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.

October 20 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
Near-Term Weather for Friday, October 20, 2016
Blowing Dust Advisory remains in effect for Imperial County until 6 p.m. Friday, October 20.
Wind Advisory remains in effect for Imperial County until 11 p.m. Friday, October 20.
Gusty winds this afternoon will lead to areas of blowing dust across parts of southeast California and southwest Arizona. Winds will decrease into Saturday, except across the lower Colorado River Valley. Primary concerns in the short term revolve around blowing dust and strong winds, especially across southwest Arizona and southeast California. Satellite imagery and observations indicate plumes of blowing sand and dust have developed across Imperial and Yuma Counties, with visibilities locally restricted down to one mile. This is in response to strong westerly flow moving across southern California into Arizona, supporting gusts of 40-50 mph across the I-8 corridor primarily from Yuma County westward. Some increase in west-southwesterly winds has been noted this afternoon across south-central Arizona, but the best phasing of the strongest flow aloft with peak heating will remain focused west of the Phoenix area. The Blowing Dust Advisory, mainly for Imperial and Yuma Counties, remains in effect until 01Z, while a Wind Advisory remains in effect until 06Z. By tomorrow, winds should generally weaken area-wide, except near the lower Colorado River Valley, where north winds of 15-25 mph will remain possible.

SYNOPSIS FROM THE SAN DIEGO OFFICE
A trough of low pressure will move through California tonight, with isolated showers ending and mountain and desert winds decreasing. Offshore flow will develop this weekend and continue through at least Tuesday, bringing hot and dry weather along with occasional gusty northeast winds, especially through and below passes and canyons. Weak onshore flow is forecast to develop Wednesday and Thursday for a modest cooling trend. Winds are gusting to over 45 mph mainly in the mountains and locally into deserts, and those will continue through this evening, then decrease overnight. It will even be breezy along the coast. The trough axis moves east tonight and high pressure aloft begins to build this weekend. The trough will leave behind cold air into the Great Basin, which will lead to surface high pressure and an offshore pressure gradient aligned toward Southern California. That will force offshore winds through and below mountain passes starting Saturday morning mainly through and below Cajon Pass and into eastern Orange County. For more on anticipated critical fire weather conditions, see fire weather discussion below. These locally breezy offshore winds continue Sunday, then increase in coverage and strength Monday through Tuesday. Top gusts Monday and Tuesday mornings will exceed 40 mph in, and adjacent to, foothills. With strong high pressure aloft combining with dry offshore flow, temperatures will soar each day. The hottest days Monday and Tuesday will feature some areas exceeding 100 degrees west of the mountains and even exceeding 90 along parts of the coast.

FROM THE PHOENIX OFFICE
Near-normal temperatures will make a brief return this weekend, before a strong area of high pressure builds over the Western U.S. This will result in another warming trend with dry conditions and well above normal temperatures throughout much of next week. By tomorrow, winds should generally weaken area-wide, except near the lower Colorado River Valley, where north winds of 15-25 mph will remain possible. The coolest daytime temperatures in awhile will also occur in the wake of the fast-moving storm system. High temperatures in the mid-80s are expected across most lower-desert locations. Unfortunately, a rapid return to well above-normal temperatures will occur by Monday, as the large-scale pattern becomes highly amplified with a ridge building across the Pacific coast. Temperatures in the mid-upper 90s are expected Monday through Wednesday. Longer-range models are now trending towards another pattern change by next weekend, developing the coldest and most expansive upper trough of the season across the northern Rockies/northern Plains into the Four Corners region. This will likely result in a strong cold front sweeping south-southeastward across the Great Basin, potentially clipping western/central Arizona and bringing cooler temperatures by next weekend.
Weather Story Phoenix Station Weather Story San Diego Station
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