In Brief:

What looks to be the last gasp of Summer occurs Saturday through Tuesday this week. Mostly dry conditions and above normal temperatures will be the story. Temperatures might make it to 90F at least once more (Sunday and maybe Saturday and Monday). Next week we return to normal temperatures (or or below normal) and see rain chances return.

10:30pm Update 9/15:

Things are on track with our forecast with a cool down beginning today! More later today!

End 10:30pm Update 9/15.

10:30am update 9/14:

We are on track for highs around 88F today and mostly clear skies. Go have fun as summer really ends and fall begins (this upcoming week).

As for our tropical system, it did achieve tropical storm strength and was named Humberto last night. The approaching cold front (related to what we enjoyed the last couple of days) will shove it out to sea. Wind shear looks like it will keep much of the heaver rain/thunderstorms tilted off to the east side of the storm, so there will be less impact on much of the Bahamas than we might have seen and almost no effect seen on the mainland U.S. (Figure 1 update). It is expected to at least become a minimal hurricane Sunday afternoon out in the ocean.

Figure 1 update: The tropical storm Humberto 5 day forecast map from the NHC and the NWS.

End 10:30am update 9/14.

Forecast Discussion:

A cool high pressure system sits over Colorado Friday (Figure 1). We are comfortable and dry.

That’s all I’ve got to say about that.

The Longer Range Forecast:

The long-entrenched high pressure center to our south begins to exert its influence over us again through the weekend (Figure 2). We stay much above normal with some 90’sF possible through Tuesday next week. Channel 7’s weather speculated that these might be the last 90F+ temperatures for the year 2019 in Denver. I might buy that.

The next trough (that looks a lot like the hail-maker of Wednesday) passes Tuesday night. We at least get a cold front with this and cool towards normal temperatures (Figure 3). For Thursday, we see a deeper trough entering the West with strong southwest flow over the state (Figure 4). It should be cooler and wetter starting Wednesday.

I’ve put the days of above normal temperature in a red box in Figure 5 and have circled the rain chances later in the period in green. It is a pretty simple picture for now.

Just because the Bahamas don’t need any more difficulties, I am pointing out that an admittedly much weaker, tropical system has the potential to develop over the next day or two in that region. It may get named and threaten many of the same areas as Dorian did. This is currently expected to only achieve tropical storm strength before it gets suddenly shoved out to sea next week when it may reach hurricane status. We’ll watch it if it forms (Figure 6).

Figure 1: The surface analysis weather map from the weather channel.com for Friday late morning.
Figure 2: The 500mb forecast upper air analysis for Saturday PM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
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 500mb forecast upper air analysis for Thursday PM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 5: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 6: The potential next tropical system 5 day forecast map from the NHC and the NWS.
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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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