Cool and Wet Weather Ahead

October 31, 2013

October will end cooler than average for most of us in the region.  The temperature at PDX (53.5) will end up the coolest in 5 years.   Eugene will be the coolest since 1981.  Of course all that sunny weather means only about 1/2 of our normal rainfall.

Now November is our wettest month of the year on average here in Portland…5.63″ is the average.  And in accordance with that we get a much wetter weather pattern once we get past the 1st day of the month.

Several items of interest.  First is the surface low pressure system that tracks into the Strait of Juan de Fuca Saturday.  Models have slowed it down a bit, and the 00z GFS has pushed it a little farther south.  Still, gusts shouldn’t get much above 60 mph on the northern Oregon Coast and 35-45 mph here in the valleys.  It WILL be the strongest storm we’ve seen in a month though.  Wind should pick up nicely just before daybreak Saturday here in the Portland area.

Here’s the 00z WRF-GFS showing the low inland over Washington and the tight southerly pressure gradient:

slp.42.0000

Then, behind the cold front, strong and cold westerly flow behind the cold front will push a continuous stream of snow into the Cascades through sometime Sunday.  This will be the first dump of snow down to below pass elevations so far this season.  Government Camp could easily see 6-10″ from midday Saturday through midday Sunday.  A good 10-15″ more likely higher up in the mountains. Watch out travelling through the Cascades from near sunset Saturday through midday Sunday; expect mid-winter driving conditions!

MarkSnow_MtHoodFcst_2013

Another system comes through Monday afternoon through Tuesday, but snow levels will be rising to around 6,000′ briefly.  Then snow levels fall again the 2nd half of next week.  So the snow this weekend will be sticking around and we’ll see additional base accumulations next week.  Maybe most important is that we don’t see any sign of significantly warmer weather in the long-range.

Take a look at the 00z GFS ensemble chart:

tseries_850t_000-384_Portland

and the 12z ECMWF ensemble chart:

tseries_850t_000-360_Portland

Both show atmospheric temperatures over our area well below average through most of the foreseeable future (after tomorrow).  By the way, those of you planning to get on the “Wishcast Express”?  Based on the 00z operational GFS it appears to be cold enough for snow in Portland about 11 days from now.  But note the operational run was an outlier, the average of the ensembles is significantly warmer, but still below average.  We’ll see…

Chief Meteorologist Mark Nelsen


Another Dry Trick or Treating Night

October 31, 2013

For the first time in about 10 years I’m not going out with my kids…they are getting too old!  I’m just going to pout about it in the weather center instead.

But YOU should have a good time…radar has pretty much dried up and I just expect a cloudy and mild evening…enjoy!

Halloween2010

Chief Meteorologist Mark Nelsen


ECMWF Monthly Run Maps

October 31, 2013

The usual…last night’s run of the ECMWF out to one month.  One map for each week.  The common thread is the upper level heights remaining well above normal out in the Pacific around 160W.  That’s often a good location for us to get colder than normal weather.

500za_week1_bg_NA

500za_week2_bg_NA

500za_week3_bg_NA

500za_week4_bg_NA


A Quick Evening Post: Plus A Winter Thought or Two

October 29, 2013

Real quiet weather out there this evening.    Temperatures are running a bit cooler than 9pm last night,

PLOT_Temps_24HrChg_Metro

although last night we were dealing with the last of the breezy northeast wind.  Assuming little or no cloud cover makes it here before sunrise (likely), temps will be just about the same as last night.  Here are a few of the morning lows:

MarkCold_FrostyOvernightLowsMetro

Interesting to note that downtown Portland didn’t have a frost (not expected there anyway), but Aurora only reported a lowest hourly of 34 (ignore the 36).  It’s possible it was lower, but still a little warmer than I would have expected down there.

Just for fun this evening, I spent 30 minutes comparing current fall conditions with some previous fall weather and the ensuing winter.  Should be interesting to see what you all think.

We’re going to end up with less than 1.50″ rainfall for October here in Portland, less than half of normal. So…

I looked up all the Octobers since 1950 with less than 2″ of rain

2008, 2006, 2002, 1993, 1991, 1989, 1988, 1987, 1986, 1983, 1980, 1978, 1976, 1972, 1964, 1958, 1952

Then just those in the group that followed a wetter than average September

1986, 1978, 1976, 1972

And those (of the initial “dry Octobers” group) that were ENSO-neutral through the following winter

1993, 1989, 1980, 1978, 1952

The only year that featured a wet September, followed by a dry October, that was an ENSO-neutral winter, was 1978.

If you look at just the autumns that are wet in September, followed by a dry October, regardless of ENSO conditions, what happened the following winter?  There are only 4 of those as you see above.  2 had no snow in Portland (1976 & 1986).  One had a historic arctic blast in December and 6.5″ snow (1972), and one had several blasts of cold arctic air and 8.4″ for a seasonal total (and a crazy ice storm in January!).  That was 1978 again.

 

WHAT DOES THIS MEAN?  I don’t know, but it filled an entire blog posting didn’t it?

I think the possibilities are WIDE OPEN for this coming winter.  We could have some good action or it might be a shutout.  The general consensus at the OMSI meeting Saturday was that we’ll see some action this winter.  Pete Parsons went crazy forecasting the worst January in years (in a good snowy/cold way).

Chief Meteorologist Mark Nelsen

 


ECMWF Month-Long Maps: Chilly 1st Half of November?

October 28, 2013

Last night’s ECMWF monthly run.  Some interesting changes from the previous two runs.  Appears that upper-level high wants to be a little farther west, leaving some sort of troughing (cool) over us through mid-November.  That says cooler than average temps for the first half of the month.  If the trough is over or west of us, that’s also very wet.

500za_week1_bg_NA

500za_week2_bg_NA

500za_week3_bg_NA

500za_week4_bg_NA

The cool trend shows up nicely in the 12z ECMWF ensemble 850mb chart:

tseries_850t_000-360_Portland
Note the red line showing the average of all the ensembles; it’s below the average of +4 to +6 during this period.

Chief Meteorologist Mark Nelsen


Time For An Outbreak of Arctic Air This Winter?

October 25, 2013

Just finished up my presentation for OMSI tomorrow; I wrap up the past year’s worth of weather before the forecasters stick their necks out (for the meteorological guillotine?).  Made a new graphic this time, showing the coldest winter high temp at PDX:

WINTERWXMEET2013

You can pick out the years where we saw a big intrusion of cold arctic air here into the Pacific Northwest.  I figure if the high temp was 30 or below it counts, especially if the lows were down in the teens.

I would say there have been 4 real “big freezes” the past 20+ years:  December 1990, late January 1996, December 1998, and December 2009.  All of these involved several days of high temps well below freezing or extremely cold nights (in the case of 2009).

The Dec 1990 and Jan/Feb 1996 events were especially cold; 3 days of highs 19-21 in 1990, and 5 days below 30 degrees  in 1996.  The 2009 event saw no snow cover and totally sunny skies, allowing high temps to reach 30-34 each day, a little warmer than those other events.  The 2 other events on the chart above?  January 2004’s cold only extended down into far northern Oregon and didn’t last too long.  December 1998 was pretty cold, but no real strong east wind and it went out with a whimper.  Dec 2008 was mainly about the snow…we never had a several days long string of sunny and cold weather, so cold-wise it wasn’t that severe.

For region-wide severity, I would rank them this way:

  1. Dec 1990
  2. Dec 1998 (widespread)
  3. Jan/Feb 1996 (#2 if we’re talking Portland area only)
  4. Dec 2009

That shows how rare a BIG FREEZE really is here in the Pacific Northwest.  We only get a big one every 5-8 years I suppose.  We haven’t seen any “arctic action” for 3 winters, but it would not be unusual if we went another winter or two without it.

So what do YOU think?  That’s what the comments are for.

Chief Meteorologist Mark Nelsen


Big Change In The Forecast: Gray and Cool Friday

October 24, 2013

Friday (and maybe Saturday) will be MUCH different from the past few days.  Expect a gray and cool day with high temps only in the 50s instead of sunshine and 70-75 degree temps.

Take a look at this great chart, created by Brian Schmit.  It shows what has been going on the past week or so:

photo_brian

  • Elevations above 1,000′ or so have been above all fog and low clouds, with the warmest temps in our area between 1,000′ and 3,000′.  Larch Mtn. Washington is around 1,100′ east of Battle Ground.
  • In the lowest elevations (where most of us live) in NW Oregon and SW Washington we’ve had just enough offshore flow, with its breezes and drier air, to keep the fog/low clouds to a minimum.
  • Farther north, in Puget Sound, there hasn’t been enough drier air mixing down to the surface to break up the fog and clouds.
  • As a result, it’s been a miserable gray and cold period up there, pretty nice here in our area, and similar to late summer in the foothills and mountains.

That setup is changing quickly this evening.

I have been expecting the offshore flow to weaken the next few days, and that has happened the past few hours;  the east wind blowing through the Gorge has disappeared.  It’s calm at Crown Point at 9pm.  But what I didn’t expect is the stratus/fog that’s been on the coastline the past few days is suddenly lifting a bit and coming up the Columbia River and over the Coast Range.  Tidewater RAWS at 2,000′ just SE of Astoria dropped from 68 to 50 degrees from 2-4pm.  So it’s safe to say that marine layer thickened rapidly at that location in the middle of the “peak heating” of the day.  This satellite loop shows the surge of moisture (clouds/fog) pretty well too after dark:  http://sat.wrh.noaa.gov/satellite/alternative.php?wfo=pqr&area=west&type=fog&size=2

Models now show solid low clouds/fog west of the Cascades tomorrow morning, note our RPM model at 9am.  It’s visibility, but you get the idea:

rpm_9am

In the last week of October, when you get low clouds/fog in the morning with warmer air above (an inversion) and no offshore flow, they sure aren’t going anywhere in the afternoon!  The screaming message is that we’re going to be like Puget Sound tomorrow.  I cringed this afternoon on the way to work when I heard a DJ on a local radio station say “SUNNY EVERY DAY THROUGH THE MIDDLE OF NEXT WEEK”.  Ughhh!  Now everyone that heard that will wonder how the forecasters “screwed up the forecast” so badly.  We all get lumped together in the public’s mind.

No other changes to yesterday’s thinking for the cold trough early next week.  It sure moves out of here quickly.  In fact both the ECMWF and GFS both have cloud cover moving in already next Wednesday.  As a result there may only be one real chilly night (Monday night) before high clouds keep us milder Tuesday night.  I raised the low temp forecast to 32 for PDX at that time as a result.  AND, for the average John Q. Citizen, the clouds and 50s for tomorrow is going to feel cooler than the sunny and 50s for Monday/Tuesday, so I took the COOLER wording off the 7 Day Forecast.

Chief Meteorologist Mark Nelsen