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  • Posted

Thursday, September 16th, 5:00 P.M. 

It was a beautiful day out there, with plenty of sunshine and nice warm temperatures! Tonight will be a warmer evening too, with lows in the mid-50s. We will continue to see more clouds move in throughout the night.
 
Tomorrow will stay mostly cloudy through the day, but temperatures will be similar in the Portland area to what we saw today. However, along the coast, we will start to see showers popping up early in the day before wet weather moves inland. Rain will hit Portland late tomorrow night, starting a very wet weekend. 
 
Showers will be on and off through the weekend, with thunderstorms possible at times too. Expect breezy conditions to move in starting tomorrow night as well. Models show we could accumulate between 1.5-2.0" of precipitation in Portland by Monday morning. 
 
Things dry out Monday and start to warm slightly. By Tuesday we will see another sunny day with temperatures getting close to 80° for the last official day of summer. 

  • 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

10pm Thursday...

Our mild winter (minus one cold week in mid-February) has come to a conclusion in the lower elevations west of the Cascades. As I look into the first week of March on our various models, it's pretty obvious that

It's time to put a fork in Winter 2020-2021.  This season is finished

So what kind of a statement is that?

It means I'm quite confident we're done with most of our typical winter weather events.  But not all!  Read on...

First, this winter (December 1st to now) is running 13th warmest on record at PDX.  Those records extend back to 1940.  Spokane is 14th warmest out of 72, and Baker City is experienced its 12th warmest winter.  So not a record warm winter, but definitely at the upper end for many spots. This "La Niña Winter" will go down as warmer than average.

Looking at the models for the next 10-14 days...

  1. I don't see an outbreak of cold arctic air.  For that matter I don't see unusually chilly air for this time of year.   We have not seen a region-wide arctic air-mass descend across the Pacific Northwest since December 2013!  Sure, some cold-air intrusions to some areas at times, but no big arctic blast.
  2. I don't see a setup for lowland snow west of the Cascades.  Even a brief & wet morning snowfall.

Point #1 on the graphic below is most important; the chance of a widespread snow/ice event in the metro area is down to just about zero.  I mean the type of event that shuts down our area for a day, or even part of it.

  • Other than the cold spell with the snow/ice storm, we didn't have a major freeze this winter. Portland's low temperature was 24.
  • Sure, we can still get a chilly east wind, but in early March we don't get long periods of the screaming cold easterly wind.
  • As for flooding, for the first time in my career we DID see some significant April flooding in Spring 2018.  But otherwise all of our big floods have occurred during the winter months.

What could we still see as we head into March?

We have seen March windstorms in the past and even one April event a a few years ago.   And of course in recent years we've seen close calls with snow in March, including last year.  Although it's still far more rare than December-February snow.

What actions can YOU take at this point?   Get those snow tires off and turn on the exposed water line to the chicken coop (mine is back on).

There you go.  Basically it's time to "de-winterize" WEST OF THE CASCADES.

SUMMARY

We transition from late winter to early spring weather over the next 2-3 weeks as temperatures gradually rise.

In the short term, we've got big-time winter in the Cascades! Winter Storm Warnings are up for there and in Northeast Oregon.

The Mt. Hood area has the best snowpack since 2008 for late February!

Chief Meteorologist Mark Nelsen

  • Posted

9:30pm Wednesday…

We’ve had three mild days with sunbreaks at times, and that’s melting the snow nicely west of the Cascades. After peaking out around 14″ at home, I’m down to just a few inches now (quite a bit denser!). But during this time a big snowstorm has been ongoing in the Cascades.

At this moment Mt. Hood Meadows has a 132″ base, Timberline 154, and 70″ (six feet!) is on the ground down at Government Camp.

I just checked out the numbers at the Mt. Hood Test Site (SNOTEL) at 5,400′. This is a long term snow measurement site in operation for over 40 years now. It’s close to the bottom of Pucci Lift in the Timberline Ski Area. What a surprise! Snow depth is 138″. If you could snap your fingers, immediately melting all that snow, it would be the equivalent of 47.7″ rain. That is referred to as “Snow Water Equivalent” or SWE. This is how our summer water supply is measured. Snow “stored” in the Cascades (and other Oregon mountains) gradually melts March through June, delivering water into reservoirs and recharging groundwater. We have a long dry season so snowpack is very important.

What surprised me is how well the snowpack is doing; at that elevation on Mt. Hood, AND down around 4,000′ (two separate sites), it’s THE BEST SNOWPACK ON FEBRUARY 17TH SINCE 2008!

To get a more complete picture, scientists at USDA average many stations across the region and state. For the Mt. Hood area, we’ve gone from 66% of average early in the month to 99% today…big improvement in just a couple weeks! All of Oregon looks like this…

We are in good shape, best across the northern part of the state. It appears we’ll be staying on the “cool-ish” side of things for the next 7-10 days. The chart below shows 850mb temps from each of the 51 ECMWF ensemble members for the next week. That’s temperature around 5,000′ elevation for the next two weeks. The green line is the average for this time of year. Red line is average of all 51 members. What sticks out? Much of the time the next two weeks, the overhead atmosphere is below that green line = cooler than normal. Good for Cascade snow, bad if you want some (very early) spring weather in the lowlands. That said, we need a temperature below -7 this time of year for a wet morning snowfall. That can still happen into mid-March, although rare. There are a few members implying that could happens in the next two weeks…we’ll see. Regardless, I’m turning my outdoor chicken water back on; no sign of a cold freeze.

Speaking of lowland weather, plenty of rain ahead, although I don’t see any sort of flooding setup. There are hints that MAYBE later next week it might turn slightly drier. You can see more gaps in the Euro ensemble 24hr QPF chart beyond the 24th.

On another subject, we picked up some new numbers from PGE today. They now say that at one point 350,000 customers were out of power. That makes this the most disruptive power event since the Columbus Day Storm (in pure numbers). That’s about 40% of their customers! In terms of percentage of customers, the December 1995 windstorm put 46% of customers out, so these two events are comparable in that way I suppose. Just a devastating ice storm for utilities and life-altering for many of you this week.

On the snow front, it turns out I had a bad number for 1955 (see previous posts). So the 10.1″ that fell in Portland (officially) through this event gives us the 2nd snowiest February on record

That’s it for tonight, I’ll be off for a few days and back Sunday…Chief Meteorologist Mark Nelsen