May Begins Mild & (Mainly) Dry

May 5, 2015

9:30pm Tuesday…

It’s been awhile since I last blogged; but I’ve got a few random notes tonight:

1.  Mt. Bachelor is closing.  They are the last ski area to throw in the towel on the horrid ski season.  They typically stay open daily through Memorial Day since USUALLY there is plenty of snow left on the ground.  Not this year!  You can read all about it on their web page.  This coming Sunday will be the last day.


2.  Detroit Lake has stopped filling.  I noticed the level hasn’t changed in a week; it appears the very low flows on the streams feeding into the lake aren’t keeping up with the discharge.  That’s due to little rain and hardly any snow to melt.  A neat graphic here shows the leveling off.


Rainfall has only been around 50% of normal for much of Oregon in the past 30 days.


This is exactly what you DON’T want after the worst snowpack on record.  Forecasts of decent stream flow across parts of the state have been based on NORMAL precipitation in April and May, before the dry season really kicks in.  If May continues dry, we’re probably even going to see some issues on the westside of the state too.

3.  Split-Flow and/or Ridging seems to want to hang around.  Here is the forecast for next Monday from tonight’s GFS:


A pattern of systems cutting off and dying as the approach the West Coast has been causing problems with models in the 5-10 day range.  The warm stretch we just had late last week and over the weekend was forecast very well way out in time.  Over the past couple of weeks models have repeatedly shown cool/wet conditions in the long-range only to have the splitty pattern reappear.  That seems to be happening again for this coming weekend and early next week.  Some of that is not unusual in the spring season, but it IS strange to see upper-level lows diving down towards California in May.

The 12z ECMWF Ensemble 500mb height anomaly for NEXT Wednesday shows the troughing to the south…


But ridging returns to our north again mid-month, note Monday the 18th…


I have a feeling May is going to return us back into “Above Average Temperature” territory.

4.  Short term we have a chance for thunderstorms tomorrow afternoon/evening, although most action appears to be over the mountains.  There’s always a chance that we get something to drift out over the valleys though so maybe we’ll get lucky.  Today was sure underwhelming with many spots getting very little rain.   Then it’s back to 70s and maybe even touching 80 for Friday and Saturday.  It appears we have ANOTHER very nice weekend ahead.  Moms will be happy with that.

Chief Meteorologist Mark Nelsen

Siberian Smoke Likely Back For Bright Orange Sunrises & Sunsets

April 29, 2015

10pm Wednesday…

Did you see the sunset tonight? Some areas were clear enough that we could see a very orange sun as it sank to the horizon. It appears another “cloud” of smoke/haze is back…most likely from fires in Siberia. Here’s the 6pm smoke discussion from NESDIS:

…A large area of unknown aerosols is moving in from the Pacific Ocean over the US Pacific Northwest and southwestern Canada. Models suggest this area may contain blowing dust from Asia as well as smoke from Siberian fires…

And a blog from NASA says the smoke is moving across the Pacific on the east-flowing jet stream.  Here’s a quick screen capture:


So enjoy the bright sunsets we’ll probably see the next few days.

Chief Meteorologist Mark Nelsen

82 Degrees Monday: Warmest This Year

April 27, 2015

Quite an April “scorcher” out there today:


The 82 degree high at PDX was above our forecast of 80 degrees.  Not quite a record (86 in 1987), but 18 degrees above average!  The Salem sounding at 5pm showed an 850mb temp of +14.6 degrees.  In non-meteorological jargon: The temperature around 5,000′ elevation over Salem was about 58 degrees.  It could have been even warmer;  my chart for April shows easterly flow, solid sunshine, and a +14 has seen a Portland high temp as high as 85!  Models had shown +12 or +13, thus the forecast of 80.

Maybe more amazing is the jump from yesterday.  The high temp jumped 21 degrees in one day, which I haven’t seen happen in the spring.  Of course we’ve seen it drop 20 degrees in one day (tomorrow?) due to a major marine push and/or a cold front passage.

The easterly pressure gradient has increased this afternoon and evening, giving a peak gust over 50 mph at Crown Point and 40 mph at Corbett.  It’ll back off dramatically by sunrise as low marine clouds flood into the valley.

We’ve got a weak cold front moving inland tomorrow so expect some showers but not a big soaking.  In fact I don’t see any other decent chance for rain in the next 7-8 days.  This might be a year in which we start watering in May unless a trough materializes the middle of next week with a nice soaking (.50″ or more).  Both the 18z GFS meteogram and 12z ECMWF meteogram showed less than 1/2″ in the next 7-10 days.



It does looks like a very mild and “settled” weather pattern over the next week.  By that I mean that after tomorrow’s disturbance moves past we see the action lift north.  This is typically what we see later in May and June.  So temperatures warm to above average over the next week.  This may be a re-emergence of the ridging we’ve seen so often over the past year or so.  Take a look at last night’s ECMWF monthly run.  One map representing the average height anomalies for each week.





Same sort of splitty pattern we’ve seen recently with lower than normal heights to our south and higher than normal to our north and northwest.

Chief Meteorologist Mark Nelsen

Will Detroit Lake and other Willamette Reservoirs Fill? Maybe Not, But Don’t Panic

April 23, 2015

Have you driven by one of the Willamette Reservoirs lately and wondered if they will actually fill for summer recreation?  Good question!

Now let me point out that it’s perfectly normal to drive by Detroit Lake, Green Peter, Lookout Point, Cougar, & Hills Creek reservoirs in winter time and see them extremely low.  That’s all the extra space left each fall for rainy-season flood events.  The storage built into these reservoirs keeps us from seeing regular flood events in the Willamette River system (including Eugene, Salem, & Portland!) each winter.

Here’s a graph with a bunch of lines…it’s for Detroit Lake (east of Salem):


First, ignore the entire bottom half of the chart and focus instead on the thick red line on the upper part.  That’s the “control curve” showing, in a perfect world, where officials want the level of the lake to be during each part of a normal year.  Notice the lake is normally kept “full” from around May 1st to September 1st, then the level is dropped to the winter minimum by December 1st each year.  It is kept there (if possible) through February 1st, then filling begins.  That gives the Corp 3 months to “empty” reservoirs in the fall and 3 months to fill them in the late winter and spring.  In the case of Detroit Lake the lake level varies about 113 ft. from “empty” to “full”.

Now look at the blue line…that’s the actual level over the past 12 months.  Notice last summer the lake dropped a bit lower than preferred in the 2nd half of summer and then followed the “curve” more or less through the fall and early winter.  As a meteorologist it’s interesting to note the wintertime spikes when heavy rainfall suddenly fills the reservoir.  In late December the level jumped about 40′ in a very short period of time!  February 1996 must have been crazy!  On that blue line you can also see that right after a heavy precipitation event lots of water is poured downriver to quickly bring the level back down to where it should be in winter.

Two things I’ve noticed in the past few months:  They started allowing it to fill earlier than normal this year (mid/late January) since it was obvious ridging was going to stick around that point with its dry weather.  Then you can see how the filling is going much more slowly this year.  A week from now (May 1st) the lake would typically be “full”.  Not this year!  Looks like it is running about 45′ below the curve right now, which means as you drive by it’s only as full as it would typically be in late February or early March.

So will it fill?  Most likely NO.  But that doesn’t mean no boating! Here’s a forecast from the Army Corps of Engineers from about a week ago:


The purple line on the left side is the past and then future forecasts (and levels right now) begin at the dotted line.  The blue line is the most likely scenario, assuming normal precipitation/conditions over the next month or two.  The red line is the line in which there’s only a 5% chance it’ll get above that.  Looks like officials think it’s most likely the lake will top out around 1450’…about 13-14′ below full pool.  What does that mean for boating?

Take a look at (ONE MORE) chart for the past 7 days:


This one shows all the boat ramp elevations.  There is one that’s available all year long…the low water ramp.  But the current level is still at least 20-55 feet below all the other ramps.  The good news is that most of those ramps should be available this summer according to the forecast levels up above.  You’re just going to have to wait a bit longer to get on the water this year!

I didn’t look into any forecast for other reservoirs…although you can find all the info on the Army Corps of Engineers Willamette Basin Web Page.  You can see all the reservoirs are well below normal in this graphic:


So don’t panic if you have party plans on “the lake”…there WILL be some water to play on!

Chief Meteorologist Mark Nelsen

Air Force Dumping USA models

April 21, 2015


I just read some interesting articles and blog posts about a major change in the US Air Force.  They are dumping their WRF model (and support) and instead going with a UK model!

Here’s an article from The Capital Weather Gang.

And a blog post from Cliff Mass up at the UW.

I don’t have any great thoughts about it because I just now read the articles myself.  Seems like a bad move in general though.

Today was crazy wasn’t it?  We dropped from 81 yesterday to 62 today.


At one point this evening (around 5pm) we were running about 25 degrees below yesterday at the same time!

That’s all, not much weather happening except a huge cooldown in progress.  Snow flurries may stick down to around 3,000′ tomorrow morning!

Chief Meteorologist Mark Nelsen

First 80 Degree Day!

April 20, 2015

6pm Monday…

We hit 81 in Portland today


The first of the season.  Almost all of us in the metro area hit 80.  Quite a warmup over the past week!


This year we hit 80 a bit earlier than average…which has been around May 10th


Remember 2010 & 2011?  Some were worried endless slugs, rotted veggies, and April-June downpours were the new normal.  Apparently not.  As of today, we’ve seen 5 days at/above 70 degrees, the most real warm days in April since 2009.


By the way, we could see the start of the Government Camp condo fire this afternoon from the Mt. Hood Adventure Park camera at Skibowl East.  Note the left side of the timelapse:

Chief Meteorologist Mark Nelsen

Another Smoky/Dusty Sunrise: Could Keep Us Below 80 Degrees

April 20, 2015

7:30am Monday…

You’ve probably noticed the haze in the air the past 48 hours, especially Sunday.


It’s smoke from fires in Siberia, with probably some dust thrown in too.  Here’s a detailed description from NESDIS (your tax dollars at work!):

A relatively expansive plume of smoke is capture in morning visible satellite imagery extending from southern Saskatchewan across central Montana, northern two-thirds of Idaho, Washington, Oregon, and northern California. This area of smoke (with a low probability of dust/sand mixed in) has been traced back to numerous large wildfires burning across Siberia. These fires produced pyrocumulus clouds that enabled the smoke to rise quickly and become entrained in the atmospheric jet stream. The first plume of smoke that has been since transported across the northern Pacific and is now located over the Pacific Northwest and southwestern to south-central Canada. Additional large detached smoke plumes were seen yesterday beginning to follow the same trajectory.

That was yesterday, but this morning the satellite image shows thick smoke over us once again.

Beijing also had their worst sandstorm in a decade from the same system that brought the strong winds across the border in Siberia:

Cliff Mass blogged about this yesterday too:

For us, this means we have the hazy skies and slightly reduced heating from the sun.  A great example is from USFS RAWS sites.  This one from Mt. Wilson SE of Timothy Lake:

Look at the SOLAR RADIATION column and you’ll see the values each hour in Watts per Square Meter (W/m^2).  Notice on Friday and Saturday it is around 900-920 max, but then only around 830 yesterday, so maybe a 10% decrease in solar radiation reaching the ground.  That could be enough to chop a couple of degrees off the high and that COULD keep us below 80 again today.  Offshore flow is a bit weaker than I expected too…less than 2 millibars through the Gorge.

Nevertheless, a GREAT day again today with highs near 80…enjoy!

Chief Meteorologist Mark Nelsen


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