Saturday, August 28, 2010

Area Forecast Discussion - South Central/Southwest Missouri

FXUS63 KSGF 282357
AFDSGF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPRINGFIELD MO
657 PM CDT SAT AUG 28 2010

..UPDATE TO AVIATION...

DISCUSSION...

SHORT TERM (TONIGHT THRU MONDAY NIGHT)...

HIGH PRESSURE REMAINS IN CONTROL ALOFT AND AT THE SURFACE
TODAY...WITH REGION SITUATED ON THE WESTERN PERIPHERY OF BROAD UPPER
LEVEL RIDGE...WITH THE ASSOCIATED VERY DRY SURFACE HIGH STRETCHING
FROM THE MID ATLANTIC WEST TO THE EASTERN PLAINS. 12Z SGF RAOB
NICELY DEPICTS LARGE SCALE SUBSIDENCE THAT IS IN PLACE...WITH A
WHOPPING 0.55 INCH PWAT AND IMPRESSIVE MID LEVEL INVERSION. WITH THAT
IN MIND...SHOULD HAVE ONE MORE CLEAR OVERNIGHT TONIGHT...ALBEIT
SLIGHTLY WARMER THAN THE LAST FEW EVENINGS.

ON SUNDAY...DISORGANIZED SUBTROPICAL DISTURBANCE CURRENTLY OFF THE
LOUISIANA COAST IS EXPECTED TO BEGIN EJECTING NORTH AROUND THE
AFOREMENTIONED UPPER RIDGE. MOISTURE AND LARGE SCALE LIFT ASSOCIATED
WITH LEAD SHORTWAVE/VORT MAX FROM THIS FEATURE SHOULD BEGIN TO WORK
INTO THE EASTERN HALF OR SO OF THE CWA DURING THE DAY TOMORROW...
AND SHOULD RESULT IN A FEW SCATTERED THUNDERSTORMS DURING PEAK
HEATING TOMORROW. WITH THE AIRMASS REMAINING DRY OVER THE ENTIRE
AREA...DO THINK THAT NORTH AND WESTWARD EXTENT OF
SHOWER/THUNDERSTORM ACTIVITY WILL BE SOMEWHAT LIMITED. LATE SUNDAY
NIGHT AND MONDAY...THINK THAT PRECIP CHANCES WILL EXTEND SOMEWHAT
FURTHER WEST AS PRIMARY VORT WORKS INTO THE AREA...BUT
AGAIN...AMBIENT DRY AIR RAISES SOME QUESTION AS TO HOW FAR NORTH AND
WEST PRECIP WILL EXTEND.

TEMPERATURES LOOK TO BE FAIRLY SEASONABLE THROUGH THE PERIOD...WITH
SOUTHERLY RETURN FLOW BEGINNING TO BRING A MORE LATE AUGUST-LIKE
AIRMASS NORTH INTO THE AREA FROM THE SOUTHERN PLAINS. ONLY
EXCEPTION WILL BE ACROSS THE EASTERN PORTION OF THE CWA...WHERE
SCATTERED PRECIP AND MORE DENSE CLOUD COVER SHOULD KEEP TEMPS IN THE
MID 80S SUNDAY AND MONDAY.

HEADING INTO TUESDAY...DEEP UPPER SHORTWAVE/CLOSED LOW CURRENTLY
OVER NORTHERN CALIFORNIA WILL BE MAKING ITS WAY EAST ACROSS THE
NORTHERN PLAINS...WITH AN ASSOCIATED SLOW MOVING SURFACE FRONT
EXTENDING SOUTH ACROSS MUCH OF THE CENTRAL CONUS.

BOXELL

LONG TERM (TUESDAY THRU SATURDAY)...

INTO THE MIDDLE OF THE WEEK...MODELS HAVE THE STRONG EAST COAST
RIDGE SLOWLY DEAMPLIFYING AND THE 500MB FLOW BECOMING GENERALLY MORE
FLATTENED DUE TO THE ABOVE MENTIONED TROUGH. BUT THERE IS SOME
VARIATION BETWEEN MODELS IN THEIR HANDLING OF THE TROUGH AS IT PUSHES
ACROSS THE ROCKIES INTO THE NORTHERN MIDWEST. THE ECMWF IS MORE
PROGRESSIVE WITH THE TROUGH AND KEEPS THE SURFACE SYSTEM CLOSER TO
THE TROUGH AXIS...WITH THE MAIN FRONT SLIDING THROUGH ON THURSDAY.
INSTEAD...THE GFS HAS AN INITIAL SURFACE BOUNDARY PUSHING QUICKLY
NORTHEAST WHILE THE MAIN FRONT LAGS ACROSS MISSOURI INTO FRIDAY.

WHILE THE BREAKDOWN OF THE 500MB RIDGE WILL DETERMINE THE
PROGRESSION OF THIS SYSTEM...FEEL THAT THE ECMWF SOLUTION OF A
FASTER WEAKENING OF THE RIDGE IS MORE LIKELY FOR THE EXTENDED FCST.
HPC ALSO NOTED THIS PREFERENCE IN THEIR MORNING DISCUSSION AND HAVE
USED THIS AT THE BASE OF THE EXTENDED.

AFTERNOON TEMPS WILL PUSH THE 90S AHEAD OF THE FRONT AND DEWPOINTS
WILL POOL AHEAD OF THE BOUNDARY...BUT HEAT INDEX VALUES SHOULD NOT
BE ANY PROBLEM. INTO THE WEEKEND...ANOTHER SHOT OF COOLER AND DRY
AIR WILL BUILD IN BEHIND THE FRONT AND BRING TEMPS BACK DOWN TO
NEAR NORMAL VALUES OF HIGHS IN THE LOW 80S AND LOWS IN THE LOW
60S.

CROWE

&&

AVIATION...
/ISSUED 646 PM CDT SAT AUG 28 2010/

FOR THE 29/0000Z KSGF/KJLN/KBBG TAFS...A SOUTHEAST WIND IS
CONTINUING TO SPREAD MOISTURE INTO THE AREA. AREAS NEAR KJLN ARE
STILL BONE DRY...BUT LOW LEVEL MOISTURE IS EXPECTED TO SPREAD INTO
THAT REGION OVER THE NEXT FEW HOURS. OTHERWISE...THE SFC PATTERN IS
EXPECTED TO REMAIN THE SAME...WITH LOW PRESSURE OVER THE NORTHERN
AND CENTRAL HIGH PLAINS AND HIGH PRESSURE OVER THE EASTERN CONUS.
SOUTHEAST WINDS WILL CONTINUE THROUGH THE TAF PERIOD...WITH A FEW
MODERATELY STRONG GUSTS EXPECTED DURING THE DAYLIGHT HOURS. THE
ADDITIONAL MOISTURE WILL LEAD TO MORE AFTERNOON CUMULUS WITH BROKEN
HIGH END MVFR OR VFR CEILINGS POSSIBLE SUNDAY...ESPECIALLY ALONG
THE MO/AR STATE LINE. ALSO CAN'T RULE OUT AN ISOLATED AFTERNOON
TSTM...MAINLY EAST OF THE TAF SITES AFTER 29/1800Z. DSA

&&

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

$$


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