Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 241511
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1011 AM CDT FRI OCT 24 2014

.DISCUSSION...
326 AM CDT

SHORT TERM...THROUGH FRIDAY NIGHT...
FOR THE REMAINDER OF THE NIGHT AND INTO FRIDAY MORNING...THE INITIAL
CONCERN WILL BE CLOUD COVER...AND IMPACTS ON VISIBILITY.  FOLLOWING
THE PASSAGE OF A WEAK SFC TROUGH/PACIFIC-SOURCED WEAK COLD
FRONT...WEAK HIGH PRESSURE HAS BUILT ACROSS THE REGION.  A LOW
STRATUS DECK HAS BEEN IN PLACE FOLLOWING THE FROPA...BUT THE STRATUS
DECK IS ERODING IN PLACES...AND WITH CALM TO LGT/VRBL WINDS IN
PLACE...THE CLEARING LOCATIONS ARE EXPERIENCING RAPID FOG
DEVELOPMENT.  THE FOG IS INITIALLY MOSTLY IMPACTING NWRN IL...ARND
THE ROCKFORD AREA...BUT AS THE STRATUS CONTINUES TO
DISSIPATE...ADDITIONAL FOG MAY DEVELOP...BUT ANY DENSE FOG SHOULD BE
LIMITED TO NORTH CENTRAL AND NWRN IL...AWAY FROM THE CHICAGO METRO
AREA.  EXCEPT FOR LOCATIONS THAT CLEAR OUT...TEMPERATURES SHOULD
GENERALLY BOTTOM OUT IN THE LOWER TO MIDDLE 50S...EXCEPT FOR SOME
ISOLATED...SHELTERED LOW LYING AREAS...WHICH COULD RADIATE DOWN INTO
THE UPPER 40S.

FOR THE REMAINDER OF FRIDAY...THE WARMING TREND SHOULD CONTINUE AS
UPPER RIDGING CONTINUES TO BUILD OUT OF THE ROCKIES AND INTO THE
WESTERN PLAINS.  THE MORNING STRATUS AND STRATOCU SHOULD DISSIPATE
THROUGH THE MORNING HOURS...BUT TOTAL SUNSHINE WILL BE LIMITED AS A
THICK CIRRUS LAYER AND SOME MID LEVEL CLOUDINESS WILL OVERSPREAD THE
REGION THROUGH THIS AFTERNOON AND EVENING AS A STRONG UPPER LEVEL
JET STREAM DIVES OVER THE UPPER MISSISSIPPI VALLEY AND INTO THE
MIDWEST. THE SHORT RANGE GUIDANCE IS ALSO INDICATING SOME SHORTWAVE
ENERGY OVERTOPPING THE RIDGE THIS EVENING...WITH SOME GUIDANCE
INDICATING A LITTLE QPF.  HAVE A HARD TIME INTRODUCING ANY
MENTIONABLE POPS WITH THIS SYSTEM AS MOISTURE PROFILE FORECASTS ALSO
INDICATE LITTLE DEEP LAYER MOISTURE.  HOWEVER...SOME OF THE HIGH RES
SHORT TERM GUIDANCE IS SHOWING SOME INCREASE RH LATE FRIDAY NIGHT
UNDER INCREASINGLY SWLY FLOW...BUT AS FLOW OFF OF THE GULF OF MEXICO
WILL BE LIMITED BY HIGH PRESSURE RIDGING EXTENDING FROM THE CNTRL
APPALACHIANS THROUGH ERN TX...FEEL THAT THIS INCREASED RH COULD BE
MORE INDICATIVE OF SOME FOG POTENTIAL RATHER THAN PCPN POTENTIAL.
AS FOR TEMPERATURES...UNDER INCREASING LOW LEVEL WARM ADVECTION AND
BUILDING HEIGHTS ALOFT...EXPECT THAT TEMPERATURES FOR FRIDAY WILL
LIKELY BE AROUND 5 DEGREES HIGHER THAN THURSDAY WITH HIGHS IN THE
MIDDLE 60S. FRIDAY NIGHT SHOULD REMAIN MILD WITH DEWPOINTS
INCREASING INTO LOWER TO MIDDLE 50S THROUGH FRIDAY AND INTO FRIDAY
EVENING...SO OVERNIGHT LOWS SATURDAY MORNING SHOULD BE UNSEASONABLY
MILD...AND ONLY DROP INTO THE LOWER TO MIDDLE 50S.

KREIN

SATURDAY THROUGH MONDAY...
500MB TROUGH AXIS WILL BE PIVOTING EAST ACROSS THE GREAT LAKES
REGION...WITH A TRAILING FRONTAL BOUNDARY STRETCHING SOUTH AND
EXPECTED TO PUSH EAST ACROSS THE FORECAST AREA SATURDAY MORNING.
MID-LVL HEIGHTS WILL STEADILY RISE AS THE RIDGE PARKED ACROSS THE
CENTRAL CONUS PUSHES EAST...BRINGING MILDER AIR TO THE REGION SAT
WITH HIGHS IN THE MID/UPR 60S. THE FAR SOUTHERN CWFA COULD TOUCH 70
DEG SAT. TEMPS SUN ARE EXPECTED TO BE SLIGHTLY COOLER AS THE FLOW
BEGINS TO TRANSITION BRIEFLY INTO A QUASI-ZONAL SETUP. HOWEVER THIS
DOES NOT LOOK TO REMAIN VERY LONG...AS RIDGING RETURNS FOR MON AND
TEMPS SHUD QUICKLY WARM INTO THE 70S ACROSS MUCH OF THE AREA. A WARM
FRONTAL BOUNDARY WILL LIFT ACROSS THE AREA EARLY MON...AS SOUTHERLY
FLOW STRENGTHENS. EXPECT MUCH OF THE DAY MON TO REMAIN DRY...HOWEVER
LATE AFTN/EVE A DEVELOPING LOW ACROSS THE CENTRAL PLAINS MAY HELP TO
GENERATE A FEW SHOWERS/THUNDERSTORMS LATE MON.

TUESDAY-WEDNESDAY...
TOWARDS THE MIDDLE OF NEXT WEEK ENSEMBLES CONTINUE TO SUGGEST THE
RIDGING OVERHEAD WILL SHIFT EAST...WITH FLOW TRYING TO FLATTEN.
SUGGESTING THAT A SEMI-ZONAL SETUP MAY DEVELOP BY WED...WHICH WILL
LIKELY RESULT IN PERIODIC CHANCES FOR SHOWERS. TEMPS SHUD RETURN TO
MORE SEASONAL CONDS TUE/WED.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 15Z...

* MVFR CIGS/VSBY LIKELY AGAIN LATE TONIGHT. IFR CIGS/VSBY POSSIBLE.

MDB

//DISCUSSION...UPDATED 15Z...

CLOUDS CONTINUE TO ERODE FROM PWK TO DPA TO JOT TO PIA AND POINTS
EAST WITH A LARGE GAP IN COVERAGE HAVING DEVELOPED. EXPANSIVE AREA
OF LIFR AND LOWER CIGS/VSBY REMAINS PERSISTENT TO THE WEST. THE
EASTERN FLANK OF THIS HAS SHOWN SOME VERY SLOW DRIFT TO THE EAST
SO AM A LITTLE CONCERNED THAT CLOUDS COULD FILL IN A BIT AGAIN AT
DPA SO WILL KEEP SCATTERED MENTION THERE BUT THE LONGER IT TAKES
FOR ANY CLOUDS TO ARRIVE THERE THE HIGHER THEY WOULD LIKELY BE
THANKS TO SOME WARMING IN THE MEANTIME. OTHERWISE HAVE FURTHER
SLOWED IMPROVEMENT AT RFD AND MAY STILL BE A BIT FAST...ESPECIALLY
SINCE FAIRLY DENSE CIRRUS IS MOVING IN OVERHEAD. OTHERWISE LIGHT
AND VARIABLE SOUTHWEST TO NORTHWEST WINDS ARE EXPECTED.

MDB

FROM 12Z...

FOLLOWING THE PASSAGE OF A WEAK SFC TROUGH...HOWEVER...AN AREA OF
STRATUS FILTERED IN BEHIND THE WEAK BOUNDARY. LATEST SATELLITE
IMAGERY INDICATES THAT THE STRATUS IS BREAKING UP OVER NRN IL AND
IN LOCATIONS THAT HAD SEEN SOME PCPN YESTERDAY...MAINLY ARND THE
RFD AREA...SOME PATCHY DENSE FOG HAS FORMED...THOUGH OF THE TAF
SITES...ONLY RFD HAS OBSERVED THE DENSE FOG. BASED ON THE LATEST
HIGH RES MODEL GUIDANCE AND SATELLITE TRENDS...ANTICIPATE THAT
CONDITIONS SHOULD IMPROVE TO VFR OVER THE AREA BY LATE MORNING.

ANOTHER SFC TROUGH WILL TRACK ACROSS THE CNTRL PLAINS TO THE
UPPER MISSISSIPPI VALLEY BY EARLY EVENING. WINDS WILL BECOME SSWLY
THOUGH THE DAY...THOUGH WITH A WEAK PRESSURE GRADIENT...WIND
SPEEDS SHOULD BE LESS THAN 10KT THROUGH THE DAY. FOR THE EARLY
EVENING HOURS...A MODEST MID LEVEL IMPULSE IS EXPECTED TO CROSS
THE AREA INVOF THE WI/IL BORDER. THERE IS A CHANCE THAT THIS
SYSTEM COULD TRIGGER SOME ISOLD/SCT -SHRA...BUT CONFIDENCE IN
TIMING AND COVERAGE IS TOO LOW TO INCLUDE PCPN IN THE TAFS AT THIS
TIME. CONFIDENCE IS A LITTLE HIGHER THAT MORE FOG SHOULD DEVELOP
OVERNIGHT TONIGHT...PER THE LATEST HIGH RES MODEL RH
TIME SECTIONS...SO HAVE INTRODUCED IFR VIS FOR LATE THIS EVENING
AND OVERNIGHT. SOME GUIDANCE IS POINTING TOWARD THE POSSIBILITY OF
VIS DROPPING TO 1/4SM...BUT GIVEN THE AMOUNT OF CLOUD COVER
EXPECTED...DO NOT HAVE HIGH ENOUGH CONFIDENCE TO DROP VIS LOWER
THAN 1SM FOR NOW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 15Z...

* MEDIUM CONFIDENCE IN CIG TRENDS LATE TONIGHT.

* LOW TO MEDIUM CONFIDENCE IN VSBY TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

MDB

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

SATURDAY NIGHT...VFR. WX NIL.

SUNDAY...VFR. WX NIL.

MONDAY...VFR. WX NIL.

MONDAY NIGHT AND TUESDAY...CHANCE SHRA/SLIGHT CHANCE TSRA.

TUESDAY NIGHT...SLIGHT CHANCE SHRA.

WEDNESDAY AND THURSDAY...VFR. WX NIL.

KREIN

&&

.MARINE...
215 AM CDT

A WEAK RIDGE OF HIGH PRESSURE EXTENDS FROM WESTERN QUEBEC
SOUTHWEST THROUGH THE CENTRAL GREAT LAKES...INTO THE TENNESSEE
VALLEY. THIS RIDGE WILL CONTINUE TO DRIFT EAST OF THE REGION THIS
AFTERNOON...MEANWHILE A TROUGH OF LOW PRESSURE OVER CENTRAL CANADA
CONTINUES TO SLIDE EAST TOWARDS HUDSON BAY SATURDAY. THE GRADIENT
WILL REMAIN LIGHT THROUGH THIS AFTERNOON...THEN SLOWLY TURN
SOUTH/SOUTHWESTERLY. AS THE LOW NEARS HUDSON BAY ON SATURDAY...A
FRONTAL BOUNDARY WILL TRAIL AND SLOWLY SLIDE SOUTH ACROSS LAKE
MICHIGAN. THIS WILL RESULT IN WINDS TURNING WEST/NORTHWEST
SATURDAY AFTERNOON/EVENING. COOLER AIR WILL FLOW ACROSS THE LAKE
ALONG WITH A TIGHTENING GRADIENT...RESULTING IN INCREASING WINDS
NEARING 30KT AT TIMES. THEN ANOTHER RIDGE OF HIGH PRESSURE WILL
QUICKLY SLIDE SOUTHEAST FROM THE UPPER MIDWEST/NORTHERN PLAINS
SUNDAY...STEADILY DIMINISHING THE GRADIENT. ANOTHER TROUGH OF LOW
PRESSURE IS EXPECTED TO DEVELOP EARLY NEXT WEEK ACROSS THE CENTRAL
PLAINS...THEN APPROACH LAKE MICHIGAN CLOSER TO MID-WEEK. THIS WILL
BRING WINDS BACK TO THE SOUTHWEST WITH OCCASIONALLY WINDS GUSTING
TO 30KT.

BEACHLER

&&

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

$$

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