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"

Wednesday, October 28, 2015

The start of the Wet Season

The bar graph below shows the average precipitation for Chicago, New York, and Spokane.

Much of the U.S has the majority of their precipitation in the summer (Chicago), or it's fairly evenly distributed throughout the year (New York).  In the West, it's the other way around. We have a distinct dry season in the summer, and wet season in the winter. 

After the hot dry summer, Pacific storms in September and October typically become more frequent, and increasingly wet.  And then in November, the storm door really opens; it's twice as wet as October.  In fact, for most of the Inland Northwest, November is the wettest month, followed closely by December and January.  (The exception to this is Lewiston, which has it's wettest month in May).  

This year, the storm door looks like it will open rather suddenly.  The storms for October have been fairly weak and temperatures have been near record warmth.  But all of that will change this weekend.  Below is the forecast rainfall for the next 5 days from 2 forecast models, the GFS and Canadian.

GFS Predicted Precipitation Oct 29 - Nov 2 2015

Canadian predicted precipitation 29 Oct - 2 Nov 2015

Now, before you go thinking that Wenatchee is going to get 0.5" to 1" of rain, or Spokane is going to 2" of rain, these models are notorious for spreading the rain too far away from the mountains into the lower elevations.  They know that the Mountains exist, but they don't have enough resolution to account for just how sharp the rain shadow is.  

The weather pattern that's going to bring us all this rain is a strong jet stream from west to east.  That kind of pattern produces a large rain shadow east of the Cascades, that extends at times all the way to Coeur d'Alene.  So for the area from Wenatchee to Spokane to Lewiston, take those computer forecasts and cut them in half, and you're probably in the ball park of what will happen.  For the Cascades and Panhandle mountains, the computer forecasts are probably a bit too low.  In other words, the western Cascades could see a foot of rain by Monday morning, and the Panhandle Mountains could see 6" or so.  That's a really nice start to the wet season.

This weather pattern is also a windy one.  Here's the wind gust forecast for Saturday afternoon.

One other thing.  These weather patterns are usually quite mild.  This will mean high snow levels.  They'll start off around 6,000 feet, and then rise to 8,000 feet on Friday and Saturday.  So this won't start building a mountain snow pack.  Yet.  

Colder air moves into the area on Sunday.  Snow levels will be dropping through the day, so that by the evening they'll be 4,000-5,000 feet.  Unfortunately, this will be as the precipitation is ending.  Still, there's a good chance for the mountains to pick up a few inches.  Here's the average computer forecast for mountain snowfall Sunday and Monday.  

OK, it's not enough to ski on, but it's a start.  The cooler air will stick around through much of the week, so any snow that does fall in the mountains won't be going anywhere. Here's the computer temperature forecasts for the next 7 days in Spokane.  Notice that next week, high temperatures will be in the mid-40s.

In fact, many locations will see their first freezing temperatures of the season by Tuesday or Wednesday morning.  This weather pattern won't change for awhile.  Here's the 8-14 day temperature outlook.

This shows below-normal temperatures in the West, with a good chance of above-normal temperatures in the East.  So a rather cool start to November.

Saturday, October 3, 2015

Is the end of fire season expected soon?

So while we can't argue that the worst of fire season is behind us, it should be noted there are still fires burning across portions of the Inland Northwest. Here's is what satellite information was showing on the last day of September:

MODIS Visible Satellite Imagery from 9/30/15

While these fires are far from the raging infernos we saw earlier this summer, it's still rather impressive for the end of September or beginning of October.  However, as we all know this year is different. First off, look at these precipitation totals since the beginning of April

Idaho Precipitation % of normal 4/2/15-10/1/15

Washington Precipitation % of normal 4/2/15-10/1/15
That is a lot of red and dark red shading over the Inland Northwest which correlates with meager precipitation amounts ranging 25-70% of normal. That's pretty dry. In fact, since the beginning of April through the beginning of October it was the driest period on record for both Spokane and Boundary Dam, WA (extreme NE corner of the state).

So combine the record dry conditions with nearly record warmth for both sites and it is no wonder the fire season has been so long. Here is a look at the temperatures for both sites.

So obviously record warm and dry conditions led to our active fire season, but unlike a typical year, things just aren't winding down as quickly as we are accustomed to. Climatologically, the days of active fires will be limited. We say that because the shorter days are leading to cooler temperatures and higher relative humidity levels  (both items are generally detrimental to good fire growth) while the chances for measurable precipitation are rising quickly. Climatologically the chance of measurable rain ranges from 20-25% over locations where the fires are currently burning. However by the end of the month those chances nearly double. So despite these facts, look at the latest fire danger ratings for the Inland Northwest:

Current Fire danger ratings
That map shows the fire danger is still high (yellow) or even very high (orange) across a sizable portion of the Inland Northwest, with moderate conditions (light green) found everywhere east of the Cascades. So what does that mean? According to the Wildland Fire Assessment System (WFAS) a high fire danger means, "All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape. Fires spread rapidly and short-distance spotting is common. High-intensity burning may develop on slopes or in concentrations of fine fuels. Fires may become serious and their control difficult unless they are attacked successfully while small.

So is this danger level unusual for the beginning of October? Since 2006 (earliest year of  the graphical archive), the current fire danger has only been matched one time. That was in 2012. All other years saw low to moderate fire danger ratings across the area.

So what was the fire weather like in 2012? This satellite picture tells the story

MODIS Satellite imagery from 10/4/12

Just like this year, there were quite a few fires burning during the beginning of October. In fact, based on the satellite image, they were much bigger and included the Wenatchee Complex (southwest of Wenatchee) and the St. Mary's Misson Rd fire south of Omak. So what happened that year? The dry weather and fires continued to burn through the middle of the month, but several days of rain (not necessarily heavy) and cooler temperatures put an end to that fire season.

So what did the weather pattern look like for the end of that fire season? Well leading up to the end of the fire season, the upper-level pattern exhibited a large ridge parked right off the BC/WA coast with dry northwest flow over the region. Also, note the low-pressure area off the California Coast.

Early October 2012 500 mb pattern. 
So how does the pattern look for most of this week? Although it's far from identical, it does have some similarities, including the low near California, and the ridge over the Pacific Northwest.
500 mb pattern for Monday afternoon (10/5/15)
So what did the weather pattern that led to the end of the fire weather year in 2012 look like? The ridge broke down quite quickly and was replaced swift southwest flow into the Pacific Northwest and a deep low over the Gulf of Alaska. Again this brought cooler temperatures, periods of light rain (moderate in places), as well as significant cloud cover.
Mid-October 2012 500 mb pattern (Oct12-14)
How about this year? Is anything similar expected? Again although not a perfect match, there are some good similarities including a deep Gulf of Alaska low and deep southwest flow pointed into the Pacific Northwest from the eastern Pacific.
500 mb forecast for Oct 10, 2015
So how is our confidence in this solution and will this be the end of the fire season?  There are a few additional tools we can look at. One of the more interesting ones is called the NOMADS ensemble probability tool. This tool queries 21 GFS ensemble members or model runs and calculates the chances of any given parameter. Using this tool we can look at things such as what is our chance of seeing over a tenth of an inch of rain in a day?  When asking that particular question, here is the answer for the Grizzly Complex located over northern Shoshone County, ID.

The probability of seeing 0.10" of rain or more in 24 hrs over northern Shoshone County. 
So if you key in on the clustering of the blue bars, you can see that there is some consensus that by next weekend (10/10 and 10/11) that the weather pattern will support an increasing chance of rain (it peaks at 25% for the 24 hrs between 5pm Saturday through 5pm Sunday). Notice also that there is a small chance of light rain during the middle of the week.

Stay tuned and we shall see if this will truly be the end of a historically warm and dry fire season across the Inland Northwest.

Thursday, September 10, 2015

What will El Nino bring this winter?

After such a dismal snow year last year, many of you may be asking what kind of winter we will have this year.  Many may have already heard that a strong El Nino is present.  El Nino often brings warmer temperatures, so does this mean another bad year for snow?  In this blog we'll try and answer this question.

First of all, what patterns tend to set up during El Nino Winters?  Here is a graphic from the Climate Prediction Center...

Idealized weather pattern during an El Nino winter.  During El Nino winters, a strong and persistent Jet Stream over the Pacific is oriented over the southern tier of states.  Cold air intrusions from Canada into the northern states are infrequent.

Typically during El Nino winters, the jet streams splits with the cold northern branch over southeast Canada while the wet Pacific Jet Stream sends weather systems to our south across California.  This tends to give us warmer winters, while precipitation tends to be more variable with some years a bit wetter than normal while other years a bit drier.

What is the official forecast from the Climate Prediction Center calling for?  The graphics below issued August 20th shows highly increased odds for a warmer-than-normal winter, with slightly elevated chances for drier-than-normal conditions.

To evaluate the current state of El Nino, we need to look at the equatorial region out in the Central and Eastern Pacific.  Here is map showing the current SST (Sea Surface Temperature) anomalies over the past month through September 5th.

Sea Surface Temperature (SST) anomalies in the Pacific for 9 Aug - 5 Sep 2015.  Red shading indicates warmer-than-normal while blue shading shows lower-than-normal SST's.

The important area to key on is along the equatorial region in the Central and Eastern Pacific (middle part of graphic).  Values warmer than 1.5C are an indicator of Strong El Nino conditions.  Currently there are values greater than 2.0C, which supports a strong El Nino.

So how does this compare to past events?  Let's take a look.

Three-month average sea surface temperatures in the Nino 3.4 region of the equatorial Pacific for 2015 and the past 6 strong El Nino winters.
The purple line on this map is this year's current and projected trace.  While some uncertainty still remains regarding the peak of this event, it should end up as one of, if not the strongest El Nino, most similar to the strength of the 1997-1998 Strong El Nino.

So what has happened in past winters during Strong El Nino episodes?  There have been six cases since 1950.  First let's look at temperature composites for December, January, and February for past strong El Nino years.

As you can see, for the Inland NW, three of the six were much warmer than normal (1957-58, 1982-83 and 1991-1992) and two were near to slightly above normal (1965-66, 1997-98).  The 1972-73 Strong El Nino was actually cooler than normal.

What about precipitation?  Let's take a look...

In this graphic the yellow and orange shaded areas indicate drier than normal while the greens and blues indicate wetter than normal.  There's even more variability than with temperatures.  Two of the strong El Nino winters were wet (1957-58 and 1982-83), two were dry (1965-66 and 1991-92), and two were near normal (1972-73 and 1997-98).

So what do we gather from all of this?  The most important point is that every El Nino year is different.  Some of the differences are related to the timing of when the typical El Nino pattern develops.  During the 1972-73 event it wasn't until mid-February before an El Nino-like pattern kicked in.  Other years El Nino conditions start by January.  The main message here is that El Nino conditions are most favored during the second half of winter.  Thus, parts of November and December are at times more prone to fall and winter storms over the region.

Strong El Nino years also differ in terms of snowfall depending on where you live.  Below are images for snowfall for past episodes with the value on the far right the current 1981-2010 normals.

As you can see, for Spokane, every strong El Nino has brought at or below normal snowfall, with three of the six having less than 20 inches.  Meanwhile for Wenatchee amounts have varied greatly with each year different.  For Republic each strong El Nino year has brought close to normal snowfall, except for a snowy 1965-1966 year.  Bonners Ferry was also very snowy during the 1965-1966 El Nino, with at or below normal snow the other years.

The strong El Nino of 1991-92 saw an early season cold snap in late October. During the 1965-66 El Nino, most areas received near to above normal snowfall.  In 1972-73, a prolonged cold snap occurred in December with high temperatures several days in the teens and lows as cold as -11F in Spokane.  This was followed by another cold snap in January that lasted a week.  Take a look at the Spokane graphic below.

Spokane temperatures in the 1972-73 winter.  Blue bars show daily observed temperatures.  Brown shading shows the normal temperature range.  Red shading indicated above-normal temperatures.  Blue shading shows below normal temperatures.

The strong El Nino of 1997-1998 saw a brief cold snap with highs in the lower teens in January.

Meanwhile the El Nino of 1957-1958 saw no such cold snaps.  Here is the Spokane trace for that winter.

Spokane temperatures in the 1957-58 winter.

So while El Nino years tend to be warmer, most have at least brief periods of very cold or snowy conditions.

For this upcoming year are there any indications of what type of El Nino year we will have?  First, persistent high pressure has been evident in the Eastern Pacific Ocean off the Washington, Oregon, and British Columbia coast.  Note the large positive anomalies (yellow, orange, red colors) in the graphic below.

500mb Height anomalies for April 1 - August 31, 2015.  Red shading indicates higher-than-normal pressure while blue shading shows lower-than-normal pressure.

The longer this persists, the more likely we will prone to early season fall and winter storms as high pressure in the Eastern Pacific results in north-northwesterly flow over the area bringing cooler and potentially wet storms into the area.  However with the current strong El Nino the tendency for upper ridging may not last long.

To summarize, despite the current strong El Nino, be prepared for winter like conditions especially for the early part of the winter.  As winter continues on, El Nino like conditions becomes increasingly favored.  Thus after this winter is over, most will look back and probably think of this being a mild winter.

What does this mean for our mountain snow pack?  We'll address this in another blog in the near future.


Monday, August 31, 2015

Does this mean summer is over?

Our hot summer came to a screeching halt on Sunday with a Pacific cold front bringing our first widespread rain in what seems like months.  The forecast for this week is decidedly cool, with daytime highs in the 70s and lower 80s.  And one look at the calendar begs the question:  Did summer just end without any warning?  Kinda felt like autumn on Sunday didn't it?  And we often say that on average, summer in the Inland Northwest is between Independence Day and Labor Day.

It's hard to define when one season ends and another begins.  But of all 4 seasonal transitions, the summer-to-fall transition is typically the most marked.  A marked transition doesn't happen every year.  Some are more noticeable than others.  The most impressive "autumn arrival" was probably 1959.  Here's a plot of the temperatures for that summer and fall in Spokane:

On September 12, the mercury reached 90F in Spokane.  A cold front moved in, dropping the temperature to 83F on the 13th, 65F on the 14th, and only 51F on the 15th.  But what's most impressive is that after that, the temperature never warmed above 67F for the rest of the autumn.  In other words, Spokane said good bye to the 90s, 80s, and 70s all with one cold front.

At this point we're not expecting a dramatic repeat of that event for 2015.  Spokane averages one day in the 90s in September and 7 days in the 80s.  The record is 10 days in the 90s, back in 1938.  And no, Spokane has never hit 100F in September.

Looking at the warmest 8 summers (based on June, July, and August average temperatures), only one (1958) had a normal September.  The other 7 were all much warmer than normal in September.  

Year Jun Jul Aug Sep
1922 +7.6 +3.2 +2.2 +3.1
1938 +4.5 +5.0 -0.9 +8.2
1940 +6.0 +2.8 +1.9 +5.1
1958 +3.3 +3.0 +4.9 -0.9
1967 +1.2 +0.6 +5.7 +5.7
1998 +0.2 +5.3 +3.0 +5.5
2013 -0.6 +3.9 +3.5 +3.4
2014 -0.6 +5.7 +3.5 +3.5
2015 +9.1 +4.2 +4.2 ???

The folks at the Climate Prediction Center are also favoring a warm and dry September.  Here's the outlook they produced today:

It calls for below-normal precipitation with above-normal temperatures for the month of September.

We typically look at a model called the GFS for forecasts of the weather for the next 7-14 days.  But when we want to look farther into the future, we look at the CFS (Climate Forecast System).  So let's see what it says for September.  First, we'll look at the CFS that was run back on August 10th.

The yellow and orange colors indicate areas where the model thinks temperatures will be above normal in September.  Large area of abnormal warmth over Alaska and Canada, spreading into most of the western US.

Now let's see the CFS from August 20th:

Notice the change.  The model still expects warmth in the West, just not nearly as strong or widespread.

Now here's the latest run of the model, which was fed the data from August 20-30:

We're back to a large area of abnormal warmth over Alaska and Canada, but only a minor area in the northern Rockies.  

The folks at CPC look at this (and a lot of other data) and concluded a warm September for the West.  So don't put away your summer clothes just yet.