I thought today I would discuss a question raised by Justin about why the Southland’s temperatures go from 100 degrees to 60’s in just a few days... You asked and so you shall receive! The LA basin’s weather is primarily dominated by large scale weather patterns, such as Highs and Lows, but the primary weather changer is the Jet Stream. During this time of year the Polar Jet and the Subtropical Jet are in transition to more northerly positions (summer). This causes very deep troughs and ridges to develop in the central part of the Pacific. As these move onto the west coast the strong ridges drive temperatures thru the roof, while the troughs drop temps back below normal. This is the nature of weather. Occasionally a trough is so deep that the bottom tip of it breaks away from the rest of the Jet Stream, becoming a Cut Off Low Pressure. These will drop temperatures well below normal, and bring chances of rain, and low level clouds to the Southland. On the opposite side, when a High pressure takes up residency over the Four Corner States, or Las Vegas, winds shift off shore causing compressional warming as the Santa Ana Winds force there way up and over the mountains. This causes low humidity, gusty winds, and a massive spike in temperatures. Even with our up and down variations, the LA basin is calm in comparison to Buffalo’s Lake Effect storms, or the Nor’easters in New England. We go from 100 to low 70’s or upper 60’s, while places like Washington DC, go from 90’s and humid, to 20’s and covered in snow. Personally I love huge changes in the weather, and as an Atmospheric Scientist, roller coaster temperature changes is what I live for.