In Brief:

Upper atmospheric high pressure and dry air keeps things quiet on Saturday. Moisture in place and a shifting of the high center allows for afternoon storms and seasonable high temperatures for many days to come.

1am update 8/6:

A bunch of work and home stuff crowded out the forecast discussion today (8//6) but the story is pretty simple. The high that either blocks the moisture and convection or pumps it into the state is in a no-so-great location for storms Tuesday and (somewhat) on into Wednesday. After that it does drift to the southeast of Colorado again. Moisture will return Thursday-Saturday (at least) and short waves will be able to interact with this moisture to really kick off some better thunderstorm coverage Thursday +. More later!

End 1am udpate.

Forecast Discussion:

There is quite a big blob of tropical moisture over the southwest U.S., (Figure 1) but the high has wobbled over Colorado Saturday which will keep things quiet except for a few isolated thunderstorms up in the mountains and on the Palmer Divide (Figure 2). For Sunday, the high center drifts to Arizona which will allow some afternoon storms to form and drift east off the mountains.

The Longer Range Forecast:

Little changes in the longer range – you can watch the animation of the 500mb pattern and the closed set of circles that is the high (like a mountain with lines of equal elevation) drift this way and that around the southwestern U.S. over the next 5 days (Figure 3). The upper atmospheric relative humidity gives an indication of the moisture flow around this high – the animation in Figure 4 shows blobs of moisture getting pulled into the circulation. Because of this, we’ll see varying amounts of afternoon convection over the next 10 days with peak activity occurring when the high is more distant or to the southeast of us, and when the higher moisture values are in place at the time of maximum daytime heating (Figure 5).

Figure 1: the water vapor satellite image (browns/reds are dry air, whites and light grey is moist air, purple/blue is ice and high cloud tops). From the the Weather Channel from Satruday.
Figure 2: The 500mb forecast upper air analysis for Friday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 3: Animation of the GFS 500mb pattern and anomaly for the next 5 days from tropicaltidbits.com
Figure 4: Animation of the GFS upper air moisture representation for the next 5 days from tropicaltidbits.com
Figure 5: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
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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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