FXUS63 KEAX 282338
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
538 PM CST SAT NOV 28 2009
...UPDATED FOR AVIATION...
.DISCUSSION...
/305 PM CST SAT NOV 28 2009/
SHORT TERM (TONIGHT-MONDAY NIGHT)...
20Z SURFACE ANALYSIS DEPICTED A WEAK SURFACE BOUNDARY EXTENDING
ROUGHLY FROM HAYS KS TO OMAHA TO DES MOINES. SOUTHWARD COLD
INTRUSION (ALBEIT QUITE MODIFIED BY LATE NOVEMBER STANDARDS) WAS
MOST AGGRESSIVE ACROSS THE HIGH PLAINS...AND SIGNIFICANTLY LAGGED
FURTHER EAST AS EXPECTED IN THESE SHALLOW AIRMASSES. DIURNAL COOLING
AND A PROGRESSIVE SHORTWAVE ADVANCING THROUGH THE NRN PLAINS WILL
ACCELERATE THIS COLD FRONT OVERNIGHT...REACHING THE FAR SRN CWA
AROUND DAYBREAK.
AS THE FRONT ENTERS THE CWA AFTER MIDNIGHT...IT WILL BEGIN TO
INTERCEPT A NARROW PLUME OF ELEVATED MODIFIED GULF MOISTURE. GIVEN
THE VERY SHALLOW NATURE TO THE INCOMING COLDER AIRMASS...EXPECT THAT
A STEEP AND SATURATED LOW LEVEL TEMPERATURE INVERSION WILL RAPIDLY
BECOME ESTABLISHED IN THE WAKE OF THE BOUNDARY...LEADING TO A BAND
OF LOW STRATUS THAT WILL PREVAIL THROUGH MUCH OF THE DAY SUNDAY. A
SLIGHTLY WARMER/MORE MOIST BOUNDARY LAYER OVER THE SRN CWA MAY
PROVIDE ENOUGH VERTICAL MOTION IN THE LOW LEVELS TO SUPPORT SOME
PATCHY LIGHT RAIN/DRIZZLE SUNDAY MORNING...BUT ANY QPF WILL BE
NEGLIGIBLE. WITH THE TIMING OF THIS BOUNDARY AND ITS INCIPIENT COLD
ADVECTION/LOW CLOUDS...HIGH TEMPERATURE FORECAST FOR TOMORROW IS A
BIT OF A MISNOMER WITH SOME AREAS LIKELY TO HAVE 7 AM HIGHS FOLLOWED
BY STEADY/SLOWLY FALLING TEMPERATURES. DIURNAL RANGES SHOULD BE 5
DEGREES OR LESS FOR MOST OF THE CWA WITH SOME LATE DAY CLEARING
ALLOWING FOR A MODEST IMPROVEMENT OVER THE NORTHEAST.
WITH THE GROWING SEASON LONG OVER...THE PROSPECTS OF A KANSAS CITY
HARD FREEZE SUNDAY NIGHT ARE MERELY FOR THE RECORD BOOKS WITH ABOUT
A 50/50 SHOT AT THIS POINT. READINGS SHOULD REBOUND NICELY MONDAY
INTO TUESDAY AS A WEAK PRESSURE RIDGE PASSES AGAIN TO OUR SOUTH
ALLOWING FOR A MODIFIED WESTERLY COMPONENT TO RESUME. STILL A VERY
SOUTHERN STREAM DOMINANT FLOW WHICH SHOULD KEEP US SEASONABLE AND
QUIET FOR THE NEXT FEW DAYS.
BOOKBINDER
MEDIUM RANGE (TUESDAY THROUGH SATURDAY)...
DISCREPANCIES AMONG OPERATIONAL AND ENSEMBLE MEDIUM RANGE MODELS
REMAIN RATHER LARGE TODAY...EXACTLY FOR THE SAME REASONS DISCUSSED
IN YESTERDAY AFTERNOONS DISCUSSION. FOR THE SAKE OF BREVITY...WILL
NOT REHASH THE ENTIRE ARRAY OF FORCING AND FEEDBACK MECHANISMS ON
THE HEMISPHERIC SCALE WHICH WILL EVENTUALLY DICTATE SENSIBLE WEATHER
ACROSS THE CNTRL CONUS. HOWEVER...SUFFICE IT TO SAY...IT WILL STILL
LIKELY BE SEVERAL DAYS BEFORE SUFFICIENT MODEL CONSISTENCY CAN BE
ACHIEVED TO YIELD A HIGHER THAN AVERAGE CONFIDENCE ON SPECIFIC
DETAILS OF THE FORECAST.
RECENT RUNS OF THE OPERATIONAL GFS WERE ALMOST ENTIRELY IGNORED PAST
WEDNESDAY...AS ANY SEMBLANCE OF CONSISTENCY IS POOR TO SAY THE
LEAST....MUCH LESS CONTRADICTING A GOOD CONCEPTUAL MODEL. IN AN
INTERESTING REVERSAL OF ROLES...THE RECENT GFS RUNS HAVE ADVERTISED
MUCH DEEPER CLOSED LOW HEIGHT ANOMALIES OVER THE GREAT LAKES FOR THE
END OF THE WEEK (A SOLUTION FIRST ADVERTISED BY THE ECMWF
YESTERDAY...YET WITH LITTLE AGREEMENT WITH THE MAJORITY OF
ENSEMBLES...AND SINCE RESCINDED BY MORE CURRENT ECMWF RUNS). THE
OPERATIONAL MEMBER ALSO CONTINUES TO DRIVE EAST PACIFIC ENERGY FAR
TOO AGGRESSIVELY THROUGH THE WRN CONUS RIDGE...CREATING AN
UNREALISTIC SHORT WAVELENGTH SET OVER THE CONUS. THE PAST SEVERAL
ECMWF SOLUTIONS HAVE VERY GOOD SUPPORT FROM MULTI-MODEL ENSEMBLES
DEPICTING NOTABLE ERN CONUS TROUGHING...YET SOMEWHAT WEAKER AND MORE
TRANSITORY IN NATURE. AT THE SAME TIME...THE ACTIVE SET OF
PACIFIC WAVES DOES BREAK DOWN THE WRN CONUS RIDGE (MUCH MORE
GRADUALLY THAN THE OPERATIONAL GFS)...WHILE MAINTAINING A PREFERENCE
FOR DEVELOPING SPLIT FLOW (DEFINITELY A PREFERRED TREND GIVEN THE
BASE EL NINO STATE AND ENHANCED SUBTROPICAL JET). THUS...A GENERAL
BLEND OF AN ENSEMBLE MEAN AND ECMWF WAS UTILIZED FOR THIS FORECAST
PACKAGE.
ALTHOUGH MODEL UNCERTAINTY AND SPREAD IS RATHER HIGH THROUGH THE
MEDIUM RANGE...THERE ARE SEVERAL CONSTANTS AND TELECONNECTIONS THAT
SHOULD ADD SKILL OVER BASE NUMERICAL GUIDANCE OR CLIMATOLOGY.
FIRST...REGARDLESS OF THE MODEL...THE TREND THROUGH MUCH OF THE
MEDIUM RANGE IS THAT OF WEAK NEGATIVE HEIGHT ANOMALIES OVER THE ERN
CONUS...WITH POSITIVE ANOMALIES ARCING FROM THE PACIFIC NORTHWEST
THROUGH CNTRL CANADA AND INTO GREENLAND (THOUGH CERTAINLY BY FAR THE
LARGEST SEASONALLY STANDARDIZED NEGATIVE ANOMALIES ARE ASSOCIATED
WITH THE EL NINO INFLUENCED SUBTROPICAL JET FROM THE SOUTHEAST
PACIFIC THROUGH THE GULF OF MEXICO). THIS PATTERN STRONGLY
TRANSLATES TO A -NAO/AO TELECONNECTION THOUGH MOST OF THIS
PERIOD...WHICH SEASONALLY HAS A FAIRLY HIGH FEEDBACK PROBABILITY OF
BELOW AVERAGE TEMPERATURES THROUGH THE CNTRL CONUS.
HOWEVER...THERE ARE SEVERAL MITIGATING FACTORS WHICH ARGUE FOR
TEMPERATURES FALLING TO ONLY AROUND ONE STANDARD DEVIATION BELOW
AVERAGE. AS DISCUSSED YESTERDAY...SNOW COVER IS ALMOST COMPLETELY
LACKING BETWEEN THE LOWER MISSOURI RIVER VALLEY AND NORTHERN
ALBERTA/SASKATCHEWAN...AND WITH UNUSUALLY WARM WEATHER FOR THE
ENTIRE PAST MONTH...UPPER SOIL TEMPERATURES REMAIN RATHER
WARM...BOTH FACTORS WHICH WILL INFLUENCE SIGNIFICANT AIRMASS
MODIFICATION ON ITS PROGRESSION SOUTH. IN ADDITION...TRAJECTORY
ANALYSIS ON THE ENSEMBLE MEAN OF THE POST FRONTAL SFC HIGH FOR THE
END OF THE WEEK SHOWS THE SOURCE REGION PRIMARILY FROM WRN CANADA
RATHER THAN THE NORTHWEST TERRITORIES OR ALASKA...WHERE CURRENT
TEMPERATURES ARE NOT REALLY UNSEASONABLY COLD FOR THE END OF
NOVEMBER. AND FINALLY...WITH DEEP TROUGHING IN THE GULF OF ALASKA
AND ERN PACIFIC GRADUALLY PUSHING ONSHORE INTO THE PACIFIC
NORTHWEST...A GENERAL LOW LEVEL ONSHORE FLOW AND LOWERING SFC
PRESSURE PATTERN ACROSS THE CANADIAN ROCKIES WILL KEEP THE TRUE
ARCTIC AIRMASS LOCKED UP FROM THE NUNAVUT ARCHIPELAGO POLEWARD AND
THEN OUT INTO NRN ASIA. IN FACT...THE PREFERRED ENSEMBLE MEAN (AND
TO A DEGREE THE ECMWF) INDICATES A GOOD MEASURE OF WLY DOWNSLOPE
RETURN FLOW AT THE VERY END OF THIS PERIOD...ARGUING FOR A BRIEF
RESUMPTION OF NEAR OR SLIGHTLY ABOVE AVERAGE TEMPERATURES.
REGARDLESS...SAW NO REASON TO ADD ANY SIGNIFICANT PRECIPITATION
MENTION TO THIS FORECAST GIVEN THE OVERALL EXPECTED PATTERN...THOUGH
CERTAINLY WILL NEED TO WATCH FOR ANY ENHANCED WAVE DIVING SOUTH IN
THE NWLY FLOW ALOFT THAT COULD LOCALLY PRODUCE FLURRIES WITHIN BANDS
OF MARGINALLY CONVECTIVE STRATOCUMULUS FIELDS.
21
&&
.AVIATION...
FOR THE 00Z TAFS...VFR CONDITIONS WILL PREDOMINATE AT ALL THREE
TERMINAL SITES FOR THE EARLY PART OF THE FORECAST...WITH CEILINGS
EXPECTED TO DROP RAPIDLY AFTER THE PASSAGE OF WEAK COLD FRONT IN THE
04-08 UTC TIMEFRAME. WEAK SHORT WAVE ADVANCING OUT OF THE SOUTHERN
HIGH PLAINS WILL ENHANCE ISENTROPIC LIFT ACROSS THE FORECAST AREA
DURING THE LATE NIGHT HOURS. EXPECT ALL THREE TERMINAL SITES WILL
EXPERIENCE A PERIOD OF VFR CIGS BETWEEN 4K AND 5K SEVERAL HOURS
BEFORE FRONTAL PASSAGE...THEN BASED ON CIGS LEVELS ASSOCIATED WITH
SMALL AREA OF STRATUS/STRATOCU CURRENTLY ACROSS SOUTHEAST
TEXAS...EXPECT CIGS TO FALL TO AT LEAST THE LOWER END OF MVFR RANGES
IN THE HOUR OR TWO AFTER FROPA. NAM AND GFS MOS GUIDANCE BOTH HINT
AT A BRIEF PERIOD OF IFR CIGS IN THE 11Z TO 14Z TIMEFRAME...THOUGH
CONFIDENCE IS LOW THAT CEILINGS WILL FALL INTO IFR CATEGORY. WILL
LEAVE TEMPO GROUP OF IFR CIGS IN FOR TIME BEING...AND WILL MONITOR
TRENDS AT UPSTREAM ASOS/TERMINAL SITES AND DETERMINE WHETHER IFR
TEMPO SHOULD BE REMOVED WITH 06Z TAFS. FINALLY...BASED ON
RH/SPECIFIC HUMIDITY PROGS...EXPECT MVFR CIGS TO LINGER MOST OF THE
DAY AT KMKC AND KMCI...SCATTERING CIGS OUT AROUND 22Z AT BOTH
SITES. CIGS WILL IMPROVE A LITTLE EARLIER AT KSTJ...SCATTERING
AROUND 20Z.
24
&&
.CLIMATE...
THE CURRENT FORECAST LOW TEMPERATURE AT KANSAS CITY THROUGH SUNDAY
MAKES IT UNLIKELY THAT A HARD FREEZE (TEMPERATURES AT OR BELOW 28
DEGREES) WILL OCCUR THROUGH AT LEAST NOVEMBER 29TH. THAT DATE STANDS
AS THE LATEST OCCURRENCE OF 28 DEGREES. HERE ARE THE TOP 5 LATEST
OCCURRENCES OF 28 DEGREE LOW TEMPERATURES IN KANSAS CITY:
RANK DATE YEAR
----- ------ ------
? ?????? 2009
1 NOV 29 1905
2 NOV 27 1944
3 NOV 26 1902
4 NOV 26 1958
5 NOV 25 1928
FOR ADDITIONAL INFORMATION...PLEASE VISIT OUR WEBSITE AT
WWW.WEATHER.GOV/KC.
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&
$$
