Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 221720
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1120 AM MDT SUN MAY 22 2016

.Update...
Issued at 900 AM MDT Sun May 22 2016

Cold front is moving across western SD...with southeasterly winds
and dewpoints in the 50s/60s ahead of the front, and westerly
winds and 30s/40s dewpoints behind. Clouds are diminishing and
temps are already warming into the 60s. No precip on the radar so
removed PoPs this morning. Since most models are showing precip
over the area now, have little confidence in their forecasts for
this afternoon and evening. Would think storms would be most
likely to develop across central SD this afternoon, along the
front and the area of highest CAPE. However, hi-res convective
models are indicating storms initiating farther west, where there
is better shear but less CAPE. Increased PoPs across northeastern
WY and western SD, but kept highest chances over south central
SD.

&&

.SHORT TERM...(Today Through Monday Night)
Issued at 330 AM MDT Sun May 22 2016

Current surface map shows trof/cold front across far eastern
Montana into northeast Wyoming. Convection lifting north out of
northeast Wyoming with isolated shra/tsra developing across south
central South Dakota. Upper low located in southern Alberta with
110kt jet streak lifting across Utah into Wyoming.

For today, cold front slowly slides through western South Dakota
as jet streak shifts into eastern Wyoming/western Dakotas. MLCAPE
of 2000-3000j/kg forecast along cold front, with 25-35m/s bulk
shear. Model reflectivity suggest discrete supercells developing
this afternoon, mainly east of a line from Pine Ridge to Phillip.
Large hail, greater than 2 inches, and damaging winds likely
across south central South Dakota late this afternoon into this
evening. also some potential for tornado development.
Thunderstorms will push east of the forecast area overnight. As
boundary layer flow turns southwest to west behind cold front,
drier air bring a decrease in low clouds across western South
Dakota. With the additional sunshine, high temperatures across
western South Dakota will be warmer than yesterday even with the
passage of the cold front. Dry weather expected for Monday.

.LONG TERM...(Tuesday Through Saturday)
Issued at 330 AM MDT Sun May 22 2016

Mean upper trough over the western CONUS will change little
through much of the upcoming week. Southwest flow aloft will
prevail over the CWA with periodic shortwaves and a couple of
transient upper lows passing through. Hard to pin point timing at
this point, so PoPs generally broad-brushed. The weather does
look unsettled with daily chances for storms Tuesday through next
weekend. Temperatures will be seasonal.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1117 AM MDT Sun May 22 2016

(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 520 AM MDT Sun May 22 2016

Scattered to numerous thunderstorms will develop over much of
northeast Wyoming and western South Dakota later this afternoon
and last into the evening hours before pushing east. Outside of
the storms VFR conditions are expected. In and near storm, IFR
ceilings and visibilities are expected along with the potential
for strong gusty winds and hail.

&&

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

$$

Update...Pojorlie
SHORT TERM...7
LONG TERM...15
AVIATION...Helgeson


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