New Mexico Weather Patterns and Fire

A comment from my friend Denise over at Mom in Madison led us to do a little information gathering about New Mexico's seasonal weather patterns and how they relate to our weird fire seasons. Thanks, Denise!


On the California Coast, fire danger is greatest in the late summer-fall, due to extreme dryness, heat, and winds coming off the ocean--like Southern California's Santa Ana Winds.


But the New Mexico pattern is different.


Much of the state is Chihuahuan Desert country with associated high desert grasslands, shortgrass prairie, and montaine forests. The life zones are pushed higher because much of the state lies below the 36th latitude. That means that in central New Mexico--where we live--we don't see Pinyon-Juniper Woodland below about 6,000 feet (depending on which side of the mountain) and Ponderosa Pine Forest does not become well-established below about 7800 feet. Also, average annual precipitation in the Rio Grande Valley is less than 10 inches a year, and in the Central Mountains, it is about 16 inches a year--less further south and more further north. Twenty inches is about the upper limit on annual precipitation for anywhere in the state.


New Mexico has the bi-modal precipitation pattern common to the Chihuahuan Desert.
We typically have a dry and windy spring and fall due to to movement of the jetstream high altitude pattern during those seasons. Starting in late June of early July, we get the summer monsoon storms, which are influenced by the ENSO pattern (El Nino-Southern Oscillation). In a good El Nino year, we get more precipitation--as in the summer of 2006, and in a strong La Nina year, we get less precipitation. In an ordinary year (neither El Nino or La Nina) we get an precipitation somewhere between the two. If we have a long string of weak El Nino's, or strong La Ninas, we have summer drought conditions. The monsoonal winds last until late August or early September, and then we return to a fall dry, warm and sunny situation. Our winter snowfall is also influenced by ENSO, and we watch the mountain snowpack carefully, because our overall drought conditions depend a lot of whether we get good snowpack or not. Also, if spring conditions come too soon, we can end up with a summer drought situation and an earlier fire season. (This picture is from the NOAA website and you can learn all about the North American Monsoon by clicking the link).


What all of this adds up to is that our most extreme fire seasons tend to be spring and fall.
During La Nina years, if the monsoon fails, we can end up with a fire season that extends from March-October or even November. Last year, the worst fire in Central New Mexico happened at the end of November--the Ojo fire--which was not far from the current Trigo fire.



Last year, we had a good but normal monsoon which helped mitigate the fire danger in summer. This year it looks like the La Nina pattern could persist, causing us more fire problems. The last two summers have also increased grasses and forbs, so a dry summer means a heightened grassland fire danger.

This year, too, the March winds have lasted into the beginning of May. Since mid-March, we have had more days of Red-Flag Fire Warnings than not. A Red-Flag Fire Warning requires the combination of warm, sunny days--which lifts the thermals over the mountains in the afternoon--lack of precipitation and low relative humidity, and high regional winds from fast moving storm systems that mix downward as the day progresses.

Yesterday, the Trigo fire jumped containment due to high winds. Slightly lower pressures due to a fast moving storm system from which we do not expect precipitation means that these high-wind conditions will continue through Friday. Exacerbating the problem is that fixed-wing planes cannot drop retardant in the high winds, so they usually only get a few hours near sunset to to their drops. The fire is already relatively inaccessible, being on peaks and in canyons, but the high winds mean that the hot-shot crews are pulled off the mountain frequently.


What has made all of this much worse is that the fuel loads of the central mountains are high due to what we call "dirty woods"--lots of snags and deadfall--created by the USDA's misguided fire-suppression policies of the past 50 years. You know what they say about "good intentions."


Fire is a natural part of this ecosystem--and small, frequent fires keep the fuel loads down, preventing the kind of crown forest fires that have extremely high heat, create their own weather, and burn the entire forest.


Live and learn.