textproduct: Great Falls

KEY MESSAGES

- It will be windy this afternoon along the Northern Rocky Mountain Front.

- It will be windy in Southwestern Montana on Wednesday.

- Widespread precipitation returns Wednesday evening through Friday morning with colder temperatures on Thursday and Friday.

DISCUSSION

- Meteorological Overview:

This afternoon there will be upper-level zonal flow over North- central, Central, and Southwestern Montana. This will keep warm weather over the area. Due to a strong surface pressure gradient this afternoon it will be windy along the Northern Rocky Mountain Front and plains west of I-15. This evening due to an upper-level shortwave there will be snow along the Northern Rocky Mountain Front. On Wednesday there is an upper-level ridge ahead of an approaching upper-level trough over North-central, Central, and Southwestern Montana. This combined with the southerly winds aloft will bring warm temperatures to the area with windy conditions in the valleys of Southwestern Montana. Due to the warm temperatures and southerly flow aloft instability will increase and isolated locations could see a rumble of thunder Wednesday afternoon. See the Forecast Confidence & Scenarios Section for details. On Wednesday snow will continue along the Northern Rocky Mountain Front. Wednesday afternoon/evening a Pacific Front will move across North- central, Central, and Southwestern Montana. This will bring a heavy band of snow along the I-90 Corridor late Wednesday afternoon through early Wednesday evening. Wednesday afternoon and early evening across North-central and Central Montana initially there will be rain showers before transitioning to snow showers Wednesday night.

On Thursday an upper-level trough is over North-central, Central, and Southwestern Montana. This combined with the cold front will bring well-below seasonal averages for temperatures on Thursday. During the day on Thursday there will be snow showers across North- central, Central, and Southwestern Montana. On Friday the upper- level trough remains over North-central, Central, and Southwestern Montana. On Friday due to the upper-level trough it will be cold in the morning with temperatures warming up some in the afternoon with mostly dry weather. On Saturday and Sunday an upper-level ridge moves over North-central, Central, and Southwestern Montana. This will bring warm and dry weather to the area for the weekend. -IG

- Forecast Confidence & Scenarios:

Across southwestern Montana there is greater than an 80% chance for snowfall rates in excess of 1 inch per hour Wednesday evening. Along the I-90 corridor Wednesday afternoon/early evening there is greater than a 50% chance for surface instability combined with a tenth of an inch of snowfall accumulation (i.e. a snow squall). The greatest risk from any snow squall will be a sudden reduction in visibility. On Wednesday south of the Montana Highway 200 Corridor there is a 15 - 30% chance for thunder.

From Wednesday tonight through Friday morning there is greater than a 90% chance for 9 inches of snow or greater across the Madison and Gallatin Mountains. As a result a Winter Storm Watch remains in effect for those areas from Wednesday evening through Friday morning. From tonight through Thursday morning there is greater than a 50% chance for 6 inches of snow or greater along the Northern Rocky Mountain Front. As a result a Winter Weather Advisory is in effect for the Northern Rocky Mountain Front from midnight tonight through Thursday morning. Across the valleys of Southwestern Montana from Wednesday evening through Thursday evening there is a greater than a 50% chance for 2 inches of snow or greater. Across the lower- elevations of North-central and Central Montana from Wednesday evening through Thursday evening there is greater than a 35% chance for 1 inch of snow or greater. Wednesday evening through Thursday evening across the Little Belts, Highwoods, and Southern Rocky Mountain Front there is greater than a 75% chance for 4 inches of snow or greater.

On Wednesday there is a 30 - 60% chance for wind gusts of 55 mph or greater across the valleys of Southwestern Montana. As a result across the Madison and the Beaverhead River Valleys a High Wind Watch remains in effect during the day on Wednesday. Friday morning there is greater than a 50% chance for a low temperatures of 15 degrees or colder along the Hi-Line. -IG

AVIATION

14/18Z TAF Period

Breezy west to southwest winds pick up this afternoon, with the strongest winds along the Rocky Mountain Front. Wind gusts of up to 45kts will be possible at KCTB through 15/03z. Winds will decrease overnight but will pick back up again mid to late Wednesday morning. A Pacific whether system will bring in mountain snow Wednesday morning and light isolated showers at lower elevations. The isolated nature of the showers makes it difficult to pin point start times in the TAFs, as better chances arrive later Wednesday. -Wilson

PRELIMINARY POINT TEMPS/POPS

GTF 41 59 27 37 / 0 40 90 60 CTB 34 54 20 31 / 10 20 60 50 HLN 38 58 27 39 / 10 80 90 80 BZN 36 59 27 38 / 10 60 100 80 WYS 28 45 26 33 / 10 90 100 100 DLN 36 57 26 36 / 0 50 100 80 HVR 39 61 25 35 / 0 20 80 50 LWT 37 58 26 35 / 10 60 90 60

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from midnight tonight to 9 AM MDT Thursday for East Glacier Park Region.

Winter Storm Watch from Wednesday evening through late Thursday night for Gallatin and Madison County Mountains and Centennial Mountains.

High Wind Watch from Wednesday morning through Wednesday afternoon for Beaverhead and Western Madison below 6000ft- Madison River Valley.