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000
FXUS63 KFSD 141538
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1038 AM CDT TUE MAY 14 2013

.UPDATE...
ISSUED AT 1029 AM CDT TUE MAY 14 2013

FORECAST LOOKS IN PRETTY GOOD SHAPE. RED FLAG WARNING LOOKS
GOOD...WITH BLUSTERY SOUTHWEST WINDS AHEAD OF THE COLD
FRONT...TRANSITIONING TO NORTHWEST BEHIND IT. EXPECT FREQUENT GUSTS
INTO THE 25 TO 35 MPH RANGE WITH RELATIVE HUMIDITY DROPPING TO AROUND
20 PERCENT...OR EVEN A LITTLE LOWER AHEAD OF THE FRONT THIS
AFTERNOON. LEADING EDGE OF THE ACCAS IS A SOME SORT OF BOUNDARY WITH
WINDS TURNING MORE WEST SOUTHWESTERLY BEHIND IT. HOWEVER THE TRUE
COLD FRONT IS BEHIND THIS...HAVING JUST GONE THROUGH CHAMBERLAIN AND
HURON WITH THEIR WINDS TURNING NORTHWEST. WENT AHEAD AND RAISED
HIGHS A FEW DEGREES FOR TODAY...WITH READINGS AROUND 100 LOOKING
LIKELY ACROSS NORTHEAST NEBRASKA AND NORTHWEST IOWA...LOCATIONS THAT
WILL STAY JUST AHEAD OF THE COLD FRONT THROUGH THE PEAK OF DAYTIME
HEATING. CONVECTION CHANCES WITH THE FRONT STILL LOOK LOW WITH
DEWPOINTS MIXING OUT. HOWEVER HRRR IS SHOWING SOME ACTIVITY AFTER
21Z. AND GIVEN THAT ITS BOUNDARY LAYER DEPICTION SEEMS DECENT...CAN
NOT COMPLETELY IGNORE THE CHANCE. HOWEVER IT DOES APPEAR THAT THE
BEST CHANCE WILL STAY SOUTH OF OUR CWA ACROSS NEBRASKA...THUS WILL
KEEP THE FORECAST DRY FOR NOW. ALTHOUGH ANY STORM THAT IS ABLE TO
FORM WOULD BE CAPABLE OF POTENTIALLY SEVERE WIND GUSTS GIVEN THE DRY
PROFILES.

&&

.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 UNTIL 8 PM CDT THIS EVENING FOR SDZ255>258.

MN...RED FLAG WARNING UNTIL 8 PM CDT THIS EVENING FOR MNZ900.

IA...RED FLAG WARNING UNTIL 8 PM CDT THIS EVENING FOR IAZ300-301.

NE...RED FLAG WARNING UNTIL 8 PM CDT THIS EVENING FOR NEZ249.

&&

$$

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