228
FXUS63 KFSD 171137
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
537 AM CST TUE DEC 17 2024
KEY MESSAGES
- A CLIPPER SYSTEM MOVES THROUGH THE AREA TODAY WITH
ACCUMULATING SNOW. HIGHEST SNOW TOTALS EXPECTED BETWEEN US
HIGHWAY 14 AND I-90, WITH 3 INCHES OR MORE OF SNOW. SNOW
TOTALS HAVE SHIFTED HIGHER AND FURTHER SOUTH THIS MORNING.
ADDITIONAL SHIFTS MAY STILL OCCUR.
- DUE TO INCREASING SNOWFALL AMOUNTS, A WINTER WEATHER ADVISORY
HAS BEEN ISSUED. EXPECT HAZARDOUS TRAVEL AND REDUCED
VISIBILITY IN FALLING SNOW.
- CONFIDENCE IS INCREASING IN THE POTENTIAL FOR ANOTHER ROUND OF
SNOW ON THURSDAY. HOWEVER, THE HIGHEST PROBABILITIES FOR SNOW
REMAIN ACROSS CENTRAL MINNESOTA.
- DRY CONDITIONS RETURN FOR THE END OF THE WEEK AND WEEKEND WITH
TEMPERATURES MODERATING BACK TO NEAR SEASONABLE.
DISCUSSION
ISSUED AT 407 AM CST TUE DEC 17 2024
TODAY AND TONIGHT: AWAITING THE ARRIVAL OF OUR NEXT SYSTEM THIS
MORNING, WITH THE SNOW TRACKING INTO WESTERN AND CENTRAL SD AS THE
WAVE EJECTS OUT OF WY. SNOW SHOULD MOVE INTO THE WESTERN PORTIONS OF
OUR AREA BY DAYBREAK, EXPANDING TOWARD THE I-29 CORRIDOR BY MID
MORNING. CONTINUE TO EXPECT A BAND OF SNOWFALL TO DEVELOP, WITH
INCREASING LIFT IN THE DGZ, VORTICITY MAXIMUMS AT 700 AND 500 MB,
700 MB WAA, AND STRENGTHENING FRONTOGENESIS (ESPECIALLY AT 850 MB
AND 700 MB) LINING UP LATER THIS MORNING THROUGH THE AFTERNOON
HOURS, SLIDING EAST THROUGH THE EVENING. OUR AREA IS ALSO FAVORED IN
THE LEFT FRONT ENTRANCE REGION OF THE UPPER LEVEL JET. SOME
SOUNDINGS THIS MORNING SHOW A DRY LAYER BETWEEN THE STRATUS AND THE
DGZ, WHICH COULD PLAY A ROLE IN THE DELAYING ONSET TIMING.
TRENDS HAVE CONTINUED TO WOBBLE THE BAND SOUTH, WITH THE HIGHEST
AMOUNTS NOW EXPECTED FOR THE SD HWY 34 AND MN HWY 30 CORRIDOR. QPF
TRENDED UP WITH THIS FORECAST PACKAGE AS WELL. THEREFORE, NOW EXPECT
A BROAD SWATH OF 1-3 INCHES NORTH OF A MENNO/BERESFORD/SPENCER IA
LINE TOWARD US HWY 14, WITH HIGHER AMOUNTS OF 3 TO 5 INCHES FOR THE
SD HWY 34/MN HWY 30 CORRIDOR. MOST OF THE DETERMINISTIC GUIDANCE IS
IN AGREEMENT WITH AMOUNTS AND PLACEMENT, ALTHOUGH THE NAM AND
CANADIAN REMAIN OUTLIERS (HIGHER AND/OR FURTHER SOUTH). THINK THE
PROGRESSIVE NATURE OF THE SYSTEM SHOULD KEEP AMOUNTS BELOW WARNING
CRITERIA (6 INCHES). SNOW MAY BE MODERATE AT TIMES, WITH VERY PATCHY
LOW (< 20%) PROBABILITIES OF HOURLY SNOWFALL RATES OVER 1". PERIODIC
SNOWFALL RATES OF 0.5" ARE MORE LIKELY, AROUND A 40-60% CHANCE.
GIVEN THE UPWARD TRENDS IN AMOUNTS, ISSUED A WINTER WEATHER ADVISORY
IN COLLABORATION WITH NEIGHBORS FOR THE AREAS MOSTLY LIKELY TO SEE 3
OR MORE INCHES OF SNOW. WINDS SHOULD BE LIGHT, WITH THE GUSTS AROUND
OR LESS THAN 20 MPH, AND STRONGEST OFFSET FROM HEAVIEST NOW. CAN'T
RULE OUT PATCHY BLOWING/DRIFTING. VISIBILITY WILL BE REDUCED IN
FALLING SNOW SO BE PREPARED FOR HAZARDOUS TRAVEL.
NOW, WATCHING SOME OF THE EARLY 17.06Z DATA, CONCERN REMAINS THAT
THE HEAVIER BAND MAY WOBBLE SOUTH THROUGH THE MORNING - NAMELY WITH
THE 06Z CANADIAN. ADDITIONALLY, WITH FORCING MECHANISMS AT DIFFERENT
LAYERS BEING FAVORED THROUGH TODAY, SOME GUIDANCE POINTS TO MORE
THAN ONE LOCALIZED AREA OF HEAVIER SNOWFALL (ONE NORTH OF I-90 AND
THE OTHER SOUTH). THEREFORE, CONFIDENCE IS A LITTLE LOWER THAN
AVERAGE WITH EXACT PLACEMENT OF THE BAND. WILL CONTINUE TO MONITOR
TRENDS, BUT FURTHER SHORT TERM ADJUSTMENTS TO AMOUNTS AND HEADLINES
ARE POSSIBLE.
TEMPERATURES TODAY IN THE 20S AND 30S. LOWS TONIGHT IN THE TEENS.
WEDNESDAY: A REPRIEVE FROM SNOW CHANCES ON WEDNESDAY WITH SHORT
LIVED SURFACE HIGH PRESSURE TO THE EAST AND MID/UPPER LEVEL RIDGING.
A COOLER DAY WITH NEW SNOW COVER AND PREVAILING CAA - HIGHS IN
THE UPPER TEENS IN SOUTHWESTERN MN TO THE LOWER 30S IN SOUTH CENTRAL
SD.
WITH THE NEXT SYSTEM BEGINNING ITS APPROACH WEDNESDAY NIGHT, WE'LL
SEE INCREASING WINDS SOUTHEASTERLY WINDS THROUGH THE OVERNIGHT AS
THE SURFACE PRESSURE GRADIENT (SPG) TIGHTENS - GUSTS TO 25 MPH COULD
LEAD TO PATCHY BLOWING AND DRIFTING SNOW FOR AREAS WITH NEW SNOW
PACK.
THURSDAY AND ONWARD: AFOREMENTIONED NEXT SYSTEM MOVES THROUGH OUR
AREA THURSDAY AND THURSDAY NIGHT. GUIDANCE IS COMING INTO BETTER
AGREEMENT WITH THE LOW PRESSURE TRACK, SO CONFIDENCE IS INCREASING
IN ACCUMULATING SNOWFALL THURSDAY AND THURSDAY NIGHT. HIGHEST
PROBABILITY (40%+) OF A TENTH OF AN INCH OR MORE OF QPF CONTINUES TO
BE FOR THE BUFFALO RIDGE AND NORTHEASTWARD. THIS PARAMETER ALSO CAN
BE AN ESTIMATOR OF WHERE THE HIGHEST CHANCES OF ROUGHLY 1.5 INCHES
OR MORE OF SNOW ARE POSSIBLE, USING SNOW RATIOS 15:1. PROBABILITY IS
MODERATE TO HIGH (50% OR MORE) THAT MOST OF THE AREA WILL SEE
ACCUMULATING SNOW. WINDS WILL BE MUCH STRONGER WITH THIS SYSTEM, SO
EVEN MINOR SNOW ACCUMULATIONS COULD LEAD TO BLOWING AND DRIFTING.
STRONGEST GUSTS WILL BE OFFSET IN LOCATION FROM THE HEAVIEST SNOW.
REGARDLESS, IF YOU HAVE TRAVEL PLANS THURSDAY, KEEP AN EYE ON THE
FORECAST AND PREPARE TO ADJUST PLANS.
AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 524 AM CST TUE DEC 17 2024
MVFR STRATUS OVERNIGHT HAS LINGERED THIS MORNING, WAVERING IN
SPATIAL COVERAGE. GUIDANCE IS NOT HANDLING THIS DECK WELL, AND
WITH MID AND HIGH CLOUDS INCREASING, IT IS DIFFICULT TO DISCERN
HOW WIDESPREAD THIS IS ACROSS SOUTHWESTERN MN AND EASTERN SD.
OTHERWISE, VFR CONDITIONS DETERIORATE FROM WEST TO EAST THIS
MORNING THROUGH THE AFTERNOON HOURS AS SNOW MOVES IN. EXPECT
MVFR/IFR CEILINGS AND VISIBILITY WHILE SNOW IS ON-GOING.
GREATEST CHANCES FOR SNOW AND HIGHEST ACCUMULATIONS ARE EXPECTED
NORTH OF I-90 TOWARD US HIGHWAY 14. LIFR VISIBILITY EXPECTED IN
THE HEAVIEST SNOW.
SNOW MOVES EAST THROUGH THE AFTERNOON, TAPERING OFF FROM WEST TO
EAST DURING THE EVENING HOURS AND INTO TONIGHT. SNOW LINGERS
LONGEST ALONG/EAST OF IA/MN STATE HIGHWAY 60. WINDS THROUGH THE
PERIOD SHIFT FROM EASTERLY TO NORTHWESTERLY. GUSTS AROUND 15 TO
20 KNOTS EXPECTED - STRONGEST IN SOUTH CENTRAL SD AWAY FROM THE
HEAVIEST ANTICIPATED SNOWFALL.
AS SNOW ENDS, EXPECT IMPROVING CONDITIONS AFTER MIDNIGHT TONIGHT.
FSD WATCHES/WARNINGS/ADVISORIES
SD...WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 9 PM CST
THIS EVENING FOR SDZ039-040-054>056.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR SDZ038-
052-053-057>059.
MN...WINTER WEATHER ADVISORY FROM 9 AM THIS MORNING TO 9 PM CST
THIS EVENING FOR MNZ071-072-080-081-089-090-097.
IA...NONE.
NE...NONE.
DISCUSSION...SG
AVIATION...SG
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