Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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510 FXUS65 KRIW 301735 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1135 AM MDT Sun Jun 30 2024 .KEY MESSAGES... - Hot and dry today, with elevated fire weather conditions. Red Flag Warning for much of Natrona County this afternoon. Burning is discouraged. - A cold front brings rain chances and cooler temperatures Sunday night and Monday. - Seasonal temperatures and afternoon showers and thunderstorms for the middle of the week. Warmer and drier towards the end of the week. && .DISCUSSION... Issued at 205 AM MDT Sun Jun 30 2024 Current water vapor imagery shows the current synoptic pattern well, that being a ridge over Wyoming shifting eastward, with an incoming trough over the Pacific Northwest. Starting with the ridge, this brings hot temperatures and dry air to the area today. Temperatures east of the Continental Divide peak in the 90s, with near 100 for warm places like Greybull. West of the Divide, temperatures will generally be in the mid-80s. Afternoon relative humidities (RH) drop to the low teens for many locations across the area, with upper single digits for the Bighorn Basin. Northwest Wyoming and eastern Sweetwater County look to be around 20%. There is some uncertainty in RH values in an area from roughly Rock Springs to Midwest. Moisture moving up from the high to our south brings slightly better moisture and clouds. Both these would act to limit how low RHs get. The approaching trough tightens the pressure gradient for today, with a west-to-southwest wind gusting 20 to 40 mph for most of the area. The Wind Corridor may be closer to that 40 mph mark. A Red Flag Warning is in effect for the lower elevations of Natrona County this afternoon for these conditions, as well as the critical fuels there. Again, there is a bit of uncertainty due to incoming moisture and cloud cover, which could keep RHs above 15% (about a 20% chance). That same incoming moisture may spark some afternoon convection for Sweetwater County northeast through roughly the Natrona County area. Current models have isolated (about 20%) showers and thunderstorms during the afternoon and evening. With such dry conditions, not expecting these to be big rain producers. Instead, outflow winds will be the bigger concern. Gusts 40 to 50 mph are possible with any downbursts. Depending on the extent of the cloud cover, these winds could vary; less cloud cover would allow more afternoon heating and thus increase the risk for higher winds. Any of this convection should end by around 10PM MDT. Now onto the other feature, the approaching trough. The associated cold front begins to move through northwest Wyoming around midnight Sunday night. Rain chances accompany the front, moving south and east overnight. Chances continue through the day Monday. The best chance for rain occurs over the north half of the area, through Monday afternoon may see an isolated shower or storm over southern areas. Temperatures will be noticeably cooler Monday behind this front, with places in the the middle 70s to middle 80s. Wind looks to be the main threat with any storms at this time. The trough is broad, and its influence continues into Tuesday, with rain chances remaining over the northern third of the area. Tuesday also look to be a cool day, with highs below normal. An upper-level low moves out of Canada and into the Dakotas Thursday. This brings another cool day with rain chances, mainly across the northern half of the area. Past Thursday, a strong high pressure system builds over the western U.S. This acts to shut down much of the moisture into the area. Depending on its exact position, there may be a few upper lows that pass through the area, or they would be pushed to our east. Either way, looks like there is favoring for drier and warmer conditions for next weekend. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1135 AM MDT Sun Jun 30 2024 Winds begin to increase at most terminals within the first hour or two of the forecast period. Gusts 20 to 25kts should be expected at most terminals through the afternoon, then diminishing by around sunset. KRKS and KCPR will be the two terminals with the best chance of seeing any showers or thunderstorms today as Pacific moisture begins to push through. Spotty convection has been observed across the south and central portions this morning, but convection will generally be weak. A few stronger storms would be possible at the aforementioned terminals late in the afternoon, as diurnal heating and instability increases. Monday morning, a cold front will move west to east across the region. Showers are possible with the front, but confidence is not high on intensity of these showers, so have included several PROB30 groups to account for any stronger showers or storms that might occur along and behind the front. The cold front will not bring a strong wind shift, but gusty west winds will occur ahead of and behind the front for most terminals Monday morning. 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 205 AM MDT Sun Jun 30 2024 Elevated fire weather conditions today across most of the area. Afternoon RHs drop to 8%-25%. Afternoon wind gusts of 20 to 40 mph. A Red Flag Warning is in effect for Zone 280 this afternoon, from 1PM to 7PM MDT. Some afternoon showers and storms are possible across Sweetwater, southern Fremont, and Natrona Counties this afternoon and evening. Not expecting any good rain with these, but outflow gusts 40 to 50 mph are possible. A cold front moves in tonight from the northwest, bringing cooler temperatures and rain chances. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 7 PM MDT this evening for WYZ280. && $$ DISCUSSION...Wittmann AVIATION...Hensley FIRE WEATHER...Wittmann