Memorial Weekend Forecast

Memorial Day is not a dependable weekend around the Northwest...never has been, never will be.    Generally we have a sunny, warm period in the middle of May (early May this year) and then we move towards the June gloom mode of low clouds.

During the past few days we have had a closed upper low hanging over us (see graphic), with showers circling around, sometimes from the unusual easterly direction.

With the low right over western Washington today, most of the shows have gone south of Puget Sound, hitting the Oregon coast and Willamette Valley quite hard, with some places getting 1-2 inches of rain.   The next 24h will be more of the same (see graphic), with rain over Oregon, but very little north of Olympia.  Northwest Washington would be a good place for a Friday hike or walk.

I have good news and bad news for the rest of the weekend.  The good news is that low will open up and weaken.  There will be major breaks.  The bad news is that the low/trough will hang around for much of the weekend, with some showers and plenty of clouds in the west.  Oregon will be much wetter than Washington.

Saturday will be bring clouds and some light rain showers over and west of the Cascade crest.  Here is the 24 h total precipitation ending 5 PM on Saturday.  Not the best day for a hike on the western slopes of the Cascades, and the Oregon coast will be damp.

But Sunday looks much better over Washington, but still quite wet  over western Oregon. (24 h precipitation ending 5 PM Sunday is found below).

On Monday, a frontal system will be approaching the NW,  but it will begenerally dry over Washington, except for the crests and windward slopes of the Cascades.  Here is the forecast of precipitation at 5 PM on Monday. 

Eastern Washington is a good bet over the weekend for sun and warm temperatures (60s and 70s).    And with the I5 bridge over the Skagit River collapsed, it will be a tough ride north on I5 through Mt. Vernon.

One good thing about the cool, damp period of the past few days has been a substantial freshening of the snow about 3500 ft.  Some good late-season cross country skiing and the Cascade and Olympic Mt. snowpack is well above 100% of normal.

The Lessons of the Moore Oklahoma Tornado

On Monday, an EF-5 tornado struck Moore, Oklahoma resulting in substantial loss of life, hundreds of injuries, and economic losses that will run into the billions of dollars.  The storm had winds reaching 200-210 mph, was on the ground for 17 miles, and was observed from 2:45-3:35 PM CDT (19:45-20:35 UTC).

How did the National Weather Service and the weather forecast enterprise do?  Can we do better?  This blog will provide some analysis and a few recommendations.

Let me say at the outset, a lot went right and this event demonstrates the substantial improvements in weather prediction technology during the past decades. 

For several days before, based on a range of numerical forecast models and substantial knowledge of severe thunderstorms, the National Weather Service forecasters at the Norman, Oklahoma NWS office and staff at the NOAA/NWS Storm Prediction Center (SPC) had predicted the threat of severe thunderstorms on Monday over Oklahoma.   Here is the graphical outlook for severe convection released on Sunday.  Central and eastern Oklahoma was clearly in a high risk area.

And the Storm Prediction Center's discussion highlighted the threat for Monday

TSTMS MAY DEVELOP BY 20-21Z ACROSS OK ...AND THE 

PROSPECT FOR A VERY MOIST WARM SECTOR FAVOR 

NUMEROUS SUPERCELL STRUCTURES...VERY LARGE HAIL AND
TORNADOES ARE POSSIBLE WITH SUPERCELLS ... 

One of my graduate students, Luke Madaus, happened to be in Oklahoma on Sunday and several people commented on the potential severe storm threat for the next day.

The next morning it was clear that the threat of severe weather was enhanced.  Many of the numerical models showed the development of strong convection, although their solutions differed considerably in strength and position.  The radiosonde (balloon-launched weather instruments) sounding at Norman, Oklahoma showed extraordinary instability (CAPE of roughly 5000 Joules per kilogram and plenty of vertical shear; CAPE stands for Convective Available Potential Energy.  Northwest locations rarely gets above a few hundred, a few thousand is very large, 5000 is extreme).  PLUS, there was a frontal boundary and a dry line that intersected near Norman, Oklahoma.  A very, very big threat. 
 
Our nation is lucky to have the best severe storm forecasters in the world, backed by world-leading research at the National Severe Storms Lab, the University of Oklahoma, the National Center for Atmospheric Research, and many others).   They proved themselves on Monday.  The 11 AM CDT forecast (communicated via YouTube among other ways), painted out the threat and even talked about dangers to schools. (see image, click on it to see the video).

  http://www.youtube.com/watch?feature=player_embedded&v=9Q7iUn9YfWA

You will notice that the warnings of severe thunderstorms was over an area.  Our current level of forecasting technology, coupled with the substantial uncertainty and the chaotic nature of convection, made it impossible to do better.  But an extraordinarily valuable forecast.  A major threat was communicated well. 

Then the next level of warming technology took over:  the U.S. Doppler radar network.  The U.S. has invested heavily in state-of-the-art Doppler radars across the country, radars that have recently been upgraded to dual-polarization (allows the radar to determine the type of precipitation or the nature of the "targets" it view).  

Around 2:30 PM the CDT the Doppler radar in Norman, OK observed the classic signs of a rotating, supercell tornado, including a hook echo and a mesocyclone (an area of rotation 5-10 km wide).  The image below (at 3:06 PM CDT) shows the hook echo, with a "debris ball" at the end.

With the radar image and reports from spotters, a tornado warning went out  at 2:40 PM, 36 minutes before the tornado hit Moore.  You may not think that is much, but 36 minutes is a far larger compared to the pre-radar days (average of 5 minutes in the 1980s).  (Thanks to Mike Smith's blog for an analysis of the lead time issue). This is enough time to run the tornado sirens, put out warnings in the media, and to give folks a chance to move to safe locations...if there ARE safe locations.

That is one big problem.  For an EF-4 or 5 storm the damage can be catastrophic, with buildings either being blown away or experiencing severe structural damage.  Safety can only be found in specially hardened rooms or enclosures.  And such protective spaces were not available to many resident of Moore and for several of the schools.  This needs to be changed.

In short, National Weather Service forecasters did a magnificent job for this event.  But could we do better?  I believe the answer is yes.

Because the atmosphere is chaotic (which means small errors in the initial state can have large negative impacts on the subsequent forecasts, impacts that increase in time) and the requirement of very detailed information to describe the initial environment for thunderstorm forecasts, it is virtually impossible to predict the details of severe thunderstorms a day or more ahead.   And this is not going to change soon. Yes, we can predict that  a major threat exists, but we can't get the exact locations or strength of the future storms correct.    So the day ahead forecast will have to be broad brushed.

But there IS the potential for major forecasting advances in the period from 1 to roughly 6 hours before the storm, if we can run models with enough resolution and can get enough information to describe the initial 3D atmosphere with lots of detail.  And we need to run many simulations (called ensemble forecasts) to get a handle on the uncertainties of the forecasts.

What kind of model resolution am I talking about?  Probably 1-2 km between the grid points, which requires huge computer resources.  We need to apply new ensemble-based data assimilation approaches (data assimilation is the technology of using data to describe the structure of the atmosphere).  And this modeling system needed to be frequently updated, at least once per hour.

We also need much more detailed information about the structure of the atmosphere, using innovative new data sources.  For example, I have a graduate student, Luke Madaus, who is using pressures from smartphones to improve weather forecasts and he is planning on testing this approach with strong thunderstorms.  A potentially huge advance for convective storm forecasting.  Unfortunately, the NWS support for this work (through the NWS CSTAR program) was cancelled for lack of funds....a tremendous frustration.  One of the weaknesses of the NWS is its inability to support and take advantage of university research.

The NOAA and the National Weather Service has been developing an early version of an advanced short-term, high resolution prediction system (the 3-km grid spacing High Resolution Rapid Refresh System, HRRR), which is only run in research mode because of the lack of sufficiently powerful computers in the NWS.  Below is an example of the HRRR forecast 6 and 3 hour out for 2100 UTC (4 PM CDT)----not bad, but not perfect).

Skillful 1-6 hr forecasts are potentially achievable since the forecasts are short enough that the growth in forecast error is modest.  And a few hour warming of a major storm allows sufficient time to evacuate folks from areas which severe weather is probable.

To achieve better short-term predictions, more model  development is needed, including higher resolution, state-of-the-art data assimilation, and moving to an ensemble approach.   But with enough research and sufficient computer resources, we can do better.  But the NWS did very well in this case.
 

Weather Impacts of the Mount Saint Helens Eruption

Yesterday was the 33rd anniversary of the eruption of Mt. St. Helens, an event that devastated the mountain and surroundings and caused terrible problems on nearby rivers.

But there is another story of the eruption and one far less known:  its impact on local weather.

The eruption produced a huge volcanic dust cloud that was mainly blown downwind (towards eastern Washington) by the prevailing winds.  Here are a few weather satellite images that day (May 18,1980 at 8:32 AM), that clearly shows the eastward dispersion of the volcanic dust.

Imagine if the volcano had erupted a few months earlier when the winds are more typically from the south--the nearby Puget Sound region would have been crippled.

What were the meteorological impacts of this dust cloud?   I decided to investigate this with the help of Professor Alan Robock of the University of Maryland (now at Rutgers). 

Here are the temperatures at Yakima and Spokane during that period (this is from a paper we wrote in Monthly Weather Review).  As the plume went over Yakima, day turned to night.  There was a slight cooling as the sun was obscured and then the temperature remained virtually constant for over 12 h.  Why?   The thick volcanic cloud acted as a very effective blanket:  solar radiation couldn't get in, infrared radiation couldn't get out.   The cloud hit Spokane a bit later in the day (they had more time to warm) and was a bit thinner there, so the impacts were less.

How much did the cloud influence temperatures that day?  We estimated this by taking the difference between a very skillful forecast system (MOS, Model Output Statistics) and what actually happened.  The next plot, which shows the estimated cooling in Celcius at 5 PM that day,  shows what we found.  Over portions of eastern Washington the volcanic cloud caused temperatures to cool by around 8 C (14.5F), with cooling of roughly 9 C extending to the Idaho border.

The dust cloud rapidly spread into Idaho, Montana, and Wyoming (although thinning as it moved eastward).   Those locations were able to warm up during the day and then the dust spread over during the night.   The volcanic cloud, like all clouds, reduced the amount of infrared cooling (we cool at night because the earth radiates infrared radiation day and night, and at night there is no warming from the sun).  Thus, the cloud caused the temperatures to be much warmer than they would be otherwise (there were few meteorological clouds). 

Here is the proof:  the estimated temperature changes due to the volcanic cloud at 5 AM the next morning:  8-12 degrees (C) warmer over western Montana!

The weather effects of the Mt. St. Helen's dust cloud rapidly weakened during the next few days as the dust thinned and moved to the east. 

Interestingly, this eruption had virtually no climatic effects.  The reason:  the effluent from the volcano had relatively little sulfur content (SO2).  Injecting this gas into the stratosphere is the main way to produce long-lived volcanic hazes that spread around the planet and cool the lower atmosphere for a few years.  In fact, some folks would like to try cooling our warming planet by doing this artificially--injecting large amounts of particles into the stratosphere to reflect some of the solar radiation.  But that is the subject of another blog!

Announcement:   I will be teaching Atmospheric Sciences 101 (WEATHER) at the UW this fall.  This class is accessible folks 60 or older at very little cost (the UW Access Program) and, of course, to regular UW students.  This class will give you a good basic understanding of the atmosphere and Northwest weather.

Biking Dry

Today is bike to work day and thus there is no better time to discuss how you can bike on most days without fear of getting wet....or at least very wet.

Yes, even here in the Pacific Northwest a little meteorological knowledge and technology can help you avoid those raindrops and enjoy a very pleasant ride on your bicycle.

You might be surprised, but the Northwest is one of the best places to bike commute or enjoy recreational biking in the nation.

Think about it.  What are the worst conditions for biking?  That's easy:  icy and snowy roads.  It's cold and accidents are inevitable.   Good news: western Oregon and Washington have very little snow and ice.

Biking is miserable in hot, humid weather like during summer in the southeast U.S. and the extreme heat of the southwest.  Again, we luck out:  we rarely see such conditions.

Very heavy precipitation, such as in thunderstorms. is really bad for biking and lightning is dangerous.  No problemo here!--we get less thunderstorms than almost anyone else.

Ah, yes, the rain.   But consider our rains are concentrated in only a few months (November through February) and the rest of the year is really pretty dry.  Our annual precipitation (e.g.,  Seattle gets about 37 inches a year) is far less than most of the central and eastern parts of the U.S.  And when it does rain, it is generally quite light;  a rain resistant jacket and pants, coupled with our mild temperatures, leads to a pleasant ride.

 Heavy showers like this are very rare in the Northwest.

But it gets even better for you bicycle commuters and enthusiasts!  Even when we have wet days it rarely rains steadily for a long period of time.  If you can shift your trip by a few minutes, you can often escape the rain.  I bike to work nearly every day and rarely get very wet.

Case in point, the in famous shower and sunbreaks.   Much of our precipitation comes after a front goes by and we get into cool, unstable air.  Such precipitation is convective, meaning we get hit by a shower and then there is a break, followed by another shower an hour or more later.    Here is a radar image showing you an example of this....the showers are coming in from offshore.

Such rain is easy to avoid, wait for the shower to pass and then head out on your bike.
And even in other weather situations rain is almost never uniform and all you have to do is make sure you wait for the dry or light rain areas. 

How can you do that?   Smartphone technology solves this problem!    There are now hundreds of weather radar apps that give you the latest radar image and a radar animation.  It even shows where you are on the image using the GPS or cell-tower navigation function on your phone.  Easy to see the dry spots coming!  And some radar apps will even tell you exactly when the radar will start.  Some are free, but the best ones cost a few dollars.   I use Radarscope (see image below) and some folks use DarkSky, which gives you the timing (but reviews are mixed on this one).

Radarscope (left) and DarkSky (right).

I have been trying to convince a few of my students to create a weather-radar-based bicycle app, where you put in your route and tells you when the coast is clear.

And one more thing.  It is virtually NEVER raining everywhere around here because of our mountains.  If there is a convergence zone going on, with precipitation over north Seattle, head north or south for a dry ride.   Wet frontal system over the entire region, with typical southwesterly flow?  No problem, head to Sequim, Port Townsend, or northern Whidbey.  

Announcement:   I will be teaching Atmospheric Sciences 101 (WEATHER) at the UW this fall.  This class is accessible folks 60 or older at very little cost (the UW Access Program) and, of course, to regular UW students.  This class will give you a good basic understanding of the atmosphere and Northwest weather.

 Our Mayor knows how to find the dry spells.

A New Chapter for U.S. Numerical Weather Prediction

Major news to report.

The National Weather Service will be acquiring a radically more powerful computer system during the next year, one that could allow the U.S. to regain leadership in numerical weather prediction.  Used wisely, this new resource could result in substantial improvements in both global and regional weather predictions.

Using 24 millions dollars from the Superstorm Sandy Supplemental budget, the National Weather Service will be acquired two computers with a capacity 37 times greater than it uses today.  We are talking about a transition from 70 teraflops right now (and 213 teraflops this summer) to 2600 teraflops in 2015.  (A teraflop denotes a trillion calculation per second).    Such computations are spread over tens of thousands of processors.

This new system would give the National Weather Service world-class computer resources and should nudge its Environmental Modeling Center a bit ahead of the current gold-standard weather prediction entity, the European Center, in raw computer power...the essential requirement for weather prediction.

Although this is unalloyed good news, one should note a few important facts:

1.  The National Weather Service does FAR more than the European Center, which only runs global models.   The U.S. has done an inadequate job in regional and national prediction, most acutely in running high-resolution ensemble forecasts--which need to be at 2-4 km grid spacing, not the current 16 km.  My back-of-the-envelope estimate is that the NWS needs at least ten times more computing power than even this new acquisition will give it to be truly state-of-the-art BOTH globally and locally.

2.  The new computer only gives the NWS the potential to be the best.  It needs to use the best approaches for data assimilation, model physics, and use of observations, which often it is not now.  In the past there have been all kinds of excuses about lack of computer power.  Excuses are gone now.  And the NWS needs to develop a closer and more interactive relationship with the research community, something its has failed at in the past.

3.  Even the creaky, small computer they use now has been applied inefficiently and wastefully.  This kind of approach, with lots of legacy products, old models, and lack of cost/benefit analysis, needs to be changed.  For example, a huge amount of the current computer time is used for four times a day runs of the Climate Forecast System (several month simulations using the global GFS model).  This makes little sense..why four times a day?  And why run their global model (the GFS) to 16 days, four times a day?  The European Center doesn't!.   Perhaps do so twice a day, with shorter runs (192 hours) for the other times.

4.  The NWS needs to use other available computers more effectively for operations.  For example, there is the huge NOAA Fairmont machine that is available for NWS use.  Move over less time-critical operational runs, such as the Climate Forecast System runs noted above.

I can provide many other examples of inefficiency and waste in the current usage.

You think that the new computer is so big that we don't have to worry about efficiency?  Think again.
If you want to double horizontal resolution in a weather prediction model (and we REALLY want to do this), you need roughly EIGHT TIMES more computer power.  There is a reason that numerical weather prediction requires the most powerful computers on the planet!

I will end by noting that this huge improvement did not occur because NOAA management had planned carefully and worked to garner the necessary resources over time.  They have irresponsibly let U.S. numerical weather prediction and the NWS slide during the past decade, and Congress has not been sufficient attentive to the problems.   This great advance occurred due to the intense hue and cry by the meteorological community, users of weather information, and the media.  Blogs and newspaper articles documented the deficiency, and private sector companies have complained about paying exorbitant fees to the European Center to get state-of-the-art forecasts.   It shows the power and influence of the public and the weather community when they can document both the need and deficiency, and push their case with the new communication tools of the 21st century. 

Without Hurricane Sandy we would have the same old computer!

And it took a great disaster, Hurricane Sandy, to display the decline in U.S. numerical weather prediction in a concrete and compelling way.  U.S. weather prediction can now move on a new and better road if NWS and NOAA leadership are willing to follow it.