Questions from Reader

We like answering reader questions:

How did you generate your 4 day precip total map? Is it doppler estimated or based on ground obs?

Asking because the map implies that a 20 mile radius (if not more) of the Denver metro area received 1.5" to 3". The KDEN "official" precip for the MONTH is 0.74". Clearly a mismatch.

I also believe the 7 day precip forecast is misleading in highly variable areas (such as the Colorado Front Range) other than to predict "you may receive above/below normal precip." Areas of Boulder County received 6+" of rain overnight and are experiencing major flooding. However, KDEN has reported a mere 0.11" yesterday and 0.00" as of 6a today.

The map is what is called a "gauge-adjusted radar estimate" of the amount of rain. The maps are broken into 4 X 4 km (2.5 X 2.5 miles) squares and the amount averaged over that square. If, for example, the west third of the square has 2", the middle third 1" and nothing falls in the east third of the square the entire square will display the average of 1".

Here is a closeup of the Denver area during the last four days:

You can see that more than eight inches of rain have fallen near and south of Boulder where major flash flooding, including two fatalities, have occurred. Unfortunately, rains continue to move from south to north along the Front Range so more flooding is possible. The green polygons are flash flood warnings. This radar data is valid at 10:50am MDT. 

With regard to forecast rainfall amount maps they ,too, are on a grid and forecast average amounts for that grid square. We often caution readers to "blur their eyes" a little bit as they look at the forecast maps we put on the blog because they are not meant to be exact point forecasts. 

Hope this answers the questions. Thanks for asking!