650
FXUS63 KUNR 272316
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
516 PM MDT Mon May 27 2024

.KEY MESSAGES...

-Mainly dry and warmer into Wednesday.

-Showers and thunderstorms return for the last half of the week.
 Severe storms possible Wednesday afternoon and evening.

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 123 PM MDT Mon May 27 2024

Active flow over the northern Pac will continue to offer
progressive mean westerly flow through most of the forecast
period. Mainly quiet weather ongoing across the fa today.
Shortwave trough is progressing across ND, with an associated sfc
trough supporting a few showers/storms there. Current ob trends
(supported by hires models) shift all precip east of the FA this
afternoon/evening, with dry conds expected. However, if enough
instability and forcing arises over far NW SD, an isold shower
would be possible there through early evening. Have continued with
a dry forecast attm. The next stronger upper trough will advect
into the region Tue, supporting WAA and shortwave ridging.
Expected a quiet day Tues with warmer temps than today into the
70s most areas. Upper trough will shift east with sfc pressure
falls ensuing Tues night, supporting the the development of a LLJ.
This will allow sfc winds to increase trough the night. In
addition, Pos theta-e adv combined with steep mid-level lapse
rates may support elevated nocturnal showers/storms on the SD
plain late Tue night. Did add a low pop for this. Thermal ridge
will pass over the region Wed with gusty SE winds per ongoing
pressure falls. Temps will climb into the 80s most places, but may
struggle a bit at first given SE winds under a strong inversion.
Decent ridge of ll moisture will nose into the region along the
high plains, with dewpoints expected into the upper 50s and lower
60s. Lee side trough will kick out in the afternoon, timing with
the upper trough, supporting increasing chances for showers and
storms, first over NE WY and the northern BH (per eddy
convergence). Expecting storms to organize into a broken line with
embedded strong to severe cells, esp over NW SD where the
strongest forcing will be. Bulk shear is not that great, but ML
CAPE in the 1.5-2kJ/kg will me more than ample to support a few
severe storms as the line shifts east in the evening. Cold front
will progress through Wed night with shower chances shifting east.
Much cooler Thurs, with instability showers possible in the
afternoon, esp SE of the BH. Large upper trough will slowly
progress through southern Canada through the end of the week
offering seasonal temps into the weekend locally, with continue
near daily chances for showers/storms as impulse ladden flow
(stemming from the parked NE PAC upper trough) continues to
traverse the region. Warmer temps do look possible by Sunday into
the following week, as flow amplifies and WSW flow becomes
established in mean model solutions.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 516 PM MDT Mon May 27 2024

VFR conditions will continue through the forecast period. Breezy
northwesterly winds will decrease early this evening. A light
shower or two could clip portions of far northwest SD early this
evening, mainly across the Lemmon area.

&&

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

$$

DISCUSSION/KEY MESSAGES...JC
AVIATION...26