Spring Break

March 25, 2014


I will be on vacation through March 31st, so probably no posts through that time.  Enjoy the rain!

3 Nice Days, then Very Wet!

March 21, 2014

Oregon’s Spring Break has begun and it looks glorious for Saturday, Sunday, and Monday.  We’ll see slight warming over the weekend, then a warming overhead atmosphere combined with offshore flow and Monday will push temperatures up to the warmest we have seen so far this year.


The GFS, ECMWF, and WRF-GFS show temperatures just shy or at 70 degrees for a high Monday afternoon.  That wouldn’t be unusual because about every other year we hit 70 at some point in the month.  Maybe similar odds to hitting 98-100 degrees in July?  OR, maybe we’ll just top out at 68 as my current forecast shows.  Either way, try to take a sick day Monday to enjoy the warmth.  Because then we turn very wet.

All models are in strong agreement that we’ll be seeing several weather systems Tuesday through at least the following weekend.  The ECMWF shows rain beginning Monday night with no 12 hour period dry for the following 7 days!


That graphic shows the actual rain accumulation in blue on the bottom chart and the ensemble average as green; note ensembles are quite close to the deterministic forecast.  The chart on the top shows each individual ensemble member’s rainfall accumulation.  By the way you’ll notice I use Salem instead of Portland since the terrain on the ECMWF seems to shove heavier Clark County foothills precipitation too far southwest into the metro area,  The GFS meteogram shows the same thing; this is the 00z run this evening:


Probably not such good graphics to use on TV eh?  Might be mildly confusing.

So enjoy the next 3 days, and then hunker down for lots of rain and some windy systems too.  It IS possible to have a weak windstorm this late in the season, but right now I don’t see any real deep lows close to the coast or strengthening as they approach.

On another note, our overnight temps should warm a bit the next two days.  There were record low temps in Pendleton, John Day, and Burns this morning.  12 in late March…that’s chilly!


Chief Meteorologist Mark Nelsen


Equinox Thursday: Halfway to Summer

March 19, 2014

Tomorrow morning at 9:57am we’ll see the Spring (Vernal) Equinox in the northern hemisphere.


What does that mean?

The earth orbits around the sun, but the poles are not lined up directly perpendicular to the orbital plane.  Our planet is actually tilted about 23 degrees from vertical.  That means that at one point in our orbit the southern hemisphere is receiving more energy from the sun than the north and six months later it is reversed.  That’s how we end up with summer and winter, the effect being more pronounced (generally) the farther you head away from the tropics.  If you visit a tropical area you’ll find that “summer’ and “winter” aren’t really in their vocabulary since the sun is always almost directly overhead.  Tomorrow we’ll be halfway between the two points, thus the Equinox which means “equal night”.  Day/night are very close to equal in late March and in late September.

Of course you might then wonder why we aren’t halfway to the hottest time of the year climate-wise?  If the average high in Portland is 44 at the coldest and 82 at the warmest, why isn’t the average high in the lower 60s?  It’s because it takes time for the heat to accumulate on the land and in the oceans, and they are both slow to lose it, thus the delayed seasons.  If we’re talking just energy from the sun, we should be halfway through spring right now.  Obviously we aren’t.

Another misconception is that it’s winter right up until tomorrow morning.  That’s not really true either; because the coldest 3 months of the year at our latitude are December-February, not mid December through mid-March.  Take a look at the average monthly temperatures here in Portland:


Notice that March is not only warmer than December, but even a bit warmer than November!  Even if you take the coldest four months of the year, March still isn’t included and is definitely not a winter month in the Pacific Northwest.  That said, it’s a little easier to get snowfall to lower elevations in March than November.

Meteorologically we consider winter in the Northern Hemisphere as December-February for the reasons mentioned above.  How was this winter in our area temperature-wise?  Take a look at the national temperature departure from normal:


Note we were generally near normal across Washington and Northern Oregon and above average farther into the state (of Oregon).  Now I’m not into conspiracy theories, generally, but I do notice what someone else already did.  You have to look very closely to see the below average temperature areas but the opposite, above average, sticks out great due to the color table chosen by NCDC.  Much of the nation was very cold, yet this map seems to minimize it a bit.  But, maybe it’s just me.  Anyway, if you look closely at Oregon you see something interesting:


The chart above shows temperatures for Zone 2 in Oregon, the Willamette Valley area.  We had our coldest winter since 2008-2009.  Yet:


This chart shows the high desert areas of Oregon east of the Cascades had their warmest winter in about 8 years.   What?  Most likely due to the frequent inversions.   Remember all the days Salem sat in the 30s while Bend and Burns made it into the 50s?  That explains it.

What about precipitation?  No big surprise here, parts of the Pacific Northwest, especially along the coastline are in the MUCH BELOW NORMAL category.  The farther south you go along the West Coast the drier it was:


Poor California, and they are just about out of time to get significant rain this season.

So this winter was definitely drier than normal and a bit cooler than normal here in the lowlands.  Once again…a weird winter.  So far March is running wetter and warmer than average.

By the way, do you know what would happen if we were orbiting the sun without that 22 degree tilt?  There wouldn’t be any (temperature) seasons.  We would just stay the same year-round.  And you can probably guess what it would be like if we were tilted a full 45 degrees?  Even more extreme changes from summer to winter.  In that case the sun would be directly overhead at the summer solstice and it would be on the “arctic circle” with the sun hardly rising at all at the winter solstice…brrr!

Chief Meteorologist Mark Nelsen

Lowest Snow Level In A Month (or so)

March 17, 2014

8:30am Monday…

Happy St. Patrick’s Day! 

We’ve got some chilly Irish weather for you; appropriate enough for Ireland at least.

Yesterday’s cold front held off long enough to give MOST of the metro area a dry and warm day.  Looks like the ECMWF was wrong this time pushing in the precipitation early in the day.  It sure was close though!  Kelso was in the upper 40s or 50 all afternoon while we hit the lower 60s in a good chunk of the metro area.   Models really did quite well (even the ECMWF) showing the band of steady rain holding nearby all day and then suddenly swooping in from the northwest in the evening.

Then the cold air came in with the moisture, bringing us the first snow below 2,000′ since the arctic blast back in early February.  This morning I have a snow/rain mix at 1,000′ and you can see there was snow during the night on these ODOT cameras around 1,000-1,200′ along Highway 26 east of Sandy:


US26 at Cherryville Dr_pid2332

The mountains FINALLY have some decent snow today too; looks like 6-12″ has fallen up there and it’s all powder for the first time in a month too!

Showers taper off today and will be mainly up against the Cascades where the air rises, cools, and moisture condenses out of the clouds.

The weather will continue to be relatively quiet/calm the next week.  We get a cool trough swinging through on Wednesday/Thursday, then split flow COULD mean another nice weekend with rain headed into California.  We’ll see about that later this week.  You can see the gradual warming on the ECMWF maximum temperature forecast through early next week:


The ECMWF is also drier than other models too, showing just a few hundredths on Wednesday afternoon and then nothing until next Tuesday or Wednesday.  That’s because it has the Wednesday/Thursday trough a bit flatter and the air isn’t as cold with it.  We’ll see.  Once we get more clearing and the chillier airmass, expect overnight frosts to return Thursday-Saturday mornings too.

 Chief Meteorologist Mark Nelsen

Tricky Weekend Forecast

March 13, 2014

I admit my blogging has slowed down dramatically the past couple of weeks; that’s because the weather itself is quite slow and I don’t feel as inspired.  Sorry, that’s how it works.

But this weekend’s forecast has been interesting to watch.  We kept showers in Sunday’s forecast all this week based on the ECMWF model.  The ECMWF has been steadfastly sticking to a rainy Sunday with a system crashing the mild ridge much more quickly than the GFS.  Here is this morning’s forecast for Sunday at 11am:


Then in the past 24 hours the GFS has now pretty much come around to that idea…no big surprise that it’s playing catch-up to the ECMWF once again.    So here’s our latest forecast for the Shamrock Run early Sunday morning:


Now you’ll notice areas to the south and east of a Portland to Lincoln City line could stay dry for a good part of Sunday.  So the forecast is still not set in stone; a slight northward shift would mean a dry Sunday morning here in Portland…Stay Tuned!

There is one interesting tidbit that I first noticed on the ECMWF and now I see on the WRF-GFS.  On Sunday evening/night it looks like we may get a rare “Anafront”.  That’s when most of the precipitation occurs just behind the cold front as opposed to ahead of it.  There is a sharp wind shift and a dramatic drop in snow level.  The WRF-GFS shows the temperature in Portland dropping from 55 to 40 in just a few hours with the wind shift.  That would imply snow could stick down below 2,000 or 1,500′.  It also generates 8-12″ along the west slopes of the Cascades.  This may be the heaviest snowfall of the “winter” around 2,000′ other than what we saw during the 2nd arctic blast in February.  Something to watch the next day or so.

Other than that, real slow weather continues next week, the 3rd week of March.  Milder midweek with weak ridging, then a colder trough again near the end of next week.

Chief Meteorologist Mark Nelsen

Wednesday: Warmest Day So Far Ahead

March 11, 2014

Today was a wonderful early spring day with temperatures up around 60 degrees in the metro area and sunshine most of the day.  Sure, a real chill in the air this morning but a comfortable afternoon.  We hit 59 in Portland.

Now all signs point to a very warm day Wednesday.

1. The atmosphere overhead warms quite a bit

2. Weak low-level flow turns easterly for the first half of the day; it will be a breezy morning in the western Gorge and eastern edge of the metro area

3. That easterly flow will mix drier air down into the lower elevations and also warm the lowest elevations.

My chart I use for the month of March shows a high temp at PDX between 65-69 degrees tomorrow afternoon.  Our RPM model goes with a high of 70 tomorrow, the WRF-GFS around 66-68.  My 10pm forecast will be 66.  We’ll see how that turns out.  We might have a decent variation around town with warmest temps near the mouth of the Gorge.  I think Troutdale could touch 70, or Hillsboro could be close…we’ll see.  So enjoy Wednesday!

It sure won’t be like 2005 though; remember that year?  We had a long stretch of record warm & dry weather from late February into mid March.



The first 11 days of the month are running above average; a bit of a change from a chilly February and chilly winter overall.  Signs point to the above-average temperatures continuing for at least another 5-7 days.  What happens beyond that is a little uncertain.  Although it appears to me we are probably headed for cooler than average temps as we head toward Oregon’s spring break.  That’s the last week of the month.

Last night at 10pm I mentioned the disparity in snowfall totals vs. elevation this winter.  In fact two rainstorms and mild weather in between have only made that more noticeable.  Take a look at two locations.  The first is just below Timberline Lodge.  The other is west of Kingsley Reservoir near Mt. Defiance (west of Hood River).  The bars represent February 10th and March 10th % of average snowpack.  Notice higher elevations improved a little, in fact above 5,000′ snowpack is only slightly below average on Mt. Hood. Yet it is abysmal below; down to 35% of average at 3,000′.  Basically there is very little snow below the 4,000′  elevation.  This highlights what I mentioned in my winter wrapup; that we’ve seen very little 1,000-3,000′ snowfall this winter.  And the warm temps the last 3 weeks (above the cold Gorge influence) has actually started the normal melt a little early.  March could have been the big “make up” month, but it isn’t this year.  Even SkiBowl at 4,000′ only has 2.5′ on the ground, and in a normal year the snowpack starts to decrease just a couple of weeks from now.


Here is the snow depth the past few winters at 3,000′ just a few miles SE of Larch Mountain (OR):


No better than the El Nino winter of 2009-2010 at that location, at least for mid-March.

As I mentioned, it does appear we’ll have cooler weather coming up in 7-10 days, but not sure it’ll be a decent snow-producing pattern.

Chief Meteorologist Mark Nelsen

The Migration Has Begun: Thousands of Birds Overhead Tonight

March 7, 2014

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.  Although I guess it did happen in the mid-1800s when many of our ancestors came west to Oregon.


And it shows up on weather surveillance radar quite well at times.  I just noticed it on the Portland radar for the first time this season.  We usually see it on the 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 10,000′ or so.

Tonight was a great example.  Soundings show a westerly wind from 5,000-10,000′, yet the current radar screen shows a strong SOUTH TO NORTH movement…20-40 kts.  And at sunset the radar suddenly fills in with those “targets” moving from SOUTH TO NORTH.    Ornithologists call that the “exodus” as thousands of birds suddenly take flight at sunset.   Here it is on the radar loop:


Here is the VAD wind display from the Portland radar around 7pm showing the strong southerly wind, which is really moving birds:


The wind arrows are all northerly up to around 11,000′, then no echos to get a speed/direction from above that level.  Birds don’t like to fly too high.

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:  http://virtual.clemson.edu/groups/birdrad/index.htm

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 to relax you before bedtime:

By the way, my duck (ChitChat) quacks when she flies…across the yard.  So for some reason waterfowl like to chat as they fly…you can hear that in the video.

Chief Meteorologist Mark Nelsen