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Mountain West Discussion


Chinook
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Just for fun, I checked the SREF plumes for Fort Collins-Loveland, which have QPF values of 0.44" to 1.90", which could be 4.4" to 19.0" at 10:1 ratio.

The GEFS plumes for GXY (Greeley) have 0.44" to 1.13" which could be 4.4" to 11.3".

Also, just for fun, if you check the SPC web page, the HREF (high-resolution models ensemble) is within range to give a max snowfall amount.

The regular NAM has 0.8" of QPF (Denver) up to 1.6" of QPF (Fort Collins-Loveland).

Let's just say, in my entire time in Fort Collins/Loveland, the best November snowstorms were 7.4" in 2006, and 9.0" in 2011. When I lived in the Midwest, November did not produce this type of snow.

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OK, just as things were getting consistent with around a foot of snow for Denver metro, some models are pulling the plug less than 12 hours before things start, especially in my neck of the woods. WTF?? I can look at GFS, NAM and HRRR. GFS is backing off some (6-9 inches); NAM backing off a bit more (like 5-7), and HRRR keeps the Metro area completely dry through midnight while whacking Fort Collins with over an inch of precip. Jeesh.

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16 minutes ago, ValpoVike said:

Snow ratios are going to be important tonight.  What is the current thinking on that?  I saw NWS discussion of 15:1 +, but that was a day or so ago...

BoulderCAST was saying 15:1 for the most part with periods of up to 18:1. I haven't taken time to look at the soundings though. I'd tend to think you'll get in on some of the upslope action where you are.

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40 minutes ago, MidlothianWX said:

Here is QPF from the 18z NAM for the Front Range:

S3iEDho.png

I know it's the NAM but it's fun to look at. If you are in Longmont/Berthoud right now, watch out. Boulder looks to be just shy of 2" on that. I'm getting really pumped about this one - I haven't seen over 16" IMBY since PDII in 2003.

That’s a huge increase from the last run. Not sure if that’s indicative of a legitimately higher impact than anticipated but it’s sure fun to look at, and last-minute trends can be meaningful. I imagine that’d be a top-five storm for at least Boulder and Fort Collins if it verified.

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19 minutes ago, snowfan789 said:

That’s a huge increase from the last run. Not sure if that’s indicative of a legitimately higher impact than anticipated but it’s sure fun to look at, and last-minute trends can be meaningful. I imagine that’d be a top-five storm for at least Boulder and Fort Collins if it verified.

Yeah, someone is going to get pounded with 2-3" /hr rates and I think the models are just honing in on where the upsloping/convergence takes place. Seems like NE Boulder and SE Larimer are the place to be right now for the qpf max but other factors could cause areas just west to win out.

I lived in the Mid-Atlantic long enough to be NAM'd several times. Will be interesting to see what the 18z runs of the globals do. For Boulder proper, 23" would be top 10 all time and 26" would be top 5.

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8 minutes ago, MidlothianWX said:

18z High Res GFS:

esEEqCW.png

Models seem to like Erie-Longmont-Berthoud for the QPF max.

That’s also a little better than the last run for Denver, but not as dramatically so as the NAM. Still, latest trends = encouraging. Things could still change in the other direction but I think it’s reasonable to be cautiously optimistic at this point.

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46 minutes ago, MidlothianWX said:

Yeah, someone is going to get pounded with 2-3" /hr rates and I think the models are just honing in on where the upsloping/convergence takes place. Seems like NE Boulder and SE Larimer are the place to be right now for the qpf max but other factors could cause areas just west to win out.

I lived in the Mid-Atlantic long enough to be NAM'd several times. Will be interesting to see what the 18z runs of the globals do. For Boulder proper, 23" would be top 10 all time and 26" would be top 5.

In my anecdotal experience, the NAM tends not to significantly over predict in Colorado. That is in contrast to the Nor’easters I used to experience when living in New England.

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7 minutes ago, snowfan789 said:

In my anecdotal experience, the NAM tends not to significantly over predict in Colorado. That is in contrast to the Nor’easters I used to experience when living in New England.

That's good to hear. I've been let down by way too many NAM fantasy maps in the DC/RIC area. Hoping Denver gets solid totals out of this one too.

I wish I knew more about local snow climo, just haven't lived here long enough. From looking at historic "big ones", it appears that the bullseye outside of the upsloping spots is usually somewhere along I-25.
 

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36 minutes ago, snowfan789 said:

In my anecdotal experience, the NAM tends not to significantly over predict in Colorado. That is in contrast to the Nor’easters I used to experience when living in New England.

I know, right?! When I was in SNE it would have stupid high amounts, and here in CO it lives up to its name: the No Accumulation Model.

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Sometimes I'm not sure how the NAM deals with upslope flow when things are less obvious with upslope flow direction and speed. The GFS is more consistent at predicting snowfall amounts near my place.

Anyway, the snow has started here at about 2:00 or slightly earlier. We already have 1" of snow in less than 2 hours. Greeley is above freezing with rain, currently. That will change quickly.

At the end of the storm, I will make a loop of 850mb temps, 500mb vorticity, composite radar, and GFS-6hr precip/SLP.

note: 18z models still have 10-12" at locations of 5-10 mi southeast of Denver, with ECMWF still at 10" (8" on map, but ratios will be higher than 10:1)

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1 hour ago, ValpoVike said:

Coming down pretty good up here northeast of EP.  Nearly 3" so far over about 2.5 hours.  So far so good on ratios as the flake size is good.

It's nearly the same here, the radar shows a max of precipitation here at Loveland, Lyons, and Estes Park.

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