A National Weather Service WSR-88D Doppler Radar
This report describes the situation and what needs to be done to correct it.There is little useful weather radar coverage over Northwest coastal waters or along the immediate coast. Northwest meteorologists lack radar information about crucial weather features along the NW coast, such as heavy precipitation and strong winds. In contrast to the rest of the country, Northwest weather forecasters cannot view the details of weather systems approaching the coast.
The lack of a coastal weather radar degrades warnings and forecasts for the entire region from what would be possible with proper coverage. Major storms can hit our coastal regions with little warning and short-term forecasts are degraded. Research on Northwest coastal meteorology is greatly hindered by the absence of an operational coastal radar.
The National
Weather Service completed a major modernization in the 1990s, a central
component being the installation of powerful Doppler weather radars
across
the country. Such units, known as WSR-88Ds or NEXRADs,
describe precipitation and winds in their environs and have
revolutionized forecasting and meteorological research.
The range of
useful radar coverage is controlled by a number of factors.
Terrain
blockage is important in mountainous regions like the Northwest.
Furthermore, the height of the radar beam increases with distance
from the radar--resulting in an inability to see important low-level
features at distances from the radar. Under perfect conditions,
the maximum range
of the WSR-88D for wind information is 230 km (138 miles) and for
precipitation sensing roughly twice as far.
An official
National Weather Service map of national weather radar coverage (for
precipitation)
is shown below. A second image with a blow-up of the Northwest
section
is also provided. These radar coverage maps are valid at 10,000
ft
ABOVE THE RADAR SITES (many of which are already thousands of feet
above
the surface!), not at the surface. Radar coverage near the
surface
is far poorer, particularly over the western U.S. where blockage by
terrain
is significant. Even for the optimistic 10,000 ft coverage, the
Northwest coastal zone is poorly served compared to the California,
Gulf
of Mexico, and Atlantic coastal regions. But as shown below, the
NWS radar coverage maps do not provide the real story.
The National Weather Service installed three radars to provide coverage over western Washington and western Oregon: Camano Island (WA), Portland (OR) and Medford (OR). The figures shown below indicate their locations and provide more exact coverage maps using high-resolution terrain data.
The left diagram
shows the location of the National Weather Service
radars (tower symbols) and some other sites of interest. The
right diagram indicates
the effective coverage of the Weather Service radars (at 3-km,
approximately 10,000 ft above mean
sea level), with hatching indicating
substantial blockage. Coverage at lower levels is far worse.
Notice that low-level coastal coverage is virtually absent.
The western entrance to the Strait of Juan de Fuca and the dangerous Columbia River bars do not have useful low-level weather radar coverage. Offshore military exercises run out of Whidbey Island Naval Air Station, McChord Air Force Base, the Everett Home Port, and the Bangor Submarine base are without the comprehensive meteorological oversight that coastal radars could provide. Weather Service forecasters cannot garner critical information on weather systems approaching the Northwest coast, clearly degrading short-term forecasts. Some examples are given below.
Incidents such as the grounding of the New Carisa and the loss of Coast Guard personnel during a rescue attempt in 1997 demonstrate the need for timely weather information over the Pacific coast for emergency situations. For the New Carisa, poor weather guidance resulted in the initial salvage attempt failing.
Doppler winds from the Weather Service radar are only available within 230 km (138 miles) of the radar. Considering that the nearest coastline is 160 and 100 km away from the Camano Island and Portland radars, respectively, offshore wind coverage would be very limited even without the mountains . Radar beams ascend higher the farther they get from the radar. By the time they get to the coast (approximately 150 km out), the radar beams are already at approximately 1500 m (approximately 5000 ft). Thus, current radars cannot determine low-level coastal and offshore precipitation and wind features of great interest to mariners and people living on the coast, even if the coastal terrain wasn't there.
When the New Carisa grounded Near Coos Bay, Oregon, there
was no radar coverage to help manage salvage operations.
What Would We See With Radars on the Northwest Coast?
To illustrate
the kind of radar coverage two coastal radars could provide, the
potential
coverage of the lowest radar beam for the current and proposed radar
networks
is shown below. The current network (left figure below) provides
little radar coverage along most of the Oregon and Washington coasts,
and
what coverage does exists is for higher altitudes. In contrast,
northern
California enjoys excellent coastal coverage due to the Eureka radar
site.
Wth the addition of two radars along the central Washington coast
(perhaps Westport, WA) and the
central Oregon Coast (perhaps Newport), the Pacific Northwest gains
excellent
coastal radar coverage, allowing a clear view of storms approaching
from
the Pacific.
Radar coverage maps for the lowest beam (.5 degree elevation angle)
for the current
network (left) and the proposed network (right) with radars at Westport
(WA) and
along the central Oregon coast. Red areas indicate no coverage
below 8000 m (25,000 ft).
Note that someof the coastal terrain without coverage would be included
at a higher scanning angle.
Meteorologists would be able to see the details of incoming weather systems during the 6-18 hr period before they arrived. Forecasts and warnings for the entire Northwest would improve. Coastal search and rescue, as well as offshore military operations, would gain critical weather radar information on winds and precipitation. The data from coastal radars could help provide a real-time detailed description of the weather in the coastal zone. Not only could this information be provided to the public and interested users, but it could be used in numerical weather prediction models to improve downstream predictions. Such data is particularly critical in the Northwest where we lack detailed observations upstream over the eastern Pacific. For the first time, the distribution and intensity of coastal precipitation could be diagnosed, aiding more accurate streamflow and flood forecasting. Researchers would gain a continuous view of the interaction of Pacific weather systems with Northwest coastal terrain, thus improving our understanding of these features, which should lead to better forecasts. The radar would provide crucial data for homeland security needs. For example, the data from the radars would enhance local weather prediction, thus providing better forecasts of toxic plume dispersion. It would also help protect the population from major storms.
To address at least one and more optimally two additional Weather Service radar need to be place on the Pacific Northwest coast. With two radars, one radar could be place on the central Washington Coast--Westport would be a good placement--with the other radar along the central Oregon Coast, perhaps near Newport. If only one radar could be acquired, the central Washington coast would probably be the best location, since it would provide surveillance for the entrances to both the Strait of Juan de Fuca and the Columbia River, would provide crucial precipitation information over the flood prone southern flanks of the Olympics, and would give upstream weather information for the highly populous region stretching from the northern Willamette Valley to Puget Sound.
The acquisition costs for an additional radar would be substantial (roughly 4 million), with additional costs for land, utilities and maintenance each year . But such costs are small compared to the substantial benefits such coastal radars would provide. A single improved forecast could save millions of dollars and several lives. It is of interest that several local TV stations have been able to afford weather radars (although far less capable than the NWS units). Other regions of the country (e.g., Indiana) have requested and secured additional radars to fill in holes in coverage. The Pacific Northwest has a strong claim to similar treatment.
How do we proceed from here? Perhaps the best approach would be to contact our representatives in the Senate and the House of Representatives, asking them to supply additional funds to the National Weather Service to add one or two Northwest coastal radars. (Click here for Senatorial contact information). Additional funds are crucial because the NWS does not have support for extensions to the current radar network. It would also be useful to directly contact higher officials in the National Weather Service and NOAA, letting them know about our concerns regarding this major deficiency in the national observing network.
For more information: Cliff Mass, Professor of Atmospheric Sciences, University of Washington (206-685-0910), cliff@atmos.washington.edu
Acknowledgment
Ken Westrick of 3-Tier, Inc. provided several of figures shown above and provided several useful comments.