Sunday, December 20, 2015

Monday storm

A strong storm will pass through Washington and north Idaho on Monday.  This is a storm that is worth paying attention to and is expected to produce a swath of heavy snowfall as well as windy conditions near the Foothills of the Blue Mountains.  A small adjustment to the storm track could result in big forecast changes depending on where you live.  So keep informed of the latest forecast for your area.

Our current forecast favor the band of heavy snow to set up over the Wenatchee area extending east along the Highway 2 corridor into Spokane, Coeur D'Alene and the Central Panhandle Mountains.  Here is a look at our latest forecast for snow amounts Monday into Tuesday.

A slight shift north in the storm track could give places like Omak, Republic, Colville, and Bonners Ferry more snow compared to what the current graphic shows.  Meanwhile a further north track could give less snow to Moses Lake, Ritzville, and Pullman.  People in these areas should keep a close eye on the forecast.  Let's take a look at what the models are showing for this storm so  you can see what we are talking about.

Here is a look at what the 18z GFS model from today is projecting for Monday.   Note the position of the low as the day progresses.  The image is moisture and the bright green areas represent a high amount of relative humidity which often leads to precipitation in form of rain or snow.  Areas on the south side of the low track will be prone to milder air and windy conditions with highly reduced snow amounts (if any for the valleys). Locations on the north side of the low track will be colder with snow.  Thus narrowing down this track will be critical for snow totals with this storm.

Now there one alternate scenario that is possible.  The graphic below represents the two possible storm tracks for this storm.  The scenario above represents scenario one which is the preferred solution.  However another model (ECMWF) tracks the low further north placing the band of heaviest snowfall further north.

So, everyone with the exception of the Lewiston area and lower portions of the Palouse and Blue Mountain Foothills should be prepared for a significant storm producing heavy snow.  For the Pomeroy and Alpowa Summit areas very windy conditions will be the big story, and are expected to develop late Monday afternoon into the early evening as the low tracks north of these areas.  Here is the wind forecast from 4 pm to 7 pm Monday.  The graphic shows sustained winds but we could see gusts even stronger around 45-55 mph in this area.

Please keep updated with latest forecasts with this dynamic weather system.

Friday, December 18, 2015

Snowy weather ahead

After a very wet and mild start to the month of December, the pattern has changed with storms now coming at the region from the west and northwest.  This will bring several opportunities for snow and the chances of a White Christmas are looking good for most of the Inland NW.  Let's dig deeper into where we are now and what lies ahead.

The first colder storm that tracked through Thursday and Friday has blanketed the region with snow.  Here's an analysis of snow on the ground.

This is just the beginning of the snow.  A storm Saturday night and Sunday will bring light to moderate accumulations.  Here is our forecast as of Friday afternoon for Saturday night and Sunday.

It looks like snow will reach the Cascades Saturday night and then the remainder of Eastern Washington and North Idaho on Sunday.

A stronger storm is on tap for Monday.  Here is what one of the forecast models is showing.

Dec 18th/18z GFS model run valid 10 am Monday showing 500mb height and 700-500mb Relative Humidity
Note the large area of green over the region indicating lots of moisture.  Here is our forecast as of Friday afternoon for snow amounts Monday into Monday night.

This one could bring moderate to heavy snow amounts for most of the area.  Exception could be around Moses Lake, and Lewiston areas where milder air coming up from the south may limit accumulations as rain may mix in with the snow.

The snow that falls is expected to hang around a while as a cooler northwest flow sets up for the middle to end of next week.   Models are showing an upper ridge building in the Gulf of Alaska with a cool trough over the region.  This could bring cool weather and snow showers to the region especially in the mountains.  Here is what one of the model forecasts look like for Christmas Eve.

Dec 18th/18z GFS model run valid 10 am Christmas Eve showing 500mb height and 700-500mb Relative Humidity
And the latest CPC outlooks agree with this cooler pattern.  Take a look at the temperature outlook below valid Dec 24th-28th.

So, after a mild and wet start to December, it looks like the month will finish colder and snowy with a White Christmas for most.

Tuesday, December 15, 2015

Could we really have a White Christmas?

After all of this mild and wet El Nino weather, is it really possible to still have a White Christmas?  Believe it or not, the answer is actually "yes".  And the odds are actually starting to improve.  Let's show you what we mean.

First, let's start with the current situation.  The warm and wet weather so far this month gave us a respectable mountain snow pack, but left the lower elevations with very little snow.  About the only exception to this is in the Cascade valleys and the Waterville Plateau.  Here's an analysis of snow on the ground:

As you can see, not very Christmas-like for much of the populated areas.  Just for comparison, here's the morning satellite image:

MODIS satellite image for 15 Dec 2015

It's hard to tell the difference between the clouds and the snow.  The white areas that have a herring-bone appearance are clouds.  But you can definitely see snow on the Waterville Plateau.  They're looking good for a White Christmas.

So what about the rest of us?  Is there any hope?  Yes, and not from just one storm.  There's actually a series of weather systems during the next 7-9 days that could bring us snow.  The first is tonight.  Here's the forecast of snowfall:

OK, so it's nothing to write home about.  The system is a rather weak one, coming at us from the north.  This flow pattern favors locations south and east of Spokane.  Here's what it looks like on satellite:

IR Satellite image 15 Dec 2015

The lack of clouds over British Columbia shows how weak tonight's event is.  The bigger storm just off the Pac NW coast will dive into California, missing us.  But the one behind it (on the left side of the image) will arrive on Thursday for a good chance of snow.  Here's the expected snow totals from that storm:

Definitely a more respectable storm, and probably the first significant snow for most residents.  Will it last for a week?  For the Palouse and L-C valley, it might not survive the day.  Here's the Friday afternoon high temperatures:

Temperatures around 40 along with some afternoon wind could melt most if not all the snow for Lewiston, Pullman, and Ritzville.  But don't fear.  There are still more opportunities for snow.  The reason is that the overall weather pattern will be changing.  Gone will be our warm and moist flow from the southwest.  Instead we'll be getting air from the Gulf of Alaska.

As we get farther out in time, the details are typically in doubt.  Rather than show you a bunch more maps, let's look at a computer snowfall forecast for Spokane.

You can see the first "bump" of snowfall (on the left side of the graph) will bring 1-2" of snow (probably closer to 1").  The 2nd bump on Thursday night and Friday shows another 3-5" of snow.  Then there's another system on Sunday, and yet another possibly next Tuesday.  

Now, don't go thinking we're going to have 14-18" of snow on the ground by next Wednesday.  Even if (and that's a big "if") we get all of the snow from these 4 storms that the computer is predicting, it doesn't account for melting and compaction.  However, all that said, there is a good chance that by next Wednesday, most locations will have at least some snow on the ground.  How much remains to be seen.

By the way, if you like White Christmases, be thankful this year that you live in the West.  Our friends in the East will be celebrating the holiday week in their shorts.  The trough of low pressure over the western US means a warm ridge of high pressure in the East.  Here's the forecast for next week's temperatures:

You don't typically see probabilities that high.  Above normal temperatures east of the Mississippi next week are a done deal.  Here's the precipitation outlook:

Wet in the West and the Ohio valley.  While we're getting snow next week, the Southeast and Gulf Coast will be getting thunderstorms.  

Buffalo, NY still is waiting for their first 0.1" of snow of the season, the latest that it's ever taken.

Oh, if you're wondering what the historical probability of a location seeing a White Christmas, NCDC has a story on that at:

Here's their results:

We'll update this blog in a few days to see if we're still looking at a White Christmas.

Friday, December 11, 2015

Wet December - Will it continue?

December has been off to a WET start!  Some may be wondering if this will continue through the month.  We will address some of the impressive numbers so far this month and also take a peak into the future.

So, how wet has it been?  Here is a map showing total precipitation from December 1st through the 10th for selected areas.

Quite the impressive precipitation totals especially in the Cascades.  Some locations on the west slopes of the Cascades have received amounts in excess of 10 inches.  It's also been wet in the Idaho Panhandle with Mullan Pass coming in with 6.70 inches, and 5.38 inches in Prichard.  

So how do some of these totals compare to normal?  Well these amounts only cover ten days, so its no surprise that these totals are well above normal.  Take a look at the values below.

So what has caused this abnormally wet period.  The answer is a very strong and active jet stream that stretched across the entire Pacific Ocean which brought numerous storms into the area.  

NCEP reanalysis of 300mb zonal mean wind Dec 1st through Dec 8th, 2015

So what does the future hold in store?  More active weather is in store with the parade of storms persisting.  Let's begin with Saturday...

     18z/11th GFS forecast of 500mb height and 700-500mb Relative Humidity
4 PM Saturday

The bright screen shading on the map is indicative of high moisture content in the atmosphere.  A deep low pressure system is located near Vancouver Island.  This storm is expected to bring snow to the Cascades and northern valleys and mountains.  Locations from Interstate 90 south from Ellensburg to Lookout Pass are expected to see mostly rain in the valleys with snow in the mountains.

So how about Sunday?  

18z/11th GFS forecast of 500mb height and 700-500mb RH 10 AM Sunday
You can see the wet weather continues with the best focus of moisture (with valley rain and mountain snow) over Oregon, Southeast Washington, and Idaho. This day could bring significant snow to the Blue Mountains, Camas Prairie, and Lookout Pass areas.

After this the pattern turns cooler and drier with a potential weak system Tuesday night bringing light snow to the Idaho Panhandle.  But after that models show potential another wet storm on or around Thursday.  

18z/11th GFS forecast of 500mb height and 700-500mb RH 4 PM Thursday
It's too far out to have much confidence in the specifics for this storm, but more rain and snow looks like a good bet.  Beyond this forecast confidence drops, but long range outlooks from the Climate Prediction Center for Dec 19th through Christmas day are favoring elevated chances of wetter and cooler than normal conditions.  

Overall it looks like December is going to finish out much wetter than normal.

Tuesday, December 8, 2015

Another Wind Storm? Not a repeat of 17 November.

Yes, there is another wind storm heading for the Inland Northwest.  But it will NOT be as strong as the 17 November wind storm.  While this event is similar to the storm last month, there are differences.  Let's see in what way.  First, take a look at our blog that we put out before that wind storm.  It's at:

You'll see that we talked about 2 main weather patterns for strong winds.  The November 17 storm was a pattern #2.  Tomorrow's storm will be more of a hybrid between pattern #1 and #2, which is much more common.  In other words, tomorrow's wind storm will be more like what we are used to getting.

For the November wind storm, the surface low that passed by over southern BC was 985mb when it was to our north, and then 977mb in the lee of the Rockies over Alberta.  Below are the surface pressure forecasts for tomorrow's storm.

GFS forecast of Sea Level Pressure for 830am 9 Dec 2015

GFS forecast of Sea Level Pressure for 200 pm 9 Dec 2015
This time around, the low will be about 991 mb over southern BC, and 985 mb in Alberta.  That's about 6-8mb weaker than the 17 November storm.  Also note that the track is slightly south of the storm last month.  This would suggest that the stronger winds will also be shifted farther south than last month.  That's good news for the northern counties (i.e. Bonner, Boundary, Pend Oreille, Stevens), but may be bad news for the southern counties like Whitman, Latah, Nez Perce, Asotin, Garfield, and Lewis.

Also, the jet stream is displaced farther south, over Oregon instead of Washington.  All of this points to a weaker system than November, but still a respectable event that could cause some damage.

Here's the forecast of peak winds:

Comparing this forecast to the previous month, you'll notice that wind speeds are overall weaker by about 10 mph.  The exception to this is in the southeast (Pullman, Lewiston, Winchester), where the forecast is about 10 mph stronger.  So the focus for potential damage will be in those areas.

There is one fly-in-the-ointment to all of this, that wasn't a factor in November.  There is the potential for thunderstorms on Wednesday.  (Yes, this is mid-December.)  We have a VERY moist air mass in place, and the cold front on Wednesday is strong.  This combination could lead to a few thunderstorms.  They won't be "severe".  But, a thunderstorm can bring down stronger winds from the upper levels of the atmosphere.  So any thunderstorms that do form will have to be watched closely.

After the wind on Wednesday, the weather pattern will change to cooler with a better chance for snow in the lower elevations. 

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"

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.