879
FXUS63 KFSD 111950
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
250 PM CDT TUE MAR 11 2025
KEY MESSAGES
- A STRONG SPRING STORM SYSTEM REMAINS ON TRACK FOR THE FRIDAY
THROUGH SATURDAY TIMEFRAME. MULTIPLE HAZARDS ARE POSSIBLE IN
THE FORMS OF THUNDERSTORMS, HIGH WINDS, AND SNOW. CONTINUE TO
CHECK THE LATEST FORECAST FOR THE MOST UP TO DATE INFORMATION.
- AS OF THIS TIME, THERE IS A 30-60% CHANCE FOR SNOWFALL TO
EXCEED AN INCH FRIDAY NIGHT THROUGH SATURDAY. THIS IS THE
SAME TIME PERIOD WHERE STRONG WINDS ARE LIKELY (30-60% CHANCE
FOR GUSTS TO EXCEED 50 MPH) TO OVERSPREAD MUCH OF THE AREA AND
PERSIST THROUGH THE DAY ON SATURDAY. THE STRONG WINDS
COMBINED WITH FALLING SNOW MAY RESULT IN TRAVEL IMPACTS ACROSS
THE AREA.
- ABOVE AVERAGE TEMPERATURES REMAIN ON TRACK TO CONTINUE THROUGH
MUCH OF THE UPCOMING WEEK. HIGH TEMPERATURES INTO THE 60S AND
70S ARE LIKELY FOR THE SECOND HALF OF THIS WEEK.
- ELEVATED FIRE DANGER IS POSSIBLE ON THURSDAY, MAINLY ALONG AND
WEST OF THE JAMES RIVER WHERE THE LOWEST HUMIDITY LEVELS LOOK
TO LIE.
DISCUSSION
ISSUED AT 249 PM CDT TUE MAR 11 2025
SEASONABLE CONDITIONS PERSIST ACROSS THE AREA THIS AFTERNOON AS HIGH
TEMPERATURES HAVE WARMED TO THE UPPER 30S AND 40S. WINDS REMAIN
LIGHT OUT OF THE EAST/SOUTHEAST, AS SURFACE RIDGING SLIDES EAST OF
THE FORECAST AREA. THIS WILL PUT A LOOSE SURFACE PRESSURE GRADIENT
(SPG) IN PLACE AND KEEP LIGHT WINDS GOING THROUGH THE NIGHT. A WEAK
SURFACE LOW WILL BEGIN TO PUSH IN FROM THE WEST LATE TONIGHT THOUGH.
THIS COULD RESULT IN PATCHY FOG TO DEVELOP IN LOW LYING AREAS AND IN
RIVER VALLEYS. OTHERWISE, LOW TEMPERATURES WILL FALL TO THE UPPER
20S TO LOW 30S.
850MB TEMPERATURES WILL WARM TO THE SINGLE DIGITS ALOFT ON WEDNESDAY
IN RESPONSE TO UPPER LEVEL RIDGING PUSHING INTO THE NORTHERN PLAINS.
MIXING THESE TEMPERATURES TO THE SURFACE WILL RESULT IN HIGH
TEMPERATURES INTO THE 60S ACROSS THE AREA. UPPER LEVEL RIDGING
PERSISTS THROUGH THURSDAY BUT WARM AIR ADVECTION (WAA) WILL
STRENGTHEN ACROSS THE REGION, PUSHING 850 MB TEMPERATURES UP TO THE
LOW TEENS ALOFT. THIS WILL RESULT IN WELL ABOVE AVERAGE HIGH
TEMPERATURES INTO THE 70S. AT THE SAME TIME, LOW LEVEL PRESSURE
GRADIENTS WILL TIGHTEN, LEADING TO BREEZY WINDS ACROSS THE AREA. THE
VERY WARM TEMPERATURES WILL RESULT IN LOWER RELATIVE HUMIDITY
VALUES, LOWEST WEST OF THE JAMES RIVER. WITH LOWER HUMIDITY AND
BREEZY WINDS IN PLACE, ELEVATED FIRE DANGER IS POSSIBLE, ESPECIALLY
ALONG AND WEST OF THE JAMES RIVER WHERE HUMIDITY WILL BE LOWEST.
THIS POTENTIAL IS SUPPORTED BY THE HOT DRY WINDY INDEX (HDWI) AS IT
SHOWS NEARLY 100% OF ITS MEMBERS EXCEEDING THE 75TH PERCENTILE OF
ITS CLIMATOLOGY. FIRE DANGER TRENDS WILL BE MONITORED.
THE POWERFUL STORM SYSTEM REMAINS ON TRACK TO BEGIN IMPACTING THE
AREA ON FRIDAY AS THE MAIN WAVE EJECTS INTO THE PLAINS FROM THE
ROCKIES. WITH AN UNSTABLE ENVIRONMENT IN PLACE, THIS WAVE WILL
DEVELOP A STRONG SURFACE LOW PRESSURE SYSTEM VIA LEE CYCLOGENESIS.
THIS LOW WILL TRAVEL NORTHEASTWARDS THROUGHOUT THE DAY, RESULTING IN
BROAD SOUTHEAST FLOW INTO THE FORECAST AREA. THIS WILL BEGIN "PHASE
1" OF THIS SYSTEM AS THE WARM SECTOR FOR THIS SYSTEM SETS UP.
HOWEVER, THERE REMAINS UNCERTAINTY IN HOW FAR WEST THE BETTER
MOISTURE CAN BE PULLED. LATEST ENSEMBLE PROBABILITIES FOR EXCEEDING
A 50F DEW POINT CONTINUE TO KEEP THE BETTER MOISTURE ALONG AND EAST
OF I-35. THIS LEAVES ONLY A 20-50% CHANCE FOR THESE DEW POINTS TO BE
PULLED INTO PARTS OF NORTHWEST IOWA. THAT SAID, AN ELEVATED MIXED
LAYER (EML) WILL BE ADVECTED INTO LOCATIONS DOWNSTREAM OF THE
INCOMING WAVE, RESULTING IN STEEP MID LEVEL LAPSE RATES AND
INSTABILITY. GIVEN THE LACK OF BETTER MOISTURE, INSTABILITY VALUES
LOOK TO BE ON THE LOW SIDE. THIS IS SUPPORTED BY THE ENSEMBLES AS
THEY SHOW ONLY A 40-60% CHANCE FOR CAPE VALUES TO EXCEED 500 J/KG.
HOWEVER, THERE IS ENOUGH INSTABILITY IN PLACE WHERE THERE IS A NON-
ZERO CHANCE FOR STRONG TO SEVERE STORMS GIVEN THE STRONG LIFT WITH
THE SYSTEM. AS OF NOW, PARTS OF NORTHWEST IOWA LOOK TO HAVE THE
HIGHEST POTENTIAL FOR SEEING ANY STRONG TO SEVERE STORMS.
ANY CHANCE FOR STORMS WILL COME TO AN END FRIDAY EVENING. WHILE THIS
PHASE OF THE SYSTEM WILL BE ENDING, "PHASE 2" WILL BEGIN. THIS IS
THE TIME PERIOD WHERE TEMPERATURES WILL BE QUICKLY FALLING AND
PRECIPITATION WILL BE TRANSITIONING FROM RAIN TO SNOW. ON TOP OF THE
SNOW, WINDS WILL BE STRENGTHENING AS WELL GIVEN HOW 850 MB WINDS
LOOK TO TOP OUT AT ABOUT 50 KNOTS. THESE STRONG WINDS ARE SUPPORTED
BY THE NATIONAL BLEND OF MODELS (NBM) AS IT SHOWS A 30-60% CHANCE
FOR WIND GUSTS TO EXCEED 50 MPH FROM FRIDAY NIGHT THROUGH SATURDAY.
IN TERMS OF SNOW, THE SNOW LOOKS TO BE DRIVEN BY A TROUGH OF WARM
AIR ALOFT (TROWAL) THAT DEVELOPS AS THE SYSTEM OCCLUDES. SNOWFALL
AMOUNTS REMAIN UNCERTAIN AT THIS TIME DUE TO THE QUICK MOVEMENT OF
THE SYSTEM AND THE POTENTIAL FOR THUNDERSTORMS TO PULL SOME OF THE
MOISTURE AWAY FROM THE AREA. AS OF NOW, THE ENSEMBLES SHOW A BROAD
30-60% CHANCE FOR EXCEEDING AN INCH OF SNOW. THEY ALSO SHOW A 20-40%
CHANCE FOR EXCEEDING 3 INCHES OF SNOW (ADVISORY LEVEL SNOWFALL).
HOWEVER, ANY FALLING SNOW COMBINED WITH THE STRONG WINDS WILL RESULT
IN POTENTIAL NEAR BLIZZARD TO BLIZZARD CONDITIONS, MAINLY WHEN SNOW
IS FALLING. THESE CONDITIONS MAY RESULT IN DIFFICULT TRAVEL ACROSS
THE AREA. THIS SECOND PHASE OF THE SYSTEM WILL PULL NORTHEASTWARDS
BY SATURDAY EVENING, LEAVING DRY CONDITIONS IN ITS WAKE.
THE DRY CONDITIONS ARE EXPECTED TO CONTINUE THROUGH SUNDAY AND EARLY
NEXT WEEK. SUNDAY WILL SEE COOLER HIGHS ONLY UP TO THE MID 30S TO
MID 40S BEFORE TEMPERATURES REBOUND BACK INTO THE 50S AND
POTENTIALLY 60S ON MONDAY AND TUESDAY.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1223 PM CDT TUE MAR 11 2025
VFR CONDITIONS ARE EXPECTED FOR THE TAF PERIOD. MAINLY CLEAR SKIES
AND LIGHT NORTHEAST/EASTERLY WINDS BEGIN THE TAF PERIOD. WINDS WILL
REMAIN LIGHT WHILE VEERING TO OUT OF THE SOUTHEAST BY THIS EVENING
WITH SPEEDS UP TO ONLY 5-10 KNOTS. THE LIGHT SOUTHEASTERLY WINDS
WILL PERSIST THROUGH THE OVERNIGHT HOURS BEFORE WINDS BEGIN TO TURN
OUT OF THE NORTH TOMORROW MORNING. THERE COULD BE SOME PATCHY FOG
DURING THE OVERNIGHT HOURS, MAINLY IN LOW LYING AREAS AND RIVER
VALLEYS. HOWEVER, CONFIDENCE IS FAR TOO LOW TO INCLUDE IN A TAF AT
THIS TIME.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...MEYERS
AVIATION...MEYERS
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