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Chinook

Mountain West Discussion

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From a Larimer County Emergency Services text today with county snow totals:

S: Winter Weather Update 11/26/2019 11:07am Winter Storm Update 11/26/2019 11am - Latest radar shows that the current storm system should be moving out of Larimer County in the next hour or so. Road crews are working to catch up in all cities and the county. Big snow in western parts of Larimer with Red Feather and Stove Prairie winning the award with 32" of snow. 

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4 hours ago, MidlothianWX said:

Snow has completely finished here in Boulder. I measure 21" IMBY but the official COOP station right up the road appears to have at least 22" - we'll have to wait for their final report. Looks like the Euro was pretty much dead on with QPF, down to the hundredth of an inch.

This is a top 5 or 6 storm for Boulder since the modern COOP station went up in 1990. This is also likely to be a borderline top 10 event all-time. What a fun ride it was - probably the 2nd most I've ever seen IMBY.

@donsutherland1 I thought I would tag you, as I know you pop in here from time to time. Didn't want you to miss this!

Rbd8H6d.png

Many thanks for tagging me. It was an exciting event for Colorado and it will be interesting to see the storm as it continues to track eastward.

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The upcoming western US storm will hit New Mexico, and western Colorado. There is more uncertainty regarding the impacts in the northern Plains, Wyoming, and Montana mountains. Things are always complicated in New Mexico. What's not too hard to understand is the San Juan Mountain range (CO) getting heavy snow with southwest flow aloft. 

If you are interested, there is a 975mb low moving onshore near Eureka CA/ Southwest Oregon, with some wind gusts of 50-60mph close to the coast and snow starting to hit mountainous areas.

odhhs2j.png

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I went with 0-3" <5200 feet, 2-5" 5200-5600 feet, and 3-7" 5600-6100 feet in Albuquerque. It's a wet bulb storm for us in the city, we'll begin the day with temps in the low 20s or high teens (thanks for the cold dry air), before warming to the high 30s or low 40s, then the rain starts, but the sunsets, the dew point rises, but it cools the air as the moisture evaporates. Window for Albuquerque is likely 8 pm to 4 am for accumulating snow if you buy the 3-km NAM. Higher areas will start out earlier and last longer. But it's a 16 hour precip event before the next storm, and something lie 8-12 hours of it should be snow for the city. But, it is complicated here. I generally like this setup though, we had very low dew points in Feb 2015 at the surface, and then subtropical moisture moved on top of it. The subtropical warmth won, eventually, but first we had 6-12 in the city, 2/26-2/28. It's not super different from this setup.

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Every run of the models seemed to get better and better for this area. There were a couple of weird model runs, but not too many. Inaccurate predictions of snow sometimes just happen, but this time, the NWS Watches/Warnings were pretty decent.

The first banding started on the east side of the Rockies at about 12PM - 2PM on Monday. Then I started to notice snow at 2PM. It was steady snow. I noticed 6" or more by 8PM, 10 to 11" by 10:30PM. At 9:30 PM, the radar was starting to fill in for Denver. Some snow banding was just north of Denver started in after 6:00PM, though. I measured 16.0 - 16.5" by Tuesday morning.

Not many storms have produced 1" per hour for so many hours. Many storms around here seem to be 5-6" in several hours, usually a night time. Some storms last 9 hours, with a band that is north of a cold front. Not a lot of storms have stronger 700mb easterly winds like this one. It's weird though, because this wasn't much of a closed circulation at 500mb, but did have that closed circulation at 700mb. I don't know how this one pulled in the Pacific moisture just right. 

There has not been a 12" storm in Fort Collins since February 2nd, 2016, if I remember correctly.

 

watches, warnings, advisories

UjYTwvi.jpg

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I had 3.5" with the New Mexico storm by 10:50 pm on 11/27 in my backyard, about 10-miles due north of the airport site, at the same elevation.

As of 1:30 am on 11/28, I'm up to 5.0". Airport in Albuquerque has had 0.19" fall as snow with temperatures between 28-32F the entire time. I think they're probably around 2.3" so far.

The cold dry air has really held it's own so far. We went from 37F / 14F dew point to 32F / 25F dew point in an hour flat from 6 pm to 7 pm. 

 

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A large area of the Dakotas, Minnesota, and Wisconsin got more than 12" of snow yesterday and today. Some western areas had blizzard conditions. Cheyenne and areas near me had a ground blizzard. Winds gusted to 60-70mph at Cheyenne, Wellington CO, the Boulder foothills, the open plains of Colorado, and western Nebraska This created ground blizzards. Around here, we had winds to 20 mph winds gusting up to 42mph yesterday, which created snow drifts that made new ice on the sidewalks and streets.

WX1N3jp.jpg

 

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My basic idea for December for New Mexico & Colorado & West Texas is that the storminess of November dies off somewhat, but we still finish wetter than average, with temperatures probably not that far from average either way, despite impressive cold at times later in the month.

In recent El Ninos, the US temperature pattern for Oct 16-Oct 31 has tended to become the December temperature pattern nationally, but shifted somewhat East. We had near to record cold in that period this year. My objective high temperature & precipitation matches for the July-November period include six very cold Decembers locally, including the record and near record cold of 1943, 1952, 1953, 1992. Only 1939 was warmer than normal, and that was the weakest of the ten objective matches.

Objective matches for the subsurface in the Tropical Pacific, years with a big warm up Sept to Oct, and then a cool off in Oct to Nov also support somewhat cold temps in the SW. Additionally, if you blend all years when Nino 4 is above 29.3C (there aren't too many of them) in Fall/Dec, the composite looks a lot like the map below. The top SOI matches for Sept-Nov also look like the map below. Years with positive NAO readings in December. 

Image

I do expect the pattern in early November to repeat at some point later in the winter - probably January, but its worth remembering most of the severe cold was destroyed pretty quickly.

Image

It's obviously amplified, but the very warm coast/colder middle thing repeated last Nov 1-15 in January. It's just it came in much more severely, even though it was similar spatially.

Image

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I should say, I don't actually expect the tropical forcing map I posted to verify for December - it's just what you get from blending the years that match. I think my blend of 1953 (x2), 1983 (x2), 1992, 1995, 2009 (x3), 2018 should hold fairly well. November behaved, with the warm West look, and a colder East. I did warm up the raw blend 2F because my blend is too cold in Nino 4 - around 28.6C and it's close to a degree above that.

Anyway, snow pack is good here too:

Image

PDO still looks somewhat negative to me with the warmth east of Japan and NOT by Alaska & Canada on the immediate coast.

SOI has been going positive past couple days - have to watch that. First time we've had two positive days above +4 in six weeks I think.

Image

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That system has SOI support - I think it may drift south from where it is depicted currently by 12/15 though. But you had a big SOI drop 12/3-12/5. So there should be something in the "SW domain" - I  look for a low between 30-37N, 103-118W after those big drops.

Snow pack / precip generally has been very low in Washington and SW Canada - part of me thinks that will snap hard the other way later, probably sometime in Feb-Apr if it happens.

Image

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