FXUS63 KEAX 220441
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1041 PM CST MON DEC 21 2009
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
SHORT TERM (TONIGHT-WEDNESDAY NIGHT)...
NCEP AND GLOBAL MODELS CONTINUE TO TREND TOWARD A CONSENSUS THAT
NEARLY MIMICS THE FAVORED ECMWF OVER THE PAST FEW DAYS. THUS...
FORECAST CONFIDENCE CONTINUES TO INCREASE FOR THE SHORT TERM
ALLOWING FOR SOME FINE TUNE ADJUSTMENTS.
IN THE NEAR TERM...A WEAK SHORTWAVE CENTERED OVER CENTRAL NEBRASKA
WILL CONTINUE TO MIGRATE RAPIDLY EASTWARD THROUGH EARLY THIS
EVENING...SPREADING A PERIOD OF MID CLOUDS OVER THE REGION. MODIFIED
SOUTHERLY LOW LEVEL FLOW IN RESPONSE TO THIS WAVE HAS HELPED DRAW
DEWPOINTS TO AROUND 30 DEGREES THIS AFTERNOON...AND A MORE
AGGRESSIVE MOISTENING LATE TONIGHT WILL RESULT IN THE ONSET OF
WIDESPREAD LOW STRATUS OVER THE WRN CWA TOWARD DAYBREAK. RECENT
STATISTICS SHOW AN SIGNIFICANT COLD BIAS WITH MINIMUM TEMPERATURE
FORECASTS OVER THE PAST FEW DAYS...INCLUDING ALL OBJECTIVE GUIDANCE.
WILL TRY TO BUCK THIS TREND AND FAVOR WARMER MINS GIVEN THE BOUNDARY
LAYER MOISTENING AND LOW LEVEL WARM ADVECTION.
IN RESPONSE TO INITIAL HEIGHT FALLS OVER THE SRN ROCKIES BROAD
SURFACE CYCLOGENESIS SHOULD EVOLVE OVER THE TX PANHANDLE
TOMORROW...WITH A LONG WARM FRONT EXTENDING NORTHEAST THROUGH OK/KS
AND BISECTING THE CWA. STILL LIKE THE PROSPECTS OF DRIZZLE/FREEZING
DRIZZLE DURING THE DAY TOMORROW...GRADUALLY BECOMING A STEADIER
LIGHT RAIN/FREEZING RAIN INTO TOMORROW NIGHT. RIGHT NOW ONLY THE NRN
TIER OR TWO OF COUNTIES WOULD BE SUSCEPTIBLE TO MINOR ICING (MAINLY
ELEVATED SURFACES) WITH TEMPERATURES FORECAST TO BE JUST UNDER
FREEZING. HOWEVER...GIVEN THE CRITICAL LOW LEVEL THERMODYNAMICS AND
+4 TO 6C TEMPS ATOP THE INVERSION...IT IS POSSIBLE THAT DIABATIC
EFFECTS COULD WARM THE BOUNDARY LAYER SUFFICIENTLY TO AVOID
SIGNIFICANT PROBLEMS. A SHORT TERM FREEZING RAIN ADVISORY MAY BE
NEEDED IF SUFFICIENT COLD AIR IS MAINTAINED NORTH OF THE BOUNDARY.
OTHERWISE...EXPECT THAT THE SURFACE WARM FRONT WILL GRADUALLY
RETREAT NORTH AND WEST...ULTIMATELY REFORMING JUST WEST OF THE CWA
AS A NORTH-SOUTH ORIENTED INVERTED TROUGH AS DEEPER SOUTHERLY FLOW
IS ESTABLISHED. FIRST WAVE OF PRECIPITATION IS EXPECTED TUESDAY
NIGHT/WEDNESDAY MORNING...ACCENTUATED BY A LEAD SHORTWAVE PIVOTING
NORTHWARD THROUGH THE MEAN TROUGH. THIS UNUSUAL SHORTWAVE TRAJECTORY
WILL FURTHER ENHANCE THE FLOW OUT OF THE GULF...AND WITH A POSSIBLE
LULL IN THE PRECIP FOR A PORTION OF WEDNESDAY...WARM ADVECTION
SHOULD ALLOW TEMPERATURES TO RISE TO AROUND 50 DEGREES ALONG AND
SOUTH OF THE MISSOURI RIVER.
STRONG VERTICAL ASCENT ALONG WITH HIGH PRECIPITABLE WATER ANOMALIES
WILL AGAIN OVERSPREAD THE AREA WEDNESDAY NIGHT AS THE UPPER WAVE
BEGINS TO EJECT NORTHEAST ACROSS THE SOUTHERN PLAINS. CONCERNS OF
HEAVY RAIN INCREASING...ESPECIALLY CONSIDERING THE FROZEN GROUND AND
LIKELIHOOD THAT EXCESSIVE RUNOFF COULD LEAD TO RIVER FLOODING OVER
THE SRN/ERN CWA. HPC GUIDANCE SUGGESTS HIGH POTENTIAL FOR > 1" QPF
AND AGREE WITH THAT ASSESSMENT. IN ADDITION...MODEL FORECAST
SOUNDINGS SHOW AMPLE MUCAPE (200-400 J/KG) AND UPPER DIFFLUENCE FOR
THUNDERSTORMS OVER WEST CENTRAL/CENTRAL MO....THE EXTENT OF WHICH
MAY BE DICTACTED BY MORE WIDESPREAD DEEP MOIST CONVECTION OVER THE
OZARKS AND POINTS SOUTH.
GIVEN THE SLIGHTLY SLOWER AND MORE WESTERN TRACK OF THE DEEPENING
OCCLUSION...FEEL MORE CONFIDENT THAT THE ENTIRE CWA WILL REMAIN
WITHIN THE MODIFIED WARM SECTOR OVERNIGHT. THUS...HAVE KEPT
PRECIPITATION ALL RAIN AND HAVE ALSO MADE SIGNIFICANT UPWARD
ADJUSTMENTS TO MIN TEMPS FIGURING THAT READINGS SHOULD REMAIN STEADY
IF NOT CLIMB SLOWLY AS MODERATE SOUTHERLY WINDS PERSIST THROUGH THE
OVERNIGHT HOURS.
BOOKBINDER
MEDIUM RANGE (THURSDAY THROUGH MONDAY)...
MAIN CONCERN THROUGH THE MEDIUM RANGE CONTINUES TO BE WITH POTENT
STORM SYSTEM EXPECTED TO EVOLVE ACROSS THE CENTRAL CONUS THROUGH THE
LATTER PART OF THE WEEK. OVERALL MODEL TRENDS CONTINUE TO BE IN
DECENT AGREEMENT THROUGH THE END OF THE WEEK BEFORE SIGNIFICANT
DIFFERENCES ARISE WITH RESPECT TO THE TRACK AND TIMING OF THE UPPER
LOW. WENT WITH A ECMWF/GFS ENSEMBLE MEAN BLEND WHICH SEEMED TO BE A
GOOD COMPROMISE AMONG THE VARIOUS SOLUTIONS.
BY THURSDAY...MEAN TROUGH AXIS WILL SWING INTO THE SOUTHERN PLAINS
WHILE BECOMING NEGATIVELY TILTED AS IT LIFTS NORTHWARD TOWARDS THE
AREA. VIGOROUS WAA WILL BE ONGOING BY THURSDAY MORNING AHEAD OF THE
UPPER TROUGH ARRIVAL WITHIN LARGE SCALE DIFFLUENCE AND VIGOROUS
ISENTROPIC ASCENT. THIS SHOULD LEAD TO FAIRLY WIDESPREAD PRECIP BY
THURSDAY MORNING...MAINLY IN THE FORM OF RAIN INITIALLY AS WARM AIR
IS DRAWN NORTHWARD INTO THE SYSTEM. MAIN CONCERN WILL BE WHERE
INVERTED TROUGH AXIS SETS UP DURING THE DAY THURSDAY AND THE
SUBSEQUENT TRANSITION LINE FROM LIQUID TO FROZEN PRECIP. ATTM THE
BEST LOCATIONS TO RECEIVE FROZEN PRECIP DURING THE DAY THURSDAY
APPEARS TO BE ACROSS FAR NORTHWEST MISSOURI WHERE THE HIGHEST
PROBABILITY OF COLDER AIR REMAINING IN PLACE WILL EXIST.
BY THURSDAY NIGHT...SIGNIFICANT HEIGHT FALLS TAKE SHAPE AS THE
SYSTEM INTENSIFIES ACROSS THE CENTRAL PLAINS AND MIDWEST. THERE WILL
LIKELY BE A TRANSITION PERIOD WHERE PRECIP MAY SHUT OFF FOR A TIME
AS EXPECTED DRY SLOT ROTATES INTO THE SYSTEM. THE EXACT TRACK OF THE
SYSTEM IS STILL TO BE DETERMINED AND A DEVIATION TO THE RIGHT OR
LEFT MAY LEAD TO MORE ABUNDANT PRECIPITATION FOR ANY GIVEN
LOCATION. ON THE WESTERN SIDE OF THE SYSTEM...COLDER AIR WILL BE
ALLOWED TO WRAP AROUND ALLOWING A TRANSITION FROM RAIN TO SNOW.
AGAIN...PORTIONS OF FAR NORTHWEST MO/NORTHEAST KS WILL LIKELY
TRANSITION FIRST BEFORE THE SYSTEM LIFTS NORTHWARD AND THE REMAINDER
OF THE AREA IS ALLOWED TO CHANGE OVER. SNOW AMOUNTS ARE STILL
UNCERTAIN...ALTHOUGH GREATER AMOUNTS ARE MORE LIKELY ACROSS FAR
NORTHWEST MO/NORTHEAST KS. HOWEVER...DYNAMIC COOLING UNDER THE COLD
CORE MAY ALLOW A TRANSITION TO SNOW...WITH PERIODS OF MODERATE TO
HEAVY SNOW POSSIBLE...ALTHOUGH THE DURATION MAY NOT LAST LONG. LIGHT
SNOW OR FLURRIES MAY LINGER INTO THE BEGINNING OF THE WEEKEND AS THE
SYSTEM DEPARTS NORTHEASTWARD. OTHERWISE...COLDER AIR FILTERS
SOUTHWARD BY THE WEEKEND LEADING TO SUB-FREEZING TEMPS ACROSS MOST
LOCATIONS...MUCH COLDER IN SNOW PACKED AREAS.
DEROCHE
&&
.AVIATION...
FOR THE 06Z TAFS...CONCERN IS ONCE AGAIN IFR STRATUS. VFR CONDITIONS
WILL PREVAIL THROUGH EARLY MORNING. HOWEVER...A COLD FRONT PRESSING
SOUTH FROM CNTRL NEBRASKA WILL SHIFT SOUTHEAST INTO THE TERMINALS BY
THE LATE MORNING OR EARLY AFTN HOURS. IFR STRATUS WAS PRESENT BEHIND
THE FRONT IN CNTRL NEBRASKA WITH THE CURRENT TIMING SUGGESTING THAT
THE STRATUS WILL ARRIVE AFT 15Z. MVFR FOG MAY ALSO OCCUR. THE CIGS MAY
RISE TO ABOVE 1KFT DURING THE AFTN...BUT INCREASING MOISTURE ABOVE THE
FRONT WILL LEAD TO THE DEVELOPMENT OF IFR CIGS AND MVFR/IFR VSBYS
WITH DRIZZLE DURING THE EVENING ON TUESDAY.
DB
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&
$$
