Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 131641
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1041 AM MDT Wed Mar 13 2024

.KEY MESSAGES...
153 AM MDT Wed Mar 13 2024

- Splitting upper-trough brings light precipitation, windy, and
  cooler weather today and Thursday
- Dry weather returns with breezy/windy spots over the weekend as
  a cold front brings a glancing blow of cooler air

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 153 AM MDT Wed Mar 13 2024

07z surface analysis had weak cool front just south of CWA
curving southwest into CO. Water vapour loop had upper trough
across the Rockies with main energy diving southward from northern
ID. Clouds streaming ahead of trough over the CWA as lift
encounters dry air in place. Effect of trough main forecast
concern.

Today through Thursday, upper trough splits with main energy
diving well south into the southwest US with weaker northern
stream energy caressing the US/Canadian border. Most guidance has
trended further southwest with the main energy and thus, main
cyclogenesis is further south. Result will be initial fetch of
drier northeast boundary layer flow into the CWA, which will
impede saturation ahead of upper trough. Main precipitation
delayed a bit with focus shifting southwest along inverted
surface trough. Upslope flow for the northern Black Hills present,
but less moisture/flow has cut back QPF amounts by 50%. QPF
>0.10" chances around 50% along the SD/NE border into east-
central WY. QPF >0.25" chances around 50% in far southwest
Campbell County. This translates to substantial reduction in snow
amounts with a marginal chance of local 4" amounts southwest of
Wright, WY. Recent warm temperatures and marginal wet bulb zero
heights will also impede snowfall during the day. Will forgo
headlines this morning and let day shift reassess as main effects
come later tonight/Thursday. Breezy/windy spots expected late
tonight/Thursday as gradient increases (40-70% chance of 41kt
gusts for a small small area just east of the Black Hills). Have
bumped up temperatures a tad per precipitation delay across
northeast half of CWA. Otherwise, near guidance.

Friday, breezy spots expected as temperatures rebound. Cold front
associated with upper trough zipping from central Canada into the
Midwest brings glancing blow of cold air for the area this weekend.
Temperatures rebound for the first half of next week as upper
ridge builds from the west coast into central North America.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1041 AM MDT Wed Mar 13 2024

Areas of MVFR/IFR conditions in SHRA/SN will expand across
northeastern WY and potentially into the Black Hills through 00z,
though with the parent system taking an increasingly southward
track, these reduced conditions are expected to cover a smaller
area than in previous forecasts. MVFR/IFR conditions are then
expected to erode from northeast to southwest after 00z, with VFR
conditions prevailing for most by 06z. More widespread MVFR to
LIFR conditions may arrive behind a secondary front late in the
period (09z onward). Breezy to windy winds, predominantly out of
the north, are anticipated through much of the period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Sherburn


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