Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 191728
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1228 PM CDT TUE AUG 19 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 356 AM CDT TUE AUG 19 2014

A QUIET AND NOT AS HUMID DAY AHEAD AS THE AREA IS IN THE WAKE OF AN
EXITING SYSTEM TO THE EAST. THIS HAS LEFT DRIER AIR AND A WEAK HIGH
PRESSURE ACROSS THE REGION WHICH WILL RESULT IN WARM TEMPERATURES
AND WINDS MAINLY LESS THAN 10 MPH THROUGH THE DAY. AFTER SEEING
YESTERDAYS HIGHS POP UP A LITTLE MORE THAN EXPECTED WENT AHEAD AND
SIDED WITH SOME OF THE WARMER GUIDANCE AND RAISED HIGHS ABOUT 2
DEGREES IN MOST LOCATIONS...EXPECTING MAINLY LOWER TO MIDDLE 80S
WITH A FEW UPPER 80S IN CENTRAL SD.

BY TONIGHT A WAVE WILL MOVE INTO WYOMING WHICH WILL SPREAD WARM AIR
ADVECTION ALOFT INTO SOUTHERN AND WESTERN PARTS OF THE CWA. THIS
WILL BRING A GOOD CHANCE FOR THUNDERSTORMS TO THOSE AREAS BUT SEVERE
WEATHER SHOULD REMAIN LIMITED. WHILE THERE IS SOME BETTER
INSTABILITY IF LIFT IS AROUND 850MB OR LOWER IT APPEARS THAT THIS
LAYER MAY BE TOO DRY AND LIFT WILL TAKE PLACE FARTHER ALOFT...WHERE
LESS INSTABILITY EXISTS. HOWEVER IF AN UPDRAFT CAN BECOME ROOTED A
LITTLE LOWER IN THE ATMOSPHERE AN ISOLATED SEVERE THUNDERSTORM WILL
BE POSSIBLE. OTHERWISE SEASONABLY MILD WITH LOWS IN THE LOWER TO
MIDDLE 60S.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 356 AM CDT TUE AUG 19 2014

MID LEVEL WARM AIR ADVECTION CONTINUES INTO THE DAY WEDNESDAY. GIVEN
THE DIURNAL WEAKENING OF THE LOW LEVEL JET AND DRY AIR IN THE LOWER
LEVELS...UNCERTAIN IF MUCH IN THE WAY OF ELEVATED SHOWER AND
THUNDERSTORM ACTIVITY WILL LINGER INTO THE DAY. BUT SHOULD AT LEAST
SEE SOME MID LEVEL CLOUDINESS...AND POSSIBLY ISOLATED TO SCATTERED
CONVECTION. HIGHS ARE TRICKY DUE TO CLOUD COVER CONCERNS...AND THERE
IS A LARGE SPREAD AMONG THE MODELS. FOR NOW TRIED TO STAY NEAR A
CONSENSUS OF THE MODELS...AS EVEN WITH MORE SUN...SOUTHEASTERLY
WINDS AND HIGH DEWPOINTS WILL LIKELY HINDER MIXING AND PREVENT HIGHS
FROM GETTING TOO HIGH. FOR NOW WENT WITH LOW TO MID 80S SOUTHWEST
MINNESOTA TO MID AND UPPER 80S ALONG THE MISSOURI RIVER...WITH HEAT
INDICES IN THE MID 80S TO MID 90S.

CONVECTION CHANCES SHOULD INCREASE WEDNESDAY EVENING INTO THE
OVERNIGHT HOURS AS BETTER UPPER FORCING OVERSPREADS THE
AREA...ACCOMPANIED BY AN EASTWARD ADVANCING COLD FRONT AND
INCREASING LOW LEVEL JET. STILL SOME UNCERTAINTY ON WHETHER WE WILL
BE ABLE TO GET NEAR SURFACE STORM DEVELOPMENT ALONG THE COLD FRONT.
CLOUD COVER COULD REALLY HURT LOW LEVEL LAPSE RATES AND KEEP THE
NEAR SURFACE LAYER CAPPED. HOWEVER IF WE CAN GET ENOUGH SUN AND
STORMS DO FORM ALONG THIS FRONT...THERE WOULD BE A SEVERE THREAT.
DEEP LAYER SHEAR FORECAST TO BE AROUND 40 KTS...WITH A WARM FRONT
ENHANCING LOW LEVEL SHEAR AS WELL. SO WILL NEED TO MONITOR
CLOSELY...AS SUPERCELLS WOULD BE POSSIBLE IF WE ARE ABLE TO
DESTABILIZE...BUT AGAIN THIS IS NOT A SURE THING. DOES LOOK LIKE
MORE OF A SURE BET ELEVATED STORMS WILL FORM NORTH OF THE WARM FRONT
AS THE LOW LEVEL JET PICKS UP. GIVEN THE LOCATION OF THE BEST UPPER
SUPPORT AND LOW LEVEL JET CONVERGENCE...HIGHEST THREAT FOR THESE
ELEVATED STORMS WOULD BE NORTH OF INTERSTATE 90...SO WILL KEEP
HIGHEST POPS THERE.

THURSDAY SHOULD SEE SUBSIDENCE ALOFT BEHIND THE DEPARTING
WAVE...LEADING TO A PARTLY TO MOSTLY SUNNY DAY. WILL BE A WARM ONE
AS WELL...WITH HIGHS IN THE MID 80S TO AROUND 90. COMBINED THIS WITH
DEWPOINTS IN THE 60S AND 70S...AND HEAT INDICES WILL BE IN THE 90S
ACROSS MOST OF THE AREA. LOWERED POPS ON THURSDAY NIGHT...AS THE GFS
SEEMS TO BE ON ITS OWN WITH TRACKING A WAVE ACROSS THE AREA AND
GENERATING AN AREA OF STORMS.

HOWEVER BY FRIDAY INTO THE WEEKEND THE PATTERNS SHOULD GET ACTIVE
AGAIN AS THE TROUGH OVER THE WESTERN PORTION OF THE COUNTRY BEGINS
TO PUSH EAST AND SEND WAVES OF UPPER ENERGY INTO THE PLAINS. STILL
SOME DIFFERENCES ON TIMING...BUT THUNDERSTORM THREAT SHOULD INCREASE
BY LATER FRIDAY INTO SATURDAY MORNING. TOUGH TO ASSESS SEVERE THREAT
THIS FAR OUT...AS THIS PATTERN WILL PROBABLY HAVE A DECENT AMOUNT OF
ACCAS TYPE CLOUDS AND PRECIP AROUND...SO SURFACE INSTABILITY IS
UNCERTAIN. HOWEVER DECENT DEEP LAYER SHEAR WOULD SUPPORT A SEVERE
RISK SOMETIME LATER FRIDAY INTO SATURDAY SHOULD WE GET ENOUGH SUN TO
DESTABILIZE. FRIDAY SHOULD BE ANOTHER WARM AND HUMID ONE WITH HIGHS
IN THE 80S AND HEAT INDICES IN THE 80S AND 90S.

THE TREND OVER THE WEEKEND INTO EARLY NEXT WEEK SHOULD BE COOLER
TEMPERATURES...JUST A MATTER OF HOW QUICKLY AND HOW COOL. NOT REAL
CONFIDENT ON EITHER OF THESE...BUT A CONSENSUS APPROACH YIELDS A
SLIGHT THUNDERSTORM THREAT EACH DAY...WITH HIGHS INTO THE LOW AND
MID 70S BY SUNDAY AND MONDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1221 PM CDT TUE AUG 19 2014

VFR WILL PREVAIL THROUGH THIS AFTERNOON...TONIGHT AND WEDNESDAY
MORNING. AS TONIGHT PROGRESSES...SURFACE WINDS WILL BECOME
INCREASINGLY FROM THE SOUTHEAST OR EAST/SOUTHEAST...AND SETTLE
INTO A 10 TO 20 MPH RANGE WEDNESDAY MORNING. THERE IS A SUBTLE
WARM FRONT LIFTING NORTHWARD LATE TONIGHT AND WEDNESDAY. THIS
BOUNDARY WILL GIVE A CHANCE FOR SHOWERS AND ISOLATED STORMS MAINLY
FOR OUR MISSOURI RIVER VALLEY ZONES LATE TONIGHT AND EARLY
WEDNESDAY. BUT WOULD NOT BE SURPRISED TO SEE SOME ACTIVITY SNEAK
UP TO THE KFSD TAF SITE A BIT LATER WEDNESDAY MORNING. THERE
CERTAINLY IS ELEVATED INSTABILITY. BUT AT THIS TIME CHOSE NOT TO
MENTION THUNDER IN THE KSUX AND KFSD TAF SITES...JUST SHOWERS. THIS
IS BECAUSE THE TIMING IS OF COURSE A BIT UNCERTAIN THIS FAR OUT...
AND CONFIDENCE IS RATHER LOW PIN POINTING THUNDERSTORMS. BUT DO BE
AWARE THAT THE POSSIBILITY EXISTS FOR A THUNDERSTORM WITH THE
PASSING SHOWERS AS THE SYSTEM LIFTS NORTHWARD.

&&

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

$$

SHORT TERM...08
LONG TERM...CHENARD
AVIATION...MJ





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