Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 271742
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1242 PM CDT SAT JUN 27 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 340 AM CDT SAT JUN 27 2015

EXPECT QUIET WEATHER TO PREVAIL THROUGH THE DAYTIME HOURS TODAY...
GENERALLY A PLEASANT SUMMER DAY WITH WEST-SOUTHWEST WINDS AT OR
BELOW 10 MPH AND A FAIR AMOUNT OF SUNSHINE. THE LOW LEVEL FLOW
FAVORS GOOD MIXING...WHICH SHOULD AID IN WARMING TEMPERATURES INTO
THE 80S...WARMEST ALONG/WEST OF THE JAMES RIVER VALLEY. THE MIXING
SHOULD ALSO ALLOW FOR COMFORTABLE HUMIDITY LEVELS THIS AFTERNOON AS
DEW POINTS MIX BACK DOWN INTO THE MID-UPPER 50S. RAP/HRRR SUGGEST
DEW POINTS COULD MIX EVEN LOWER...WITH TEMPERATURES LIKEWISE MIXING
A FEW DEGREES HIGHER...SO THIS WILL HAVE TO BE MONITORED THROUGH THE
DAY. SOME HI-RES MODELS ALSO DEVELOPING SPOTTY AFTERNOON CONVECTION
ACROSS MAINLY EASTERN PORTIONS OF THE CWA TODAY. NOT AS CONFIDENT IN
THIS DEVELOPMENT AS YESTERDAY GIVEN SUBTLE RIDGING ALOFT AHEAD OF
STRONGER WAVE MOVING INTO THE AREA TONIGHT. LOW LEVEL WARM ADVECTION
AHEAD OF THE WAVE COULD PROVIDE NEEDED LIFT...SO CANNOT COMPLETELY
RULE OUT SOME ISOLATED INSTABILITY SHOWERS/STORMS AS SEEN IN THE
MODEL OUTPUT...BUT WITH AFOREMENTIONED UNCERTAINTY...OPTED TO
LEAVE OUT FOR NOW.

GREATER FOCUS FOR PRECIPITATION THREAT LIES ON THE WAVE SLIDING
SOUTHEAST THROUGH THE NORTHERN PLAINS TONIGHT. TIMING OF THE WAVE
APPEARS PRETTY SIMILAR AMONG THE MODELS...BRINGING MAIN THREAT OF
STORMS INTO NORTHERN PARTS OF OUR FORECAST AREA TOWARD SUNSET...
THEN TRACKING SOUTH-SOUTHEAST THROUGH THE REGION OVERNIGHT...
MAINLY EAST OF DE SMET-SIOUX FALLS-CHEROKEE LINE. MARGINAL SEVERE
RISK OUTLINED BY SPC SEEMS REASONABLE GIVEN OVERNIGHT TIMING
RESULTING IN OVERALL LOWER INSTABILITY. EFFECTIVE SHEAR OF 30-40KT
COULD STILL SUPPORT HAIL TO QUARTER/HALF-DOLLAR SIZE IN STRONGEST
STORMS THROUGH 06Z...EVEN WITH RELATIVELY NARROW CAPE PROFILES.
ISOLATED SEVERE GUSTS ALSO POSSIBLE GIVEN INVERTED-V LOOK TO
SOUNDINGS ABOVE THE SHALLOW SURFACE BASED INVERSION WHICH DEVELOPS
WITH LOSS OF HEATING. EXPECT LIMITED SEVERE THREAT TO DIMINISH
FURTHER THROUGH THE OVERNIGHT HOURS...WITH MOST ACTIVITY EXITING
THE FORECAST AREA PRIOR TO 12Z SUNDAY.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 340 AM CDT SAT JUN 27 2015

A FEW CHANGES MADE TO THE MEDIUM RANGE FORECAST THIS MORNING.
OVERALL LONGWAVE PATTERN REMAINS MUCH THE SAME AS PREVIOUSLY
DISCUSSED...HOWEVER MODELS ARE BEGINNING TO CONVERGE ON A SOLUTION
THAT WOULD PRODUCE A BIT MORE RAIN OVER THE AREA TUESDAY NIGHT INTO
WEDNESDAY.

THE START OF MEDIUM RANGE CONTINUES TO LOOK DRY AS SHORTWAVE ENERGY
EXITS SOUTHEAST EARLY SUNDAY MORNING. DESPITE THE BREEZY NORTHERLY
WINDS...SUNDAY SHOULD BE A VERY NICE EARLY SUMMER DAY.  BY
MONDAY...SHARP NWLY FLOW ALOFT WILL PREVAIL. SOME INDICATIONS OF A
WEAK WAVE MOVING THROUGH MONDAY AFTERNOON THAT COULD SPARK AN
ISOLATED SHOWER/STORM OVER THE MINNESOTA/IOWA COUNTIES. AS FAR AS
TEMPERATURES ARE CONCERNED...QUITE THE ARRAY OF READINGS.  GFS SEEMS
UNCHARACTERISTICALLY WARM AS COMPARED TO THE MUCH COOLER ECMWF.  NAM
SEEMS LIKE A GOOD COMPROMISE AS MIXING SHOULD PROMOTE READINGS
APPROACHING THE 90S WEST OF THE JAMES RIVER.

CLOUDS WILL BEGIN TO THICKEN ON TUESDAY AS RETURN FLOW AMPLIFIES.
GFS/ECMWF SUGGESTING THAT A BROAD NW TO SE ALIGNED BAROCLINIC ZONE
WILL BECOME ESTABLISHED BY LATE TUESDAY AND EARLY WEDNESDAY. A
SLIGHTLY STRONGER SHORTWAVE MAY TRAVEL ALONG THIS ZONE...WITH THE
NOCTURNAL LLJ DEVELOPING SHOWERS/THUNDERSTORMS ALONG THIS BOUNDARY.
GFS REMAINS ABOUT 6 HRS FASTER THAN THE ECMWF WHICH WOULD LINGER
PRECIP WELL INTO WEDNESDAY.  THE GEM...WHICH ACTUALLY CAPTURED THIS
IDEA BEFORE THE OTHER SOLNS...HAS SHIFTED THIS WAVE FURTHER SW
OVERNIGHT...A TREND THAT MAY BE POSSIBLE.  REGARDLESS...HAVE BUMPED
UP POPS TUESDAY NIGHT INTO WEDNESDAY BY 10 TO 20% ON AVERAGE.

HAVE DEVIATED A BIT FROM BLENDED MODEL SOLNS FOR WEDNESDAY NIGHT
INTO THURSDAY AS SFC HIGH PRESSURE SLIDES INTO THE WESTERN GREAT
LAKES AND SHOULD DRY OUT AND COOL OFF THE AREA TEMPORARILY.

THIS DRY SPELL WILL BE BRIEF AS ANOTHER WAVE ENTERS THE PLAINS FOR
THURSDAY AND FRIDAY BRINGING INCREASING RAIN CHANCES. OUTSIDE OF
MONDAY/TUESDAY HARD TO SEE CLIMB TO MUCH ABOVE NORMAL GIVEN LONG-
WAVE SETUP. THAT SAID...FAIRLY SUBSTANTIAL ENSEMBLE ANOMALIES
BEGIN TO APPEAR BY THE HOLIDAY WEEKEND LOWERING OVERALL FORECAST
CONFIDENCE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1242 PM CDT SAT JUN 27 2015

VFR IS ANTICIPATED THROUGH THE TAF PERIOD. HOWEVER ONE THING TO
WATCH FOR IS THE NAM IS AGGRESSIVE IN BRINGING MVFR CEILINGS INTO
OUR FAR NORTHEAST ZONES LATE TONIGHT AND EARLY SUNDAY MORNING IN
AN AREA PRIMARILY FROM MARSHALL MN TO WINDOM MN. THIS IS PLAUSIBLE
BEHIND THE SHORT WAVE PASSAGE TONIGHT. BUT THE TAFS SHOULD STAY
VFR. CONCERNING PRECIPITATION CHANCES...WILL KEEP AN EYE ON ANY
ISOLATED SHOWER OR TSRA DEVELOPMENT UNDER THE CUMULUS FIELD THIS
AFTERNOON. THE ACTIVITY WILL NOT BE AS PREVALENT AS YESTERDAY
HOWEVER. THEN AS BRIEFLY MENTIONED ABOVE...A SHORT WAVE WILL DIVE
DOWN THE NORTHWEST FLOW ALOFT TONIGHT. CURRENT TRACK OF THE WAVE
WILL GIVE OUR EASTERN ZONES A CHANCE FOR SHOWERS AND THUNDERSTORMS
BETWEEN 03Z AND 12Z SUNDAY. IT APPEARS AS ONLY KFSD HAS A CHANCE
FOR THUNDERSTORMS IN THIS FORECAST AREA SO INCLUDED THE MENTION OF
THAT IN THE TAF SITE WITH THE TIMING IN THE OVERNIGHT HOURS.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...JH
LONG TERM...DUX
AVIATION...MJ



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