Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 020538
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1138 PM CST SUN MAR 1 2015

.UPDATE...
ISSUED AT 1030 PM CST SUN MAR 1 2015

AFTER SOME COORDINATION WITH SURROUNDING OFFICES...DECIDED TO GO
AHEAD AND PULL THE TRIGGER ON A BLIZZARD WATCH FOR OUR NORTHERN
AND WESTERN ZONES. THE 00Z GEM REGIONAL COLLABORATED THE 00Z NAM
IN TIMING OF THE WIND AND SNOWFALL AMOUNTS...AS GOING SOLELY WITH
THE NAM MODEL IS ALWAYS A SCARY PROPOSITION. INTERESTINGLY...THE
00Z GFS ALSO HAS THE LEADING EDGE OF THE COLD FRONT STILL IN
CENTRAL SD WEST OF OUR FORECAST AREA AT 06Z TUESDAY...VERY SIMILAR
TO THE NAM AND GEM REGIONAL. BUT THE GFS CONTINUES TO BLAST THE
FRONT THROUGH NEARLY OUR ENTIRE FORECAST AREA IN JUST 6 HOURS BY
12Z TUESDAY. ALTHOUGH THIS IS NOT IMPOSSIBLE...AT THIS TIME IT
DOES NOT SEEM PLAUSIBLE TO MOVE THE FRONT QUITE THIS FAST THROUGH.
SO THUS THE TIMING OF THE BLIZZARD WATCH IS BASED OFF OF THE GEM
AND NAM.

THESE MODELS SHOW VERY VERY STRONG PRESSURE RISES AND COLD AIR
ADVECTION JUXTAPOSED ENTERING INTO OUR WESTERN ZONES BETWEEN 12Z
AND 15Z TUESDAY. THEN MOVES IT EASTWARD THROUGH THE DAY. MIXED
LAYER WINDS BEHIND THE FRONT ARE 35 TO 40 KNOTS FROM THE NORTH AND
NORTHWEST...SO WOULD NOT BE SURPRISED TO SEE 30 TO 50 MPH FOR
ABOUT A 6 HOUR WINDOW POST FRONTAL. THESE WINDS COMBINED WITH
FALLING SNOW COULD PRODUCE A REAL MESS WHERE 2 TO 4 INCHES OF SNOW
COULD RAPIDLY FALL...AND THIS WOULD BE ALONG AND NORTH OF A
GREGORY SOUTH DAKOTA...TO SALIM AND FLOUNDER SOUTH DAKOTA...TO
WINDOM MN LINE. SIOUX FALLS ITSELF IS CLOSE...AND IT WILL
CERTAINLY BE VERY WINDY ON TUESDAY...BUT NOT SURE IF THE SNOWFALL
WILL BE INTENSE ENOUGH FOR 3 TO 6 HOURS TO WARRANT A BLIZZARD
WATCH SO LEFT SIOUX FALLS OUT FOR NOW. FURTHERMORE...THIS STORM
HAS BEEN CORRECTING TO THE NORTH IN TERMS OF MODEL PLACEMENT SO IF
THIS TREND CONTINUES...SIOUX FALLS WILL GET EVEN LESS SNOW THAN WE
THINK. SIOUX CITY BEING EVEN FURTHER SOUTH SHOULD ONLY SEE LIGHT
AMOUNTS OF SNOW. WITH NO SNOW COVER THROUGH OUR ENTIRE SOUTHWEST
ZONES...AND GLACIATED SNOW COVER ELSEWHERE...THE BLIZZARD
CONDITIONS IF THEY MATERIALIZE WILL MOST CERTAINLY HAVE TO BE
ACCOMPANIED BY FALLING SNOW...AS THERE IS LITTLE TO NO EXISTING
SNOW COVER TO BLOW AROUND. THEREFORE DID NOT WANT TO LINGER THE
BLIZZARD WATCH PAST THE ENDING TIME OF THE FALLING SNOW.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 318 PM CST SUN MAR 1 2015

UPPER TROUGH ACROSS NORTHERN SOUTH DAKOTA WILL STEAM EASTWARD THIS
EVENING. STRATOCUMULUS FIELD AS A RESULT OF SURFACE BASED MIXING
WILL QUICKLY DISSIPATE THIS EVENING...AS WILL THE FEW SCATTERED
FLURRIES WHICH WILL GLANCE THE NORTHERN/NORTHEASTERN CWA LATE
AFTERNOON...AND THE GUSTY WESTERLY WINDS AS SURFACE RIDGE BUILDS
ACROSS THE CWA TONIGHT. DIFFERENCE IN SURFACE CONDITIONS SHOULD
AGAIN BE EVIDENT OVERNIGHT...AND WHERE RIDGE AXIS AND CLEARING
COINCIDE WITH MINOR SNOW COVER...WOULD NOT BE SURPRISED TO FIND LOWS
PLAYING WITH NEAR ZERO READINGS ONCE AGAIN...WHILE SNOW FREE AREAS
STAY CLOSER TO 10 ABOVE.

CLOUDS WILL START TO INFRINGE ON THE SOUTHWESTERN CWA DURING THE
EARLY MORNING...WITH BUILDING HEIGHTS/WARM AIR ADVECTION INCREASING
THROUGH THE DAY. PROSPECT OF GETTING MUCH TO REACH THE GROUND IN THE
INITIAL WARM ADVECTIVE PULSE IS FAIRLY LOW INITIALLY WITH DRY AIR AT
LOWER LEVEL. GRADUALLY...SHOULD SEE SOME LOWER CHANCES FOR
PRECIPITATION DEVELOPMENT AS THE BAND LIFTS NORTHEAST THROUGH THE
DAY.  A BIT OF DISCONNECT BETWEEN THE SURGING MID LEVEL LIFT AND
MOISTURE...AND LAGGING LOWER LEVEL MOISTURE COMING UP LATER IN THE
DAY. WILL LIKELY HAVE A GREATER STRATUS DEVELOPMENT GOING THROUGH
THE AFTERNOON COMING OUT OF EASTERN NEBRASKA ON LOW LEVEL JET.
SURFACE WINDS WILL BE QUITE BRISK FROM THE SOUTH...AND SHOULD SEE
SOME WINDS APPROACHING ADVISORY CRITERIA OVER THE WESTERN CWA.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 318 PM CST SUN MAR 1 2015

THE MAIN STORY CONTINUES TO BE THE SYSTEM PROJECTED FOR MONDAY NIGHT
INTO TUESDAY. SOME FAIRLY SIGNIFICANT CHANGES IN THE MODELS TODAY.
THE TREND BEGAN LAST NIGHT AND HAS BEEN REINFORCED WITH THE 12Z
RUNS...MAINLY ON SHIFTING THE FORCING FARTHER NORTH. THE FAR
SOUTHERN CWA NOW CLOSER TO AN ELEVATED DRY SLOT AND ALSO TO THE
DEEPER LOW LEVEL MOISTURE THUS SOUNDING ANALYSIS INDICATING THAT
FREEZING DRIZZLE SHOULD BE MORE OF A THREAT THAN WAS PREVIOUSLY
EXPECTED. BETWEEN ABOUT 9Z AND 15Z...THE BETTER CHANCE FOR FREEZING
DRIZZLE...THERE IS A LITTLE ELEVATED INSTABILITY SO WITH WET BULB
TEMPERATURES SUPPORTING SNOW IF SNOW SHOWERS CAN DEVELOP NOT AN EASY
SOLUTION TO GO JUST FREEZING DRIZZLE. AND WITH A SURGE OF WARM/MOIST
ADVECTION DURING THE EVENING DO EXPECT SOME SNOW SHOWERS TO PUSH
INTO THE EASTERN CWA BUT SHOULD REMAIN MOSTLY DISORGANIZED. THE MAIN
WAVE COMES OUT AND CONVERGENCE ON THE MID LEVEL BAND INCREASES IN
THE SOUTHWEST CWA AROUND MIDNIGHT...THEN SHOULD QUICKLY COLLAPSE
EASTWARD OVERNIGHT. STILL EXPECTING PRETTY MUCH ALL SNOW. THIS BROAD
BAND SHOULD START TO THEN COLLAPSE SOUTHEAST AND PRETTY MUCH BE
SOUTH OF THE CWA BETWEEN 18Z AND 21Z TUESDAY. THE CONCERN THEN TURNS
TOWARDS NORTH WINDS OF 25 TO 40 MPH ON TUESDAY LATE MORNING INTO THE
AFTERNOON WHICH WILL LIKELY CAUSE SOME DECENT BLOWING SNOW. FOR NOW
BELIEVE THIS EVENT WILL REMAIN BELOW WARNING CRITERIA SO NO WATCH
PLANNED. SINCE IT ALSO IS MOSTLY A 4TH PERIOD ISSUE WILL HOLD OFF ON
ANY ADVISORIES AND TRY TO IRON OUT WHETHER OR NOT THIS NORTHWARD
SHIFT IS CORRECT.

STRONG WINDS AND PATCHY DRIFTING SNOW WILL CONTINUE INTO TUESDAY
NIGHT AND WEDNESDAY MORNING AND WITH TEMPERATURES LIKELY BELOW ZERO
IN MANY LOCATIONS WIND CHILLS WILL DROP TO ABOUT 15 BELOW TO 25
BELOW.

WEDNESDAY WILL BE JUST PLAIN COLD WITH GRADUALLY DIMINISHING
NORTHWEST WINDS AND HIGHS MAINLY IN THE SINGLE DIGITS. A LITTLE
WARMER ALONG THE MISSOURI RIVER WITH TEMPERATURES IN THE TEENS.

DID GO AHEAD AND LOWER LOWS A BIT WEDNESDAY NIGHT WITH EXPECTATION
OF FRESH SNOW COVER AND A RIDGE OF HIGH PRESSURE PASSING THROUGH.
THE COLDEST TEMPERATURES SHOULD BE FROM THE BIG SIOUX RIVER VALLEY
EAST WHERE WINDS WILL BE LIGHTEST TOWARDS SUNRISE THURSDAY MORNING.

IN THE OUTER PERIODS(THURSDAY THROUGH SUNDAY)...STILL VERY MUCH ON
TRACK FOR A WARM UP...ESPECIALLY ALOFT...WITH THE MAIN CHALLENGE
FIGURING OUT HOW MUCH OF THIS TRANSLATES TO THE SURFACE GIVEN THE
EXPECTED FRESH SNOW COVER. FOR NOW WITH THE EXPECTATION BEING A BAND
OF 2 TO 4 INCHES DO NOT FEEL IT WILL COMPLETELY WIPE OUT THE WARM UP
BUT WILL TEMPER HIGHS AND LOWS A BIT INTO THE WEEKEND. REGARDLESS
STILL LOOKING AT HIGHS IN THE 40S SOUTH AND WEST AND 30S NORTH AND
EAST. THE WEAK SYSTEM ON SATURDAY HAS BEEN AVERAGED OUT BETWEEN
YESTERDAYS VERY COLD GFS AND YESTERDAY VERY WARM ECMWF TO SOMETHING
MORE BELIEVABLE TODAY WITH JUST A BRIEF SHOT OF COOL AIR. NO PLANS
ON ANY PRECIPITATION DURING THIS TIME FRAME.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1134 PM CST SUN MAR 1 2015

VFR WILL PREVAIL FOR THE REST OF TONIGHT AND MONDAY. ON MONDAY
EVENING...THE CONTINUING SOUTHERLY FLOW OF AIR COULD VERY WELL
BEGIN TO USHER IN STRATUS FOR THE KSUX AND KFSD TAF SITES. BOTH
THE NAM AND GFS ARE SHOWING THIS STRATUS...HOWEVER THE GFS IS A
FEW OF HOURS SLOWER WITH THE ONSLAUGHT OF IT. FOR NOW...BLENDED
THE TWO SOLUTIONS TO COME UP WITH THE TIMING OF THE STRATUS FOR
KSUX AND KFSD BETWEEN 00Z AND 06Z TUESDAY. RIGHT NOW...IT APPEARS
THE STRATUS WILL BE LOWER END MVFR...BUT COULD NOT RULE OUT THE
POSSIBILITY OF IFR CONDITIONS.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...BLIZZARD WATCH FROM TUESDAY MORNING THROUGH TUESDAY AFTERNOON
     FOR SDZ038>040-050-052>061-063-064.

MN...BLIZZARD WATCH FROM TUESDAY MORNING THROUGH TUESDAY AFTERNOON
     FOR MNZ071-072-080-081-097.

IA...NONE.
NE...NONE.
&&

$$

UPDATE...MJ
SHORT TERM...CHAPMAN
LONG TERM...08
AVIATION...MJ


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