Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 310254
AFDLOT

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

.UPDATE...839 PM CDT

MAIN CONCERN IS AGAIN WITH FOG POTENTIAL THANKS TO CALM
WINDS AND CLEAR SKIES WITH EXCEPTION OF HIGH-LEVEL HAZE FROM
WILDFIRE SMOKE. ONE OF THE TYPICAL SPOTS TO FOG UP...KARR...HAS
BEEN DOWN TO 2-3 MI VISIBILITY AS OF THIS WRITING...BUT ONLY A
FEW OTHER LOCATIONS WITH 5 MI VISIBILITY SO FAR. UNLIKE LAST
NIGHT...GFS LAMP GUIDANCE IS NOT HITTING THE FOG AS HARD. HOWEVER
...HI-RES GUIDANCE AND NAM DO SHOW DENSE FOG DEVELOPING IN PREDAWN
HOURS. WILL MONITOR TRENDS FOR NEXT FEW HOURS FOR POSSIBLY NEEDING
TO ISSUE A DENSE FOG ADVISORY. CURRENTLY DO NOT YET HAVE ENOUGH
CONFIDENCE TO ISSUE ONE. UPDATED ZONES WILL BE SENT SHORTLY.

RC

&&

.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 SLIGHTLY 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 03Z...

* POTENTIAL FOR FOG DEVELOPMENT OVERNIGHT.

BMD

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS CENTERED OVER THE MID-OHIO RIVER VALLEY THIS
EVENING PROVIDING LIGHT WINDS AND VFR CONDITIONS TO MUCH OF THE
REGION. A LAKE BREEZE HAS PUSHED ACROSS THE CHICAGO TERMINALS
TURNING WINDS EASTERLY...WHICH SHOULD VEER AND WEAKEN OVERNIGHT.
LIGHT AND AT TIMES CALM WINDS OVERNIGHT AND CLEAR SKIES SHOULD SET
THE STAGE FOR RADIATIONAL COOLING...THOUGH THE RELATIVELY THICK
SMOKE ALOFT THAT HAS SETTLED OVERHEAD MAY HINDER THIS PROCESS TO
SOME DEGREE. IN ADDITION...WHILE GUIDANCE DOES HINT AT THE
POTENTIAL FOR FOG DEVELOPMENT...IT ISNT AS PRONOUNCED AS
YESTERDAY. BACKED OFF ON THE TIMING SEVERAL HOURS AND TAPERED THE
MAGNITUDE SLIGHTLY AT THE CHICAGO TERMINALS.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* LOW CONFIDENCE IN VSBY TRENDS OVERNIGHT.

BMD

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

TUESDAY THROUGH THURSDAY... VFR. SOUTH TO SOUTHWEST WIND.
FRIDAY THROUGH SATURDAY...VFR. SOUTH TO SOUTHEAST WIND.

BMD

&&

.MARINE...
235 PM CDT

RATHER 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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