633 
FXUS63 KILX 152323
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
523 PM CST SUN JAN 15 2012

.DISCUSSION...
ISSUED 300 PM CST SUN JAN 15 2012

SEVERAL SYSTEMS ARE INCLUDED IN THIS 7 DAY FORECAST...WITH THE FIRST 
ONE ARRIVING ON MARTIN LUTHER KING JR DAY...AND LINGERING THROUGH 
TUESDAY. THE NEXT SYSTEM WILL AFFECT OUR AREA ON THURSDAY WITH A 
THIRD ON FRIDAY. 

SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT.
INITIAL FOCUS IS ON LATER TONIGHT WHEN WARM AIR AND MELTING SNOW 
WORK TO SATURATE THE BOUNDARY LAYER...PRODUCING FOG AND POSSIBLY 
DRIZZLE/FREEZING DRIZZLE LATE TONIGHT AND EARLY MON MORNING IN OUR 
FAR NORTHERN COUNTIES. COULD BE A BIT SLIPPERY IN AREAS NORTHEAST OF 
PEORIA...WHERE FREEZING TEMPS ARE EXPECTED. THE MAIN THING THE COULD 
PREVENT DRIZZLE IS THAT THE SATURATION LAYER APPEARS TO BE A BIT 
SHALLOW /1000FT/ THAN YOU WOULD NORMALLY NEED FOR DRIZZLE
/3000FT/. IF WE GET ENOUGH TURBULENT MIXING...WE COULD GET ENOUGH
COLLISION COALESCENCE TO GET THE DROPS BIG ENOUGH TO DRIFT TO THE
GROUND. FOG LOOKS LIKE A PRETTY GOOD BET TONIGHT
THOUGH...ESPECIALLY IN THE NORTHERN AREAS WHERE THE SNOW COVER WAS
MORE THAN AN INCH.

ON MLK JR DAY...TEMPS WILL BE ON A STEADY RISE ALREADY BY 
SUNRISE...AS SOUTHERLY WINDS INCREASE AND A 40-50KT LOW LEVEL JET 
CRANKS UP THE WARM AIR ADVECTION. MOISTURE LEVELS ALOFT DO 
EVENTUALLY INCREASE...BUT THE OVERALL COLUMN SATURATION IS NOT VERY 
IMPRESSIVE DURING THE DAY...SO WE KEPT THE POPS ONLY IN THE CHANCE 
CATEGORY. THE DAY MAY BE DOMINATED BY FOG AND PATCHY DRIZZLE MORE 
THAN MEASURABLE LIGHT RAIN.

AS LOW PRESSURE PASSES OVER CENTRAL IL MON NIGHT...WE EXPECT 
INSTABILITY PARAMETERS TO BECOME FAVORABLE FOR TSTMS...MAINLY 
SOUTHEAST OF I-72. MU CAPE VALUES CLIMB TO 300 J/KG, WHICH IS ENOUGH 
FOR STORMS THIS TIME OF YEAR. CAN NOT RULE OUT SOME HAIL FROM A FEW 
OF THE STORMS. RAIN CHANCES INCREASE MON NIGHT...WITH 80+ 
CATEGORICAL POPS IN THE SOUTHEAST...AND LIKELY POPS /60-70/ NW TO 
THE I-55 CORRIDOR. 

COLD AIR WILL BEGIN TO FLOW INTO OUR NW COUNTIES AFTER MIDNIGHT...AS 
THE LOW MOVES EAST INTO INDIANA. RAIN MAY CHANGE TO SNOW NW OF THE 
IL RIVER...WITH SOME SNOW ACCUMS LESS THAN A HALF INCH POSSIBLE. LOW 
TEMPS ON MONDAY NIGHT WILL BE A TOUGH CALL...AS TEMPS RISE STEADILY 
IN THE SOUTHEAST OF THE PATH OF THE LOW...WHILE NW AREAS REMAIN 
STEADY BY MILD UNTIL LATE. THEN TEMPS FALL THROUGH THE DAY ON 
TUESDAY. WE KEPT SNOW CHANCES FOR MOST OF CENTRAL IL ON 
TUESDAY...EXCEPT FOR THE SOUTHEAST WHERE TEMPS WILL REMAIN ABOVE 
FREEZING LATER INTO THE DAY.

SNOW AMOUNTS FROM MON NIGHT AND TUESDAY SHOULD REMAIN LESS THAN AN 
INCH TOTAL...WITH THE HIGHER AMOUNTS NORTH OF A LINE FROM RUSHVILLE 
TO LINCOLN TO CHAMPAIGN. TEMPS WILL LIKELY DROP BELOW NORMAL TUESDAY 
NIGHT...WITH SOME SINGLE DIGIT LOWS PSBL N OF PIA-BMI. 

LONG TERM...WEDNESDAY THROUGH SUNDAY.
HIGH PRESSURE WILL KEEP WEDNESDAY DRY BUT CHILLY AS THE CANADIAN 
AIRMASS MOVES OVER THE AREA. 

THE NEXT COLD FRONT WILL BE DRAGGED ACROSS ILLINOIS BY A FAST MOVING 
CLIPPER THAT PASSES ACROSS S MN AND WIS INTO MICH. SNOW CHANCES WILL 
BE BETTER NORTH OF OUR COUNTIES...BUT WE DECIDED TO INCREASE POPS TO 
THE CHANCE CATEGORY FOR OUR FAR NORTHERN COUNTIES AS ISENTROPIC LIFT 
AND LOW CONDENSATION PRESSURE DEFICITS LOOK SUFFICIENT FOR AT LEAST 
SOME LIGHT SNOW. MOST AREAS WILL PROBABLY ONLY SEE FLURRIES AND 
TRACE AMOUNTS OF SNOW ON THURSDAY. THE LOW WILL BE JUST A BIT TOO 
FAR NORTH THIS TIME.

THE NEXT SYSTEM QUICKLY COMING OUT OF THE PLAINS ON FRIDAY HAS 
SEVERAL SOLUTIONS POSED BY THE MODELS. THE GFS AND CANADIAN GEM 
DISSIPATE THE SURFACE LOW AS IT REACHES IL...BUT CONTINUE THE 
FORCING FOR PRECIP ACROSS OUR COUNTIES ON FRIDAY. THE ECMWF 
DISSIPATES THE INITIAL LOW AS WELL...BUT REDEVELOPS A DIFFERENT LOW 
TO OUR SOUTHEAST OVER KENTUCKY. THE EC THEN WRAPS RAIN INTO OUR AREA 
FROM THE SOUTH. SO THAT SECOND LOW MAKES THE EC SOLUTION WARMER THAN 
THE GFS/GEM. THE GFS/GEM SOLUTION WOULD BE LEANING MORE TOWARD A 
SNOW EVENT. THE UNCERTAINTY THIS FAR OUT KEPT US FROM MAKING TOO 
MANY CHANGES TO FRIDAY...AND WE KEPT CHC POPS GOING DURING THE DAY. 
FRIDAY NIGHT WE PROGRESSED THE PRECIP EASTWARD...WITH CHANCE ONLY E 
OF I-57. 

THERE IS POTENTIAL FOR SIGNIFICANT WARMING INTO SUNDAY PER THE GFS 
SOLUTION...WITH MUCH ABOVE NORMAL TEMPS POSSIBLE. 

SHIMON
&&

.AVIATION...
ISSUED 523 PM CST SUN JAN 15 2012

SOUTH WINDS AND WARM ADVECTION WILL CONTINUE THROUGH THE NIGHT OVER 
THE TAF SITES. MAIN CHALLENGE WILL BE IF/WHEN LOW CLOUDS DEVELOP 
AFTER 06Z...THEN THE CLOUD/PRECIPITATION EVOLUTION ON MONDAY. WINDS 
WILL REMAIN AT OR ABOVE 10 KT OVERNIGHT...ALTHOUGH THE GUSTINESS 
WILL SLOWLY DIMINISH. MEANWHILE...THE STRONG WARM ADVECTION ABOVE 
THE SURFACE WILL BRING 2K FT WINDS 23050KT. WILL THEREFORE INCLUDE 
LLWS FOR THE TAFS LATER TONIGHT. STRATOCU AROUND 3K FT IS FORECAST 
TO INCREASE BY 12Z MON ALONG AN ELEVATED PSEUDO-WARM FRONT OVER 
NORTH-CENTRAL TO EASTERN IL. LOW LEVEL MOISTURE BELOW THAT DOES NOT 
BEGIN SATURATING UNTIL AFTER 12Z...SO WILL HOLD OFF ON MENTION OF 
PRECIPITATION THROUGH 12Z-14Z. FOG WILL INCREASING THOUGH AS THE 
SNOW MELTS IN TEMPERATURES MAINLY ABOVE 32F. BY MID MORNING 
MONDAY...WARM ADVECTION LIGHT RAIN WILL BE INCREASING AHEAD OF A 
COLD FRONT THAT WILL EXTEND FROM NORTHWESTERN IL TO NORTHWESTERN MO 
BY 18Z. AT LEAST MVFR FOG WILL BE HANGING IN THERE AS WELL. COVERAGE 
UNCERTAINTIES PRECLUDE ANY MENTION OF PREDOMINATE PRECIPITATION... 
BUT WILL HAVE TEMPO RAIN BEGINNING AT PIA AROUND 16Z...THEN AT 
SPI-BMI-DEC BY 18Z. WILL JUST HAVE VCSH FOR CMI...THEN TEMPO FOR 
THEM BY 20Z. THE FRONT TO THE NORTHWEST IS NOT FORECAST TO COME 
SOUTHEAST INTO THE CENTRAL IL TERMINALS UNTIL AFTER THIS TAF PERIOD.

04
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$