Billings, Montana

• Widespread fog is likely through this morning across much of the region; and again Saturday night into Sunday.
• The chance of precipitation has increased today ahead of the late weekend weather system, although precip amounts remain light.
• A weather system will bring widespread precipitation (70-90% chance) and breezy conditions (20-40 mph) Sunday into Monday.
• Stronger winds are possible over the Bighorn foothills and along the Dakota border Monday. There is a 60% chance for gusts greater than 50 mph.

Next 7 Days (through Friday)

Very appropriate Halloween weather is in store over the next 24 hours. Low stratus that lingered through the entirety of the day Friday is transitioning into widespread fog tonight, including an expansion in area. The plains will likely see the most widespread dense fog this morning with visibility of 1/4 mile or less possible. This is all being aided by weak upslope (easterly) winds across the CWA. Due to this, the other area that could see dense fog will be in the foothills of the east facing aspects of the mountains.

Also occuring this morning are some scattered showers, especially over the western 2/3 of the CWA. Ahead of the main upper level low, a lobe of energy is pivoting through eastern ID into Central Montana. This is bringing us scattered rain and snow showers this morning. As the vort max continues to move through the area quickly, the coverage in showers is forecast to decrease through the afternoon and evening hours. That being said, there is still a 20-40% chance of precip for much of the CWA through the evening hours. So it might be a good idea to carry an umbrella this evening in case you need keep that costume dry.

Due to the fact that there will be minimal change in the overall weather regime through the day today, another round of fog is forecast tonight as well. All of the same conditions remain in place, however as the parent system moves in Sunday morning, this will help clear out some of the fog west of Billings as rain showers begin. In the same way we saw last evening, the fog could develop right after sunset so be prepared for a potentially foggy Halloween Night!

The upper level low that is currently situated just off of the coast of the PNW will slowly move due east into the Northern Rockies through the day today and Sunday. By Sunday AM, much of south-central MT will be seeing some form of precip. Note that snow levels will start out high before falling overnight Sunday into Monday morning as we start to see more cold air advect in. Even the NBM 25th percentile keeps the snow at or above 8kft through the day Sunday before gradually dropping down to 5kft Monday. This is the low end solution so levels will likely be a touch higher than this. Precipitation will end from west to east during the day Monday.

In terms of precip totals there is actually some good news. The current forecast is that as surface cyclogenesis occurs to our south, the wrap-around precip band will set up over our eastern CWA. This region has missed out on much of the rainfall events over the past several months and is therefore in an extreme drought (D3). The current forecast is for this region to see widespread totals of around 0.5" with locally higher amounts. The NBM 75th percentile even has some locations seeing up to 1.5" of rainfall for the entire event.

Although snow will not be a big part of this event, it will likely be the first impactful snow of the year for the Bighorn Mountains. The current 10-90 percentile spread for Burgess Junction is 2-14" with the mean sitting around 7". This will impact any recreation in the high country. One of the largest forecast questions surrounding the Bighorns is the forecast wind direction on Monday. This system will have PWAT values around 200% of normal so there will be ample moisture wrapping around the cyclone, however a few degrees change in the wind direction could make a huge difference regarding just how much upslope the eastern side of the terrain sees. As of right now, most models are showing nearly a perfect north direction in the wind to start the day Monday before slowly becoming NW. This will be something we have to keep a close eye on as more high-res models solutions come in. Speaking of the wind for this area, it may just be the most impactful part of this system.

As the surface low develops and quickly deepens Monday, winds will pick up as a result. By Monday afternoon, the ECMWF ensemble shows a 997mb low over the Great Plains, while the GFS ensemble shows it as low as 995mb. With a tight gradient between the low and the developing 1024 high associated with the CAA, a good gradient will set up over eastern MT/WY. This flow will be locally enhanced near Sheridan as it funnels around the Bighorn Mountains. Gusts in the 40s mph Monday afternoon in Sheridan are almost certain at this point, however there is a greater than 50% chance that we see gusts in the mid 50s mph range Monday afternoon/evening as well. These wind speeds are also forecast in the Bighorns during this timeframe as well. This could result in sharply reduced visibility due to the winds in combination with falling snow.

Although details are still quite fuzzy past this early week event, the overall pattern seems to be decently clear. It looks like we will see a more progressive pattern over the next week or so with repeated upper level lows / troughs pivoting through North America. Models still disagree on strength, timing, and placement so it is hard to pick out any details at right now. WMR

Areas of fog and low stratus will persist across the region through at least 18Z...and perhaps longer over the east (KMLS, KBHK). IFR and LIFR conditions will be common. Confidence is low in exact ceilings and visibility which may significantly vary at times...particularly as light showers move in after 12Z. Conditions should begin to improve by midday at most locations with fog ending in the early afternoon. Areas of light showers develop over portions of south central MT this morning and shift northeast through the day, lingering over east central MT through the afternoon. Mtns may be frequently obscured. BT

    Tdy Sun     Mon     Tue     Wed     Thu     Fri
-------------------------------------------------------
BIL 052 037/051 041/053 033/057 034/055 032/056 036/056
    8/W 06/W    +8/W    00/U    00/B    00/B    01/B
LVM 054 034/049 033/046 024/053 028/054 028/053 028/051
    4/W 26/W    +6/W    00/B    00/B    01/B    21/B
HDN 051 032/055 038/053 028/059 028/056 028/058 029/058
    5/W 14/W    +9/W    10/U    00/B    00/B    00/B
MLS 053 037/056 041/050 030/054 032/053 031/055 032/056
    2/W 23/C    +9/W    20/U    00/B    00/B    00/B
4BQ 060 037/062 041/047 031/054 032/053 031/054 033/056
    1/E 14/W    +9/W    40/U    00/B    00/B    00/B
BHK 061 037/059 039/051 028/052 029/053 028/053 029/055
    3/W 32/E    +9/W    41/B    00/B    00/B    00/B
SHR 056 031/056 032/045 025/057 029/056 027/056 028/057
    2/W 04/W    9+/W    20/U    00/B    00/B    01/B

MT

None.

WY

None.