Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 231752
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1152 AM CST MON FEB 23 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 349 AM CST MON FEB 23 2015

THE DUTY OF THE DAY FOR THE LOCAL ATMOSPHERE WILL BE TO SHAKE OFF
THE EARLY DAY CHILL RESULTING FROM LIGHTER WINDS AND CLEAR SKIES. BY
EARLY DAY...SURFACE RIDGE AXIS ALREADY WILL HAVE SETTLED SOUTH OF
THE CWA...AND WILL UNDERGO AN INCREASE IN THE GRADIENT AND SOUTHWEST
WINDS ACROSS THE REGION THROUGH THE DAY. COMBINATION OF WINDS OF 5
TO 8 MPH AND EARLY DAY COLD TEMPS ACROSS PARTS OF SW MN WILL LEAD TO
A COUPLE HOURS OF -20 TO -25 WIND CHILL READINGS...BUT AT THIS TIME
HAVE NO PLAN TO RAISE A WIND CHILL ADVISORY WITH THESE FAIRLY LIGHT
WINDS. THIS INITIAL AIR MASS IS COLD AND DENSE...AND GROUND HAS HAD
TIME TO CHILL DOWN A BIT MORE OVER PREVIOUS WARMING DAYS...AND
CHALLENGE IS HOW MUCH OF THE WARMING POTENTIAL WILL BE REALIZED.
SUNSHINE WILL BE QUITE PREVALENT AS JUST A FEW EARLY DAY HIGH CLOUDS
BRUSH BY TO THE SOUTH WITHIN UPPER LEVEL CONFLUENCE...WITH A MORE
NOTABLE INCREASE IN HIGH CLOUDS FROM NORTHERN STREAM WAVE DURING THE
AFTERNOON AND EVENING. OFTEN THERE IS A COLD BIAS TO BOUNDARY LAYER
ON THESE STRONG WARM ADVECTION DAYS WITHOUT SNOW COVER...SO HAVE
HEDGED JUST A BIT MORE TOWARD ECMWF BASED DATA WHICH HAS A BETTER
TRACK RECORD ON THIS REGIME.

MOST SIGNIFICANT FEATURE OF THE SHORT TERM WILL PROBABLY TILT TOWARD
THE STRONG WINDS. STRONGEST GRADIENT IN PLACE DURING THE UPCOMING
NIGHT...AND WOULD NOT BE SURPRISED TO LOCALLY MEET WIND ADVISORY
CRITERIA NEAR AND DOWNSTREAM OF THE BUFFALO RIDGE DURING THE
OVERNIGHT PERIOD...ESPECIALLY LATER EVENING THROUGH EARLY OVERNIGHT.
WITH INVERSION STRENGTH A BIT WEAKER AND SPREAD OUT OVER A GREATER
DEPTH...CAN LIKELY AVOID THE STRONGEST POTENTIAL WIND GUSTS OVER 50
MPH...BUT SOME TO AROUND 45 MPH CAN BE EXPECTED IN THE USUAL
LOCATIONS. WILL LIKELY HAVE AN UNEVEN NON DIURNAL TREND TO TEMPS
ACROSS THE AREA...WITH SOME LOCATIONS EAST NO DOUBT REACHING THE
WARMEST TEMPS DURING THE NIGHT...ESPECIALLY ELEVATED LOCATIONS.
PASSAGE OF PREFRONTAL TROUGH LATER IN THE NIGHT WILL COMMENCE A
TOUCH OF COOLING ALOFT WHICH SHOULD FURTHER ENHANCE MIXING OF THE
WEST TO NORTHWEST COMPONENT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 349 AM CST MON FEB 23 2015

BREEZY NORTHWEST WINDS BEHIND THE EXITING FRONT WILL KEEP CONDITIONS
MIXY THROUGH THE DAY ON TUESDAY. WITH A DELAY IN THE COLD AIR
ADVECTION...TEMPERATURES WILL BEGIN THE DAY MILD AND PEAK IN THE
UPPER 20S TO LOWER 40S - WARMEST NEAR THE MISSOURI VALLEY. COULD SEE
A FEW FLURRIES DEVELOP ACROSS SOUTHWEST MINNESOTA MAINLY IN THE
MORNING.

THE MAIN FORECAST CONCERN IN THE EXTENDED HOWEVER ARRIVES ON TUESDAY
EVENING AS A FRONTAL BAND SETS UP ACROSS THE REGION WHILE A MID
LEVEL WAVE DROPS ALONG THE NORTHWEST FLOW. MODELS SEEM TO BE COMING
INTO BETTER AGREEMENT...WITH ONLY SLIGHT DIFFERENCES IN PLACEMENT.
OF COURSE...SHIFTS IN THE FRONTAL BAND WILL GREATLY IMPACT SNOWFALL
AMOUNTS. THE NAM AND GFS ARE FURTHER WEST THAN THE ECMWF AND
GEM...BUT THE DIFFERENCES MINOR. FOLLOWED A MIDDLE ROAD SOLUTION
WHICH PLACES THE BULK OF THE BAND NEAR THE JAMES RIVER VALLEY IN
SOUTH CENTRAL SD AND SOUTHEAST ALONG THE MISSOURI INTO NORTHWEST
IOWA. WITH COLDER AIR ADVECTING INTO THE AREA AND A DEEPENING
DENDRITIC GROWTH ZONE...SNOW RATIOS INCREASE LATE TUESDAY NIGHT
NIGHT AND WEDNESDAY POSSIBLY TOPPING 14:1. EXPECT AROUND 1 TO 3
INCHES OF SNOW ALONG AND SOUTH OF A HURON TO SIOUX FALLS TO STORM
LAKE LINE WITH THE HEAVIEST AMOUNTS NEAR THE MISSOURI RIVER. THE
NORTHEASTERN HALF OF THE FORECAST AREA...PARTICULARLY ACROSS
SOUTHWEST MINNESOTA WILL BE CONTENDING WITH DRY AIR ISSUES AS THE
WAVE DROPS THROUGH THE REGION...SO THINK THAT ACCUMULATIONS WILL BE
MINIMAL HERE.

THE SYSTEM EXITS THE AREA WEDNESDAY AFTERNOON...WITH COOL
TEMPERATURES ONCE AGAIN SETTLING IN FOR THE REMAINDER OF THE WEEK.
DRY NORTH TO NORTHWEST FLOW WILL KEEP THE WEATHER QUIET...BUT
TEMPERATURES WILL BE WELL BELOW NORMAL. LATE FRIDAY INTO SATURDAY
THE UPPER PATTERN TURNS WEST TO SOUTHWEST...WHICH SHOULD MODERATE
TEMPERATURES. THE GFS AND ECMWF SWING A DEEP UPPER LEVEL TROUGH INTO
THE FOUR CORNERS REGION AND FEED WARM AIR ADVECTION MOISTURE INTO
THE CENTRAL PLAINS. STILL QUITE A BIT OF UNCERTAINTY...BUT BOTH
MODELS BRING A GOOD CHANCE OF PRECIPITATION INTO OUR SOUTHERN HALF
SATURDAY AND SATURDAY NIGHT. HAVE CONTINUED WITH AN UPWARD TREND
ABOVE THE ALLBLEND - TO REACH HIGH END CHANCES DURING THIS PERIOD
FOR FAR SOUTHEAST SD INTO NORTHWEST IOWA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1139 AM CST MON FEB 23 2015

VFR CONDITIONS WILL DOMINATE THROUGH MUCH OF TONIGHT...WITH MVFR
CEILINGS EXPECTED TO FOLLOW A COLD FRONT PUSHING SOUTHWARD INTO
THE REGION AFTER 24/09Z. MOST CONFIDENT ABOUT MVFR CEILINGS AT
KHON. CONFIDENCE OF MVFR CONDITIONS AT KFSD A LITTLE LOWER...BUT
STILL LOOKS PROBABLE ENOUGH TO INCLUDE THERE.

GUSTY WINDS WILL ALSO BE AN AVIATION CONCERN...AS SOUTHWESTERLY
LOW LEVEL JET INCREASES TO 40-45KT ACROSS EASTERN PORTIONS OF THE
AREA THIS EVENING. THINK THE BOUNDARY LAYER WILL REMAIN MODESTLY
MIXED...PRODUCING GUSTS TO AROUND 25KTS THIS EVENING INTO THE
OVERNIGHT. THIS SHOULD INHIBIT DEVELOPMENT OF A SHARP SURFACE
BASED INVERSION...WHICH SHOULD LIMIT THE LOW LEVEL WIND SHEAR
EFFECTS.

&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...
AVIATION...JH



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