FXUS63 KILX 061743
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1143 AM CST SUN DEC 6 2009
.DISCUSSION...
ISSUED 1036 AM CST SUN DEC 6 2009
MORNING SURFACE ANALYSIS SHOWS SLOW-MOVING COLD FRONT EXTENDING
FROM SOUTHERN WISCONSIN TO AN AREA OF LOW PRESSURE OVER THE TEXAS
PANHANDLE. AHEAD OF THE FRONT...SOUTHERLY FLOW IS GRADUALLY
SPREADING MOISTURE NORTHWARD FROM THE WESTERN GULF OF MEXICO.
LATEST SATELLITE IMAGERY SHOWS THICK VEIL OF HIGH CLOUDS STREAMING
INTO THE MIDWEST...WHILE LOWER CLOUDS ARE CONFINED TO LOCATIONS IN
THE IMMEDIATE VICINITY OF THE SURFACE LOW AND ACROSS EASTERN
TEXAS. 12Z NAM-WRF 1000-850MB RH PROFILES KEEP LOW CLOUDS WELL TO
THE W/SW TODAY...THEN GRADUALLY SPREAD THEM INTO CENTRAL ILLINOIS
LATER TONIGHT INTO MONDAY MORNING. MEANWHILE...12Z KILX UPPER AIR
SOUNDING SHOWS A THICK LAYER OF CIRRUS EXTENDING FROM 15000 TO
25000FT ALOFT. WITH THIS BLANKET OF HIGH CLOUDS IN PLACE...THE SUN
IS BEING SUFFICIENTLY OBSCURED TO GO WITH MOSTLY CLOUDY WORDING IN
THE FORECAST. IN ADDITION...HAVE LOWERED AFTERNOON HIGH TEMPS BY A
COUPLE OF DEGREES...WITH READINGS MAINLY IN THE UPPER 30S.
&&
.AVIATION...
ISSUED 1143 AM CST SUN DEC 6 2009
LOW PRESSURE CURRENTLY OVER THE OKLAHOMA PANHANDLE WILL LIFT
NORTHEASTWARD...BRINGING A PERIOD OF LIGHT SNOW TO CENTRAL
ILLINOIS LATE TONIGHT. BEFORE THE SYSTEM ARRIVES...HIGH CLOUDINESS
AOA 15000FT WILL PREVAIL. BOTH NAM AND GFS ARE SHOWING LOW-LEVEL
MOISTURE RAPIDLY INCREASING FROM THE SOUTHWEST STARTING AT 06Z
AT KSPI...THEN SPREADING TO KCMI BY AROUND 10Z. LOWEST CEILINGS
AND BEST PRECIP CHANCES WILL OCCUR FROM 09Z THROUGH 15Z. AT THAT
TIME...WILL BRING CEILINGS DOWN TO 2500FT AND INTRODUCE VCSH.
AFTER THAT...THE LOW WILL LIFT INTO NORTHEAST ILLINOIS AND ANY
LIGHT PRECIP WILL TAPER OFF AND COME TO AN END. WILL THEREFORE
RAISE CEILINGS TO 3500FT AFTER 15Z. WINDS WILL INITIALLY BE FROM
THE SOUTH AT AROUND 10KT THIS AFTERNOON...THEN WILL BACK TO
SOUTHEASTERLY TONIGHT...BEFORE VEERING TO SOUTHWESTERLY MONDAY MORNING.
BARNES
&&
.PREV DISCUSSION...
ISSUED 1127 PM CST SAT DEC 5 2009
MAIN FORECAST CHALLENGE CONTINUES TO BE THE EXACT TRACK OF THE
TUESDAY NIGHT AND WEDNESDAY SYSTEM...AND ASSOCIATED PRECIPITATION TYPE.
COLD FRONT EXTENDING FROM A LOW IN EASTERN MN...TO NE IA AT 07Z.
SOUTH WINDS OF 5 TO 10 MPH NOTED ACROSS THE AREA...RESULTING IN
OVERNIGHT TEMPERATURES A FEW DEGREES WARMER THAN YESTERDAY. CI
STREAMING INTO THE FORECAST AREA AHEAD OF THIS LOW.
SHORT TERM...SUNDAY THROUGH MONDAY NIGHT
NEARLY ZONAL UPPER LEVEL FLOW...WITH A DISTURBANCE ACROSS NV...WHICH
WL TRACK EAST AND HELP MOVE THE FRONT A BIT EAST...AND PUSH THE
LOW NE ALONG THE FRONT. LIGHT SNOW WL DEVELOP ACROSS THE FORECAST
AREA SUNDAY EVENING AS THE SYSTEM PASSES. FORECAST SOUNDINGS
INDICATE DRYING IN THE MID LEVELS...ESPECIALLY SOUTH OF I-74. AFTER
12Z...MOISTURE IS JUST BELOW THE 10C LEVEL. THIS WOULD INDICATE A VERY
LOW LIKELIHOOD OF ICE CRYSTALS IN THE CLOUDS...RESULTING IN THE
PRECIPITATION TO BE DRIZZLE OR FREEZING DRIZZLE. SLIGHTLY DEEPER
MOISTURE PRESENT ACROSS THE NORTH...SO FLURRIES POSSIBLE. NO MAJOR
CHANGES MADE TO PRECIPITATION TYPE OR SNOW ACCUMULATIONS FOR THIS SYSTEM.
HIGH PRESSURE BRIEFLY BUILDS IN MONDAY AND MONDAY NIGHT...BRINGING
AN END TO THE PRECIPITATION. MOSTLY CLOUDY SKIES WILL PERSIST
AHEAD OF THE NEXT SYSTEM.
LONG TERM...TUESDAY THROUGH SATURDAY
NO CHANGES MADE TO THE FORECAST BEYOND THURSDAY. FORECAST MODELS
ARE ALL SHIFT THE TRACK OF THE TUESDAY NIGHT/WEDNESDAY LOW A BIT
FURTHER NORTH. THE ECMWF NOW TRACKS THE LOW JUST A BIT FURTHER
NORTH THAN THE GFS...HOWEVER TRACK POSITIONS WERE CLOSE...ALTHOUGH
THE GFS WAS FASTER. PREFERRED A BLEND OF THE GFS AND ECMWF. A MORE
NORTHERLY LOW TRACK WOULD SHIFT THE HEAVIER PRECIPITATION
NORTHWEST OF THE FORECAST AREA...AND PLACE A BETTER CHANCE OF
MIXED PRECIPITATION ACROSS THE CENTRAL PART OF THE FA. ACROSS THE
SE...TEMPERATURES ARE WARM ENOUGH FOR RAIN...UNTIL MUCH COLDER AIR
IS PULLED INTO THE AREA ON WEDNESDAY. INCREASED THE COVERAGE OF
THE RAIN AND SNOW MIX...AND CUT BACK ON SNOWFALL TOTALS A BIT TO
THE EAST OF INTERSTATE 55.
VERY TIGHT PRESSURE GRADIENT ON THE BACKSIDE OF THE DEPARTING LOW
WILL RESULT IN GUSTY NW WINDS ON WEDNESDAY. THESE WINDS WILL
RESULT IN SOME MUCH COLDER AIR TO POUR INTO THE STATE WEDNESDAY.
VERY COLD TEMPERATURES WEDNESDAY AND THURSDAY MORNING CAN BE
EXPECTED. MORNING LOW TEMPERATURES WL BE ESPECIALLY COLD OVER
AREAS WITH A SNOWPACK...TO THE NW OF THE IL RVR.
DPK
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
