A tight pressure gradient ahead of an advancing low pressure system brought high wind to eastern Sweetwater County. The strongest wind gust was 67 mph at the Snow Springs RAWS site.
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The episode as NWS RIW wrote it up.
A tight pressure gradient ahead of an advancing low pressure system brought high wind to eastern Sweetwater County. The strongest wind gust was 67 mph at the Snow Springs RAWS site.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Riverton, WY wrote its last area forecast discussion before the first event at Apr 5, 10:25 AM MST, 35 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Riverton WY 1125 AM MDT Fri Apr 5 2024 .KEY MESSAGES... - One more warm day today with elevated fire weather across the area and strong to high wind. - Turning much colder for the weekend with mountain snow and rain and snow in the lower elevations along with continued strong wind. - Moderate to heavy snow is likely in the northern mountains. Uncertainty remains very high in the lower elevations in regards to snowfall amounts. && .DISCUSSION... Issued at 317 AM MDT Fri Apr 5 2024 It is days like this when I question why I made the decision many years ago to become a meteorologist and suffer trough many semesters of advanced math that I rarely use in my daily activities. Uncertainty remains very high in some portions of the forecast that have the potential to be very impactful. There are some things that are more certain though, so that is some consolation. Tonight we are listening to old school rhythm and blues, funk and New Jack Swing. (Two Gen Xers are working tonight). And this reminds me of one of my favorite groups on this station, Earth, Wind and Fire. Expect, with the concerns with the forecast, we will replace Earth with snow. So, in similar fashion to the previous forecast discussion, we will approach each of these individually, but not in that order. We will start with fire. This will be only a one day concern, and that day is today. Expect another warm day today before a cold front sweeps across the area and smacks us back into the reality of Wyoming in April with temperatures 25 to 35 degrees colder over the weekend when compared to today. South to southwest flow ahead of the front will bring one more day of well above normal temperatures, with highs in the 70s. The tight pressure gradient will bring strong wind and with humidity dropping into the teens this afternoon, elevated to near critical fire weather is likely across most areas East of the Divide and in southern Wyoming. We can't rule out isolated critical fire weather, but nothing widespread. We will issue fire weather statements to cover for this. Next we move on to wind. We have a good set up for high wind across portions of the area, especially southern Wyoming. First, a tight pressure gradient across the area with the advancing cold front to the west. The models also show two things that are favorable. First, 50 knots or greater at 700 millibars. Second, we will have some downward forcing from the right front quadrant of a 90 knot jet streak. With that we will maintain the high wind watch. There could be high wind tomorrow as well, but with west flow behind the front, this would be restricted to eastern portions of Sweetwater County. Elsewhere, it will be toupee and trash can alert day, but the chance of high wind gusts is less than 1 in 3. So, now other wind highlights for today. On Saturday, concerns also shift to the opposite scenario, those favored by post frontal / northwest flow / cold advection patterns, mainly the northern Bighorn Basin and especially Johnson County. Guidance is showing sustained wind over 34 knot in some areas, averaging out to around a 3 in 4 chance of high wind. No highlights here though. Mainly because, it will likely be snowing when this occurs and a winter weather advisory or warning may be more appropriate for expected impacts. This would not be until Saturday night, so there is still time. And now for the one that would be the most impactful, but also by far the most uncertain, snow. The mountains have more certainty. The hardest hit areas by far will be the Bighorns and Casper Mountain, where there is at least a 9 in 10 chance of a foot or more of snow above 8000 feet. We went ahead and upgraded the watches to warnings here. The impacts look less in the west though. For the watches in the northwestern mountains, snow amounts have trended down a bit. There could be a few spots that receive warning amounts but it would be over a long period of time. So, we have opted for winter weather advisories. As for maximum impact, in the west, the heaviest periods of snow would be this evening with the cold front, and Saturday evening with the trailing trough. It is more of a continuous event East of the Divide in the mountains. The lower elevations and population centers are where the uncertainty ramps up, the quote Spinal Tap, up to 11. We have many factors for the uncertainty. First is the time of day. We are now into April. The sun is now as strong as it is around Labor Day in early September. So, it has a lot of power. And this will have an impact on snow accumulations during the daylight hours, especially on paved surfaces. This could limit accumulation unless the snow is heavy, reducing impacts. The second is temperatures, both surface and aloft. The air mass behind the front is Pacific, not Canadian, and as a result, it is not really cold. Much of the snow will be falling when it is above freezing, again limiting accumulation unless rates are heavy. As for aloft, 700 millibar temperatures are a good rule of thumb for snow levels. During most of this event, they will vary between minus 6 and minus 8, which would put levels between 4500 and 5500 feet, and many of the population centers are below this elevation. And next is elevation, this is a situation where 500 feet of elevation can make a difference between a cold rain and wet, heavy snow. And finally, there is precipitation rate, which tends to increase evaporational cooling and can turn rain to snow. And, to add in one more factor, strong wind, especially in Johnson County, may bring very difficult travel with the snow Saturday night even if amounts aren't that great. So, with the uncertainty, we will turn to probabilistic guidance. The areas that look most likely to get highlight amounts of snow are exclusively Casper and Buffalo, with a 2 in 3 and 4 in 10 chance respectively. Casper has the best chance of the biggest snow, with around a 1 in 7 chance of a foot of snow. But that depends on position of a strengthening low, if flow is more northwest rather than north, it could limit upslope. As a result, the high and low ranges of expected snow in Casper range from 1 to 12 inches. So, although we are confident is some snow, exact amounts are still highly uncertain. Some snow showers may continue into Monday as well, especially in northwest flow areas with cyclonic curvature remaining over the area. And, unfortunately, it does not look good for viewing of the solar eclipse. Quieter weather returns on Tuesday into the rest of the week. We could see some snow showers in the mountains, but no impactful systems are expected the rest of the week. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1125 AM MDT Fri Apr 5 2024 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals. Approaching trough and Pacific cold front will cross the region early Friday evening. Strong southerly wind frequently gusting 30- 40kts continues through 00Z/Saturday before gradually slowing. The passage of the front switches the wind to the west to northwest, while KJAC lightens up from the south. However, KJAC has the best chance for MVFR conditions as rain switches to snow between 01Z- 05Z/Saturday. Confidence is lower for a persistent period of snow or rain showers at the southwest terminals, so VCSH has been continued. After this initial push, MVFR may be more difficult to come by until after sunrise Saturday at KJAC. West to northwest wind increases to 20-30kts at the southwest terminals between 15Z-18Z/Saturday. Mountain tops frequently obscured, especially after 00Z/Saturday. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals. All terminals remain VFR through the period. Approaching trough and Pacific cold front will cross the region later Friday evening. Strong southerly wind frequently gusting 30-40kts continues through 00Z/Saturday before gradually slowing by 02Z. Dry lower levels should limit convection this afternoon despite favorable instability. Westerly wind increases at all terminals between 15Z-18Z/Saturday. Cloud cover does lower after sunrise Saturday at KCOD and KWRL, but west-northwest flow aloft should hinder the development of MVFR cloud cover. Showers of rain, perhaps mixed with snow above 5K ft MSL, are most possible over the Bighorn Basin later Saturday morning. Mountain tops obscured after 12Z/Saturday. 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 from 3 PM this afternoon to noon MDT Sunday for WYZ001-012. Winter Weather Advisory from 6 AM Saturday to noon MDT Sunday for WYZ002. Winter Storm Warning from 6 AM Saturday to 6 PM MDT Monday for WYZ008-009. Winter Storm Warning from 6 AM Saturday to 6 AM MDT Monday for WYZ022. High Wind Warning until 8 PM MDT this evening for WYZ028>030. && DISCUSSION...Hattings AVIATION...CNJ
Hazardous Weather Outlook National Weather Service Riverton WY 733 AM MDT Fri Apr 5 2024 WYZ001>020-022>030-061300- Yellowstone National Park-Absaroka Mountains-Cody Foothills- North Bighorn Basin-Southwest Bighorn Basin- Southeast Bighorn Basin-Owl Creek and Bridger Mountains- Bighorn Mountains West-Bighorn Mountains Southeast- Northeast Johnson County-Southeast Johnson County- Teton and Gros Ventre Mountains-Jackson Hole- Wind River Mountains West-Wind River Mountains East- Upper Wind River Basin-Wind River Basin-Lander Foothills- Green Mountains and Rattlesnake Range- Natrona County Lower Elevations-Casper Mountain-Star Valley- Salt River and Wyoming Ranges-Upper Green River Basin Foothills- Upper Green River Basin-South Lincoln County- Rock Springs and Green River-Flaming Gorge-East Sweetwater County- 733 AM MDT Fri Apr 5 2024 ...Winter Storm Warnings in Effect for the Bighorn Mountains and Casper Mountain Beginning Saturday... ...Winter Weather Advisories in Effect for the Northwest Mountains for Much of the Weekend... ...High Wind Warning Posted for Most of Sweetwater County Friday... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...Today and Tonight. Strong southerly wind across Sweetwater County, with windy conditions likely for much of the remainder of the area. The gusty wind combined with dry conditions and warm temperatures leads to elevated fire weather conditions Friday afternoon for many portions of central and southern Wyoming. Snow spreads into the western mountains late Friday afternoon and tonight. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Saturday and Sunday...Turning much colder with snow, which will be heavy at times in some mountain locations. Rain and snow likely across the lower elevations, especially in the northern half of the state. Snow amounts in the lower elevations remain uncertain as daytime accumulations will be limited. The best chance for accumulating snow across the lower elevations will be Saturday night. Please see forecasts and winter weather products for details. Sunday Night and Monday...Snow ending, but temperatures will remain cooler than normal. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to Standard Operating Procedures.
The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
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NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1170674.