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FXUS65 KMSO 170113 CCA

Area Forecast Discussion
National Weather Service Missoula MT
245 PM MST Sat Nov 16 2019

.DISCUSSION...A warmer air mass is working its way into the region, 
and the mild start to the day has helped to bring high temperatures 
to above average readings. Mild conditions are expected tonight with 
a plume of moisture moving into north-central Idaho and western 
Montana. Snow levels will quickly rise tonight and all but the 
highest terrain will have rain. Rain showers will start in northwest 
Montana and move southward during Sunday. There is an outside chance 
for freezing rain Sunday morning mainly near Seeley Lake, Ovando, 
and Helmville, but confidence is low for temperatures to be at 
freezing once the rain starts. Rain showers and cloud cover will 
linger into Sunday night.

Areas that experience enough clearing Sunday night, will likely have 
fog during Monday morning. Mild temperatures are expected again for 
Monday afternoon, with showers developing over northwest Montana 
during the evening. Showers will develop into the rest of the region 
Monday night.

These showers are associated with another moist system moving 
towards our area on Monday evening. The initial impacts will be 
limited to above 5500 feet, although at this time we are thinking, 
with very low probability, some of our colder valleys could start as 
freezing rain. Some of the locations would be valleys east and west 
of the Flathead, along Interstate 90 between Drummond and Anaconda, 
and portions of MT-200 east of Clearwater. 

By mid-day Tuesday, winds will shift to the northeast along Highway 
2 causing snow levels to drop sufficiently for Marias Pass to 
quickly change over to all snow. Throughout the late afternoon, the 
cold air will advance west and south, and by around midnight should 
be into the Missoula Valley. After a very dry first half of 
November, we will see widespread precipitation amounts of a 0.50" to 
0.75. Currently, most of our climate stations range from a third to 
a half an inch below normal. Although most valleys in Western 
Montana will see a changeover to snow by Wednesday morning, there 
will be little to no accumulation, except near Butte, where an inch 
or 2 is possible. Mountain Passes like Marias and Lolo could see 4 
to 8 inches, with higher amounts around Marias. 

From Wednesday onward, expect cooler temperatures than the
previous week, although only slightly colder than normal. Highs will 
be in the upper 30s to lower 40s in western Montana and upper 40s 
to 50 in Central Idaho. Low temperatures will be in the teens to 
middle 20s in western Montana to central Idaho. Weather models do 
not agree on any specific system, but it does look to be an active 
northwesterly flow, with a couple of relatively dry disturbances 
moving through the overall flow. 


.AVIATION...Periodic obscured terrain will continue through the 
afternoon with lingering mid-level moisture. Cloud cover will 
lower during this evening in northwest Montana as a plume of 
moisture arrives. Rain will expand in coverage overnight and 
transition southward during Sunday. Snow levels will be high and 
generally range between 8000 and 9000 feet. Model cross-sections 
show widespread obscured terrain for most of Sunday and visibility 
reductions are expected under rain showers.  



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