618
FXUS65 KRIW 142253
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
353 PM MST Thu Nov 14 2024

.KEY MESSAGES...

- Gusty mountain winds will decrease this evening, with gusty
  winds redeveloping over southern Wyoming Friday afternoon.

- Light snow accumulations for western Wyoming valleys and
  moderate snow for mountain passes Friday evening into Saturday
  morning. Only a dusting expected east of the Divide.

- Another weather system moves through the region Monday into
  Tuesday of next week, bringing the next chance for widespread
  light snow accumulations.

&&

.DISCUSSION...
Issued at 230 PM MST Thu Nov 14 2024

The zonal flow pattern with a jet stream aloft over Wyoming
will shift to become more southwesterly overnight as a trough
develops over the West Coast. Gusty winds in the terrain will
ease overnight.

Friday will be an active weather day. By the late morning, a
shortwave rotating through the larger approaching trough will
tighten the pressure gradient over southern Wyoming, with gusty
winds in the 40 to 50 mph range expected along the I-80
corridor in southern Wyoming. These winds will be south-
southwesterly, so expect a strong crosswind component for high
profile vehicles traveling I-80.

In addition to wind, snow will be moving into the western
portions of the state by the afternoon hours. Friday evening
through the overnight hours will bring light snow accumulations
to westerly valleys. The more impactful snow amounts will be
over the mountain passes, such as Teton Pass and Togwotee Pass.
A Winter Weather Advisory is in effect for these higher
elevation travel corridors, given storm total snow
accumulations in the 4 to 6 inch range.

By daylight Saturday, precipitation rates will decrease, and
only a dusting of snow is forecast for areas east of the
Continental Divide. Temperatures will be about 10 degrees colder
than on Friday (and a few degrees below season normals) as
cooler Canadian air moves into the region.

Sunday`s temperatures moderate slightly as the region sits
between weather systems. Another trough develops over the
Pacific Northwest Sunday night into Monday, bringing the chance
for widespread light snow over Wyoming Monday into Tuesday.
Precipitation details are uncertain for this system, with a
complex jet streak forcing pattern over the CONUS. Have stuck
with consensus model guidance for the time being. Two forecast
details are fairly high confidence at this point: Cooler
temperatures about 10 degrees below seasonal normals, and gusty
north winds for the Powder River Basin on Tuesday. A ridge
quickly builds in behind the large trough deepening over the
Great Plains, leading to a dry and warming trend late in the
week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 450 PM MST Thu Nov 14 2024

With high pressure to the east of WY and low pressure along the
West Coast, moderate southwest flow continues to stream high-
level clouds over western and central WY today and overnight.
Some low- to mid-level clouds are also over the northwest
mountain areas, with the highest peaks being obscured. A few
showers may occur over the mountains overnight, but shouldn`t
impact any TAF sites. Wind has been the story today at a few
sites, including KJAC, KCOD, and KCPR, with 25-30 kt gusts
across central WY after a very gusty early morning. Winds should
decrease after sunset and remain relatively light through early
Friday morning. As the West Coast low pressure system
approaches on Friday, the surface flow pattern will become more
southerly, and winds will increase by 15/18Z at most sites, with
several TAF sites going 15-20G25-30 kt. Moisture and clouds
increase during the afternoon hours over western WY, with KJAC
likely seeing some showers before 16/00Z, and showers spreading
into KBPI/KPNA right around 16/00Z. A cold front then spreads
west to east Friday evening, shifting winds to the west and
northwest, and bringing chances of precipitation into Saturday
morning. Western WY into northwestern WY into northern WY
appear to have the best chances of precipitation with this next
storm system.

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


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 2 PM Friday to 8 AM MST Saturday
for WYZ012.

&&

$$

DISCUSSION...VandenBoogart
AVIATION...McDonald/LaVoie