Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 141156
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
556 AM CST SUN DEC 14 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 555 AM CST SUN DEC 14 2014

WHILE STRATUS HAS BEEN PREVALENT THROUGHOUT THE NIGHT...LOWER
VISIBILITY FOG HAS BEEN SPOTTY AT BEST. STILL CONCERNED ABOUT
VISIBILITY DROPPING THROUGH THE NEXT FEW HOURS AS LOW LEVEL MOISTURE
CONTINUES TO BUILD NORTHWARD...AND HAVE SEEN SOME INDICATION OF THIS
WITH 0915Z OBS IN NORTHWEST IA/SOUTHWEST MN...SO DECIDED TO KEEP IT
GOING IN THOSE AREAS FOR NOW BUT WILL DROP FROM I-29 CORRIDOR/SD
COUNTIES. OTHERWISE THICK STRATUS WILL PERSIST AHEAD OF THE COLD
FRONT...CURRENTLY POSITION NEAR/JUST WEST OF THE MISSOURI RIVER.
SHOULD SEE LOWER STRATUS SCOUR OUT IN THE WEST WITH FRONTAL PASSAGE
BUT GREATER AMOUNT OF MID-HIGH CLOUDS THERE WILL STILL RESULT IN A
MOSTLY CLOUDY DAY. MOISTURE SURGE SHOULD PUSH TEMPERATURES UP A FEW
DEGREES FROM CURRENT READINGS AHEAD OF THE FRONT...GIVING HIGHS IN
THE MID-UPPER 50S IN MANY AREAS EAST OF DE SMET-TYNDALL LINE. OUR
FAR WESTERN AREAS ARE LIKELY NEAR THEIR DAILY HIGH NOW AND SHOULD
SLOWLY DECLINE AFTER SURFACE WINDS SWITCH AROUND TO THE WEST EARLY.
HOWEVER...DO NOT EXPECT TO SEE SHARP COLLAPSE UNTIL COLDER AIR ALOFT
BEGINS TO MOVE IN THIS AFTERNOON.

MAIN FOCUS FOR THE FORECAST CONTINUES TO BE THE WINTRY SCENARIO
EVOLVING OVER THE AREA AS DEEP TROUGH IN SOUTHERN ROCKIES LIFTS
THROUGH THE PLAINS. CONSENSUS HAS BEGUN TO BECOME STRONGER IN THE
TRACK AND TIMING OF THE LARGER SCALE SYSTEM...A BIT SLOWER AND
WARMER SYSTEM TO START...WITH MAX PRECIPITATION BAND EXPECTED
ACROSS THE FSD CWA IN DEFORMATION BETWEEN THE NORTHERN STREAM AND
SOUTHERN STREAM COMPONENTS TO THE SYSTEM. STILL HAVE A BIT OF
DIVISION BETWEEN A MORE SOUTHERN ECMWF/CANADIAN AND NORTHERN
NAM/GFS...BUT PRESENCE OF WEAK NORTHERN STREAM JET SUGGESTS A BIT
BETTER TIE TOWARD THE NORTHERN SOLUTION. SOUTHERN STREAM NATURE
OF THE MAIN LOW MEANS A VERY WARM PRE STORM ENVIRONMENT...WITH
COLD AIR GRADUALLY BECOMING INCORPORATED INTO THE SYSTEM HEADING
LATER TONIGHT AND ESPECIALLY ON MONDAY. MIXED PHASE PRECIPITATION
IS A CERTAINTY WITH MAIN COOLING OCCURRING AT LOWER LEVELS FIRST
AS SURFACE WAVE DEEPENS TO THE SOUTH...AND LAYER OFF SURFACE
MAINTAINS AN EASTERLY COMPONENT FEEDING INTO INVERTED TROUGH.

LOW LEVEL BOUNDARY REALLY SLOWING TO A CRAWL AS WRAPPED UP LOW TO
THE SOUTH BEGINS THE SLOW WANDER NORTHEAST THROUGH THE SHORT TERM.
LIGHT PRECIPITATION SHOULD PERSIST NEAR AND AHEAD OF LOW LEVEL
BAROCLINICITY...AS WELL AS INITIAL ELEVATED LIFT AND WEAK SIGNAL
OF MID LEVEL MOISTURE ALLOWING FOR A FEW LIGHT SHOWERS. WARM
TEMPS FOR CONTINUATION OF ALL LIQUID THIS EVENING...WITH SOME
POTENTIAL MIXED PRECIPITATION IN THE FAR WEST LATE EVENING. DOES
NOT APPEAR THAT ANY MORE WIDESPREAD PRECIPITATION WILL WORK INTO
THE CWA UNTIL APPROACH OF BETTER DIV Q BANDING WORKS NORTHWARD
AFTER 06Z. AT THIS TIME...FAIRLY DECENT BAND OF SHOWERS WILL WORK
NORTHWARD. WHILE CENTRAL AND EASTERN CWA WILL REMAIN MILDER
SURFACE AND ALOFT...WARM LAYER BETWEEN 850-800 HPA HOLDS ON IN THE
WEST THROUGH THE NIGHT...WITH EXCEPTION OF THE EXTREME WEST WHERE
COOLING BEGINS TO TAKE STRONGER HOLD. THIS WILL YIELD AN
INCREASING POTENTIAL FOR MIXED PRECIPITATION THROUGH THE JAMES
VALLEY. PRECIP FURTHER EAST WILL ALMOST CERTAINLY BENEFIT FALLING
THROUGH VERY WARM LAYER 900-800 HPA WHERE ONLY THE NEAR SURFACE
FREEZING LAYER TOWARD KMDS/KBKX WILL ALLOW FOR SOME FREEZING RAIN
TOWARD DAYBREAK. CURIOSITY WITH SYSTEM IS THAT AS DISTINCT LOBE
WRAPS NORTHWARD ON NOSE OF DRYING ALOFT...MAY EVEN SEE A COUPLE
RUMBLES OF THUNDER WANDER INTO LOWER MISSOURI VALLEY AND NW IA
LATE TONIGHT OR EARLY MONDAY MORNING.

PRECIPITATION BAND WILL LIFT INTO THE DEFORMATION ZONE BETWEEN
SYSTEMS THROUGH THE MIDDLE OF THE DAY.  LIFT IN THE DEFORMATION
ZONE WILL BECOME MORE FAVORABLY LOCATED WITH DENDRITIC GROWTH ZONE
DURING THE MORNING TOWARD WESTERN CWA...AND THUS EXPECT SNOWFALL
WILL BECOME MODERATE TO BRIEFLY HEAVY IN BANDING ACROSS SOUTH
CENTRAL SD EXTENDING EAST/NORTHEAST. AS WINDS INCREASE TO 20 TO 35
MPH AND GUSTY...MAY GET SOME ADDITIONAL REDUCTION IN VISIBILITY
WITH BLOWING SNOW DURING THE AFTERNOON...BUT A MUCH GREATER
PORTION OF THE REDUCED VISIBILITIES ARE LIKELY TO BE RESULT OF
SNOW RATE. FURTHER EASTWARD...WARM LAYER ALOFT WILL CONTINUE TO
PLAGUE TRANSITION ZONE WITH GOOD SET UP FOR SOME FREEZING RAIN AND
SOME SLEET WORKING EASTWARD. MID PORTION OF THE CWA FROM THE
MORNING TO EARLY AFTERNOON HAS THE MOST CRITICAL THERMAL PROFILES
FOR MIXED PRECIPITATION...WITH A LITTLE MORE OF A RAIN TO SNOW
CHANGE FURTHER EAST LATER IN THE DAY. ALSO...WITH DRY SLOT
HOVERING CLOSE TO THE FAR SOUTHERN CWA...HAVE DROPPED BACK THE
PRECIPITATION CHANCE JUST A BIT DURING THE LATER MORNING AND EARLY
AFTERNOON.

WITH EXPECTATIONS OF AN AREA OF ICE ACCUMULATION ACROSS EASTERN
SD INTO SW MN /IMPACTS LIMITED SOMEWHAT INITIALLY BY WARMER
SURFACE TEMPERATURES AND HIGH DEWPOINTS/ FOLLOWED BY A BAND OF
2 TO 6 INCHES SNOWFALL...HAVE OPTED TO ISSUE A WINTER WEATHER
ADVISORY FOR MUCH OF SD CWA EXTENDING INTO SW MN...STARTING FAR
WEST AFTER MIDNIGHT...AND CONTINUING THROUGH 00Z TUE. SNOW WILL BE
CONTINUING AFTER 00Z OVER THE EASTERN HALF OF AREA...BUT WORST
APPEARS TO BE WINDING DOWN BY THIS TIME. WINDS WILL ALSO BE FAIRLY
BRISK...BUT FOR NOW HAVE LIMITED ANY BLOWING SNOW MENTION TO THE
LOWER BRULE AND LOWER JAMES VALLEY AREAS WHERE SNOW CONSISTENCY
MORE FAVORABLE AND THERE IS A LONGER DURATION OF SNOWFALL/WIND
OVERLAP. HOWEVER...WILL HAVE TO WATCH SPEED OF TRANSITION AS WILL
HAVE A GREAT IMPACT ON BOTH ICE AND SNOW ACCUMULATION...AS WELL AS
LOCATION OF EACH.

DEFORMATION ZONE WILL UNDERGO A FAIRLY STEADY WEAKENING DURING THE
EVENING HOURS...SO HAVE GRADUALLY TRENDED DOWN THE CHANCE FOR
ADDITIONAL SNOWFALL...AND THE AMOUNTS IN THIS BAND AS WELL
OVERNIGHT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 555 AM CST SUN DEC 14 2014

BY LATE MONDAY NIGHT AND EARLY TUESDAY...UPPER WAVE CONGEALING TO
EAST WILL SHEAR WRAP AROUND BAND OUT AND WILL BE LEFT WITH STOUT
NORTHWESTERLY FLOW SURFACE AND ALOFT. PRECIPITATION WILL END...BUT
WILL LIKELY HAVE A FAIR AMOUNT OF CYCLONIC STRATUS WRAPPING ACROSS
AT LEAST THE NORTHEAST CWA. TEMPS SUGGEST MAY EVEN THREATEN TO
HAVE A FEW FLURRIES ACROSS THE NORTHEAST...BUT HAVE NOT MENTIONED
THOSE SPECIFICALLY AT THIS TIME. TEMPS HARD PRESSED WITH EARLIER
SNOWFALL TO CLIMB A GREAT DEAL...MOST LOCATIONS NO MORE THAN 3-6
DEGREES OVER MORNING LOWS...MEANING UPPER TEENS TO MID 20S.

GOOD TO SEE BETTER AGREEMENT IN PULLING THE CLOSED UPPER LOW
THROUGH THE GREAT LAKES THROUGH MID WEEK. HIGH PRESSURE WILL
SETTLE IN BEHIND THE EXITING LOW...WITH COLD AIR CONTINUING TO
POUR IN THROUGH WEDNESDAY. WITH DIMINISHING WINDS AND SOME
CLEARING ON TUESDAY NIGHT...HAVE NUDGED TEMPS DOWN A BIT MORE.
ONCE IT BECOMES MORE OBVIOUS THAT WILL NOT BE DEALING WITH A
STRATUS FIELD BEHIND THE UPPER LOW...WILL CERTAINLY HAVE TO WORK
ANOTHER HALF DOZEN OR MORE OFF THE TEMPS FOR WEDNESDAY MORNING.

DRY AND COOLER CONDITIONS EXPECTED TO DOMINATE THE LONGER RANGE
WEDNESDAY NIGHT THROUGH SATURDAY. 12Z ECMWF WAS STILL A BIT MORE
WOUND UP WITH LATE WEEK SYSTEM...WHICH SPREAD PRECIPITATION CHANCE
OVER MOST OF THE FORECAST AREA THURSDAY THROUGH FRIDAY. HOWEVER 00Z
RUN TRENDED TOWARD THE WEAKER/DRIER GFS/CANADIAN SOLUTIONS. WILL
HANG ONTO MINIMAL SNOW CHANCE IN OUR WESTERN/SOUTHERN AREAS DUE TO
SOME UNCERTAINTY FROM POOR RUN-TO-RUN CONSISTENCY...BUT LOW
CONFIDENCE ANYTHING WILL OCCUR THIS FAR NORTH.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 547 AM CST SUN DEC 14 2014

IFR-LIFR CONDITIONS WILL DOMINATE THROUGH THE PERIOD...THOUGH
BRIEF IMPROVEMENT TO MVFR-LOW END VFR IS POSSIBLE...MAINLY IN
AREAS WEST OF THE I-29 CORRIDOR. PRIMARILY LIGHT-MODERATE DRIZZLE
AND FOG THROUGH THE DAY WILL GRADUALLY INCREASE TO BONAFIDE RAIN
SPREADING OVER THE AREA TONIGHT. LOCATIONS WEST OF I-29 WILL SEE
THE RAIN BECOME A WINTRY MIX OF FREEZING RAIN/SLEET AFTER 06Z AS
COLDER SURFACE AIR BEGINS TO UNDERCUT LINGERING WARM LAYER ALOFT.
EVENTUALLY THE MIXED PRECIPITATION WILL SWITCH TO SNOW AS LAYERS
ALOFT COOL...HOWEVER THIS NOT LIKELY TO OCCUR AT KHON UNTIL AFTER
THIS TAF PERIOD.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY FROM 4 AM TO 6 PM CST MONDAY FOR SDZ039-
     040-053>055-059-060-065-068.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM CST MONDAY
     FOR SDZ050-052-057-058-063-064.

     WINTER WEATHER ADVISORY FROM 8 AM TO 6 PM CST MONDAY FOR SDZ056-
     061-062-066-069.

MN...WINTER WEATHER ADVISORY FROM 8 AM TO 6 PM CST MONDAY FOR MNZ071-
     072-080-097-098.

     DENSE FOG ADVISORY UNTIL 10 AM CST THIS MORNING FOR MNZ089-090-
     097-098.

IA...DENSE FOG ADVISORY UNTIL 10 AM CST THIS MORNING FOR IAZ001>003-
     012>014-020>022.

NE...NONE.
&&

$$

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


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