In Brief:

We have a cool down from a mild Saturday (that might not be as warm as expected if the high clouds stay in place and keep the cold air at the surface from mixing out) on to a chilly Monday. A storm system arrives Sunday into Monday putting fresh snow down in the mountains, but little moisture and warm temperatures (again) will keep us snow-less and possibly dry. Next week looks seasonably normal with no storms on the horizon.

12/8 8am Update:

This is just a quick check-in Sunday AM looking at the snow accumulation up to 9pm tonight according to the HRRR map (Figure 1 update) and total precipitation (rainfall too – Figure 2 update) for that same time period. Right now it doesn’t look like much will fall -at all- in Longmont. There is a slightly better chance of snow showers between 5am and 11am Monday, but the GFS doesn’t show anything falling in town (just up in the nearby mountains).

Figure 1 update: The forecast snowfall for the next 15 hours from the HRRR and weather5280com for Colorado (up to 9pm Sunday) made Sunday at 6am.
Figure 2 update: The forecast precipitation for the next 15 hours from the HRRR and weather5280com for Colorado (up to 9pm Sunday) made Sunday at 6am.

End 12/8 8am Update.

Forecast Discussion:

High pressure at the surface and aloft is sitting over Colorado today (Figure 1). The only problem keeping us from an almost hot day (65F) is the thickness of the high clouds. If they remain in place through much of the morning and afternoon, the thin layer of cold air (inversion) near the surface won’t destabilize enough to mix out and let us warm up fully. It will still be nice and the slow melt will continue.

The Longer Range Forecast:

We will see a slight downhill slide in temperatures from today to Monday (Figure 3) with a small chance of precipitation Sunday PM to Monday AM. This cooling and slight shower chance will be created by a weak trough sliding by (Figure 2).

For this storm, the mountains get a foot plus in the higher elevations but Longmont sees no snow (the GFS Figure 4). Even rainfall probably won’t make it to 0.05″ level (Figure 5).

The NAM agrees keeping snow to the foothills to our west (Figure 6).
The GEM says the same (Figure 7).

An interesting footnote: Figure 8 shows a deep south storm moving up across New Mexico and Texas (and beyond) mid-week. If you have friends in the DFW area, they might slip and slide going to work Wednesday.

Figure 1: the current surface analysis map from Saturday AM and the weather channel.
Figure 2: The 500mb forecast upper air analysis for Sunday night. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 3: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 4: 10:1 (snow to liquid) snowfall totals through through Monday noon from the GFS and weather5280com for Colorado made Saturday morning.
Figure 4: precipitation totals through through Monday noon from the GFS and weather5280com for Colorado made Saturday morning.
Figure 6: 10:1 (snow to liquid) snowfall totals through Saturday noon from the NAM and tropicaltidbits. com for Colorado made Saturday AM.
Figure 7: 10:1 (snow to liquid) snowfall totals through Saturday noon from the GEM and tropicaltidbits. com for Colorado made Saturday AM.
Figure 8: 10:1 (snow to liquid) snowfall totals through Thursday early morning/midnight from the GEM and tropicaltidbits. com for Colorado made Saturday AM.
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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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