Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 160917
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
417 AM CDT WED APR 16 2014

.DISCUSSION...
313 AM CDT

WEATHER WITHOUT ANY SIGNIFICANT IMPACTS LOOKS TO BE THE RULE THROUGH
THE EARLY PART OF THE WEEKEND WITH MUCH OF THE ATTENTION ON
TEMPERATURES AND WIND SPEEDS TODAY AND THEN SMALL CHANCES FOR
PRECIPITATION THURSDAY NIGHT AND FRIDAY.

TODAY AND TONIGHT...
THE UPPER TROUGH RESPONSIBLE FOR THE CHILLY DAY YESTERDAY IS
ADVANCING EAST OVER EASTERN CANADA AND NEW ENGLAND AND IS
RESPONSIBLE FOR PORTIONS OF AT LEAST 22 STATES UNDER FREEZE WARNINGS
THIS MORNING! STRONG MID-LEVEL DRYING IS SEEN ALL THE WAY DOWN TO
THE NORTHERN GULF AND AT THE SURFACE THE DRY AIR HAS ADVANCED
SOUTHWARD ALL THE WAY INTO THE GULF WITH SEVERAL PLATFORMS/BUOYS
REPORTING DEW POINTS IN THE 30S. SO BASICALLY THE GULF IS NOT
AVAILABLE FOR THE NEXT SYSTEM PASSING ACROSS THE REGION TONIGHT AND
THAT WILL BE A MAIN REASON WE LOOK TO REMAIN PRECIPITATION FREE.
THIS SYSTEM IS A FAIRLY WELL-DEFINED LOW AMPLITUDE UPPER WAVE THAT
IS MOVING EAST ACROSS SD THIS MORNING AND WILL FOLLOW ITS PARENT JET
STREAK/DIVERGENCE ALOFT TO THE EAST NORTHEAST OVER THE UPPER GREAT
LAKES TONIGHT WHERE A SNOW STORM IS FORECAST ACROSS NORTHERN WI/U.P.
OF MICHIGAN.

THE QUICK EASTWARD PROGRESSION OF THE SYSTEM SURFACE LOW BY
AFTERNOON WILL TIGHTEN THE PRESSURE GRADIENT ACROSS THE LOCAL AREA.
WHILE THERE WILL BE SOME HIGH CLOUDS...MIXING WILL AID THE PRESSURE
GRADIENT IN CREATING SUSTAINED SPEEDS AROUND 20 MPH AND GUSTS PLUS
10 MPH OF THAT. SOME 35 MPH GUSTS SHOULD EVEN BE REALIZED IN NORTH
CENTRAL IL. TEMPERATURES LOOK TO BOUNCE BACK 15 DEGREES OR EVEN
HIGHER THAN YESTERDAY GIVEN WARMING OF THE BOUNDARY LAYER AND
LOW-LEVEL ADVECTION. A SLIGHT COMPONENT OFF THE LAKE INTO CITY OF
CHICAGO AND NORTHWARD WILL KEEP THESE LAKE ADJACENT AREAS A HANDFUL
OF DEGREES COOLER...BUT COMPARED TO 33 DEGREES YESTERDAY...THE
FORECAST OF AROUND 50 TODAY FOR THESE LOCATIONS SHOULD BE WELCOME.
OUTLYING AREAS LOOK TO REACH THE MID 50S. UPSTREAM DEW POINTS ARE IN
THE UPPER TEENS TO MID 20S ACROSS DOWNSTATE IL/IN INTO THE TENNESSEE
RIVER VALLEY...SO EXPECTING A FAIRLY DRY AIR MASS TODAY WITH
HUMIDITY IN THE 25-35 PERCENT RANGE IN MOST AREAS.

AS THE UPPER WAVE PASSES TO THE NORTH TONIGHT THE PACIFIC MOISTURE
REMAINS NORTH AS WELL AND THE WARM AIR ADVECTION ASCENT HERE REMAINS
WITHIN A LOW PWAT ATMOSPHERE. WOULD NOT BE SURPRISED TO SEE SOME
RADAR ECHOES/VIRGA ACROSS FAR NORTHERN IL BUT THAT SHOULD BE ABOUT
IT. WITH MORE CLOUD COVER TONIGHT AND SOUTHERLY WINDS OF 10-20 MPH
CONTINUING...LOWS LOOK TO ONLY DIP INTO THE LOWER-MID 40S.

THURSDAY AND FRIDAY...
THE SYSTEM SURFACE FRONT/TROUGH IS EXPECTED TO MOVE INTO THE
FORECAST AREA THURSDAY MORNING AND BECOME STATIONARY. THIS DOES NOT
LOOK TO BE A VERY PRONOUNCED BAROCLINIC BOUNDARY. HAVE CONSIDERABLY
LOWERED CLOUD COVER DURING THURSDAY MORNING AND EARLY AFTERNOON AND
WITH THAT BOOSTED TEMPERATURES SOME...WITH 55 TO 60 PROBABLE. A
SHEARING UPPER WAVE IS EXPECTED TO MOVE NORTHEAST OVER THE BOUNDARY
THURSDAY NIGHT. A LOOK AT THE DPROG/DT...OR TREND...OF SEVERAL
MODELS OVER THE PAST FOUR CYCLES SHOW CONSIDERABLY LESS FORCING AND
MOISTURE AVAILABILITY FOR PRECIPITATION. HAVE CONTINUED THE FORECAST
TREND TO CUT BACK POPS BUT ALSO TO CONFINE THE AREA WHERE
CONVERGENCE/FRONTOGENESIS IS DEPICTED NEAR THE BOUNDARY. BY FRIDAY
THE ENVELOPE OF GUIDANCE HAS FORCING EAST OF THE AREA...HOWEVER ONE
FINAL SEPARATE MID-LEVEL IMPULSE SEEN ON THE NCEP MODELS PASSES OVER
THE AREA FRIDAY AFTERNOON. CONTINUE A SMALL CHANCE OF RAIN SHOWERS
WITH THIS. THE NORTH TO NORTHEAST FLOW BEHIND THE FRONT ON FRIDAY
SHOULD LEAD TO A DECENT TEMPERATURE DIFFERENCE FROM NEAR THE LAKE TO
OUTLYING AREAS...WITH MID 40S TO MID 50S PRESENTLY FORECAST ACROSS
THAT CROSS SECTION. LOCAL CLIMATOLOGICAL RESEARCH FAVORS SUCH A
SPREAD THIS TIME OF YEAR WITH ONSHORE FLOW.

THIS WEEKEND INTO EARLY NEXT WEEK...
WHILE THE FLOW IS PROGRESSIVE ACROSS THE FAR NORTHERN CONUS/SOUTHERN
CANADA IT LOOKS TO BE FAR ENOUGH NORTH TO HAVE LITTLE INFLUENCE ON
THE AREA SATURDAY AND POTENTIALLY EVEN SUNDAY...ESPECIALLY IF GOING
TOWARD THE EC AND GEM WHICH WE HAVE LEANED OUR FORECAST. THESE
MODELS INDICATE THAT A CLOSED UPPER LOW OVER THE SOUTHEAST U.S.
DEPICTED BY MODELS LATE IN THE WEEKEND MAY LEAD TO A SLOWING OF THE
NEXT SYSTEM TO APPROACH THE AREA FROM THE ROCKIES...MORE SO SUNDAY
NIGHT AND MONDAY. TEMPERATURES LOOK TO BE BACK TO NORMAL SUNDAY AND
MONDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY SOUTH WINDS DEVELOPING DURING THE DAY WEDNESDAY...WITH
  OVER 30 KTS AT TIMES DURING THE AFTERNOON.
* LOW LEVEL WIND SHEAR WEDNESDAY EVENING/NIGHT.

BMD

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

OVERNIGHT HOURS WILL REMAIN QUIET WITH VFR CONDITIONS AND A LIGHT
SSE BREEZE DEVELOPING. LOW PRESSURE WILL TRANSLATE EAST ACROSS THE
NORTHERN PLAINS OVERNIGHT WITH THE GRADIENT INCREASING THROUGH THE
PERIOD. BY MID MORNING WEDNESDAY...EXPECT TO START MIXING DOWN MID
20 KT GUSTS...AND BY EARLY AFTERNOON...GUSTS TO AROUND 30 KT ARE
POSSIBLE. WITH THE SURFACE LOW STARTING TO FILL AND SOME DEGREE OF
DECOUPLING WEDNESDAY NIGHT...WIND GUSTS AT THE SURFACE SHOULD TAPER
SOME MID TO LATE IN THE EVENING. MEANWHILE...A 50 KT OR SO LOW LEVEL
JET IS PROGGED TO DEVELOP...ESPECIALLY OVER NORTH CENTRAL ILLINOIS
AND COULD SET THE STAGE FOR MARGINAL LOW LEVEL WIND SHEAR. OPTED TO
REMOVE THE LLWS AT ORD AS IT APPEARS THE THREAT WILL BE BETTER
FARTHER WEST SUCH AS AT RFD. AS THE LOW MOVES EAST...EXPECT AN
INCREASE IN HIGH AND MID LEVEL CLOUD COVER...BUT VFR CONDITIONS WILL
PREVAIL THROUGH THE CURRENT TAF PERIOD.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* LOW CONFIDENCE IN LLWS WEDNESDAY NIGHT.
* MEDIUM CONFIDENCE IN MAGNITUDE OF WINDS/GUSTS DURING THE
  AFTERNOON/EVENING.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

BMD

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

THURSDAY...CHC RA LATE AFTN/NGT. MAINLY VFR.

FRIDAY...CHC RA/MVFR EARLY...THEN VFR.

SATURDAY...VFR.

SUNDAY...CHC RA.

MONDAY...SLGT CHC RA.

RATZER

&&

.MARINE...
242 AM CDT

HIGH PRESSURE WILL CONTINUE TO MOVE AWAY FROM LAKE MICHIGAN TODAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE NORTHERN PLAINS ALLOWING A
SOUTHERLY GRADIENT TO SET UP ACROSS LAKE MICHIGAN. WINDS WILL
STEADILY INCREASE THROUGH THE DAY TOPPING OUT AROUND 30 KT THIS
EVENING AND TONIGHT. A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR
THE INDIANA AND ILLINOIS NEARSHORE WATERS TODAY THROUGH TONIGHT.
STABLE CONDITIONS WILL PREVENT STRONGER WINDS FROM REACHING THE LAKE
SURFACE. THE LOW WILL BEGIN TO FILL THURSDAY AS IT LIFTS ACROSS FAR
NORTHERN LAKE MICHIGAN...THEN HIGH PRESSURE WILL BUILD OVER LAKE
MICHIGAN LATE IT THE WEEK INTO THE WEEKEND.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM WEDNESDAY TO 4 AM THURSDAY.

&&

$$

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