FXUS65 KRIW 031105
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
505 AM MDT Sat May 3 2025

.KEY MESSAGES...

- Warm and dry conditions expected today. Temperatures will peak 
  around 15 degrees above normal.

- A system will begin to push into the area Sunday. Isolated
  showers and thunderstorms are expected across the area,
  especially across western and southern Wyoming.

- Widespread rain and mountain snow is expected Monday through
  Tuesday, especially across central Wyoming.

- Precipitation may lead to elevated river levels Tuesday, mainly 
  across central Wyoming.

&&

.DISCUSSION...
Issued at 502 AM MDT Sat May 3 2025

High pressure will dominate today as the ridge reaches its maximum 
extent over Wyoming. Accordingly, mostly clear skies are expected, 
with little chance of precipitation across the area. High today will 
peak around 15 degrees above normal as 700mb temperatures reach 
nearly 10C. Humidity values will drop into the low teens today 
across lower elevations, though relatively light wind will help to 
mitigate fire weather concerns.

The ridge begins to break down on Sunday as a longwave trough 
approaches from the West Coast. At the same time, an associated 
500mb low will deepen across southern California. This will bring 
the leading impacts from this system to Wyoming as moisture surges 
northward. Showers and thunderstorms should kick off by early 
afternoon, moving from southeast to northwest across the area given 
the location of the low to our southwest. This activity will be 
fairly widespread through the afternoon, though with the best 
chances across western and southern areas. In reality, much of the 
area will remain warm and dry again, with temperatures possibly even 
peaking a little higher than Saturday for locations east of the 
Divide. While brief heavy rainfall is possible with any storms, the 
primary concern will be strong outflow winds given the still drier 
boundary layer. Fire weather concerns may creep up a bit given the 
outflow wind potential, though widespread strong winds are not 
expected.

Guidance is coming into better agreement with the progression of the 
low by Monday. The most likely scenario is for the low to track from 
southern Arizona to the Four Corners region Monday afternoon, and 
then move more easterly through Tuesday. This will further increase 
moisture over Wyoming, leading to a respectable precipitation event 
over the area. This will be most notable across central Wyoming 
where a prolonged period of northeasterly upsloping flow will be 
realized. Forecast precipitable water values are over 0.60", which 
would put it near the climatological maximum for this time of year 
at KRIW (SPC Sounding Climatology). Precipitation amounts across 
central Wyoming are generally in the 0.50" to 1" range, with the 
higher values toward the northeasterly facing mountain slopes. This 
includes the Lander and Casper areas, which currently have about a 
70% chance of seeing at least 1" of precipitation during the period 
from Monday through Tuesday. Elsewhere, accumulations are generally 
expected to be under half an inch. 700mb temperatures approaching 
negative 6C Tuesday morning certainly mean mountain snow, and likely 
even a mix or a change to all snow for a time in the lower 
elevations as well. The primary concern with this event, while not 
particularly high, is the potential for river and small stream 
flooding. Elevated river levels can be expected, aided in part by 
the warm weekend preceding the rain. 

Precipitation will come to an end Tuesday evening. Further ahead, 
ensemble cluster guidance continues to indicate a quick return to 
rising 500mb heights by Wednesday. This favors warmer and drier 
conditions through the end of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 422 AM MDT Sat May 3 2025

High pressure will bring VFR conditions to all TAF sites through
12Z Sunday. Wind will be generally 15 knots or less everywhere.
The only clouds will be some cumulus over the mountain ranges
and a few mid level clouds generally from Interstate 80 and
southward.

&&

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

&&

$$

DISCUSSION...Myers
AVIATION...Hattings