Strong System For Sunday and Long Range Thoughts

November 29, 2012

Some interesting twists and turns on models and maps the past 24 hours, probably the first time this season we’ve seen the possibility of strong wind here in the Valleys show up.  The key word is POSSIBILITY in that sentence.

The area of interest is later Saturday night or early Sunday morning.  Various runs of various models show some sort of surface low deepening and moving very quickly SW to NE somewhere across the Pacific Northwest.  If you want a good windstorm west of the Cascades, you want something like what showed up on the 00z GEM (Canadian) model LAST NIGHT:

A deep low making landfall around Astoria and tracking quickly east or northeast.  When that happens we get a great rush of wind from the south and southwest behind it; a classic windstorm.  And you want the isobars perpendicular to the valley so the wind can rush straight south to north.

In the past 24 hours other models have had the low much weaker, or farther south, or moving through as an open wave (weaker than a closed low), and now a couple don’t even show a consolidated low, but more of a double structure.   This evening the GFS, WRF-GFS, and GEM are showing the open wave or double-type structure.  That would imply nothing too exciting.

WHAT DOES THIS MEAN?

There is no good model consensus as of this evening what’s going to happen; but those 3 models might be a trend developing for a weaker wave that just gives us more rain and breezy conditions only.   We may get a strong surge of wind later Saturday night or very early Sunday morning OR just normal breezy conditions and no one will even notice.  As we say in this business; we’ll see what the next run of models holds.

LONGER RANGE:

Some chatter today about possible colder weather showing up on the maps.  I have several thoughts on that, especially for the newbies out there:

  • #1  You shouldn’t get excited about anything beyond 6-8 days unless it consistently shows up on most or all models.  That means run after run of similar results.  That did happen just before the 2008 cold spell; day after day of models showing a major change.  Otherwise you’re getting yourself worked up over nothing; and it sure isn’t worth arguing about
  • #2  We have 4 runs per day of the GFS that go out to 16 days, 2 runs of the ECMWF that go to 10 days, 1 run of the GEM that goes out to 10 days.  Plus a few other models.  There will be something “coldish”,  “near snowy/snowy”, or even an “arctic blast”  on ONE of those models almost every day between now and February.  Another reason to not get too excited unless #1 (above) occurs.
  • #3  Ignore the surface temps on the IGES output after about Day 3.  They’ll lead you astray; often extremely cold for the pattern.  Just keep an eye on 850mb temps, surface wind (Southerly or Westerly = Bad for Cold/Snow), and actually look at the maps instead of just reading text output.

That said, I don’t see anything too interesting in the next 7-10 days.  Cool troughs Sunday/Monday and again next Wednesday/Thursday will keep highs in the 40s then and maybe snow down around 2,000′ with that 2nd trough.  If so, that’ll be just about the lowest so far this season.  Here’s the 850mb ensemble chart from the 12z ECMWF:

Note the cold trough later next week with pretty good agreement on 850 mb temps down around -4 to -5.  Then most members seem to get a little milder but a WIDE variation (thus the “spaghetti plot” name).  Note a few members of the 51 members show -6 to -9 850mb temps in the 10-15 day range.

A few of you may have noticed my blogging frequency is down a bit the past couple of weeks.  I’m doing all 5 evening shows while Stephanie is gone (she’ll be back in two weeks).  Not much room in the workday for anything other than getting graphics put together, emails etc…  Luckily for me (but not for you) most of this Fall the weather has been relatively slow.

Chief Meteorologist Mark Nelsen