151
FXUS63 KILX 210807
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
207 AM CST SAT NOV 21 2009
DISCUSSION
ISSUED 205 AM CST SAT NOV 21 2009
LATEST SURFACE MAP SHOWING THE CWA UNDERNEATH AN EAST-WEST HIGH
PRESSURE RIDGE...CENTERED IN SOUTHEAST OHIO. SATELLITE FOG
IMAGERY SHOWING PATCHES OF STRATOCUMULUS CLOUDS ACROSS THE EAST
CENTRAL CWA AROUND CHAMPAIGN AND DANVILLE...AS WELL AS SCATTERED
NEAR THE ST LOUIS AREA. DENSE FOG HAS MAINLY BEEN PATCHY THUS
FAR...WITH AVERAGE VISIBILITIES OVER THE CWA IN THE 3 TO 7 MILE
RANGE.
MAIN SHORT TERM CONCERN INVOLVES THE FOG THIS MORNING. IN THE
LONGER RANGE...EVOLUTION OF THE NEXT STORM SYSTEM IN THE TUESDAY-
WEDNESDAY TIME FRAME IS THE PRIMARY FORECAST CONCERN.
SHORT TERM...TODAY THROUGH MONDAY...
THE FOG HAS BEEN SLOWER TO EVOLVE THAN LAST NIGHT...BUT LATEST
SURFACE PLOT SHOWING FOG BECOMING MORE WIDESPREAD ACROSS IOWA AND
ADJACENT AREAS OF MISSOURI AND ILLINOIS. RUC MODEL SUPPORTS SOME
EXPANSION OF THIS AREA...AND WILL KEEP THE DENSE FOG ADVISORY
GOING ACROSS THE NORTHERN CWA. ACROSS THE SOUTH...BELIEVE THE FOG
WILL BE MORE PATCHY IN NATURE...DUE TO THE DRYING THAT TOOK PLACE
IN THE SUNSHINE ON FRIDAY.
OTHER THAN THAT...MODELS IN DECENT AGREEMENT THROUGH MONDAY...
KEEPING THINGS DRY. TEMPERATURES EXPECTED TO REMAIN SEVERAL
DEGREES ABOVE NORMAL. MET/MAV MOS GUIDANCE FAIRLY CLOSE AND DID
NOT SIGNIFICANTLY DEVIATE FROM IT.
LONG TERM...TUESDAY THROUGH FRIDAY...
MAIN FORECAST CHALLENGE INVOLVES EVOLUTION OF UPPER TROUGH THAT
WILL MOVE INTO THE PACIFIC NORTHWEST ON SUNDAY. THE MAJOR MODELS
ALL HAVE A CLOSED CIRCULATION DEVELOPING OVER THE CENTRAL PLAINS
BY TUESDAY MORNING...BUT THE SPEED AND TRACK OF THE SURFACE
FEATURES REMAIN IN QUESTION. GFS HAS SLOWED A BIT BUT CONTINUES TO
BE THE FASTER OF THE EXTENDED MODELS...BRINGING THE COLD FRONT
THROUGH THE CWA BY ABOUT MIDDAY TUESDAY AND HAVING WRAPAROUND
PRECIP AFFECTING THE AREA TUESDAY NIGHT. MEANWHILE...THE ECMWF
PLACES THE SURFACE LOW IN SOUTHEAST NEBRASKA AT 12Z TUESDAY AND
MOVES IT TO NEAR ROCKFORD BY 12Z WEDNESDAY...WITH THE SURFACE
FRONT PASSING THROUGH OUR AREA SHORTLY AFTERWARD. TRENDED TOWARD
THE SLOWER SOLUTION AND THUS REDUCED POPS TO SLIGHT CHANCE ACROSS
THE EASTERN CWA MONDAY NIGHT. WENT AHEAD AND ADDED SOME LOW CHANCE
POPS TUESDAY NIGHT AND WEDNESDAY ACROSS THE NORTH...AS THAT AREA
SHOULD AT LEAST BE GETTING SOME WRAPAROUND PRECIPITATION FROM THE
GFS SOLUTION...OR FROM THE FRONT ITSELF IN THE ECMWF SOLUTION.
SOUTHERN CWA IS NOT AS CLEAR CUT AT THIS TIME...AND WILL NOT
CHANGE THE POPS IN THAT AREA. UNTIL MORE CONSISTENCY DEVELOPS.
1000-500MB THICKNESS...AS WELL AS BUFKIT SOUNDINGS...WOULD SUGGEST
THAT PRECIP TYPE WOULD BE A CONCERN AS WELL. CURRENTLY PLAN TO
LIMIT ANY MIXED PRECIP TO THE FAR NORTHERN CWA FOR TUESDAY NIGHT.
BOTH MODELS SHOWING WEAK TROUGHS MOVING THROUGH ON THANKSGIVING
DAY...FOLLOWED BY HIGH PRESSURE RIDGING BUILDING IN FROM THE WEST.
HOWEVER...NO CHANGES WERE MADE TO THIS PORTION OF THE FORECAST.
GEELHART
AVIATION
ISSUED 1116 PM CST FRI NOV 20 2009
LIGHT FOG HAS DEVELOPED AT SOME SITES TONIGHT WHILE OTHERS ARE
SLOW. HOWEVER...DENSE FOG...VLIFR VIS CAN BE EXPECTED BY MORNING
AT BMI AND PIA WHILE SPI...DEC AND CMI WILL SEE VIS DOWN TO AROUND
A MILE BY MORNING. CLOUD COVER OVER CMI HAS FINALLY MOVED
NORTHEAST AND EXPECT MOSTLY CLEAR SKIES AT ALL TAF SITES
OVERNIGHT. BY MID MORNING...MODEL BRING SOME HIGHER RH VALUES INTO
THE WESTERN HALF OF THE REGION AND AM EXPECTING BKN CIGS AT AROUND
4KFT TO ADVECT INTO SPI...DEC AND THEN AT BMI AND PIA LATER THIS
MORNING AND INTO THIS AFTERNOON. CLOUD COVER SHOULD BECOME
SCATTERED IN THE LATE AFTERNOON TO EARLY EVENING HOURS AS THE
CLOUDS MOVE NORTH THROUGH THE AREA. CMI SHOULD REMAIN SCATTERED
ALL DAY AS THE HIGHEST RH VALUES REMAIN WEST OF THE TAF SITE.
LIGHT WINDS WILL BECOME SOUTHEAST TOMORROW AND REMAIN LESS THAN 10MPH.
AUTEN
ILX WATCHES/WARNINGS/ADVISORIES
DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR ILZ027>031-
036>038-040-041.
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