Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 240827
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
327 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 06Z...

* MVFR CIGS/VIS DURG THE LATE NIGHT/EARLY MORNING HOURS. CHANCE
  CIGS COULD DROP TO IFR LEVELS.

KREIN

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

FOLLOWING THE PASSAGE OF A WEAK SFC TROUGH...ANY RESIDUAL PCPN
REMAINS ISOLD AND SOUTH OF THE TERMINALS. HOWEVER...THERE IS SOLE
RESIDUAL LOW LEVEL MOISTURE AND AS HIGH CLOUD PUSHES AWAY...A BAND
OF STRATUS CAN BE SEEN IN THE LATEST SATELLITE IMAGERY. AS A
NOCTURNAL SUBSIDENCE INVERSION LOWERS OVERNIGHT...CLOUD BASES
SHOULD GRADUALLY LOWER TO LOWER END MVFR LEVELS. THERE IS A CHANCE
FOR SOME PATCHY IFR CIGS DURG THE EARLY MORNING HOURS...ESPECIALLY
OVER NWRN IL WHERE SOME RAIN FELL EARLIER...WHICH WOULD MOST
LIKELY AFFECT RFD AND POSSIBLY DPA. AS WINDS BECM LGT/VRBL
OVERNIGHT...VIS SHOULD DROP TO 3-5SM DURG THE EARLY MORNING
HOURS...AND IF THE WESTERN EDGE OF THE STRATUS DECK CAN ERODE OVER
NWRN IL BEFORE SUNRISE...THERE IS A CHANCE FOR RFD TO DROP INTO
IFR OR EVEN LIFR VIS LEVELS. HOWEVER...THAT WOULD BE HIGHLY
DEPENDENT ON THE CIG TRENDS.

THROUGH THE DAY ON FRIDAY...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...SOME OF THE MODELS ARE
SUGGESTING THAT THERE COULD BE SOME LIGHT PCPN WITH THE PASSAGE OF
THE NEXT SFC TROUGH. HOWEVER...SINCE FORCING WITH THIS TROUGH AXIS
LOOKS TO BE RATHER WEAK...CONFIDENCE IS TOO LOW TO ADD PCPN TO THE
TAFS AT THIS TIME.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/VIS TRENDS OVERNIGHT.

* LOW CONFIDENCE IN SPECIFIC TIMING OF IMPROVEMENT TO VFR FRIDAY.

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS THROUGH THE DAY ON
  FRIDAY.

* LOW CONFIDENCE IN THE CHANCES FOR PCPN FRIDAY EVENING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

* FRIDAY NIGHT...MAINLY DRY. MVFR/FOG POSSIBLE.
* SATURDAY...DRY/VFR. GUSTY WEST/NORTHWEST WINDS.
* SUNDAY...DRY/VFR. SOUTHEAST WINDS.
* MONDAY...DRY/VFR. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF SHRA. STRONG/GUSTY WESTERLY WINDS.
* WEDNESDAY...CHANCE OF SHRA. WEST-SOUTHWEST WINDS.

KMD

&&

.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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