The National Weather Service has issued their Monsoon 2010 Forecast for the southwestern portion of the United States. The overall forecast is neutral while we wait for El Nino/La Nina patterns to stabilize, and while we wait to see how wet the central plains will be. If you track this stuff like I do, you’ll find the forecast to be both interesting and informative.
As the temperatures in Southern Arizona heat up, and the moisture in the air decreases, we start getting a lot of Red Flag Warnings for the various parts of the state. I’ve known intuitively what these warnings are about, especially since I was a wildland firefighter for a season, but wanted to find out some more details.
Red Flag Warnings are issues by the National Weather Service to inform firefighting authorities and land management offices that the conditions are right for wildland fire ignition and propagation. For these offices, the issuance of a Red Flag Warning helps them prepare for the potential fires brought on by drought, low humidity and high winds with potential lightning. For the general public, a Red Flag Warning means there is a high fire danger with increased probability of a quickly spreading vegetation fire in the area in the next 24 hours.
The weather criteria for fire weather watches and red flag warnings varies with each Weather Service Office’s warning area based on the local vegetation type, topography, and distance from major water sources but usually includes the daily vegetation moisture content calculations, expected afternoon high temperature, afternoon minimum relative humidity and daytime wind speed.
Related to, but of less severity than, a Red Flag Warning is a Fire Weather Watch. which alerts the public and fire fighting agencies that conditions may exist for a Red Flag Warning after the initial forecast period (12 hours). It is generally issued 12 to 48 hours in advance of the conditions, but can also be issued up to 72 hours in advance. That watch then remains in effect until it expires, is canceled, or upgraded to a Red Flag Warning.
Here’s an example of a Red Flag Warning for Flagstaff, AZ.
WWUS85 KFGZ 120342 RFWFGZ RED FLAG WARNING NATIONAL WEATHER SERVICE FLAGSTAFF AZ 842 PM MST WED JUN 11 2008 AZZ111>117-140-120445- /O.EXP.KFGZ.FW.W.0023.000000T0000Z-080612T0400Z/ CHUSKA MOUNTAINS AND DEFIANCE PLATEAU (FIRE WEATHER ZONE 111)- LITTLE COLORADO RIVER VALLEY IN COCONINO COUNTY (FIRE WEATHER ZONE 112)- LITTLE COLORADO RIVER VALLEY IN NAVAJO COUNTY (FIRE WEATHER ZONE 113)- LITTLE COLORADO RIVER VALLEY IN APACHE COUNTY (FIRE WEATHER ZONE 114)-WESTERN MOGOLLON RIM (FIRE WEATHER ZONE 115)- EASTERN MOGOLLON RIM (FIRE WEATHER ZONE 116)- WHITE MOUNTAINS (FIRE WEATHER ZONE 117)- NORTHEAST PLATEAUS AND MESAS SOUTH OF HWY 264 (FIRE WEATHER ZONE 140)- 842 PM MST WED JUN 11 2008 ...RED FLAG WARNING WILL EXPIRE AT 9 PM MST THIS EVENING... THE RED FLAG WARNING WILL EXPIRE AT 9 PM MST THIS EVENING. WINDS WILL CONTINUE TO DIMINISH AND RELATIVE HUMIDITIES WILL INCREASE THIS EVENING...THUS THE RED FLAG WARNING WILL BE ALLOWED TO EXPIRE. $$
A couple days ago, as a storm was moving out of the area, we got some classic cirrus clouds in the upper atmosphere. These types of clouds are very high in the atmosphere, are traditionally thin with wispy strands, and can often herald the arrival of a storm (in this case they were remnants of a previous storm). Cirrus clouds like to live at levels above 26,000 feet (8000 meters), and are formed when water vapor freezes into ice crystals. The lack of moisture at such high altitudes is one of the reasons these clouds tend to present so thin and wispy.
Cirrus Clouds in Tucson, AZ
A lot of times in Tucson we see hair like filaments of ice crystals precipitating out of the clouds in the form of what’s called virga. These streaks often indicate the difference in the motion of air between the upper part of the cirrus cloud and the lower air below it. It appears as though rain is coming from the cloud, but it’s actually ice crystals, most of which evaporates before it hits the ground (especially in Arizona). On some days, cirrus cloud development is so extensive that they become virtually indistinguishable from one another, forming what’s called cirrostratus clouds.
Another type of cirrus cloud that you’re already very familiar with is the condensation trails, or contrails, seen in the sky coming from planes. These trails are basically artificial clouds formed by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets. If the air is cold enough, this trail will comprise tiny ice crystals. On some days, with a high level of air traffic, you can see contrails crisscrossing the sky, and these contrails often hang around for some time. It’s pretty neat!
Clouds are very cool, and an obviously integral part of weather. I intend to eventually go through all the various cloud types, hopefully using images I’ve shot with my camera. If you understand why a particular cloud type is in the area, you have a good idea of what sort of weather might be on the way.
For those of you living in Arizona and New Mexico, and who own Garmin GPS receivers, I have created a mapset called Southwest Trails that you may find useful on your outdoor adventures.
Southwest Trails is a transparent map overlay that you can put on your map-enabled Garmin GPS receiver. This allows you to see, and follow, trails using whatever maps you normally would on your GPSr…be it topo maps, City Navigator, or any other sort of map that you have on your GPS. Using data provided by The Trails Co-Op, as well as my own data and user submitted data, I hope to build an extensive mapset of trails across the Southwest. This should help make your outdoor experiences more enjoyable, and more safe.
Using Southwest Trails on your Gamin GPSr extends your ability to have a fun, safe time in the wilderness. No longer are you contrained to adding a few trails or tracks to your GPSr, limited by the design of the device. Since Southwest Trails is a complete mapset, you simply load it with all the other maps you want to have on your device, and any trail in the mapset is available for your use at all times. Now, the only limitation is the number of trails that come with Southwest Trails! It’s my hope that Southwest Trails will enhance your wilderness enjoyment, and keep you safe on your travels.
Southwest Trails is available for both Windows and Mac users. The current version, v0.51a, is available for download at Outdoor Resources.
Here is a link to my 12 of 12 for May 2009. The subject this month is the Esmond Station train wreck of 1903 in Esmond, AZ.