River Flood Warning 265, NWS Kansas City, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
237 PM CDT WED JUL 7 2010

.DISCUSSION...

SHORT TERM (TONIGHT-FRIDAY NIGHT)...

COMBINATION OF LOW-MID 80F TEMPERATURES AND LOWER 70F DEWPOINTS HAS
ALLOWED BOUNDARY LAYER PARCELS TO REACH THEIR LFC PER MODIFIED 12Z
KTOP SOUNDING. EXPECT A FAIRLY WIDESPREAD COVERAGE OF SHOWERS AND
STORMS THROUGH THE REST OF THE AFTERNOON AS SUBSEQUENT OUTFLOW
COLLISIONS YIELD ADDITIONAL DEVELOPMENT. GIVEN THE RATHER HAPHAZARD
NATURE TO THE CONVECTION AND WEAK VERTICAL SHEAR...IT IS LIKELY THAT
MANY OF THE MORE ISOLATED CELLS MAY FIND THEMSELVES ANCHORED TO
WHATEVER LED TO THEIR DEVELOPMENT...THUS LEADING TO LOCALLY
TORRENTIAL RAINFALL GIVEN PRECIPITABLE H20 VALUES IN EXCESS OF 2
INCHES.

ALTHOUGH THIS ACTIVITY IS LARGELY DIURNALLY DRIVEN...LARGE SCALE
ASCENT AHEAD OF A BROAD SHORTWAVE TROUGH OVER SW KS AND A SMALLER
TROPICAL LOW OVER EASTERN OKLAHOMA WILL PERSIST THROUGH MID EVENING
AS THESE FEATURES APPROACH...WITH SEVERAL SURFACE CONVERGENCE
TROUGHS SERVING AS ADDITIONAL FOCI. THUS EXPECT HIGHER PROBABILITIES
OF RAIN TO PERSIST THROUGH AROUND 02Z BEFORE COVERAGE BEGINS TO
QUICKLY WANE.

LONG WAVE TROUGH PASSAGE SHOULD ULTIMATELY FORCE A VERY WEAK SURFACE
BOUNDARY SOUTHWARD THROUGH THE REGION TOMORROW...SCOURING THE DEEP
MOISTURE AND GRADUALLY ENDING THE THREAT FOR WIDESPREAD DEEP
CONVECTION. WILL FEATURE CHANCE POPS SOUTHERN ZONES TOMORROW...WITH
A DRY FORECAST FOR FRIDAY AND SATURDAY (INCLUDING MUCH MORE
TOLERABLE DEWPOINTS). CURRENT TEMPERATURE FORECAST LOOKS KOSHER SO
NO CHANGES PLANNED.

BOOKBINDER

MEDIUM RANGE (SATURDAY THROUGH WEDNESDAY)...

PRIMARY CONCERN THROUGH THE MEDIUM RANGE PERIOD WILL BE SEVERAL
SHORTWAVES PROPAGATING IN BROAD NWLY FLOW...EVENTUALLY DIGGING OUT
WEAK NEGATIVE HEIGHT ANOMALIES ACROSS THE GREAT LAKES/OHIO RIVER
VALLEY BY THE END OF THE PERIOD. 12Z OPERATIONAL GFS ACTUALLY HAS
GOOD SUPPORT FROM ENSEMBLE CLUSTERS AND PARALLEL GFS RUN...VERSUS
THE OPERATIONAL ECMWF WHICH DEPICTS A SLOWER...WEAKER...AND MORE
SHEARED SOLUTION (YET MOST LIKELY STILL CARRIES SOME SKILL MEASURE).
THUS...FAR MORE OF THE OPERATIONAL GFS WAS UTILIZED IN THIS FORECAST
PACKAGE (SANS APPARENT CONVECTIVE FEEDBACK PROBLEMS) THAN PREVIOUS
FORECASTS.

MODEL TRENDS STILL INDICATE A PRIMARILY (IF NOT ENTIRELY) DRY
WEEKEND...WITH TEMPERATURES NOT STRAYING FAR FROM CLIMATOLOGY. FIRST
CHANCE FOR ORGANIZED CONVECTION LOOKS TO ARRIVE SUNDAY EVENING/NIGHT
AHEAD OF A WEAKENING FRONTAL BOUNDARY AND SHORTWAVE EJECTING INTO
THE CNTRL PLAINS. MOST LIKELY AREA TO RECEIVE PRECIPITATION APPEARS
TO BE NRN MISSOURI MONDAY MORNING ON THE SRN PERIPHERY OF AN ASSUMED
CONVECTIVE COMPLEX...AND HAVE STARTED THE TREND OF PUSHING POPS
HIGHER IN THIS REGION. EFFECTIVE BOUNDARY WILL EVENTUALLY SLIDE INTO
THE BULK OF THE FORECAST AREA...SUCH THAT RAINFALL CHANCES WILL
CONTINUE INTO TUESDAY MORNING. SHOULD THE BETTER DEFINED AND MORE
AMPLIFIED GFS TYPE SOLUTION COME TO FRUITION...RIDGING IN THE WAKE
OF THE NORTHWEST FLOW SHORTWAVES WOULD PROMOTE SFC PRESSURE
RISES...AND A MORE RAPID SOUTHWARD EXIT TO THE AFOREMENTIONED
FRONTAL BOUNDARY (WHICH IS CURRENTLY ADVERTISED IN THIS FORECAST).
HOWEVER...SHOULD FLOW ALOFT REMAIN MORE BROAD NWLY OR QUASI-ZONAL
(ALA 00Z ECMWF) THIS BOUNDARY MAY LINGER ACROSS MISSOURI MUCH
LONGER...AND PRECIPITATION CHANCES WOULD NEED TO BE SPREAD OVER A
MUCH LONGER TIME SPAN.

21

&&

.AVIATION...

FOR THE 18Z TAFS...KTOP 12Z SOUNDING SHOWED AN UNSEASONABLY LOW
CONVECTIVE TEMPERATURE OF ONLY 80F...WITH MODERATE INSTABILITY AS
COMPARED TO RECENT DAYS WITH UPWARDS OF 2000 J/KG OF MLCAPE. WITH
SUFFICIENT SUNNY BREAKS EARLY THIS AFTERNOON...EXPECT CONVECTIVE
TEMPERATURE WILL BE BREACHED BY 19Z...ALLOWING FOR MORE NUMEROUS
SHOWERS/STORMS TO DEVELOP...AIDED BY LARGE SCALE ASCENT ARRIVING
FROM SW KS AND A SECONDARY CIRCULATION LIFTING NORTH THROUGH EASTERN
OKLAHOMA. THESE FEATURES WONT ARRIVE UNTIL EARLY EVENING...ALLOWING
THE THREAT FOR DOWNPOURS TO PERSIST THROUGH MID EVENING.

WITH CB TOPS EXPECTED AROUND 40KFT AGL...SHOULD SEE MORE PRONOUNCED
LIGHTNING ACTIVITY TODAY AND WILL GO WITH A PREDOMINANT VCTS
GROUP...FOCUSING TEMPO CHANCES BETWEEN 2 AND 6 PM. CB BASES SHOULD
AVERAGE MVFR...WITH THE CAVEAT OF LOCALLY IFR VISIBILITIES EXPECTED
IN BRIEF TORRENTIAL DOWNPOURS.

WINDS WILL BE NEARLY CALM FOR THE AFTERNOON...TRENDING TOWARD THE
LIGHT NORTH BY LATE EVENING WITH A WEAK FRONTAL PASSAGE. WINDS MAY
BE GUSTY AND VARIABLE IN AND AROUND THUNDERSTORMS.

BOOKBINDER

&&

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

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