From Daniel Swain at the California Weather Blog:
” … Another extremely warm and moist atmospheric river, with a moisture transport corridor originating near the Hawaiian Islands (hence, “Pineapple Express), is once again steaming toward California. By several meteorological measures, the airmass associated with this storm is pretty extraordinary: the amount of atmospheric water vapor (precipitable water) expected to be present near San Francisco on Saturday morning may be close to the all-time record value for any time of year. (It’s worth noting that early April is actually the *least* likely time of year for really extreme PW to occur; it’s more likely during the heart of winter (during extreme AR events) or during the late summer months (during our relatively rare “hurricane remnant” events.)
This airmass is also expected to be incredibly warm for a California precipitation event; freezing levels could be as high as 10,000 feet or even higher during the initial part of the storm, with rain (instead of snow) expected at even very high mountain locations. Daytime temperatures during cloudy and rainy conditions on Fri/Sat will be in the 60s, and could even approach 70 in some spots (so things will feel very muggy and subtropical indeed). … ”
Continue reading from the California Weather Blog here: April surprise: warm and wet late-season atmospheric river to soak NorCal
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