However, despite the proliferation of such models, the idea of a completely integrated approach, says Koch, is something that NOAA is still working out. “We don’t have one gigantic model that solves all the problems,” he says. Even so, one result of this intensive focus on modeling is that NOAA has made measurable progress at improving the ability to predict extreme weather more accurately. However, at NSSL, the focus of which is tornadoes, hail, and high winds, the difficulty of such predictions is acute.

Until recently, weather prediction has mostly relied on a few central prediction models, but that strategy has given way to running an ensemble of models, sometimes upward of 40 models, each with slightly different physics or other configurations. The idea is to create models that can capture the wide variability in the atmosphere and then combine them so there is sufficient spread in the characteristics of a complete ensemble. The ultimate goal of ensemble modeling, then, is to develop a broader representation of plausible outcomes while also producing useful estimates for forecasting.

One problem, however, is that even with an ensemble of models, the prediction results are limited by the quantity and quality of input data. In the U.S., for example, 142 weather radars cover the lower 48 states, with an average spacing of approximately 260 kilometers between them. Because of the Earth’s curvature, more

until recently,
weather prediction
has largely relied
on a few central
prediction models,
but that strategy has
changed to running
an ensemble of
models, each with
slightly different
physics or other
configurations.

than 70% of the U.S. is not covered
by radar in the lowest 1 kilometer of
the atmosphere, which is, of course,
where humans live. It is also where
severe thunderstorms develop. “To
overcome the Earth’s curvature prob-
lem,” says Koch, “you would need to
develop a cost-effective, much-denser
coverage system.”
Another challenge is the weather
processes. What creates severe tur-
bulence, for example, is far from be-
ing completely understood. “There
are gaps in our understanding of pro-
cesses within thunderstorms, and one
of the biggest gaps is the physics of
the precipitation process itself,” says
Koch. “We have an unsatisfactory un-
derstanding of what generates orga-
nized thunderstorms.”

a matter of Volume

Beyond these issues, which have drawn much attention by researchers in recent years, the sheer volume of data produced by an ensemble model configuration, which scientists now believe is the most effective way to predict extreme weather, is much more than the bandwidth of the most advanced networks can handle. In addition, while an ensemble of models can be tuned to the particular aspect of the weather it is designed to simulate, rendering the ensemble quickly enough to be useful for real-time forecasting remains a challenge, even with today’s fastest supercomputers.

The power and cooling requirements are formidable for supercomputer-class systems, and the maintenance costs can be exorbitant. So Koch and other NOAA scientists are looking beyond traditional supercomputer systems and are exploring systems based on graphical processing units (GPUs). While GPUs are not general purpose, they do offer performance advantages over general-purpose CPUs for certain applications. NOAA has not made a decision yet about implementing GPU systems, but trials are in an advanced exploratory phase run at NOAA’s ESRL.

Mark Govett, chief of the advanced computing lab at ESRL, has been di-

Technology

PC and Tablet Sales Forecast

industry analysts are less optimistic now than earlier this year about PC sales for 2011. But the personal computer’s woes have little to do with the public’s enthusiasm for tablets as some believe, says Stephen Baker, vice president of industry analysis for the nPD Group.

research company Gartner has trimmed its forecast for 2011 PC sales from 9.8% growth just three months ago to 3.8%, while rival research firm iDC lowered its forecast from 7.1% to 4.2%.

the nPD Group would not
release specific numbers, but
Baker characterizes U.S. PC
sales as having been mostly flat
to slightly down, mainly due to
the weak economy. “And also
because people bought record
numbers of computers these last
two years ever since the launch
of Windows 7,” Baker says.
“those new computers won’t
need to be replaced or upgraded
for a while.”
dominated by Apple’s iPads—
have grown dramatically from a
first-year small base, Baker says.
there was no tablet market
until the iPad was released in
April 2010.