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Snow Level Planning Tools and Strategy

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Snow Level Planning Tools and Strategy

Postby dofdear » Tue Feb 23, 2016 10:47 am

In addition to Postholer's recent update and the Trail Snow Conditions pages, I've previously written on the subject of snow level planning tools and strategies. The Trail Snow Conditions pages are a great addition but it may be considered a higher level planning tool. Postholer's Google Maps offer map skins that offer a visual depiction of the actual trail status and I've also described how to use the maps to acquire historical overlays (map skins), including a technique to create an quasi annotation using your browser cache. (Note: I've only tested using Chome.)

Postholer may consider this strategy for the FAQs

This is a rather long post and may appear technical in nature. Please contact me if there are questions or if I can offer some assistance. Thumper

This is a repost from the PCT-L:

So after a great deal of discussion today I thought I’d write a little
about two snow level information resources.

The first is United States Department of Agriculture, Natural Resources
Conservation Service, Water Climate Center. This is the agency that
operates and manages the Snow Telemetry (SNOTEL) and Snow Course Data
and Products. Most individuals who follow this list-serv have heard of
the SNOTEL reference. The following link will open a page that will
then have links to clickable maps of Northern California, Oregon and

From there select the state you are interested in and then the
particular site. For purposes of demonstration I’ll select Washington
and then Harts Pass. Once on the Harts Pass page there will be a list of
reports. Let’s select the second report, “7-Day In-Depth Report -
Hourly data for standard SNOTEL sensors” Once the page opens unclick
the check-box titled “Fit Table To Screen” to view all the data. I do
not recommend using this page for historical data unless you want hourly

Next let’s get daily historical data. From the Harts Pass page select
the first report, “7-Day Summary Report - Midnight data for standard
SNOTEL sensors”. Again, unclick the “Fit Table to Screen” box. What
is presented is the last 7 days data. Now in the header area is a
drop-down titled “Time Period”. Set as desired and the historical data
will present itself. Note that a Water Year is the same as the Federal
fiscal year, 1 October through 30 September.

There are 2 methods of outputting the data, first is to copy and special
paste into a spreadsheet and the second is to use the “Output” drop-down
in the header to output into a CSV format which you then need to copy
and paste. Personally I like the first copy and paste method better as
it is quicker.

So that’s SNOTEL in a nut shell. There are many reports and many years
of data available. A few comments; There are no SNOTEL sites in NORCAL
that would be of any value to a PCT hiker; SNOTEL sites are a set of
specific measurement tools and as such do not necessarily reflect the
surrounding areas. The position in the topography and exposure to sun
are just two major variables that contribute to accuracy, or lack
thereof; SNOTEL sites are not necessarily in close proximity to the PCT
so data may be deceptive as it relates to trail conditions; Finally,
there are some SNOTEL sites referenced via the maps,
Location Type Snow Sensor, but not all that are relatively close to the
trail are listed (Harts Pass) and other that are listed are no longer
active (Miners Ridge). Additionally on the does list many
of The California Data Exchange Center (CDEC) sites along the PCT.

So that’s a great segue into the second snow level information resource.
It is the US Department of Commerce, National Oceanic and Atmospheric
Administration (NOAA). NOAA operates and maintains a series of
satellites that report all kinds of useful data. This link is for Snow
and Ice offered products: . Like anything else
in this life there are very technical things happening in the
background. Our friend at has made a very hard thing
pretty easy. Subscribing to the NOAA data and their
on-line trail maps has many of google maps. The overlays, or as they
call them, “Map Skins” contain subject areas including Weather, Snow
Analysis, Fire, Miscellaneous and Wilderness areas. The Snow Analysis
features are discussed in a journal entry found at

The snow data is updated by NOAA each day at 0400EST and
accesses the data through web-services which makes it somewhat
transparent to the user. To access the trail maps go to the following; and then in the header click on “GMaps” and
then select your map. Once the map opens you will note the trail line
laid on the typical Google maps we all use on a daily basis. You can
select the map type using the drop-down and select My Topo, Map,
Satellite or Terrain. Note on the right area of the map header is a
drop-down titled “Map Skins”. This has the list of available map
overlays. It’s that simple.

So let’s make it a little harder and also show a real-life illustration.
First off, historical overlays are available, and yes through the website but you will need to understand how to construct
the URL.

Look closely at the following 2 urls:

trail_id=1 is the PCT (2 is the CDT, 3 is the AT, 4 is the JMT and so
on. Remember the link, well you
can decode the trail_id from there)

&depth=1 is the Snow Depth for the current date

&depth=20151201 is the Snow Depth for December 1, 2015 in YYYYMMDD
format (this is historical information)

So basically you can put in any date back to mid-October 2005.

SNOTEL historical data is tabular where map overlays are visual. There
are no animations for the overlays but maybe I can offer a quasi
animation. A quasi animation could be setup as follow. Lets say you
wanted to look at the weekly snow depth since 20151130, a Monday. You
would then paste in the first date into your browser, enter, and then
modify the date , enter and so on. When done you can use your back and
forward buttons to sort of scroll through the date range and get an idea
of the snow levels. Each URL would look like this;

Okay now let’s do the same thing but zoom in on a particular area of the
map. I selected where the PCT crosses Hwy 2 near Stevens Pass as the
map center and a zoom level of 8. The map is now viewable between Rainer
and Harts Pass. Using the same dates as above the URLs now look like

Note the insertion of “&lat=47.74750&lon=-121.08750&zoom=8” which is the
Lat Long of the selected map center and the desired zoom level.

I only have 3 more points and then I’m done with this for a while.
Remember the link: . Near the
bottom of the page is a list of the Snow Page reports available to the maps. Look at the Snow Depth URL and you will see
“&depth=1” Well we know the =1 is the current date and =YYYYMMDD is
some historical date. The “&depth” is the report identifier. So if you
wanted the SWE report change “&depth” to “&SWE”. Or the 24 Hour Snow
Melt would be “&meltday”, and so on. The point is you can get
historical overlays back into 2005.

Next, if you’re a journalist on the postholer site these overlay, “Map
Skins” are available on your personal maps including last SPOT Location
which auto-zooms the map to a zoom level 10.

Finally, and as a test, I promised a real life example. I began a hike
on June 25, 2010 SOBO from Manning Park. We arrived at Harts Pass on
the 30th. Using the SNOTEL historical data look at the reported snow
depth for that date range. The use the following url to compare

What’s your conclusion?

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Re: Snow Level Planning Tools and Strategy

Postby postholer » Tue Feb 23, 2016 1:42 pm

Hey Dan, thanks again for the great write up! It's a good addition to the info provided here.
The Trail Snow Conditions pages are a great addition but it may be considered a higher level planning tool.

For a hiker or in the case of Blades350 a trail maintainer, I think the charts would be the 'go to' tool to use for planning and the overlays as a higher level tool. That charts and overlay both represent the same data (depending on the zoom level of the map). With the charts it's quickly evident how any trail location compares to average for the date or Apr 1 min/max.

For instance, a quick peek at the chart tells me Olallie Lake is exactly normal for Feb 22, 13" SWE, with an Apr 1st max of 44" SWE and an Apr 1st min of 0" SWE. It's simply impossible to tell that from the overlays.

For the overlays, Olallie Lake appears to have an SWE of 10-20" and that's all you can say for sure. Is that a little or a lot? You just don't know.

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