Elsewhere in Weather News: August 23rd, 2014

More Wildfires out West

Wildfires continue to be the story out west as large areas of not only western Canada, but also the western United States are experiencing tinder dry conditions. As explained in last week’s EIWN, these conditions are due to the persistent ridging that took place in most of July and early August over the region. The ridge brought limited precipitation and warm, dry air to the western half of North America. The Drought Index reveals this well, showing a large chunk of the western US under severe to exceptional drought.

The Drought Index for this week continues to show significant drought in the west. (Source: USDM)
The Drought Index for this week continues to show significant drought in the west. (Source: USDM)

California which has seen no reprieve from the drought and saw another large wildfire flare up this week near Yosemite National Park. The fire, which started on August 18 just to the north of Oakhurst, quickly grew into a large wildfire that was out of control. Numerous air tankers, as well as 1,300 firefighters on the ground, are actively fighting the blaze. Yesterday the crews were able to gain more control of the fire, which was 95% contained as of Friday night. The wildfire is expected to be under full control by the end of this weekend. Some 500 structures in the path of the wildfire were at risk of getting torched on Tuesday and about 1,000 people had to evacuate from Oakhurst. As of Friday most homes had been saved though, with only 47 structures destroyed by the fire. The wildfire burnt an area totaling 612 acres, a small fire compared to the China Nose Fire discussed in last week’s EIWN which reached 9,100 acres in size this past week.

Map of current wildfires that are burning throughout California, Yosemite fire identified by the arrow. (Source: CAL Fire)
Map of current wildfires that are burning throughout California, Yosemite fire identified by the arrow. (Source: CAL Fire)

The next chance for rain in drought-stricken parts of California looks to be Tuesday as a trough digs into California and brings with it a chance of showers, however, there is signficant uncertainty regarding the strength of the trough.

Elsewhere in Weather News: May 17th, 2014

Wildfires Torch California, Helped by Strong Winds and Drought

This past week several wildfires have been burning out of control in San Diego County, just north of San Diego. It is not known whether any of the fires were started intentionally or not, however, the weather has played a significant role in hampering firefighting efforts. As of Friday evening there were four wildfires burning in the county which were all over 1,000 acres in size, and only one of these four was above 25% contained. There are two main points to note of as to why weather has played such a significant role in fueling the fires.

A large pyrocumulus cloud could be seen on Wednesday from San Diego looking towards the Cocos San Marcos fire. (Source: Mashable/Kent Horner)
A large pyrocumulus cloud could be seen on Wednesday from San Diego looking towards the Cocos San Marcos fire. (Source: Mashable/Kent Horner)

The Santa Ana Winds are the first to have a big impact on wildfires currently burning out of control in Southern California. These winds occur when air blows towards the Pacific Ocean from the mountain ranges to the east. As the air descends the mountain sides it warms and its relative humidity decreases causing for hot and dry winds. This past week, relative humidity as low as 3% was observed by stations in southern California, coupled with winds of 50km/h, this produced prime wildfire conditions. The second reason as to why the wildfires have been difficult to contain is the current drought situation in the region. A large ridge of high pressure has been persistent over the west coast for most of this past winter and part of this spring, making precipitation difficult to come by. The drought index currently indicates that an extreme drought (second highest tier) is occurring in the region where the fires are burning. In turn, the wildfires have little trouble spreading to moisture-starved vegetation and dried out brush.

This weekend offers a mixed-bag to firefighters. Strong winds and scorching temperatures will persist during the day, but winds will now be out of the west causing for slightly moister air coming onshore from the Pacific. Regardless, the Storm Prediction Center maintains an “elevated” fire risk for this weekend.

Elsewhere in Weather News: August 24th, 2013

California Wildfires Threaten National Park

A small wildfire started about a week ago in the back country trails of the California forests near Yosemite National Park has now turned into a raging wildfire. The wildfire which was initially located outside park boundaries has recently encroached on the national park territory. Covering about 425 square kilometers, the fire is only 2% contained bringing concern to many residents in the area who are under voluntary evacuations. Twelve buildings have been damaged or destroyed by fire already and another 4,500 around Yosemite are at risk. In all, 7,000 firefighters were brought in to battle the wildfire.

Wildfire smoke

Visible satellite shows extensive amount of smoke in eastern California. Smoke outlined in orange, red the location of the Yosemite fire. (Source: CoD satellite)

Very dry heat has been in place over the region for the last week priming the conditions for wildfires. Relative humidity values are expected to remain in the single digits, combined with temperatures in the mid to high twenties, no relief will be provided to the firemen battling the blaze. Drought has persisted since the beginning of summer for much of California and as of Friday 98% of the state is experiencing drought, with the severity ranging from moderately dry to extreme. Due to the dry conditions, 15-20 large wildfires are currently burning in California.

Usually, the wildfire risk peaks in late September in California as the Santa Ana winds come into play. Santa Ana winds are severe winds that are funneled through the mountains. As these winds are funneled through and descend in height (moving towards the coast) they are heated by natural processes, namely, adiabatic heating, causing for extremely hot and dry weather. These easily spread wildfires by blowing embers towards flammable vegetation.