textproduct: Great Falls

KEY MESSAGES

- Precipitation largely subside later this evening.

- Two cold nights ahead, with lows in the 20s for many areas.

- Slowly trending warmer through the week, with a few rounds of precipitation at times.

UPDATE

/Issued 747 PM MDT Sun May 17 2026/ Updated forecast is out. Main change was to end the winter weather advisory over the far northern and souther portions of the area, along with increasing pops over Central MT this evening. A band of light rain/snow continues to move southward through the Fort Benton/Great Falls/Sieben Flats area. Additional snowfall through this evening of an inch or two is possible in the remaining advisory area that goes through Midnight. Otherwise, any snow at lower elevations will mostly just melt on contact. Some patchy fog is possible by morning in areas that had rain/snow today. Overnight lows look on track, with a potential frost for some areas as well Mon morning. A few isolated storms Mon/Tue along the divide from Lincoln north to the St. Mary and across the Hi-Line area on Tue, otherwise, the next more widespread lower elevation rain and mountain snow arrives on Wed. Brusda

DISCUSSION

/Issued 747 PM MDT Sun May 17 2026/

- Meteorological Overview: The core of the upper level troughing is beginning to track east of the region this afternoon, resulting in a northerly flow aloft. Northerly/northwesterly upslope precipitation continues this afternoon, with additional precipitation developing in the form of showers, mainly across Southwest MT and vicinity.

Loss of daytime heating and upslope flow will allow for precipitation to come to an end this evening. Lighter northerly flow aloft continues into tonight though, which will allow for quite a cold night across the region. Most locations look to fall into the 20s, with a few cold prone locations dipping into the teens. Some patchy fog cannot be ruled out tonight, though coverage will depend on where most precipitation falls through the remainder of the day today.

Cool air aloft persists into Monday, which will combine with daytime heating to result in a mix of rain and snow showers across the region. Slightly warmer air aloft begins to move in Monday night, though lingering cooler air at the surface will result in another cold night before temperatures trend closer to average during the day Tuesday. A few afternoon showers will be around Tuesday, but overall coverage of the showers is questionable at this time.

Several disturbances pass across the region within a northwest flow aloft Wednesday onward, which will allow for a couple stretches of precipitation. Temperatures over this timeframe slowly trend warmer, though this trend will be briefly interrupted by the showery conditions at times. -AM

- Forecast Confidence & Scenarios:

Cold temperatures tonight and Monday night:

The probability for an overnight low below 32F is nearly 100% in all areas tonight. That probability isn't quite as high for Monday night, but is at or greater than 50% in the overwhelming majority of areas.

Precipitation Wednesday:

A sharper trough looks to pass across the region Wednesday into Wednesday night. This trough looks cool enough to result in some mountain snow, but most precipitation looks to fall as rain. Areas along the Rocky Mountian Front and across Central Montana terrain have a roughly 30% probability for 0.25" liquid from this system. -AM

AVIATION

18/06Z TAF Period

Southwest Montana (KBZN, KEKS, KWYS): VFR conditions will generally prevail through the TAF period. Low to mid-level clouds are expected to persist through the night as some lingering mountain snow starts to taper off heading towards the late morning. As for fog chances, because a BKN to OVC mid-level cloud deck is expected to stick around through most of the night, the probability of fog development across Southwest Montana remains rather low. KWYS still has the highest probability at 20% but even then it is unlikely unless the clouds start to clear out overnight. Should the clouds clear at any of the three terminals then fog will be a concern. But otherwise mountain obscuration will be the primary concern through the first half of the TAF period.

North-Central and Central Montana: Low clouds will gradually start to push out of the region as the night goes on but, in the meantime, some low-VFR/high-MVFR CIGs are possible at KHVR, KGTF, and KHLN. At KLWT, light snow is possible on and off throughout most of the night with IFR to LIFR CIGs possible at times. Mountain obscuration will remain a concern through the night across portions of Central Montana. In terms of fog, the main concerns will be KCTB, which has already cleared out, and KGTF which is set to clear out in the next couple hours. For both locations there is around a 40% chance of fog development during the night. Additionally, there is a 20% chance for fog developing at KHVR, however, there is less confidence that the clouds will be able to clear out in time to pose a significant fog threat tonight. Otherwise VFR conditions are expected across North- Central and Central Montana after 18/18Z. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 28 52 29 63 / 90 10 0 30 CTB 24 54 31 63 / 20 20 10 20 HLN 31 55 29 62 / 30 10 10 20 BZN 25 51 22 60 / 20 10 0 10 WYS 21 41 16 51 / 10 10 10 20 DLN 25 48 23 60 / 20 10 10 20 HVR 27 54 26 66 / 40 10 0 50 LWT 27 46 23 59 / 60 40 0 30

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until midnight MDT tonight for Little Belt and Highwood Mountains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.