Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 310820
AFDLOT

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

.SHORT TERM...
320 AM CDT

THROUGH TONIGHT...

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

&&

.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 06Z...

* FOG THIS MORNING...WITH MVFR/IFR VIS LIKELY.

RODRIGUEZ

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

HIGH PRESSURE CENTERED ACROSS THE REGION WILL HELP FOR DRY/VFR
CONDITIONS WITH LIGHT WINDS THIS FORECAST PERIOD. HOWEVER...FOG
IS DEVELOPING OVER MUCH OF THE AREA EARLY THIS MORNING AND EXPECT
THIS TO PERSIST THROUGH THE MORNING. DO THINK VIS WILL RANGE FROM
1-3 MILES...BUT WILL NEED TO MONITOR VIS POSSIBLY DROPPING BELOW
THIS FOR A TIME LATER THIS MORNING. FOG WILL DISSIPATE BEFORE MID
MORNING...WITH LIGHTER WINDS MAKING WAY FOR A WIND SHIFT TO THE
EAST WITH LAKE INFLUENCE. SPEEDS WILL REMAIN WELL BELOW 10 KT
THOUGH.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH FOG/VIS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//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...DENSE FOG ADVISORY...ILZ006-ILZ022-ILZ023 UNTIL 9 AM MONDAY.

IN...DENSE FOG ADVISORY...INZ001-INZ002-INZ010-INZ011 UNTIL 9 AM
     MONDAY.

LM...DENSE FOG ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM MONDAY.

&&

$$

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