In Brief:

Light snow dusted the Front Range Monday night – now we look out at three more small chances for more snow Wednesday PM, Saturday AM, and Monday/Tuesday next week. Temperatures remain below normal (except for Friday and Sunday when they are back to near normal in town). Conditions are going to go back towards “quiet weather” again.

Update 2/13 1:30pm:

A quick peek at the snowfall from the Wednesday storm. Longmont had 3-4 inches across town (a bit more than I called for by about an inch- Figure 6 udpate). Boulder saw 2-3.5 inches.

Figure 6 update : 24 hour snowfall reports through 7am Thursday in Boulder Co. from CoCoRaHS.

End 2/13 1:30pm update.

Update 2/12 1:30pm:

The snow should start shortly… and the NWS has now issued a winter weather advisory:

Winter Weather AdvisoryIssued: 2:26 PM Feb. 12, 2020 – National Weather Service

...WINTER WEATHER ADVISORY IN EFFECT UNTIL 11 PM MST THIS
EVENING... see Figure 5 update

* WHAT...Snow expected. Total snow accumulations of 1 to 5
inches.

* WHERE...The Northern Front Range Foothills, The Southern Front
Range Foothills, Boulder and the western suburbs of Denver,
Denver and Castle Rock.

* WHEN...Until 11 PM MST this evening.

* IMPACTS...Plan on slippery road conditions. The hazardous
conditions could impact the evening commute. Reduced visibility
is possible under the higher intensity snow showers.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Slow down and use caution while traveling.

The latest road conditions for the state you are calling from can
be obtained by calling 5 1 1.
Figure 5 update: NWS winter weather advisory map

End 2/12 1:30pm update.

Update 2/12 8:30am:

A fast moving cold front with a period of high winds will blow ground snow around while light snow begins later in the morning. Snow should be falling off and on from 1pm to 8pm and snow showers may continue until after midnight. The NWS is concerned that models may be missing the strength of the system with a stronger quicker front and jet stream support for additional atmospheric lift. There could be some surprise 10 inch snow amounts in the mountains.

Snowfall roundup:

The Longmont forecast from the:
GFS (Figure 1 update): 1/2-2 inches (more to the west).
HRRR (Figure 2 update): 0.1-1 inch (more to the south).
NAM (Figure 3 update): 1.2-2.5 inches (more to the west).

The Video briefing for the end of the week can be found in Figure 4 udpate.

Figure 1 update: 10:1 (snow to liquid) snowfall totals through Friday PM from the GFS and weather5280com for Colorado made Wednesday morning.
Figure 2 update: The forecast snowfall for the next 15 hours from the HRRR and weather5280com through 9pm Wednesday.
Figure 3 update: 10:1 (snow to liquid) snowfall totals through Friday PM from the NAM and weather5280com for Colorado made Wednesday morning.
Figure 4 update: The Longmont Public Media forecast discussion

End update 2/12 8:30am.

Forecast Discussion:

We still have a big ridge off the west coast with northwest flow over the state and an approaching trough (with a cut-off low down in southern AZ – Figure 1). The water vapor satellite image shows this same pattern with some moisture flowing across AZ, NM and CO. This will move out into the southern Plains Tuesday/Wednesday (Figure 2).

By Wednesday AM, there is widespread snow/ice mix down in NM and the panhandle of TX (Figure 3). Just a tiny bit of mountain snows linger in Colorado. The snowfall for just Monday/Tuesday: the GFS gives us 1-2 inches (about 1/2 of an inch has fallen so far with decreasing snowfall on radar). This might be overdone already – Figure 5.

The Longer Range Forecast:

Temperatures remain below normal for the next 10 days except for Friday and Sunday when we get to, or climb just a bit above, normal (Figure 4). You can see the general warmth over the eastern Plains Sunday in Figure 6.

In the much longer range look – there are tiny snow chances Wednesday PM, Saturday AM, and Monday/Tuesday next week (Figure 4). The GFS over the next 10 days doesn’t really give Longmont any additional measurable snow – even while the central, northern, and (especially) southern mountains get a foot or more of new snow.

Before we go today, let’s see what NOAA is calling for out to the end of the month (19 days). Figure 8 has us really close to normal temperatures (but cooler than normal just up in Cheyenne and northward). Figure 9 paints us as receiving just a bit more moisture than normal for the next 19 days. Given warm ocean temperatures in the eastern Pacific right now, that looks pretty reasonable.

Figure 1: The 500mb upper air analysis for early Monday night. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 2: 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 from Monday PM.
Figure 3: The forecast surface map for Wednesday am from NCEP.
Figure 4: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 5: 10:1 (snow to liquid) snowfall totals through Tuesday PM from the GFS and weather5280com for Colorado made Monday afternoon.
Figure 6 : the surface temperature anomaly (departure from normal) from the GFS for Sunday morning from weather5280.com.
Figure 7: 10:1 (snow to liquid) snowfall totals through the next 10 days from the GFS and weather5280com for Colorado made Monday afternoon.
Figure 8: The temperature outlook for the rest of February 2020 from NOAA.
Figure 9: The precipitation outlook for the rest of February 2020 from NOAA.
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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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