May Grey is a little late setting up this year but this forecast is showing more signs of development this week, and even more so next week.
The night and morning low clouds near the coast are common in May because high pressure starts being more common and we see fewer transitional weather systems in the jet stream. This generally means lower wind speeds and a higher contrast of temperatures between beach locations and interior valleys. Not only do you have that temperature contrast you also get what is called "temperature inversion" where temperatures above the ground layer can actually be warmer (not cooler as is more common in an idealized model of the atmosphere). This happens because water temperatures are cooler than land air temps and cooler air is more dense. Without much wind condensation takes place at low levels and the clouds can be trapped under the warmer "inversion" layer. Now these clouds can burn off with sunshine or mix out with increasing winds but occasionally they linger much if not all day at beaches and some coastal valleys. This is so common in May you get the name "May Grey", there is also "June Gloom", "No Sky July" and of course "Fogust". While this can annoy beach goers, this is also the reason the Central Coast is not a sprawling desert. It is free air conditioning.
The modeling is showing patchy cloud development for the Central and Southcoast tonight into Thursday morning. More consistent and more stubborn clouds look more likely for the Southcoast. Interior areas will not be impacted by the marine clouds and stay warm Thursday.
Friday and Saturday look cooler as a trough of low pressure digs into the western U.S. states. This isn't ideal position for cold weather but definitely will allow some moderation of temperatures into the weekend.
Next week the jet stream looks set to amplify into a larger arching ridge which will warm inland areas up but May Grey looks more likely at beaches and near coastal valleys setting up large temperature ranges for the area much of next week.
Late next week models are indicating a trough into NorCal which could again ease off inland heat.
