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
43
273 FXUS65 KRIW 250350 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 950 PM MDT Fri May 24 2024 .KEY MESSAGES... - Dry through the end of the day. - Unsettled conditions return this evening with showers moving into southern Wyoming. - Widespread showers and thunderstorms expected Saturday. - Sunday will see lingering showers east of the Divide. - Warmer and drier Memorial Day through the middle of next week. && .DISCUSSION... Issued at 156 PM MDT Fri May 24 2024 Transitory ridging has taken over in the wake of yesterday`s system. This has led to a warmer and drier day across the area, though highs will still peak about five degrees below normal for this time of year. Returning southwest flow near the surface will make for a breezy afternoon for most locations while mixing down drier air that has moved in aloft. This will lead to a few hours of slightly elevated fire weather conditions for portions of central and southern areas where humidity will drop below 20 percent. The quiet weather will be short-lived as unsettled conditions return this evening. Pacific moisture will increase with the arrival of a shortwave within the southwest flow. This should lead to some light showers overnight, mainly limited to the southern half of the area. This first wave will be quickly followed by a stronger shortwave trough that will move into western Wyoming by late morning. This will bring a reinforcing shot of moisture that will contribute to fairly widespread convection. Showers and thunderstorms will move from west to east through the afternoon. Hi-resolution models have been keying in on southern portions of the CWA for the best parameters for a few stronger storms by mid-afternoon (CAPE over 500 J/kg and bulk shear 30-45 knots). There is some uncertainty on how quickly clouds can clear from the first wave there which could limit instability later on. Otherwise, this system is not very cold, and high temperatures won`t be too much different than today. Snow will be limited to the mountains with only light accumulations. The entire area has a good chance (~60 percent) of at least a little rain, with the most accumulation along and west of the Divide (40-60 percent chance of a quarter inch or more). Showers will mostly come to an end Saturday evening save for some lingering activity across northern Wyoming into Sunday morning due to another quick shortwave clipping the area. Sunday continues to trend drier for most locations with Saturday`s wave moving off to the east. The exception will still be across northern Wyoming, and especially the Bighorns and the Powder River Basin. These areas will see another weak wave dipping down from Montana, as well as a better moisture pool for an additional round of showers in the afternoon. Memorial Day will be dry as stronger ridging returns to the area. Temperatures will return to around or a few degrees above normal. Further out, ensemble guidance still favors ridging to persist through midweek before weakening by the weekend. This would keep drier conditions and temperatures around or above normal through much of next week. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 949 PM MDT Fri May 24 2024 Prevailing VFR conditions through about the first half of the period. Two rounds of showers move through the area over the next 24 hours. The first occurs at the start of the period, with most likely impacts at KRKS through about 15Z. Models have shifted the best precipitation chances southward, so KRKS could see very little precipitation. Have kept prevailing rain in the TAF for now, but confidence is lower. KCPR has about a 10% chance to see a shower. The next round comes Saturday late afternoon through the evening. Showers and thunderstorms are possible with this push of moisture. High-resolution models have a slightly better grasp on starting times, but struggle with the speed of the system and how long precipitation chances linger into the evening and early night. Have attempted to put average start and end times in the TAFs but would not be surprised to see timings adjust a few hours in either direction for future issuances. 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...Myers AVIATION...Wittmann