FXUS63 KEAX 112343
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
542 PM CST FRI DEC 11 2009
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
/324 PM CST FRI DEC 11 2009/
SHORT TERM (TONIGHT THROUGH SATURDAY NIGHT)
HIGH PRESSURE WILL CONTINUE TO BE THE DOMINANT WEATHER FEATURE OVER
THE REGION THROUGH TONIGHT BEFORE SHIFTING EASTWARD TOWARD THE MID
ATLANTIC COAST TOMORROW. WITH THE HIGH SITUATED JUST SE OF THE
CWA...SOUTHERLY WINDS HAVE SUPPORTED CONSIDERABLE WAA OVER THE
REGION TODAY. THE ABUNDANT SUNSHINE HAS ALSO BEGUN TO MINIMIZE THE
SNOW PACK ACROSS THE NORTHWESTERN CWA...PARTICULARLY ALONG THE
SOUTHERN EDGE WHERE SNOWFALL AMOUNTS WERE THE LEAST.
SOUTHERLY WINDS WILL CONTINUE TO PREVAIL FRIDAY NIGHT AND SATURDAY...
HELPING TO WARM OVERNIGHT LOWS AND SATURDAY HIGHS TO NEAR SEASONABLE
NORMALS. THUS HAVE BUMPED TEMPS UP A FEW DEGREES TO REFLECT THIS
PERSISTENT SOUTHERLY FLOW. BY SATURDAY MORNING...LOW LEVEL MOISTURE
FROM THE GULF OF MEXICO WILL BEGIN TO SURGE NORTHWARD ACROSS THE
SOUTHERN PLAINS...PROGRESSING NORTHWARD THROUGH THE AFTERNOON AND
EVENING HOURS. BUFR SOUNDINGS SHOW MOISTURE DEPTHS TO BE QUITE
SHALLOW ACROSS MUCH OF THE REGION...WITH THE GREATEST MOISTURE
DEPTHS OVER CENTRAL MISSOURI. THE MAIN CHANGE THAT WAS MADE TO THE
PREVIOUS FORECAST WAS WITH PRECIP TYPE. SINCE SATURDAY TEMPS HAVE
BEEN BUMPED UP DUE TO THE CONTINUED SOUTHERLY FLOW...HAVE
TRANSITIONED MUCH OF PRECIP TO DRIZZLE RATHER THAN FREEZING DRIZZLE.
THE ONLY EXCEPTION IS ACROSS THE EXTREME NW CORNER OF THE CWA THAT
HAS THE GREATEST AMOUNT OF SNOW PACK. CENTRAL MISSOURI...WHERE
MOISTURE DEPTHS WERE GREATEST...MAY ACTUALLY RECEIVE INTERMITTENT
LIGHT RAIN AMONGST THE PATCHY DRIZZLE. ANALYZED 280-292K ISENTROPIC
SURFACES TO GET A BETTER SENSE OF THE FLOW OF THIS SOUTHERLY
MOISTURE. BY SATURDAY EVENING...ISENTROPIC SURFACES SHOW THE
MOISTURE BARELY CLIPPING THE NW CORNER OF THE CWA...KEEPING THE BULK
OF THE PRECIP TO THE SE. AS WE PROGRESS THROUGH SATURDAY EVENING AND
OVERNIGHT HOURS EARLY SUNDAY...PRECIP WILL PUSH EASTWARD ACROSS THE
CWA...AND FINALLY EXIT THE REGION BY SUNRISE SUNDAY MORNING.
ALTHOUGH THE NW CORNER HAS THE GREATEST CHANCE OF RECEIVING FREEZING
DRIZZLE...SOUNDINGS OVER THIS AREA SHOWED THE MOST SHALLOW MOISTURE
DEPTHS...THUS RESULTING IN MINIMAL EXPECTED QPF OVER THIS AREA.
ACH
MEDIUM RANGE (SUNDAY THROUGH FRIDAY)...
OPERATIONAL AND ENSEMBLE MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT
WITH THE OVERALL HEMISPHERIC FLOW PATTERN...DEPICTING PREDOMINANT
NORTHERN LATITUDE POSITIVE HEIGHT ANOMALIES...IN CONJUNCTION WITH
MORE SOUTHERN LATITUDE OCEANIC BASIN NEGATIVE ANOMALIES. THE
RESULTING LONGWAVE ALIGNMENT THROUGH THE MAJORITY OF THIS PERIOD
DEFINES AN ALMOST TEXTBOOK -NAO/AO TELECONNECTION PATTERN...WITH THE
STRONG NORTH ATLANTIC REX BLOCK REPRESENTING NORMALIZED HEIGHT
ANOMALIES GREATER THAN 4 STANDARD DEVIATIONS ABOVE AVERAGE OVER
GREENLAND. RESULTANT UPSTREAM JET WILL FEATURE QUASI-ZONAL
FLOW...GRADUALLY BECOMING MORE NWLY WITH TIME...WHILE NORTHERN
LATITUDE RIDGING PROMOTES SFC PRESSURE RISES AND THE EQUATORWARD
PROPAGATION OF HIGHER PRESSURES TOWARDS STRONGER BAROCLINICITY ALONG
THE PRIMARY JET AXIS. THE OVERALL -NAO/AO TELECONNECTION PATTERN
ALONG WITH THE MAGNITUDE OF THE ANOMALY CENTERS (ENSEMBLE NAO
MEASURES SOME 2 SIGMA LEVELS TOWARDS THE NEGATIVE SIDE...WHILE AO
MEASURES AROUND 4 SIGMA LEVELS NEGATIVE) STRONGLY CORRELATE TO BELOW
AVERAGE TEMPERATURES ACROSS THE CNTRL CONUS. JUST BEYOND THIS MEDIUM
RANGE PERIOD...THERE ARE SOME INDICATIONS OF A +PNA TELECONNECTION
PATTERN BECOMING LINKED WITH THE -NAO/AO PATTERN...WHICH COULD GIVE
AN EVEN HIGHER PROBABILITY OF BELOW AVERAGE TEMPERATURES...THOUGH
ENOUGH UNCERTAINTY EXISTS REGARDING THE LONGITUDINAL ORIENTATION OF
THE ANOMALY CENTERS (OR PERSISTENCE OF SAID ANOMALIES) TO KEEP THE
FORECAST WITHIN THE MEAN ENSEMBLE GUIDANCE TOWARDS THE END OF NEXT
WEEK.
SPREAD AMONG NUMERICAL GUIDANCE IS ABNORMALLY HIGH CONSIDERING THE
GOOD AGREEMENT ON THE POSITION AND STRENGTH OF THE TROPOSPHERIC
FEATURES. THIS MAY BE IN PART DUE TO THE PRESENCE OR EXTENT OF SNOW
COVER IN THE NRN CWA (AND FOR THAT MATTER THE FETCH OF SNOW COVER
HIGH PRESSURE MUST TRAVEL BEHIND A FRONTAL PASSAGE MONDAY). EVEN THE
SPREAD BETWEEN DIFFERENT RUNS OF THE SAME MODEL LEAVES MUCH TO BE
DESIRED...AND HAVE GENERALLY KEPT NEAR AN ENSEMBLE MEAN PRIOR TO
FROPA SUNDAY AND MONDAY...AND CUT BELOW THE MEAN POST FRONTAL
THROUGH THURSDAY MORNING. COULD SEE QUITE A SPREAD IN HIGH TEMPS
SUNDAY AFTERNOON...HIGHLY CONTINGENT UPON THE AMOUNT OF (OR LACK
THEREOF) LOW CLOUD EROSION. TRIED TO STAY RATHER CONSERVATIVE HERE
CONSIDERING THE LOW SUN ANGLE AND REDUCED MIXING DEPTH. WILL LIKELY
SEE ONLY MINOR NOCTURNAL FALLS SUNDAY NIGHT WITH LOW LEVEL MOISTURE
ADVECTION...FOLLOWED BY MORNING HIGHS AHEAD OF A SHARP COLD FRONT
RACING SOUTH THROUGHOUT THE DAY. DEEPER CAA MAY ACTUALLY LAG THIS
FRONT SLIGHTLY...SO DID ALLOW FOR SOME MINOR DIURNAL RISES
MONDAY...BEFORE CRASHING TEMPS DURING THE LATE AFTERNOON AND
EVENING. SHOULD SEE LITTLE IF ANY PRECIPITATION ASSOCIATED WITH THIS
FRONT...WITH BETTER SATURATION AND LIFT RELEGATED CLOSER TO THE I-80
CORRIDOR. SEASONABLY CHILLY WEATHER (SLIGHTLY MORE THAN 1 SIGMA
LEVEL BELOW AVERAGE) WILL PREVAIL THROUGH THURSDAY...BEFORE
REBOUNDING CLOSER TO CLIMATOLOGY BY THE END OF THE WEEK. THE GOOD
NEWS IS POST FRONTAL PRECIPITATION CHANCES IN THE COLD AIR BEYOND
MONDAY EVENING LOOK SLIM TO NONE.
21
&&
.AVIATION...
FOR THE 00Z TAFS...SATELLITE IMAGERY SHOWS EXTENSIVE AREA OF VFR
CEILINGS BETWEEN 3500-5000 AGL SPREADING NNE ACROSS SOUTH
CENTRAL/SOUTHEAST KS AND SOUTHWEST MO. NONE OF THE MODELS HAVE
PICKED UP ON THIS. LATEST RUC DID SHOW SOME POCKETS OF MOISTURE AT
850MB BUT NOWHERE NEAR WHAT WE ARE SEEING. HAVE BROUGHT IN VFR
CEILINGS AROUND 4K FT AGL INTO THE TERMINALS USING LINEAR
EXTRAPOLATION. HAVE SEEN SOME HOLES IN THE CLOUD DECK START TO FORM
OVER CENTRAL OK SO THIS CLOUD LAYER MAY BE RELATIVELY THIN AND PRONE
TO BREAKING UP AS IT MOVES NNE THIS EVENING.
BETTER MOISTURE AND DEEPER ISENTROPIC LIFT ARRIVES SATURDAY MORNING
WILL SATURATE THE BOUNDARY LAYER AND LOWER CEILINGS INTO THE MVFR
CATEGORY. BY MID AFTERNOON...AND POSSIBLY EARLIER...SHOULD START TO
SEE SOME MVFR ADVECTION FOG ARRIVE. NAM/GFS BUFR SOUNDINGS SUGGEST
DRIZZLE COULD BECOME AN ISSUE. WANT TO SEE HOW THE 00Z MODEL RUNS
LOOK BEFORE ADDING TO THE FORECAST.
MJ
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&
$$
