Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 180245
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
945 PM CDT THU APR 17 2014

.DISCUSSION...
309 PM CDT

A RELATIVELY BENIGN WEATHER PERIOD IS IN STORE FOR THE NEXT FEW
DAYS...WITH THE ONLY CHANCE OF ANY PRECIP THROUGH SUNDAY BEING
TONIGHT. THE MAIN FORECAST CONCERNS OVER THE NEXT FEW DAYS WILL BE
TEMPERATURES...AS THERE WILL LIKELY BE SOME DECENT TEMPERATURE
GRADIENTS ACROSS THE AREA...DUE IN LARGE PART TO THE ONSHORE FLOW
EXPECTED ACROSS NORTHEASTERN ILLINOIS ON FRIDAY AND SATURDAY.

CURRENTLY THERE IS A GOOD AMOUNT OF MID AND HIGHER LEVEL CLOUDINESS
STREAMING NORTHEASTWARD ACROSS THE AREA AHEAD OF A SHEARED OUT SHORT
WAVE...CURRENTLY IN PLACE ACROSS THE MID AND LOWER MISSOURI VALLEY.
MODEL GUIDANCE CONTINUES TO SPARK OFF AN AREA OF SHOWERS ACROSS
PORTIONS OF THE REGION THIS EVENING AND OVERNIGHT AS THIS SHORT WAVE
DISTURBANCE APPROACHES AND INDUCES SOME ISENTROPIC ASCENT ACROSS THE
AREA. OVERALL...I FOLLOWED CLOSE TO THE INHERITED FORECAST...WHICH
PLACES THE CHANCES FOR THIS ACTIVITY MAINLY FROM MID EVENING THROUGH
LATE TONIGHT FOR AREAS ALONG AND SOUTH OF A LINE FROM CHICAGO TO
MENDOTA.

A 1030 MB SURFACE HIGH IS EXPECTED TO BUILD IN ACROSS THE UPPER
GREAT LAKES REGION ON FRIDAY. THIS WILL SET UP A NORTH-NORTHEASTERLY
ONSHORE FLOW ACROSS THE AREA DURING THE DAY. AS SUCH...EXPECT CHILLY
CONDITIONS ON FRIDAY ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA...WHERE A ENHANCED LAKE BREEZE WILL LIKELY KEEP TEMPERATURES
IN THE 40S FORE AREAS NEAR THE LAKE. FARTHER
INLAND...HOWEVER...TEMPERATURES SHOULD WARM INTO THE 50S...WITH EVEN
SOME LOW 60S POSSIBLE WELL INLAND.

TEMPERATURES BEGIN TO MODERATE AREA-WIDE ON SATURDAY AS THE LOWER
LEVEL FLOW TURNS OUT OF THE SOUTHEAST IN RESPONSE TO LOW PRESSURE
MOVING ACROSS THE NORTHERN PLAINS AND SOUTHERN CANADA. TEMPERATURES
LOOK TO CLIMB INTO THE 60S FOR MOST AREAS...WITH THE EXCEPTION OF
FAR NORTHEAST ILLINOIS...WHERE SOUTHEASTERLY ONSHORE FLOW LOOKS TO
KEEP THINGS COOLER. SUNDAY DEFINITELY LOOKS TO BE THE BEST DAY OF
THE WEEKEND. SOUTH-SOUTHWESTERLY FLOW IS EXPECTED TO TRANSPORT AN
EVEN WARMER AIR MASS IN ACROSS THE AREA. MODEL GUIDANCE IS IN VERY
GOOD AGREEMENT IN ADVECTING IN 15 (9) DEGREE CELSIUS 925 MB (850 MB)
TEMPERATURES. LOCAL CLIMO FOR THESE VALUES THIS TIME OF YEAR
INDICATE HIGH TEMPERATURES GETTING INTO THE LOW TO POSSIBLY MID 70S
ACROSS THE AREA.

THE NEXT CHANCE FOR PRECIPITATION LOOKS TO BE ON MONDAY AS ANOTHER
WEAK FRONTAL SYSTEM AND MID LEVEL DISTURBANCE PUSHES ACROSS THE
AREA. FOLLOWING IN THE WAKE OF THIS FRONTAL MONDAY...LOOKS TO BE
ANOTHER DAY OR TWO PERIOD OF NORTHEASTERLY ONSHORE COOLING
FLOW...WHICH WILL AGAIN COULD SET UP A DECENT THERMAL GRADIENT
BETWEEN THE LAKE SHORE AND AREAS FARTHER INLAND.

WAY OUT...TOWARDS THE END OF THE CURRENT FORECAST PERIOD...GUIDANCE
IS IN GOOD AGREEMENT IN DEVELOPING A GOOD STORM SYSTEM ACROSS THE
PLAINS..THEY JUST DIFFER SIGNIFICANTLY WITH THE TIMING. THIS  SYSTEM
LOOKS TO PRODUCE A PERIOD OF MUCH WARMER WEATHER AND ALSO ANOTHER
THREAT FOR SHOWERS AND THUNDERSTORMS AT THE END OF THE PERIOD.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* WINDS SHIFTING FROM WSWLY TO NELY LATE EVENING.

KREIN

//DISCUSSION...UPDATED 00Z...

THE LOW PRESSURE SYSTEM OVER NRN WISCONSIN IS WEAKENING RAPIDLY AS
IT MOVES OVER NRN LAKE MICHIGAN EARLY THIS EVENING. AN ASSOCIATED
WEAK COLD FRONT EXTENDS SWWD INTO SRN MO...BUT THE BOUNDARY IS
VERY DIFFUSE OVER NRN IL. THROUGH THE EARLY EVENING...THE BOUNDARY
IS EXPECTED TO WASH OUT AND THAT WINDS SHOULD TURN NELY AS EITHER
A LATE LAKE BREEZE OR INVERTED TROUGH FORMS ALONG THE LAKEFRONT
AND MOVES INLAND. THE LATEST RUNS OF THE HIGH RES SHORT RANGE
MODEL GUIDANCE INDICATE THAT WINDS AT ORD/MDW/GYY COULD TURN NELY
AS EARLY AS ARND 02Z. WINDS SHOULD THEN REMAIN GENERALLY NELY AT
THE TERMINALS THROUGH THE REMAINDER OF THE FCST PERIOD AS HIGH
PRESSURE BUILDS ACROSS THE UPPER MISSISSIPPI VALLEY AND ACROSS THE
WESTERN GREAT LAKES REGIONS. A MID LEVEL DISTURBANCE TRACKING NEWD
THROUGH THE MIDDLE MISSISSIPPI VALLEY COULD BRING SOME RAIN TO
CNTRL IL AND NRN IN THIS EVENING...BUT ANTICIPATE THAT ANY PCPN
SHOULD REMAIN SOUTH OF THE TERMINALS...BUT THERE IS A CHANCE THAT
GYY COULD SEE SOME RAIN LATE THIS EVENING IF THE PCPN CAN OVERCOME
THE LOW LEVEL DRY AIR AND REACH THE SFC. OTHERWISE...CONDITIONS AT
THE TERMINALS SHOULD BE VFR/WX NIL THROUGH THE DAY TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN TIMING OF WIND SHIFT...WITH HIGHER
  CONFIDENCE IN WIND TRENDS LATTE TONIGHT AND TOMORROW.

* MEDIUM TO HIGH CONFIDENCE THAT ANY PCPN WILL REMAIN SOUTH OF THE
  TERMINALS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

SATURDAY...VFR/WX NIL.

SUNDAY...VFR/WX NIL.

MONDAY...CHANCE RAIN WITH MVFR CIGS/VIS LIKELY. IFR CIGS POSSIBLE.

TUESDAY...VFR/WX NIL.

WEDNESDAY...CHANCE RAIN WITH MVFR CIGS/VIS LIKELY. IFR CIGS
POSSIBLE.

KREIN

&&

.MARINE...
216 PM CDT

WEAKENING LOW PRESSURE OVER NORTHEAST WISCONSIN THIS AFTERNOON
WILL CONTINUE TO LIFT NORTHEAST AND WEAKEN...REACHING NORTHEAST
ONTARIO BY DAYBREAK FRIDAY. THIS LOW HAS A FRONTAL BOUNDARY THAT
WILL CONTINUE TO SLIDE EAST ACROSS THE LAKE THIS AFTERNOON...WITH
WINDS SLOWLY TURNING WESTERLY TO NORTHWESTERLY. THE GRADIENT WILL
BE CONTINUE TO WEAKEN THIS EVENING...AS AN AREA OF HIGH PRESSURE
LOCATED ACROSS CENTRAL CANADA WILL SLIDE EAST AND ELONGATE
COVERING THE WESTERN GREAT LAKES REGION BY MIDDAY FRIDAY.

THE NEXT WEATHER SYSTEM WILL BEGIN TO DEVELOP FRIDAY NIGHT ACROSS
THE CENTRAL PLAINS...ALLOWING A TIGHTENING GRADIENT TO DEVELOP
ACROSS THE SOUTHERN HALF OF THE LAKE EARLY SATURDAY. IT DOES NOT
APPEAR AT THIS TIME ANY SUBSTANTIAL INCREASE IN THE WINDS WILL
OCCUR. OTHERWISE THE NEXT CHANCE FOR MODERATE TO STRONG WINDS WILL
BE FROM EARLY NEXT WEEK ON AS A STRONGER LOW PRESSURE SYSTEM COULD
IMPACT THE REGION.

BEACHLER

&&

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

$$

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