textproduct: Great Falls

KEY MESSAGES

- Cold air filters in today, coldest in Hill and Blaine Counties where a Cold Weather Advisory is in effect. - Light, mainly mountain snow showers through the weekend. - Warming trend through the weekend, but cold air lingers to the northeast.

DISCUSSION

- Meteorological Overview:

Cyclonic northwesterly flow aloft will persist across the region through at least the weekend. Surface high pressure centered over the central AB/SK border this afternoon will slide southeastward through the day towards ND and vicinity, which will continue to induce a northeasterly winds across much of the plains through the day. Cooler air will continue to filter into the area, which will result in a cold night tonight, particularly in the Havre area and vicinity. Winds, however, will decrease overnight tonight which should keep wind chill values from getting below Extreme Cold Warning criteria (-35F).

Weak waves diving through the cyclonic flow will result in occasional periods of light snow through the rest of the week into the weekend. The first period of is ongoing this afternoon, though impacts will continue to be minimal/isolated at this point. The cold temperatures slowly moderate after Friday, given the lack of a reinforcing shot of cold air (That would keep temperatures cold), nor persistent westerly/southwesterly downslope winds developing (That would quickly warm temperatures up).

Upper level ridging looks to build in near the Pacific coast heading into next week, but struggles to make quick progress eastward. This keeps the door open for low-end probabilities for light precipitation into early next week as temperatures continue to moderate. -AM/Ludwig

- Forecast Confidence & Scenarios:

Cold overnight lows/wind chill tonight:

Largely light, but non-zero, winds will combine with the much cooler temperatures moving in through the day today to result in quite a chilly night across the region. Areas near Havre will be the coldest, with the Chinook, Harlem and up to the Big Flat area being the coldest. Hourly probabilistic guidance gives roughly a 50/50 probability for wind chills of -35 or less across Northern Blaine county late tonight into early Friday. The probability for wind chills that cold is lower across adjacent areas, including Hill county and southern Blaine county. -AM

AVIATION

22/18Z TAF Period

VFR conditions will prevail across all terminals during this TAF Period except for at the KGTF, KHVR, and KLWT terminals. At the KCTB, KGTF, and KLWT terminals by the end of this TAF Period ceilings will be reduced to MVFR-levels. At the KGTF, KHLN, and KCTB terminals there is a 15 - 30% chance for snow between 23/00Z and 23/12Z. Snow will reduce visibility periodically to at least MVFR- levels at the KLWT terminal during the majority of this TAF Period. During this TAF Period there is at least a 60% chance for visibility to be reduced periodically to IFR-levels. There will be periods of mountain obscuration during the duration of this TAF Period. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 0 10 1 22 / 30 10 0 30 CTB -5 11 -1 19 / 20 0 0 10 HLN 3 13 2 21 / 20 20 0 20 BZN 3 16 -1 20 / 10 20 0 0 WYS 0 19 -15 16 / 0 20 0 10 DLN 8 20 2 24 / 0 10 0 0 HVR -14 3 -5 11 / 0 0 0 10 LWT -5 6 -6 17 / 50 30 0 30

TFX WATCHES/WARNINGS/ADVISORIES

Cold Weather Advisory until 10 AM MST Friday for Bears Paw Mountains and Southern Blaine-Hill County-Northern Blaine County.