Fire Activity

The dramatic change in the weather pattern across Alaska has produced a belated start to meaningful wildfire activity, and according to the AICC, about 47,000 acres have now burned in the state - and virtually all of this in the last week.  This is no longer the lowest fire acreage on record for the date, and it won't be the least active fire season on record: 1995 ended up with only 44,000 acres burned for the season.

Most of the (still very limited) fire activity is south of Nenana and between Salcha and Delta Junction, but there are some fires in the hills around Fairbanks, and the Fairbanks airport reported this year's first instance of smoke in the ASOS observation on Saturday morning.

The remarkable change to persistent and unusual warmth across Alaska occurred right after the middle of the month, and obviously the drier, warmer pattern is partly responsible for the modest fire growth in recent days.

However, it was lightning that started the fires, and there was a tremendous amount of it during the recent heat wave.  According to data from the ALDN, over 40,000 lightning strikes occurred between Monday and Thursday last week, and last Monday's 19,000 or so strikes ranks as the 5th highest daily total in the modern history of the ALDN (2012-present).  It was also the highest since July 11, 2019.

The recent lightning outbreak is even more impressive considering the date on the calendar: late July is certainly past the seasonal peak in lightning activity.  It seems the electrical storms were greatly enhanced by high humidity and therefore greater convective instability.  Both Tuesday and Wednesday last week achieved the rare feat of having a daily mean dewpoint above 60°F in Fairbanks, and the week ending Saturday had very nearly the highest 7-day mean dewpoint on record (it was marginally higher in late July and early August 1994).

The chart below shows daily average temperature, dewpoint, and relative humidity for Fairbanks since May 1st this year.  The upward climb in dewpoint is typical, but the normal value peaks at about 50°F in late July.

This chart also suggests a reason why the recent fire starts haven't yet produced very dramatic acreage growth - the relative humidity hasn't dropped much below 40% on most days recently, whereas values of 25% or below are generally regarded as favorable for fire growth.  This too is typical for the time of year: it's rare to get very low humidity days this late in the summer.  See here for an old post on the seasonality of fire weather in Fairbanks:

http://ak-wx.blogspot.com/2015/07/fire-weather-climatology.html

Having said all this, we shouldn't assume that major fire problems can't or won't happen in the next few weeks.  The forecast is again very hot, with the NWS predicting temperatures near 90°F for the eastern interior again this weekend.  It would be unusual, but fire activity can ramp up in August; there have been 4 years since 2000 when more than a million acres burned in August (2002, 2004, 2005, 2009).  Let's hope this year doesn't make a run at that joining that group.