The State of the Atmosphere: Sunday, August 2, 2015

Well, it's official, our streak of above-average monthly precipitation officially came to an end in July after three months of above average readings. Denver International Airport only recorded 1.06" of precipitation, which is a notable 1.02" below normal. We did, however, see some above normal precipitation across the state, with north-central and western Colorado seeing the greatest positive departures from normal for July. While "normal" isn't much for California during the month of July, note the huge departures across much of the state, especially southern CA thanks to tropical storm Dolores earlier in the month:

July precipitation departure from normal (percent) | NWS

The July temperature forecast did work out well for us, with widespread cool across the middle of the country. Denver ended the month 1.5° below normal, with cooler than normal temperatures extending from the southwest U.S. into the Great Lakes:

July calculated temperature anomalies CFSv2 | WeatherBell Analytics

Oh to be average
The State of the Atmosphere has been nothing short of boring of late, at least for those weather nuts around here (you know who you are) craving the active streak to continue. For Denver, the weather over the last week to 10 days has been about as interesting as the temperature chart below.

Daily max temperatures compared to average | Weather5280

Unfortunately, there's not a tremendous amount of support that shows a real up-tick in reliable monsoon moisture for the Front Range in the next week or so. There will be an okay chance of storms Monday for the metro areas (around 20-30%), but not overly impressed with coverage at this time. We'll see better storm coverage across the higher terrain to the west, and again east of Denver through Tuesday. In fact, all of the global models show a similar precipitation pattern as shown in today's 12z GFS below, best totals for the mountains and again far eastern plains through the week:

GFS precipitation forecast through 00z Aug 9, 2015 | Weather5280 Models

By next weekend we may see a little better flow of tropical moisture return to the state, but I hesitate to include the Front Range in that for now. It does appear that better storm coverage for the mountains at least will be a pretty good bet by the weekend, but we'll have to see how things shake out over the coming days.

The culprit keeping us high and dry? The positioning of the southern ridge. The monsoonal flow has certainly been present, just not aligned favorably for the Front Range. With that, it could be the moisture plume remains too far west for the foreseeable future to give us much reliable thunderstorm activity along the I-25 urban corridor. Meanwhile western Colorado continues to see storms, including the risk for Flash Flooding across southwest Colorado through tonight.

GFS precipitation over the next week with greatest moisture west | Weather5280 Models

I'd really like to see the mean ridge shift a bit further east before getting too excited about the return of the monsoon for the Front Range. A look at global ensembles, however, just really doesn't support this happening over the next 7 - 10 days. A few shifts here and there? Yes. Consistently further east, maybe not. Maybe, just maybe, things will start to look a bit different as we head into the second week of August.

Some interesting years showing up in the 6 - 10 day analogs from the CPC. Unfortunately, most of these dates are pretty dry signals for us. Even the 1997 date (which was a wet August overall) really dried out by the 26th.

CPC analogs

For now enjoy the quieter weather, and we'll keep looking down the road for when things may finally turned around for us once more. Plan on highs each day running near normal, with a few days climbing a bit above, and a few days running a few degrees below.

Quick note on today...
Today is a big day for those eager for cooler temperatures. Denver's average high dropped from 90 to 89 degrees today, and will continue to drop through the end of the year. By month's end, the average high for the city will have dipped to 84 degrees, with an average low of 54. Those late summer warm days and crisp nights are not too far away now!

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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