Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 270245

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
845 PM MDT Wed Apr 26 2017

Issued at 844 PM MDT Wed Apr 26 2017

Fairly quiet evening in store across the region as mid/high clouds
have dissipated...and low cloud shield has slowly shrunk over
time. Am a bit concerned that with snow melt this afternoon and
fcst models showing light low level winds...that there might be
some shallow ground fog setting up. Fcst soundings from the HRRR
and NAM12 lean toward that possibility. Not sure that it is worth
mentioning in the grids...but did make a mention in the TAFs.


.DISCUSSION...(This Evening Through Wednesday)
Issued at 337 PM MDT Wed Apr 26 2017

Current surface analysis shows weak high pressure nosing south
out of central Canada and into the Dakotas. Low pressure is
located across southern BC, with cold front stretching across the
Pacific NW. Upper level analysis shows weakening low moving
northeast away from the Dakotas, with cutoff low over southwest
Canada. Strong jet in place from the Pacific NW to the Southern
Plains, with developing shortwave sliding east-southeast across
eastern portions of OR and WA. Clouds have been very slow to
dissipate across our area today, especially from west central to
south central SD. Skies are variably cloudy in most places with
very cool temps, mid 30s to mid 40s. Some showers have developed
south of our northeast WY zones, moving eastward. A few light
showers could clip far southern Campbell County through early

The next system will begin to impact the area on Thursday, with
chances for showers increasing across northeast WY into southwest
SD, especially by the afternoon. Most of the pcpn should be in the
form of rain during the day as slightly milder air pushes in. Highs
will be in the 40s and lower 50s, warmest over eastern areas where
there will be more sun.

Medium range models still showing differences on track of the system
as it slides down the east slopes of the Rockies and how far east
pcpn will reach into our CWA. Latest GFS and NAM further east with
more significant pcpn compared to EC. A general blend seems
appropriate at this point. For Thursday night, pcpn will expand a
bit further east across the area Thursday night, with the more
significant pcpn moving across southern portions of northeast WY and
possibly into far southwest SD. Rain will change over to snow
overnight across northeast WY and into the Black Hills, and likely
across far southwest SD toward daybreak Friday. This system is not
quite as cold as the last one, so snow can be expected across these
areas in the morning, with a mix or change over to rain in the
afternoon in many areas. Snowfall amounts look to be on the lighter
side in most areas, up to a few inches from the Black Hills to far
southwest SD and most of northeast WY. However, across southern
Campbell County where the heaviest pcpn is forecast, amounts
approaching 6 inches are possible, especially the higher elevations
of southwest Campbell County Thursday night into Friday. Pcpn will
dissipate and shift south of the area Friday night as system moves
into the Central Plains.

The weekend looks mainly dry, but remaining cool, as large trough
lingers over the region. Will see temperatures possibly approaching
average early next week, but unsettled weather will return for at
least the first half of the week. Active northwest flow on the back
side of the trough will bring several disturbances across the area,
with daily chances for showers in most areas. The bulk of the
activity should come during the afternoon and evening hours.


.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 605 PM MDT Wed Apr 26 2017

MVFR cigs have become SCT over the last hour as diurnal
heating begins to wane over the KRAP terminal. Additionally, expect
winds to diminish to less than 10kts for both KGCC and KRAP with
FEW/SCT sky conds. Fcst soundings show potential for some light fog
to develop...especially with the melting that occurred today in the
KRAP have inserted brief mention for both locations.
Otherwise look for an increase in cloud cover ahead of next system
during the day Thursday. Inserted some pops for light rain chances
in the KGCC terminal toward the end of the valid period.




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