Billings (BYZ) — the National Weather Service forecast in plain English · Plaincast

Messages

Occasional chances of showers (mainly light) today through Sunday night. Scattered thunderstorms possible in southeast Montana Sunday.

Snow showers in the mountains above 10000 feet Sunday and Sunday night; minimal to no accumulation.

Update

Cold front has pushed through the entire cwa and temperatures/winds have responded accordingly, with temperatures in the mid 40s to mid 50s and easterly surface winds extended all the way to Livingston (a few hours earlier than previously thought). Weak shortwave is producing light showers mainly from Melville to Judith Gap as of 14z, but there are also showers near Livingston and Emigrant. Shower potential, though it should remain isolated to scattered, will extend eastward across the plains this afternoon and evening. Cloud cover is steadily increasing and looking upstream there is low stratus from Cut Bank to Great Falls. As low level cool advection continues and upslope winds deepen, would be shocked if low clouds and perhaps upslope fog don't become issues for us by this evening. All told, today will be 15-25F cooler than Thursday with highs in the 60s to lower 70s. Have dropped forecast highs a bit and adjusted winds/chance of rain per current mesoanalysis. JKL

Discussion

The forecast for Friday and Saturday remains roughly the same as what we have been seeing for the past 1 to 2 days. A cold front is forecast to move through the forecast area this morning which will bring with it our first taste of fall. In addition to the notable increase in moisture, the high temperatures today will be roughly 10 degrees below average for most locations, or 20 degrees colder than what we saw Thursday. Just behind this frontal passage, and lingering through the day Friday, there will be scattered showers and thunderstorms. The highest coverage of precipitation will be in the mountains and foothills of south-centeral Montana and decreasing in coverage with eastward extent. Saturday will be fairly similar to Friday with temperatures 10 degrees below average and isolated showers across the region. Coverage of precipitation will decrease through the day leading to widely isolated showers by evening.

Over the past day or so models have trended the Sunday shortwave farther to the north. This would result in warmer and drier conditions then previously forecast. At one point there was a few inches of snow forecast above 9kft and a high chance of a wetting rain across the entire forecast area Sunday, there is now a less than a 50% chance region-wide for a wetting rain Sunday. With this more northerly track of the low now, we will actually see a slight temperature rebound on Sunday. There is still a large model spread on how much temperatures will rebound, but highs near average are possible before another push of cool air to start the work week.

With parts of our forecast area now in the "dry slot" of the low on Sunday, there is a slight chance that some stronger thunderstorms may develop in the eastern portion of the forecast area. During the afternoon and evening Sunday, a cold front will push from west to east across the area acting the the primary source of lift for any convection. Due to the cooler temperatures, modeled MU-storm energy values remain under 1000 J/Kg, however this would be plenty sufficient given the strong source of lift aiding CI as the front pushes through late afternoon and evening. Additionally, shear values in SE Montana will be in the 30-50kt range due to the proximity and location of the upper level low. In terms of moisture, precipitable water values are forecast to exceed 1" in the eastern 1/3 of the forecast area ahead of the frontal passage which will be plenty for thunderstorm development. With this event just now being depicted on models, plus it being several days away, there is still several questions surrounding the event. The few CAMs that run out that far are depicting some strong storms in NE WY and just clipping SE Montana. This signal will be monitored as we get closer to the potential event.

To start the work week we will remain under the main branch of the jet stream which will allow for near to just below average temperatures to linger through the first part of the week. There is a chance that isolated showers continue with these cooler temperatures due to the strong jet dynamics overhead. WMR