Monday, July 24, 2006

Horse Fire II

Given what we saw on yesterday’s reconnoiter of the fire, we were not terribly concerned about risk to our home, but still we didn’t think it was prudent to just go to sleep — after all, this rather large wildfire was burning just over the hill from us! But around midnight, it became clear that we simply weren’t going to get any more news — every source of information shut down for the night. The MODIS satellite only makes a few passes a day over any given spot, so we’d be waiting six or eight hours between updates on it. We assessed the risk as so low that making the long road trip out to the fire wasn’t worth it (the fire was only two or three miles in a straight line from our home, but to get there on roads is about 15 miles) — so finally we just gave up, and went to bed.

As of 7 am this morning, the CDF has not posted any news for today (their message is unchanged from last night). But…the MODIS satellite data (publicly available, in near realtime) shows a huge change from last night when I finally went to sleep. The map is at right, this time shown overlayed on a US Geodetic Service topo map instead of the simple shading as I used previously. As before, the green splotch on the left is where our home is. Now, however, we’ve got all kinds of MODIS data.

The orange slant-shaded areas (two splotches) are the 24-hour old data from yesterday. The red slant-shaded areas are between 4 and 24 hours old. The red solid-shaded areas are current as of about 6:45 am this morning; they show where the fire is burning right now. The blue arrow is my hand-drawn inferred path of the main fire.

Last night the CDF message was reporting 6,000 acres burned. My very rough estimate (from the MODIS data) is that 12,000 to 15,000 acres have burned as of this morning.

For us, the most immediately concerning thing is those two solid red splotches near where the fire started. Those are in the same area that I photographed last night; likely that means there has been no firefighting activity there (and we saw none last night). If those areas started burning toward the west, we could have problems. Obviously we will be keeping an eye on that. The center-of-mass of the fire, however, is about six miles due east of the observation point where we reconnoitered last night. The fire moved a long, long way in the still evening air (my weather station recorded no wind at all last night). To some extent, I’m sure that’s due to a combination of the rugged terrain (channeling air flow) and the heavy fuel loads. The area that’s burning is very difficult to get access to — my maps don’t even show any trails, let alone roads. The easternmost front has almost reached Lake Morena (a large man-made reservoir); if it makes it past the lake, every direction is populated. And south of the entire path of the fire is also populated; the beautiful Deerhorn Valley area. If it headed north from where it is currently burning, there are several more miles of wilderness and one of the last remaining large family ranches in San Diego County, then more populated areas (and also the areas burned three years ago in the Cedar Fire).

All in all, it appears that the risk to our home is still quite low. If I lived in Deerhorn Valley or Campo, I’d be considerably less sanguine right now. And as I have said earlier, the fuel consumed by this fire is substantially lowering our risk of the particularly deadly Santa Ana-driven wildfire, because all that fuel would be upwind of us in a Santa Ana…

Update 8 AM:

The CDF is now reporting 6,600 acres burned and 5% contained. They’re also reporting exactly the expected areas as “of concern", a lesser risk than “threatened”. I can’t make sense of the 6,600 acres given the clearly larger area burned on the MODIS data — either there’s something I don’t understand about the MODIS data, or the ground reports haven’t caught up with it…

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