000
FXUS63 KLOT 161940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
240 PM CDT SUN JUN 16 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 18Z...

* NONE.

JEE

//DISCUSSION...UPDATED 18Z...

A BROAD AREA OF LOW PRESSURE STRETCHES FROM MANITOBA THROUGH NEW
YORK AND A STATIONARY FRONT LIES ACROSS NORTHERN IL. WINDS ARE
MUCH LIGHTER THAN PREVIOUSLY EXPECTED DUE TO THE WEAK BOUNDARY AND
A LAKE BREEZE HAS FORMED. STILL EXPECTING THE LAKE BREEZE TO
REMAIN EAST OF THE TERMINALS. DRIER AIR IS SLOWLY PUSHING IN AND
THE MVFR STRATUS DECK IS LIFTING AND MOVING SE OUT OF THE
TERMINALS. EXPECTING SKIES TO CLEAR FROM NW TO SE AND WINDS WILL
DIMINISH ACROSS THE REGION TO LESS THAN 5 KT OVERNIGHT AS THE
GRADIENT WEAKENS. MAY SEE FOG AT DPA LATE TONIGHT...BUT KEPT FOG
OUT OF THE TAF FOR NOW AS CONFIDENCE IS LOW TO MEDIUM.

EXPECTING SW WINDS ARND 10 KT BY MID MONDAY MORNING AND WINDS
WILL REMAIN ARND 10 KT AS THE THE LOW SINKS SOUTH DOWN THE LAKE
AND THE GRADIENT TIGHTENS. WINDS MAY BECOME MORE WESTERLY OR EVEN
WNW LATE MONDAY AFTERNOON DEPENDING ON HOW QUICKLY THE LOW
PROGRESSES. SHOWERS AND THUNDERSTORMS MAY ACCOMPANY THE LOW AND
MOVE IN MONDAY AFTN/EVENING. HOWEVER KEPT THE TAFS DRY BECAUSE
MODEL SOUNDINGS LOOK VERY DRY AND LIMITED MOISTURE WILL PROBABLY
LIMIT PRECIP COVERAGE.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS.

JEE

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

MON...VFR. CHC TSRA.

TUE THROUGH THU...VFR. NO SIG WX.

FRI...VFR. SLGT CHC TSRA.

TRS

&&

.MARINE...
404 PM CDT

LARGE HIGH PRESSURE OVER THE EASTERN UNITED STATES WILL SLOWLY
CONTINUE EAST WHILE A TROUGH OF LOW PRESSURE AND FRONTAL BOUNDARY
OVER THE UPPER MISSISSIPPI VALLEY SHIFT EAST ACROSS THE LAKE
TONIGHT. WITH THIS IN PLACE...EXPECT GENERALLY SOUTHERLY FLOW TO
SPAN THE LAKE BEFORE WINDS TURN MORE TO THE SOUTHWEST OVERNIGHT.
WEAK HIGH PRESSURE WILL THEN BUILD EAST ACROSS THE SOUTHERN GREAT
LAKES ON SUNDAY...WITH A TROUGH OF LOW PRESSURE EXTENDING FROM
SOUTHERN QUEBEC WEST TO SOUTHERN ONTARIO. THIS TROUGH OF LOW
PRESSURE WILL SLOWLY SHIFT SOUTH DOWN THE LAKE SUNDAY NIGHT INTO
MONDAY. WESTERLY WINDS WILL TURN TO THE NORTHWEST AND NORTH AS
THIS TROUGH AND ASSOCIATED BOUNDARY WORK DOWN THE LAKE. WINDS AND
WAVES WILL INCREASE BEHIND THIS TROUGH/BOUNDARY...BUT STILL
REMAINING AT 10 TO 20 KT. HIGH PRESSURE WILL THEN MOVE SOUTHEAST
FROM THE CANADIAN PRAIRIES INTO THE GREAT LAKES BEHIND THIS FRONT
BY MIDWEEK.

RODRIGUEZ

&&

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

$$

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