Wunderground launches high-definition radar product

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

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

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I believe this is the best weather website I've ever been to! So much awesome stuff here!!!
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At least the Miami radar hasn't been down for a whole month now as the KIAH (North Houston) one has been. We're suppose to be getting our first front tomorrow and was looking forward to seeing the squal lines on it, doesn't look like its gonna happen
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All South Florida radars are now down, at least according to the map. Palm Beach, Ft. Lauderdale and Miami TDWR radars have been down for about 2 wks now w/no comment whatsoever on their respective pages. Miami radar went down 2 days ago but at least they posted a comment that it was down due to replacing parts of the radome. What gives?
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I believe that this sentence: "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."
should actually read "...the traditional WSR-88D radar to ENSURE..." ensure and insure are similar, but I believe inappropriately mixed here.
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Looking for the 1st Hail of the Season here.
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Will be nice to have the Greer SC TDWR data!
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Lots of new TWDR stations have been added. Still waiting on New Orleans, though.
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Quoting Orcasystems:
Oh man... its almost time to leave sunny Mexico.. the bus will be here in 1 hour to pick us up to go home.. to sunny Victoria.. where it is SNOWING and a windchill of -11... WTF happened?

Santa left the door open.
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out of season area of interest west atlantic

Watch it closely.
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Looks like they could make a "combined" radar using the old 88 and new HD...... taking the strengths of each and combining them.

It is nice to have new weather tools, hopefully we can get more along the atlantic and gulf coasts.....
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Oh man... its almost time to leave sunny Mexico.. the bus will be here in 1 hour to pick us up to go home.. to sunny Victoria.. where it is SNOWING and a windchill of -11... WTF happened?
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BBC Article on something we kinda figured.
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110. GBlet
Good morning! BOY, it's cold here! Working on getting water to thaw out in back bathroom as our heat bulb blew out last night. We got snow that was not expected to be this bad. The county trucks are working double time to get roads passable. Now I hear we are getting freezing drizzle later. YIPPY!!!!
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Good evening from Spain!

We've got another possible case of MEDICANE (cyclone with some tropical characteristics over the Mediterranean Sea):

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out of season area of interest west atlantic
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South Florida StormWatch
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106. viter
DC Metro Area - Composite Image?

It looks like those of us in the DC Metro area are going to have 4 of these radars surrounding us. (BWI, IAD, DCA & NHK ???)

It would seem that this level of coverage could eliminate the drawbacks associated with the higher resolution...IF we could get some sort of composite image of all 4.

So, who's gonna hook this up?
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Quoting P451:

I have noticed that as well. So has the "New York Area" with the Ramapo fault. I also feel that the St Louis area as reminded us it is also not dead.

With these things it is always a question of WHEN and never IF...because it's going to happen.

The thing with these areas is they have all these lower level quakes but never a big pressure release event like California has. So that energy is constantly building - and when it goes out East - it GOES.

It's going to happen it's just a matter of when. These little quakes remind you that the plates are grinding but there has been no release with these events in fact they are a hint that the pressure is BUILDING and not RELEASING.

It's just a fact of life though and when it happens it's going to be deadly and we will have to respond to it.

I feel this country...our government... does NOT have a fail safe plan to save those affected by these seemingly imminent events.

That's the big one. The reaction to the event.

Hey, we always knock 3rd world countries but look at the Tsunami response from years back - those countries were right on top of taking care of their own as best they could.

The USA? We get a hurricane and it's 3 weeks later and we're in bread and water lines - be it North Carolina, Florida, or New Orleans. That's....disconcerting to say the least.

That is what we must focus on. Not prevention but reaction to an event. We're one of the WORST in the world when it comes to reaction to a big event.

Why have we not improved upon this!? Politics, Money be damned... we MUST improve our ability to respond to disasters. We haven't and we will continually be reminded that we haven't as each new disaster gets handled terribly.

Couldn't agree with you more. There is one major problem we have in this country that no other country has. We all feel that we're invincible and that we can overcome anything. Its more a psychological problem than anything.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Seems like the Southeastern US has become more seismically active over the past couple years. Just hoping that this is not becoming a trend.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Quoting Rainman32:

Hmmm.. took a look at the location map, the epicenter is across the street from Charleston Naval Weapons Sta.. blame it on the neighbors?

more: Magnitude 3.6 - SOUTH CAROLINA

Mod: Oh, isn't that interesting? they changed the location.. where the heck is my tinfoil hat?

I used it to grill sausages.

Sorry. :(
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Back. Trying to get overstretched plumbers out to my house before this malstrom happens.

Yea NE appears that all my wishing is paying off =) But I dont like the ice wording in the forecast.

Morning conchy =) Yes folks up this way dont need another round of ice, snow yes. Still have a ton of branches and two trees left to clear from the property, get the boiler back online finally (hopefully today), and work crews are still removing branches from wires and fixing infastructure.

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Local News is reporting an outbreak of the Norovirus at an assisted living Facility here in Wilmington.
This is not good news!
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vort....that's SJ's neck of the woods...too many Krystals again....
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Quoting HadesGodWyvern:
as for how many cyclone for the southern hemisphere I seen about 10 for Australia and 10 for Fiji region.. so it might be an active season down south.

There is also a cyclone potential for Australia right now (Western Australia region)

What about Queensland and Northern Territory, that's the north and east coast of tropical Australia. I will endevour to bring everyone the latest info when the s@#t hits the fan here in OZ.
Cheers and Happy Festive Season, God Bless, and a Happy New Year to one and all.
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yea rain....maybe something went "Boom!"
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Hmmm.. took a look at the location map, the epicenter is across the street from Charleston Naval Weapons Sta.. blame it on the neighbors?

more: Magnitude 3.6 - SOUTH CAROLINA

Mod: Oh, isn't that interesting? they changed the location.. where the heck is my tinfoil hat?

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Hey,Bone,are you ready to rock and roll this week?All your snowcasting looks like its going to pay off
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Magnitude 3.6
Date-Time Tuesday, December 16, 2008 at 12:42:15 UTC
Tuesday, December 16, 2008 at 07:42:15 AM at epicenter
Time of Earthquake in other Time Zones

Location 32.970°N, 79.997°W
Depth 5 km (3.1 miles) set by location program
Distances 4 km (2 miles) SE (134°) from Goose Creek, SC
6 km (4 miles) N (359°) from Hanahan, SC
10 km (6 miles) N (11°) from North Charleston, SC
146 km (90 miles) NE (45°) from Savannah, GA
418 km (260 miles) E (101°) from Atlanta, GA

Location Uncertainty horizontal +/- 23.1 km (14.4 miles); depth fixed by location program
Parameters NST= 14, Nph= 14, Dmin=22.7 km, Rmss=1.11 sec, Gp=234°,
M-type="Nuttli" surface wave magnitude (MLg), Version=6
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Yikes Bonedog: You all sure don't need another ice storm. Good Morning by the way!
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LOL MissNadia

Looking at a couple of rounds of nastiness coming my way. Might be another ice storm also =( still recovering from the last one.

Hopefully all stays well for everyone.
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Morning All
ILM is
Cloudy 54F
Forecast is for 67F with rain.
NO ICE here Bone!
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thanks bonedog :)
Member Since: August 14, 2008 Posts: 0 Comments: 675

current outlook

12/21 - 12/25

12/26 - 12/29
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Hi all just popped in to say 2 things:

1) Good Morning all of you WU bloggers! :)

2) anyone have the maps of the temperature outlook and precipitation outlook for the US? TIA

PS its cold again and I'm a bit sick now time to get that soup
Member Since: August 14, 2008 Posts: 0 Comments: 675
It's to early. I mean off to the sw.
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out of season area of intrest 25n/55w

I see a ull off to the se with a llc around 28n 55w under a developing convective blowup.
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out of season area of intrest 25n/55w
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Night to everyone. Work calls tomorrow.
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Have to walk the furry kids, so g'nite!! Take care all.
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nght Baha, thanks for info
Member Since: January 1, 2008 Posts: 0 Comments: 4397
Quoting conchygirl:
Hi Sugarsand: Ready for the holidays? Blog pretty quiet but as to be expected this time of the year!

I do see that Pottery is around too!

Still have a few things to do for the "holidays"...fun stuff, like baking and wrapping.
Sorry to hear about your Aunt.
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Sorry to check out on u guys so early. I've been under the weather [admittedly great!] today, and I need to get out early tomorrow. So I'm heading to bed.

Goodnight, all!
Member Since: October 25, 2005 Posts: 20 Comments: 26810
I'm off - take a look at the santas on my blog - some great pics posted by Pat.

Member Since: August 13, 2007 Posts: 10 Comments: 4304
I've been kinda curious about the final number of deaths for Ike as well. I notice the NHC report doesn't seem to be out as yet. I dunno if that is one of the holdups. Then again, neither are Fay, Gustav, or Hanna, so they may be waiting on other info like wind confirmations, reanalysis data, or complete damage reports.
Member Since: October 25, 2005 Posts: 20 Comments: 26810
Sorry to hear that, not fun when family is sick over the holidays.
Member Since: August 13, 2007 Posts: 10 Comments: 4304

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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