Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 292144
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
444 PM CDT SUN MAR 29 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 22Z...

* STRONG SOUTHWEST WINDS THROUGH 23-00Z POSSIBLY GUSTING OVER 30KT
  AT TIMES
* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE AROUND
  00Z.
* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT AN EARLY 22Z AMENDMENT TO BACK OFF ON GUSTS THROUGH 23Z.
ACARS SOUNDINGS SHOW WINDS IN THE MIXED LAYER SLOWING EASING A
BIT. STRONGEST PRESSURE FALLS CONTINUE TO PUSH AWAY AND ANY
CLEARING LOOKS TO BE VERY SHORT LIVED AND CHANCES OF TOP OF THE
CHANNEL MIXING DOWN OF 35KT+ GUSTS ARE QUICKLY FADING. A BRIEF
GUST OR TWO UP TO 35KT CANNOT COMPLETELY BE RULED OUT BUT
PREVAILING GUSTS SHOULD REMAIN MOSTLY BELOW 30KT REST OF THE
AFTERNOON. BAND OF -RA/-SHRA IS DEVELOPING OVER SOUTHERN WI WITH
THE FRONT SO HAVE ADDED A SHORT PERIOD OF PREVAILING -RA/MVFR CIGS
AHEAD OF THE FRONT.

IZZI

UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THIS EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

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

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.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...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

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