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  • Posted

A short blog post tonight! Just to point out how quickly the snow/water situation is going downhill as this warm-ish and VERY DRY spring continues…

Snowpack on April 1st…pretty good across Northern Oregon, below average across the southern half of the state

Today…what a change! Much worse. The extremely dry April and warm temperatures have taken a big toll

Now it’s important to point out that early & end of season maps can be deceiving. For example there are many lower elevation stations that don’t typically still have snow on the ground in early May. That could skew the average. But the point is that things are heading downhill quickly and I don’t see any change through mid-May. Take a look at the Mt. Hood Test Site near the bottom of Pucci lift at Timberline (5,400′)

The GREEN line is the typical accumulation of “snow water” through the season. The colored areas represent lowest to highest snowpack on record on any one date. Green area is an “average” year. At this elevation, the abundant February snows brought the snowpack up well above average (BLACK line). And a cool March preserved that snow. However the lack of precipitation in March means a peak occurred a bit earlier than normal. Now it has slipped below average! Basically A GREAT SNOWPACK IN LATE FEBRUARY AND EARLY MARCH IS NOW MELTING FASTER THAN NORMAL. The whole snowmelt season is earlier and more condensed this year. At this rate there won’t be snow on the ground more than another month…unless we go back to cool and wet weather.

Farther east, in the Blue Mountains, this site shows something similar…well above normal snowpack in March, then a rapid melt right now. It’ll be gone in a couple days…earlier than normal!

This spells trouble for our water supply. In fact Willamette Valley Project reservoirs are running well below where they should be in late spring. Most of these lakes reach their maximum “full pool” level at the end of the spring filling season. That’s right now. But two months of very little rain is a big problem.

Detroit Lake (one example) is about 17 feet below where it should be.

So…we need rain, but I don’t see anything significant through the next week. I’ve never seen it this dry at this point in the spring.

Chief Meteorologist Mark Nelsen

  • Posted

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

  • Posted

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

  • Posted

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