FXUS63 KILX 250257
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
857 PM CST THU DEC 24 2009
.DISCUSSION...
ISSUED 857 PM CST THU DEC 24 2009
HOURLY TEMPS AND OVERNIGHT LOW TEMPS NEED TO BE ADJUSTED TONIGHT
TO ACCOUNT FOR CURRENT TRENDS AND WHAT IS EXPECTED OVERNIGHT AND
INTO TOMORROW. BASED ON CURRENT RADAR TRENDS AND NEW MODEL
OUTPUT...WILL LIKELY EXTENDED FLOOD WATCH TIL 6AM IN MORNING. RAIN
WILL STILL TAPER OFF AND DIMINISH AFTER MIDNIGHT BUT FLOODING
POTENTIAL WILL LIKELY CONTINUE UNTIL MORNING. CLOUD COVER...POPS
AND WINDS ALL LOOK OK.
AUTEN
&&
.AVIATION...
ISSUED 508 PM CST THU DEC 24 2009
SITES WHERE PCPN HAS ENDED FOR NOW HAVE SEEN CIGS RISE TO VFR
CATEGORY OR MVFR FOR BMI. ONLY SITE STILL AT IFR CIGS IS SPI. VIS
IS GOOD AT ALL SITES DUE TO STRONG GUSTY WINDS FROM THE EAST.
BELIEVE THE HIGHER CIGS WILL AFFECT SPI AS WELL WITH TEMPO IFR AT
TIMES. PCPN AND VCSH WILL CONTINUE INTO THE EVENING HOURS. THEN
THE DRY SLOT WILL MOVE INTO THE REGION FROM THE SOUTHWEST AND MOST
PCPN SHOULD END...AROUND 06Z. PCPN REMAINDER OF THE TAF PERIOD
WILL BE WIDELY SCATTERED AND THEN CHANGE TO ALL SNOW BY LATE
TOMORROW MORNING. SNOW WILL THEN CONTINUE INTO THE AFTERNOON.
WINDS WILL BE EAST TO SOUTHEAST NEXT 12HRS AND THEN BECOME MORE
SOUTHERLY TO SOUTHWESTERLY FOR THE MORNING AND AFTERNOON TOMORROW.
AUTEN
&&
.PREV DISCUSSION...
ISSUED 300 PM CST THU DEC 24 2009
MAIN FORECAST CONCERNS TODAY REVOLVE AROUND ONGOING MAJOR WINTER
STORM SYSTEM. THESE CONCERNS INCLUDE HOW MUCH RAIN WILL STILL FALL
IN OUR AREA...WHEN PRECIPITATION WILL CHANGE OVER TO SNOW...HOW
MUCH SNOW WILL FALL AS THE SYSTEM VERY SLOWLY PULLS AWAY HEADING
INTO THE WEEKEND...AND HOW WINDY IT WILL BE. 12Z MODELS IN GOOD
OVERALL AGREEMENT WITH ONGOING SYSTEM...SO DO NOT REALLY HAVE A
PREFERRED SOLUTION.
SHORT TERM...TONIGHT THROUGH SUNDAY...WE ARE CURRENTLY SEEING THE
MAIN EVENT WITH RESPECT TO THE STORM IMPACTS OVER CENTRAL AND
SOUTHEAST ILLINOIS. A PLUME OF RICH MOISTURE IS STREAMING NORTH
FROM THE GULF OF MEXICO TO THE EAST OF THE MAIN SYSTEM.
STRONG/DEEP ISENTROPIC ASCENT AND UPPER DIFFLUENCE ARE BOTH
HELPING TO EFFICIENTLY WRING THIS MOISTURE OUT IN THE FORM OF
MODERATE TO HEAVY RAIN. THE SURFACE LOW...CURRENTLY CENTERED OVER
ARKANSAS...WILL LIFT INTO MIDWEST/GREAT LAKES TONIGHT AND LINGER
THROUGH MUCH OF THE WEEKEND. THE STRONG UPPER LOW...CURRENTLY
DRIVING THE SURFACE LOW...WILL LIFT NORTHEAST FROM THE SOUTHERN
PLAINS TONIGHT. THEN...THIS UPPER LOW WILL DUMBBELL AROUND ANOTHER
VIGOROUS WAVE THAT IS STARTING TO DIVE INTO THE NORTHERN PLAINS.
THESE TWO UPPER FEATURES WILL DEVELOP INTO A MUCH LARGER UPPER LOW
THAT WILL BE VERTICALLY STACKED OVER THE SURFACE LOW.
EXPECT RAINS TO CONTINUE THROUGH THE NIGHT...THOUGH THEY SHOULD
BEGIN TO TAPER OFF OVERNIGHT AS THE RICHER MOISTURE PUSHES OFF TO
OUR EAST. FOR THIS REASON...WILL CONTINUE TO LET THE FLOOD WATCH
EXPIRE AT MIDNIGHT. THE DRY SLOT ASSOCIATED WITH THE SOUTHERN
PLAINS WAVE WILL ARRIVE BY CHRISTMAS MORNING AND GREATLY REDUCE
THE MEASURABLE PRECIPITATION. THE COLD AIR THAT IS ASSOCIATED WITH
THIS FEATURE WILL ALSO CHANGE ANY LINGERING RAINFALL OVER TO SNOW
CHRISTMAS MORNING.
ONCE THE SNOW SHOWERS BEGIN CHRISTMAS DAY...THEY WILL BE WITH US
PERIODICALLY THROUGH THE WEEKEND. THE VERTICALLY STACKED SYSTEM
WILL KEEP US IN DEEP CYCLONIC FLOW...WITH OCCASIONAL ENHANCEMENTS
IN LIFT/MOISTURE DEPTH AS IMPULSES ROTATE AROUND THE SYSTEM.
HOWEVER...THERE ARE A COUPLE THINGS GOING AGAINST MUCH IN THE WAY
OF SNOW ACCUMULATION FRIDAY INTO SUNDAY. FIRST...THE MOISTURE DEPTH
IS EXPECTED TO BE SHALLOW FOR MUCH OF THE TIME AND SHOULD NOT
SUPPORT MORE THAN FLURRIES. SECOND...THE AIR MASS OVERHEAD DURING
THE PERIOD WILL BE VERY COLD AND SHOULD RESULT IN SMALL SNOW
FLAKES THAT WILL NOT ACCUMULATE MUCH. SO...HAVE KEPT SNOW CHANCES
NO HIGHER THAN THE CHANCE CATEGORY. HOWEVER...USED SCATTERED
WORDING RATHER THAN CHANCE SINCE IT WILL SNOW...JUST NOT VERY
MUCH.
AS FAR AS WIND CONCERNS...WHILE IT WILL BE WINDY THE NEXT FEW
DAYS...WE SHOULD STAY BELOW ADVISORY CRITERIA. THE STRONGEST WINDS
AT THE MOMENT ARE JUST WEST AND EAST OF THE MAIN SURFACE LOW. BY
THE TIME THE SURFACE LOW GETS HERE BY EARLY FRIDAY...IT WILL BE
STARTING TO OCCLUDE AND RESULT IN WEAKER WINDS ACROSS THE MIDWEST.
LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MODELS/ENSEMBLES IN
REASONABLE AGREEMENT THROUGH THE PERIOD. THE LARGE UPPER/SURFACE
LOW THAT WILL BE WITH US THROUGH MUCH OF THE WEEKEND WILL FINALLY
DEPART... RESULTING IN MAINLY DRY WEATHER AND MODERATING
TEMPERATURES. THE MEAN UPPER FLOW WILL SPLIT AGAIN AFTER THE
CURRENT SYSTEM DEPARTS...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/THURSDAY. HAVE
ADDED 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...
FLOOD WATCH UNTIL MIDNIGHT CST TONIGHT FOR ILZ027>031-036>038-
040>057-061>063-066>068-071>073.
FLASH FLOOD WATCH THROUGH FRIDAY AFTERNOON FOR ILZ051.
&&
$$
