In Brief:

We have two more warm/hot (for this time of year) days to go – Tuesday and Wednesday. A very power front blasts down the Front Range around 5pm Wednesday and the temperatures drop. Rain will form behind the front and change quickly to snow. The Longmont snow total (ignoring melting) will be about 1-3 inches. Banding of snow could double this range if we are ‘lucky.’ We’ll spend about 30 hours below freezing dropping to a low Friday AM of 13F or lower. We will be about 33F below normal on Thursday. We snap back to the 60’sF for the weekend and beyond.

Forecast Discussion:

What a beautiful day Monday was. It will be more beauty-fuller Tuesday and the first half of Wednesday. Some locations will approach 80F around the Plains with dry winds creating some fire danger in the mountains.

Our next storm is visible gathering its icy clutches in western Canada (Figure 1). By Wednesday AM the front has blasted down through most of Wyoming (Figure 2). We’ll be some 12-15F above normal Wednesday before the cold air gets here (Figure 3). Can you see the front entering at the top of the graphic?

The Longer Range Forecast:

This big storm is powered by an amazing trough – red line in Figure 4. The front arrives around 5pm Wednesday followed by a brief chance of rain before the change over to snow occurs. Some folks along I25 may see snow first (Figure 5). We should see about 30 hours with temperatures below freezing from Thursday early morning to midday Friday.

With the jet stream roaring overhead – there will be snow bands forming. The computer models pictured won’t get the exact location of the banding right (thin red lines I’ve added), but the approximate spacing and existence of banding is well indicated.

The GFS – Figure 6 gives us about 2-3 inches.
The GEM – Figure 7 gives us about 2-3 inches.
The NAM – Figure 8 gives us about 2.5-3.5 inches. gives us 1-2 inches.

A part of the story that can’t be ignored is the bitter cold. By far the coldest we’ve felt in a long long time. Friday AM could be in the single digits on locations in the Plains and up in the mountains. We should be about 30-35F below normal on Thursday alone (Figure 9). Get everything ready!

Figure 1: The forecast surface map for Tuesday morning/midnight from NCEP.
Figure 2: The forecast surface map for Wednesday noon from NCEP.
Figure 3: the surface temperature anomaly (departure from normal) from the GFS for Wednesday noon from
Figure 4: The 500mb forecast upper air analysis for Thursday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 5: the graphical forecast for the next 10 days for Longmont, CO from
Figure 6: The forecast snowfall totals for the next 5 days from the GFS and weather5280com for Colorado made Monday noon.
Figure 7: The forecast snowfall totals for the next 5 days from the GEM and for Colorado.
Figure 8: The forecast snowfall totals for the next 5 days from the NAM and for Colorado.
Figure 9: the surface temperature anomaly (departure from normal) from the GFS for Thursday noon from
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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 – . 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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