Springtime across portions of the Inland Northwest has been very dry at least compared to climatology. We can measure just how dry using various tools in our meteorological tool box. One of the conventional tools we use is simply looking at precipitation maps across the region. So how have things looked over the past 90 days?
As you can see things are highly variable across the region. near the Cascades it has actually been quite wet, with precipitation amounts nearly twice the average amount over the past 90 days. Also near the Washington/Idaho border amounts have been close to normal (aside from the southern Palouse, LC Valley, and Blue Mountains). However one area that stands out is a portion of central Washington in the lee of the Cascades stretching from Omak down to Moses Lake and The Tri-Cities and Yakima areas. Some of these locations have seen only a quarter of the normal precipitation during this period.
If we add the November precipitation amounts to the mix, the resulting map doesn't look much different for the dry areas.
So that got us thinking is this a record of some sort? Now granted these statistics are rather arbitrary, After all, who calculates records from 11/23 through 3/21? Not many people, but just for fun we will examine some of these odd records. First we will look at Yakima.
 |
| Yakima, WA precipitation 11/23-3/21 |
So in fact this is a top 10 driest period for Yakima, but it was actually drier in 2018. Now how about Omak? Not quite top 10 but close.
And finally lets look at the Ephrata:
Only in 16th place out of the last 70 years and the driest since 2014. So although this is noteworthy, it isn't really a historic dry spell.
But precipitation alone does not tell the entire story about a dry spell of weather. Other things to take into consideration during this period include; winds, temperatures, relative humidity levels, and solar radiation. All of these parameters will impact the amount of evaporation or evapotranspiration that can take place and how quickly the soils will dry out. That is a lot of information to keep track of, however fortunately we have a relatively new and very useful tool called the Evaporative Demand Drought Index or EDDI. This takes all the aforementioned parameters into account and states how thirsty the atmosphere is. So what is this index showing for the area? If we go back to November things look particularly bad:
Over the entire Lower 48, no area has seen more widespread and harsh drying conditions compared to normal. The categories on the map correspond to our typical drought outlooks. In this case the shading over eastern Washington corresponds to an ED4 or an exceptional drought. Does that mean this area is now in an exceptional drought? Not necessarily. A drought is not built on four months of weather alone, but if these trends continue we will certainly be faced with worsening drought conditions over this portion of eastern Washington. Since November here is how the drought monitor has been evolving across Washington.
These images start in the middle of November and advance two weeks at a time. The last image shows the drought conditions as of the middle of March. 
Specifically looking at the March 17th the outlook:
This map shows that almost 23% of Washington is in a D1 or moderate drought which just so happens to correspond closely to the first precipitation maps we showed. But what is interesting is the EDDI maps show worse conditions than what's depicted by official drought maps and sometimes this can foretell the trends. EDDI itself is not a drought prediction, but at short timescales (such as what we have shown), it indicates the potential for drought (or trends). So this area certainly bears watching.
So looking past the EDDI values what do the longer range weather forecasts tell us? That is always a tough question to answer, but lets look. The 8-14 day outlook through the beginning of April calls for near normal precipitation and cooler than normal temperatures. Near normal precipitation amounts would certainly help. The cooler than normal readings should also temper the thirstiness of the atmosphere however that could be overcome by having unusually dry air masses in place or prolonged windy conditions.
And finally, if we want to peer even farther into the future (April-June) the prognostication right now would suggest worsening drought conditions. But we will just have to wait and see.
So what are the ramifications of a drought over the Columbia Basin? While much of the area is irrigated for agriculture, there are areas which also have a considerable amount of sagebrush which could eventually lead to quick burning fires this spring. It could also lead to more blowing dust than normal on a windy day. Part of this dry area also encompasses some denser fuels both east and west of Omak. Right now the nearest snotels (snow measuring sensors) depict a snowpack around 65%. It's too early to say if this will lead to a busier than normal fire season in these areas as we have found the leading cause of a big fire season is a hot and dry summer.
We will revisit this topic later this Spring to see how things panned out.
