Wednesday, May 20, 2020

Fire Season Speculation

News of a small wildfire that started north of Wasilla on Saturday brought a reminder that Alaska's fire season is imminent, and recent dry conditions have created high fire risk.  According to,

"With no significant precipitation since the snow pack melted off a month ago and greenup still in process, conditions in the Mat-Su Valley are extremely dry and the wildfire danger is very high. A burn permit suspension has been in effect since May 1 prohibiting the use of burn barrels and debris burning for the Mat-Su area and the rest of the state with the exception of Southeast Alaska."

The fire risk seems ironic after such wet weather in late winter and early spring, but it doesn't take very long to dry things out with long hours of sunshine and low humidity.  Check out how suddenly the deluge was shut off at the CRN site near Fairbanks:

Are there any indications of what the fire season might hold for Alaska?  As of May 1, the NIFC fire potential outlook suggested no reason to expect anything other than "normal" fire conditions this summer, although they indicated that the start of fire season might be later than normal because of the healthy snowpack.

A couple of years ago (see here) I noted a modest connection between fire season acreage and May ocean/atmosphere conditions across the North Pacific and Alaska; of course a warm, dry May tends to set up an active season.  It was also interesting to see that significant El Niño episodes tend to occur after active fire years, so if El Niño is showing signs of developing during summer, then enhanced fire activity might be expected.

Last year my exploration continued with a closer look at May North Pacific SSTs, and rather remarkably it turns out that all of the very active fire seasons in recent decades have occurred in tandem with a positive North Pacific Mode (NPM), indicating unusual ocean warmth to the south of Alaska.

The chart below illustrates the connection between Alaska fire acreage in the last 30 years and the May NPM index and August ONI (Oceanic Niño Index); both of these "predictors" are significantly positively correlated with statewide fire acreage.  The top 10 fire years all had a positive NPM phase, but we should note that a positive NPM doesn't quite guarantee an active fire year; 2014 was the major exception, with an extremely warm North Pacific but less than a quarter of a million acres of fire in Alaska.

If we create a standardized index from the May NPM and August ONI, the scatter plot shows a remarkable absence of bad fire years when the index is negative; but again a positive index is not quite a guarantee of a busy year.

So what can we deduce for 2020?  Well, we're certainly don't seem to be heading for El Niño, and in fact it's quite the reverse, with a cooling trend developing recently and expected to continue in the equatorial Pacific.  La Niña appears to be considerably more likely than El Niño in the latter part of the year, but it's also quite possible that near-neutral conditions will persist.

As for the North Pacific, it's warm.  Here's the last month's SST anomaly map:

Consequently the North Pacific Mode is positive, although not nearly as positive as it was last summer and autumn.

So far this month we've seen above-normal 500mb heights over most of Alaska, and as mentioned earlier it's been dry.

All in all, then, it seems there are mixed messages.  The trend towards La Niña is perhaps hinting at a relatively low fire year, but on the other hand the North Pacific is unusually warm, and Alaska has been dry and warm in recent weeks.  Perhaps the main conclusion is that there's no strong signal in either direction; a very active fire year would be a surprise, I think, given the tropical cooling; but a very quiet year would perhaps also be unexpected, given the North Pacific warmth.  So I'll go for near-normal, i.e. between about 0.3 and 1.0 million acres.  We'll find out soon enough.


  1. One thing that affects snow to soil water is frozen soils. A cold winter, late high snow water equivalent, and potential late spring thaw over frozen soils can lead uncertain predictor for fires. The melt water goes away in a fresh drying breeze and surface runoff and we are left with uncertainty until unstable air brings the ignition of flammables.

    We've had very little recent precipitation in fairbanks. All it takes is a spark and off go the fires.


  2. There's a regime change forecast for Interior Alaska around Memorial Day weekend and onward a bit:

    Might bring some thunderstorms to create sparks for fires?


  3. And so it begins... 5/31/20

    I called in that McDonald Creek fire south of Fairbanks while driving through the UAF this pm. Barely visible then and not on my to-do list. It's in Limited Protection on Military land so may burn away.


    1. Yes, there it goes: lightning and fire, just like clockwork. But Rick noted that thunder in Nome yesterday was the first to occur in May in 15 years.

  4. Without lightning would fire have been available to ancient people? I suspect not. And what gives sometimes takes away to renew the Earth.