In Brief:

The moisture is arriving, the cool fronts are arriving – it will rain a good amount over the next four days with temperatures dropping each day. We have a chance of morning snow Thursday and Friday. After that we dry out some and warm up a bit for the weekend.

Forecast Discussion:

The water vapor satellite image (moist air is white/pink/teal, dry air is red/orange/black) shows that the center of the upper level low is coming on shore Monday PM. The river of tropical moisture (green arrow – Figure 1) is flowing northward ahead of the system. The air feels really moist outside and big storms formed east of I-25 to kick off this blustery wet week.

The graphical forecast in Figure 2 shows very little break in the high rain chances through Friday morning. Today (Tuesday) we should pick up our first 3/4ths of an inch of water. The GFS based output in Figure 3 shows storm chances Monday PM then storms returning by dawn.

The Longer Range Forecast:

The highs drop to the lower 40’sF Wed/Thur and we have a chance of early morning snow Thursday and Friday. According to the latest weatherundeground.com model output – we get an inch of snow Thursday AM.

The GFS snowfall map – Figure 4 – gives us a coating to 1 inch over the course of this storm. The mountains pick up 1 to 1.5 feet. Wow.

Rainfall Roundup:

Figure 5 – the GFS gives us 1.25-1.5 inches of water over the next 5 days.
Figure 6 – the GEM gives us 1.75 to 2 inches of water over this time.
Figure 7 – the JMA (Japanese model) gives us 1.25-1.5 inches of water (a new model for this column).

Remember that the models went precipitation crazy before the last storm, and we only got about a third of that amount. Still, this will be a wet and chilly week. Keep warm and dry!

Figure 1: The water vapor satellite image from Monday night from NOAA and aviationweather.gov. Longmont is the pink dot.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 3: 7Timer (GFS) forecast for sky conditions and precipitation type for the next 3 days for Longmont.
Figure 4: the forecast accumulated snowfall map from the GFS and weather5280.com for Colorado,over the next 5 days.
Figure 5: the forecast accumulated precipitation map from the GFS and weather5280.com for Colorado,over the next 5 days.
Figure 6: the forecast accumulated rainfall map from the GEM and tropicaltidbits.com for Colorado, through the next 5 days.
Figure 7: the forecast accumulated rainfall map from the JMA and tropicaltidbits.com for Colorado, through the next 5 days.


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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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