Last of the Warm & Dry Weather

October 22, 2018

6:30pm Monday…

It’s been glorious hasn’t it?  Day after day of sunny skies, cool mornings followed by warm afternoons.  If you’ve lived west of the Cascades most/all of your life (like me), now you know what it’s like east of the mountains in a typical October.  Eastside sees a wider diurnal temperature range and more sunshine in mid-Autumn.

Today is our 14th day without measurable precipitation in Portland.  It just has to be a record right?  Not even close!

Dry Spells October

I remember October 1987; my first year in college up in Centralia.  It didn’t rain until Halloween; poor timing for the little kids.  And of course none of us were around in 1895 when no measurable rain fell the entire month!  So we can have long dry spells in October, but most years just see occasional shorter dry periods.

What’s ahead?  BACK TO NORMAL is what I’m seeing.  Not a sudden plunge into the storm season by any means, but we’ll be “easing in” to cloudier/wetter/cooler weather through the end of the month.  A very weak system moves inland tomorrow and pretty much falls apart, then a little wetter one for Thursday will wet the ground nicely.  Most likely a nice soaker is on the way for Sunday/Monday too.  That’s because our big ridge of high pressure breaks down and is replaced by southwesterly flow in the upper atmosphere.  I figure we could see 1.00-2.00″ in the next 7 days…it’s a start at least.  As of today the past 6 months (mid-April to mid-October) have been the 2nd driest on record in Portland after 2015.

What about mountain snow?  Not yet, this southwest flow isn’t good for mountain snow, especially so early in the season.

ECMWF Snow Level From 850mb Temps LONG TERM

Is this the beginning of a stormy period?  That’s somewhat common to see the last week of October.  But I don’t think that’s the case.  Take a look at the 10 day forecast 500 millibar height/anomaly from the GFS/ECMWF/GEM models.  Red indicates higher than average heights.  All 3 are for November 1st, a week from Thursday

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That’s the same pattern we had earlier this month with a big ridge somewhere in the far eastern Pacific.  This is a drier than average setup for us this time of year.  Whether it’s warmer or cooler than average will be determined by the location.  Regardless, it appears a stormy start to November is unlikely even though October will go out wet.

Keep in mind we are entering an El Nino winter/wet season.  It has been quite a delayed start but today’s weekly ENSO update shows the important Nino 3.4 region is up to 0.9, approaching moderate El Nino status.  You can see the warming on the right-side chart

Nino_ThisWeek_ONI

So what has happened in November in El Nino years in Portland?  I just took at look at the last 10.

LAST 10 EL NINO WINTERS:  1987-88, 1991-92, 1994-95, 1997-98, 2002-03, 2004-05, 2006-07, 2009-10, 2014-15, 2015-16

NOVEMBER TEMPERATURE:  6 of 10 milder/warmer than average, 2 near average, 2 cool

NOVEMBER PRECIPITATION:  6 of 10 drier than average, 2 near average, 2 wetter

NOVEMBER SNOW:  It’s always rare in November of course, and we’ve only seen snow one of those 10 years.  That snow/freezing rain mix in mid-November 2014.  Just a trace officially.   East metro and hills had freezing rain with that very early season freeze.

By the way, I crunched the February El Nino winter numbers too.  I was thinking of a vacation and wondered what the threat of snowy/icy weather could be.

TEMP:  7 of 10 milder/warmer than average, 3 average, None colder than average

PRECIP: 4 of 10 drier than average, 4 average, 2 wetter

SNOW:  Only 1 in 10 had any snow, the February 1995 snowstorm.  Apparently snow in an El Nino winter is very rare!  Booking tickets soon…

Chief Meteorologist Mark Nelsen