Update 1pm:

With plenty of moisture brought in on easterly flow behind this morning’s weak front – and daytime heating getting under way – there is a marginal risk of severe weather just along I-25 and to the east. Hail and high winds are the most likely threat – tornadoes will occur further east and to the distant southeast of our quarter of the state.

Figure 1 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK.

End 1PM Update.

In Brief:

A wind shift (weak cold front/gust front) arrives in the morning Monday followed by a larger cold front later in the afternoon. Rain chances increase and continue through Friday with some chance of morning/night time snow Wednesday AM and Thursday AM. Some rain chances continue on off to the middle of the month each day.

Forecast Discussion:

Our first taste of north winds arrives earlier than expected today. This will cut off what could have been 80’sF to just the upper 60’sF. This is a lot cooler than our forecast last week. The front is backing up against the mountains today (Figure 1). There are a number of surges of cold /cool air (blue lines in Figure 2) that will keep rain chances very high and even snow chances possible in the early mornings.

You can see the easterly flow bringing in the water by Tuesday morning (Figure 3). It is time for that water proof coat/umbrella.

The Longer Range Forecast:

By Wednesday morning, there is a huge trough over the western U.S. and many short waves to keep the moisture flowing and instability over the region (Figure 4). We will be cloudy for days.

The 5 day precipitation total from the GFS (Figure 5) stands at about 1.25 inches. Snowfall from the GFS (Figure 6) is confined to the foothills and mountains – but it will come very close to town and I-25 including Denver and Ft. Collins. The GEM (Figure 7) does give us a trace to an inch of snow now. We’ll watch for thunderstorm chances, but with a cooler lower atmosphere, instability will be low around here.

Figure 1: The forecast surface map for Monday PM from NCEP.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 1: The forecast surface map for Tuesday AM from NCEP.
Figure 4: The 500mb forecast upper air analysis for Wednesday morning. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 5: the forecast accumulated precipitation map from the GFS and weather5280.com for Colorado,over the next 5 days.
Figure 6: the forecast accumulated snowfall map from the GFS and weather5280.com for Colorado,over the next 5 days.
Figure 7: the forecast accumulated snow map from the GEM and tropicaltidbits.com for Colorado, through the next 5 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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