In Brief:

A vigorous short wave trough is passing to the north over the next couple of days . This will give us a small chance of afternoon storms and cool temperatures first to the lower 80’sF then upper 70’sF for the end of the week. We see highs climb back up to the mid and upper 80’sF – somewhat above average – temperatures next week. Dryness will be the overall rule.

3pm 9/10 Update:

The apology tour update: Note, a recent forecast called for quiet weather the rest of the week, but this short wave is looking quite strong and will impact northern Colorado more than appeared a few days ago.

Also, I mentioned that the GFS created a hurricane that hit around New York City later this week. That has vanished from the model, but it continues to create wandering storms around the Atlantic Basin and even in the Gulf over the next 2 weeks. Anything is possible, but long range hurricane forecasting is not a GFS strength. (It is entertaining to watch though <grin>.

Look for an earlier update tomorrow (Wednesday) to catch the details of the severe weather chances in the afternoon.

End 3pm 9/10 Update.

1:30 pm 9/10 Update:

The strong short wave will be doing “it’s thing” tomorrow (Wednesday) with very large hail and supercells up in Nebraska. Areas just north of Denver and in the northern mountains of Colorado may see some of this severe thunderstorm activity with large hail as well. The SPC has issued a Marginal Risk for the Front Range with a Slight Risk and Enhanced Risk up in the northeast corner of the state.

Figure 1 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Tuesday for Wednesday.

End 1:30pm 9/10 Update.

Forecast Discussion:

Even though there is some surface moisture around, the bulk of the atmosphere over the state is really dry (red and oranges in Figure 1). The next trough is pretty dry and most of the energy is to the north of the state. As it approaches, we cool down and do see a chance of afternoon showers (Figure 2 and Figure 5).

The Longer Range Forecast:

The trough cools us the most on Thursday (Figure 3 and Figure 5) and things dry out (as far as rain chances go). We warm next week as the jet stream really flattens out (becomes zonal Figure 4). We stop seeing ‘weather’ for a while (Figure 5).

Taking a peak at our drought conditions, there are larger regions of abnormally dry and some regions of moderately dry (near the Four Corners area) forming. This is to be expected in the hot dry summer, but it is the most-moist I’ve seen the state at the end of summer since I’ve been watching it here. (Figure 6).

Figure 1: 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 Weather Channel from Monday afternoon.
Figure 2: The 500mb forecast upper air analysis for Tuesday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 3: The 500mb forecast upper air analysis for Thursday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 4: The 500mb forecast upper air analysis for Sunday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 5: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 6: The Colorado drought index map issued Thursday Sept 5 from NOAA/NWS/NCEP and the CPC.
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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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