Tuesday, September 15, 2015

Some Relief on the Way for Washington, Oregon, Northern California.

A large trough of low pressure moving in from off of the Pacific will bring some much needed rain to the Pacific Northwest and some of northern California the next couple of days.

500 millibar map forecast for 5:00 a.m. PDT Wednesday, September 16
showing upper level trough moving on to the West Coast.

The rain, along with a turn to cooler weather will be most welcome by firefighters battling the many wildfires in progress in Washington, Montana, Oregon, and northern California.

Major wildfires in the U.S.

It's not in the news much, but there are also numerous wildfires in progress across the northern half of Alberta.

Major wildfires in Canada

However, it appears northern and central Alberta may see only scattered showers and miss out on any substantial widespread rainfall with the system affecting the northwestern U.S.

Rainfall amounts of the next 72 hours are expected to be from 0.75 to more than 1.50 inches along the coast of Oregon and Washington to as well as the Cascades. Rainfall is expected to be less in the Willamette Valley and in central and eastern Washington. Rainfall in northern California is likely to be heaviest in the extreme northwest portion of the state, in the higher coastal ranges, with amounts falling off to the south and east.

Quantitative Precipitation Forecast for the 72 hour period ending 5:00 p.m. PDT September 18.

Significant rain should fall on a few northern California wildfires, but the two largest and least controlled fires, the Butte and Valley fires, will likely only see lighter rain amounts. While the rain likely won't be significant in the worst fire areas,the increasing humidity and cooler weather should be beneficial in controlling the fires. The down side could be strong winds in some areas as the low pressure center moves inland..

The cooler weather marks a big change in the weather pattern in the Pacific Northwest. Seattle (SEATAC Airport) experienced 51 days of temperatures equal to or greater than 80°F, the most on record.  Portland, OR recorded 29 days with high temperatures equal to or greater than 90°F, breaking the old record of 24 set in 2009. The average number of days 90°F or above is 12.

Some more good news is that the latest 6-10 day outlook favors cooler and wetter than normal weather for these same areas.

Much further down the coast in southern California, moisture streaming ashore the remnants of Hurricane Linda produced some impressive rainfall totals this morning.

Radar image for southern California at 8:53 am PDT this morning showing rain showers
extending from near San Diego to northwest of Los Angeles.

CoCoRaHS observers in Los Angeles County, northern Orange County, and northwestern Riverside County measured more than an inch of rain this morning with 2.08 inches at CA-LA-48, Santa Monica 1.3 NNE. Lesser but still very welcome amounts occurred through much of southern California.

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