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. && $$