textproduct: Western and Central Wyoming

KEY MESSAGES

- Snow shower activity is expected to increase this afternoon across much of the area before decreasing in coverage shortly after sunset. Periods of moderate to heavy snow and gusty winds could cause reduced visibilities.

- Additional snow accumulations between 2-4 inches are possible across the Bighorns, Casper Mountain, and northern Johnson county where a Winter Weather Advisory remains in effect until 6PM this evening.

- Scattered, less widespread snow showers are forecast again Thursday afternoon through Friday across the area.

- Warmer and drier weather continues to look favorable this weekend into next week.

UPDATE

Issued at 1257 PM MDT Wed Apr 2 2025

A surface boundary situated near the Montana/Wyoming border (as of 18Z) will push south over the next few hours. As the boundary makes it's southward move, a slight increase in moisture will occur along and north of the boundary. This mornings mostly sunny skies have allowed for sufficient daytime heating to occur as well with afternoon SBCAPE values between 100-250 J/kg. This slight uptick in moisture, instability, and the frontal boundary will support scattered convective snow showers with some thunder potential across much of the area this afternoon and early evening; however, chances (50-70%) for snow showers are greatest across the northern half of Wyoming.

Portions of the eastern half of the CWA (the Bighorn Mountains, Casper Mountain, and northern Johnson County) remain in a Winter Weather Advisory through 6PM this evening. Enhanced convergence along the boundary combined with daytime instability will allow for periods of moderate to heavy snowfall rates across the aforementioned locations and these areas could see an additional 2-4 inches of snow now through 6PM.

The boundary stalls this evening and bisects the state roughly along the Divide. Cloud cover is forecast to gradually dissipate overnight along and south of the boundary. This will allow for sufficient radiational cooling where clouds do clear, potentially cooling temperatures a degree or two colder than what is currently forecast. Otherwise, widely scattered convective showers are forecast Thursday along and north of the boundary with the help of a shortwave trough traversing the region.

DISCUSSION

Issued at 106 AM MDT Wed Apr 2 2025

Areas of snow showers moving across the Wind River Basin down into eastern Sweetwater County ongoing through near sunrise Wednesday morning. The NAMNest is handling this pretty well, although other HiRes models not too far off having it dissipate by this timeframe. Otherwise, the near stationary boundary to the north will bring in another round of snow showers out of Montana along the shortwave skirting around the main upper level trough dipping to the south of the CWA. By early afternoon, the Bighorns and northern Johnson County will see continuous snow showers. Additional accumulations of higher confidence up to 4 to 8 inches (70-80%) for the Bighorns and 1 to 3 inches for northern Johnson (50-60%). As winds increase through the afternoon with the stronger gradient from the aforementioned surface boundary, expect north to northwesterly gusts up to 25 to 35 mph that will limit visibility for these stretches of interstate out of Buffalo. Mid to late afternoon, the highest snow rates across Casper Mountain as the boundary sage south, east of the Bighorns, also coupled with the stronger winds. Elsewhere, some sporadic snow showers across the Absarokas and Yellowstone, and more organized through the Wind River Basin. By 4-5PM, expect a subtle low to push a rain/snow mix through about sunset before lingering as snow into the late evening hours as it pushes southeast into Sweetwater County once again. Regardless, the showers will dissipate towards midnight lingering for Yellowstone by sunrise Thursday morning.

With the lingering surface boundary near the Montana state line, another round of developing showers by mid afternoon, mainly across the northern parts of the CWA. With a bit stronger daytime heating, some instability off the Absarokas into the western Bighorn Basin could see some isolated thunder chances with 100-200 J/kg expected. This is where the stronger of the PVA anomalies will be from the more elongated upper level trough progressing a bit further east. Coverage a bit more limited, mainly driven by daytime heating with more limited accumulations expected for the higher terrain. With the upper trough continues eastward dipped well to the south, more limited coverage for eastern counties for any shower activity Friday afternoon.

Overnight Friday into early Saturday morning, expect the main finger of the PFJ finally eject the upper trough to the east of the CWA allowing for the cold front to drop southeastward into the high plains. This will give way to the more seasonable and slightly cooler Saturday afternoon high temperatures with improved conditions expected. Strong ridging builds into the CWA from the west with increasing convergence aloft. The PFJ remains well north and eastward aiding in dry weather into next week, despite the more meridional upper level pattern. This ridge will set in place through about mid next week giving way to a warming trend, resulting in above average temperatures. A couple shortwaves look to pass to the north with the southward moving PFJ but impacts look to be limited with minor precipitation chances for northern zones Tuesday through Thursday. Otherwise, long term outlooks trend towards stronger ridging, and dryer/warmer than average conditions expected heading into the middle of the month.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 414 PM MDT Wed Apr 2 2025

Unsettled conditions continue today, with another round of isolated convection expected through this evening. Brief MVFR to IFR conditions are possible with any direct terminal impact, but confidence is low on this and have kept Prob30 groups for several terminals. KCOD is more favored to see a shower or two and do have a Tempo group there late this afternoon. This activity will clear up after sunset, leaving prevailing VFR conditions overnight through Thursday morning. Otherwise, several terminals will see a breezy wind through this afternoon, subsiding this evening. Isolated convection is again possible Thursday afternoon though should be even less widespread; for now have added a Prob30 group for KCOD for impacts after 21Z.

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 6 PM MDT this evening for WYZ008>010-022.