Friday, August 30, 2019

This smoke season's anomalies explained, with a Labor day smoke forecast tacked on

Easy part first:

Western WA Labor day weekend smoke forecast
After a welcome dousing of rain yesterday and consistent on- shore flow this weekend, the fire risk will remain low. No major smoke impacts expected over the Labor day weekend so go ahead & enjoy the Good air, but please be diligent and prevent new fires. Too many reports of abandoned campfires, dragging chains and discarded cigarettes starting new fires.

Eastern WA smoke forecast
Two issues worth mentioning, although one of them may not amount to much:

  1. Some spotty smoke is present around Asotin County, likely from the Cow Fire in Oregon, and the area is likely to see intermittent Moderate air over the next few days. 
  2. All the smoke models are assuming that a few fires in the Okanogan- Wenatchee National Forest are actively pumping out smoke and they maybe right to some extent, but are likely overstating the magnitude. Haven't seen any measurable smoke impacts at Leavenworth, Chelan, the Methow Valley or Stehekin as yet and don't expect area air quality to degrade beyond Moderate on occasion.

Other than that, we're mostly expecting Good air provided there are no new fires. Warmer, dryer conditions are predicted to return mid week, reminding us that the fire season is not over yet.

WZUP with this wildfire smoke season?

Here's an animation showing how the worst air quality days in the last 2 wildfire seasons compared with this year. While 2019's worst day thus far wasn't even close to those of the previous two anomalously smoky years, it occurred so early in the season (May 31) and got us all worried about what might transpire. More so since the seasonal outlook available at that time called for a slightly warmer-than-normal and dryer-than-normal summer.
Thankfully, that smoky scenario hasn't played out this year. The chances of the smoke monster making a comeback are diminishing as the sun becomes more preoccupied with baking the southern hemisphere.

The # of wildfires burned by today in 2019 is lower than the low- smoke years of 2013 & 2016. How nice to be lagging behind!

Year-to-date
# of fires nationwide
2019 (1/1/19 - 8/29/19)
32,887
2018 (1/1/18 - 8/29/18)
43,448
2017 (1/1/17 - 8/29/17)
45,981
2016 (1/1/16 - 8/29/16)
39,997
2015 (1/1/15 - 8/29/15)
43,511
2014 (1/1/14 - 8/30/14)
38,454
2013 (1/1/13 - 8/30/13)
34,256
Data source: National Interagency Fire Center

Here are some of the main meteorological factors that mitigated the build-up of smoke that was released from the few fires that did burn. I've only considered the anomalous smoke years of 2017 & 2018 in one of the graphics below (#2. wind vector animation).
  1. Less frequent high pressure systems over us
    Here's a comparison of the height at which atmospheric pressure reaches 500mb (usually around 18K feet above), showing differences between 5 recent summers (excluding 2017 & 2018), and 2019. Data are June- July composites from global weather models that have been re-analyzed after the observational data became available. 2019 August data aren't yet available.
    The yellow over our region suggests that upper level pressure in past years were 10- 20m higher than what we saw in June- July this year. Not an insignificant difference. Include 2017 & 2018 and the difference jumps to about 35m.

    Higher pressure = lighter winds, warmer temperatures and dryer air. All the factors needed for conducive fire behavior and poor smoke dispersion happened less frequently this year.

    An aside: notice how areas to our north & the Arctic had higher pressure this year than the last few. We had several early season fires in northern Alberta & Alaska. In fact the May 31 2019 smoke shown in the air quality map animation above mostly originated from northern Alberta.
  2. Stronger upper level winds aimed at the Pacific Northwest

    Here's how the 700mb level (about 10K feet above) winds in recent summers compared with 2019. Notice how 2019 winds aimed at the Pacific NW are stronger than their 2012- 2018 counterparts. More active weather impacting our region = less chance for air to stagnate. 
  3. Cooler upper air temperatures

    And now, a 850mb level (4500 feet above) temperature difference plot. 2-3C warmer in other years than 2019. For a two month average, that's quite a difference. Cooler upper level air temps this year = less ground level warming & drying out.
Why the region's seasonal climatic variables behaved this way is beyond the scope of this blog. This season's fire behavior is compared & contrasted in a recent interview. The interested reader can compare ground- based observations of temperature and precipitation each year, against historical norms using the following NWS links.




No comments:

Post a Comment

We monitor this site during business hours, Monday through Friday, 8AM to 5PM. We encourage your questions, comments, and feedback. We ask that everyone be respectful of the opinions of others, and avoid comments that are defamatory, inappropriate or off-topic. If you have an emergency, please call 911.

We moderate all comments to prevent spam. Your comment will publish upon review