In Brief:

Beautiful warm weather is the only story through Monday. Then a trough and cold front move in. We cool 20-30F starting Tuesday and rain (and possible snow) continues off through next weekend – and beyond.

Forecast Discussion:

High pressure at the surface (Figure 1) and a ridge aloft (not shown) mean mostly clear skies and warm temperatures in the 70’sF this weekend (Figure 2). This is an excellent time to get out and play.

The Longer Range Forecast:

As advertised for days now, a strong cold front (blue front line in Figure 2) arrives Monday afternoon/evening. The trough is so large that it has other troughs in it (Figure 3). This is a big, slow-to-change pattern change. Temperatures drop and mountain snows resume. Higher elevations will see a foot or more before next weekend.

From Tuesday to Sunday, the weatherunderground.com model (Figure 2) gives Longmont about 2 1/4 inches of rain. The GFS (Figure 4) now gives us 2 inches (a big jump up again after yesterday’s run, more like the output a day before). The GFS still doesn’t give us snow, but the GEM still has about 1-2 inches over this time period (not shown). We’ll keep tracking rain and snow totals as the weekend passes.

Figure 1: The forecast surface map for Saturday PM from NCEP.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 3: The 500mb forecast upper air analysis for Tuesday PM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 4: the forecast accumulated precipitation map from the GFS and weather5280.com for Colorado,over the next 10 days.


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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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