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
502 FXUS65 KRIW 241736 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1136 AM MDT Fri May 24 2024 .KEY MESSAGES... - Mainly dry and milder today. - A half and half 3 day weekend on tap: Saturday unsettled, Sunday less wet but breezy to windy; nice on Monday. - Warmer for midweek. More uncertainty for chances of convection for the middle and end of next week. && .DISCUSSION... Issued at 309 AM MDT Fri May 24 2024 The storm that brought the variety of weather over the past 24 hours is finally exiting stage east into the Dakotas. Shortwave ridging will build across the area today and bring a decent end to the workweek and entrance to holiday weekend with sunshine and somewhat below normal but comfortable temperatures. There will still be a bit of a breeze but nothing substantial. There is a small chance of a shower or thunderstorm over the northwestern mountains, but the chance is less than 1 in 5. One fact about this part of the country is that May is typically our wettest month on average. And Memorial Day weekend, for some reason, is usually rather wet and sometimes chilly. And this will be the case again, at least for part of the weekend. A weak shortwave will approach southern Wyoming Friday night and will have enough jet energy for a few showers and thunderstorms, stretching across roughly the southern third of the state. The chance of showers is at most 2 in 5 across the far south, tapering down further north. A Pacific cold front and trough will then begin crossing the state on Saturday. At this point, this looks to be the wettest day of the weekend with all areas having a chance of showers and thunderstorms. There will be a decent amount of cloud cover. This should limit instability a bit. There is some CAPE (generally less than 500 J/KG) and lifted indices top out at minus 2. So, most thunderstorms will be of the garden variety and not severe type. The most numerous activity this day will be found in areas West of the Divide (anywhere from a 1 in 2 to a 4 in 5 chance of showers or storms. This chance tapers to around 2 in 5 at the most East of the Divide. And we still have to talk about the S word, snow.. Temperatures are not as cold with this system though, bottoming out around minus 1 to minus 2 for the most part, so this should stay confined to the mountains. Sunday is starting to look more optimistic. Most guidance is now showing this system as an open wave and not a closed low, and progression will be faster as a result. So, areas West of the Divide should dry out for Sunday. East of the Divide will still have a chance for showers, but what we have in the forecast is probably the worst case scenario. POPs will be highest across Johnson County and the Bighorns (greater than 1 in 2), tapering to less than 1 in 5 in the Wind River Basin. The culprit for this is a shortwave brushing by the north and some jet energy diving in from Montana. The main thing will be some gusty wind that will develop in many areas. This will especially be the case in central Wyoming, where mid level convergence and the right front quadrant of the jet enhancing downward momentum. The 700 millibar winds do not look sufficient for high wind though. These showers should end Sunday evening. Ridging should then build in for Monday and bring a nice end to the 3 day weekend with sunshine and near normal temperatures. Mainly dry conditions should last into Tuesday as well with warmer temperatures as flow turns southwesterly. Guidance diverges more starting Wednesday with some models wanting to bring some shortwaves across the area with chances of convection and other keeping activity to the north of the state. We split the middle for now, keeping lower end POPs across northern Wyoming with mainly dry conditions further south. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1134 AM MDT Fri May 24 2024 Relatively quiet weather expected through the first 18 hours of the forecast period. Westerly winds gusting 20 to 25kts will be possible at most terminals through the afternoon, diminishing by sunset. Otherwise, VFR conditions prevail at all terminals with only FEW to SCT mid- and high-clouds through the evening hours. Cloud cover begins to increase overnight, especially west of the Divide as the next shortwave pushes into the region. Models indicate two separate waves of moisture with this system. The first, looks to impact KRKS overnight, between 09Z and 14Z Saturday. Have kept VFR for now, but occasional MVFR conditions are certainly possible (30% chance) during heavier showers. There is also a 20% chance of showers reaching KLND, KRIW, and KCPR with this wave, but have left any shower mentions out of the TAF due to low confidence. With the second wave, hi- res models are struggling to resolve exact timing, but for now, no impacts are expected before the end of the TAF period. 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...Hattings AVIATION...Hensley