Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
808 FXUS65 KRIW 201828 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1228 PM MDT Fri Sep 20 2024 .KEY MESSAGES... - Breezy today, with elevated fire weather for portions of central Wyoming. A cold front moves through late today. A cool north to northeast wind follows. - Saturday is much cooler, with a gusty northeast wind for the Wind Corridor and Sweetwater County. Patchy frost is possible Sunday morning for low-lying or cold prone areas. - A quick moving system Monday brings a north wind and low rain chances. - Warm-up for the latter half of next week, with little to no rain chances. && .DISCUSSION... Issued at 1226 PM MDT Fri Sep 20 2024 In the middle of high pressure over Texas and low pressure up in Canada, today should be a fairly typical mid-September day. West to southwest flow today brings a breezy afternoon, with gusts 10 to 20 mph for much of the area. The Wind Corridor, from roughly South Pass to Casper, is a bit windier in this favored direction, with afternoon gusts up to near 30 mph. High temperatures are the warm side today, with the high pressure having a greater influence. Temperatures in the mid-60s to mid-70s occur west of the Continental Divide, with mid-70s to low 80s east of the Divide. There are some fire weather concerns this afternoon and early evening. The gusty winds of the Wind Corridor, in addition to the drier air, brings elevated to critical fire weather to portions of the area. Red Flag Warnings are in effect to cover this. A cold front drops down from the north late this afternoon through the overnight hours. The main impact from this will be a breezy north wind and cooler temperatures. Starting with the wind, north wind prone locations, such as the Bighorn Basin and Johnson County, could see gusts up to 35 mph through about sunrise Saturday. A few high-resolution models are developing very light rain showers with the front. These would mainly be over Yellowstone National Park, the northern Absaroka range, and the northern half of the Bighorn Basin. If lucky, a hundredth of liquid may fall, but expect a few drops at most, if a shower does pass over. Have kept chances mainly 15% or lower, with some spotty 30% chances for Yellowstone into the Absarokas. Post-front Saturday features a cool northeast wind. Highs peak in the 60s for most of area. An approaching low pressure system to the south will aid in bringing a gusty northeast wind to the Wind Corridor, and especially Sweetwater County, starting Saturday morning. Gusts increase, with speeds of 30 to 35 mph by the afternoon. These winds decrease into the night. That low to the south remains out of the CWA as it tracks eastward. A very isolated (15%) shower is possible over far southeast Sweetwater and Natrona Counties late Saturday afternoon and through about sunrise Sunday. Models continue to reduce these chances, however. Sunday morning will likely be the coldest morning in at least the next week. The focus for the colder temperatures is lower elevations east of the Divide - places that haven`t seen growing season ending temperatures yet. Overall, not looking at widespread freezes (32F or less), but morning temperatures in the middle to upper 30s look to be widespread. Models are hinting at the potential for a few colder locations, such as near Worland and Casper, where temperatures near, or less than, 32F could occur (about 40% chance based on NBM, but less than 10% based on HREF). The takeaway here is that widespread freezes are not expected, but there could be some patchy frost areas for a few locations, and low-lying areas. For the day Sunday, relatively light winds, with no precipitation chances. Highs will climb a little bit, but are still seasonal. A trough quickly sweeps down through the state Monday. Models are still in disagreement on the strength of this system, though would likely bring a breezy north wind, with low precipitation chances. This system exits the area for Tuesday, which looks dry as high pressure begins to build in. Temperatures are on the warm side for the second half of the workweek, with little to no rain chances. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1120 AM MDT Fri Sep 20 2024 VFR conditions at all terminals through midday Saturday. A shortwave sweeps east across Montana Friday afternoon and evening, nudging a cold front south through areas east of the Continental Divide. There is enough lift and mid-level moisture to generate isolated showers over far northern Wyoming late today, but no impacts beyond SCT-BKN mid-cloud deck at KCOD. Gusty westerly wind 10-20kts increases at almost all terminals by 21Z/Friday before slowing again by sunset. The cold front begins a southward trek Friday evening and generates gusty northerly wind 10-20kts overnight. The front does make it to KRKS around 08Z/Saturday, but fails to reach other western terminals. 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 1226 PM MDT Fri Sep 20 2024 Elevated to critical fire weather conditions today across fire zones 280, 281, 289, and 300. A southwest wind increases this afternoon, with gusts 25 to 30 mph. Areas of critical RHs occur through this evening, with values around 15%. A cold front passes through this evening and overnight, bringing a north to northeast wind and cooler temperatures. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 7 PM MDT this evening for WYZ280-281- 289-300. && $$ DISCUSSION...Wittmann AVIATION...CNJ FIRE WEATHER...Wittmann