Forecast Discussion:

The stage is being set for our storm (I’ll still use the word loosely, but I’m excited we’ll see cloudy skies and falling water soon). Figure 1 shows the low tonight forming in SE Colorado and a hint of moisture being drawn in from the Pacific (purple arrow). The first snows are hitting Utah, Nevada and spots in Western Colorado already.

By tonight, the upper air trough is in as far as western Arizona and western Utah (red line in Figure 2).

The timing of the storm, from weatherunderground: precipitation will start in the morning Friday, before sunrise. The peak precipitation occurs late morning into late afternoon with showers tapering off into the evening (Figure 3).  Again, it should be all snow with temperatures not getting far into the 40’sF early in the day.  It may not stick on pavement and bare ground at first.

The GFS ensembles are in much more agreement that this period of precipitation will hit on Friday (Figure 4) and have temperatures only in the upper 30’sF at the start of the precipitation period. Even the model (7! Timer) used for astronomical purposes has snow falling after 8am and by 11am (Figure 5).

The totals are still light though, the GFS (Figure 6) gives Longmont 1/10th inch to 1 inch of snow over the next 5 days (this storm is it). The NAM (not shown) has more like 2-3 inches building up.  The weatherunderground model (Figure 3) keeps us in the trace to coating area.

Figure 1: The forecast surface map for Thursday PM. From NCEP.
Figure 2: The 500mb forecast upper air analysis for Thursday PM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 3: a snippet of the graphical forecast for the next 10 days forecast for Longmont, CO from
Figure 4: 10 day meteogram from for DIA.
Figure 5: the next 3 days forecast of sky conditions and precipitation showing snow beginning Friday 8-11am.
Figure 6: The forecast accumulated snow map from the GFS and for Colorado, for the next 5 days (through end of weekend).

The longer range forecast:

Temperatures return to the 50’sF and things dry out in the long term.  I don’t have much to say about that beyond that!

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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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