Wunderground launches high-definition radar product

By: Dr. Jeff Masters , 2:46 PM GMT on December 15, 2008

Share this Blog
22
+

The Terminal Doppler Weather Radar (TDWR) is an advanced technology weather radar deployed near 45 of the larger airports in the U.S. The radars were developed and deployed by the Federal Aviation Administration (FAA) beginning in 1994, as a response to several disastrous jetliner crashes in the 1970s and 1980s caused by strong thunderstorm winds. The crashes occurred because of wind shear--a sudden change in wind speed and direction. Wind shear is common in thunderstorms, due to a downward rush of air called a microburst or downburst. The TDWRs can detect such dangerous wind shear conditions, and have been instrumental in enhancing aviation safety in the U.S. over the past 15 years. The TDWRs also measure the same quantities as our familiar network of 148 NEXRAD WSR-88D Doppler radars--precipitation intensity, winds, rainfall rate, echo tops, etc. However, the newer Terminal Doppler Weather Radars are higher resolution, and can "see" details in much finer detail close to the radar. This high-resolution data has generally not been available to the public until now. Thanks to a collaboration between the National Weather Service (NWS) and the FAA, the data for all 45 TDWRs will be made available in real time over the next few months via a free satellite broadcast (NOAAPORT). Six radar sites are already available (Figure 1), and the remaining radars will be added by June 2009. I'm pleased to announce that the Weather Underground is now making the TDWR data available to the public, and will be adding new sites as they become available. We're calling them "High-Def" stations on our NEXRAD radar page. The six TDWR sites available so far are:

Detroit, MI
Cleveland, OH
Fort Lauderdale, FL
Miami, FL
West Palm Beach, FL
Newark, NJ

Since thunderstorms are uncommon along the West Coast and Northwest U.S., there are no TDWRs in California, Oregon, Washington, Montana, or Idaho.


Figure 1. The network of 45 Terminal Doppler Weather Radar (TDWR) stations in the U.S.

Summary of the TDWR products
The TDWR products are very similar to those available for the traditional WSR-88D NEXRAD sites. There is the standard radar reflectivity image, available at each of three different tilt angles of the radar, plus Doppler velocity of the winds in precipitation areas. There are 16 colors assigned to the short range reflectivity data (same as the WSR-88Ds), but 256 colors assigned to the long range reflectivity data and all of the velocity data. Thus, you will see up to 16 times as many colors in these displays versus the corresponding WSR-88D display, giving much higher detail of storm features. The TDWRs also have storm total precipitation available in the standard 16 colors like the WSR-88D has, or in 256 colors (the new "Digital Precipitation" product). Note, however, that the TDWR rainfall products generally underestimate precipitation, due to attenuation problems (see below). The TDWRs also have such derived products as echo height, vertically integrated liquid water, and VAD winds. These are computed using the same algorithms as the WSR-88Ds use, and thus have no improvement in resolution.

Improved horizontal resolution of TDWRs
The TDWR is designed to operate at short range, near the airport of interest, and has a limited area of high-resolution coverage--just 48 nm, compared to the 124 nm of the conventional WSR-88Ds. The WSR-88Ds use a 10 cm radar wavelength, but the TDWRs use a much shorter 5 cm wavelength. This shorter wavelength allow the TDWRs to see details as small as 150 meters along the beam, at the radar's regular range of 48 nm. This is nearly twice the resolution of the NEXRAD WSR-88D radars, which see details as small as 250 meters at their close range (out to 124 nm). At longer ranges (48 to 225 nm), the TDWRs have a resolution of 300 meters--more than three times better than the 1000 meter resolution WSR-88Ds have at their long range (124 to 248 nm). The angular (azimuth) resolution of the TDWR is nearly twice what is available in the WSR-88D. Each radial in the TDWR has a beam width of 0.55 degrees. The average beam width for the WSR-88D is 0.95 degrees. At distances within 48 nm of the TDWR, these radars can pick out the detailed structure of tornadoes and other important weather features (Figure 2). Extra detail can also been seen at long-ranges, and the TDWRs should give us more detailed depictions of a hurricane's spiral bands as it approaches the coast.


Figure 2. View of a tornado taken by conventional WSR-88D NEXRAD radar (left) and the higher-resolution TDWR system (right). Using the conventional radar, it is difficult to see the hook-shape of the radar echo, while the TDWR clearly depicts the hook echo, as well as the Rear-Flank Downdraft (RFD) curling into the hook. Image credit: National Weather Service.

No change to time resolution
Like the old NEXRAD data, the new TDWR data will update once every six minutes. The NWS advertises that the TDWR data will be sent out within one minute of when it is measured. The TDWR does scan the atmosphere once per minute at the lowest elevation angle of the radar, but unfortunately, there are no plans to make this rapid scan data available via the free public NOAAPORT feed.

Attenuation problems
The most serious drawback to using the TDWRs is the attenuation of the signal due to heavy precipitation falling near the radar. Since the TDWRs use the shorter 5 cm wavelength, which is closer to the size of a raindrop than the 10 cm wavelength used by the traditional WSR-88Ds, the TDWR beam is more easily absorbed and scattered away by precipitation. This attenuation means that the radar cannot "see" very far through heavy rain. It is often the case that a TDWR will completely miss seeing tornado signatures when there is heavy rain falling between the radar and the tornado. Hail causes even more trouble (Figure 3). Thus, it is best to use the TDWR in conjunction with the traditional WSR-88D radar to insure nothing is missed.


Figure 3. View of a squall line (left) taken using a TDWR (left column) and a WSR-88D system. A set of three images going from top to bottom show the squall line's reflectivity as it approaches the TDWR radar, moves over the TDWR, than moves away. Note that when the heavy rain of the squall line is over the TDWR, it can "see" very little of the squall line. On the right, we can see the effect a strong thunderstorm with hail has on a TDWR. The radar (located in the lower left corner of the image) cannot see much detail directly behind the heavy pink echoes that denote the core of the hail region, creating a "shadow". Image credit: National Weather Service.

Range unfolding and aliasing problems
Another serious drawback to using the TDWRs is the high uncertainty of the returned radar signal reaching the receiver. Since the radar is geared towards examining the weather in high detail at short range, echoes that come back from features that lie at longer ranges suffer from what is called range folding and aliasing. For example, for a thunderstorm lying 48 nm from the radar, the radar won't be able to tell if the thunderstorm is at 48 nm, or some multiple of 48 nm, such as 96 or 192 nm. In regions where the software can't tell the distance, the reflectivity display will have black missing data regions extending radially towards the radar (Figure 4). Missing velocity data will be colored pink and labeled "RF" (Range Folded). In some cases, the range folded velocity data will be in the form of curved arcs that extend radially towards the radar.


Figure 4. Typical errors seen in the velocity data (left) and reflectivity data (right) when range folding and aliasing are occurring. Image credit: National Weather Service.

Ground clutter problems
Since the TDWRs are designed to alert airports of low-level wind shear problems, the radar beam is pointed very close to the ground and is very narrow. The lowest elevation angle for the TDWRs ranges from 0.1° to 0.3°, depending upon how close the radar is to the airport of interest. In contrast, the lowest elevation angle of the WSR-88Ds is 0.5°. As a result, the TDWRs are very prone to ground clutter from buildings, water towers, hills, etc. Many radars have permanent "shadows" extending radially outward due to nearby obstructions. The TDWR software is much more aggressive about removing ground clutter than the WSR-88D software is. This means that real precipitation echoes of interest will sometimes get removed.

For more information
For those of you who are storm buffs that will be regularly using the new TDWR data, I highly recommend that you download the three Terminal Doppler Weather Radar (TDWR) Build 3 Training modules. These three Flash files, totaling about 40 Mb, give one a detailed explanation of how TDWRs work, and their strengths and weaknesses. There is also a full product documentation guide available. I'll be adding the info in this blog entry into the radar help link available on each of our radar pages.

No Atlantic named storm likely this week
The models continue to indicate an extratropical storm that has the potential to evolve into a named subtropical storm will form in the middle Atlantic by Thursday. However, it now appears that there will be too much wind shear for Subtropical Storm Rene to form out of this system.

I'm in San Francisco this week for the annual meeting of the American Geophysical Union, the world's largest climate change conference. I'll be posting daily "post cards" from the conference this week.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 22 - 1

Page: 1 | 2 | 3 — Blog Index

Bravo Weather Underground your commitment to technology makes your website superior to others! Oh by the way, Dr.Masters thank you for the terrific innovative update.
Member Since: Posts: Comments:
You never know... From the latest discussion:

...SATELLITE IMAGES INDICATE AN INCREASED AREA OF CYCLONIC TURNING IN THE MID/UPPER LEVELS NEAR 27N59W....THIS SURFACE TROUGH WILL LIKELY GAIN VORTICITY FROM THE WEAKENING FRONT AND POSSIBLY DEVELOP INTO A CLOSED LOW ON TUE/EARLY WED ACCORDING TO MANY OF THE NWP MODELS.

Would be quite interesting so late.

The turning is quite clear in RAMSDIS loop.

Member Since: Posts: Comments:
Stopping by to say hi. Glad the season has calmed.
Member Since: Posts: Comments:
Quoting Dr. Masters:

No Atlantic named storm likely this week
The models continue to indicate an extratropical storm that has the potential to evolve into a named subtropical storm will form in the middle Atlantic by Thursday. However, it now appears that there will be too much wind shear for Subtropical Storm Rene to form out of this system.

(end quote)



Looks like 08 season died onward to a hopefully peaceful 09 season
Member Since: Posts: Comments:
Mauritius Meteorological Services
Tropical Cyclone Warning Number ONE
ZONE PERTURBEE 04-20082009
12:00 PM UTC December 15 2008
======================================

At 12:00 PM UTC, Area of Disturbed Weather (1003 hPa) located at 9.4S 69.8E has 10 minute sustained winds of 20 knots with gust of 30 knots. The disturbance is reported as moving west-southwest at 5 knots.

Dvorak Intensity: T1.5

Forecast and Intensity
=========================
24 HRS: 10.2S 66.1E - 30 knots (DEPRESSION TROPICALE)
48 HRS: 10.7S 63.4E - 30 knots (DEPRESSION TROPICALE)
72 HRS: 11.2S 61.1E - 30 knots (DEPRESSION TROPICALE)

Additional Information
======================
This system evolves within a neutral environment: Windshear has decreased over the area, low inflow is established poleward but not equatorward and mid level lack of humidity.
Available NWP models analyze this low and track it globally westward without deepening it significant at short to medium range.

AT THIS STAGE, THIS SYSTEM DOES NOT JUSTIFY ISSUANCE OF REGULAR WARNINGS.
Member Since: Posts: Comments:
Tropical Cyclone Advisories #30 (1800z 15DEC)
=================================================

Subject: CATEGORY THREE TYPHOON EAST OF THE PHILIPPINES

At 3:00 AM JST, Typhoon Dolphin (970 hPa) located near 15.5N 130.5E has 10 minute sustained winds of 65 knots with gusts up to 95 knots. The cyclone is reported as moving north at 6 knots.

Storm Force Winds
================
60 NM from the center

Gale-force Winds
================
240 NM from the center in north quadrant
180 NM from the center in south quadrant

Dvorak Intensity: T4.5 - Stronger than 65 kts.. wonder why JMA kept the wind speed for 4.0 then.

Forecast and Intensity
=====================
24 HRS: 17.2N 130.4E - 60 knots (CAT 2)
48 HRS: 18.8N 131.6E - 50 knots (CAT 2)
72 HRS: 19.4N 132.7E - 40 knots (CAT 1)

Philippines Atmospherical Geophysical Astronomical Services and Administration

Typhoon "ULYSSES" has gained more strength as it moves northwestward slowly.

Tropical Cyclone Bulletin #6 (1500z)
==============================
At 11:00 PM PhST, Typhoon Ulysses (DOLPHIN) located at 15.1°N 130.2ºE or 620 km east-northeast of Virac, Catanduanes has 10 minute sustained winds of 130 km/h (70 knots) with gustiness up to 160 km/h (85 knots).

Additional Information
=======================
This disturbance is still far to affect any part of the country.
Member Since: Posts: Comments:
When I see words like "Attenuation", my mind tends to drift and I can't finish the blog entry.

Anyone got an Idiot's guide to fancy new radars?
Member Since: Posts: Comments:
Just stopping by to check up on everyone. Been quite some time since I last visited the blogs. Been having a rough semester that just came to an end last Thursday.

Anyways, yet another well-written and impeccable blog post by Dr. Masters. Will be looking forward to using this new radar technology to track thunderstorms here in South Florida come the spring. Seems like the resolution will be much better and this new radar technology will provide so much more data.

By the way, it seems like all the computer models are onboard with brief subtropical development in the Central Atlantic before wind shear takes control. Will be watching this region throughout the week in case.

If you have been visiting my site within the past month, I apologize for not having updated it for quite some time. Just been really busy with finals and trying to overcome some emotional hurdles that have come over the past couple months. This morning, I did a full update on my site.

Well, thanks for the update Dr. Masters and hope everyone has a great holiday season. I will be stopping in from time to time during the "offseason".
Member Since: April 14, 2007 Posts: 8 Comments: 5163
Hello everyone! I am currently working on my Blog as some of you can tell. I am making each MAP and GRAPHIC INTERACTIVE.....go to my blog an click on the Airport Delays to see what i am doing..
Member Since: Posts: Comments:
Nice WU! Will look forward to ATL and DFW added, as well as other hubs.
Member Since: Posts: Comments:
stsimon-Yeah, I'm feeling kinda left out over here on the gulf coast too.

Member Since: Posts: Comments:
Cool to know how it all works and what the current limits are. Thank you.
Member Since: Posts: Comments:
Good morning... and Thx Doc.

Always good to have more tools in your arsenal. :P
Member Since: Posts: Comments:
Great to see this new data and it's product suite available on a public site. I was employed by the research lab that developed the TDWR and actively involved in the algorithm fine-tuning for many years. It has been in use by the FAA for wind shear detection and the like for probably a decade, but getting access to the data in the public realm has been a long time coming. One of my mentors, who has unfortunately passed away now, was part of the original TDWR development team. Thanks for this post, Dr. Masters, and for WU jumping onboard to provide this data to the weather community.
Member Since: Posts: Comments:
Its good to see the strong focus on south fl with the new radar coverage. I'm sure the hurricane researchers are loving the new data sets these radars provide and statistically south fl is the best place in the us to put land based sensing devices as far as tropical cyclone data is concerned.
Member Since: Posts: Comments:
Too bad we don't get one in southern CA... although usually we just have a massive cold front (like right now), or no rain at all (95% of the time)
Member Since: Posts: Comments:
Thanks Doc.

Been viewing that new radar since it appeared on WU last week. Neat stuff and I am lucky to have one close by that covers my area.

Greatly appreciate the explanations because it did seem that there was quite a diff between traditional and the hi-def. Good to know the limitations.
Member Since: Posts: Comments:

Viewing: 22 - 1

Page: 1 | 2 | 3 — Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.