textproduct: Great Falls

KEY MESSAGES

- Temperatures continue to trend cooler through Monday, with near normal temperatures arriving by Tuesday.

- Another night of fog is possible across the region, most notably in the valleys of Southwest and Central Montana

- Numerous opportunities for precipitation during the upcoming work week.

UPDATE

Lingering fog and low clouds across portions of Hill and Blaine counties has increased in coverage the past hour or as insolation has waned. This fog looks to remain in place across these areas for at least a couple more hours before southwest winds look to build in and dry out the low-levels. At this time the fog is not widespread, so we will opt to forego a Dense Fog Advisory, instead opting for a Special Weather Statement. Should this fog increase in coverage and be more persistent than initial thinking, a Dense Fog ADvisory will be considered. The main update this evening was to increase fog mention in areas where it is already occurring as well as adjacent areas. -AM

DISCUSSION

/Issued 409 PM MST Sat Nov 14 2026/

- Meteorological Overview:

The upper ridge axis over the CONUS Central Plains will continue to propagate eastward with strong southerly flow over Montana transitioning to Southwesterly flow over the next 12 to 24 hours. With support from a broad negatively tilted trough extending from the PNW through Western CONUS, a weak upper-level disturbance will perturbate through the flow bringing generally light showery precipitation over Southwest MT through the afternoon hours. Due to surface warming and ABL mixing, WBZ heights will stay around 3000 FT so snow will be contained to the mountain ranges. There is a stable layer over the Northern regions of the state with weak easterly flow keeping low-level fog producing moisture trapped along the Milk River Valley until early this afternoon when diurnal boundary layer mixing occurs.

For Sunday, warm and dry conditions will persist with Southwesterly flow aloft maintaining warm air advection to keep temperatures in the 50s and 60s. With the approaching Pacific trough, pressure gradient winds will increase over Southwest MT with gusts up to 40 mph expected within the valley downslope regions Sunday morning into the afternoon.

Beginning Monday night, the Pacific system will kick a strong upper-level shortwave trough out over western CONUS bringing deep ascending moisture and instability over Montana into Wednesday and fueling cyclogenesis over the Yellowstone area. This low pressure system will deepen and move eastward across the Continental Divide pulling colder Canadian air south into the region and creating widespread snow across the CWA by Tuesday night. Moisture laden Southwesterly flow aloft with cold northerly advection will provide healthy snow growth zone profiles over much of the state. Most likely placement for a weak deformation zone to develop will be Northwest of the low over Western and Central MT. - Akins

- Forecast Confidence & Scenarios:

Strong Winds in the Madison River Valley Sunday...

NBM5.2 probabilistic data suggests a 10-30% chance that sustained winds from the southern end of the Madison River Valley to Norris Hill could exceed 40 mph from the late morning hours through early evening hours on Sunday, with a 5-10% chance that gusts could exceed 55 mph over this same timeframe. BUFKIT soundings and deterministic guidance support southwesterly wind speeds of 20-30kts through H700 over this timeframe, with a weak-to-moderate surface pressure gradient orientated from west to east along the I-90 corridor from Cardwell to Livingston. While these wind speeds and the overall strength of the gradient are not high enough to warrant a High Wind Warning there is a low end chance that during peak mixing on Sunday that sustained winds within the Madison River Valley could approach high wind criteria (i.e. 40 mph for 1+ hours). - Moldan

Precipitation this Work Week...

For the upcoming winter event Tuesday, ensembles are signaling a potential weak deformation zone for moderate snowfall setting up approximately over Helena and Great Falls. ECMWF and GFS show similar mesoscale band placement within the broader pattern however intensity, exact location, and duration still diverge. Most snowfall estimates for lower elevation areas are 1-4 inches over the Monday night to Wednesday timeframe. Next run will bring event time within most short-medium range ensemble members for higher fidelity scenario creation.

The table below lists the reasonable low end (25th Percentile), most likely (50th Percentile), and high end (75th Percentile) QPF (liquid equivalent) and snowfall amounts within the NBM5.2 for select locations across North Central, Central and Southwest Montana from Monday through Wednesday and then Thursday through Friday. The low end scenario has a 75% chance that amounts will exceed the listed value or a 25% chance that amounts will be lower than what is listed while the high end scenario has a 75% chance that amounts will be lower than what is listed or a 25% chance that amounts will be higher than what is listed.

Reasonable QPF Scenarios Monday thru Wednesday LOCATION 25Pct | 50Pct | 75Pct Browning 0.00 | 0.00 | 0.09 Cut Bank 0.00 | 0.00 | 0.14 Havre 0.04 | 0.19 | 0.50 Great Falls 0.06 | 0.25 | 0.65 Lewistown 0.05 | 0.18 | 0.35 Helena 0.12 | 0.40 | 0.65 Bozeman 0.25 | 0.50 | 0.80 Dillon 0.19 | 0.35 | 0.60 Ennis 0.35 | 0.65 | 0.95 West Yellowstone 0.35 | 0.50 | 0.80

Reasonable QPF Scenarios Thursday thru Friday LOCATION 25Pct | 50Pct | 75Pct Browning 0.00 | 0.00 | 0.08 Cut Bank 0.00 | 0.00 | 0.09 Havre 0.00 | 0.00 | 0.11 Great Falls 0.00 | 0.00 | 0.19 Lewistown 0.00 | 0.03 | 0.19 Helena 0.00 | 0.01 | 0.24 Bozeman 0.00 | 0.12 | 0.35 Dillon 0.00 | 0.06 | 0.25 Ennis 0.08 | 0.21 | 0.40 West Yellowstone 0.19 | 0.40 | 0.65

Reasonable Snow Scenarios Monday thru Wednesday LOCATION 25Pct | 50Pct | 75Pct Browning 0.0 | 0.0 | 0.2 Cut Bank 0.0 | 0.0 | 0.0 Havre 0.0 | 0.0 | 0.2 Great Falls 0.0 | 0.1 | 0.3 Lewistown 0.0 | 0.2 | 1.8 Helena 0.0 | 0.0 | 0.3 Bozeman 0.8 | 1.2 | 2.3 Dillon 0.0 | 0.4 | 1.5 Ennis 1.0 | 1.5 | 2.6 West Yellowstone 1.9 | 2.6 | 4.4

Reasonable QPF Scenarios Thursday thru Friday LOCATION 25Pct | 50Pct | 75Pct Browning 0.0 | 0.4 | 3.4 Cut Bank 0.0 | 0.3 | 2.0 Havre 0.0 | 0.1 | 1.1 Great Falls 0.0 | 0.7 | 2.5 Lewistown 0.0 | 0.9 | 3.4 Helena 0.0 | 0.9 | 2.6 Bozeman 0.6 | 1.8 | 3.8 Dillon 0.1 | 1.1 | 3.6 Ennis 0.3 | 2.2 | 5.0 West Yellowstone 1.7 | 5.0 | 9.0

- Akins/Moldan

AVIATION

15/00Z TAF Period

Initial concern will be for some lingering low clouds across portions of SW MT associated with precipitation and across portions of the Hi-Line associated with lingering patchy fog. Gradual clearing will mitigate concerns across SW MT through the evening, with surface southwesterly winds helping mix out any lingering low clouds or fog on the Hi-Line. Gusty winds will lessen somewhat overnight in many areas before increasing again late Sunday morning or early afternoon. I can't quite rule out some LLWS on the plains in areas where surface winds become light this evening. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 36 57 36 54 / 20 0 0 0 CTB 30 54 34 50 / 0 0 0 0 HLN 30 55 31 51 / 20 0 0 0 BZN 30 53 29 52 / 20 0 0 0 WYS 24 41 21 45 / 20 0 0 10 DLN 30 49 30 48 / 10 0 0 10 HVR 32 59 32 55 / 0 0 0 0 LWT 34 57 36 56 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.