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A Look At The Winter Season 2010-2011 for Montana March 6, 2011

Posted by mikeheard in Uncategorized.

The winter season of 2010-2011 was greatly influenced by a La Nina event in the equatorial pacific with much colder than normal sea surface temperatures. This La Nina event was a stronger event than the La Nina in the 2008-2009 winter season. Moderate to Strong La Nina episodes typically lock Montana into a colder and wetter winter weather pattern. Also the stronger the event the more likely it is to redevelop again, not a guarantee, but La Nina’s typically run in back to back years. The data is showing the current La Nina weakening and should be in a neutral state by late spring or early summer and by late summer we should have enough data to determine if La Nina conditions will redevelop or not.

Looking back at this winter season the data is showing that overall Montana endured one of the coldest winter season in many years. Listed below is the average monthly temperature from November to February and overall the data shows well below average temperatures with the exception of January for southwest Montana.

Average Monthly Temperatures winter season 2010-2011
……………….Butte    Bozeman  Helena  Dillon………………………
November -2.5           -3.1             -3.5         -6            COLD
December -.5            -2.2            -3.3         -4.2           COLD
January 3.6            4.5              6.3         -.7           MILD
February -5.2           -6.4             -5.1        -8               VERY COLD

The month of February-2011 across Montana was Extremely Cold especially for the northern half of the state and far eastern cities. February avg temperatures: Great Falls -9.5, Cut Bank -10.6, Havre -8.9, Glasgow -10.9, Miles City -10.5, Billings -9.6, Bozeman -6.4, Dillon -8, Lewistown -8.7, Missoula -6, Kalispell -5.8, Butte -5.2, Helena -5.1. When we analyze climate data and see average temperatures vary a few degrees is not unusual, however, when we see average temperatures vary more the 3 to 5 degrees is alarming but when the vary 8 to 12 degrees is exceptional. So most of Montana saw below average temperatures in February -5 to -11 degrees and again that signals an extreme event.

An interesting side note on the winter season was the month of January. Average temperatures for January 2011 saw a complete reversal with above to well above average temperatures. La Nina was still in a very strong state but apparently there were other atmospheric conditions offsetting the normal La Nina effects on Montana during that month. A few record highs were noted within Southwest Montana during January as max values reached the lower to mid 50’s.

Arctic Cold below zero mornings

Gallatin Field

Nov 8 mornings below zero

Dec 9 mornings below zero

Jan 7 mornings below zero

Feb 8 mornings below zero

Total 32 mornings with below zero lows Nov through Feb.

Gallatin Field -10 to -20 Nov to Feb = 15 mornings

Gallatin Field -20 or colder Nov to Feb = 5 mornings and 4 of those in Feb.

Coldest morning low this past winter season 2010-2011 at Gallatin Field -22, Feb. 25th

Butte – Bert Mooney Airport

Nov 7 mornings below zero

Dec 10 mornings below zero

Jan 9 mornings below zero

Feb 10 mornings below zero

Total 36 mornings with below zero lows Nov through Feb.

Bert Mooney Airport -10 to -20 Nov to Feb = 16 mornings

-20 or colder = 6 mornings Nov to Feb and 4 of those where in February.

Coldest morning low at Bert Mooney Airport for the winter season 2010-2011 was -25, February 26th.

The 30 to 90 day forecast continues to bring more of the same with La Nina still controlling the overall weather pattern so colder than normal temperatures will likely persist into the early half of spring. Climate Prediction Center longer range forecast for this summer is showing a complete reversal with above to well above normal temperatures July through September due to the La Nina reaching a neutral state.

This is the time of the year we start to see how the upcoming spring/summer could fair as far as forest fires and/or flooding. The current data shows average to well above average snowpack across the entire state of Montana. The highline and NE counties of Montana has a double threat with colder than normal temperatures and well above normal ground snow which increases the potential for moderate to major flooding this spring. North and South Dakota through Minnesota has a high probability for major flooding as well as the high plains has been inundated with plenty of snow and a colder than normal winter season as well. The rest of Montana has a good chance for minor flooding due to snowmelt especially on those rivers and tributaries that are free flowing or not augmented by reservoir storage.

The next 4 to 6 weeks will determine the severity of spring flooding across the state, if forecasts trends continue with colder than normal temperatures and near normal precipitation flooding will occur in Montana this spring. Hardest hit areas will be the NE and far eastern counties, minor for the rest of Montana with some moderate flooding possible in isolated areas if conditions are just right. One possible weather pattern I am most concerned with is the colder than normal pattern will keep most of the snowpack in place up to the beginning of the rainy season in May. If a warm and very wet pattern where to hit the above normal snowpack flooding probabilities will increase substantially.

I’ll continue to monitor the weather patterns to see how fast the current La Nina weakens to a neutral state, how mountain snowpack data trends develop and we will keep a very close eye on the longer range forecast for this summer to see how the summer fire season could develop. Right now we are most concerned with the increasing possibility of flooding this spring.



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