Front awakens hare

Rain Or Shine Report for February 19th
The Hare wakes from Winter Slumbers for 2-day record

The story of the week, of course, was the front.

As predicted, it was a rain maker: waking The Hare from its winter slumbers and sprinting it back into the annual water cycle race with The Tortoise. The Hare actually moved ahead in some watersheds (Big Cypress), but is still lagging far behind in others (Lake O).

There’s still plenty of Dry Season ahead of us on the March, April, and May calendar pages.

Look for The Tortoise to make up the ground it lost to The Hare in the coming weeks, especially now that temperatures are starting to rise, and the springtime bloom is in the air: both factors that put an extra skip in The Tortoise’s step as we move into the second half of the Dry Season.

But here’s the numbers.

Big Cypress National Preserve took the brunt of the front in terms of rainfall: 4.5 inches of rain fell preserve-wide for the week. The 10-year February average is 2 inches. So twice over the monthly average fell in 2 days, and we still have a week and a half left on the February calendar. And don’t forget it’s a Leap Year.

That gives us an extra day in February, and one extra day to add to the rainfall (and evaporation) total.

As a hydrologist, I’ve always pushed for them to add that extra Leap Year day during the summer, say by adding a 32nd day to July or August — especially during drought years — instead of tacking a 29th day onto the end of a dry-season month, thereby increasing our chance for more rainfall! (Don’t chew too much on that on, it’s just my poor attempt at a Leap Year joke!)

In all sincerity, the Leap Year is a nuisance when it comes to number crunching, it really throws a monkey wrench in the works when looking at the daily data streams. I’m definitely not the crème-de-la-crème of the number crunchers – what I call the “super crunchers”, or also known in the financial industry as the “quants”, I’m just a semi-super cruncher, if that.

But back to the front.

You have to go all the way back to February of 1998 to find a wetter February for Big Cypress National Preserve.

Around 5.3 inches fell in February 1998, which was preceded by a 7.1 inch December and followed by a 5.3 inch March.

If those numbers look strange, it’s because they are strange.

The Dry Season of 1997-98 was an El Nino. Actually it was the El Nino of the century, or more correctly stated, it was the second “El Nino of the Century”, a monicker it almost stole from, but more or less shares the honors with the originally-dubbed “El Nino of the century” in 1983.
In the neighborhood of 20 inches of rain fell during both those Dry Seasons – as counted from November 1st through the end of April. That’s about twice as much as the 10-year average for that 6-month Dry Season period.

Many remember an equally wet winter, even more so, in 1995 – and it was: in the neighborhood of 20 Dry season inches fell between Nov 1994 and April 1995. The icing on the cake for that year was the 60 inches of Wet Season rain that followed.
Its somewhat of an esoteric debate among the inner circle of the ENSO researches over how past El Nino episodes rank, and 1995 always creeps into the argument, not because of the magnitude of the signal (it was lower than both 1983 and 1998), but by merit of its length: it spanned multiple years. In Florida Weather, Winesberg makes mention that the potential for El Nino events to amplify the chance for winter rainfall in Florida increases during the second year.

So the duration of the ENSO event can be just as significant as amplitude of the signal, especially with respect to the teleconnections.

But that was then and this is now.

Currently the ENSO signal has swung towards El Nino’s twin sister: La Nina. The La Nina phase tends to decrease the chance for winter rainfall in south Florida.

Keep in mind that those correlations are more or less Winter specific. Now that we are moving toward Spring, other factors will come into play – such as when and if we get more fronts, and whether they will be rain makers. We had a 5 inch March in 2005 and over 8 inches in May 2003.

But they are the exceptions which prove the rule.

Over the past 10 years, the months of November through May have averaged just around 2 inches on the nose (for Big Cypress Nat’l Preserve). That means sun is more likely over the next dozen weeks.

What’s perhaps most amazing is that last week’s 4.5 inches was the highest 2-day rain total in the preserve since October 2000.

Last week’s 2-day rain total beat out the 20 inch June 2005 – it maxed out at a 3.4 inch total on consecutive days – and Wilma which chimed in at 3.6 inches.

Interestingly, I’m having trouble placing the storm system in early October 2000 that dropped so much rain in the preserve. I’m thinking it was a tropical system, but nothing is jumping off the radar screen at me. Before that, there was Mitch, which tops the 2-day rainfall list with over 8 inches in the early part of November 1998. And a year later there was Irene’s 7 inches two-day total in mid October 1999.

How has all this affected the watersheds?

The rain largely missed the Upper Kissimmee.

But the Lake rebounded back above 10 ft. Currently its at 10.14 ft msl: that’s still an all-time February low, but the rain effectively rewound the Big Lake’s Dry Season clock around a month, to the same level it was in mid January.

Wetland stage at Loxahatchee did not rebound dramatically from the storm, just a few inches.

But that was enough to put Loxahatchee and Water Conservation Area 2 at new 5-year high-water levels for mid February. Mid-February water levels haven’t been this high since February 2000 for WCA2 and February 2002 for Loxahatchee.

The big story in the Northern Everglades is that the S10s and S11s are both open and flowing at high rates. Over 3,000 and 2,500 cfs are spilling through the S10s and S11s, respectively. That’s the highest daily flow rate through the S10s since September 2006.

Down in Water Conservation Area 3, regulatory stage jumped up a few inches, moving it above the 5-year February low-water mark it was tracking at, and actually placing it an inch or two above mid-February of last year. Like the Lake, that jump in stage rewound the Dry Season clock about a month.

But the real chart-topper was over in Big Cypress National Preserve.

Prior to the front, water levels were starting to vanish below ground into the aquifer. But that 4-5 inches of rain raised preserve-wide water levels over a foot, moving the wetting front back into the wet prairies, and temporarily rewinding the Dry Season clock back three months.

I’ve noted with similar Dry Season deluges that while they can raise the water table in dramatic fashion, its staying power at that level erodes quicker than at a similar height during the early part of the Dry Season.

Another reason to stay in tune to south Florida’s water cycle, and to tune in next week.

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