Radar — KTFX
Surface Analysis — Western U.S. (North)
Satellite
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Nearest monitored road: Helena Avenue (Secondary)
- periods of dense fog will continue through sunday morning, most widespread over central and north-central montana.
- precipitation becomes more widespread by sunday, with accumulating snow most prevalent over the higher terrain of southwest montana sunday night into monday morning.
- temperatures trend closer to average next week.
/issued 815 PM MDT sat oct 31 2026/
Southerly flow ahead of an incoming upper level trough is importing deeper moisture aloft into the the region over already very moist low levels, leading to widespread low clouds with a few light showers also tracking north in association with an initial disturbance ahead of the trough. Main concern through the overnight period will be the redevelopment/expansion of fog. A dense fog advisory continues for much of north-central mt, where conditions are most favorable and latest high resolution model ensembles support this with a 70% or higher probability for visibility less than 1/2 mile. Temperatures, and more importantly dewpoints are at or above freezing across most areas where either dense fog or light precipitation is expected tonight, limiting the potential for icing or freezing precipitation and overnight forecast grids were refreshed to reflect this and incorporate latest guidance and observed trends. Hoenisch
/issued 815 PM MDT sat oct 31 2026/
- meteorological overview:
Low level easterly flow continues to support low stratus and areas of dense fog development over central and north-central mt, while a moist southwesterly flow aloft overruns the cooler air mass and sends waves of light showers, sprinkles, and even some isolated instances of freezing drizzle. This general pattern will more or less persist through sunday before a closed mid -level low over the pacific NW heads towards the northern rockies and brings more widespread rain and snow sunday through early monday. The fog impacts will be most widespread over central and north-central areas during the overnight and early morning hours.
The closed low will begin migrating towards the northern rockies late saturday night into sunday while being weakened and elongated by synoptic shearing. With the colder air aloft not scheduled to arrive until sunday night, snow levels will be over 7000 ft for most locations, except along the continental divide. This will bring mostly liquid precipitation for lower elevations with the exception of some isolated instances of light freezing drizzle over the plains west of i15. Some freezing precipitation may also occur for the colder southwest valleys along the mt/id/wy borders.
H700 temperatures finally fall to around -5c by sunday night into early monday and this will bring more efficient accumulating snow, heaviest over the madison/gallatin ranges above 6000 ft. There will be a brief period with snow levels falling to the valley/plains floors monday morning, although it does not appear that this will be long enough to support widespread accumulating snow impacts. Northwesterly winds may get gusty monday morning, though gusts look to stay below 40 MPH. Ensembles continue to favor ridging aloft to bring drier conditions and near average temperatures for the remaining first half of next week, with unsettled conditions looking to return later in the week. - rcg
- forecast confidence & scenarios:
...dense fog through sunday...
Hi-res ensemble forecast (href) guidance supports the development of fog between 9PM this evening and 3AM sunday over the plains of central and north central montana, with this area of fog persisting through 9AM to 3PM sunday before an area of precipitation lifting northeast from southwest montana brings an end to the reduced visibilities. The aforementioned href guidance largely support probabilities of between 40-60% with respect to visibilities falling below 1/4 mile during the overnight hours, and for this reason a dense fog advisory has been issued yet again through 12 PM sunday. Confidence is highest in visibilities falling to 1/4 mile or less along and west of the i-15 corridor, mt hwy 200/US hwy 87 corridor, and in milk river valley where persistent low level east to north flow will support upslope fog. - moldan
...light mountain snow and lower elevation rain, snow, and some mixed precipitation sunday through monday morning...
The main trough moves through sunday through early monday and brings a wave of widespread precipitation to much of the forecast area. Aside from some light snow along the continental divide and perhaps some spotty freezing drizzle over the plains west of i15 and over the higher southwest valleys, most of the precipitation will be falling in the form of rain until sunday night. The overall pattern and nbm probabilities favor the madison and gallatin ranges for the best chance (60 to 80%) for snowfall amounts in excess of 3 inches. Lighter snows, generally up to a couple inches, look to fall along the continental divide and the central island ranges. The colder air is still not looking to be optimally aligned with the moisture for lower elevation snows, but will monitor the gallatin valley where there is around a 30 to 40% chance for a couple inches of snow on the south/eastern fringes of the valley monday morning. - rcg
01/06Z taf period
Initially, low level clouds, patchy dense fog, and drizzle will be the primary concern through the morning hours. Greatest risk of visibilities below 1/2 mile are across north-central mt where northeast flow is aiding surface moisture. While the threat is lower across southern terminals, isolated dense fog cannot be ruled out especially terminals kbzn, kwys, and keks. Moving into sunday afternoon, rain becomes increasingly widespread pushing in from the southwest. This will bring renewed concerns of decreased visibility with rainfall in combination of fog as well as low cloud bases through the later half of the taf period. Mountain obscuration will continue through the entire taf period. -jr
Gtf 45 35 39 36 / 0 20 90 100 ctb 45 29 41 29 / 0 10 60 50 hln 46 35 43 36 / 10 50 100 90 bzn 42 34 41 34 / 30 20 90 100 wys 42 32 39 26 / 90 80 100 90 dln 44 37 40 33 / 70 70 100 90 hvr 39 30 42 33 / 20 0 70 90 lwt 40 34 45 33 / 20 0 60 100