How Did Those "Maxed-Out" Probability Forecasts Work Out?

By -
For sixteen years, the National Weather Service has been producing severe weather forecasts in a probabilistic form. Only twice in all that time have they maxed out (forecast the highest value) their numbers the day before the event (known as "Day 2"). So, with the help of the NWS's Greg Carbin, I wanted to see how well those forecasts worked out.

The Friday Day 2 severe weather forecast was for all types of severe weather (tornado, large hail, damaging thunderstorm winds). The highest the forecast (reproduced below) probability can go is 60%. Here is the forecast issued early Friday morning for Saturday:


Through a technique called "hindcasting," Greg re-ran the forecast using the actual reports of severe weather. In other words, to produce a "perfect hindcast" for comparison. Here it is:

With the exception of west central Texas, the forecast is excellent. The 60% maxed out probabilities were warranted.


Now, let's take a look at the tornado (only) probabilities issued 11:30am Saturday morning before the first tornado occurred. The 45% is very high and rarely attained, but they can go as high as 60%.

Here is the perfect hindcast:
Turns out they could have maxed the probabilities out at 60% in Kansas! The forecast of tornadoes also went too far south. Still, this was a difficult-to-forecast extraordinary event and these extraordinarily high numbers attracted the attention of the media, bloggers, and even a newspaper. They, in turn, got the word to the general public of the exceptionally high risk in the central Plains.

I would give the Day 2 forecast an A and the Day 1 tornado forecast an A-. 

Nice work National Weather Service Storm Prediction Center!

Comments

Post a Comment

Popular posts from this blog

Hilary's Forecast Path Shifts West; Updated 9:20am PDT

By -
Image
The forecast path of the center of Hilary has shifted a bit to the west. This increases the threat to the Southland, especially in terms of flooding.  Rainfall Note the heavy rains are forecast for Los Angeles County. Serious flash flooding may result. Because the forecast path has shifted to the west, that increases the threat of serious flooding in Los Angeles County north into Yosemite and the southern Sierra. It lessens the threat in Utah and western Arizona. While the threat of widespread flooding in Utah and Arizona lessens, note that some thunderstorms with localized heavy rain show up on the map.  In Nevada, the more western path increases the risk of serious flooding around Mt Charleston and into the central part of the state.  Here is the updated  (9am PDT) flash flood risk map. Wind There are already about 40,000 people without power in California, mostly in the center of the state.  The maps above are the peak gusts forecasted with the storm. The highest winds, in general,
Read more

Dangerous Travel Conditions - People Reportedly Stranded

By -
Image
-- Note, more current info available. Scroll up. --- Updated Information as of 8am PDT You are risking your life if you attempt to travel through the purple area.  While the rain has not begun in coastal California, I would urge you to use this time to make any preparations. Power outages have occurred already in southeast California. Here is the latest radar as of 7:55am PDT. As of 6:40am PDT , the radar indicates moderate to heavy rain falling over desert areas of Southern California and far western Arizona (click to enlarge).  Rainfall amounts for the 24 hours ending at 7am PDT show more than two inches have already fallen. There are reports from reliable sources that roads are already washed out and that people are stranded in isolated parts of the desert.  Below is a high-resolution computer model's rainfall forecast from 5am PDT to 11pm PDT Sunday. More than a foot of additional rain is forecast to fall. This will lead to catastrophic flooding.  Here is a map of current watc
Read more

Update on Tornado and Wind Potential; 12 Noon PDT

By -
Image
There was at least one tornado and at least one funnel cloud yesterday.  --- original forecast --- Hilary (the swirly symbol) continues to move NNW paralleling the coast of Baja California, Mexico. The area outlined in red has a significant risk of tornadoe s the rest of the afternoon.  Below is a list of peak wind gusts so far.  Peak winds may increase farther north as the afternoon progresses.  Addition at 12 noon PDT: Sure enough, winds have increased.  Note: If you are in the San Diego area, I recommend not  traveling east on I-8. Heavy rains may cause flash flooding that will involve the highway. 
Read more