Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 250302
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1002 PM CDT FRI OCT 24 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 03Z...

* LOWERING CIGS LATE EVENING/OVERNIGHT...MVFR PROBABLE WITH
  IFR/LIFR A LOW POSSIBILITY.

* MVFR VSBY POSSIBLE OVERNIGHT.

* IMPROVING CIG/VIS SATURDAY MORNING WITH BREEZY WEST-NORTHWEST
  WINDS.

RATZER

//DISCUSSION...UPDATED 03Z...

IFR/LIFR CIGS AND VIS EXPANDING ACROSS PARTS OF CENTRAL AND
EASTERN IOWA THIS EVENING...EXPECTED TO SPREAD INTO PARTS OF
NORTHWEST AND WESTERN/CENTRAL IL LATE TONIGHT. LATEST MODEL
GUIDANCE CONTINUES TO INDICATE POTENTIAL FOR LOW CIGS/VIS MAINLY
WEST AND SOUTHWEST OF THE CHICAGO TERMINALS. HAVE INDICATED A
PERIOD OF IFR CONDITIONS AT RFD DURING THE EARLY SATURDAY MORNING
PERIOD...WITH LOWER MVFR CONDITIONS LIKELY FARTHER EAST ACROSS
ORD/MDW/GYY/DPA.

RATZER

PREVIOUS DISCUSSION FROM 00Z...

SUBTLE SURFACE LOW PRESSURE WAVE WAS OVER EASTERN IOWA EARLY THIS
EVENING...AND WILL MOVE EAST ACROSS THE TERMINALS OVERNIGHT. AN
AREA OF IFR/LIFR CIGS AND FOG WAS LOCATED JUST AHEAD OF THIS WAVE
ACROSS EASTERN IOWA/SOUTHWEST MINNESOTA...AND IS EXPECTED TO
ADVANCE INTO PARTS OF SOUTHWEST WISCONSIN AND WESTERN ILLINOIS
OVERNIGHT...AS LIGHT SOUTH-SOUTHWEST WINDS CONTINUE TO ADVECT LOW
LEVEL MOISTURE AHEAD OF THE WAVE. A FASTER MOVING COLD FRONT WITH
A STRONG PUSH OF DRIER AIR WILL OVERTAKE THE WEAKER WAVE
OVERNIGHT. A FEW SPRINKLES WILL BE POSSIBLE LATER THIS EVENING AS
AN ASSOCIATED UPPER LEVEL DISTURBANCE ENHANCES LIFT...THOUGH THESE
SHOULD BE VERY LIGHT AND FAIRLY ISOLATED.

LOW END VFR AND MVFR CIGS ARE EXPECTED TO SPREAD EAST AS FAR AS
THE CHICAGO TERMINALS DURING THE LATE EVENING/OVERNIGHT HOURS...
THOUGH CONFIDENCE IS LOW THAT THE LOWER IFR/LIFR CIGS OVER IOWA
WILL MAKE IT THIS FAR EAST AS THE LOW LEVEL MOIST AXIS GETS
PINCHED OFF BY THE FASTER COLD FRONT. THE SECOND FRONT WILL CLEAR
THE TERMINALS SATURDAY MORNING...WITH MUCH DRIER AIR SCOURING OUT
ANY LOW CLOUDS THAT DO FORM OVERNIGHT.

SOUTH-SOUTHWEST WINDS LESS THAN 10 KT THIS EVENING WILL SHIFT TO
THE WEST WITH THE FRONTAL PASSAGE PRE-DAWN SATURDAY. WEST-
NORTHWEST WINDS AROUND 10 KT WILL BECOME BREEZY WITH GUSTS NEAR 20
KT LATER SATURDAY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE CIGS LOWERING TO LOWER END VFR LATER THIS
  EVENING...MEDIUM CONFIDENCE IN MVFR CIGS OVERNIGHT. LOW
  CONFIDENCE IN CIGS IFR/LIFR DEVELOPING.

* MEDIUM CONFIDENCE IN MVFR CIGS OVERNIGHT.

* HIGH CONFIDENCE THAT -SHRA COVERAGE WILL BE LOW LATE THIS
  EVENING.

* HIGH CONFIDENCE IN IMPROVEMENT TO VFR AND WEST WINDS SATURDAY.

RATZER

//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...
228 PM CDT

HIGH PRESSURE IS SLOWLY PUSHING EAST WITH LIGHT SOUTHWEST WINDS OVER
THE LAKE. A WEAK LAKE BREEZE HAS TURNED WINDS ONSHORE OVER LAKE
COUNTY IL.  SOUTHWEST WINDS INCREASE TO 20-25 KT THIS EVENING WITH
OCNL 30 KT GUSTS PSBL OVER THE NORTH HALF OF THE LAKE OVERNIGHT.
WINDS TURN W 20-25 KT BEHIND THE FRONT AND SLOWLY BECOME NW SATURDAY
NIGHT. POINTS NORTH OF WILMETTE HARBOR MAY SEE OCNL GUSTS TO 25 KT
TOMORROW...BUT THINKING SUSTAINED SMALL CRAFT CONDITIONS WILL NOT BE
MET. WINDS DIMINISH AS A HIGH MOVES OVER THE LAKE SUNDAY.  WINDS
BECOME SOUTH BEHIND THE LOW AND THEN TURN SE AND INCREASE TO 20-25
KT AS THE NEXT LOW APPROACHES SUNDAY NIGHT.  THERE IS STILL A LOT OF
VARIABILITY IN THE STRENGTH AND PATH OF THE NEXT LOW SO CONFIDENCE
IS LOW IN THE EXACT WIND SPEEDS. ONE MODEL DOES FEATURE WESTERLY
GALES ON THE BACKSIDE OF THE LOW TUESDAY NIGHT...BUT DO NOT HAVE
ENOUGH CONFIDENCE TO GO THAT HIGH IN THE FORECAST JUST YET.  HIGH
PRESSURE MOVES IN MID NEXT WEEK AND WINDS SLOWLY DIMINISH WEDNESDAY.

STILL THINKING THERE IS A MARGINAL CHANCE FOR SMALL CRAFT CONDITIONS
TO BE MET MONDAY NIGHT THROUGH TUESDAY...BUT WILL HOLD OFF ON
HEADLINES FOR NOW.

JEE

&&

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

$$

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