Stormy Weather Ahead; Winter Meeting Today

November 17, 2012


It appears that REAL November weather is on the way, with many storms/frontal systems ready to impact the Pacific Northwest in several different ways over the next week (and beyond).   The main issues (threats) will be possible flooding and/or damaging wind.

First, don’t forget the previous posting, the OMSI winter weather meeting starts in just 2.5 hours!  I’ll be manning the rafffle box.


Now, on to the weather:

We have a cold front just offshore this morning, with rain showers ahead of it in the mild airmass.  The steady rain with the front will be here in the middle of the day with a break behind the main rain band occurring in the late afternoon and evening.   This first system is pretty weak, it’s just “opening the door”…

From Sunday afternoon through Tuesday morning, a baroclinic zone (boundary between warm and cool air) sets up right over Oregon and Washington, first mainly over Washington, then sliding well down into Oregon Tuesday.  This is an “atmospheric river” event with plenty of moisture to work with; thus a flooding threat depending on where the heaviest rain falls.  

Our 12z RPM (sometimes too wet in the past, but not always) shows the heavy rain:

Several deep areas of low pressure will track along this zone during the period:

Low #1:  This one is somewhat weak, maybe even just an open wave (not a closed area of low pressure).  It is that cluster of clouds/rain behind the main cold front.  It’ll move up along Vancouver Island late this evening and very early Sunday morning.  A decent burst of wind/rain in the middle of tonight with this.

Low#2:  Much stronger/deeper low, maybe 982-988 mb runs right into central Vancouver Island late Sunday evening.  Strong wind at the coast tomorrow evening through the middle of night.

Low#3:  Similar strength and only 8-12 hours behind the first one as it rides along a baroclinic zone (frontal system) sitting just to our north.  Similar location for landfall, maybe a little farther south.

So if you want to go see stormy weather at the Coast, the 24 hour period from Sunday afternoon through Monday afternoon looks best.

Neither of these lows (as of this morning) is enough to give us a big windstorm, but gusts to 70 mph along the coast and 40-45 mph here in the valleys will be the strongest we’ve seen so far this season.

We’ll see about the rain, it’s always tough to know exactly where the heaviest rain will line up.  I remember exactly one year ago we had the heavy rain band sit right over us a little longer than expected the Tuesday before Thanksgiving, giving us some minor flooding.

Finally, snowfall in the Cascades.  Good news and bad news.  The good news is that we could see 10-15″ in the norhtern Oregon Cascades in the next 3 days. 

Most of that will be later today through Sunday morning and then again Monday night and Tuesday morning.  The bad news is that the Mt. Hood ski resorts will be in the warm part of the storm from Sunday evening through Monday afternoon.  Many inches of rain will fall all the way up to 7,000′ during that time.  You can see the difference on the map above; note most of the Washington Cascades on the colder side of the baroclinic zone more of the time equals much higher totals.  Add the new snow and heavy rain together and I’d gamble base totals won’t change between now and midday Tuesday.  Or, pray that the whole zone is 100 miles farther south and feet of snow will dump on Mt. Hood the next few days.

Okay, off to the meeting and on to exciting weather!

By the way, no sign of real cold air for lower elevation snow in the next 7-10 days…in case you were wondering.

Chief Meteorologist Mark Nelsen