Forecast Discussion:

The ridge still rules, the atmosphere is dry, there is no smoke in the state, and a cool down is visible – 8 days out from now.

Figure 1 shows the dry weather on this side of the stationary west coast trough (purple is center of moist axis). The surface map for later today shows dry conditions and high pressure over Colorado (Figure 2). The temperatures will continue to be about 10-13F above average (Figure 3). Toasty!

Figure 1: the water vapor satellite image from Wednesday afternoon. Reds/Oranges are dry air, greys/whites are moist air regions.
Figure 2: The forecast surface map for Thursday PM. From NCEP.
Figure 3: the departure from normal temperature at noon Thursday – surface temperatures from weather5280.com

The longer range forecast:

Figure 4 is the animation of the upper air pattern showing Colorado sitting under the same pattern for most of the next week.  You can see Florence drift in, die inland and zip off to the northeast on this run of the GFS. Finally, about 7 days out, you can see the ridge modify and break down. Troughs start to enter the West.

The first big cold front roars into the state the early morning of Thursday the 20th (Figure 5).  That is a 30F drop from the week between now and then.

Looking at Florence, there is coverage of this storm everywhere now, and is often updated more frequently than this column as landfall is hours away.  Figure 6 shows the push-me-pull-me of the two highs will now result in the storm drifting VERY slowly to the southwest for 48 hours or more before heading deep inland to die.  Some folks in the Carolina’s will see feet of rain. The tangle of models all pretty much agree.  The pink arrow in Figure 7 is the approx. location of the earlier path.  That is quite a southward drift!!

Figure 4: The animated 500mb forecast upper air analysis for next 9 days. from tropicaltidbits.com
Figure 5: the departure from normal temperature at noon Thursday next week 9/20- surface temperatures from weather5280.com
Figure 6: the five day cone of uncertainty plot forecast from the NHC for Florence.
Figure 7: the five day multi model plot forecast from the NHC for Florence.
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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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