742
FXUS63 KUNR 031919
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
119 PM MDT Wed Jul 3 2024

.KEY MESSAGES...

-Lingering thunderstorms through the evening
-Cool and showery Independence day
-Possible thunderstorms again on Saturday
-Hot/dry pattern develops next week

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 116 PM MDT Wed Jul 3 2024

Current surface analysis shows a weak s/w pushing into western
NE...resulting in mid-morning convection across parts of western
NE and southwestern SD. Additionally...a much stronger s/w and
associated 500hpa trough is now dropping into northwest WY with
associated convection in central MT. At the sfc...there is a lee
trough from central MT into southeast WY/NC CO.

For the rest of the afternoon and into the overnight
hours...models  are still pretty bullish on two distinct areas of
convection developing. An area across southwest and southcentral
SD associated with the NE shortwave sliding through...and on the
nose of the best low level moisture found in NE. Although not
easily defined...there still appears to be a boundary draped
across the NE/SD border...with 60s dwpts south with southerly
winds...and 50 dwpts north with easterly winds. Latest ensembles
cont to show ample amounts of 0-6km bulk shear (45-60kts) through
22-23z, SBCAPE values AOA 1K J/Kg through the afternoon and CIN
amounts becoming near zero. Of interest...HRRR and NAM show 2
distinct 700hpa areas of theta-e forcing during the afternoon. One
across the southcentral along the pesky E/W boundary...and
another narrow area setting up along the Black Hills ahead of the
main s/w and associated trof before they move through. Current
thinking is that there will be 2 separate areas of convection that
develop with possibly 2 modes. One coming out of MT/WY that will
start off as distinct supercells...developing into a strong line
as it moves east. The other across the southcentral that will be
more distinct as well. Another thing of interest is looking at
ensemble hodographs...there are a couple for sites in the northern
hills (Spearfish, Sturgis areas)...that are more curved in nature
for a couple of hours this afternoon before becoming more
straight in nature. Once into the overnight hours, subsidence
behind the exiting wave will aid in bringing everything to an end.
Some low level moisture indicators in the models show that low
clouds may be an issue across our western counties.

Independence Day will looks to be rather cool and unsettled as
cyclic  flow remains over the region. The day may start off
partly cloudy...but with cool temps aloft and enough instability
remaining...still envision quite a bit of cloud
cover/sprinkles/showers/thunderstorms developing during the
afternoon. With this being mostly diurnally driven...envision it
drying out toward late afternoon/early evening. Clouds/pcpn will
most likely keep many areas at or below guidance values.

Northwest flow remains through the weekend. Noticed that there are
some height falls during the day Saturday as an ill-defined wave
pushes through in the NW flow. Moisture remains pretty scant, but
the mention of thunder is warranted. Otherwise things still look
on track for western CONUS ridge to start building early next week
with associated height rises over the region. Confidence is
building that we will begin to see temperatures warm to above to
well above normal by weeks end.



&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1033 AM MDT Wed Jul 3 2024

Scattered showers and thunderstorms will develop this afternoon across
NE WY and western SD. Gusty, erratic winds and large hail can be
expected near any stronger cores. Expect transient MVFR conditions
near any stronger convective cores. Otherwise, VFR conditions
will prevail outside of showers and storms through the forecast
period. Northwesterly winds will become breezy Thursday morning.

&&

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

$$

DISCUSSION/KEY MESSAGES...Hintz
AVIATION...Pojorlie