Thursday, January 29, 2015

Is Winter Over in the Inland NW?

As we expected, this winter has not been very wintry.  Aside from a few cold outbreaks, the temperatures have been very mild without much snow.  So, even though it's still January, folks are asking if winter is over.

First, the official outlook for February doesn't look very promising.  Above normal temperatures and below normal precipitation is expected for the Inland Northwest.

Of course, that doesn't mean we won't see any snow, and that every day will be warmer than normal.  But if you're a snow lover, our chances of seeing more white stuff are getting slim.

On that note, there is hope for some Inland NW residents to see some snow in the upcoming days.  A weak storm will move through the area on Sunday.  Right now, the timing is ideal for snow, arriving during the late night/morning hours.  Most locations will be too warm for snow.  But the northern valleys could see an inch or two.  Here's the NAM model meteogram for Republic, WA:

The snowiest forecast is 2", while the least amount is a half inch.  For Bonners Ferry, ID, the story is similar:

For Spokane, it's a more difficult call.  Here's the same meteogram for Spokane:

This plot shows both the NAM (in red) and GFS (in blue).  The GFS predicts an inch or 2 for Spokane, but this would fall with temperatures just above freezing, so it may be tough to get much accumulation.  And if the precipitation does start as snow, it would probably change to rain in the afternoon.  The NAM is decidedly less excited about the snow chances for Spokane.  This is largely because it expects the precipitation to start later in the day.

Another minor system arrives on Monday but the timing of it looks like mainly rain for the lower elevations, while the mountains will get a few inches of snow.  More storms are expected during the latter half of the week.  Again, timing will be a major importance in determining snow type for the lower elevations, mainly north of Interstate-90.  The mountains will see mostly snow but some rain is also possible for them as well.

So, to answer the original question, no, winter isn't quite over.  But don't expect any major valley snow storms.  Instead, we'll see some threats of lowland snow depending on the time of day (late night/morning), with rain favored for the afternoon/evening hours. 

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