Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 140801
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
301 AM CDT SUN SEP 14 2014

.DISCUSSION...
915 PM CDT

EVENING UPDATE...

SURFACE RIDGE OVERHEAD...DRY AIR MASS AND MOSTLY CLEAR SKIES ARE
PROVIDING NEARLY IDEAL RADIATIONAL COOLING SET-UP THIS EVENING.
PATCHY HIGH CLOUDS PASSING OVER THE REGION OVERNIGHT ARE NOT
EXPECTED TO HAMPER ATTAINING EXCEPTIONALLY COLD LOWS FOR MID
SEPTEMBER. HAVE MADE MINOR ADJUSTMENTS DOWNWARD IN LOW
TEMPERATURES FOR SOME PARTS OF THE AREA...YIELDING MID TO UPPER
30S OUTSIDE OF CHICAGO AND MID 40S IN AND NEAR DOWNTOWN CHICAGO.
ADDED PATCHY FOG WORDING IN FOR MORE OF THE AREA AS A RESULT OF
MINOR TEMPERATURE ADJUSTMENTS BUT NOT EXPECTING WIDESPREAD FROST
DUE TO WARM GROUND CONDITIONS AND NEARLY SATURATED SOIL FROM ALL
THE RAIN THIS WEEK. UPDATED ZONE FORECAST HAS BEEN SENT.

SEE THE CLIMATE AFD BELOW FOR A NOTE ON THE RECORD LOW IN CHICAGO
TONIGHT.

RC

//PREV DISCUSSION...
315 PM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH ANOTHER COLD NIGHT
TONIGHT...WITH FROST POSSIBLE ACROSS THE CWA.

QUIET BUT COOL AFTERNOON AS EARLY MORNING STRATUS LINGERED AND
THEN EXPANDED WITH STRATOCU STILL PRESENT OVER THE CWA. CONTINUED
CAA AND THIS CLOUD COVERED LIMITED DAYTIME WARMING TODAY WITH MOST
LOCATIONS ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA NOT
RISING OUT OF THE 50S TODAY. ANY LINGERING CLOUD COVER THIS
AFTERNOON WILL DIMINISH THROUGH THE EVENING WITH MOSTLY CLEAR
SKIES THEN EXPECTED TONIGHT. WITH HIGH PRESSURE CONTINUING TO
SHIFT EAST THIS EVENING AND THEN REMAINING SITUATED OVER THE CWA
TONIGHT INTO SUNDAY MORNING...SETUP FOR ANOTHER COLD NIGHT WILL BE
IN PLACE. SOME WEAK WAA IS STILL ANTICIPATED TONIGHT AS WINDS
BECOME MORE SOUTHERLY...BUT THIS SLIGHT WARMING MAY ARRIVE TOO
LATE TO HAVE AN OVERALL IMPACT ON LOW TEMPS TONIGHT. MADE ONLY
MINOR ADJUSTMENTS TO MIN TEMPS TONIGHT MAINTAINING MID TO UPPER
30S ACROSS NORTH CENTRAL ILLINOIS BUT DID LOWER TEMPS TO THE UPPER
30S OVER AREAS IN EAST CENTRAL ILLINOIS AND NORTHWEST INDIANA...AS
WELL AS EXPANDED MENTION OF FROST IN THE GRIDS. WITH WARMER
SURFACE TEMPS STILL IN PLACE AS WELL AS HIGHLY SATURATED
CONDITIONS OBSERVED OVER THE ENTIRE AREA...ANY FROST DEVELOPMENT
SHOULD REMAIN LIMITED TONIGHT AND HAVE NOT ISSUED ANY HEADLINES
THIS AFTERNOON BUT WILL CONTINUE MENTION IN THE ZONES/HWO.

SUNNY AND DRY CONDITIONS WITH SLIGHTLY WARMER TEMPS IN THE LOW TO
MID 60S EXPECTED ON SUNDAY...AS THIS HIGH PROGRESSES TO THE EAST.
INCREASING CLOUD COVER WILL BE OBSERVED SUNDAY NIGHT AND
ESPECIALLY TOWARDS EARLY MONDAY MORNING...WITH CHANCES FOR SHOWERS
INCREASING ACROSS NORTHERN ILLINOIS DURING THIS TIME. CURRENT
SHORT WAVE PROGRESSING EAST THROUGH THE NORTHERN PLAINS WILL
CONTINUE EAST TONIGHT THROUGH SUNDAY NIGHT AND EARLY MONDAY
MORNING...WITH ASSOCIATED SURFACE LOW/TROUGH DROPPING EAST
SOUTHEAST TOWARDS THE REGION. THIS WILL LIKEWISE KEEP MOST OF THE
PRECIP TO THE WEST AND NORTHWEST INTO EARLY MONDAY MORNING BUT
WITH PRECIP CHANCES INCREASING QUICKLY THROUGH MONDAY. A SECOND
AND STRONGER SHORTWAVE WILL MOVE IN BEHIND THE FIRST WAVE AND DIVE
SOUTHEAST TOWARDS THE CWA ON MONDAY...WITH SURFACE TROUGH PUSHING
THROUGH THE CWA. EXPECT AREA OF SHOWERS TO THEN MOVE THROUGH THE
CWA ON MONDAY WITH GUIDANCE IN AGREEMENT OF OVERALL TRENDS...AND
HAVE MAINTAINED LIKELY POPS IN THE GRIDS. PRECIP WILL THEN QUICKLY
DEPART MONDAY EVENING AS HIGH PRESSURE BUILDS BACK OVERHEAD.

RODRIGUEZ

&&

.CLIMATE...
915 PM CDT

THE RECORD LOW IN CHICAGO FOR SEPTEMBER 14TH IS 40 DEGREES SET IN
1985. WE ARE FORECASTING A LOW OF 41 AT CHICAGO-OHARE...SO A TIE
IS POSSIBLE AND A NEW RECORD NOT OUT OF THE QUESTION.

RC

&&

.AVIATION...

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

* POTENTIAL FOR FOG/STRATUS OVERNIGHT.

BMD

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

SHOULD BE A QUIET PERIOD OF WEATHER UNDER THE INFLUENCE OF HIGH
PRESSURE FOR THE LATEST TAF PERIOD EXCEPT FOR THE POSSIBILITY OF FOG
EARLY SUNDAY. THE HIGH IS CENTERED OVERHEAD TONIGHT RESULTING IN
VERY LIGHT WINDS...CALM AT TIMES. THIS ALONG WITH MOSTLY CLEAR SKIES
WILL SET THE STAGE FOR STRONG RADIATIONAL COOLING SO WILL HAVE TO
MONITOR FOG DEVELOPMENT OVERNIGHT AND SEVERAL MODELS DO HINT AT THE
POTENTIAL FOR DENSE FOG DEVELOPING. WITH TEMPERATURES ONLY A FEW
DEGREES FROM SATURATION ALREADY ACROSS MUCH OF THE REGION...HAVE
OPTED TO AT LEAST CONSERVATIVELY INTRODUCE VSBY RESTRICTIONS
OVERNIGHT AND MAY HAVE TO LOWER VSBY FURTHER. THE HIGH WILL SHIFT
EAST OF THE TERMINALS SUNDAY WITH MODEST SOUTHWESTERLY FLOW SETTING
UP FOR THE REMAINDER OF THE FORECAST PERIOD.

BMD

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

* LOW CONFIDENCE ON VSBY DETAILS LATE TONIGHT/EARLY SUNDAY.
* HIGH CONFIDENCE IN REMAINDER OF FORECAST.

BMD

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

MONDAY...SHOWERS LIKELY WITH MVFR. SOUTHWEST WINDS SHIFTING
NORTHWEST LATE.

TUESDAY...VFR. WEST TO NORTHWEST WINDS.

WEDNESDAY...VFR. NORTHWEST WINDS SHIFTING NORTHEAST IN THE
AFTERNOON.

THURSDAY...VFR. EAST WINDS.

FRIDAY...VFR. SOUTHEAST WINDS.

MDB

&&

.MARINE...
256 AM CDT

HIGH PRESSURE IS IN PLACE OVER SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH LIGHT SYNOPTIC FLOW ALLOWING LAND BREEZES/OFFSHORE
FLOW TO DEVELOP. FARTHER NORTH...SOUTHWEST WINDS HAVE BEGUN TO
FRESHEN UP AHEAD OF AN AREA OF LOW PRESSURE OVER SOUTHERN MANITOBA
THIS MORNING. WINDS ARE EXPECTED TO INCREASE INTO THE 20 TO 25 KT
RANGE...MAINLY OVER THE NORTH HALF OF THE LAKE BY LATER TODAY. A
COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN ON MONDAY TURNING WINDS
WEST/NORTHWEST. A SECONDARY FRONT WILL MOVE ACROSS THE LAKE
WEDNESDAY...BUT THE REMAINDER OF THE WEEK WILL SEE RELATIVELY
MODEST WINDS AS HIGH PRESSURE BUILDS BACK OVERHEAD. BMD

&&

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

$$

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