Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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378 FXUS65 KRIW 232223 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 423 PM MDT Mon Sep 23 2024 .KEY MESSAGES... - Slightly above normal temperatures Monday and Tuesday with partly cloudy skies becoming mostly sunny along with some gusty north winds east of the Divide. - High pressure strengthens Tuesday night into Wednesday, bringing well above normal afternoon temperatures and gusty southwest wind for elevated fire weather conditions. - Similar situation creates elevated fire weather conditions on Thursday with gusty west winds and partly cloudy skies across northern Wyoming. - Dry and very warm conditions continue Friday and Saturday, with the next chance (20-30 percent) of precipitation Sunday afternoon and evening into Monday as a disturbance moves through the northern Rockies. && .DISCUSSION... Issued at 113 PM MDT Mon Sep 23 2024 Dry northwest flow continues over western and central WY today as a low pressure system moves out of southern Canada into the Northern Plains. High-level clouds have increased today with a northerly component, and some mid-level wave clouds have also developed in response to the increase in moisture. One or two high- resolution models are showing a 5-10% chance of showers over the east-central Bighorn Mountains late this afternoon and early evening, but feel that the better chance is well to the northeast. Near the surface across north-central WY, winds are generally from the NW to N and are gusty, especially around Buffalo. In response to the "boundary", gusty west- southwest winds continue today from southwest WY into central WY, though central WY should see some north winds this evening. With 700 mb temps around +6 to +8 C today and tomorrow, max temps will be about 3-6 degrees above normal in the 70s to around 80. Upper- level high pressure is expected to move from OR to the northern Intermountain West overnight, and then over northern UT Tuesday afternoon. Skies will thus clear from west to east on Tuesday, and the surface pressure gradient will weaken to bring relatively light winds for an amazing fall day across the state. Wednesday will see the ridge axis move over WY during the morning and then eastward through the day. A lee-side low is expected to develop over eastern MT, strengthening the gradient across the forecast area, and increasing southwest winds during the afternoon. Skies will still remain mostly clear, but surface temperatures will increase in response to 700mb temps also increasing to +12 to +15 C. Expected max temps will be from the high 70s to around 90, which is 14-16 degrees above normal for Sept. 25. Models are showing drier air moving in Wednesday afternoon as well with min RH values dropping to around 15 percent, to create elevated fire weather conditions during the afternoon and early evening. The shortwave trough over the PACNW then moves into MT on Thursday with no precipitation expected across northern WY. Dry and very warm air continues over the forecast area as winds shift from southwest to west and remain gusty. Again, elevated fire weather conditions are expected. As the trough moves eastward across MT, a weak surface cool front then shifts the winds to the north across north- central and northeast WY Thursday afternoon. Weak mid-level southwest flow will return to WY Friday and Saturday as the pressure gradient weakens. Temperatures will cool slightly to the mid 70s to mid 80s, but still remain 10-12 degrees above normal for late September. Skies should remain mostly clear until late Saturday night as a shortwave trough moves from the West Coast toward the MT/WY area. Winds and clouds will increase Sunday morning with the advance of a strong cold front and some showers and thunderstorms are possible (25 percent) through the day. The north- south uncertainty with this wave though is likely to bring a better chance of storminess to northern WY, with considerable cooling behind the system. Ahead of the front in central WY, gusty southwest winds and dry conditions will again elevated fire weather concerns. Hopefully a better picture will develop over the coming days, as well as some autumn precipitation to keep drought categories from worsening. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 420 PM MDT Mon Sep 23 2024 Lingering high cirrus clouds will continue moving southward across the region this evening, but no low or middle atmosphere clouds are expected over the next 24 hours. Breezy north winds continue this evening east of the Continental Divide, while northwest winds prevail west of the Divide. Wind gusts over 20 kts will quickly decrease after sunset, with sustained winds becoming more light and variable. Winds on Tuesday afternoon will be lighter than those experienced today. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...McDonald AVIATION...VandenBoogart/LaVoie