Fire Weather Outlook: April - June, 2013

RECENT CONDITIONS

In total, this past winter for Florida was one of the warmest on record, and near normal in precipitation. However, only the warmth was a constant through the winter. Rainfall patterns took a strange path, sometimes dominated by extreme events. December saw near normal rainfall overall, but split with a dry Panhandle and a wetter peninsula. January was uniformly dry across the state, the seventh driest January on record. February, on the other hand, appeared to be heading on its way to be a drier month, mostly due to a lack of rainfall over the peninsula. But, just before the month ended, a very heavy rain event over North Florida tipped the state the other way – in the books as the fifteenth wettest February on record. But this is entirely on the back of that one event, where even in this abnormally wet month at the state level, three of Florida’s five climate divisions saw near or below normal rainfall.

The El Niño-Southern Oscillation (ENSO) was in a neutral phase this winter, and as such did not exert a clear influence over Florida weather patterns that we typically see during El Niño or La Niña periods. Although, for much of January, the sea surface temperature anomalies did resemble a La Niña pattern somewhat; this may have played a role in the dry January seen statewide. With the general lack of an ENSO influence though, other factors also flexed their muscle over state weather patterns. As in January 2010 and 2011, another stretch of historically low values in the Arctic Oscillation (AO) have resulted in a dramatically colder March, and for much of northern Florida, also a continuation of the pattern of increased rainfall that ended February. Unfortunately for the bulk of the peninsula, only isolated areas saw increased rainfall, while the majority of that area has remained significantly drier than usual.

LONG-RANGE WEATHER OUTLOOK

Models currently predict the ENSO phase to remain neutral into the summer. Beyond that, there is significant uncertainty in precisely how long neutral conditions will persist, as this is the time of year in which ENSO forecasts show the least skill (For instance, at this time last year, a forecast was for an emerging El Niño event through the winter – in reality, El Niño conditions collapsed in the early fall). Modeling does indicate, though, that neutral conditions will persist through much of the year.

Both neutral conditions and the time of year represent a minimum of influence from the ENSO phase in Florida. In the near term, blocking continues to be present over Greenland, keeping the AO low and continuing the potential for colder, unsettled weather in the first half of April. However, the AO is a relatively fast-changing index and its strongly negative phase is already quite old. It should at least back away from the extreme values we have been seeing lately. Deeper into spring, very long range models indicate the potential for a return to seeing above normal temperatures, but also drier than normal conditions during a period that is already dry to begin with. There is a good deal of uncertainty for the late spring into summer without a strong influencing signal by features that are better predicted at this time scale. Unforeseen extreme events, such as those that have occurred in late February and March can dramatically alter the picture.

SUMMARY AND FIRE POTENTIAL OUTLOOK

A continued blocking pattern indicates the continuation of our recent weather patterns into the early part of April. This includes colder than normal temperatures and, at least for the northern half of the state, more rainfall. Eventually it is expected that a general trend of above normal temperatures and below normal rainfall will again emerge late in the spring, though confidence in the forecast at the later stages grows significantly with the lack of a strong driving climatic signal. This may help to alleviate some of the drought conditions in Northeast Florida, but help less in the rest of the peninsula.

Assuming the forecast verifies, the recent rains in the Panhandle will help reduce wildfire potential. That area has seen significant rainfall deficits in the past couple years, which may reduce the benefit of the rains, but as long as future rain comes with sufficient frequency, wildfire activity will be held in check. The same is true in the northern peninsula, but the more significant background drought conditions imply that somewhat consistent rainfall this spring is more essential to keeping wildfire activity from increasing much above normal. Conditions appear to be more serious in the rest of the peninsula – even in this recent rainy period, sufficient rainfall there has been difficult to come by. If we do indeed return to a period of below normal rainfall, there will continue to be greater wildfire potential as drought conditions persist or worsen. The end of this forecast period is also the beginning of hurricane season – any early season tropical cyclones could significantly alter conditions, but any discussion of that impact would be purely speculative at this time.