Not Much Rain & A Look Ahead Into May

April 25, 2021

9pm Sunday…

Well, it rained a bit yesterday, but officially nothing in Portland today. Showers were widely scattered and mainly concentrated over the Coast Range and Cascades. Saturday’s showers showed up and were about what I expected, but not today.

Officially nothing measurable fell in Portland, which means it’s still the driest April on record with just five days left this month. I think there’s a very good chance it’ll remain the driest April we’ve seen…more on that below

WHAT’S AHEAD

A cool upper-level low (pool of cold air overhead) is sitting along the West Coast this evening. It’s going to stick around for one more day

But that trough leaves late tomorrow as strong and very warm high pressure builds in the upper atmosphere. By Thursday its hot anywhere south of southern Oregon and quite warm here. We could be close to 80 again Thursday

The ridge flattens for the first weekend of May, which may (or may not) lead to some decent showers

But there doesn’t appear to be another cold trough headed our way for at least 10 days! By Wednesday the 5th of May, weak ridging is overhead again

I’m only showing you one operational model, the ECMWF, but others are similar with upper level heights running higher than average the next 10 days…which takes us into the first week of May. It’s pretty clear that the much anticipated turn towards a wet spell is looking a bit weak. The GFS, ECMWF, & GEM models barely produce 1″ of rain in the lowlands of western Oregon & southwest Washington the next 10 days. And these numbers seem “irrationally exuberant” when compared with the upper-level maps.

To summarize:

  1. This record dry spring will continue into the first week of May.
  2. You will need to continue watering this week, since I don’t see any significant rain (0.25″ or more) until at least Friday evening
  3. It’s possible we still don’t get a soaking next weekend either, but we don’t know yet.
  4. We have three guaranteed dry days Tuesday through Thursday as the ridge builds overhead

RECORD DRY SPRING

I figured we could get at least 1/2″ of rain this weekend through tomorrow plus a bit more later next week. Not typically a tough feat in April. That’s why I was poo-pooing the idea of seeing our driest April on record. But as of tonight it’s looking quite likely once the clock strikes midnight this Friday. The last 7 years…

Notice last year was also in the top 5 driest Aprils… If we get more than .27″ rain before midnight Friday, it WON’T be the driest April on record at PDX. That may happen

Of course something we have been talking about for the past few weeks has been the record dry spring. It’s amazing to think we’ve seen less than 2″ rain in all of March and April! This year just 1.81″ at PDX so far. These records go back to 1940. I also checked the downtown location (records back to around 1880); there appear to be only two other springs so dry, 1885 & 1926. Its the driest spring in Salem since 1926 as well…so far

This is the 2nd spring with very dry March-April conditions. 2017 was a soaker eh?

WHAT DOES THIS MEAN FOR MAY/JUNE, OR SUMMER?

First, there’s no reason to freak out (yet) over the lack of spring rain.

IF we get deep into May with these conditions, I’ll start getting concerned. If the dry pattern continues into early-mid June then we have a serious problem. That’s only six weeks away.

We already know that we need at least normal rain from this point forward to fill reservoirs like Detroit and Green Peter. And we also know drought conditions continue to creep north through Oregon.

Lack of mountain snow and warm temperatures have caused a faster-than-normal melt in the Cascades. The snow melt season had been delayed due to a chilly March, but now snowpack is below average in most of Oregon

Does a dry March+April mean we’re headed for a serious drought? Possibly, I did a little bit of research this evening. I looked at the ten driest springs (up to this point) and then looked forward into May and June to see what happened. Here you go:

Yep, it was a divided verdict. In 2-3 years we saw a soaking in May, or June, or a combo of both in 4 of those years. But in 6 of those years, drier than normal conditions continued as we headed into early summer (June). It is interesting that only one May saw less than 1″ of rain. That shows you how unusual it is to have a sub 1″ rain month in spring in Portland. That’s what we’re seeing right now.

The following summers? I didn’t check rain since we don’t get much in July/August anyway, but I did check temperatures. Only 1 of the 10 summers could be considered a “cool” one. All the rest were average or hot. Does that mean we will see a 9th consecutive warm/hot summer? We don’t know, but this would imply a dry spring can lead to at least a normal/warm summer.

So…there’s a decent chance we continue with a dry-ish spring, but there’s no reason it can’t still turn around.

For now, keep watering! Chief Meteorologist Mark Nelsen


11 Consecutive Sunny Days in April, But Clouds & Rain In Sight

April 21, 2021

9pm Wednesday…

Drought and fire weather concerns aside, this has been an amazing stretch of summer weather…in mid-April! Today we made it to 78 degrees in Portland; similar to an early July day

Think back…how many times can you recall waking up to sunshine for 11 consecutive days? It’s nothing unusual if you live east of the Cascades of course (drier climate). But west of the mountains, even in summer, it’s rare. From fall through spring it doesn’t happen because we have weather systems moving through from time to time. In July and August we get occasional surges of cooler marine air and low clouds. So even in the peak of summer we typically don’t see more than 7 cloudless days. Sure, we’ve seen some high clouds a couple mornings recently, but no significant cloud cover since Saturday the 10th! I don’t have stats for cloud cover, but I think it’s quite likely we haven’t seen this in April in a long time!

APRIL TEMPERATURES

Today is the 8th consecutive 70 degree day in Portland.

This is the longest stretch in the 70s ever observed here in April. Those records go back to 1940.

We set one record high for the date last Saturday, but no other warm temperature records. In fact, as of this moment it’s just the 13th warmest April on record; well below 2016, 2004, and just last year. It’s probably fair to assume the ranking will drop once we hit the cool/showery weather this weekend. So it’s not a spectacularly warm April, but consistently warm. I’ve never seen such a long stretch of offshore flow and extremely low humidity in March or April. Probably not in May either. Dewpoints have regularly been in the 30s, or even 20s for multiple days. The woods around my house are as dry/crunchy as mid-summer after repeated bouts of the dry easterly wind. I’ve watered my deck pots several times over the past week or so. Luckily much of the Cascades remains under at least some snowpack and we still have the subsoil wet from winter rains.

APRIL RAIN

So dry…only 2 days with measurable rain in the first three weeks of the month. So far, just .09″ rain this month.

Of course we can easily get 1-2″ rain in a week this time of year so don’t assume it’s going to be any sort of record dry April.

WHAT’S AHEAD

An upper-level trough will move through the Pacific Northwest this weekend, with the first rain arriving Friday evening (late). You can see the well below average heights in the atmosphere on the Sunday ECMWF ensemble 500mb chart. This screams cold showers, maybe hail and thunder too.

By the middle of next week, a (transitory) upper-level ridge is overhead, cutting off the rain again. More rain should return the latter half of next week as April wraps up.

On the ECMWF 24 hour precipitation ensemble chart, you see the solid chance for a soaking rain this weekend, but plenty of gaps the middle of next week (Tuesday/Wednesday). Then more widespread rain again later in the week. Each horizontal line is one individual ensemble member. On a side note, these ensembles are run at a lower resolution than the “operational” ECMWF run, but about a year from now the resolution will be upgraded significantly.

The GEFS (GFS ensembles) are similar

Could we see an inch or more in the lowest/driest areas west of the Cascades before the month wraps up? Possibly. Both the GEFS & EPS are showing 1-2″ in the last 7 days of the month in the lowlands with 2″ or more in the foothills and Cascades/Coast Range

So I wouldn’t be surprised if we end up with a drier than average April, but it’s unlikely we’ll see a record dry month. Let’s hope for a soaking at some point in May!

Chief Meteorologist Mark Nelsen


A Big Taste of Summer…In April

April 18, 2021

9:30pm Sunday...

What a weekend it has been! Both days in the 80s west of the Cascades, no rain, sunny from sunrise to sunset, and not much wind either. Must be mid-July right? No, just mid-April.

Portland ended up with these numbers the past three days…

A marine push of cooler air arrived on the central coast yesterday, but didn’t make it the Astoria and Long Beach until early today. So a few spots hit 80 yesterday up north, but ALL areas were much cooler today. Newport couldn’t even make it to 50. Keep in mind that in these situations proximity to the ocean determines how warm a location gets. Newport’s observations are taken at the airport, very close to the beaches. Yet Tillamook airport is quite a few miles inland = warmer when the marine layer is very shallow. Just a few miles inland at Toledo it was around 70 degrees today.

Typically I’d expect lots of that marine air to pour inland tonight. Then, since it’s so early in the season, we’d wake up to low clouds and afternoon highs only reaching to 65 or so tomorrow. But while we do have some marine air pushing inland this evening, a fresh round of “cool” and dry Canadian air is surging south through Eastern Washington. This is due to an upper-level disturbance moving down the back side of the warm ridge we are under. There was a gusty WEST wind in the Gorge today with the onshore flow, but by tomorrow morning models tell us we’ll be back to 3-5 millibars EASTERLY gradient. Expect gusts 30-50 mph at Vista House the first half of the day…quite a change. Spokane’s airport just reported blowing dust and a squall this hour as the late season “arctic front” passes by. Strong northeast wind is spreading south quickly this evening. So we’re back to a mild easterly wind tomorrow = no marine push and/or low clouds. Of course we’ll still be a bit cooler, but 10-12 degrees above normal instead of 20-22 above. To summarize, we have three more beautiful days, just some high clouds at times. That will give us 11 totally dry and mainly/all sunny days. Extremely rare in April! Check out that slow temperature rise since the cool/showery 53 degree day on Saturday the 10th

It’s back to onshore flow and a cooler atmosphere Thursday through next weekend…back to normal. We’re going for this right now. Typical late April weather for next weekend.

Of course we badly need rain, it’s now officially the driest spring (at this point) we’ve seen in Portland since at least 1940. The ground is chalky dry in my garden; although I see the woods still have moisture an inch or so below.

How much rain is ahead? Enough to wet things down for sure, but we could use a nice 2-3″ over the next two weeks to start soaking the ground again. ECMWF ensembles say most likely it begins Saturday and continues off/on through the end of the month. So wrap up your deck-staining and other outdoor activities this Thursday/Friday and assume we’re headed into a wet period.

So is this very dry spring unusual? Yes, of course. But this isn’t a trend we’ve been seeing in springtime. In fact we’ve been turning a bit WETTER west of the Cascades in springtime compared to 100 years ago. I just checked the entire NCDC Oregon Climate Zone #2 (western valleys) for March-April-May precipitation. This average ALL climate stations in the lower elevations westside. The last three years have been a bit on the dry side, but not excessively so.  One thing to keep in mind, we still have 6 weeks of “spring” left and a May soaker could make up for this very dry start.

What about temperatures? Here are spring temperatures for this same western lowlands climate zone. What really sticks out is the cyclical stuff; we go through several years of cool/wet springs (2008-2012), then warmer periods. The last 8-9 springs have been above average…we haven’t seen a “cold spring” since 2012. That’s good for gardening, but as we know, it can be bad for summer fire season. Also notice temperatures have NOT been rising dramatically at all during this spring period. Winters are warming, summers are warming, but not much with spring…so far.

That’s it for now. Enjoy a few more bright days with more comfortable temps than we’ve see the past two days. Eventually the cool showers WILL return.

Chief Meteorologist Mark Nelsen


It’s Portland’s Driest Spring So Far, Plus Summerlike Temps

April 15, 2021

9:30pm Thursday…

It’s been nice waking up to sunshine every one of the past five days. And we’ll do it for at least another five, but now it’s getting a bit…weird. It’s been nice, but we don’t live in Sacramento. Most of our viewers live in western Oregon and Washington.

Take a look at those temperatures the past few days. We’ve gone from a high of 53 Saturday to 76 today in Portland…the warmest day of the year.

VERY DRY SPRING

We’ve only seen .09″ rain so far this month and now we’ve reached the midpoint of meteorological spring. March-April-May is spring in the northern hemisphere (officially defined by NOAA). Take a look at the numbers…in the past 7 weeks we’ve seen less than 2″ rain in Portland.

Assuming it doesn’t rain by Sunday (it won’t), this will be the driest March 1st – April 18th on record at PDX. Those numbers go back to 1940. I checked Salem, Astoria, & Olympia. Similar extremely dry numbers.

Last year was a bit dry, our 5th driest April. Luckily last year we had a wetter May and very wet June to make up for it.

I remember the flooded sports fields back in 2017 & 2018. Each year is different, but this spring (so far) is exceptionally dry.

The NWS has a Red Flag Warning out for much of western Oregon, also quite rare for April

WHAT’S AHEAD?

A strong ridge of high pressure in the upper atmosphere is centered in British Columbia with a cool low just to our southeast. It’s been a chilly mid-week from Boise over to western Colorado, snow in spots

That warm ridge slides down right over us by Saturday…warmer atmosphere overhead

Then it weakens a bit by Monday, but at the same time another pocket of cool air is sliding down just to our east

The result will be offshore (easterly) flow and warming temps tomorrow & Saturday. 850 millibar temps to around +12 to +13 imply we could get as high as 84, but we’re going slightly conservative with a high of 82 Saturday. That would be enough to break a record for the day

Then onshore flow arrives on the coast Saturday afternoon and tries to push a bit inland Sunday. I don’t think that will drop our temperature more than a degree or two Sunday. The result is a very summerlike 3 days ahead. Then as the cool air drops in to our east Monday, that’s high pressure which renews the easterly flow across the region. A cooler airmass Monday, but offshore flow returns quite strong. Looks like more sunshine for Monday and Tuesday. This all adds up to five more days of sunshine.

When does the rain return? Each operational model is different, but they all suggest a pattern change later next week. The ECMWF ensemble forecast suggests not much rain Wednesday/Thursday, but by Friday and into that last full weekend of April we could be back to a more typical wet/showery weather pattern

We can’t do anything about the lack of rain, so enjoy the sunshine while we have it. And there’s no reason to panic thinking that we’re going to have a “terrible fire season”…remember last June we had soaking rains the first part of the month.

Chief Meteorologist Mark Nelsen


Cold Nights & A Sunny April Week Ahead

April 11, 2021

9:30pm Sunday…

I’ve been on vacation the past 9 days, a bit of bike riding down in the Moab (Utah) area with my son. Sorry, not many pictures because I was having fun. Actually I was home part of that time as well; but I’m back at work this evening. Calling it “work” is a bit of a stretch meteorologically since we are in a VERY stable weather pattern for at least the next 7 days.

THE COLD

First, the record cold this morning. We’ve seen LOTS of late season frost the past month, because we’ve seen much drier than normal weather. Keep in mind we’ve seen less than 2″ of rain in six weeks in Portland! Drier air = less cloud cover = colder nights. Basically west of the Cascades we’ve been in more of a “continental climate” than usual. Right now dewpoints are down in the 20s in the metro area. Sometimes we don’t see them get that low all April long. Our spring in Portland (so far) is similar to a typical spring you would experience east of the Cascades. Wide temperature range; nights running cooler than average, but daytime slightly warmer. Last night we saw widespread cold readings. Look at the Portland metro lows:

Lots of upper 20s, even a few mid 20s…pretty cold for mid April! Portland airport dropped to 32 degrees, the first time we’ve seen frost beyond April 10th since 1982. Quite an impressive reading considering the metro area is much larger than 40 years ago, more of an urban “heat island” now. Plus our climate has warmed a bit in general. We don’t see many record lows in Portland the last couple of decades. Record lows were also set in several other locations west of the Cascades

My peach tree is blooming and still LOOKS okay. Maybe it needed to be under 27 degrees to do significant damage, we will see within the next couple of weeks.

Tonight won’t be quite as chilly as the airmass has warmed a bit. Sure, some frost for outlying areas, but everyone should be at least 2-3 degrees warmer than last night.

AN AMAZING WEEK AHEAD

When I came in and looked at the maps/models today, it became obvious we are in for almost continuous sunshine for the next week for much of Oregon and SW Washington. That includes the coastline.

In the upper atmosphere, a ridge of high pressure (zigzag blue line) and its sinking airmass is developing just to our west and north, keeping weather systems away. But a cold pool of air (upper-level trough) is coming down the back side of that out of Canada. By Tuesday it is centered over the Idaho/Nevada/Utah area.

It’s far enough south and east of us to keep cloud cover away. But we get a relatively strong northeast flow overhead. That’s offshore flow. Even though the air starts cool, this pattern under strong April sunshine will push our temperatures above normal. By Thursday the setup is strong high pressure to the north with a low south. This can be (and will be) a very stable weather pattern. It’s called a “Rex Block”.

Then between Thursday and Saturday the warm ridge expands south and east over us as the low moves away. A warming atmosphere means high temperatures climb from just above average to MUCH above normal. We’re headed from the lower 60s tomorrow to mid-upper 70s Saturday west of the Cascades. After tonight the widespread frosts west of the Cascades should disappear as well.

Meanwhile a deep layer of offshore wind flow continues all week, although it may weaken briefly Wednesday/Thursday. Check out the WRF-GFS cross-section over Portland; Wednesday afternoon (right side) through Sunday afternoon (left side). Yellow line is around mountain pass elevation.

Offshore flow almost the entire time, plus a warming atmosphere. No cloud cover (maybe a few thin high clouds). It doesn’t get better than this anytime April through June!

At this point we don’t appear to be setting up for record high temperatures…all in the 80s mid-April and beyond. But we’ll go from a perfectly average 60, to around 70 by Wednesday/Thursday, to upper 70s Saturday and possibly Sunday. For the weather geeks, 850mb temps need to make it to at least +10 over Salem this time of year to hit 80 in Portland with perfect conditions. That COULD happen Saturday, we will see. Regardless, this 7 Day forecast is something else for mid April!

When will it end? ECMWF ensemble precipitation forecasts imply the ridge breaks down somewhat next week, so it’s safe to assume showers will appear at some point after NEXT Monday

That’s it for now, enjoy the sunshine!

Chief Meteorologist Mark Nelsen


April Begins Warm & Dry

April 1, 2021

9:30pm Thursday…

It was another fantastic spring day across the region wasn’t it? Just a few thin high clouds drifting lazily by at times. We made it to 68 in Portland, just a few notches down from the 71 yesterday (March 31st). Salem and Eugene were a bit warmer than yesterday.

March Recap

In my opinion, we’ve had a great start to spring if you like to get outdoors. March was drier than average, with plenty of partly cloudy or sunny days. It was our 7th driest on record at PDX (out of 81), and the 2nd driest during a La Niña winter/spring.

Just as interesting? We’ve now gone through four consecutive years with drier than normal conditions in March. Payback will be a real tough in some future March!

And you can see most of the West has been quite dry this past month

What about temperatures? A bit cooler than average. Not a huge departure, but most of Oregon has been cooler than normal.

Is this unusual? Not really. Looking back at past La Nina springs, there is a very strong signal for cooler than normal across the Pacific Northwest. This is a composite of April-June temperatures for the last 20 La Nina springs. Pretty clear signal isn’t it?

One would think a cool spring would also be wet, but that’s not the case. April through June precipitation from those same 20 springs…well below average.

I don’t mind these springs too much; plenty of sunny or partly cloudy days mixed in with the wet days. Plenty of chilly nights and late frosts (like this year), but a cold/clear night is followed by very strong April/May sunshine too!

Snowpack is still running well ahead of average in northern Oregon; no significant spring melt yet due to the cooler temps. Southern Oregon is not in good shape as of April 1st. Lots of drought issues are likely across the Klamath and Good Lake basins

What’s Ahead?

April is what I call the “greening up” month west of the Cascades. Most deciduous shrubs and trees come alive this month; bare of foliage to start, then flush with fresh leaves & green by April 30th. It’s very dramatic in the woods around my home. Right now the ground is pretty much bare and bright sunshine makes it down to the forest floor. But four weeks from now all the ferns will have popped out of the ground, alder/maple trees will be leafed out. It turns darker and shady in the woods from that point through October.

Portland’s average high temperature rises from 59 > 64, and we typically see 5 days at/above 70 degrees. Last year we made it to 76 degrees late in the month

We have also entered the drier half of the year…just barely. April is slightly drier than October in a typical year as the rainy season slowly winds down

In the short term, we’ve got a dying cold front that brings a few sprinkles to the northern Oregon coastline tomorrow. Then (unfortunately) on Easter a splitting upper-level trough brings another dying front overhead. Lots of clouds that day but not much rain! The fresh 00z GRAF model shows how little rain we expect through Sunday afternoon. If there is no color on this map, that means less than 0.10″ precipitation.

The result? Not much rain and temperatures near normal for this first week of April. And…

EASTER WILL NOT BE A WASHOUT, JUST LOTS OF CLOUDS PLUS A FEW SPRINKLES OR A SHOWER

Chief Meteorologist Mark Nelsen