Rain Or Shine Report for Nov 4
Cold front brings chill, but still not Fall in SFL
Hoover Dike’s Lake Okeechobee versus Hoover Dam’s Lake Mead
Day-time highs in Naples have been steadily declining since mid October. Naples weekly-averaged day-time high had stayed at or above 90°F for 4 consecutive months from mid June through late August. The recent onslaught of cold air finally dropped our day-time high down into the mid 80s.
Shark Valley Tram and Tower. Read below to find out more about current water levels at the Tower in comparison to previous years.
The cold air has also brought some chill to the night air, at least by south Florida standards.
Naples has had three consecutive nights drop at or below 60° F. Winsberg (Florida Weather)defines the onset of Fall in Florida as occurring when night-time lows, averaged for 7 consecutive days, drop below 60°F.
That still hasn’t happended yet this year for Naples — but has occurred upstate in Pensacola (late Oct), Tallahasee (mid Oct), Jacksonville (early Nov), Gainesville (mid Oct), and Atlanta (early Oct).
The onset of Fall typically occurs during the 3rd or 4th week for Naples, but not until late December for Miami, and, if you use the 60°F standard, never for Key West. Average night-time lows bottom out at 65° F.
By the way, last year we had an early onset of Fall, with a 7-day dive below 60° F in late October — and, if you’ll remember, a month after that we had another batch of very cold air blow low across the peninsula right around Thanksgiving. It was relatively mild the rest of the winter, even by Naples standards, until a late winter downturn for the colder in February.
So the start of Fall, using Winsberg defintion, is something fun to keep an eye on — but it has little relation to the degree of coldness or deepness of the freezes to come.
Winsberg points out that the winters with the deepest freezes tend to occur when the ENSO index is in its neutral phase. That frees the meterological palette for the Jet Stream to dip high polar latitudes and low into the subtropics of the North American continent. The Jet Stream becomes more narrowly corralled in the mid latitudes of the continent when the ENSO index swings in the El Nino and La Nina phase.
The ENSO index is currently swinging into a La Nina. That means we are less likely to see any deep freezes.
One other interesting temperature note related to the water cycle. The lack of rains in Naples and Ft Myers — which typically have a cooling effect by blocking out the afternoon sun and dousing day-time heat with rain — made it a hotter summer in Naples than usual. That was especially reflected in above average night-time lows that were routinely in the high 70s. That made this year’s summer nights in Naples more like Miami and Key West — both of which have historical night-time lows in the high 70s — instead of Naples normal low 70s night-time low.
Its the end of the rains that define Fall in Florida more than anything. South Florida averages around 2 inches of rain in November, as it does for the rest of the Dry Season through April. (SFL-wide rain history)
Around 5 inches of rain fell across south Florida in October. As we know, it didn’t fall evenly. Miami-Dade recorded 10 inches of October rain, whereas Naples and Ft Myers and Lake O only recorded 3 inches in comparison. The Kissimmee Valley recorded around 5 inches of October rain, which bodes well for inflows to the Lake. Big Cypress National Preserve matched its historical October average with 4 inches of rain.
Lake O is at an all-time November low, but the good news is that Lake stage has continued to slowly creep up. Its current elevation at 10.4 ft msl is just around 2 ft lower than early November of last year. Just two months ago in mid September Lake stage was almost 4 feet lower than mid September of the previous year. The difference has been this year’s October inflows from the Kissimmee Basin (through the S65E) in comparison to none for October of last year.
Going back almost two years to the date, Lake O stage stood higher than 17 ft msl in November 2005 as a result of Wilma. In the two years since, the Lake’s withstood two consecutive Wet Seasons with under 25 inches of rain, and last year’s sub-par 5 inches of Dry Season rain, plus lack of rain in the upstream Kissimmee Basin — all of which have had the combined effect of dropping Lake stage to its current historic November low.
The hope was to have an above average Wet Season this year, and although that didn’t pan out as hoped, at least there was a mild dose of October rain that kept the onset of the dry season at bay until the first of November, intead of last year’s early Dry Season start because of a rainless October.
Lake stage is around 5 ft below its 5-year early November average. The last time November Lake stage was close to this low was in 2000 when it started November at a 12 ft msl stage, and before that in 1981 when November Lake stage was also in the 11-12 ft range.
Lake stage has now been below 13.5 ft msl — the point below which most of the Lake’s littoral marsh goes dry — for 18 consecutive months.
Below is a hydrograph showing Lake Okeechobee’s stage since 1990 in comparison to the Colorado River’s Lake Mead (the pool of water behind Hoover Dam). Lake Mead is also in the midst of a drought that has steadily dropped water levels behind Hoover Dam 100 ft over the past 10 years.
Both are multi-use water bodies. Lake O looks bigger from a map, but actually holds a lot less water — only 4-5 million acre feet in comparison to Lake Mead’s 28 million acre feet, which is currently holding half that volume due to the multi-year drought. The difference is the depth — Lake Mead is around 400 ft deep, and over 100 miles long. The deepest point on the Lake around 8 ft under current conditions and only 25 miles from bank to bank.
Lake Okeechobee’s drought stricken 30 inches of annual rain is gargantuan compared to Lake Mead’s 4 inch annual average. Lake Meade relies on snow melt from its upstream Rockie Mountains in the same way that Lake Okeechobee depends on inflows from the Kissimmee Valley.
This comparison also highlights Florida’s abundance of water, but lack of storage, versus the American West’s large storage capacity, but relative lack of water to keep it filled.
The big news in the Everglades is the S11s. They are currently discharging around 2,500 cfs into Water Conservation Area 3, and have been flowing at or over 1,000 cfs for almost a full month now. That was after a 12 months of not flowing at all.
Further upstream, the S10s are still closed. That and all the rain that fell on the east coast has pushed regulatory stage in Loxahatchee up to a new 5-year high-water mark. Loxahatchee stage is currently perched 7 ft above nearby Lake Okeechobee.
Flow also continues to discharge into Everglades National Park through the S12 structures — at around 400 cfs — which incidently has been this Summer’s maximum flow rate for the S12s to date.
That puts the S12s on track to discharge less than 100,000 acre-feet for the first time since the drought years of 1989 and 1990. The S12s peaked in 1995 at over 2 million acre-feet in comparison, and most recently recorded over 1 million acre-feet in Wilma influenced 2005. This year the S12s are actually on track to fall under 1989’s 30,000 acre-feet annual flow volume.
That lack of upstream flows, despite all the rain in Miami-Dade, has dropped water levels in the downstream Park. Wetland water depths at the Park’s Shark Valley Tram are over foot lower than November of 2003, 2004, and 2005 — but at about the same level as early November of last year. That makes it the second consecutive dry start to the Dry Season for the Park.
Sheetflow volumes in Big Cypress National Preserve are also down for the year. USGS flows monitored under the preserve’s 35 length of the Tamiami Trail are at a 30-year low. Interestingly, preserve-wide stage are tracking at the same level as last year, which also matches the 5-year early November average for the preserve. The difference maker this year was the abundance of rain south of US41.