April 2021 was by far the driest April on record for Portland, with only 0.39″ of rain falling at Portland Int’l Airport. This record-dry April occurred on the heels of a much drier-than-average March. As I explained in my last blog post, the entire Western US is experiencing drought conditions, and although the drought is most severe over California and the Desert Southwest, the drought has intensified over the Pacific NW over the past two months. According to the US Drought Monitor, much of the Willamette Valley is now in a “Moderate” drought, while much of Eastern Oregon is in a “Severe,” “Extreme,” or even an “Exceptional” drought, the highest on the scale.
Portland reached 69 today with mostly sunny skies and a strengthening ridge overhead. I shot a few hoops & did a bit of skateboarding this afternoon at Grant Park and the weather was just perfect. The ridge will reach peak strength tomorrow and a thermal trough will form along the I-5 corridor, resulting in well-above-average temperatures and light offshore flow. Current forecasts have Portland and much of the Willamette Valley hitting the low-mid 80s tomorrow… I’m hoping to go for a nice spring swim in the Willamette if I have some free time! Just remember that rivers are still running high and are extremely cold this time of the year, so use extra caution in some of the slower-moving rivers like the Willamette by downtown Portland, and simply stay out of the colder, swifter rivers like the Clackamas or Sandy.
A thermal trough will build over the Willamette Valley & SW Washington tomorrow, bringing low 80s to much of the Portland metro despite increasing high clouds ahead of an approaching front. Temps will fall to the low 60s on Thursday as this cold front moves inland. #wawx #orwx pic.twitter.com/tQZy82wOH1
— Charlie Phillips (@GeoduckChuck) May 5, 2021
Temperatures will plummet on Thursday as a system offshore (visible in the image below as the trough and accompanying clouds 1000-1500 miles west of the West Coast) moves inland. Thankfully, this system should bring us some much-needed rain, with an initial front arriving on Thursday afternoon & showers persisting through Friday afternoon/evening.
There’s a fairly large spread in models – the European model only gives us a tenth of an inch, while the GFS gives us anywhere from 0.25″ – 0.5.” I sure I’m not alone in rooting for the rainier GFS solution!
The 12Z Euro keeps most of the rain expected Thursday & Friday over Washington, while the 12Z GFS brings it south into the Willamette Valley. If the GFS is right, Portland could get more rain Thursday & Friday than the entire 0.39″ they saw in April! #fingerscrossed #orwx #wawx pic.twitter.com/ckaTyR19l8
— Charlie Phillips (@GeoduckChuck) May 5, 2021
Saturday & Sunday should be dry with a slight warming trend, and I think next week will be slightly warmer-than-average with continued drier-than-average conditions. Apart from tomorrow, I don’t see any “early spring heat waves” through at least the middle of next week.
On another note, NOAA released their updated 30-year climatology today! NOAA’s 30-year climatology datasets are the “gold standard” for climatology data, but because they are so robust and take so much effort to create, they are only updated once a decade. The image below shows the change in temperatures and precipitation over the US from the old, 1981-2010 climatology dataset to the newly-released 1991-2020 dataset. As you can see, the 1991-2020 dataset is warmer just about everywhere and drier over much of the Western US, apart from the Pacific NW.
After much anticipation, today @NOAA releases the new U.S. Climate Normals for 1991–2020. Normals help you compare what’s happening in your neck of the woods with the last 30 years. Find out: https://t.co/3pFfT2tIfV @NWS @CommerceGov #ClimateNormals #NOAAClimateNormals pic.twitter.com/KtYF7upaeD
— NOAA NCEI Climate (@NOAANCEIclimate) May 4, 2021
We have less confidence in how precipitation will change with global warming than how temperatures will change, but many climate models show the Western US becoming drier with more severe droughts, which is awful news for wildfires and water supplies. It’s discouraging to see how well this has verified over the past 10 years, and although there’s no guarantee that the West will continue to trend drier in future decades, it’s clear that we need to be proactive and prepare for a drier West than we’ve seen in the past.
On that sober note, enjoy the warm weather tomorrow and rain Thursday afternoon & Friday, and I hope you’ll join me in doing some rain dances to bring more precipitation to the Western US later this month!
Charlie
