In Brief:

An encroaching trough will hold off the heat wave this weekend. The moisture flow is also remaining fairly healthy – we see another chance of severe thunderstorms tonight (Friday). We dry out for the weekend but only hit the upper 90’sF on Sunday.

After that we slowly cool until a strong cold front brings in a taste of Fall at the end of next week and weekend.

Forecast Discussion:

The trough to our west is holding stronger than expected – this is keeping temperatures a bit cooler through Saturday than expected earlier in the week (Figure 1). We still have tropical moisture from the south and east and Pacific moisture from the west coming in at different levels (Figure 2).

The SPC has us on the very western edge of a Marginal Risk of severe weather (1 on a scale of 1-5) for hail and high winds (as usual).

2pm Friday Update:

The forecast for today going into the weekend is on track. The Marginal Risk (1 on a scale of 1-5) for severe weather (for hail and high winds this afternoon) has been nudged westward to include most of Longmont (Figure 1 update). The Slight Risk (2 on a scale of 1-5) is just a few miles further east. There is a chance for tornadoes in the middle of the Slight Risk region.

For Saturday – we warm up to around 90F and have almost no chance of a storm at all (dry air and lack of upper level support – Figure 2 update). The real heatwave (almost 100F) is still confined to Sunday only.

Figure 1 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Friday for Friday.
Figure 2 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Friday for Saturday.

End 2pm Friday Update.

The Longer Range Forecast:

We hover just around 90’F Friday and Saturday then the ridge hits us hard for a day (see the ridge in Figure 5). We hover in the 80’sF through mid-week then a powerful cold front is still coming in Thursday PM. Highs in the lower 70’sF (or only upper 60’sF ?!) are possible on the Plains. Rain showers (not so thundery) are possible Thursday night into the weekend as well. Exciting!

Figure 1 The 500mb forecast upper air analysis for Friday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 2: 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 NWS from Thursday PM.
Figure 3: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Thursday for Friday.
Figure 4: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 1 The 500mb forecast upper air analysis for Sunday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
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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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