Done With April; On to May

April 30, 2012

By one measure this Spring is doing far better than last year.  Check out the number of 60 degree days so far this year:

Compared to last year, and the chilly spring of 2008, it’s a decent improvement.  Looks like April temperatures ran quite close to average across the Pacific Northwest, here’s a graph showing temperature anomaly over the past 4 weeks across the west from Western Region Climate Center…the rest of the country has been warmer than average too, although not as extreme as March:

Well, the first week of May, or at least the first 6 days, will be quite cool.  This has been a well forecast cool and wet spell (see previous blog postings).  Cool westerly flow in the upper atmosphere turns more into a cool upper level trough as we get to the end of the week.  Then that trough “closes off” into a chilly upper level low and takes it’s time getting out of here this weekend.  As a result, this upcoming weekend will probably be the coolest we’ve seen in a month.  850mb temps Saturday morning bottom out around -4, impressive for May. 

The surface low and associated moisture may give us quite a soaking Thursday; that appears to be the wettest day of the week.

Models are in pretty good agreement on upper level heights rising Sunday and into next week for a return to normal or above average temps.  Here is the 00z GFS ensemble chart:

Interesting to note the last few weeks that as we move into the warm season, even these 5,000′ temps are affected by the strong diurnal heating.  You don’t see that October-March. 

And here’s the 12z ECMWF, showing above average 850mb temps beginning next Monday, at least in the mean:

Chief Meteorologist Mark Nelsen


Quick Sunday A.M. Check In

April 29, 2012

Hmmm, thick low clouds over the western Valleys this morning and cool onshore flow airmass appears quite deep.  Very first glance would say “hard to clear out today”, but I didn’t look at much.  Not exactly a forecast there.

Rainy most of the upcoming week still.

The 00z ECMWF definitely shows hope for much warmer weather about 7 days from now as a cold trough digs into California and we get ridging behind it starting next Sunday:

The 6z GFS is similar to the ECMWF mean, not the operational:


Enjoy the Weekend; A Wet & Chilly Week Ahead

April 27, 2012

Hard to believe, but our 4th weekend of April appears either dry and mild or mainly dry and mild.  Tonight’s warm front, spreading light rain into the northwest part of Oregon, will fizzle and dissipated right over the top of us later tonight and into Saturday morning.  That leaves us with a gray start Saturday, but increasing afternoon sunshine.  Sunday will just be partly cloudy or mostly sunny.  Both days our RPM is trying to generate weak convective showers over the Coast Range and Cascades in the light westerly upper-level flow.  Thus the “mainly dry” wording.  Most likely we have a dry weekend ahead.

Then, it’s on to May!  Unfortunately, the first week of May looks to be unusually wet and chilly.  Early on in the week we get “zonal” flow which is our usual westerly jet stream bringing in cool and wet systems.  Then the latter half of the week (and probably next weekend) a colder upper-level trough digs down over us.  Take a look at the 00z ECMWF’s 500mb anomaly forecast for the 7 day period starting next Monday-Tuesday:

Note the large negative anomaly over the West Coast, western Canada, and Alaska.  In fact the next 7-10 days sure looks like the March weather pattern doesn’t it?  Nice that the heat returns to the eastern USA too.  A peek at the 12z ECMWF 850mb ensemble chart shows below average temps (around 5,000′ elevation) from Monday to next Sunday, the lots of variation after that time.

The 12z GFS is similar, although it holds onto the cooler than average temps a good 1-2 days longer.  Brrr!  

The screaming message is that next week will feature lots of cancelled spring sports practices and games, along with chilly temps and mountain snow down to 3,000′ or even lower at times.  Hopefully you didn’t plant your tomatoes or corn yet!  I just planted tomatoes in my greenhouse I built last Fall.  In there, even on days like today, it gets up to around 80.  A little bit of climate change going on at the Nelsens.

So once again…enjoy the mild and dry weekend!

Chief Meteorologist Mark Nelsen


Take Your Kid to Work Day

April 26, 2012

Relatively slow in the weather center this afternoon, not quite as much action (lightning-wise) as I expected.  Good time for Andrew to hang out with his old man.  Today is officially “Take Your Kid to Work Day”, and my son looks forward to coming in and hanging out.  Plus “Aunt” Stephanie brings in treats too. 

Weatherwise, plenty of  towering cumulonimbus clouds plus blue skies in-between made for nice time-lapse today. The showers should die down dramatically after 7pm as we lose the daytime heating. Not that we had much daytime heating; highs somehow made it into the upper 50s between the showers. But most of the day was spent in the low-mid 50s.

A big slowdown in the weather now through the weekend. Tomorrow we get approaching warm front clouds for more gray than blue. Just not much (or any) rain. Then the warm front dies right over the top of us Saturday…in fact the afternoon that day might end up mostly sunny! Sunday looks nice again, then we start a fresh round of rain next week. The ECMWF shows below average 850mb temps through most of the next 7-10 days (after Sunday).

So no sign of an early May warm spell!

I had some fun on the way to work today.  Highway 26 was totally stopped near Murray Ave…cars started moving again slowly, and I pass by a pair of Canada Geese with their brand new goslings walking down the left emergency lane!  How did they end up there?  No pond nearby, the right side of the freeway is a 15 foot high wall, and the 3 foot barrier on the left.   They then decided to walk ONTO the freeway, maybe because I had parked in the emergency lane blocking them to get a picture…oops.  That would explain the lady screaming at me to move my car.  Anyway, they walked another 30 feet and were able to walk onto the grassy median to slop around in the mud puddles and I headed on to work.  Hope they made it…

Chief Meteorologist Mark Nelsen


Thunderstorm Rain Totals: Big Soaking Out East

April 25, 2012

Those thunderstorms eastside sure dumped a pile of rain in Clackamas and eastern Multnomah County. The Eagle Creek RAWS site (on the highway between Eagle Creek and Sandy) reported almost 1.00″ of rain. Other spots saw around 1/2″.


A “Bolt From the Blue” In Gresham

April 25, 2012

5:00pm:

That cluster of thunderstorms continues moving up through the far east side with heavy rain, some hail, and frequent lightning strikes.  Boring, Sandy, and now Corbett getting a good show.

But check this out just 5 minutes ago…a strike well outside the thunderstorm very close to Centennial High School, just east of 181st ave.

This proves the point that lightning can leap well outside of the thunderstorm, in this case 5-7 miles west of the center of the storm!

Chief Meteorologist Mark Nelsen


Thunder Moving Up East Side of Valley

April 25, 2012

A cluster of heavy showers is racing quickly up the far east side of the Willamette Valley right now.  Lightning breaking out east of Silverton, headed for Molalla, Colton, and eventually Estacada, Sandy, and Gresham…they are moving 30-40 mph from south to north.


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