Forecast Discussion:

The giant trough continues to be trough-y. That is keeping us cool. There are smaller short-wave troughs embedded the flow that will kick down cold fronts of various strengths through the weekend (red lines in Figure 1). A cold front came down Wednesday afternoon and weak up-slope and lift may drop a bit of snow along I-25 Wednesday PM into Thursday AM. Figure 2 shows the midnight scattered showers and front nearby. Figure 3 shows the main storm off to the east by noon today (Thursday).

Figure 4 is the HRRR model for the 15 hours up to 5 a.m. Thursday. There are a couple of bands of snow out on the plains, but not much of note around Longmont. Figure 5 is the GFS for the next 18 hours (through Thursday AM). It shows snow closer to Longmont, but there isn’t much.

Figure 6 is the the 10 day graphic from the model, and it gives  only a small chance of rain overnight.


Figure 1: The current 500mb upper air map for Wednesday evening from NCAR/UCAR.
Figure 2: The forecast surface map for Thursday AM. From NCEP.
Figure 3: The forecast surface map for Thursday noon. From NCEP.
Figure 4: The forecast accumulated snow map from the HRRR and for Colorado for the next 15 hours. Longmont is the pink dot, as always.
Figure 5: The forecast accumulated snow map from the GFS and for Colorado for the next 18 hours. Longmont is the pink dot, as always.

The longer range forecast:

There is another front that passes on Friday that keeps us cool. The weekend storm may come from two short wave troughs that extend precipitation chances through Monday. More on that later!

Figure 6: the next 10 days of the graphical forecast for Longmont, CO 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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