textproduct: Great Falls

KEY MESSAGES

- Warmer temperatures continue to work into the region tonight and into the day Monday as winds increase.

- Periods of mountain snow this week, mostly along the Continental Divide.

- The vast majority of the week looks at least breezy, with the latter half of the week bringing strong winds to most areas at times.

DISCUSSION

- Meteorological Overview:

Upper level ridging will keep the remainder of the afternoon and evening on the benign side across the region. Warmer temperatures will continue to make inroads across the plains into Monday as increasingly stronger zonal flow aloft will help to develop at least a weak pressure gradient. The risk for localized drifting snow will persist in areas adjacent to the Rocky Mountain Front later tonight into early Monday, but confidence in widespread impacts remains on the lower side.

Winds Monday largely appear to be diurnally driven, which will focus the timeframe for the strongest winds to the afternoon hours. Regardless of whether winds become strong or not, they will result in temperatures that rise well above average. These milder temperatures largely look to persist through the week.

Pacific moisture streaming through the zonal flow will result in a few periods of snow along the Continental Divide this week. The first period of snow that looks more impactful arrives early during the day Monday, lasting into Tuesday, primarily impacting areas north of Lincoln - including Marias Pass. A rather potent wave then arrives Tuesday night, which will help propel a Pacific front across the region. A band of snow is increasing in likelihood with the Pacific front late Tuesday night into early Wednesday, mostly across Southwest Montana. Should this timing trend any later, there would be impacts to the morning commute across much of Southwest Montana Wednesday.

Potent zonal flow develops behind the Pacific front and persists through Friday across the Northern Rockies, which will result in an extended timeframe of stronger winds, some of which will be higher- end. As mentioned prior, this zonal flow will result in additional snow along the Continental Divide over this timeframe, mainly north of Lincoln.

Confidence in specifics wane Friday night toward the weekend, but it does appear that at least a weaker Canadian cold front will drop south across the region under a west-northwest flow aloft. The more benign scenario involves minor cooling below freezing with some light snow over the plains, while a more aggressive scenario would send a stronger cold front through into Southwest Montana with much colder temperatures and more notable lower elevation snow. -AM

- Forecast Confidence & Scenarios:

Blowing snow late tonight and early Monday:

Confidence remains on the lower side that the winds that develop will be sufficient to blow around any of the existing snowpack along the Rocky Mountain Front, adjacent plains, or across portions of the highway 200 corridor early Monday. Should confidence increase in impacts from blowing/drifting snow occurring, a short-term Winter Weather Advisory would be necessary. Temperatures quickly rise well above freezing into the day Monday which will rapidly decrease the risk for any blowing or drifting of snow.

Winds Monday:

Winds Monday will be almost exclusively driven by diurnal mixing, as the pressure west and south of the Continental Divide isn't particularly high compared to the pressure across the forecast area. Winds in the mid level do look potent out of the west to southwest, on the order of 50 kts or so at times. The main question is if the diurnal mixing will be strong enough to tap into these strongest winds aloft. At this point BUFKIT soundings are quite split, with some mixing just enough to realize these higher end winds/gusts, while others are much less optimistic. Areas around Cut Bank look to see the greatest probability of realizing these higher end gusts, but it is not necessarily a slam dunk. With that in mind there are no upgrades being made at this time, though some adjustments in timing to the High Wind Watches have been made.

Snow Along the Continental Divide This Week:

Most snow this week looks to be confined to areas north of Lincoln along the Rocky Mountain Front. A few Winter Weather Advisories are the most likely scenario for the more intense periods of snow. An initial Winter Weather Advisory for Marias Pass has been issued from Monday through early Tuesday morning.

Pacific Front and potential for snow squalls late Tuesday Night:

As the Pacific front moves across the region late Tuesday night into Wednesday morning, a band of snow looks to develop with it across Southwest Montana. Rapid transitions from little to no snow to briefly heavy snow with some wind is increasing in likelihood late Tuesday night into early Wednesday morning. Should this trend a bit slower, greater impact to the Wednesday morning commute across Southwest Montana would occur. Trends for this timeframe will be monitored closely.

Wind behind the Pacific Front Wednesday through Friday:

Ensemble guidance and anomaly indicators show high confidence in a period of strong winds Wednesday through Friday. As an example of confidence in stronger winds, the probability for an 80 mph gust in Browning Thursday is between 50 and 60%. Further east in Cut Bank that probability is roughly 30% on the same day. -AM

AVIATION

22/18Z TAF Period

VFR conditions generally prevail under passing mid- and higher level cloudiness. East to southeasterly surface breezes over the plains will become more south to southwesterly and increase in a west to east fashion tonight into Monday as stronger westerly flow aloft begins to transfer to the surface. Winds will gust over 40 kts at times at KCTB and KGTF Monday afternoon. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 13 53 33 50 / 0 20 30 20 CTB 9 49 26 45 / 0 20 10 10 HLN 22 52 33 49 / 0 20 50 50 BZN 24 52 32 49 / 0 10 30 50 WYS 7 39 24 36 / 0 0 40 90 DLN 21 50 32 50 / 0 0 20 30 HVR 3 50 22 43 / 0 10 20 10 LWT 29 49 30 43 / 0 10 40 40

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 5 AM Monday to 5 AM MST Tuesday for East Glacier Park Region.

High Wind Watch from Monday morning through Monday evening for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains-Southern High Plains.

High Wind Watch from Monday morning through Monday evening for Cascade County below 5000ft-Judith Basin County and Judith Gap.