311
FXUS63 KUNR 282240
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
440 PM MDT FRI MAR 28 2025
KEY MESSAGES
- MILD AND ELEVATED FIRE WEATHER CONDITIONS THROUGH THIS
AFTERNOON, PARTICULARLY ACROSS SOUTHWESTERN SOUTH DAKOTA.
- WIDESPREAD PRECIPITATION BEINGS TONIGHT AND PERSISTS THROUGH
SUNDAY. HEAVIEST PRECIPITATION ALONG AND SOUTH OF I-90.
- CONFIDENCE REMAINS LOW ON FINAL SNOW AMOUNTS, PARTICULARLY
ACROSS THE WYOMING AND SOUTH DAKOTA PLAINS.
DISCUSSION
(THIS EVENING THROUGH FRIDAY)
ISSUED AT 246 PM MDT FRI MAR 28 2025
WATER VAPOR IMAGERY DEPICTS ACTIVE SOUTHWESTERLY FLOW WITH LEAD
SHORTWAVE TROUGH LIFTING THROUGH WESTERN ND INTO SOUTHERN
SASKATCHEWAN/MANITOBA. FURTHER UPSTREAM, A STRONG SHORTWAVE IS
EVIDENT LIFTING OUT OF THE FOUR CORNERS REGION INTO THE CENTRAL
ROCKIES. LEE CYCLOGENESIS IS OCCURRING ACROSS EASTERN CO/WESTERN KS
WITH ONE SURFACE BOUNDARY STRETCHING FROM SOUTHERN MT THROUGH
EASTERN NE INTO WESTERN KS/OK; A SECOND BOUNDARY (WITH MUCH COLDER
AIR BEHIND IT) IS ANALYZED SURGING SOUTHWARD ACROSS NORTHWESTERN SD.
THE UPPER LEVEL SHORTWAVE OVER THE FOUR CORNERS WILL LIFT THROUGH
THE FORECAST AREA EARLY SATURDAY WITH A SECOND SHORTWAVE TROUGH
ARRIVING IN THE FORECAST AREA EARLY SUNDAY MORNING. AMPLE SYNOPTIC
LIFT WILL OVERSPREAD THE AREA COUPLED WITH STRENGTHENING LOW-LEVEL
FRONTOGENESIS ACROSS SOUTH-CENTRAL SD INTO CENTRAL SD.
WIDESPREAD PRECIPITATION WILL OVERSPREAD THE REGION EARLY SATURDAY
MORNING WITH HEAVIEST RAIN/SNOW FALLING DURING THE DAY AND EVENING
SATURDAY. RECENT MODEL TRENDS HAVE SHIFTED THE AXIS OF HEAVIEST QPF
SLIGHTLY SOUTH WITH NORTHEASTERLY LOW-LEVEL FLOW ADVECTING DRIER AIR
INTO THE NORTHERN PORTION OF THE FORECAST AREA DURING THE AFTERNOON
AND EVENING SATURDAY. LATEST NBM AND ENSEMBLE GUIDANCE HAS HIGHEST
QPF POTENTIAL ALONG AND SOUTH OF I-90, FROM NORTHEASTERN WY INTO
SOUTH-CENTRAL SD; CHANCES OF >0.1" ~95%; >0.25" ~70-85%; AND
>0.5" ~50-75%.
BEFORE WE GET TO A DISCUSSION REGARDING THE UNCERTAINTY ASSOCIATED
WITH THIS STORM, IT WOULD HELP TO SUMMARIZE THE CURRENT SNOW AND
QPF FORECAST TONIGHT THROUGH SUNDAY: 2-5" OF SNOW IN THE BLACK
HILLS WITH 1-3" ACROSS THE PLAINS (SOUTH OF I-90); HIGHEST AMOUNTS
FOCUSED INTO SOUTH-CENTRAL SD. WIDESPREAD LIQUID PRECIPITATION
AMOUNTS >0.25" IS LIKELY FROM NE WY INTO WESTERN SD, AGAIN, MAINLY
ALONG AND SOUTH OF I-90.
AS IS TYPICAL FOR SPRING STORMS, CONSIDERABLE UNCERTAINTY REMAINS
REGARDING SNOW AMOUNTS. THE LOWEST CONFIDENCE AND HIGHEST UNCERTAINTY
WITH THIS STORM REVOLVES AROUND SNOW AMOUNTS ACROSS THE WESTERN SD
PLAINS INTO SOUTH-CENTRAL SD. FACTORS COMPLICATING THE SNOWFALL
FORECAST: 1) THE EXTENT OF DRY AIR INTRUSION OUT OF THE NE, 2)
DYNAMIC COOLING/EXTENT OF LOW-LEVEL COOLING, 3) DIURNAL EFFECTS, AND
4) SNOWFALL RATES AND/OR BANDED PRECIPITATION POTENTIAL. THE LATEST
FORECAST BRINGS AN INTRUSION OF DRIER AIR INTO THE AREA ALONG WITH A
MORE SOUTHERLY TRACK OF THE SYSTEM, WHICH HAS RESULTED IN THE QPF
AXIS SHIFTING SOUTHWARD FROM PREVIOUS FORECASTS. ADDITIONALLY, THE
CURRENT FORECAST REFLECTS THE POTENTIAL FOR CONSIDERABLE MELTING
GIVEN THAT THE HEAVIEST PRECIPITATION FALLS DURING THE DAY SATURDAY
WITH MARGINAL SURFACE TEMPERATURES. SHOULD COLDER AIR FILTER IN
MORE QUICKLY AND/OR DYNAMIC COOLING RESULT IN COLDER LOW-LEVEL
THERMAL PROFILES, THE SNOW POTENTIAL WILL BE HIGHER THAN FORECAST.
FINALLY, SNOWFALL RATES MAY ULTIMATELY MAKE OR BREAK THIS FORECAST;
RECENT CAMS AND THE 12Z HREF SUITE SHOW THE POTENTIAL FOR HEAVIER,
BANDED PRECIPITATION ACROSS SOUTH-CENTRAL SD DURING THE AFTERNOON
AND EVENING SATURDAY. ANY HEAVIER, MESOSCALE BANDS OF SNOW WOULD
YIELD STRONGER DYNAMIC COOLING AND HIGHER SNOWFALL RATES, WHICH
WOULD YIELD MORE EFFICIENT SNOW ACCUMULATION. HIGHER SNOW AMOUNTS
CLOSER TO 3-6" COULD BE POSSIBLE WITH ANY BANDED SNOW LATE SATURDAY
ACROSS SOUTH-CENTRAL SD.
ACTIVE FLOW IS EXPECTED TO PERSIST THROUGH THE WEEK WITH ANOTHER
SYSTEM BRINGING WIDESPREAD QPF TO THE AREA MID-WEEK. ENSEMBLES AND
CLUSTER ANALYSIS DEPICT ACTIVE, WETTER PATTERN WILL CONTINUE THROUGH
AT LEAST NEXT WEEKEND.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 437 PM MDT FRI MAR 28 2025
GUSTY NORTH-NORTHWEST WINDS ACROSS THE WESTERN SD PLAINS WILL
DECREASE THROUGH THIS EVENING. CLOUDS WILL INCREASE THIS EVENING
AS A SYSTEM APPROACHES THE AREA. MVFR CONDITIONS WITH RAIN WILL
SPREAD ACROSS MUCH OF THE AREA TONIGHT, THEN BECOMING IFR/LIFR AS
PRECIP CHANGES TO SNOW OVERNIGHT INTO SATURDAY MORNING. THERE IS
STILL LOW CONFIDENCE IN THE TIMING OF THIS TRANSITION TO SNOW.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...SE
AVIATION...WONG
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