000
FXUS63 KLOT 061142
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
540 AM CST TUE JAN 6 2009
.DISCUSSION...
317 AM...MODELS COMING INTO A LITTLE BETTER AGREEMENT THIS MORNING
REGARDING LIGHT PRECIP ACROSS MAINLY THE SOUTHEAST CWA THRU THIS
AFTERNOON. BULK OF THE QPF STAYS GENERALLY SOUTHEAST OF THE CWA
WITH ONLY A HUNDREDTH OR TWO THROUGH THE DAY ACROSS THE SOUTHEAST
CWA. HOWEVER...THERMAL PROFILES AND SOUNDINGS SUGGEST THAT THE
BULK OF ANY PRECIP THAT FALLS TODAY WILL BE IN THE FORM OF
FREEZING DRIZZLE...OR PERHAPS LIGHT FREEZING RAIN SHOULD QPF
AMOUNTS END UP BEING HIGHER THAN EXPECTED. PERHAPS A LITTLE SNOW
TO START UNTIL WARMER TEMPS PUSH NORTH AND THE MID DECK SHIFTS
EAST. WHILE GUIDANCE DOES WARM TEMPS TO NEAR FREEZING LATER THIS
AFTERNOON...MIGHT BE STRUGGLE TO GET THERE WITH CLOUD COVER AND
DRIER EASTERLY FLOW. DON/T HAVE A PARTICULARLY HIGH DEGREE OF
CONFIDENCE WITH THIS EVENT AND SINCE IT ONLY TAKES A SMALL AMOUNT
OF FREEZING DRIZZLE/RAIN TO CAUSE PROBLEMS...WILL ISSUE A FREEZING
RAIN ADVISORY FOR BENTON COUNTY WITH THIS FORECAST... WHICH MAY
NEED TO BE EXPANDED NORTH...DEPENDING ON HOW PRECIP
DEVELOPS/EVOLVES THRU THE MORNING.
UPPER TROUGH APPROACHES LATE THIS AFTERNOON AND THIS EVENING WITH
A WEAK SHORTWAVE RIDING NORTHEAST AHEAD OF IT. THIS SHOULD PROVIDE
ENOUGH LIFT FOR SOME VERY LIGHT SNOW...NO MORE THAN A DUSTING AND
THIS WILL BE MAINLY OVER NORTHEAST IL/NORTHWEST INDIANA BUT WILL
ONLY HAVE CHANCE POPS DURING THIS TIME.
THE UPPER LOW MOVES RIGHT ACROSS THE CWA WEDNESDAY AFTERNOON AND
THIS MAY ENDED UP PROVIDING THE BEST CHANCE OF LIGHT SNOW OR SNOW
SHOWERS. HAVEN/T MADE TOO MANY CHANGES DURING THIS TIME WITH JUST
CHANCE POPS AND A FEW TENTHS OF AN INCH OF SNOWFALL IN THE GRIDS.
THIS SHIFTS EAST WEDNESDAY EVENING WITH LINGERING FLURRIES ENDING.
TEMPS WARM TO THE LOWER/MID 30S TODAY. LOWS TONIGHT WILL BE
WEDNESDAY MORNING AS A COLD FRONT PASSES. GUIDANCE SHOWING SOME
RECOVERY IN HIGH TEMPS ON WEDNESDAY AND THIS LOOKS A BIT OVERDONE
WITH STRONG CAA. HIGHS LIKELY WILL BE IN THE MORNING WITH SLOWLY
FALLING TEMPS THRU THE AFTERNOON.
WAA DEVELOPS THURSDAY NIGHT INTO FRIDAY MORNING AS A CLIPPER
SYSTEM MOVES ACROSS THE LAKES REGION. ECMWF HAS BEEN RATHER
CONSISTENT WITH THIS SYSTEM...SHOWING PRECIP TO REMAIN ACROSS THE
NORTHERN CWA OR NORTH OF THE AREA WITH THE GFS NOW TRENDING THIS
DIRECTION. HAVE TRIMMED POPS FROM THE SOUTH AND WARMED TEMPS UP
SEVERAL DEGREES...CLOSER TO BUT NOT AS WARM AS THE LATEST MEX.
TEMPS MAY END UP BEING A FEW DEGREES WARMER. NO CHANGES AFTER
FRIDAY NIGHT. CMS
&&
.AVIATION...DISCUSSION REGARDING 12Z TAFS...
540 AM CST
PRESSING QUESTION THIS MORNING IS WHETHER OR NOT PRECIP SHOWING UP
ON RADAR OVR CNTRL IL WILL BE RACHING THE SFC AS IT LIFTS NEWD
ACROSS NERN IL/NWRN IND. FOR NOW HAVE OPTED TO KEEP TAFS
DRY...ESPECIALLY AT RFD AND ORD WHERE ACARS AND FCST SOUNDINGS
SUGGEST THERES A LOT OF DRY AIR FOR FALLING PRECIP TO OVERCOME.
FURTHER TO THE S AND E EXPECT SOME LIGHT SNOW OR MIXED PRECIP TO
REACH SFC...BUT THIS MOST FAVORED AREA FOR PRECIP IS EXPECTED TO BE
S OF TERMINALS.
THIS FIRST WAVE OF REFLECTIVITY HAS DEVELOPED AHEAD OF SHORT WAVE
NOW MOVING INTO W CNTRL IL...AND LIFTING QUICKLY NEWD AT ARND 50 KTS
BASED ON IR SATLT FIX. THIS FEATURE WILL BE PASSING NEWD THRU AREA
ERLY THIS MRNG AND WILL BE OFF TO N AND E BY 16Z. THIS SHOULD END
PRECIP THREAT UNTIL LOW PRESSURE GETS BETTER ORGANIZED OVR UPR OH
VLY THIS EVENING. PRECIP SHIELD FROM THIS STORM IS EXPECTED TO BE
OFF TO E OF RGN...SO WILL KEEP TERMINALS DRY TNGT...AND DONT EXPECT
ANY WIDESPREAD PCPN UNTIL UPR LVL LOW CENTER DEEPENS AND DROPS DOWN
OVR AREA ON WED. AS TROPOSPHERE COOLS WITH THE APCH AND DEEPENING
OF THIS LOW...EXPECT OCNL LGT SNOW TO DVLP DURG 24-30 HR PERIOD.
OTHER FACTOR TO NOTE BASED ON SATLT IMAGERY AND SFC OBS IS THAT CIGS
DROP INTO MVFR RANGE AS SHORT WAVE TROF AXIS MOVES THRU. LEADING
EDGE OF THIS LWR CLOUD DECK IS NOW LIFTING NNEWD ACROSS SERN IA AND
W CNTRL IL...SO HAVE TIMED IT ACROSS AREA BASED ON ARRIVAL OF SHRT
WAVE TROF AXIS. FCST SOUNDINGS THEN LWR THIS DECK TO BLO FL020 BY
LATE THIS AFTN. EXPECT IMPROVEMENT BACK TO VFR CIGS AS SFC TROF
MOVES THRU DURG 04Z-07Z TIME FRAME...CAUSING WINDS TO SHIFT TO W AND
INCR TWD 12Z. THIS ADVECTION OF DRIER/COLDER AIR IN LLVLS SHOULD
ERODE LWR STRATUS DECK.
MERZLOCK
&&
.MARINE...
335 AM CST
HIGH PRESSURE OVER THE UPPER OHIO VALLEY WILL GIVE WAY
TO DEVELOPING LOW PRESSURE OVER THE PLAINS STATES. INITIALLY...THIS
LOW PRESSURE AREA WILL BE POORLY ORGANIZED AND COMPOSED OF TWO
CENTERS. ONE OVER SOUTH DAKOTA AND THE OTHER OVER THE
OKLAHOMA PANHANDLE REGION. THESE LOWS WILL MOVE EASTWARD TO THE
WESTERN GREAT LAKES AND MISSISSIPPI VALLEY TODAY AND TONIGHT
BEFORE EVOLVING INTO ONE CENTER OVER OHIO BY EARLY WEDNESDAY. THIS
LOW IS THEN FORECAST TO INTENSIFY AS IT MOVES TO NEAR TORONTO
WEDNESDAY EVENING. HIGH PRESSURE WILL THEN BE BUILDING SOUTHEASTWARD
ACROSS THE DAKOTAS AND MINNESOTA. THIS COMBINATION WILL CAUSE WEST
TO NORTHWEST WINDS TO DEVELOP LATE TONIGHT ON THE SOUTH END OF LAKE
MICHIGAN...AND BY WEDNESDAY EVENING IN THE NORTH. SUSTAINED WINDS
WILL INCREASE TO NEAR 30 KNOTS...WITH A FEW GUSTS OCCASIONALLY
REACHING GALE FORCE WEDNESDAY NIGHT.
MERZLOCK
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...FREEZING RAIN ADVISORY...INZ019...8 AM TUESDAY TO 6 PM TUESDAY.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...NOON
WEDNESDAY TO 6 AM THURSDAY.
SMALL CRAFT ADVISORY...LMZ744-LMZ745...NOON WEDNESDAY TO NOON
THURSDAY.
&&
$$
