North Zone Fire Danger
July 24, 2018
Matt Butler
Questions are coming up about the fire danger at this point in the year and where we might be headed given a warm and drier forecast predicted the next couple of weeks. Here is some insight into how things are shaping up.
Precipitation this Spring/Summer:
90 Day precipitation anomalies for the period April 25 – July 23. The North Zone is showing generally 50%-75% of normal with the south end of the Zone showing 25%-50%.
30 Day precipitation anomalies for the period June 24 – July 23. The North Zone is 25%-50% of normal precipitation for the time period.
Drought Monitor showing the North Zone in an abnormally dry area. The Sesonal Drought Outlook identifies the North Zone being characterized as “Drought Development Likely” (map not shown).
Where are we now?
• The North Valleys and North Mountains have been listed as High Fire danger.
• Looking at July 23rd indices the Ignition Component spiked due to RH’s in the mid-teens. With RH’s in the mid 20’s, the Ignition Component doesn’t spike as much and actually moderates a bit. So the 23rd may have been a bit of an outlier but shows what warm and low RH days may do to the Ignition Component.
• Given this:
o The North Valleys are solidly in Very High. The 23rd they crept into the low end of Extreme….but that could be due to the lower RH’s causing the Ignition Component to spike. The next several days RH’s are forecasted to be in the 20’s which would still put the North Valleys in Very High.
o The North Mountains are on the High/Very High breakpoint. Given a few more days of warm and dry conditions the North Mountains will likely creep into Very High and stay there for a while given the predicted weather forecast.
Below are the ERC graphs out of WFDSS showing the current ERC curve (yellow line) and forecasted 7 day trend (green line) based on the weather forecast. Note that WFDSS pulls the years of the entire weather history and the 90th/97th percentiles may look different than our NFDRS thresholds using the years of 2003-2017. The point is the ERC trend that is forecasted. For our actual current ERC values and Percentiles…look at the table below:
Actual ERC and percentiles based on 2003-17 are shown in the table:
ERC on 7/23 Percentile
Priest Lake 47 88
Bonners 63 92
Saddle Pass 51 90
Hoo Doo 54 96
Expected Conditions for the next several weeks:
6-10 Day Temp and Precip Forecast:
3-4 Week Temp and Precip Forecast:
Summary
• The past few months have resulted in drier than normal conditions and have resulted in lower fuel moistures and higher indices. The area is under a “Drought Development Likely” category
• Current conditions are showing Fire Danger as solidly Very High in the North Valleys with the North Mountains likely solidly in Very High within a few days.
• Forecast conditions show hot and drier than normal. The next several days may moderate RH’s slightly which will moderate the ERC, BI, and IC curves somewhat….but….conditions are still above the 90th percentile and the curves will remain high.
• We are in our normal summer drought period and not much precipitation falls this time of year and usually is associated with a thunderstorm. The forecast shows continued warm and dry and the indices will likely continue to creep upward without precip or days with lower RH’s below 20%.
• 1000 hr fuels are also showing signs of the warm and dry conditions. 1000 hrs range from 11-14% on the 4 RAWS stations on the zone. I’ve always figured that at 15% and below fire show more resistance and burn deeper. At 12% and below….fires show a lot more resistance and more tend to have more activity.
Recommendation is to move the North Valleys to Very High and make the determination for the North Mountains in another 2-3 days to move to Very High.
