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.

Mid-May Blow

A front associated with a line of thunderstorms and followed by very strong winds raked western Washington this afternoon, resulting in the loss of power to tens of thousands of homes and a major blockage of I5.

WSDOT photo of a big tree blocking parts of I5

First, what were the wind speeds like?  Here is a map of the max winds during the past 24 h; virtually all of the high winds occurred this afternoon.  Plenty of folks experienced gusts of 30-45 mph, with some marine locations to 50 or a bit more.  Interestingly, the winds were worse over the inland waters than along the coast.  Strong winds are a problem now because trees have their leaves and thus are more prone to catching the wind.  Furthermore, this has been a pretty wimpy windstorm season, so there was only modest "pruning" by winter winds.

During the morning it became clear that we were in for something special.  The coastal radar at Langley Hill showed an intense convective band approaching the coast, as shown by the image below at 10 AM.  You will also notice a second band behind it.

 The UW WRF model forecast substantial winds during the afternoon (gusts reaching 25-35 kt, see below), although it did underplay them by 5-10 mph in places.  That is unfortunately typical.

The convective line reached the Puget Sound lowlands around 12:30-1 PM and was associated with intense rain and some lightning.  I was teaching my forecasting class at the time and let's say none of us were giving full attention to the lecture.  Visiblity plummeted to a few hundred feet in the downpour and driven by the winds, water pushed through the closed windows of my lecture room (dripping to the room below on to some computers!).

Here is the radar image right before it hit the UW (1:20 PM).  Pretty impressive line.  You don't see reds (very, very heavy rain) on Northwest radar imagery very often.

Winds picked up modestly with the first band, but the REALLY strong winds followed the second band, which was not associated with much rain.  Thus, this front was distributed over two steps, each associated with a rain band.  Here is a plot of the weather at the UW to illustrate.  The top panel shows sustained winds at gusts.  The sixth panel is rainfall.  A short spike of wind with the first band (around 21z), but the real winds were later (around 00z--5 PM) following the second band.

Why the sustained strong wind behind the front?   Because a large north-south pressure difference set up behind the front as its associated trough of low pressure passed to the north (see graphic).

The air behind the front is cooler and much drier, with far lower dew points.  It almost feels like fall outside right now.    Here is a plot of temperature and dew point the last few days at Sea Tac.  The dew point dropped from 55 to 42F today.  You will notice that.  And temperature is down to the lower 50s.

Tomorrow will be a sunny and cooler day, but temperature should still get into the mid-60s.  After the torrid, dry weather of the past few weeks, this is almost welcome.