In the last post a week ago I mentioned the possibility of the first dusting around the 20th of this month.  That looks like it may still happen a week later today, but we have some better details now that we are closer.

You should already have noticed much colder weather over the past week as a cold trough has settled over the West.  Highs have only been in the 60's instead of the 80's.  That weather will continue tomorrow before we see colder air move in with the next trough.

A fairly dry cold front should move through on Tuesday with the chance for a few showers.  We could see a few flakes and even a dusting of snow over the upper elevations.

A second storm may dive in Thursday bring a reinforcing shot of colder air and this system looks a little wetter and could bring a couple inches of snow above 7000 feet.  We will have to keep watching how much moisture could come with this system.  The snow levels could drop near lake level so everyone could see a few flakes. 

Here is a our first look of the season at the GFS total precip forecast for the next 5 days.

and the first snowfall forecast map of the season...

Temperatures will drop into the low 50's for highs at lake level and 40's on the mountains for the 2nd half of the week.  We will see some strong winds up high with both systems.  

By next weekend high pressure builds off the coast with the return of drier and slightly warmer weather.  This colder weather may just be a fluke this week, as the long-range models show the ridge of high pressure building in over the West going into October.  Looking at the latest European weekly model runs they show the pattern possibly turning colder again for the 2nd half of October.

The Data:

I knew the questions about the snowfall and temperature trend would come up this time of year as they always do.  I had the data last week but wanted to keep the length of the post down.  All I do when looking at snowfall and temperature data is to present the data I find recorded by reporting stations, ski resorts, or data I collect.  I leave the interpretation up to the reader.  I do my best to try and create charts to show data you have been asking for using the data I can find from around the area.

I get a lot of questions on temperature trends or how temperatures in a month or season compare to past seasons.  You have to remember that the forecasting I do or we do at opensnow is very micro.  We are focused on a small area of high elevation mountains where ski resorts are located.  The data in these micro climates can vary from data or trends in large areas like states, the country, the continent, or the globe.  

I have been keeping the average temperature reported at the Truckee Airport reporting station for each month since 1980 (the year I was born), in an excel spreadsheet.  I have it tied to a chart plotting the point of the average temperature reported for each month.  I have the average annual temperature calculated from the average of the monthly average temperatures reported for each year since 1980.  I have that tied to a line graph that shows the average temperature reported for each year, with the average annual temperature calculated of 43.3 degrees as the red line.

Here are the average temperatures reported...

and the graph...

Here is the snowfall graph for total snowfall by year recorded for Truckee, CA since 1934.

A lot of the snowfall data I post is from the Central Sierra Snow Lab located on Donner Summit near 7000'.  Here is the October to May snowfall for that location since 1970.

Here are the updated snowfall averages for that location by month, with March showing as the snowiest month.

The main question I usually get is whether there is less snow falling at lake level compared to the higher elevations.  This is a hard number to calculate as you rely on the measurements from ski resorts for a lot of the data, or reporting stations around the lake.  There are more factors for lake level snowfall besides snow levels, like how much moisture spills over the crest into the basin with each storm, or the snow ratios at lake level versus the higher elevations.  

For this question this time I decided to take the snowfall (Oct-May) against the average for the Snow Lab at 7000' on Donner Summit and to compare that to the snowfall against the average recorded for Truckee at 5800' for each year (Oct-May) since 1998, so for the last 2 decades.  I then put the % difference between the two elevation for each year.  Then I put the Truckee temperature departure from average for averaged months of (Oct-May).

So here is the chart.  I do see that on the colder Winters the snowfall average is greater at the lower elevation than the higher elevation  4 of 9 times.  Those winters the higher snow ratios may have carried down to the lower elevations and snow levels may have been below 5,800' more than average resulting in a higher snowfall against the average than at 7000', but also storms could have tracked in from the North or East more than average resulting in more snow East of the Sierra Crest than average, or more snow spilled over to the basin than average.  So there are more possible variables than just temperature for the higher snowfall against the average at the lower elevations versus the higher elevations.

9 of 10 Winters with above average temperatures the snowfall against the average was greater at 7000 feet, which you would expect in a milder Winter with higher than average snow level levels with each storm, and also the other variables could factor in.  There is a variance of more than 25% 4 of the last 9 winters, but half of those had below average temps.  When there is less snowfall in Truckee versus Donner Summit against the averages those years it seems to be tied more to the below average precip (all 4 years) than the temperatures.

 

We will keep tracking along each year and adding in more data.  Again, this data is just that, data from local reporting sites put into tables and graphs for you to see.  It is for a very micro climate area.  But it is interesting to look at the temperature and snowfall trends over time.  

Looking forward to hopefully lots of snow for all elevations this Winter!

Stay tuned...BA