIFTS NORTHEAST ACROSS LOWER MICHIGAN.
THIS COULD PRODUCE A PERIOD OF WEST GALES TUE NGT/EARLY WED...THEN
ANOTHER RIDGE OF HIGH PRESSURE BUILDS BACK INTO THE WESTERN LAKES
TOWARDS THE MIDDLE OF THE WEEK.

BEACHLER

&&

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

$$

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