textproduct: Great Falls

KEY MESSAGES

- Warm and dry conditions persist through Friday.

- Windy conditions on Friday will lead to elevated fire weather concerns.

- A shift to cooler and wetter conditions is expected this weekend with a chance for impactful mountain snow.

DISCUSSION

- Meteorological Overview:

Low amplitude upper level ridging across the western US will maintain unseasonably warm and dry conditions across the area through Friday beneath a west-northwest flow aloft. Afternoon temperatures will run slightly lower than those of Monday but still around 15 degrees above early October climatological averages. Afternoon mixing and a moderate surface pressure gradient across the Rockies will support some breeziness this afternoon, mainly across the plains, with overall lighter winds Wed and Thu as surface high pressure slides east across the Canadian Prairies.

An upper level trough digging southeast through BC Friday will bring a significant weather pattern change for the weekend with windy conditions developing Friday as southwesterly mid-level flow increases ahead of the approaching trough. Warm, windy and dry conditions Friday will bring elevated fire weather concerns ahead of a cold front Friday night that brings in much cooler and wetter conditions for the weekend. Model guidance is in reasonable agreement to dig the trough southward into the NW US Saturday with typical differences and spread still at this time range among models/ensemble members in the eventual evolution of the trough through the rest of the weekend into early next week. Hoenisch

- Forecast Confidence & Scenarios:

With warm and dry conditions expected to continue through the rest of the week, there is a concern for elevated fire weather conditions (see FIRE WEATHER for more information).

Wintry Conditions This Weekend:

Confidence continues to increase in the potential for cold temperatures and widespread snow along the mountains this weekend with the potential for some lower elevation snow Sunday morning. Temperatures on Saturday will be 25-30 degrees cooler compared to Friday and continue to drop another 15-20 degrees by Sunday.

There are hints in the models that some of the heavier mountain snow could arrive Saturday evening instead of early Sunday morning. This has the potential to impact more of the Continental Divide and the island ranges of Central Montana with some additional snow possible compared to the previous storm totals. The main impacts would be along mountain passes, particularly Logan and Marias Pass initially followed by Rogers Pass over the next few hours. Those who plan on recreating or traveling this weekend should have a plan for cold temperatures and wet snow.

Across the northern plains there is a potential for snow levels to fluctuate right around ground level through Sunday afternoon which could produce a rain/snow mix at times. Additional snowfall accumulations are expected to be on the lighter side by this point in the event but a larger concern might be if there is any rain/snow mix plus daytime melting on Sunday followed by subfreezing temperatures overnight into Monday morning which could make roads and sidewalks slick across the area.

Given the level of uncertainty still present in the models it is hard to pin down exactly how much snow will fall during this event but there is at least a 50% probability of locations below 5000 feet seeing at least one inch of snow total. -thor

AVIATION

06/12Z TAF Period.

VFR conditions will prevail throughout this TAF period. Relatively mild winds will occur across the Southwest terminals (KBZN, KEKS, KWYS and KHLN). For the Central terminals (KGTF and KLWT), expect westerly-southwesterly winds gusting up to around 20 kts from 20Z to 01Z. KCTB will have westerly winds gusting up to around 25 kts during this time frame. Cloud cover will begin to increase around 22Z, mostly over Central/North-Central MT, but ceilings will remain high. -Dzomba

FIRE WEATHER

While wind speeds through Thursday will not be significant, warm afternoon temperatures and low afternoon humidity will persist with only moderate to locally poor overnight humidly recovery, especially over the central MT mountains and adjacent slopes. These condtions may advance the curing and drying of lighter (grass/shrub) fuels that are already headed into seasonal dormancy. Increased winds with potential for gusts in excess of 40 mph Friday, alongside the continued warmth/dryness will bring an elevated fire weather risk. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 45 72 42 75 / 0 0 0 0 CTB 41 67 39 72 / 0 0 0 0 HLN 43 77 43 78 / 0 0 0 0 BZN 42 75 40 76 / 0 0 0 0 WYS 34 73 31 72 / 0 0 0 0 DLN 42 77 40 77 / 0 0 0 0 HVR 42 71 37 73 / 0 0 0 0 LWT 46 73 42 75 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.