No!…The Dreaded Split Flow!

November 18, 2008

Junk I don't usually post this early, but I'm sitting here with all 3 weather graphics computers down while doing an upgrade.  So I had to share this image.  Click on it to get the full deal.  It's the 12z GFS at 144 hours, next Monday morning.  It shows a "perfect" split flow pattern on the way.  The previous model run didn't show it quite so strongly, but I see the 12z ECMWF is quite similar.  Bad news for skiers/snowboarders.  If this verifies, along with the maps that go out to 10 days, the ski season is going to have to wait until after the Thanksgiving Weekend.  There are worse weather patterns than a big ridge in winter in my opinion.  This would be it.  I also realized that we never once saw this pattern last winter.  Doesn't mean anything for this winter, but shows how consolidated and chilly last winter's pattern was.  More later…

Okay, it's 10:00pm and we just finished hootin', hollerin' and clapping at the beginning of the show (you don't hear that, we stop just before the anchors begin).  So here's a quick update.  00z GFS and Canadian show either ridging or split-flow through the first of December.  Quite a turnaround from the wet start to the month. 

In the short term, I did some quick touch-up surgery to the metro and Gorge forecasts for tomorrow.  Gradient PDX-DLS is switching around quickly to easterly and our RPM shows 6-7 millibars by midday tomorrow.  That should produce wind gusts to 50 mph at the west end of the Gorge and 35 mph at TTD, Gresham, Camas etc…  That will finally clear out the low-level muck for most of us though.

No other deep thoughts for this evening; I think I exhausted my brain cells on those life-altering thoughts in last night's post…Mark Nelsen


Inversion Season

November 17, 2008

Snapshot The last couple of days show that we've moved into inversion season, although we're clearly right on the "edge" of inversion weather.  Valley temps today struggled to get much above 50 degrees AWAY from the Columbia River Gorge.  In fact Hillsboro only made it to 49 degrees.  PDX was only 2 degrees short of the record (61) for the date.  Somehow, with a light southerly wind, Eugene made it to 70.  Not nearly as surprising was the summer like 75 degree high at Redmond.  That blew away the old daily record by 9 degrees!  The family and I stayed the night over at Warm Springs last night and drove back over Mt. Hood between 8-10am.  Quite a change in temps as we went in and out of the warm air.  At one point it rose from 37 to 50 in just a couple miles.  West of the Cascades the cool Valley air appears to be quite shallow, maybe just over 1,000' thick at most in the Tualatin Valley.

I find these temperature variations fascinating when we have slow winter time weather.  I didn't always feel that way.  WAY back in 1992, in the second year of my career I was working for a company called Micro-Forecasts in Hood River.  We forecast on the computer (no internet yet!) and phone line for windsurfers in the Gorge at the time.  Erik Moldstad, who still forecasts weather up in Washington, came to work for the company and about the same time I had to make a move from the Portland area out there.  So two weather geeks had to decide where to live in an exciting new climate (to us).  We had both grown up in dreary westside climes and yearned for something new.  The choices we made were vastly different.  I wanted SNOW…as much of it as possible without too long of a commute.  So I rented a place 17 miles from Hood River in the Upper Valley (near Parkdale) around 1500'.  Whew, cold nights up there in winter, although I moved back to Portland to work at KOIN sometime in mid-January so I didn't get to see a full winter.  Erik was really big into temperature variations…which I thought was very strange and boring.  So he chose to rent a place 20 miles upriver in Dallesport.  He wanted to watch the temp go up and down dramatically.  I also found wind pretty interesting, but he hated it because it didn't allow much of a diurnal temperature change.  The point of this is:  each of us weather geeks finds a different part of weather or climate most fascinating.  Some of us HATE hot weather, others like it.  Some HATE wind, others stay up all night posting pressure gradients. 

So there is no great point to that last little bit.  But I do find that as I approach the twilight, the closing book, the final act, the last hurrah…of my life (almost 40), that I find almost any sort of weather interesting.  I suggest you try to do so as well…Mark Nelsen


A Slow Night

November 13, 2008

Snapshot  I took a bit of grief from the newsroom today about the sudden flooding in Tillamook County last night.  As you can see on the image, the Wilson River made it almost 4 feet above flood stage.  Up to 4pm yesterday the forecast was for it to stay below flood stage.  I told the news folks that it was pretty much out of my hands and that the Northwest River Forecast Center takes care of rivers.  So I ducked that issue somewhat well.  Sounds like the hydrologic models didn't handle this one well though.  The meteorological models we all look at did quite well with the rainfall as I mentioned on last night's posting.

Moving on to the current weather:  there's nothing happening right now.  It's mid-November, skies are clear, and it's getting cold outside at 9pm.  Any surprises there?

Back here in the weather center, we're watching houses burn in California near Santa Barbara on the satellite feed (a really slow night).  A strong Santa Ana wind has found a wildfire.  We'll probably show more live pictures during the 10pm newscast.

We'll have a longwave ridge over us in some form or another for the next 5-7 days.  Maybe a change beyond that point, but not enough to start the ski season NEXT weekend…Mark Nelsen


Rain Moving Out

November 12, 2008

Snapshot I'm very happy with how things have turned out with our midweek stormy weather.  Models have done an excellent job handling rainfall totals and timing, wind, and snow levels.  I suppose the wind speed was a bit lighter, by about 5 mph, than what I expected this morning.  That's about all the fault I can find in models or the forecasting this evening.  As I write this, the back edge of the solid rainband is now sliding over the metro area.  Models had consistently shown the rainfall quickly and dramatically tapering off over the Metro area sometime in the late evening.  They had also shown the very light totals over the Valleys yesterday and mainly dry weather this morning.  As of 8pm, if my addition is correct, it appears that the 48 hour rainfall totals look like this:

Portland- 1.43"
Salem- 1.09"
Kelso- 4.06"
South Fork (Coast Range)- 5.42"
Blazed Alder RAWS (Near Mt. Hood 2600')- 5.10"
Yacolt- 4.77"

I assume the mountain locations may have up to one more inch on the way, so a 5-7" storm total seems pretty reasonable.  If you look two posts back, you can see what our model was forecasting.  I heard someone elsewhere in TV weather land this evening state that we were getting more rain than expected.  I would disagree, these numbers look pretty good!  Kelso was a bit heavy though.

9:05pm addition:  I see that we have a nice front moving through the metro area right now.  It shows up on radar through Clark County, about to hit PDX.  The wind behind it has switched to northwest along with a temperature drop.

Moving on…a very straightforward forecast the next 7 days or so.  A longwave upper level ridge is going to be lingering somewhere near the West Coast.  So not much rain and mild temps, at least outside of the Valleys.  If we get a significant area of surface high pressure centered overhead, fog or low clouds are a sure bet this time of year, keeping temps cool.

Long range models seem to imply a bit more of a change later next week (8-10 days) in LaLa land.  But one thing seems likely…the ski/snowboard season is not going to start early this year.  Probably not even by next weekend since the first possible significant snow in the mountains isn't until right around next weekend itself.  Let's aim for Thanksgiving week…Mark Nelsen


Orographic Flow

November 11, 2008

Snapshot This evening's rain totals, up to 8pm, clearly show strong orographic flow in progress over us.  That means the strong westerly flow is running right into the mountains head on.  Over the next 24 hours wind around 4,000-5,000' (850mb) averages 60 mph.  Add a very moist and warm airmass to that and you get a ton of rain over elevated terrain.  The graphic here shows about 5 times as much rain at the crest of the Cascades compared to the driest part of the Valleys.  The areas just downwind of the Coast Range tend to be the driest, generally the west side of the Portland Metro Area.

Quite a break in the rain at midday today…actually the models did better than I did.  I saw the big rain-shadowed hole over us yesterday evening (for today), but just said the rain would be a bit lighter.  Models still show the same thing coming up for later tonight through midday tomorrow as the main jet and cold front are aimed at Western Washington.  So quite a break in the rain again the 1st half of tomorrow, then the heavier cold front rain moves down over us from Noon-6pm or so.  I still don't see much more than another 1" at most here in the valleys.  But maybe another 4" in the Cascades and Coast Range.

I notice the wind is picking up on the roof right now…due to the warm front moving in and tightening the southerly pressure gradients again.  The North Bend to Forks gradient made it up to around 13 millibars early today, dropped to less than 8 this afternoon, but now is back up close to 14 mb.  Wind seems to be responding…I see gusts to 47 the last hour at Yaquina Bay Bridge in Newport.  Gradient seems tightest later tonight through tomorrow morning.  The WRF-GFS from the UW has consistently shown a leeside-type low developing near Yakima overnight too.  It shows 15mb from Eugene to Yakima by daybreak.  This may bring strong west wind through the Gorge later tonight, but there's no sign of that for now.

Not much to talk about beyond tomorrow evening.  Some sort of longwave ridging sits over us for many days, through some time next week or even longer.  Looks like November will end up milder than average…unless we have a really cold 2nd half of the month that doesn't show up on the maps yet…Mark Nelsen


Lots of Rain

November 10, 2008

Snapshot This image is the output from the 18z run of our RPM model here at the station.  It pretty much shows the story for the next 48 hours.  Lots of rain…maybe 1-2" in valleys and 5-8" in the Cascades.  I see the freezing level gets up to around 11,000' by Wednesday morning too.

Now, that said, our new 00z run is somewhat drier.  It shows 4-5"
 totals in the Cascades and closer to 1+" in the valleys.  This goes with the 00z GFS which along with the other GFS runs today has been gradually pushing the core of the heaviest rain to the north.  That means another flooding cycle for already-wet Washington.

The IR satellite and water vapor images sure look impressive with a very long fetch of subtropical moisture extending from the West Coast to the Dateline.  Plenty of juice out there for lots of rain, but the bullseye is going to be slightly north of us.

As for wind, I sure don't see a windstorm.  Just a lot of gusty south wind beginning tomorrow and continuing through Wednesday.  Earlier model runs today had cut off the wind quickly early Wednesday as a weak cold front (and most of the rain) sagged to our south.  Now it's looking like it'll take most of Wednesday to get the front through here.  So gusty south wind both days.  I don't see a gradient that would produce gusts much above 35-40 mph, so that's my top range for the valleys.

For the Thursday and beyond period?  Back to dry with some sort of longwave ridging nearby for quite a long period.  Each model run has been a bit different, but they all say mild and mainly dry into the 3rd week of November.  Don't lose hope skiers and snowboarders.  It will only take 2 good storms to put the ski areas in business and that can happen quickly!  Mark Nelsen


Warm Air Moves In

November 6, 2008

Snapshot  Finally, after waiting all day for the south wind to take over, the warming suddenly arrived at PDX a few hours ago.  I don't think the cool east wind will make a return for tonight, so we'll be well into the 50's all night long.  Check out the rainfall totals up north in Western Washington.  1.20" in 6 hours at Olympia, 6"+ at a spot in the Olympics too.  4 rivers already have flood warnings up there with more to follow as the rain continues tomorrow.

I think we probably won't have much rain here in the Metro area until about midday tomorrow.  The frontal zone and it's good lifting stays to the north most of the day tomorrow and Saturday.  A wave comes through tomorrow afternoon/evening, so we do get a decent surge of rain.  Then cooler rain Saturday and Sunday.

I see Timberline has had 2.20" snow, then rain today.  The 20" or so is melting quickly with temps into the 40's at that elevation.  It'll all be gone by Saturday morning.  There will be some new snow at/above Pass elevations Sunday and Monday, but now it looks like another warm period the middle/latter part of next week.  00z GFS and 12z ECMWF have very warm 850mb temps at +7 to +10 again during that time.  So no early start to the ski season in sight yet…Mark Nelsen