A wintry mess before the very wet and milder arrives next week?

So as we mentioned in our previous blog post, we are expecting to finally break out of this latest cold and dry weather pattern by early next week. So what is going to be responsible for this change? Here is a look at the current weather maps which are supported by what we see on satellite (a good sign if we want to follow a particular weather model):

500 mb map (left) with Integrated Vapor Transport (shows atmospheric rivers denoted by bright colors). Water vapor satellite imagery  on right. 

The most noticeable things on the left chart are the large high pressure ridge centered over the Inland Northwest (Large H) as well as the atmospheric river developing north and west of Hawaii. Over the next several days we expect the presence of the high to persist over our area. This means more fog, low clouds, and very cold temperatures in the valleys with light winds. This is because high pressure systems in the winter typically lead to strong inversions (temperature increasing with height). This is especially true when there is widespread snow cover over an area and clearing skies. This is certainly the case right now as we have seen many mornings recently with sub-zero temperatures and mainly clear skies. Here is a look at just how strong the inversion was this morning at our office.

1/14/17 4am weather sounding at NWS Spokane. The red line shows how the temperature varied with elevation. The farther to the right the red line is the warmer the atmosphere is. Notice how the temperature increases all the way from the ground up to 4700'. That is what we would call a strong inversion. 

So why are we telling you about this inversion? Because what happens between now and Monday night will be critical into producing an accurate weather forecast. But more on that later. So first, what do we expect to happen to that atmospheric river forming north of Hawaii? By Monday night here is what most of the weather models are showing.

Atmospheric river position 10 pm Monday 1/16/17

According to this we should see the ridge being rapidly replaced by the atmospheric river moving in from the Pacific. Not only is this air stream moist, but it will be warm as well. So that should mean we would see a rapid transition from the current chilly air mass to a much milder one, right?. In other words we should see any threat of snow changing to rain and probably in a short amount of time. But if only it were that easy! This upcoming system will likely provide us with all sorts of weather conundrums simply based on the inversions we showed you earlier.   Here is an example from Moses Lake.

Weather Sounding from Moses Lake 4am Tuesday with the freezing line denoted in pink.

So as the precipitation arrives it could begin as all snow as the entire atmosphere will have temperatures below freezing. But as the atmospheric river comes into the area (being ushered in by southwest winds of 30-40 mph 3000-10,000 ft above the ground) the temperatures above the ground will warm faster than those near the ground and this will create what we call a melting layer or warm nose of air aloft. What this means is any snow which forms in upper portions of the atmosphere will melt as it traverses the melting layer. If the melting layer is deep enough it will melt anything which falls into it. If it's not deep enough it will only partially melt the snow falling into it. In this case we are looking at a melting layer around 4000-5000' thick which should be plenty deep to melt most of the snow falling through it. That's not the whole equation though. What happens after that depends on how deep the freezing layer near the ground is. For the sounding above the freezing air near the ground is around 1500' thick so the question is "is this deep enough to completely freeze what melted before hitting the ground"? If the answer is yes the melted snow would completely refreeze producing sleet or ice pellets. If its not deep enough the melted snow will not refreeze and instead fall as a very cold rain which can easily refreeze once it contact a sub-freezing object on the ground. Here is a nice weather schematic the NWS office in Omaha created that shows the complexity of forecasting winter weather precipitation types.

So what does the profile in the Moses Lake sounding favor? That is always a tough question to answer as any perturbation in the strength/depth of the above ground melting layer and near ground freezing layer has a direct impact on the precipitation type.  If nothing were to change in the models we think this would lead to freezing rain. However the no change argument isn't one that often appears as much as we would desire. Since this event is still a few days away there are numerous answers as to what might occur. While we are confident we will see precipitation, we are far less confident in what the prevailing type of precipitation will consist of. Each model is advertising a different scenario. When we see such great differences we sometimes like to defer to what we call an ensemble model solution. This is were we take the same initial model and introduce very small changes at the very beginning of the run. These small initial changes can lead to vastly different solutions as you get farther into the forecast. So here is a snapshot of the various precipitation chances associated with the incoming weather make during the Tuesday morning commute.

4-panel ensemble solution for the precipitation type on Tuesday morning. Upper left corner=Sleet chance, upper right=Snow chance, lower left=freezing rain chances, lower right=measurable precipitation chances

The image above is about as messy as a weather forecast can get around here. As for sleet or ice pellets (upper left), we'd expect to see the best chances to occur over the western Columbia Basin and into the northern valleys east of Omak. The snow chances (upper right panel) would be highest near the north Cascades, northeast Washington, and over the northern Panhandle. Meanwhile the threat of freezing rain looks most prevalent over the remainder of the the Inland Northwest. But that is what the latest ensemble model runs suggest and this could change significantly as the event nears. Previously we were expecting to see a lot more snow with a brief changeover to freezing rain and then all rain. If we see snow first the freezing rain impacts could be somewhat mitigated as freezing rain falling onto fresh snow has much less impact on driving conditions then freezing rain falling onto bare pavement. Stay tuned to the latest changes in this evolving portion of the forecast.

Eventually (how long is uncertain) the atmospheric river will bring the warm moist over the entire region and mix it down to the ground with the most of the snow or freezing rain chances remaining near the north Cascades or over the far northern valleys. Here is what the temperature profile looks like for Moses Lake at 10 am Tuesday. Notice it's entirely above freezing which means we would see all rain.

10am Tuesday temperature profile for Moses Lake

Once the lower atmosphere warms above freezing we expect it to remain above freezing through the end of the event.The end of the event will likely consist of a good amount of time as the atmospheric river remains fixed over the area. Here is the expected position on Wednesday afternoon and then on Thursday.

Atmospheric River position on Wednesday 1/18/19 4pm.

Atmospheric river position by Thursday morning 1/19/17

That means the atmospheric river will be over the region beginning Monday night and persisting into early Thursday. Needless to say that can result in a lot of precipitation. Just how much are we expecting? Here are four distinct model runs.

72 hour precipitation ending 4 pm Thursday

Surprisingly there is very good agreement for a forecast this far out. We are quite confident that the precipitation over the western Columbia Basin and in the lee of the Cascades is a little bit overdone, and near the Cascade Crest and over north Idaho it might be underdone. Nonetheless these are some very impressive precipitation amounts. Looks like the eastern third of Washington and the Idaho Panhandle should generally see anywhere from 1.50"-3.00 inches. If there were no snow on the ground this alone could produce some issues with low-land flooding and perhaps some ice jam flooding as the ice breaks up on area rivers. However that is not the case as we have an appreciable amount of snow on the ground. Here is a look at the approximate amount of water tied up in the snow pack.

That is quite a bit of water or potential runoff sitting on the ground and will only add to the runoff totals. Based on the forecast temperatures, we expect to see temperatures remaining above freezing from Tuesday through much of Thursday (including nighttime low temperatures). The above freezing temperatures will combine with breezy winds resulting in a great setup for appreciable melting. The best melting potential will occur the SE third of our forecast area with the least amount near the Cascades and far northern valleys. We still expect to see most if not all the snow to melt over the Palouse, LC Valley, and eastern Columbia Basin. So combining the expected rainfall with the water from the snow melt could equate to up to 2.50 to nearly 5.00 inches of water which could potentially runoff. This increases the odds for flooding appreciably. Here is a map of where we anticipate the greatest flooding problems to occur.

We expect most of the flooding issues will involve low-land flooding, ice jam flooding, and urban flooding (think snow clogged storm drains...clear them now if you can!). Small rivers and streams could also flood, especially over the Palouse and nearby areas. As of now we are not expecting any mainstem flooding, however that could change especially if we melt more snow than expected.

If we look into the longer range weather forecasts, we don't expect to totally dry out, but we will cool considerably. Not down to current levels, but certainly enough to refreeze what doesn't melt. The pristine snow cover we have over us will look completely different by next Friday and could feature hard snowpack and frozen slush.

Please stay tuned to the latest forecasts for this upcoming situation...it will likely be a messy situation and is certainly subject to change. Oh yes...the countdown to spring is now 64 days and counting.

Is a significant snow event possible for Spokane,Coeur d'Alene or the Palouse Tuesday morning?

Although the weather of late has been quite wet, the overwhelming majority of the precipitation has fallen as rain (or melting snow) in the valleys of eastern Washington and north Idaho including the Spokane/Coeur d'Alene area and the Palouse. That might change however as an unusual weather pattern materialises on Tuesday morning resulting in the possibility of significant snow. So what is the weather pattern which might lead to this unusual snow? To get significant snow in the valleys this time of year you need several things. First, you want to have a fairly strong upper-level trigger. In this case, we will be dealing with a slow moving upper-level disturbance or vorticity maximum.

500 mb pattern 2 am-2 pm Tuesday

The emphasis is on slow. The loop above shows the disturbance quite nicely between 2am-2pm Tuesday. The green area represents where the forecast model is placing the best moisture. Notice the feature also looks like a semi-circle indicating a tight circulation in the upper atmosphere which should lead to increased upward motion.

Another ingredient we like to see to enhance this upward motion is deep instability. This helps enhance the upward vertical motion between the ground and the upper atmosphere. So will the atmosphere be unstable? You bet. The orange and red shading indicates where we expect to see the most instability (however it's unstable everywhere across the region.

Lapse Rates through the mid-atmosphere 2am Tue

So couple the presence of the instability and the upper-level disturbance and here is where one model solution suggests we will see the greatest lift. Areas in purple and light purple are where the models expect to see the greatest ascent and thus the best potential for precipitation.

Upward motion through the mid-atmosphere 2am Tuesday

Finally, you need an atmosphere which is cold enough to support snow. This is the least confident part of the forecast. Model solutions are suggesting that the temperatures before the precipitation arrives early Tuesday will be above freezing, but then they slowly fall as the precipitation intensifies during the morning at least over a very small area (denoted in light or dark blue).

8am Tuesday Temperatures

So we have the ingredients in place for a heavy precipitation event (albeit fairly localized). Now the question is where will this band of precipitation set up and will it become heavy enough that it can produce accumulating snows in the valleys. That is a tough question to answer since there has been considerable model variability. What we can gather is more often than not the model solutions have depicted a northwest-southeast or west-east oriented band of precipitation similar to the two panes in top portion of the image below. Some of these amounts are quite impressive. The areas in purple show precipitation amounts above 0.75 inches and the red areas are showing more than an inch. So is it possible that most of not all this will fall as snow? It is certainly a possibility. 

12hr precipitation amounts forecast between 2am-2pm Tuesday

So just how much snow are we talking about?  Well here is a plume diagram showing 27 different model possibilities or solutions for the Pullman/Moscow area. While some of the models are hinting at a little more than a trace of snow, the most impressive solution is showing nearly 8 inches! The average snow amount from all the variations is just over 1" of snow.  For the Spokane area, the forecast is nowhere close to as snowy as for Pullman. The maximum snow forecast is around 2.25" but the average is around a quarter inch. That's a lot of variation, to say the least. 

Plume Diagram for snow for Pullman (Click image for larger view)

Plume diagram for snow for Spokane (Click image for larger view)

So what do we expect to happen? We are fairly confident we will see a band of moderate to locally heavy precipitation develop on Tuesday morning. Again the question is where will this occur and will the atmosphere be cold enough to support heavy snow? The other variable is will the ground be cold enough allow accumulations to occur on the roads? If the snow gets heavy enough (quite possible) we suspect the answer will be yes. Motorists are urged to prepare for the possibility of winter driving conditions for the Tuesday morning commute. Chances are the afternoon commute will be much easier as any threat of accumulating snow diminishes. Hopefully, as the event nears our confidence will grow as to where we expect to see the greatest risk of significant snows. 

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

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!