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Phoenix-Area NEXRAD (KIWA): Beam Geometry over the Desert

Phoenix-area NEXRAD (KIWA) coverage of Mesa: beam height over desert, clutter, and range. This page is not a live Doppler loop.

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The Phoenix metropolitan area is not seen by a radar on a downtown roof. It is sampled by a WSR-88D whose site identifier is KIWA, the Phoenix-area NEXRAD in Maricopa County. NOAA NCEI’s station list places KIWA at 33.289233°N, 111.66991°W, 1,426 feet elevation—southeast of Mesa, in the Florence / Queen Creek approach to the valley. This article is about that geometry: what the beam is doing over desert and city when a personal weather site said “Phoenix Doppler.” It is not a live loop, not a Weather Underground gallery, and not an NWS warning page.

TNET Weather does not rehost KIWA imagery. Current official products: NWS Radar — KIWA and the NWS Phoenix forecast office. TNET is not a warning service. Monsoon flooding, severe thunderstorms, and dust hazards are official NWS decisions.

Historical context

The recovered page at /weather-doppler.php was formatted 25 April 2005, 23:28:30 MST. It advertised Doppler images “from the WeatherUnderground,” a clutter-removed view, and a “scientific” view with clutter left in, covering “the Arizona Area from about Flagstaff to Nogales.” Navigation chrome, access counters, and those GIFs are not restored. They were historical third-party mosaics and loops, already delayed in 2005, and they are not current KIWA data.

What the URL still names is local Doppler for people who lived in Mesa and used the TNET Weather station pages. The scientific object behind that menu item is KIWA’s volume, not a 25-minute WU animation. Neighboring station articles still treat rain detail and lightning as separate observation types; this page stays on the radar’s view of the valley.

Where KIWA sits relative to Mesa

NCEI HOMR lists KIWA as PHOENIX, Maricopa County. Public NWS Radar uses the station path /station/kiwa/. Consumer maps often label the same site Phoenix-Mesa or Florence because the antenna is not at Sky Harbor; it is out the southeast side of the metro, closer to the desert edge than to downtown Phoenix. Mesa, Gilbert, Chandler, Tempe, and the Salt River valley therefore sit at short to moderate range from KIWA. Flagstaff, Nogales, and Yuma do not.

That range split is the whole lesson. A rain gauge in Mesa and a KIWA lowest-tilt pixel over Mesa are at least arguing about the same neighborhood. A pixel “over Flagstaff” on a Phoenix-centered GIF is often KIWA’s beam already thousands of feet up, or it is another radar entirely if the image is a mosaic. The 2005 copy that stretched one loop from Flagstaff to Nogales described a map extent, not uniform low-level coverage. Map extent is a cartographic choice. Coverage is physics.

Nearby NEXRAD sites that actually own other Arizona basins include Flagstaff (KFSX) and Tucson. NCEI also lists a Phoenix TDWR (TPHX) as a separate, shorter-range airport radar. A PWS page that says “Phoenix Doppler” should name KIWA when it means the NWS WSR-88D, and should not silently mix TDWR, KFSX, and a national mosaic.

Beam height over a hot, dry column

NOAA JetStream’s WSR-88D primer is the right starting geometry for any desert metro. The antenna steps through a volume coverage pattern. The lowest tilt is typically about 0.5°. At 100 miles, that beam is about 12,000 feet above the ground. The beam also spreads—on the order of 1,000 feet of width per 10 miles—so distant cores are smeared.

Apply that to the valley without inventing a custom KIWA ray-trace:

  • Mesa and the east valley are close enough that the lowest tilt can still see relatively low in the column, subject to local terrain and clutter. That is why a Mesa rain gauge and KIWA often tell a comparable storm story during a monsoon cell that actually reaches the ground.
  • The Mogollon Rim and Flagstaff are far enough that KIWA’s lowest beam is sampling mid-levels, not the rain shaft at the pines. Shallow rain, virga, and terrain blockage are expected disagreements.
  • South toward Tucson and Nogales is another long radial. Tucson’s own WSR-88D is the honest low-level sensor for that corridor.
  • West toward Yuma is similar: long range, high beam, dry sub-cloud layer.

The sub-cloud layer is not a footnote in Arizona. High bases and dry air evaporate hydrometeors. Radar can show a robust core while streets stay dry (virga). Conversely, a brief microburst or outflow can wet a gauge after the elevated core has already been the radar’s story. Those are observed disagreements between a remote-sensing volume and an in-situ funnel. They are not proof that either instrument failed. The station rain article and the radar article should both keep units and times so a later reader can see the split.

Standard refraction is an assumption. Super-refraction and ducting—temperature inversions, sharp moisture drops—bend the beam into the ground and paint anomalous propagation. Desert nights and monsoon moisture gradients both produce AP. The 2005 TNET split between clutter-removed and “scientific” views was an attempt to show that choice. Clutter suppression is derived. It can hide AP; it can also nibble real echoes. Neither view is a warning.

Ground clutter in a built valley

KIWA looks across cities, irrigation, freeways, and mountains as well as open desert. Near-radar returns from the surface, buildings, and terrain are ground clutter, strongest on the lowest tilt, often quasi-stationary. Dual-polarization products (network-wide from 2012, after the 2005 page) help classify biologicals, debris, and hydrometeors; they were not what that Wayback GIF showed.

A PWS operator in Mesa who compared the gauge to a clutter-filtered WU loop was comparing a point depth to a processed mosaic. The cleaner comparison is: station rain versus KIWA base reflectivity at a named tilt and time, plus a note on range. Composite reflectivity will fill in elevated monsoon turrets and can look “rainier” than the surface. Echo tops will look dramatic in deep cells and still will not be GOES cloud-top temperature.

How to use KIWA from a station site

Do not archive a 2005 loop and call it live. Link KIWA on NWS Radar. If you embed, keep the timestamp and legend, and caption KIWA, product, and UTC. State that the antenna is the Phoenix-area WSR-88D southeast of the metro, not “radar on site.” Put the rain gauge in a separate panel (rain detail). Lightning is another family (weather-lightning.php for the station sensor; lightning.php for lightning versus satellite). For monsoon safety, send readers to NWS Phoenix.

Level III product codes are on /radar/grlevel3. Remote-sensing physics: /radar. Third-party mosaics that once filled this URL’s images: /radar/wunderground.

What the 2005 Flagstaff–Nogales frame actually implied

A single GIF covering Flagstaff to Nogales is a wide cartographic window. At KIWA’s latitude it includes short-range, relatively low-beam sampling over the east valley; long-range, high-beam sampling toward the Rim and the border; likely mosaic pixels from other radars if the publisher was WU; and clutter filtering as a binary aesthetic rather than a documented algorithm. Reading that GIF as “Doppler of all Arizona at the ground” is the error this article exists to block.

Modern relevance

Place matters: which radar, which range, which desert column. Precipitation and storm structure as weather evidence are grouped under evidence families. The Horizon study review is independent context for weather and Starlink; it does not map KIWA dBZ onto a Mesa street-level speed.

A dated connection estimate for a chosen city and interval is the Connection Outlook. That estimate is not a Doppler loop and not an NWS warning. How observed, modelled, and derived information are labeled is how the service works. Regional studies: regional performance and weather studies.

This PHP path does not animate KIWA. Historical observation pages: observations hub.

Sources