Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 010917
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
417 AM CDT FRI MAY 1 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 416 AM CDT FRI MAY 1 2015

BAND OF SHOWERS IS CONTINUING TO WORK ACROSS THE AREA EARLY THIS
MORNING...BUT LIMITED MOISTURE HAS DOOMED AMOUNTS TO A QUITE LIGHT
LEVEL...A TENTH OF AN INCH OR LESS. MAIN DYNAMICS CONTINUE TO PLOW
EAST TOWARD NORTHERN MINNESOTA...AS SLIGHTLY BETTER THERMODYNAMICS
HOVER TOWARD THE SOUTH. SOME SUB 100 ELEVATED CAPE INDICATED IN A
FEW SOLUTIONS...BUT HAVE NOT EVEN HAD ANY INTRACLOUD LIGHTNING IN
LAST 4 HOURS IN BAND...AND UNLIKELY TO GET A GREAT DEAL MORE
FAVORABLE CONDITIONS THROUGH THE EARLY MORNING. ISOLATED THUNDER
THREAT IS PERHAPS A BIT STRONG...BUT WILL ADD IN SOME NEAR KSUX
THROUGH EARLY MORNING. COULD END UP A SPLIT OF PRECIPITATION ACROSS
THE CWA AS A RESULT...WITH RELATIVELY HIGHER AMOUNTS ACROSS THE
NORTHEAST CWA AND SOUTH OF I90. UPPER FORCING WILL CONTINUE TO CLIP
ALONG AND WILL EVENTUALLY OUTRUN THE LOWER LEVEL BOUNDARY...AND A
SLIGHTLY FASTER TIMING TO THE EXIT OF PRECIPITATION LOOKS TO BE IN
ORDER. CLOUDS WILL LINGER SOMEWHAT LONGER THAN PRECIP THREAT...BUT
EVEN A NOTED CLEARING WILL PUSH INTO THE NORTH AND WEST AREAS BEFORE
DAYBREAK.  A LOT OF 30S DEWPOINT READINGS BACK IN CLEAR AIR AND WILL
BE THIS SOURCE OF AIRMASS FOR THE DAY. A COUPLE OF THE LATEST HRRR
RUNS ARE SUGGESTING THAT THERE MAY BE SOME INSTABILITY SHOWERS WHICH
DEVELOP DURING THE MID TO LATER AFTERNOON HOURS ACROSS AREAS EAST
OF I29...ESPECIALLY SW MN TOWARD THE IOWA GREAT LAKES. HOWEVER...
APPEARS TO BE A CASE WHERE THE DRYING OF LOWER LAYERS IS
UNDERESTIMATED...AND THE NET SURFACE BASED INSTABILITY WOULD BE
LESS...MUCH AS INDICATED BY COARSER MODEL SOLUTIONS. MIXING WELL
WITH WESTERLY COMPONENT...HIGHS FROM AROUND 70 IN LONGER CLOUD
DURATION SOUTHEAST TO MID TO UPPER 70S WEST.

WIND LIKELY A BIT CHAOTIC THIS EVENING AS POST FRONTAL WEAK RIDGE
WASHES OUT AND BROAD WEAK SOUTH TO SOUTHEAST FLOW RETURNS TO THE
AREA BY 06Z. LIKELY TO HAVE A COUPLE OF ROGUE STORMS POP UP ALONG
BOUNDARY TOWARD I 80 WHICH COULD SPILL A FEW MORE CLOUDS TOWARD THE
SIOUX CITY AREA AND EASTWARD LATER TONIGHT...BUT WITH EXPECTED DRY
AIR INTRUSION THROUGH THE AFTERNOON AND MAINLY CLEAR SKIES...HAVE
HEDGED LOWS DOWN JUST A TOUCH MOST LOCATIONS...WITH MID 40S TO NEAR
50.


.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 416 AM CDT FRI MAY 1 2015

SATURDAY REMAINS RATHER INTERESTING IN TERMS OF SMALL CHANCES FOR
CONVECTION. BUT OVERALL IT WILL BE A PLEASANT AND VERY WARM SPRING
DAY. THE GFS AND HIGH RESOLUTION NAM SOLUTIONS CONTINUE TO LOCK ONTO
CONVECTIVE CHANCES PRIMARILY IN EXTREME NORTHEAST NEB AND NORTHWEST
IA. THE MECHANISM FOR THIS IS THE LOW LEVEL JET...WHICH HAS 30 KNOTS
IN THE CENTRAL PLAINS FEEDING INTO 10 TO 20 KNOTS IN NORTHWEST IA
CREATING GOOD SPEED CONVERGENCE. THE MIXED LAYER IS BUOYANT WITH
VERY LITTLE IN THE WAY OF CIN AND ML CAPE IN THE 1000 TO 1500 J/KG
RANGE FOR THE AFOREMENTIONED AREAS. SO SLIGHT CHANCE TO LOW END
CHANCE POPS ARE WARRANTED. LATE IN THE AFTERNOON JUST AHEAD OF A
SLOW MOVING WIND SHIFT...THERE COULD ALSO BE AN ISOLATED STORM IN
OUR EXTREME WESTERN ZONES BUT THAT AREA IS MORE CAPPED. PROBABLY THE
MAIN STORY THOUGH IS THE WARMTH...WITH BIAS CORRECTED READINGS ONCE
AGAIN RULING THE DAY WITH HIGHS WIDESPREAD OF 80 TO 85 DEGREES.

SOUTHERLY WINDS CONTINUE SATURDAY NIGHT AHEAD OF THE NEXT COLD FRONT
AND SHORT WAVE HELPING TO USHER IS SOME REBOUND IN SURFACE TO
BOUNDARY LAYER DEW POINTS. THERE COULD BE A LINGERING ISOLATED STORM
IN OUR FAR EASTERN ZONES IN THE EVENING LEFTOVER FROM ANY AFTERNOON
CONVECTION TALKED ABOUT ABOVE. AND THERE MIGHT BE SOME ISOLATED
STORMS IN OUR WESTERN ZONES JUST AHEAD OF THE COLD FRONT. BUT
OVERALL CONVECTIVE CHANCES SATURDAY NIGHT WILL BE VERY SPOTTY.

SUNDAY AND SUNDAY EVENING IS STILL THE DAY TO WATCH FOR MORE
ORGANIZED STORM ACTIVITY. DECENT SHORT WAVE AND ACCOMPANYING WIND
SHIFT ALONG A COLD FRONT WILL ACT AS A FOCUS MECHANISM FOR
CONVECTIVE DEVELOPMENT. IN THE MORNING HOURS...IT APPEARS THE BEST
CHANCE FOR SPOTTY CONVECTION WILL CONTINUE TO BE IN OUR WESTERN
ZONES ALONG THE WIND SHIFT...AND IN SOUTHWEST MN WHO IS PLACED ON
THE NOSE OF A BOUNDARY LAYER TO 850MB WARM FRONT. AS THE AFTERNOON
PROGRESSES...THE STORM ACTIVITY WILL BECOME MORE WIDESPREAD...
ESPECIALLY EAST OF INTERSTATE 29 IN NORTHWEST IA AND MOST OF
SOUTHWEST MN. THERE IS A MARGINAL TO SLIGHT RISK OF SEVERE WEATHER
GENERALLY ALONG AND EAST OF A YANKTON...TO SIOUX FALLS TO MARSHALL
MN LINE BY MID AFTERNOON. BUT THE SEVERE CHANCES WILL WANE RAPIDLY
IN THE EARLY AND MID EVENING AS THE 850MB WIND SHIFT PROCEEDS
QUICKLY SOUTHEASTWARD. BUT JUST AHEAD OF THE WIND SHIFT...ML CAPES
ARE ONCE AGAIN IN THE 1000 TO 1500 J/KG RANGE AIDED BY 30 TO 35 KNOT
0-3KM LAYER BULK SHEAR WINDS. THE BULK SHEAR VECTORS ARE ORIENTATED
RATHER PARALLEL WITH THE MID LEVEL FLOW WHICH MAY INHIBIT A WIND
EVENT...SO AT THIS TIME WORRIED A LITTLE MORE ABOUT HAILERS.
CONCERNING TEMPERATURES...IT SHOULD ONCE AGAIN BE WARM BUT THE BIAS
CORRECTED VALUES ARE HINTING AT A LITTLE MORE COOLING IN OUR WESTERN
ZONES BEHIND THE COLD FRONT IN THE AFTERNOON. ACTUALLY THE GFS BC
VALUES LOOKED REALLY GOOD GIVEN THE 850MB TEMPERATURES. THEREFORE
RANGED HIGHS FROM 87 DEGREES IN SIOUX CITY TO 76 IN CHAMBERLAIN SD.

IN THE EXTENDED MONDAY THROUGH THURSDAY...TRENDED POPS SOUTHWARD TO
SOUTH OF INTERSTATE 90 MONDAY AND MONDAY NIGHT...WHEREAS THE
SUPERBLEND BASICALLY SPLASHED POPS EVERYWHERE WHICH IS UNREALISTIC.
STRONG HIGH PRESSURE IS NOSING SOUTHWARD CREATING STABLE AIR... AND
THE CHANCES FOR RAIN EVEN IN OUR FAR SOUTHERN ZONES ARE VERY SMALL.
THE MID WEEK STILL LOOKS UNSETTLED...WITH BIG UPPER TROUGHING IN THE
SOUTHERN ROCKIES LIFTING NORTH TO NORTHEASTWARD. IT APPEARS WHEN
BLENDING THE MODELS THAT THE ABSOLUTE BEST CHANCES FOR STORMS WILL
BE WEDNESDAY AND WEDNESDAY NIGHT WITH WHAT LOOKS LIKE FINALLY A
DECENT MOISTURE FEED IN THE SURFACE TO 850MB LAYER. HAVE NOT REALLY
HAD THAT THIS SPRING YET...NOT WIDESPREAD ANYWAY. SO THERE COULD
FINALLY BE SOME BENEFICIAL RAINFALL.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1033 PM CDT THU APR 30 2015

VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD. A FRONTAL
BOUNDARY WILL PUSH ACROSS THE AREA LATE TONIGHT INTO FRIDAY. THIS
SYSTEM WILL TRIGGER SCATTERED SHOWERS AS IT MOVES ACROSS THE
AREA...THOUGH SHOULD HAVE LITTLE IMPACT TO VISIBILITY. WINDS WILL
BECOME NORTHWESTERLY BEHIND THE FRONT.


&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...MJ
AVIATION...JM



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