415
FXUS65 KRIW 011715
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1115 AM MDT Wed May 1 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected today, mostly
  across the northern half of the area. Light snow accumulation
  is expected for the western valleys, possibly spilling east
  of the Divide this evening.

- Elevated to near critical fire weather conditions are again expected
  across much of central and southern Wyoming this afternoon.

- Cooler and unsettled weather continues through the end of the week.

- Warmer and drier conditions return Saturday, though another
  system is likely to approach on Sunday.

&&

.DISCUSSION...
Issued at 456 AM MDT Wed May 1 2024

Similarly to the previous few nights, light showers are scattered
across portions of the area early this morning, most widespread
across western Wyoming. This is due to a shortwave rotating around
the longstanding trough to our north. A reinforcing, stronger wave
ejecting off the trough will begin to push in by late morning. This
will increase shower and thunderstorm coverage across the northern
half of the area through this evening. Given the colder temperatures
that will remain in place today, some of this will fall as light
snow or a rain/snow mix across the valleys of western Wyoming. In
fact, light snow will likely spill east of the Divide as well as
700mb temperatures drop to around -8C. In particular, the Dubois
area and far western portions of the Bighorn Basin could see light
accumulation through this evening; the latest HREF run suggests a 50
to 60 percent chance of at least a half inch there through tonight.
As for other areas east of the Divide, temperatures will certainly
be cold enough for light snow overnight. The saving grace for these
areas (at least, for those of us who have tired of snow and would
like to move on to spring now that May is here) will be that
precipitation will be ending as temperatures drop with the wave
passage.

Otherwise, it will be another windy and mostly dry day for much of
central and southern portions of the area. Westerly wind gusts of 25
to 35 mph will be widespread from Uinta County through central
Fremont County and Natrona County. Accordingly, elevated to near-
critical fire weather conditions are expected again here as the wind
combines with afternoon relative humidity of 15 to 20 percent.

Precipitation will end overnight as the wave departs. However, the
next wave ejecting off the trough still to our north will arrive by
Thursday afternoon. This will make for a continued cool and
unsettled day, with showers focused on northern and western Wyoming.
Elevated to near-critical fire weather conditions will continue as
well, though wind does look a little lighter than Wednesday.

A stronger wave within the cyclonic flow will arrive in the Thursday
night / Friday timeframe. This will spread shower chances across the
entire area through Friday. Temperatures will be cold enough during
the morning hours Friday for some of this to fall as snow, including
in the basins. As has been the theme this week, however, available
moisture looks underwhelming, and precipitation in any form looks
pretty light at the moment.

Saturday will buck the trend we`ve seen this week as the low to our
north finally moves east. Transitory ridging will take over, leading
to dry conditions and temperatures returning to near or above
normal. Elevated fire weather conditions do look to persist
Saturday.

There is growing model and ensemble guidance consensus that a strong
low pressure system will move onto the West Coast by late Saturday.
In this scenario, Sunday could be an active weather day as this
system quickly approaches Wyoming. While there are still timing and
position uncertainties, warm, southerly flow ahead of the low could
lead to another day of elevated/critical fire weather conditions for
southern and central Wyoming. At the same time, showers and
thunderstorms should spread across western Wyoming during the
day, and then east across the rest of the area through Monday as
the associated cold front arrives. While these details will
likely change in the coming days, guidance is certainly favoring
another active and unsettled pattern to begin next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1115 AM MDT Wed May 1 2024

A weak weather system passes through today, with the main impacts
being precipitation chances and wind. Starting with precipitation,
chances will be limited to more northern Wyoming sites through the
afternoon. Chances (about 15%) sweep through KCPR, KLND, and KRIW
this evening. Best chances occur at KCOD and KJAC this afternoon.
Showers will be more scattered, so although the TAFs have prevailing
groups of snow, there may be times it is not snowing. Thunder is
also possible (about 10-15% chance), and given the most likely
precipitation type is snow, thundersnow is possible.

Wind-wise, gusts 20 to 30 knots are common this afternoon, with a
few sites favoring slightly higher gusts during peak heating this
afternoon. For the most part, gusts decrease after sunset, with most
locations ending the gusty winds by 05Z/Thurs. KRIW may see a
northwest drainage wind later than that time. Winds look to increase
again for Thursday.

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...
None.

&&

$$

DISCUSSION...Myers
AVIATION...Wittmann