In Brief:

Dry stabilizing air is moving in overnight Sunday into Monday cutting off storm chances. A giant ridge is forming across the southern U.S. turning off tropical moisture flow. We warm to the 90’sF this week with very small chances of an afternoon storm – and even then, only on some days.

11:30 am 8/13 update:

Some moisture has sneaked back into northern Colorado. With daytime heating and the direction that winds are coming from up through the atmosphere, there is a risk of a few supercell thunderstorms getting started along the Front Range this afternoon. The SPC has painted us with a Marginal Risk again (1 on a scale of 1-5 – Figure 2 update) and hail is the primary risk near Longmont and I-25 (Figure 3 update).

Further out on the Plains in the Slight and Enhanced risk (Figure 2 update) zones, high winds and tornadoes become a threat to watch for.

Figure 2 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Tuesday for Tuesday.
Figure 3 update: The large hail forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Tuesday for Tuesday.

End 11:30am 8/13 update

2pm 8/12 Update:

Just to follow up on the promise made yesterday – here is the water vapor image from midday Monday (Figure 1 update) showing the river of dry air flowing over the state. Looking out the window – it is really clear out there as well.

Figure 1 update: 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 midday Monday.

End 2pm 8/12 Update.

Forecast Discussion:

The real storms formed out over eastern Colorado with only light rain around I-25 and westward. The Denver NWS was right to be concerned about the dampening effect of too much morning cloudiness in the Marginal Risk zone Sunday. Dry air is replacing the moisture (it will be really different water vapor satellite image in the next 24-48 hours (Figure 1)). We return to the 90’s with a very small chance of rain Monday (Figure 2). The SPC doesn’t even give us a chance of convection on Monday (Figure 3).

The Longer Range Forecast:

On Tuesday, healthy daytime heating will interact with what remaining moisture we still have in the atmosphere and a storm or two may form around I-25. Most will not see a drop fall (Figure 4). The dominant story is a big ridge over the western U.S. and a ridge stretching almost from Bermuda to Hawaii to our south (Figure 5). Say goodbye to rich moisture (or monsoon like) flow.

Because of this sudden onset of quiet hot weather, I’ll turn to some family time and post double-day posts until things cool down and get moist again. The longer range does hint at a big cool down for later August. Wait for it!

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 Sunday.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 3: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Sunday for Monday.
Figure 4: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Sunday for Tuesday.
Figure 5: The 500mb forecast upper air analysis for Wednesday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Previous articlePodcast: Interview With Joan D. Heiman, Author Of Life With An Impossible Person
Next articleSubmit Your Questions For the 2019 Longmont City Council Election Debates
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.

Leave a Reply