La Nina Update - Winter Outlook 2024-25

Have you been wondering what kind of winter the Inland NW will be granted with this year?  In this blog post we take a look at what a possible La Nina Winter will bring.

Our partners from the Climate Prediction Center wrote a fantastic blog about the influence of La Nina on snowfall across the region, that we highly recommend checking out.  The link to their blog can be found here.

As the blog states, for La Nina winters there is a tendency for above normal snowfall.  Indeed, local research we've conducted for several cities across our region show a tendency for above normal snowfall.  As shown below, on average snowfall ranges from 110-125% of normal for La Nina Winters.

% of normal snowfall for all La Nina winters from 1950-2017

For the interactive version of this map, where you can view charts for individual locations, click here.  Unfortunately the map isn't mobile friendly, so it is best viewed from a computer.

The latest probability for a La Nina this winter is around 70% according to the chart below.

% chance of La Nina (blue), Neutral (gray), El Nino (red) for each 3 month period.  DJF would be the chances for this upcoming winter

What do some of the latest climate models suggest for the winter?  The NMME (North American Multi-Model Ensemble) shows what one would typically expect for La Nina, cooler and wetter than normal conditions for the northwest.

NMME temperature and precipitation anomaly forecast for Dec 2024-Feb 2025

What about the official outlooks from the Climate Prediction Center?  These are weighted towards cooler and wetter than normal as well.

CPC Temperature Outlook valid Dec 2024 - Feb 2025

CPC Precipitation Outlook Valid Dec 2024 - Feb 2025

We have said this in previous blogs and will say it again in this one.  La Nina is only one piece of the puzzle, and while the outlooks favor increased odds for above normal snow, it is certainly not a guarantee.  This is because other oscillations in the atmosphere impact the weather pattern that sets up.  For instance, take a look at Spokane snowfall for all La Nina Winters since 2000.

My oh my!  Anywhere from 27"-98"!  And interestingly, those two winters (2005/06 and 2008/09) were both weak La Nina events.  So, while the average La Nina snowfall for Spokane is between 55-60", the precise number Spokane ends up with this winter may be much higher or lower.  

But given that a weak La Nina is favored and latest outlooks side towards the cooler and wetter, it would be best to prepare now if you haven't already.

Excessive Heat, Smoke, and Critical Fire Weather

For residents of the Inland Northwest, the heat has likely felt relentless to most of us.  While hot temperatures may feel normal given that it's July, the data suggests otherwise.  The current stretch of hot weather is about to break some more records (more on that later).

Most of the region had a much drier than normal spring and early summer.  Here is a look at percent of normal precipitation over the past 120 days.  

Percent of normal precipitation past 120 days (March 20th - July 17th, 2024)

Enhancing the dry conditions, has been the relentless heat over the region.  Spokane has now reached the 90 degree mark for 14 consecutive days (including today).  The chart below shows the normal range in temperatures (brown shading), with the observed values shown by the blue bars.  The readings on July 8th, 9th, and 10th set records for the date.

Spokane International Airport Observed, Normal, and Record Temperatures for July 2024

The record streak of 90 degree days is 15, so this will easily be broken.  In fact, the heat will intensify.  Here is a look at a map of Excessive Heat Warnings that are in place over much of the region.

Map of NWS Excessive Heat Warnings and Heat Advisories as of 8 PM July 18th, 2024

The number of 100 degree days is also noteworthy.  So far Spokane has reached 100 degrees three times this season (through July 18th).  The record is 6, which recently happened twice in 2022 and 2021.  With the forecast reaching that mark Saturday, Sunday, and Monday there is good chance that record will be tied yet again.  Of course one more heat wave this summer could push us above that.

Here is a look at forecast high temperatures from July 19th-23rd, from the forecast published on July 18th.

The heat is likely to peak on Sunday for most of the region (except parts of North Idaho).  And you'll notice a cool down on Tuesday with highs in the lower 90s.  This could cause some problems (more on that later).

Of great concern is the recent lightning event that occurred on July 16th and 17th across the northwest.  Several wildfires were ignited, especially across Oregon, just east of Grand Coulee, and in the North Cascades of Washington.  There were also some new fire starts in the Central Panhandle Mountains in Idaho.  Here is a snapshot of fires across the region as of July 18th. 

With so many fires, several areas of smoke were noted on satellite this evening (July 18th)

Satellite image evening of July 18th, with smoke highlighted inside pink area.

With record heat this weekend, the expectation is that several of these fires will become larger, putting out an increasing amount of smoke.  Here is one model projection showing smoke over the region the next couple of days.

5 PM July 18th HRRR Total Smoke forecast valid from 8 PM July 18th-5 PM July 20th, 2024

Surface smoke impacting air quality is expected to continue to be most impacted near wildfires.  But hazy skies from regional wildfire smoke will be prevalent over all of the region.

Finally, as mentioned earlier, with fires becoming more active through the weekend, there is a concern of dry, breezy winds as temperatures begin to trend cooler early next week.  Below is the National Blend of Models output for the chance of wind gusts exceeding 30 MPH on Monday.

Any new or existing fires in Central Washington will have the potential to spread rapidly.  These gusty winds will likely continue through at least Tuesday.

So, be prepared for excessive heat, potential for increased smoke into early next week, and then critical fire weather conditions in Central Washington on Monday (and likely into Tuesday as well).

And so, summer heat begins!

   In case you haven't heard we are on the verge of a prolonged spell of summer heat set to arrive right after the 4th of July. Years ago, it seemed summer would always begin right after the 4th of July in the Spokane however is that really true? According to statistics, perhaps not. Interestingly enough, we can define summer by looking at the warmest 91 (3-month period) of the year which according to our climate statistics occurs around June 16th. Also interesting is the fact, that the beginning of the summer season has been getting later and later each year, however there is a significant amount of disparity when looking at the chart below.  

Also interesting is noting the abundance of red dots since 2000 signifying a warmer than normal summer. Since 2000, 75% of the summers have been warmer than normal with a current streak of 12 warmer than normal summers. Below is a closer examination of that factoid plotted against the 30-year moving average.  The blue line represents the average summer temperature (based on June-August data and not the 91-day period shown above. 

So enough of the summer background, let's take a look at the upcoming forecast and heat-filled details. This burst of heat will arrive care of a very strong ridge of high pressure. If we look at the 500 mb charts (~18,000') in the atmosphere we can see how this scenario is going to play out. On Friday, the ridge will begin to build off the coast and this should begin the heat event.

500 mb heights Friday

By Sunday the ridge will migrate toward the center of Washington ensuring we warm up even further. 

500 mb heights Sunday

By Tuesday the ridge axis shifts into eastern Washington and then the heat will really get going across the Inland Northwest. 

500 mb heights Tuesday

But that's not the end of it, as it looks like the heat will peak on Wednesday or Thursday with the ridge shifting to the Montana/Idaho border. 

500 mb heights Thursday

So how confident are we this scenario is going to pan out? At this point, quite confident. In the past we only had a few weather models at our disposal and run-to-run changes were common, especially at the latter ends of the forecast (for instance days 4-7). However now we utilize ensemble forecasting which takes multiple models (over 100 for the days 1-2 forecast and 100 for days 3-7) and complies them for us. This method can show us the range of possible outcomes and in this upcoming pattern there just aren't a lot of outcomes other than just plain hot. The easiest way to determine how uncertain the forecast is by examining a chart that shows the different model solutions and plotting them on top of one another. 

Let's start by examining the model possibilities for Sunday.  Note the ridge positioned along the West Coast and the pale-yellow shading over the region. The shading represents the differences in the 500 mb heights between the 100 model runs. In this case, the differences are only around 2 decameters, which signifies good model agreement. If you look farther west, over the Gulf of Alaska note the purple shading which signifies large model differences (13 decameters, which is significant). Seeing model agreement only 2-3 days into the forecast isn't unusual, especially for a ridge. 

500 mb ensemble model differences on Sunday 7/7/24

By Tuesday the model differences with the ridge increase, but not by much (only 1 decameter over the Pacific Northwest). This still suggests high forecast certainty. 

500 mb ensemble model differences on Tuesday 7/9/24

By Thursday the model differences increase slightly, but again not to the point where we would think the ridge will be replaced by the offshore trough, delivering cooler weather. All the significant model differences remain on the eastern or western periphery of the ridge. 

500 mb ensemble model differences on Thursday 7/11/24

If we go out even further to next Saturday, there still is a higher-than-normal chance that the ridge is going to stick around, however we'd have to imagine we'd see some cooling by then. 

500 mb ensemble model differences next Saturday 7/13/24

So far, we've only examined the 500 mb heights, which are indicative of sinking air and generally fair weather, but how does that translate to temperatures on the ground?  First, we will examine the mean temperatures forecast by the National Blend of Models. This represents the most likely outcome. 

NBM mean temperature forecast for the Inland Northwest

However, what would we expect if the warmest 25% of the model solutions came to fruition? That would certainly support a historic heat wave. There's no reason to believe this will occur, however it just hints at a possibility. 

NBM 75th percentile temperature forecast for the Inland Northwest

So, what are our chances of exceeding 100°F during the next week or so? It's a done deal for the LC Valley, as well as the Columbia Basin and Okanogan Valley. There's a slightly lesser chance for Spokane, while the "cool" escape will be to Sandpoint. Below is a list of the chances:

Chances of hitting 100°F or hotter

As you can see, the odds are quite good that a large portion of the Inland Northwest will see a multi-day period of triple digit heat. Currently our forecast doesn't suggest we will break any records for consecutive 100°F days however once again we could easily see 4 consecutive days of triple digit heat in Spokane. Something which occurred in both 2021 and 2022 but not many years other than that. The record is 6 set in 1928. 

Other daily records could be broken beginning on Sunday and continuing at least through Thursday. Spokane's records are as follows: 7/7 99°F, 7/8 99°F, 7/9 100°F, 7/10 102°F, 7/11 103°F. All are certainly within reach. We also got the question is Spokane's all-time record in peril? Just 3 years ago Spokane set a new record of 109°F (6/29/2021). While we don't expect to break this record during this spell, it is not a 0% chance. In downtown Spokane, the chance is around 10% on Thursday (in other words 10% of the ensemble model runs are forecasting temps of 109°F or warmer), while at the Airport (the official forecast spot for Spokane) the chance is around 2%. 

Chance of 109°F or warmer on Thursday 7/11/24. 

So far we've discussed the daytime highs which will be trying enough to those who don't tolerate heat well. But we also have to factor in the nighttime lows. Unfortunately, these won't cool off too much either. The table below reveals overnight lows only dipping into the mid 60s to mid 70s for most locations. That means folks without air conditioning will have a tougher than usual time cooling off their houses during the night. And the length of this event will only exacerbate this issue. 

Nighttime low temperature forecasts

If you add these factors together, we are looking at a trying environment for many denizens of the Inland Northwest. We can characterize this using an index we call HeatRisk. By Sunday a large portion of the region will experience Major heat risk which means the heat will impact anyone without effective cooling and/or having access to adequate hydation. 

Sunday HeatRisk

By Tuesday (the last day available for the HeatRisk as of this blog post), we begin to see extreme values popping up around the area. Remember, we expect the heat to peak on Wednesday or Thursday which suggests the magenta will become more widespread. 

Tuesday HeatRisk

Needless to say, we urge all of our friends to take the necessary precautions ahead of time and prepare for this upcoming heatwave. Here are a few hints from the CDC to help you beat the heat. We also want you to treat your loving pets with the utmost care to keep them safe during this heatwave. Please stay tuned to our latest forecast to see how hot it is going to get. 

Safety advice from the CDC and the NWS for you and your pet

Inland Northwest White Christmas Outlook

 Are we going to see a White Christmas this year?  Now that Christmas is less than a week away, there is increasing confidence with the upcoming forecast but a few details are still unknown.  Let's dive into it!

Historical chances

Let's begin with a map of the climatological chances for a White Christmas.  

Source: NCEI.  Based off 1991-2020 Normals

As you can see, the chances depend quite a bit on location.  It's no surprise that for the Inland NW, the further north you go, the better the chances.  Historically chances are only around 10-20% for the Tri-Cities area into the Lewiston-Clarkston Valley, increasing to near 60% for the Spokane area, while chances are 90% or higher for Republic and the Methow Valley.

This year

So far we have only talked about historic chances and you may be asking, "What about this year?"

Great question; let's take a look

We will begin with our current snow depth as of this morning courtesy of our CoCoRAHS and COOP observers.  

Snow depth reports (inches) on December 19th, 2023

Areas along the East Slopes of the Cascades have snow on the ground, as does the Republic area and the areas around Deer Park, Elk, and Athol.  Some other areas have light amounts of 0.5-1.0" of snow on the ground.  The Wenatchee area, Columbia Basin, Spokane area, and down through the Palouse and Lewiston area have little to no snow on the ground.  

So for many areas, chances of a White Christmas will come down to the weather leading up to Christmas.

For the next several days, mild temperatures are forecast before a cool down to normal temperatures from Dec 23rd-25th, so we expect there will be more melting of our current snow through Friday.  Here is a look at the forecast high temperatures from Dec 20th-25th.

NWS Forecast of High Temperatures, issued 3 PM December 19th, 2023

What is going to cause this cool down?  A weather system will usher in a cold front by Friday night.  Snow levels will also lower, with the best chances for lower elevation snow into Saturday across the Idaho Panhandle.  Here is a map showing the chances for 1" or more of snow:

NBM (National Blend of Models) probability of 1" or more of snow from 4 AM PST Dec 22 - 4 AM PST Dec 24th, 2023

The map shows little to no chances for 1" of snow for the Okanogan Valley down through the Columbia Basin and Lewiston area, a 10-20% chance for the Spokane area down through the Washington Palouse, increasing to 30% or higher for the Idaho Palouse and much of the Idaho Panhandle.

What about after that? Another weak weather system may arrive Christmas Eve night into Christmas Day.  Given the colder air that will be in place most of the precipitation is expected to fall as snow if any develops.  As of this writing (Dec 19th), there is a 20-30% chance of light snow for most of the region with a 40-50% chance along the East Slopes of the Cascades.  It's possible high pressure will be strong deflecting all precipitation north of the region. Stay tuned to the forecast for updates.  For the latest forecast for your area, head to weather.gov/spokane   

So for this year a White Christmas is forecast for the East Slopes of the Cascades, Republic area, and in the mountains.  Elsewhere, not all hope is lost yet.  Merry Christmas!

El Niño and the Winter Outlook 2023-24

What will this winter bring?  In a previous blog post, found here, we talked about how El Niño could impact our fall weather.  Now we will take it a step further and examine the winter.

In case you haven't heard, there is a 100% chance of an El Niño this winter!  This is guaranteed.  And there is an 80% chance the event will be classified as a strong El Niño.  Below is the typical pattern associated with an El Niño winter.  Typically the polar jet stream stays well to our north and east while an active Pacific Jet Stream sends wet weather into the west coast (especially California).  But as you'll see later that is certainly no guarantee.

Typical Jet Stream Pattern associated with El Nino

While the impacts locally are not the same for every El Niño winter,  the winters favor warmer than normal temperatures.  We will talk about precipitation and snow later.

So how is the current El Niño looking?  As the graphics below show, there is plenty of warmer than normal water along the Central and Eastern Equatorial Pacific.

Average Sea Surface Temperature Anomalies Sep 24-Oct 21, 2023 (left image).  Specific anomalies for Nino regions (right image)

The Niño 3.4 region already has an anomaly of 1.6C (3 F).  Anything 1.5C or warmer would classify as a strong event if this intensity maintains itself for three or more months.

The model predictions are calling for not only for these warm waters to maintain themselves, but to get even warmer through the remainder of the fall and early winter

Model predictions of Nino 3.4 Sea Surface Temperature Anomalies through JJA (June, July, August 2024)

Why does this warm water matter when it is so far away?  The why can be found in this September 29th blog post from the Climate Prediction Center (CPC), found here.

Since 1980, composite temperature and precipitation anomalies of Strong El Niño winters (shown below) reveal that on average, Strong El Niño winters result in warmer than normal temperatures, while precipitation has been slightly above normal in Central Washington, and slightly drier than normal over SE Washington into the south Idaho Panhandle.

Left Image: Average temperature anomalies of the 1982-83, 1991-92, 1997-98, 2009-10, and 2015-16 Strong El Niño Events.  Right Image: Averaged Standardized Precipitation Anomalies for those same events

It is important to mention here that this only includes five events (small sample size).  Due to the influence of climate change, there is some reluctancy to put as much weight into earlier cases.  However, the maps below show all strong events (8 in total) since 1950.  Let's begin with temperature:

Temperature anomalies observed from previous Strong El Niño events

And now precipitation:

Precipitation anomalies observed from previous Strong El Niño events

Here are the key takeaways from previous Strong El Niño Winters

• Every event since 1980 has been warmer than normal
• Precipitation varies significantly.   Some years have been wet, some dry, and some near normal.

So, what do the official outlooks call for this winter?  The CPC is calling for an 89% chance that temperatures will finish near to above normal (56% above normal, 33% normal), and only a 11% chance of the winter finishing cooler than normal as shown below.

Climate Prediction Center Dec 2023 - Feb 2024 Temperature Outlook.  The green icon on map is over Spokane, WA with the pie charts on left side of graphic showing various temperature and precipitation probabilities for the period

Note the bottom left pie chart which is the precipitation forecast.  Consistent with previous cases, there isn't much weight put into any one category, with all outcomes carrying nearly equal weight.

The warmer than normal temperatures themselves tends to reduce snowfall amounts for the lower elevations.  Below is a map of % of normal snowfall for ALL El Niño Winters from 1950-2015

Percent of normal snowfall averaged over all El Nino years from 1950-2015

As you can see, just about every town on average sees below normal snowfall.  Want to fiddle with this page some more?  Well you are in luck, an interactive version can be found here.  Each location when clicked on will bring up a chart showing average snow amounts for all three ENSO States (El Niño, La Niña, and Neutral).

There are two important things to point out regarding snowfall for the Inland NW.  

1. The Palouse area and Spokane area historically received the greatest reduction in snow during El Niño events compared to normal.  Since we are heading into a strong El Niño, we examined previous events for Moscow and Spokane (shown below).  
2. Communities from the East Slopes of the Cascades up into the Okanogan Highlands including Leavenworth, Chelan, Winthrop, and Republic show much more variability with amounts. 

Let's start with Moscow, ID.  Every strong El Niño event since the 1970s has brought below normal snow, with most years only receiving around 20-30" versus a normal near 50"!

For the Spokane International Airport, EVERY strong El Niño event since 1950 has brought below normal snow except 1965-66 which was near normal.

And for Wenatchee, snow amounts are quite variable.

If you live in North Central Washington, the presence of El Niño won't really help much regarding the seasonal snow prediction.  Because of this there is higher uncertainty with the snow forecast for these areas.

Interested in reading more about how El Niño can impact snow over North America?  The Climate Prediction Center recently published a blog post going into more detail, found here.

Finally, while El Niño plays a role for the winter as a whole, short term variations in the weather (lasting 1-3 weeks) commonly occur as other atmospheric variables impact the weather pattern.  These can have impacts over the region including strong winds, flooding, cold temperatures, and a variety of winter precipitation types including snow, sleet, and freezing rain.  With that in mind, it is always wise to be prepared for winter weather.  In fact, winter weather already struck parts of the region on October 27, 2023 creating slick roads as these images from WSDOT showed on I-90 near the Four Lakes area.

Oct 27th, 2023 - Photo courtesy of WSDOT on X (Twitter)

Oct 27th, 2023 Photo courtesy of WSDOT on X (Twitter)