textproduct: Great Falls

KEY MESSAGES

- Dry with near to a bit above average temperatures through Monday. - Next opportunity for precipitation arrives Tuesday, mainly along the Continental Divide.

- Windy on Wednesday in most areas, with cooling temperatures into Thursday.

DISCUSSION

- Meteorological Overview:

Nearly all of the upcoming week will be characterized by different variations of a zonal flow aloft across the Northern Rockies. Initially this flow aloft is more anticyclonic in nature, as broad, low amplitude ridging overspreads the entire west. This will keep the area dry through Monday night, with breezy winds over the plains in the late morning through early evening timeframe. Temperatures look be on the warmer side of average, particularly for Southwest Montana.

By Tuesday the leading edge of Pacific moisture associated with the southern extent of a large upper level trough in the Gulf of Alaska moves onshore across the Pacific Northwest, nosing into the Northern Rockies by the afternoon. A mix of rain and snow develops as a result, mostly for areas along the Continental Divide Tuesday into Wednesday. An embedded wave with stronger mid-level flow ejects from the broader troughing off the Pacific NW and BC coastline toward the Northern Rockies through the day Wednesday. Ample daytime mixing through the day Wednesday will allow for these stronger winds to be readily mixed to the surface across the vast majority of the region.

Cooler air moves in behind this system for Thursday. Although surface temperatures look to cool close to average, temperatures aloft look to cool even more, resulting in some instability developing by Thursday afternoon. Scattered snow showers develop by the afternoon across the region, though coverage looks uncertain given the upper level ridging that will begin building in across the west late Thursday afternoon.

Upper level ridging builds in and remains in place Friday through the weekend, which looks to result in a warming trend. Dry conditions are also forecast over this timeframe. -AM

- Forecast Confidence & Scenarios:

The most impactful timeframe this week looks to be during the day Wednesday when a period of strong winds looks to develop over the plains. Strong zonal flow aloft looks to be mixed to the surface during daytime hours Wednesday, even with some upper-level cloud cover in place. An added nudge giving confidence in these strong winds materializing over the plains is that cooler air will be filtering in through the day Wednesday, resulting in steep low to mid-level lapse rates that promote ample mixing. Further south in Central and Southwest Montana valleys, the cooler air will be slower to arrive, but ample mixing will still result in a windy day. The probability for a 75 mph gust between Cut Bank and Browning is roughly 30% Wednesday, increasing above 50% west of Browning closer to the Rocky Mountain Front. -AM

AVIATION

22/18Z TAF Period.

VFR conditions prevail at all north-central and southwest MT terminals through the TAF period. A moderate westerly flow aloft persists across the Northern Rockies and MT with initially little or no cloud-cover giving way to a gradual increase in mid-high level clouds from west to east tonight. Somewhat breezy (gusts 20-30kt) west to northwest winds will affect most terminals as atmospheric mixing increases this afternoon before winds subside this evening. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 32 59 38 51 / 0 0 0 20 CTB 23 55 28 44 / 0 0 0 30 HLN 31 62 37 61 / 0 0 0 20 BZN 32 65 38 65 / 0 0 0 10 WYS 21 56 30 53 / 0 0 0 20 DLN 33 65 40 64 / 0 0 0 10 HVR 28 56 32 47 / 0 0 0 20 LWT 29 57 35 54 / 0 0 0 10

TFX WATCHES/WARNINGS/ADVISORIES

None.