000
FXUS63 KFSD 160941
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
441 AM CDT THU MAY 16 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 441 AM CDT THU MAY 16 2013

VERY IMPRESSIVE WAVE MOVING EAST NORTHEAST ACROSS COLORADO EARLY
THIS MORNING...AND WILL BE THE MAIN PLAYER IN THE SHORT TERM ACROSS
THE AREA AS IT TRACKS NORTHEAST INTO NEBRASKA BY THIS EVENING. WEAK
LOW LEVEL DRY RIDGE NUDGED INTO THE EASTERN CWA EARLY THIS MORNING...
BUT STARTING TO SHOW SIGNS OF PULLING EAST WITH DEVELOPING EAST TO
SOUTHEAST LOW LEVEL FLOW. ABUNDANCE OF HIGH LEVEL AND SOME MID LEVEL
CLOUDS STREAMING NORTHEAST AHEAD OF THE APPROACHING WAVE. A MID
LEVEL BOUNDARY REMAINS IN PLACE...AND HAVE SEEN ISOLATED SHOWERS AND
THUNDERSTORMS POP AT TIMES FROM EAST CENTRAL NEBRASKA TO SOUTHERN
IOWA ALONG ELEVATED INSTABILITY GRADIENT. FOR THE MOMENT...ARE
ENTERING SHORT PERIOD OF SHORT WAVE RIDGING ALOFT AND SHOULD GO
THROUGH SEVERAL HOURS WITH VERY LITTLE ALONG THE NEBRASKA PORTION OF
THE BOUNDARY. HOWEVER...EMERGENCE OF THE VIGOROUS UPPER WAVE INTO
THE PLAINS WILL INCREASE THE CROSS FRONTAL FLOW AND WILL SEE UPSURGE
IN THE MID LEVEL THETA E ADVECTION COMMENCE LATER THIS MORNING BACK
TOWARD SOUTH CENTRAL SOUTH DAKOTA...AND LIKELY SLOW NORTHWARD SHIFT
TO THE INSTABILITY GRADIENT TOWARD MIDDAY AS WELL. WILL START TO
INTRODUCE POPS THROUGH THE MISSOURI RIVER CORRIDOR TOWARD MIDDAY.
HOWEVER...MAIN GROWTH OF PRECIPITATION IS LIKELY TO START DURING THE
AFTERNOON AS DIV Q INCREASES ACROSS SOUTH CENTRAL SOUTH DAKOTA AND
SHIFTS EASTWARD THROUGH THE LATER AFTERNOON. PUSHED UP POPS A BIT
FROM THE JAMES VALLEY AND WEST DURING THE LAST HALF OF THE AFTERNOON
TO COINCIDE WITH ARRIVAL OF FORCING. DEEPER MOISTURE HAMPERED BY THE
SOUTHERN PLAINS CLOSED LOW...SO PRETTY MUCH WILL BE WHAT CAN BE
STRIPPED FROM THE PERIPHERY ALONG WITH WHAT THE WAVE CARRIES
ALONG...AND AT A GLANCE THE NEARLY 75 TO 100 PERCENT INCREASE IN
PRECIPITABLE WATER OVER THE ENTIRE PLAINS SEEMS SOMEWHAT UNREALISTIC.
KEPT QPF LEVELS SOMEWHAT LOWER THAN MORE EXTREME ECMWF/GFS TOTALS
FOR THE AFTERNOON. POSSIBLE THAT ELEVATED LIFT FORCING COULD
GENERATE SOME MORE ISOLATED COVERAGE LIFTING NORTHEAST AHEAD OF THIS
FEATURE...AND CARRIED SOME LOWER POPS FOR THAT POSSIBILITY SOMEWHAT
EAST OF THE MAIN FORCING. ALL IN ALL...INSTABILITY IS REALLY NOT
THAT IMPRESSIVE /500-1000 J/KG MLCAPE ALONG AND SOUTH OF I 90/...
ALTHOUGH THE DEEP LAYER BULK SHEAR BECOMES SOMEWHAT INTERESTING
REACHING 35 TO 40 KNOTS. WILL BE INTERESTING TO SEE HOW MUCH OF THIS
WILL BE EFFECTIVE...FOR COULD GET ENOUGH FOR SOME MARGINAL STORM
ORGANIZATION IN/AROUND THE LOWER JAMES/LOWER BRULE AREAS THIS
AFTERNOON.

WILL HAVE POSSIBILITY TO AGAIN MIX SOME DRIER DEW POINT TEMPERATURES
ON THE EASTERLY FLOW OUT OF RETREATING RIDGE IN THE EAST. MIXING
WOULD BRING SOME LOWER 80S AGAIN TO THE MIX...BUT WILL CERTAINLY BE
DEALING WITH THE WRONG CLOUD TRENDS TODAY TO MAKE THE MOST OF
POTENTIAL...UNLIKE YESTERDAY. WORKED IN A LITTLE DROP IN
TEMPERATURES THIS AFTERNOON WITH FAIRLY WIDESPREAD PRECIPITATION
EXPECTED.

POTENT SHORTWAVE WILL TRACK NORTHEAST ACROSS THE FORECAST AREA
TONIGHT...WITH INITIAL EARLY EVENING PRECIPITATION THREAT CLOSER TO
THE MISSOURI/LOWER JAMES RIVER VALLEYS BECOMING REFOCUSED ACROSS
NORTHWEST HALF OF THE CWA BY LATE EVENING AND THROUGH THE OVERNIGHT
HOURS AS WAVE TRACKS ALONG/NORTH OF WARM FRONT LIFTING NORTH THROUGH
THE AREA. DEEP LIFT ALONG NOSE OF MOISTURE SURGE INTO THE BOUNDARY
SHOULD RESULT IN FAIRLY EFFICIENT RAINFALL PRODUCTION...AND HAVE
BOOSTED OVERNIGHT QPF AMOUNTS INTO 1/2-3/4 INCH RANGE ACROSS MUCH OF
SOUTHEAST SD/SOUTHWEST MN. CLOUDS AND INCREASING LOW LEVEL MOISTURE
SHOULD HOLD TEMPERATURES IN THE UPPER 50S TO AROUND 60 FOR LOWS.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 441 AM CDT THU MAY 16 2013

SHOULD SEE SOME LINGERING THUNDERSTORMS ACROSS THE NORTHEAST CWA
FRIDAY MORNING AS SHORTWAVE EXITS THE AREA...WITH DRIER CONDITIONS
EXPECTED FOR FRIDAY AFTERNOON WITH WEAK MID-UPPER LEVEL RIDGING...
THOUGH THIS IS SHORT-LIVED AS ANOTHER QUICK MOVING WAVE BRINGS A
PRECIP THREAT BACK TO THE WEST FRIDAY EVENING. NOT AS CONFIDENT IN
TIMING/LOCATION OF THIS WAVE SO WILL KEEP POPS ON THE LOWER END OF
CHANCE RANGE...WITH BETTER CHANCE OF RAIN REMAINING NORTH OF THE AREA
FRIDAY NIGHT.

WARM FRONT MAKES STRONGER NORTHWARD PUSH THROUGH THE DAY SATURDAY...
WITH DRY AND WARMER WEATHER EXPECTED ACROSS OUR FORECAST AREA THROUGH
MOST OF THE DAY. FOCUS REMAINS ON LATE SATURDAY AFTERNOON...AND MORE
SO SATURDAY EVENING FOR POTENTIAL SEVERE WEATHER...AS STRONGER WAVE
LIFTS OUT OF SLOWLY EASTWARD MOVING UPPER TROUGH INTO THE HIGH PLAINS
BY 00Z SUNDAY. WILL KEEP A CHANCE OF THUNDERSTORMS IN OUR FAR WEST
LATE SATURDAY AFTERNOON...ALTHOUGH INITIAL FOCUS SHOULD BE FARTHER
WEST AND NORTH...WITH DRY LINE OVER THE HIGH PLAINS OF SOUTH DAKOTA
AND NEBRASKA...AND WARM FRONT FROM WESTERN THROUGH NORTHEAST SOUTH
DAKOTA. DECENT CAP SHOULD LIMIT DEVELOPMENT IN OUR AREA UNTIL THE
WAVE MOVES INTO CENTRAL NEBRASKA/SOUTH DAKOTA SATURDAY EVENING...AND
THIS WOULD BE OUR GREATEST CHANCE FOR SEVERE WEATHER WITH MODEL CAPE
VALUES ON THE ORDER OF 2000-3000 J/KG. DEEP LAYER SHEAR LACKING A
LITTLE WITH SOUTH-SOUTHWEST MID LEVEL FLOW AHEAD OF THE WAVE...BUT
DEEP LIFT AND INSTABILITY STILL SUPPORTIVE OF PRIMARILY HAIL/WIND
THREAT WITH STORMS THAT CAN BREAK THE CAP ACROSS OUR WEST SATURDAY
EVENING. SEVERE THREAT EXPECTED TO DIMINISH AS STORMS SHIFT EASTWARD
WITH THE UPPER TROUGH DURING THE OVERNIGHT HOURS.

SUNDAY THROUGH MONDAY CONTINUES TO LOOK FAIRLY WET AND COOLER AS
UPPER LOW CLOSES OFF AND MOVES VERY SLOWLY EASTWARD THROUGH THE
NORTHERN PLAINS. SOMEWHAT LESSER CHANCES OF RAIN TOWARD THE MIDDLE OF
THE WEEK AS THE LOW MEANDERS AROUND THE REGION. HOWEVER WHILE ALL
MODELS SHOW THE DEVELOPMENT/PERSISTENCE OF THE CLOSED LOW...THEY
DIFFER ON PLACEMENT AND THUS STILL LOW CONFIDENCE ON TEMPERATURE
FORECAST THROUGH THE LATTER PORTIONS OF THE FORECAST. GEM AND ECMWF
SWING THE CLOSED LOW FARTHER SOUTH...ALLOWING COOLER AIR TO WRAP INTO
THE REGION FOR TUESDAY/WEDNESDAY...WHILE GFS TRACKS THE LOW INTO
NORTHERN MINNESOTA AND KEEPS OUR AREA ON THE WARMER SIDE OF THE
SYSTEM. WITH UNCERTAINTY AT THIS RANGE...DID NOT DEVIATE FROM MODEL
CONSENSUS FOR TEMPERATURES...THOUGH POTENTIAL DEFINITELY THERE FOR
HIGHS ABOUT 5-10 DEGREES COOLER THAN CURRENT FORECAST.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1050 PM CDT WED MAY 15 2013

VFR CONDITIONS ARE EXPECTED THROUGH 18Z THURSDAY. THEREAFTER...THE
PATTERN BECOMES MORE UNSETTLED WITH A PROGRESSION OF SHORT WAVES
ACROSS THE AREA. TIMING IS SOMEWHAT ILL DEFINED...BUT APPEARS AS
THOUGH STORMS WILL BECOME MORE WIDESPREAD TOWARDS THURSDAY
EVENING. STORMS APPEAR TO BE ROOTED AROUND 5K FEET...AND SHOULD
ONLY HAVE TEMPORARY RESTRICTIONS TO VISIBILITY WITH LIMITED
INSTABILITY.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...CHAPMAN/JH
LONG TERM...JH
AVIATION...