FXUS63 KEAX 060557
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1156 PM CST SAT DEC 5 2009
...UPDATED AVIATION DISCUSSION...
.DISCUSSION...
MAIN THING TO FOCUS ON IN THE VERY SHORT TERM IS THE SHORT WAVE AND
ASSOCIATED PRECIPITATION SUNDAY AFTERNOON AND SUNDAY NIGHT BEFORE
THE BIGGER SYSTEM HANDLED IN THE MEDIUM RANGE DISCUSSION BELOW.
MODELS CONTINUE TO AGREE ON THIS INITIAL SYSTEM RAPIDLY PROGRESSING
FROM THE NORTHERN ROCKIES/NORTHERN GREAT BASIN RAPIDLY INTO UPPER
MIDWEST BY SUNDAY AFTERNOON. ISENTROPIC UPGLIDE AHEAD OF THE WAVE
WITH INITIATE PRECIP ESPECIALLY IN NW MO DURING THE MIDDAY. THE
PRECIPITATION SHOULD INCREASE BY LATE AFTERNOON INTO THE EVENING
HOURS OVER FAR NW MO. EXPECT THE PRECIPITATION UP THERE TO BE LIGHT
SNOW WITH AN INCH OR TWO ACCUMULATION BY THE TIME IT ENDS BY LATE
EVENING. AS STATED IN PREVIOUS DISCUSSIONS DRY MID LEVEL AIR MAY
PRECLUDE ICE CRYSTAL SEEDING MEANING AN AREA OF FREEZING DRIZZLE
MAINLY ALONG AND N OF I70. FLY IN THE OINTMENT WILL BE LOW LEVEL
TEMPERATURES. WE MAY NOT COOL OFF FAST ENOUGH IN THE EVENING FOR THE
PRECIP TO BE FREEZING ALONG AND NORTH OF THE I70 CORRIDOR. FURTHER
SOUTH FROM THERE TEMPS WILL ALMOST CERTAINLY REMAIN ABOVE FREEZING
SO ONLY LIGHT DRIZZLE EXPECTED. DONT THINK THERE WILL BE ENOUGH
TURBULENCE IN THE LOWER LAYERS TO PRODUCE HEAVY DRIZZLE...SO EXPECT
ANY DRIZZLE THAT DEVELOPS...FREEZING OR NOT...TO BE LIGHT.
BAILEY
MEDIUM RANGE (MON NIGHT-SAT)...
GENERALLY SPEAKING...LITTLE HAS CHANGED IN THE MEDIUM RANGE PORTIONS
OF THE FCST REGARDING THE PENDING WINTER STORM FOR TUE AND WED. AS
ANTICIPATED YESTERDAY FROM ENSEMBLE PROGNOSTICATIONS...DETERMINISTIC
GUIDANCE HAS CONVERGED ONTO A SIMILAR SYSTEM EVOLUTION THROUGH THE
MIDDLE OF THE WEEK. PATTERN HAS TRANSITIONED NICELY TOWARDS A
CLIMATOLOGICALLY FAVORED PROGRESSIVE UPR WAVE...A PATTERN CONDUCIVE
TO LOCALLY HEAVY SNOWFALL. THIS MORE PROGRESSIVE WAVE MAY FEATURE
THREE DISTINCT TRANSITIONS. STRONG WAA AND ISENTROPIC LIFT WILL
COMMENCE AFTER 06Z TUE AND BEGIN TO FOCUS IN PORTIONS OF NORTH
CENTRAL KS AND NW MO AIDED WITH A BIT OF EXTRA LIFT BY A DUAL JET
STRUCTURE ALOFT. THIS WAA PRECIP WILL RANGE WELL AHEAD OF THE UPR
WAVE AND MAY CONTINUE FOR SOME TIME. INITIALLY IT APPEARS SOUNDINGS
MAY QUICKLY SATURATE AS NO STRONG EAST DRY AIR ADVECTION APPEARS
LIKELY. SOUTH OF THIS AREA...MAY NEED TO WATCH INTRUSION OF DRY AIR
ALOFT IN AREAS FROM CLINTON TO SEDALIA AS THESE LOCATIONS COULD BE
CUTOFF FROM SIGNIFICANT PRECIP FOR A PERIOD IN THE DAY. BY THE
MIDDLE TO LATER PARTS OF TUE...AS WAA BEGINS TO SHIFT
EAST...INCREASING DYNAMICS OF THE UPR WAVE WILL COME INTO PLAY
ENHANCING THE MOISTURE INFLUX INTO THE CWA. THE FINAL STAGE OF
PRECIPITATION WILL LIKELY FALL ON THE BACKSIDE OF THE UPR WAVE AS A
SHORT DURATION OF FRONTOGENESIS AND Q-VECTOR CONVERGENCE MAY PRODUCE
AN INTENSE LAST BAND OF PRECIP AS COLDER AIR RUSHES IN. IT APPEARS
THIS EVENT WILL BE STRETCHED OVER ABOUT A 12-18 HOUR WINDOW.
DESPITE A VERY CONSISTENT UPR FLOW PATTERN...THERE WILL BE SEVERAL
DETAILS OF THE LOWER TROPOSPHERE THAT WILL HAVE SIGNIFICANT
IMPLICATIONS ON THE PRECIP TYPE INCLUDING BOUNDARY LAYER TEMP AND
WARM NOSE TEMPS. THIS BEING SAID...EXCELLENT CLUSTERING FROM THE
GEFS ENSEMBLE MEMBERS ALONG WITH CONSISTENT LOWER PROFILE SOLNS FROM
THE 12Z ECWMF/GFS AND TO SOME DEGREE THE GEM HAVE PRODUCED HIGHER
THAN NORMAL CONFIDENCE THAT A PRECIP TRANSITION LINE WILL LIFT
SOMEWHERE ALONG A KANSAS CITY TO MACON LINE BY 18-21Z TUE. FURTHER
NORTH AND NORTHWEST...ATMOSPHERIC SOUNDINGS AND CONCEPTUAL MODELS
INDICATE THAT COLDER AIR SHOULD REMAIN IN PLACE IN THE MID-MO VALLEY
SUPPORTIVE OF PREDOMINATELY SNOW IN NE KS AND NW MO. ATTM...THE 12Z
NAM/SREF IS CONSIDERED AN OUTLIER.
AS FAR AS THE PRECIP TRANSITION AREA...SOUNDINGS SUGGEST A RATHER
UNIFORM WARMUP IN THE LOWER COLUMN NOT COMPLETELY SUPPORTIVE OF
FREEZING RAIN. HOWEVER...DO SEE A SOLN THAT COULD PLACE A MIXTURE
OF SNOW/RAIN/SLEET FOR A SUSTAINED PERIOD IN AREAS ALONG AND SOUTH
OF THE MO RIVER. PERHAPS A COMPLETE TRANSITION TO RAIN MAY OCCUR
WELL SOUTH.
CONTINUING THE THEME FROM YESTERDAY...FROM A PROBABILITY STANDPOINT
USING CURRENT DATA...INDICATIONS POINT TO THE HIGHEST PROBABILITY OF
HEAVY SNOW (+6") TO FALL IN NORTHERN KANSAS AND NORTHERN MO IN AREAS
ALONG AND NORTH OF HWY 36. PROBABILITIES AND SNOWFALL TOTALS ARE
EXPECTED TO DECREASE FURTHER SOUTH INTO CENTRAL/SOUTHERN MO DUE TO
THE PENDING UNCERTAINTY IN THE INFLUX OF WARM AIR ALOFT. AS TYPICAL
IN THESE SYSTEMS THERE WILL LIKELY BE A SHARP CUTOFF/GRADIENT TO
SNOWFALL WITH THE POTENTIAL FOR SOME AREAS TO RECEIVE LITTLE
SNOWFALL. THEORETICALLY THIS ALL COULD SHIFT N OR S.
BEHIND THIS SYSTEM...REMAIN CONFIDENT IN A TEMPORARY INTRUSION OF
VERY COLD TO PERHAPS ARCTIC AIR (GIVEN POTENTIAL CROSS POLAR FLOW
SETUP AND SHIFTING OF POLAR LOW FURTHER SW). WITH A GOOD LIKELIHOOD
OF SNOW COVER IN NORTHERN MO BY WED NIGHT INTO THUR MORNING HAVE
FURTHER DROPPED LOWS TO SINGLE DIGIT READINGS. WINDS WILL ALSO BE A
MAJOR CONCERN ON WED GIVEN THE EXPECTED DEEPER CYCLOGENESIS AT THE
SFC. THIS BEING SAID WILL INTRODUCE BLOWING SNOW WORDING TO AREAS
WHICH MAY RECEIVE THE HIGHEST SNOW.
DUX
&&
.AVIATION...
HIGH CLOUDS WILL CONTINUE TO THICKEN AND THEN SLOWLY LOWER THROUGH
THE DAY TOMORROW TO AROUND 15KFT. MORE ROBUST TOP-DOWN SATURATION
WILL OCCUR TOWARD 00Z AS LARGE SCALE ASCENT INCREASES AHEAD OF A
PROGRESSIVE UPSTREAM SHORTWAVE. AN INVERTED TROUGH WEST OF THE
TERMINALS WILL HELP FOCUS A BAND OF LIGHT SNOW DURING THE EVENING
HOURS...AND CONDITIONS COULD QUICKLY DETERIORATE TO IFR SHORTLY
AFTER DARK. DEPTH OF THE SATURATED LAYER IS MARGINAL SO THERES A
CHANCE THAT SNOW COULD MIX WITH OR CHANGE TO FREEZING DRIZZLE AT
TIMES OVERNIGHT. THIS WILL BE A CONCERN FOR AIRPORT CREWS AS
TEMPERATURES FALL BACK THROUGH THE 20S.
WINDS WILL REMAIN FROM THE SOUTH TONIGHT AT LESS THAN 8 KNOTS AND
GRADUALLY BACK INTO THE SOUTHEAST AND EVENTUALLY EAST BY 00Z MONDAY
AS A WEAK SURFACE WAVE RIDES NORTHWARD ALONG THE INVERTED TROUGH
AXIS.
BOOKBINDER
&&
.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&
$$
