textproduct: Great Falls

KEY MESSAGES

- Snow will fall this afternoon into Monday along the Continental Divide with portions of the rest of North-central, Central, and Southwestern Montana seeing a light rain/snow mix tonight through Monday.

- It will cool down for Monday and Tuesday before briefly warming up on Wednesday.

- There is the potential for a spring storm with widespread precipitation Wednesday night through Friday.

DISCUSSION

- Meteorological Overview:

This afternoon there is upper-level zonal flow over North-central, Central, and Southwestern Montana. Tonight an upper-level shortwave moves across the Canadian/Montana Border. This shortwave brings with it a Pacific Cold Front to North-central Montana. This shortwave will bring snow to the Rocky Mountain Front this afternoon through the day on Monday. The snow will be the heaviest tonight into Monday morning. Across the plains of North-central Montana isolated locations will see light rain this afternoon into tonight. On Monday the upper-level shortwave trough continues to track eastward across the Canadian/Montana Border. This will bring rain/snow showers to isolated locations of North-central, Central, and Southwestern Montana. Due to the cold front passage, it will be colder across North-central Montana on Monday with well-below seasonal average temperatures expected along the Hi-line. The cold front will eventually make it to Southwestern Montana Monday afternoon and allow isolated snow showers to form in Southwestern Montana. Due to a strong surface pressure gradient it will be windy on Monday with the strongest winds along the Rocky Mountain Front and in Southwestern Montana.

On Tuesday upper-level zonal flow remains over North-central, Central, and Southwestern Montana. This will allow the area to dry out with cool temperatures across the area. On Wednesday an upper-level ridge forms over North-central, Central, and Southwestern Montana ahead of an approaching upper-level trough. This will breifly allow temperatures to warm up with mostly dry weather. Wednesday evening an upper-level trough (closed low) begins to move over North-central, Central, and Southwestern Montana. This upper-level trough will remain over North-central, Central, and Southwestern Montana through Friday. This upper-level trough will bring cooler temperatures and widespread precipitation to North-central, Central, and Southwestern Montana. The precise track of this upper-low remains uncertain at this time. See the Forecast Confidence & Scenarios section for details. -IG

- Forecast Confidence & Scenarios:

For snow tonight into Monday there is a 60 - 80% chance for 4 inches of snow or greater along the Rocky Mountain Front. As a result a Winter Weather Advisory remains in effect for the Northern Rocky Mountain Front from 8 PM tonight through 10 AM Monday morning. Across the mountains of Central and Southwestern Montana there is a 30 - 50% chance for 2 inches of snow or greater tonight through Monday.

On Monday along the Rocky Mountain Front there is a 50 - 80% chance for wind gusts of 55 mph or greater. On Monday across the higher elevations of Southwestern Montana there is greater than a 70% chance for wind gusts of 55 mph or greater. On Monday across the north-south oriented valleys of Southwestern Montana there is a 30 - 50% chance for wind gusts of 55 mph or greater.

For the Wednesday night through Friday system there remains uncertainty in precipitation types due to uncertainty in the low track. Clusters and ensembles currently exhibit large differences in the track and speed of the upper-level low. If the low tracks further south than currently the deterministic models have it, that will reduce precipitation amounts across North-central Montana. If the low tracks further north that would increase precipitation amounts across North-central Montana. -IG

AVIATION

29/18Z TAF Period

VFR conditions will prevail across all terminals during this TAF Period. At the KHVR terminal between 29/20Z and 30/11Z there is a 20 - 40% chance for rain. At the KLWT terminal between 29/21Z and the end of this TAF Period there is a 25 - 50% chance for rain with a rain/snow mix possible after 30/15Z. At the KGTF and KHLN terminals after 30/02Z through the end of this TAF Period there is a 15 - 30% chance for rain and or a rain/snow mix. At the KBZN terminal between 30/16Z and 30/20Z there is a 25 - 30% chance for rain. At the end of this TAF Period there will be periods of mountain obscuration across North-central, Central, and Southwestern Montana. Between 30/00Z and 30/15Z there will be isolated instances of low-level wind shear and mountain wave turbulence across North-central, Central, and Southwestern Montana. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 37 45 17 47 / 40 30 10 0 CTB 24 35 11 42 / 20 20 10 0 HLN 35 48 20 50 / 30 50 10 0 BZN 38 55 20 50 / 10 70 40 10 WYS 33 54 23 46 / 10 60 70 50 DLN 40 58 23 54 / 0 30 20 10 HVR 32 43 15 45 / 50 10 0 0 LWT 33 43 15 42 / 50 70 20 10

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 8 PM this evening to 10 AM MDT Monday for East Glacier Park Region.