Lander, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

477
FXUS65 KRIW 152355
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
555 PM MDT Fri May 15 2026

.KEY MESSAGES...

- Warm, dry and windy this evening, with elevated to critical
  fire weather conditions. Conditions will improve after sunset.

- Warm on Saturday, with a bit less wind. A few dry showers or
  thunderstorms are possible, with outflow winds up to 50 mph
  the main hazard.

- A weather system brings much colder temperatures for Sunday
  and Monday, along with widespread moisture. The cooler air
  will hang around through the middle of the week.

- Snow is looking very likely (80%) for lower elevations Sunday
  night into Monday, possibly impacting Monday morning travel.
  Confidence remains low on where the heaviest precipitation
  falls.

&&

.UPDATE...
Issued at 1236 PM MDT Fri May 15 2026

The warm, dry, and windy forecast remains on track for today and
tomorrow, with no notable adjustments made. Focus remains on the
weather system for Sunday and Monday. Like the full discussion
mentions, models have trended towards a deeper trough, though there
remains uncertainty on where/if the heaviest precipitation falls.
Current trends bring better liquid amounts further south than
previous model runs, with the Wind River Mountains, South Pass, and
east towards Casper being the most favored locations for the
greatest totals. For actual liquid amounts, most of the area has a
good chance (widespread 40 to 90 percent chances) for moisture, with
those aforementioned favored locations having the potential for 0.75
to 1.00 of liquid. Cluster analysis would suggest about a 40 percent
chance for higher than currently forecasted values, and about a 30
percent chance for less - again indicating the current uncertainty
with this event.

All that said, the main impacts will likely be with snow that falls
Sunday night into Monday morning. Initial snow would likely melt,
but with sub-freezing temperatures, wet surfaces could freeze, with
then accumulating snow on top. The Monday morning commute could be
impacted by this. South Pass would be a location of note, with
higher snow totals and gusty winds. Furthermore, a strong northerly
wind is expected Sunday night with the front. This could further
impact travel as snow and blowing wind create lower visibilities
across the Bighorn, Wind River, and Powder River Basins, and down
into Sweetwater County. Again, there is still some uncertainty with
this system, so stay tuned though the weekend for further
updates.

&&

.DISCUSSION...
Issued at 219 AM MDT Fri May 15 2026

May is typically a very volatile month across Wyoming. It is
traditionally our wettest month, and can see anything from severe
thunderstorms to blizzards, sometimes at the same time. And over the
next several days, volatile will be a good way to describe it.

Today looks like more of the same when compared to Thursday. That
means another day of above normal temperatures and low humidity. A
gusty wind will still be present. However, with the jet moving
further north, it should be down a few notches when compared to
yesterday. However, gusts over 25 mph are still a greater than 1 out
of 2 chance for many locations and as a result, it will be another
day of elevated to critical fire weather. No fire weather highlights
though because fuels are not critical. And across the border, we
can`t completely rule out a stray shower. However, the chance is at
most 1 out of 10 so we left for forecast dry. And with dew point
depressions approaching 60 degrees, they would likely be virga
showers. They could produce some wind gusts past 50 mph though if
your are one of the people that get caught near one.

Saturday looks like the transition day. Most areas will have one
more dry and warm day. There are a couple of exceptions though. One
is across southern Wyoming where a bit of energy may bring a couple
of showers or thunderstorms. But the second, and more important
system, will be an upper level low moving in from the Pacific
northwest. It could bring a few showers to northwestern Wyoming, but
even there most of the day should be dry with most precipitation
holding off until after sunset. With humidity remaining low,
elevated fire weather again looks likely across much of the area.
However, with somewhat less wind and somewhat higher humidity,
concerns might be down a bit when compared to Friday.

Sunday is when things begin to get interesting as the upper level
low moves towards Wyoming. Most guidance now shows the low opening
up into a fairly deep trough as it crosses the state. Most guidance
does show the main impacts from later Sunday through Sunday night
into Monday. However, this is where the agreement ends. Some
deterministic models, like the GFS, as well as some ensemble
members, show a more progressive system that exits by Monday evening
and keeps the heaviest precipitation across Colorado. Other ensemble
members, as well as the European model, have a slower and wetter
system (which is badly needed given the current drought). However,
even it has shifted a bit further south and east with the heaviest
precipitation. So, what we are saying is that although most areas
should see some precipitation, amounts and placement of the
heaviest is still very much in flux. However, one thing we have
fairly good confidence in is that much of it will be in the form
of snow, even in the lower elevations. Largely rain will fall
during the day on Sunday. However, as cold air gets pulled in ,
700 millibar temperatures will fall to minus 6 celsius or less,
dropping snow levels to the valley and basin floors. The
National Blend of Models Ensemble shows at least a 2 out of 3
chance of an inch or snow across most of the area for the 48
hours ending at 6 pm Monday, with the exception of the Bighorn
Basin. As snowfall amounts go up, things become very elevation
dependent, as would be expected in mid May. The greater than 1
in 2 chance of 3 inches of snow or more is largely restricted to
locations above 5500 feet or so. The greater than 1 in 2 chance
of 6 inches or more is largely restricted to the mountains.
There is a greater than 1 in 2 chance of over a foot of snow
across the higher elevations of the Wind River Range and
Bighorns though. One thing to note, the official snow will
probably not be what people see in their yards. The warm ground
will melt some of the snow on contact and a lot of the snow that
falls during the day on Monday will have trouble sticking with
the very high mid May sun angle. Temperatures will be below
normal starting Sunday and especially into Monday.

On Tuesday a second system may impact the area, especially the west,
but this one has less moisture to work with. Cyclonic curvature will
linger over the area into Wednesday, keeping temperatures below
normal and a few showers in the forecast. More zonal flow returns
for the end of next week, bringing a drier and warmer pattern.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 530 PM MDT Fri May 15 2026

VFR conditions are forecast over the next 24 hours. Gusty winds are
likely to be the most impactful aviation-related weather this
evening with many sites seeing gusts in the 20 to 30 kt range. No
precipitation is in the forecast for TAF sites, but COD has isolated
showers well to the northwest, while RKS has scattered showers to
the southeast. Apart from these two TAF sites, western and central
Wyoming will have mostly clear skies through the overnight hours.

Winds decrease quickly around sunset. Saturday brings increased high
and mid-level cloud cover ahead of the next weather system, with a
10 to 20% chance of brief afternoon showers for most airports.

&&

.FIRE WEATHER...
Issued at 219 AM MDT Fri May 15 2026

It will be another warm day today with humidity falling under 15
percent for many locations. Wind will be somewhat lighter than
yesterday. However, with a greater than 1 out of 2 chance of
wind gusts over 25 mph across much of the area, elevated to
critical fire weather will occur this afternoon. There should be
some improvement Saturday with somewhat higher humidity and less
wind. Much cooler and potentially wetter weather moves in for
Sunday and continues into early next week.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Wittmann
DISCUSSION...Hattings
AVIATION...VandenBoogart
FIRE WEATHER...Hattings