Weather Service Report


578 
FXUS65 KMSO 280851
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
251 AM MDT Thu Mar 28 2024

.DISCUSSION...
Surface pressure analysis early this morning shows a surface low 
moving northeastward across southern Idaho. A mesoscale 
precipitation band has developed west-northwest of the lows 
center as seen in regional radar imagery. The latest round of 
model guidance suggests this low will move across eastern Lemhi 
County between 400-700 AM MDT, before reaching southwest Montana 
thereafter. Precipitation will spread across the southern 
Clearwater Mountains, the Bitterroot/Sapphire Mountains, and 
across Lemhi County and southwest Montana with snow levels 
initially around 5,000-5,500 feet. High resolution guidance 
suggests moderate precipitation intensity will help drive snow 
levels down towards 4,000-4,500 feet. A short period (1-2 hours) 
of moderate snow will impact Montana 1 from Drummond to Georgetown
Lake and I-90 from Garrison Junction through Butte. Winter 
weather advisories remain in effect for the southern Clearwater 
Mountains and Bitterroot/Sapphire Mountains Mountains through this
morning, where higher confidence exists for winter driving 
conditions across Lolo and Lost Trail Passes. 

The atmosphere will destabilize this afternoon as a Pacific 
trough passes overhead. Modest instability will produce vigorous 
mountain snow showers. Valley areas will see a mix of rain, snow,
and graupel from convective showers. The primary impacts will be 
short lived visibility reductions, with periods of slushy roadways
at the higher elevations. 

As mentioned in previous discussions, model guidance continues to
show high confidence for a digging Pacific low to move into 
southern California Friday into the weekend. The Northern Rockies 
will remain under the influence of a broad trough under 
southwesterly flow keeping showers in the forecast, mainly across 
the higher elevations. The Pacific low will begin to track 
eastward into the great Basin on Sunday. Model guidance continues 
to advertise a mid-level low moving into northern UT, southern ID,
and WY. Its worth highlighting the low probability snowfall 
event (15% percent) for Lemhi County and southwest Montana 
continues to exist within model cluster members. This snowfall 
event would occur if this mid-level low tracks further north; 
however, most guidance (85% of members) suggest this will not be 
the case. 

Long range models are in strong agreement for a ridge of high 
pressure to develop over the region early next week (Monday- 
Tuesday), bringing warmer and drier conditions. Overall however, 
model ensembles indicate this being a shortlived ridge, with 
nearly 80 percent of forecast models returning us to cool, showery
and potentially quite windy conditions by Thursday (April 4). 
/Lukinbeal

&&

.AVIATION...Precipitation continues to spread across the
Clearwater Mountains, Lemhi County, and portions of southwest
Montana early this morning as a surface low approaches into 
central Idaho. Precipitation rates will increase between 
28/1100-1800Z as the low pushes across eastern Lemhi County into 
southwest Montana. Snow levels will fall from 5,000-5,500 to 
4,000-4,500 feet, with a mix of rain/snow at KSMN and KHRF, 
bringing lower ceilings and visibility reductions. Confidence is 
high for at least IFR visibility reductions at KBTM this morning 
as snow spreads across the area with the low passing to the 
south. Furthermore, there is a 20-30% chance for a brief period 
of moderate to heavy snow at KBTM between 28/1500-1700Z. 
Convective showers will develop across the Northern Rockies 
airspace this afternoon, with brief visibility reductions being 
possible for all terminals from a mix of rain, snow, and/or 
graupel. /Lukinbeal

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until noon MDT today for 
     Bitterroot/Sapphire Mountains. 

ID...Winter Weather Advisory until 11 AM PDT this morning for 
     Southern Clearwater Mountains. 

&&

$$

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Western Regional Climate Center, wrcc@dri.edu