695
FXUS63 KEAX 092319
AFDEAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
520 PM CST MON NOV 9 2009
..UPDATED AVIATION
..DISCUSSION
NARROW BAND OF ELEVATED CONVECTION WHICH FORMED OVER NORTHEAST KS
THIS AFTERNOON WILL SPREAD NORTHEAST BETWEEN STJ/MCI AND ACROSS
NORTHERN MO THIS EVENING. FOR THE PAST SEVERAL MODEL RUNS THE
NAM/GFS/SREF/GEM HAVE ALL BEEN POINTING TO THIS AREA FOR
DEVELOPMENT...SO NOT TOO SHABBY OF A JOB. COMBINATION OF A WEAK
SHORTWAVE/NOTED IN WATER VAPOR IMAGERY/...INCREASING ISENTROPIC LIFT
ON THE 300 THRU 310K SURFACES...AND DEVELOPMENT/FAVORABLE ALIGNING
OF LAYERED FRONTOGENETICAL FORCING ARE ALL CONTRIBUTING TO THIS
PRECIPITATION. WITH BETTER CONFIDENCE FEEL COMPELLED TO USE
CATEGORICAL POPS TONIGHT. ISOLD THUNDER ALSO OCCURRING WITH THIS
ACTIVITY DUE TO ELEVATED INSTABILITY. 18Z NAM 850-300MB MU CAPE
SHOWS GOOD CORRELATION BETWEEN THUNDER AND 100-200 J/KG.
HOWEVER...THIS INSTABILITY IS FORECAST TO WEAKEN THIS EVENING AND
THE 12Z MODELS SUPPORT THIS FORECAST. SO WILL ONLY INSERT ISOLD
THUNDER FOR THIS EVENING WITH THE HIGHEST POPS. HAVE RAISED LOW
TEMPERATURES AS SURFACE DEWPOINTS REMAIN HIGH AND LOW LEVEL MOISTURE
NOW APPEARS TO BE TRAPPED UNDER THE FRONTAL INVERSION.
SHOWERS WILL BE SLOW TO EXIT THE CWA AND WILL HANG ONTO LOW CHANCE
POPS INTO TUESDAY MORNING OVER THE SOUTHERN COUNTIES AS THE BETTER
ISENTROPIC LIFT EXITS THE REGION. HAVE ALSO SLOWED DOWN CLEARING AS
CONCERN OVER LOW LEVEL MOISTURE TRAPPED BENEATH THE FRONTAL
INVERSION. NORTHERN CWA SHOULD CLEAR OFF FINE BY AFTERNOON AND WITH
ONLY MARGINAL COLD AIR ADVECTION MAX TEMPERATURES SHOULD REMAIN
ABOVE NORMAL. THIS SAME CONCERN ABOUT TRAPPED LOW LEVEL MOISTURE
RAISES A YELLOW FLAG THAT STRATUS AND/OR FOG WILL NEVER TOTALLY
CLEAR THE SOUTHERN CWA OR REFORM TUESDAY EVENING. CONFIDENCE NOT
HIGH ENOUGH TO GO WITH TOTAL OVERCAST SO WILL TREND THAT WAY WITH
BROKEN CLOUDS. THIS SHOULD ALLOW LATER SHIFTS FLEXIBILITY TO GO
EITHER WAY.
WEDNESDAY WILL BE A BENIGN BUT MILD DAY WITH WEAK RETURN FLOW UNDER
A SLOWLY DEPARTING SURFACE HIGH. NET EFFECT IS CONTINUED WARMER THAN
NORMAL TEMPERATURES.
MJ
MEDIUM RANGE/DAYS 4-7...
HIGH PRESSURE WILL REMAIN OVER THE GREAT PLAINS THROUGH THURSDAY AS
AN UPPER LEVEL RIDGE CONTINUES TO INFLUENCE THE REGION. THE UPPER
LEVEL RIDGE WILL BEGIN TO PROGRESS EASTWARD OUT OF THE AREA ON
FRIDAY...AS A LOW PRESSURE SYSTEM STARTS TO DIP INTO THE SOUTHERN
GREAT PLAINS. THIS LOW PRESSURE SYSTEM WILL MOVE NORTHEASTWARD ON
MONDAY...WITH AN ELONGATED AND WEAK COLD FRONT STEMMING OUT FROM IT.
RIGHT NOW HAVE JUST SLIGHT CHANCE POPS FOR THE ENTIRE CWA ON SAT AND
SAT NIGHT DUE TO THIS FRONTAL PASSAGE.
THE NEXT FEATURE THE GFS/ECMWF/GEM ARE PICKING UP ON IS AN UPPER
LEVEL TROUGH DIGGING ACROSS THE ROCKIES AND INTO THE CENTRAL PLAINS
BY SUNDAY. HOWEVER...THERE ARE NOTABLE DIFFERENCES IN THE 12Z
GFS/ECMWF MODEL RUNS REGARDING THE PROJECTED STRENGTH AND PATH OF
THIS SYSTEM. GFS IS SUGGESTING A TIGHTLY CLOSED OFF LOW WILL
POSITION ITSELF OVER THE NW CORNER OF THE CWA SUNDAY EVENING...WITH
WRAP AROUND PRECIP CONTINUING TO AFFECT THE REGION THROUGH MONDAY
EVENING. CURRENTLY AM LEANING MORE TOWARD THE ECMWF THOUGH...WHICH
IS PUSHING A SLIGHTLY WEAKER UPPER LEVEL DISTURBANCE...COMPARED TO
THE GFS...FURTHER NORTH OVER THE NORTHERN PLAINS BY MONDAY MORNING.
WILL NEED TO KEEP AN EYE ON HOW FUTURE MODEL RUNS HANDLE THE
TRACKING AND INTENSITY OF THIS SYSTEM. ONE PARTICULAR FEATURE WORTH
NOTING...IN THE 12Z GFS...THE 500 MB HEIGHTS WRAPPED AROUND THE
UPPER LEVEL LOW DROP DOWN TO AS LOW AS 534 ACROSS THE NORTHERN TIER
OF OUR CWA AND FURTHER NORTH OVER MUCH OF IOWA. IF THIS SCENARIO
WERE TO PAN OUT...WE COULD BE LOOKING AT THE POTENTIAL FOR SOME
WINTER PRECIP WITH THIS SYSTEM.
ACH
AVIATION
NARROW BAND OF SHRA/TSRA CURRENTLY BISECTING TERMINAL CORRIDOR WILL
ONLY SLOWLY OSCILLATE NORTH THROUGH THE EVENING...WITH SLIGHT
SOUTHWARD AREAL EXPANSION OF RADAR ECHOES LIKELY AS WELL. SHORTWAVE
APPROACHING CNTRL KANSAS WILL ENSURE MORE EXTENSIVE SHRA COVERAGE
INTO THE LATE EVENING AND OVERNIGHT HOURS. EMBEDDED TSRA WILL
CONTINUE THROUGH THE EVENING HOURS...THOUGH INSTABILITY IS EXPECTED
TO SHIFT MORE INTO SERN KANSAS/SWRN MISSOURI OVERNIGHT...LEADING TO
MERELY -SHRA ACTIVITY. VERY LOW CONFIDENCE IN VSBY/CIG FORECAST FOR
THE NEXT 6 HOURS...LARGELY TIED TO PRECIPITATION INTENSITY AND
COVERAGE...WITH UPSTREAM OBSERVATIONS WIDELY VARYING BETWEEN VFR AND
IFR. TRIED TO TREND FROM PRIMARILY VFR TO UPPER REACHES OF MVFR
DURING THE INITIAL PRECIPITATION ONSET...THEN TOWARDS THE LOWER END
OF MVFR AS THE SHORTWAVE GETS CLOSER. ACTUALLY A BIT BETTER
CONFIDENCE AFTER 06Z...AS ALL MODEL GUIDANCE POINTS TOWARDS SOLID
LOWER END MVFR FOR AN EXTENDED PERIOD (EVEN SOME HINT OF IFR CIGS
POSSIBLE AS WELL). EXCEPTION MAY BE AT KSTJ IF DRIER BOUNDARY LAYER
AIR CAN ADVECT SOUTHWEST AND RAISE CIGS TUESDAY MORNING.
21
EAX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
KS...NONE.
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