Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 192019
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
219 PM MDT THU MAY 19 2016

.SHORT TERM...(This Evening Through Friday Night)
Issued at 215 PM MDT Thu May 19 2016

20z surface analysis had lee trough over central MT into central
CO with nice southerly flow over the CWA. Convergence along lee
trough assisting high based convection over northeast WY per local
radar. Activity also on the tail end of a weak shortwave from
southeast MT into central WY. Storms will move slowly east this
afternoon and evening, moving into an area of 250-500J/kg MLCAPE
created by mid-upper 40s dew point pooling ahead of lee trough. 0-
6km bulk shear quite weak and expect storms to wane around sunset
and as they approach better MLCIN on the SD plains. However, low
level jet will develop this evening from southwest into south
central SD which may result in isolated elevated convection
overnight. Temperatures tonight will be near to slightly above
guidance.

Friday, upper low currently over central WA will drop into western
NV with shortwave ridge over the CWA. Boundary layer moisture
continues to increase on southerly flow with lee trough moving
little. 1-1.5KJ/kg MLCAPE develops over western SD during peak
heating in the afternoon. MLCIN 25-50J/kg over the far west and
near higher terrain. MLCIN on the plains 100+J/kg. Given rising
heights and implied subsidence over the CWA, thunderstorms may be
few and far between and likely rooted near terrain or occur along
lee trough. 0-6km bulk shear around 15m/s. Perhaps an isolated
severe thunderstorm with wind given highly mixed boundary layer in
the west or wind and hail over the Black Hills may occur. Activity
should die quickly after sunset with little synoptic support and
increasing MLCIN. Temperatures will average about 10F above
normal.

.LONG TERM...(Saturday Through Thursday)
Issued at 215 PM MDT Thu May 19 2016

Upper low over the Pacific NW Saturday will begin to slowly move
east-northeast over the weekend as ridge shifts east of the area.
Chances for showers and thunderstorms will continue to gradually
increase through the weekend from west to east. Medium range
models in better agreement on pushing the low to the north and
west of the area, into the Canadian Prairie provinces by Monday
morning. Several shortwaves will slide through the area, with a
cold front also slowly passing through late Saturday night and
Sunday. The potential for strong to severe storms looks greatest
over far northeast WY into far western SD late Saturday, then
possibly across central SD on Sunday.

The first half of next week still looks somewhat unsettled at times
as southwest flow continues ahead of a slow moving Pacific trough.
Chances of storms will continue through mid week. Temperatures will
be near or slightly above average through the first half of the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 215 PM MDT Thu May 19 2016

VFR conditions generally expected through the forecast period.
Isolated to scattered showers and thunderstorms are expected across
the Black Hills and ne WY this afternoon. Isolated activity is
possible east of the Black Hills tonight as southerly low level
jet intensifies. Local MVFR conditions are possible in and near
any showers.

&&

.UNR Watches/Warnings/Advisories...
SD...None.
WY...None.
&&

$$

SHORT TERM...Helgeson
LONG TERM...13
AVIATION...13



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