Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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781 FXUS65 KRIW 201122 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 522 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 /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 516 AM MDT Thu Jun 20 2024 High clouds continue to sweep across the state this morning. A bank of lower clouds associated with increasing surface moisture has been building toward KCPR, which will bring cigs down to MVFR for the next few hours, before lifting again by 18Z. Winds east of the Divide will remain light from the east, generally 10 mph or less. A few higher gusts are possible at KCPR this afternoon. Areas west of the Divide will see southwest winds 5 to 10kts, with some gusts to 20kts at KRKS. Showers and a few thunderstorms will develop this afternoon, but will stay mainly in central and eastern WY, withholding effects to just KCPR this afternoon. Between 00Z and 06Z tonight, winds will all shift from the east around 10kts, bringing in more near sfc moisture. This will build low clouds earlier into KCPR, and possibly reaching KLND/KRIW around 12Z/21. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wittmann AVIATION...Straub