Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280928
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
428 AM CDT THU APR 28 2016

.SHORT TERM...
333 AM CDT

THROUGH FRIDAY...

STRONG UPPER LOW OVER WESTERN IOWA IS FORECAST TO QUICKLY WEAKEN
AND OPEN UP AS IT MOVES INTO WISCONSIN TONIGHT. BAND OF SHOWERS
AND ISOLATED THUNDERSTORMS MOVING ACROSS THE AREA NOW SHOULD
CONTINUE TO PIVOT NE ACROSS THE AREA EARLY THIS MORNING WITH
MAJORITY OF THE PRECIP WITH THIS BAND EXPECTED TO SHIFT NORTH INTO
WISCONSIN BY MID-MORNING. DEEP LAYER OF LOW LEVEL
MOISTURE/SATURATION AND CONTINUED WEAK ISENTROPIC ASCENT TODAY
SHOULD RESULT IN AT LEAST THE POTENTIAL FOR SOME LIGHT RAIN OR
SHOWERS THROUGH THE DAY AND PERHAPS SOME DRIZZLE THIS MORNING INTO
THE EARLY AFTERNOON BEFORE CIGS BEGIN TO SLOWLY LIFT DIURNALLY.
THE EXTENSIVE CLOUD COVER AND AT LEAST INTERMITTENT RAIN TODAY
SHOULD HELP KEEP TEMPS UNSEASONABLY CHILLY...ESPECIALLY NORTH OF
I-80 WHERE BRISK EASTERLY WINDS OFF THE LAKE THIS MORNING WILL
HELP LOCK TEMPS IN THE 40S. WINDS WILL GRADUALLY EASE A BIT THIS
AFTERNOON AS SFC LOW FILLS BUT SHOULD MEAN MUCH FOR TEMPS. FAR
SOUTHERN CWA WILL BE CLOSER TO THE WARM FRONT...COULD SEE A FEW
BREAKS IN THE CLOUDS AND LESS PRECIP...SO TEMPS EXPECTED TO MILDER
THAN POINTS FARTHER NORTH.

CLOUDINESS LIKELY TO STICK AROUND TONIGHT SO NOT EXPECTING TEMPS
TO DROP MUCH NORTH. SHOULD SEE SOME PARTIAL CLEARING FRIDAY AS WE
ENJOY A SHORT BREAK IN BETWEEN SYSTEMS. THE SEEMINGLY NEVER ENDING
NORTHEAST FLOW WILL KEEP TEMPS QUITE CHILLY WITH MAINLY 50S FOR
HIGHS...THOUGH MID-UPPER 40S EXPECTED NEAR THE LAKE.

IZZI

&&

.LONG TERM...
333 AM CDT

FRIDAY NIGHT THROUGH THURSDAY...

THE NEXT STRONG WESTERN UPPER LOW IS PROGGED TO MOVE OUT ONTO THE
PLAINS SATURDAY WITH GUIDANCE CONTINUING TO FLUCTUATE ON THE
TIMING OF ARRIVAL OF RAIN INTO OUR AREA IN ASSOCIATION WITH THIS
SYSTEM. THE GFS IS NOW THE SLOW OUTLIER WITH A LATE AFTERNOON
SATURDAY ARRIVAL TIME...WHILE ECMWF AND NAM FAVOR AN EARLIER START
TIME. SATURDAY LOOKS TO LARGELY BE A REPEAT OF WEDNESDAY EXCEPT
WITH THE POTENTIAL FOR MORE WIDESPREAD COVERAGE OF RAIN AND
PERHAPS TEMPS A BIT COOLER THAN TODAY. LEANING TOWARD THE FASTER
NAM/ECMWF SOLUTIONS HAVE SCALED TEMPS BACK FOR SAT...BUT IF THESE
FASTER SOLUTIONS VERIFY THEN EVEN THE GOING FORECAST TEMPS WILL
END UP TOO WARM WITH HIGHS MORE LIKELY HOLDING IN THE MID TO UPPER
40S. COMBINE THAT WITH RAIN AND FAIRLY STRONG NORTHEAST WINDS
KNOCKING WIND CHILLS INTO THE 30S AND SAT WILL FEEL MUCH MORE LIKE
EARLY MARCH THAN THAN LAST DAY OF APRIL!

THE POWERFUL PLAINS UPPER LOW IS FORECAST TO OPEN UP AND RAPIDLY
WEAKEN AS IT MOVES INTO THE MORE CONFLUENT FLOW ALOFT OVER THE
UPPER MIDWEST. SUNDAY LOOKS TO BE A SIMILAR SET UP TO TODAY WITH
SOME SPORADIC LINGERING SHOWERS POSSIBLE ALONG WITH A CONTINUATION
OF CHILLY NORTHEAST WINDS OFF THE LAKE AND UNSEASONABLY COOL
TEMPS.

FORECAST CONFIDENCE HEADING INTO NEXT WEEK IS LOWER THAN AVERAGE
AS MEDIUM RANGE MODELS STRUGGLE TO HANDLE THE EVOLUTION OF THIS
VERY BLOCKY UPPER FLOW OVER NOAM. THE LATEST ECMWF AND GFS DO
SUGGEST THAT THE REX BLOCK LIKE PATTER WITH THE HIGH AMPLITUDE
RIDGING OVER SOUTH CENTRAL CANADA WILL RETROGRADE WEST POTENTIALLY
ALLOWING A MORE SUBSTANTIAL DEEP LONG WAVE TROUGH TO DEVELOP OVER
THE EASTERN CONUS BY MID TO LATE WEEK. WE COULD SEE A BRIEF WARM
UP DURING THE TRANSITION PERIOD EARLY IN THE WEEK WITH WESTERLY
WINDS AHEAD OF AN APPROACHING CLIPPER ACTUALLY ALLOWING LAKE FRONT
TEMPS TO GET ABOVE 50 FOR THE FIRST TIME IN NEARLY A
WEEK...HOWEVER THERE ARE INDICATIONS THAT WE COULD BE HEADING INTO
ANOTHER BOUT OF UNSEASONABLY COOL AIR BY LATE IN THE WEEK INTO
EARLY NEXT WEEKEND. ONE CAVEAT IS THAT THE BLOCKY FLOW PATTERN
WITH SEVERAL LARGE CLOSED LOWS EARLY IN THE PERIOD DOES LEND SOME
UNCERTAINTY TO MEDIUM RANGE GUIDANCE`S HANDLING OF THE FLOW
PATTERN LATER IN THE MEDIUM RANGE PERIOD...THOUGH THE CONSISTENCY
BETWEEN THE LATEST EC AND GFS DOES LEND IT A BIT MORE CREDIBILITY.

IZZI

&&

.AVIATION...
FOR THE 09Z TAF AMENDMENTS...

VSBYS AND CIGS REMAIN THE MAIN QUESTION FOR THE REMAINDER OF THE
NIGHT AND INTO THE MORNING. THE LINE OF SHOWERS AND ISOLATED
TSTORMS HAS MOSTLY CLEARED THE AREA. SUPPORT FOR WIDESPREAD IFR
CIGS AND VSBYS APPEARS TO BE SHORT LIVED IN THE NEAR TERM AND WE
HAVE ALREADY SEEN AN INCREASE TO MVFR IN THE ONE-MINUTE DATA AT
ORD...BUT TRENDS TOWARD MORNING APPEAR TO BE LOWER AGAIN.

AFTER SUNRISE...A BIT OF A WET MURKY DAY IS IN STORE WITH
PERIODIC SHOWERS AND MAYBE SOME PATCHY DRIZZLE. TIMING IS TOUGH TO
PIN DOWN...BUT A BREAK IN THE EARLY MORNING WITH RENEWED ACTIVITY
TOWARD LATE MORNING AND AFTERNOON STILL LOOKS REASONABLE. LATER
UPDATES MAY EXTEND SHRA PAST 21Z AS WELL.

LENNING

&&

.MARINE...
252 AM CDT

A SMALL CRAFT ADVISORY IN THE ILLINOIS NEARSHORE WATERS...MAINLY
FOR WAVE ACTIVITY WITH ONSHORE WINDS TODAY...LOOKS ON TRACK TO
EXPIRE BY MID AFTERNOON WHEN WINDS RELAX AND ALLOW WAVES TO BEGIN
SUBSIDING. ADDITIONAL CHANCES FOR EXCEEDING ADVISORY CRITERIA
APPEAR POSSIBLE SATURDAY AFTERNOON AND AGAIN SUNDAY. OTHERWISE
RELATIVELY LIGHT NORTHERLY TO EASTERLY FLOW SHOULD PERSIST
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM THURSDAY.

&&

$$

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