FLORIDA CAN EXPECT A MILD AND DRIER THAN AVERAGE WINTER, WITH SOMEWHAT BELOW AVERAGE CHANCES OF CITRUS-DAMAGING FREEZES…
- Summer and fall datapoints, including ENSO, Northern Hemisphere snowpack, Arctic sea ice, and the persistent fall longwave pattern, were used to make a forecast of projected temperature and precipitation anomalies for the winter of 2016-2017 in Florida.
- Overall, temperatures are expected to be near to slightly above normal in the state over December through February, with below average precipitation continuing through the winter. Though mild freezes are likely in central Florida, the seasonal risks of severe, citrus-damaging cold are lower than average this winter.
In Florida, they say the only two seasons are summer and the two-to-four (depending on the part of the state where you live) months that you can get away with not running the air conditioner. As the rarer of these two seasons is now upon us, it’s time to look ahead to the rest of winter, to see what can be said about the temperature, precipitation, and citrus freeze risk trends in Florida for the months ahead. For those who want to skip the discussion and go straight to the predictions, scroll to the Florida Winter Forecast for 2016-17 heading below or click here. Also, don’t forget to sign up for a free trial to get 10-day forecasts of Florida freeze risk from WeatherTiger’s weekly winter outlooks.
Forecast Method and Discussion
The first step in seasonal forecasting is to identify cases in the historical record in which the primary driver of global weather patterns—the El Niño/Southern Oscillation, or ENSO— is a reasonable match for this year’s Pacific sea surface temperature anomalies. In 2016, a long-awaited La Niña event has slowly come to fruition over the fall. As shown above left, the central Pacific is seeing -0.5 to -0.75C or so SST anomalies (at left, above). The uncertainty regarding the future evolution of this –ENSO event is declining; most models, including WeatherTiger’s proprietary “ENSO Whisperer,” now suggest little additional intensification over the next couple months, with weakening back to neutral-negative conditions by early 2017 continuing into spring.
Of course, ENSO state can cover a multitude of sins, especially when the phase amplitude is weak like this year. Fall weather in Florida has been rather Niña-like in terms of precipitation, as the last two months have been extremely dry over most of the state. Hurricane Matthew, which dumped 5-10″ or more in southern Florida and up the East Coast, was the last significant rain event in many locations. However, while drier conditions are often coupled with warmer temperatures, that has not necessarily been the case, with heat in October giving way to a very mild November. To understand whether such conditions are likely to continue into winter, we need to dig deeper.
Despite Florida’s renegade near normal temperatures, most of the country has been torched relative to average this fall, with a powerful drought developing in the Southeast. The feature that is responsible for all this is a persistent, strong area of upper-level low pressure over the Gulf of Alaska, which has driven a ridiculously robust Pacific jet stream straight across the continental U.S. for the past six weeks. This jet stream has flooded the central U.S. with mild oceanic airmasses, as well as blunting the southward progress of troughs and keeping moisture well away from the Deep South and Florida. This Pacific jet is finally starting to shift south a bit, which will allow some much-needed rainfall to spread across the Southeast and Florida in late November and early December.
However, while it may not remain in the average October/November position shown above right, a stronger than average zonal (west-to-east, as opposed to north-to-south) jet stream is likely to persist through the winter over the Pacific and continental U.S. The reason for this lies in some very weird climate dynamics currently being observed in both the Arctic and Siberia. Starting with the Arctic, the fall of 2016 is very unusual as sea ice area has struggled mightily to expand south from the Poles as it usually does at this time of year. In fact, the area of Arctic sea ice has actually shrunk somewhat in November, as shown at left, as temperatures have been running 30-40F degrees above average at the Poles for this time of year.
You may be wondering at this point, if North America was crazy warm in the fall, and the Arctic was also insanely warm, was it cold anywhere? It’s been equally absurdly cold in eastern Europe, Russia, and central Asia, where temperatures have been running 25-35 degrees below average. In fact, schools in Russia have cancelled classes due to unsafe cold– and when Russia is cancelling school due to cold, you know it’s serious. Unusual cold over central Asia in October and November is often a signal that precedes severe winters in the eastern U.S., including bringing citrus damaging freezes to Florida. Specifically, we look at Russian snowpack relative to average, as the most punishing cold airmasses in Florida freeze history often develop in central Asia, cross the North Pole, and swoop down out of the north-northwest into the Florida peninsula to wreak havoc. Sure enough, snows are running far above average in that region so far in 2016– but of course, there’s also no year quite like 2016 in the historical record when it comes to Arctic sea ice, either.
And that’s the key for this winter in Florida. For technical reasons, the lingering temperature contrast between the warmer than average Arctic and colder than average central Asian landmass is likely to continue driving a stronger than average jet, on average, over the next three months. So while the presence of heavy snowpack in Siberia is often a good indicator of future severe cold outbreaks, this winter, those cold airmasses are going to struggle to push all the way south into Florida at full strength, because their approach will be blunted by stronger than average west-to-east winds at upper levels. That goes along with my general idea, backed by both physical reasoning and WeatherTiger’s suite of proprietary seasonal climate models, of a fairly cold and snowy winter in the northern tier of the U.S., including the Great Lakes and Upper Midwest, with more normal temperature and precipitation anomalies across the Upper South and some drier and warmer than average conditions in the southern Plains and Southeast.
Florida Winter Forecast for 2016-17
For Florida, these inputs add up to a winter that is more-or-less average, as unlike the rest of the eastern United States, the warm bodies of water swaddling our state like chicken tenders nestled in a Publix sub make the delivery of pristine polar airmasses to our state the winter exception, not the winter rule. The expected temperature and precipitation anomalies between December and February in north, central, and south Florida are summarized in the table below.
Overall, I expect north Florida to be warmest relative to average, while the rest of the state averages out to close to normal temperatures over the next three months. As is typical for even weak La Nina years, all regions of the state are expected to see below average rainfall accumulations, with the driest weather relative to average coming in south Florida. Nevertheless, I do not expect a continuation of the complete lack of rain chances observed over the last month and a half, just a decrease in their frequency compared with normal, and even this tendency may vanish by later in the winter as La Niña weakens.
Of course, for citrus concerns, the average weather really doesn’t tell the whole story, as it is those individual severe cold snaps (especially the wildcat freeze events not preceded by weeks of cool weather) that are dangerous for fruit and trees. To address this, I took a granular look at the lowest temperatures of the year in five historical years resembling the pattern in 2016-17 (55-56, 66-67, 75-76, 98-99, 00-01) over three representative observation stations in key citrus growing regions:
- North (Winter Haven/Polk): Average of 3.2 freezes per year, with lowest observed temperature of 28 (three times).
- Southeast (Ft. Pierce/St. Lucie): Average of 2 freezes per year, with lowest observed temperature of 31 (multiple).
- Southwest (Clewiston/Hendry): Average of 0.8 freezes per year, with lowest observed temperature of 26 (Jan. 2001, which was a particularly cold event in SW Florida, as shown at right).
None of these years featured extreme cold outbreaks, though several of the years in the set recorded repeated minor freeze events, like 1975. Nevertheless, all of the years saw at least one drop to seasonal minimum temperatures around 30 in the North and Southeastern citrus zones. This is evidence that while I do not foresee an elevated chance of damaging citrus freezes in 2016-17, it is also unlikely that Florida will simply skate through the winter scot-free. There will likely be at least one or two frontal passage events that need to be watched, with a particular emphasis on the latter half of the winter for this risk as the persistent protective jet may be weakening or gone by late January or February.
In summary, I expect a drier than average but temperate winter over the majority of Florida this year– real Chamber of Commerce weather, as they say. Persistent hemispheric weather patterns generally auger against the type of sustained, severe cold outbreaks that would damage citrus production, and WeatherTiger models predict lower than average risks of citrus freeze events in 2016-17. However, the exceptional nature of early season Northern Hemispheric snowpack and Arctic sea ice trends that we have observed to date lower confidence in this forecast somewhat. In particular, if the Pacific jet influence weakens, that will be a signal that long-term freeze risks are rising. WeatherTiger will be monitoring the 10-day freeze impact potential in Florida citrus country in weekly outlooks issued each Monday; we invite you to sign up for a free trial and follow those risk assessment discussions. In the meantime, however, the baseline seasonal forecast is for mostly sunny skies, with perhaps both heaters and A/Cs switched off (for the time being).