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Tuesday August 15, 2017 - The Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory

By John Ensworth Discussion: Just as we get our first 90+F temperature since the early days of the month, a cold front is coming in and knocking the temperatures down and bringing rain.
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This content was originally published by the Longmont Observer and is licensed under a Creative Commons license.

By John Ensworth

Discussion:

Just as we get our first 90+F temperature since the early days of the month, a cold front is coming in and knocking the temperatures down and bringing rain.

Figure 1 shows mid-level moisture streaming in from the west (dark green arrow) along with the next front.  Surface easterly winds are still bringing in moisture from the dying southerly source (light green arrow).

Figure 1:  Water vapor satellite image from Monday PM.

Figure 2 shows the ridge on the move (blue line) with a trough to the west and trough to the east (red lines). When troughs or ridges are far apart enough to be about the width of the US, the ridges and troughs don’t move much.  When they are wider than the US, they move westward (retrograde).  When they are shorter than the US in size, they move to the east (progress). This is a progressive pattern (as well see just below in Figure 5).

Figure 2:   The 500mb map from Monday mid-day from the GFS model.

In a look at the longer range:

The cold front has pushed through by Wednesday morning and we will have had a cooler and showery Tuesday and Wednesday (Figure 3). Figure 4 shows the accumulated precipitation (24 hours’ worth) just through Tuesday night. It does seem to favor Denver or the Palmer Divide more than us. Figure 5 shows the upper air pattern again Wednesdaymorning--- the ridge is out over the Ohio Valley and a deepening trough in the west is transporting moisture up from the tropics to us. We go back to remaining mostly below normal (which we’ve done very well doing so far in August).

Figure 3: The Wednesday morning surface analysis forecast.

Figure 4: The GFS forecasted 24 hour accumulated precipitation before Tuesday night.

Figure 5: The GFS forecasted 500mb pattern for Wednesday morning.

 

Eclipse forecast special:

We continue to build a trend chart here for a sampling of eclipse viewing locations.  Each forecast will be for the expected % cloud cover (0% is clear, 100% is overcast) at 12pmMountain Time for Teton Village, WY, Casper, WY, Glendo, WY, Lusk, WY, Alliance, NE, and Longmont, CO (Longmont is included for reference… it will NOT be in the totality path).

I’ll add each day’s model forecast for that time from Sunday night to Sunday night.  The important thing to watch is the trend.  Does your city look clearer as the week goes on, or more cloudy, or pretty constant?  My expectation is that you will not be able to move far from where you are Monday morning due to traffic.  You’ll need to pick your destination a day out and plan for that.

Monday commentary: all locations are forecasted to have more clouds.  Don’t panic yet. With the sun this high during the eclipse, partly clouds skies will still let you see the eclipse off and on.

Monday 8/21 12pm MT

Percent Cloud Cover Forecasted for Sun 8/13 Mon 8/14 Tue 8/15 Wed 8/16 Thur 8/17 Fri 8/18 Sat 8/19 Sun 8/20
Teton Village 26% 30%
Casper 9% 27%
Glendo 13% 31%
Lusk 9% 26%
Alliance 7% 36%
Longmont 23% 45%

A Map Version of Cloud Forecasts

These maps were created by www.weather5280.com (you should visit them for weather discussion as well!). These maps are a cloud forecast map (future satellite image, sort-of) with percent cloud cover plotted and the eclipse path added for reference by those talented forecasters and programmers. All of these are for the same time and date – noon on Monday, Mountain Time, near totality of the eclipse.  As with the table above, keep an eye on the trends and patterns.  If they change a lot day to day, confidence is low that the models are getting it right. If they are consistent, then you can place some confidence in this forecast.  This is a different model than the one creating the percentage table above, so if these numbers match those, you can be even happier that you know what Monday will be like. Never allow yourself to be completely confident that this is what Monday will yield.

Monday commentary:  there is, understandably, a lot of variation in these images so far. We are still a week out.  I doubt either of these forecasts will match reality much when Monday noon actually happens.

Forecast created Sunday 8/13

Forecast created Monday 8/14

*** This feature will run as close to daily as possible in this location on the Longmont Observer. ***

This article will provide a brief discussion concerning the ‘why’ behind the weather with a focus on severe weather, unusual weather, and snow (especially trying to predict snow depth and its human impact in Longmont).

*** This feature will run as close to daily as possible in this location on the Longmont Observer. ***

This article will provide a brief discussion concerning the ‘why’ behind the weather with a focus on severe weather, unusual weather, and snow (especially trying to predict snow depth and its human impact in Longmont).

Bio:

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.