Forecast Discussion:

8pm Thursday Update:

The National Weather Service has issued a Winter Weather Advisory

Area included in alert: Boulder And Jefferson Counties Below 6000 Feet/West Broomfield County; Elbert/Central and East Douglas Counties Above 6000 Feet; North Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe Counties/East Broomfield County
Alert brief: Winter Weather Advisory issued January 10 at 2:42PM MST expiring January 12 at 12:00AM MST by NWS Denver CO
An upper level weather disturbance will move into the area tonight and intensify through Friday as it moves across the state. Snow will first develop in the mountains along and south of the I-70 Corridor toward midnight tonight, and then spread across the rest of northeast and north central Colorado late tonight and Friday morning. The main travel impacts will be in the mountains, foothills, and Palmer Divide late tonight through Friday evening, when snow covered roads and hazardous travel conditions can be expected. On the I-25 Corridor, mainly wet roads can be expected through most of Friday, but as temperatures drop Friday evening snow will start to accumulate on roads. Bridges and overpasses will be first affected. Significant winds will not occur during this snowfall.
* WHAT…Snow expected. Total snow accumulations of 3 to 5 inches expected.
* WHERE…Boulder and the western suburbs of Denver, Denver and Castle Rock.
* WHEN…From 5 AM Friday to midnight MST Friday night.
* ADDITIONAL DETAILS…Plan on slippery road conditions Friday evening. The hazardous conditions could impact the late evening commute. The Palmer Divide may see slick and hazardous travel as early as Friday morning.
The forecasters at are becoming more bullish as well (more snow than I called for below…)
Figure 1 Update:
The hand-drawn forecast for snow totals (mainly) Friday from the forecasters at

End 8pm Thursday Update.

I’m posting early again as the storm will begin to change travel conditions across the state before January 11th arrives. The surface forecast map (Figure 1) shows the low that deepened early on Friday in SE Colorado moving across the Texas panhandle later in the day. A good moisture flow is arcing around the low up into Kansas and “up slope” into Colorado for all day Friday. The strongest period of up slope (heavier snow rates) is a briefer window of time (around 6 am to 11 am – Figure 2). Snow should begin around midnight and continue into the late evening. Figure 3 (a model from China based on the GFS, 7timer) has snow falling from 9 m to 11 pm.

What is interesting is that some models are beginning to go nuts on the snow totals for Longmont and Colorado in general. The NAM (Figure 4) seems to paint 3-5 inches for Longmont. The WRF (Figure 5) gives Longmont a whopping 5-8 inches. The forecasters at cite the government shut down to blame for the calculated high amounts on (maybe) the fact that there aren’t humans conducting quality control in observations being fed into the U.S. models.

To go outside the U.S. model world…The Canadian model (Figure 6) puts us in the 2.5 inch+ (but less than 5 inches – which is a pretty wide color key). The European (not shown) does agree pretty well with the GFS (currently) – Figure 7. The GFS has Longmont in the 1-2 inch area with 3 inches just west of town and is less bullish about snow all over.

My take is: Longmont 1-3 inches. I’ll update it if things seem to get colder, wetter, or slower.

A selection of other towns: Fort Collins 1/2-2 inches. Berthoud 1-2 inches. Boulder 2-4 inches. Estes park 3-6 inches. West Denver 2-4 inches. Eastern Denver 1-3 inches. The Palmer Divide communities 2-5 inches.

If things change, it would probably be to add an inch or two to these totals (since I’m wary about throwing out the U.S. models entirely – they ‘may’ be seeing something real in the atmosphere).


Figure 1: The forecast surface map for Friday PM. From NCEP.
Figure 2: the graphical forecast for the next 10 days forecast for Longmont, CO from
Figure 5: the next 3 days forecast of sky conditions and precipitation.
Figure 4: The forecast accumulated snow map from the NAM and for Colorado, for the next 48 hours.
Figure 5: The forecast accumulated snow map from the WRF and for Colorado, for the next 48 hours.
Figure 6: The forecast accumulated snow map from the CMC (a Canadian model) and for Colorado, for the next 48 hours.
Figure 7: The forecast accumulated snow map from the GFS and for Colorado, for the next 48 hours.

The longer range forecast:

The jet stream will stay a bit more depressed to the south over the next week than was previously forecasted (there will be more cold air in the northern and central states) so temperatures will recover only to the upper 40’s F and lower 50’s F for the next 8 days.  There is something wet to watch next Friday. Fun fun.

Previous articleLongmont PD Beat Map
Next articleHow Do Patients Determine Hospital Medical Costs at Longmont Hospitals?
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.

Leave a Reply