Mountain West Discussion

[Chinook]

On Wednesday, a 500mb low will develop and slosh around under the blocking scenario. Normally this would be a big storm for us as it would have brought in moisture from the Pacific, but it's kind of a non-event this time.

[raindancewx]

There it is guys - the big wet storm of 12/10/2007, right on time. It actually starts much earlier than this 174 hours in terms of precipitation. The first moisture would be ~150 hours on the Euro from now. This is the last two runs. Was shown on the prior run too.

[smokeybandit]

 

[Chinook]

On 11/30/2020 at 12:11 AM, raindancewx said:

There it is guys - the big wet storm of 12/10/2007, right on time. It actually starts much earlier than this 174 hours in terms of precipitation. The first moisture would be ~150 hours on the Euro from now. This is the last two runs. Was shown on the prior run too.

 

 

Maybe the Euro will bring this storm back. I am rooting for you to have your SOI change prediction come true, and I'm rooting for any precipitation in the Southwest whatsoever.

[raindancewx]

I actually don't think that Euro storm is going to come back as depicted unfortunately. The GFS has had something similar a bit later though.

The SOI thing I've mentioned - that's the systems now. The crash was 11/21-11/23, and the rule is you wait ten days.

It more or less did work as it is snowing across our northern mountains pretty heavily (really squalls with low qpf snow). There is a low over the area in the correct time frame too.
But the NAM and HRRR were hinting at snow even down here earlier today. There is a winter weather advisory out, and the local NWS learned their lesson this time, waiting for the snow to actually develop before issuing an advisory. I want to see how December goes, but I find replicating July-December precipitation patterns is a good predictor for Jan-June. So if this holds up, there is a pretty strong precipitation signal for January here. Each blue period is wetter than average.

The 12/1-12/5 high for the city as currently forecast looks ~top 20 for cold for the past 100 years. So some cold and some snow isn't a terrible way to start of a La Nina down here. I'm much more concerned about the Spring than the Winter for moisture. December has a bunch of ways it can be wet regardless of the outcome the next ten days. 

MJO phase five is usually pretty good in December, La Nina rapidly weakening would be good, another SOI crash could help. I'm a little bit optimistic for March too, just because every year we've seen snow in October in the city has seen snow in March. The years with October snow have all seen storms come through in the time frames we've seen them this year. The weird pattern of a lot of early cold days is unusual too (highs <=55), but it has some similarities to 1936 when I looked.

[raindancewx]

Let's try this again: There was another big SOI crash today. As far out as it is, the three models I look at all have a day ten storm tapping subtropical moisture. Are they going to be right, or even close this far out? No. But...this is the first time they've all had something depicted that far out since the October storm.

Date	Tahiti (hPa)	Darwin (hPa)	Daily Contribution	30 day Av. SOI	90 day Av. SOI
2 Dec 2020	1014.81	1008.05	15.78	8.74	7.73
1 Dec 2020	1014.91	1007.10	21.23	8.99	7.70
30 Nov 2020	1013.51	1006.20	28.18	9.24	7.69

There was an associated SOI drop in this time frame in December 2007 ahead of a big storm.

2007 332 1012.91 1006.95   19.59 (Nov 28)
2007 333 1013.66 1009.50    8.14 (Nov 29)
2007 334 1013.05 1010.90   -4.65 (Nov 30)(-23 in two days)
2007 335 1012.80 1010.30   -6.33 (Dec 1) (-15 in two days)

Ten days later in Albuquerque:

Date	Hi	Lo	Mean	Dpt	HDD	CDD	Precip	Snow
2007-12-10	40	32	36.0	-0.7	29	0	0.49	T	0
2007-12-11	43	33	38.0	1.5	27	0	0.24	0.3	0

Too early to expect anything useful from the models, but it is rare to see something on all three so far out here. The GFS has actually had something around 12/11 for a while already...but I had been ignoring it.

[raindancewx]

The airport of course got literally nothing. But areas north and west of it in the metro did very well overnight. So that SOI crash from 11/21-11/23 did well here. I had a dusting.

[Chinook]

If you are bored with the weather here, a strong trough in Europe is bringing in a moist southerly cloud band, may produce 200cm to 350cm (138") of snow in Italy.

[Solution Man]

18 minutes ago, Chinook said:

If you are bored with the weather here, a strong trough in Europe is bringing in a moist southerly cloud band, may produce 200cm to 350cm (138") of snow in Italy.

I know that area well, East Tirol....the Austrian side, my wife is from there

[raindancewx]

The 12/10-12/12 periods needs to be watched. The GFS, Canadian, Euro all at least have precipitation for NM and CO in that time frame.

[smokeybandit]

GFS has nearly lost that 12/10-ish storm the last few runs

[raindancewx]

You jinxed it.

One for me -

One for Colorado. (I really think the models may try to phase these somewhere).

 

[Chinook]

Every single model run seems to be different, at about hour ~126

[raindancewx]

Once the system is over the waters west of Los Angeles and the models see how much moisture it has, I think you'll see rapid re-conciliation toward one solution. Curious to see what the Euro has in a few minutes though. The members above, 2,3,5,10,11,19 seem about right in terms of that "SOI rule" I use.

Actually think the ICON has about the right idea on the last run, it goes to the Gulf of California, crosses SE Arizona, runs north north east, loses a lot of moisture, but western NM, SW Colorado get good moisture - rain and snow, southern NM gets rain. Then another system comes in with snow but less moisture.

[raindancewx]

GFS and Canadian are different, but the NAM looks like the Euro to some degree. The northern stream system is more of a mess at this point, but still expect some snow for Colorado.

[Chinook]

The models have struggled with some of the features of the upcoming storm system. At this point, there seems to be some agreement that most of CO/NM will get lighter snows of 1"-4" on the mountains, maybe some for Denver. Along with that, some larger precip values will be in SW New Mexico. The main 500mb shortwave will create a low-impact rain/snow event for the Plains/Midwest. At this time, the whole region is falling behind on snowpack, as some higher elevations of Colorado should be getting 30" per month, but that rate of snow is not happening right now. The Canadian/Euro have some more substantial snow for NE New Mexico over to Texas at some on Friday night/Saturday.

[raindancewx]

The GFS run from Tuesday was honestly better for this time frame than runs of the recent days. This is the most recent five day period depiction on the GFS and the Canadian:

The Canadian is probably too optimistic but I like to use it as a "bust up" ceiling for the high end of what is possible. A lot of this is Thursday-Saturday, so not exactly in la-la model land anymore, but the details are still going to change.

 

[raindancewx]

Make it happen Chinook. You guys in Colorado will get at least some snow out of this Thu-Sat period.

[Chinook]

Tonight's No-Accumualtion Model (NAM) is doing the exact opposite: lots of accumulation for Colorado, New Meixco, ansd southeast Nebraska. I think these values are overdone, to some degree.

[raindancewx]

Whenever there is some huge surge of subtropical moisture, my default is the 3-km NAM and Euro will eventually have the right sense of the totals, but not until within 48 hours of the event finishing. Until then, I just assume 0.2"-0.6" of liquid equivalent for the NM valleys for each full day of precipitation until proven otherwise, higher or lower.

[mayjawintastawm]

I was inside but apparently about 2 PM my local airport had a temp of 70 F with a dew point of -8 F. I think that's the driest I've seen it in December here (RH 4%). Gonna have to drag out the hose and sprinkler again, never had to do that with the Xmas decorations up before.

[Amos83]

how is Park City, UT looking in the coming weeks? Trying to get out there to ski before everything gets shutdown again.

[ValpoVike]

12 hours ago, mayjawintastawm said:

I was inside but apparently about 2 PM my local airport had a temp of 70 F with a dew point of -8 F. I think that's the driest I've seen it in December here (RH 4%). Gonna have to drag out the hose and sprinkler again, never had to do that with the Xmas decorations up before.

Yesterday was crazy dry.  My home station dipped to 4% as well.

[beavis1729]

Yeah, very dry and mild.

Denver is currently 64/0, RH 7%...and may dry out a bit more later this afternoon.  Limon is 63/-7, RH 6%.

[mayjawintastawm]

5 hours ago, Amos83 said:

how is Park City, UT looking in the coming weeks? Trying to get out there to ski before everything gets shutdown again.

Check out opensnow.com. Long term forecasts have a paywall but they are as accurate as any. Unfortunately it's looking really dry for the foreseeable future.

[snowfan789]

Actually, I think based on what I’ve seen that Utah may be in for a snowy stretch starting soon. But it has been very dry in the West lately, so there’s a lot of making up to do re: snowpack. I think pretty much everywhere is requiring reservations to ski, so I definitely recommend checking on that before traveling anywhere.

[Chinook]

sunset tonight

I guess our area will get a second (mostly light) snow event from a northwest-flow shortwave on Saturday night. It may start to come in as early as 18z Saturday.

 

[raindancewx]

I find the 3-km NAM is a pretty good model at short ranges, unlike it's exaggerating cousin the 12-km NAM. Pretty good snows depicted for Western Colorado and Northern New Mexico.

 

[Chinook]

I guess we are at the point where the NWS digital forecast contains the snowfall total for both storms, since they are so close together in time.

 

[raindancewx]

I got some more snow today. Very light. The local NWS has a lot of trouble estimating lows, but they do real well for highs. But with subtropical moisture initially moving over dewpoints of 5-10, it isn't surprising we hung out in the low 30s for a while with some snow. This La Nina is infinitely better than the 2017-18 La Nina, when the city had three days with 0.1" or more from Oct-May. We're already at three for 10/1-12/10. No rain or snow in the whole state that December, this is already storm two, and I'd imagine there will be another around 12/19 given the SOI drop, and something will probably come through 12/26-12/30 too.