FXUS65 KRIW 161230 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 630 AM MDT Thu Apr 16 2026 .KEY MESSAGES... - A weather system will move across the state and bring snow and rain changing to snow today and tonight. The highest snowfall amounts will be in the western mountains. Gusty wind will bring blow and drift the snow at times. - A hard freeze is likely (4 out of 5 chance) in the lower elevations to the East of the Divide Friday night. - Drier and warmer weather returns for Sunday and early next week. && .DISCUSSION... Issued at 207 AM MDT Thu Apr 16 2026 There have times through my rather lengthy meteorology career that I have felt guilty for things. And this is a system when I am having these feelings. The last time I did the forecast, back on early Monday morning, it looked like we had a decent chance of some badly needed moisture across the area. However, trends for much of the area that need the moisture, like the Green River, Wind River and Big Horn Basins, have been for less and less moisture. At the time, chances looked rather good. Needless to say, chances have diminished substantially over the past few days. Radar now shows the first area of precipitation moving into western Wyoming. The cold front is still back in Idaho, so snow levels remain fairly high right now, generally above 7500 feet. Snow will levels will gradually drop through the night and day. As for highlights in western Wyoming, these still look reasonable. Probabilistic guidance shows at least a 2 out of 3 chance of 8 inches or more across most of the warned area. Thought about a Winter Weather Advisory for the Salt and Wyoming Range, but the only areas with a greater than 1 in 2 chance of 6 inches of new snow or more are the highest elevation above the mountain passes. So, we will hold off for now. In the valleys and lower elevations, no location has more than a 1 in 6 chance of 4 inches or more, so no highlights here. Some snow will continue through Thursday night, but the bulk of the snow will fall through midnight with light snow following that. In Sweetwater County, with some surface instability, snow squalls will be possible late today and this evening with the front, mainly to the east of Rock Springs. Amounts here should remain under 3 inches though. The only areas with a greater than 1 in 3 chance are across far southern Sweetwater County where impacts will be slim to none. Any snow squalls could be handled by short fused statements. And now on the area where I feel guilty, East of the Divide. Trends continue to be down in this area. I gave serious thought to canceling the advisories for the Wind River Basin and Lander foothills. However, I am holding off now for a few reasons. For one, guidance is indicating some instability, with up to 250 J/Kg of CAPE this afternoon with lifted indices as low as minus 1. In addition, the area will be under the right rear quadrant of the jet this evening. This could lead to some snow squalls as the front moves through the area this afternoon and evening. The other is a feature I saw on the GFS early this morning. There is the presence of a weak 700 millibar circulation around midnight tonight near the Natrona / Fremont County border, giving a decent amount of QPF (as much as a a quarter of an inch). If this further moves a bit further west, it could impact Riverton and Lander. Eastern portions of the basin still have a 1 in 2 chance of 3 inches of snow as well. So, we will leave them up for now. Highlights still look good for Johnson and Natrona Counties though, with most probabilistic guidance giving at least a 1 in 2 chance of 3 inches of snow or more. In this area, the highest impact will be Thursday night. Wind will also be an issue, especially in the favored northwest flow / cold advection locations, like Johnson County and the Bighorn Basin, bring blowing snow and more impacts with gusts over 40 mph at times later this afternoon and evening. Conditions should begin to improve on Friday as the trough and front move away to the east. Unstable northwest flow and cyclonic curvature will keep snow showers going through much of the day. Then we turn to Friday night with the potential for a freeze. As I have stated before, the concern is not with crops and gardens as Wyoming residents know not to plant this early. The main concern will be for flower gardens, trees and sprinkler systems. The variables remain the same. First, if it can clear out enough. Chances are better for this across the north and west, with decreasing chances further south. The other is snow cover, chances of lows below 20 have decreased somewhat across the Bighorn Basin and Wind River Basin with the smaller amounts of snow reducing albedo. Probabilistic guidance still gives a greater than 2 in 3 chance of lows below 25 across almost all the area though. We will hold off on any freeze products with the greater concern of the snow but some will likely be needed. The remainder of the forecast period looks largely tranquil as ridging builds back over the Rockies for this weekend and early next week. Temperatures will begin to moderate Saturday and likely return to near to above normal levels by Sunday for most. Most areas look dry and warm from Monday through at least Wednesday. The next system is the form of an upper level low may then approach for later next week with the next chance of moisture but these are very fickle this far out so details are still highly uncertain. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 630 AM MDT Thu Apr 16 2026 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals A system continues to impact the area this period. Conditions will hover right around VFR/MVFR through most of the day, with occasional IFR impacts during periods of heavier snow. Conditions should improve this afternoon before a snow band moves in this evening dropping conditions back to MVFR/IFR at KJAC. At KBPI and KPNA chances are too low for prevailing precipitation, but there is a 30% chance of some rain showers late this morning into early afternoon. Rain showers will develop at KRKS this afternoon, with some isolated thunder possible (30%). Rain will transition to snow at KRKS late this afternoon, with snow ending by 03Z Friday. A cold front will pass through this afternoon and evening, with wind shifting from southwest to northwest behind the front. Wind will remain breezy through the TAF period, with strong wind from mid-morning Thursday through Thursday afternoon. Mountain obscuration will be prevalent through the TAF period. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals VFR conditions prevail through this morning, but rain will spread east of the Continental Divide this afternoon and quickly transition to snow this evening. Most terminals will have minimal impacts through the daylight hours. KCPR is the exception as convective rain/snow bands will develop this afternoon into the evening. Conditions will drop to IFR at KCPR this evening once rain transitions to snow. AT KRIW, KLND, and KWRL PROB30 groups have been added for a rain/snow mix. At KCOD and KWRL there will be a better chance for prevailing light snow showers and MVFR conditions this evening. A cold front will pass through this morning into the afternoon, with wind shifting from southwest to northwest behind the front. Wind will remain breezy through the TAF period, with strong wind from mid-morning through this afternoon. Mountain obscuration will become more frequent once the front passes through. 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 Storm Warning until 6 AM MDT Friday for WYZ001-002-012. Winter Weather Advisory until 6 AM MDT Friday for WYZ008-009. Winter Weather Advisory from noon today to 6 AM MDT Friday for WYZ010-011. Winter Storm Warning until 6 PM MDT Friday for WYZ014-015. Winter Weather Advisory from 3 PM this afternoon to 6 AM MDT Friday for WYZ016>018. Winter Weather Advisory from 3 PM this afternoon to noon MDT Friday for WYZ019-020-022. && $$ DISCUSSION...Hattings AVIATION...Rowe/Myers