Cold in Illinois, December 25, 2005

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
745 PM CST SAT DEC 24 2005

.EVENING UPDATE...

DENSE FOG DEVELOPING ACROSS PARTS OF EASTERN IL AND NORTHWEST IN
THIS EVENING. EXPECT DENSE FOG TO BECOME MORE WIDESPREAD ACROSS THIS
AREA DURING THE REST OF THE EVENING AND OVERNIGHT AND HAVE ISSUED A
DENSE FOG ADVISORY FOR THESE AREAS. AREA OF RAIN DEVELOPING ACROSS
WEST CENTRAL IL IS SLOWLY CREEPING NORTHEAST AND THIS SHOULD PREVENT
WIDESPREAD DENSE FOG FROM DEVELOPING WEST OF THE ADVISORY AREA BUT
WILL NEED TO KEEP AN EYE ON THIS OVER THE NEXT FEW HRS. IF RAIN DOES
HELP KEEP VISIBILITIES UP...AS IT CREEPS EAST OVERNIGHT...DENSE FOG
MAY IMPROVE ACROSS EASTERN PART OF ADVISORY AREA. OTHER CONCERN FOR
TONIGHT IS CHANGEOVER OR MIX WITH ANY FREEZING DRIZZLE OR FLURRIES
TOWARD MORNING. WITH LOW CLOUDS ACROSS ALL THE MIDWEST...LITTLE IF
ANY COLD AIR ADVECTION...EXPECT MAINLY STEADY TEMPS IN THE LOWER TO
MID 30S. DID NOT MAKE ANY CHANGES TO PRECIP WORDING ATTM AND WILL
TAKE A LOOK AT 00Z RUNS BEFORE MAKING ANY SIGNIFICANT CHANGES.

&&

.DISCUSSION FOR AFTERNOON ZFP/GRIDS...
305 PM CST

MAIN FOCUS REMAINS HOLIDAY WEEKEND LOW PRESSURE SYSTEM.

SHORT WAVE TROUGH/SPEED MAX ROTATING THROUGH BASE OF UPPER
TROUGH/CLOSED UPPER LOW OVER LOWER MISSOURI VALLEY THIS AFTERNOON.
BAROCLINICITY RATHER WEAK WITH THIS SYSTEM...AT LEAST THIS FAR
NORTH...WITH LITTLE IN WAY OF SIGNIFICANT THERMAL OR VORTICITY
ADVECTION. THEREFORE DEFORMATION AXIS ALONG NORTH/NORTHWEST SIDE OF
SYSTEM PROVIDING MAIN FORCING IN VICINITY OF LOT CWA...WITH BAND OF
GENERALLY LGT RAIN FROM WEST CENTRAL IL NORTHEAST ACROSS SRN LAKE
MICHIGAN. DEFORMATION ZONE AND ASSOCIATED PRECIP BAND TO MOVE SLOWLY
EAST ACROSS FORECAST AREA OVERNIGHT AND SUNDAY MORNING...WITH PRECIP
ALREADY DIMINISHING ACROSS FAR WESTERN PORTIONS OF CWA.

AS STATED IN EARLIER UPDATE...EACH SUCCESSIVE MODEL RUN HAS TRENDED
WARMER WITH THIS SYSTEM...AND 12Z RAOB ANALYSIS BEARS THIS OUT.
FORECAST SOUNDINGS AND THICKNESS FIELDS CONTINUE TO SUPPORT RA AS
MAIN PRECIP TYPE...AND DO NOT INDICATE COLUMN COOLING ENOUGH TO
SUPPORT A TOTAL CHANGE TO SNOW UNTIL AFTER PRECIP ENDS...OR
MID/UPPER LEVEL DRYING ROBS ICE NUCLEATION TO PRODUCE ONLY DRIZZLE
IN SATURATED LOW LEVELS. THUS AM EXPECTING ONLY RA...WITH SOME WET
SNOW MIXING IN WITH NO ACCUMULATIONS BEFORE PRECIP TAPERS TO DRIZZLE
WEST TO EAST LATE TONIGHT/EARLY CHRISTMAS MORNING. DEFORMATION BAND
LINGERS IN THE EAST SUNDAY...WHERE WILL KEEP MENTION OF RA/SN MIX
INTO AFTN HOURS NW INDIANA. AGAIN...EXPECTING NO ACCUMULATION WITH
TEMPS REMAINING ABOVE OR RISING ABOVE FZG AND POTENTIAL FOR MORE OF
A MIX THAN A TOTAL CHANGE OF PHASE TO FROZEN PTYPE. GIVEN SATURATED
LOW LEVELS...LIGHT FOG/STRATUS AND DEWPOINTS IN THE 30S WILL STAY ON
THE HIGH SIDE OF GUIDANCE FOR MINS TONIGHT. ONLY FRZG TEMPS EXPECTED
TO BE NW CWA...AND WILL MENTION PATCHY DZ/FREEZING DZ THOUGH EXPECT
PCPN VERY LGT AND NOT LIKELY TO CAUSE ANY GLAZING PROBLEMS.

UPPER TROUGH PULLS AWAY SUNDAY NIGHT WITH SFC HIGH PRESSURE RIDGE
MOVING IN OVERNIGHT. MODEL TSECTS/SOUNDINGS CONTINUE TO INDICATE
MOIST LOW LEVELS SO WILL ADD SOME LIGHT FOG ESPECIALLY WESTERN AREAS
WHERE MORE LIKELY TO SCT OUT LOW CLOUDS AND IN CLOSER PROXIMITY TO
APPROACHING RIDGE AXIS.

REMAINDER OF FCST...TREND CONTINUES TO BE GENERALLY ABOVE NORMAL IN
TEMPS IN SLIGHTLY AMPLIFIED BUT RATHER PROGRESSIVE UPPER PATTERN.
PRECIP CHANCES WED/WED NIGHT SOUTHERN PARTS...THEN CHANCE CWA WIDE
FRIDAY/SATURDAY. WITH ABOVE NORMAL TEMP TREND...MODEL THERMAL FIELDS
SUPPORT MAINLY MIX RA/SN BOTH EPISODES...THOUGH ADMIT A LONG WAYS IN
ADVANCE FOR TOO MUCH DETAIL AT THIS POINT.

RATZER

&&

.AVIATION...
1040 PM CST...25/06Z TAFS

MORE SUSTAINED NLY WIND WORKING INTO TAF SITES NOW AS PRECIP TANDS
TO FADE. CIGS HAVE SETTLED DOWN BELOW 5HND FT MOST SPOTS BUT VIS
MORE VARIABLE BUT OCNL DOWN TO 1/4 MI. CONDS SHOULD NOT CHANGE MUCH
REST OF THE NIGHT WITH BIG QUESTION WHETHER VIS WILL FALL FURTHER
GIVEN REMAINING SNOW FIELD AND WET AIRMASS. IN ANY EVENT IFR TO LIFR
CONDS WILL PREVAIL NEXT 12 HRS OR MORE. AS UPPER TROUGH AND SURFACE
LOW RETREAT EAST SOME IMPROVMENT LIKELY SUNDAY ESP WITH VIS. NO
CLEARING EXPECTED UNTIL MONDAY THOUGH AS MODEL SOUNDINGS SUGGEST
STRENGTHENING INVERSION SUN NIGHT AND MONDAY AS WARM AIR RUSHES IN
ALOFT. IFR CONDS ARE PROBABLE MOST AREAS THROUGH MOST OF SUN.  KML

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
.IL...DENSE FOG ADVISORY UNTIL 8 AM CST SUNDAY...FORD...IROQUOIS AND
      KANKAKEE.
.IN...DENSE FOG ADVISORY UNTIL 8 AM CST SUNDAY...LAKE...PORTER...
      NEWTON...JASPER AND BENTON.
.LM...SMALL CRAFT ADVISORY SUNDAY MORNING THRU SUNDAY NIGHT.

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
755 PM CST SAT DEC 24 2005

ILZ003>006-008-010>014-019>022-023-032-033-039-INZ001-002-010-011-
019-251200-
WINNEBAGO-BOONE-MCHENRY-LAKE IL-OGLE-LEE-DE KALB-KANE-DU PAGE-COOK-
LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-IROQUOIS-FORD-
LAKE IN-PORTER-NEWTON-JASPER-BENTON-
755 PM CST SAT DEC 24 2005

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL
AND NORTHEAST ILLINOIS...AND NORTHWEST INDIANA.

.DAY ONE... TONIGHT

A DENSE FOG ADVISORY IS IN EFFECT FOR AREAS EAST OF A LINE FROM
GARY TO BONFIELD TO GIBSON CITY...GENERALLY EAST OF INTERSTATE 57.
DENSE FOG WILL BECOME MORE WIDESPREAD ACROSS THESE AREAS.

LIGHT RAIN WILL TAPER OFF TO PATCHY DRIZZLE ACROSS MUCH OF THE
ILLINOIS PORTION OF THE OUTLOOK AREA TONIGHT. TEMPERATURES ARE
EXPECTED TO REMAIN ABOVE FREEZING FOR THE MOST PART...BUT MAY FALL
TO...OR JUST BELOW FREEZING MAINLY NEAR THE WISCONSIN BORDER BY
EARLY SUNDAY MORNING. THUS PATCHY FREEZING DRIZZLE COULD CAUSE SOME
SLICK SPOTS ON LIGHTLY USED ROADS...PARKING LOTS OR SIDEWALKS.
FARTHER SOUTH AND EAST...SOME WET SNOW MAY MAY MIX IN WITH THE RAIN
ACROSS SOUTHEASTERN PARTS OF THE OUTLOOK AREA. NO SIGNIFICANT
ACCUMULATION IS EXPECTED HOWEVER.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

A DENSE FOG ADVISORY IS IN EFFECT UNTIL 8 AM CST FOR AREAS EAST OF
A LINE FROM GARY TO BONFIELD TO GIBSON CITY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NECESSARY.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)

LMZ740>745-766-251200-
WINTHROP HARBOR IL TO MICHIGAN CITY IN-
LAKE MICHIGAN-
755 PM CST SAT DEC 24 2005

THIS PORTION OF THE HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS
AND INDIANA WATERS OF LAKE MICHIGAN.

.DAY ONE... TONIGHT

AREAS OF FOG WILL BE POSSIBLE ACROSS SOUTHERN LAKE MICHIGAN.

.DAYS TWO THROUGH SEVEN... SUNDAY THROUGH FRIDAY

A SMALL CRAFT ADVISORY IS IN EFFECT SUNDAY MORNING THROUGH LATE
SUNDAY NIGHT. NORTH WINDS WILL INCREASE TO 25 KNOTS AND WAVES WILL
BUILD TO 6 FEET OR MORE.

&&

COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE
NWS CHICAGO WEBPAGE: WEATHER.GOV/CHICAGO (LOWER CASE)