(Cover photo credit: Clifford Paguio Jr.)

If you garden or have been outdoors recently, you’re probably aware of what a dry spring it has been in Portland and the northern Willamette Valley. In many years, springtime is a rather mushy and marshy kind of season, with frequent rain keeping the ground muddy and the soil cold – sometimes lasting into May before conditions start to improve.

Not this year. Actually, not last year either. Over the past decade (or more accurately, beginning in 2013!) we seem to have caught a trend of dry weather in the spring, unlike what we traditionally would have expected. We’ve also had at least a couple springs where overall precipitation is pretty normal, but there’s a gaping 2-3 week stretch of bone-dry weather in between all the rain.

The month of March was very dry at PDX. Only 1.55″ of rain compared to the “old” normal of 3.68″. Somehow, with a bunch of cool upper-level troughs and orographic flow, the mountains managed to end up with above-normal snowpack by month’s end (actually some late February storms also helped with that part). And we’ve seen only 0.04″ at the airport so far in April, when we “should” be close to an inch at this point in the month! That goes a long way in explaining why the soil outside looks more like June or early July, than it does April.

By the way, our area is technically not in a drought at the moment. Drought conditions are horrible across most of the rest of the West, though:

One final tidbit: it hasn’t been all that warm this spring. March was actually slightly cooler than normal, with quite a few frosty nights for just about everyone outside the immediate downtown or the airport area.

LOOKING AHEAD

Other than a few light showers tomorrow, it’s going to remain VERY dry over the next 10 days, with tons of sunshine for most of next week. Our extremely dry spring is going to continue!

But temperatures? That question is a little tougher to answer. To illustrate the problem, I’m going to show you the 500mb anomaly maps for North America’s GFS model, over the past 3 days. Next week we are going to see a warm upper-level ridge over the Pacific to our immediate west – but a cold upper-level trough will dig down over the Interior West, Rockies, and parts of the Northern Plains. Different model runs have disagreed on the exact placement of the ridge and trough, however. Earlier runs from 2-3 days ago, showed the ridge a little closer to us and pushed the cold air more definitively to the south and east. That would have meant several days well into the 70s, possibly even flirting with 80 if everything lined up perfectly.

But now, models are bringing the cold air closer to the Pacific Northwest. Let’s take a look at the 12z WRF models from today, to get a better look at how the airmasses are playing out. First, 11am tomorrow Saturday:

Looks chilly! 925mb = approximately 2,500 feet elevation, so this would mean freezing levels over PDX around 1,500 feet. Possibly cold enough to see a few snowflakes at the top of the West Hills? Who knows. But shower activity is somewhat limited, and will die out during the daytime, leading us into the BIG DRY STRETCH.

Surface winds turn slightly offshore by Sunday, notice that the black pressure lines go NW to SE over Eastern Oregon.   This is a sign of higher pressure building on the east side:

By Monday, the lower atmosphere is beginning to warm up both east and west of the Cascades:

But then the Columbia Basin turns cooler again Tuesday as an arctic high pressure center begins to sink into the Northern Rockies! This will amplify the dry NNE wind across the region, and result in very low humidity levels.

By early Wednesday morning we see the full “punch” of the cold air east of the Cascades, with 925mb temps at or below freezing in most locations:

Things gradually begin turning warmer as we head toward Friday and Saturday, but the east side appears to remain quite cool through Thursday. What this means for Portland? Still tons of sunshine next week, but the airmass now looks cool enough to keep our highs in the 60s and lows in the 30s for a few days.

By the way….this cold air is originating from central Alaska – where April records have been falling in many towns and cities.

One final thought on the matter: If models were to continue to “retrograde” the pattern over the next couple days, and even more cold Canadian air makes it into the Pacific Northwest next week? Then we’d be looking at a very unusual situation for mid-April: high temps only in the 50s under full sunshine and offshore flow! Probably very painful spring freezes in NW Oregon and SW Washington as well, with the cold air and clear nights. Luckily for us it’s getting kind of late for the pattern to keep evolving, but there’s always that slight possibility…

THE FORECAST

Expect clouds to build in overnight, and showers to commence early tomorrow morning. They won’t be very long or heavy, probably just 0.1″ to 0.2″ rain in the metro area. Colder air will be filtering in during the day tomorrow, and continuing into tomorrow night as the skies clear. Expect high temps tomorrow to barely reach 50 degrees in Portland, and be down near freezing tomorrow and Sunday nights. (Record lows for PDX on Sunday and Monday morning are 33 and 30, by the way – we could definitely come close!).

Sunday and beyond looks very sunny with low humidity and either northerly or northeasterly wind at the surface. There will likely be a second punch of cool air into the Columbia Basin late Monday into Tuesday; that means high temps stay in the 60s for Portland at least through Wednesday and will likely be several degrees cooler in spots like The Dalles and Pendleton.

We will probably begin to warm up at some point between Thursday and Saturday…but we are expected to remain dry throughout this entire period.

One thing the maps are NOT showing, is a strong east wind through the Columbia River Gorge. This will be more of a regional NNE wind, as the cold air slides south.

So there you have it folks. This is going to go down as a historically dry first half of April, once we get through tomorrow’s showers. Luckily we have enough snow in the mountains, that things aren’t too dire for drought at the moment.

Enjoy the spring sunshine, regardless of the temps! -Karl