Area Forecast Discussion

KEY MESSAGES

- Areas of fog will be found across the area this morning and may impact the morning commute. Another period of widespread fog is possible tonight (Friday night) into Saturday morning.

- A slight chance of light precipitation has been added to the lower elevations for Saturday ahead of the late weekend weather system.

- Confidence is increasing on a weather system bringing precipitation, windy conditions, and somewhat cooler temperatures to portions of the region Sunday into Monday, though exact impacts remain uncertain.

UPDATE

Satellite, ground observations and webcams are suggesting areas of fog, with pockets of dense fog, developing across much of our CWA. Worst seems to be along the US-191 corridor, and also to the east over Fallon and Carter Counties. We have issued Dense Fog Advisories for these areas through 11 am. Will monitor other areas this morning as dewpoint depressions becoming rather narrow at many locations. BT

DISCUSSION

Today through Thursday...

Fog will impact portions of the region this morning as temperatures drop into the 20s to mid 30s (F). While fog will likely become locally dense in spots, passing high clouds combined with a slight breezy may limit or completely inhibit fog in other locations, mainly in far southern Montana and northern Wyoming. With that said, make sure to stay alert if traveling this morning as fog could significantly reduce surface visibility at times. As temperatures warm into the 40s and 50s today, expect any fog that does develop to gradually dissipate through the morning hours, with some locations north of Billings potentially seeing fog linger into the early afternoon hours (medium chance). Over the plains of far eastern Montana, winds will also increase out of the southeast today with peak wind gusts in the teens to around 30 mph. Low temperatures tonight into Saturday morning then look to be a few degrees warmer than this morning, however, fog is forecast once again. With this, fog could become locally dense, significantly reducing visibility in spots.

The forecast for Saturday has now changed a bit as models are suggesting a more robust shortwave trough will traverse through the area ahead of the Sunday into Monday weather system. With this, a slight chance of precipitation has been introduced to much of south-central Montana, including the plains. While precipitation during this time looks to remain mostly light, with some areas just seeing cloud cover at times, a few pockets of moderate lower elevation rain and mountain snow are possible with precipitable water values near 0.50 to 0.75 inches, which is above normal for this time of year. These elevated atmospheric moisture values may also allow fog to linger through the morning into the early afternoon hours again.

Sunday into Monday, a weather system is expected to move through the region, bringing precipitation, wind, and a slight cool down to much of the area. While uncertainty still remains regarding the evolution of this system through our area, a cold front looks to push through late Sunday into Monday. This will bring the windy conditions to the area with peak wind gusts generally in the 20s to 40 mph. Some of the higher hills around the area, especially in Sheridan County, Wyoming and far eastern Montana, could also see wind gusts approach 50 mph (medium chance). The chance of seeing 60 mph wind gusts (High Wind criteria) remains very low. Winds are expected to peak during the day Monday before coming to an end Monday night. Along with the wind, the cold front looks to bring some precipitation to the region. However, the main player for precipitation looks to be the surface low pressure system that develops as the system moves off the Rocky Mountains. With this, models are starting to hint that this could occur over far eastern Montana into North Dakota and South Dakota. With this, the best chance of seeing a half inch (0.50") or more of liquid precipitation (rain or melted snow) is over south-eastern Montana and north-central/eastern Wyoming (50 to 70 percent chance). Outside of this area, chances decrease to the west. As far as precipitation type goes, snow is expected in the mountains initially above 9,000 feet before snow levels decrease to near 7,000 feet on Monday. Over the plains, there does not appear to be enough of a cold push with this system for snow, so precipitation will likely be all rain. With the snow in the mountains, the Bighorn Mountains are favored the most where there is currently a 50 to 80 percent chance of seeing at least 6 inches of snow over the higher elevations.

Tuesday into Thursday look to remain mostly dry with high temperatures in the 40s and 50 (F), however, cannot rule out isolated precipitation at times, mainly over the mountains. LA

.AVIATION...

Areas of fog and low stratus ceilings will impact the region through 17Z today leading to IFR and LIFR conditions. Conditions after 17Z will trend to VFR across the area. Expect another round of fog and low clouds developing tonight (Friday night) across the area. BT

PRELIMINARY POINT TEMP/POPS

Tdy Sat Sun Mon Tue Wed Thu ------------------------------------------------------- BIL 046 034/053 035/052 039/052 033/058 034/053 031/053 0/E 13/W 02/W 76/W 00/U 00/B 00/B LVM 053 031/055 032/050 028/047 023/055 027/052 024/053 0/E 22/W 24/W 94/W 00/B 00/B 01/B HDN 050 030/053 031/057 036/053 028/060 031/056 028/057 0/E 02/W 01/E 98/W 20/U 00/B 00/U MLS 054 039/053 035/057 040/050 032/055 032/053 030/054 0/E 02/C 21/E 88/W 21/U 00/B 00/U 4BQ 058 041/057 035/060 041/046 033/055 033/052 031/054 0/B 00/E 00/E 98/W 41/U 00/B 00/U BHK 054 039/060 036/058 038/049 028/053 028/051 025/052 0/E 00/C 10/E 78/W 51/B 00/U 00/B SHR 055 032/057 029/058 031/046 026/058 029/054 026/056 0/B 01/E 02/W 98/W 20/U 00/B 01/U

BYZ WATCHES / WARNINGS / ADVISORIES

MT...Dense Fog Advisory in effect until 11 AM MDT this morning FOR ZONES 29-33-37-42-63-141-172-228. WY...None.