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January 2011 Montana Precipitation Trends January 25, 2011

Posted by mikeheard in Uncategorized.
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Late January precipitation trends look varied across Montana with some of us well above average on month to date precipitation and others well below normal. It’s been an interesting month for moisture in regard to type and intensity as well, rain, snow, freezing rain.
Here is the data in terms of percent of average. Any values below 100% are below normal and any values above 100% are above normal.

Dry Areas:
0-25% of average
Gallatin Field – Belgrade 23%
Dillon 17%
Helena 24%
Cut Bank 0%

25-50%
Billings 32%

50-100%
Bozeman MSU 56%
Wisdom 54%
Livingston 82%
Miles City 95%
Great Falls 46%
Butte 52%
Lewistown 54%

Wet Areas:
100-200%
Kalispell 187%
Seeley Lake 192%
West Glacier 135%
Big Sky 128%
Ennis 121%
Havre 125%

Very Wet Areas:
200+%
Missoula 211%
Anaconda 200%
Glasgow 557%
Glendive 244%

A general overview shows that SW, Central and SE Montana will end up on the drier than normal side for January precipitation with a few exceptions. Western and Northern Montana will end up with well above normal precipitation. Why?
The month was very active with regard to strong pacific storms rolling in from the pacific NW. This type of weather pattern is prone to upslope and downslope factors. Mountain ranges running North to South and a perpendicular flow from the west creates strong lifting on the windward side (west) of the various mountain ranges from the pacific NW, inland NW through to the continental divide. Just the opposite occurs on the Lee side (east) of the various ranges, downsloping dries the air and produces very windy conditions at times.
For SW Montana our variety of mountain ranges shielded many of the valleys with downsloping and thus drier conditions than normal for the month of January.
Another interesting factor with this weather pattern during the month was the tug of war between the numerous warm moist pacific storms and the Arctic air over Canada and Northern U.S. Temperature contrasts between Western Montana and Central to Eastern Montana varied more than 50 degrees at times with highs in the 40’s around Missoula, Butte, Bozeman vs. single digits below zero highs on the highline and NE counties. Temperatures statewide did moderate by the end of the month.
The varied temperatures produced varied precipitation. Moderate to heavy rain occurred across Western and NW Montana and did mix with a little snow at times which in turn produced some minor flooding at times. The colder than normal temperatures kept the precipitation in the form of snow across central and eastern and northern Montana. Blowing and drifting was a major problem across NE Montana during the month and on the I-90 corridor between Livingston and Big Timber.
Snowpack

Despite the varied precipitation trends across Montana, statewide snowpack continues to run at or slightly above normal to above normal. In general statewide snowpack percent of average values for water content is running 105% to 130%.

Interesting side note on snowpack is the pacific NW snowpack data is running below normal! The reason is that the numerous pacific storms slamming the pacific NW have produced mostly heavy rain and not much snow.

ICE Jams

Another noteworthy weather event was the on again off again ice jams in SW Montana. As temperatures started out well below zero to begin the month all area rivers and streams iced up considerably and as temperatures moderated mid month that ice broke up and produced ice jams and flooding on the Gallatin River, Madison River and Beaverhead river.

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