Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 271949
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
249 PM CDT WED APR 27 2016

.UPDATE...

1110 AM CDT

THE MAIN CONCERNS THIS MORNING CONTINUE TO CENTER AROUND TIMING
OF SHOWERS THIS AFTERNOON INTO TONIGHT. CURRENTLY IT APPEARS THE
AREA OF SHOWERS TO OUR SOUTHWEST WILL CONTINUE TO GRADUALLY WORK
THEIR WAY TO THE NORTHEAST THROUGH THE AFTERNOON. AREAS ACROSS THE
CHICAGO METRO LOOK TO REMAIN DRY THROUGH AT LEAST 3-4 PM THIS
AFTERNOON...IF NOT LATER...BEFORE THE THREAT OF RAIN SHOWERS
BEGINS TO INCREASE. THE THREAT OF THUNDER WITH THIS INITIAL SURGE
OF MOISTURE LOOKS LOW. HOWEVER...ANOTHER ROUND OF THUNDERSTORMS
EXPECTED TO DEVELOP THIS AFTERNOON OVER NORTHERN MISSOURI COULD
TRACK EAST-NORTHEASTWARD AND POSSIBLE IMPACT SOUTHERN SECTIONS OF
THE AREA THIS EVENING BEFORE THEY WEAKEN.

OVERALL...WE HAVE NOT MADE ANY MAJOR CHANGES TO THE
FORECAST...JUST SOME MINOR TWEAKS TO TIMING OF PRECIPITATION THIS
AFTERNOON. OTHERWISE...PERSISTENT EASTERLY FLOW AND CLOUD COVER
SHOULD KEEP AREAS NEAR THE LAKE IN THE MID 40S...AND ONLY INTO THE
LOWER 50S INLAND.

KJB

&&

.SHORT TERM...
320 AM CDT

THROUGH THURSDAY

PRIMARY SHORT TERM CONCERN REVOLVES AROUND TIMING THE PRECIP
ARRIVAL AND OF COURSE TEMPS. WHILE LOW CLOUDS WILL PROBABLY CLEAR
OUT IN SPOTS AT TIMES...HIGH CLOUDINESS LIKELY TO KEEP CHARACTER
OF THE DAY CLOUDY. STIFF NORTHEAST WINDS WILL CONTINUE TO ADVECT
DRY AIR INTO THE LOW LEVELS WHICH COMBINED WITH THE VERY SLOW
MOVEMENT OF THE APPROACHING UPPER LOW WILL LIKELY KEEP MOST OF THE
AREA DRY THROUGH EARLY TO MID AFTERNOON. AN ARC OF SHOWERS AND
PERHAPS A THUNDERSTORM WILL LIFT NORTHEAST ACROSS THE AREA VERY
LATE THIS AFTERNOON AND TONIGHT.

CLOUDINESS AND COOL NORTHEAST FLOW WILL CONTINUE THURSDAY WITH
SOME FOG POTENTIAL EVEN NEAR THE LAKE AS HIGHER DEWPOINTS ATTEMPT
TO SPREAD NORTH AND INTERACT WITH THE CHILLY MARINE LAYER. UPPER
LOW SHOULD MOVE ACROSS THE CWA THURSDAY AND SHOULD BE ENOUGH TO
SUPPORT ISOLD TO SCTD SHOWERS EVEN THOUGH IT WILL BE WEAKENING
QUICKLY. ANY SHOWERS SHOULD END THURSDAY EVENING AS THE SYSTEM
MOVES EAST OUT OF THE AREA.

IZZI

&&

.LONG TERM...
248 PM CDT

THURSDAY NIGHT THROUGH WEDNESDAY...

A PROGRESSIVE...COMPLICATED UPPER LEVEL PATTERN IS SETTING UP FOR
THE EXTENDED FORECAST PERIOD.  MULTIPLE SYSTEMS ARE EXPECTED TO
IMPACT THE REGION...OR COME CLOSE ENOUGH THAT THERE MAY BE SOME
POTENTIAL IMPACTS SHOULD SOME CHANGES OCCUR DURING THE EXTENDED
FORECAST PERIODS.

BY THURSDAY NIGHT...A SLOW MOVING UPPER LOW TRACKING THROUGH THE
CENTRAL PLAINS WILL MAKE A TURN TO THE ENE...ACROSS SRN WISCONSIN.
THE LONGER RANGE GUIDANCE IS RATHER CONSISTENT ON THE PATH OF THE
UPPER SYSTEM AND WILL REPRESENT THE TAIL END OF THE PCPN EVENT
MOVING INTO THE REGION WEDNESDAY AFTERNOON.  WITH THE MAIN FORCING
TO THE NORTH OF THE CWA...THE HIGHEST POPS SHOULD BE OVER THE NRN
TIER COUNTIES AND SRN WI...BUT THERE SHOULD BE ENOUGH WRAPAROUND
MOISTURE AND WEAK INSTABILITY ON THE BACK SIDE OF THE EXITING
ASSOCIATED SFC LOW FOR THE CHANCE FOR SOME LINGERING SHOWERS THROUGH
THURSDAY NIGHT.  FRIDAY INTO FRIDAY NIGHT SHOULD BE DRY AS HIGH
PRESSURE BUILDS OUT OF CANADA AND ACROSS THE GREAT LAKES REGION.
THIS SHOULD BE A COOL...DRY AIRMASS...WITH TEMPERATURES ONLY
EXPECTED TO BE IN THE UPPER 50S TO LOWER 60S ACROSS AREAS AWAY FROM
LAKE MICHIGAN.  PREVAILING NELY FLOW OFF OF LAKE MICHIGAN WILL KEEP
LAKEFRONT LOCATIONS MUCH COOLER...WITH HIGHS ONLY IN THE UPPER 40S
TO AROUND 50F.  BY SUNDAY...A SLOW MOVING SHORTWAVE LIFTING OUT OF
THE CENTRAL PLAINS WILL BRING THE NEXT CHANCE FOR PCPN ...POSSIBLY
AS EARLY AS SATURDAY MORNING.  BROAD WARM ADVECTION SHOULD BE
CONDUCIVE TO INCREASING MOISTURE...BUT SFC TEMPERATURES WILL HAVE
TROUBLE REBOUNDING MUCH HIGHER THAN THE PREVIOUS FEW DAYS AS STRONG
HIGH PRESSURE BUILDING OUT OF CANADA AND ACROSS THE UPPER GREAT
LAKES WILL LIMIT THE NWD PROGRESSION OF A SFC WARM FRONT.  WHILE
THERE ARE SOME DIFFERENCES AMONG THE LONGER RANGE MODELS IN THE
FINER SCALE DETAILS...THE GENERAL IDEA IS THAT THE WARM FRONT SHOULD
STAY TO THE SOUTH OF THE CWA THROUGH SUNDAY...KEEPING RELATIVELY
COOL FLOW OFF OF THE LAKE IN PLACE.  SO...WHILE INLAND TEMPERATURES
MAKE BE ABLE TO REACH AROUND 60 F ON SUNDAY...THE LAKEFRONT WILL
REMAIN MUCH COOLER WITH HIGHS AGAIN ONLY AROUND 50F...AND POSSIBLY
ONLY UPPER 40S.

BY EARLY NEXT WEEK...SIGNIFICANT UNCERTAINTY ENTERS INTO THE
FORECAST...WITH THE GFS ADVERTISING AN UPPER RIDGE BUILDING ACROSS
THE CENTRAL PLAINS...TO THE WESTERN GREAT LAKES TUESDAY
NIGHT...WHILE UPPER LEVEL NWLY FLOW AND DEEP LAYER COLD ADVECTION IS
SHUNTED EAST TO THE NERN CONUS. THIS WOULD SUGGEST A WARMING TREND
FOR THE LOCAL AREA.  HOWEVER...THE ECMWF IS SIGNIFICANTLY
DIFFERENT...WITH A NRN STREAM SHORTWAVE DROPPING OUT OF CANADA AND
SWINGING THROUGH THE UPPER MISSISSIPPI VALLEY AND UPPER GREAT
LAKES...ALONG WITH A LONGWAVE TROUGH EXTENDING SOUTH THROUGH THE
MIDDLE  MISSISSIPPI VALLEY.  AN ASSOCIATED COLD FRONT WOULD PUSH
THROUGH THE REGION ON TUESDAY LEADING TO COOLER CONDITIONS FOR
TUESDAY AND WEDNESDAY.  THE GEMNH LENDS SOME SUPPORT TO THE ECMWF
SOLUTION...INDICATING A NORTHERN STREAM SHORTWAVE DROPPING THROUGH
THE WESTERN GREAT LAKES BY TUESDAY MORNING...BUT THAT IS THE END OF
THE AVAILABLE GUIDANCE FROM THAT PARTICULAR MODEL.  GIVEN THE
SIGNIFICANT FORECAST UNCERTAINTY...HAVE OPTED TO MAINTAIN LITTLE
SIGNIFICANT CHANGE TO THE GOING FORECAST...WHICH WOULD SUGGEST
SEASONABLE TEMPERATURES AND LOW PCPN CHANCES.

KREIN

&&

.AVIATION...
FOR THE 18Z TAFS...

A STORM SYSTEM TO OUR WEST WILL GRADUALLY SPREAD SHOWERS
NORTHEASTWARD ACROSS THE TERMINALS LATE THIS AFTERNOON THROUGH EARLY
THIS EVENING. MAIN CHANGE TO THE TAFS WAS TO REMOVE THE VCTS
MENTION...AS IT APPEARS MOST OF THE THUNDERSTORM ACTIVITY MAY REMAIN
SOUTH OF THE TERMINALS. THERE IS STILL A SMALL CHANCE OF STORM AT
THE TERMINALS THIS EVENING...BUT THE PROBABILITY AND DURATION OF IT
IS TO LOW TO CONTINUE A MENTION IN THE TAFS AT THIS TIME. SHOWER
ACTIVITY SHOULD MOVE INTO KRFD BY EARLY THIS AFTERNOON...AND ACROSS
THE EASTERN TERMINALS AFTER 21-22 UTC. THESE SHOWERS WILL CONTINUE
INTO THIS EVENING BEFORE ENDING BY LATE EVENING. ADDITIONAL SHOWERS
ARE POSSIBLE ACROSS THE AREA LATER TONIGHT INTO THURSDAY...BUT DUE
TO UNCERTAINTIES ON THE EXACT TIMING...WITH JUST LEAVE A VCSH IN THE
FORECAST.

EXPECT WINDS TO CONTINUE TO BE GUSTY AT TIMES OUT OF THE EAST-
NORTHEAST THROUGH THE PERIOD. CIGS WILL IMPROVE SOME THIS
AFTERNOON...BUT LOWER MVFR CIGS AROUND...OR JUST BELOW 1,000 FT AGL
ARE LIKELY AGAIN BY THURSDAY MORNING.

KJB

&&

.MARINE...
250 AM CDT

HEADLINES...THE SMALL CRAFT ADVISORIES LOOK GOOD AS IS.

LOW PRESSURE OVER KANSAS WEAKENS AND PASSES OVER CENTRAL IL
THURSDAY. MEANWHILE HIGH PRESSURE OVER CENTRAL CANADA REMAINS
STATIONARY THROUGH THE END OF THE WEEK AND THEN SHIFTS EAST OVER
QUEBEC EARLY NEXT WEEK.  NORTH TO EAST WINDS ARE EXPECTED OVER THE
LAKE THROUGH MONDAY. THE ONSHORE FLOW RESULTS IN HAZARDOUS WAVES FOR
SMALL CRAFT INTO THURSDAY FOR THE IL NSH WATERS.  ANOTHER WEAK LOW
PASSES SOUTH OF THE LAKE SUNDAY...AND THEN HIGH PRESSURE SPREADS
OVER THE LAKE MONDAY. A LOW PRESSURE SYSTEM MOVES ACROSS SOUTHEAST
CANADA MONDAY NIGHT INTO TUESDAY...AND WINDS ARE FORECAST TO BECOME
SOUTH OR SOUTHWEST AS THE HIGH SHIFTS EAST OF THE LAKE TUESDAY.

JEE

&&

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

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 PM THURSDAY.

&&

$$

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