Does Monday still look like a severe day?

A few days have come and gone since our last post about the potential severe weather event for the first day of June. So how are things looking now that the event is nearing? Well according to the water vapor imagery below, it's looking pretty good. See the swirl off the northern California Coast? That's the deep low-pressure system which will deliver the active weather as it moves toward the Inland Northwest. Why is this low important? Well for a good thunderstorm day we need three key ingredients: lift, instability, and moisture. The low will provide us with the first ingredient.

Animated water vapor imagery. Note the swirl off the Northern California coast. 

The models are very consistent in taking this low from its current position off the California Coast toward the Washington/Oregon border by afternoon and then toward the Washington/BC border by evening. This pattern resembles the typical negative tilted pattern we associate with severe weather in the Inland Northwest. The track of the low will ensure that the region will be subject to strong lifting potential beginning in southern Washington and central Idaho in the morning and spreading northward through the day. 

500 mb forecast with precipitable water forecast

Notice the shading in the 500 mb map above? That represents the precipitable water forecast. The greens, blues, and purples depict where the juiciest air will be located, Initially the pool of moisture, currently over far northern Oregon, will shift northward tonight and then become enhanced with even more moisture from the incoming low. How much moisture will we see? We forecast that using  a parameter termed precipitable water. Precipitable water is a figure used to represent how much water the atmosphere is holding. The precipitable water forecasts are expected to reach  values are forecast to exceed an inch over portions of the Inland Northwest by afternoon. How unusual is that? According to the graphic below, it would be placed in the 97.5-99th percentile for this time of year. So it will be far from typical. 

Precipitable Water anomaly

So with the two key pieces in place, what about the third, instability? Well it looks like that piece of the puzzle will be realized as well. If you recall our previous blog post, one of the ways to measure potential instability is looking at the lifted index values. If we see negative lifted index values, that indicates potential instability. So as early as 5 am, we begin to see some of this instability. Notice the yellow and orange shading over southeast Washington? This is enough instability to support thunderstorms even without the benefit of daytime heating. 

5am Monday Lifted Index Forecast

How about later in the day? Suffice it to say the instability will not be lacking. The entire region is expected to see negative lifted index values, with the best instability represented by the -6 to -8 values over extreme eastern Washington and north Idaho. That's about as good of a lifted index as you can expect to see over the region. 

5 pm Monday Lifted Index Forecast

So with all the pieces in place what would we expect to happen? We think there will be a band of showers and thunderstorms early in the morning spreading across the Washington/Oregon border, which should slowly work their way northward through the morning. How extensive this band will be remains rather uncertain. One of the weather models is forecasting the radar to look like the image below. Notice the nice cluster of showers and thunderstorms near the Blue Mountains in SE Washington. This coincides nicely with the good pocket of instability forecast by another model.  

7 am simulated radar image

By midday, this band is expected to drift farther north, but could lose some of its definition and strength.  

11 am simulated radar

However, the first band which moves through will further moisten and destabilize the atmosphere before the strong upper-level disturbance tracks toward our region. So what will the afternoon look like? This is far from certain, and there are as many answers as there are high-resolution models. Here's just one of the forecasts for 5 pm. 

5 pm simulated radar

That is a pretty impressive simulation with strong thunderstorms located across the northern portions of Washington as well as in the southern Idaho Panhandle. However recall that the best instability (or lifted index values) were located over the Idaho Panhandle. So we have better faith in the eastern portions of this radar simulation verifying. Another thing we can look at is an ensemble of simulated radar returns. The image below shows where the greatest risk will be for the biggest thunderstorms (chances of having a 40 dbz or stronger radar echo). The regions shaded in purple have the best chances (over 90%) followed closely by the reds (over 70%). This would highlight two areas. The Cascade crest and over the southeast corner of Washington and the southern Idaho Panhandle.

Ensemble chances for 40dbz or higher echoes

So what will the main risk of severe weather involve tomorrow? Based on the instability, the biggest risk looks to be large hail. If we look at the model soundings they are likely a little too moist to support widespread wind damage, however, we still expect to see some strong wind potential with a few of the storms. 

So what is the typical weather we experience with this type of upper-level pattern? We can utilize a fascinating tool produced by the Cooperative Institute for Precipitation Systems (CIPS) at Saint Louis University. They created a tool that makes an analog of the 15 closest weather patterns (since 1980) to what the forecast weather pattern is supposed to be. So below we see the forecast for tomorrow in red compared to the mean of the top 15 analogs (or pattern matches). This looks like a pretty good fit.

500 mb forecast for tomorrow (red) plotted against the 15 top weather analogs since 1980

So what weather was experienced on those days? Interestingly enough, quite a bit. Of those 15 days that matched Mondays expected weather, there were widespread severe reports. Most of them were related to hail, but a good sample of the reports were related to wind as well. Also, notice there were 3 tornado reports in the Inland Northwest. We do not expect to see tornadoes on Monday, as the wind patterns are not quite right to support violently rotating storms, however, they have occurred in this weather pattern before. 

Severe reports from the top 15 analog days to Monday's weather pattern

The other risk we see tomorrow will be for flash flooding. The storms which develop tomorrow will obviously contain copious amounts of moisture. And more importantly they could be slow movers. 

The risk of heavy rains will likely continue through Monday night before tapering off. Here's a look at the 24-hour precipitation forecast from 4 different weather models.

Precipitation forecast from 11am Mon-11am Tue

That's a lot of precipitation (purple amounts are above  0.75") and there is a fairly consistent message that the bulk of it will occur across the northern quarter of Washington, the Cascade Crest, and over the Idaho Panhandle. Since much of this will be attributed to thunderstorms, there is likely to be a high variability over short distances, with some areas likely to receive much heavier amounts. 

Stay tuned for updates to the forecast as this will likely be a very active weather pattern. 

How is this Memorial Day Weekend looking weather-wise?

Last year at this time, we composed an extensive blog discussing the connotations associated with Memorial Day weekends in the Inland Northwest.  In many parts of the country, this weekend typically kicks off the summer season. However here in the Inland Northwest that really isn't the case, due to continued cool and unsettled weather. So is this year going to fit the weather mold, or will we see warm and dry weather?

Before we delve into this year's weather scenario, lets look at what the typical weather pattern is for this time of year. Looking at the mean 500 mb (18k ft MSL) maps below we see that the typical weather pattern is to see moist southwest flow pointed into the Pacific Northwest with a ridge setting up just downstream of the Continental Divide in western and central Montana. 

500 mb mean map 5/23-5/31

So what about the temperatures associated with this average pattern? Here's  the average temperatures for a couple locations as well as the average chance of precipitation:

So not bad. An average high around 70°F with rain expected on roughly 1 out of 4 days doesn't sound too terrible. But that's climatology and this weekend's weather could vary significantly from the norm. Why you ask? Well, let us take a look at the 500 mb pattern for this weekend to get an idea what sort of weather we might be dealing with. First off, here's a look at the weather for Saturday. 

GFS 500 mb heights for Saturday

This does not look promising if you enjoy plenty of sunshine and warmth. Note the closed low-pressure system (yellow L) centered over northwest Washington. Low-pressure systems like this are typically associated with cool and unsettled weather, especially if your are under or near the low. But this is only one model run. Surely there are other ideas out there in weather land. Well, here's a look at 4 distinct weather models for the same time period.

500 mb pattern from 4 different weather models for Saturday

Notice all these model runs place a low somewhere over the Pacific Northwest. That raises our confidence that the weather will be cool and unsettled over portions of the region, but maybe this unsettled weather will only last for a day. So let us take a look at the Sunday weather pattern.

500 mb pattern from 4 different weather models for Sunday

If the upper left model solution verifies (the GFS), the Inland Northwest could really be stricken with another cool and wet day. The other model solutions would hint at some modest improvements, but far from what we would deem summer like weather. How about Monday then?

500 mb pattern for Monday

The upper left solution (the GFS) still keeps the low parked over Washington while the others either drop it south of the region or weaken it. We shall see. But what if the GFS solution were to verify? What would our weather be like? If you love rain, well then you will love this forecast. Here's a look at the total precipitation forecast for Saturday and Sunday.

Rainfall forecast for Saturday and Sunday

The swath of red shading indicates rainfall amounts in excess of an inch. This includes Spokane, Kellogg, Coeur d'Alene, Pullman, Lewiston, Banks Lake, Lake Roosevelt, and Colville. If you look even closer there are a few locations which are expected to see in excess of 2 inches (shaded in tan)!
Now that is a lot of rain, regardless of the time of year. If the precipitation were to materialize, it would equate to our wettest Memorial Day weekend since 1997 and the second wettest on record (since 1970). So what is our confidence level in this precipitation panning out at this point?

Another tool we can look at in addition to just a few deterministic model runs is from an ensemble forecast approach. This is where you look at multiple model runs (initialized from the same model) and try to gather where the forecast confidence in the precipitation swath is greatest. Using this approach, the news isn't great either.

NAEFS/GEFS Ensemble precipitation amounts for the 48 hrs ending Sunday Afternoon

Without delving too deep into the specifics of the image above, the black lines depict the average precipitation amounts from the ensemble mean precipitation forecast while the green and blue shading (well any shading really) is bad if you like dry weather.  Notice the black lines hint at a swath of precipitation extending from southern British Columbia to the central Idaho Panhandle. The green and blue shading suggests the 48-hour precipitation amounts are in the 99-99.9% percentile for an early April-early July event. In other words, it is a 1 out of 100 or 1 out of a 1000 event for this particular time of year! There is even a small area of pale blue which hints that rain of this magnitude for this time of year has not been experienced since between 1985-2011!  This map suggests the GFS isn't entirely alone in forecasting a wet weekend, but we would like to see much better model agreement before buying off on this solution.

Now, if the rain does materialize, what impact will  this have on our temperatures?

7-day Spokane Forecast

Our current forecast is showing highs above average through the workweek with a cooldown by the weekend. Notice by the weekend we are forecasting highs right around 70 each day. That's not bad. Right around average actually. But we discounted the wet GFS solution. What if the GFS were to verify? How warm would it get then?

7-day temperature meteogram for Spokane

See the green line on the chart above? That is our official NWS forecast. However the blue lines (from the GFS) show the highs on Saturday could struggle to escape the mid-50s on Saturday and then slowly rebound into the lower to middle 60s for Sunday and near 70 on Monday.

Stay tuned to later forecasts this week to see how wet this weekend might really get. In the meantime, you might want to procure yourself one of these if you have camping plans this weekend.

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. 

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!

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