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
070 FXUS65 KRIW 230430 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1030 PM MDT Wed May 22 2024 .KEY MESSAGES... - A period of moderate to heavy snowfall is expected tonight across the Tetons and Gros Ventres, generally between 6 PM and midnight. - Cooler and wetter conditions Thursday behind a cold front. Snow continues in the mountains but especially across the Bighorns. Windy for most locations Thursday. - Warmer and drier on Friday. The next system will arrive this weekend bringing widespread precipitation chances. && .DISCUSSION... Issued at 400 PM MDT Wed May 22 2024 The next system is beginning to push into western Wyoming after a short period of relatively tranquil conditions within transitory ridging. Mid-level flow has become southwesterly in response to a low pressure system that is dropping south into northeast Oregon. Rain and snow showers will continue to increase across the west through the afternoon as moisture is funneled up the Snake River Plain. The rest of the area will remain on the drier side through the afternoon, though a few showers will make their way east of the Divide into the Bighorn Basin. Otherwise, the rest of the afternoon will be breezy across the usual Wind Corridor as southwest wind increases in response to a building pressure gradient ahead of a cold front. Wind will quickly drop off after sunset. Precipitation rates will ramp up further across western Wyoming this evening with the arrival of increasing upper level divergence due to a favorably placed ~100 knot jet. This should make for a fairly heavy period of snowfall across the Tetons before midnight, perhaps as much as an inch an hour for the higher elevations. While the passes won`t get quite that much, it may still make for a difficult drive this evening. Shower coverage east of the Divide will also increase a bit, but most locations here will remain dry through midnight. There will be a relative lull across western Wyoming after midnight as the low quickly approaches, turning the prevailing flow northerly as a cold front surges east. This will shift the precipitation focus to northern Wyoming by sunrise as moisture is wrapped back over the state. Showers will spread to the rest of areas along and east of the Divide through Thursday as the low skirts east across central Wyoming. The cold front will result in temperatures much cooler than today. Snow levels will drop to around 5,000 feet in the morning, rising to around 7,000 feet in the afternoon. With upslope favoring the Bighorns Thursday, a Winter Weather Advisory remains in effect for generally 6 to 12 inches there. Given the heavier period of snow tonight and continued lighter snow tomorrow, we have issued a Winter Weather Advisory for the Tetons/Gros Ventres as well. That said, impacts there may be limited tomorrow due to spring temperatures and long daylight. Another aspect of Thursday`s forecast will be wind as the front passes, as well as when the northerly flow ramps up behind the low. Accordingly, west wind will increase after sunrise across most of the area. Then a northerly push will arrive in the Bighorn Basin by early afternoon. Wind gusts generally look lower than needed for highlights, but occasional gusts over 55 mph are possible (30 to 40 percent) in northern Johnson County Thursday afternoon. Precipitation and wind will quickly decrease around sunset as the system pulls away. Friday looks to see warmer and drier conditions return as a weak ridge takes over. Guidance is then favoring the next system arriving for the weekend. Details on this system are uncertain as the pattern is not clearly organized. However, trends remain favorable for a fairly widespread precipitation event Saturday and Sunday before ridging returns on Monday. Currently, this looks to be a warmer system than the current one, limiting snow to higher mountain elevations. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1028 PM MDT Wed May 22 2024 The next weather system continues to approach Wyoming tonight with moderate to heavy precipitation impacting the western part of the state. Rain has turned over to snow at KJAC and should remain IFR through 07-08Z as the area of precip moves northeast. A mid-level cold front will move west to east overnight, bringing snow and rain to KBPI and KPNA between 06-12Z/Thu. A low chance of showers is possible at KRKS around sunrise too, not enough to mention in the TAF though. Behind the cold front, surface winds will increase from the west and gust 30-40 kts at most sites through the day Thursday. As the storm center moves across the middle of the state, wrap- around precipitation with SW then NW winds will bring showers to KJAC during the middle of the day. And then as the storm center moves to eastern WY in the afternoon, a surface cold front will push southward into the Bighorn Basin to bring MVFR/IFR conditions to KCOD and KWRL with gusty north winds and rain turning to snow. The cold front will push into central WY around 00Z/Fri for 1-2 hours of gusty north winds at KRIW/KLND/KCPR and a 30 percent chance of light showers. Some east winds then push into KRKS just before 06Z/Fri. The mountains will be mostly obscured for the TAF period with moderate snow in the west-central mountains tonight, and moderate snow over the Bighorns from early morning through sunset Thu. 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... Winter Weather Advisory from 3 AM to 6 PM MDT Thursday for WYZ008-009. Winter Weather Advisory until 4 PM MDT Thursday for WYZ012. && $$ DISCUSSION...Myers AVIATION...McDonald