Bay Area weather: How unusual is rain in May?

Remember umbrellas and windshield wipers Bay Area residents woke Monday morning to something they hadn t seen in six weeks Rain A fast-moving cold front from the Gulf of Alaska brought several hours of showers across Northern California on Monday providing countless free car washes clearing the air and wetting down vegetation after a hot dry weekend It was the first important rain in the Bay Area since April How rare is rain in May Not unheard of experts explained Monday We don t get a lot But we usually do get certain commented Jan Null a meteorologist with Golden Gate Weather Services in Half Moon Bay More precisely of the Bay Area s annual average rainfall inches out of a yearly total of inches measured by the gauge in downtown San Francisco falls in five months November December January February and March a feature of the state s Mediterranean environment And falls in just three months December January and February May Normally sunny On average the Bay Area receives inches of rain each May or of the annual total That puts May as the th wettest month of the year well behind December January February March November April and October and ahead of June September August and July We re in the shoulder months between spring and summer explained Karleisa Rogacheski a meteorologist with the National Weather Utility We get weak low pressure systems that sometimes come across Northern California This was beneficial rain The rain cleared the air reduced fire danger for a short time and helped boost seasonal totals she noted Selected years there isn t any On average it rains days a year in May Monday s showers came in before dawn causing flight delays of about minutes on average at San Francisco International Airport and minutes at Oakland and San Jose airports It was gone by mid-morning The wettest areas were across Bay Area hills and peaks Tilden Park in the East Bay Hills had nearly half an inch with inches Mount Diablo near Walnut Creek had inches the same as Ben Lomond in the Santa Cruz Mountains Marin County s Mount Tamalpais saw inches while Hayward had Concord Oakland San Francisco Mt Hamilton San Jose Palo Alto Richmond and Watsonville It was the the greater part rain in the Bay Area since The bulk rain in the Bay Area since April when San Jose receive inches The forecast Dry weather for the rest of the week I m looking at nice blue skies Null disclosed Since Oct rainfall totals have been higher in Northern California than Southern Santa Rosa on Monday was at of normal San Francisco at San Jose at Los Angeles at and San Diego at But after three above-average or near-average winters in a row reservoirs across the state are full and no summer water shortages are expected It s been a real gradient from the Oregon perimeter to Mexico this year with higher numbers in the north and less and less as you go south Null commented A lot of the storms we saw in the winter got cut off around Interstate Average Bay Area rainfall amounts by month Downtown San Francisco - with of annual total January February March April May June July August September October November December Total average