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000
FXUS63 KLOT 170541
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1241 AM CDT MON JUN 17 2013

.DISCUSSION...
238 PM CDT

ANTI-CYCLONIC FLOW OVER THE NORTHERN PLAINS WILL CONTINUE TO PROVIDE
AN INFLUENCE ACROSS THE WESTERN GREAT LAKES REGION TONIGHT. THE
GRADIENT REMAINS MINIMAL...ALLOWING WINDS TO DIMINISH OVERNIGHT TO
LESS THAN 10 KT. VISIBLE IMAGERY SHOWS THE BACK END OF THE CHANNEL
OF CLOUDS/BOUNDARY ORIENTED FROM SOUTHEAST IOWA STRETCHING NORTHEAST
THROUGH A PORTION OF THE SOUTHERN CWFA...THEN MEANDERING INTO LOWER
MICHIGAN. THE DEEPER MOISTURE WAS ALSO PEELING SOUTHEAST AWAY FROM
NORTHERN IL/NORTHWEST IN...ALLOWING THE CLOUD DECK TO THIN. ALSO
AIDING IN THINNING THE CLOUDS WAS THE MIXED LAYER...WHICH HAS BEEN
PRODUCING OCCASIONAL GUSTS TO 15-20MPH. THIS HAS PROVIDED SOME
SUBSIDENCE AT THE SFC...AS DEW POINTS ARE BEGINNING TO FALL INTO THE
UPR 50S/ARND 60 DEG.

GIVEN THE SFC WILL REMAIN MOIST...IT IS CONCEIVABLE THAT WITH
MINIMAL CLOUD COVER EXPECTED AND LIGHT WINDS SOME PATCHY FOG MAY
OCCUR ARND MIDNIGHT THROUGH DAYBREAK MON. TEMPS OVERNIGHT WILL COOL
TO ARND 60/LOW 60S.

CONFIDENCE...HIGH.

MONDAY THROUGH MONDAY NIGHT...
THE ANTI-CYCLONIC FEATURE WILL SLOWLY DRIFT SOUTHEAST ACROSS THE
OHIO VALLEY..WITH A DRY MID-LVL. THIS IS SUPPORTED BY GUIDANCE
SOUNDINGS. AT THIS TIME THE GREATEST CHALLENGE FOR MON WILL BE IF
THUNDERSTORMS DEVELOP...AND PLACEMENT/COVERAGE/TIMING. GUIDANCE HAS
BACKED OFF ON ARRIVAL OF PRECIP WITH A SLIGHTLY LONGER INFLUENCE
FROM THE DEPARTING SFC RIDGE...KEEPING THE LOW/MID LVLS DRY. AS A
RESULT HAVE REMOVED MENTION OF PRECIP PRIOR TO 18Z. THEN THE
CHALLENGE IS TRYING TO PIN-DOWN WHEN PRECIP MAY ACTUALLY OCCUR...AND
THE COVERAGE/INTENSITY OF POSSIBLE THUNDERSTORMS.

500MB WEAK TROUGH FEATURE SLIDES SOUTHEAST ACROSS THE UPPER MIDWEST
WITH A LOBE OF VORTICITY ASSOCIATED WITH THIS FEATURE. GUIDANCE
CONTINUES TO DIFFER ON PLACEMENT/TIMING OF PRECIP IN THE
AFTERNOON/EVENING HOURS. THE CURRENT CYCLE OF THE LOCAL HI-RES
GUIDANCE SUGGESTS THAT PRECIP MAY ACTUALLY HOLD OFF UNTIL CLOSER TO
00Z TUE AS A RESULT OF THE DEPARTING SFC RIDGE. A BOUNDARY WILL SAG
SOUTH AND EVENTUALLY REACH NORTHERN IL IN THE MID TO LATE AFTN
HOURS. THIS WILL SERVE AS A FOCAL POINT FOR BETTER LIFT. CLOUD COVER
DOES NOT APPEAR TO BE ABUNDANT. DESPITE GOOD SFC HEATING MOST OF THE
DAY...INSTABILITY DOES NOT APPEAR TO BE TOO ABUNDANT. SOUNDINGS
INDICATE CAPE WILL BE A FEW HUNDRED J/KG AFT 18Z. HOWEVER AS TIME
PROGRESSES INTO THE EVENING HOURS...BETTER MOISTURE WILL ARRIVE FROM
THE NORTHWEST ASSOCIATED WITH THE APPROACHING BOUNDARY. THUS IT
APPEARS THE MOST PROBABLE TIME FOR CONVECTION/PRECIP WILL OCCUR AFT
21Z AND CLOSER TO 00Z TUE.

TEMPS MON WILL WARM INTO THE LOW/MID 80S AGAIN. THERE WAS SOME
INITIAL INDICATIONS THAT A LAKE BREEZE MAY DEVELOP...HOWEVER WITH A
SLIGHTLY STRONGER FLOW AT 950MB...THIS BREEZE MAY REMAIN ANCHORED
ALONG THE SHORELINE OR POSSIBLY MOVING INLAND ACROSS LAKE COUNTY IL.

CONFIDENCE IN TEMPERATURES...HIGH.
CONFIDENCE IN PRECIPITATION/THUNDERSTORMS...LOW/MEDIUM.

TUESDAY THROUGH WEDNESDAY...
BROAD ANTI-CYCLONIC FEATURE CONTINUES TO BE POISED FOR ARRIVAL
TUE/WED ACROSS THE GREAT LAKES/OHIO VALLEY REGIONS. 850MB THERMAL
TROUGH OF 8 TO 10 DEG C COUPLED WITH A 500MB TROUGH...WILL KEEP
TEMPS IN THE 70S FOR MANY LOCATIONS BOTH DAYS. WITH AN ONSHORE FLOW
EXPECTED TUE...TEMPS ADJACENT TO LAKE MICHIGAN MAY REMAIN IN THE MID
60S. OVERNIGHT LOWS WILL EASILY RADIATE INTO THE 50S WITH LIGHT
FLOW. TUE NIGHT A FEW AREAS ALONG AND NORTH OF I-88 COULD SEE TEMPS
COOL INTO THE UPR 40S.

CONFIDENCE IN TEMPERATURES...HIGH.
CONFIDENCE IN DRY WEATHER...HIGH.

THURSDAY THROUGH SATURDAY...
EXTENDED FORECAST INDICATES SOME CHANGES WILL OCCUR IN THE LONGWAVE
PATTERN. THE MID-WEEK 500MB TROUGH OVER THE GREAT LAKES REGION WILL
SLOWLY DISSOLVE AS IT PIVOTS EAST. IN ITS WAKE WILL BE A DEVELOPING
MID-LVL RIDGE ACROSS THE PLAINS THUR. WITH A STRENGTHENING
MID-ATLANTIC RIDGE...THIS WILL SLOW THE DEPARTING/WEAKENING TROUGH
OVER THE NORTHEAST CONUS. THE BY-PRODUCT OF THIS WILL BE A
STRENGTHENING RIDGE IN THE MID CONUS AND A WARMING TREND TOWARDS THE
END OF THE UPCOMING WORK WEEK. 850MB THERMAL RIDGE WILL STEADILY
WARM WITH TEMPS PUSHING INTO THE LOW 20S IN THE CENTRAL PLAINS
THUR/FRI. THIS TONGUE OF WARM AIR WILL SLIDE EAST AND ARRIVE ACROSS
THE CWFA LATE IN THE WEEK...WITH SFC TEMPS WARMING INTO THE MID/UPR
80S FRI/SAT.

IN ADDITION THE STEADILY WARMING TEMPS LATE IN THE WEEK AND FIRST
HALF OF NEXT WEEKEND...MOISTURE WILL BE STREAMING NORTH FROM THE
WESTERN GULF INTO THE WESTERN OHIO VALLEY/GREAT LAKES. ENSEMBLES
CONTINUE TO POINT TOWARDS AN ACTIVE PERIOD OF WEATHER.

CONFIDENCE...MEDIUM/HIGH.

BEACHLER

&&

.AVIATION...

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

* WIND SHIFT MONDAY AFTERNOON.
* POTENTIAL FOR THUNDERSTORMS MONDAY AFTERNOON.

BMD

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

A WEAK PRESSURE GRADIENT IS IN PLACE LATE THIS EVENING AS A BROAD
FRONTAL TROUGH SLOWLY SAGS SOUTH ACROSS THE GREAT LAKES REGION.
WINDS WILL REMAIN FAIRLY LIGHT OVERNIGHT AND MAY GO VARIABLE AT
TIMES...BUT SHOULD GENERALLY KEEP A WESTERLY COMPONENT. DEEP MIXING
ON MONDAY WILL ALLOW WINDS TO PICK UP DURING THE DAYTIME AHEAD OF
THE FRONT...AND A FEW GUSTS INTO THE TEENS WILL BE POSSIBLE. THE
COLD FRONT IS EXPECTED TO MOVE FASTER DOWN THE LAKE AND THEN ONSHORE
AS AN ENHANCED LAKE BREEZE. IT SHOULD PASS OVER THE TERMINALS EARLY
TO MID EVENING WITH A SHARP SHIFT IN WINDS FROM W OR WNW TO NE.
MODEST INSTABILITY AHEAD OF THE FRONT MAY ALLOW A FEW THUNDERSTORMS
TO DEVELOP...BUT COVERAGE APPEARS TO REMAIN LOW AND MAY NOT IMPACT
THE TERMINALS. WILL MAINTAIN THE PROB30 FOR TSRA NOW BUT AT THIS
POINT SEE LITTLE CHANCE FOR UPGRADING THAT TO TEMPO/PREVAILING
LINE. STABLE AIR BEHIND THE FRONT SHOULD QUICKLY END THE THREAT
FOR PRECIP.

BMD


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

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS/TIMING.
* LOW CONFIDENCE IN THUNDERSTORMS IMPACTING TERMINALS.

BMD

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

TUESDAY THROUGH THURSDAY...VFR. NO SIGNIFICANT WEATHER.

FRIDAY AND SATURDAY...SLIGHT CHANCE OF TSRA.

LENNING

&&

.MARINE...
245 PM CDT

LOW PRESSURE OVER SOUTHERN ONTARIO WILL MOVE INTO SOUTHERN QUEBEC
OVERNIGHT TONIGHT...WHILE DRAGGING A COLD FRONT DOWN THE LENGTH OF
LAKE MICHIGAN...TURNING THE GENERALLY SOUTHERLY WINDS TO GENERALLY
NORTHERLY. WHILE COLD ADVECTION BEHIND THE FRONT MAY GENERATE A
FEW GUSTS TO 25 KT...WINDS SHOULD GENERALLY BE AROUND 10 TO 20 KT
WHILE AT THEIR STRONGEST MONDAY NIGHT. MEANWHILE...HIGH PRESSURE
WILL BUILD OUT OF THE NORTHERN ROCKIES AND SPREAD OVER THE
NORTHERN PLAINS ON MONDAY. THE HIGH PRESSURE WILL CONTINUE TO
SPREAD EAST ACROSS THE GREAT LAKES REGION AND WILL THEN DOMINATE
THE GREAT LAKES REGION THROUGH WEDNESDAY NIGHT. BY THURSDAY...A
TROUGH OF LOW PRESSURE AND AN ASSOCIATED COLD FRONT WILL MOVE OUT
OF THE ROCKIES INTO THE WESTERN PLAINS.

KREIN

&&

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

$$

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