A Hot May Day

May 22, 2017

11pm Monday

Forecasts turned out just right today with 80s along parts of the coastline and low 90s around the metro area.  Aurora was the warm spot in our area with a 93 degree high.

Todays Observed Highs OrWa 2017

Somehow Eugene only hit 85…not sure what was going on down there.

Tomorrow will be much cooler at the Coast as a strong NW wind kicks in during the afternoon.  That will also pour inland and cap our temperatures off in the lower 80s.  Good news, no hot weather for tomorrow but a warm and sunny late May day.

Now today’s 91 at PDX was the warmest in May in 3 years but short of the record for the date.


We have entered an unusually long warm/dry period for late May.  Since I don’t expect showers Wednesday, that means ridging will take hold again for the end of the week through early next week.  No model shows any decent chance for significant cooling and/or showers until at least the middle of next week.  Wow, what happened to the cool/wet spring???

Enjoy the sunshine in the days ahead, it’ll be accompanied by low dewpoints Wednesday through Friday so night will be cool with pleasant afternoons.

Chief Meteorologist Mark Nelsen

Excellent “Early Summer” Weather Ahead

May 21, 2017

9pm Sunday

What a beautiful day across the Pacific Northwest!  Even the coastline cleared out as temperatures rose into the 70s out there

Here in Portland we saw our 2nd warmest day of the season so far (May 4th at 85 was warmest).  Easterly wind came over the Cascades and through the Columbia River Gorge…it was light but it got the job done (warming).  Troutdale was the warmest spot in the metro area as the easterly wind mixed down dry and warm air from above.    You can see a thick layer of easterly flow on the Troutdale profiler (current time on left side, two days ago on right)

850mb temps are expected to top out around +19 over Salem tomorrow afternoon as a 588dm ridge centers just offshore of the Pacific Northwest.  This means that warm easterly flow of warm and dry air increases tonight and tomorrow, warming the atmosphere further.  As a result the western valleys should see a 5-10 degree warming Monday and a few spots on the coastline will get above 80 degrees (Tillamook).  Monday is going to be a “May Scorcher”.  The good news is that it’ll only be for one day.  A couple of nights ago models began to show the ridging “squashing down” much faster as a cold system drops through SW Canada late Tuesday & Wednesday.  They have stayed with that idea which means a few things:

  1. Temperatures will likely peak earlier than normal Tuesday (early to mid-afternoon) as a strong northwest wind begins to blow west of the Cascades.  Gusts to 30 mph are likely by 5-8pm as a much cooler airmass pours inland.
  2. Highs will just get a few degrees above 80 on Tuesday…it won’t be a hot day
  3. Wednesday will be dramatically cooler
  4. Wednesday will NOT be a gloomy day.  That’s because a cold and quite dry upper-level airmass will disrupt the typical warm season marine layer that would give us gray skies and drizzle.  Wednesday will be breezy, cool-ish, and nice late May day

What happens beyond Wednesday as we head toward the first big holiday of Summer 2017?

Believe it or not, there is some good news…it’s possible we have a very nice 3 day weekend on the way.  I’m scared to jinx it, but as of now there is pretty good agreement that upper-level ridging is going to rebuild along the West Coast.  Nothing extreme, but a very pleasant June-like pattern with above normal temps and mainly (or all) dry weather.   Check out the 12z ECMWF model 850mb ensemble chart.  This shows the next two weeks.

The green line is average temperature in celsius for the date at around the 5,000′ elevation.  Blue line is operational ECMWF run, red is ensemble average.  The screaming message here is that we’ll have that brief chilly day or two Wednesday & Thursday, then a warming trend that just happens line up with Memorial Day Weekend.  I’ll have to check the records and see when we last had a warm and mostly sunny Memorial Day Weekend…can’t remember.  Confidence is relatively high since NO ensembles are below average until AFTER the weekend.

One other interesting tidbit…from the GEFS (GFS ensembles).  This is a rainfall chart for the next 16 days, each horizontal line represents accumulated rain as you go from left to right (current time is left side).  Note only 1 of the 21 ensemble members has measurable rain before May 31st.  That’s a week from Wednesday.

 It appears May is going to end on a mild and mainly (or all) dry note.  That’s quite a change.  If this is the case, it’ll break the 5 month cold streak we’ve had going since December.  And it’ll be our first drier than normal month since January…it’s time I suppose.

Enjoy the sunshine and stay cool tomorrow.  At least it’ll only be hot for a few hours in the afternoon.

Chief Meteorologist Mark Nelsen

May Heat Ahead…Forecast Numbers Going Up

May 18, 2017

6pm Thursday

Today was sure a nice day after 7 days of rain showers.  Other than a sprinkle or two late this afternoon, we saw partly cloudy skies and much warmer temps.  This is about as normal as it gets in the latter half of May

High pressure is strengthening over the Pacific Northwest as the cold upper-level trough has moved off to the east.  In general high pressure will dominate our weather for the next week.  Temperatures climb tomorrow with very weak onshore flow and a warmer atmosphere overhead.

Saturday will be cooler with even a chance of a shower or drizzle through midday.  That’s because a weak system rides through the building high pressure, allowing a surge of cool marine air inland.  That marine layer will be quite thick Saturday…up to about 4,000′ or so.  When it does that the possibility for a shower or drizzle exists.  The ECMWF is sure seeing this, although less than .10″ in any lowland location

Sunday through Tuesday a big upper-level ridge builds with 500 millibar heights above 585 dm.  That is a summertime ridge and air overhead will be warm like summer.

Models are in excellent agreement that 850 millibar temperatures (the temperature around 5,000′ elevation) will rise to around +15 (celsius) Sunday, +19 Monday, and +20-21 on Tuesday.  That’s just plain hot overhead.  On Monday and Tuesday easterly flow at that elevation lowers pressure west of the Cascades.  It appears all day Monday through early Tuesday what we call a “thermal trough” will be located quite close to the coastline.  A thermal trough is a very warm area of low pressure that forms in the lee of the Cascades/Coast Ranges.  In this case, with it getting out along the coastline, temperatures should skyrocket at the beaches just like in the valleys.  Most likely that happens on Monday; that IS the one day that should be a scorcher on the beaches…80-90 is possible out there.

Here in the metro area, if we combine May sunshine, offshore wind flow (both Monday & Tuesday), and those 850mb temps?  We get a high temperature somewhere between 92-98 based on past setups in May just like this.  Highest temps are likely on Tuesday assuming no onshore flow begins.  As a result I raised 7 Day forecast high temps a could degrees again today.




So when might it rain again?  Some ensemble members of some models imply a weak upper-level low could bring showers/clouds Thursday and beyond next week.  That said, more members are remaining dry through Memorial Day Weekend than wet.  Only 5 of the 21 GEFS ensemble members give PDX .10″ or more rainfall by the end of that holiday weekend.  Each of the horizontal lines below represents 1 of those 21 members.  Time goes from now on the left to the 3rd of June on the right.

The ECMWF ensembles are similar…11 of 51 members produce .10″  rain in the next 10 days.   Only 4 have .50″ or more.

Basically we MIGHT get a few showers as we head toward/into Memorial Day weekend, but as of now there’s no reason to believe a long spell of cold and showery weather is coming back before the end of the month.  There’s also no sign that hot weather continues beyond Tuesday.

Chief Meteorologist Mark Nelsen

Snow, New Baby MacMillan, & Summer Heat Next Week

May 16, 2017

10pm Tuesday

What a chilly and occasionally wet day today.  We were only around 50 degrees during the evening commute and topped out at 56 earlier in the day.  It felt more like an early April day didn’t it?  Today was the 6th day with some sort of rain in Portland, that was after a relatively mild & dry start to the month

Today a cold upper-level low was moving over the Pacific Northwest, setting off hail and thundershowers.  Plus a huge snowstorm in the Cascades.  Snow is still falling up there, and about 2 feet has fallen at Timberline Lodge!

Other than some leftover snow on the passes briefly Wednesday AM, we warm up and you can forget about mountain snow.  A big warmup is on the way.

Models have done a very good job forecasting a big change to warm and mainly dry weather beginning the middle of this week.  Sure enough, we’ve got a cold love moving overhead now, but check out the big upper-level ridge that develops right along the West Coast late this week and into early next.  This map is the forecast for Sunday PM.

With 850mb temps moving into the +10 degree range Friday and Saturday, we’ll get well into the 70s (tempered a bit Saturday by onshore flow).  Then Sunday through Tuesday the airflow over us goes northeast or even light easterly.  We’re in “prime sun angle” time of the year now.  We’re getting just as much energy from the sun as we would be in late July.  So with clear skies, 850mb temps +17 to +20, and weak/moderate offshore flow…temperatures are going to soar.  Sunday we should make it into the low-mid 80s.  Then 90 is definitely achievable both Monday and Tuesday.  All global models are in quite good agreement with this “hot” period Sunday-Tuesday.  The record high for Monday is 95 and 93 for Tuesday…it’s not unheard of to see 90 in late May.  Still, it’s hard to believe but we’ll be watering the plants on our decks and in patio containers 6-7 days from now or that Timberline will be in the low 70s next Monday and Tuesday.

As for rain, I think we’re also entering a long dry & mild period, more like what we’d see in June.  As mentioned early next week we’ll see ridging (ECMWF ensemble average 500mb height for Monday)

Then later next week the ridging weakens and backs slightly farther offshore (Friday the 26th, start of Memorial Day weekend)

Then 5 days later…the last day of May…looks similar with that ridging to the west.  This is typically a very dry pattern in spring or early summer with no wet systems approaching from the west.

Check out the ECMWF ensemble 24 hour rainfall chart:

This chart shows the 51 members of the ECMWF model’s “ensemble”.  That’s 51 different versions of the same model run with slightly different initial conditions.  When they are all in pretty good agreement our confidence goes up.  When they are each different, confidence goes down.  In this case each horizontal line is one member and represents 24 hour rainfall.  Notice extremely good agreement that no rain falls Thursday through next Wednesday.  Beyond that you only see scattered showers trying to show up here and there.  So a drier than normal pattern for the next weeks.

On another note, we’ve got a new member of the weather team!  I’d like to call him “Mini-Mac”.  Brian MacMillan & his wife Ashley have a new family member.  Little Evan MacMillan was born late yesterday evening…a solid 8 lbs too.  Congratulations!


Chief Meteorologist Mark Nelsen

Wettest Spring On Record In Portland

May 14, 2017

3pm Sunday…

Well, I take that back, we can start whining about the amount of rain this spring.  Note the previous post.  But now the soaking Friday and Saturday has put us in record territory…

As of midday this Sunday, the 13.00″ precipitation (mainly rain) that has fallen since March 1st is the MOST WE’VE EVER SEEN IN A SPRING THROUGH MID-MAY!  That’s pretty bad.  The airport records go back to the late 1930s…so that’s just about 80 years.


Note the chart just goes through midnight last night.  We’ve had .05″ since that time, putting us up to 13″.  Most interesting is that the top 4 wettest have occurred in the past 7 years.  Note that if we get 1.51″ of rain in the next 2+ weeks (by May 31st) that will be the wettest spring on record at PDX.  We’ll see what happens.


Salem’s weather records go back further in time…124 years.  It appears you folks are at #5 wettest.  Yet there have only been 2 wetter (1963 & 2012) in the past 80 years.  Yeah, it’s time to start whining…I’m right there with you.

Luckily another taste of summer is coming later this week.  More on that later…

Are We All Whiners? A Look At Spring So Far

May 11, 2017

10pm Thursday

The last 5 days were sure nice…totally dry with warming temperatures each day.  By yesterday the soil around my home was all dry and it finally looked like late spring out there as I planted a few more veggies.  Then a strong cold front moved through the region today with much cooler air behind.  Scattered heavy showers, hail, & even a few thunderstorms have popped up this evening…that chilly spring of 2017 is back!  But is it REALLY that bad?  I’d say no.  Take a look at our spring so far.  It began March 1st and of course we’ve gone through May 10th:

This really surprised me.  In the past 20 years, we’ve seen two 5-year periods in which temperatures were colder than this one so far.  1999-2003 springs were all colder than this one and 2008-2012 were all cooler too.  So no, this year is pretty close to normal temperature-wise; just slightly on the cool side.  What we’re really noticing is the dramatic shift from 4 warm springs (especially last year) to this one.  Back to normal!

Now check out rainfall:

I think we have a right to whine a bit about the rain…it has been WET.  We haven’t seen it this wet since 2012.   In fact it’s one of the wettest springs on record here in Portland.  Only 2011 & 2012 were wetter.  It’s also interesting to note our springs have been gradually turning wetter since around 1980.  But again, we have been spoiled by the past two years of warmer and drier than normal weather.  Not it’s back to “reality”.

The Big Picture:  It’s not Global Warming, Chemtrails, or HAARP.  We don’t live in San Francisco, Sacramento, Denver, or Salt Lake City.  We just live in a wet maritime climate; this is what happens here every few years.

It is pretty clear that this cool & showery weather will continue for about 6 days then we get a break again.  The 12 Day Trend I use in the 2nd half of the 10 O’Clock newscast shows that with milder and drier May weather beyond next Tuesday.

So if the cool and showery weather annoys you just wait…it’ll turn a bit more pleasant again in less than a week.

Chief Meteorologist Mark Nelsen

3 More Sunny Days, Then Back to Wet & Cool

May 7, 2017

9pm Sunday…

It’s a new workweek for me but for most of you it was a fantastic end to the weekend.  Sunshine covered the entire Pacific Northwest this afternoon and we ended up right at normal here in Portland = 66 degrees.

If you’ve been outside the past couple of hours you know temps are cooling off quickly.  With high pressure overhead, a dry airmass, and clear skies, temperatures will plummet tonight.  Lows drop way down into the 40s with even a few upper 30s in the colder outlying parts of Portland.  Hopefully you didn’t plant your warm weather veggies yet…it’s a bit too early.  Not just because of another chilly night but we see quite a change in the pattern after Wednesday.

The good news is that we have 3 warmer days ahead.  We should be somewhere between 70 and 80 degrees each of the next 3 afternoons.  But then the cold showers return.  Take a look at the ECMWF ensembles showing 24 hour precipitation amounts the next 15 days:

You can see the very good agreement among the ensemble members showing pretty solid .10 to .30″ 24 hour rain totals for at least an 8 day period beginning Thursday.  This goes along with the 850mb ensemble chart

A nice warmup for 3 days, and then those pass-level temperatures (in the free atmosphere) plummet down to around freezing during that 8 day period.  Of course with the strong May sunbreaks we’ll get very little snow down to 4,000′, but the point is snow returns to the higher elevations late this week and the valleys will feel more like early April again.  Lots of showers, hail showers, and probably cold thundershowers here and there.  Also note there is a tick upward about 12 days out.  You see the decreasing rain totals on that previous chart as well.  The GEFS (GFS ensembles) have more ridging near the end of the 16 day period too.  You can see the upward trend in temps when average.    Of course the blue line is the operational run and it appears to be much warmer than the mean (average) of the ensembles.  Remember these charts show the temperature around 4,000′ or so.  The GEFS surface temps look like this, showing the same 8-10 day cool spell ahead:

So buckle up, enjoy the 3 warm days ahead, put off all your indoor tasks and enjoy the sunshine!

One more bit of good news…ALL Willamette Basin reservoirs are full and it’s just the first of May.  You can see it on the Army Corps of Engineers “teacup diagram” page.

There will be PLENTY of water for this summer, including irrigation (more of an issue typically east of Cascades) and water recreation.

Chief Meteorologist Mark Nelsen