Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 241745
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1145 AM CST TUE FEB 24 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 348 AM CST TUE FEB 24 2015

STRONG TROUGH OBSERVED DIGGING TOWARD THE WESTERN GREAT LAKES EARLY
THIS MORNING...WITH PUSH OF MILDER AIR ACROSS THE AREA. PREFRONTAL
TROUGH ABOUT SPLITS THE CWA NORTHWEST AND SOUTHEAST...WITH MOST WELL
MIXED TO THE NORTHWEST. STRONGEST WINDS FOR THE TIME BEING HAVE
DIMINISHED IN LEE OF BUFFALO RIDGE AS FLOW DIRECTION HAS SHIFTED
MORE WESTERLY AND GRADIENT WEAKENED NEAR LOCATION OF THE INVERTED
TROUGH...BUT NOT BEFORE SOME LOCAL 45 TO 50 MPH WIND GUSTS DURING
THE EVENING HOURS. MAIN COLD FRONT WITH UPPER WAVE PUSHING SOUTHWARD
AT A FAIR CLIP ACROSS EASTERN NORTH DAKOTA.

SHORT RANGE MODELS COMING UP SHORT THIS MORNING WITH THE MIXING AND
WARMER AIR MASS ACROSS MUCH OF SD AND INTO SW MN EARLY THIS MORNING.
AS A RESULT...MOST SHORT RANGE MODELS...INCLUDING RAP/NAM/GFS SEEM
TO SHOW FAR TOO MUCH LOW LEVEL COOLING FAR TOO QUICKLY. IT WILL GET
THERE...JUST NOT QUITE SO FAST...AND IN REALITY...TEMPS IN THE CLOUD
BEARING LAYER WILL LIKELY NOT FALL INTO A REASONABLE ICE FAVORING
PROFILE UNTIL LATER MORNING OR EARLY AFTERNOON AT BEST...AND
PROBABLY NOT IN TOO LONG A WINDOW WHILE THE MOISTURE IS PRESENT.
ALSO HAVE QUITE A BIT OF FORCED SUBSIDENCE THROUGH THE MORNING AND
EARLY AFTERNOON PERIOD ON THE LARGER SCALE...WHICH REALLY DROPS ANY
CHANCE OF MEASURABLE PRECIPITATION TODAY BACK TO VERY SHALLOW AND
TERRAIN DRIVEN OFF THE GLACIAL HILLS. THUS...HAVE DECIDED TO REMOVE
MENTION OF ANY MEASURABLE SNOWFALL FOR THE DAYTIME PERIOD.  HAVE
MAINTAINED TEMPERATURES TOWARD THE WARM SIDE OF GUIDANCE GIVEN THE
SHORT TERM SHORTCOMINGS...AND THE MIXED ATMOSPHERE REGIME. WILL
EVENTUALLY SEE THE ARCTIC FRONT SURGE SOUTHWARD INTO THE AREA BY
MIDDAY...AND SHOULD TURN THE TEMPS AROUND WHICH WILL VARY FROM A
STEADY TO SLOW RISE IN THE LOWER TO MID 30S PRIOR TO FRONTAL PASSAGE
IN THE NORTHEAST...TO A NICE WARMING INTO THE LOWER 40S THROUGH THE
MISSOURI RIVER CORRIDOR.  WINDS WILL BECOME QUITE GUSTY AGAIN BY
LATER MORNING AND AFTERNOON...ESPECIALLY EAST OF INTERSTATE 29.

FOCUS FOR THE SHORT TO EARLY MEDIUM TERM OF THE FORECAST WILL BE PUT
IN MOTION DURING THE LATTER EVENING HOURS...AND CONTINUE THROUGH THE
REMAINDER OF THE NIGHT...WHICH WILL BE BAND OF SNOWFALL DEVELOPING
ACROSS THE AREA. DECENT LOWER TO MID LEVEL BAROCLINIC ZONE WILL LIE
IN WAIT ACROSS THE CWA...AS DECENT WAVE SLIPS INTO THE AREA BY LATER
TONIGHT AND EARLY WEDNESDAY.  WHILE THERE ARE SOME ABERRATIONS IN
PRECIPITATION PLACEMENT...THE OVERALL SUITE IS STARTING TO SETTLE ON
A BETTER BAND OF SNOWFALL FROM THE LOWER JAMES RIVER TO THE LOWER
MISSOURI RIVER CORRIDOR... OR ROUGHLY BETWEEN K9V9 AND KMHE TOWARD
KSUX.  FOR THE MOST PART...STRONGER LIFT IS NOT COLLOCATED WITH THE
DENDRITIC GROWTH ZONE...AND TEMPS AND LACK OF INSTABILITY ABOVE
FRONTAL SURFACE ARE EXPECTED TO KEEP SNOW-LIQUID RATIOS IN CHECK...
PROBABLY AVERAGING 12-14/1 IN THE MAIN BAND. WILL ALSO HAVE THE
COMPLICATION OF LOWER LEVEL DRY AIR TO THE NORTHEAST...COMPLIMENTS
OF THE JET STREAK EXITING TOWARD MINNESOTA AND WHICH FEATURES RIGHT
ENTRANCE WILL ACT TO ENHANCE THE FRONTAL FORCING LATER TONIGHT
ACROSS THE AREA.  ALL WORK TO PRODUCE A BAND OF 1 TO 3 INCHES
SNOWFALL ACROSS THE AREA BY DAYBREAK SOUTH AND WEST OF THE SIOUX
FALLS METRO...WHILE THE FAR EAST AND NORTHEAST MAY YET TO SEE
MEASURABLE IF DRY AIR CAN HOLD OFF PRECIPITATION LONG ENOUGH.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 348 AM CST TUE FEB 24 2015

ONGOING LIGHT TO MODERATE SNOWFALL BAND WILL CONTINUE THROUGH
WEDNESDAY MORNING FOR THE MAJORITY OF THE FORECAST AREA. OUR
NORTHEAST CORNER - MAINLY NEAR THE BUFFALO RIDGE AREA OF SOUTHWEST
MINNESOTA WILL CONTINUE TO SEE MOISTURE ISSUES IMPACTING SNOWFALL AS
DRY NORTHEAST LOW LEVEL WINDS LIMIT SNOWFALL IN THIS REGION.
SNOWFALL POTENTIAL REMAINS GREATEST TO THE SOUTHWEST...FOR AREAS
NEAR THE JAMES RIVER VALLEY INTO THE MISSOURI VALLEY AND NORTHWEST
IOWA. CONTINUED TO FOLLOW A MORE MIDDLE GROUND SOLUTION FOR HIGHEST
QPF PLACEMENT - BETWEEN THE MORE SOUTHERLY GFS SOLUTION AND
NORTHERLY ECMWF. WHILE THERE IS NOT A HUGE DIFFERENCE BETWEEN THE
MODELS...ANY SLIGHT CHANGE IN THE QPF AXIS WILL NUDGE THE LOCATION
OF THE HIGHEST SNOWFALL TOTALS IN THIS SOMEWHAT NARROW BAND. FOR NOW
IT LOOKS LIKE UP TO 3 TO 5 INCHES OF TOTAL SNOWFALL CAN BE EXPECTED
ALONG AND WEST OF A WESSINGTON SPRINGS TO BERESFORD TO STORM LAKE
LINE...WITH AMOUNTS QUICKLY TAPERING OFF TO THE EAST OF THIS LINE.
SIOUX FALLS LOOKS TO BE AROUND 2 INCHES OR SO...BUT COULD EASILY SEE
MORE IF THE MORE NORTHERLY SOLUTIONS PAN OUT. EXPECT THAT A WINTER
WEATHER ADVISORY WILL BE NECESSARY WITH THIS SYSTEM...BUT AFTER
CONSULTING WITH NEIGHBORING OFFICES...WILL HOLD OFF GIVEN THE
MODEL UNCERTAINTY OF WHERE THE HEAVIER ACCUMULATIONS WILL FALL.
TEMPERATURES WILL BE NEARLY STEADY IN THE TEENS AND LOWER 20S OR
SLOWLY FALLING DURING THE DAY ON WEDNESDAY. WINDS WILL BE AROUND
10 TO 20 MPH FROM THE NORTHEAST.

ARCTIC HIGH PRESSURE SLIDES SOUTHEAST ACROSS THE NORTHERN PLAINS
LATE WEDNESDAY...MOVING OVERHEAD ON THURSDAY. CLOUDS WILL DECREASE
THURSDAY MORNING...BUT DESPITE THE SUNSHINE FRIGID CONDITIONS WILL
GRIP FORECAST AREA. AFTER EARLY MORNING LOWS IN THE SINGLE DIGITS
BELOW ZERO...HIGHS WILL ONLY RECOVER INTO THE SINGLE DIGITS ABOVE
ZERO. CHILLY NORTHERLY WINDS WILL DROP WIND CHILLS INTO THE 20S
BELOW ZERO IN THE EARLY HOURS WITH LITTLE IMPROVEMENT IN THE DAYTIME.

UPPER FLOW BEGINS TO WEST TO SOUTHWEST THIS WEEKEND AS A DEEP
PACIFIC TROUGH SWINGS INTO THE FOUR CORNERS REGION. UNCERTAINTY
INCREASES WITH THIS EVENT WITH THE ECMWF AND GFS SHOWING LARGER
TIMING AND POSITIONAL DIFFERENCES THAN EARLIER RUNS. IMPULSES RIDING
ALONG THE SOUTHERN OR NORTHERN STREAM WILL BRING THE POTENTIAL FOR
SNOWFALL...BUT THE LOCATION OF THESE WAVES OR THERMAL BOUNDARIES ARE
HARD TO PINPOINT. THE GFS IN PARTICULAR IS TRENDING FURTHER SOUTH
AND IT STILL LOOKS LIKE THE BEST BET FOR ANY PRECIPITATION IN OUR
FORECAST AREA WILL BE SOUTH OF I90.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1137 AM CST TUE FEB 24 2015

STILL EXPECTING A PERIOD OF SNOW LATER TONIGHT INTO WEDNESDAY
REDUCING CIG AND VIS INTO THE IFR TO MVFR CATEGORY. LIKELY TO SEE
SOME BRIEF LIFR VIS IN THE HEAVIER BAND. THIS LOCATION HAS
SHIFTED NORTH...WITH FORECAST HEAVILY WEIGHTED TOWARDS THE GEM AND
ECMWF. BLUSTERY NORTHWESTERLY WINDS THIS AFTERNOON WILL TURN
EASTERLY TONIGHT AND SETTLE INTO THE 10 TO 15 KT RANGE. MAIN
UNCERTAINTY WITH THIS TAF ISSUANCE IS THE START TIME OF THE LOWER
VISIBILITY...AS THE NORTHWARD TREND MAY DELAY THIS AT KFSD AND
KSUX.

&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...
AVIATION...CHENARD


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