Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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482 FXUS65 KRIW 192344 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 544 PM MDT Thu Sep 19 2024 .KEY MESSAGES... - Dry and seasonal today and tomorrow. - A weak cold front moves through Friday evening, bringing a cool north wind shift. - Cool to seasonal through the weekend, with isolated (20%) rain chances for portions of southern Wyoming. && .DISCUSSION... Issued at 1238 PM MDT Thu Sep 19 2024 A very seasonal day today. Highs are in the 60s to mid-70s across the area this afternoon. Winds will be light, with gusts around 20 mph for the Wind Corridor (approx. South Pass through Casper). Some low clouds have hung around portions of northwest Wyoming. Of note is Jackson Valley, where mid-level clouds have kept the eroding sunshine from breaking up the lower clouds. Models have been struggling to resolve this. Would expect these lower clouds to erode by mid-afternoon as the sun becomes stronger. For Friday, temperatures increase a little, with highs in the 70s for most of the area. Not expecting any precipitation. Afternoon winds do increase, with 20 to 30 mph gusts for the Wind Corridor and portions of northwest Wyoming. Elevated fire conditions may occur for the Wind Corridor, but winds will be marginal, and critical RHs may not be widespread enough to warrant any highlights. A weak cold front pushes through in the evening. This shifts winds to the north and northeast, with a slight breeze and cooler temperatures. The cold front leaves Saturday cooler, with highs in the 60s. No strong signals for precipitation chances, but an approaching low to the south could bring an isolated (20%) shower for southern Wyoming areas. This low also brings a tighter pressure gradient, so gusty winds across the Wind Corridor of 20 to 35 mph. Models still track this low southeast of the CWA, so its impacts will be minimal to none through the weekend -cooler temperatures and isolated (20%) rain chances for southern areas. Sunday morning looks to have the coldest temperatures through the next week. Even so, Sunday morning lows look to remain in the middle 30s to around 40 degrees for lower elevation locations that have yet to hit freezing (mainly east of the Divide locations). The HREF has less than 10% chances for 32F or less Sunday morning. The low exits to the east Monday, allowing another trough to dip down into the state. There is some uncertainty with this low. The ECMWF brings a closed upper-level low, while the GFS keeps it an open trough as it passes through Wyoming. Continued cool temperatures and some precipitation chances are the main result in either case. High pressure looks to make a return for the middle and end of next week. This would favor warmer temperatures and less precipitation chances. Long range models are keeping these conditions until the start of October. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 544 PM MDT Thu Sep 19 2024 VFR prevails at all terminals through 00Z/Saturday. Any lingering 10 to 20 kt wind gusts end between 01Z and 02Z/Friday. KCPR, KCOD, and KJAC see surface winds increase from the west to southwest between 15Z and 18Z/Friday. Most other terminals see westerly 10 to 14kt surface winds develop between 18Z and 21Z/Friday ahead of a cold front approaching from the north. The passage of a weak shortwave across the region leads to little more than a few more mid and high cloud decks late Friday, especially across the far north. Cold frontal passage occurs just beyond the valid period of this forecast. Expect occasional mountain top obscurations until 02Z/Friday over northwest Wyoming. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wittmann AVIATION...CNJ/VandenBoogart