Area Forecast Discussion · National Weather Service Billings (BYZ) · issued Thursday, July 16 at 2:26 PM MDT.
Revised in 10 passages since the 5:28 AM discussion. See every revision.
Messages
Isolated to scattered showers and thunderstorms today and Friday. A few thunderstorms may become strong to severe over central and western Montana. Heavy rain, strong winds, and hail are the main threats. The severe weather risk is greatest today.
Slow moving thunderstorms capable of producing heavy rain may lead to localized flooding, or even flash flooding, today, Friday, and Saturday. Marginal Risk (Level 1/4) of flash flooding over portions of central and western Montana and northern Wyoming.
Daily chance of showers and thunderstorms this weekend into next week with high temperatures in the 80s and 90s, warmest this weekend.
Discussion
An upper level ridge, with moisture and occasional shortwave disturbances rounding the ridge, will continue to dominate our weather pattern into next week. With this, temperatures near to above normal in the 80s and 90s are forecast, along with a daily chance of showers and thunderstorms over at least some of the area each day.
For today, isolated to scattered showers and thunderstorms are forecast, first over the mountains and foothills this afternoon before spreading over the plains this evening. This forecast delay over the plains is due to a capping inversion that looks to limit convection over the plains initially. While the showers and thunderstorms will decrease in coverage tonight, a weak low level jet may allow showers and weak thunderstorms to continue over eastern Montana tonight into Friday morning, though the chance of precipitation remains low (around a 15 percent chance). With good instability and modest wind shear, a few thunderstorms may become strong to severe over central and western Montana this afternoon and evening. While the instability is also high over eastern Montana, wind shear is much less, limiting the ability for thunderstorms to organize and become strong to severe. Currently, the Storm Prediction Center has a Marginal Risk (Level 1/5) of severe thunderstorms over much central and western Montana, with a small pocket of Slight Risk (Level 2/5) over western Montana. The main threats are heavy rain, strong wind gusts, and hail. The hail threat is greatest over western Montana where the wind shear is greatest. The Weather Prediction Center also has a Marginal Risk (Level 1/4) of excessive rainfall leading to flash flooding today over south- central Montana and north-central/western Wyoming due to slow moving thunderstorms.
Friday, isolated to scattered showers and thunderstorms are forecast once again, with a low chance of precipitation over eastern Montana in the morning and a low to medium chance of precipitation across much of the area in the afternoon and evening. A low level jet may also once again allow showers and weak thunderstorms to linger over eastern Montana into the night, but the chance remains low. With good instability, but limited shear, the main risk with any thunderstorm Friday afternoon and evening is heavy rain as thunderstorms will be slow moving. With this, the Weather Prediction Center has a Marginal Risk (Level 1/4) of excessive rainfall leading to flash flooding over south- central and western Montana and north-western Wyoming. Over western Montana where wind shear looks to be a bit stronger, there is also a Marginal Risk (Level 1/5) for severe thunderstorms. East of this area over south-central/eastern Montana and northern Wyoming, there is a risk of thunderstorms, but they are expected to remain non-severe with the limited wind shear.
While a daily chance of precipitation remains in the forecast Saturday into next week, Sunday into Monday looks to be slightly drier days behind a cold front passage as atmospheric moisture content decreases back near normal, compared to the above normal values we have been seeing. This will limit precipitation mainly to the mountains and foothills these days. The return of above normal atmospheric moisture across much of the area Tuesday into the second half of the week will then resume at least a daily chance of precipitation across much of the area for mid-week. LA
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