In Brief:

Light rain will change to snow later this evening and snow will fall, now and then, through early afternoon Thursday when temperatures warm enough to turn it back to rain. We warm up and dry out by the weekend with nice weather most of next week.

Forecast Discussion:

The surface map for Thursday AM (Figure 1) shows a big shield of snowfall over most of Colorado. Light rain should turn to snow about 9-10pm with snow showers continuing until around 1pm Thursday.

Longmont should pick up about 0.25-0.50 inch of water over the next 48 hours (Figure 3). For snowfall, the GFS gives us about 1 inch of snow (Figure 4). The HRRR model (which only runs through 4am Thursday – Figure 5) does not give Longmont measurable snow. The forecasters at are giving us 0-2 inches (Figure 6).

I’m calling for 1/2 to 3 inches on grassy cool surfaces (including elevated bridges and overpasses).

The Longer Range Forecast:

The storm pulls away (to the south and west!) Friday morning (when a bit more snow might fall – but not much to measure). We warm to the 70’sF by the end of the weekend and have nice weather on into next week. We’ll look at afternoon storm chances in a future post.

Figure 1: The forecast surface map for Thursday AM from NCEP.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from
Figure 3: the forecast accumulated precipitation map from the GFS and for Colorado,over the next 2 days.
Figure 4: the forecast accumulated snowfall map from the GFS and for Colorado,over the next 2 days.
Figure 5: the forecast accumulated snowfall map from the HRR and for Colorado up to 4am Thursday.
Figure 6: the “hand drawn” snowfall forecast map from the forecasters at
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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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