Forecast Discussion:

Snow has fallen most of the day Wednesday with some accumulation on cold surfaces before sunrise and again in the afternoon when snow rates increased. We had enough moisture to create puddles! (Take that GFS, you were wrong.)

The surface map shows one front passing back to the east while a cool air mass is still pushed down to the south. When there is a front over the state, we can see up-slope flow and showers from passing upper level short waves. Rain chances don’t vanish today even though things warm up and dry out a bit (Figure 1).

We approach 60°F tomorrow/Friday, then the next system sets up…

Figure 1: The forecast surface map for Thursday p.m.. From NCEP.
Figure 2: The 500mb forecast upper air analysis for Saturday a.m.. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.

The longer range forecast:

Our next cold front enters the state Saturday afternoon after about 3 p.m. Before that, we’ll have a high up at about 60°F again. Temperatures keep dropping through the night to drop below freezing before midnight. Temperatures won’t go above freezing again until about 11 a.m. Monday. With that front, very cold air (a high of 30°F on Sunday!!), we are expecting more snow.

The GFS (Figure 3) gives us about 4-5 inches.

The GEM (Figure 4) gives us 4-5 inches.

The NAM (Figure 5) gives us 1-3 inches (up through midnight Sat-Sun, so not the whole storm).

The weatherunderground model gives us 2-6 inches. It seems like a consensus!
Prepare for a Saturday p.m. to Sunday snow.

Figure 3: The total snowfall accumulation from Wednesday p.m. up to noon Monday from the GFS model and weather5280.com
Figure 4: The total snowfall accumulation from Wednesday p.m. up to noon Monday from the GFS model and weather5280.com
Figure 5: The total snowfall accumulation from Wednesday p.m. up to late night Saturday from the NAM model and weather5280.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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