Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 300547
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1247 AM CDT MON MAR 30 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

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

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

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

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC


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

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

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

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

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