FXUS63 KILX 081154
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
554 AM CST TUE DEC 8 2009
.DISCUSSION...
ISSUED 254 AM CST TUE DEC 8 2009
SIGNIFICANT WINTER STORM TO IMPACT CENTRAL ILLINOIS TODAY THROUGH
WEDNESDAY.
06Z SURFACE CHART SHOWS LOW PRESSURE DEEPENING OVER NORTHERN
ARIZONA...WHILE LIGHT WARM-ADVECTION SNOW HAS ALREADY BROKEN OUT
WELL IN ADVANCE OF THE SYSTEM FROM KANSAS INTO WEST-CENTRAL
ILLINOIS. ALOFT...SHARP TROUGH CONTINUES TO DIG OVER THE DESERT
SOUTHWEST.
SHORT TERM...TODAY THROUGH THURSDAY
MODELS INDICATE THE SNOW CURRENTLY ACROSS THE NORTHWEST KILX CWA
WILL GRADUALLY LIFT NORTHWARD BY MID-MORNING...AS 850MB FRONT/BEST
FORCING SHIFTS TOWARD THE SOUTHERN GREAT LAKES. AFTER A BRIEF
LULL...A MORE SIGNIFICANT AREA OF PRECIP WILL DEVELOP FURTHER
SOUTH AND BEGIN LIFTING INTO CENTRAL ILLINOIS BY AROUND MIDDAY.
NAM-WRF/GFS FORECAST SOUNDINGS INDICATE ALL RAIN SOUTH OF
I-70...WITH A SNOW/SLEET MIXTURE ACROSS THE REMAINDER OF THE AREA
UPON INITIAL ONSET. AS WARMER AIR FLOWS NORTHWARD...THE PRECIP
WILL GRADUALLY CHANGE TO RAIN ALONG AND EAST OF THE I-55 CORRIDOR
BY 00Z WED. FURTHER NORTHWEST...SNOW/SLEET WILL CONTINUE ACROSS
THE ILLINOIS RIVER VALLEY.
00Z 8 DEC MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE TRACK AND
STRENGTH OF APPROACHING LOW PRESSURE TONIGHT...WITH THE GFS
CONTINUING ITS TRACK FROM THE OKLAHOMA PANHANDLE...UP THE ILLINOIS
RIVER...AND INTO THE CHICAGO AREA BY 12Z WED. MEANWHILE...NAM-WRF
HAS SHIFTED ITS TRACK A BIT FURTHER WEST...TAKING THE LOW ALONG
THE MISSISSIPPI RIVER INTO SOUTHEAST WISCONSIN. AT THIS
POINT...WILL FOLLOW THE MORE CONSISTENT GFS...AND WILL MONITOR THE
12Z SUITE TO SEE IF THE FURTHER NORTHWEST TREND CONTINUES.
VIGOROUS UPPER DYNAMICS WILL BE IN PLACE TONIGHT...AS 130-140KT
300MB JET STREAK ROUNDS THE TROUGH...PLACING THE REGION IN THE
LEFT EXIT REGION OF THE JET. IMPRESSIVE VALUES OF OMEGA WILL
ENSURE WIDESPREAD PRECIP...ESPECIALLY LATER THIS AFTERNOON THROUGH
THE EVENING. AS LOW CONTINUES TO DEEPEN...60 TO 65KT 850MB JET
STREAK NOSES INTO SOUTHERN ILLINOIS/OHIO VALLEY...FURTHER
ENHANCING LIFT. HAVE THEREFORE MENTIONED A CHANCE FOR
THUNDERSTORMS SOUTH OF I-70 THIS AFTERNOON...THEN FURTHER NORTH
INTO THE CHAMPAIGN-URBANA AREA THIS EVENING.
FURTHER WEST...RAIN WILL CONTINUE ALONG THE I-55 CORRIDOR AND A
SNOW/SLEET MIX WILL PREVAIL ACROSS THE ILLINOIS RIVER VALLEY. WITH
TEMPS REMAINING STEADY OR EVEN RISING A FEW DEGREES TONIGHT AS
WINDS SWITCH TO SOUTHERLY...SNOW WILL BE QUITE WET...WITH 8:1
LIQUID TO SNOW RATIO LIKELY. BASED ON EXPECTED QPF AND PRECIP
TYPE...A 5 TO 7 INCH SNOW WITH LOCALLY HIGHER AMOUNTS...IS STILL
ON TARGET FOR THE FAR NORTHWEST KILX CWA AROUND GALESBURG. THE
SNOW TOTALS WILL RAPIDLY DECREASE FURTHER EAST...WITH 2 TO 4
INCHES ALONG THE ILLINOIS RIVER...AND PERHAPS AROUND 1 INCH ALONG
I-55. WILL THEREFORE CONTINUE THE WINTER STORM WARNING FOR KNOX
AND STARK COUNTIES...AND THE WINTER WEATHER ADVISORY FURTHER EAST
TO WOODFORD...TAZEWELL...AND MASON COUNTIES.
AS THE LOW LIFTS INTO THE SOUTHERN GREAT LAKES ON WEDNESDAY
MORNING...WINDS WILL SWITCH TO WESTERLY AND MUCH COLDER AIR WILL
POUR INTO THE REGION. ANY LINGERING PRECIP WILL CHANGE OVER TO
LIGHT SNOW...HOWEVER ONLY A LIGHT ACCUMULATION OF A HALF INCH OR
LESS IS EXPECTED ACROSS EAST-CENTRAL ILLINOIS...WITH LITTLE OR NO
SNOW SOUTH OF I-70. MAIN PROBLEM ON WEDNESDAY WILL BE THE
WINDS...AS TIGHTENING PRESSURE GRADIENT RESULTS IN SUSTAINED WINDS
OF 30 TO 35 MPH. FORECAST SOUNDINGS AND NUMERIC GUIDANCE SUGGEST
GUSTS UP TO 45 MPH...WHICH WILL LIKELY REQUIRE A WIND ADVISORY OR EVEN
A HIGH WIND WARNING BY LATER SHIFTS. WITH THESE WINDS...BLOWING
SNOW WILL BE A CONCERN ACROSS THE NORTHWEST...WHERE VISIBILITIES
MAY BE SIGNIFICANTLY REDUCED AT TIMES. IN ADDITION...TEMPS WILL
FALL INTO THE TEENS AND 20S ACROSS THE BOARD BY WEDNESDAY
AFTERNOON...RESULTING IN ICY SPOTS DEVELOPING ON ROADWAYS ACROSS
THE ENTIRE CWA.
LONG TERM...FRIDAY THROUGH MONDAY
DID NOT MAKE MANY CHANGES TO THE EXTENDED...AS RELATIVELY QUIET
WEATHER IS EXPECTED. GFS/ECMWF ARE BOTH INDICATING A WEAK SYSTEM
SKIRTING BY TO THE SOUTH ON FRIDAY...WITH A COLD FRONT PUSHING
THROUGH ILLINOIS ON SATURDAY. NEITHER SYSTEM APPEARS TO BE VERY
IMPRESSIVE AND BOTH WILL BE LACKING IN MOISTURE...SO WILL MAINTAIN
A DRY FORECAST INTO EARLY NEXT WEEK.
BARNES
&&
.AVIATION...
ISSUED 554 AM CST TUE DEC 8 2009
WINTER STORM APPROACHING AREA WILL BRING A MIX OF PCPN TO TAF
SITES. PCPN AT SPI...DEC AND CMI WILL BE RAIN WHEN IT STARTS
AROUND 18Z...WITH CIGS BELOW 1KFT. THIS RAIN WILL CONTINUE INTO
THE EVENING HOURS AND THEN CHANGE TO SNOW ONCE THE LOW MOVES
NORTHEAST OF THE AREA...AT AROUND 08Z. PIA PCPN WILL RETURN AS A
MIX OF SNOW...RAIN AND SLEET FOR THE AFTERNOON...BUT AS WARM AIR
MOVES NORTH...THE PCPN WILL JUST BE RAIN AND SLEET THEN CHANGE TO
ALL RAIN FOR THE EVENING. THE PCPN WILL THEN CHANGE TO SNOW AFTER
MIDNIGHT. BMI WILL BE SIMILAR WITH THE PCPN STARTING IN THE
AFTERNOON AS A MIX OF RAIN AND SLEET...THEN CHANGE TO ALL RAIN
UNTIL AFTER MIDNIGHT CHANGING TO ALL SNOW. WINDS WILL BE EASTERLY
MOST OF THE DAY AND THEN SWITCH TO SOUTHEAST AS THE LOW LIFTS INTO
THE AREA...THEN BECOME SOUTHWEST AND GUSTY ONCE THE LOW PULLS INTO
NORTHERN NORTHERN IL.
AUTEN
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM NOON TODAY TO 6 PM CST WEDNESDAY
FOR ILZ029>031-036-037-040-041.
WINTER STORM WARNING FROM NOON TODAY TO 6 PM CST WEDNESDAY FOR
ILZ027-028.
&&
$$
