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

Unusually wet February and March

Greetings folks, sorry it's been a while since we last posted to this blog, but we have been focused on implementing a new computer system for our office used to compose our complete suite of products and weather grids. Now that we have gotten our feet wet, it's time to discuss the unusually wet February and March the Inland Northwest endured.

So the weather pattern that took a dramatic shift in February unexpectedly continued into March. What was the cause? Recall that a highly anomalous ridge was fixed over the extreme eastern Pacific through the first half of the winter. Here's what it looked like on a 500 mb chart (approximately 17-18k ft). Notice the strong buckling in the flow just off the west coast. This is rather unusual and resulted in almost a record breaking dry spell for the first half of a winter.

500 mb mean map for 10/1/13-1/15/14

Well as the calendars changed to February, the unrelenting ridge gave way and opened the doors to countless storms which surged through the Pacific Northwest for the following 2-month period.
The mean 500 mb charts for February and March exhibited this ridge flattening.

500 mb mean map for 2/1/14-3/29/14

Notice although the ridge is still present (albeit flatter), its actually a much more favorable setup for precipitation since the amplitude of the ridge allows sub-tropical moisture to be wrapped into passing weather systems. Here's is what the anomaly of the atmospheric moisture (called precipitable water) looked liked for the period. Notice the well defined connection of moisture extending from southwest of the Hawaiian Islands northwest to the coast from northwest California to southern Washington (red, orange and green shading).

Precipitable Water Anomaly 2/1/14-3/29/14

So how wet was the two month period? Very was the answer. The map below shows the departure from normal of precipitation for February and March. Every location saw wetter than normal conditions, with the Cascades and Idaho Panhandle mountains leading the pack with well over 10" more than the normal amount of precipitation.

Rainfall departure from normal February & March 2014

From a percentage standpoint vs. normal it was also an impressively wet period. Note the dark blues and purples over the Cascades and north Idaho mountains, indicating where precipitation amounts were 2 to 4 times the normal for that period.

Rainfall % of normal February & March 2014

The unusually wet period has also brought the snow water equivalent (amount of water in the mountain snow pack) to normal or just above normal over the entire region. Note that although conditions were moist over Washington, Idaho, and western Montana, things were still quite dry across Oregon and California (not shown).

Not only did a considerable amount of precipitation fall, but it also did so on an unusually high number of days. Here's a look at the numbers compared to the normals.

Days of measurable rainfall for various locations across the Inland Northwest Feb-Mar 2014

Over locations where the temperature was cold enough, most of this equated to snow. In Holden Village, WA the snowfall for the two-month period was 180.7". That shattered the old record of 166.7" (set in 1999). Not quite as impressive was the 14.0" which fell in Lewiston, ID. This was the most since Feb-Mar in 1985.

So will this unusually wet weather continue? Showers are still fairly common this time of year. In Spokane we typically see some precipitation about 50% of the time during the first half of April. That number drops to around 40% of the days by the end of the month.  In Wenatchee and Moses Lake, the percentage of wet April days is a mere 25%!

The 8-14 day outlook for precipitation shows near normal conditions for most of eastern Washington and north Idaho.

8-14 day precipitation outlook. 

Well that was a quick recovery!

Our blog posted on 2/6 hinted that changes were coming which would be conducive for snowfall across the Inland Northwest. While that prognostication proved true, we had no idea just how much snow was going to fall. Since February 7th the region has been pummeled by a relentless parade of storms. Just look at some of these snow totals below.

All of these locations have seen more than the normal amount of snowfall for February in the brief two-week period. Some locations much more. The hardest hit locations have been near the Cascades with most locations seeing 2-3x the monthly normal already. While the 100" that fell at Holden Village was not a record (117.2" fell in February 1999), there is still more snow expected through the remainder of the month. The record could also be attained at Plain (66.5" in 1937). The Lewiston number isn't a record either but it is the most amount of snow that has fallen during the month of February since 1985. Below is a picture of what the snow depth looked like in western Chelan County.

Buried pickup truck in western Chelan County...care of Chelan County Sheriff Office. 

So how has this snow impacted what was nearly a record low snow pack earlier this winter. First lets take a look at some individual SNOTEL sites and then a broader scale map of the region. For those not familiar, a SNOTEL is a site, typically set in a remote mountain location which measures things such as temperature and snow depth. You can check this link for more details.  So here's the data from Harts Pass SNOTEL located in western Okanogan County at an elevation of 6490'. If we just look at the blue dotted line it suggests that since the 9th of February nearly 40" of snow has accumulated. While 40" is a good amount of snow it is a large underestimation since the snow undoubtedly compacted from the shear amount that's fallen. Since February 6th, nearly 8" of precipitation has fallen (red line). If we use a climatologically average snow to liquid ratio of 14:1 that would yield around 112 inches of snow.

Hart's Pass in western Chelan County. 

Now if we look at a different site, (Blewett Pass in Chelan County) in a different format we can compare how we stack up compared to normal conditions. The important lines to look at are the navy one which shows the snow water equivalent for the 2014 water year (October 2013-current) and the lavender line which show the median conditions. Notice the navy line almost went straight up over the past couple weeks, falling just shy of the median. That is an awfully swift recovery.

Blewett Pass SNOTEL 

Now lets zoom out a little and look at things from a regional perspective. Below is a look at the snow pack as of the middle of January. Notice the widespread yellow and orange shading over the Cascades and some reds over the Olympics and Oregon Cascades. This denoted near record dry conditions over much of the region.

Snow water equivalent as of 1/14/14

Now fast forward just over a month later and the recovery has been rather impressive. Most of the Washington Cascades have now nearly attained a normal water equivalent in the snow pack, while the Clearwater Mountains of north-central Idaho have actually exceeded normal. Meanwhile the mountains stretching from the Okanogan Highlands to extreme northern Idaho have generally kept pace since mid-January.

Snow Water Equivalent as of 2/20/14

So will this wet trend continue? If we look at some of the model prognostications the answer is a resounding yes. Below is a look at precipitation forecast using some ensemble model data and associating it with similar weather patterns from the past (termed an analog). This analog suggest that from now through the end of the month, up to another 1-2" of precipitation can be expected near the Cascades with just a little bit less for the Idaho Panhandle.

Precipitation analog through 4pm  2/26

Does a dry winter lead to a bad fire season?

We have received many questions from the public inquiring whether our dry start to the winter will equate to a bad fire season this summer. Common sense would suggest that if the fuels begin the fire season on a dry note that should increase the risk of fires later in the year. But is that necessarily true? Before we address that notion, lets review the weather pattern thus far this water year and what the weather looks like for the remainder of the winter. For climate purposes in the western U.S., the water year is defined as the 12-month period beginning in October. Since October, the western U.S. has generally been affected by a persistent ridge of high pressure fixed just off the coast. Meanwhile, the remainder of the U.S. has seen a rather persistent trough of low pressure. This scenario is reflected in the mean 500 mb (~18k ft MSL) seen below. Notice the large buckle in the flow centered just of the western coast of North America and the dip over the eastern half of the continent.

500 mb pattern October 1-January 12 2014

This is a rather unusual flow pattern. The typical flow pattern for this time period generally features swift west-southwest flow into the region as seen on the map below. This southwesterly flow often draws deep moisture from the sub-tropics and slams it into the Pacific Northwest (think Pineapple connection or atmospheric river). This setup produces frequent and heavy precipitation, especially west of the Cascades. 

Typical 500 mb pattern October-early January.

When we compare the top image (October 2013-early January 2014) to the bottom were are left with some pretty sizable departures from the normal which is termed an anomaly. The biggest anomaly this wet season was the huge red bulls-eye centered over the Gulf of Alaska. This is the culprit responsible primarily for our unusually dry winter thus far. 

500 mb anomaly (red=higher than normal heights, blue=below normal heights)

So climatologically speaking, how has that translated to the precipitation departures from normal across the area? As you can probably guess, the precipitation this wet season has been quite meager.  Most locations across eastern Washington have seen less than half the normal amount of precipitation with locations near Wenatchee, Omak, and Moses Lake seeing less than 25% of the normal precipitation (dark red). As of January 13th, both the Omak and Wenatchee areas have received less than an inch of precipitation since October 1st, and both were the 2nd driest on record, only trailing an even drier 1976. 

October-December 2013 precipitation percentages of normal. 

An obvious implication of this lack of precipitation was an even more impressive lack of snow pack and the water contained in that pack. Needless to say our snow pack is running much below normal, especially in the Cascades where totals were hovering between 50-75% of normal (yellow and orange shading). Conditions were significantly worse across Oregon and California (not shown).

Current snow water equivalent 

So being as dry as it's been can we expect to recover to near normal conditions by the end of winter. Based on past winters with similarly dry beginnings, the answer is no. See this previous blog link for more details. So does the weather in the next 8-14 days look promising for ending or at least lessening this dry winter pattern? The answer to that is also no, as as the strong eastern Pacific ridge is expected to rebuild and remain fixed over the region (note ridge axis right off the coast) for the next couple weeks. Below is a map of the mean 500 mb pattern expected over North America through the end of the month. 

Mean 500 mb pattern expected through end of January

This translates to little promise for appreciable precipitation (dark brown area over Washington is a 60-70% chance of below normal precipitation) 

Precipitation probability Jan 24-30, 2014

Based on the current dry conditions and little improvement expected anytime soon, can we assume that will translate to a busy fire weather season? To determine that answer we took a look at annual fire acreage across the Inland Northwest since 1970 and compared it to the winter precipitation conditions that preceded it. We first took a look at the precipitation measured at the Spokane Airport between October 1st and January 15th and ranked those values. We then compared these precipitation rankings to the amount of acreage which burned in the following fire season. Below are the results. 

Of the 10 driest October-January 15th periods in Spokane,  4 of the following fire seasons resulted in above-average fire acreage (average burned acreage is 61,000), while 5 saw well below-average fire activity. That alone would suggest there isn't any correlation between a dry winter and a bad fire season.  In fact, the driest year, 1976-77 only resulted in the 26th ranked fire season. But note that 4 of the top 6 fire seasons are in this list (2001, 2012, 1994, 1970).

Top 10 driest Oct-Jan 15th since 1970  in Spokane and the following amount of burnt acreage

  If we rank the seasons based on precipitation in Wenatchee, the message is still muddy. Four of the following summers were active fire years, but the other 5 were below normal.

Top 10 driest Oct-Jan 15th periods since 1970 in Wenatchee and the following amount of burnt acreage

This suggests that a dry beginning to winter doesn't necessarily lead to a busy fire season. What about the opposite? Does a wet season lead to a quiet fire season? 

Top 10 driest Oct-Jan 15th periods since 1970 in Spokane and the following amount of burnt acreage

Similar to the dry winters, the numbers are about evenly split. Four summers following wet winters had active fire seasons, and 5 were less active.  In fact, the wettest Oct through mid-January (2006/2007) was followed by the largest fire season since 1970.

              

Top 10 driest Oct-Jan 15th periods since 1970 in Wenatchee and the following amount of burnt acreage

In Wentachee the 10 wettest winters since 1970 led 6 of the quietest fire seasons (ranks of 35 or higher). So perhaps a wet winter could yield a fair prediction to a slow fire season, especially when considering the Wenatchee precipitation. After all, most of the fire acreage in the Inland Northwest typically burns near the Cascades. This all makes sense, since a wet winter will typically yield a large snow pack which will take longer to melt.  So the higher elevations have no chance of wild fires until much later in the summer, if at all, which reduces the amount of forest available to burn during the summer.

So what does all this mean?  Most large fire seasons are the result of the combination of lots of lightning and dry fuels.  Just because you have one, doesn't mean you'll get the other.  So even if you have a dry winter, a quiet lightning season will result in a quiet fire season.  However, as we saw from the tables above, a dry winter lead to 4 of the top 6 fire seasons.  Meaning, if you do happen to have an above-average fire year, it has the potential to be a really bad year.