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Mountain West Discussion


Chinook

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For anyone who saw the Accuweather winter outlook, it had a decent winter for much of the West, excluding maybe S. NM and S. AZ.

Their long range forecaster apparently used a blend of 1960, 1979, 1981, 1983, 1996, 2013, 2014, and 2016, with 1981, 1996, and 2013 each double weighted. I'm not a fan of that blend, 1979 & 2014 were both borderline El Ninos, and most of those years are a lot colder in the Atlantic, and they tend to have high solar activity. More generally, 1983 & 2016 were both after super El Ninos, which tend to have lingering impacts. The PDO is super positive overall in those years too (largely from 2014, 1983, and 2016) which I don't buy for this year.

http://www.city-data.com/forum/weather/2822099-winter-thread-2017-18-northern-hemisphere-10.html

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4 hours ago, ValpoVike said:

Currently it is 60 degrees at my home, and we just had a 5 minute snow shower.  WTH?  I guess the warm air is very shallow at this elevation...

Its rare, but even down here we occasionally get accumulating snow into the upper 30s and 40s. It routinely snows / sticks (on cold surfaces) when over freezing and snowing in Oct/Nov, Mar-May. The record here is supposedly like 47F with snow because it was dry and in the low 30s even 500 feet off the ground.

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Regarding Monday: the 18z GFS has about 0.4" to 0.9" for Larimer County (me and ValpoVike), and about 0.34" for Denver. Some snow and some rain will fall at lower elevations. Have fun with this one, Valpovike. For me, it's too early for snow. Hopefully it's not too heavy for the trees and hopefully the tree colors won't be impacted too much by freezing temps. The cold temps of 15-20F at *exactly* this time of year (Oct 9) in 2009 really killed the tree colors later in that month.

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NWS Boulder discussion

Quote

Each of the medium range models have nearly similar timing with
the arrival of the upper trough Sunday night. Cold temperatuers
and snowfall are expected to continue through Monday as upslope
low level flow continues with the upper trough also remaining over
the state. Snow amounts along the I-25 corridor could be in the 3
to 6 inch range by Monday evening. The combination of gusty
winds, falling snow and local vegetation still nearly in full leaf
will make some highlight necessary.

 

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first winter storm warning for me

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* WHAT...Heavy snow expected. Some secondary roads and bridges and
  overpasses may become snow or slush covered. Plan on slow and
  hazardous travel conditions, including during the morning
  commute on Monday. Total snow accumulations of 4 to 7 inches are
  expected, heaviest amounts near the foothills.

 

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We're in a freeze watch down here. Don't think the city gets to 32F on Tuesday morning, but nice to see - we didn't drop below 44F at all last October. Our first frost is usually right around Halloween. Didn't happen til November 18th last year. Historical range here for first frost is 10/31, +/- 3 weeks, so it was definitely very late last year. These nights in the mid 40s have been nice for the Balloon Fiesta, since we still warm into the 70s during the day.

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The snow packed down a lot with temps of about 34. Maybe we had 2.5" with 0.30" or 0.40" liquid equivalent. The snow rate was pretty respectable, in the sense that a lot of decent sized snowflakes were falling. Fort Collins has gotten about 0.67" combination of rain and snow. There was definitely at least 0.17" of rain.

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Given the lag between Nino 3.4 and the ENSO state, seems like we'll be in a Neutral pattern through December, with the weeklies rising now for three weeks in a row. Neutrals are good for CO snow early... La Ninas are good in the core of winter and El Ninos are good in Spring. So if we switch to more of a La Nina base in Dec-Feb, could be a pretty good Oct-Feb for snow in CO.

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We only received 7 inches up here, and the roads stayed relatively clear.  I was down in FoCo much of today for meetings and it seemed to melt as fast as it was coming down, which is great news for the trees given the apparent high water content.

Edit: I checked my weather station rain gauge and it shows .99 inches, which would be 7:1 and is very close to Chinook's estimates.  This puts me at 18.05 inches for the year and a realistic shot of closing over 20, which would be in excess of 20% over what limited climatological data I can find.

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On 10/10/2017 at 2:15 PM, beavis1729 said:

Laramie WY dropped to -2 this morning, shattering the old record of 7 set in 2009.  Records go back to 1948.

This has to be Laramie's earliest sub-zero temp on record...or close to it.

A lot of years with 0F or lower readings by Oct 31 were used in my winter forecast - nice to see! I was considering using 1985-86 but the Atlantic was frigid that winter. 1970-71 came up as a 'Summer Conditions' analog. Used 1996 as a main analog. 2002, believe it or not came up as a similar Summer analog too. 

xG8Qybn.png

 

 

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I guess Rapid City, snow-wise, is kind of a mix between the very snowy northern Black Hills (north wind blizzards,) and normally dry western Dakotas. And when I say normally dry, I mean the western half of the Dakotas, (Black Hills excluded) have relatively low amounts of snow and rain, although the snow could last a long time.

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Just a bit of amplification in the pattern this month. The look so far is actually not super far off from what I put out what for winter, but I think it relaxes/reverses at times, and its further south as the cold air builds. We shall see. Pretty sure Nov is going to be quite warm for much of the West though.

 

DMN8Sn-VoAA5NHD.jpg:large

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Last year, the La Nina was starting to peak about this time. With cold Neutral conditions for the moment, Nino 3.4 is way warmer than last year. The changes y/y resemble a Modoki El Nino, although the tropical Pacific is cold overall in absolute sense.

Atlantic is colder near the US - always a good sign for wetness/moisture out here.

hI7YOOT.png

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Moderate to strong La Nina years:  (see list of years.) If you composite these temperatures vs. the 1981-2010 normal temperatures, you find below normal to normal temps from Los Angeles to Denver. That does not mean that all these Southwestern areas have above normal precip; they do not. North Central and West Colorado climate divisions average above normal precip, but most of the Southwest is below normal. The upcoming winter is not necessarily a strong La Nina-- it hasn't even formed into a La Nina yet.

bPgF0Wd.png

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