textproduct: Great Falls

KEY MESSAGES

- Patchy fog early Monday morning.

- Above average temperatures return this week.

- Next system arrives late week bringing wind and rain.

UPDATE

Updated forecast is out. Just minor adjustments to the forecast for current trends. Removed showers for the rest of tonight, along with adjusted temps a bit in colder valleys of the Rocky Mountain Front and across Southwest MT. Main concern overnight will be the potential for fog/reduced visibility. With recent rainfall, areas of fog are possible, some dense. Midnight shift will monitor the potential for any SPS or NPW's for fog concerns that develop overnight. Otherwise, the remainder of the forecast is on track. Brusda

DISCUSSION

/Issued 200 PM MDT Sun Sep 20 2026/

- Meteorological Overview:

Southwesterly upper level flow will be the predominant weather pattern this week as upper level ridging stalls out over the center of the North American Continent this week, keeping us generally warm and dry for most of this week. Expect temperatures to generally be either side of 80 along the Missouri River corridor, with temperatures not as warm in the higher terrain and along the Rocky Mountain Front. Winds will also be uncharacteristically light for much of the week, with winds generally struggling to gust over 20 mph through Thursday. Our next weather system will arrive Friday or Saturday, which will bring cooler temperatures, gusty winds, and the possibility for some widespread precipitation, though the amount of rainfall remains fairly uncertain at this point in time.

- Forecast Confidence & Scenarios:

Friday/Saturday system: an upper level trough and associated surface front embedded in the upper level flow are expected to arrive in the Northern Rockies Friday or Saturday. Current model forecasts suggest that this setup will bring some widespread precipitation, with the potential for many areas to receive over a quarter inch of liquid equivalent. The other concern will be the wind, as the strengthening trough may produce a bit of a sting jet on its southwest side, which would produce some gusty westerly winds thanks to the sinking air behind a cold front. As of Sunday afternoon, probabilities for 60 mph wind gusts appear low (generally under 20 percent), but this event will need to be watched in case probabilities increase. Ludwig

AVIATION

21/00Z TAF Period

Weak ridging aloft moves over the Northern Rockies tonight into Monday and brings mostly clear skies and light winds; however, lingering surface moisture combined with the light wind regime will encourage areas of fog to develop, most widespread along the Hi- Line between 21/09 and 21/16Z. Probabilities for visibility falling below a half mile are currently running highest (above 50%) for KHVR and KCTB. Other than the categorical degradations from morning fog/low stratus, general VFR conditions will prevail. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 46 79 49 80 / 0 0 0 0 CTB 44 76 45 77 / 0 0 0 0 HLN 44 76 45 77 / 0 0 0 0 BZN 39 73 41 75 / 0 0 0 0 WYS 27 67 28 69 / 0 0 0 0 DLN 39 72 40 74 / 0 0 0 0 HVR 45 79 47 81 / 0 0 0 0 LWT 42 75 46 79 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.