Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 250903
AFDLOT

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

.DISCUSSION...
314 AM CDT

SHORT TERM...THROUGH SATURDAY NIGHT...
FOR THE REMAINDER OF THE NIGHT AND INTO SATURDAY MORNING...THE INITIAL
CONCERNS WILL BE CLOUD COVER...AND IMPACTS ON VISIBILITY.  A WEAK
MID LEVEL IMPULSE THAT TRACKED ACROSS THE REGION FRIDAY EVENING
BROUGHT SOME SCT SPRINKLES.  AS THE MID AND HIGH CLOUD PUSHES AWAY
FROM THE AREA...FOG AND LOW STRATUS ARE BLOOMING.  NWRN IL AND ERN
IA HAVE ALREADY SEEN DENSE FOG AND LOW STRATUS FORM...AND IN THE
MOIST AIRMASS IN PLACE...WITH DEWPOINTS IN THE LOW 50S...EXPECT THAT
THE AREA OF FOG/STRATUS SHOULD INCREASE...THOUGH THE LOWEST
CONDITIONS SHOULD BE ALONG AND WEST OF THE I-39 CORRIDOR.  EAST OF
I-39...ANY DENSE FOG SHOULD BE LIMITED TO SHELTERED...LOW-LYING
AREAS.

THROUGH THE MORNING HOURS...A WEAK FRONTAL BOUNDARY WILL CROSS THE
AREA...WITH SFC HIGH PRESSURE BUILDING ACROSS THE CNTRL PLAINS WHILE
UPPER LEVEL RIDGING ALSO BUILDS OUT OF THE ROCKIES AND ACROSS THE
CENTRAL PLAINS.  THE UPPER RIDGING WILL SET UP A SUBSIDENCE PATTERN
ACROSS THE AREA...LEADING TO MOSTLY SUNNY SKIES.  LOW PRESSURE
MOVING THROUGH SERN CANADA...COMBINED WITH THE HIGH PRESSURE OVER
THE PLAINS WILL SET UP A GENERALLY NWLY GRADIENT ACROSS NRN IL/IN.
DAYTIME WARMING SHOULD ALLOW ANY RESIDUAL FOG/STRATUS TO DISSIPATE
BY LATE MORNING...WHILE THE AMPLE SUNSHINE AND LARGER SCALE
SUBSIDENCE SHOULD ALLOW TEMPERATURES TO QUICKLY RISE INTO THE LOWER
70S ACROSS THE SRN PORTIONS OF THE CWA...WHILE LOCATION CLOSER TO
THE WI BORDER WILL BE A BIT COOLER...BUT STILL SIGNIFICANTLY WARMER
THAN NORMAL...WITH HIGHS IN THE UPPER 60S.  STEADY NWLY WINDS AT THE
SFC AND ALOFT SHOULD PREVENT ANY KIND OF LAKE BREEZE FROM FORMING
AND THE WARMER AIR SHOULD COVER THE AREA UP TO THE LAKEFRONT.  WHILE
DEWPOINTS WILL BE IN THE 50S FOR THE MORNING HOURS...DEEP MIXING
SHOULD DRAW MUCH DRIER AIR TO THE SFC...WITH DEWPOINTS DROPPING INTO
THE UPPER 30S FOR THE AFTERNOON HOURS.  SO...OVERALL...SATURDAY IS
SHAPING UP TO A VERY PLEASANT DAY...WITH TEMPERATURES AROUND 10
DEGREES ABOVE NORMAL.  THE SFC HIGH PRESSURE WILL BUILD ACROSS THE
MISSISSIPPI VALLEY AND INTO THE MIDWEST OVERNIGHT TONIGHT WHILE THE
UPPER RIDGE SLOWLY PROGRESSES AS WELL.  WITH A DRIER AIRMASS IN
PLACE TONIGHT...THE CHANCES FOR ANOTHER ROUND OF FOG AND STRATUS IS
UNLIKELY...THROUGH THE CLEAR SKIES...LIGHT WINDS AND LOWER DEWPOINTS
SHOULD ALLOW TEMPERATURES TO RADIATE DOWN INTO THE UPPER 30S TO
LOWER 40S.  THE CHICAGO AREA URBAN HEAT ISLAND SHOULD REMAIN A
LITTLE WARMER...WITH LOWS IN THE MIDDLE 40S.

KREIN

SUNDAY THROUGH TUESDAY...
GUIDANCE HAS BEEN RELATIVELY CONSISTENT IN THE MEDIUM TERM FEATURING
MID-LVL RIDGING OVER THE UPPER MIDWEST/GREAT LAKES REGION WITH A SFC
RIDGE PROVIDING ABUNDANT SUNSHINE AND DRY CONDS FOR THE SECOND HALF
OF THE WEEKEND. HOWEVER THIS RIDGE WILL ONLY BE TEMPORARY AS THE
MID-LVL HEIGHTS BEGIN TO FALL AND A QUASI-ZONAL FLOW BEGINS TO SETUP
FOR EARLY NEXT WEEK. FORTUNATELY IT REMAINS LIKELY THAT MON WILL
REMAIN DRY...WITH VERY MILD TEMPS EXPECTED. THE SFC RIDGE WILL BE
SHIFTING EAST OF THE FORECAST AREA...BUT SHOULD CONTINUE TO KEEP
CLOUDS TO A MINIMUM AND PRECIP WEST OF THE AREA. THE COMBINATION OF
THIS AND AN ANOMALOUS THERMAL RIDGE WILL ALLOW TEMPS TO SOAR INTO
THE MID/UPR 70S...WITH A FEW 80 DEGREE READINGS IN THE SOUTHERN CWFA
MON AFTN.

BROAD SFC TROUGH OVER THE CENTRAL/NORTHERN PLAINS WILL SLOWLY
CONSOLIDATE AS THIS FEATURE NEARS THE GREAT LAKES MON EVE. THERE IS
A SMALL CHANCE THAT A FEW SHOWERS/THUNDERSTORMS COULD SKIRT THE
NORTHERN CWFA MON AFTN...BUT EXPECT THE BULK OF THE PRECIP TO OCCUR
POST SUNSET. MID-LVL TROUGH WILL AMPLIFY ACROSS THE CENTRAL PLAINS
TUE MORNING...AS THE SFC LOW DEEPENS ACROSS LOWER MICHIGAN. HAVE
HELD ONTO THE MENTION OF THUNDER INTO TUE MORNING...AS IT APPEARS
SOME INSTABILITY/FORCING WILL CONTINUE. MON NGT TEMPS WILL LIKELY
NOT FALL MUCH...PRODUCING A MILD OVERNIGHT. THEN FOR TUE WITH
CONTINUED CLOUD COVER/PRECIP...EXPECT TEMPS TO REMAIN IN THE UPR
50S/LOW 60S. DEPENDING ON THE TIMING OF THE FROPA TUE...TEMPS COULD
BEGIN TO FALL TUE AFTN INTO THE LOW 50S.

WEDNESDAY THROUGH FRIDAY...
FOR THE SECOND HALF OF THE WEEK IT APPEARS THE PATTERN WILL BE
TRANSITIONING TOWARDS A COOLER AND SOMEWHAT ACTIVE SETUP. ENSEMBLES
CONTINUE TO PROG MID-LVL RIDGING DEVELOPING ACROSS THE WESTERN
CONUS...ALLOWING BROAD TROUGHING DOWNSTREAM FOR THE GREAT LAKES
REGION WED/THUR. THEN FRI THE 500MB RIDGE MAY BEGIN TO FURTHER
AMPLIFY AS A POTENT SHORTWAVE IS PROGGED TO APPROACH THE PAC-NW AND
RIDGING REMAINS ACROSS THE NORTH ATLANTIC. TROUGHING WILL LINGER
ACROSS THE GREAT LAKES FRI. TEMPS WILL TREND BACK TOWARDS
SEASONAL...WITH PERHAPS FRI BEING SUB-SEASONAL WITH HIGHS IN THE UPR
40S/LOW 50S. PERIODIC CHANCES FOR SHOWERS THROUGHOUT THE EXTENDED
TIMEFRAME.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* 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 09Z...

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

* LOW TO 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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