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Chinook

Mountain West- Winter

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Here is our new thread for the winter. As I am typing this, I am thinking about how pleasant October and early November have been. It is actually kind of nice to have blue skies and 70 without worrying about the next crazy weather change. The GFS, GFS ensembles, and other models showing a trough in the Rockies on Nov 16-17. The GFS is even getting consistent at showing a fairly significant snow for Wyoming.

8BAO12w.png

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Today's 12z GFS brought the snow back to NE Colorado on Thu-Fri. I thought for sure the models had trended north with the low pressure, and would stay north. There's still several days to go.

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I still like my general idea for the winter - dry to near normal for much of NM, AZ, CO, UT, in winter but turning colder late. These -50F anomalies in Asia probably have to break apart and move to North America at some point. I had NM warm & wet in Nov, which looks pretty good right now. We're already "wet" by the standards of the month, i.e. >=1.2x mean rain 1931-2015 base). This is what I had - https://t.co/Zx6yobAlBI. Also did an update where I compared my forecast to some others, and incorporated October precipitation and temperature ideas - https://t.co/ZdLDRW5uxY

Also think the MJO (i.e. patterns repeating with much more rigidity than in an El Nino) is a bigger factor this year. For instance - early Aug v. early Nov had nearly identical rains at about two MJO cycles of 45-days apart.

The "weather" analogs I picked based on similar conditions in Albuquerque from June to September compared to the Summers of 1931-2015 suggested an increased likelihood of a big snowstorm or several little snow events around Feb 1, Jan 29 - Feb 2. That is largely consistent with the timing of big precip events in the SW recently and in line with the MJO - we had good rains in early May, then early August, then early November.

Still like February for a big snow overall - the temperature profile of the Summer-Fall transition is very similar to years ahead of big February snowstorms, including Summer 2014, ahead of the ~10 inch snowstorm Albuquerque had Feb 26-28. The northern mountains of New Mexico had 40-100" of snow from Feb 22 - Mar 5 in 2015, following a warm October after a mild September, as we had this year. The ten warmest Octobers in the SW have ALWAYS been followed by big snows in Jan-Apr in NM/ Southern Colorado, and often for the rest of CO and AZ too.

Frigid Asia.PNG

Rain early November 16 2.gif

Rain early August 16.gif

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The Canadian and, to some degree, the ECMWF, give some hope for snow here at low elevations in Colorado on Thursday. It seems rather likely this will be a 3-6" snowstorm for many populated areas of Wyoming and Montana. Perhaps somewhat dangerous blizzard conditions in the Dakotas. My area may be totally dry Thursday, or may get up to 2" of snow.  I think there will be 3-10" for areas over 9000ft in northern Colorado.

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November 1-13 temperature departures. Regardless of the upcoming cold and snowy conditions, the large amount of warmth will be the biggest story of the month in the northern US.

y7SbZ3A.jpg

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The upcoming storm might be a little more significant for the mountains and foothills near here. The GFS has 1.0" of QPF at Rocky Mountain Natl Park, (10-15" of snow) and 0.2" to 0.3" of QPF at Fort Collins and Denver. The ground is so warm around here, little snow will stick to the streets, assuming we get any.

UKiBw4q.png

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700mb temps and winds here are part of the reason why the GFS predicts fairly high QPF here- easterly wind at 700mb, upslope and weak warm advection in a terrific -7C layer.

 

O9qjy7U.png

 

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We had a reasonably snowy afternoon. We got 1" from 12:15pm to 1:15pm, then lighter snow that probably had accumulation less than 1 extra inch.

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How close was this event to being your latest date for a (first) snowfall on record?

I know here, depending on how things play out, our first snow can be anywhere from early October (as recently as 2009) or as late as February (as recently as 2002).

There is a fairly strong relationship between first snowfall date and accumulating snow for the season too, at least in my area. If y=total snowfall in Albuquerque from Oct 1-May 31, knowing the date of the first snowfall (as x) gives you an idea of whether the winter has a good shot as being snowy or not. 

For Albuquerque, it's typically snowy if it snows for the first time in November, and there is a strong cut-off date around December 15th - we've had 18 winters where the first snow came after Dec 15th, but none of them had over 13 inches of snow...which is unusual as ~1/4 of winters here get 13"+ snow.

 

First Snow v. Total Snow ABQ.png

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1 minute ago, raindancewx said:

How close was this event to being your latest date for a (first) snowfall on record?

I know here, depending on how things play out, our first snow can be anywhere from early October (as recently as 2009) or as late as February (as recently as 2002).

There is a fairly strong relationship between first snowfall date and accumulating snow for the season too, at least in my area. If y=total snowfall in Albuquerque from Oct 1-May 31, knowing the date of the first snowfall (as x) gives you an idea of whether the winter has a good shot as being snowy or not. 

For Albuquerque, it's typically snowy if it snows for the first time in November, and there is a strong cut-off date around December 15th - we've had 18 winters where the first snow came after Dec 15th, but none of them had over 13 inches of snow...which is unusual as ~1/4 of winters here get 13"+ snow.

 

 

Pretty amazing that the R squared was only about 0.1 though, so 90% of the variability is due to other things.

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Considering how fluky one snow event can be, in terms of timing, patterns and everything else, I was actually fairly surprised it was even that high. The main thing to me from the relationship is that there is a cut off date for when you can expect a "much snowier than normal" cold season here - December 15th. We've had 18 winters with a first snow after Dec 14th. None of them had >13" snow. But...in the 85 years of snow records, 22 winters have had >13" snow (you'd expect around five - (18)(22/85). To me that's the main take away. I was trying to see if you all had passed a threshold in Denver in the way that Dec 15 is a threshold here. 

Another way I look at it is if it snows by December 14th, there is a 22/67 shot (~1/3) of >13" snow here. All others...near 0 (0/18 historically - if I'm being cute with uniform priors we can pretend it's 1/19).

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According to a recent tweet by NWS Boulder, Fort Collins latest first snow was Dec 13th, but for Denver, it is Nov 21st.

1 hour ago, raindancewx said:

How close was this event to being your latest date for a (first) snowfall on record?

 

 

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Let's do an experiment: Everyone look at the four ensembles estimating snow that came out for the CFS through Dec 31 today. Write down what you think it is saying for your area based on each ensemble. In January, we can look back at this and see if there is one CFS ensemble for our areas that isn't completely out to lunch.

For me, (ABQ), from 11/18-12/31 I get:

A - 6"

B - 1"

C - 10"

D - 3"

For New Mexico I kind of like D the best for most realistic, B seems worst case scenario. D>A>C>B in order of realistic to least in my area. What do you all think for your areas? C is sort of awesome - more snow in MS than by Salt Lake City...

Snow Coming.png

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After hitting 81° on Wednesday, we picked up 4" of snow yesterday, and bottomed out at 18-19° this morning. I left work early yesterday afternoon and am glad I did. It took a couple of my coworkers over an hour to get up this way around rush hour, when it's normally a 20-25 minute drive.

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Fort Collins was 79 on Wednesday, which was a record high (possibly the warmest temp for this late in the season.) Considering the highest and lowest temps at the Fort Collins-CSU electronic thermometer it was 78.8F on Wednesday and 19.7F this morning, a difference of 59.1 degrees.

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It was about 35 degrees here. It has been a very long time since we had a day that was about 15 degrees below average on the high temperature

The next storm event is on the horizon for Tuesday. It would appear that snow may be rather light for elevations under 6000 ft around here, but perhaps this could bring 10"+ to southwestern Colorado.

q2A83ET.png

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recent snow reports from Thursday. I thought there would be many more mountain snow reports of over 6". The Denver metro area had 4-4.5" in a couple of spots.

jkzlB8Y.jpg

 

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