May 10, 2011

Clouds do not equal rain

When will the meteorological wet season start?

Usually by mid May the big clouds are popping up.

Cumulonimbus cloud of early May

But rainfall, not cloud formations, is the metric that matters.

The bubble chart above plots a point for each day over the past twenty years in which over a quarter inch of rain fell, as an average, across south Florida. Anywhere you see a “purple rain drop” in the center of those points marks what we call a Big Rain Day. That’s our non-technical catch term that we use (as coined by meteorologists over in West Palm Beach) for describing a day in which the south peninsula gets thoroughly drenched.

It’s the Big Rain Days which give the wet season the biggest boost.

Consistent rains kick in towards mid and late May

Over the past few weeks the tell-tale towers of cumulonimbus clouds have returned, and – locally at least – they’ve dropped rain by the buckets and even some hail, but they haven’t been big enough to get picked up on our regional bubble chart (shown above.)

Some wet seasons start of early (i.e., 1997, 2009) while others sputter into June (i.e., 1998, 2000) and others benefit by a Big Rain Day right out of the gate (i.e., 2005.)

This year the wet season hammer has yet to fall,

Which, when it does, will have a lot of filling up to do.


jabblog said...

We're hoping for lots of rain to drench the forest floor and hopefully prevent any further fires.

Janie said...

Clouds do not = rain, but no clouds does = no rain. That's my statistical and philosophical offering for the day. He's hoping you get clouds = rain one day soon.

Robert V. Sobczak said...

So true about the corollary formula, Janie! Despite the waiting game for the start up of the true meteorological wet season we got lucky with pop up showers two consecutive days last weekend that fell right over top the fire. Last word is that it should be fully contained in the coming days.