textproduct: Great Falls

KEY MESSAGES

- Patchy fog is expected in Southwestern Montana this morning.

- Cool (below seasonal-average) temperatures are expected through this upcoming work week.

- There will be periods of precipitation from Monday evening through the rest of the work week.

DISCUSSION

- Meteorological Overview:

Today there will be an upper-level ridge over North-central, Central, and Southwestern Montana. This will allow skies to be clear with light winds. As a result at some lower-elevation locations there is the potential for patchy fog to form. See the Forecast Confidence and Scenarios section for details. Today it will be dry with well-below normal temperatures across North-central, Central, and Southwestern Montana. On Monday the upper-level ridge remains over North-central, Central, and Southwestern Montana. By Monday evening an upper-level trough begins to move over the area. This will bring slightly warmer and dry weather to North-central, Central, and Southwestern Montana through the day on Monday. Monday evening snow-levels will begin to fall and snow will begin across the mountains of Southwestern Montana.

On Tuesday the upper-level trough remains over North-central, Central, and Southwestern Montana. This will bring widespread precipitation primarily in the form of lower-elevation rain and Mountain snow. See the Forecast Confidence & Scenarios section for details. Due to lingering southerly flow temperatures will warm up a few degrees on Tuesday but remain below seasonal averages. On Wednesday an upper-level ridge briefly builds in over North-central, Central, and Southwestern Montana. This will allow warm temperatures to persist with mostly dry weather. Thursday through Saturday an upper-level trough returns to North-central, Central, and Southwestern Montana. This will bring multiple rounds of precipitation to the area with cooler temperatures. -IG

- Forecast Confidence & Scenarios:

For fog this morning there is around a 30 - 50% chance along the Rocky Mountain Front, the lower-elevations of Cascade County, and the West Yellowstone area. However based on current satellite imagery and model soundings this is most likely due to low clouds and not fog. In the Helena and Gallatin Valley there is a low chance for fog to form this morning as well, which is suggested in some model soundings. Based on current satellite imagery the Gallatin Valley and West Yellowstone area have the highest chance for fog to form out of any of the areas listed above.

For the Monday evening through Tuesday morning system there is a 50 - 80% chance for 4 inches of snow or greater across the higher peaks of the Madison and Gallatin Mountains. For the Monday evening through Tuesday morning system there is a 40 - 70% chance for 2 inches of snow at pass-level in the Madison and Gallatin Mountains. From Monday evening through Tuesday there is a 40 - 80% chance for a quarter inch of liquid precipitation or greater across Southwestern Montana. From Monday evening through Tuesday morning across the Gallatin and Madison River Valleys and the Lewistown area there is greater than a 60% chance for a tenth of an inch of snow or greater. On Tuesday across Blaine and Fergus Counties there is a 40 - 60% chance for a quarter inch of total liquid precipitation or greater. -IG

AVIATION

25/06Z TAF Period

The main weather concern over the next day or so will be the potential for low clouds and fog. Southwest MT has the best chance for seeing fog, as high clouds have moved over much of North Central MT. Expect the fog to diminish by late morning. Some light rain/snow showers possible over the northern Rockies today as well. Mountains/passes will be obscured at times by clouds/fog through the period. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 40 24 38 22 / 0 0 0 0 CTB 41 22 41 20 / 0 0 0 0 HLN 42 23 38 22 / 0 0 0 0 BZN 41 20 45 18 / 0 0 0 0 WYS 45 15 51 17 / 0 0 0 0 DLN 43 24 43 25 / 0 0 0 0 HVR 44 21 46 22 / 0 0 0 0 LWT 41 20 40 23 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.