In Brief:

We have temperatures a touch above normal through Friday – and dry. Our next storm system begins to dump a prolonged period of snow on the mountains starting today (Thursday) but snow doesn’t begin to fall until later Friday night. We’ll see a snowy weekend (Saturday and Sunday) but with only moderate accumulation. Next week starts very cold – the thaw will be delayed.

Update 12/12 at 12pm:

Just a quick check-in looking at the snow this weekend. Even it isn’t a lot of snow for Longmont, it will be cold and wet from late late Friday night through late Sunday night. The GFS (Figure 1 update) is trending towards more snow for all in Colorado. We are up to 2-3 inches expected for the weekend. Daytime highs will still make it to the mid-30’s so it isn’t the best for accumulation. It may be more a wet snow that melts as it hits the ground for a while before building up. Old snow surfaces will see the full snow depth. You will really notice the winds on Friday – tie down your Christmas decorations!

The CMC still puts Longmont in the 2-3 inch zone. The NAM, on the other hand, seems to make down slow flow the rule and we get no snow (or rain) at all (not shown). This is an interesting weekend to watch!

You will really notice the winds on Friday – tie down your Christmas decorations!

Figure 1 update: 10:1 (snow to liquid) snowfall totals through noon Monday from the GFS and weather5280com for Colorado made Wednesday afternoon.

End 12/12 12pm update.

Forecast Discussion:

A juicy low level pacific flow with strong jet stream flow aloft plus three significant short waves will bring winter weather back to the state (Figure 1). I still have snow in the yard and ice on the street out front.

Snow starts today (Thursday) with strong winds and a short wave number 1 (Figure 2) up in the mountains. Snow will continue to fall for almost the next 100 hours up high and out west. Longmont makes it through dry (even if it is very windy Friday) until Friday night when the second short wave moves by and up slope flow begins east of the Rockies.

The Longer Range Forecast:

The precipitation begins in the evening Friday (Figure 3) with snow showers moderate at times and light at times from later Friday night through late night Sunday.

By the end of shortwave number 2 (see figures 2 and 3) there is 1 to 1.5 feet of new snow in the higher mountains. From the NAM (Figure 4) we may have a coating up to 1 inch.

For all three shortwaves – the GFS (Figure 5) gives us a coating to 1 inch with over 1.5 feet of snow over a broad stretch of the mountains.

The GEM – for all three waves – is more bullish with 2-4 inches of snow for Longmont and 2 feet of snow up in the high country (Figure 6).

Fantasy Christmas Snow Watch:

Figure 7 is the closest snow of any kind before Christmas that the GFS is printing out. This time there are a few very light snow showers here and there across the state Christmas Eve evening. Here’s hoping!

Figure 1: The forecast surface map for Friday morning from NCEP.
Figure 2: the graphical forecast for the next 10 days for Estes Park, CO from weatherunderground.com
Figure 3: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 4: 10:1 (snow to liquid) snowfall totals through Sunday morning from the NAM and weather5280com for Colorado made Wednesday afternoon.
Figure 5: 10:1 (snow to liquid) snowfall totals through noon Monday from the GFS and weather5280com for Colorado made Wednesday afternoon.
Figure 6: 10:1 (snow to liquid) snowfall totals through Monday noon from the GEM and tropicaltidbits. com for Colorado made Wednesday afternoon.
Figure 7: The 6 hour precipitation type forecast for Christmas Eve evening from the GFS from tropicaltidbits.com
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John Ensworth works from Longmont as the Principle Investigator for the NASA Science Mission Directorate Earth and space science education product review through the IGES (The Institute for Global Environmental Strategies – www.strategies.org) . He is in his 14th year running this review. He is an astronomer (from the 2nd grade onward) and became a meteorologist (in the 5th grade) when a thunderstorm in Arizona rained on his telescope when the weather service had only forecasted a 10% chance of rain. He has college degrees in physics and astronomy and climatology and a graduate degree in meteorology and earth science. He lectures at the Little Thompson Observatory in Berthoud, the Estes Park Memorial Observatory in Estes Park, and for a number of online universities. He built and runs a backyard observatory near Pace and 17th in northeast Longmont where he has lived for 8 years with his wife, daughter, son, and two cats. Invitations to open house nights at this observatory, LTO, and EPMO will be posted with future discussions when they are scheduled. Forecasting severe weather and snow amounts via text lead to this column. He began texting friends about the weather right after the September 2013 flood. The readers of this column will, hopefully, keep him honest in what he ‘thought’ he had forecasted for ‘the most recent’ storm.

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