000
FXUS63 KEAX 061130
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
529 AM CST TUE JAN 6 2009
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
/320 AM CST TUE JAN 6 2009/
EARLY MORNING WV IMAGERY SHOWS TROUGH AXIS NOW CROSSING THE
ROCKIES...WITH A DISTINCT SHORTWAVE DIVING SOUTHEAST THROUGH NEW
MEXICO...AND A SECONDARY SHEARED NRN STREAM WAVE ENTERING THE
DAKOTAS. PRIMARY SUBTROPICAL FEED AND LOW LEVEL BAROCLINICITY HAS
BEEN SHUNTED SOUTH TO A LINE FROM ERN OKLAHOMA TO THE OHIO RIVER
VALLEY...WITH NOTABLE DRY AIR INTRUDING FROM THE SRN HIGH PLAINS
THROUGH WRN MISSOURI. LOW CLOUD DECK HAS PUSHED JUST NORTH OF THE
MISSOURI RIVER OVERNIGHT...AIDED BY WEAK ISENTROPIC LIFT THROUGH THE
280K-285K LAYERS...WHILE A BKN ACCAS DECK HAS RAPIDLY FORMED IN
RESPONSE TO H7-H6 FRONTOGENETICAL FORCING AHEAD OF THE EJECTING
TROUGH AXIS. HOWEVER...THE SUBSTANTIAL DRY AIRMASS BETWEEN BOTH THE
ACCAS DECK AND THE LOWER CLOUD TOPS...AND IN THE BOUNDARY LAYER HAS
PRECLUDED ANY OF THE PRECIPITATION ECHOES SEEN ON LOCAL RADAR
IMAGERY FROM REACHING THE SFC.
SFC OBSERVATIONS AND MODELS CLEARLY SHOW TROUGH AXIS EXTENDING FROM
ERN SOUTH DAKOTA THROUGH NWRN KANSAS THIS MORNING.
ESSENTIALLY...THERE IS NO CAA IN THE WAKE OF THIS BOUNDARY (WITH
TEMPERATURES BEHIND THE BOUNDARY ACTUALLY WARMER THAN THOSE
PRECEDING THE TROUGH DUE TO DOWNSLOPING)...AND DESPITE MORE
EXTENSIVE MID/HIGH CLOUDS ADVECTING TOWARDS THE CWA...THE FAVORABLE
WLY LOW LEVEL TRAJECTORIES SHOULD WARM AFTERNOON TEMPS A GOOD 5F+
ABOVE AVERAGE...AND HAVE HEDGED TOWARDS MET GUIDANCE IN THIS
RESPECT. ALL PRECIPITATION SHOULD REMAIN SOUTH AND EAST OF THE
AREA...THOUGH WILL NEED TO CLOSELY MONITOR ACCAS VIRGA EARLY THIS
MORNING.
WEAK BACKDOOR FRONT WILL SLIDE THROUGH NERN MISSOURI ON
WEDNESDAY...LEADING TO A STEEPER NE-SW TEMPERATURE GRADIENT ACROSS
THE CWA. BOUNDARY LAYER WINDS WILL LARGELY KEEP A WLY
COMPONENT...PROMOTING CONTINUED BETTER MIXING...AND ONLY WEAK CAA AT
THE H9 LEVEL WILL PUSH TEMPS ACROSS NORTHEAST MISSOURI COOLER THAN
EXPERIENCED TODAY. CANNOT TOTALLY RULE OUT A FLURRY OR SPRINKLE
ALONG AND BEHIND THIS FRONTAL BOUNDARY...THOUGH SATURATION AROUND
THE H8 LEVEL LOOKS TO BE SOMEWHAT LIMITED...AND WILL KEEP NO WEATHER
MENTION FOR THIS FORECAST PACKAGE.
CONTINUED ABOVE AVERAGE TEMPERATURES WILL REMAIN IN THE FORECAST
BOTH THURSDAY AND FRIDAY...AS SFC HIGH PRESSURE SLIDES EAST...AND
MODIFIED RETURN FLOW DEVELOPS ACROSS THE PLAINS. VERTICAL MIXING MAY
BE SOMEWHAT LIMITED ON THURSDAY WITH LIGHT SFC WINDS...HOWEVER WITH
WARMING H9 LAYER AND PLENTY OF SUN...FELT WARMER END OF THE GUIDANCE
ENVELOPE WAS JUSTIFIED. PROBABLY THE LARGEST CHANGE TO THE FORECAST
WAS TOO BOOST HIGH TEMPS FRIDAY SIGNIFICANTLY...AS H9 TEMPS WARM TO
+5C TO +8C IN A REGIME OF SLY/SWLY BOUNDARY LAYER WINDS...AND
COMPRESSIONAL WARMING AHEAD OF A STRONGER COLD FRONT DIVING
SOUTHEAST TOWARDS NWRN MISSOURI. FOR THE TIME BEING...HAVE FORECAST
HIGHS ABOUT 5F ABOVE MEX GUIDANCE (AROUND 20F ABOVE
CLIMATOLOGY)...FEELING THE CLIMO INFLUENCE IS ARTIFICIALLY TEMPERING
GUIDANCE OUTPUT. OVERALL...STILL FEEL THESE FORECAST HIGHS ARE VERY
CONSERVATIVE...AND WOULD NOT BE SURPRISED IF ANOTHER 5F NEEDS TO BE
ADDED ON.
FOLLOWED SLIGHTLY SLOWER FROPA (PER ECMWF) FOR LATE FRIDAY
AFTERNOON/EVENING...AND HAVE CONTINUED SLIGHT CHANCE POPS...THOUGH
PRECIPITATION MECHANISMS DO NOT LOOK OVERLY IMPRESSIVE. LITTLE TO NO
CHANGES MADE TO THE FORECAST DURING THE WEEKEND...THOUGH
MODIFICATION OF POST FRONTAL AIRMASS MAY KEEP CONDITIONS NOT TOO FAR
CLIMATOLOGY VERSUS BEHIND A TYPICAL JANUARY FRONTAL PASSAGE WITH
MORE EXTENSIVE CNTRL PLAINS SNOW COVER THAN CURRENTLY REPORTED.
21
&&
.AVIATION...
FOR THE 12Z TAF...VFR CEILINGS WILL PREVAIL THROUGH THE PERIOD. A
WEAK TROUGH WILL MOVE THROUGH THE TERMINALS BY 18Z VEERING WINDS
FROM THE SOUTHWEST TO WEST WITH HIGH LEVEL CLOUDINESS DURING
PASSAGE. WINDS WILL BECOME MORE NORTHWEST BY 00Z AND DECREASE AS
INVERSION SETS UP. HIGH CLOUDS WILL ALSO START TO THIN BY 00Z AS
HIGH MOVES IN.
DNB
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
$$
