705
FXUS63 KFSD 181133
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
633 AM CDT SUN MAY 18 2025
KEY MESSAGES
- AREAS OF FROST ARE POSSIBLE TONIGHT INTO SUNDAY MORNING,
MAINLY FOR LOCATIONS ALONG AND NORTH OF A HURON, SOUTH DAKOTA
TO SIOUX FALLS, SOUTH DAKOTA TO JACKSON, MINNESOTA LINE.
LINGERING STRATUS CLOUDS MAY PREVENT TEMPERATURES FROM
FALLING LOW ENOUGH FOR WIDESPREAD FROST, BUT PATCHY FROST IS
STILL POSSIBLE.
- ISOLATED SEVERE WEATHER IS POSSIBLE SUNDAY NIGHT INTO MONDAY
MORNING. LARGE HAIL WILL BE THE MAIN HAZARD.
- WIDESPREAD RAIN ALONG WITH SOME THUNDERSTORMS IS EXPECTED
MONDAY THROUGH WEDNESDAY. CHANCES FOR EXCEEDING ONE INCH OF
RAIN REMAIN HIGH AT (70-100%). CHANCES FOR EXCEEDING 2 INCHES
IS MODERATE (30-50%).
DISCUSSION
ISSUED AT 309 AM CDT SUN MAY 18 2025
TODAY AND TONIGHT: LOOKING AT GOES SATELLITE WE SEE LINGERING
STRATUS NORTH OF A LINE FROM DE SMET SOUTH DAKOTA TO SPIRIT LAKE
IOWA. HREF GUIDANCE SHOWS THIS STRATUS HANGING OUT THROUGH THE
OVERNIGHT AND EVEN PUSHING SOUTHWEST A BIT. AT THE SAME TIME CLOUDS
ARE INCREASING FROM THE SOUTHWEST AS A STRONG LOW PRESSURE SYSTEM
WORKS ITS WAY THROUGH THE ROCKIES AND OUT ONTO THE PLAINS. THE
INCREASED CLOUD COVER WILL LIKELY KEEP OUR LOW TEMPERATURES A BIT
WARMER THAN THE FORECAST FROM 24 HOURS AGO. HOWEVER, DEWPOINTS ARE
STILL EXPECTED TO FALL INTO THE LOW 30S. SO WHILE CONFIDENCE IN
WIDESPREAD FROST HAS DECREASED, PATCHY FROST IS STILL POSSIBLE IN
THE AREA OUTLINED IN THE FROST ADVISORY. WITH THIS UNCERTAINTY IN
MIND, HAVE DECIDED TO LEAVE THE HEADLINE AS IS, AND WE'LL SEE WHERE
THE TRENDS TAKE US. CURRENTLY THE FROST ADVISORY RUNS FROM 1 AM
UNTIL 9 AM THIS MORNING.
LOOKING AGAIN AT GOES SATELLITE WATER VAPOR IMAGERY WE CAN SEE THE
STRONG LOW PRESSURE SYSTEM DIGGING SOUTH THROUGH THE CENTRAL
ROCKIES, WHILE ZONAL FLOW ALOFT IS THE STORY FOR OUR REGION TODAY.
WINDS THIS MORNING WILL BE EASTERLY AND LIGHT. WAA AHEAD OF THE
APPROACHING WAVE HELPS THE 925 MB TEMPERATURES WARM TO 12-16 DEGREES
C. MIXING THESE DOWN WE CAN EXPECT HIGHS IN THE LOW 60S TO LOW 70S.
BY THIS AFTERNOON WE WILL SEE THE UPPER TROUGH BEGIN TO TAKE ON A
SLIGHTLY NEGATIVE TILT AS THE SURFACE LOW EJECTS OUT OF COLORADO
ONTO THE CENTRAL PLAINS. THIS LOW WILL ACCELERATE NORTHEASTWARDS,
CONTINUING TO PUSH STRONG WAA AHEAD OF IT. IN ADDITION, WINDS WILL
REMAIN EASTERLY BUT INCREASE IN RESPONSE TO THE TIGHTENING SPG. BY
AFTERNOON GUSTS OF 25-30 MPH WILL BE FREQUENT, WITH LOCALLY HIGHER
GUSTS TO 35 MPH POSSIBLE OVER CENTRAL SOUTH DAKOTA. BY THIS EVENING,
A STRONG LOBE OF PVA WILL WORK WITH THE WAA TO ENHANCE THE POTENTIAL
FOR EVENING AND OVERNIGHT THUNDERSTORM DEVELOPMENT. TRENDS HAVE KEPT
THE BEST DYNAMICS JUST TO THE SOUTH OF OUR AREA. HOWEVER, MODEST
ELEVATED CAPE OF AROUND 600 J/KG AND 30-40 KTS OF 0-6 KM BULK SHEAR
HAS THE POTENTIAL TO SUPPORT SOME ISOLATED AND ELEVATED STRONG TO
SEVERE THUNDERSTORMS CAPABLE OF PRODUCING HAIL UP TO THE SIZE OF
QUARTERS. THE LATEST GUIDANCE INDICATES STRONGER STORMS ARE MOST
LIKELY TO DEVELOP ALONG THE MISSOURI RIVER. THE SPC DAY 1 MARGINAL
RISK (LEVEL 1 OF 5) FOR SEVERE THUNDERSTORMS APPEARS TO BE IN GOOD
SHAPE.
MONDAY-WEDNESDAY: SHOWERS AND THUNDERSTORMS WILL MOVE NORTH THROUGH
THE DAY MONDAY INTO THE EVENING AND OVERNIGHT. EASTERLY WINDS ARE
EXPECTED TO REMAIN BREEZY OVERNIGHT AND INCREASE MONDAY MORNING.
GUSTS OF 30-35 MPH ARE LIKELY WITH LOCALLY HIGHER GUSTS UP TO 40 MPH
POSSIBLE. THESE WINDS WILL CONTINUE TO ADVECT IN MOISTURE RICH,
UNSTABLE AIR. MUCAPE OF 800-1300 J/KG MAY BE ENOUGH TO KEEP
INSTABILITY SHOWERS AND THUNDERSTORMS GOING THROUGH THE DAY.
CONFIDENCE IN STRONG TO SEVERE STORMS IS LOW DUE TO THE FACT THAT
THE ACTUAL BOUNDARY AND SOURCE OF GREATEST LIFT REMAINS SOUTH OF THE
REGION. HOWEVER, IF THIS BOUNDARY SHOULD MOVE FARTHER NORTH WE COULD
SEE MORE DEVELOPMENT OF SEVERE THUNDERSTORMS ALONG THAT BOUNDARY.
THE PRIMARY THREAT REMAINS HAIL, BUT STRONG WIND GUSTS ARE ALSO
POSSIBLE, AND THOUGH UNLIKELY, A TORNADO ALONG THE BOUNDARY CANNOT
BE RULED OUT. THIS IS SUPPORTED BY THE SPC DAY 2 OUTLOOK FOR A
SLIGHT RISK (LEVEL 2 OF 5) OF SEVERE THUNDERSTORMS. TIMING FOR
STRONGER STORMS IS MONDAY AFTERNOON INTO EARLY TUESDAY MORNING.
BY EARLY TUESDAY MORNING THE SURFACE LOW MOVES TO OUR SOUTHEAST AND
MOISTURE WRAPS AROUND TO THE BACKSIDE OF THE LOW. SHOWERS MAY THEN
INCREASE IN INTENSITY, ESPECIALLY FOR AREAS ALONG AND EAST OF I-29.
THIS IS DUE TO ANOTHER STRONG PUSH OF WAA AND LOBE OF STRONG PVA.
THE SYSTEM STALLS HERE FOR MOST OF THE DAY TUESDAY, WHICH COULD
RESULT IN TRAINING SHOWERS AND THUNDERSTORMS. WHILE FIELDS, STREAMS,
AND RIVERS SHOULD BE ABLE TO ABSORB HIGHER RAINFALL TOTALS, URBAN
AREAS MAY EXPERIENCE LOCALIZED FLOODING. THIS SYSTEM WILL BE
SLOW TO MOVE OFF, AND SHOWERS WILL CONTINUE TUESDAY EVENING AND
INTO WEDNESDAY. SOUNDING PROFILES REMAIN SATURATED WITH MODEST
OMEGA LIFT THROUGH THE DGZ, KEEPING SHOWERS GOING THROUGH MOST
OF WEDNESDAY AND POSSIBLY EVEN INTO THURSDAY MORNING. WHEN IT'S
ALL SAID AND DONE, WE CAN LOOK FORWARD TO BENEFICIAL RAIN ACROSS
THE REGION. ENSEMBLES CONTINUE TO INDICATE A HIGH PROBABILITY
(70-100%) OF SEEING AN INCH OR MORE OF RAIN ACROSS THE ENTIRE
REGION. THERE IS EVEN MODEST PROBABILITY (30-50%) OF 2 INCHES OR
MORE. THE AREA MOST LIKELY TO SEE THE HIGHER AMOUNTS IS
NORTHWESTERN IOWA, AND CENTRAL SOUTH DAKOTA. WHILE THERE IS
STILL TIME FOR CHANGES IN THE TIMING AND TRACK OF THIS SYSTEM,
ALL SIGNS CURRENTLY POINT TO A GOOD, SOAKING RAIN THE FIRST HALF
OF NEXT WEEK.
THURSDAY-AND-BEYOND: THE LINGERING SHOWERS THURSDAY SHOULD TAPER OFF
BY LATE MORNING. A HIGH PRESSURE RIDGE BUILDS IN FOR THE LATTER HALF
OF THE WEEK. SOUTHERLY SURFACE WINDS BRING WARMING TEMPERATURES
THROUGH THE WEEKEND, BACK INTO THE 70S. THE ACTIVE PATTERN CONTINUES
AS A "RIDGE RIDER" SHORT WAVE BRINGS CHANCES FOR PRECIPITATION AGAIN
SUNDAY.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 633 AM CDT SUN MAY 18 2025
VFR TO IFR CEILINGS THIS MORNING WILL GRADUALLY LIFT THIS MORNING.
STRATUS HAS LINGERED THIS MORNING FROM HURON SD SOUTHEAST TO IDA
GROVE IA. AT THE SAME TIME, CLOUDS ARE BEGINNING TO FLOW IN FROM THE
WEST-SOUTHWEST AHEAD OF A WAVE THAT IS CURRENTLY WORKING ITS WAY OUT
OF THE ROCKIES. THERE MAY BE PEAKS OF SUNSHINE THIS MORNING, BUT BY
THIS AFTERNOON A FAIRLY THICK LAYER OF STRATUS WILL SETTLE OVER THE
REGION.
WINDS WILL BE EASTERLY AND INCREASING THIS AFTERNOON. GUSTS OF 20-27
KTS ARE LIKELY THIS AFTERNOON, WITH SOME GUSTS TO 30 KTS OVER SOUTH
CENTRAL SOUTH DAKOTA. WINDS RELAX SLIGHTLY OVERNIGHT BUT THEN BEGIN
TO INCREASE AGAIN AFTER SUNRISE MONDAY. GUSTS 30-35 KTS ARE POSSIBLE
ACROSS MUCH OF THE REGION MONDAY. LLWS LOOKS TO BE POSSIBLE FROM
19.06Z UNTIL 19.12Z FROM THE JAMES RIVER VALLEY AND WEST. THIS WILL
LIKELY IMPACT KHON.
SHOWERS AND THUNDERSTORMS ARE POSSIBLE THIS EVENING AND OVERNIGHT.
SOME OF THESE MAY BE STRONG TO SEVERE WITH THE MOST LIKELY THREAT
BEING HAIL THE SIZE OF QUARTERS. PERIODIC AND SOMETIMES HEAVY
RAINFALL ARE EXPECTED THROUGH THE END OF THIS PERIOD INTO MONDAY AND
TUESDAY.
FSD WATCHES/WARNINGS/ADVISORIES
SD...FROST ADVISORY UNTIL 9 AM CDT THIS MORNING FOR SDZ038>040-
054>056-062.
MN...FROST ADVISORY UNTIL 9 AM CDT THIS MORNING FOR MNZ071-072-080-
081-089-090-097-098.
IA...NONE.
NE...NONE.
DISCUSSION...AJP
AVIATION...AJP
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