Sunday, August 29, 2010

Area Forecast Discussion - South Central/Southwest Missouri

FXUS63 KSGF 292217 CCA
AFDSGF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPRINGFIELD MO
248 PM CDT SUN AUG 29 2010

DISCUSSION...

SHORT TERM (TODAY THROUGH TUESDAY NIGHT)...

FORECAST ISSUES THROUGH THE SHORT TERM CENTER AROUND CHANCES FOR
THUNDERSTORMS WITH A SUBTROPICAL MOISTURE MOVING NORTH FROM THE
GULF TODAY THROUGH EARLY TUESDAY...AND THEN PRECIP CHANCES IN
RESPONSE TO UNSETTLED SOUTHWEST FLOW ALOFT ALONG/AHEAD OF AN
APPROACHING FRONT.

BROAD PLUME OF TROPICAL MOISTURE WITH EMBEDDED SHORTWAVES/VORT
MAXES CONTINUES TO STREAM NORTH INTO THE AREA TODAY. PWAT VALUE ON
THIS MORNING'S 12Z SGF RAOB IS NEARLY 3 TIMES HIGHER THAN JUST 24 HRS
AGO (0.55 YESTERDAY TO 1.59 TODAY) AS GULF MOISTURE HAS SURGED INTO
THE AREA. SCATTERED TO BKN CU HAS DEVELOPED ACROSS THE ENTIRE REGION
THIS AFTERNOON...WITH THE DENSEST CLOUD COVER OVER THE FAR
SOUTHEASTERN CWA...COINCIDENT WITH HIGHER PWATS. SUBTLE SHORTWAVE
EMBEDDED IN THIS FLOW IS EVIDENT ON WATER VAPOR IN THE VICINITY OF
MEMPHIS AT 1830Z...AND DO THINK THAT DESPITE MEDIOCRE INSTABILITY IN
PLACE ACROSS THE REGION...A FEW SCATTERED THUNDERSTORMS MAY DEVELOP
IN RESPONSE TO THIS FEATURE OVER THE SOUTHEASTERN CWA LATE THIS
AFTERNOON AND INTO THIS EVENING. ADDITIONAL CHANCES APPEAR POSSIBLE
OVERNIGHT...AND THEN ESSENTIALLY A REPEAT PERFORMANCE ON MONDAY.
AGAIN...BEST CHANCES FOR ANY CONVECTION SHOULD BE OVER THE
SOUTHEASTERN CWA.

ON TUESDAY...BROAD HEIGHT FALLS ALOFT IN RESPONSE TO PAIR OF
SHORTWAVES TRAVERSING THE NORTHERN CONUS SHOULD BEGIN TO OVERSPREAD
THE REGION DURING THE DAY. THIS SHOULD ALLOW SLIGHTLY FASTER AND
UNSETTLED UPPER FLOW TO BEGIN TO SETTLE INTO THE NORTHERN AND
WESTERN PORTIONS OF THE FORECAST AREA. THE COMBINATION OF THIS LARGE
SCALE BUT SUBTLE FORCING AND WHAT SHOULD BE A MOISTURE-RICH AIRMASS
IS EXPECTED TO RESULT IN A SMATTERING OF THUNDERSTORMS DURING THE
DAY ON TUESDAY...MAINLY WEST OF U.S. 65. MORE ORGANIZED
SHOWER/THUNDERSTORM ACTIVITY WILL LIKELY INITIATE OVER SOUTHERN
NEBRASKA/NORTH CENTRAL KANSAS DURING THE DAY/EVENING TUESDAY...AND
THE SETTLE INTO THE AREA FROM THE NORTHWEST TUESDAY NIGHT IN AT
LEAST A SCATTERED FASHION.

BOXELL

LONG TERM (WEDNESDAY MORNING THROUGH NEXT SUNDAY)...

MODEL DIVERGENCE IN THE LONG TERM WAS AGAIN EVIDENT
TODAY...ESPECIALLY AFTER DAY 5. THE ECMWF CONTINUES TO BE A LITTLE
MORE PROGRESSIVE WITH THE TROUGH THAT WILL BRING THE FRONT THROUGH
THE MIDWEST ON THURSDAY. BOTH THE EC AND GFS HAVE COME INTO BETTER
AGREEMENT IN THE HANDLING OF THE MIDWEEK SYSTEM BUT STILL WENT WITH
MORE OF THE ECMWF SOLUTION THAT FULLY KICKS THE FRONT OUT OF THE
AREA BY FRIDAY AFTERNOON AND BUILDS IN A WEAK SURFACE HIGH RIGHT
OVER THE CWA.

BEYOND DAY 5...CONFIDENCE IN MODEL OUTPUT SIGNIFICANTLY DECREASES
BECAUSE THE ECMWF SUGGESTS THE DEVELOPMENT OF A THREE WAVE LOW
PATTERN ACROSS THE US INTO SUNDAY AND ANOTHER FRONT MOVING THROUGH
THE MIDWEST EARLY NEXT WEEK. THE GFS SOLUTION SEEMS MORE LIKELY
WITH A WEAK RIDGE BUILDING BACK INTO THE MIDWEST...WHICH HAS BEEN
THE ROUTINE OF LATE. A GOOD AMOUNT OF COOL AND DRY AIR COULD RETURN
TO THE AREA IF THIS PANS OUT BUT FOR NOW HAVE TEMPERED THE LOW DEW
POINTS AND OVERNIGHT TEMPS BECAUSE THE GFS MAY BE OVERDOING IT A BIT.

CROWE

&&

AVIATION...

FOR THE 18Z TAFS...

CHALLENGING AND SOMEWHAT UNCERTAIN AVIATION FORECAST FOR THE
TERMINALS TODAY...WITH POSSIBILITY OF IFR CIGS OVERNIGHT TONIGHT
AND EARLY IN THE MORNING MONDAY. LOW AND MID LEVELS HAVE MOISTENED
SIGNIFICANTLY SINCE LAST NIGHT...AND WITH GULF MOISTURE SURGING
NORTH AHEAD OF A SUBTROPICAL DISTURBANCE APPROACHING THE
AREA...EXPECT THIS TREND TO CONTINUE. LATE TONIGHT...COMBINATION
OF RICHER MOISTURE AND WEAK LARGE SCALE LIFT ASSOCIATED WITH
AFOREMENTIONED DISTURBANCE MAY RESULT IN LOW STRATUS DEVELOPMENT
ACROSS THE AREA...ESPECIALLY AT KSGF AND KBBG. GUIDANCE HAS BEEN
HITTING IFR CIGS QUITE HARD AFTER 07Z OR SO TONIGHT...AND DESPITE
CLIMATOLOGICAL TENDENCY FOR CIGS TO REMAIN MVFR OR HIGHER THIS
TIME OF YEAR...THE NEAR UNANIMOUS MODEL AGREEMENT IS HARD TO IGNORE.
SO FOR THIS TAF ISSUANCE...HAVE HINTED AT IFR POSSIBILITY AT
KSGF...THOUGH FORECAST IS TECHNICALLY FOR MVFR CIGS ATTM. DO FEEL
LIKE KJLN WILL LIKELY STAY MVFR TO VFR WITH A SLIGHTLY DRIER
AIRMASS IN PLACE. DID TAKE KBBG DOWN TO IFR...CONSIDERING THAT
CLIMATOLOGICALLY BBG TENDS TO BE THE MOST PRONE TO SUB-MVFR
CIG/VIS. IT SHOULD BE NOTED THAT IF MODEL GUIDANCE CONTINUES TO
SHOW IFR THIS EVENING/TONIGHT...WOULD ANTICIPATE LATER FORECAST
SHIFTS DROPPING CIGS FURTHER THAN WHAT IS CURRENTLY SHOWN.

BOXELL

&&

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

$$

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