Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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360 FXUS65 KRIW 060915 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 315 AM MDT Mon May 6 2024 .KEY MESSAGES... - Showers continue to spread across areas east of the Divide this morning. Moderate to heavy rain will be possible across parts of Natrona and Johnson County. - Strong gusty winds continue today with widespread gusts of 30+ mph this afternoon and evening. - Showers will periodically continue across western and northern WY through the first half of the week. The remainder of the state will likely see a brief lull in action. - Another round of precipitation looks possible for the second half of the week. Winds are expected to remain breezy or even gusty at times through most of the week. && .DISCUSSION... Issued at 314 AM MDT Mon May 6 2024 Winds howled across parts of the Cowboy State on Saturday, with some locations, such as Lander and Rock Springs seeing gusts of 55 mph. Besides the gusty winds, the day was a pleasant taste of typical May weather, with highs east of the Divide reaching the 70s. However, conditions quickly deteriorated as a cold front swept across the state. Along the frontal passage showers and thunderstorms developed and continued to linger after the front moved through. That leads us to this morning where showers are still spreading across the state and will linger through the day. The hardest hit areas look to be western and eastern portions of the CWA. The unsettled weather pattern continues today, with the main culprit behind this pattern change being a deep Pacific low. The low continues to track across the the state this morning and afternoon. There are two parts of this upcoming system. The first will be winds which are going to be the main concern, as strong 700 mb winds of 60 to 70 knots set up over the region by the afternoon and evening. Similar to Saturday winds begin to increase shortly after sunrise, with the first impacts seen across the southern CWA before gradually spreading north through the early afternoon. There is a slight deviation from Saturday, as the low is now going to be mainly east of the CWA, which will create predominantly northwesterly/westerly flow. 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. Due to the change in flow, places such as the upper Wind River Basin and Northern Johnson County may see strong wind gusts as well, with a (60-80%) chance of seeing 45+ mph gusts. The High Wind Watch for part of Natrona County has been cancelled due to the lack of confidence in criteria strength winds. However, this area will still likely see periodic gusts around 50 mph. High Wind Warnings remain in effect for parts of Sweetwater, Fremont, and Natrona Counties through Monday evening. Special Weather Statements have been issued for parts of Sublette, southern Lincoln, Fremont, Natrona, and northern Johnson Counties. The SPS is due to strong wind gusts that may be near or exceed 45 mph this afternoon and evening. Some areas of concern will be along the I-80 corridor and South Pass. Gusts in these areas likely exceed 60+ mph on Monday which may make travel difficult, especially for high profile vehicles. Precipitation for West of the Divide... Precipitation continues this morning across western WY and will gradually ramp up intensity throughout the remainder of the morning. Snow levels have dropped compared to Saturday, mainly thanks to colder air from northwesterly flow. Snow is expected to continue across western ranges through 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 remains in effect 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 are now in effect for western ranges including the Wind Rivers as they will likely see 6 to 12 inches of snow through this evening. Lower elevation valleys in western WY will likely have a period of snowfall starting early Monday morning. Periodic snow/rain showers look to fall through Tuesday evening. Temperatures will likely climb above freezing during the day and drop to or below freezing during the night. This will limit most of the low elevation snow accumulation to the overnight and early morning hours. Snow totals range from 2-4 inches in parts of Jackson Hole and Star Valley. There is a good chance that some of the snow in lower elevations will melt in between showers, leading to lower amounts. Prevailing westerly flow will likely keep showers over western WY through at least Wednesday. Precipitation for East of the Divide... Showers continue to spread south to north this morning as the Pacific low gradually moves across the state. Central portions of the CWA will see showers dissipate after sunrise. Some showers are possible through the remainder of the day with a (20-40%) chance of an isolated shower this afternoon/evening. The main bulk of precipitation will shift east across Natrona and Johnson Counties this morning. Recent model guidance has indicated QPF amounts greater than 0.50 inches by the evening in these areas. Probabilities look good, with a (50-70%) chance of >0.50 inches of QPF in parts of Natrona and Johnson Counties by the evening. The eastern half of the Bighorn Basin looks to get a period of some much needed precipitation this morning. Models are showing a (40- 70%) chance of QPF values >0.30 inches by the evening for places such as Worland and Greybull. Another place seeing some much needed moisture will be the Bighorn Mountains. Snow totals across the Bighorns look to range from 6 to 14 inches with lower amounts in the southern portion of the mountains. Winter Weather Advisories are in effect through Monday evening as a result. The main bulk of precipitation comes to an end by Tuesday morning with a few lingering showers possible Tuesday and Wednesday. Remainder of the week... The remainder of the week is looking active and interesting in regards to the track of this Pacific low. Models are showing this low make its way north into Montana Tuesday and Wednesday as a result of strong ridging over the Central CONUS. By Wednesday morning things look to get interesting as models show the low being guided back south moving over WY and ending up in the Great Basin by Thursday. If this occurs flow would shift back to the north/northeast by Wednesday evening, possibly bringing another round of precipitation for the second half of the week. One thing to monitor will be northeasterly flow prone areas such as the eastern Winds. There are early indications of rounds of precipitation across this area as a result of this flow shift. Winds will also likely be sticking around as the low will keep the pressure gradient tight, leading to breezy or even gusty conditions through a large chunk of the upcoming week. Overall, most of the state will continue to see breezy winds, below normal temperatures, and chances for precipitation through most of the upcoming week. There may be a light at the end of this unsettled, damp, and cool tunnel of weather most of the state is currently in. While still numerous days out models are showing a break in the action and a return to May-like weather for the upcoming weekend. However, there are some models which are showing the exact opposite, so that should give a good indication of just how volatile the weather will be for the next week or so. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1037 PM MDT Sun May 5 2024 Messy forecast overnight with rain and snow showers overspreading the state. Areas west of the divide will fluctuate overnight with showers, with cigs holding down to right near the 3000 foot level. Winds have relaxed overnight, but will jump up again tomorrow morning, with gusts again 25 to 35kts, and even higher at KRKS. Precipitation will gradually end at KRKS by 18z, but will continue into the afternoon for KBPI/KPNA and all day at KJAC. While showers will not be overly heavy, some brief vis lowerings and variably gusty winds in the vicinity can be expected. East of the divide, showers have begun to spread into the region, and will continue through the night. Winds here have also relaxed, but will also jump back up to 25 to 40kts through the afternoon. Showers continue at all sites through 00Z/07 before tapering off in the evening. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 6 PM MDT Tuesday for WYZ001. Winter Weather Advisory until 11 PM MDT this evening for WYZ008-009. Winter Storm Warning until 11 PM MDT Tuesday for WYZ012. Winter Weather Advisory until 6 PM MDT this evening for WYZ014- 015-024. High Wind Warning until 9 PM MDT this evening for WYZ019- 028>030. && $$ DISCUSSION...Dziewaltowski AVIATION...Straub