Unusually high tides filled many streets of Venice on Wednesday as atmosphericforces lifted the northern Adriatic Sea.The official water level in the city reached 56.6 inches (144 cm) above theaverage, the highest of the year. City authorities reckon that about 60 percentof the city's streets and piazzas were put under water. On St. Mark's Square,flood waters stood knee deep, forcing tourists to wade or follow raisedboardwalks.

The flooding stopped well short of last year's mark of 63 inches, which yieldedthe city's worst flooding in more than 20 years.

The atmospheric setting that most often leads to tidal flooding in Veniceblends low pressure over northern Italy with high pressure over southeasternEurope and the eastern Mediterranean Sea. The result is a gradient in pressurethat lifts the level of the northern end of Adriatic Sea. The pressure gradientalso drives southerly and southeasterly winds over the open Adriatic, which addto the lift at the northern end of the sea.

The trigger of this latest incident of flooding lay with a storm tracking fromSpain to the Alps. More bouts of flooding will take place during the next fewdays as more low pressure areas will follow this overall track.

Story by Accuweather.com Senior Meteorologist Jim Andrew