Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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412 FXUS65 KRIW 050937 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 337 AM MDT Sun May 5 2024 .KEY MESSAGES... - Showers develop across western WY this morning and gradually spread east as a cold front moves through the state this afternoon/evening. - High elevation snow will be possible after the frontal passage with chances for light snow in western valleys. - Winds will be gusty late this morning through the evening with many seeing gusts of 30+ mph. Parts of Sweetwater, Fremont, and Natrona Counties likely see gusts exceeding 55 mph. - The first half of the week looks to be unsettled with chance for precipitation, breezy winds, and below normal temperatures. && .DISCUSSION... Issued at 332 AM MDT Sun May 5 2024 Saturday saw pleasant and sunny weather across the Cowboy State. Unfortunately change is around the corner, as a potent upper-level Pacific low is currently making its way across the Great Basin this morning. This low will bring gusty winds, chances for precipitation and cooler temperatures over the next couple of days. Temperatures do make a brief rebound ahead of the FROPA today, with highs west of the Divide in the 50s/60s and highs east of the Divide reaching the 70s. Today will be the start of an unsettled weather pattern, with the main culprit behind this pattern change being a deep Pacific low. The low continues to near the state during the morning and impacts look to begin to ramp up around the same time. There are two parts of this upcoming system. The first will be winds which are going to be the main concern, as a strong 100+ knot jet sets up over the region by the afternoon. Southerly winds begin to increase shortly after sunrise, with the first impacts seen across the southern CWA before gradually spreading north through the early afternoon. Gusts of 30+ mph will be widespread with a (70-90%) chance across most of CWA during the afternoon and evening. Stronger gusts of 50+ mph are likely (50-80%) in parts of Sweetwater, Fremont, and Natrona Counties. Models continue to indicate these strong wind gusts and due to that, the High Wind Watches have been upgraded to High Wind Warnings. Winds have slightly decrease for the Lander Foothills and much of Natrona County. So, the High Wind Watches for these areas have been cancelled. Winds look to decrease Sunday night and then once again increase after sunrise Monday. For this reason these Warnings will be in effect from Sunday afternoon through Monday evening. Some areas of concern will be along the I-80 corridor and South Pass. Gusts in these areas likely exceed 60+ mph on Sunday and Monday which may make travel difficult, especially for high profile vehicles. West of the Divide... Precipitation arrives this morning across western WY and will gradually spread eastward throughout the day. Showers will be periodic with steady precipitation not arriving over this area until Monday morning. Temperatures on Sunday look to be too warm to support snow even at high elevations, with snow levels during the day exceeding 10,000 feet. However, snow levels look to quickly drop this afternoon/evening as a cold front sweeps across the state. After the front pushes through the heaviest snowfall is expected to fall over western mountains with snowfall rates nearing 1 inch per hour. Snow is expected to continue across western ranges through Monday into Tuesday evening. Snow accumulation will mainly be limited to the higher elevations with totals ranging from 6 inches to over 2 feet. A Winter Storm Warning has been issued for the high elevations of the Tetons and Gros Ventre ranges as they look to see 1 to 2 feet of snow. Winter Weather Advisories have been issued for the remaining western ranges including the Wind Rivers as they will likely see snow totals of 6 to 12 inches. Lower elevation valleys in western WY will likely have a period of snowfall starting early Monday morning. Periodic snow showers look to fall through Tuesday evening, with snow totals ranging from 2-4 inches in parts of Jackson Hole and Star Valley. One thing to keep in mind is that the snow will likely have difficulty accumulating on surfaces due to the strong Sun angle. There is a good chance that some of the snow in lower elevations will melt in between showers, leading to lower amounts. East of the Divide... Most of the CWA east of the Divide looks to remain dry for much of today. The best chance for precipitation comes with the nearing FROPA during the late afternoon and evening. Central portions of the CWA such as most of Fremont, Natrona and the Bighorn Basin will see little QPF as a result of the FROPA. Monday will be a slightly different story, as the low begins to shift northward due to a persist area of ridging over the central CONUS. As the low tracks north winds will shift to the NW, leading to enhanced upsloping for portions of the eastern Bighorn Basin. Natrona and Johnson Counties will also have a good chance seeing some showers during this time with a (40-70%) of seeing at least 0.20 inches of QPF by Monday night. Daily showers will be possible over the Bighorn Basin and the eastern portion of the CWA through midweek as the low wobbles around Montana. Remainder of the week... Uncertainty remains in regards to the impacts the low will have on the CWA as it moves over Montana during the first half of the week. The best chances of precipitation do look to remain across western and northern Wyoming, as flow and proximity to the low will be the most favorable. Overall, most of the state will continue to see breezy winds, below normal temperatures, and chances for precipitation through at least the first half of the upcoming week. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1042 PM MDT Sat May 4 2024 Most sites will be VFR through the night, with slowly lowering cirrus shield overspreading the region. Exception remains KJAC, which will see shower activity becoming more numerous through the night. While most of the night should stay VFR, some brief lowered cigs are possible with passing showers. Sunday will see numerous showers at KJAC through the day, with isolated thunder possible in the afternoon. Shower activity will spread into KPNA/KBPI early afternoon, and to remaining sites late afternoon to early evening. Most periods will still remain VFR, but lower cigs will continue through the night, with tempo MVFR cigs expected. Other concern remains gusty winds during the day for all except KJAC. Still expected 25g40kts for all sites west of the divide, with gusts approaching 60kts at KRKS during the afternoon. Winds will relax some after 00Z, but will still remain gusty at all sites through the overnight hours. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 11 PM this evening to 6 PM MDT Tuesday for WYZ001. Winter Storm Watch from Tuesday evening through late Tuesday night for WYZ001-012. Winter Storm Watch from Monday morning through Tuesday morning for WYZ008-009. Winter Storm Warning from 6 PM this evening to 11 PM MDT Tuesday for WYZ012. Winter Weather Advisory from 6 PM this evening to 6 PM MDT Monday for WYZ014-015. High Wind Warning from 9 AM this morning to 9 PM MDT Monday for WYZ019-028>030. High Wind Watch from Monday morning through Monday evening for WYZ020. Winter Weather Advisory from 11 PM this evening to 6 PM MDT Monday for WYZ024. && $$ DISCUSSION...Dziewaltowski AVIATION...Straub