599 
FXUS63 KUNR 070428
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1028 PM MDT Sun May 6 2018

.DISCUSSION...(This Evening Through Sunday)
Issued at 223 PM MDT Sun May 6 2018

Active WNW flow will persist through the period as impulses eject
out of the eastern PAC. Lingering LL trough INVOF the western FA 
today, with weak instability supporting isold shra over mainly the
BH. Diurnal heating may support a few shra, maybe a lone TS in 
that area through early evening. Compact/strong upper impulse will
shift east toward the region supporting pressure falls and an 
associated increasing LL jet tonight. Some elevated instability 
indicated over the far NW FA combined with forcing from the jet 
may fire a shower or TS late tonight. Left in a low chance pop for
this. LL moisture will increase across the region through Monday,
although limited. Upper impulse will support sct- isold shra/ts 
to the NE of an expected sfc trough/dry line late Monday 
afternoon/eve, esp from the BH into NW SD where the best overlap 
of pos theta-e adv and convergence will be found. Sufficient LL 
moisture with steeping lapse rates will support increased CAPE 
over western SD, with values of 1-1.5 KJ/KG. However, deep layer 
bulk shear will remain very limited at 25-30 knots or less. Hence,
severe threat looks marginal at this time, with gusty winds and 
small to moderate sized hail the main threats. Shower/TS chances 
will linger through Tues with unstable cyclonic flow overhead. Wed
does look dry attm. A backdoor cold front looks to advect into 
the region Thur-Friday. This could support support much cooler 
conds than current forecast numbers. Associated longwave trough 
will drop into the region for the weekend, with cool and unsettled
conds looking more likely. Some places may not even rise out of 
the 40s Sat if colder solutions verify. Snow still looks possible 
in the higher elevations Sat night.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1028 PM MDT Sun May 6 2018

A few widely isolated TS/SH are possible overnight through 
tomorrow morning across northeastern WY and western SD, which 
could bring brief MVFR cigs. Scattered TS/SH will develop 
tomorrow across northeastern WY beginning around 18z, then 
gradually overspread the remainder of the area during the 
afternoon. Localized MVFR conditions will be possible with this 
activity. A few TS could also be severe, with large hail and 
damaging winds possible. While TS/SH will likely impact both TAF 
sites at some point tomorrow, will wait for future TAFs to 
pinpoint timing.

In locations that do not experience TS/SH, VFR conditions are 
expected.

&&

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

$$

DISCUSSION...JC
AVIATION...Sherburn