Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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518 FXUS65 KRIW 020943 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 343 AM MDT Thu May 2 2024 .KEY MESSAGES... - Mainly dry today with critical fire weather for Natrona County this afternoon. - A weather system will spread showers across the much of the area tonight and tomorrow. Small accumulations of snow are possible late tonight and Friday morning, including in the lower elevations. - Unsettled weather returns Sunday night and continues much of next week with below normal temperatures, gusty to strong wind and rounds of showers. Details of the placement in intensity of the rounds of precipitation remains highly uncertain. && .DISCUSSION... Issued at 338 AM MDT Thu May 2 2024 Lets play a game this morning. Let us see if you can guess the word that will describe the over the next week or so. It is a nine letter word. Still don`t know? OK, it starts with a U. Still don`t know? If means that the weather will be active but some up and downs. If you guessed unsettled, you are correct. No prizes will be given though. We are a government agency after all. Today will be somewhat more settled. Other than a few mountain showers, most of the day will be dry, with only a 1 in 5 chance of showers through the daylight hours. The main concern will be fire weather; ore specifically, in Natrona County. Some areas had Red Flag Conditions for several hours today. And with a gusty wind expected to develop and dew points expected to drop into the single digits, we have issued a Red Flag Warning for this location. In other zones, fuels are not critical and one that is, Johnson County, wind will be less and humidity only has a 1 in 5 chance of reaching criteria. The first shortwave and cold front will move into the area tonight and move across through Friday. It could get interesting in a few locations. Models have come into decent agreement with the main impacts across the southern two thirds of the state. The system does not have a ton of moisture to work with though. I do have some concerns though. There will be some left front quadrant jet energy for the system to tap into. In addition, temperatures will be cold enough for snow across most areas, including the lower elevations. The problem is that, given the dynamic nature of the system, with snow will be of the showery and banded variety and models all have different solutions in placement of the bands. Impacts would not be widespread though. In addition, with the warm ground snow would have trouble sticking to the roads, especially anything that falls after around 8 am or so given the high May sun angle. So to sum it up, we have high confidence that some locations will wake up to a coating of snow Friday morning (more than 1 in 2). However, pinpointing locally higher amounts has low confidence (less than 1 in 4). As for specific amounts, probabilistic guidance gives the western valleys have less than 2 in 5 chance of an inch or more of snow, and the chance is less than 1 in 10 in almost all locations East of the Divide. Friday looks rather chilly as well, with temperatures averaging 10 to 15 degrees below normal. If there is some good news, it is that at least part of weekend looks fairly nice for most locations. This will especially be the case for Saturday as ridging moves over the area, bring the nicest day of the period with near to somewhat above temperatures and dry conditions. This will not last though as the next Pacific cold front and trough approaches. This will spread snow showers into the west much of the day. In areas East of the Divide, most areas will be dry most of the day courtesy of southwest, downsloping flow. This will bring gusty to strong wind to many areas though. And there are some 50 knot barbs at 700 millibars appearing as well. This brings the possibility of some high winds into the picture. The chance is less than 1 in 4 at this point, but we will have to watch it carefully. Much of next week looks rather unsettled with below normal temperatures and rounds of precipitation. An upper level low will move towards Wyoming on Monday and bring an unsettled day with rain and snow across portions of the area. This first storm looks warmer for Monday, with 700 millibar temperatures of minus 5 or warmer, which would keep snow levels about 6000 feet so most populated areas would have mainly rain, with snow at the higher elevations. With a tight pressure gradient, strong to high is possible as well. Uncertainty then increases starting on Tuesday, some models are showing a blocking ridge developing over the central portions of the country, which would keep the upper level low and general troughiness of the area at least through Thursday and possibly into Friday. With tight pressure gradient remaining, wind will likely remain strong to high for much of the time as well. This will especially so in areas favored by west to northwesterly flow, Like Buffalo, the northern Big Horn Basin and Sweetwater County. However, slow moving and meandering upper level lows make details of the forecast like precipitation amounts, timing and intensity very hard to predict this far out. So, to sum things up starting Monday, we have fairly high confidence (around a 3 in 4 chance) of a cool, blustery and unsettled pattern continuing through much of the week. However, confidence in the details of each day remains very low. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 942 PM MDT Wed May 1 2024 VFR conditions through the entirety of the period for all TAF sites. Mid level clouds and ceilings for all locations overnight into Thursday morning with relatively light winds less than 10-15kts. Winds will increase at locations up to 18-25kts but less at JAC as per usual after 16-18Z with daytime heating and mixing. These winds will push through sunset around 01-02Z before diminishing into the overnight hours with radiational cooling. Clouds will lower to around 5kft west of the Divide ahead of the next shortwave that will affect those locations into the next couple of TAF cycles for Friday and Friday night. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued at 338 AM MDT Thu May 2 2024 A combination of relative humidity falling toward 10 percent and wind gusting to 30 to 40 mph will bring critical fire weather to Natrona County this afternoon. Elsewhere, local elevated fire weather is possible but wind or humidity is not expected to reach critical levels. Concerns will ease tomorrow as showers and higher humidity spreads across the area. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from noon today to 8 PM MDT this evening for WYZ280. && $$ DISCUSSION...Hattings AVIATION...Lowe FIRE WEATHER...Hattings