Monday, November 30, 2015

What's a typical El Nino?

So by now you've probably heard that a strong El Nino episode is underway and will continue through this winter.  We wrote about it earlier this fall:

Since we wrote up that blog, not much has changed.  El Nino continues to be strong.  Here's the sea surface temperature anomaly for the past week.  This is a classic El Nino signature.

El Nino typically means milder winters in the Pac NW.  But after our really mild winter last year, does that mean that this winter will be even milder?  In other words, what is a typical El Nino winter like?  Let's take a look at some of the recent moderate and strong El Nino winters to see if we can answer that.


This was the most recent El Nino winter, and was technically a moderate El Nino, not in the strong category like this winter.  But it's still worth a look.  Here's some notes from that winter.
  • A cold snap in early December dropped daytime temperatures into the teens and sub-zero at night.  The month was colder than normal, but the month was rather dry so there wasn't much snow either.
  • January was just the opposite.  All but a few days were warmer than normal with very little snow.
  • February continued the mild trend, but precipitation was near normal.

This too was a moderate El Nino.
  • December was mild and wet, with rain or snow on just about every day.  Temperatures turned a little colder after Christmas resulting in a few inches of low-elevation snow.
  • January was also mild and wet.  Very few days remained below freezing during the day.  And precipitation was twice the normal amount.  There were a couple of snowy days.
  • February was mild but dry, with little in the way of snow.

This is the most recent strong El Nino.  So how did it compare to other winters?
  • December temperatures were about normal, but it was rather dry.  As a result, there were only  a handful of snow days.  3.4" fell in Spokane one day, but Moscow had 6" just after Christmas.
  • January was similar to December.  There was a cold snap in the middle of the month with a couple of sub-zero nights.  But most days of the month were in the 30s and 40s.  Spokane had about 7 snow "events", each of which amounted to less than 2 inches.  Wenatchee Airport had a 13" snow storm in the middle of the month.
  • February was more like spring than winter, with day time temperatures in the 40s and 50s, and quite a bit of rain.

Another strong El Nino.
  • December got the winter off to a mild start.  Nearly every day warmed above the freezing mark.  As a result, there were only a couple of snow days.
  • Temperatures in January were closer to normal with about 6 snow days.
  • Aside from a 2-day cool snap, February was very mild and snow free.

This strong El Nino is really the first winter when the "El Nino" phrase was used in the general public.
  • Winter started early with a couple of cold snaps in November.
  • December was typical for the last month of the year.  A significant snow storm early in the month was followed by a short cold spell.  More snow fell in the middle of the month, and then just before Christmas.
  • After a cold snowy start to January, mild weather arrived on the 4th and remained for pretty much the rest of the month.
  • The mild weather continued in February, although there were a couple of cold snowy days in the middle of the month.
We could go on, but you probably get the basic idea.  El Nino brings milder winters to the Inland Northwest.  But there will still be some wintry days, just not as many as normal.

So using the past El Nino winters as an indicator, here's what we can most likely expect this winter:
  • December
    • Temperatures will probably be normal or just a tad warmer than normal.  But it will probably be the coldest month of the winter.  Might have a cold episode or two with near zero temperatures at night.
    • Expect 3-5 days of snow, but most of these will probably be 1-3".  Might see a one day snow storm with more than 3".
  • January
    • Temperatures will be warmer than December.  Sub-freezing day time readings will be rare.
    • Might see 2-3 days of snow, probably about 1" each.
  • February
    • Expect an early spring.  Daytime temperatures will be in the 40s and 50s.
    • Snow in the lower elevations will be rare.
Remember, last winter had very little snow for the lower elevations.  A "normal" El Nino winter will likely have more snow than last winter, but less than a typical winter.  So the odds are you'll use your snow shovel/blower more than last winter, but not as much as "usual".  

So what is an El Nino winter like in the mountains?  Let's take a look at two locations.  Bear Mountain in the northern Idaho Panhandle, and Blewett Pass in the Cascades.  Here's the graph of Snow Water Equivalent (SWE) for those 2 sites.  SWE measures the total amount of water in the snow pack.

Snow Water Equivalent at Blewett Pass for various years as well as the Average (black line)

Snow Water Equivalent at Bear Mountain for various years as well as the Average (black line).  Data for Feb-Apr was missing.
There's a few points to make from these 2 graphs.
  • The 1982/83 Strong El Nino actually had an above-normal snow pack in the mountains.
  • The other El Nino winters had normal to somewhat below-normal snow pack for the mountains.  
  • The below-normal snow pack years were still at least 75% of a normal snow pack.
  • The snow pack from these El Nino winters melted off sooner than normal, typically by 2-5 weeks.
  • All of the El Nino winters had a lot more snow than last winter.
The last of these points is perhaps the most important.  The mountain snow pack last year was the lowest ever observed, and melted off sooner than any other winter.  Could the upcoming winter see the same?  It's possible, but the odds are that we'll see a mountain snow pack that's at least 75% of normal.

Monday, November 16, 2015

Widespread Damaging Wind Storm Tuesday

In the Inland Northwest, we get several windy storms every winter.  It comes with the territory of living at this latitude, as well as being a frequent "gateway" for storms to enter the US.  But many of these windy storms aren't considered "extreme".  A typical wind storm in our area will result in gusts somewhere in the 50-60 mph.  A wind gust over 60 mph becomes much more rare.  The table below shows the wind records for the Spokane Airport.

Spokane Airport Wind Record (by month)
Fastest Mile (1949-1995)
Peak Gust (pre-1984)
Peak Gust (since 1984)
59 MPH (Jan 9, 1972) 
67 (Jan 9, 1972)
56 MPH (Jan 11, 2014)
54 MPH (1949)
58 MPH (Feb 28, 2011)
54 MPH (Mar 16, 1971) 
64 (Mar 26, 1971)
66 MPH (Mar 15, 2009)
52 MPH (Apr 17, 1987)

62 MPH (Apr 17, 1987)
49 MPH (1957)
59 MPH (May 3, 2010)
44 MPH (1986)
77 MPH (Jun 21, 2005)
43 MPH (1970)
67 MPH (Jul 23, 2014)
50 MPH (1982)
54 (Aug 9, 1982)
54 MPH (Aug 25, 2013)
38 MPH (1999)
55 MPH (Sep 6, 2009)
56 MPH (Oct 27, 1950)
65 (Oct 27, 1950)
62 MPH (Oct 16, 1991)
54 MPH (Nov 27, 1949)
65 (Nov 27, 1949)
64 MPH (Nov 16, 2010)
51 MPH (1956)
63 MPH (Dec 12, 1995)

The all-time wind speed at Spokane is 77mph, but that was caused by a thunderstorm gust front, not a widespread winter storm.  So ignoring that, a really strong winter storm will typically gust into the 60-65 mph range.  The highest non-thunderstorm wind at Spokane is 67 mph from January 1972.

The storm on Tuesday will have the potential to do that.  Here's some of the damage reported by the Spokesman Review in  January 1972:

  • Communities of Beverly, Shawana, and Mattawa (along the Columbia River south of Wenatchee) sustained extensive damage.  Six trailer houses were overturned and destroyed.  Other low-income homes were leveled.  All three towns were without power and phones.
  • Rattlesnake Mountain near Richland measured a wind gust of 150 mph, the top speed of the instrument.
  • Gusts of 60-65 mph and higher were prevalent.
  • The wind blew away the upper mechanical room of the University of Idaho Physical Science Building in Moscow.
  • Wind toppled chimneys in Colfax.

Another strong wind storm occurred on Nov 19, 2003.  Here's some reports from that storm:

  •  In the northern Idaho panhandle a dozen large pine trees fell on summer homes along Lake Pend Oreille. 
  • In the Coeur d'Alene area numerous trees fell on houses and power lines.
  • At Pomeroy a wind gust was measured at 65 mph. 
  • Over the Palouse region a wind gust blew the roof off of a barn near Colfax. 
  • Near Newport a tree was blown onto a house. 
  • The heaviest damage occurred in the Spokane area where numerous trees were toppled onto houses and power lines. Up to 16,000 people were without power in Spokane's South Hill neighborhood. 
  • Fairchild Air Force base recorded a wind gust of 68 mph which ripped the roof off of a recreation center. 
  • At Spokane International Airport a wind gust of 63 mph was recorded and at the Spokane National Weather Service office the wind gusted to 61 mph. 

There are two predominate weather patterns for high winds in the Inland Northwest.

Weather patterns for high winds in the Inland Northwest

The first pattern is where a deep low approaches the Washington/Oregon coast from the south or southwest.  This pattern is fairly common, and most storms produce high winds along the coast.  The stronger storms also deliver high winds to the inland areas of western Oregon/Washington (i.e. I-5 corridor).  But strong winds east of the Cascades in this pattern are rather rare.  Only the strongest storms of this pattern can produce damaging winds in eastern Washington.  Some of these are the Columbus Day storm of 1962, December 10th 1995, and the Hanukkah Eve storm of 2007.

Track #2 is more rare, but is the more favored pattern for high winds in eastern Washington and north Idaho.  The low tracks west-to-east across southern British Columbia.  If the low is strengthening as it does this, then high winds are more likely.

Here's what the forecast for Tuesday looks like:

GFS MSLP forecast valid 7am Tue 17 Nov 2015

GFS MSLP forecast valid noon Tue 17 Nov 2015

GFS MSLP forecast valid 6pm Tue 17 Nov 2015

The low follows Track #2 across southern BC.  The central pressure starts at 993 mb off the BC coast, and deepens to a 977 mb over Alberta.  In other words, this is a classic set up for high winds in the Inland Northwest.  

So how strong will the winds be?  Here's the current forecast:

You'll notice that the 68 mph forecast for Spokane is higher than the January 1972 storm.  We don't have the skill to predict the winds to the nearest mile-per-hour.  But we do think that this storm has the potential to rank as one of the strongest ever in the Inland Northwest. The areas in the mountainous regions have lower wind speeds forecast, but don't let that fool you.  There's a lot more trees in those locations, so there's more trees to blow over.

Be prepared for lots of downed trees, power lines, fence and roof damage, and maybe even some blowing dust in the Columbia Basin.

Tuesday, November 3, 2015

Halloween Weekend Atmospheric River Event

Over the Halloween weekend, an atmospheric river brought widespread precipitation and wind to the Inland Northwest. Here are some of the highlights from the weekend.

Friday October 30
    • 50 mph Wind Gust across the Columbia Basin and Palouse region creating blowing bust and closing down a portion of I-90.
      • Ephrata - 55 mph
      • Mission Ridge - 92 mph

    • Record high temperatures at several locations.
      • Ephrata - 74F
      • Wenatachee - 73F
      • Moses Lake - 73F
      • Grand Coulee - 67F
    • Thunderstorms developed over the central Panhandle Mountains.
    • An inch of rain fell in the higher terrain with around 2 tenths of an inch in the Columbia Basin.
24-hour Precipitation ending 5am Saturday 31 Oct

Saturday Oct 31
    • Thunderstorms over the Palouse.
Radar image Saturday afternoon

    • First snowfall of the season above 5000 feet.

    • Areas along the east side of the Cascades like Leavenworth, Plain, and Winthrop received over one inch of rain.
    • Areas along the Cascades crest received 4+ inches of rain
    • In the Idaho Panhandle and extreme Eastern Washington, areas received around a half to three quarters of an inch of rain. 
24-hour Precipitation ending 4am Sunday 1 Nov
    • Stehekin River (Chelan County) and Paradise Creek (Moscow, ID) rise rapidly

Sunday Nov 1
    • The moisture associated with the atmospheric river begins to dip South and exit the region.
    • The Idaho Panhandle received the most rain with most locations getting a quarter to half an inch of rain
24-hour Precipitation ending 4am Monday 2 Nov

    • The Cascades and Northern Mountains experienced a drop temperatures and began to receive snow Sunday.

The total precipitation for the weekend was impressive, as expected.  Some parts of the western Cascades picked up over 10" of moisture, while the Panhandle mountains generally received 3-5" of rainfall.
7-day Precipitation ending 4am Tuesday 3 Nov

Here's some weekend totals from the local area

Spokane: 0.61"
Coeur d'Alene: 0.88"
Lewiston: 0.43"
Wenatchee; 0.08"
Omak: 0.15"
Ephrata: 0.03"
Moses Lake: 0.08"
Pullman: 1.08"
Deer Park: 0.92"
Republic: 0.48"
Bonners Ferry: 1.13"