205
FXUS65 KRIW 271147
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
547 AM MDT Sat Apr 27 2024

.KEY MESSAGES...

- Rain showers and mountain snow will continue today.

- Some showers linger tomorrow, but coverage looks to be less.

- The forecast has trended more unsettled next week with a
  couple of rounds of showers and strong wind, but confidence in
  details remains rather low.

&&

.DISCUSSION...
Issued at 242 AM MDT Sat Apr 27 2024

Precipitation is ongoing across approximately the western half of
the area, with emphasis on the easterly upslope areas against the
Wind River Range, Absarokas and the Salt and Wyoming Range. One
place that has overperformed has been Dubois, where a perfect low
level upslope flow (around 120 to 130 degrees) and good
precipitation rates have cooled temperatures to around freezing to
bring a couple of inches of snow, including some on the roads. Most
other areas have just wet roads, with the exception of South Pass
where the Winter Storm Warning is in effect. Snow levels look to
remain around 7500 feet or so through the day.

Precipitation will continue today, although intensity East of the
Divide should begin to decrease this afternoon as low pressure over
Colorado begins to move away, starting to shut off the moisture. It
still looks like some good rates in the morning though, so we will
continue the highlights as is for now. A trailing trough axis will
move into western Wyoming this afternoon and bring a round of
showers into the evening. It is possible a few locations may receive
advisory level amounts, especially in the Tetons and Salt and
Wyoming Ranges. We will not issue any highlights though. The
heaviest precipitation will fall in the afternoon, and given recent
warm weather and the almost May sun angle, snow should have
trouble sticking to roads. In addition, the heaviest snow would
fall above pass level where impacts would be minimal. We will
issue some Special Weather Statements to cover for this though.
This trough axis will then slowly move across the state on
Sunday, and bring some additional showers and isolated
thunderstorms. Coverage will be less though, especially East of
the Divide where the chance will be generally less than 1 out of
2.

Past Sunday, uncertainty in the forecast increases significantly.
The main driver of the weather will be an upper level low moving in
from the northern Pacific, into the Pacific northwest and across the
northern Rockies through at least midweek. Deterministic and ensemble
guidance has trended further south with some shortwaves rotating
around the low, which would increase shower coverage across the area
through midweek. There is some agreement on the main waves moving
through on Monday and Wednesday, with a break on Tuesday. There are
still differences on exact timing and placement of the heaviest
precipitation. Guidance also differs on when the low kicks east of
the area, differing by as much as 36 hours. There has been poor
consistency though, with the deterministic models flip flopping over
the past couple of days. So, although we around a 1 in 2 chance
in confidence on some unsettled weather continuing, confidence
is very low in the details. Strong wind is also possible Monday
through at least Wednesday with the jet over the area, but
confidence in meeting high wind criteria is mixed, basically a 1
in 2 chance or a coin flip. Ridging should bring some drying
toward the end of the next work week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 546 AM MDT Sat Apr 27 2024

An unsettled weather pattern will continue to bring scattered rain
showers to much of the area today. The best chance of prevailing
impacts will be at KLND through the morning given the more favorable
easterly flow. Showers will then become more focused west of the
Divide for the afternoon. Given the nature of showery precip
confidence is low on specific terminal impacts and timing; MVFR
ceilings are likely with any rain through the day. Most terminals
will see rain chances decrease late this afternoon. KJAC will be the
exception, holding on to rain chances and/or MVFR ceilings through
the period as the next shortwave passes through western Wyoming.

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 3 PM MDT this afternoon for
WYZ002.

Winter Storm Warning until 9 PM MDT this evening for WYZ015.

&&

$$

DISCUSSION...Hattings
AVIATION...Myers