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Chinook

Mountain West Discussion

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Now that it has snowed in Denver and this area, we will start the winter discussion for our region.

To recap: On Wednesday it was 78 degrees here, but a cold front with 30 mph wind gusts brought the temp to about 39 by evening. On Wednesday night, I saw thunder and lightning with numerous graupel bits which would normally be called 1" of snow. Then, when I got home, there was just a bit of graupel on the ground. Then, Thursday morning, my place got 2" of snow or more. Then, on Thursday evening, there were snow flurries when I was at work. So, I had to go out to my car and clear off another 1/2" of snow off my car. I was wondering if the road would be icy, but I didn't notice anything slippery.

Today, things are getting back to being a somewhat normal chilly day.

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Yup, other than the fact that all outdoor plants including trees look like they were blasted by a death ray, you can't tell that anything is too different from the way it was last Wednesday. The trees went from green to gray, skipping all the colors in between. Yuck.

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Nino 1.2 is currently under 20.0C in October on the weeklies. The monthlies usually come in warmer for Nino 1.2...still, if the month finishes under 20.0C in Nino 1.2, a -PDO is likely for winter. Since 1950, 17/18 years with a <20.0C Nino 1.2 in October have finished with a -PDO for Nov-Apr.

With an El Nino forming, that can be an incredible pattern nationally. The temperature pattern for October (super cold NW / super hot SE) is consistent with the PDO correlations to winter when the PDO is negative.

This is the composite for when the PDO finishes under 0 for the Nov-Apr period, in an El Nino (it is the same idea - cold West / mild East if you use only 1950+ years)

Image

 

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That is a large area of similarly cold temperatures in the composite.

A couple of notes: the last month or so has had a strong ridge in the Southeast and Ohio Valley. I wonder if this will break down this winter or maybe it will continue to pop up and help weather disturbances affect the Upper Midwest, as opposed to Mid Atlantic or Southeast

bmJMsWy.gif

 

Other note:

this looks like a cool snake!

 

qUF9w9b.png

 

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Image

Not quite as warm as last year....but pretty close now in Nino 3.4. I think the Jamstec is too cold in the SE, but I'm broadly on board with what it has. A Modoki El Nino (ish) with a neutral or -PDO (colder right by Alaska for SSTs, with a warmer tongue east of Japan. I really struggle with places in the mid-south going from +8 to +12 in October, after a warm September, to a very cold winter like the model shows. The Jamstec is a bit drier than I am in the Rockies (I think we're near to slightly above average, it has near- to below).

Image

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What do you think about this large sector of +2C to +3C in the north Pacific? Will there be a ridge in the Gulf of Alaska for most of the winter?

YuVgtla.gif

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The (relatively) cold backwards C by the Alaskan Coast around that blotch of warmth is a pretty canonical -PDO, especially with the warm waters east of Japan. 2014 was the opposite - super warm by the coast of Alaska, and cold east of Japan. Will the -PDO ish look now last all winter? I kind of doubt it. Just because Nino 1.2 falling below 20.0C in October is a leading indicator that the PDO will fall. It did on the weeklies. But now it looks like it will warm up. So it probably reverses, at least somewhat, by December or January. Even with the El Nino last year, the Nov-Apr PDO only recovered to +0.5 from +0.3 in 2017-18. With a weaker El Nino this year, it could easily be closer to 0. The trend has been down. I think the PDO is weak enough that the SE ridge won't get squashed or destroyed for any length of time, and when the subtropical jet is strong, and the SE ridge is strong, that is the best shot at major storms (cut offs) for where I am, as the two battle it out.

Nov-Apr PDO

2013 0.38
2014 2.07
2015 1.70
2016 1.06
2017 0.30
2018 0.51

Image

With the NAO negative, the winter -PDO correlations seem to work about perfectly for October so far.

Image

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This is what I had for snow nationally in my winter outlook - but I think for Colorado after a quick start there is something of a break until late winter.

JuE8Jyu.png

My snow map was fairly good last year. Montana and Virginia did better than I thought, and I should have had an elevation component for the West last year since the valleys in NM were much closer to average than the mountaintops everywhere.

Ygz7Xbf.png

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Forecasting seasonal snowfall in the CO Front Range other than during strong El Niño and La Niña winters (generally snowy and not snowy respectively) seems to be unusually difficult. What I understand to be your top analog years, Raindance, average out to slightly below average snowfall in Denver but those seasons individually ranged from quite bad to very good.

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18z GFS has 8" of snow and 0.91" of QPF for downtown Denver on Wednesday to Thursday. This is likely a case of the GFS being precipitation-happy in the 120hr-168hr period, but it's worth watching.

12z Euro prediction:

fp8ikSC.png

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Some normal weather last evening changed to windy weather of 30-50mph wind gusts in the Front Range cities. For my area, the greatest gusts were in the middle of the night at about 4:00AM. Currently, DIA has the strongest gusts of the day.

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There is a fairly strong signal in the years I like for a big snow storm around Nov 20 for New Mexico, likely parts of Colorado too. The pattern in ocean temperatures kind of looks like 2004 which I believe had some big storms in November. if I had done fall analogs, 2004 would have made the cut, I just don't like it for winter. 2012 is actually pretty good for Fall too.

November might be something like a blend of 1994, 2004, 2012, 2017, 2018 and then the 2012/2017 will vanish from relevancy for winter from rapid cooling. 1994/2018 will likely fall off too once the MJO match in October wanes a bit. The blend matches reality fairly well for temps - cold West/warm East (and the warmth by end of Oct will be a lot less than now even int he SE like in the blend), and then the West is fairly warm in Nov, with average or slightly wetter than average precipitation.

The blend respects the warm Atlantic, positive IOD, warm tongue east of Japan relative to cooler waters by NA to some degree, with extensive cold on both sides of South America. We'll see. 

Image

 

 

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This is new. I didn't see this on the NWS web page yesterday.

Quote
...HIGH WIND WARNING IN EFFECT FROM 6 AM THIS MORNING TO 7 PM MDT
THIS EVENING...

* WHAT...West winds 35 to 45 mph with gusts up to 75 mph
  expected.

 

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Quote
...WINTER STORM WATCH IN EFFECT FROM WEDNESDAY EVENING THROUGH
THURSDAY MORNING...

* WHAT...Heavy snow possible. Total snow accumulations of 5 to 8
inches possible, with some localized areas seeing up to 12
inches.

* WHERE...The Southern Front Range Foothills and Palmer Divide.

* WHEN...From Wednesday evening through Thursday morning.

* IMPACTS...Travel could be very difficult. The hazardous
conditions could impact the morning commute.

 

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Last night, we had another period of wind gusts of 30-60mph. I was in Fort Collins at 10:00PM and there were some 30mph wind gusts blowing leaves all over the place. There were brief 60mph winds recorded at the west side of Fort Collins.

There is a winter weather advisory for Denver for tonight and tomorrow, with a winter storm warning from the Palmer Divide down to New Mexico border.

NWS forecast for Colorado Springs:

Quote

Rain before 7pm, then rain and snow between 7pm and 8pm, then snow after 8pm. The snow could be heavy at times. Low around 24. Blustery, with a north wind 15 to 20 mph decreasing to 10 to 15 mph after midnight. Chance of precipitation is 90%. New snow accumulation of 4 to 8 inches possible.

The GFS and other models show another cold front and snow for WY and CO on Sunday-Monday.

Our area already has a temperature departure of -2.9F for the month (Denver.)

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1 hour ago, Chinook said:

The GFS and other models show another cold front and snow for WY and CO on Sunday-Monday.

Our area already has a temperature departure of -2.9F for the month (Denver.)

Seems like we skipped Sept and Oct and went right from August to November.

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Today my area was 42 degrees and breezy by late afternoon. I saw a few rain drops out of the first band of precipitation at about 1:00PM. Such things remind me of late November and December in the Midwest. Right now, Denver has 34 degrees and snow with 1/2 mile visibility, with moderate dBz values on the radar.

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A meh event up here, with maybe 2 inches.  Sunday looks more interesting in my part of the foothills.  Curious to hear how Conifer Mtn Man did on last night's snow.  

Regardless, the mountains seem to be off to the races again this year so far.

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The good stuff seemed to stay a bit further south and west than forecast with a pretty sharp cutoff.  MBY got 3" of the 5-8" forecast, yet they got double that 8 miles south.

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The cold front and snow storm system for Sunday to possibly Tuesday looks like it could be more significant than previous runs showed. Previous runs of the Canadian showed a lot of snow, at slightly later time frames. Now the Canadian is bonkers with 1.2" of QPF for Denver. The Euro has 1.2" of QPF for the city of Denver and northwards.

QV7zfrq.png

 

iEHGhj2.png

 

 

MacS9hb.png

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Hoping for a good one -- models seem to be consistent with two waves, with around .4 for each one... With the colder temps ratios will help a bit. 

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Our area has a winter storm watch. I am wondering about this will play out time-wise. The models have a 2nd wave of snow on Tuesday (GFS has this at about 12z-18z Tuesday). Nevertheless, there is a lot to be concerned about.

Quote
...WINTER STORM WATCH REMAINS IN EFFECT FROM LATE SATURDAY NIGHT
THROUGH MONDAY AFTERNOON...

 

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Several inches of snow have fallen in central Wyoming. Areas around here are in the 20s. My place has had light snow. I think Cheyenne may be getting a little closer to 1"

aeEWycz.png

 

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Kind of busting here so far... 2" of light fluff you can blow off your car with your breath. QPF from the NWS went from 0.5" 24 hours ago to around 0.25", and I think we'll be lucky to get 0.2". Maybe the second round on Tues-Wed will be better.

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Snow is continuing here. It's not falling fast. We have over 2" and it has been accumulating on the grass since early afternoon. The radar right now shows there are higher dBz values in south Denver than here. That could sort of mean anything though. With colder temps, radar is not always super good at estimating QPF rates, so that's why you need people to measure and report on road conditions.

D4Kvtuq.jpg

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5" total on my snow board, with a bit over 3" overnight, assuming this round is done. There are spots on my very slow greased-road commute to Aurora that look over 6". Even though there was little wind, there was probably some drifting in spots because it was so fluffy.

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