Forecast Discussion:

Will you have to shovel snow in the morning, or scrape the windshield? The short answer is – almost to probably. Figure 1 is the HRRR 15 hour snowfall accumulation and there is 2+ inches of snow drawn right up to Airport road, then nothing significant beyond that. Aarug! Figure 2 shows how much super cold air is still in place today with temperatures about 25°F below normal. This is our coldest day yet.

The GFS (Figure 3) still paints a hole on Longmont with no snow, but up to an inch all around. What is up with that!? The GEM model gives us about 1 inch by the end of tomorrow (Figure 4).

Figure 5 says the highest chances of snow and precipitation for Longmont occur between 5 a.m. and 2 p.m. There are smaller chances of precipitation beyond that. The weatherunderground model (also Figure 5) says approximately an inch. Since there is light sleet falling this evening at 10 p.m., getting some ice in the morning is pretty likely.

 

 

Figure 1: The 15 hour snowfall accumulation up to noon today from the HRRR model and weather5280.com
Figure 2: The surface temperature anomaly (departure from normal) for Wednesday noon.
Figure 3: The total snowfall accumulation from Tuesday p.m. up to noon Thursday from the GFS model and weather5280.com
Figure 4: The total snowfall accumulation from Tuesday p.m. up to Wednesday night from the GFS model and weather5280.com

The longer range forecast:

As we get our possible snow, hurricane Michael is hitting the Florida panhandle possibly as a category 4 storm (not shown here). We moderate a bit for Friday and Saturday getting up to only 10°F below normal – then our next storm moves in with 3-5 inches predicted on weatherunderground for Saturday night into Sunday a.m.

The GFS gives us a total of about 4-5 inches (Figure 6) and the NAM gives us about 3-4 inches. This weekend storm is looking significant! More later!

Figure 5: the next 10 days of the graphical forecast for Longmont, CO from weatherunderground.com
Figure 6: The total snowfall accumulation from Tuesday p.m. up to noon Monday from the GFS model and weather5280.com
Figure 7: The total snowfall accumulation from Tuesday p.m. up to Sunday noon from the GFS model and weather5280.com
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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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