Severe thunderstorms tomorrow? It's possible.

After a seemingly endless barrage of weather systems, yet another is already beginning to show its stripes. Take a look at the satellite picture below. This is a water vapor image.Notice the green area covering the western portions of Oregon and Washington. That's associated with a plume of sub-tropical moisture which should deliver rain (and high mountain snow) to most of the Inland Northwest between tonight and Thursday morning.  Also notice the dark area over the eastern Pacific and the kink in the blue lines located along 130w. This is associated with a fairly vigorous shortwave trough. This trough will become a crucial player for our weather across the Inland Northwest by tomorrow afternoon.

10pm PDT Water Vapor image and 500 mb heights

So as mentioned before we expect widespread rains (and mountain snow) tonight into early Thursday. This will likely prime the atmosphere full of moisture and could set the stage for some active weather tomorrow afternoon across portions of the Inland Northwest. Lets look at some model data for details. First we will start with a course resolution model, the 90km GFS. Here's a look at what that models is showing as far as the shortwave trough moving through the region. The first image shows the previously displayed 500 mb heights combined with what we term Q-Vector convergence. This is a fancy term that essentially shows upper level lifting. In this case the purple shading shows where the lifting in the upper levels is strongest. The top image shows the trough extending from the central Washington Cascades to the SE corner of Washington around 11 am with the best upper level lifting focused over most of the region. The second image shows the same thing only at 5 pm. Notice by this time the trough is focused along a line from Sandpoint to Missoula, however the strongest lifting by that time has shifted into eastern Montana and SE British Columbia. That's all well and good but what does that translate to weatherwise?

11am PDT Thursday 500 mb heights and Q-vector convergence

5pm PDT Thursday 500 mb heights and Q-vector convergence

Lets take a look at one more 90km GFS image before moving on. This time we will look at CAPE values. CAPE or Convective Available Potential Energy is simply the amount of potential energy that can be released should we be able to lift an air parcel. You can read more about it here if you desire. Suffice it to say, the higher the CAPE values there more energy or explosiveness there is in the atmosphere. So what is explosiveness tomorrow afternoon? Its actually fairly impressive at least for this region and this time of year. Notice the axis of the highest CAPE values extend from the NE corner of Washington southeast toward the Clearwater Mountains southeast of Lewiston. Keep in mind this area of instability coincides with the passage of the shortwave trough and upper level lifting...a good thing for producing thunderstorms.

CAPE forecast for 5pm Thursday

The parameters shown above are what we meteorologist have looked at for many years, however we are now also getting more refined and specific data from finer resolution models and simulated radar data. So what is this newer model data showing? Its actually quite interesting. Here a look at simulated radar for 5 pm Thursday that was run 42 hours previously (at 11 pm Tue). Notice over NE Washington and the SE corner of Washington there are a pair of bright orange and yellow cells. This model was suggesting that there could be thunderstorms over this area. We see this a lot from the finer resolution models but often can't put a lot of faith in them unless there is some consistency.

Simulated 42hr Composite reflectivity (radar) from 11pm Tue Model run

 So has there been consistency? Lets see the next model run. This one was run 6 hours later and sure enough there are the two yellow and orange areas over NE Washington and a slightly larger one over SE Washington.

Simulated 36hr Composite reflectivity (radar) from 5am Wed  Model run

So that gives us some confidence. Now how about the latest model run? If you look at the image below you can see that the information isn't  quite as convincing as the previous two but it still showed two yellow and orange areas in the same general vicinity. Interesting. So is this enough information to convince us that we will see severe thunderstorms tomorrow afternoon. Probably not, but it does at least hint at a possibility of it. Our confidence is much higher that we will see some thunderstorms...a few of which will produce hail and possible some gusty winds. If the latest models were showing what we see depicted from northern Louisiana toward northern Illinois our confidence would be much higher!

Simulated 24hr Composite reflectivity (radar) from 5pm Wed  Model run

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

How long can this stagnant weather go on?

By now, most of you may be getting tired of our boring, foggy weather.  On the positive side, you haven't had to shovel any snow, and the roads have been in decent shape, except for some occasional icy spots from freezing drizzle.  But the gray skies do tend to wear on some folks.  Here's what it looks like from space.

Visible Satellite 1/23/14

That white area in the middle of the picture is the fog and stratus that has filled in the Columbia Basin of eastern Washington and north-central Oregon.  You can see some mountains above the fog near the Washington/BC border, as well as the Washington Cascades.

Why are we stuck in this pattern?  High pressure over the western US is steering storms away from our area.  As we've discussed in past blogs, this is causing a severe drought in the western US.  But for many in the West, they're enjoying sunshine and warmth.  Take a look at this satellite image to see what we mean:

Western US Visible Satellite picture 1/23/14

So why are we so cloudy while the rest of the West is sunny?  Professor Cliff Mass of the University of Washington wrote about this in his blog.  You can find it at:  http://cliffmass.blogspot.com/2014/01/cloud-bowl-of-eastern-washington.html  We highly recommend it.

But in short, the reason is three-fold.  First, the Columbia Basin acts as a topographic bowl.

 The Columbia Basin is bordered by the Cascades to the west, the Selkirks to the north, the Panhandle mountains to the east, and the central-Oregon mountains to the south.    A perfect bowl.  Note in the above picture of the western US, the Central Valley of California also provides a nice elongated topographic bowl.

Second, you need moisture in order to form fog.  And while we have been very dry, we still have had weather systems providing some moisture.  Coupled with the cold nights, and you get fog and stratus to form.  The Central Valley of California has been so dry this winter, they can't even produce fog! 

The third ingredient is a lid to put on the bowl of fog, to prevent it from going anywhere.  This is provided by the ridge of high pressure.  High pressure results in sinking air.  Sinking air warms. So while at the surface we're stuck in cold, sub-freezing temperatures, the air above us is much warmer.  Locations in the mountains as high as 5000-6500'' have been reaching the mid-40s each day.   The high pressure also keeps storms away from our area.  Storms mean wind, and wind mixes the air which dissipates fog. Below is a temperature and moisture sounding or profile taken at our office on 1/23 at 3 pm. There are two pink lines on this chart, the one on the right denotes how the temperature changes with height. The line on the left is the moisture profile. The farther away the two lines are from one another, the drier the air.  So on this sounding, most of the atmosphere is clear and dry. The exception is near the ground where our temperatures have been stuck in the mid 20s to lower 30s for days and the sun has been a rather rare site. Notice how the temperature increases with height and peaks at 47° at an elevation around 6500'. So if you seeking sun and warmth, the mountains are the place to go. 

Spokane temperature sounding 3pm Thursday. Light pink line or right denotes the temperature profile. 

One positive of this weather has been the beautiful natural flocking which has adorned most of the objects stuck in fog for the past week. This flocking is being produced from the deposition of small sub-freezing water droplets on objects resulting in riming. The rime in this event is covering everything from trees, fences and power lines.  We wrote about this back in December.  You can read about it at: http://inlandnorthwestweather.blogspot.com/2013/12/another-kind-of-white-weather.html  

Here's some pictures from our office:

So this kind of weather can't last forever, can it?  No, but it can last for a few weeks.  This episode started on January 16th, and today is the 24th.  Yep, it's only been going on for a week.  Seems like a month though.  Have we seen longer episodes in the past?  Of course.  One of them occurred during the 1976/77 drought.  After a few storms brought rain and snow to the area in the middle of January 1977, a huge area of high pressure developed over the area, just like our current episode.  Spokane and the Inland NW were stuck in the fog from the 19th of January through February 10th.  That's 22 days!  Although there were a few peaks of bright sunshine during that streak they quite brief.  A weak weather system moved through at the start of February, but it was too weak to get rid of the fog.  Instead, they had some freezing rain.

How long will our current episode last?  Aside from a few possible sun breaks, we're likely stuck in the fog through the weekend and into early next week.  There's a outside chance that some locations in the Panhandle and northeast Washington will see more sun on Monday.  This is due to an arctic high pressure system centered over eastern Montana and the Dakotas that may push a bit of drier air into our area from the east.

7am 1/27/14 precipitation and sea-level pressure forecast from GFS model. 

Despite the presence of the weak system notice the 500 mb ridge (below) remains very amplified and basically centered over the Pacific Northwest. 

500 mb pattern for 7am 1/27/14  GFS model.

Starting on Tuesday, some very weak Pacific weather fronts might be able to break up the low clouds as well as bring us a dusting of snow as the ridge gets progressively weaker each day.   By the end of next week, there is more confidence that the weather pattern will have changed and we can get a respite from the fog and low clouds.

4am 1/28/14 500 mb map from GFS.
Ridge gets flattened a little by weak front. 

7am 1/30/14 500 mb map from GFS.
Ridge is virtually gone now over PacNW and is replaced by a trough off the coast. 

And this ridge breakdown could actually persist for more than a couple days. The map below is the mean 500 mb pattern projected for the period from January 30th-February 3rd. Notice the ridge has generally shifted into western Alaska and has left a broader trough over most of the US, including our area. The 8-14 day outlook (bottom image) through February 7th looks similar as well. 

6-10 day outlook. Mean 500 mb map. 

8-14 day outlook., Mean 500 mb map 

Snow, Rain, Wind, (and Thunder?)

Yesterday's weather system brought a nice 1 to 3" of snow to many locations.  You can see an extensive list of snow reports on the National Weather Service website.  Now we have Storm #2 arriving 24 hours later.  This one will be a little different in a couple of ways.  First, this storm is a little wetter and more extensive than the first.  This means more people will see precipitation.  Here's the radar forecast from the HRRR model valid at 5pm this evening:

5pm radar forecast from the HRRR model

This is a forecast from a computer, not an actual radar image.  But it gives you an idea what the radar will look like around 5pm.  And just about everyone in the Inland NW will be seeing some sort of precipitation at this time.  Which leads us to the other difference.  While Storm #1 was all snow, this one will be more of a mixed bag of rain and snow.  The HRRR forecast for precipitation type at 5pm is shown below.

5pm precipitation type forecast from HRRR

This graph is a little hard to read, but the horizontal blue lines represent snow, while the vertical green lines are for rain.  The HRRR expects the precipitation by 5pm to be rain south of a line from Deer Park to Grand Coulee.  This includes Spokane and the Palouse.  The precipitation may initially start in the metro area as wet snow, but it won't be able to accumulate much and will change to rain later this afternoon. Also notice there are some small pockets of red scattered around the region. This represents a chance of freezing rain. If freezing rain really does occur it will be rather isolated and likely quite brief. 

Here's the storm total snow forecast from the National Weather Service.

Storm total snow ending 4pm Thursday

Most of the valleys across the north (Republic, Colville, Sandpoint) will see all snow and pick up 2-6" of snow, while the mountains will receive up to a foot.

Storm #3 will follow on Thursday afternoon/evening this will be a weaker system.  It will once again bring rain or snow to Spokane and the Palouse while the northern valleys will pick up a little more snow.

Storm #4 is still taking shape but it consistently looks like it will be the strongest of the bunch.   Today's GFS model forecast backed off a little from it's previous forecast, while some of the other models came out a little stronger today.  As a result, they're all in very good agreement at this time.  We often take this as a sign to increase our confidence in the forecast.  Even though they all agree, could they all be wrong?  Yes, but the odds are growing increasingly slim.  

Here's a breakdown of how this storm will unfold:

• Precipitation will spread over the area on Friday around or shortly after sunset.
• Spokane and the Palouse will see rain from this storm, with a possible mix of snow at the onset.
• Saturday morning will be rainy and breezy.  Spokane will be in the lower 40s by sunrise and top out in the mid 40s during the day.
• The northern valleys will start as snow and will accumulate a few inches.  They will gradually change to rain overnight.  Colville will probably change to rain before midnight, while Bonners Ferry could hold on to snow until Saturday morning.
• The cold front will move through the area during the middle of the day.  Behind the front winds will really blow.  Below is our forecast peak winds for Saturday.  Areas in white can expect gusts in excess of 50 mph.

Peak wind gusts expected on Satuday

We will likely be issuing Wind Advisories for much of the area and possibly High Wind Warnings.  You'll want to stay tuned to this forecast.

Here's a couple of other things to consider with this storm.  The rain along with the melted snow won't be able to soak into the ground since the ground is solidly frozen (from our early December cold snap).  So expect some water  ponding, even on your lawn.

The other interesting tidbit is the outside chance of a thunderstorm.  Thunder?  In early January?  Yes, it's happened before, and this is pretty much the classic set up for it:  warm moist air ahead of a strong cold front.  Below is the SREF model probability of thunderstorms. 

24 hr thunder chances ending 10pm Saturday. 

You can see a small area of 10% over southeast Washington.  If thunder does occur, we don't expect to see hundreds of lightning strikes. However a few claps of thunder are a possibility especially over southeast Washington and the southern Idaho Panhandle, including Pullman and Lewiston.