How confident should you be in the weather forecast for tonight, two days from now, or next week?  The answer to that question depends on the answers to a number of other questions, one of which is, what is the source of the forecast?

Some of you may still swear by the Old Farmer’s Almanac. The technologically savvy may look to tweets on Twitter. A couple of weeks ago, I overheard someone in a store in Picayune tell a customer, “It’s going to snow 12 inches this weekend.”

As entertaining as these sources can be, I recommend you check with the National Weather Service (NWS). On the Internet type your zip code into the search box at www.weather.gov. Or, you can listen to broadcasts by the weather persons on the local New Orleans or Gulfport television stations. While these weather casters have varying degrees of expertise in meteorology and communications, their forecasts usually don’t differ much from those issued by the NWS. That’s because these weathercasters read the NWS’s forecasts and look at the data and model predictions provided to them by the NWS.

The NWS forecast for our area is produced by the NWS Forecast Office in Slidell. That office is responsible for issuing forecasts for southeast Louisiana, much of southern Mississippi, and the north central Gulf waters. The Slidell forecasters focus their attention on our area and have experience and understanding of our local weather.

Another question to consider is, which weather factor in the forecast is of most interest to you? Precipitation forecasts are generally harder to get right than temperature forecasts. That’s one reason that the NWS includes a probability of precipitation – in other words, percent-chance-of-precipitation – for the forecasts out to three days. Beyond three days, precipitation forecasting gets even harder, and the NWS drops the numerical percent-chance-of-rain and talks about a “slight chance” or “chance” of rain. If the forecaster’s confidence of dry weather is high, he won’t mention rain at all in the four through seven day forecasts.

This Tuesday and Wednesday southerly flow will bring warm air from the Gulf supporting highs in the 70s. There will be plenty of moisture. As of Monday the NWS forecast put our chance of showers at 20 percent for Tuesday and Tuesday night. Of course, that means that there’s an even better chance, 80 percent, that you won’t see a shower during that time. But, as a strong cold front approaches, the rain chances go up to 40 percent on Wednesday and 70 percent on Wednesday night.

After the cold front moves through on Wednesday night, you will notice a drastic cool down on Thursday through Friday with a light freeze possible early Friday morning. Some rain may linger early Thursday behind the front, but that will come to an end as the colder, drier air blows in.

The outlook for the weekend is an example of a low confidence forecast. One of the main computer weather models predicts a return of showers, while another keeps us dry. So, the NWS is forecasting a “slight chance of rain” for Friday night and Saturday, and a “chance of showers” for the rest of the weekend.

By Skip Rigney.