As we’ve gone through the holidays this past year and move into 2021 I’ve noticed this winter has brought something that hasn’t been seen in a while, fog. It has been a number of years since we’ve had more than a few days of dreary, cold foggy days. Seems like this December and first few weeks of January we’ve experience a good stretch of long foggy days. For those of us that grow tree and vine crops, fog is very helpful in getting the “rest” or accumulated chill hours that many trees and vines need for the next season. Having chill hours really helps with budbreak, leaf out and ultimately yields. The fog blanketing the valley in December and January keeps temperatures below 45F which gives us our chill hours. Warm December and January temperatures cause the trees to expend its energy in respiration and therefore cause the lack the carbohydrate reserves for budbreak and leaf out resulting in poor fruit production.
Most of us probably hate the dark, bleak days without sunshine, long, cold nights and difficult driving conditions but we need these days for most of our trees and vines to thrive. Various theories abound on why we don’t have long foggy winters anymore all centering around climate change. However, if one just looks at our surroundings in the San Joaquin Valley over the last 40 years, you’ll notice how the cities have grown tremendously and the increase in population generating heat in the expanding urban areas. As an example, Madera has grown from around 22,000 in 1980 to 66,000 in 2020. This definitely has some effect on our foggy winters. The downside of having fog is that it forms when there is lack of air movement and it usually means no rain. A big storm can push out the high-pressure areas over the valley, get rid of the fog for a few days and give us much needed rain. As I write this in late January it seems like winter is over and springtime is beckoning. If we have a normal winter there is usually about 6 weeks of foggy weather punctuated by storms and moisture. So maybe we’ve had 3-4 weeks of foggy weather and not much rain this year. Hopefully the storms that are forecast in the waning days of January and early February will at least give us at least a normal rain/snow season for the year.