Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 222330

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
530 PM MDT Thu Mar 22 2018

.DISCUSSION...(This Evening Through Thursday)
Issued at 133 PM MDT Thu Mar 22 2018

Water vapor shows upper ridge over the Rockies with large trof
over the far western CONUS. At the surface, nearly stationary
frontal boundary extends across eastern WY. Some radar returns
showing up over central/eastern WY but likely not much if any pcpn
reaching the ground due to drier low/mid layers.

Upper ridge axis will move into the plains overnight as large trof
west coast trof advances eastward. Lead short wave embedded in
southwest flow aloft will overrun the tightening surface gradient
east of the surface boundary, resulting in rather widespread pcpn
spreading eastward across the forecast area tonight. While some
of the pcpn could fall as light freezing rain across northwest SD,
the amount of warm advection should keep the pcpn elsewhere in
the form of rain. Fog/low stratus also likely especially in the
foothills/plains north and east of the Black Hills given the
strong east southeast boundary layer flow.

Main band of pcpn will lift north/east of the forecast area on
Friday, but could be some showery pcpn develop in the afternoon as
upper wave passes overhead (and possibly enough instability for a
thunderstorm near the NEB border with temps well into the 60s).

Short wave ridge behind departing system will bring dry weather
for Saturday, but southwest flow aloft returns for early next week
as large scale trof works slowly through the Rockies. Pcpn likely
again late Sunday into Monday as a piece of northern stream
energy works through the Northern Plains. Northwest flow aloft
develops mid/late week bringing a chance of more unsettled

As far as temps are concerned, readings expected to run near
average through the end of next week with little chance for
extreme warm or cold weather.


.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 524 PM MDT Thu Mar 22 2018

VFR conditions can be expected early tonight as clouds continue to
develop with lowering cigs. Rain will develop, especially north
and east of the Black Hills along with some possible mixed precip
across northwestern South Dakota. Rain and possible patchy fog
could yield IFR/LIFR at KRAP and the South Dakota plains after 3Z.
Some gradual improvement to flight conditions is expected during
the day Friday, although VFR/MVFR cigs may develop in northeast
Wyoming by late Friday morning.

As the surface low pressure shifts southeast tomorrow, winds will
turn northwesterly with gusts 20 to 25 knots Friday afternoon.




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