The previous a number of days haven’t precisely been crisp or cool like they’d be throughout a typical October. Fog has been prevalent and right now’s fog advisories proceed by means of 10 a.m. throughout a lot of the realm.
Fog isn’t uncommon on this a part of the world, however a lingering fog that lasts for therefore many hours is a bit atypical. I ran some numbers to see how usually we get dense fog advisories in higher Boston. It occurs about 5 occasions annually, though that quantity is far greater over Cape Cod, which is surrounded by water.
So as to get fog, the relative humidity should principally be close to or at 100%, which means temperature and the dew level have to be equal. This may occur in two methods; moisture might be added to the air, elevating the dew level and thus equaling the temperature, or the air can cool to the dew level. Both method, or a mixture of them, can get us to a relative humidity of 100%.
The chart from Logan Airport under exhibits the temperature and the dew level have been virtually equivalent for a lot of hours. Because of this there’s a lot fog. Fog isn’t a assure when the relative humidity is 100%, generally we’ll get clear skies with a variety of dew or frost on the bottom.
Within the early mornings, when it’s cool and infrequently clear, radiation fog kinds within the low-lying areas the place the relative humidity turns into 100%. Over the previous few days, moist air has moved in from the south. This air mass was advected into the realm. When the temperature falls at evening, it meets that dew level and the thick fog kinds. As soon as the temperature warms up a bit and the relative humidity falls, that fog dissipates. Just lately although, due to the cloud cowl, the temperature hasn’t modified a lot from day to nighttime so the fog is lingering.
Within the winter, lots of heat air might be advected over snow cowl to create fog. We name this advection fog. Likewise steam fog can type over a physique of water like a lake because the moisture is evaporated into the air. However regardless of how or the place the fog kinds, it’s nonetheless fog. If the droplets get sufficiently big, it might begin to drizzle.
After the fog lifts late this morning we’ll be left with a couple of showers and temperatures within the 60s. The rain clears out tomorrow and also you’ll discover the air feeling a lot drier. Temperatures may attain the excessive 60s, however will fall rapidly later within the day. Readings are within the 40s for Friday morning and the 30s at dawn on Saturday and Sunday. There’s doubtless going to be a tough frost or perhaps a freeze over many inland areas. Sunshine can be prevalent for the weekend, with temperatures within the 50s on Saturday and 60s on Sunday. Apart from some localized early morning floor fog, will probably be the sunshine, not the fog, that can dominate the climate this weekend.
