textproduct: Great Falls

KEY MESSAGES

- Periods of dense fog and even some isolated instances of icing over elevated surfaces will continue through Sunday morning, most widespread over central and north-central Montana.

- Precipitation becomes more widespread by Sunday, with accumulating snow most prevalent over the higher terrain of southwest Montana Sunday night into Monday morning.

- Temperatures trend closer to average next week.

..Dense fog through Sunday

Hi-Res Ensemble Forecast (HREF) guidance supports the development of fog between 9pm this evening and 3am Sunday over the plains of Central and North Central Montana, with this area of fog persisting through 9am to 3pm Sunday before an area of precipitation lifting northeast from Southwest Montana brings an end to the reduced visibilities. The aforementioned HREF guidance largely support probabilities of between 40-60% with respect to visibilities falling below 1/4 mile during the overnight hours, and for this reason a Dense Fog Advisory has been issued yet again through 12 pm Sunday. Confidence is highest in visibilities falling to 1/4 mile or less along and west of the I-15 corridor, MT Hwy 200/US Hwy 87 corridor, and in Milk River Valley where persistent low level east to north flow will support upslope fog. - Moldan

...Light mountain snow and lower elevation rain, snow, and some mixed precipitation Sunday through Monday morning...

The main trough moves through Sunday through early Monday and brings a wave of widespread precipitation to much of the forecast area. Aside from some light snow along the Continental Divide and perhaps some spotty freezing drizzle over the plains west of I15 and over the higher southwest valleys, most of the precipitation will be falling in the form of rain until Sunday night. The overall pattern and NBM probabilities favor the Madison and Gallatin ranges for the best chance (60 to 80%) for snowfall amounts in excess of 3 inches. Lighter snows, generally up to a couple inches, look to fall along the Continental Divide and the central island ranges. The colder air is still not looking to be optimally aligned with the moisture for lower elevation snows, but will monitor the Gallatin valley where there is around a 30 to 40% chance for a couple inches of snow on the south/eastern fringes of the valley Monday morning. - RCG

AVIATION

31/18Z TAF Period

KCTB is expected to have its dense fog and VLIFR conditions end by 20Z this afternoon.

Low level easterly flow combined with a moist southwesterly flow aloft will bring periods of IFR/LIFR conditions and mountain obscuration from low stratus, fog, and spotty light showers. Additionally, steadier rainfall will begin moving into the region out of the SW around 10Z. The worst and most widespread degraded conditions will be over central and north- central MT after 05Z. - RCG/ESH

PRELIMINARY POINT TEMPS/POPS

GTF 35 39 36 47 / 20 90 100 0 CTB 29 41 29 50 / 10 60 50 0 HLN 35 43 36 49 / 50 100 90 10 BZN 34 41 34 41 / 20 90 100 30 WYS 32 39 26 39 / 80 100 90 0 DLN 37 40 33 43 / 70 100 90 0 HVR 30 42 33 46 / 0 70 90 10 LWT 34 45 33 42 / 0 60 100 40

TFX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory from 9 PM this evening to noon MDT Sunday for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft-Eastern Glacier, Western Toole, and Central Pondera- Eastern Pondera and Eastern Teton-Eastern Toole and Liberty- Fergus County below 4500ft-Hill County-Judith Basin County and Judith Gap-Northern Blaine County-Northern High Plains-Southern High Plains-Western and Central Chouteau County.