It rained most of the day in north Florida Sunday. It was also cloudy and rainy for several hours in a row on Monday. If history is any clue, there will be many more days like this than Floridians are used to in the coming months. Normally during the cool season (November - April), the majority of the days are sunny and dry. This year, however, the UF Weather Team anticipates the current El Niño event in the Pacific Ocean will cause a shift in the jet stream that results in more cloudy, cool and rainy days than usual. Unfortunately, it could also make the state more susceptible to flooding and severe weather events as well.
A typical winter weather pattern in Florida includes several cold fronts or storm systems, but they usually pass through with little or no rain. Even though the state is surrounded by water on three sides, the upper levels of the atmosphere are often lacking adequate moisture to produce significant precipitation. During an El Niño event, however, a shift in the jet stream occurs whereby it splits into two separate currents. Rather than one dominant polar jet that occasionally delivers cold dry air masses from the north, a stronger flow from the Pacific Ocean to the Gulf of Mexico is established. This subtropical jet stream carries more moisture and stronger storm systems across the southern tier of the nation, resulting in a more active (and wet) pattern in Florida. Rainfall is usually much higher than normal, there are more rainy days overall, and sometimes even a few severe weather outbreaks during an El Niño winters. In fact, the top two deadliest tornado outbreaks occurred in February of strong El Niño's (2007, 1998).
An El Niño event is the largest and most influential weather phenomenon around the globe. Meteorologists and scientists have been studying it since 1950, and the data strongly correlates to the following notable weather trends during the winter and spring months across the United States.
The aforementioned split in the jet stream will likely leave parts of the Ohio and Tennessee Valleys with less precipitation than usual this winter, as storms systems are forced to move north or south of these areas.
The warmer Pacific waters typically induce a stronger upper-level ridge of high pressure over the Northwest and North-Central US, thereby preventing intrusions of arctic air from Canada and resulting in warmer-than-normal temperatures.
An unusually stormy pattern will likely unfold, and potentially even last for weeks, over the Intermountain West and in California. Multiple heavy rain and snow events will likely occur, some even possibly producing flooding and mudslides.
It should be noted that not all El Niño events are the same. This year's warmest waters, for example, are in a slightly different location than the other comparable events. How this may play into the overall weather pattern across the nation remains to be seen. The Florida Public Radio Emergency Network will continue to monitor the progress of El Niño and update you on the potential influences it may have on our weather in the coming weeks.