368
FXUS63 KUNR 011740
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1140 AM MDT Wed May 1 2024

.KEY MESSAGES...

-Cool/unsettled weather continues through Friday

-Warmer this weekend

-Strong storm with wet/windy conditions early next week?

&&

.UPDATE...
Issued at 859 AM MDT Wed May 1 2024

A band of widespread showers is spreading northward across western
SD due to strong jet streak overrunning the low level baroclinic
zone, so have raised pops quite a bit for much of western SD.
Activity will increase further into the afternoon as inverted
surface trof, currently over southeast WY, lifts northeast.

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 230 AM MDT Wed May 1 2024

Current surface map places low across northern Minnesota with high
pressure across eastern Montana into western South Dakota.
Mid/high clouds are spreading across the forecast area. A few
radar echoes show up across northern Nebraska. Persistent upper
low located across southern Alberta/Saskatchewan spins another
vigorous impulse across the area later today/tonight. Shower
activity across northern Nebraska spreads northward this morning
as better isentropic lift shifts north. Showers/thunderstorms
will increase in coverage this afternoon/evening as stronger mid
level forcing arrives. A bit of buoyancy/marginal shear will
support some stronger updrafts with sub-severe hail/wind threat.
Secondary impulse swings through early Thursday with additional
showers. Showers linger into Friday with cyclonic flow aloft and
steep mid level lapse rates. Thermal profiles support the
potential for some snow in the higher elevations of the Black
Hills. LREF gives a 30-40% probability of 2" of accumulation
through Friday afternoon...mainly for elevations above 5500ft agl.

Canadian upper low shifts east this weekend as strong low digs
across the western CONUS. Upper ridge builds across the Northern
Plains with robust low level warm advection. Highs climb into the
70s Sunday/Monday. 00Z deterministic runs of GFS/ECMWF/GEM are in
decent agreement with western CONUS swinging through the Rockies
into the eastern Dakotas by Tuesday. That would result in wet and
windy conditions across the forecast area. At this time, low
confidence in overall forecast details that far out given the
spread in ensemble guidance.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1130 AM MDT Wed May 1 2024

Scattered to numerous showers, and a few thunderstorms, are
expected through this evening. LCL MVFR conditions are possible,
especially with the stronger showers and storms. AREAS MVFR/LCL
IFR conditions will develop over parts of western and south
central South Dakota after 06Z tonight. With conditions gradually
improving from west to east and becoming all VFR conditions after
16Z on Thursday morning.

&&

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

$$

UPDATE...Johnson
DISCUSSION/KEY MESSAGES...7
AVIATION...10