Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281850
AFDLOT

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


.SHORT TERM...
140 PM CDT

THROUGH FRIDAY...

ANOTHER COOL/CLOUDY AFTERNOON ACROSS THE REGION...WITH NORTHEAST
WINDS USHERING IN MUCH COOLER TEMPERATURES INTO NORTHEAST
ILLINOIS WITH TEMPS LOCKED IN THE MID/UPR 40S. FURTHER INLAND AWAY
FROM LAKE MICHIGAN TEMPS HAVE WARMED INTO THE MID/UPR
50S...ESPECIALLY ACROSS THE SOUTHWEST CWFA. THERE IS SOME BREAKS
IN THE THICK STRATUS ALONG THE SOUTHERN CWFA...AND WITH A WARM
FRONTAL BOUNDARY DRAPPED ACROSS CENTRAL ILLINOIS SLOWLY LIFTING
NORTH...IT IS POSSIBLE SOME OF THE SOUTHERN PORTIONS OF THE
FORECAST AREA COULD TOUCH THE LOW/MID 60S BEFORE SUNSET THIS
EVENING.

THE LACK OF MECHANICAL MIXING THIS AFTERNOON/EVENING WILL ALLOW
CLOUDS TO REMAIN...WITH MINIMAL SCOURING OF THE STRATUS LAYER
PROGGED THROUGH THIS EVENING/OVERNIGHT. SOME OF THE GUIDANCE
CONTINUES TO PROG SCATTERED SHOWERS LIFTING NORTHEAST AHEAD OF THE
FRONTAL BOUNDARY THIS EVENING/OVERNIGHT...HOWEVER FEEL THAT
COVERAGE WILL REMAIN MINIMAL. IN ADDITION WITH THE LACK OF A LIFT
COMPONENT...EXPECT DROPLET SIZE TO BE MINIMAL WHICH COULD RESULT
IN PRECIP BEING MORE IN THE FORM OF DRIZZLE WITH PERHAPS SOME
LIGHT RAIN. AS THE OVERNIGHT PROGRESSES AND THE UPPER LEVEL SYSTEM
DRIFTS EAST...THE COVERAGE AND PROBABILITIES FOR PRECIP WILL
STEADILY DWINDLE FROM SOUTHWEST TO NORTHEAST. TEMPS OVERNIGHT WILL
ONLY COOL INTO THE LOW/MID 40S.

SHORTLY AFTER DAYBREAK FRI MID-LVL HEIGHTS WILL BE ON THE
RISE...WHICH WILL USHER IN DRIER AIR...HOWEVER WITH THE CONTINUED
LACK OF MIXING THE CHALLENGE IS HOW QUICKLY DO WE ERODE THE THICK
STRATUS LAYER. GUIDANCE HAS SLOWED THE RATE OF IMPROVEMENT UNTIL
MIDDAY...TO PERHAPS LATE AFTERNOON. THIS WILL END UP CONTROLLING
HIGHS FOR FRI...SO HAVE HELD ONTO THE TEMPS GENERALLY IN THE
MID/UPR 50S WITH PERHAPS SOME LOW 60S IN THE FAR SOUTHERN CWFA.
ELSEWHERE THE NORTHEAST FLOW OFF OF LAKE MICHIGAN WILL CONTINUE TO
SEE TEMPS REMAIN IN THE MID/UPR 40S AGAIN FRI.

BEACHLER

&&

.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 18Z TAFS...

VISIBLE SATELLITE IMAGERY CONTINUES TO SHOW A THICK LAYER OF
STRATUS CLOUDS LINGERING ACROSS NORTHERN IL/NORTHWEST IN AIRFIELDS
THIS AFTERNOON...WITH VERY MINIMAL BREAKS. THE LACK OF PRESSURE
GRADIENT HAS ALLOWED WINDS TO REMAIN VERY LIGHT FROM THE
NORTHEAST/EAST DIRECTION...WITH SPEEDS AROUND 8-10KT. THIS WILL
ALSO MAINTAIN THE LOW STRATUS THROUGH THIS EVENING. GUIDANCE
CONTINUES TO INDICATE THERE WILL BE SOME DEVELOPMENT TO SCATTERED
SHOWERS THIS AFTERNOON THROUGH EARLY EVENING...HOWEVER COVERAGE IS
NOT EXPECTED TO BE VERY LARGE AND HAVE OPTED TO PULL THE MENTION
OF VCSH AT THIS TIME. AS THE UPPER LEVEL SYSTEM BEGINS TO DEPART
THE REGION EARLY FRIDAY MORNING...SKIES ARE EXPECTED TO THIN WITH
VFR CONDS EVENTUALLY ARRIVING LATE FRIDAY MORNING.

BEACHLER

&&

.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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