763
FXUS65 KRIW 090512
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1112 PM MDT Wed May 8 2024

.KEY MESSAGES...

- The upper low continues to rotate through the region, bringing
  more rain and mountain snow to much of the region today and
  tonight. Northeasterly upslope flow will cause showers to
  linger through much of the day Thursday across favored areas,
  particularly the east slopes of the Wind River Mountains.

- Northerly winds will continue to decrease through the evening
  as the low weakens. Strongest winds through the rest of today
  will be post-frontal northerly winds across the Bighorn
  Basin.

- Warmer, drier, and much less windy weather will finally arrive
  Friday and continue through the weekend.

- A series of shortwaves look to move through next week, which
  could produce scattered afternoon showers and thunderstorms,
  but confidence is low regarding locations or intensity of any
  of these shortwaves and associated shower activity.

&&

.DISCUSSION...
Issued at 330 PM MDT Wed May 8 2024

Rain and snow have spread across most areas east of the Divide late
this morning into the early part of the afternoon. The precipitation
is associated with the same upper low that has persistently been
plaguing the region for the past several days. , we should
be largely done with the wind impacts that have been the most
persistent, it seems, with this upper low. Now that we have moved on
from wind, we will now be dealing with some rain and snow that will
persist through tomorrow and even into Thursday night for some
areas. We are not entirely done with the wind, as gusty post-frontal
north to northeast winds will persist across the Bighorn Basin
through this evening. The Wind River Basin and locations across the
southwest will also see some breezy winds through the rest of the
afternoon, but these will continue to decrease through evening hours
and be mostly light by Friday morning. Then, easterly winds will
develop across the south tomorrow late morning, gusting through the
afternoon, but gusts will be in the 25 to 35 mph range, rather than
the 45 to 55 mph range that we have seen over the past few days.

As for precipitation, northeasterly flow over the next few days will
enhance the precipitation across favored east slopes, particularly
in the Winds and Casper Mountain. Note that precipitation amounts
have increased significantly across the Wind River Range, and thus,
snowfall amounts have also increased rather significantly. Peaks of
the eastern Winds could see over 2 feet of snow through Friday as a
result of the upslope. Hence, have upgraded that zone to a Winter
Storm Warning. Meanwhile, to the north, precipitation across the
Bighorns is not expected to be as heavy as previously thought. Have
thus decided to downgrade to an Advisory for those zones. All other
highlights remain the same from the previous shift.

Snow will be mostly relegated to the mountains, however, evaporative
cooling, particularly in foothill locations along the east slopes of
certain ranges (Lander, Casper) could lead to a period of wet snow.
Other higher low elevation areas such as the higher elevations of
20/26 between Shoshoni and Casper, as well as across Sweetwater
County could also see some snowfall. Overall, given time of year,
snow accumulations in these areas will be minimal and will mostly be
on grassy surfaces, while road surfaces should remain mostly wet,
especially during daylight hours.

The bulk of the precip will fall this evening through tonight.
Thursday, precipitation becomes more showery in nature, but steady
rain and mountain snow will still be ongoing for upslope favored
locations (Wind River Mountains, Casper Mountain, Lander Foothills,
Green Mountain/Rattlesnake Ranges, east slopes of the Absarokas)
through Thursday afternoon and even lasting through Thursday night
across the east slopes of the Winds. Elsewhere, precipitation will
mostly end by Thursday night, though lingering light showers are
certainly not out of the question.

Friday, we finally begin to see a warming and drying trend, which
will continue through the weekend. Temps climb to above normal
values by the weekend and winds will remain light as well.
Temperatures remain warm through about mid-week next week, but a
series of shortwaves could bring some scattered showers and
thunderstorms to the region through much of the week. Confidence
remains low regarding intensity or location of these showers. Models
hint at a cooler, more potent shortwave for mid-week, but again, low
confidence at this time.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1112 PM MDT Wed May 8 2024

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

A series of minor shortwaves will continue to parade across the
forecast area through midday Thursday. The north to northeast flow
aloft leads to downsloping and hinders precipitation chances at
KJAC, KBPI, and KPNA through the period. VFR prevails at these
terminals. KRKS sees a northeast surface wind gradually strengthen
between 09Z-15Z/Thursday as the pressure gradient tightens. The weak
upslope in the vicinity of KRKS combined with shortwave energy
should still lead to a period of IFR/MVFR conditions with light snow
from 08Z-14Z/Thursday. Conditions and ceilings improve at KRKS
around midday with VFR after that time. Gusty east to northeast
surface wind 20-35kts will be common at KRKS by late morning. KBPI
and KPNA see easterly wind 10-20kts develop around midday, while
KJAC sees downvalley northerly wind at similar speeds. The winds at
all terminals decrease around 02Z/Friday, with KRKS seeing breezy
conditions all evening. Mountain tops frequently obscured.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

A parade of shortwaves rotate southwestward through the forecast
area through midday Thursday. In general, MVFR conditions prevail
until 15Z-18Z/Thursday. The potential for IFR and light snow at KCPR
and KLND has decreased and have shifted the forecast to a TEMPO
mention with this package. The favorable north to northeast upslope
flow keeps intermittent light rain in the central basins through
late Thursday morning. There could be some breaks in the clouds
Thursday afternoon, but cold air aloft enables low-end VFR
stratocumulus to reform in the moist environment. VFR returns to all
terminals between 16Z-20Z/Thursday with the exception of KCPR, where
VFR may not return until around 00Z/Friday. Mountain tops obscured,
especially above 8-9K ft MSL through much of the period.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MDT Thursday for WYZ002-008-
009-022.

Winter Storm Warning until 6 PM MDT Thursday for WYZ015.

&&

$$

DISCUSSION...Hensley
AVIATION...Hattings