textproduct: Great Falls

KEY MESSAGES

- Patchy to areas of dense fog will bring localized sharp visibility reductions across short distances and isolated slippery spots from frost deposition again tonight in Monday morning.

- Pacific weather systems will bring periods of light snow this week, most widespread over the higher terrain along the Continental Divide and southwest Montana Monday night into Tuesday.

- Temperatures will generally remain below average heading into the latter part of October.

UPDATE

The only update for the evening was to increase mention of cloud cover across the valleys of SW MT. Low clouds have persistent there, but are still forecast to lower further and become fog overnight tonight. Consideration was given toward expanding the Dense Fog Advisory further north, between the Helena and Great Falls area, but high level clouds moving in were a nudge to hold off for now. Trends will be monitored through the night for any additional Dense Fog Advisories. -AM

..Light mountain snow Monday night into Tuesday

A cold core aloft will bring a period of accumulating snow Monday night into early Tuesday. H700 temperatures quickly drop off to around -5C, which will be supportive of the 1 to 4 inches snow being depicted by model guidance. Areas along the Continental Divide and the southwestern mountains along and south of I90 look to see the heaviest snowfall amounts with lighter snows over the central ranges. Impacts will mostly be slippery passes and reduced visibility. - RCG

AVIATION

26/00Z TAF Period

VFR conditions will prevail at the KHLN, KGTF, KHVR, and KLWT terminals during this TAF Period. At the KBZN and KWYS terminal there will be fog from 26/03Z through 26/16Z. This fog will reduce visibility to at least one mile with intermittent visibility reductions down to one half mile expected at the KBZN terminal. During the first 16 hours of this TAF Period at the KBZN terminal there will be at least IFR-level ceilings with a period of LIFR- level ceilings. During the first 6 hours of this TAF Period there will be periods of mountain obscuration across North-central, Central, and Southwestern Montana. Between 26/06Z and 26/18Z there will be mountain obscuration across Southwestern Montana. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 18 43 30 50 / 0 0 40 40 CTB 19 43 25 50 / 0 0 30 40 HLN 22 48 32 50 / 0 0 80 30 BZN 19 52 28 47 / 0 0 90 60 WYS 17 49 18 38 / 0 10 100 70 DLN 22 52 30 46 / 0 0 90 20 HVR 23 52 28 49 / 0 0 40 70 LWT 22 50 29 45 / 0 0 60 70

TFX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until noon MDT Monday for Beaverhead and Western Madison below 6000ft-Canyon Ferry Area-Elkhorn and Boulder Mountains-Gallatin Valley-Gallatin and Madison County Mountains and Centennial Mountains-Madison River Valley-Missouri Headwaters-Northwest Beaverhead County.