FXUS63 KEAX 111728
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1128 AM CST FRI DEC 11 2009

...UPDATED AVIATION DISCUSSION...

.DISCUSSION...

GENERALLY SPEAKING...ONLY MINOR ADJUSTMENTS MADE TO THE SHORT TERM 
PORTIONS OF THE FCST.  TEMPS NOT DROPPING OFF AS MUCH AS PREVIOUS 
FCST INDICATED...THIS IS DUE IN PART TO A SLIGHTLY STRONGER SWLY 
BOUNDARY LAYER WIND WHICH HAS ALLOWED FOR HIGHER SFC DEW POINTS TO 
ADVECT NORTHWARD. NEVERTHELESS...THIS HASN'T PREVENTED TYPICAL COLD 
SPOTS IN THE DEEPER SNOWPACK AREAS TO DROP NEAR TO BELOW ZERO.

FOR TODAY...SFC HIGH PRESSURE WILL CONTINUE TO SHIFT OFF TO THE 
EASTERN PORTIONS OF THE UNITED STATES AHEAD OF OUR NEXT WEAK S/W 
TROUGH PUSHING ONTO THE CALIFORNIA COAST THIS MORNING.  AS THIS 
FEATURE MOVES INLAND AND VORTEX OVER THE CENTRAL CANADIAN PROVINCES 
FLATTENS...A BROAD ZONAL FLOW WILL DEVELOP OVER THE HEART OF THE 
COUNTRY.  A RESPONSE TO THESE FEATURES HAS ALREADY DEVELOPED AS 
PROFILERS IN THE SOUTHERN PLAINS HAVE ALREADY BACKED TO THE SOUTH. 
PROFILERS SUGGEST THAT THE EDGE OF THIS LOW-LVL WARM AIR ADVECTION 
IS STILL OKLAHOMA...WITH MODEL GUIDANCE SUGGESTING THESE WARM MOIST 
AIR TRAJECTORIES INTENSIFY OVER THE CWA AFTER 12Z.  THIS BEING 
SAID...HAVE BUMPED UP DAYTIME HIGH TEMPS IN NEARLY ALL AREAS.  AS 
EVIDENT FROM THURSDAY...SNOW PACK WILL HAVE SOME IMPACTS IN NORTHERN 
MISSOURI...BUT STRONGER SFC WAA SEEMS TO MITIGATE THESE EFFECTS.
MET/MAV GUIDANCE BLEND SEEMS REASONABLE.  

FRI NIGHT AND SAT...WEAK S/W TROUGH WILL BEGIN TO PRESS EASTWARD
INTO THE CENTRAL PLAINS OVERNIGHT...WITH STRONG LOW-LVL THETA-E
AIRMASS ADVECTING OUT OF THE GOM AND AHEAD OF THE S/W. AS PREVIOUS
FORECASTER SUGGESTED...I ALSO HAVE CONCERNS FOR ADVECTION FOG FRI
NIGHT INTO SATURDAY AS MUCH HIGHER DEWPOINTS LIFT NORTHWARD OVER THE
SNOWPACK. HOWEVER...AN INITIALLY LIGHT SFC WIND SHOULD BEGIN TO
INCREASE IN INTENSITY MITIGATING THE FOG THREAT SOMEWHAT. BY MID- DAY
SATURDAY SOUNDINGS INDICATE THE ARRIVAL OF THIS RICH LOW-LVL AIRMASS.
ATTM...SOUNDINGS CONTINUE TO SUGGEST PRECIP MAINLY IN THE FORM OF
DRIZZLE...SPRINKLES OR FREEZING DRIZZLE (NORTH). LITTLE TO NO ICE
CRYSTALS CAN BE FOUND IN THE SOUNDINGS...WITH THE HEIGHT OF THE
SATURATION LVL ONLY TO AROUND 850-825 MB. ATTM...SOUNDINGS SUPPORT A
LATE MORNING ARRIVAL OF MOISTURE...WHICH GIVEN THE EXPECTED WARMUP
ABOVE FREEZING...WOULD MITIGATE A FREEZING DRIZZLE THREAT.
HOWEVER...ANY LOW-LVL SATURATION THAT WOULD ENTER PRIOR TO 15Z WOULD
LIKELY BE FREEZING DRIZZLE. IT APPEARS MUCH OF THE CWA WILL RISE 32
OR ABOVE BY THE AFTN...WITH PERHAPS THE AREAS OVER THE SNOWPACK
REMAINING BELOW FREEZING. THUS...WILL KEEP A MENTION OF FREEZING
DRIZZLE OVER THE DEEPER SNOWPACK AREAS SAT AFTN.

SUNDAY COULD POSE A VERY TRICKY FCST...ESPECIALLY REGARDING TEMPS.  
AS THE WEAK S/W MOVES EASTWARD...BROAD ZONAL FLOW WILL CONTINUE 
DURING THE DAYTIME HOURS BEFORE OUR NEXT WEAK S/W ENTERS THE PICTURE 
FOR SUNDAY NIGHT AND MONDAY.  HOWEVER...FIRST CONCERNS WILL BE ONCE 
AGAIN ON FOG POTENTIAL FOR SUNDAY MORNING AS MODELS CONTINUES TO 
SUGGEST SFC DEW POINTS IN THE LOWER 30S ADVECTING NORTH DURING THE 
NIGHT.  THIS SAID...HAVE SIGNIFICANTLY INCREASED OVERNIGHT TEMPS SAT 
NIGHT AND INTRODUCED FOG WORDING.  HAVE ALSO BUMPED UP SUNDAY HIGH 
TEMPS WITH THE POTENTIAL FOR MANY AREAS REACHING 40 DEGREES. CLOUD
COVER MAY BE THE LIMITING FACTOR.

AS THE NEXT S/W ENTERS THE REGION SUNDAY NIGHT...EXPECTING LITTLE OR 
NO DROPOFF IN OVERNIGHT LOWS.  IN FACT...TEMPS MAY RISE THROUGH THE 
NIGHT AS BREEZY SOUTHERLY WINDS AHEAD OF A DEVELOPING SFC LOW IN THE 
WESTERN PLAINS PREVAIL. HAVE USED A NON-STANDARD DIURNAL CURVE WITH
MONDAYS HIGH TEMPS NEAR DAYBREAK.  PERHAPS AN ADDITIONAL BOUT OF
DRIZZLE WILL BE POSSIBLE HEADING INTO MONDAY...BUT NO SIGNIFICANT
PRECIP EXPECTED. A STRONG COLD FRONT WILL PLUNGE THROUGH
MONDAY...ONCE AGAIN HIGH TEMPS NEAR DAYBREAK WITH PLUMMETING READINGS
THROUGH THE DAY.

DUX     

&&

.AVIATION...

FOR THE 18Z TAFS...HIGH PRESSURE SITUATED OVER THE REGION WILL KEEP
CONDITIONS DRY WITH 5 TO 10 KT SOUTHERLY WINDS. WILL START SEEING A
SURGE OF MOISTURE FROM THE SOUTHERN PLAINS LATE SATURDAY
MORNING OVER THE TAF SITES...RESULTING IN INCREASED CLOUD COVER AND A
DROP IN CIGS. HOWEVER...VFR CONDITIONS ARE EXPECTED TO CONTINUE
THROUGH THE TAF PERIOD.

ACH

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&

$$