Forecast discussion:

Note: I’m nearing the end of my two week family camping trip.  My available bandwidth is very low so I’m keeping posts shorter than normal and less graphically intensive.

We are clearly in the where’s-the-monsoon-moisture? time of year.  The giant upper air ridge and high center (Figure 1) are parked almost on top of Longmont Tuesday.  It won’t move far by Wednesday, explaining the 100°F + temperatures. Remember, we average one 100°F + day every other year… so we’ve really hit the heat hard this year so far.  I’ve indicated the tropical moisture flow as dark green arrows.  The circulation around the high is pushing it all to the south and up into the west and over us to the north.

This high is also stirring the smoke from various Western U.S. fires making the skies mildly milky.  This probably won’t clear out in the near future.

You can see the above mentioned moisture as the grey and white colors in Figure 2 – the water vapor satellite image. The change that is coming over these two days comes from the high migrating eastward and the moisture plume bending eastward with it to give Colorado cooler temperatures and chances of thunderstorm rainfall.  Thursday and Friday will see a chance of storms statewide, but no severe weather is predicted at this time.


Figure 1: The 500mb upper air analysis for Tuesday PM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 2: the water vapor satellite image from Tuesday PM. Reds/Oranges are dry air, greys/whites are moist air regions.
Figure 3: The forecast precipitation map from the GFS and NCEP for Friday morning.

The longer range forecast:

After cracking 100°F early week, we cool to around 90°F (just a bit above average) and thunderstorm chances return.  Saturday looks dry and hot again (as the plume moves east of us briefly) then the moisture rocks back to cover Colorado early next week.

Figure 4: 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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