FXUS63 KILX 221735
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1135 AM CST TUE DEC 22 2009
.DISCUSSION...
ISSUED 1028 AM CST TUE DEC 22 2009
LOW CLOUDS CONTINUE TO BLANKET CENTRAL ILLINOIS THIS MORNING...AS
A WARM FRONT TAKES SHAPE FURTHER SOUTH ACROSS THE OZARKS INTO THE
TENNESSEE RIVER VALLEY. EASTERLY FLOW NORTH OF THE BOUNDARY WILL
KEEP THINGS ON THE CHILLY SIDE TODAY...WITH HIGHS ONLY RISING A
FEW DEGREES FROM CURRENT READINGS. MOST LOCATIONS WILL SEE HIGH
TEMPS TOPPING OUT IN THE MIDDLE 30S...ALTHOUGH AREAS ALONG AND
SOUTH OF I-70 COULD EXPERIENCE READINGS APPROACHING THE 40 DEGREE
MARK. THE 12Z KILX UPPER AIR SOUNDING SHOWED A SHALLOW MOIST LAYER
FROM THE SURFACE UP TO ABOUT 925 MB...WITH A CONSIDERABLE POCKET
OF DRY AIR ABOVE THAT. AS A SOUTHERLY LOW-LEVEL JET BEGINS TO
STRENGTHEN AND NOSE INTO THE AREA THIS AFTERNOON...FORECAST
SOUNDINGS SHOW A DEEPER SURFACE-BASED LAYER OF MOISTURE
DEVELOPING...SUPPORTING PATCHY DRIZZLE AFTER 21Z. THE DRIZZLE WILL
PERSIST INTO THE EVENING HOURS...BEFORE EVEN DEEPER MOISTURE
ARRIVES AFTER MIDNIGHT. WITH WARM FRONT LIFTING NORTHWARD...LIGHT
RAIN WILL DEVELOP LATER TONIGHT...PARTICULARLY ACROSS THE CENTRAL
AND SOUTHERN ZONES. FURTHER NORTH...SOUNDINGS MAINLY SUPPORT
DRIZZLE...OR PERHAPS FREEZING DRIZZLE WHERE TEMPS HOVER NEAR 32F.
BEST CHANCE AT A LIGHT ACCUMULATION OF ICE WILL BE ACROSS AREAS
THAT PICKED UP A LIGHT SNOW COVER LAST NIGHT...MAINLY NORTH OF THE
I-74 CORRIDOR. WILL THEREFORE KEEP ANY FREEZING DRIZZLE MENTION
CONFINED TO THE FAR NORTHERN TIER OF COUNTIES.
&&
.AVIATION...
ISSUED 1135 AM CST TUE DEC 22 2009
LOW CEILINGS AND POOR VISIBILITIES WILL PREVAIL THROUGH THE ENTIRE
18Z TAF PERIOD...AS A STORM SYSTEM SLOWLY APPROACHES FROM THE
SOUTHWEST. CURRENT OBS INDICATE CEILINGS BELOW 1000FT AND VISBYS
LESS THAN 4SM...AND THESE CONDITIONS ARE EXPECTED TO PERSIST FOR THE
BALANCE OF THE AFTERNOON. AS LOW-LEVEL MOISTURE AND LIFT
INCREASES...DRIZZLE WILL DEVELOP AT THE TAF SITES AFTER 21Z. WITH
SURFACE TEMPS DROPPING TO AROUND 32F ACROSS THE NORTH TONIGHT...A
PERIOD OF FREEZING DRIZZLE WILL BE LIKELY AT BOTH KPIA AND KBMI
FROM 06Z THROUGH 13Z. FURTHER SOUTH...LIGHT RAIN WILL DEVELOP AT
KSPI AND KDEC WELL AFTER MIDNIGHT AND PERSIST INTO WEDNESDAY
MORNING. THE RAIN WILL SPREAD FURTHER NORTH AND IMPACT THE
REMAINING TERMINALS AFTER 13Z. WINDS WILL INITIALLY BE GUSTY FROM
THE E/SE THIS AFTERNOON...THEN WILL BECOME MORE EASTERLY AND
INCREASE LATER TONIGHT. BUFKIT DATA SUGGESTS GUSTS REACHING 25KT
BY WEDNESDAY MORNING.
BARNES
&&
.PREV DISCUSSION...
ISSUED 332 AM CST TUE DEC 22 2009
WEAK PRESSURE PATTERN CONTINUES ACROSS THE MIDWEST THIS
MORNING...WITH A VERY WEAK RIDGE FROM THE UPPER MIDWEST TO THE
SERN CONUS. QUASI ZONAL FLOW ALOFT AS UPPER LOW FINALLY MOVING ON
SHORE IN THE PAC NW AND TROF BEGINNING TO TAKE SHAPE OVER THE PAC
COAST. QUICK WAVE PUSHING ACROSS NRN PORTIONS OF THE CWA BRINGING
SOME ACCUMULATING SNOW NORTH OF 74...BUT OVERALL STRONGEST BANDS
OF SHOWERS LIFTING NE. LINGERING OF THESE SHOWERS IS THE FIRST
TROUBLE FOR THE FORECAST. MODELS ARE MAINTAINING A FAR WARMER
TAKE ON THE SYSTEMS FOR MIDWEEK THROUGH THE HOLIDAY...KEEPING THE
SYSTEM RAIN DOMINATED BEYOND TUE NIGHT WED MORNING. INITIAL COLD
TEMPERATURES WILL RESULT IN A CHANCE OF SOME LIGHT ICE
ACCUMULATION IN THE NORTH...MAKING MANY HOLIDAY SHOPPING/TRAVEL
ISSUES A CONCERN. STRONG SYSTEM PUSHES INTO CENTRAL ILLINOIS
THURSDAY...WITH HEAVY RAIN...STRONG WINDS...AND THE CHANCE FOR
THUNDERSTORMS...FEELING A BIT MORE LIKE A SPRING FORECAST THAN A
DECEMBER ONE. THAT BEING SAID...LIGHT SNOWFALL AND FLURRIES LINGERING
INTO CHRISTMAS MORNING AS THE SYSTEM SLOWS CONSIDERABLY.
MODELS ARE IN PRETTY DECENT AGREEMENT OVERALL...AND CURRENT
FORECAST HAS VERY LITTLE SHIFT FROM PREVIOUS.
SHORT TERM...TODAY AND TOMORROW...
WAVE PASSING THROUGH TAKING THE MOST EFFICIENT SNOW SHOWERS OUT OF
CWA EARLY THIS MORNING...THOUGH OVERALL EFFECT OF THE WAVE AND
LIFT ACROSS THE REGION IS SCT SHOWERS. WITH PLENTY OF RETURNS
STILL POPPING UP ON RADAR...HAVE EXPANDED A SLIGHT CHANCE OVER
MUCH OF THE CWA FOR THIS MORNING. AND WITH A WEAK BOUNDARY
STARTING TO PUSH UP THRU KS/MO ON SAT IMAGERY AS WE GO THRU A
PATTERN SHIFT...KEEPING THE CHANCES THROUGH THE AFTERNOON. RAMPING
UP THE CHANCES A BIT IN THE OVERNIGHT. FORECAST MODELS BEING
SUBTLE WITH THE CHANCES FOR PRECIP WITH THE LAST RUN...BUT JUST
NOT WILLING TO ABANDON THEM AS A WEAK INVERTED TROF MAINTAINING ON
SFC PATTERN AS THE THERMAL GRADIENT INCREASES WITH SFC LOW
DEVELOPING IN THE SRN PLAINS. LIGHT ICE ACCUMULATION/GLAZING
POSSIBLE NORTH OF INTERSTATE 74 TONIGHT AND INTO TOMORROW MORNING
AS THE PRECIP SPREADS INTO COLD AIR ALREADY IN PLACE.
SLOWLY WARM AIR PUSHING INTO THE MID LEVELS FIRST ON WED WHILE SFC
FLOW REMAINS EASTERLY...THOUGH IN COMBINATION WITH SOME SIMPLE
DAYTIME WARMING...THE CHANCE FOR FREEZING PRECIP PUSHES NORTHWARD
AND ILX BECOMES DOMINATED BY RAIN. AS THE LOW PUSHES CLOSER...THE
CHANCE FOR THUNDER MOVES INTO THE SOUTHERN CWA. SCT HEAVY RAINFALL
AMOUNTS ARE POSSIBLE AT THIS TIME...BUT THE BEST CHANCES FOR HEAVY
RAIN LIKELY THE NEXT DAY.
LONG TERM...THURSDAY THROUGH SATURDAY...
NOT A LOT OF CHANGE OVERALL...HEAVY RAINS AND WINDY THROUGH
CHRISTMAS EVE...WITH A CHANGE OVER TO SNOW FOR FRI MORNING ON THE
BACKSIDE OF THE SYSTEM AS THE LOW WRAPS UP AND COLD AIR SOAKS IN.
FLURRIES INTO SAT MORNING AS THE LOW SLOWS ON ITS PROGRESSION
THROUGH THE GREAT LAKES. ONE MAJOR THING TO WATCH OUT FOR IN THE
NEXT FEW RUNS OF THE OPERATIONAL MODELS IS THE 06Z NAMS TAKE ON
THE SYSTEM. IT SEEMS TO BE CATCHING ON TO THE BROADER TROF CONCEPT
IN THE MIDDLE OF THE CONUS...AND NOTHING TO PUSH THE UPPER TROF
INTO A NEG TILT. AS A RESULT...THE SFC SYSTEM IS QUITE A BIT
WEAKER WITH FAR LESS EXPLOSIVE DEVELOPMENT. GOOD NEWS...COULD BE
LESS BLUSTERY. BAD NEWS...COULD MEAN REDUCED WAA WHICH MIGHT
CHANGE PRECIP TYPES HERE AND THERE.
HJS
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
