Atmospheric River (Wednesday PM update)

Wednesday, November 28, 2012 at 9:37 am

Wednesday PM update:

Got a good look at 12z Euro guidance and 18z GFS just to help us fine tune the 3 waves of this storm we wrote about this morning. Tonight’s wave might bring a few showers to the Idaho border. Friday night’s wave is looking a bit better so maybe a few inches will be possible, especially north of I-80. Continuing to gain confidence in the late Sunday/Monday system as well. It’s fast moving and lacks great dynamics, but it has truly insane amounts of moisture to work with — so it could very well be a significant event for the Wasatch. I’m praying this works out and Monday will be a first true lift-serviced powder day of the season. Think snow!



The Atmospheric River, or firehose, as I referred to it the other day, is taking aim at northern California today. NorCal is getting itself ready for one of the more impressive rain storms of the last few years. The atmospheric river is a moisture plume, usually with tropical origins, that gets funneled over a specific area creating a river in the atmosphere (duh) of very moist air that can drop intense rainfall or high elevation snowfall. We are a bit too far from the Pacific and from the Low pressure system that is powering this river to see much of the effects. North and especially west of Utah will see the majority of the precipitation. GFS model has depicted 5-day storm totals of up to 15″ of rain in places of Northern California. We think that is overdone and the EC isn’t quite as robust. But even 10″ of rain will cause some flooding issues. If you’re wondering what that means for skiing in the Sierra Nevada — it means lots of precip, but very high snow levels. Above 9,000 ft in the Sierra, there will be a lot of snow… some 3-8 feet. However, between 7K – 9K feet, it will be a gross fluctuation between rain and snow. Lots of slush!

Over here in Utah, we’ll watch as three impulses rotate around this low. The first one will move well to our northwest late today and tomorrow. It won’t bring anything in the way of rain or snow to Utah. But it will increase winds today and scour out the valleys which are mildly inverted.

The second wave is timing itself for late Friday into Friday night, this one will move a little closer to northern Utah and therefore bring more clouds and a chance for valley rain and snow above 7,000 ft. Best chance will be closer to the Idaho border. Most likely scenario — we’ll only see an inch or two of wet snow for Saturday morning. Winds on Friday ahead of this system will likely be very strong.

The third and final wave from this series is scheduled for late Sunday and Sunday night into early Monday. This is the strongest wave of the three and it is progged by all models to track the farthest south. GFS/GEM/GFES all bring a good open wave and cold front into Utah, allowing for decent snow accumulations. The EC is farther north and would only give us light accumulations. But we think the GFS has a better handle on this system as it’s been very consistent for about 5 runs now. Northern Utah will likely see snow starting Sunday afternoon with snow levels at about 7,000 ft initially. As the cold front moves through Sunday night, snow levels will fall to 5,000 or possible lower. This will create a nice layering system with wet base and lighter on top. Monday could be a good powder day if you’re able to take the day off work. It’s a bit early to start talking snowfall totals, but it looks like moderate amounts to me, that usually means anywhere from 4-18″, which is a huge range. So we’ll probably just have to fine tune it as we get closer. I think 6-12″ is more likely. Again, a bit too early so we’ll make a formal prediction in the next couple days.

After Monday of next week, we’ll clear out for at least a couple days. GFS has been trying to build a ridge off the west coast, which would develop a trough in the Great Basin and Northern Rockies if the ridge retrogrades westward enough. If this occurs, we might see a series of quick-hitting systems starting the end of next week. This is all far out, so we’ll address this again later when it moves within range.


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3 thoughts on “Atmospheric River (Wednesday PM update)

  1. Steve

    Looking forward to seeing some snow on webcams. Looks like NWS came around to your way of thinking about this storm.

    1. wasatchsnowcast

      We’re looking forward to skiing fresh snow! NWS is usually on top of it weather-wise, but since they are a government agency, they can’t just got around spewing hypotheticals like we can. One of the great things about running our weather blog is that we can discuss the possibilities and leave the solid facts to the NWS. Sometimes those possibilities come to fruition!

  2. Pingback: Snow Coming to the Blog

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