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Mountain West Discussion


Chinook

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I'm sure it will change with the warm up coming for the East for much of the rest of the month, but for 12.1 to 1.5 its fun looking at how non-canonically this La Nina is performing. Last year, it was wet in the SW, and warm in the NE, but otherwise, fairly canonical, with the warm Southeast and Southwest, and the cold/wet Northwest.

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We had 0.03" of rain today, that damned streak is over. I put a forecast on my Twitter on January 1 saying I expected it to end on Jan 7 - Jan 13, so reasonably happy with that.

We went 96 days without any measurable precipitation. The last time we've had over 0.05" was in September...so you know would still be nice to have a bigger storm, but one thing at a time. My forecast for winter had a dry, but not "historically" dry winter in the West/SW - if the PNA flips as the models are suggesting that may still verify in this area of the world. Its difficult for me to see Flagstaff finishing with three inches of snow instead of 100, or for Albuquerque to finish with 0.03" precipitation, instead of say 0.9" (average is 1.33").

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The European-seasonal forecast from January apparently does favor increasing wetness over time, I guess it can't get any drier huh?

It's kind of interesting for February, since the Canadian trended much wetter for February too in its January update. Historically, a dry Nov-Jan is a strong signal for a wet June here, and the European has that too. We haven't had a wet March in 11 years in the city, I'm assuming that streak ends soon, and I do have a funny feeling about Spring.

UF0eqAS.png

 

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2 hours ago, raindancewx said:

The European-seasonal forecast from January apparently does favor increasing wetness over time, I guess it can't get any drier huh?

It's kind of interesting for February, since the Canadian trended much wetter for February too in its January update. Historically, a dry Nov-Jan is a strong signal for a wet June here, and the European has that too. We haven't had a wet March in 11 years in the city, I'm assuming that streak ends soon, and I do have a funny feeling about Spring.

UF0eqAS.png

 

It does seem like the SW is destined for a wet Feb and March as the PNA relaxes and the pattern overall changes.  The Spring Break ski season could be great for the southern Rockies and hopefully the whole SW.

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After splitting out Springs in non-El Nino years by whether a major hurricane hit Texas prior to winter, I could only find two signals for the SW that held up to any kind of statistical scrutiny:

1) Very wet Marches rarely happen in non-El Ninos in the SW...but if a major hurricane hit Texas before winter, its roughly as likely as in an El Nino winter. Even then, its merely "possible" and not likely. There aren't a lot of major hurricanes to hit Texas, but this does seem to hold up on the difference in proportions test I did. I have no idea why.

2) There will be at least one fairly normal precipitation month in March-May in a non-El Nino year after a major hurricane. This is a 10/10 thing v. 34/49. Normal here is 0.5" in March/April, so I went with >0.39" for the test. Every non-El Nino Spring after a major hurricane had at least one month with >=0.39". It's close to being significant at p=0.05, up to 0.6" or so, but it is significant at >0.3" to >0.39".

DHb9Yub.png

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My area got 2.5" of snow today. It was pretty much a surprise. Global models have had some agreement on a storm system moving into Colorado on Sat/Sun. In general, models have about 0.3" to 0.6" of QPF on Sat/Sun with temps of 25 degrees and possibly a favorable upslope or at least a weak flow at 700mb with -12C. Reasonably good 500 mb trough.

 

MIO8Qp5.png

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5 hours ago, Chinook said:

My area got 2.5" of snow today. It was pretty much a surprise. Global models have had some agreement on a storm system moving into Colorado on Sat/Sun. In general, models have about 0.3" to 0.6" of QPF on Sat/Sun with temps of 25 degrees and possibly a favorable upslope or at least a weak flow at 700mb with -12C. Reasonably good 500 mb trough.

 

This trough looks interesting.  The Cascades look to get crushed.

 

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Global models still have the storm for Saturday/Sunday here - averaging out at 0.3" of QPF for low elevations, more or less (WPC forecast also has this.) This could be a moderate impact storm for the foothills/mountains above 6000 ft. There could be 7-18" of snow for higher elevations, maybe even a decent period of upslope snow on the east side of the Continental Divide.

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I'm a fan of the 3-km NAM, but it isn't in range yet. The GFS had 0.10" to 0.15" for the city, would be the biggest precipitation event here since September if it verified. Lows have been colder than forecast for days now, so if this system has moisture, would expect the drier / colder than initialized air to turn us from rain to snow at the end of the event. But would need 0.10" or more to happen otherwise its very light rain (0.05") to jack.

It took a while with the all-time heat in November, but we're ahead of the pace from last year for frosts and very cold nights (<20F).

Oct 2016 - May 2017 had only three nights <20F, already at five through 1/18/18.

Oct 2016-May 2017 had seven frosts through 11/30, but only 38 through 1/18/18.

We had only two frosts through Nov 2017, but are at 41 through 1/18. So only 31 frosts from 12/1 to 1/18 last year, but 39 frosts from 12/1 to 1/18 this year. 

I had forecast 92 frosts (<=32F lows) for Oct 2017 to May 2018. I'm probably a bit high, but it looked terrible on Nov 30, not so bad now, particularly if it stays this dry.

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NAM and 3km NAM are upping the snow totals in the areas of Fort Collins to Denver. GFS still has in the range of 4". The NWS has not issued a Winter Storm Watch for the most populated areas. Here is their reasoning.

 

 Could see northeasterly
winds gusts to around 40 mph along this axis during afternoon,
namely across Sedgwick, Phillips, Washington, Lincoln and eastern
portions of Adams and Arapahoe Counties. Could see snow totals in
this area anywhere from 4 to 8 inches by evening and with the
gusty winds, areas of blowing snow. Closer to the Front Range,
snow amounts not expected to be as great due in part to an earlier
shut down in snowfall with nwly winds downsloping off the Front
Range during the afternoon. The I-25 corridor may still see
anywhere from 3 to 6 inches by early Sunday afternoon, with the
greater totals in and around the Denver metro area.

 

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Local weather service has 6-10" for the Northern Mountains of NM, although I'd expect locally more than that. This system seems like it could have pretty good wrap around for the mountains. Not expecting much in the city. We usually get 30-120 minutes of rain, or rain to snow with these strong Pacific cold fronts in the city if we get anything. It should be near 60F tomorrow during the day anyway, so the snow will be fighting a fairly warm ground. 

Was doing some math earlier - out of all possible streaks where the same month is drier than average for 10 years in a row, ala March 2008-2017 in Albuquerque, the odds of that happening are 1%, or 1 month in 100 months (8.33 years) should be the 10th year in a row that the same month is dry for that long. This is based on the real frequency of dry-streaks in the 1932-2017 airport era of data for Albuquerque.

That said, the same month being dry 11-years in a row (2008-2018) is much rarer - 0.44%, or one month in 19 years. Since we had an 11-year dry streak in May in 1996-2006, I lean towards this being the "March Year" for the city and southern regions of the SW that has been missing for the last decade. The 7-year dry June streak is in some trouble, as our wettest Junes come after our driest November-January periods here, and we're currently at a staggering 0.03" for Nov-Jan. Odds of neither streak ending, as best I can tell are 1 in 9,239 - up by over five fold from last year, when the June streak nearly ended (0.48", average is 0.61"), and probably would have ended had one thunderstorm moved west by one mile.

The 96-day dry streak here was roughly a 1/7,000 event when it broke, based on all 96-day periods through the day it ended, so I finally, finally have some confidence that one of these months will be wet, since 1 in 9,239 is even less common than 1/7000

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Yes! The first winter storm warning for me (or Denver) this season

Fort Collins-Greeley-
Including the cities of Fort Collins, Hereford, Loveland, Nunn,
Eaton, Fort Lupton, Greeley, and Roggen
524 AM MST Sat Jan 20 2018

...WINTER STORM WARNING IN EFFECT FROM MIDNIGHT TONIGHT TO 2 PM
MST SUNDAY...

* WHAT...Freezing drizzle is expected late this evening and will
  change to snow early Sunday morning. Plan on difficult travel
  conditions. Total snow accumulations of 4 to 8 inches and light
  ice accumulations are expected.

* WHERE...Fort Collins and Greeley.

* WHEN...From midnight tonight to 2 PM MST Sunday.

 

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17 hours ago, Chinook said:

NAM and 3km NAM are upping the snow totals in the areas of Fort Collins to Denver. GFS still has in the range of 4". The NWS has not issued a Winter Storm Watch for the most populated areas. Here is their reasoning.

 


 Could see northeasterly
winds gusts to around 40 mph along this axis during afternoon,
namely across Sedgwick, Phillips, Washington, Lincoln and eastern
portions of Adams and Arapahoe Counties. Could see snow totals in
this area anywhere from 4 to 8 inches by evening and with the
gusty winds, areas of blowing snow. Closer to the Front Range,
snow amounts not expected to be as great due in part to an earlier
shut down in snowfall with nwly winds downsloping off the Front
Range during the afternoon. The I-25 corridor may still see
anywhere from 3 to 6 inches by early Sunday afternoon, with the
greater totals in and around the Denver metro area.

 

It looks like they are counting on 20:1 ratios.  That's pretty high, especially with winds of 40 mph, so I would guess that the potential risk for downside on these totals is significant.

 

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3 hours ago, ValpoVike said:

It looks like they are counting on 20:1 ratios.  That's pretty high, especially with winds of 40 mph, so I would guess that the potential risk for downside on these totals is significant.

 

From NWS AFD late this AM, GFS and EC were talking about 0.5" QPF. 18Z GFS points to about 0.4" and latest WPC (it says 00Z but it isn't even 00Z yet) has a range of 4.5-9 inches of snow, so 5-6" for the Denver Metro still seems about right. I'm going to go wash my car for good luck.

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If we get 0.02" here from this storm, it becomes our wettest month, at 0.05" or more, since September.

Weatherbell apparently thinks February will be a blend of 1996 & 2011, via the daily update the other day. Feb 1996 was insanely warm here, and Feb 2011 had our second coldest day in 125+ years of records, with a low of -7F and a high of +9F. It may not be too crazy, some of the long-term looks on the models favor a "mother of all cold shots" look for the middle of the US in early February....but it is fantasy range.

 

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We are getting some pretty decent snow here. We probably have 2" on the ground. There's 1/2 mile visibility at the airport. I am not entirely sure this is all going to get up to 6" though. I think a lot of the area had freezing drizzle before it starting snowing - around 10PM.

My GRLevel3 program is not getting radar data off the internet!

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