In Brief:

The front has arrived and anchored itself to topography of Colorado. It is serving as a trigger for thunderstorms that will ride over the cooler air and feed on easterly up slope flow. We will cool to a low high temperature of around 77F Monday then return to seasonable warm weather with afternoon storms.

7:30am Update:

Wind shear (the change in direction and speed of winds at different heights of the atmosphere) and daytime heating (the stratus clouds are remaining further east that was expected yesterday) will be significant enough to create strong thunderstorms again today. A Marginal Risk of severe weather has been forecasted for the Front Range and much of eastern Colorado (Figure 1 update).

Hail and high winds (and a few spots of locally flooding rains) are the primary risk. We are still expecting 1/4-1/2 inch of water across the region mainly after 2pm on to late morning Monday with thunderstorms capable of dropping an inch or two in local spots.

Storms will be moving out of the northwest direction – so watch those dark skies and your weather alert apps!

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

End 7:30am Update.

Forecast Discussion:

Figure 1 shows that the SPC has expanded the Slight Risk (2 on a scale of 1-5) back to Hwy 287 and the first round of storms got pretty severe around Lyons. The front is visible anchored down the mountains almost to New Mexico (Figure 2). Monsoonal moisture from the southwest and Mexico is leaking into the state from the south (Figure 3).

The cooler air Sunday will inhibit severe weather but rain and thunderstorms are still possible (Figure 4). By 6am the HRRR gives us a about 1/4th inch more than we received mid afternoon Saturday (Figure 5).

The Longer Range Forecast:

The site gives us a bit more than 1/2 inch more rain on Sunday and maybe 1/10th inch up to Monday (not shown). The GFS gives us 3/4th of an inch to 1 inch over the next 48 hours (Figure 6).

We hover just above and just below the 90F mark Tuesday through the next weekend with a return of afternoon thunderstorms.

Figure 1: The 3:40pm screen capture of the radar and SPC thunderstorm risk map from MyRadar app from iOS.
Figure 2: The current surface map analysis from
Figure 3: 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.
Figure 4: The forecast surface map for Sunday AM from NCEP.
Figure 5: the forecast accumulated precipitation map from the HRRR and for Colorado, for the next 15 hours through 6am Sunday.
Figure 6: the forecast accumulated precipitation map from the GFS and for Colorado, for the next 2 days.
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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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