Sunrise 5:38 AM   Sunset 8:00 PM Moonrise 3:37 AM   Moonset 2:41 PM

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FXUS63 KUNR 031124 AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 524 AM MDT Fri May 3 2024

KEY MESSAGES

- Cool with showers today. Minor snow accumulations possible in the Black Hills.

- Warmer and windy this weekend

- Strong Storm system early next week with potential for several hazards; severe thunderstorms Monday, locally heavy rain Monday/Tuesday (northeastern Wyoming/northwestern South Dakota), high winds Tuesday/Wednesday, snow for the Black Hills Tuesday/Wednesday.

DISCUSSION
(Today Through Thursday)
Issued at 240 AM MDT Fri May 3 2024

Current surface map places low across northwestern Minnesota with cold front across eastern South Dakota into northern Nebraska. Water vapor shows shortwave over eastern Montana and another over southern Idaho. The pair of shortwaves track eastward today. Best lift occurs later this morning through early evening over southern half of the forecast area along low level baroclinic zone. Thermal profiles support snow in the Black Hills. High resolution models point to accumulating snow for the higher elevations with HRRR mean around 3" (10:1 SLR) and the 25th-75th percentile is 1"-5". Given expected snowfall rates (<0.5"/hour)
and time of day, SLR's should be 25-50% lower. That still gives an inch or two of snow accumulation which should mainly be limited to grassy/elevated surfaces.

Surface high drops across the area early Saturday with dry weather expected. As the high shifts east during the day southerly flow increases. Shortwave ridge aloft crosses the area early Sunday as deep low tracks through the Great Basin. Tight pressure gradient will result in windy conditions Sunday. Highs warm into the 60s for Saturday and 70s on Sunday.

Upper low swings through the Rockies into the Northern Plains Monday with low stalling out over Dakotas Tuesday. Low then slowly drifts southeast on Wednesday. Decent agreement with deterministic GFS/ECMWF/GEM, through there are some minor differences in the details. Chance of showers/thunderstorms increase late Sunday/Sunday night with an uptick in buoyancy/theta-e advection on nose of low level jet. Looks to be widespread showers/thunderstorms Monday as robust QG forcing lifts through the area. Timing of best lift/buoyancy/shear could result in a threat of severe thunderstorms Monday afternoon. Focus for widespread rains will come as TROWAL wraps around the upper low Monday night through Wednesday. At this time, the heaviest rains appear to be north/northwest of the forecast area, though the LREF paints 40-50% probability of >1.50" QPF for parts of northeastern Wyoming into the northern Black Hills and northwestern South Dakota. Even with the potential for locally heavy rain, threat of any flooding is very low. Biggest issue with the storm will be very strong west-northwest winds. Will likely see gusts of 50-60 mph, especially on the plains north and east of the Black Hills.
Thermal profiles marginally cold enough that there could be some snow in the northern Black Hills Tuesday/Wednesday. However there is a wide spread in low level temperatures resulting in low confidence in any snowfall amounts. LREF has small area in the higher elevations with 30-60% probability of >6".

AVIATION
(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 522 AM MDT Fri May 3 2024

MVFR/local IFR conditions expected in rain/snow today, across parts of northeastern WY and SW to south central SD. Conditions will gradually improve to VFR from west to east this evening.

UNR WATCHES/WARNINGS/ADVISORIES
SD...None.
WY...None.

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