The State of the Atmosphere: Monday, September 4, 2017

The state of the atmosphere is hazy! Satellite imagery has been showing smoke flowing into Colorado all weekend long, as the west bakes under record heat and high fire danger. The smoke is especially evident along a cold front set to bring MUCH cooler temperatures to the state on tonight and Tuesday.

GOES-16 imagery showing smoke spreading across the U.S.

Denver set a record high on Sunday of 97°F at Denver International Airport, two degrees warmer than the previous record of 95° set in 1995. Today wasn't a whole lot better, with our station topping out at 96° downtown, and DIA so far climbing to 91° this afternoon.

Relief is on the way. Highs Tuesday should be some 20 degrees cooler than we saw today, and perhaps a bit more than that for some spots. A pretty big range in MOS guidance, with the GFS at 77°F for Tuesday and the NAM at 69°. We will split the difference a bit, and go with 72°F, a well-earned break from the heat in any case.

Cooler air is already spilling into the state at this hour:

So, those above average temperatures we're experiencing today...

Get replaced by below average temperatures for Tuesday...

Unfortunately, the cool down looks short-lived, although the return to record heat doesn't look imminent. If we look at the 12z GEFS high/low forecast for the next 16 days, we see our cool down on the way tomorrow (it has 75° for a high), and then warming back into the upper 80s for Thursday, Friday and Saturday. Ridging will continue to be an issue for the west for some time to come, so more warm days will be likely any time that ridge shifts a little east.

Despite some cooler days showing up in the chart below, it's likely we'll have more heat than cold to contend with over the next 16 days or so. You see our cold front for tomorrow, but then more heat up across Canada and across the western United States which spills into Colorado from time to time. The greatest occurrence of cooler than average temperatures will be across the eastern half of the country over the period:

As for precipitation, we'll struggle a bit in this regard too, though models are showing some hints of moisture from time to time over the period as well. Both the GFS and EURO show best precipitation chances hanging up over the mountains for the remainder of the week, with the GFS trying to pull in a bit of moisture for next weekend across the metro areas as well – we'll see. Unfortunately, the front moving through bringing tomorrow's cool down is mostly a dry one for us.

Here's the GFS precipitation forecast through Sunday:

WeatherBell Analytics

And here's the EURO ensemble precipitation anomaly forecast, showing below average precipitation for eastern Colorado through the period.

Irma
A quick note tonight on hurricane Irma, for which forecasts continue to trend further west in recent days – which is not great news for the U.S. Hope for Irma recurving out into the Atlantic without a U.S. landfall is at the moment not looking great, as the latest NHC track pulls Irma through the Bahamas, then grazes Cuba as we head into next weekend.

Where it might go from there is still up in the air. Some models take it almost due north swiping Florida and on into the Carolinas, while others bring it even further west before eventually moving north/northeast. A complex upper level pattern will eventually determine where Irma will end up going, but for now, if you know anyone along the eastern seaboard, or are planning travel there this coming weekend, PLEASE have them make appropriate preparations in the event of a Irma landfall.

A look at the latest GEFS ensemble forecast shows potential tracks for Irma, with pretty good agreement over the next several days, then a spread in solutions as we head toward next weekend. Running out of good solutions for the United States, unfortunately.

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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