Sun and Warm Weather Is Here!

April 22, 2013

What a huge change in the past 24 hours!  We’ve from gloomy, cool, & damp to bright, sunny, & warm.  The long-awaited dry spell is here:

  • Dry weather is likely for at least 5 days, possibly through Saturday…possibly
  • Warmest weather should be Wednesday…somewhere in the mid 70s.
  • Onshore flow brings cooler temps and/or more cloud cover Thursday/Friday.

Hard to believe that 5 days ago models were showing an upper-level ridge building directly over us today through Wednesday.  Instead it has decided to park itself out around 140W, well offshore:


That location is just about the “sweet spot” in winter that you want to get arctic air moving south into the Pacific Northwest on the back side of the upper level high.  In fact today’s dewpoints in the 20s with a NORTHERLY wind instead of more easterly is an obvious indication that a “cool” Canadian air mass has descended on the Pacific Northwest.  That’s similar to an October east wind period when we get frosty mornings and  cool afternoons in the 60s.  The huge difference is that we get as much energy from the sun in late April as we do in mid August!  Far different from October.  So our temps will jump the next two days by 7-10 degrees.

Nighttime temps will remain chilly; those areas that go calm will drop well down into the 30s.

I was tempted to make Thursday and Friday’s temps much cooler on our 7 Day forecast due to onshore flow developing ahead of an approaching upper-level trough.  But both our RPM and the WRF-GFS aren’t getting too crazy with the low-level moisture yet, so I left it alone.  Just be aware that Tuesday-Wednesday are the guaranteed nice days, Thursday-Friday are a bit up in the air.

Models are keying in on a cold trough swinging through the Pacific Northwest early next week (Sunday-Monday).  The ECMWF was very chilly and now the 18z GFS looks real cool as well.  So yes, another cool and possibly wet weekend is on the way.  Here are the two latest GFS/ECMWF ensemble charts:




That 18z GFS sure says SPRING with the up and down troughs and ridges doesn’t it?

Here are the 4 weekly maps from last night’s ECMWF monthly run:





Nothing that really sticks out beyond the 2nd week.

Enjoy the warm spring weather the next few days!

Chief Meteorologist Mark Nelsen

A Bunch of Maps

April 18, 2013

I’ve got some maps/model info for the weather geeks…

First, last night’s run of the ECMWF out to one month: These are ensemble average maps. Nothing too spectacular except the large upper level ridge in the next 7-10 days slightly west of us:





To go with that, today’s story with the long range forecast is that models have all shifted that upper level ridging next week slightly to the west, which means a bit cooler weather.  Still a fantastic week ahead, but we may not see 80 degree temps.  This is “model-riding” at its finest!  We’ll see how the 00z models look, but here are the ensemble averaged 500 mb heights for next Wednesday afternoon.  Compare these to the maps on the previous post.  They are for the same forecast time and you can see the shift westward:

can12z ecmwf12z gfs12z

Then the 12z ECMWF ensemble chart and the 12z GFS ensemble chart:

tseries_850t_000-384_Portland tseries_850t_000-360_Portland

Agreement hasn’t totally fallen apart, but not as good as yesterday and 850mb temps are a good 5 degrees cooler the middle of next week.

Today was sure a (nice) forecast bust with no rain the first half of the day and now just a few sprinkles showing up this evening.  I looked out the window at 9am, rubbed my eyes, and thought “where’s the rain”?  A great surprise that ended with an unanticipated bike ride.

Chief Meteorologist Mark Nelsen

Is That Really an 80 Degree Day in the Forecast?

April 17, 2013

The short answer is yes, here’s the longer answer…

We’re increasingly confident that the early-middle part of next week will be quite warm for several reasons.  Here’s our 7 Day forecast as of Wednesday evening:

7 Day


Models today have suddenly come into great agreement for the 4-8 day period (Sunday through next Thursday).  The past few days they have been all over the place beyond Sunday; this is common when models are struggling with an upcoming pattern change.  But now they’ve settled on the change.

That change is strong offshore surface flow (an east wind event) from Monday through Wednesday next week, plus 850mb temps peaking out around +11 to +17 next Wednesday, depending on the model.  The 12z ECMWF was the warmest with the +17.    For comparison, in the 18 Aprils from 1992 to 2009, only 3 days saw a +17 degree or warmer temp.  All three of those days were 85-90 degrees.  But, that ECMWF temp was an outlier.  Regardless, a +15 degree temp with easterly flow and 100% sunshine will push us into the 80-85 degree range this time of year.

10pm UpdateMaybe I should have checked the blog & high temps from April 22/23rd just one year ago!  Exact same situation pushed us to 82 degrees two days in a row!

Continuing on…

Here are two of the usual ensemble charts I show, compare them to charts from just two days ago; far more agreement:

12z ECMWF…


12z GFS…


And here are the ensemble 500 mb anomaly maps for next Wednesday from the ECMWF, GFS, and GEM (Canadian model).  Notice they all show ridging right along the West Coast:




Almost 3 weeks ago we hit 77 two days in a row (remember Easter Weekend?), upper 70s isn’t a huge deal in late April.  Most records are in the 80s in those last 10 days of the month.  Next Wednesday’s record high is 79 at PDX.

Chief Meteorologist Mark Nelsen

The Birds On Radar

April 16, 2013

The twice-yearly migration of millions of birds from warmer climates to colder northern regions has always fascinated me.  It would be like half the USA getting up and walking a few hundred miles twice a year.


And it shows up on weather surveillance radar quite well at times.  We notice it here on the Portland radar from early-mid spring and then again in early-mid Fall.  You can see the echoes suddenly appear right after sunset, rise in height, and peak out around 8,000′ or so.

Tonight was a great example, the last of the daytime showers were fading away at sunset, moving from NORTH to SOUTH.   Then right after sunset the radar screen fills in with “targets” moving from SOUTH TO NORTH.  Here is the VAD wind display from the Portland radar around 7pm:


The wind arrows are all northerly up to around 12,000′, then no echos to get a speed/direction from above that level.

Then the same display around 11pm:


The arrows are all southerly or southeasterly, probably the birds flying straight north contaminated a bit by the northerly flow of the atmosphere?  The southerly flow seems to top out around 7,000′ too.  And how do we know the actual wind direction didn’t suddenly shift through thousands of feet of atmosphere in just a few hours?  All models show the northerly flow continuing through another 12+ hours.

Most birds prefer to migrate at night due to smoother airflow (no daytime heating for strong up/down motions), and they need to eat during the day down on the ground.

It doesn’t take that many birds to make a radar show “rain” (what it looks like to you).  Think of the surface area of a flock of geese or ducks compared to raindrops.  Or dozens of flocks of smaller birds scattered around the region.  Several studies have been done showing 20-30 dBZ echoes equal 200-1800 birds per CUBIC kilometer.  That’s a cube 1 kilometer  wide/high.  Lots of birds!

You can read more about it here:

By the way, there is a movie called WINGED MIGRATION (a documentary) produced about 10 years ago using hand-raised birds. They follow the birds (usually geese) while flying and migrating using some sort of very light aircraft. Or, actually I suppose the birds follow the aircraft since they imprinted on humans at hatching.  That means they think humans are part of their family. Now, believe me, this is no “party movie”, actually it’s REALLY slow, but great visuals for little kids to watch. Filming was done all over the planet. Here’s a clip for a little mid-day relaxation:

I like how they have short conversations with each other while flying

Chief Meteorologist Mark Nelsen

A Warm and Sunny Weekend Ahead? Probably Not!

April 15, 2013

I was on forecast duty early this afternoon after barely looking at maps the past two days.  Some minor changes in the general weather pattern over our region means a major change to the extended outlook.  3 days ago I was thinking 70s were very likely this coming weekend.  Of course that wasn’t within the 7 Day forecast at that time so you never saw them  in a forecast graphic.

For those just tuning in for the basics:

  • More clouds than sun this week
  • Rain is most likely on Friday
  • Showers are possible again tomorrow afternoon, late Wednesday, or early Thursday.
  • This weekend’s forecast is very much up in the air, models are all over the place beyond Saturday.
  • I’d put a couple of big question marks for Sunday and Monday, but that doesn’t make for good TV.
  • In general, temperatures will be warming a bit the next 7-10 days.

The big change in the maps/models compared to what I saw Friday?  A building upper level ridge late this week is much flatter (heights are lower), and slightly farther offshore.  Sound familiar?  This is a similar setup to the pattern we have seen several times since early January.  One in which weak disturbances ride over the top of the ridge and then scoot across the Pacific Northwest.  They are quite weak, but northwest flow running into the Cascades is quite efficient at squeezing lots of moisture  out of the clouds and keeps us gray here in the lowlands.  That seems to be the case from late Wednesday through at least Saturday.  Interesting that a setup like that keeps reappearing.

Of course with an upper-high just offshore, slight variations in the position make for a huge variation in our weather.  If the ridge is a little closer we get very sunny and warm spring weather.   Position it farther offshore and we get onshore flow/showers with a surface high to our west.  Here’s a good example of the variation on the 12z ECMWF ensemble chart:


Remember the blue line is the operational run that we all get maps/data for.  The red line is the average of all 51 ensemble members.   Good general agreement through Saturday the 20th (the line “21”).  Then they diverge wildly.  Just two days later, they are anywhere from a -4 at 850mb (similar cold temps that we’ve seen the last two days) to a +14 (high temps well into the 70s or even 80).  The ensemble mean and operational are both around +4 at that time with lots of cloud cover and showers just to our north.  The 12z GFS is similar:


a wide spread after Saturday.  The 18z GFS was even cooler and wetter, although that run was nearly the coldest of its ensemble members from Sunday through most of next week.  Then it swings way up to the warmest beyond that point.


This is a good example of how you can use ensembles to forecast…in this case it’s probably safest to go for a “middle ground” until models calm down a bit and settle on a reasonable solution.

One item hasn’t changed on the ensemble average on all three charts the past few days:   Upper level temps are generally average to above average starting Thursday through most/all of the extended period.  We’ll see if that holds in the coming days.

Chief Meteorologist Mark Nelsen

Cool and Showery Weekend Ahead

April 12, 2013

It’s been well advertised that we have another cool and showery weekend ahead.  Maybe not quite as wet as last weekend but just as cool.  The bulk of the next 48 hours we’ll have temperatures in the 40s here in the metro area.  Snow levels briefly dip to around 2,000′ the next two mornings.

Where might you go to stay dry?  Take a look at our RPM model forecast of rainfall between Friday evening and Sunday evening.


Areas colored are greater than .10″.  Notice just about all the lower elevations of eastern Oregon will be dry or nearly so.

One area that will just see very light showers (mainly dry) will be the Hood River Valley.   Fruit trees are blooming, at least in the lower valley where this picture was taken by Don Grasley:


Enjoy the weekend.

Chief Meteorologist Mark Nelsen

Arctic nearly free of summer sea ice during first half of this century?

April 12, 2013


An interesting piece from NOAA detailing a few possibilities related to future summertime ice in the Arctic Ocean.  Obviously it has nothing to do with our current weather, but some good reading.

Arctic nearly free of summer sea ice during first half of 21st century.