000
FXUS63 KFSD 200128
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
828 PM CDT SUN MAY 19 2013

.UPDATE...
ISSUED AT 828 PM CDT SUN MAY 19 2013

PARTIAL CLEARING THIS EVENING IN THE FORECAST AREA HAS ALLOWED
MLCAPES OF 500 TO 1500 J/KG TO DEVELOP IN THE BIG SIOUX VALLEY
SOUTH OF INTERSTATE 90. WHILE DEEP LAYER SHEAR REMAINS BELOW 30
KTS...0 TO 3 KM SHEAR OF 20 TO 30 KTS EXISTS IN SE SD. EXPECTATION
THIS WILL ALLOW STORMS TO PERSIST AT LEAST TO I90 AS THE MOVE UP
THE BIG SIOUX VALLEY AND ADJACENT AREAS OF NW IA AND SW MN. WHILE
WE DO NOT ANTICIPATE SEVERE WEATHER...WOULD NOT BE SURPRISED TO
SEE SOME PEA TO DIME SIZE HAIL AND FEW WIND GUSTS TO 40 OR 45
MPH...ESPECIALLY JUST WEST OF I29 WHERE SHEAR VECTOR IS PARALLEL
TO MOTION VECTOR. AS STABILITY INCREASES LATER THIS
EVENING...EXPECT TO SEE STORMS SLOWLY WEAKEN AS THE PUSH NORTH
TOWARD BROOKINGS AND MARSHALL BUT STILL WORTH A VERY HIGH POP.

AS NOTED BELOW A STRONG PV ANOMALY WILL MOVE NORTH TONIGHT AND
THIS SHOULD ALLOW SHOWERS AND THUNDERSTORMS TO PERSIST WEST OF I29
IN THE JAMES VALLEY THROUGH LATE TONIGHT. EXPECT THAT EAST OF
I29...RAINFALL CHANCES WILL DECREASE AFTER MIDNIGHT AS STABILITY
INCREASES AND CONVECTION WEAKENS AND MOVES NORTH AND EAST OF AREA.
RAINFALL OF UP TO ONE INCH STILL SEEMS LIKELY FROM YANKTON TO
SIOUX FALLS AND SOME LOCATIONS COULD SEE OVER AN INCH NEAR
INTERSTATE 29 SOUTH OF SIOUX FALLS WITH STRONGER CELLS.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 347 PM CDT SUN MAY 19 2013

SURFACE ANALYSIS SHOWS THE LEADING EDGE OF AN OCCLUSION GENERALLY
WHERE IT HAS BEEN ALL DAY...ALONG A HURON TO YANKTON SD LINE.
ALOFT...UPPER LOW IS SPINNING AWAY IN CENTRAL NEBRASKA. AHEAD OF
THE OCCLUSION...WE HAVE HAD A LOT OF RAIN COOLED AIR MOVE INTO OUR
EASTERN ZONES ALONG AND EAST OF THE I 29 CORRIDOR WHERE PV IS STRONG
PER THE 1.5 PRESSURE SURFACE. THERE IS SOME CLEARING SKIES JUST
BEGINNING TO WORK INTO OUR FAR SOUTHEAST ZONES AROUND STORM LAKE
MOVING NORTHWARD. BUT SOME OF THAT CLEARING IS LIKELY SUBSIDENCE
DRIVEN FROM THE CONVECTION THAT FIRED RECENTLY ALONG I 35 TO THE
EAST OF OUR AREA. ALL IN ALL...BEGINNING TO THINK THAT OUR WINDOW OF
OPPORTUNITY FOR SEVERE WEATHER IS BEGINNING TO CLOSE DUE TO THE RAIN
COOLED ATMOSPHERE. CERTAINLY CANNOT RULE OUT SOME SEVERE...GENERALLY
ALONG AND EAST OF A SIOUX CITY TO MARSHALL MN LINE THROUGH EARLY
EVENING. HOWEVER BOTH 0-1KM AND 0-3KM BULK SHEAR VECTORS SHOW THE
BEST POTENTIAL EAST OF OUR FORECAST AREA...WITH BOTH ML AND ELEVATED
MU CAPES VALUES NOT ALL THAT UNSTABLE. IN ADDITION AS THE EVENING
PROGRESSES...DIRECTIONAL SHEAR IN OUR EASTERN ZONES POINT TO A COLD
AIR ADVECTION BACKING IN THE LOW LEVELS...BEFORE BECOMING MORE
UNIDIRECTIONAL AS THE EVENING PROGRESSES. WILL CONTINUE TO MONITOR
THIS SITUATION BUT IT INCREASINGLY LOOKING MULTICELLULAR FOR OUR
EAST.

OTHERWISE PERSISTENT PV ADVECTION PER THE 1.5 SURFACE CONTINUES ALL
NIGHT AHEAD OF THE UPPER LOW ENCOMPASSING THE EASTERN HALF OF OUR
FORECAST AREA. AFTER MIDNIGHT IN OUR WESTERN ZONES...FAIRLY STRONG
TROWALING SETS UP IN THE 300K TO 315K LAYER INCLUDING 700MB TO
600MB. THEREFORE WITH ALL OF THIS IN MIND...IT IS DIFFICULT TO GO
REAL LOW POPS ANYWHERE. IN OUR WEST BECAUSE OF THE TROWAL...DECIDED
TO GO CATEGORICAL POPS IN THE JAMES VALLEY. IN THE CLOSER TERM...THE
UPPER LOW IS WELL PLACED WITH ITS PV ADVECTION TO DEVELOP AN AREA OF
CONVECTION IN OUR SOUTHWEST TO SOUTH CENTRAL AREAS...THEN WILL MOVE
NORTHWARD UP THE VERMILLION RIVER VALLEY THIS EVENING TOWARD SIOUX
FALLS. ONE CAN SEE CONVECTION FIRING UP RIGHT NOW IN EAST CENTRAL
NEBRASKA. BUT AGAIN...IT IS DOUBTFUL IF THIS ACTIVITY WILL BE SEVERE
AT ALL.

ON MONDAY...THE UPPER LOW GRUDGINGLY MOVES TOWARD NORTHEAST SOUTH
DAKOTA. DRY SLOTTING WILL THEREFORE PROBABLY TAKE OVER TO THE
SOUTHWEST QUAD OF THIS LOW...GIVING THE LOWEST POPS IN THE YANKTON
TO SIOUX FALLS LOCATIONS. TROWALING PERSISTS IN THE MORNING IN OUR
WESTERN ZONES AROUND THE JAMES VALLEY BEFORE GREATLY WEAKENING. AND
IN THE AFTERNOON...A SUBTLE SURFACE FEATURE WILL MOVE ALONG A STRONG
UPPER VORT FILAMENT WHICH COULD FIRE A STRIPE OF AFTERNOON
CONVECTION IN OUR SOUTHEAST ZONES INCLUDING NORTHWEST IA AND THE
SOUTHERN SECTIONS OF SOUTHWEST MN. LATE IN THE AFTERNOON...WOULD NOT
RULE OUT A BRIEF WINDOW OF SEVERE IN OUR EXTREME SOUTHEAST ZONES AS
THEY HEAT OUT RIGHT ALONG THE VORT FILAMENT...WHICH IS A FAVORED
AREA ON THE  SOUTHEAST SIDE OF THE UPPER LOW. WILL HAVE TO WATCH FOR
SPINUP TORNADOES AND FUNNELS IN THOSE AREAS UNTIL EARLY EVENING.
ELSEWHERE...STRATOCUMULUS CLOUDS WILL GREATLY ADD TO STABILITY.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 347 PM CDT SUN MAY 19 2013

ON MONDAY NIGHT MODELS IN FAIRLY DECENT AGREEMENT WITH THE UPPER
LEVEL LOW BEING CENTERED OVER THE EASTERN DAKOTAS. MODELS ALSO
HINTING AT A VORT LOBE SWINGING SOUTHWARD AROUND THE MAIN LOW
DURING THE NIGHT...AND WHILE IT LOOKS TO BE MAINLY DRY IN THE EAST
DURING THE EARLY PART OF THE NIGHT...HAVE SOME HIGHER POPS
ADVECTING TO THE EAST THROUGH THE NIGHT AS THIS LOBE TRACKS ACROSS
THE REGION. BY THIS TIME...ANY INSTABILITY HAS MOVED TO THE EAST
OF THE CWA SO LOOKING AT PLAIN SHOWERS OVERNIGHT. THERMAL PROFILES
CONTINUE TO COOL WITH THE LOW...AND LOWS WILL DROP ABOUT A
CATEGORY...INTO THE LOWER TO MID 50S.

THE UPPER LEVEL LOW CONTINUES TO WOBBLE OVER THE PLAINS STATES ON
TUESDAY AND WEDNESDAY...BEFORE BEGINNING TO FILL AND PUSHING
EASTWARD BY THURSDAY. WITH THIS...POPS ARE WARRANTED BOTH TUESDAY
AND WEDNESDAY...THOUGH STAYED PRETTY GENERAL WITH DIFFICULTY IN
TIMING VARIOUS SHORTWAVES FLOATING AROUND THE LOW. DOES APPEAR THAT
PRECIPITATION WILL TAKE ON A MORE SCATTERED NATURE AS THE BETTER
UPPER LEVEL LIFT MOVES OUT OF THE REGION. STILL LOOKING AT THE
POSSIBILITY OF ISOLATED FUNNEL CLOUDS/LANDSPOUTS ON TUESDAY...MAINLY
SOUTH AND EAST WITH A NEARLY VERTICALLY STACKED LOW PRESSURE OVER
THE AREA...IN CONJUNCTION WITH DECENT LOW LEVEL LAPSE
RATES/VORTICITY. THE COOLEST THERMAL PROFILES WILL BE SITUATED
ACROSS THE REGION ON TUESDAY AND WEDNESDAY...AND LOOKING AT HIGHS
ONLY IN THE UPPER 50S TO 60S WITH WEDNESDAY BEING THE COOLEST DAY.

SURFACE HIGH PRESSURE AND UPPER LEVEL RIDGING BUILD BACK INTO THE
REGION FOR THURSDAY AND FRIDAY...WITH DRY CONDITIONS AND A SLOW
WARMING TREND. AS THE SURFACE HIGH PULLS OFF TO THE EAST...WARMER
AND MORE MOIST AIR BEGINS TO RETURN TO THE REGION ON THE BACKSIDE OF
THE HIGH FOR NEXT WEEKEND...BRINGING ANOTHER CHANCE OF THUNDERSTORMS
ALONG WITH TEMPERATURES JUST EITHER SIDE OF NORMAL.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 800 PM CDT SUN MAY 19 2013

AREA OF SHOWERS AND THUNDERSTORMS CURRENTLY ACROSS NORTHEAST NEBRASKA
WILL MOVE NORTHEAST TONIGHT...APPROACHING SIOUX CITY AROUND 0130Z AND
SIOUX FALLS CLOSER TO 03Z. SMALL HAIL AND WIND GUSTS OF 30 TO 40 KTS
ARE POSSIBLE IN THESE STORMS THROUGH AROUND MIDNIGHT. IN GENERAL
EXPECT THE ACTIVITY TO WEAKEN AFTER THIS POINT. THERE COULD BE SOME
ISOLATED THUNDER THAT LINGERS THROUGH THE NIGHT...BUT FOR NOW WILL
KEEP IT JUST SHOWERS IN THE TAFS. MAINLY VFR CONDITIONS THIS
EVENING...WITH REDUCTIONS TO MVFR AND BRIEFLY IFR IN ANY
THUNDERSTORM. LATER TONIGHT INTO TOMORROW MORNING LOOKS LIKE A GOOD
CHANCE OF MVFR STRATUS FORMING AS THE SHOWERS TAPER OFF. THE CLOUD
BASES SHOULD TEND TO LIFT INTO THE VFR RANGE BY LATE
MORNING...ESPECIALLY EAST OF THE JAMES RIVER. TO THE EAST...RAIN
CHANCES LOOK ON THE LOW SIDE THROUGH THE DAY TOMORROW...ALTHOUGH
THERE COULD BE SOME ISOLATED ACTIVITY. TO THE WEST OF THE
JAMES...LOWER CIGS AND SHOWERS MAY LINGER FOR MUCH OF THE DAY.


&&

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

$$

UPDATE...SCHUMACHER
SHORT TERM...MJF
LONG TERM...JM
AVIATION...CHENARD