Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 091117
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
517 AM CST TUE FEB 9 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 414 AM CST TUE FEB 9 2016

STILL SEEING SPORADIC WIND GUSTS SPIKE UP TO 35-40KT IN PARTS OF
SOUTHWEST MN/NORTHWEST IOWA EARLY THIS MORNING...BUT WITH GENERAL
DOWNWARD TREND AND STRONGER WINDS BECOMING MORE ISOLATED...WILL LET
REMAINING WINTER WEATHER ADVISORY EXPIRE WITH THIS FORECAST PACKAGE.
WILL CONTINUE TO CARRY MENTION OF BLOWING SNOW IN THESE LOCATIONS
THROUGH THE DAY HOWEVER...AS FAVORABLE MIXING WILL ALLOW NORTHWEST
WINDS TO REMAIN BREEZY IN 25 TO 30 MPH RANGE UNTIL SUNSET. NEUTRAL
TO WEAK COLD ADVECTION ALSO PERSISTS IN OUR EAST THROUGH THE DAY...
SO TEMPERATURES MAY ONLY REBOUND INTO THE MID TEENS FOR HIGHS THERE
TODAY. SLIGHTLY MORE SEASONABLE TEMPERATURES ARE EXPECTED CLOSER TO
LOW LEVEL WARM FRONT IN OUR WEST...THOUGH STILL A FEW DEGREES BELOW
NORMAL WITH A HIGH NEAR 30.

FOCUS THEN SHIFTS TO INCREASING THREAT OF LIGHT SNOW DEVELOPING IN
WESTERN PARTS OF THE FORECAST AREA BY LATER TONIGHT...AS MID LEVEL
WAVE DROPS SOUTH-SOUTHEAST ALONG LOW LEVEL BAROCLINIC ZONE NEAR/WEST
OF THE JAMES RIVER VALLEY. EXPECT TO SEE MID-HIGH CLOUDS INCREASE
OVER THE AREA BY MIDNIGHT...WHICH SHOULD HELP KEEP TEMPERATURES IN
CHECK...THOUGH EASTERN AREAS LIKELY TO SEE A FEW SUB-ZERO READINGS
AS CLOUDS WILL STILL BE RELATIVELY THIN AS SURFACE RIDGE AXIS SHIFTS
INTO THAT AREA TOWARD DAYBREAK. DEEPEST SATURATION PRIOR TO 12Z
APPEARS TO REMAIN WEST OF I-29 CORRIDOR...AND WILL LARGELY CONFINE
CHANCE POPS FOR LIGHT ACCUMULATIONS LESS THAN A HALF INCH TO THESE
AREAS.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 414 AM CST TUE FEB 9 2016

WAVE IN NORTHWEST FLOW WILL TRAVERSE THE CWA DURING THE DAY...WHILE
BAROCLINIC ZONE WANDERS FIRST NORTHEAST...THEN SETTLES IN WAKE OF
WAVE BACK A BIT SOUTHWEST BY EVENING. BROAD BAROCLINIC ZONE FEATURES
A FAIRLY DECENT SLOPE...AND CROSS SECTIONS ACTUALLY SUGGEST THERE
MAY BE A BIT OF WEAK INSTABILITY ABOVE THE FRONTAL BOUNDARY ALONG
AND EAST OF A KHON-KFSD-KCIN LINE TO AID IN FOCUSING/NARROWING THE
BAND A BIT MORE. ISENTROPIC LIFT IS GENERATED BY INDUCED CROSS
FRONTAL FLOW AS JET IMPULSE SLIPS PAST THE AREA. HOWEVER...OVERALL
SIGNATURE FOR LIFT FORCING IS FAIRLY WEAK...SO SHOULD NOT GET OUT OF
HAND. THERMAL PROFILES ALSO WOULD INDICATE THAT PROSPECT FOR SUPER
EFFICIENT PRECIPITATION IS PROBABLY OUT OF THE QUESTION...WITH MOST
OF THE DENDRITIC TEMPS INVOLVED TOWARD THE EAST...AND TENDENCY WILL
BE FOR LAYER TO MODERATE JUST TO THE WARM SIDE OF THE BEST THERMAL
RANGE. WEST OF THE DEEPER SATURATION...EVEN POSSIBLE THAT WILL LOSE
THE NECESSARY DEPTH TO OBTAIN ICE DEVELOPMENT...AND COULD BE LOOKING
AT PATCHY FREEZING DRIZZLE TOWARD THE JAMES VALLEY BY AFTERNOON. THE
LIKELY SNOW TO LIQUID RATIOS WILL AVERAGE 13-15 TO 1...HIGHER TOWARD
THE EAST. BEST OF THE DEEPER FORCING WILL OCCUR THRU 18Z-21Z...AT
WHICH POINT LARGE SCALE SUBSIDENCE WILL BE A BIT MORE AT ODDS WITH
THE FRONTAL ZONE...WITH EXPECTED DECREASE IN OVERALL SNOW COVERAGE
OVER THE EASTERN CWA THROUGH EARLY EVENING. BY THE TIME
PRECIPITATION WINDS DOWN...LIKELY TO FIND BAND OF AN INCH OR LITTLE
MORE ACROSS THE MID/EASTERN CWA.

SURFACE TROUGH IN MOST SOLUTIONS PUSHES INTO LOWER BRULE AREAS
DURING THE MIDDAY AND EARLY AFTERNOON...ALLOWING A STRONG MODERATION
TO TEMPS INTO THE MID TO UPPER 30S...WHILE ECMWF STANDS FIRMLY ALONE
IN KEEPING THE COLDER AIR LOCKED IN. HAVE SIDED MORE TOWARD THE
MAJORITY...WHICH MAKES SENSE GIVEN THE BEHAVIOR OF THE NEAR SURFACE
THERMAL BOUNDARY.

SOUTHWARD PUSH OF COOLER TEMPS ON WEDNESDAY NIGHT AS ARCTIC RIDGE
OOZES TOWARD THE EASTERN CWA. WITH TEMPS COOLING TOWARD VERY
DENDRITIC RANGE...WOULD NOT BE SURPRISED TO GET SCATTERED FLURRIES
AS LOWER LEVEL BOUNDARY DRIFTS SOUTHWESTWARD. THURSDAY A QUIET DAY
AS FLOW WORKS TO TURN AROUND TOWARD SOUTHERLY. ANOTHER WAVE IN THE
FRANTIC NORTHWEST FLOW WILL TRAVERSE THE REGION THURSDAY NIGHT. AS
HAS BEEN THE CASE...THE LOCATION OF THE BAROCLINIC ZONE CONTINUES TO
WAVER SPATIALLY BOTH BETWEEN DIFFERENT MODEL RUNS AND SUCCESSIVE
RUNS OF THE SAME MODEL...THUS THE BETTER CHANCE FOR LIGHT SNOWFALL
IS HARD TO PLACE AT THIS TIME. MOST ARE FOCUSING ON THE THURSDAY
NIGHT PERIOD...SO FOR NOW WILL BROAD BRUSH IN SOME LOWER POPS...
FAVORING MAINLY THE NORTHEAST HALF OF THE AREA WHERE STRONGER MID
LEVEL FRONTAL FORCING IS ADVERTISED.

AS IN THE CASE OF THE WEDNESDAY WAVE...THIS WAVE WILL ALSO ACT TO A
GREATER DEGREE TO AMPLIFY THE PATTERN...DRIVING A STRONG ARCTIC
ANTICYCLONE SOUTHWARD THROUGH THE EASTERN HALF OF THE REGION FRIDAY
INTO SATURDAY. TEMPERATURES WILL STRUGGLE TO RISE A GREAT DEAL ON
FRIDAY...LIKELY STEADY TO FALLING THROUGH MUCH OF THE AREA. BITTERLY
COLD AIR IS EXPECTED SATURDAY MORNING...WITH PERHAPS HIGH CLOUDS AND
A LESSER SNOW COVER KEEPING THE WESTERN HALF OF THE AREA FROM
REACHING TEMPS FROM CRASHING WELL BELOW ZERO. WIND CHILLS COULD
REACH ADVISORY LEVELS LATER FRIDAY NIGHT AND SATURDAY MORNING IN THE
EAST. PRESENCE OF ARCTIC RIDGE WILL KEEP SATURDAY TEMPS STRUGGLING
IN THE SINGLE DIGITS EAST.

STRONG SOUTHERLY WINDS ON BACK SIDE OF THE ARCTIC RIDGE DEVELOP
SATURDAY NIGHT INTO SUNDAY. WITH PROSPECT OF AT LEAST A COUPLE OF
LIGHT SNOWFALL EVENTS AND VERY COLD INTERVENING TEMPERATURES... WILL
BE A SNEAKY SET UP FOR ELEVATED LOCATIONS FROM EAST CENTRAL SD INTO
HIGHER LOCALES OF SOUTHWEST MINNESOTA AND NORTHWEST IOWA TO DEVELOP
SOME BLOWING SNOW.

ANOTHER TROUGH PROGRESSING OUT OF THE PACIFIC THIS TIME AROUND WILL
AMPLIFY ACROSS THE AREA ON SUNDAY. LEADING WARM AIR ADVECTION MAY
PRODUCE SOME SPOTTY PRECIPITATION ON SATURDAY NIGHT ACROSS THE
NORTH/EAST...WITH BETTER CHANCES ON SUNDAY. MOISTURE WILL BE A BIT
OF A CHALLENGE TO EARLY PRECIP PRODUCTION...BUT BY SUNDAY ENOUGH
DYNAMIC FORCING TO BRING UP SOME CHANCE POPS NORTH/EAST.

THE OVERALL SIGNAL IS FOR THE LARGER SCALE AMPLIFICATION TO BREAK
DOWN EARLY NEXT WEEK...ALLOWING A MORE ZONAL PUSH OF MILDER AIR TO
SURGE ACROSS THE REGION. ECMWF IS A BIT MORE HESITANT...BUT
EVENTUALLY GETS THERE LATER TUE AND WED. A BIT CONCERNED THAT A FEW
THINGS COULD IMPEDE THE STRONGER WARMING SIGNAL FOR MONDAY INTO
TUESDAY...ESPECIALLY IF THE SOLUTION TRENDS TOWARD THE ECMWF.
OPERATIONAL ECMWF IS TOWARD THE COOLER SIDE OF ENSEMBLE...SO FOR
NOW...HAVE STUCK CLOSER TO THE BLEND...WITH SMALL HEDGE DOWN IN THE
DEEPER SNOWCOVERED AREAS EAST.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 517 AM CST TUE FEB 9 2016

AREAS MVFR-IFR VISIBILITY IN BLOWING SNOW WILL CONTINUE TO IMPACT
PARTS OF SOUTHWEST MN/NORTHWEST IA TODAY DUE TO PERSISTENT NORTH
TO NORTHWEST WINDS GUSTING OVER 25KT AT TIMES. SUB-VFR CONDITIONS
SHOULD GRADUALLY DECREASE IN COVERAGE AS WINDS GRADUALLY SUBSIDE
THROUGH THE AFTERNOON. OTHERWISE EXPECT VFR CONDITIONS TO DOMINATE
FOR THE TAF LOCATIONS AND POINTS WEST THROUGH 06Z TONIGHT. AFTER
THAT TIME...LOWERING CEILINGS WILL BE ACCOMPANIED BY A DEVELOPING
BAND OF LIGHT SNOW. THIS ONLY EXPECTED TO IMPACT KHON TAF LOCATION
BY THE END OF THIS TAF PERIOD...BUT WILL LIKELY SHIFT INTO KFSD
AND KSUX AFTER 12Z WEDNESDAY.

&&

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

$$

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


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