Cloudy Northwest Montana

Most of us that live in this beautiful and remote part of Northwest Montana in Lincoln and Sanders Counties know that our region is rather different than much of the rest of the state of Montana. The biggest comment I often hear from those who are visiting during the winter months or those who relocate to the area is how surprised they are at how cloudy conditions are generally between late October to mid April. Many of us are simply used to that and appreciate the rare times we do get to see the mountains such as the Coeur d’ Alene’s and Scotchman Peaks in Sanders County or the Cabinet Mountains and Whitefish Range in Lincoln County any time of the year but especially during the winter. Have you ever wondered why we do have so much cloud cover in our part of our magnificent state?

Consider this interesting fact about our region. Libby, Montana averages 155 days of sunshine a year and Coeur d’ Alene, Idaho averages 125 days of sunshine a year. (I have included Coeur d’ Alene simply for statistical purposes as we don’t have records for other regions in our area). That means that the other 210 days of the year are either mostly cloudy or cloudy, a rather dull picture overall. Yet it’s this “dullness” that allows our region to have the beautiful and magnificent forests that we would not have if we had a lot more sunshine. Our region is relatively dry with Libby only averaging 17.81 in of precipitation, Troy averaging 24.36 in of precipitation, Heron averaging 33.67 in of precipitation, Trout Creek averaging 28.46 in of precipitation and Eureka averaging 14.44 in of precipitation. Except for the locations in Sanders County of Heron and Trout Creek those precipitation totals are all on the low side and one would think that this would not support the little amount of sunshine for our region. The key here though is when the majority of this precipitation falls along with our latitude at 48.5 degrees north and the terrain. Overall our region sees the majority of it’s precipitation during the fall, winter and spring months when daylight hours are considerably shorter and nights are cool to cold. We are also in a region that is generally in the North Pacific storm track which tends to keep the frequency of systems approaching from the west rather consistent even during the warmer summer months. These systems typically have an abundance of cloud cover both low, mid and high level cloudiness associated with them. In addition, we also are vulnerable to systems that dive southward from Canada, commonly referred to as “Alberta Clippers” which usually have low to mid level cloudiness associated with them. Last, but not least we are also influenced by dynamically induced cloud cover and thunderstorm outbreaks in the summer months from the south, all of which contribute to our abundance of cloud cover for our region. The biggest factor however in our persistent cloudy conditions, especially in the the lower elevations where we reside are valley inversions. Under “normal” conditions, temperatures decrease with altitude while under inversion conditions temperatures actually increase with altitude. The picture below shows the typical set-up for inversion conditions in our part of the country.

Mountains on all sides of our valleys in Northwest Montana allow extensive inversions to develop during the fall winter and spring months. Cold air pools on valley bottoms with warmer air aloft with cooler air well above the warm inversion layer.

Mountains on all sides of our valleys in Northwest Montana allow extensive inversions to develop during the fall winter and spring months. Cold air pools on valley bottoms with warmer air aloft with cooler air well above the warm inversion layer.

The common set up for inversion conditions to persist in our part of the country occur during the fall, winter and spring months when nights are long allowing cold air to pool in the valleys and not mix effectively during the day along with a lack of wind. This is more common later in October through mid March and becomes less persistent as the daylight hours increase through the Spring months. Here is another interesting fact concerning the days on end during the winter months when it is cloudy and damp outside during the winter. If you are one who enjoys hiking and the challenges associated with that in the winter months, once you rise above around 5000 feet in our region you will likely be greeted with a scene that looks something like the one below.

A picture taken at Big Mountain near Whitefish during the winter with clear skies above an extensive blanket of freezing fog and low clouds down below. This is common during the winter months when both upper level high pressure and surface high pressure are parked over our part of the country with clear skies in the mountains along with light winds in the valleys.

A picture taken at Big Mountain near Whitefish during the winter with clear skies above an extensive blanket of freezing fog and low clouds down below. This is common during the winter months when both upper level high pressure and surface high pressure are parked over our part of the country with clear skies in the mountains along with light winds in the valleys.

The picture above is typical during stretches of upper level high pressure along with a surface high pressure area over our region during the winter months. In order for inversions to develop winds need to be light and skies generally clear. Once you rise above the top of the inversion layer, which for our part of the country typically occurs around 5000 feet, you most likely will encounter clear conditions above that elevation and cloudy, foggy and snow flurry conditions below that elevation. It is these same inversion conditions that often give our valleys here in Lincoln and Sanders Counties freezing rain when the pattern begins to break down and storm systems begin to move back into our region. The warmer temperatures aloft in the mountains cause snow levels and freezing levels to be rather high which means that any snow that falls into the warmer air above the inversion melts. Once it falls back into the cold air trapped in our valleys it will either re-freeze and fall as sleet or if the below freezing layer is less than 500 feet thick, will fall as freezing rain. It’s this cloud cover associated with the inversions that allow the little precipitation we receive in our area to soak into the ground, keeping the ground much wetter and thereby allowing the forests we have to flourish. During the summer months, those of you hiking in the mountains will notice that the nights are considerably warmer on slopes and ridges than down in valley locations. This too is due to inversion conditions although with summer being a drier time of year around here and the ground often dry along with much longer daylight hours, any low clouds or fog that do develop quickly dissipates to leave sunny skies. The final point here is that locations under the inversion will often be considerably colder, as much as 20 or more degrees colder than those in the “thermal belt” above the inversion. This can be very noticeable during the summer months when those of you who live on mountain sides and ridges will not cool off very effectively as those who live on the valley bottoms. This leads to uncomfortable sleeping conditions during periods of hot weather when the atmosphere does not cool off and remains hot. An example of this from the summer of 2018 near Libby occurred during the heatwave at the beginning of August when the high temperature was 108 degrees. On the valley floor the morning low that day was a very pleasant 50. At 500 feet above the valley floor the low temperature that same morning was 77 degrees, a whopping 27 degrees warmer! That is a strong inversion! Winds later that morning along with the long daylight hours of summer allowed the valley bottom to warm up and mix out with high temperatures being the same at both locations. So now when someone asks you about why it’s so cloudy in our beautiful part of the state you can tell them it’s the inversion.

An inversion free day across south Libby in Lincoln County. The absence of low clouds and haze in the lower elevations indicates ventilation or rising air also evident by the cumulus clouds. This picture was taken during the late spring when inversion conditions are less persistent and less noticeable during the daylight hours.

An inversion free day across south Libby in Lincoln County. The absence of low clouds and haze in the lower elevations indicates ventilation or rising air also evident by the cumulus clouds. This picture was taken during the late spring when inversion conditions are less persistent and less noticeable during the daylight hours.

Winter 2018-2019 Outlook for Northwest Montana’s Lincoln and Sanders Counties

So here we are closing out the first week of November as of this writing on November 8, 2018. So far the autumn season has been pleasant with a mix of sunshine and periods of wet weather but not much in the way of cold which has made some people very happy and some not so happy. After another hot summer, September came and brought much relief from the hot summer with temperatures ending up cooler than average for the month across all of Lincoln and Sanders Counties. October started off on a cool note but ended up on the warm side of the column. Now we are in November and up to now it has continued to be mild. What will the upcoming winter season bring? I will try to answer that here in this article.

There is much discussion going on about the Climate Prediction Center’s (CPC for short) winter outlook which is calling for a weak El Nino to continue to develop across the Pacific and how that may affect the weather across the continent. While El Nino is a significant factor in the weather patterns across North America, it is only one factor of many that can contribute to how our winter will shape up. In any case I keep hearing people say that we are going to have a warm and dry winter because of El Nino or that’s what they heard on TV. Take a look below at these two maps that the CPC has put out for the Winter months of December/January/February 2018-2019. The first one below is a temperature probability map.

off02_temp.gif

This map is valid for the months of December, January and February 2018-2019 and was made on October 18, 2018. The way the media and most people are reading this is that the darker orange shading for our region means that we are going to have a warm winter. In reality that is not what this map is saying. What it is saying is that the probability of above average temperatures for the months of December through February is between 50% to 60% or that the odds favoring above average temperatures for the winter months is 50% to 60%. Now take a look at the next map below. This is a precipitation probability map.

off02_prcp.gif

Again this map was made October 18, 2018 and is valid for the months of December through February 2018-2019. Once again the way the media and most people are reading this map is that the brown shading over our region means we are going to have a dry winter. This too is not what this map is saying. What the map is stating is that the probability of below average precipitation for the months of December through February are between 33% and 40% or that the odds of below average precipitation are 33% to 40%, a long shot difference of stating that we are going to have a dry winter. The explanation here is that in looking at past winter’s with similar conditions we have seen more years with warmer than average temperatures for a stronger correlation and odds favoring warmer than average temperatures but not as clear a signal for precipitation with the overall tending to favor below average precipitation. These maps cover a large area but what about our specific region in far Northwest Montana specifically here in Lincoln and Sanders Counties? I have included temperature and precipitation comparisons for two communities in our region for the months of December through February. For this example I have chosen two years that most closely resemble the pattern we currently have along with the long range forecasts. I have also included the climatic normals for the 3 winter months of December through February.

Normals for December through February:

Libby, MT

Month: Avg high ‘F: Avg low ‘F: Avg precip (inches):

December 31.7 21.1 2.20

January 33.5 21.3 1.78

February 40.7 22.3 1.25

Thompson Falls, MT

December 34.4 23.7 2.35

January 36.4 24.6 2.32

February 42.6 25.3 1.83

Next I’ll include the data from two years that we have on file for the same two locations for the two years that most closely resemble this one.

Winter 1958-1959

Libby, MT

Month: Avg. high’F Avg. low’F Avg. precip(in)

December 33.1 21.2 5.29

January 32.1 17.7 1.94

February 37.1 18.3 3.27

Thompson Falls, MT

December 38.0 26.7 3.45

January 36.2 23.3 3.75

February 37.2 23.7 1.41

Winter of 2014-2015

Libby, MT

Month Avg. high‘F Avg. low’F Avg. precip(in)

December 34.9 23.7 1.99

January 35.4 23.2 1.40

February 45.3 27.0 1.34

Thompson Falls, MT

December 35.2 26.1 2.12

January 35.0 25.5 2.22

February 46.9 28.7 1.44

As you can see from the data provided above the 2 years that most closely resemble where we are right now and closely resemble what is forecasted for the upcoming winter show some variability. The winter of 1958-1959 brought a milder start in December but then turned considerably colder in January and February at both Libby and Thompson Falls. Precipitation was consistently above average throughout the entire winter especially in Libby. For the winter of 2014-2015 we see just the opposite with temperatures running considerably warmer throughout the winter but precipitation running only slightly below average except for February when readings were fairly close to average. Sure there are some other years as well that are similar to what this winter is forecasted to become but these two years most closely resemble where we are now. While El Nino does play a factor in our weather especially during the winter months, it is only one of several factors that can determine our winter weather. One of the main factors that seems to greatly affect our region is the Pacific North America Pattern or PNA for short. Looking back at history for the two winters I have referenced notes that the PNA pattern went from weakly positive in November and December to weakly negative in January and February for 1958-1959 while for the same time period in 2014-2015 the PNA remained in the weakly positive phase but a little bit more so in the positive phase for that winter verses the same period in 58-59. There is a correlation between the positive phase of the PNA pattern and El Nino along with a corresponding negative phase of the PNA pattern and La Nina which is the opposite of El Nino. At this point in time the odds favor a positive phase of the PNA pattern throughout the upcoming 2018-2019 winter which looks much like the chart below.

The dotted line represents the upper level ridge axis during the positive phase of the PNA pattern.

The dotted line represents the upper level ridge axis during the positive phase of the PNA pattern.

In addition to El Nino or La Nina and the PNA pattern, one other aspect I like to look at is North American snow cover which so accurately predicted the last 2 winters around here. From the charts I looked at as of November 8, 2018 most of the snow cover across North America, specifically in Canada is located across the eastern part of the region. This in part explains why the pattern across the continent for the end of October into November so far has been cold and stormy in the east and mild and relatively dry in the west, a result of a positive phase of the PNA pattern. Hudson Bay is also beginning to show signs of beginning to freeze over and if it does and the pattern continues to favor continued below average temperatures and snowfall across eastern Canada with upper level ridging across western Canada and the US that may end up locking us into the positive phase of the PNA for the winter with the weak El Nino helping to maintain that pattern. If, on the other hand, the pattern flips, then the opposite is possible. The take away point here is that wherever the snowcover sets up across the continent early i the season often will determine where the so called Hudson Bay low or polar vortex sets up which is what largely governs the patterns across our region.

So what does all this mean for our region you may ask and what does it mean for our winter outlook. From the research that I have been able to do the winter outlook for 2018-2019 for Lincoln and Sanders Counties looks something in-between the 1958-1959 winter and the 2014-2015 winter. In other words I believe that we will see a decent start to the winter in late November into December with some snowfall and near average temperatures that will likely persist into the beginning of January. Beyond that, it appears to me that our region may then dry out and ridge up with the jet stream splitting with the southern or subtropical branch shifting more to our south into California and the northern or polar branch shifting well to our north into Northern BC leaving our neck of the woods dry and mild(in the mountains as this type of pattern often results in widespread valley inversions marked by an abundance of low clouds and fog) pattern. So as a whole, I tend to agree with the CPC that odds favor a milder than average winter, although I have to say that I do not necessarily believe it will be a warmer than normal winter except for perhaps in the mountains and also that the odds favor a near normal to slightly drier than normal winter. I do not think that our region will see the amounts of snowfall that have been common around here the past 2 winters but some significant snowfalls are certainly possible. Also I would not be surprised to see some significant cold air outbreaks particularly if a strong positive phase of the PNA develops. Those cold air outbreaks are more likely to occur in December some time and again later into January or February. Towards the end of the winter season in later February or March we may see some wetter weather in our region but that is only a guess at this point. So in summary for Lincoln and Sanders Counties I expect populated areas in the lower elevations to see near to perhaps slightly above average temperatures for the winter and near to slightly below average precipitation for our region. Will I be correct? Time will tell. Please feel free to leave comments and share with others.

Summer 2018 Outlook

The first official day of summer arrives on June 21 this year for our region although we have been in meteorological summer since June 1. After a cool and wet start to our Spring and a very warm and dry end to it many are wondering what the summer looks like for our region.

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