FXUS63 KILX 042327
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
527 PM CST FRI DEC 4 2009

.DISCUSSION... 
CORRECTED WORDING AND ADDED ADDITIONAL DISCUSSION TO EXTENDED.

ISSUED 300 PM CST FRI DEC 4 2009

MAIN CONCERN IS ON THE STORM SYSTEM FOR TUES-WED NEXT WEEK...AND
POTENTIAL FOR MEASURABLE SNOWS AND/OR MIXED PRECIP. THE TRACK OF
THE LOW REMAINS A QUESTION MARK...AS THE 12Z GFS AND ECMWF NEARLY
SWAPPED SOLUTIONS WITH THEIR 00Z COUNTERPARTS. THE 12Z GFS SHOWS A
FARTHER NW TRACK...TAKING THE LOW FROM SW TO NE ACROSS OUR
CWA...WHILE THE ECMWF TAKES THE LOW FARTHER SE...ACROSS THE
SOUTHERN TIP OF IL/IN. EACH TRACK WOULD PRODUCE SIGNIFICANTLY
DIFFERENT PRECIP OUTCOMES...WITH THE NEW ECMWF COLDER AND MORE
SNOWY FOR OUR CWA...AND THE GFS WARMER IN THE SE HALF OF OUR
CWA...WITH MORE RAIN IN THAT AREA.

BASICALLY TRENDED WITH A SLIGHTLY WARMER SOLUTION...CLOSER TO THE
00Z ECMWF/12Z GFS. ADDED HIGHER RAIN CHANCES TUESDAY NIGHT SE OF
I-70...AS WARMER AIR SOUTH OF THE LOW WOULD INVADE OUR E-SE CWA.

SHORT TERM...TONIGHT THROUGH MONDAY.

A SHEARED OUT H5 VORT AXIS COUPLED WITH RESIDUAL BOUNDARY LAYER
MOISTURE TO KEEP CLOUDS AND FLURRIES LINGERING ALL DAY ACROSS
CENTRAL IL. THE FOCUSED ARE OF DPVA WILL SLIDE EAST OF THE CWA
DURING THE EVENING...BUT EXPECT FLURRIES TO CONTINUE FOR A FEW
HOURS THIS EVENING. 

CLEARING SKIES AND COLD CONDITIONS WILL PREVAIL THE REMAINDER OF
THE NIGHT...WITH LOWS WELL BELOW NORMAL IN THE TEENS EVERYWHERE. 

HIGH PRESSURE CENTERED SOUTH OF IL WILL MOVE EAST ON SAT AND
SUNDAY. IT WILL STILL PROVIDE DRY CONDITIONS FOR OUR AREA BOTH
DAYS...AND SLIGHTLY WARMER HIGHS AS H85 TEMPS CLIMB TO 6-8C ABOVE
TODAYS NUMBERS BY SAT AFTERNOON. STILL BELOW NORMAL TEMPS HOWEVER.

SUNDAY NIGHT A QUICK MOVING UPPER WAVE AND RESULTANT SURFACE LOW
WILL PASS OVER CENTRAL IL. ALL THE SHORT TERM MODELS HAVE VARYING
SOLUTIONS TO THE PLACEMENT OF THE MID LEVEL FRONT AND BEST FOCUS
FOR PRECIP. GENERAL CONSENSUS IS FOR SCATTERED SNOW SHOWERS TO
DEVELOP SUNDAY NIGHT...BUT NO SIGNIFICANT ACCUMULATIONS IN ANY ONE
AREA. UP TO A HALF INCH MAY ACCUMULATE IN AREAS FROM LINCOLN AND
NORTH...WITH A DUSTING TO A FEW TENTHS SOUTH OF THERE. THE GFS IS
TRYING TO FOCUS SOME HIGHER SNOW TOTALS SOUTH OF I-70...BUT FOR
NOW WILL KEEP LIGHTER SNOW SOUTH OF THE TRACK OF THE H85 LOW. A
FEW FLURRIES MAY LINGER MONDAY MORNING...WITH NO ADDITIONAL
ACCUMULATION.

LONG TERM...TUESDAY THROUGH FRIDAY.

THE MORE SIGNIFICANT SYSTEM WILL BEGIN TO AFFECT OUR AREA ON
TUESDAY. A WIDE SPREAD OF MODEL SOLUTIONS HAS RAISED CONCERNS
ABOUT THE PLACEMENT OF THE HEAVY SNOW BAND...AND THE RAIN/SNOW
LINE. IT APPEARS THAT THIS DYNAMIC SYSTEM WILL HAVE PLENTY OF
ENERGY AND FORCING TO PRODUCE HAZARDOUS TRAVEL CONDITIONS ACROSS
PORTIONS OF CENTRAL IL. THE BEST BET FOR AROUND 2 INCHES OF SNOW
STILL REMAINS NORTHWEST OF LINCOLN...BASED ON THE WARMER 12Z
GFS/00Z ECMWF SOLUTIONS. A RAIN/SNOW LINE WOULD MOST LIKELY SET UP
NEAR SHELBYVILLE TO DECATUR TO DANVILLE TUES NIGHT...THEN SLIDE
EAST ON WEDNESDAY AS THE COLDER AIR WRAPS IN FROM THE WSW CORNER OF
THE CWA. SOME SLEET OR FREEZING RAIN WILL BE POSSIBLE TUES NIGHT...BUT
THIS SYSTEM DOES NOT LOOK LIKE IT WILL PRODUCE AN EXTENDED PERIOD
OF MIXED PRECIP AT THIS POINT. RAIN OR SNOW SHOULD BE THE PROMINENT
PRECIP TYPES.

THE COLDER 12Z ECMWF SOLUTION ACTUALLY PUSHES THE
RAIN/SNOW LINE FARTHER SE...AND EXPANDS THE AREA OF MEASURABLE
SNOW INTO SE IL.

WE STAYED CLOSER TO PERSISTENCE WITH OUR FORECAST...AND WENT
SLIGHTLY WARMER IN THE SOUTHEAST HALF OF THE CWA. UNDER THAT
SCENARIO...WE EXPECT A NON DIURNAL TEMPERATURE SWING ON TUESDAY
NIGHT...WITH RISING TEMPS SOUTHEAST OF THE LOW...OR SE OF
LINCOLN...AND STEADY TEMPS NW OF THERE. THEN WEDNESDAY WOULD
LIKELY SEE FALLING TEMPS AFTER MORNING HIGHS...AS WEST WINDS
BEHIND THE SURFACE LOW PULL COLD AIR INTO C IL.

THE COLDEST AIR WITH THIS SYSTEM SHOULD REMAIN N OF IL...BUT STILL
HIGHS WILL STRUGGLE TO GET OUT OF THE 20S ON THURSDAY...UNDER HIGH
PRESSURE. 

WARM FRONTAL SNOWS ARE INDICATED FOR THURSDAY NIGHT...WITH LOW
PRESSURE AND SNOW SHOWERS FOR FRIDAY. WE WENT WITH SLIGHT CHANCE
POPS FOR SNOW DURING THAT TIME.

&&

.AVIATION...
ISSUED 527 PM CST FRI DEC 4 2009

MAIN AVIATION CONCERN WILL BE DEPARTING LOW-LEVEL CLOUD SHIELD
THIS EVENING. LATEST SATELLITE IMAGERY SHOWS BACK EDGE OF CLOUDS
ALONG A KAA TO K1H2 LINE...AND STEADILY ADVANCING NORTHEASTWARD.
TIMING TOOLS INDICATE CLEAR SKIES AT KCMI BY AROUND 01Z AND AT
KBMI SHORTLY BEFORE 02Z. BKN CLOUD COVER MAY LINGER AT KPIA A BIT
LONGER DUE TO A FETCH OF CLOUDS STRETCHING BACK INTO NORTHEAST
MISSOURI TO NEAR KIRK. HAVE THEREFORE DELAYED CLEARING AT KPIA
UNTIL 04Z. WITH HIGH PRESSURE OVERHEAD ON SATURDAY...SKIES WILL BE
MOSTLY SUNNY...HOWEVER CU RULE INDICATES THE POTENTIAL FOR A FEW
DIURNAL CU AROUND 5000FT. WINDS WILL INITIALLY BE WESTERLY AT 5KT
TONIGHT...THEN WILL BACK TO SOUTHERLY AND INCREASE TO AROUND 10KT
ON SATURDAY.

BARNES
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$