Northwest Wildfires: Any Relief Ahead?

The 2012 drought disaster is not only impacting agriculture in the nation's heartland.  

Drought conditions in the northern Rockies and Great Basin, coupled with persistent heat, low humidity and lack of rain have laid the foundation for a destructive period of wildfires recently in the Northwest and northern Rockies.  

In some locations, it hasn't rained (measurably) for over a month!  Sheridan, Wyo. is approaching their all-time record dry streak of 46 days, set in Dec. 2002-Jan. 2003.  

Seattle and Portland set and tied, respectively, their record driest August, each measuring only a trace of rainfall.  Even during the "summer dry season", this is exceptionally dry for the Pacific Northwest.  

As of Monday morning, 28 large wildfires were burning across 7 states from Washington and Oregon to North Dakota.  

Particularly problematic have been a cluster of fires in central Washington, north of Ellensburg and near Wenatchee.  Those clusters have now charred just over 87,000 acres.  

According to a story from KING-TV in Seattle, fire incident commander Rex Reed said, "We are in unprecedented weather conditions for the 20th of September.  It's something in my career that started in 1974 I've never experienced in the month of September."

What's the cause of this parched scenario?

Blame the Jet Stream

The crux of the problem, here, is that the polar jet stream was diverted north into Alaska and western Canada, before taking a plunge into the Great Lakes, forming a configuration resembling the Greek letter omega.  

Therefore, the main storm track was also channeled well away from the fire-fatigued Northwest and northern Rockies.  

Therefore, a dome of high pressure aloft produced sinking, stable air, squashing the formation of clouds, and, thus, rain.  This sinking, stable air can lead to dangerous air quality.

On a night with few clouds, air near the ground cools faster than air a few hundred feet aloft.  This "warm over cool" vertical configuration, called an inversion, does not allow the air in the lowest layers to mix.  

(AIR QUALITY ALERTS:  Wash. | Ore. | Idaho)

Usually, visibility improves in the afternoon, as increased surface heating adds at least some instability to the lower layers of the atmosphere, increasing vertical mixing and some dispersion of the smoke.  However, if the warm air aloft is sufficiently strong, this afternoon "breather" may not necessarily occur.

(LIVE CAMS:  wunderground.com)

Relief...or Another Nuisance?

The good news is that we could see some rain in the Northern Rockies. Unfortunately, it appears the better chance of showers will stay east of the fires in Washington.

An upper-level disturbance has snuck under the powerful "omega block" upper ridge.

(MAP: Alaska moist plume satellite loop)

So while the upper-air disturbance will bring the threat of thunderstorms and unwelcome lightning strikes, there will also be an opportunity for wetting rains with many of the spotty showers and thunderstorms popping up in the Northern Rockies into Tuesday.

Of course, this type of pattern can be a double-edged sword; even thunderstorms that do bring beneficial rains can still send lightning strikes outside the rain zone into dry areas, potentially igniting new fires and posing a personal risk to fire crews on the ground. And the shifting winds that usually accompany these storms are the exact opposite of what firefighters are looking for.

A broad, gentle, soaking rain or snow event would be better for fire suppression, but that doesn't appear to be in the cards this week.

(FORECASTS:  Missoula | Boise | Spokane | Wenatchee)

While precipitation typically picks up in the Northwest and northern Rockies starting in October as the jet stream migrates south into the U.S., the three-month outlook from NOAA released Thursday paints a dry picture, with below-average precipitation expected in the Pacific Northwest, eastward to the Bitterroots of Montana and Idaho.  

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