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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 46 °
• Low: 32 °
• Chance Rain

• Thursday
• 
• High: 48 °
• Low: 32 °
• Chance Rain

• Friday
• 
• High: 48 °
• Low: 32 °
• Chance of Rain

• Saturday
• 
• High: 45 °
• Low: 27 °
• Chance of Snow

• Sunday
• 
• High: 45 °
• Low: 25 °
• Chance of Rain

Area forecast discussion 
National Weather Service Missoula Montana 
250 PM MDT Tue may 22 2012 


..significant storm expected this weekend... 


Discussion...convective rain showers have begun popping up 
across the northern rockies and will continue to bring pockets of 
rain through this evening. Breezy conditions are another feature 
that will be quite persistent through this evening, at least until 
nightfall. Gusts between 20 and 30 mph are likely across western 
Montana and central Idaho. A few lightning strikes are also 
possible in areas of showers. More persistent rain will once again 
develop overnight, particularly over Clearwater and Idaho counties 
in Idaho. Breaks in precipitation will be few and far between, 
with showers likely to continue through Wednesday. 


Thursday and Friday will remain unsettled as the intermountain 
region remains under an elongated upper level trough with two 
distinct circulations at either end. The northwest circulation 
along the Canadian rockies will send moisture and impulses 
southwest over western Montana Thursday. Thursday evening and 
Friday...the western-most circulation will take over and bring 
more Pacific moisture to the area. There's cold enough air aloft 
that some of the showers Thursday afternoon and evening may fall 
in the form of snow. The snow will melt on contact at most valley 
locations, but the higher valleys and passes may see some light 
accumulations mainly on grassy surface. Georgetown Lake, McDonald 
pass, and Lost Trail Pass will likely see these conditions. 
Temperatures will remain well below average, with highs mainly in 
the 50s to end the week. 


Forecast models continue to come into better agreement regarding a 
significant storm system impacting the northern rockies this 
weekend. The European model (ecmwf) model has been the most consistent with the 
path, strength, and subsequent precipitation, so it remains the 
model of choice. However, it is Worth mentioning that the latest 
run of the GFS is beginning to show a trend towards the European model (ecmwf) and 
into better agreement with its own ensemble mean. 


All things considered, those with plans for the Holiday weekend 
will want to be judicious in checking the forecast before 
embarking on their adventures to ensure they have the appropriate 
gear for inclement, winter-like conditions in the mountains, and 
cold, persistently wet conditions in valleys. Light precipitation 
will begin to develop on Saturday as the weather system approaches 
from the southwest and then overspread western Montana and central 
Idaho overnight through Sunday. The snow level is forecast to fall 
considerably, with accumulations possible down to between 5000ft and 
6000ft by Sunday morning, coincident to the locations with the 
heaviest precipitation. 


At this time: confidence is high that snow will impact the higher 
terrain and highest mountain passes (lost trail, MacDonald and 
Homestake passes) this weekend. But actual amounts are still too 
challenging to pin down. Meanwhile, persistent light to moderate 
rainfall across the lower elevations will amount to some areas 
receiving another 1.0 to 1.5 inches of rainfall over the weekend, 
which may result in additional rises on some area rivers, creeks 
and streams. Temperatures area-wide this weekend will be 10 to 20 
degrees below normal Saturday and Sunday. Some improvement is 
expected in both weather conditions and temperatures on Memorial 
Day (monday), though scattered showers cannot be ruled out 
throughout much of the day. 


Beyond the extended Holiday weekend, forecast models show a weak 
weather feature producing some showers on Tuesday as it quickly 
moves across the region. This appears to be followed with a weak 
ridge, though confidence in this remains very low at this time 
with only a little more security held in a gradual return to more 
normal temperatures next week. 




&& 


Aviation...rain showers will continue over the region today with 
thunderstorms possible this afternoon across southwest Montana and 
central Idaho, mainly affecting kbtm and ksmn. Gusty west- 
northwest winds will continue until sunset tonight. Most 
locations will experience gusts between 20 and 30 mph across the 
entire northern rockies before diminishing. Rain will be the 
persistent feature for the next 24 hours, if not longer. 




&& 


Mso watches/warnings/advisories... 
Montana...none. 
Idaho...none. 
&& 


$$ 


Allegretto/Dickerson/Mead