June 28, 2017

Due to our mild & dry pattern, it appears the big holiday will be pretty reasonable this year.  Most likely high temperatures somewhere between 70-80 degrees, pretty normal for this time of year.

Mark IndependenceDayHistory

I remember sitting through some very chilly fireworks shows here in Northwest Oregon, but my 16-year-old son hasn’t seen a wet Independence Day.  You have to go all the way back to 2000 to find a wet one!

That’s especially strange considering that any one July 4th has a 24% chance of getting measurable rain in Portland.  And this one is always surprising…JULY 4TH HAS A HIGHER RAIN CHANCE THAN ANY OTHER JULY DAY!  It’s just a fluke of course, but bizarre that it happens to occur on a holiday.

You may remember the sweltering 4th just 2 years ago during the great heat wave of 2015.  Last year was a bit cool though.

Mark IndependenceDayHistory2

Regardless, we’re in pretty good shape this year!

Chief Meteorologist Mark Nelsen

Stable & Dry Summer Weather Pattern Arrives Early

June 27, 2017

10pm Tuesday

Today was about as “average” as it gets for a late June day.  We hit our typical high of 76 with afternoon sunshine following the morning cloud cover.  And of course it was dry as well.  Here in Portland we haven’t seen measurable rain in 11 days:

Mark Dry Spells Summer Recent

Remember that 2012 dry spell?  It didn’t start until early September!  That was a strange early fall dry period.

We have turned dry because those showery spring upper-level lows have weakened and are staying well to the north.   So basically weather maps and models look just like July/August right now and we have entered the warmest/driest time of the year in the Pacific Northwest.  It’s time to hit the rivers, mountain lakes, Gorge, Coast, hiking, camping, bicycling and anything else you wait all fall/winter/spring for. We’ll get just enough onshore flow over the next week to keep hot weather away, but we WILL see a thinner marine layer the next few days.  That means slightly warmer temperatures.

Then a few weak disturbances slide by later this weekend and the first half of next week; that will increase the onshore flow = increasing morning clouds & cooler temps.

Take a look at the Global Ensemble Forecast System (GEFS) temperature anomaly (departure from normal) over the next 16 days.  The general trend is clear…warming the next few days, a downturn but only to around or slightly below average around the 3rd/4th.  Then warming again after the 4th.  A very stable pattern with mainly above average temps.


A different way to look at it; the ECMWF ensemble chart showing maximum temperature from its 51 different members


You see quite a few members showing this Friday as the warmest day (the 30th) and then warming again around the 5th/6th.  This shows good agreement among two different models.

As for rain…it looks very dry.  Sure, we can always sneak in some sprinkles or marine air drizzle, but that’s about it.  The GEFS says little or no rain the next 16 days.  Each horizontal line below is one of the 21 ensemble members.


So enjoy the weather…you’ve waited MANY months for these few guaranteed warm and dry weeks of the year.

By the way, on a side note, today is “melt-out” day at the Mt. Hood SNOTEL Test Site.  This evening the snowpack is just about all gone at that 5,400′ elevation.  The last week it has been melting very quickly.  3 days ago there was 10″ of water content in the snowpack, this evening it will be down to just under 2″ by midnight.  That’s the threshold I use for this graph showing the melt-out date for the past 36 years:


Until the last 3 years the average date hadn’t changed much, but the very early melt-out the past two years (late May and early June) mean the trend is EARLIER for snowmelt AT THIS ELEVATION on the mountain.  We’re only talking a few days, but something to keep an eye on in coming years.  With a warming climate one would assume the date will gradually creep earlier and earlier.  We’ll see.

Chief Meteorologist Mark Nelsen


June 25, 2017

5:15pm Sunday

The numbers are in…and as expected it was hotter today in the metro area with hot easterly wind holding off the cooling breezes until AFTER the 5pm high temperature.  Here are the numbers, which are unlikely to change in the next 2 hours:

Check out the 5pm temperature map…

Portland sticks out like a (hot) sore thumb as they say.  100 here, but 10 degrees cooler in Salem and 20 cooler in Kelso & Eugene.  The heat wave has ended all areas west of the Cascades except right in the immediate metro area.  Gusty southwest and northwest wind will be converging in the middle of the city in the next 2 hours as we are getting a major marine push…that’s cooler ocean air pouring inland.  This will end our heat wave by sunset.  So let’s look at the numbers:

In the middle/latter part of this past workweek we forecast 92-100-102, so we were within 2 degrees with each forecast.  See what I mean about forecasting heat waves compared to other “extreme” events west of the Cascades?  Models handle these sunny periods pretty well, at least here in the metro area.    They nailed the idea of easterly wind holding on in the western Gorge through the mid-late afternoon, allowing PDX to max out its high temperature around 100.

What about tomorrow?  It looks REFRESHING.  High temperatures under partly cloudy skies (just a slight chance for a sprinkle) around 78 degrees…very nice.

Chief Meteorologist Mark Nelsen


Today’s Numbers: Heat Records Fall

June 24, 2017

6:00pm Saturday

Here’s a first look at the initial high temperatures for today, a couple of these may change since the cutoff time is 5pm.  Check out Astoria, Tillamook, & Salem!

The 93 at Astoria was the 4th warmest temperature on record out there.  The all-time high at Astoria Airport is 98, set just last August.  The 1st, 2nd, & 4th highest temperatures ever observed at AST have been set in the past 15 years.  I think a coastal heat wave blog post is in order at some point…”Is Heat Becoming A More Regular Visitor to the Oregon Coast?

Most of the metro area cruised in just below 100 degrees.  It’s possible a few of these will bump up one degree since once again the cutoff time is around 4:53pm.  We may have had a little too much easterly wind. The 98 (or will it be 99?) at PDX broke the old record of 96 degrees

One thing that makes our heat waves far more tolerable than say…a 100 degree day in Louisiana?  The humidity is EXTREMELY low.  Check out the 12% value at this hour!

Tonight will be warmer than last night, but nothing like a heat wave anywhere east of the Rockies.  If it was 98 in St. Louis during the day, I can guarantee you it sure wouldn’t drop down into the upper 50s and lower 60s at night!

That’s because we have that very dry air overhead.  That said, because the east wind will keep blowing at the west end of the Gorge and on some hilltops, those areas will remain in the 70s tonight…similar to those warm tropical trade winds you pay $$$ to fly to Hawaii for?  Tonight it’s free if you live in those spots.  So open up the windows and feel the breezes blowing through…after 10-11pm of course once we’ve cooled off.

Tomorrow’s general weather forecast is easy…SUNNY & HOT.  But the temperature details are very tricky.  That’s because a southwesterly surge of cool marine air moves up the coastline during the night, stalls over the Coast Range the first half of the day, then surges into the CENTRAL & SOUTHERN Willamette Valley in mid-late afternoon.  The timing is critical to reaching 100 or over in the valleys; an early arrival would mean no 100 degree day tomorrow.  If we ignore that southwest push…our atmosphere will be warmer tomorrow and we start with a warmer morning low; easterly flow through early afternoon should mean between 2-5 degrees warmer Sunday in the valleys and then the wind goes calm by mid-afternoon.  This is the perfect setup for maximum heating in the metro area; east wind early that backs off later in the day.  But from Salem south that  afternoon onshore push means your temperatures will likely be capped below 100 degrees.  In this pattern (I’ve seen it many times over my career here), the LAST place to see the cooling is the Portland/Vancouver metro area with a southwesterly surge.  As a result I’m forecasting 101 at PDX tomorrow, 2-3 degrees warmer than today, but down about 5 degrees in Salem.  Eventually that cooler air will make it in here AFTER the peak heating of the day as the east wind disappears too.  That will finish our 3 day heat wave.

Monday should be glorious with a good 20 degree drop in temperatures, then a morning cloud/afternoon sun routine with highs in the 70s Tuesday and Wednesday.

Chief Meteorologist Mark Nelsen



Saturday Scorcher Arriving

June 24, 2017

8:45am Saturday

Everything is proceeding according to plan for this last weekend of June.  This is one of the easiest forecasts we make…heatwaves west of the Cascades involve sunshine only.  But the numbers are just larger, sometimes even three digits instead of two.  It’s nothing like forecast snow/wind/ice/flooding.

At 9am some foothill locations are already over 80 degrees around Estacada, Colton, & Battleground…it’s gonna get hot!

We expect a high temperature around 100 both today and tomorrow.  In reality at the official observing site (PDX) it could be somewhere between 98 and 102 either day.  It won’t matter, it feels the same.

The morning balloon sounding is in from Salem and it shows an 850 millibar temperature of +21 degrees C, easterly wind flow from near the surface all the way up to 7,000′, and relative humidity of only 10-25% above 2,000′.  That’s some hot and dry air that will surface later this afternoon.  It’ll do that because we’ve also got a 3-4 millibar easterly gradient through the Gorge and over the Cascades.  East wind blew all night in Corbett and temperatures there only dropped into the upper 60s.  Tonight those of you in the windy areas will remain in the 70s…like those Hawaiian trade winds.

Today is also the one day we’ll see a scorcher at the coastline.  Expect highs around 90 on the north coast and well into the 80s from Newport north.  Then a surging southwesterly wind arrives tonight and tomorrow morning cutting off the heat…much cooler Sunday.

Stay cool!

Chief Meteorologist Mark Nelsen


Hottest Weekend of Summer? Could Be!

June 22, 2017

10pm Thursday

Our heat wave is still on for this weekend.  And it’s going to be a scorcher.  This is what we are forecasting as of Thursday evening here at FOX12:

Sunday will likely be the warmest day, that’s based on models showing a weak marine push just beginning to head into the Willamette Valley late afternoon Sunday.  In these cases of a “southwesterly push” of the cool air, the Portland metro area is typically the last to see cooling, or technically I suppose it’s the last area west of the Cascades to see the end of the hot temps.  I wouldn’t be surprised if Portland reaches 102 Sunday but Eugene only gets up to 95 for example.  Both Saturday and Sunday we’ll see perfect “offshore” windflow with a hot airmass overhead combining with easterly wind through the Gorge and down off the Cascades.  This pattern is just about as “perfect” as it gets for a heat wave west of the Cascades if you want maximum heating.  We don’t have many weekends with both days around 100 degrees, even in July or August so it’s always possible this weekend WILL be the hottest of summer.  But we won’t really know until late August of course.

So I think it’s pretty obvious we have a scorcher coming up, but what about the coastline?  The next two days will be cloudless with warming temperatures.  Saturday is the “scorcher” along the coastline since light offshore wind could push high temperatures (especially up north) up around 90 degrees.    Then a southerly wind reversal, which means a push of cooler air scoots north along the coastline, drops temperatures into the 60s or lower 70s Sunday.  A bank of fog/clouds will likely move north too.

A few questions you might have?  I’ve heard a few about humidity and nighttime temperatures.  Don’t worry about humidity, it’ll be dry.  Nighttime temperatures will be warming, but nothing too unusual due to the low humidity.

And the biggie…isn’t this unusual this early in June?  Yes, two highs right around 100 ARE unusual this early in the season, but it happens sometimes.  Back in 2006 we had a 101 followed by 102 in late June.  Summer temperatures ARE gradually increasing west of the Cascades, check out the change during my lifetime, or at least the part of my life that I would remember:

This is a graph showing average June through August temperatures for ALL stations in the Willamette Valley climate zone.  A few are in cities, but most are in rural areas, so this isn’t just a case of urban heating.  If you’re my age (around 50) and have lived here your whole life then you’ve probably noticed the same thing.  The last 4 summers have been quite warm with 2015 our warmest on record.  Assuming this warming trend continues, earlier heat will become more normal in our lifetimes.  Better get an air-conditioner!

Chief Meteorologist Mark Nelsen



June 21, 2017

7pm Wednesday

We’re just three weeks into summer but our first heat wave of the season is closing in on us.  So far this year we’ve been as warm as 91 (May 22nd, just before Memorial Day), but June has seen very “average” temps and rainfall.

What’s going on?  We have a strong upper-level ridge developing offshore, that’s a large area of warmer than normal air.  It will move right over the West Coast Friday through Sunday, then weaken and head south Monday and beyond.

Jet Stream Forecast 2017


Headlines Spring Summer

Heat waves are FAR easier to forecast than any other extreme weather in our area.  In fact I can’t remember screwing up a heat wave forecast in the past 20 years.  Sure maybe a 100 degree day became a 90 degree day because of high clouds, but in general we’re talking sunny skies and it’s just a matter of “HOW HOT IS IT GOING TO BE?”.

Well this time the answer is “pretty darn hot!”.  The all-time record June temperature at PDX is 102 degrees, set 11 years ago.

Models are in good agreement that 850 millibar temps over Salem (the temp in Celsius at 5,000′) will peak around 20 Friday, 23-24 Saturday, and 22-25 Sunday.  With neutral to slight offshore flow Friday turning to relatively strong offshore flow Saturday and Sunday, temperatures are going to skyrocket.

How hot?  Looking back at the 2006 heat wave, 850mb temps peaked out around +24 to +25 and we ended up with two 100+ days (101 and 102).  My “magic” chart for June says with offshore flow there’s no reason we can’t hit 100 (or higher) with the forecast temps, especially off the ECMWF model on Sunday; it’s the warmer model that day.  To summarize, afternoon temperatures both Saturday and Sunday will be somewhere in the 97-102 degree range in the Portland metro area.

Will it be humid with this heat wave?  The short answer is NO…good news.

How much wind? I think Saturday and Sunday will be breezy, especially Saturday afternoon and early Sunday.  That’ll mainly be a northerly wind in the western valleys.  In the Gorge it’ll be breezy Saturday and then windy the first part of Sunday with that easterly wind.  Most likely no westerly wind in the Gorge for windsurfers and kiteboarders until Monday.

90s at the Coast?  I think that’s unlikely this time around unless we get the east wind out over the beaches.  Mostly likely 70s to 80 Friday, 80s Saturday, and then 60-80 Sunday as c chilly southwest wind kicks in first on the central coast and then works its way north.  Saturday should be the warmest day on the Oregon and SW Washington coastline.

Get your air conditioners and pool ready!

By the way, there is no substantial rain in sight, at least through the end of June.  Check out the ECMWF model’s ensemble of rain accumulation forecasts:


Each horizontal line up above represents one member of the ensemble.  Green indicates .10″ rain accumulation.  Notice only 8 of 51 members produce a tenth of an inch of rain over us through the 6th of July.  That gives some confidence to the idea that we MAY have already entered the very dry season.  If so, vegetation is going to be drying out quickly with the warm temps.

Chief Meteorologist Mark Nelsen