FXUS63 KILX 040930
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
330 AM CST FRI DEC 4 2009

.DISCUSSION...
ISSUED 320 AM CST FRI DEC 4 2009

00Z SHORT RANGE MODELS ARE IN FAIR AGREEMENT THROUGH THIS WEEKEND
AS DRY AND SEASONABLY COOL WEATHER PREVAILS THROUGH SUNDAY. LIKED
THE COOLER NAM/MET TODAY AND SAT ESPECIALLY WITH MORE LOW CLOUDS
MOVING INTO CENTRAL IL TODAY. 00Z EXTENDED MODELS LIKE GFS...ECMWF
AND GEM HAVE TRENDED FURTHER NW WITH TRACK OF DEEPENING LOW
PRESSURE EJECTING NE FROM THE SOUTHERN ROCKIES/GREAT PLAINS MON
NIGHT/TUE ACROSS ILLINOIS LATE TUE NIGHT AND INTO THE CENTRAL GREAT
LAKES WED WITH 980 MB OR DEEPER LOW PRESSURE BY THEN. MODELS
CONTINUE TO SHOW A STORM STORM SYSTEM AFFECTING THE MIDWEST WITH
EITHER SNOW OR A MIXTURE OF PRECIPITATION DEVELOPING OVER
CENTRAL/SE IL TUE WITH BEST CHANCES TUE NIGHT AND DIMINISHING
DURING WED AS COLDER AIR USHERS IN ON BACK SIDE OF STRONG STORM.
HPC/NCEP APPEARED TO FOLLOW FURTHER SE TRACK OF LOW PRESSURE NEAR
I-70 MORE LIKE THE DGEX AND GFS ENSEMBLE MODELS WHERE GFS AND
ECMWF MODELS ARE FURTHER NW WITH THE LOW TRACK ALONG THE IL RIVER
VALLEY.

09Z/3 AM SURFACE MAP SHOWS 1030 MB HIGH PRESSURE OVER WESTERN
KS/OK AND RIDGING EAST INTO THE MID MS AND OHIO VALLEYS. THIS HAD
PROVIDED SOME TEMPORARILY CLEARING OF LOW CLOUDS OVER PARTS OF
CENTRAL AND EASTERN IL INTO INDIANA. A WEAK SURFACE TROF EXTENDED
FROM 1010 MB LOW PRESSURE OVER EASTERN SHORES OF LAKE SUPERIOR
INTO NW LOWER MI INTO SE WI AND ALONG THE IA/IL BORDER. SOME
FLURRIES NEAR THIS BOUNDARY IN NW IL AND ALONG A FAIRLY STRONG
SHORT WAVE TROF NEAR THIS BOUNDARY. ALOFT A STRONG 520 DM 500 MB
LOW WAS OVER NORTHERN ONTARIO NEAR HUDSON BAY WITH A STRONG TROF
EXTENDING ACROSS THE MIDWEST AND SOUTHERN HIGH PLAINS. COOLER
TEMPERATURES WERE IN THE LOW TO MID 20S WITH WSW WINDS 5 TO 15 MPH
AND GUSTING TO 15 TO 25 MPH OVER NORTHERN IL.

SHORT TERM...TODAY THROUGH MONDAY.

UPPER LEVEL SHORT WAVE AND SURFACE TROF TO PIVOT SE ACROSS CENTRAL
IL TODAY BRINGING PARTLY TO MOSTLY CLOUDY SKIES AS LOW CLOUDS
INCREASE ESPECIALLY NORTH OF I-70. COULD BE A FEW FLURRIES NORTH
OF PEORIA THOUGH BETTER CHANCE ACROSS NORTHERN IL FROM I-80 NORTH 
TODAY. HIGHS ONLY IN THE LOW TO MID 30S TODAY WHICH IS CLOSE TO
THE COOLER NAM/MET HIGHS. WSW WINDS 8 TO 15 MPH AND GUSTS NEAR 20
MPH WILL ADD A CHILL TO THE AIR TOO. LOW CLOUDS WILL DECREASE FROM
SW TO NE DURING TONIGHT AS UPPER LEVEL TROF SHIFTS SE OF IL ACROSS
THE OHIO VALLEY AND 1025 MB SURFACE HIGH PRESSURE BUILDS INTO IL.
WEST WINDS BECOME LIGHTER TOO AND THIS SUPPORTS COOLER LOWS IN THE
UPPER TEENS TO NEAR 20F. 

MOSTLY SUNNY SKIES SAT WITH HIGHS IN THE MID TO UPPER 30S WHICH IS
CLOSER TO COOLER NAM/MET HIGHS SINCE 925-850 MB TEMPS ARE STILL
PRETTY COOL AND WARM AIR ADVECTION PATTERN SETS UP LATER IN THE
DAY AS HIGH PRESSURE DRIFTS EAST OF IL. HIGHS PRESSURE DRIFTS INTO
THE MID ATLANTIC STATES SUNDAY WHILE WEAK SURFACE LOW NEAR 1015 MB
EJECTS NE FROM THE TX PANHANDLE INTO NW IL BY DAWN MON. THIS TO
INCREASE HIGH CLOUDS SUNDAY WITH SEASONABLE HIGHS IN THE LOWER 40S
MOST AREA THOUGH A BIT COOLER NORTH OF I-74. HAVE ABOUT A 40%
CHANCE OF LIGHT SNOW SUNDAY NIGHT WITH BEST CHANCES NW OVER THE IL
RIVER VALLEY WHERE HALF TO 1 INCH OF SNOW POSSIBLE. CONTINUED A
CHANCE OF LIGHT RAIN TOO SW OF A SPRINGFIELD TO ROBINSON LINE. BEST
CHANCES OF LIGHT SNOW SHIFT NE OF CENTRAL IL MONDAY.

LONG TERM...MONDAY NIGHT THROUGH THURSDAY.

DRY WEATHER RETURNS BRIEFLY TO IL MONDAY NIGHT AS HIGH PRESSURE
RIDGE DRIFTS INTO THE OHIO VALLEY. MEANWHILE A STRONG UPPER LEVEL
TROF DIGGING SOUTHWARD ACROSS THE ROCKIES MON WILL DEVELOP A
SURFACE LOW OVER THE SOUTHERN ROCKIES THAT EJECTS INTO THE
SOUTHERN PLAINS MON NIGHT AND THEN LIFTS NE ACROSS IL LATE TUE
NIGHT. HPC/NCEP FAVORS A FURTHER SE TRACK OF LOW PRESSURE NEAR
I-70 LIKE DGEX AND GFS ENSEMBLE SHOWS VERSUS FURTHER NW TRACK OF
THE ECMWF AND GFS MODELS ACROSS THE IL RIVER VALLEY WITH ECMWF
BEING FASTER. FURTHER SE TRACK OF LOW WILL SUPPORT MAINLY SNOW
OVER CENTRAL IL WHICH DEVELOPS TUE...WITH A MIXTURE OF PRECIPITATION
OVER SE IL WHICH WOULD PROBABLY START AS RAIN DEVELOPING
TUE...THEN CHANGEOVER TO SNOW TUE NIGHT. SNOW SHOULD DIMINISH FROM
SW TO NE DURING WED AS DEEPENING LOW PRESSURE LIFTS INTO THE GREAT
LAKES. THIS STORM SYSTEM SHOULD BE MONITORED CLOSELY AS IT APPEARS
LIKELY PARTS OF IL ESPECIALLY NORTH OF I-70 WILL SEE THEIR FIRST
MEASUREABLE SNOW OF THE SEASON AND IT COULD BE SIGNIFICANT. COLDER
AIR USHERS INTO IL WED/WED NIGHT ON BACK SIDE OF STORM WITH DRY
WEATHER RETURNING WED NIGHT/THU.

HUETTL

&&

.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

&&

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

&&

$$