National Weather Service Weather Forecast Office

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

000
FXUS63 KFSD 131835
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
111 PM CDT MON MAY 13 2013

.UPDATE...
ISSUED AT 1023 AM CDT MON MAY 13 2013

IN GENERAL EARLIER FORECAST IS BEHAVING FAIRLY WELL WITH A LITTLE
SLOWER DECREASE IN THE HIGH CLOUD COVER. STILL EXPECT WITH THE
CLOUDS THINNING OUT BY AFTERNOON THAT THE HEATING AND WARMING WILL
PUT TEMPERATURES CLOSE TO FORECAST HIGHS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 347 AM CDT MON MAY 13 2013

OBVIOUSLY THE MAIN CONCERN TODAY IS FIRE WEATHER. TEMPERATURES WILL
BE WELL ABOVE SEASONAL NORMALS AS A SURFACE TROUGH OF LOW PRESSURE
MOVES EASTWARD ACROSS OUR FORECAST AREA. THIS SURFACE TROUGH WILL
CAUSE A WIND SHIFT FROM THE SOUTHWEST TO NORTHWEST BEFORE IT STALLS
OUT LATE IN THE DAY IN NORTHWEST IOWA. GIVEN THE WINDS OFF THE
SURFACE AND MIXING POTENTIAL...OUR ZONES IN IOWA AROUND THE IOWA
GREAT LAKES AND STORM LAKE AREAS...AS WELL AS SOME OF THE SOUTHERN
SECTIONS IN SOUTHWEST MINNESOTA...WILL PUSH RED FLAG CRITERIA BUT
PROBABLY ONLY FOR A COUPLE OF HOURS. THIS IS BECAUSE BETWEEN 21Z AND
00Z...THE WINDS SHOULD DECREASE A FAIR AMOUNT IN THE AXIS OF THE
SURFACE TROUGH WHICH IS RIGHT IN THOSE AREAS. THEREFORE IT WILL BE A
BREEZY TO MODERATELY WINDY DAY IN THOSE AREAS...GOOD FOR A VERY HIGH
FIRE DANGER...BUT POSSIBLY JUST NOT QUITE THERE FOR A BONAFIDE RED
FLAG WARNING. THE SAME HOLDS TRUE FOR BEHIND THE SURFACE TROUGH...
WHICH IS ALONG AND WEST OF THE JAMES RIVER VALLEY. MINIMUM HUMIDITY
VALUES WILL LIKELY REALLY TANK IN THOSE ZONES TO LESS THAN 20
PERCENT. HOWEVER IN OUR WESTERN ZONES THIS AFTERNOON...SUSTAINED
NORTHWEST SURFACE WINDS WILL LIKELY STAY LESS THEN 20 MPH MUCH OF
THE TIME...WITH GUSTS FREQUENTLY AROUND 25 TO 27 MPH. SO AGAIN...
JUST A BIT BELOW RED FLAG CRITERIA...BUT CERTAINLY ELEVATED FIRE
DANGER. THE ONE THING THAT COULD REALLY ALTER THIS SCENARIO
SIGNIFICANTLY IS IF THE MIXED LAYER WINDS WHICH ARE FORECAST TO BE
AROUND 25 KNOTS IN OUR FORECAST AREA...BECOME STRONGER THEN
ANTICIPATED. IF THAT HAPPENS...WE COULD GO RED FLAG OVER MANY AREAS.
CONCERNING HUMIDITY...MUCH OF THE MODEL DEW POINT GUIDANCE IS WAY
TOO HIGH. PRIMARILY BLENDED THE REALLY DRY RAP MODEL DEW POINTS INTO
CONSENSUS SHORT. THIS SEEMED TO GIVE REASONABLE VALUES...AS IT SEEMS
THAT EACH DAY WE CANNOT GO LOW ENOUGH ON THE DEW POINTS...AND THUS
THE HUMIDITY VALUES. RIGHT NOW...DEW POINTS ARE IN THE 30S WEST
RIVER...AND LOWER TO MID 40S IN SOUTH CENTRAL NEBRASKA. THEREFORE
LOOKING AT TRAJECTORIES EITHER FOR A SOUTHWEST WIND OR NORTHWEST
WIND...MADE SURE NOT TO GO ABOVE THOSE VALUES UPSTREAM.
OBVIOUSLY THE MAIN CONCERN TODAY IS FIRE WEATHER. TEMPERATURES WILL
BE WELL ABOVE SEASONAL NORMALS AS A SURFACE TROUGH OF LOW PRESSURE
MOVES EASTWARD ACROSS OUR FORECAST AREA. THIS SURFACE TROUGH WILL
CAUSE A WIND SHIFT FROM THE SOUTHWEST TO NORTHWEST BEFORE IT STALLS
OUT LATE IN THE DAY IN NORTHWEST IOWA. GIVEN THE WINDS OFF THE
SURFACE AND MIXING POTENTIAL...OUR ZONES IN IOWA AROUND THE IOWA
GREAT LAKES AND STORM LAKE AREAS...AS WELL AS SOME OF THE SOUTHERN
SECTIONS IN SOUTHWEST MINNESOTA...WILL PUSH RED FLAG CRITERIA BUT
PROBABLY ONLY FOR A COUPLE OF HOURS. THIS IS BECAUSE BETWEEN 21Z AND
00Z...THE WINDS SHOULD DECREASE A FAIR AMOUNT IN THE AXIS OF THE
SURFACE TROUGH WHICH IS RIGHT IN THOSE AREAS. THEREFORE IT WILL BE A
BREEZY TO MODERATELY WINDY DAY IN THOSE AREAS...GOOD FOR A VERY HIGH
FIRE DANGER...BUT POSSIBLY JUST NOT QUITE THERE FOR A BONAFIDE RED
FLAG WARNING. THE SAME HOLDS TRUE FOR BEHIND THE SURFACE TROUGH...
WHICH IS ALONG AND WEST OF THE JAMES RIVER VALLEY. MINIMUM HUMIDITY
VALUES WILL LIKELY REALLY TANK IN THOSE ZONES TO LESS THAN 20
PERCENT. HOWEVER IN OUR WESTERN ZONES THIS AFTERNOON...SUSTAINED
NORTHWEST SURFACE WINDS WILL LIKELY STAY LESS THEN 20 MPH MUCH OF
THE TIME...WITH GUSTS FREQUENTLY AROUND 25 TO 27 MPH. SO AGAIN...
JUST A BIT BELOW RED FLAG CRITERIA...BUT CERTAINLY ELEVATED FIRE
DANGER. THE ONE THING THAT COULD REALLY ALTER THIS SCENARIO
SIGNIFICANTLY IS IF THE MIXED LAYER WINDS WHICH ARE FORECAST TO BE
AROUND 25 KNOTS IN OUR FORECAST AREA...BECOME STRONGER THEN
ANTICIPATED. IF THAT HAPPENS...WE COULD GO RED FLAG OVER MANY AREAS.
CONCERNING HUMIDITY...MUCH OF THE MODEL DEW POINT GUIDANCE IS WAY
TOO HIGH. PRIMARILY BLENDED THE REALLY DRY RAP MODEL DEW POINTS INTO
CONSENSUS SHORT. THIS SEEMED TO GIVE REASONABLE VALUES...AS IT SEEMS
THAT EACH DAY WE CANNOT GO LOW ENOUGH ON THE DEW POINTS...AND THUS
THE HUMIDITY VALUES. RIGHT NOW...DEW POINTS ARE IN THE 30S WEST
RIVER...AND LOWER TO MID 40S IN SOUTH CENTRAL NEBRASKA. THEREFORE
LOOKING AT TRAJECTORIES EITHER FOR A SOUTHWEST WIND OR NORTHWEST
WIND...MADE SURE NOT TO GO ABOVE THOSE VALUES UPSTREAM.

WINDS WILL TAPER DOWN THIS EVENING AND TURN SOUTHERLY OVERNIGHT.
WITH THERMAL PROFILES CONTINUING TO WARM...IT WILL BE A MILD NIGHT
WITH LOWS IN THE MID 50S TO LOWER 60S.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 347 AM CDT MON MAY 13 2013

A STRONG SOUTHERLY FLOW SETS UP ON TUESDAY OUT AHEAD OF A SURFACE
TROUGH/FRONTAL BOUNDARY WHICH WILL PUSH ACROSS THE AREA IN THE
AFTERNOON. MOISTURE LOOKS TO BE MINIMAL WITH THIS SYSTEM...SO
EXPECTING IT TO BE A DRY FRONTAL PASSAGE. IT WILL BE A VERY MIXY DAY
WITH STRONG SOUTHWESTERLY WINDS OUT AHEAD OF THE FRONT...AND STRONG
NORTHWESTERLY WINDS BEHIND THE FRONT. MODELS AGAIN SEEM TO BE
OVERDOING DEWPOINTS ON TUESDAY...MOST LIKELY OVER DOING
EVAPOTRANSPIRATION...AND PROGGING DEWPOINTS WELL INTO THE 50S.
INSTEAD USED THE MIXDOWN TOOL WHICH YIELDED A BETTER ESTIMATION OF
DEWPOINTS...GENERALLY IN THE 40S...WITH SOME MOISTURE POOLING ALONG
THE FRONTAL BOUNDARY...THOUGH STILL MAY BE SLIGHTLY TOO HIGH ON
VALUES. IN ANY EVENT...WITH THE STRONG WINDS AND AFTERNOON RELATIVE
HUMIDITY VALUES FLOATING AROUND 20 TO 25 PERCENT...ISSUED A FIRE
WEATHER WATCH FOR THE ENTIRE CWA. AS HAS BEEN ADVERTISED OF
LATE...TUESDAY WILL GENERALLY BE THE WARMEST DAY OF THE WEEK WITH
ALL MODELS PROGGING 850 MB TEMPERATURES IN THE LOWER TO MID 20S C
OVER OUR EAST IN THE AFTERNOON...SO KEPT WITH LOWER TO MID 90S
THERE. WITH COLD AIR ADVECTION BEHIND THE FRONT...IT WILL BE LITTLE
COOLER TO THE WEST...WITH HIGHS IN THE MID AND UPPER 80S.

COOLER AIR WILL FILTER INTO THE REGION ON TUESDAY NIGHT WITH WINDS
DYING OFF OVERNIGHT. LOWS LOOKING TO BE IN THE UPPER 40S TO MID 50S.
WEDNESDAY AND WEDNESDAY NIGHT APPEAR TO BE PLEASANT WITH WEAK HIGH
PRESSURE BUILDING INTO THE REGION...WITH HIGHS IN THE 70S AND LOWS
IN THE 50S.

FARTHER INTO THE EXTENDED...THURSDAY THROUGH SUNDAY...LOOKS TO BE A
FAIRLY ACTIVE PERIOD WITH A NEARLY ZONAL UPPER LEVEL FLOW AT THE
START OF THE PERIOD...TRANSITIONING TO RIDGING ON FRIDAY AS A TROUGH
BEGINS TO LIFT OUT OF THE WESTERN U.S. AND INTO THE AREA BY LATE IN
THE WEEKEND. THINK MOST OF THURSDAY WILL BE DRY AND LITTLE WARMER AS
A SOUTHERLY FLOW BEGINS TO RETURN TO THE REGION WITH HIGHS IN THE
MID AND UPPER 70S. CANNOT RULE OUT SCATTERED THUNDERSTORMS FOR
THURSDAY NIGHT AND FRIDAY WITH INCREASING THETA E ADVECTION INTO THE
REGION...THOUGH WOULD BE HARD TO PIN POINT EXACT TIMING ON ANY
CONVECTIVE DEVELOPMENT THIS FAR OUT. A BETTER CHANCE OF CONVECTION
WOULD APPEAR TO BE LIKELY ON FRIDAY NIGHT AS LOW PRESSURE BEGINS TO
LIFT OUT OF THE ROCKIES. WITH CONVECTIVE PARAMETERS INCREASING
DURING THAT TIME FRAME...SEVERE STORMS WOULD SEEM MORE
LIKELY...THOUGH MODELS ARE DIFFERING A BIT ON THE PLACEMENT OF A
BOUNDARY LAYING SOMEWHERE CLOSE TO OUR AREA ON FRIDAY NIGHT AND
SATURDAY. THE UPPER LEVEL TROUGH SWINGS THROUGH THE REGION ON
SUNDAY...KEEPING A CHANCE OF CONVECTION...WITH COOLER AIR BEGINNING
TO PULL IN BEHIND THE SYSTEM.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 108 PM CDT MON MAY 13 2013

VFR EXPECTED TO CONTINUE THROUGH 14/18Z EVEN AS COLD FRONT ENTERS
THE NORTHWEST CORNER OF THE AREA INCLUDING HON BY 14/18Z. SURFACE
GUSTS TO 25 TO 30 KNOTS FROM THE WEST TO SOUTHWEST IN SOUTHWEST MN
AND NORTHWEST IA WILL DECREASE BY 23Z BUT MAY REDEVELOP AFTER
14/15Z OVER THE AREA. WINDS WILL SHIFT TO THE NORTHWEST OVER THE
NORTHWEST CORNER OF THE AREA INCLUDING HON NEAR END OF PERIOD BY
14/18Z.

&&

.FIRE WEATHER...
ISSUED AT 1023 AM CDT MON MAY 13 2013

FIRE WEATHER WAS DISCUSSED EXTENSIVELY IN BOTH SHORT AND LONG TERM
SECTIONS EARLIER. MAIN PROBLEM WITH WINDS COMING UP A LITTLE
FASTER THAN EXPECTED IN OUR EAST IS A POSSIBLE NEED FOR A RED FLAG
WARNING FOR THIS AFTERNOON IN OUR EAST...EVEN THOUGH DEW POINTS
ARE COMING UP ABOUT AS WE HAD. WILL TRY TO ISSUE BY THE START OF
THE AFTERNOON IF WE DECIDE ONE IS NEEDED. OF COURSE WILL ALSO BE
CHECKING ON A POSSIBLE UPGRADE OF TUESDAY WATCH TO A WARNING.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...FIRE WEATHER WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY
     EVENING FOR SDZ255>258.

MN...FIRE WEATHER WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY
     EVENING FOR MNZ900.

     RED FLAG WARNING UNTIL 6 PM CDT THIS EVENING FOR MNZ900.

IA...FIRE WEATHER WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY
     EVENING FOR IAZ300-301.

     RED FLAG WARNING UNTIL 6 PM CDT THIS EVENING FOR IAZ301.

NE...FIRE WEATHER WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY
     EVENING FOR NEZ249.

&&

$$

UPDATE...
SHORT TERM...MJF/JM
LONG TERM...JM
AVIATION...
FIRE WEATHER...