Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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654 FXUS65 KRIW 111934 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 134 PM MDT Tue Jun 11 2024 .KEY MESSAGES... - Dry, breezy, and very warm conditions are expected through Thursday. Elevated fire weather conditions will occur as a result for the basins and valleys and into the foothills. - The above normal temperatures are continuing mountain snowmelt and keeping river and stream levels elevated for the next few days. Water levels should decrease toward the end of the week. - Isolated thunderstorms are possible this afternoon across far northern Wyoming, with isolated showers and thunderstorms across northern WY and far southern WY Wednesday afternoon and early evening. Isolated showers and thunderstorms are expected over some mountain areas Thursday, with higher chances on Friday. && .DISCUSSION... Issued at 1230 PM MDT Tue Jun 11 2024 Weak ridging over the Great Basin with zonal flow over the northern Rockies has brought mostly clear skies to western and central Wyoming today, along with above normal temperatures in the 70s and 80s. This pattern will also continue breezy and gusty WSW winds for much of the area this afternoon and early evening before decreasing around sunset. Models are showing a low chance (10-15%) of showers and thunderstorms over the northern portions of Yellowstone and the Absarokas as well as the Bighorn mountains late this afternoon as a weak shortwave trough moves eastward through Montana. Drier mid-level flow then pushes eastward in the zonal flow on Wednesday. WSW winds should be a bit stronger tomorrow with some areas gusting 25-40 mph during the afternoon. Lingering moisture around NW WY could develop some showers and thunderstorms (15-20%) during the afternoon. A weak trough moving from northern UT into northern Colorado should also bring a slight chance of showers and thunderstorms (15-25%) to southern Sweetwater County (developing off the Uintas). Outflow wind gusts from the storms could reach 50 mph. Afternoon max temperatures should be increase a couple of degrees Wednesday to range from around 80 to the low 90s. A similar pattern continues on Thursday though winds will not be as strong as the previous day. Models are showing a very weak boundary moving north-south during the afternoon into central WY. Around this boundary from west-central WY toward Casper, there may be a few showers and thunderstorms during the late afternoon and evening. Better chances are around southern Natrona County. With the large-scale high over SE CO, some moisture is finally brought northward from eastern UT to keep a slight chance of showers across southern and central WY through the night into Friday morning. Models are indicating a shortwave trough moving from the PacNW into Montana on Friday as well. The resulting pattern is likely to bring modest chance of the showers and thunderstorms (40-60%) to both the northwest and southern into central parts of the state. Temperatures should drop a few degrees on Friday with the increased cloud cover and precipitation. Saturday looks to be a little cooler but still above normal, along with breezy to windy west winds in the post-storm environment. A few showers are possible over northern WY during the late afternoon and evening. Indications at this time are for a much colder system to move into the PacNW on Sunday, which will bring 700-mb temps below 10C to the forecast area. Sunday and Monday should then be near normal for temperatures. The strong system then moves westward on Tuesday, warming temperatures and increasing the south-southwest wind. There are some timing issues with model forecasts with the ECMWF being 18-24 hours faster than the GFS. However, it appears that this system will bring a cold front to western WY and some showers and thunderstorms to the northern half of the forecast area. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1130 AM MDT Tue Jun 11 2024 VFR conditions are expected at all terminals through the period with mostly clear skies. Breezy west to northwest winds will continue to increase through the first 2 hours of the period. Winds will remain gusty through the afternoon, then decease after 02 to 03Z. Winds will increase again late in the period. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .FIRE WEATHER... Issued at 1240 PM MDT Tue Jun 11 2024 West to southwest winds with gusts of 25-30 mph and RH values in the teens will result in elevated to near- critical fire weather conditions today and Wednesday. High temperatures in the 90s will be much more widespread east of the divide Wednesday with RH values in the teens, along with wingspread wind gusts up to 30-50 mph. These conditions will once again result in elevated to near-critical fire weather conditions. Agricultural burning of any kind is highly discouraged today and Wednesday. Although temperatures will still be above normal on Thursday, winds will be weaker and RH values in the teens will be pushed south to southwest and southern WY. && .HYDROLOGY... Issued at 1250 PM MDT Mon Jun 10 2024 Rivers and creeks will continue to run high at or just below action stage, but remain steady for the next 24-26 hours. Snow Water Equivalent (SWE) at SnoTel sites continues to fall, with most remaining locations at 5 inches or less. A couple of notable exceptions, Grand Targhee in the Tetons and Two Ocean Plateau in southern portions of Yellowstone NP, still have 30 and 20 inches, respectively. It looks like any widespread flooding threat is diminishing and will likely only impact localized areas, if at all. Water levels are expected to decrease quite a bit by the weekend. && .RIW WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...McDonald AVIATION...Hensley FIRE WEATHER...LaVoie/McDonald HYDROLOGY...LaVoie/McDonald