Author: WeatherFlow Forecaster

Mystery Fog Bank Drifts Into the SC Coast on 3/27/20.

By WeatherFlow meteorologist Shea Gibson written on 3/29/20.

Lots of folks on the water (and meteorologists alike) saw a fog bank encroach the coastline late Friday afternoon and into the evening. It was rather peculiar because we generally would see a marine layer (fog) build along the coast as ambient air temps surpass the water temps by a substantial amount through the day, or leftover from nighttime into the morning.  This fog bank; however, was one that crept up on us in the afternoon and we can definitely can understand how legendary nostalgic maritime vessel and pirate stories would have started.

The setup at the coast was a classic warm pattern for the SE Region with Atlantic High pressure bringing somewhat moderate SW/SSW Sea Breezes into the coast. As with all successful Sea Breeze circulations, humidity was very low at the beaches and just inland. Sea surface temps (SST’s) were in the mid to upper 60’s and ambient air temps topped out around ~86°, making a difference of around 14-16 degrees. This is not very much of a difference to create a marine layering along the coast, but rather would be a very shallow surface layer if anything.

Here is a snapshot is what the cooler shelf waters were on that day. You can see the Gulf Stream offshore as the warmer body of water in the low 80’s.

At some point in the afternoon, a cool and stable pool of air managed to develop over the shelf waters. It was curved around the Atlantic High pressure and was nudged into the coast along the Sea Breezes. Here is what I caught off the GOES16 visible imagery:

To many on the water and beaches that day, it came as quite a surprise. Not only did it make air temps drop several degrees, it also eventually killed off the winds by several knots as this pool of stable air was injected into the Sea Breeze circulation.

Here are a few pics of the area from the locals:
This one from Daniel Cubberly Goldston at Kiawah Island just south of Charleston.

This one from Andy Lassiter at Folly Beach:

And this one from Eric Angermeier at the back marshes of Folly:

The NWS Charleston even issued a Dense Fog Advisory to cover the time for the effects:
With the Sea Breeze being so moderate before the fag bank moved in, it was pushed into the coast where warmer, unstable air existed and dispersed by 7:00PM.

You can see the air temp drop starting just after 4PM inside the Charleston harbor at our Fort Sumter Front Range Light.

And here are the winds dropping after the cool air injected itself into the Sea Breeze circulations. It was not immediate, but rather gradual. This data was pulled from our weather stations at both the Isle of Palms pier and the Folly Beach pier.

So we already know that marine layering can hamper speeds and cause Sea Breeze decoupling where onshore flow is occurring off the cooler waters, but what about that magic number where this complication does not happen anymore? After watching SST’s and Sea Breezes for several years, I have pinned it right around 76°+ for the Charleston area when waters actually start feeding the instability factor (instability = more wind). For an additional reference point, in tropical system development we generally see 80°+ as being the fuel from the ocean surface.

As always, we are life-long students to this science and always watching, researching and sharing what we learn. Stay safe and cheers from us at WeatherFlow!

Shea Gibson
SE/East Coast Wind Forecasting
New Station Project/ Outreach
Twitter: @WeatherFlowCHAS
Facebook: Shea Gibson – Meteorologist

Sources: Our own WeatherFlow Datascope product. Nasa Sport SST: ; College of DuPage Nexlab

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CAD Burn Down Event

By WeatherFlow meteorologist Shea Gibson 3/26/2020

Ever heard of CAD? It is a term in meteorology known as “cold air damming”, where cool dense air settles under an area of High pressure under a blanket of thick stratiform clouds (mid to low level clouds). Along the East Coast, we see that this cool body of air sometimes becomes lodged between the coast and the Appalachian mountain range and can sit for hours or days at a time depending on the atmospheric setup. They can be hard to predict and keep air temps several degrees cooler until it wears off. For the East Coast, including the SE Region, the main way to get rid of CAD is to inject warm air from the east, southeast, south and southwest…which you will see below. Keep reading.

Today, Thursday March 26, 2020, we saw a rather large but disorganized pool of cold air settling down across the SE region and backing up against the mountains. A moderate area of High pressure was bottled up over the Appalachians and was pulling cool Northerly flow down around it with a thick cloud bank.

Here is the satellite imagery around 10:11AM (14:11UTC) showing a rather large cold pool extending from parts of the coast all the way to the mountains…mostly focused along the steeper up-slope of the mountains along the western foothills.

As winds started nudging in from the ocean and over the warmer land mass that was exposed earlier, we saw the curtain of stratus clouds begin to evaporate from east to west and south to north. If you look closely, you can see how the clouds were “sloshed” up-slope and overlapped the existing cloud deck due – and winds aloft nudged this overlapping . This puddling effect came out quite well in our Goes-16 satellite imagery. Just click play for some animation.

You can see that as the day progresses, the CAD is broken up by warm Southerly winds from the south and southwest from Georgia into SC….and East winds cutting across NC. Eventually just about all of it dissipates. And guess what? It allows the Sea Breezes to circulate at the coast for added bonus to the wind sports communities!

We call these warmer air masses “CAD killers” when we see this kind of dissipation/evaporation. It may seem just like a cloudy morning then a sunny afternoon to some, but if you look closer in some of the visible tools available to us now, you can find some really cool atmospheric dynamics. The sky acts like an ocean at times. Great to see it in real time. 🙂

Stay safe and cheers from us at WeatherFlow!

Shea Gibson
SE/East Coast Wind Forecasting
New Station Project/ Outreach
Twitter: @WeatherFlowCHAS
Facebook: Shea Gibson – WeatherFlow

Sources: Tropical Tidbits ; College of DuPage Nexlab 


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South Winds Speed through California’s Valleys

by Meteorologist Kerry Anderson

This past weekend my husband and I visited Death Valley National Park. How did I miss this gem? I guess the name and reports of the hottest temperatures in the nation don’t exactly make for great PR. But it was awesome. We encountered really strong south winds which of course meant I had to come home and blog about them.  They have developed due to a major pattern shift which won’t be going away for a while.

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West Coast Wind Blog: Cut-Off Low stalls California wind patterns

by Mike Godsey,

Usually, in March we have NW wind clearing winds after a storm. But this storm will seem like it will go on for days. The low pressure of storm system is normally steered from west to east by the upper-level troughs and ridges at the 500mb level at ≈ 18,000 ft. But today and the next several days we have a Cut-Off Low at ≈ 18,000 ft. that is disconnected from the flow of upper-level winds.

Once this happens the Cut-Off Low wobbles about somewhat unpredictably. And if the Cut-Off Low is supporting a surface storm as it is today then the storm’s rains and winds will continue until the Cut-Off Low opens up into a more normal upper trough and departs eastward. You can see all this happening in this annotated model imagery.

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West Coast Wind Blog: Why no NW clearing winds for California?

by Mike Godsey,

It is the gospel (Ecclesiastes 1:14) that after an early spring/late winter storm we see more blue skies and NW clearing winds along the California coast to delight wind Hungary kiters and windsurfers. This model output below for Friday, March 13 shows why we will not see much NW wind for a while.

Notice the first storm that has just passed over Southern California.

Behind the storm you can see a bit of NW clearing wind developing and that may reach Bodega late this afternoon and rest of the Bay Area during the night. But look at all the storms lined up across the Pacific. Also notice how far away from us the North Pacific High is located. Not a promising scenario.

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West Coast Wind Blog: North Pacific High brings NNW wind to the Sea of Cortez…Not!

The winter 2019-2021 season in Baja was atypical in a number of ways.

It started off with a bang in November but from that point on the winds were often unreliable unless you were on foils or big kites or sail. Or if you were there during one of the few strong wind periods.
But the main anomaly was the source of the northerly winds. Typically much of the wind comes from high pressure in the Great Basin or ideally 4 corners area of the western USA. This wind streams towards the persistent low pressure trough south of Baja. Then this N to NNE winds curves into the beaches at places like La Ventana and Los Barriles that have a warm valley inland.

But often this year the Great Basin was devoid of high pressure so we often lost that wind machine. But weirdly the North Pacific High as unusually large and atypically in a more northern location much of this winter. And this often brought solid NW wind to Baja’s Pacific side and NNW winds to the Sea of Cortez.

Unfortunately, NNW winds are at a more unfavorable angle to the La Ventana and Los Barriles and especially the El Sargento beaches. Plus some of this wind can is west enough to come down the arroyos creating weak offshore W. winds at the beaches making for unreliable wind inside. Still, any wind was welcome this season and we became to learn the routine: Strong NW wind on the Pacific side of Baja means somewhat unreliable but welcome wind for the El Sargento to Los Barriles corridor.

Until….. it doesn’t. If the models are right later this week a resurgent North Pacific High brings strong NW winds to Southern California and the entire Pacific side of Baja.

Looking at this animation you can see the North Pacific High and those strong NW winds. But notice how weak the winds are in the Sea of Cortez.

Now notice the huge low pressure in the Great Basin. This is the area where we need HIGH PRESSURE to created classic El Norte winds for Baja.

Now notice how the North Pacific High curve towards the Great Basin low pressure rather than building down the length of the Sea of Cortez. Hence the exception to rule about NW wind on Baja’s Pacific side and a windy Sea of Cortez for the El Sargento to Los Barriles corridor.

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Strong Winds drive down the California Coast and into the Bight on Sunday.

by Meteorologist, Kerry Anderson

Saturday the wind profile for California’s Central Coast and inside the Bight were dramatically different. Onshore flow increased from Santa Barbara to San Diego cooling temperatures and squelching sea breeze activity.  Consequently, winds have been anemic.  Meanwhile, the Central Coast beaches spent much the day with winds in the upper teens and even some moments in the low 20’s.

These winds developed due to a combination of systems. A very strong High-Pressure system reigns over the Eastern Pacific while Low pressure has been sinking southward out of the Plains of Canada and filling into the Great Basin.  Additionally, an upper-level Low is moving down the West Coast.  It is deepening as it moves Southward, bringing cold air back to the area.  All this has combined to create strong NW/NNW winds from Northern to Central California.

But those winds didn’t quite reach into the Bight, so most beaches were generally light.

  All that changes overnight though.  The Low sinks further south and continues to deepen.  That will start NW winds building overnight and driving southward.  Look for upper teens and low twenties across Santa Barbara by morning and working down toward San Diego by the afternoon. But make sure to get out and enjoy them tomorrow because this  pattern changes fast.  The Low exits to the east and offshore gradients build quickly for Monday.

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West Coast Wind Blog: While Baja’s big wind machines idle… back up wind engines carry the load.

by Mike Godsey

In normal years the bulk of the strong wind at the kite and windsurf sites in the Los Barriles and La Ventana areas comes from high pressure in the Great Basin area of the USA. However, the 2019-2020 winter season has seen lots of days when an unusually robust North Pacific High (NPH) has sent strong NNW winds down the Sea of Cortez.

The NNW angle of this NPH wind is not ideal for reliable wind at the beach but if there is good inland valley heating this wind does curve into the beaches.

But sometimes this season both the North Pacific High and the high pressure in the Great Basin have either been absent or too far away to help the Baja Sur winds.

Typically when this happens and we have blue skies we see kiteable mid to upper-teens winds from the local sea breeze as the inland valleys heat. These winds usually are strongest in the Rasta Beach area north of El Sargento and weaker for the La Ventana beaches and weaker yet for Los Barriles.

But there is another wind machine in our area that can ally with the local sea breezes to brings upper-teens to about 20 winds to the area. And that is the thermal trough just south of Baja’s East Cape.

Let’s look at today, February 21, 2020 as an example of this pattern.

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