FXUS63 KEAX 080540
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1140 PM CST MON DEC 7 2009
...UPDATED AVIATION DISCUSSION...
.UPDATE...
MODEL CONSISTENCY OVER A 4-5 DAY STRETCH ON A HIGH IMPACT EVENT MUST
ALWAYS BE TAKEN WITH A GRAIN OF SALT AS IT IS ALWAYS THE DEVIL IN
THE LAST MINUTE DETAILS THAT CAN MAKE OR BREAK A FORECAST. AFTER
DOING A 00Z SFC/UPPER AIR HAND ANALYSIS...THERE ARE DEFINITELY SOME
CONCERNS HEADING INTO TONIGHT AND TOMORROW.
THE MOISTURE GRADIENT IS QUITE IMPRESSIVE...WITH CONCERNS DRAWING
FROM THE FLOW TRAJECTORIES. THE 850MB CHART SHOWS A LARGE POOL OF
VERY DRY AIR EXTENDING FROM THE ARKLATEX INTO MISSOURI AND THE OHIO
VALLEY...WITH A MORE EXPANSIVE DRY LAYER NOTED AT 700MB ACROSS MUCH
OF THE SOUTH PLAINS AND LOWER MISSISSIPPI RIVER VALLEY. CURRENT FLOW
TRAJECTORIES SUGGEST THAT MUCH OF THE SOUTHERN HALF OF THE CWA WILL
MAINTAIN THE DRY AIRMASS THROUGH THE OVERNIGHT HOURS. IN FACT...WITH
THE EXPECTATIONS THAT THE FLOW WILL GRADUALLY BACK WITH TIME AHEAD
OF THE DEEPENING WESTERN TROUGH...THIS WOULD SUGGEST THAT
CONDENSATION PRESSURE DEFICITS MAY ACTUALLY /INCREASE/ AND SPREAD
NORTHWARD WITH TIME TOMORROW MORNING AS THAT DRY AIR IS ADVECTED
NORTHWARD FROM THE OZARKS AND SOUTHERN PLAINS.
FOR THE REST OF TONIGHT...WARM ADVECTION AND MODERATE ISENTROPIC
UPGLIDE WITHIN THE PRE-EXISTING MOIST LAYER SHOULD LEAD TO A RAPID
INCREASE IN RADAR ECHOES FROM CENTRAL KANSAS INTO NORTHERN
MISSOURI...WITH LIGHT TO OCCASIONALLY MODERATE SNOW OVERNIGHT. A
QUICK ONE TO TWO INCHES IS EXPECTED ALONG AND NORTH OF KCI TO
KIRKSVILLE. FOR THE AFOREMENTIONED REASONS...I'M REALLY HAVING A
TOUGH TIME JUSTIFYING ANYTHING MORE THAN OCCASIONAL FLURRIES ALONG
AND SOUTHEAST OF A KANSAS CITY TO CARROLLTON TO MACON LINE.
THIS ASCENT WILL SHIFT NORTHEAST AFTER MIDNIGHT WITH SNOW GRADUALLY
EXITING THE AREA TOWARD DAYBREAK. THIS BRINGS UP PROBLEM NUMBER TWO.
IF MY SUSPICIONS ARE CORRECT...WE MAY SEE LITTLE TO NO PRECIPITATION
ACROSS ALL BY FAR NW MO/NE KS DURING MOST OF THE DAY TOMORROW.
NEUTRAL HEIGHT ADVECTION AND DRY AIR ALOFT MAY RESULT IN LITTLE MORE
THAN SNOW GRAINS OR PATCHY DRIZZLE/FREEZING DRIZZLE UNTIL LATE IN
THE AFTERNOON.
THE BULK OF THE SNOWFALL WILL OCCUR DURING THE LATE AFTERNOON (WEST)
AND EVENING HOURS (ALL AREAS) AS STRONG HEIGHT FALLS LEAD TO RAPID
VERTICAL ASCENT AHEAD OF THE DEEPENING AND INCREASINGLY NEGATIVE
TILT UPPER TROUGH. ABUNDANT DEEP LAYER MOISTURE ACCOMPANYING THE
PACIFIC TROUGH WILL YIELD RAPID SATURATION AND THE ONSET OF MDT/HVY
SNOWFALL OVER NW MO.
OVERALL...WILL LIKELY NEED TO GREATLY ENHANCE THE SNOWFALL
ACCUMULATION GRADIENT GIVEN THE IMPACTS OF DRY AIR. EVEN WHERE
PRECIPITATION RESIDENCE TIME IS LONGEST OVER NW MO...AM NOT SURE
EVEN HERE THAT ONE TO TWO INCHES TONIGHT PLUS THE DEFORMATION SNOWS
WILL YIELD THE 10+ INCH AMOUNTS CURRENTLY PROJECTED.
WILL LET THE MID SHIFT HANDLE THE BULK OF ANY CHANGES TO THE
WATCHES/WARNINGS...BUT WILL MAKE SOME SHORT TERM MODIFICATIONS TO
LOWER POPS SIGNIFICANTLY SOUTH/EAST ALONG WITH PRECIPITATION TYPE
THROUGH TOMORROW.
BOOKBINDER
&&
.AVIATION...
FOR THE 06Z TAFS...CURRENT RADAR TRENDS CONFIRMING THE EARLIER
ANTICIPATION THAT A BAND OF SNOW WOULD DEVELOP FROM NE KS INTO NW
MO. EFFECTS OF DRY AIR RESULTING IN A LARGE REFLECTIVITY GRADIENT
RIGHT OVER MCI...AND DO NOT EXPECT THIS TO SHIFT MUCH OVERNIGHT.
FOR THE REST OF TONIGHT...
KSTJ SHOULD REMAIN IN A STEADY LIGHT TO OCCASIONALLY MODERATE SNOW
WITH SEVERAL INCHES OF ACCUMULATION.
KMCI WILL CONTINUE TO WAFFLE IN AND OUT OF THE SNOW BAND...BUT THINK
ENOUGH NORTHWARD DRY ADVECTION WILL OCCUR THAT PREDOMINANTLY THE
SNOW HERE FORWARD SHOULD BE MAINLY LIGHT (4-6SM VISIBILITIES).
KMKC WILL LARGELY REMAIN OUT OF THE PRECIPITATION WITH GENERALLY VFR
VISIBILITIES AND IFR CEILINGS.
FOR TUESDAY...LIGHT SNOW TO CONTINUE AT ST. JOSEPH...BUT AS ALLUDED
TO EARLIER...QUITE A BIT OF DRY AIR ALOFT AND WEAK FORCING TO
CONTEND WITH. WILL LIKELY BE A LONG DURATION LULL OF JUST LIGHT SNOW
AND POSSIBLE SOME INTERMITTENT FREEZING DRIZZLE. ICING ALOFT COULD
BECOME AN INCREASING CONCERN GIVEN THE SUPERCOOLED WATER DROPLETS
AND WEAK VERTICAL MOTIONS.
AS THE MAIN STORM SYSTEM APPROACHES...SNOW WILL QUICKLY OVERSPREAD
THE TERMINALS (IF NOT ALREADY ONGOING AT KSTJ) AFTER 20Z AND
BECOMING HEAVY AT TIMES IN THE EVENING. MODERATE ACCUMULATIONS
EXPECTED (POSSIBLY HEAVY STJ). WINDS WILL SHIFT ABRUPTLY FROM EAST
TO WEST-NORTHWEST WITH A MID EVENING FRONTAL PASSAGE...WITH SPEEDS
INCREASING TO 15-25 KNOTS AFTER THE END OF THE TAF CYCLE.
BOOKBINDER
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM CST
WEDNESDAY FOR MOZ032-033-037>039-043-044.
WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 6 AM CST
WEDNESDAY FOR MOZ001>008-011>017-020>025-028>031.
KS...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM CST
WEDNESDAY FOR KSZ057-105.
WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 6 AM CST
WEDNESDAY FOR KSZ025-102>104.
&&
$$
