FXUS63 KILX 081733
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1133 AM CST TUE DEC 8 2009
.DISCUSSION...
ISSUED 1040 AM CST TUE DEC 8 2009
EARLIER ZONE/GRID UPDATE WAS DONE TO REFLECT THE CURRENT
PRECIPITATION TRENDS...AS WELL AS UPDATE THE TEMPERATURES FOR
TONIGHT AND WEDNESDAY.
AREA OF RAIN HAS OVERSPRAED SOUTHEAST ILLINOIS THIS
MORNING...MIXED WITH A BIT OF SLEET ON THE NORTHERN EDGE NEAR
MATTOON. SCATTERED LIGHT SNOW HAS BEEN INCREASING A BIT WEST OF
I-55.
MAIN ISSUE FOR THE AFTERNOON CONTINUES TO INVOLVE PRECIPITATION
TYPES. UPSTREAM OBS HAVE MAINLY SHOWN RAIN OR SNOW...WITH A BIT OF
FREEZING PRECIP IN CENTRAL MISSOURI. FORECAST SOUNDINGS ON THE RUC
AND NAM MODELS CONTINUE TO SHOW NOSE OF WARM AIR AROUND 750-850 MB
WITH TEMPERATURES RISING TO NEAR 5C. MIXTURE OF VARIOUS PRECIP
TYPES AT MIDDAY SHOULD TREND MORE TOWARD RAIN AS THE AFTERNOON
PROGRESSES...WITH MOSTLY SNOW NORTHWEST OF THE ILLINOIS RIVER.
SOUTHEAST CWA WILL AT LEAST BE ALL RAIN...BUT THAT AREA WILL BE
COMPLICATED BY THUNDER POTENTIAL WITH LATEST SPC OUTLOOKS PLACING
A 5 PERCENT SEVERE HAIL RISK INTO THIS EVENING.
MORNING MODELS SHOWING THE NAM COMING MORE IN LINE WITH THE
PREFERRED GFS/ECMWF TRACK OF THE STORM. SURGE OF WARMER
AIR WILL COME INTO EASTERN ILLINOIS DURING THE EVENING AS THE LOW
MOVES INTO FAR WEST CENTRAL ILLINOIS...AS HIGH AS 9C AT 925 MB
ACROSS THE SOUTHEAST CWA. HOURLY GRIDS WERE UPDATED TO BETTER
REFLECT RISING TEMPERATURES DURING THE EVENING...CONTINUING PAST
MIDNIGHT ACROSS THE EASTERN CWA AND LEVELLING OFF IN THE WEST.
THIS ALSO REQUIRED SOME UPDATES FOR WEDNESDAY WITH HIGHS VERY
EARLY IN THE DAY. NORTHWEST CWA LIKELY TO SEE WIND CHILLS DOWN TO
ZERO BY SUNSET.
GEELHART
&&
.AVIATION...
ISSUED 1132 AM CST TUE DEC 8 2009
COMPLICATED TAF FORECAST WITH LOW CEILINGS AND VISIBILITIES...
PRECIPITATION TYPES...AND HIGH WINDS TO WORRY ABOUT.
MAIN ISSUE WITH PRECIPITATION TYPES WILL BE AT KPIA AND
KPIA...WHERE A MIXTURE OF RAIN...SLEET AND SNOW WILL TRANSITION TO
ALL RAIN AS THE AFTERNOON PROGRESSES. REMAINING TAF SITES WILL BE
WARM ENOUGH FOR ALL RAIN TO BE THE PRIMARY TYPE. THE PRECIPITATION
WILL INCREASE THROUGH THE AFTERNOON AND BECOME STEADY OVERNIGHT.
CEILINGS WILL LOWER TO NEAR 500 FEET BY LATE AFTERNOON.
A MAJOR STORM SYSTEM WILL TRACK FROM NEAR QUINCY TO THE NORTHEAST
TIP OF ILLINOIS BETWEEN 06-12Z...AND WILL RAPIDLY INTENSIFY AS IT
DOES SO. COLD AIR WILL BEGIN TO SPILL INTO THE AREA AFTER ABOUT
07Z AND CHANGE THE RAIN TO SNOW AT MOST OF THE TAF SITES THROUGH
SUNRISE...PERHAPS HOLDING OFF UNTIL LATE AT KCMI. WHILE THE
PRECIPITATION WILL TAPER OFF AFTER SUNRISE...STRONG WINDS GUSTING
TO NEAR 40 KNOTS WILL CAUSE SIGNIFICANT LOW VISIBILITIES DUE TO
BLOWING SNOW...MAINLY AT KPIA/KBMI WHERE THERE IS THE BEST CHANCE
OF THERE BEING ANY DECENT AMOUNTS OF SNOW ON THE GROUND. THESE
STRONG WINDS WILL CONTINUE BEYOND THE END OF THE FORECAST PERIOD.
GEELHART
&&
.PREV 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
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 PM CST WEDNESDAY FOR ILZ029>031-
036-037-040-041.
WINTER STORM WARNING UNTIL 6 PM CST WEDNESDAY FOR ILZ027-028.
&&
$$
