Thursday, January 22, 2015

Spring Skiing in January?

If you've looked at the forecast lately, you'll notice that we're expecting warmer temperatures next week.  Temperatures are forecast to be in the 40s, with even some lower 50s in places (i.e. the Palouse and Lewiston area).

Why will it be so warm?  Very strong high pressure will develop over the western US in the next few days.  But we often see that.  So what's so special about this?

The image below shows the temperatures at about 5000' above sea-level this morning.

Temperature at 5000 feet MSL on Thursday.

You'll notice that the warmest air (red shading) is over California, as well as in the lee of the Canadian Rockies.  Now here's the same image on Saturday afternoon:

Temperature forecast at 5000 feet MSL Saturday

Notice those bright red colors off the coast of northern California?  Where did that come from?  The wind will be "offshore" at this time, which means it will be blowing from the northeast, coming from Nevada and eastern Oregon, to the Pacific Ocean.  As it does this, it descends from the Sierra Nevada mountains down to sea level.  Air that descends warms due to compression.  So this warm air didn't move here from somewhere else, it was created by the wind flowing from the Sierra's (e.g. 8000 feet elevation) down to sea level.

Now here's the forecast of what will happen to that warm air on Monday:

Temperature forecast at 5000 feet MSL Monday morning

You can see that the warm air has spread northward, along the coast, and into the Inland Northwest.  

OK, so just how warm are we talking?  Well, in addition to keeping track of all of the record high and low temperatures at various cities, we also keep track of historical temperatures on our weather balloons.  So here's the January record high temperatures at 5000' MSL for various western locations, along with the computer model forecasts:

Max 5000’ MSL Temperature
Model 1
Model 2
Model 3

The three models differ a bit in their forecast, but they all have very warm temperatures at 5000'.  Some records (going back to 1948) could be broken.  How warm are these?  The forecast of 14.1°C at Spokane, if it verifies, would be the same as what we normally see on April 6th!!!

So what does this mean?  The answer is somewhat complicated.  Here's the forecast high temperatures for Monday:

These are about 10 degree above normal for the end of January.  But this forecast could easily be very wrong.  You'll notice that much of the western Basin (i.e. Moses Lake), and the northern valleys (e.g. Omak, Colville, Bonners Ferry) are in light blue (40-45F) while the mountains (e.g. the area between Republic and Colville) are in green (45-50F).  What gives?

The northern and Cascade valleys have snow on the ground.  Any melting of snow could lead to fog and low cloud formation.  And this would keep the valley temperatures cooler (i.e. little or now sunshine).  But if that fog doesn't form, then the temperatures could easily be 10 degrees warmer than forecast.

Typically, for a mid-winter warm spell, we need wind.  The wind helps to mix the atmosphere, taking warm air aloft and mixing it with the cold air near the surface.  But in this case, there won't be much if any wind.  So we won't have any "mechanical mixing" to stir the atmosphere. The sun will have to do all the work by itself to warm up the near-surface temperatures.  With the low sun angle of late January, this is a tough task.  Not impossible, but difficult.

Meanwhile, the mountains will be above any fog formation and they should see abundant sunshine.  So confidence is high that they will be warm.   Here's the minimum temperature forecast:

Notice that the mountains are as warm as the valleys?  The mountains won't just be warm during the day, but they'll probably be above freezing during the nighttime hours as well.  And this will likely last for 3 or 4 days.  A week cold front in the middle of next week will cool things down some, but it will still be warmer than normal for late January.

So we'll get a taste of early spring next week, especially in the mountains.  There's a big bust potential for the valley temperatures, especially north of I-90.  But if you're going skiing, make sure you bring the sunscreen and don't over-dress.

Tuesday, January 20, 2015

This winter compared to last...and will we see a normal recovery?

A couple weeks ago we posted a story on our Facebook page that said, climatologically speaking the harshest part of winter is now in our rear view mirror. Here's was the post.

We stated that since the days are getting longer, sunnier (very slowly) and temperatures are on the rise that in fact, climatologically speaking the worst is over with. However, we did put a caveat in the story which said we can still get some very good winter storms during the remainder of January into February. One astute reader mentioned that we stated something similar last year in a blog entry. Last winter we had a very dry and relatively snowless beginning to the winter and wondered what the chances were of it continuing. Needless to say we recovered quite nicely in the second half of winter. This winter, things might be just a bit tougher. Just for comparison sake, here was the mountain snowpack last year on this date.

And here's how it looked this year

Not a lot of differences. All locations were seeing below normal snow water equivalent values for both years. The Okanogan Highlands and the northern Cascades are doing a little better this year, and things are a little worse elsewhere.  Also, notice how poor the snow water numbers are for the southern Washington Cascades and the Oregon Cascades.  However, these maps aren't really telling the entire story. Why is that? If we choose to just look at the amount of precipitation which has fallen since October 1st (beginning of the water year) rather than the amount of water in the snowpack the winters are completely different. Here was 2014 through January 19th. Just like the drier than normal snowpack, the precipitation was similarly dry.
Oct 1 2013-Jan 13 2014 percent of normal precipitation
Now look at the data for this water year. What a difference a year makes! All basins are seeing normal to slightly wetter than normal conditions.

So what gives, why the big difference? In one-word temperatures. Temperatures this winter and late fall have been significantly warmer temperatures than what we saw last year. Much of what's been falling has been dropping as rain as opposed to snow. Take a look at the temperature departures from normal below. They exhibit a huge difference. In the first half of winter 2013-14 temperatures were well below normal.
Oct 1-December 2013 temperature departures. Note widespread below normal temperatures
 While this year...they have been generally well above normal. The swing from last winter to this winter is around 3-6°F warmer. That may not seem like a lot, but in terms of snow it makes a big difference.

Oct 1-Jan 18 temperature departures. Note widespread warmer than normal temperatures. 

Anyway we digress. We simply wanted to demonstrate that although we have seen similar snow totals to last winter in the mountains, how we got to those totals is completely different. Last year was an ENSO neutral year which often does not foretell what sort of winter to expect. This year is an El Nino winter (albeit a weak one). Typical El Nino winters deliver warmer than normal conditions (sure enough it has been warmer), and a variable precipitation signature. So let's examine some snowfall numbers across a few valley locations including Spokane, Wenatchee and the always snowy Holden Village (on Lake Chelan). Just like the mountains, most valley locations are seeing sharp snow deficits. In fact, most locations are seeing a top-10 least snow winter since 1949. We are utilizing 1949 since that year is when the NWS began keeping track of  El Nino/La Nina data.

Least 10 snowy Spokane winters through 1/19 since 1949

Least 10 snowy Wenatchee winters through 1/19 since 1949

Least 10 snowy Holden Village winters through 1/19 since 1949
So of those three sites, this year ranks as either the 5th or 6th least snowy winter through 1/19. But more importantly how did the rest of the winter fare and could the snowfall deficit be made up. The answer is an overwhelming no. In Spokane, none of the 10 least snowy years through 1/19 was able to recover to normal. The winter of 1989-90 was close. Last year was also somewhat close as much of the region saw a record or near record snows in February. However, those were not El Nino years. Of the El Nino years, three of them, the remainder of the winter failed to deliver more than 6 inches of snow.

For Wenatchee, two of the winters were able to recover to above normal levels after such a slow start to the snow season.  Both of those years were ENSO neutral years. During the El Nino years, the numbers were quite meager. The two El Nino winters on the list experienced snowfall of less than an inch through the remainder of the season. On average, less than 5" of snow typically falls during the remainder of the season. 

Now onto the ever snowy Holden Village area. The numbers for here spell bad news for heavy snow lovers. Of the 10 least snowy winters through 1/19, none were able to get back to normal. Last year was close (after an astounding and record breaking 142" of snow in February) as was 1989-90. Both of those years were ENSO neutral ones. The trends during an El Nino year are much less promising. Of the 4 El Nino years on the list, none were able to recover to normal levels. Additionally, 3 of the 4 El Nino years saw significantly less snow than normal through the remainder of the winter.

So climotology tells us the odds of recovering from such a slow start to the winter are slim and given our weak El Nino conditions the chances are even slimmer. However, keep in mind that long-term weather forecasting can prove a futile endeavor and ultimately anything can happen. 

Through the remainder of the month the weather pattern will not be conducive to adding significant amounts to our  snow totals. Although wet weather will likely return by the end of the week, this moisture will be accompanied by unusually warm temperatures at least over the mountains. The 6-10 and 8-14 day outlooks are calling for a good chance of warmer than normal temperatures and average or slightly wetter than normal conditions. 

8-14 day precipitation outlook

8-14 day temperature outlook

Monday, December 22, 2014

Odds for a White Christmas: Update

OK, we're only 3 days away from the Big Day, and snow is still hard to come by in my Inland Northwest locations.  Is there any hope for a White Christmas?  Here's the current snow depth analysis:

Pretty pathetic.  Folks in the Cascades are doing well, as are those in some of the northern valleys (e.g. Omak, Republic, etc).  Otherwise, lots of bare ground.  

Just to refresh your memory, here was last year's snow cover at this same time. Not stellar, but better than this year.

But there's still time to change this, right?  Actually, the answer is "yes", for some locations anyway.  As we've been discussing in earlier blogs, the computer models have been suggesting a Christmas Eve storm for over a week now, but they've been waffling on the exact timing, track, etc.  And these small differences play a HUGE role in who will get precipitation, and in what form will it fall.  But now, the models are in fairly close agreement. So let's take a look at what they're saying.

Below is the GFS forecast precipitation for the 12 hours ending 4pm Wednesday.

While this looks encouraging, unfortunately almost all of this will fall in the form of rain.  Snow levels during the morning hours will be around 6000' but will rapidly fall through the day as cold air moves in from the north.  Can the snow levels drop all the way to the valleys before the precipitation ends?  Maybe, but this is typically a poor pattern for valley snow.  And even if it does snow in the valleys, it will have a hard time accumulating on the ground during the afternoon/evening hours.

Here's the probability of 1" or more snowfall on Christmas Eve. 

Things are looking up for folks in the Idaho Panhandle.  Meanwhile things look bleak for locations in central/eastern Washington, with locations west and south of Spokane having next to no chance for snow.

So, looks like a brown Christmas for many folks.  The interesting climate tidbit in all this is that we could set an obscure record at Spokane.  The latest that it's ever taken for the Spokane Airport to have it's first 1" or greater snowfall from one storm is Dec 24th 1976.  Unless the forecast changes in a hurry, we'll break that record.  But not by much.  Why you ask?  Because it's is now looking very good for a decent snow event after Christmas.

Here's the 24-hour precipitation forecast from the GFS ending Saturday evening:

Looks similar to the Christmas Eve storm, right?.  The difference is that just about all of this will fall in the form of snow instead of rain.  The reason is that while the Christmas Eve storm might not bring much snow, it will bring colder air.  So by the time this second storm arrives, we'll be much colder.  Different models have different amounts of snow, but in general they all have a solid 2-4" for most locations with the potential for higher amounts.

Here's the snowfall forecast from the NAM (red) and GFS (blue/purple) for Spokane. 

There are different forecasts here using different techniques.  But in general they give a similar message.  Snow will start Friday evening and continue into Saturday evening.  The ECMWF (not shown) has a similar story, but doesn't start the snow until Saturday morning and continues it into Sunday.  Either way, there is the potential for several inches of snow.

It's too early to hang-your-hat on this forecast.  But one of the things we like to see is that each model forecast is similar to the previous one (GFS runs every 6 hours, ECMWF every 12).  And they've been saying a similar message for about the last 24 hours.  So that's a good sign and gives us confidence that this forecast could indeed pan out.  But the overall pattern for this storm isn't necessarily a favorable one for heavy snow in the Inland Northwest.  The mountains will almost assuredly pick up some snow from this, but the lower elevations might not see much. Stay tuned to the forecast, especially if you plan to travel this weekend.

Wednesday, December 17, 2014

Are the chances of a White Christmas improving?---UPDATED 12/18/14

...Here's an update to yesterday's blog. We replaced the images with the latest weather forecasts...  

 Since our last post, we have gotten a little more resolution on the prospects of seeing a White Christmas across the Inland Northwest. But before we answer that question we need to deal with a weak weather system tonight and Friday and then a much stronger system for the weekend. As of our latest forecast (issued 3pm Thursday). Tonight and Fridays weather system is calling for light snow, mainly confined to the mountains. Valley snow chances will be reserved for the Cascade valleys, Okanogan Valley, and a small part of the Waterville Plateau. These locations will generally see amounts ranging from 1-3 inches with locally heavier amounts near the Cascade Crest. There will likely be some travel concerns going over the Cascade passes.

Snow forecast for tonight-Friday

The storm system for Saturday and Sunday stands a much better chance of producing significant snowfall as it will contain much more atmospheric moisture. This will be care of a very well-defined atmospheric river that has its sights set on the Pacific Northwest. Here's what the atmospheric river is expected to look like by Saturday morning. This river will draw its moisture from well south and west of Hawaii.
Atmospheric river forecast for Saturday morning. The darker the colors, the more moisture content. 

While the river will assuredly produce widespread precipitation, it will also deliver steadily warming temperatures. Our confidence is high that snow levels will be low enough to produce moderate to heavy snows near the Canadian border and in the Cascades. It would not be surprising to see snow amounts approach a couple feet in the Cascades.  Meanwhile, the forecast for the nearby valleys is a much tougher call as temperatures will be critical. If they warm much above 32°F the snow accumulations could be less than forecast, in fact much less. Right now, we are forecasting temperature very close to freezing over most of these lower elevation locations and putting moderate snow accumulations in the Cascade Valleys. Most of this valley snow threat would occur between Saturday morning and early Saturday evening.

Weekend Snow forecast

By Sunday afternoon, temperatures will warm significantly as the warmth associated with the sub-tropical moisture continues its northeastward surge. Snow levels will rise to 4000' or higher over the entire Inland Northwest. This will translate to melting snow over most of these valley locations. The big question is can we melt what falls? That depends on how much accumulates over these locations. The warming will be accompanied by breezy conditions which will help melt the snow especially as the dewpoint temperatures and nighttime lows rise above freezing. And that's what we are expecting as of our latest forecasts. Here's a look at the high-temperature forecast for Sunday.

Sunday Forecast Highs

 So based on the current forecast the only valley locations which stand a chance of snow before Christmas Eve would be near the Canadian Border, or the Cascades. How about the remainder of the region? Well, as we talked about in our last blog entry we are expecting a big pattern change, right around Christmas Eve. That's still true. Our mild west-southwest flow of late will take a decided cooler turn to the northwest. Here's what the upper-level pattern is going to look like (at least something like it anyway). The wind flow will be parallel to the yellow height lines and it will deliver cooler air into the area (blue and purple shading is cold air, other colors are relatively warm) via the Gulf of Alaska. Meanwhile, the remnants of the weekend moisture stream will get hung up somewhere over the Pacific Northwest. The big question is where is that going to happen? Most likely it will occur immediately downstream or east of the curve in the yellow lines. In the picture below that suggests that will be somewhere over extreme southern Washington and northern Oregon.

500 mb Heights and temperatures

So is there good model agreement in where that curve is going to form? That is the key to this forecast. As of the latest model runs, consensus is growing. Here's a look at four various model runs all looking at the afternoon hours of Christmas Eve. We placed the precipitation forecast on top of the 500 mb yellow height lines. Notice, they all show a similar curve in the height lines or flow, however they vary on how far north to place it.  Model trends continue to support the band forming well south of I-90. Notice some don't place any precipitation over eastern Washington, while others only give us light precipitation amounts. Based on the trends, our confidence in seeing precipitation remains highest for locations near the Oregon/Washington border, such as Lewiston and Pullman. However, even in these locations temperatures may remain just a little too warm for snow.

Various weather models for Christmas Eve. Shading represents the precipitation. 

So to answer our original question. Are the chances for a White Christmas improving? For locations such as Mazama, Republic, or Plain the answer is a decided yes. For Lewiston or Pullman the answer is a maybe. Folks in Spokane, Couer d'Alene, Moses Lake, or Wenatchee the odds are not great. Of course, Christmas Eve is just under a week away and much can change between now and then. So stay tuned and maybe just maybe the yellow curve will decide to set up over the entire Inland Northwest resulting in a White Christmas for all. 

Monday, December 15, 2014

Looking for significant snow? Is there any hope soon?

  Well, another week into December and much of the Inland Northwest has yet to see any significant snow. The only exceptions have been near the Cascades and a small part of the Okanogan Valley. As of this afternoon, here what the snowpack summary looked like. Notice there is very little if any snow in the valleys. If you wanted to see significant snow, you'd have to trek into the mountains north and west of Wenatchee and Omak  or north of Sandpoint.
Snow depth as of 5pm Monday 12/15/14
Although these areas were shaded in purple indicating anywhere from 20" to 50" of snow on the ground, that pales vs. where we are supposed to be this time of year. Here's a look at the amount of water that's in the current snowpack. Generally speaking, it's right around half of where it should be this time of year (orange shading) and is actually far worse across most of the Cascades!

Snow water equivalent vs. normal

So is there any hope we can add some more snow to the forecast this week? Actually there is some hope however it won't add up to much. We have several weak weather systems set to impact the Inland Northwest this week. The first will arrive late tonight and into Tuesday. For now, here is our forecast of snow.
Snow forecast for late tonight-Tuesday
As you can see we have light snow forecast across much of the region. We are most confident about the snow totals near the Cascades and northern Valleys. Elsewhere, it looks like the snow might begin too late in the day so it might make accumulations difficult to come by. But that's not the only hope for snow. A couple weak disturbances look like they will impact the region through the remainder of the workweek. Here's our latest forecast of snow for late Thursday through Friday night. Confidence is not high as these will be weakening and warming winter storm systems. Temperatures away from the Cascades and northern valleys could be marginal for snow, especially accumulating snow.

Snow potential for Thursday afternoon-Friday night
Even if the snow materialises, it won't likely stick around long as we will see a yet another round of very warm and wet weather. This weather will be brought to us by another atmospheric river or Pineapple Express. Here is the model depiction of the latest plume. The moisture is represented by the stream or river of greens colors extending across the eastern Pacific to the Washington Coast. Notice the plume originates to the west of Hawaii (lower left corner of the picture), suggesting it will be a very juicy airmass. Temperatures should surge well above freezing over most locations which will melt most of not all of the valley snow which falls this week.
Atmospheric river forecast for Saturday

So this warm air is only forecast to persist through Monday night or so which doesn't bode well for a White Christmas. But is all hope lost? First off this would be a good time to show what the climatological odds are of seeing a White Christmas. There is a very large variability across the Inland Northwest ranging from near 100% for the northern valleys of Washington, and most of the Idaho Panhandle to less than a 25% chance by the time you go south toward the Tri-Cities and Lewiston. For a more detailed look of the map below check out this link from the National Climate Data Center.

Odds of a white Christmas. 
So enough about climatology, what about this years weather? There are actually some good indications that we could see a moderate to major winter storm on Christmas Eve. Well, why is that? It looks like we will see a very good setup where the moisture from early next week sticks around and is intercepted by much cooler arriving from the northwest.
500 mb pattern showing northwest flow from BC and Gulf of Alaska

Notice the kink in the flow setting up near the Washington/Oregon border. Where this sets up gives us a clue for where we can expect the heaviest snow.While there are model uncertainties as to where this kink sets up most of the model solutions are showing this. Here's a look at several solutions for Christmas Eve. Notice they are all showing a band of moderate to heavy precipitation (purple and red shading), they differ significantly on where to place the band.
Various model solutions for precipitation on Christmas Eve
 As this forecast period nears, we should be getting a better handle on where the band of precipitation sets up. The good news is whatever falls should easily fall as snow as we rid ourselves of the above freezing temperatures. So if you are wishing for a White Christmas this year, your wishes just might come true!

Monday, December 8, 2014

Where's the Snow?

We're now into the second full week of December, and most of us in the Inland Northwest haven't seen much snow yet.  The notable exception is the folks in the Methow Valley, which received up to 18" from a storm just before Thanksgiving.  Outside of that, most locations have seen a dusting here, half an inch there, but nothing that survived for very long.  

So the first question often is "Has this ever happened before?"  Our climate records for this area generally go back into the early 1900's with some sites having data into the late 1800's.  And some sites have good, continuous data, while others are a bit spotty.  So lets take a look at a few sites that have good data and are representative of the area.

First we have to define how to look at the early season snow.  The first measure is fairly obvious: "How much snow do we normally have by this date?"

Avg Snow through   7 Dec
Total Snow 
7 Dec 2014
Lowest Snow through 7 Dec
Spokane Airport
0.3” in 1954
Wenatchee WP
0” in 2012
0” in 1904
Priest River
0” in 2002
Trace in 1943
Trace in 1969
0” in 1920

As you can see, in most locations, we're behind our Average snow fall through December 7th.  But we're still doing better than other bleak years.  So no records there.

Another way to look at it is the average date of the first inch of snowfall. 

Avg Date First 1” Snow
2014 First 1” Snow
Latest First 1” Snow
Spokane Airport
Nov 19th
Not Yet
Dec 23rd 1976
Wenatchee WP
Dec 6th
Nov 22nd
Feb 1st 1963
Nov 22nd
Nov 29th
Jan 4th 1990
Priest River
Nov 14th
Nov 25th
Dec 15th 1926
Nov 13th
Nov 22nd
Dec 23rd 1976
Nov 12th
Nov 22nd
Dec 11th 1936
Nov 20th
Dec 4th
Dec 25th 1954

Again, most locations got a late start, but nothing that would break any records.  The exception is the Spokane metro area, which has yet to even have it's first inch of snow.

So what's been the cause of this lack of snow?  Here's the average temperature for the Nov 1st - Dec 5th period.

As you can see, for the past 30 days it's been actually colder than normal for the Inland Northwest.  Of course, this is an average of 2 cold snaps with some rather mild weather in between.  Here's the daily temperature data for Spokane:

The blue bars are the daily temperatures, while the red and blue shading shows the daily records.  Spokane hasn't had any record highs or lows during this period, but they've come close.  The mild temperatures are certainly not conducive to snow.  But what's frustrating is that the cold snaps didn't equate to much if any snow.  Typically, cold air that moves in from Canada is very dry and doesn't provide much snow, which was the case with both of these systems.  But then eventually a Pacific storm will bring moisture into the area and it will fall as snow until the cold air can be pushed out of here.  But in both of these events, that didn't happen.  Instead, the Pacific storm went south of our area, leaving the Inland Northwest largely dry.

The percent of average precipitation shows that after a promising start to the wet season in late October, we've been fairly dry over the past 30 days.

So what has this meant for the mountain snow pack?  It's not good.  Here's the Snow Water Equivalent (SWE) analysis (i.e. how much water is in the snow that's on the ground).  The color shading represents the comparison of this year to how much is typically in the snow pack by December 8th:

It shows that most of our area is lagging behind normal at this point.  While this is bad news for ski enthusiasts, it's way too early to worry about it from a water supply standpoint.

Is there any hope of a change in the weather?  Not really.  Here's the 8-14 day outlook for temperatures and precipitation from the Climate Prediction Center (CPC).

The folks at CPC see warmth for next week across just about the entire US, while precipitation is expected to be near to below normal for mid-December.  This is an average outlook for a 7 day period.  So there can still be a weak snow event buried in there, but it's not likely.  And since this outlook ends on December 22nd, the issue of a White Christmas is starting to come into play.