FXUS63 KILX 260534
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1134 PM CST FRI DEC 25 2009
.DISCUSSION...
ISSUED 842 PM CST FRI DEC 25 2009
CURRENT FORECAST APPEARS TO BE ON TRACK AS SNOW SHOWERS MOVE NORTH
OF THE REGION AND SOUTHWEST WINDS CONTINUE TO BE GUSTY. TEMPS WILL
CONTINUE TO FALL AS WELL...EVEN IN THE SOUTHEAST. THEREFORE NO
UPDATE REQUIRED AT THIS TIME.
AUTEN
&&
.AVIATION...
ISSUED 1134 PM CST FRI DEC 25 2009
ALL SITES SHOULD START AS VFR OVERNIGHT AND THEN GRADUALLY
DECREASE TO MVFR FOR MOST OF THE DAY. PIA AND BMI SHOULD DECREASE
TO IFR WITH TEMPO LIFR AS CIGS AND VIS SHOULD GET LOWER WITH
INCREASING SNOWFALL. SPI...DEC AND CMI WILL SEE TEMPO IFR
CONDITIONS AS THE BEST SNOWFALL SHOULD BE NORTH AND NORTHWEST OF
THESE SITES. ANOTHER SHORT WAVE WILL ROTATE AROUND THE SYSTEM TO
THE NORTHWEST AND BRING ANOTHER ROUND OF SNOWFALL TO THE AREA FOR
TOMORROW. BEST SITES WILL BE PIA AND BMI FOR LOWER CIGS AND VIS.
CONDITIONS SHOULD IMPROVE TO MVFR UP NORTH AND VFR FOR SPI...DEC
AND CMI AS THE SHORT WAVE ROTATES OUT OF THE AREA. WINDS WILL BE
SOUTHERLY AND THEN SWITCH TO SOUTHWESTERLY TOMORROW. SPEEDS WILL
DECREASE TONIGHT BUT THEN BECOME SLIGHTLY GUSTY AGAIN
TOMORROW...THEN DIMINISH AGAIN AFTER SUNSET.
AUTEN
&&
.PREV DISCUSSION...
ISSUED 234 PM CST FRI DEC 25 2009
A RATHER UNUSUAL WEATHER DAY IS UNFOLDING ACROSS CENTRAL AND
SOUTHEAST ILLINOIS AS RAIN SHOWERS CHANGED TO SNOW SHOWERS AND
COLDER TEMPERATURES ARE SURGING IN FROM THE SOUTHWEST. DEEP LOW
PRESSURE...CURRENTLY CENTERED OVER IOWA...WILL BE THE DOMINANT
WEATHER FEATURE ACROSS THE MIDWEST/GREAT LAKES REGION THROUGH THE
WEEKEND. NOT SURPRISINGLY...THIS FEATURE AND THE SNOW SHOWERS/COLD
TEMPERATURES/GUSTY WINDS ASSOCIATED WITH IT ARE THE PRIMARY
FORECAST CONCERNS TODAY.
12Z MODELS PRETTY SIMILAR IN THE HANDLING OF THE AREA OF LOW
PRESSURE...AS WELL AS THE UPPER FEATURES DRIVING IT. SO...NO THERE
IS NO SIGNIFICANT MODEL PREFERENCE OVER THE NEXT FEW DAYS.
SHORT TERM...TONIGHT THROUGH MONDAY...THE SURFACE LOW TO OUR
NORTHWEST WILL NOT MOVE MUCH INTO SATURDAY AS THE COMPLEX UPPER
LOW ON TOP OF IT CONTINUES TO EVOLVE/WOBBLE. AS THE SYSTEM IS
OCCLUDED/VERTICALLY STACKED...IT WILL SLOWLY WEAKEN WITH TIME.
HOWEVER...TWO STRONG SPOKES OF ENERGY WRAPPING AROUND THE UPPER
LOW WILL PROVIDE US WITH ENHANCED SNOW CHANCES. THIS ENERGY IS
CLEARLY EVIDENT ON WATER VAPOR LOOPS. THE FIRST SPOKE IS WORKING
EAST NORTHEAST ACROSS MISSOURI AT THE MOMENT. THE FORCING...MANLY
DPVA...WITH THIS FEATURE WILL KEEP SCATTERED/NUMEROUS SNOW SHOWERS
GOING THIS EVENING. THE SNOW SHOWER CHANCES WILL WANE OVERNIGHT AS
THIS FEATURE MOVES NORTHEAST OF THE REGION. THE MOISTURE
ASSOCIATED WITH THIS LEAD WAVE IS LIMITED AND SHOULD LIMIT SNOW
AMOUNTS TO A DUSTING. THE SECOND SPOKE OF ENERGY IS CURRENTLY
MOVING WEST ACROSS NORTHERN IA/SOUTHERN MN. THIS FEATURE WILL
CIRCLE THE UPPER LOW AND HELP TO SLOWLY EJECT IT NORTHEAST ON
SATURDAY. SNOW CHANCES/AMOUNTS WILL BE BETTER WITH THIS WAVE. THE
MOISTURE DEPTH IS EXPECTED TO BE DEEPER AND THE DPVA WILL BE
FAIRLY STRONG. IN ADDITION...THIS WAVE WILL ALSO HAVE A POCKET OF
WAA/ISENTROPIC LIFT TO WORK WITH THANKS TO THE COLD POCKET/LOWER
HEIGHTS TRAILING THE LEAD WAVE. THIS ADDED MOISTURE/STRONGER LIFT
SHOULD BE ABLE TO SQUEEZE OUT AN INCH OF TWO OF SNOW SATURDAY...
PRIMARILY NORTH OF THE I-72 CORRIDOR.
THE STACKED SYSTEM WILL CONTINUE TO SLOWLY PULL AWAY FROM THE
REGION SATURDAY NIGHT INTO SUNDAY NIGHT AS IT WEAKENS AND IS
DRAWN IN TO THE MEAN FLOW. HOWEVER...ENOUGH CYCLONIC FLOW WILL
PERSIST TO PRODUCE SCATTERED SNOW SHOWERS OR FLURRIES. LITTLE/NO
SNOW ACCUMULATION IS ANTICIPATED SATURDAY NIGHT THROUGH SUNDAY NIGHT.
HIGH PRESSURE SHOULD BEGIN TO RIDGE INTO THE REGION...BOTH AT THE
SURFACE AND ALOFT...BY MONDAY. THIS WILL BRING THE SNOW CHANCES TO
AN END AND ALLOW TEMPERATURES TO MODERATE.
LONG TERM...MONDAY NIGHT THROUGH FRIDAY...MODELS/ENSEMBLES DIFFER
SOME ON THE DETAILS...BUT THE AGREEMENT IS RESPECTABLE FOR FEATURES
EXPECTED TO IMPACT FORECAST AREA. THE UPPER FLOW WILL TEND TO
SPLIT IN THE WAKE OF OUR DEPARTING WEEKEND STORM SYSTEM...WITH
THE MAIN ENERGY IN THE FLOW STAYING TO OUR NORTH AND SOUTH.
HOWEVER...A WEAK IMPULSE...AND ASSOCIATED RISK OF SNOW...IS
EXPECTED TO ARRIVE BY WEDNESDAY, HAVE MAINTAINED A SLIGHT CHANCE
OF SNOW TO COVER THIS POTENTIAL...THOUGH THE BETTER PRECIPITATION
CHANCES WILL STAY MORE CLOSELY TIED TO TO THE SOUTHERN STREAM OF
THE JET NEAR THE GULF COAST.
BAK
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH SATURDAY AFTERNOON FOR ILZ051.
&&
$$
