Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 301042
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
542 AM CDT MON MAR 30 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 412 AM CDT MON MAR 30 2015

TODAY LOOKS LIKE A RATHER BENIGN WEATHER DAY ON THE SURFACE ACROSS
OUR FORECAST AREA...WITH A WEAK MID LEVEL WAVE/ASSOCIATED SURFACE
LOW TRACKING SOUTHEAST THROUGH NORTHERN/CENTRAL MINNESOTA. WEAK
TROUGH SLIDING THROUGH OUR AREA WILL SHIFT WINDS FROM SOUTHWEST TO
WEST/NORTHWEST THIS AFTERNOON...WITH JUST SOME PATCHY HIGH CLOUDS
ACROSS THE AREA.

A CLOSER LOOK REVEALS MORE FIRE WEATHER CONCERNS HOWEVER...AS THE
ANTICIPATED WEST-NORTHWEST FLOW IS VERY FAVORABLE FOR DEEP MIXING.
HAVE FOUND THAT THE RAP MODEL TENDS TO HANDLE THIS TYPE OF SCENARIO
BETTER THAN OTHER MODELS SUCH AS THE NAM/GFS...SO HAVE LARGELY BASED
FORECAST TODAY ON THE RAP GUIDANCE...THOUGH BLENDED IN SOME SLIGHTLY
LESS EXTREME GUIDANCE AS A TEMPERING FACTOR FOR NOW. RAP SOUNDINGS
INDICATE MIXING AS HIGH AS 750-700MB OVER MUCH OF THE FORECAST AREA
WHICH TAPS WELL INTO LAYER OF 30-35KT ABOVE 850MB. WITH THIS IN
MIND...ENDED UP BUMPING WINDS HIGHER THAN PREVIOUSLY FORECAST. DEEP
MIXING ALSO RESULTS IN A WARM TEMPERATURES IN THE 70S...AND LOWER
DEW POINTS IN THE UPPER 20S/NEAR 30. THIS DROPS HUMIDITY LEVELS INTO
15-25 PERCENT RANGE FOR SEVERAL HOURS THIS AFTERNOON. AFTER SEEING
HOW STRONGLY THE DRIER AIR MIXED DOWN IN THE MID-LATE AFTERNOON ON
SUNDAY...THIS DOES NOT SEEM UNREASONABLE. IN FACT...RAP SOUNDINGS
SHOW DEW POINTS 3-5F LOWER THAN CURRENT FORECAST...SO NEXT SHIFT
WILL WANT TO MONITOR CLOSELY FOR EVEN LOWER HUMIDITY VALUES. AFTER
COORDINATION WITH SURROUNDING OFFICES AND INTERAGENCY WITH MN FIRE
CENTER...WILL ISSUE A RED FLAG WARNING FOR THE ENTIRE CWA THIS
AFTERNOON/EARLY EVENING.

CONDITIONS WILL QUICKLY IMPROVE AT SUNSET AS MIXING COMES TO A HALT.
OVERALL WARMER AIR MASS IN PLACE...SO OVERNIGHT LOWS SHOULD HOLD IN
THE MID TO UPPER 30S DESPITE MOSTLY CLEAR SKIES AND LIGHT WINDS IN
ADVANCE OF APPROACHING SURFACE RIDGE.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 412 AM CDT MON MAR 30 2015

TUESDAY LINING UP TO BE A MOST PLEASANT EARLY SPRING DAY...WITH LESS
WIND AND VERY MILD TEMPS. EVEN IN A POORER MIXING ENVIRONMENT THAN
PREVIOUS DAYS...WOULD LOOK FOR TEMPS TO MIX TO AT LEAST THE WARMEST
POTENTIAL...IF NOT A DEGREE OR TWO MORE...WITH UPPER 60S SOUTHWEST
MINNESOTA TO UPPER 70S SOUTH CENTRAL. TWO DRIER AREAS MAY END UP
BEING THE FAR EASTERN CWA WHERE TRAJECTORY MORE CLEARLY OUT OF THE
RETREATING SURFACE RIDGE... AND THE FAR WESTERN AREA WHICH WILL
START TO FALL INTO A STRENGTHENING RETURN FLOW DURING THE AFTERNOON.

AS TROUGH PUSHES OUT TOWARD THE WESTERN PLAINS ON TUESDAY NIGHT...
WILL SEE LOW LEVEL JET INCREASE SIGNIFICANTLY. FAIRLY DECENT
ELEVATED MIXED LAYER SPREADS OUT AHEAD OF TROUGH WITH 700-500 HPA
LAPSE RATES OF 8 TO 9C/KM...BUT FOR THE MOST PART...LAYER JUST LACKS
ANY APPRECIABLE MOISTURE TO WORK TOWARD ANY ACCAS TYPE DEVELOPMENT
WITH MID LEVEL ADVECTIONS SHIFTING EAST OF THE AREA. COULD START TO
SEE A LITTLE LOWER LEVEL MOISTURE SURGE PUSH UP TOWARD THE CWA...BUT
FOR NOW LOOKS TO REMAIN MOSTLY ACROSS NEBRASKA THROUGH 12Z. WINDS
LATER TUESDAY NIGHT AND WEDNESDAY MORNING ARE LIKELY TO BE STRONGER
THAN GUIDANCE...AND COULD AGAIN BE GUSTING 40 TO 50 MPH ALONG AND
LEEWARD OF THE BUFFALO RIDGE GIVEN FAVORABLE INVERSION STRENGTH AND
DIRECTION OF FLOW ALOFT. LOWS AS A RESULT QUITE MILD FOR THE START
OF APRIL...UPPER 40S TO MID 50S.

POTENTIAL FOR A LITTLE HIGH BASED ACTIVITY WILL INCREASE DURING THE
MORNING ON WEDNESDAY AS LARGE SCALE LIFT BEGINS TO CREEP TOWARD THE
AREA...BUT WITH SUCH DRY AIR AT LOWER LEVELS...PROBABLY NO MORE THAN
A SPRINKLE THREAT. PROSPECT FOR STORMS DOES INCREASE DURING THE
AFTERNOON AS THE MOISTURE CONTINUES TO PUSH NORTHEAST AHEAD OF THE
BOUNDARY. CONDITIONS DO REMAIN SOMEWHAT MODERATELY CAPPED...AND
REMAINS TO BE SEEN WHETHER THE INCREASED FRONTAL FORCING WILL BE
ENOUGH TO OVERCOME...OR IF CONVECTION WILL BE LIMITED TO A HIGHER
BASED NATURE AS IT DEVELOPS DURING THE AFTERNOON. SHEAR IS FAIRLY
UNIDIRECTIONAL AND LOWER PROFILE WEIGHTED...PERHAPS GOOD ENOUGH FOR
A SEVERE HAIL OR WIND THREAT FOR STRONGER STORMS SOUTHEAST OF A
WINDOM TO VERMILLION LINE ON WEDNESDAY AFTERNOON AND VERY EARLY
EVENING. LOCATION OF STRONG FRONTAL ZONE WILL PRETTY MUCH DEFINE THE
THREAT AND NO THREAT AREAS BY MID TO LATE AFTERNOON.

EXPECT PROGRESSION OF FEATURES TO DRIVE ENDING OF PRECIPITATION
THREAT A BIT QUICKER THAN MODELS...ESPECIALLY A COUPLE SOLUTION SETS
WHICH KEEP PRECIPITATION THROUGH THE SOUTHEASTERN CWA UNTIL ALMOST
DAYBREAK THURSDAY.

SOUTH OF THE MAIN UPPER WAVE ON THURSDAY WILL PLACE THE CWA IN A
VERY MIXY ENVIRONMENT...WITH 30 TO 35 KNOTS OF WIND WITHIN REACH...
SO AGAIN FELT OBLIGATED TO HEDGE TO A BIT WARMER THAN MAX MIX OUT
TEMPERATURES...AND LOWER ON DEWPOINTS.  COOLER AIR WILL SETTLE INTO
THE AREA ON THURSDAY NIGHT THROUGH FRIDAY...BUT TEMPS WILL REMAIN
ABOVE NORMAL WITH WINDS DROPPING OFF.

MODEL SOLUTIONS VARY GOING INTO THE WEEKEND WITH HOW QUICKLY THE
ZONAL RIDGING REBUILDS INTO THE NORTHERN PLAINS. SUPPORT FROM
CANADIAN AND SEVERAL GFS ENSEMBLE MEMBERS WOULD SEEM TO FAVOR A BIT
MORE ECMWF VIEW TO THINGS...WHICH KEEPS A BIT STRONGER BACK DOOR
COOLING PUSH ON SATURDAY...THEN A STRONGER SOUTHERLY FLOW/WARMING ON
SUNDAY. FOR NOW...HAVE NOT STRAYED TOO FAR FROM INITIALIZATION
VALUES...OTHER THAN TO HEDGE A BIT WARMER IN THE SOUTH CENTRAL ON
SUNDAY. ANY SHIFT TOWARD THE GFS SOLUTION OF A FLATTER QUICKER RIDGE
WOULD RESULT IN A MUCH WARMER WEEKEND...WITH A HIGHER FIRE DANGER.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 542 AM CDT MON MAR 30 2015

VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD...WITH GUSTY LATE
MORNING/AFTERNOON WINDS THE PRIMARY AVIATION CONCERN. DEEP MIXING
WILL LEAD TO INCREASING WESTERLY WINDS AFTER 15Z-16Z...WITH GUSTS
AT OR ABOVE 25KT LIKELY THROUGH 00Z. WINDS WILL QUICKLY SUBSIDE
TOWARD SUNSET WITH LIGHT NORTHWEST WINDS EXPECTED OVERNIGHT.

&&

.FIRE WEATHER...
ISSUED AT 412 AM CDT MON MAR 30 2015

DEEP MIXING IN A DRY ATMOSPHERE ANTICIPATED THIS
AFTERNOON...WHICH WILL RESULT IN WARM TEMPERATURES...COLLAPSING
DEW POINTS...AND GUSTY WEST TO NORTHWEST WINDS. WINDS WILL AVERAGE
20 TO 30 MPH WITH GUSTS TO 35 MPH AT TIMES. WITH THE VERY DRY AIR
MIXING TO THE SURFACE... LOWEST HUMIDITY LEVELS WILL BE IN THE 15
TO 25 PERCENT RANGE FOR A GOOD PORTION OF THE AFTERNOON. THEREFORE
A RED FLAG WARNING HAS BEEN ISSUED FROM NOON TO 8 PM. CONDITIONS
WILL RAPIDLY IMPROVED BY SUNSET AS MIXING COMES TO A HALT.

IT WILL CONTINUE TO BE A WEEK OF CONCERN AT TIMES...AS PERIODS OF
ENHANCED MIXING ARE LIKELY DRIVING AFTERNOON HUMIDITY TO LOW LEVELS
AND WINDS TO STRONGER LEVELS. DESPITE A CONTINUATION OF DRY AIR...
TUESDAY WOULD APPEAR TO BE THE ONE DAY IN THE SHORTER TERM OF
SOMEWHAT LOWER CONCERN WITH MARKEDLY LESSER WINDS...STRONGEST AT 10
TO 20 MPH IN RETURN FLOW BACK ACROSS THE SOUTH CENTRAL. MIXING IN
THESE DRIER LOWER BRULE AREAS WOULD YIELD SOME 15 TO 25 PERCENT
LOWEST AFTERNOON RELATIVE HUMIDITY AND A VERY HIGH FIRE DANGER.
SOME NEAR 25 PERCENT VALUES BE LIKELY IN THE EAST WITH TRAJECTORY
OUT OF EXITING SURFACE RIDGE...BUT MUCH LIGHTER WINDS KEEPING FIRE
DANGER AT HIGH LEVELS.

ON WEDNESDAY...ANOTHER STRONG FRONTAL BOUNDARY WILL PUSH ACROSS THE
AREA. EAST OF I 29 WILL SEE AN INCREASE IN MOISTURE AND HUMIDITY
GENERALLY 35 TO 45 PERCENT. DESPITE SOME VERY STRONG PREFRONTAL
SOUTHERLY FLOW WHICH MAY GUST TO AROUND 45 MPH ACROSS PARTS OF SW MN
AND NW IA DURING THE LATE NIGHT/EARLY MORNING...HIGHER HUMIDITY WILL
RESTRICT FIRE DANGER TO VERY HIGH...PRIOR TO RAINFALL POTENTIAL
THROUGH THE AFTERNOON AND EVENING. SOME EXTREME FIRE DANGER IS
POSSIBLE DURING THE AFTERNOON WEST OF I 29 BEHIND FRONT...WHERE
HUMIDITY WILL DROP TO 20 TO 30 PERCENT...AND NORTHWEST WINDS BECOME
GUSTY.

THURSDAY IS A CLASSIC MIXING DAY ONCE AGAIN ALONG SOUTHERN FLANK OF
THE UPPER LEVEL WAVE. GENERALLY LOOKING AT 20 TO 30 PERCENT RH...
POTENTIALLY A BIT LOWER THROUGH THE MISSOURI VALLEY WHERE WILL HAVE
LONGER AHEAD OF SECONDARY COOL PUSH. WITH 25 TO 35 KNOTS OF WIND IN
THE MIXED LAYER...WILL AT LEAST END UP WITH ANOTHER DAY OF VERY HIGH
FIRE DANGER.

DIFFERENCES IN THE MODEL SOLUTIONS HAVE A TREMENDOUS IMPACT ON
THE FIRE DANGER OVER THE WEEKEND...ESPECIALLY SATURDAY. IF MORE OF
A BACK DOOR PUSH OCCURS ON FRIDAY NIGHT AND EARLY SATURDAY...THEN
WINDS WILL BE DOWN AND HUMIDITY HIGHER...WHICH WILL LIKELY KEEP
FIRE DANGER FROM REACHING VERY HIGH CATEGORY. BY SUNDAY...WHILE
GFS IS FAR MORE AGGRESSIVE IN THE ZONAL RIDGING...RIDGE DOES BUILD
IN ALL SOLUTIONS WITH STRENGTHENING SOUTHERLY FLOW. HUMIDITY WOULD
LIKELY BE QUITE LOW ACROSS AT LEAST AREAS WEST OF THE JAMES
VALLEY.

&&

.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
LONG TERM...CHAPMAN
AVIATION...JH
FIRE WEATHER...JH/CHAPMAN


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