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000
FXUS63 KFSD 070001
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
601 PM CST FRI DEC 6 2013

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 324 PM CST FRI DEC 6 2013

HIGH PRESSURE MOVES OVERHEAD SETTING UP A FRIGID NIGHT ACROSS THE
AREA. ONE REGION OF CIRRUS WILL MOVE EAST OF THE AREA THIS
EVENING...WITH MID AND HIGH LEVEL CLOUDS INCREASING AGAIN FROM THE
WEST LATE TONIGHT. BUT THESE CLOUDS APPEAR TO BE DELAYED ON RECENT
MODEL RUNS...SUGGESTING GENERALLY CLEAR SKIES THROUGH THE
NIGHT...ESPECIALLY EAST OF THE JAMES RIVER. MOS WAS TOO WARM LAST
NIGHT...AND GIVEN THE SNOW COVER AND CALMER WINDS TONIGHT...FEEL
THAT WILL BE THE CASE AGAIN. THUS TRENDED THE FORECAST MORE TOWARDS
A COMPROMISE OF THE BIAS CORRECTED GEM REGIONAL AND ECMWF...WHICH
SEEM TO HANDLE THESE SITUATIONS DECENTLY WELL. THIS RESULTS IN A
SEVERAL DEGREE DROP FROM THE PREVIOUS FORECAST...READINGS AROUND 20
BELOW ZERO OVER THE SNOW COVER...AND NEGATIVE TEENS WHERE SNOW COVER
IS ABSENT. WINDS WILL DROP OFF...BUT WITH TEMPERATURES THAT COLD IT
ONLY TAKES A FEW MPH OF WIND TO REALLY DROP THE WIND CHILL. SO WILL
KEEP THE WIND CHILL ADVISORY GOING...AND EXPAND IT TO INCLUDE ALL OF
OUR COUNTIES. LOOKING AT WIND CHILLS IN THE 20 TO 30 BELOW ZERO
RANGE. WILL LIKELY EVEN SEE READINGS AROUND 35 BELOW ZERO ALONG THE
HIGHWAY 14 CORRIDOR...BUT AT THIS TIME DO NOT THINK THESE WILL BE
PERSISTENT OR WIDESPREAD ENOUGH TO ISSUE A WARNING.

DID EXTEND THE WIND CHILL ADVISORY UNTIL 18Z ACROSS MOST OF THE
AREA...AS WITH OUR VERY COLD LOWS IT WILL TAKE SOME TIME TO
RECOVER...AND JUST A FEW MPH OF WIND WILL DROP US BELOW CRITERIA.
MID AND HIGH LEVEL CLOUDS WILL SLOWLY INCREASE FROM SOUTHWEST TO
NORTHEAST THROUGH THE DAY...WITH SOME FLURRIES OR LIGHT SNOW
POSSIBLE BY 0Z IN GREGORY COUNTY. DID LOWER HIGHS A BIT OVER THE
SNOW COVER...WHERE SINGLE DIGITS WILL BE COMMON...WITH LOW TEENS
ELSEWHERE. WORRIED THESE HIGHS MIGHT BE A BIT TOO WARM GIVEN THE
EXPECTED VERY COLD START...BUT THEY SHOULD BE CLOSE.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 324 PM CST FRI DEC 6 2013

SATURDAY NIGHT WILL SEE SATURATION AND LIFT SPREAD ACROSS THE
CWA...ESPECIALLY THE SOUTHERN CWA. OVERALL LOOKING LIKE A BROAD
FORCING EVENT WITH LITTLE IF ANY BANDING OR LOCALIZED ENHANCEMENT.
THE ONLY HINT AT SOME LOCALIZED ENHANCEMENT WOULD BE A DEEPER
DENDRITIC LAYER IN THE THE SOUTHEASTERN CWA WITH TEMPERATURES COLDER
THAN DENDRITIC TO THE NORTH. THIS WOULD HINT AT THE POTENTIAL FOR
CLOSE TO 20:1 RATIOS IN THE SOUTH AND MAYBE CLOSER TO 12:1 TO 14:1.
OVERALL THE HINT IS FOR ABOUT A QUARTER OF AN INCH OF LIQUID IN THE
FAR SOUTHERN CWA TAPERING TO ABOUT A TENTH OR SO IN THE FAR NORTH.
WITH THIS BEING A BROAD ISENTROPIC LIFT TYPE EVENT WENT AHEAD AND
RAISED POPS MOST LOCATIONS BUT OVERALL SNOWFALL AMOUNTS SIMILAR TO
PREVIOUS FORECAST WITH AN INCH OR SO IN THE FAR NORTHERN CWA AND
ABOUT 4 TO 5 INCHES IN PARTS OF NORTHWEST IOWA. MAY NEED AN ADVISORY
AT SOME POINT WITH THE MOST LIKELY LOCATION SOUTH OF A VERMILLION TO
JACKSON MINNESOTA LINE. DID LOWER THE LOWS JUST A BIT OVER MAINLY
SOUTHWEST MN BUT HAVE THEM RISING THROUGH THE NIGHT.

MOST LOCATIONS WILL SEE SOME SNOW ON SUNDAY WITH THE SNOW GRADUALLY
TAPERING OFF FROM WEST TO EAST. VERY NICE DEEP DENDRITIC LAYER IN
NORTHWEST IOWA AND FEEL THAT SOME OF THE BETTER ACCUMULATIONS WILL
BE ON SUNDAY. BECAUSE OF THE CLOUDS AND SNOWFALL SUNDAY WILL PROVE
TO BE ONE OF OUR LEAST COLD DAYS WITH HIGHS FROM ABOUT 10 TO 15
ABOVE. BY SUNDAY NIGHT THE SNOW SHOULD BE CONFINED TO MAINLY EAST
OF INTERSTATE 29. ADDITIONAL AMOUNTS SHOULD BE LESS THAN AN INCH.
COLDER DRIER AIR WILL DRIVE INTO THE AREA WITH STRONG NORTHWEST WINDS
AND COLD TEMPERATURES LATE SUNDAY NIGHT THROUGH MONDAY. WITH THE
NEW SNOWPACK WILL HAVE TO ALSO BE CONCERNED ABOUT THE POTENTIAL
FOR BLOWING SNOW LATE SUNDAY NIGHT AND MONDAY MORNING AS THE SNOW
THAT FALLS WILL LIKELY BE FAIRLY FLUFFY. ANOTHER VERY GOOD CHANCE
FOR A WIND CHILL ADVISORY SUNDAY NIGHT INTO MONDAY AS SOMETHING
CLOSE TO -20 C RETURNS AT 925MB. WITH THE FRESH SNOWPACK HIGHS
WILL LIKELY STRUGGLE TO REACH 5 ABOVE.

IN THE OUTER PERIODS (TUE/FRI)...NORTH NORTHWEST FLOW ALOFT
GRADUALLY MODIFIES THROUGH THE PERIOD WHICH SHOULD HINT AT THE
POTENTIAL FOR SLIGHTLY LESS COLD READINGS...ALTHOUGH WITH THE BROAD
SNOW COVER AND THE EXPECTED 925MB FORECAST TEMPERATURES BELOW NORMAL
READINGS ARE STILL ANTICIPATED. IN FACT THE MODELS ARE FAIRLY
AGREEABLE IN SWINGING A NEW WAVE FROM WESTERN CANADA INTO THE
NORTHERN PLAINS FRIDAY INTO SATURDAY WHICH APPEARS TO BRING A
RESURGENCE OF ARCTIC AIR FOR NEXT WEEKEND. FOR TUESDAY WILL LEAN ON
THE COLD SIDE OF GUIDANCE AS ARCTIC AIR IS IN PLACE AND MEN GUIDANCE
IS BELOW THE MEX GUIDANCE WHICH IS WELL BELOW CLIMATOLOGY AND THIS
IS USUALLY A GOOD SIGN TO GO COLD. LOOKING PRETTY DARN COLD ON
WEDNESDAY MORNING AS WELL WITH HIGH PRESSURE NEAR OR OVERHEAD THEN
EXPECT GRADUAL MODIFICATION DURING THE DAY BUT WITH WIDESPREAD SNOW
COVER TEMPERATURES MAY NOT GO FAR. SOME TIMING DIFFERENCES START TO
SHOW UP ON THURSDAY WITH THE TIMING OF THE RETURN FLOW BUT THURSDAY
STILL LOOKING LIKE THE LEAST COLD DAY OF THE WEEK. THEN FRIDAY THE
COLDER AIR WILL START TO SURGE BACK INTO THE CWA SO BACK INTO THE
DEEP FREEZE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 544 PM CST FRI DEC 6 2013

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD WITH WINDS
GENERALLY 10 KT OR LESS.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WIND CHILL ADVISORY UNTIL NOON CST SATURDAY FOR SDZ038>040-050-
     052>071.

MN...WIND CHILL ADVISORY UNTIL NOON CST SATURDAY FOR MNZ071-072-080-
     081-089-090-097-098.

IA...WIND CHILL ADVISORY UNTIL NOON CST SATURDAY FOR IAZ001>003-
     012>014.

     WIND CHILL ADVISORY UNTIL 9 AM CST SATURDAY FOR IAZ020>022-031-
     032.

NE...WIND CHILL ADVISORY UNTIL 9 AM CST SATURDAY FOR NEZ013-014.

&&

$$

SHORT TERM...CHENARD
LONG TERM...08
AVIATION...