Rain is Coming to the Northwest During the Driest Time of the Year

 Every meteorologist knows that climatology only provides typical or average conditions and that natural atmospheric variability can provide some major excursions from normal conditions.

That will certainly be true next week.  Climatologically, the last week of July is the driest of the year in western Washington (see plot at SeaTac below).  Best time of the year to plan a barbecue or an outdoor wedding.

But this year, the last week of July will bring rain...and even significant rain in some locations.

Let me show you.

The weekend will be generally dry, with a wet system moving in Sunday night/Monday morning.

The 24-hour totals ending 5 AM Monday show lots of rain along the coast, with moisture extending into NW Washington.

The next 24-h totals ending 5 AM Tuesday show western Oregon and Washington getting thoroughly dampened with as much as a half inch of rain.  A lot for this time of the year.  Even eastern WA gets a piece of it.

And light rain continues into Tuesday.

How certain are we of this rain?  

Take a look at an ensemble of many predictions for rain accumulation in Seattle for the next week using the National Weather Service's GFS model. Each gray line is a different forecast with the blue line being the high-resolution prediction.  Considerable variation (and thus uncertainty), but nearly all the forecasts predict rain.

And don't forget the temperature.  The highly accurate Weather.com website has the high on Monday not even getting into the 70s (see below).

This cool/wet period should have minimal thunderstorm activity and will help reduce subsequent wildfire activity.

Northwest wildfires are most frequently grass fires. Climate change is not an important contributor to grass fires.

When many folks think about Northwest wildfires they visualize a burning forest.

But in reality, most Northwest wildfires are grass or range fires, with trees playing a minor role.

As we will see, grass fires have little to do with climate change, but a LOT to do with flammable, human-spread invasive grasses and human ignition.   And such grass fires can subsequently contribute to wildfires in adjacent forests.

Consider a visible satellite image from early this afternoon (from a NASA MODIS satellite).  You can clearly see the smoke from some fires over eastern Washington and Oregon.  This satellite also can sense the heat from the fires (orange dots).   

Look closely and you will notice that few fires are over elevated terrain with dense forests.  Most are associated with extensive grasses and range vegetation (including small shrubs).

For reference, here are the current fires from the Northwest Fire Coordination Center.

One of the most active Washington fires is the Black Canyon fire northwest of Yakima, which has spread over 4500 acres in grass (see photo below).

The biggest fire in the region is the Lone Rock Fire of northeast Oregon, which has now spread over 131,000 acres.  Grass and shrubs.   Most of the fires in our region...and most of the smoke production..is from grass and range vegetation.

In fact, the USDA Fuelcast website diagnoses how much grass/range fuel is available (see latest determination below).  Bountiful, above-average values are in place over eastern Oregon and Washington (dark green colors) thanks to a moist spring and leftover dead grass from last year.

It is important to note that large dangerous levels of light fuels such as grasses are NOT due to drought, but rather above-normal precipitation during growth periods.

Summer heat and drought have little impact on grass fire potential since our normally dry summers are virtually always able to cure and dry out grasses and the like.

Consider the Columbia NWR RAWS site near Othello (a picture of the nearby terrain is shown).

The ten hour fuel moisture percentage (the moisture level of light vegetation) for this site for the past several months is shown below.   Under roughly 12% is dry enough for fire.  Clearly, such fuels have been dry enough to burn for months. During every summer such fuels are ready to burn.  With or without global warming.

But something HAS changed that makes grass/range fires more likely:  the replacement of native (less flammable) bunch grasses with invasive, flammable grasses such as cheatgrass (also known as grassoline).

Here is a map of where cheatgrass has moved in.  Large areas of our region.

In addition, these human-spread flammable grasses are more likely to be ignited these days, with large increases in population as well as fire-inducing human activities (from fireworks and off-road vehicles to gunnery practice to deficient power infrastructure, to name only a few.)

Strong winds play a critical role in spreading grass fires, something of particular note on the windy, lower eastern slopes of the Cascades.

Too many media outlets blame grass and range fires on climate change without factual bases or supportive information.   Grass/range fires also play a large role in inducing forest fires, something I will discuss in a future blog.