Why is the Weather Channel rainfall measurement so inaccurate??

Hey all,
So the weather.comsite has insisted for two months in a row now that there wasn’t any rain in the city (Portland, OR in this case) for several days during each month. But I certainly KNOW there was rain in a number of areas… mostly because I was rained on all day while outside doing gardening work. :rolleyes: If customers ask how much rain there has been or will be in July, I really need to know what the actual answer is, because it makes a major difference for several aspects of the family gardening business. So I found out that rainfall is measured by the city all over the place in PDX, with 38 different gauges.

The City of Portland Hydra Rainfall Network shows .37 inches for July to date. Weather.com shows .26. And .26 is lower than all but 3 of those 38 individual citywide measurements (no, none at the airport.) The city is divided up into areas (north, northwest, southeast, etc.,) and no area had an average anywhere near as low as .26. So where is weather.com getting this weird incorrect measurement from??

All ideas appreciated!:slight_smile:

I don’t use weather.com, but I’m sure that somewhere in the site selection, the exact measurement location is identified. It may be the airport, which is the one place in the metro area where the most compete records are compiled. In many cities, the airport is pretty far removed from the population center, and that ten miles or so can be the difference between over an inch of rain, or none at all.

In fact, thgere is probably an option in your weather site online where you can choose from any of several reporting stations, and each time you log on, it will default to your selection.

The radar map for Portland shows the marker in the river just north of where 5 crosses the river.
From the street pattern, I’m guessing that’s downtown. Maybe the higher building density is affecting the rainfall in that area.

Why do you think their measurement is weird and incorrect when you looked up other measurements and found that three locations reported even less rain?

If that level of detail is critical for your business, it’s not expensive or difficult to set up your own rain gauge.

Because each separate region in PDX was listed by the Hydra site as having a much higher rain average than .26. Nowhere in the city (north, northwest, northeast, southeast, etc) was the average even close to being as low as .26. Only 3 individual rain gauge locations out of 38 had a measurement even slightly lower than .26, and they were quite widely separated geographically. It still doesn’t really make any sense, but the Hydra site is clearly the way to go. It’s just strange that the national weather site would be off by so much two months in a row… you have to wonder if this is true in other regions too.

1] Indeed, rainfall can vary quite a bit even within a city. This would be especially true with this recent storm that came through. The rain was generated by a more cumulus cloud system, typically called “showers” in the forecasts, rather than stratus clouds, called regular “rain”.

2] Topography is very important in this matter as well. The west sides of the hills will receive more rain than the east sides, the rain shadow effect. Unfortunately, official rain gauges are located at airports and airports are generally sited within these rain shadows (better for air traffic). The South Willamette Valley is notorious for this as the Eugene Airport is always below what is usually measured elsewhere.

3] The Weather Channel isn’t in the business of reporting the weather, they’re in the business of selling you that new Ford F-150 4-wheel-drive pick-up with the snow plough attachment on the bumper. Use the Nation Weather Service site, [noparse]www.weather[/noparse].gov. It still has the same rainfall reporting problems but forecasts are honest … in the sense if the models are crazy all over the place, the NWS will say so … the Weather Channel will just make something up so they look smart and that sells more pick-ups with snow plough attachments.

ETA: July and August … yeah … you’ll need to irrigate … rainfall ain’t happening typically

My favorite for keeping track of local rainfall is weather underground, https://www.wunderground.com

What’s good about that site is that anyone with a weather station can register with them, and live stream data. There’s a fellow with a weather station right across my street so I get very precise rainfall numbers.

Where did you get THAT idea? It’s a commercial service and might get it’s data anywhere. It will get it from the easiest and cheapest source possible, and accuracy wouldn’t be real high on their priority list.

WeatherUnderground, unfortunately, relies on home, internet-connected, weather stations way too much. This morning I checked to see how much rain we got yesterday. (A nice round of hard rain.)

The weather station WU defaults to for me said the high yesterday was 111.9 (!) which would have been record smashing and then some. And no rain.


I keep setting my fave sites to official NWS locations, but the next time I click on the town in the header, I’m back at one of the crappy personal stations.

I quite often get at least 50% more rain than NWS reports near me. (Measured by both an electronic and old-style rain gauge.)

Just FYI, the Weather Underground (wunderground.com) and weather.com are owned by the same company, The Weather Company. The Weather Company was recently purchased by IBM (excluding the TV Weather Channel). The TV channel has a contract to acquire weather data from The Weather Company.

Huh … Weather Underground posts the NWS copy for the forecast discussion … how lazy is that?

We have the same problem in Denver. Official temperature and rainfall is determined at the Denver International Airport which is 25 miles from downtown, and in an area which is very different from the city; much more of a great plains area. Typically, the weather there is similar to that of the city, but can be much different (winds and temperatures may be quite a bit different).

This can lead to weather reports which bear no relationship to those in the city, but which are ‘official’

There are still temperature reporting stations scattered throughout the area, and I can select one or more using the weather app on my phone, but these are non-official.