Forecast Discussion:

A weak cool front traveled in before sunset and put down sprinkles around the Wyoming border and Ft. Collins Monday PM (Figure 1). Things stabilized after dark and a few drops hit Longmont.  Now we return you to your regularly scheduled warm-up.

Figure 1: MyRadarPro life radar image Monday afternoon (iOS app).

The longer range forecast:

We do have an interesting ‘bonus’ storm that may give Longmont some measurable rain come Thursday PM and Friday AM.  We’ll cover this, now, instead of the weekend pattern change and unsettled turn to the weather expected then.

The next four images will be a quick study of the difference between the GFS (Global Forecast System – from our National Weather Service) model and the ECMWF (European Centre for Medium-Range Weather Forecasts) model.

Figure 2 is Friday morning at 500mb heights with a low center in NW Kansas. Figure 3 is the European model for the same time with the low closer to Longmont.  I always cover the 500mb level for simplicity and consistency, but we have maps at lower levels (like the 850mb and 700mb) and higher (like the 300mb) heights.  Storms are not always vertically stacked in the atmosphere, which can impact their speed and severity.

Figure 4 is the 700mb map (at and below ground level for the Rockies) with the Low just east of town late Thursday PM on the GFS. Figure 5 for the same time at 850mb (even lower – so extrapolated for levels below ground level) from the European model. The Low center is off on the Kansas boundary in the lower atmosphere.

The European is better positioned for mountain snows (and rain for us) – but both now give us some weather by Friday AM.

Figures 6, 7 and 8 are the Thursday PM, Friday early AM, and Friday AM surface maps showing the surface low, from the GFS, out east of us and stalling briefly in NW Kansas.  Some nice wrap-around precipitation hits Longmont (even though there is a strip of down slope dry air that forms mid-storm, grrrr).

Figure 9 shows total water amounts by Friday morning around 1/2 inch for Longmont.  This is a nice gift out of nowhere … as long as it doesn’t vanish back into model-nowhwere.

Figure 2: The GFS 500mb upper air height and anomaly map for Friday morning from tropicaltidbits.com
Figure 3: The ECMWF 500mb upper air height and anomaly map for Friday morning from tropicaltidbits.com
Figure 4: The GFS 700mb upper air height and vorticity map for Friday morning from tropicaltidbits.com
Figure 5: The ECMWF 850mb upper air height and vorticity map for Friday morning from tropicaltidbits.com
Figure 6: The U.S. surface pressure and precipitation forecast map from the GFS and for Thursday PM from tropicaltidbits.com
Figure 6: The U.S. surface pressure and precipitation forecast map for early Friday AM from the GFS andtropicaltidbits.com
Figure 8: The U.S. surface pressure and precipitation forecast map for Friday AM from the GFS and tropicaltidbits.com
Figure 9: The total accumulated precipitation forecast map between Monday PM and Friday AM from the GFS and tropicaltidbits.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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