Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 241742
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1242 PM CDT THU JUL 24 2014

.DISCUSSION...
207 AM CDT

TODAY THROUGH TONIGHT...
EARLY THIS MORNING SKIES ARE GENERALLY CLEAR...WITH ONLY A FEW
HIGH BASED CLOUDS. TEMPS HAVE BEEN ABLE TO RADIATE INTO THE LOW
50S...AND JUST BEFORE DAYBREAK A FEW POINTS COULD DIP TO THE UPR
40S.

BROAD ANTI-CYCLONIC FLOW WILL CONTINUE TO DOMINATE THE REGION
TODAY...PROVIDING ABUNDANT SUNSHINE AND UNSEASONABLY COOL/DRY AIR
FOR A SECOND DAY. TEMPS SHUD BE ABLE TO HOLD GENERALLY IN THE MID
70S...HOWEVER WITH A NORTHEAST FLOW OFF OF LAKE MICHIGAN THE COOLER
MARINE AIR MAY KEEP TEMPS ALONG THE SHORELINE IN THE UPR 60S.

BY THIS AFTN THE SFC RIDGE AXIS WILL BE DRIFTING EAST ACROSS THE
OHIO VALLEY...WITH FLOW SLOWLY TURNING SOUTHERLY BY LATE TONIGHT.
DEPENDING ON THE TIMING...TEMPS COULD RADIATE IN THE LATE EVENING
BEFORE HOLDING STEADY OVERNIGHT IN THE MID/UPR 50S. A WEAK WAVE WILL
BE SLIDING EAST FROM THE DAKOTAS LATE TONIGHT...WITH SOME ISENTROPIC
MOISTENING ON THE LEE-SIDE ALLOWING FOR SOME SPOTTY SHOWERS AND
PERHAPS AN ISO TSRA JUST BEFORE DAYBREAK FRI IN THE WESTERN CWFA.

CONFIDENCE THRU TODAY...HIGH.
CONFIDENCE IN PRECIP OVERNIGHT/TEMPS...MEDIUM.

FRIDAY THROUGH SUNDAY...
500MB RIDGE OVER THE SOUTHERN PLAINS WILL BEGIN TO
FLATTEN...ALLOWING A QUASI-ZONAL FLOW ALONG THE NORTHERN PERIPHERY
WITH A SERIES OF WEAK MID-LVL VORTS SLIDING EAST INTO THE UPPER
MIDWEST/GREAT LAKES. GUIDANCE HAS A WEAK SFC WAVE MOVING EAST FROM
THE CENTRAL PLAINS INTO THE GREAT LAKES FRI BEFORE WEAKENING. THE
STRONGER MID-LVL VORTICITY MAXIMA REMAINS CONFINED ALONG THE HIGH
PLAINS/CANADIAN PRAIRIES FRI/SAT...WHICH WILL ALLOW A FEW ROUNDS OF
SHOWERS/THUNDERSTORMS TO PUSH ACROSS THE FORECAST AREA STARTING
FRI-SUN. AT THIS TIME THOUGH IT DOES APPEAR THE BEST CHANCE FOR
PRECIP FRI WILL BE IN THE EVENING HOURS.

A BOUNDARY LAYS OUT OVER THE MID-MISSOURI VALLEY STRETCHING EAST
THRU OHIO SAT AFTN/EVE. FOR THE SECOND HALF OF THE WEEKEND THE
PATTERN WILL ONCE AGAIN BE STARTING TO CHANGE TOWARDS A WESTERN
RIDGE AND GREAT LAKES TROUGH. THE SEMI-STATIONARY MID-LVL VORT OVER
THE HIGH PLAINS WILL SLIDE EAST EARLY SUN INTO THE NORTHERN GREAT
LAKES...WITH A SERIES OF WEAK SFC WAVES CONSOLIDATING OVER LOWER
MICHIGAN SUN MORNING.

TEMPS WILL START TO MODERATE OVER THE WEEKEND INTO THE UPR 70S/LOW
80S...AND WITH THE INCREASED LLVL MOISTURE DEW PTS WILL CREEP BACK
INTO THE MID/UPR 60S SAT EVE. THE FAR WEST/SOUTHWEST FORECAST AREA
COULD SEE DEW PTS BACK INTO THE LOW 70S.

THEN FOR SUN A FRONTAL BOUNDARY WILL BE SLIDING SOUTHEAST ACROSS THE
CWFA...HOWEVER TEMPS SHUD STILL BE ABLE TO REACH 80 TO THE LOW 80S.

CONFIDENCE...MEDIUM/HIGH.

MONDAY THROUGH THURSDAY...
ENSEMBLES FOR SEVERAL CYCLES HAVE PROGGED A NORTH ATLANTIC RIDGE
COUPLED WITH A HIGH AMPLITUDE RIDGE DEVELOPING ACROSS WESTERN
CANADA. THE RESULTING FEATURE WILL LIKELY BE A TROUGH DIGGING SOUTH
ACROSS THE GREAT LAKES/HUDSON BAY EARLY NEXT WEEK AND LIKELY
PERSISTING THRU LATE NEXT WEEK. UNSEASONABLY COOL AIR WILL BLEED
SOUTH WITH ENSEMBLES DEMONSTRATING A HIGH CONFIDENCE IN THE 850MB
ISOTHERMS OVER THE FORECAST AREA GENERALLY BETWEEN 8-10 DEG C FOR
MON/TUE...THEN VERY SLOW TO MODERATE BACK TO A 10-12 DEG C RANGE
LATE WEEK. SO TO KICK-OFF NEXT WEEK TEMPS IN THE LOW 70S LOOK LIKELY
WITH A NORTHWEST FLOW AND BROAD SFC RIDGE. AS THE WEEK PROGRESSES
TEMPS SHUD PUSH BACK INTO THE MID/UPR 70S...BUT CURRENTLY THE
NORTHWEST FLOW WOULD SUGGEST DRY CONDITIONS TO PERSIST.

CONFIDENCE...HIGH.

BEACHLER

&&

.AVIATION...

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

* NELY WINDS ARND 10KT THROUGH EARLY EVENING.

* SLY-SWLY WINDS TO ARND 10KT TOMORROW.

* CHANCE TSRA TOMORROW AFTERNOON.

KREIN

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

THE CENTER OF A LARGE AREA OF HIGH PRESSURE HAS MOVED OVER NRN IL
AND THE HIGH EXTENDS FROM LAKE MICHIGAN THROUGH THE MIDDLE
MISSISSIPPI VALLEY. WITH THE EXCEPTION OF SOME DIURNAL CU
DEVELOPMENT...SKIES REMAIN MOSTLY CLEAR WITH WX NIL. THE MAIN
CONCERN FOR THE REMAINDER OF THE AFTERNOON WILL BE WIND
DIRECTION/SPEED. WITH THE CENTER OF THE HIGH TO THE NORTHWEST OF
THE TERMINALS...A WEAK NELY GRADIENT HAS SET UP AND SOME LAKE
ENHANCEMENT/EFFECT IS ALLOWING WINDS TO REACH 10-12KT WITH AN
OCCASIONAL HIGHER GUST. AS THE CENTER OF THE HIGH MOVES ACROSS THE
TERMINALS TONIGHT...WINDS WILL BECOME LGT/VRBL...BEFORE BECMG SLY-
SWLY TOMORROW AS THE CENTER OF THE HIGH SETTLES TO THE SOUTHEAST
OF THE TERMINALS. THE GRADIENT WILL REMAIN WEAK...WITH SPEEDS ARND
10KT LIKELY AGAIN TOMORROW. THE OTHER CONCERN FOR TOMORROW WILL BE
THE CHANCE FOR THUNDERSTORMS FROM THE LATE MORNING THROUGH THE
AFTERNOON HOURS. THE MODELS CONTINUE TO SUGGEST THAT A CLUSTER OF
THUNDERSTORMS MAY DEVELOP FORM OVER THE UPPER MIDWEST LATE TONIGHT
OR EARLY TOMORROW MORNING AND ON THE NOSE OF THE LOW LEVEL
JET AND THEN MOVE SOUTHEAST ALONG THE INSTABILITY GRADIENT. THE
INSTABILITY DOES NOT QUITE REACH AS FAR EAST AS THE CHICAGO METRO
TERMINALS WITH RFD THE MORE LIKELY SITE IN THE PATH OF THE TS.
HOWEVER...WILL GO WITH A PROB30 FOR THE END OF THE TAF PERIOD AT
THIS TIME IN DEFERENCE TO THE CHANCES THAT THE TRACK OF THE TS
CLUSTER COULD BE A LITTLE FARTHER EAST THAN CURRENTLY ANTICIPATED.

KREIN

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

* LOW CONFIDENCE IN CHANCES FOR TS TO DIRECTLY IMPACT THE
  TERMINALS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

FRIDAY NIGHT THROUGH SUNDAY...PERIODIC CHANCES FOR TSRA.
MONDAY THROUGH WEDNESDAY...VFR.

BMD

&&

.MARINE...
307 AM CDT

CONDITIONS WILL CONTINUE TO GRADUALLY IMPROVE ACROSS LAKE MICHIGAN
AS HIGH PRESSURE BUILDS OVER THE AREA TODAY. WINDS HAVE ALREADY
ABATED ACROSS MUCH OF THE LAKE WITH SOME LINGERING WINDS AND WAVES
MAINLY CONFINED TO THE FAR SOUTH END OF THE LAKE EARLY THIS MORNING.
AS WINDS CONTINUE TO DISSIPATE TODAY...EXPECT LAKE BREEZES TO
DEVELOP WITH ONSHORE FLOW THIS AFTERNOON AND EVENING. SOUTHWEST FLOW
WILL FRESHEN UP ACROSS THE LAKE TONIGHT THROUGH THE WEEKEND AS A
PAIR OF LOW PRESSURE SYSTEMS DEVELOP TO OUR WEST. WHILE THE SOUTHERN
LOW IS PROGGED TO WEAKEN AND DISSIPATE...A SLIGHTLY DEEPER LOW OVER
CANADA WILL MOVE ACROSS THE GREAT LAKES SUNDAY DRAGGING A COLD FRONT
ACROSS LAKE MICHIGAN WITH NORTH/NORTHWEST WINDS ONCE AGAIN
APPROACHING 30 KT SUNDAY NIGHT INTO MONDAY BEHIND THE FRONT.

BMD

&&

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

$$

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