Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 152217
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
417 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJI-WARA WITH THE FILLING SYSTEM
TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY PUSHING
SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY EVENING. OTHER
THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER AIR...NOT MUCH
EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR ABOVE OUR
SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER THROUGH TUESDAY
NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW MOIST LAYER LOOKS TO
EVENTUALLY DEVELOP HOLES IN THE CLOUDS WEDNESDAY. IN COLDER AIR
HIGHS WEDNESDAY EXPECTED FROM THE UPPER 20S TO LOWER 30S...OR A
LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIMEFRAME.

RATZER

&&

.AVIATION...

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

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT...WITH PERIODS OF IFR POSSIBLE
  THIS AFTERNOON.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

IZZI

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

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

* MEDIUM-HIGH CONFIDENCE ON GENERAL CIG TRENDING BACK DOWN TO IFR
  AND PROBABLY LIFR TONIGHT

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT

* MEDIUM-HIGH CONFIDENCE WITH WIND SPEED/DIRECTION

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

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