FXUS63 KILX 120825
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
225 AM CST SAT DEC 12 2009

.DISCUSSION...
ISSUED 225 AM CST SAT DEC 12 2009

SOUTHERLY FLOW WAS FOUND ACROSS THE CWA EARLY THIS MORNING...ON
THE BACK SIDE OF HIGH PRESSURE CENTERED NEAR THE CAROLINA COAST.
TEMPERATURES OVER THE AREA HAVE BEEN ONLY SLOWLY FALLING THE LAST
FEW HOURS...AND WERE MAINLY IN THE 20S. JUST SOME HIGH CLOUDS
MOVING ALONG THE I-72 CORRIDOR AT THE MOMENT. LOWER DECK OF
STRATOCUMULUS TRYING TO MAKE SOME NORTHEAST PROGRESSION OUT
MISSOURI...BUT LAPS SOUNDINGS OVER OUR AREA ARE RATHER DRY.

MAIN FORECAST ISSUE FOR THIS PACKAGE INVOLVES PRECIPITATION TYPES
TONIGHT...AND ANY CHANCES OF PRECIPITATION ON MONDAY.

SHORT TERM...TODAY THROUGH MONDAY...

NO MAJOR DISCREPANCIES NOTED IN THE MODELS THROUGH THE PERIOD. DRY
WEATHER IS EXPECTED TODAY. HOWEVER...PRECIPITATION THREAT IS
EXPECTED TO BEGIN TO OUR SOUTHWEST THIS AFTERNOON...WITH
ISENTROPIC LIFT BEING SHOWN ON THE 300K SURFACE BY 00Z. MAIN TIME
FRAME OF CONCERN FOR PRECIPITATION IN OUR AREA IS FROM ABOUT
00-08Z...LINGERING A BIT LONGER EAST OF I-57. FORECAST SOUNDINGS
FROM BOTH THE NAM AND GFS SHOWING THAT RAIN WILL BE THE PRECIP
TYPE OF CHOICE ACROSS MOST OF THE AREA...PERHAPS MIXED WITH SOME
SLEET OR FREEZING RAIN AT THE BEGINNING NORTHWEST OF THE ILLINOIS
RIVER. SIGNIFICANT DRYING OF THE COLUMN FROM THE TOP DOWN WILL
RESULT IN THE PRECIPITATION TAPERING TO DRIZZLE...WHICH MAY LINGER
INTO SUNDAY MORNING. MAIN TROUGH AXIS SHOULD SWING THROUGH THE
AREA LATER ON SUNDAY.

NEXT ISSUE OF CONCERN INVOLVES A DEVELOPING STORM SYSTEM OVER
KANSAS AND OKLAHOMA. SOME MINOR TRACKING DIFFERENCES AMONG THE
MODELS WITH THE PARENT SURFACE LOW...ALTHOUGH THE SREF IS MUCH
FASTER THAN THE OTHERS. MAIN FRONTAL BOUNDARY IS PROGGED TO MOVE
THROUGH THE CWA MONDAY AFTERNOON. BEST FORCING AND LIFT WITH THIS
SYSTEM EXPECTED TO BE CLOSER TO THE GREAT LAKES REGION. AS
SUCH...WILL ONLY CARRY SLIGHT POPS IN THE MONDAY GRIDS WITH THIS
FEATURE. 

LONG TERM...TUESDAY THROUGH FRIDAY...

IN THE LONGER RANGE...UPPER RIDGING IS EXPECTED TO BUILD ACROSS
THE WESTERN U.S. AS THE WEEK PROGRESSES. SURFACE HIGH PRESSURE
WILL BUILD SOUTHEAST FROM THE NORTHERN PLAINS...WITH DRY WEATHER
PREVAILING TUESDAY THROUGH THURSDAY. NEXT UPPER TROUGH IS EXPECTED
TO MOVE THROUGH THE GREAT LAKES BY FRIDAY...BUT THE LONG RANGE
MODELS ARE IN DISAGREEMENT ON THE TIMING OF ANY ASSOCIATED
PRECIPITATION.

GEELHART

&&

.AVIATION...
ISSUED 1115 PM CST FRI DEC 11 2009

BAND OF LOW VFR CIGS ACRS SRN MO TRACKING MORE EAST THE NORTH LATE
THIS EVENING...WHILE SATELLITE DATA ALSO INDICATING ANOTHER SURGE
OF LOW LEVEL MOISTURE/CLOUDS STREAMING NWD OUT OF ERN OK. STILL 
APPEARS VFR CONDITIONS WILL PREVAIL UNTIL MID AFTN ACRS SPI AND 
PIA AND PROBABLY INTO THE EARLY EVENING ACRS CMI BEFORE A WEAK
WEATHER DISTURBANCE SHIFTS NE ACRS THE AREA SAT NIGHT INTO SUN
MORNING. MODEL DATA CONTINUING TO SHOW A 300 MB SPEED MAX TRACKING
TO OUR SOUTH TMRM NIGHT WITH OUR SRN AREAS IN THE MORE FAVORABLE
LEFT EXIT REGION...WHICH WOULD SUPPORT MORE WIDESPREAD RAINFALL
ACRS THAT AREA. FURTHER NORTH...THE LIFT IS NOT AS STRONG AND THE
MOISTURE NOT AS DEEP ON FORECAST SOUNDINGS...SUGGESTING MORE OF
A LIGHT RAIN OR DRIZZLE SCENARIO. 

INITIALLY...WITH A VERY DRY AIR MASS AT THE LOW LEVELS...THERE IS
THE POSSIBILITY THAT SFC TEMPS MAY SLIP BACK TO OR BELOW FREEZING
AS THE PRECIP STARTS WHICH WOULD BRING A BRIEF PERIOD OF FZRA/FZDZ
TO PIA AND PSBLY BMI. HOWEVER...A PERSISTENT SOUTHERLY WIND SHOULD
BALANCE OUT THE EVAPORATIVE COOLING EFFECTS AND CHANGE ANY FZRA/FZDZ
ACRS OUR FAR NRN TAF SITES TO LIGHT RAIN OR DRIZZLE LATER SATURDAY
EVENING. FOR NOW WL INCLUDE VCSH DURING THE EARLY EVENING HOURS
AND SEE HOW LATER MODEL RUNS CLARIFY ANY PRECIP TYPE ISSUES OVER
THE NORTH.

SURFACE WINDS WILL REMAIN OUT OF THE SOUTH INTO SATURDAY WITH WINDS
BACKING A BIT MORE INTO THE SOUTHEAST BY EVENING. MAY SEE A FEW GUSTS
BY LATE SAT MRNG INTO THE AFTN HOURS. 

SMITH

&&

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

$$