Tuesday Evening Update

November 26, 2013

Another 24 hours of model runs to look over…so much fun.  Looks like the weather is still going to get colder next week.    I will be on vacation and away from my computer a good chunk of the time from midday Wednesday to Saturday night.  If you are a new commenter on this blog, your comment may get approved in less than 24 hours.  And possibly no new updates on this blog until that time.   If the action starts to look REALLY good again early next week in the models, then I’ll post from a hotel room I suppose.  I’ll be out-of-town part of that time.

KEEP IN MIND THIS POSTING WAS ON TUESDAY.

Highlights for the regular folks out there that don’t need all the meteorological detail:

  • Nice weather continues through Friday
  • Showers arrive Saturday
  • Rainy and breezy Sunday
  • Rain/snow showers possible Monday before we dry out.  Details are still very uncertain with respect to getting snow down below the foothills.  We may just see a dusting on the hills Monday and then we dry out.
  • Then cold and dry next week with high temps around 40 at best

Travel looks excellent across the region through Sunday, snow levels will stay high in the mountains through Sunday afternoon, so passes may remain clear through that time.

MarkRoadConditions_I84_5_Passes

What has changed in models/maps/my thinking the past 24 hours?

1. General trend for Sunday-Tuesday is NOT AS COLD.  That’s across all the main models
Instead of seeing models with -10 to -15 degree 850mb temps, they seem to have all stabilized around -7 to -8 later Monday through early Wednesday.  This evening’s 00z runs of GFS and GEM (Canadian) are only showing thicknesses bottoming out around 520dm.  That’s cold, but not big arctic blast material.  That’ll still give us high temps close to 40.  Or 35-40 with a cold east wind.  Here is the 12z ECMWF ensemble chart, note lots of members still much colder than the operational run on Tuesday/Wednesday though.  All hope is not lost (yet) of a colder arctic blast:

tseries_850t_000-360_Portland

and the 18z GFS chart.  It was right in line with the average of its ensemble members through Monday, then a  little on the warm side Tuesday/Wednesday.  Shortly after this post, a new chart should be out.  I’ll attach it to the bottom:

tseries_850t_000-384_Portland

2. GFS speeded up the timing quite a bit last night and this morning, but has now slowed down to show almost exactly what the ECMWF shows.
GFS has a +5 still Sunday afternoon, the ECMWF was up around +2 at 850mb at the same time ahead of a wet Pacific cold front.  This does keep passes clear for the end of the weekend; very good in this case.  Sunday should be a mild and rainy day.  I saw another media site online article headline; something like “snow could arrive in the lowlands Sunday”.  That’s not going to happen.  Take a look at the Sunday 4pm map of the ECMWF:

ecmwf_apcp_f132_nw

3. Strong ridging still forecast in the Gulf of Alaska and into Alaska; generally a very good setup for cold airmasses to move south into the Pac. Northwest
All models in very good agreement on this, but the ridge is a little closer now.  Note the Thursday morning 500mb chart from the 00z GFS:

gfs_namer_204_500_vort_ht

4. NOT AS WET.  Except for the 12z ECMWF, there isn’t a whole lot of moisture once we get pass the average-looking Pacific cold front that moves through here Sunday night.  The 18z and 00z GFS are pretty much dry all of next week after midday Monday.  Just a repeat of what we’ve seen the past week, except about 10-15 degrees colder.  Brrr!  We’ll see a lot more overnight lows in the teens if that’s the case.  No more 50 degree days in this scenario either.  The 12z ECMWF was different, showing several waves riding down in the northerly flow with a snow chance later Tuesday.  Then it undercut the upper-level ridge to our west, allow a surface low to suddenly deepen offshore and then slide across Oregon.  That would be a big snowstorm across most of the state later Wednesday and Thursday.  What do you bet it won’t be there on the 00z run?  We’ll see.  But this WAS a beautiful map:

ecmwf_apcp_f216_nw

Offshore flow, a cold air mass, and a very wet low sliding by just to our south…nice.

So, right now I see a slight chance for snow for some of us if everything were to turn out just perfect early next week, then a cold spell the rest of the week.  Just not a huge arctic blast, and likely no big snowstorm either.

That said, when you have a huge upper-level ridge to the west and northerly flow, something could easily spin up in the models the next few days and put a snowstorm into our forecast…stay tuned.

Have a happy Thanksgiving!

00z GFS ensemble chart goes here:

tseries_850t_000-384_Portland

Ensemble average was a little lower than the operational run Tuesday/Wednesday, more like -10.  Notice NO warm members (warmer than -5) during that period.

Chief Meteorologist Mark Nelsen


12z GFS

November 26, 2013

A real quick post, only because of one chart I just looked at.  I’ll do a real posting for regular people who don’t need all the technical geekery) later this afternoon.

Here’s the 12z GFS ensemble chart:

tseries_850t_000-384_Portland

A few thoughts:

  • Approaching cold pattern is definitely still ON.
  • Last two runs of GFS have speeded up the timing of the cold front to Sunday midday!  That’s when we go from warm rain to snow showers below 2,000′
  • Based on this chart, the faster movement might not be correct.
  • But based on this chart, all ensemble members are down around -7 by Monday evening anyway, regardless how each run “got there”.
  • The drier arctic front is still timed for Monday night, not as well defined this time.
  • 12z operational, which wasn’t nearly as cold as ECMWF or earlier runs, is one of the warmest members by Tuesday.
  • So it’s quite possible the next run of the GFS will be colder again.
  • A lot of the “noise” has disappeared from Monday and Tuesday, very few warm members now.  Something chilly is going to happen early-mid next week.

As always, I’ll be looking forward to the ECMWF during the next hour.  It just comes out twice a day, which is probably good.  Not as many “mood swings” with either the model or me.

Chief Meteorologist Mark Nelsen