Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 301936
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
236 PM CDT SUN AUG 30 2015

.SHORT TERM...

TONIGHT AND MONDAY...

230 PM...PRIMARY FORECAST CONCERN IS DENSE FOG POTENTIAL TONIGHT
INTO MONDAY MORNING.

CLOUD COVER HAS BEEN SLOW TO SCATTER THIS AFTERNOON WITH SOME BREAKS
SHOWING UP ACROSS NORTHWEST IL AND OVER PORTIONS OF THE LAKE. CLOUD
COVER IS STEADILY ERODING FROM THE NORTHWEST ACROSS CENTRAL WI. THE
TREND FROM GUIDANCE IS FOR THIS SCATTERING AND POSSIBLE CLEARING TO
CONTINUE ACROSS THE AREA THIS EVENING AND HAVE MAINTAINED THIS IN
THE GRIDS BUT CONFIDENCE REGARDING CLEARING IS LOW. CLOUD TRENDS
WILL LIKELY HAVE A LARGE IMPACT ON FOG POTENTIAL TONIGHT. WINDS WILL
BECOME CALM IN MANY LOCATIONS TONIGHT AND IF CLOUDS DO SCATTER/CLEAR
THEN AS TEMPS DROP TO THE DEWPOINTS...AREAS OF FOG WILL DEVELOP BUT
MAY BECOME DENSE. CONFIDENCE REGARDING HOW WIDESPREAD DENSE FOG MAY
BECOME IS LOW AND SO NO MENTION AT THIS TIME...BUT TRENDS WILL NEED
TO BE MONITORED INTO THIS EVENING. IN ADDITION...WHILE FOG DID LIFT
OVER THE NEARSHORE WATERS...THERE STILL REMAINS SOME PATCHY FOG
WHICH MAY THICKEN AND THEN SPREAD INTO FAR NORTHEAST IL THIS EVENING.

CHANCE OF SHOWERS AND PERHAPS AN ISOLATED THUNDERSTORM THIS
AFTERNOON INTO THIS EVENING HAS SHIFTED A BIT FURTHER SOUTH AND MAY
JUST AFFECT THE FAR SOUTHERN CWA THRU EARLY EVENING. MAINTAINED LOW
CHANCE POPS FOR THIS POTENTIAL...BUT AFTER THIS EVENING...DRY
WEATHER CAN BE EXPECTED THRU MONDAY EVENING.

THE CLOUD COVER HAS HELD TEMPS DOWN THIS AFTERNOON...BUT TEMPS ARE
STILL WARMING THRU THE 70S AND SOME LOWER 80S MAY STILL BE POSSIBLE
WHERE THE SUN BREAKS OUT. IF THE FOG CAN BURN OFF FAIRLY QUICKLY
MONDAY MORNING WITH AT LEAST PARTLY CLOUDY SKIES...THEN MID 80S ARE
POSSIBLE WITH COOLER TEMPS NEAR THE LAKE. THESE TEMPS COMBINED WITH
DEWPOINTS IN THE UPPER 60S/LOWER 70S MAY PUSH HEAT INDEX VALUES INTO
THE LOWER 90S MONDAY AFTERNOON. CMS

&&

.LONG TERM...
235 PM CDT

MONDAY NIGHT THROUGH SUNDAY...

WEAK MID-LVL WAVE CONTINUES TO BE ADVERTISED BY A FEW OF THE
OPERATIONAL GUIDANCE SOLUTIONS...WHICH COULD TOUCH OF A FEW
SHOWERS/THUNDERSTORMS ACROSS THE REGION. CONFIDENCE IS DIMINISHING
WITH THIS SCENARIO IN THE MON NGT/TUE TIMEFRAME. HAVE TRIMMED BACK
POPS FOR TUE...BUT HELD ONTO A SLIGHT CHANCE TUE AFTERNOON FOR ANY
DIURNALLY DRIVEN PRECIP THAT MAY DEVELOP ALONG THE EASTERN HALF OF
THE CWFA. OTHERWISE WILL MAINTAIN A DRY FORECAST IN THE MON NGT/TUE
TIMEFRAME.

LOW LEVEL RIDGE CENTERED OVER THE MID-ATLANTIC REGION WILL KEEP A
SOUTHERLY TO SLIGTHLY SOUTHWESTERLY FLOW OVER THE FORECAST
AREA...WITH A PLUME OF BETTER MOISTURE STREAMING NORTH FROM THE GULF
OF MEXICO. THIS SHOULD MAINTAIN SLIGHTLY ELEVATED PWAT VALUES. TEMPS
WILL GENERALLY BE IN THE MID/UPR 60S AT NIGHT AND MID/UPR 80S DURING
THE AFTN HOURS.

WEDNESDAY THROUGH SATURDAY... BROAD MID-LVL RIDGE REMAINS CENTERED
OVER THE REGION...WITH THE BEST FORCING REMAINING SHIFTED TO THE
NORTH. THIS SHOULD KEEP THE BULK OF SHOWERS/THUNDERSTORMS IN THE
LONGER TERM NORTH OF THE FORECAST AREA. ENSEMBLES CONTINUE TO
SUPPORT A DRY EXTENDED...ALTHOUGH A DIURNALLY DRIVEN SHOWER/STORM
COULD STILL DEVELOP BUT THE ORGANIZATION OR COVERAGE SHOULD REMAIN
VERY MINIMAL.

WARM THERMAL RIDGE IN THE MID-LVLS CONTINUES TO BE PROGGED
UNDERNEATH...WHICH SHOULD ALLOW TEMPS TO APPROACH THE UPR 80S TO
NEAR 90. THE LIMITING FACTOR COULD BE HOW MUCH CLOUD COVER DEVELOPS
ALONG WITH LLVL MOISTURE. LATER IN THE WEEK HEADING INTO THE LABOR
DAY WEEKEND...ENSEMBLES ARE HINTING AT A PATTERN CHANGE THAT COULD
FEATURE THE STRONG MID-LVL HEIGHTS LOWERING AND BRINGING AN ACTIVE
PATTERN BACK TO THE REGION FOR NEXT SATURDAY.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* MVFR LIFTING TO VFR BY EARLY AFTERNOON.

* MVFR/IFR VSBY IN FOG LATE TONIGHT.

KREIN

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE REMAINS CENTERED OVER THE ERN CONUS WITH RIDGING
EXTENDING WEST TO THE MIDDLE MISSISSIPPI VALLEY WHILE A TROUGH OF
LOW PRESSURE DEVELOPS OVER THE WESTERN PLAINS. NRN IL/IN REMAINS
UNDER THE INFLUENCE OF THE HIGH WITH LIGHT AND VARIABLE WINDS. THE
STRATUS THAT DEVELOPED LAST NIGHT HAS BEEN SLOW TO IMPROVE THOUGH
VISIBILITY HAS IMPROVED TO VFR AT ALL OF THE TERMINALS. A
PERSISTENT INVERSION BASED AT ARND 2500FT HAS HELPED KEEP BKN-OVC
CIGS...THOUGH BASES HAVE LIFTED TO MVFR THROUGH THE MORNING. HAVE
BACKED OFF ON THE TIMING OF SKIES SCATTERING UNTIL 21Z AS THE
LATEST VIS SATELLITE IMAGERY HAS SHOWED SOME THINNING OF CLOUD
COVER TO THE SOUTH OF THE TERMINALS...BUT HAVE SOME RESERVATIONS
ABOUT THE NEW 21Z TIMING FOR SCATTERING. THE LATEST MODEL
SOUNDINGS STILL INDICATE THAT THE INVERSION SHOULD WEAKEN BY EARLY
EVENING AND THAT SKIES SHOULD STILL BE ABLE TO CLEAR OVERNIGHT...
BUT HAVE DECREASING CONFIDENCE IN THE INVERSION WEAKENING ENOUGH
TO ALLOW FOR DRIER AIR TO MIX TO THE LOWER LEVELS OF THE
ATMOSPHERE. HOWEVER...CONFIDENCE IS ALSO NOT HIGH ENOUGH TO MAKE
SGFNT CHANGES AT THIS TIME...SO WILL CONTINUE THE TREND OF BR
DEVELOPING AGAIN TONIGHT AS WINDS SHOULD BE WEAK TO NEAR CALM WITH
A VERY WEAK PRESSURE GRADIENT REMAINING IN PLACE. PLUS IF SKIES DO
CLEAR...RADIATIONAL COOLING SHOULD ALLOW FOR BR/FG TO DEVELOP
OVERNIGHT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE IN TIMING OF CONDITIONS IMPROVING TO VFR.

* LOW-MEDIUM CONFIDENCE IN VSBY TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

MONDAY NIGHT THROUGH SATURDAY...VFR. PRIMARILY SOUTH/SOUTHWEST
WINDS.

IZZI

&&

.MARINE...
235 PM CDT

RATHERN BENIGN PATTERN CONTINUES ACROSS THE WESTERN GREAT
LAKES...WHICH WILL LIKELY ALLOW AREAS OF FOG TO ONCE AGAIN DEVELOP
TONIGHT AND COULD LINGER INTO MONDAY AFTERNOON/EVENING. A WEAK LOW
PRESSURE WILL LIFT NORTHEAST OF LAKE SUPERIOR...WHICH COULD ALLOW A
SLIGHT INCREASE IN THE WINDS FOR THE NORTHERN PORTIONS OF THE LAKE
MON/MON NGT.

HIGH PRESSURE OVER THE CENTRAL PLAINS WILL SLIDE EAST TOWARDS THE
OHIO VALLEY...THEN REMAIN ANCHORED THROUGH THE END OF THE WEEK. THIS
WILL MAINTAIN A SOUTHERLY FLOW FOR MUCH OF THE LAKE...WITH ONLY A
BRIEF BUMP IN THE GRADIENT AND WINDS MON NGT/TUE.

BEACHLER

&&

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

$$

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