National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KFSD 141134
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
634 AM CDT TUE MAY 14 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 343 AM CDT TUE MAY 14 2013

MAIN CHALLENGE FOR TODAY WILL BE WINDS/HUMIDITY LEVELS/ASSOCIATED
FIRE WEATHER CONCERNS IN MIXY ENVIRONMENT AHEAD OF AND BEHIND COOL
FRONT WHICH WILL PUSH SOUTHEAST ACROSS THE REGION THROUGH THE DAY.
LOW LEVEL TEMPERATURES AHEAD OF THE FRONT EASILY SUPPORTIVE OF MID
90S ACROSS MUCH OF NORTHWEST IOWA THIS AFTERNOON...WITH SOME MODELS
SHOWING POTENTIAL FOR HIGHS CLOSER TO OR JUST ABOVE THE CENTURY MARK.
WITH THE STRONG MIXING COMES LIKELIHOOD OF MIXING DRIER AIR ALOFT TO
THE SURFACE. MODELS HAVE BEEN HAVING DIFFICULTY CAPTURING THE DIURNAL
DRYING TREND WITH AFTERNOON MIXING...HANGING ONTO SHALLOW MOISTURE OR
MIXING BOUNDARY LAYER MOISTURE UPWARD RATHER THAN BRINGING DRIER AIR
TO SURFACE AS DEEPER MIXING COMMENCES. RUC SEEMS TO HANDLE IT BETTER
THAN NAM/GFS...AND MORE CLOSELY FOLLOWED THAT IDEA THROUGH THE LATE
MORNING/AFTERNOON...THOUGH NOT QUITE AS DRY AS RUC INDICATES AT THIS
POINT GIVEN EXTREME DISPARITY FROM OTHER MODELS /AS MUCH AS 10-15F
DRIER THAN MOST OTHER GUIDANCE FOR 21Z/. DRIEST AIR SHOULD BE OVER
FAR SOUTHEAST AND WESTERN PARTS OF THE FORECAST AREA DURING PEAK
HEATING...WITH SLIGHT MOISTURE POOLING IN SOMEWHAT LESS MIXY AREA
RIGHT ALONG THE FRONT...FORECAST TO BE JUST EAST OF KYKN-KFSD-KMML
LINE AT 21Z. ALL THIS LEADS TO MINIMUM HUMIDITY LEVELS OF 15-25
PERCENT THIS AFTERNOON... AND THIS ALONG WITH WINDS GUSTING IN THE
25-30KT RANGE STILL SUPPORTIVE OF RED FLAG WARNING WHICH WAS ISSUED
ON THE DAY SHIFT YESTERDAY.

COLD FRONT SETTLES SOUTH OF THE AREA TONIGHT...WITH COOLING
TEMPERATURES AND DYING WINDS OVERNIGHT. LOWS LOOK TO DROP INTO THE
UPPER 40S NORTHWEST...TO MID 50S THROUGH THE LOWER MISSOURI RIVER
VALLEY INTO NORTHWESTERN IOWA.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 343 AM CDT TUE MAY 14 2013

SURFACE HIGH PRESSURE BUILDS SOUTHWARD INTO THE REGION ON WEDNESDAY
AND WEDNESDAY NIGHT...PROVIDING FOR PLEASANT CONDITIONS WITH
TEMPERATURES CLOSE TO NORMAL FOR THIS TIME OF YEAR. THIS WILL PLAY
OUT TO HIGHS IN THE MID AND UPPER 70S...WITH LOWS EARLY ON THURSDAY
IN THE UPPER 40S TO LOWER 50S.

THE HIGH MOVES EASTWARD ON THURSDAY WITH A SOUTHERLY FLOW RETURNING
TO OUR AREA ON THE BACKSIDE OF THE HIGH. THINK MOST OF THE DAY WILL
REMAIN DRY WITH WARMING TEMPERATURES...INTO THE UPPER 70S TO AROUND
80 FOR AFTERNOON HIGHS. CANNOT RULE OUT SOME THUNDERSTORM
DEVELOPMENT IN OUR SOUTHWEST LATER IN THE AFTERNOON...WITH A BETTER
CHANCE ON THURSDAY NIGHT AS A WARM FRONT BEGINS TO LIFT THROUGH
NEBRASKA AND 850 MB CONVERGENCE IS ENHANCED AS A LOW LEVEL JET
DEVELOPS THROUGH THE REGION. DOES APPEAR TO BE ENOUGH ELEVATED
CAPE...500 TO 1000 J/KG...AND EFFECTIVE SHEAR OF AROUND 30 KTS IN
THE EVENING THAT CANNOT RULE OUT A COUPLE OF SEVERE STORMS WITH
LARGE HAIL.

A MESSY PATTERN CONTINUES THROUGH THE EXTENDED...FRIDAY INTO MONDAY
OF NEXT WEEK...WITH PERIODIC CHANCES OF CONVECTION THROUGH THE
PERIOD WITH A BOUNDARY MEANDERING AROUND THE AREA AND A SERIES OF
SUBTLE WAVES TRACKING ACROSS THE REGION. HARD TO TIME THIS
CONVECTION DEPENDENT ON WHERE SYNOPTIC/MESOSCALE FEATURES SET
UP...BUT WITH INCREASING LOW LEVEL MOISTURE AND INSTABILITY ACROSS
THE REGION THROUGH THE WEEKEND THERE IS FAIRLY HIGH CONFIDENCE THAT
CONVECTION WILL OCCUR. CONVECTIVE PARAMETERS WOULD ALSO SUGGEST THAT
SEVERE STORMS WILL BE POSSIBLE FOR THOSE DAYS. AN UPPER LEVEL TROUGH
FINALLY SWINGS OUT OF THE WESTERN U.S. ON SUNDAY AND
MONDAY...KEEPING A CHANCE OF CONVECTION ACROSS THE REGION...AS WELL
AS BRINGING A COOLING TREND.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 634 AM CDT TUE MAY 14 2013

MAIN AVIATION CONCERN TODAY WILL BE GUSTY WINDS...FIRST OUT OF THE
SOUTHWEST BY 14Z AHEAD OF APPROACHING COLD FRONT...WITH THE WINDS
BECOMING NORTHWEST AS THE FRONT PROGRESSES SOUTHEAST ACROSS THE
FORECAST AREA THROUGH THE DAY. GUSTY WINDS WILL SUBSIDE WITH SUNSET
AROUND 15/01Z. VFR CONDITIONS THROUGH THE PERIOD.

&&

.FIRE WEATHER...
ISSUED AT 343 AM CDT TUE MAY 14 2013

RED FLAG WARNING STILL LOOKS WARRANTED FOR THE AFTERNOON AND EARLY
EVENING. GUSTY SOUTHWEST WINDS OF 25 TO 35 MPH AHEAD OF COOL FRONT
WILL SWITCH TO NORTHWEST BEHIND THE FRONT AND REMAIN AS STRONG. ALONG
WITH THE GUSTY WINDS WILL BE DRY RELATIVE HUMIDITY LEVELS IN THE 15
TO 25 PERCENT RANGE...AS DRY AND UNSEASONABLY WARM AIR ALOFT MIXES TO
THE SURFACE. AREAS RIGHT ALONG THE FRONT MAY NOT SEE AS SUSTAINED A
PERIOD OF RED FLAG CRITERIA DUE TO MOISTURE POOLING AND LIGHTER/LESS
GUSTY WINDS WITHIN THE FRONTAL ZONE...BUT SHOULD STILL REACH CRITERIA
AT TIMES. RECENT GREENING OF COOL SEASON GRASSES MAY SLOW FIRE STARTS
ACROSS THE AREA...BUT ANY FIRES THAT DO IGNITE WILL SPREAD VERY
QUICKLY IN THE LINGERING DORMANT TALL GRASSES.

SOME MODELS ALSO INDICATE POTENTIAL FOR EVEN WARMER/DRIER AIR MIXING
TO THE SURFACE AHEAD OF THE FRONT...MAINLY IN NORTHWEST IOWA THIS
AFTERNOON...SO THIS WILL BE WATCHED CLOSELY THROUGHOUT THE DAY.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...RED FLAG WARNING FROM NOON TODAY TO 8 PM CDT THIS EVENING FOR
     SDZ255>258.

MN...RED FLAG WARNING FROM NOON TODAY TO 8 PM CDT THIS EVENING FOR
     MNZ900.

IA...RED FLAG WARNING FROM NOON TODAY TO 8 PM CDT THIS EVENING FOR
     IAZ300-301.

NE...RED FLAG WARNING FROM NOON TODAY TO 8 PM CDT THIS EVENING FOR
     NEZ249.

&&

$$

SHORT TERM...JH/JM
LONG TERM...JM
AVIATION...JH
FIRE WEATHER...JH