But what really was maddening about the METRO folks is their decision to shut off the
bustracker software EXACTLY WHEN WE NEEDED IT!! They have a lame excuse about the
bustracker locations having errors when the bus go off the regular routes, but this make little sense. For most of the snow routes useful information IS provided. And they certainly could modify the
bustracker website to provide what information IS there...when the buses pass certain locations. The truth is that METRO has been very slow in going to a GPS tracking system and have never given sufficient emphasis to giving its patrons good information about where the buses are located. They could be doing much better even with their current old-fashioned location system.
The ForecastersYou don't expect me to be critical of my own profession, do you? The National Weather Service did about as well as the technology allows--a forecast that was good enough to provide warning of potential trouble. The day before they were going 1-3 inches, mainly in the afternoon as a coastal low moved south of the Olympics. Basically, they closely followed their main high-resolution model (the NAM,
WRF-
NMM). If you read their forecast carefully, they were only going for some flurries or light stuff in the morning, but it turned out to be considerably more (1-2 inches in places). The coastal low was more intense that expected by their model and they had to up the forecast snow amounts during the day. The
NWS was correct about cold air coming in later that day. I have to admit, my forecast was not as good regarding snow the night before. I depend heavily on the
UW high resolution system, which usually is superior to the
NWS NAM model for a number of technical reasons I won't go into here. But this situation was unusual and the NAM was better that morning (I will have a future blog telling why and steps we are taking to fix it). Essentially, the
UW system took the coastal low further south and the snow shield only extended to south Seattle. The
UW system recovered Monday morning with a very good forecast--in plenty of time to deal with the afternoon threat.
Play by Play AnalysisOn Monday morning the temperatures were near freezing as the first pulse of snow moved in. Since it had not been that cold and this was early in the season (remember it was 74F a few weeks before!), the ground and road surfaces in contact with it were relatively warm. Even the elevated structures (e.g., the Alaskan Way viaduct) hadn't cooled below freezing. So when the snow started, particularly with generous amounts of deicer
SDOT had spread around, the roads were fine. The morning commute had very little problems. People got into work and school. I even biked in with no hassles on the Burke
Gilman Trail.
So far so good.
But then the problems began. The low center along the north coast deepened more rapidly then expected and moved across the southern flanks of the Olympics (see satellite picture below)
As the low moved south, it produced moderate, mild southwesterly flow that moved northward to meet northerly flow pushing south down the Sound (the northerly flow was accelerating toward the lowering pressure over the south Sound). The converging
air streams resulted upward motion and bands of snow. But at the same time the northerly flow brought colder and colder air over Seattle starting around 3-4 PM.
Here are the temperature and wind
plots from the top of my building at the
UW that day. Temps were between 28 and 30F until just after 3 PM and then temperatures started to drop quickly.
At the same time the winds started to become much stronger and gusty (see figure).
Strong winds are important because they provide much more effective removal of heat from the surface. It is like a fan blowing cold air over the ground...much more effective for cooling.
And now it all came together. The deicer put on earlier was increasingly diluted by the larger volumes of snow falling into it until it became of marginal value. The air temperatures were rapidly dropping and the strong winds enhanced cooling. What would ice up first? You know what...the elevated roadways which did not enjoy heat conduction from the relatively warm ground below. The Alaskan Way viaduct iced. The West Seattle Bridge. And since much of I5 is elevated, it glazed over rapidly as well.
Icemageddon.
Traffic locked up on major roadways. Plow and sanders couldn't get to where they were needed. Trucks and buses got into trouble. And the rest was history.
What to Do What I am about to express is opinion...and I am probably missing key points...but I will go ahead anyway.
First, although weather forecasts are getting better, any new system for dealing with snow has to be robust enough not to depend on the forecasts being correct in the timing or amount of snow. It will be 5-10 years before the 12h forecasts are dependable enough for such work. We are quite good in telling you if the cold and winds will come. Or revealing a
threat. But getting the exact amount and distribution of snow even 6-12 hr out is not here yet.
The Nov 22 forecast by my colleagues in the
NWS were
far better than what they could have done 10 years ago. It was good enough to alert the city and various DOT agencies, and to let the general public know that something serious was possible. Certainly KING TV and other stations knew--they were hyping it up like mad the night before. Jim Forman was getting his famous parka pressed and readied.
But if the forecasts are not perfect, what is needed is good
nowcasting--a term in my field which means examining current observations carefully and intelligently extrapolating them into the future. There are 50-100 weather stations reporting in
real time in the city. With this information, one could determine exactly what the temperatures are and track the changes. As soon as the strong winds and colder air started to push in, it was time to get out there getting rid of snow on the roadways and hit them with lots of salt. Using the weather radar and temperature information it is also possible to determine the snowfall patterns over the city (this will get even better next year with the
NWS updating of all local weather radars to dual-polarization and the addition of the new coastal radar). With the information about how much snow is on the ground, where it is falling, and how temperatures are changing,
SDOT and
WSDOT should be able to do their work far more effectively...particularly in getting ahead of the storm. A software system could be created to pull all this information together...we could call it
SNOWWATCH. Furthermore, the city needs someone with meteorological training watching all the observations in real time during these events.
Once the ice forms, you are in trouble. The key is to know when snow is falling and to plow as much of it as possible off the roads and then hitting it with salt (my friends in the business suggested
prewetted salt when temps are cold). If the snow keeps up, you have to repeat.
Now at around 3 PM it was clear from the weather observations that bad things were about to happen. The surface chart showed northerly winds starting to pick up and cold air moving in from the north (see plot). The radar showed snow over the region (see plot). Click for big version.
3PM surface observations
Conclusion: it was about to get colder, winds would increase and the threat of icing was about to increase rapidly. At this point, all equipment needed to be used on elevated structures immediately, and when those were cleared and salted (solid not brine), then the other roads could be dealt with. Metro needed to pull all their articulated buses off the elevated roadways at this point...in fact, they should have replaced with with the non-articulated fleet hours before. Rapid deployment when the weather was clearly going to change seems to me the only viable option.
Question: Do any of the roadway surfaces in the city have real-time temperature measurements? If not, shouldn't this be fixed immediately?
In summary: I am suggesting a combination of the intensive use of all observational assets to provide a real-time view of the weather and road conditions around the city, and the flexibility to use the limited assets of the city and
WSDOT to hit the big threats
first, guided by these observations. The current state-of-the-art of weather forecasts are good enough to give a heads up, but not good enough today to guide hour by hour actions.
There was a considerable change in virtually all weather parameters with this front. Here are the observations at the top of the atmospheric sciences building here at the UW (click to expand). The winds gusted to 40 mph (top line), the wind direction shifted abruptly to the south, temperature plunged by 6F, pressure spiked upwards (fifth line), and lots of precipitation fell. My dog was terrified.
Was this predicted? Not really. We knew a strong front with good rain was coming in, but did not foresee such an intense event. But with a coastal radar we probably would have seen it coming and been able to provide a few hours warning.
There was a considerable change in virtually all weather parameters with this front. Here are the observations at the top of the atmospheric sciences building here at the UW (click to expand). The winds gusted to 40 mph (top line), the wind direction shifted abruptly to the south, temperature plunged by 6F, pressure spiked upwards (fifth line), and lots of precipitation fell. My dog was terrified.
Was this predicted? Not really. We knew a strong front with good rain was coming in, but did not foresee such an intense event. But with a coastal radar we probably would have seen it coming and been able to provide a few hours warning.
