Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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215 FXUS65 KRIW 200749 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 149 AM MDT Thu Jun 20 2024 .KEY MESSAGES... - Showers and thunderstorms are possible (15% to 40%) this afternoon and into the night, mainly east of the Continental Divide. More widespread showers and thunderstorms develop Friday. - Hot Sunday and Monday. Hot and dry weather continues through next week. && .DISCUSSION... Issued at 146 AM MDT Thu Jun 20 2024 Temperatures continue to climb today, with highs sitting right around, to just above, average for mid-June. A high over the eastern U.S. combines with a trough sitting over the west coast to funnel some moisture into Wyoming this afternoon. The NAM projects precipitable water (PWAT) values in the 150% to 175% of normal range mid-afternoon. The best moisture looks to remain to the east, with some isolated to scattered (15% to 40%) showers and storms developing from Sweetwater County into central Wyoming, including Fremont, Natrona, and Johnson Counties. Some development over the Absarokas are also possible (20% to 30%). Isolated chances (about 20%) continue overnight for those mentioned locations, and also the eastern Bighorn Basin, but an overall downward trend in rain coverage occurs into the night. Better moisture begins to make its way into the state late Thursday night into Friday morning. Aided by some shortwave energy entering from the west, widespread shower and thunderstorm chances occur across the area Friday. Some showers may still be going on from overnight, with some more showers developing in the morning. Showers really ramp up in coverage during peak heating Friday afternoon. The least likely (15% to 30% chances) places to get any rain will be far western Wyoming, including northern Lincoln County, north through Yellowstone. High-resolution models are projecting a fairly large swath of scattered to numerous (40% to 70% coverage) showers and thunderstorms moving across the area between 1pm and 7pm, from western Wyoming to Johnson/Natrona Counties in that timeframe. This will be the best shot for rain through the day. Rain quickly comes to an end Friday evening, leaving a dry night. Saturday starts what will be a mostly dry and hot next week. High pressure begins to build in over the Four Corners Region. This leaves the area hot and dry for the weekend. Highs Saturday begin to climb. By Sunday, highs will be firmly in the middle 90s east of the Continental Divide, with upper 80s and a few low 90s west. 700mb temperatures are around 18 to 19 degrees Celsius, which could bring 100 degree temperatures to places in the eastern Bighorn Basin. For reference, average highs this time of year are in the upper 70s to middle 80s. Temperatures look just as hot Monday. To say Tuesday looks cooler is a bit of an overstatement, but highs are looking a few degrees cooler. High pressure looks to remain through at least next Thursday, maybe Friday. This will keep these above average temperatures in place. Shift of Tails is also on board, highlighting much of the area in at least the 60th percentile for high temperatures, with some 80th percentiles Sunday and Monday. A few shortwaves look to move through during next week, though these seem to have little impact; perhaps a shower or two is possible depending if they are strong enough, but overall conditions remain dry. The GFS and ECMWF are showing a trough in the timeframe of next Friday (6/28). This could be what breaks the hot and dry pattern, but being so far out, there is low confidence in this model projection. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 941 PM MDT Wed Jun 19 2024 A weather system will approach the area over the next 24 hours and ahead of it energetic southwesterly flow will bring mid-level clouds overhead. Scattered convection is likely (60-70%) in portions of central and eastern Wyoming Thursday afternoon. Most of this convection will not impact any terminals, but there is a 20-30% chance of an isolated thunderstorm at KCPR from 21Z/Thurs to 01Z/Fri, so have included a PROB30 group to account for this threat. Conditions will remain VFR at all terminals through the TAF period. Wind will be light for most terminals (10 knots or less) and wind direction will change several times over the next 24 hours. The strongest wind will be at KCPR and KRKS Thursday afternoon. Gusts of 20 to 25 knots will occur at these terminals. Toward the end of the TAF period (Thursday evening) very isolated convection is possible (10-20%) in the Wind River Basin and southern Bighorn Basin. 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... None. && $$ DISCUSSION...Wittmann AVIATION...Rowe