Thursday, April 16, 2015

Warmer weather ahead

After one of the warmest March's on record (see previous blog entry here), April has been off to a cool start, with snow falling at times in the mountains, and even in some lower valleys at times.  Here is a look at the first half of April temperature anomaly map.

As the map shows temperatures have been running about 1 to 3 degrees below normal over the northwest.  Has the snow helped out our mountain snow situation?  Here is the latest map showing where we are at

The mountain snow pack has improved very little.  While the percent of normal values have increased slightly, they are still below 25% (dark red) or 25-50% of normal (red) for most locations across the Inland NW.  Several sites are at or below record low values dating back to the late 1970s or early 1980s.

The weather pattern is currently changing to a warmer one!  A strong ridge of high pressure is about to move in and will last awhile.  Temperatures Friday through Monday will be above normal, with the warmth possibly peaking on Tuesday.  Here is a look at a forecast model showing the general weather pattern for Tuesday.

500mb forecast map valid 5 am TUE from the 06z GFS Model run
The strong ridge will likely result in temperatures that are well above normal.  Here is our current forecast for high temperatures on Tuesday.

What about after that?  The ridge may weaken and allow for some cooling although there is quite a bit of uncertainty for the middle to end of next week.

What about May?  CPC just released their new monthly and seasonal outlooks this morning (typically issued the third Thursday of every month).

The May outlook is calling for a good chance for warmer than normal temperatures.

What about June, July, and August?

Looks pretty similar, with elevated odds for a warm summer.

Friday, April 3, 2015

Will the Inland Northwest see snow on Sunday night and Monday?

The Spring thus far has been fairly mild, and as a result we haven't had to worry about the threat of snow. The temperatures for March were some of the warmest if not the warmest on record for many locations.

March temperatures
But all weather patterns come to an end at some point and this will be no exception. So here is what the upper-level weather pattern for most of the month of March looked like. It showed a rather persistent ridge focused over the West Coast with the storm track nudged well north of our area
Mean 500 mb pattern for March 1-March 29th
However since the end of the March and continuing into April, the upper-level ridge has shifted to our east, allowing the upper-level trough to nudge into the eastern Pacific and the storm track to push through the Pacific Northwest.
Mean 500 mb pattern March 30th-April 1st
This has resulted in more typical springtime weather for the region including significantly cooler temperatures, and numerous afternoon/evening showers and thunderstorms accompanied by an Inland Northwest springtime staple: graupel. But despite the cooler weather, most of the valley locations, have yet to deal with snow. That might change though with the arrival of the next significant weather system. The model solutions are rather convincing that this system will arrive sometime between late Sunday night and Monday as the deep offshore trough heads inland.

500 mb pattern for Monday morning
Referring to  the map above, it suggests most of the upper-level energy will remain poised off the southern Oregon/Northern California coast, however look closely over extreme northeast Washington/north Idaho and notice the small yellow circles. These indicate the larger trough will also contain several small shortwave troughs.  If these troughs are accompanied by enough moisture and instability they can trigger small bands of moderate to intense precipitation, or what we
meteorologists term meso-banded precipitation or mesobands. Even more intriguing is these mesobands can often allow snow to fall (and possibly accumulate) at much lower snow levels than expected.

The odds are quite good that the region will see mesobands of precipitation form, the big question is where and what will the impacts be?

To answer the first question of where will these bands form, we first need to look at the positioning and track of any surface low tracks. Here is a look at four weather models we typically utilize and where they place the low (and resultant precipitation) as of 5am Monday morning.

4 model solutions with surface low position and 6-hour precipitation valid 5am Monday
As you can see above, all four models have a surface low located over the eastern third of Washington or north Idaho, however, the exact positioning and strength of the low is quite variable. The solution in the upper left corner is by far the most impressive solution. It has the strongest surface low (1000 mbs) and the heaviest amount of precipitation. The purple colors in this image represent precipitation amounts between 0.50-0.75" in a six-hour period. The other model solutions show a weaker low (1005-1006 mbs) and much lighter precipitation amounts.

When there are wide disparities between our core models we like to defer to ensemble modeling. This is where we take an initial model run and add small perturbations to the mix. The perturbations begin small but with time tend to grow. When the models cluster the positioning of a low, this boosts our confidence in the forecast, whereas if lows are strewn haphazardly across the region, our confidence is quite low. So here's a look at the SREF positioning of the surface lows for Monday morning.

SREF Surface low positions for 5am Monday

Although there are plentiful lows (L's) found across the Inland Northwest there is a wide scattering of their positions. The fact that there are plentiful lows is good from a standpoint of there is fair confidence of an event occurring. However, the wide scattering of the L's lowers our locational confidence significantly.  We can also look at the mean of all the low positions and the mean of all the precipitation data to come up with a preliminary snow forecast. In this case, the SREF is showing this as the mean snowfall for the 12hrs ending at 11 am Monday.

Mean 12hr snowfall ending 11am Monday
While these values themselves are not impressive (1-2" for the areas shaded in green) the fact that this model is showing such widespread snow is noteworthy. Another interesting thing we can look at from the SREF model is a plume diagram which shows all the suite of model solutions on one chart. So given the map above, it would seem locations north and east of Spokane as well as near the Cascade Crest would see the best chances of snow. So to hone our forecast a little more we will look at some plume diagrams to determine potential snow amounts. The first we will refer to is for Sandpoint.

Sandpoint snow plume diagram
Each line on this plot refers to one particular member of the SREF ensemble. In this case, most of the solutions are showing some snow on the right side of the diagram. The mean of the runs is denoted by the black line which is indicating a mean snowfall of 2". More impressive (but not probable) is the pink line which shows snowfall totals exceeding 8".  How about the plume diagram for Spokane?

Spokane snow plume  diagram
Even the Spokane plume diagram is showing some snow. Nothing compared to Sandpoint, but some snow nonetheless. The mean snowfall is right around an inch, however, there is one run which shows  totals nearing 5"!

Now despite these snow forecasts, the other factor to consider is how easily will this snow accumulate on the ground? The temperature forecast for late Sunday night and early Monday morning is for readings in the lower to middle 30s. Certainly cold enough for snow, but perhaps not enough for significant accumulations, especially in the Spokane area. After sunrise, temperatures will slowly climb into the upper 30s to middle 40s which suggest snow accumulations are even less plausible except perhaps on grassy surfaces. 

So in summary we are fairly confident a deep but compact surface and upper-level low-pressure system will track through the Inland Northwest producing locally moderate to heavy precipitation some of which will fall as snow. Where it will go and what time of day it hits will be critical for determining what it's impacts will be. Winter driving conditions are certainly possible for the Monday morning commute, especially north and east of Spokane. In the meantime, stay tuned to our latest National Weather Service Forecasts and don't put away your winter clothes quite yet. 

Thursday, March 12, 2015

When does Spring really start?

We're often asked the question "when does Spring really start?"  The easy answer is to look at your calendar.  It says March 20th.  This is "Astronomical Spring", which is the vernal equinox.  It's defined as the day when the sun is directly over the equator, and the length of a day is 12 hours no matter what your latitude (this isn't quite correct, but we won't go into that here).  But it doesn't take much thought to realize that this definition is only remotely linked to the weather.  And having one date for the entire Northern Hemisphere seems in some ways, ridiculous.  Spring starts in Miami and Fairbanks on the same day?

The "Meteorological Spring" is another definition.  It's defined as the months of March, April, May.  But again, this suffers from a "one size fits all" problem.  Surely there's a better way of defining Spring that varies from one location to another.  The Capital Weather Gang at the Washington Post addressed this same topic, and had some other ideas.  You can read their blog here.  

Some of their suggestions have this natural variability built in, such as the last day of measurable snow, last freeze, soil temperature, and first green leaves.  But many of these would be difficult to apply to all locations.  What about locations that don't receive snow, never freeze, or don't lose all of their leaves?  And if a location receives snow in May, does that mean that it's still Winter?

For central Washington, the Tree Fruit Research Center in Wenatchee tracks the average first bloom of the apple trees.  You can see those dates at this link.  The nice thing about a measure that tracks leaves, flowers, or soil temperatures, is that it will vary year-to-year (i.e. spring doesn't start on the same day every year).

The intriguing measure in the Capital Weather Gang blog was defining seasons based on average temperature.  They took the average daily temperatures at a location, and divided them into the coldest 1/4th (winter) and warmest 1/4th (summer), with spring and fall as the seasons in between.  If we do this for the Spokane Airport, we get the following:

Winter: Nov 11th - Mar 6th (116 days)
Spring: Mar 7th - Jun 8th (93 days)
Summer: Jun 9th - Sep 15th (99 days)
Fall: Sep 16th - Nov 10th (57 days)

While this is somewhat interesting, we're not quite sure if we agree with its accuracy.  Fall is the shortest season, no doubt about that.  But in reality, spring is the longest of all season in the Inland Northwest.  It typically starts in late February or early March, but it often lasts all the way through June.  We have a saying that summer in the Inland Northwest doesn't start until after the 4th of July, in Seattle, they claim that their summer starts on the 12th of July.  This means that in reality, spring lasts about 4 months while summer is just a shade over 2 months long.

For us, it's often easiest to classify the seasons by holidays:

Winter: Thanksgiving to President's Day
Spring: President's Day to the 4th of July
Summer: 4th of July to Labor Day
Fall: Labor Day to Thanksgiving

Friday, March 6, 2015's been warm! Will it continue?

Over the past 30 days the Inland Northwest has been abnormally warm, and indications are the Inland Northwest will experience well above normal temperatures next week, and maybe beyond.  Before we look ahead, take a look at the temperature anomalies over the past 30 days.

Temperatures have been running about 3 to 7 degrees above normal, with the greatest anomalies over North Central Washington, with even higher anomalies over portions of eastern Oregon, and southern Idaho.

The weather pattern ahead appears to be showing a very warm signal.  So what is going to cause this?  The atmosphere often goes through various oscillations that affect our weather pattern.  One of these that we will not dive to deep into is the Arctic Oscillation (AO).  This AO value is forecast to soar next week with the highest value seen in quite some time.  Take a look at the forecast for the AO

The black line is the observed and the red line is the forecast.  As you can see, the highest value seen since November is 3.5, and is forecast to reach a value close to 6 within the next week.
This combined with our current weak El Nino often produces warm temperatures.  Take a look at what typically occurs temperature wise with this pattern:

As you can see nearly the entire US usually sees warmer than normal temperatures in this scenario.

So, let's look at the upcoming pattern.  Here is the GFS model forecast for Tuesday

The model indicates a low pressure system over the eastern Pacific Ocean with a warm southwest flow ahead of it shown by the arrow.  This will usher in warm air from the southwest into Washington, Oregon, and Idaho.

Here is our forecast high temperatures for Tuesday, which is about 15 degrees above normal and near record values for many cities.

Now, here is the GFS model forecast for Thursday

The pattern looks similar.

How about next Saturday?  Does it look any different?

The warm pattern continues.  Regarding precipitation, this flow often brings in increased moisture as well.  At this time, it looks like the heaviest precipitation through the week will remain north of the Canadian Border.  The best threat for rain for the Inland Northwest will be Wednesday into Thursday.  

What about after that, here is the 8-14 day outlook from the Climate Prediction Center:
The pattern refuses to budge!  What about after that, what is the spring looking like?  Here is the CPC outlook for March, April, and May.

It appears that this warm weather pattern may last for awhile, with elevated odds of warmer than normal temperatures.  Of course, occasional rounds of cooler and unsettled weather typically occur in the spring.  But when all is said and done, we will probably look back at this being a warm spring.

Saturday, February 28, 2015

Update on Snow Chances

In our last blog, we talked about the chances for snow in our area on Monday and/or Tuesday.  Our conclusions were:

  • Any precipitation would fall as snow.
  • The overall weather pattern was not a good one for snow in the Inland Northwest.
  • Not all of the computer guidance agreed on exactly what was going to happen.
Two days later, those conclusions still hold true.  Usually at this point we have a pretty good idea of what's going to happen.  But in this situation, we're still no more confident than we were two days ago.  Here's why.

Here's the GFS forecast for Sunday evening.  The low is way up in northern Canada with a trailing cold front (blue line).

GFS forecast of precipitation (green shading) and sea-level pressure (thin lines) for Sunday evening.

Here's the forecast for Monday afternoon.

GFS forecast of precipitation (green shading) and sea-level pressure (thin lines) for Monday afternoon.

As you can see, the front splits.  Half of it goes into the upper plains while the other half drops down the West coast.  This leaves the Inland Northwest dry, which is pretty common for this kind of storm moving down from the northwest.

Let's look at the Canadian GEM model:

Canadian forecast of precipitation (blue green shading) and sea-level pressure (thin lines) for Monday afternoon

This looks very similar to the GFS model.  The GEM does bring a bit more snow into the Panhandle, but keeps eastern Washington dry.

So why isn't our confidence higher?  Because the ECMWF has a slightly different scenario.  It thinks the cold front will hold together as it passes over our area.  So much so, that it gives about 1-2" of snow to the Panhandle and eastern Washington, east of Moses Lake.

What's more is that each model has been consistent with itself.  Often, we'll see forecasts from the computer models that will change 12 hours later.  In those situations, our confidence is lower.  But in this case, each forecast from each model is very similar to its previous forecast.  So the GEM and GFS insist that the Inland Northwest won't see much from this storm, while the ECMWF continues to insist that we will see 1-2" of snow.  

So, are there any other computer forecast models?  Yes, there are.  Here's the UKMET forecast:

UKMET forecast of precipitation (blue and green shading), sea-level pressure (thin black lines) and 500mb heights (red lines) for Monday afternoon.

You can see that the UKMET has light precipitation over all of Washington.  This is similar to the ECMWF, just lighter on the precipitation.  If this were to verify, eastern Washington might see a dusting of snow.

The SREF model is an ensemble, which means that it's actually a group of 23 similar models.  Here's a display of the SREF forecast snowfall for Spokane:

SREF forecast of snow for Spokane

Of the 23 SREF models, only 6 of them have any snow for Spokane, and only one has nearly an inch of snow.

So given all of this, the odds are slim that eastern Washington will see any snow on Monday.  Not impossible, just not likely.  Thus, the forecast of "a 40% chance of snow showers" for Spokane.  The northern Panhandle has a bit better odds, but still not a slam dunk.

After that, we don't see any significant precipitation for at least another week.

Thursday, February 26, 2015

Is There Snow in our Future?

It's been so long since we've seen snow around here, that most of us have put away the boots and snow shovels for the season.  Is there any chance we'll have to get them back out of storage?  It's not likely, but there is a chance.  Let's take a look.

First, the stage will be set in the next couple of days.  A somewhat weak storm is moving down from the north today (Thursday), but this will largely miss our area to the west.  Some folks are getting some rain and high elevation snow, but mostly it's just clouds.  As this storm moves south of the region on Friday, it will pull down some cold and dry air from Canada.

GFS forecast precipitation (green shading) and surface pressure (thin black lines) for Saturday morning

Saturday  will be a rather raw day, with temperatures in the upper 30s to lower 40s and a brisk north wind.  This new air mass will mean that any precipitation from the next weather system will fall as snow instead of rain.  That next system will arrive Monday and Monday night.  There are three computer models that we look at for the weather 5 days out: the GFS (US model), the GEM (Canadian model) and the ECMWF (European model). 

Here's the GFS forecast for Monday night:
GFS forecast precipitation (green shading) and surface pressure (thin black lines) for Monday night
The GFS shows the majority of the next system sliding down east of the Rockies, which is what most of these storms do.  But you can see that the GFS does indicate some snow making it into the Panhandle and extreme eastern Washington.

Now take a look at the GEM model for this same time:

GEM forecast precipitation (shaded) and surface pressure (solid lines) for Monday evening

Not identical to the GFS, but similar.  The ECMWF (not shown) actually has a bit more precipitation for eastern Washington than the GEM or GFS.  Earlier runs of the ECMWF were showing a more significant storm for the Inland Northwest, but the more recent model forecasts have backed off on that idea.

Unlike storms in December or January, this system will be more spring-like.  What does that mean?  In the heart of winter, our atmosphere is typically very stable.  Snow tends to be more widespread and light.  But in the spring, the surface is warmer while the upper-atmosphere is colder.  This causes a more unstable atmosphere.  The result is precipitation which is more showery but can be heavier.  But it also can be more difficult to accumulate snow on the ground during the afternoon hours.

Temperatures on Tuesday might be rather chilly, with some locations not making it above the freezing mark.  If this happens, it would be the coldest day since January 3rd.

GFS forecast high temperatures for Tuesday March 3rd

Thus, at this point it doesn't look like a widespread heavy snow event.  Rather, some locations in the Panhandle and extreme eastern Washington could see a few inches of snow.  It's too early to have much confidence in this scenario.  In fact, it's more likely that this storm will stay to the east of our area, as they typically do.  

Stay tuned and we'll update this blog in a day or two as the forecast becomes clearer.

Monday, February 23, 2015

Mountain snow at record lows? Any relief in sight?

Many across the Inland Northwest may be wondering if our mountain snow pack is at near record levels and if there is any relief in sight.  We'll answer those questions in this blog.

First, let's look at precipitation in the mountains.  Given the lack of snow pack in the mountains, the assumption might be we haven't had much moisture.  As the image below shows, this is clearly not the case.  All of the Pacific Northwest mountains have received their normal precipitation since the start of what we call the Water Year (October 1st).

So, how does our snow pack look - not good!

Clearly, a good portion of what has fallen in the mountains has been in the form of rain.  This is especially true across the central and southern Washington Cascades, and Oregon.  Much of this rain fell early in the season (October and November) before a snow pack had been established.  There have been more mountain-rain events during the winter as well. 

So, now let's answer the question, is this a record for low snow pack?  Let's break it down by region, starting with Northeast Washington and North Idaho.  Each dot is a SNOTEL site showing where we are at this year compared to normal.  

More simply put...

red = awful snow pack
orange = not good
yellow = a little low on snow
green = doing well

As you can see, the snow pack is not good, and downright awful in spots.  Now, to see if this is a record we need to look at individual sites.  Let's look at Mount Spokane (Quartz Peak) and Lookout Pass.

Blue Line = highest recorded snow pack
Green Line = where we should be
Black Line = this season's trace (2014-2015)
Red Line = lowest recorded snow pack

So looking at the black line (this year's trace), both sites are close to a record low, but not quite there.  It's important to note that SNOTEL data started in the late 1970s and early 1980s.  Thus, the traces for "lowest" and "highest" snow pack ever only go back about 35 years at most.

How about Southeast Washington, it looks very bad.  See for yourself...

Let's look in the Blue Mountains at Touchet...

Also well below normal, just above the record low value.

And finally, the Cascades, how do they look?  The West Slopes are in bad shape.  Mission Ridge area also in bad shape.  Further north however, the mountains surrounding the Methow Valley are doing much better.

Let's see the traces from Stevens and Harts Pass

Stevens Pass isn't looking good, but is above record low value.  Harts Pass in the North Cascades is actually running right where they should be for this time of year.

So, while the snow pack is low this year, most areas are not at record levels.  You may be asking yourself "what's the problem?" since the mountains have received their normal precipitation, just in the form of rain instead of snow.  The mountain snow pack acts like summer precipitation in the western US.  By that we mean, in the West, we don't get a lot of rain in the summer.  But the mountain snow pack acts like rain in the mountains, and keeps our rivers running through the dry summer/fall months.  With a low snow pack, it will likely melt earlier than normal.  This will likely result in low stream flows in the late summer and fall months.  Whether this has an impact (e.g. irrigation, fish, etc) remains to be seen.

The Northwest snow pack typically peaks around April 1st, so we still have about a month to at least ease the bleeding.  Looking ahead, are changes in store?  Yes, but not in a big way.  Here's the GFS precipitation forecast for Thursday night and Friday.

GFS 24-hour Precipitation forecast ending Friday morning

The light green shading represents 0.01" to 0.10" of liquid, which isn't much.  The low pressure system (red L near Portland) is actually moving from north-to-south, meaning that most of the precipitation will stay west of our area.  For the mountains, all of this will fall in the form of snow.  In the lower elevations, the precipitation could be in the form of rain or snow.  But as is typical with spring weather here, snow that falls during the afternoon/evening hours probably won't accumulate.

Looking farther into the future, we get another chance of some light precipitation early next week.  Here's the same GFS forecast for next Monday and Monday night.

GFS forecast of 24 hour precipitation ending Tuesday morning, March 3rd

Again, not a strong storm by any means.  Other models (Canadian, ECMWF) are even less excited about this system.  So there's nothing coming in the next week that will bring much mountain snow.

How about farther into the future?  The 6-10 day outlook isn't encouraging.  Here's the expected temperature pattern:

Just about the entire lower-48 states will be below normal next week.  So that's encouraging.  But here's the precipitation outlook:

The dry weather continues for the western US.  That doesn't mean we won't see any more snow.  The GFS does show some other potential for snow into March.  But suffice to say, the weather pattern doesn't look cold and wet.