Forecast Discussion:

We have just about everything to discuss today- except for snow.

First, the fires of the western U.S. are still a growing problem with smoke levels increasing on west-southwest flow.  Figure 1 shows the Utah smoke source making it to Longmont.  The fires down south are adding a lot of smoke to the Great Plains.

Next, the zonal (west to east) jet stream flow still has small ripples (short waves) traveling down the stream.  One of those is over Colorado today with a weak easterly flow at the surface bringing some more moisture into our eastern Plains (Figure 2).  From these features, we have a chance of thunderstorms across the entire state (lighting is always a problem when fire danger is high!) and a marginal risk of severe weather returns backing up to I-25. Large hail and strong downdraft winds are the risk just to the east of us (unless the risk is expanded a few miles westward overnight); Figure 3.


Figure 1: The HRRR model forecast for smoke at all levels for Wednesday AM. From
Figure 2: The 500mb upper air analysis forecast from the GFS for Wednesday AM. Red lines are troughs, blue lines are ridges. Pink dot is Longmont.
Figure 3: the day 2 SPC thunderstorm and severe weather forecast made Tuesday (valid Wednesday).

The longer range forecast:

Tomorrow, the ripple is past and a moisture levels drop a bit.  Our risk of severe weather is absent from the state.  Just general afternoon thunderstorms are expected in spots (Figure 4).

That changes this weekend.  Hurricane Bud (still a category 3 storm) is headed our way via southern Arizona (as a tropical depression); Figure 5.

Figure 6 shows the cool down (out of the 90’sF again) coming for the weekend as moisture levels increase.  Moisture from Bud arrives and storm chances increase dramatically Sunday.  A cool front pushes down, in the new week, further kicking up showers and strengthening up-slope moist air flow. If this model is correct (from Longmont receives 1 1/3rd inches of rain before Thursday next week.  Keep hoping!  Let’s get some help putting fires out, from above.

Figure 7 is the total precipitation thought Monday night.  One can see a possible track of much of the moisture from Bud (from the GFS).

Figure 4: the day 3 SPC thunderstorm and severe weather forecast made Tuesday (valid Thursday).
Figure 5: The National Hurricane center prediction for the future 5 day position and strength of hurricane Bud. From
Figure 6: the total 10 days of the graphical forecast for Longmont, CO from
Figure 7: the total precipitation between Tuesday PM and Monday PM from the GFS and Red arrow is approximate moisture flow from tropical system Bud.
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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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