How To: Read a Rain Chart
I get it, charts can be boring (without narration)

Not that I’m a wildly dynamic speaker …

Nor are rain charts especially charismatic.

Bob has a one-on-one conversation with a rain chart

But combine the two together and I think you get, well — I think you’ll see the result. At the heart of the issue is what I’ve been told so many times: “Bob, you make a splendid rain chart, but most people don’t know how to read them.” And so my journey began, hours after hours, years upon years, in the quest to make the perfect rain chart. My conclusion: I think the only way to give a rain chart its due is to allow it to talk, and speak for itself. Okay, I’ll admit. I had to add the voice. And yes, I had to juice up the charts a bit (some would say with too many colors). Just don’t say I didn’t try.

Comparison of dry season rainfall, from 1970 to present. Cool color-coded bars indicate wet winters and warm color-coded bars indicate drier than normal winter.

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#Overheard: South Florida’s water year starts on May 1st, but the wet season doesn’t officially kick in until around May 20th.

Click “Read More” to see all the hydrographs!

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Weather Drop

SFWMD Weather Forecast
Courtesy of SFWMD's Meteorology Team

South Florida Water Management District Weather
10:08AM Thursday, May 16, 2022 (mrn)

Synopsis: An upper-air trough of low pressure extending from the southeast U.S. coast to the eastern Gulf of Mexico will gradually move eastward across Florida today and lie east of the SFMWD by Tuesday. A good supply of moisture and instability immediately ahead of the trough and sufficient daytime heating should cause showers and thunderstorm to form, with southwesterly steering winds favoring the rains over the eastern part of the SFWMD from around Lake Okeechobee southward and eastward through the eastern metropolitan areas. The median areal average rainfall across this region ranges from a quarter to half of an inch, with the 90th percentile or reasonable worst-case scenario in excess of half of an inch. As the trough passes across western areas and the Kissimmee Valley by this afternoon, subsidence (sinking air) and a subsequent drying with low instability should result in essentially no rainfall, or at least little of note. On Tuesday and Wednesday, large-scale subsidence in the wake of the trough is forecast to greatly suppress typical shower and thunderstorm development. However, there should be enough low-level moisture to cause isolated rains to develop along both east and west coast sea breezes on Tuesday and then isolated or widely scattered rains on Wednesday over the interior and the west when the steering winds become easterly to southeasterly. The 10% exceedance on either Tuesday or Wednesday should be no more than about a tenth of an inch. Next, a tropical wave located over the central Caribbean Sea on Tuesday should move into the western Caribbean Thursday and Friday, with its moisture feed beginning to stream northward through the Florida Keys and far southern part of the SFWMD overnight Thursday. The wave’s moisture will also be accompanied by an influx of instability, both ingredient of which should support a large increase of rainfall and rain coverage SFWMD-wide Friday and Saturday. Given the favorable large-scale conditions accompanying the wave passage south of the area, there is likely to be an enhanced risk of locally significant rainfall area wide but especially over the interior of the SFWMD. Although the most best moisture/instability seems as if will have passed by Sunday, southwesterly steering winds and daytime surface heating should still result in a good coverage of rain probably focused over the interior and the east due to southwesterly steering winds ahead of a cold front dropping southward into north Florida by Monday morning next week. For the week ending next Monday morning, total SFWMD rainfall is forecast to be at least normal and probably above normal. Monday: Very warm over parts of the SFWMD> A few showers and isolated thunderstorms developing in the east or southeast before noon. Then scattered to locally numerous afternoon showers and thunderstorms developing south and east of Lake Okeechobee through the southeastern metropolitan areas, some of which could be heavy. Rains could continue to around or after sunset before dissipating over these areas. Then quiet overnight as drier air moves across the entire area. SW to W winds 5 to 15 mph, except S near the east coast. Winds W to WSW 5 to 10 mph overnight. Tuesday: Very warm over the interior. A general lack of much rainfall area wide and far below the daily climatological average. Whatever rains do form should occur during the afternoon to around sunset inland of the east coast along the east-coast sea breeze and inland of the west-coast along the west coast sea breeze through the Kissimmee Valley. Rains diminishing by or during the early evening. Mainly W to WNW winds of 5 to 15 mph, except for E to SE winds developing by the afternoon to early evening along and near the east coast. Wednesday: A continued reduced total amount and rain coverage compared to climatology. Afternoon rains developing over parts of the interior and then over the interior and the west by late afternoon to around sunset. Isolated rains over the far west could produce heavier totals of rain. Rain chances diminishing in the east by afternoon. Mainly E to SE winds of 5 to 15 mph in the east but with W winds of 5 to 15 mph over the west during the afternoon. E to SE winds 5 to 10 mph south of Lake Okeechobee but SW winds 5 to 10 mph north and west of Lake Okeechobee overnight. Thursday: Quiet with essentially no rain in the morning. Then isolated or widely scattered afternoon rains across the SFWMD, with a few embedded heavier rain areas. However, an increase of rains should begin rising from the south into the far southern part of the SFWMD during the afternoon, followed by a good or widespread coverage of rain overnight through the Florida Keys. SSE to S winds 5 to 15 mph during the morning but then E to SE over the eastern part of the SFWMD during the afternoon and W to SW over western areas. SE to S winds area wide overnight. Friday: A large increase of rain area wide, with total rainfall likely well above the daily climatological average. Scattered to numerous showers and thunderstorms producing a widespread coverage of rainfall, some of which could be heavy. Heaviest rains probably over the interior and the west from the afternoon to early evening. An enhanced risk of locally significant rainfall accumulations. Rains diminish late in the evening and then mostly quiet overnight. SE to S winds mainly 5 to 15 mph. Saturday: Total rainfall again probably well above the daily climatological average. A good or widespread coverage of moderately heavy or heavy rains over the interior of the SFWMD but especially around and north of Lake Okeechobee from the afternoon to early evening. An elevated risk of locally significant rainfall over these areas. After evening rains diminish, mainly quiet conditions likely overnight. SE to S winds 5 to 15 mph, except S to SW north of Lake Okeechobee (0.36″). Sunday: Low-confidence forecast. Little rain in the morning, but scattered to locally numerous showers and thunderstorms forming over the interior and the east during the afternoon. Rains diminish during the early evening. SE to S wind 5 to 15 mph, except SW north of Lake Okeechobee, with winds becoming W to NW area wide overnight (0.27″).

Day 1

Go to SFWMD’s Weather Page

Thank you to the Meteorology Team at South Florida Water Management District for this forecast. I always learn something new when I read it, whether it be an atmospheric process or a new word. And more than any other forecast, it really lets you get the big picture of when and where rain may fall. The one problem is it’s buried on their website, thus my inspiration to feature it on Go Hydrology.

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Proverb: “All droughts end in flood.”

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dry season

Dry season review
A holiday guide to the dry season

How did a relatively normal dry season …

appear to be so darn wet?

Months or holidays: Which interval do you prefer for comparing rain? The advantage of months is that they are equal units. The advantage of the holidays is it allows us to partition the dry season into its various acts (i.e. opening gate, cool season, green out, spring ebb, etc.). We were headed for a “dry” dry season until the April unexpectedly kicked in.

Answer: It’s not how much but when the rain fell. And I’m not talking summer rains or fall hurricanes, which together give us about 43 inches per year. And I’m not even talking the thirteen inches of dry season we recorded this year for the 6-month span between the start of November to the end of April, which for the record was about 1-2 inches above the normal dry season total. The big difference maker when it comes to the swamp batting back the descent into deep spring drought is April rainfall. No April rain means deep drought in the swamp. This year, as indicated by the yellow bar above, the swamp recorded a solid 6 inches of rain from the spring solstice (March 22) until now. That’s twice as much as the year before (2021) and three times as much as the year before that (2020) and just the right amount of rain necessary to keep standing water in the cypress domes and strands.

Did I mention we had a subpar summer? It didn’t matter thanks to the timely April rains!

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Question: What’s your favorite dry season holiday?

Case of the Missing May
Firelight Radio Presents

What happens when the calendar …

Misses a month?

Firelight Radio is available on Apple Podcasts and Podbean

Answer: That’s what happened this year when we went from February, March, April to … June(?)  That’s right, by all indications we missed May.  You see typically the start of the summer wet season starts around Memorial Day, or the last week of May.  This year the transition occurred at the end of April, making me wonder if we either leapt a month ahead or somehow missed the month of May.  The good news: Just when I thought May was a lost cause we seem to be in the midst of receiving our final blast of dry air before the 6-month humidity hammer of Florida’s endless summer starts to bear down.

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Puzzler: Why is October (i.e. oct = 8) the 10th month?

Weather Drop

What May?
February, March, April ... June?

Usually May is that month …

That the swamp both bottoms out and bounces back.

The Everglades usually bottom out in May

Or did the water calendar jump straight to June? That’s what it feels like these past few days. A regular onslaught of afternoon rain showers — and I mean some real gully washers — are giving early May a decidedly beginning of June feel. It’s too early to tell if the pattern will persist, but if it does, then make a mental note: 2022 will be remembered as the Year Without a May.

Caption: Calendar chart showing daily rainfall in the Big Cypress Swamp from the mid 1998 to present. The black drops are Big Rain Days (i.e. when over an inch of rain fell in one day). We get a handful of those every year. Orange dots are days without rain which, as you can see, dominate from October through mid May.

Attention: The potential early start of the summer rainy pattern cannot be used as an excuse to forget Mother’s Day, Memorial Day or any other events or scheduled meetings that may occur this month.


April Showers
Bring May sheet flow?

The end of the water year …

Usually ends on a dry note.

Monthly rainfall chart for Big Cypress National Preserve

Not this year. The long-term normal for the month is around 2 inches. This year we doubled that total, which much of it coming towards the end. The start of the new water year in May typically begins the deepest and driest part of the spring dry down. This year, the start of May feels more like the start of June. Afternoon showers have been the norm. Will they last? At this point the only thing I can say for sure is that the mosquitoes can’t be far behind.