Forecast Discussion:

Let’s not bury the lead:

Winter Weather Advisory
Issued: 10:56 PM Oct. 12, 2018 – National Weather Service

* WHAT...Snow expected. Total snow accumulations of 2 to 5
inches expected.

* WHERE...Fort Collins, Boulder and the western suburbs of
Denver, Denver, Castle Rock and Greeley.

* WHEN...From 6 PM Saturday to noon MDT Sunday.

* ADDITIONAL DETAILS...Plan on icy and slippery road conditions.


A Winter Weather Advisory for snow means periods of snow will
cause primarily travel difficulties. Expect snow covered roads
and limited visibilities, and use caution while driving.

The latest road conditions for the state you are calling from can
be obtained by calling 5 1 1.

I expect this might be upgraded to a winter storm watch tomorrow. I’ll update as needed.

We’ll still have nice ‘warm-ish’ temperatures today. The front wind shift line will pass around noon, but the cold air won’t really arrive until later in the afternoon. We drop below freezing around 11 p.m. Precipitation chances begin around 7 p.m. when the temperatures are around 38°F – even if some models start the system with rain, I’m guessing it will be snow from the start. Figure one is a special graphic showing the surface front blasting through the state and a thick band of precipitation with moist up slope over much of the state.

Figure 2 shows how isolated, but stout, this storm is with precipitation tapering off later in the day Sunday. The heaviest snowfall will be between midnight and noon. We will stay below freezing, in the upper 20’sF Sunday. It will be really cold – a hard freeze.

So how much snow will we get?

My forecast for a sampling of cities is:

Ft. Collins 3-5″, Berthoud 2-4″, Estes park 5-10″, Longmont 2-4″, Boulder 3-6″, eastern Denver 2-4″, western Denver 3-5″, the Palmer Divide communities 2-5″.

Figure 3 is the hand-made forecast from the forecasters. They give Longmont 2-5″.

Figure 4 is the GFS  which has 2-3″.

Figure 5 is the NAM 3Km resolution model which has 3-4″.

Figure 1: Special weather graphic from the NWS via Twitter.
Figure 2: the next 10 days of the graphical forecast for Longmont, CO from
Figure 3: Special storm coverage graphic generated by the forecasters at
Figure 3: The total snowfall accumulation from Friday p.m. up to noon Monday from the GFS model and
Figure 5: The total snowfall accumulation from Friday PM up to Monday AM from the NAM model and

The longer range forecast:

It’s so quiet, it doesn’t get a graphic… Figure 2 shows it drying out and slowly warming for the rest of the next 10 days, but still remaining below normal for daily high temperatures.

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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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