Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 091739
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1239 PM CDT WED APR 9 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 423 AM CDT WED APR 9 2014

WARM...BREEZY AND DRY CONDITIONS TODAY WITH SCATTERED SHOWERS AND
THUNDERSTORMS POSSIBLE TONIGHT. FIRST OFF DID NOT MAKE ANY CHANGES
TO THE RED FLAG WARNING TODAY. LOOKS VERY WARM WITH 925MB
TEMPERATURES CLIMBING INTO THE LOWER TO MID 20S WHICH SUPPORTS LOWER
80S IN MANY SPOTS WITH UPPER 70S IN THE FAR EASTERN CWA. MODELS
SOUNDINGS SHOW A PRETTY DEEP MIXED LAYER SO SUSPECT A FEW HOURS THIS
AFTERNOON WHERE THE COMBINATION OF LOW DEW POINTS AND HIGH
TEMPERATURES WILL LEAD TOWARDS RELATIVE HUMIDITY VALUES IN THE 15 TO
25 PERCENT.

AS FOR THE THUNDERSTORM THREAT NOT ANTICIPATING ANYTHING CLOSE TO
SEVERE AS THE ELEVATED CAPE VALUES ONLY ABOUT 200 TO 500 J/KG AND
LIFTED INDICES ONLY ABOUT -2 OR SO. BUT ENOUGH FORCING AND
INSTABILITY TO SUPPORT A THREAT FOR SCATTERED SHOWERS AND
THUNDERSTORMS. FAIRLY STRONG WINDS WILL CONTINUE INTO THE EVENING AS
WINDS TURN TO THE NORTHWEST BEHIND DECENT COLD AIR ADVECTION.WITH A
DECENTLY MIXED ATMOSPHERE LOWS WILL REMAIN IN THE 40S.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 423 AM CDT WED APR 9 2014

A COOLER...BUT PARTLY TO MOSTLY SUNNY DAY...IS EXPECTED BEHIND THE
COLD FRONT FOR THURSDAY. ALTHOUGH GIVEN THE EXPECTED GOOD
MIXING...STAYED CLOSE TO THE WARMER BIAS CORRECTED GUIDANCE FOR
HIGHS...GENERALLY LOW TO MID 60S OVER THE AREA. WILL BE A BIT BREEZY
AS WELL...ESPECIALLY EAST OF THE JAMES RIVER...WITH SUSTAINED SPEEDS
OF 15 TO 25 MPH...BEGINNING TO WEAKEN LATE IN THE DAY AS HIGH
PRESSURE MOVES OVERHEAD AND THE GRADIENT WEAKENS. STILL SEEING A
WEAK WAVE MOVE ACROSS THURSDAY NIGHT. AS LIFT INCREASES AHEAD OF THIS
WAVE...MAY SEE A FEW SHOWERS. ALTHOUGH DOES NOT LOOK LIKE WE GET
MUCH IF ANY ELEVATED INSTABILITY...AND THERE IS QUITE A BIT OF LOW
LEVEL DRY AIR TO OVERCOME. NOT EXPECTING MUCH MORE THAN ISOLATED TO
SCATTERED SHOWERS...BUT THE WAVE IS STRONG ENOUGH TO WARRANT THE LOW
CHANCE POPS. ANOTHER MILD AND MOSTLY SUNNY DAY EXPECTED ON FRIDAY.
LOW LEVEL THERMAL PROFILES WARM A BIT FROM THURSDAY...AND WITH
EXCELLENT MIXING AGAIN EXPECTED...HIGHS SHOULD BE SEVERAL DEGREES
WARMER. DID NOT HAVE TO MAKE MUCH OF A CHANGE FROM THE PREVIOUS
FORECAST...WITH MID 60S TO LOW 70S LIKELY.

THE WEATHER BECOMES MORE ACTIVE FRIDAY NIGHT INTO THE WEEKEND.
SOUTHERLY FLOW INCREASES FRIDAY NIGHT AHEAD OF AN APPROACHING COLD
FRONT. BEST LARGE SCALE FORCING WILL STAY NORTH OF THE CWA ON FRIDAY
NIGHT...BUT WE WILL SEE STRONG THETA E ADVECTION AS WARM MOIST AIR
IS ADVECTED NORTH. THUS QUESTION BECOMES WHETHER WE SEE ENOUGH OF A
MOISTURE INCREASE TO TRIGGER ELEVATED SHOWERS AND THUNDERSTORMS
FRIDAY NIGHT. ECMWF HAS BEEN CONSISTENT IN SHOWING THIS...WHILE THE
GFS AND GEM KEEP THE QPF MORE TIED TO THE UPPER SUPPORT WITH THE DRY
AIR WINNING OUT FURTHER SOUTH. TOUGH CALL AT THIS POINT...SO WILL
JUST KEEP THE CHANCE POPS GOING. THE COLD FRONT WILL PUSH ACROSS ON
SATURDAY. COOLER AIR LAGS THE WIND SHIFT...SO EVEN WITH THE FRONT
THROUGH MOST OF THE CWA BY AFTERNOON...IT SHOULD STILL BE A WARM ONE.
THUS BUMPED HIGHS UP SOME...WITH UPPER 60S TO MID 70S EXPECTED.
STILL LOOKS LIKE WE SHOULD SEE SHOWER AND THUNDERSTORM DEVELOPMENT
ALONG AND JUST AHEAD OF THIS FRONT DURING THE AFTERNOON HOURS.
INSTABILITY AND SHEAR AHEAD OF THE FRONT DO APPEAR STRONG ENOUGH TO
SEE SOME STRONG TO SEVERE THUNDERSTORMS. SO WILL HAVE TO MONITOR
TRENDS IN TIMING OF THIS FRONTAL BOUNDARY THROUGH THE CWA. AT THIS
TIME MODEL CONSENSUS SUGGESTS MOST OF THIS ACTIVITY WILL BE SOUTH OF
THE CWA...WITH MAYBE SIOUX CITY TO SPENCER STAYING AHEAD OF THE
BOUNDARY LONG ENOUGH TO SEE STORM DEVELOPMENT.

MODEL CONSISTENCY HAS BEEN LACKING SATURDAY NIGHT INTO SUNDAY. THUS
WILL LEAVE CHANCE POPS FOR THESE PERIODS. THE INCONSISTENCY RESULTS
FROM HOW THE MODELS HANDLE A STRONGER WAVE DIVING SOUTHEAST INTO THE
PLAINS INTERACTING WITH THE FRONTAL BOUNDARY. LATEST 0Z GUIDANCE IS
MORE PROGRESSIVE AND FURTHER SOUTH WITH THIS SYSTEM. THIS RESULTS IN
MOST OF THE RAIN SATURDAY NIGHT INTO SUNDAY STAYING SOUTH OF
INTERSTATE 90...WITH THE HEAVIEST STAYING SOUTH OF THE CWA.
YESTERDAYS 12Z ECMWF WAS MUCH FURTHER NORTH...AND ACTUALLY
SUGGESTED THE NORTHWEST PORTION OF THE CWA COULD SEE SOME SNOW BY
SUNDAY. SO WHILE TRENDS SEEM TO SUGGEST THE FURTHER SOUTH SOLUTION
IS MORE LIKELY...WILL NEED TO CONTINUE TO MONITOR TRENDS. EITHER WAY
SUNDAY AND MONDAY WILL BOTH BE COOL...WITH HIGHS IN THE 40S AND A
BRISK NORTH TO NORTHWEST WIND...SO OVERALL NOT EXPECTED TO BE THE
BEST OF DAYS. MODEL SPREAD REMAINS HIGH ON TUESDAY. HIGH TEMPERATURE
DIFFERENCES OF AROUND 20 DEGREES EXISTS BETWEEN THE TWO MODELS...WITH
THE GFS BUILDING IN RIDGING...AND THE ECMWF SWINGING THROUGH ANOTHER
SHORTWAVE TROUGH. THUS FOR NOW WILL STAY CLOSE TO A MIDDLE GROUND
SOLUTION...WHICH GIVES HIGHS IN THE 40S AND 50S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1239 PM CDT WED APR 9 2014

VFR WILL CONTINUE THROUGH 10/18Z. THROUGH 10/00Z A FEW SURFACE
GUSTS FROM THE SOUTHWEST MAY APPROACH 25 KNOTS. 10/00Z-12Z
ISOLATED HIGH BASED SHOWERS AND THUNDERSTORMS MAY MOVE FROM NORTH
TO SOUTH OVER THE AREA BEHIND SOUTHWARD MOVING SURFACE COLD FRONT
WHICH WILL MOVE SOUTH OVER THE AREA 10/00Z-09Z. NORTHWEST SURFACE
WINDS WILL DEVELOP BEHIND COLD FRONT WITH GUSTS CURRENTLY EXPECTED
TO REMAIN BELOW 25 KNOTS.

&&

.FIRE WEATHER...

A COMBINATION OF VERY WARM CONDITIONS...SOUTHWEST WINDS OF 15 TO 30
MPH AND AFTERNOON RELATIVE HUMIDITIES OF 15 TO 20 PERCENT WILL LEAD
TO RED FLAG CONDITIONS. TEMPERATURES WILL QUICKLY INCREASE THIS
MORNING AS WILL SOUTHWEST WINDS. HUMIDITY VALUES WILL LIKELY REACH
CRITICAL VALUES BY NOON AND REMAIN VERY LOW THROUGH 700 PM CDT. A
COLD FRONT WILL APPROACH FROM THE NORTHWEST BUT NOT ENTER THE CWA
UNTIL AFTER SUNSET.

THURSDAY IS ANOTHER FIRE WEATHER DAY TO WATCH. POST FRONTAL
SURFACE WINDS WILL BE NORTHWESTERLY...AND IT PROMISES TO DISPLAY
ANOTHER HIGH DEGREE OF MIXING. SUSTAINED WINDS WILL BE AROUND 15 TO
25 MPH EAST OF THE JAMES RIVER...LIGHTER TO THE WEST. AFTERNOON
RELATIVE HUMIDITY VALUES WILL DROP INTO THE 20 TO 20 PERCENT RANGE.
HOWEVER BY THE TIME THE HUMIDITY DROPS THIS LOW...WINDS MAY BEGINS TO
SLACKEN AS HIGH PRESSURE MOVES IN AND THE GRADIENT BEGINS TO WEAKEN.
SO WHILE IT LOOKS LIKE IT MIGHT CLOSE TO RED FLAG CRITERIA...RIGHT
NOW IT APPEARS TO STAY JUST SHORT. BUT WILL NEED TO CONTINUE TO
MONITOR.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...RED FLAG WARNING UNTIL 7 PM CDT THIS EVENING FOR SDZ255>258.

MN...RED FLAG WARNING UNTIL 7 PM CDT THIS EVENING FOR MNZ900.

IA...RED FLAG WARNING UNTIL 7 PM CDT THIS EVENING FOR IAZ300-301.

NE...RED FLAG WARNING UNTIL 7 PM CDT THIS EVENING FOR NEZ249.

&&

$$

SHORT TERM...08
LONG TERM...CHENARD
AVIATION...
FIRE WEATHER...08






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