FXUS63 KILX 040549
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1149 PM CST THU DEC 3 2009

.DISCUSSION...
ISSUED 843 PM CST THU DEC 3 2009

CLOUD SHIELD ASSOCIATED WITH UPPER LOW OVER SOUTHERN WISCONSIN IS
NOW WORKING ITS WAY INTO CENTRAL ILLINOIS...WITH ALL AREAS ALONG
AND WEST OF THE ILLINOIS RIVER CURRENTLY OVERCAST. CLOUDS WILL
CONTINUE TO SPREAD FURTHER EAST OVERNIGHT...RESULTING IN MOSTLY
CLOUDY CONDITIONS ACROSS THE BOARD. RADAR MOSAIC/SURFACE OBS SHOW
SNOW FLURRIES AS FAR SOUTH AS SOUTHERN IOWA. THESE WILL PUSH E/NE
INTO THE FAR NORTHERN KILX CWA FROM PEORIA NORTHWARD OVERNIGHT.
BASED ON RADAR TRENDS...HAVE REMOVED CHANCE FOR FLURRIES FURTHER
SOUTH IN THE SPRINGFIELD AREA. 02Z TEMPS HAVE ALREADY SLIPPED INTO
THE UPPER 20S IN MOST LOCATIONS...SO HAVE ADJUSTED OVERNIGHT LOWS
DOWN BY A COUPLE OF DEGREES. SHOULD MAINLY SEE LOWER TO MIDDLE
20S...WITH A FEW TEENS POSSIBLE ACROSS THE ILLINOIS RIVER VALLEY.

&&

.AVIATION...
ISSUED 1149 PM CST THU DEC 3 2009

SCT-BKN LOW-LEVEL CLOUDINESS CONTINUES TO PIVOT INTO CENTRAL
ILLINOIS FROM THE WEST...AS VORT LOBE ROTATES AROUND UPPER LOW
CENTERED OVER SOUTHERN WISCONSIN. CEILINGS ALONG AND WEST OF THE
ILLINOIS RIVER ARE GENERALLY AROUND 3500FT...WITH A FEW LOCATIONS
DROPPING DOWN TO AROUND 2000FT WITH SNOW FLURRIES. WILL GRADUALLY
SPREAD 3500FT CEILINGS ACROSS THE AREA TONIGHT...STARTING AT
KPIA...THEN REACHING KCMI BY 09Z. 00Z NAM-WRF FORECAST SOUNDINGS
AND RH PROFILES INDICATE CONTINUED MOSTLY CLOUDY CONDITIONS ON
FRIDAY...AS POCKET OF VERY COLD AIR ALOFT WILL ENSURE STEEP LAPSE
RATES AND DIURNAL CLOUD DEVELOPMENT IN ANY BREAKS THAT DEVELOP IN
THE OVERCAST. WILL THEREFORE CONTINUE WITH CEILINGS OF 5000FT FOR
THE BALANCE OF THE DAY INTO THE EVENING. MODELS ARE SUGGESTING A
GRADUAL CLEARING TREND BY LATE EVENING...BUT HAVE DECIDED TO LEAVE
THE CLOUD COVER IN PLACE FOR NOW. WINDS WILL INITIALLY BE FROM THE
WEST AT 10 TO 15KT...BUT WILL DECREASE TO AROUND 5KT AND BACK TO
SOUTHWEST BY FRIDAY EVENING.

BARNES
&&

.PREV DISCUSSION...
ISSUED 300 PM CST THU DEC 3 2009

BELOW NORMAL TEMPS WILL CONTINUE THROUGH THE NEXT WEEK...AS THE
UPPER TROUGH AND COLD POOL IN PLACE GIVE WAY TO A MUCH DEEPER
TROUGH FOR TUESDAY/WEDNESDAY. 

SHORT TERM...TONIGHT THROUGH SUNDAY.

SATELLITE IMAGES THIS AFTERNOON SHOW THE SWIRL OF A SHORTWAVE
ACROSS IOWA MOVING EAST TOWARD THE NORTHERN HALF OF ILLINOIS.
LIGHT SNOW SHOWERS/FLURRIES ARE OCCURRING AS THE WAVE PROGRESSES
EASTWARD. SHORT TERM MODELS INDICATE THE BEST CHANCES OF VERY LIGHT
MEASURABLE SNOW WILL REMAIN NORTH OF OUR CWA. WE WILL KEEP
FLURRIES TONIGHT FOR AREAS NORTH OF SPRINGFIELD TO PARIS.

COLD SURFACE HIGH PRESSURE IS EXPECTED TO PREVAIL ACROSS CENTRAL
IL THROUGH THE WEEKEND...AS THE UPPER TROUGH AXIS REMAINS JUST
WEST OF IL. SUNDAY SHOULD BE THE WARMEST DAY OF THE NEXT
WEEK...AS SOUTHEAST WINDS INCREASE AHEAD OF THE NEXT SHORTWAVE FOR
SUNDAY NIGHT. STILL...BELOW NORMAL TEMPS ARE EXPECTED...DESPITE
SOME DECEMBER SUNSHINE THIS WEEKEND.

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY.

SUNDAY NIGHT THE NEXT SHORTWAVE WILL ARRIVE FROM THE CENTRAL
PLAINS. A BRIEF SHOT OF ISENTROPIC LIFT WILL ACCOMPANY A FAST
MOVING POTENTIAL VORTICITY /PV/ ANOMALY. THERE WILL BE THE
POTENTIAL FOR A DUSTING OF SNOW...AS SURFACE LOW PRESSURE LIFTS
FROM NORTHERN MISSOURI AT MIDNIGHT SUNDAY NIGHT...ACROSS NW IL...TO
EASTERN WIS BY NOON ON MONDAY.

A MORE SIGNIFICANT SYSTEM IS EXPECTED FOR LATE TUESDAY THROUGH
WED MORNING OF NEXT WEEK. A HIGH AMPLITUDE UPPER TROUGH WILL
DEVELOP IN THE SW STATES ON MONDAY AND REACH IL ON WEDNESDAY.
BY TUESDAY MORNING...SURFACE CYCLOGENESIS WILL INTENSIFY OVER THE
SOUTHERN MISSISSIPPI RIVER VALLEY...AND LIFT NORTH-NORTHEAST
TUESDAY NIGHT...REACHING NEAR OHIO BY WED AFTERNOON.

THIS STORM TRACK HAS BEEN HIGHLY VARIABLE IN THE RECENT MODEL
RUNS...SO POPS WERE HELD OUT OF THE LIKELY CATEGORY TUESDAY
AFTN/NIGHT. THE GFS TAKES A LOW WELL SE OF IL...WHILE THE ECMWF
TAKES THE LOW ACROSS THE NW CORNER OF OUR CWA. HIGHLY DIFFERENT
OUTCOMES WOULD OCCUR IN EACH CASE. FOR NOW...WE TRENDED WITH THE
ECMWF...AND KEPT A BROAD MID CHANCE POP EVERYWHERE TUESDAY AFTN
AND TUESDAY NIGHT....WITH LINGERING POPS WED MORN. IF THE GFS
SOLUTION PANS OUT...A BAND OF LIGHT SNOW COULD DEVELOP ACROSS THE
CWA FROM RUSHVILLE/JACKSONVILLE TO BMI DURING THAT TIME.

WILL KEEP A CLOSE EYE ON THE EXPECTED TRACK OF THAT LOW...AND THE
POTENTIAL FOR MEASURABLE SNOWS NEXT WEEK.

CHILLY HIGH PRESSURE IS EXPECTED TO RETURN FOR THURSDAY BEHIND
THAT MID WEEK LOW.

&&

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

$$