Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 311625
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1125 AM CDT MON AUG 31 2015

.UPDATE...
1117 AM CDT

MAIN QUESTIONS FOR TODAY PERTAIN TO POSSIBILITY OF FOG ALONG
PORTIONS OF THE LAKESHORE...AND THEN DEGREE OF AFTERNOON HEATING
ELSEWHERE. OVERALL THE TEMPERATURE TRENDS APPEAR TO BE ON
TRACK...SO NO CHANGES ARE CURRENTLY PLANNED FOR AFTERNOON HIGHS
AND WOULD EXPECT TO ONLY NEED A TWEAK OF A COUPLE OF DEGREES AT
MOST. THE QUESTION OF FOG IS MORE UNCERTAIN. HAZE IN SEVERAL
LOCATIONS IS KEEPING THE VISIBILITY IN THE 5 TO 7 MILE RANGE...BUT
WEBCAMS AND SATELLITE PICS ARE HINTING AT THE PRESENCE OF
LINGERING FOG OVER THE LAKE IN SOME AREAS. IF THIS SHOULD PERSIST
AND WANDER ONSHORE...LOCATIONS NEAR THE LAKE COULD SEE VISIBILITY
DROP CLOSER TO THE 1 MILE RANGE...THOUGH THIS WOULD STILL BE ABOVE
HEADLINE THRESHOLDS.

LENNING

&&

.SHORT TERM...
320 AM CDT

THROUGH TONIGHT...

BIG FORECAST CHALLENGE THROUGH TONIGHT IS FOG EARLY THIS
MORNING...THEN SMOKE AND ITS POTENTIAL IMPACT ON TEMPS. DENSE SMOKE
WAS APPARENT SUNDAY AFTERNOON TO OUR WEST AND NORTHWEST OVER
WISCONSIN AND IOWA. TO SEE A MAP SHOWING SMOKE LOCATION AND DENSITY
CHECK OUT OUR TWITTER (@NWSCHICAGO) AND FACEBOOK (/NWSCHICAGO)
INCLUDING A LINK TO WHERE THAT MAP AND OTHER INFORMATION CAN BE
FOUND.

FOR TODAY EXPECT FOG TO BURN OFF RATHER QUICKLY THIS MORNING LEAVING
MOSTLY SUNNY SKIES (THOUGH LIKELY HAZY THANKS TO THE SMOKE) IN ITS
WAKE. HAVE LEANED TOWARD THE COOL SIDE OF GUIDANCE TODAY DUE TO
SMOKE...THOUGH IT IS UNCLEAR HOW DENSE SMOKE WILL BE TODAY. LESS
SMOKE MEANS TEMPS COULD BE A DEGREE OR TWO WARMER AND DENSER SMOKE A
BIT COOLER PERHAPS. GRADIENT LOOKS TO BE LIGHT ENOUGH TO ALLOW A
LAKE BREEZE TODAY WHICH SHOULD KEEP TEMPERATURES IN THE 70S ALONG
THE IMMEDIATE LAKEFRONT. SOME PATCHY FOG COULD DEVELOP AGAIN
TONIGHT...THOUGH AS LOW LEVELS SLOWLY DRY OUT A BIT WILL PROBABLY
SEE LESS FOG THAN THIS MORNING.

IZZI

&&

.LONG TERM...
320 AM CDT

TUESDAY THROUGH SUNDAY...

TODAY MAY BE THE LAST DAY OF METEOROLOGICAL SUMMER...BUT IT WOULD
APPEAR THAT MOTHER NATURE FAILED TO GET THE MEMO AS A STRETCH OF
VERY WARM TO ALMOST HOT WEATHER THROUGH NEXT WEEKEND WITH
UNUSUALLY STRONG UPPER LEVEL RIDGE OVER THE REGION. LINGERING
SLIGHT WEAKNESS IN THE UPPER RIDGE FROM INDIANA SOUTH TO THE LOWER
OHIO VALLEY COULD ALLOW FOR A SLIGHT CHANCE OF MAINLY
AFTERNOON/EARLY EVENING ISOLATED STORMS THROUGH TUESDAY...THOUGH
POPS OF 20 PERCENT OR LESS LOOK APPROPRIATE. MEDIUM RANGE GUIDANCE
HINTS AT POSSIBLE CONVECTION WITH VERY SUBTLE DISTURBANCES LATE IN
THE WEEK...BUT AGAIN KEPT POPS BELOW MENTIONABLE LEVELS GIVEN THE
WEAK FORCING AND INABILITY TO REALLY PINPOINT ANY ORGANIZED
FORCING AT THIS DISTANCE.

BIG STORY THIS WEEK WILL BE THE WELL ADVERTISED HEAT WAVE THAT
SHOULD GET GOING IN FULL FORCE TOMORROW. ECMWF/NAM/GFS ALL PROG
925MB TEMPS AROUND 25-26C WHICH IS PUSHING THE LIMITS OF CLIMO FOR
EARLY SEPTEMBER. USING THE NEW SPC SOUNDING CLIMO TOOL
(WWW.SPC.NOAA.GOV/EXPER/SOUNDINGCLIMO) THE 7 DAY RUNNING AVERAGE
925MB FOR THIS WEEK IS AROUND 19-20C WITH 24C THE 90TH PERCENTILE.
OUR 925MB TEMPS ARE PROGGED TO BE CLOSE TO 3 STANDARD DEVIATIONS
ABOVE AVERAGE WITH CLIMO SUPPORTING HIGHS IN THE LOW/MID 90S WITH
925MB TEMPS OF 25C...HOWEVER DEWPOINTS LOOK TO BE A BIT HIGHER
THAN NORMAL FOR A SEPTEMBER HEAT WAVE AND ALSO THERE IS THE BIG
SMOKE WILDCARD...SO KEPT TEMPS A BIT BELOW WHAT 925MB TEMP CLIMO
WOULD SUPPORT.

SURFACE GRADIENT COULD BE STRONG ENOUGH TO PREVENT ANY SIGNIFICANT
LAKE BREEZE TUES AND WED ALLOWING THE HEAT TO REACH RIGHT UP TO
THE BEACHES...WEAKER GRADIENT LOOKS TO ALLOW SOME LAKE COOLING
LATE IN THE WEEK AND POSSIBLY OVER THE WEEKEND. OUTSIDE OF ANY
LAKE COOLING TEMPS LOOK LIKELY TO REMAIN IN THE UPPER 80S/NEAR 90
THROUGH THE UPCOMING WEEKEND.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* SLIGHT LAKE BREEZE THIS AFTERNOON BUT WIND SPEEDS UNDER 8KT.

* MVFR FOG TO RETURN TONIGHT...NOT AS DENSE AS THIS AM.

MM

//DISCUSSION...UPDATED 12Z...

MAIN FORECAST CONCERN THIS PERIOD IS WITH FOG AND VERY LOW VIS IN
THE NEAR TERM. DENSE FOG HAS MOVED OVER MOST TERMINALS EARLY THIS
MORNING AND WILL PERSIST OVER THE NEXT 1-2 HOURS...BUT WITH PATCHY
FOG POSSIBLY LINGERING INTO 15Z. THEN EXPECT VFR CONDITIONS FOR
THE REMAINDER OF THE DAY. PATCHY FOG WILL ONCE AGAIN BE POSSIBLE
LATER TONIGHT...WITH AT LEAST MVFR VIS POSSIBLE AT THIS TIME.
LIGHT WINDS THIS MORNING WILL MAKE WAY FOR A WIND SHIFT TO THE
EAST SOUTHEAST WITH LAKE INFLUENCE...WITH SPEEDS REMAINING WELL
BELOW 10 KT.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* MEDIUM CONFIDENCE WITH FOG/VIS.

MM

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR.

WEDNESDAY...VFR.

THURSDAY...SLIGHT CHANCE OF TSRA.

FRIDAY...VFR.

SATURDAY...VFR.

SUNDAY...SLIGHT CHANCE OF TSRA.

RODRIGUEZ

&&

.MARINE...
406 AM CDT

AS A LARGE RIDGE OF HIGH PRESSURE REMAINS NEARLY STATIONARY OVER
THE EASTERN THIRD OF THE COUNTRY THROUGH THIS WEEK WHILE ANY LOW
PRESSURE SYSTEMS TRACK TO THE NORTH OF THE LAKE...SOUTHERLY WINDS
WILL BE OBSERVED OVER THE LAKE. AREAS OF FOG WITH PATCHY DENSE FOG
HAS DEVELOPED ONCE AGAIN ACROSS THE LAKE THIS MORNING WITH THE
MORE DENSE FOG BEING OBSERVED OVER THE NEARSHORE WATERS. THIS
DENSE FOG WILL LIKELY PERSIST THROUGH THIS MORNING...WITH AREAS OF
FOG STILL LIKELY LATER TODAY AND TONIGHT.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...NEARSHORE WINTHROP HARBOR TO NORTHERLY IS UNTIL 10 PM MONDAY.

&&

$$

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