####018007829#### FXUS65 KBYZ 170115 AFDBYZ Area Forecast Discussion...Updated National Weather Service Billings MT 715 PM MDT Fri May 16 2025 .KEY MESSAGES... - Scattered showers and a few thunderstorms over the west half of our forecast area today and Saturday. - Another spring weather system is expected to bring lower elevation rain and mountain snow, cooler temperatures, and windy conditions back across the region Sunday through Monday. - Heavy rain Sunday into Monday may cause localized flooding in areas with saturated ground. Water rises and increased stream flows on area waterways can also be expected early next week. && .DISCUSSION... Through Sunday Night... Low pressure system over the upper midwest was slowly sliding east today. This has pulled the stronger winds and precipitation east with it. Thus, winds and rain coverage have decreased across our eastern border counties. Ths High Wind Warning for Fallon/Carter counties were allowed to expire at 100 pm. In the meantime, we have had some Pacific moisture moving into our western forecast zones with assoicated perturbation and instability. This has produced some scattered showers with a few rumbles of thunder, particularly over and near the high country. Some of this activity will linger into the evening as it slowly migrates east overnight. Skies should mostly clear out in our far east overnight allowing for temps to drop to the lower to mid 30s across Fallon and Carter Counties resulting in a threat of light frost and local fog (The probability of reaching 32F is about 25%, while there is a 60% chance of dropping to 35F or lower). Temps elsewhere will be in the 40s. We should see a period of mainly dry conditions late tonight and Saturday morning. By Saturday afternoon we start to introduce height falls in response to next approaching upper trough. There should be enough diurnal heating to achieve a bit more instability than tomorrow (300-500 j/kg of SBCAPE), but any convection should remain below severe limits...and may be limited to the higher terrain in our west thanks to some induced capping from easterly surface winds. By evening, we may see increased showers and t-storms over the western half of our CWA and some isolated activity on the eastern plains as height falls and difluent flow start to affect our region with the upper trough progged to dig into the Rockies. Look for highs in the 60s Saturday and lows in the 40s Saturday night. Sunday/Sunday night...Upper trough moves slowly across our region Sunday into Monday spreading precipiation and cooler temps over the area. As cooler air moves into the western zones (highs in the 50s), we will still see a warm sector Sunday from Billings eastward with highs in the 60s to near 70 degrees. PWAT values will broach .80 inches with decent upper forcing and instability. We could see a few stronger thunderstorm cells develop capable of heavy rain and small hail. Due to recent rainfall the past week or so, grounds may be close to saturated in some areas, especially around the Big Horns region where two to four inches of rainfall in the past 10 days has been observed. Local flooding is a concern, including the Elk fire burn scar where heavy rain in short time could cause debris flows. Heavy rainfall potential and impacts...As this early week storm system moves over the region late Sunday through Monday there is a potential for heavy rainfall with over an inch of precipitation in many areas. Snow levels are expected to be relatively high (above 8500 ft) on Sunday, droppng to around 6500-7500 ft by Monday. The high country could see 5-10 inches of new snow, with wet snow rain mix in the higher foothills. Some rain on snow is possible, but overall rainfall and saturated ground soils are currently the biggest concern, especially around the Big Horns region. Models are still bouncing around with placement of heaviest precip, with latest trends pointing to upper Musselshell region (Wheatland, Musselshell Counties) picking up half to one inch of liquid Sunday night. However, models have consistently placed over an inch of liquid over the Big Horns region Sunday through Monday. Therefore, we will issue a Flood Watch for the Big Horns, Sheridan Foothills and Southern Big Horn County from noon Sunday to 6 PM Monday with the aforementioned concerns for this area. We will monitor other areas across the CWA to possibly expand this Flood Watch, but for now our greatest concern in these areas. BT Monday through Friday... Into Monday, an upper level low set to move across Wyoming will continue to bring precipitation to the region. Precipitation will gradually diminish eastward as the low tracks into the Dakotas Tuesday morning. There still remains uncertainty of the exact track of the low and where the heaviest precip amounts will occur. Much of the region has moderate chance for at least an inch of precipitation Sunday through Monday. Through Monday and Tuesday, continued rises on waterways can be expected downstream of where any heavy precipitation occurred. No minor flooding is expected at this time. With regards to snowfall, snow levels will drop to around 6-7,000 ft Monday morning, taking away concerns for any rain on snow potential. Ensembles continue to hint at unsettled weather with lagging lower heights to our north dragging some weak energy through the area Tuesday night into Wednesday. Additional waves are possible later in the week, but ensembles are differing too much to give decent timing. Temperatures will remain around average with highs expected to be in the 50s Monday, warming into the 60s for the remainder of the week. TS && .AVIATION... An area of generally light shower activity will persist over western and central zones this evening, shifting east overnight. Local MVFR conditions can be expected near shower activity. Patchy fog is possible over the western half of the forecast area including KSHR/KBIL/KLVM/K6S0/K3HT terminals. Any fog that does develop should dissipate by 15z Saturday. Otherwise, VFR conditions are expected through Saturday. Isolated to scattered afternoon/evening convection is expected to develop Saturday afternoon across the region. Chambers && .PRELIMINARY POINT TEMP/POPS... Sat Sun Mon Tue Wed Thu Fri ----------------------------------------------------------- BIL 045/068 049/064 043/051 042/067 044/068 047/068 045/067 32/W 29/T 97/W 45/W 54/T 35/T 33/T LVM 040/064 043/054 038/056 038/064 039/067 042/064 039/065 52/T 6+/T 85/W 35/T 53/T 35/T 34/T HDN 043/070 049/069 044/052 041/066 043/068 045/069 044/069 32/T 29/T 99/W 55/W 54/T 35/T 44/W MLS 040/068 047/067 043/052 040/062 042/068 045/069 044/068 01/B 26/T 99/W 64/W 34/W 24/W 43/W 4BQ 039/067 047/068 042/048 040/059 041/066 045/067 045/066 01/B 26/T 99/W 64/W 34/T 23/W 33/W BHK 033/064 040/056 038/050 037/056 036/065 040/067 041/066 10/U 25/T 98/W 74/W 34/W 23/W 42/W SHR 037/068 043/068 039/048 037/063 038/067 041/069 040/065 21/B 29/T 99/W 55/W 45/T 24/T 33/T && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Flood Watch in effect from Sunday afternoon through Monday afternoon FOR ZONES 138-169-171. WY...Flood Watch in effect from Sunday afternoon through Monday afternoon FOR ZONES 198-199. && $$ weather.gov/billings