WRAL WeatherCenter Blog

When is our average last night of freezing temperatures? Also, have you given the projected 30 day forecast?

Posted March 7, 2007

MIKE MOSS SAYS:      Susan,    For the RDU airport, the average last date for a freezing air temperature is around April 10th, with a standard deviation of about +/- 10 days (this means in a given year, we have about a 67% chance the last freezing night will be within 10 days of April 10th, a 95% chance it will occur within +/- 20 days of that time, and a 99% chance it will occur within +/- 30 days. Keep in mind that ground and plant surfaces can become colder at night than the air temperature, so frost may occur somewhat later than the last freeze. Also, very localized terrain variations can cause significant differneces in the last freeze date over a fairly short horizontal distance, which adds even more uncertainty to that average date.

As for 30-day forecasts, we don't routinely air those or post them on our web site, although we may do so on an occasional basis or through a WeatherCenter Blog entry, etc. Since we principally focus on forecasting day to day weather changes out through 5 days or so,  we leave the long range outlooks to the folks who do that as their primary duty, such as the climatologists at the NOAA Climate Prediction Center. You can always find their latest longer range outlooks (6-10 days, 8-14 days, one month, three-month, etc) at

http://www.cpc.ncep.noaa.gov/

For now, with an El Nino pattern on the wane and a possible La Nina not yet established, it's likely those longer range forecasts will include a lot of "Equal Chance" outlooks for our area, meaning temperature and precipitation have about an equal chance of ending up near normal, above normal or below normal.

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