AIR POLLUTION
CONTROL DISTRICT

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Old Advisory Events

The information herein is NOT intended for use as a weather forecast. The Air District DOES NOT forecast but solely compiles information from both the Phoenix and San Diego National Weather Offices to relay information concerning potential changes in ambient air concentrations that may impact the public.

December 13 2017
Be Advised
High wind levels have the potential to suspend particulate matter into the air. High levels of PM10 may pose an impact to public health. It is recommended that active children and adults, and people with respiratory disease, such as asthma, limit their outdoor activities.

Potential increases in PM10 concentrations may increase to moderate or unhealthy level.

Imperial County Weather Synopsis
WINDS
NE to E winds of 20-30 mph with gusts of 50 mph and 60 mph along coastal foothills/slopes and through/below the canyon/passes.

Light surface winds to persist through Wednesday early evenings for Imperial and Blythe at time favoring north and west headings. Winds will begin to increase overnight and into Thursday am.

FIRE WEATHER
A FIRE WEATHER WATCH
Weak Santa Ana winds will continue today with humidity falling into the 5-8 percent range away from the coast. The Santa Ana winds will strength significantly early Thursday morning, first in the San Bernardino county coastal slopes, through and below the Cajon Pass, and into the Santa Ana mountains/foothills around 4 am and then into the Riverside county coastal slopes/foothills by 10 am. NE to E winds will peak at around 20-30 mph with gusts to 50 mph and locally 60 mph in those areas, with day-time humidity once again lowering to the 5-8 percent range. The winds will become less widespread Thursday evening and gradually weaken through early Friday morning. Overnight recovery will be very poor.

Late Friday through Saturday afternoon, there will be a brief period of onshore winds and slightly higher humidity. Then another burst of Santa Ana winds is likely Sunday into early Monday, with humidity falling to 10-15 percent away from the coast. Thus, we could see another round of critical fire weather conditions Sunday-Early Monday.

DISCUSSION FROM THE SAN DIEGO OFFICE
The dry air and clear skies across the region resulted in another morning of highly varying temperatures. An upper level low remained over Baja and Sonora, while an upper level ridge extended into California and Nevada. The continued offshore flow (Santa Ana winds) will continue to bring much warmer than normal weather this aftern0on, with highs 5-15 degrees above normal in most locations.

Currently the offshore pressure gradients from San Diego to Las Vegas were 4.2 mb, whereas they were 6.4 mb at this time yesterday. This will change when a short-wave trough moves through the Great Basin area tonight and down into Sonora Mexico tomorrow evening. This will result in strengthening offshore pressure gradients and upper level support - resulting in a burst of Santa Ana winds Thursday morning and afternoon then gradually weakening Thursday night into Friday morning.

SYNOPSIS FROM THE PHOENIX OFFICE
Continued high pressure over the western United States will keep the region in a generally dry and warmer than normal pattern through mid-week. A dry low-pressure system from the norther will pass through the area on Thursday followed by a second, stronger dry cold front system over the weekend, which will usher in noticeably cooler daytime temperatures for the weekend.
Weather Story Phoenix Station Weather Story San Diego Station
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