The Coastal Carolina Nocturnal Jet


by WeatherFlow meteorologist Shea Gibson

Ever heard the terms “nocturnal jetting”, “overnight jetting” or “evening surge”?  This happens when there is what is called an atmospheric “inversion” in the troposphere that traps a cool layer (radiational cooling of land overnight) at or just above the surface beneath a warm layer with a ribbon of fast moving air at the lower levels. During warmer seasons and in warmer air masses, this typically may only last until the sun comes up and the radiational heating process begins, if not diminishing earlier.  They are many times preceded by inland troughing and/or associated Low pressures, well ahead of cold fronts and stronger ones ahead of warm fronts. We see these more pronounced south of undulating fronts (rippling stationary front) and backdoor fronts (fronts that drop down from the north) to be specific for the SE Region. In fact, we had an undulating warm front to the north over northern NC and Virginia on this night and into sunrise.

Once the sun comes up, the land warms and the “thermal cap” is broken – this is where we will later get the dry line at the coast. This allows for warm air to freely rise higher up into the atmosphere (called “thermals”) for convection to form. It also allows the Sea Breeze to be drawn into land and strengthen. Sometimes, the morning jets burn off and the Sea Breeze comes ashore by midday…and other times, the sun’s heat and dissipation of the inversion (thermal cap release) can allow the Sea Breeze to push onshore earlier to get the winds moving by mid morning again. This depends on a few factors- with a couple being the overall regional pattern and allowable pre-frontal activity.

The pictures below show the mid level clouds along the warm air inversion – pics by Isle of Palms resident Rusty Williamson. Thanks Rusty!



Here is a prime example along Isle of Palms and Folly Beach of the overnight “nocturnal jet” quickly diminishing as the sun came up and radiational heating began.



And how could we forget the local US National Weather Service Charleston’s weather balloon sounding (radiosonde) for the vertical profile. Here is the 7AM sounding that shows the inversion just over the surface and another warm nose of air above it.


So now you know why there sometimes is a “nocturnal jet” overnight along the coast that keeps winds moving through sunset (with occasional higher builds) and why the winds could be elevated in the morning just before sunrise. If you ever have serious trouble tuning in your radio at night, it may be because of this occurrence which can cause signal degradation radio waves. But on the “bright” side, it can also show you that “green flash” at sunset if you can ever catch one.


Shea Gibson
WeatherFlow Meteorologist
SE Region/ East Coast
Outreach and New Station Projects
Twitter: @WeatherFlowCHAS

Posted in Coastal South Carolina

Low pressure is always a good thing for thermal winds right?


Well… only if it is in the right place.untitled

by Mike Godsey, mike AT


Up at ≈ 18,000 ft. feet a massive near record upper high pressure is expanding from Texas towards Southern California. Subsiding, descending, air from this high will compress and heat the air in the Great Basin & Southern California inland valleys and deserts creating an expanding thermal low pressure zone.

Typically low pressure in the Southern California interior means strong coast wind. But in weather as in life too much of a good thing…..

Looking at the first animation below for Sunday you can see the heat expanding from the interior towards the Long Beach coast.
This in turn creates a local low pressure zone inland so in the early afternoon the winds at Cabrillo, Belmont & Seal begin to build.

Note how the Palos Verdes Peninsula stays a bit cooler since it has cool ocean water on 3 sides.

Now look at the 2nd animation which shows the isobars going from the Pacific inland. Notice how as the heat you saw in the 1st. image approaches the coast the isobars also march towards the coast so the pressure gradient goes up.

thermal trough (aka %22heat bubble%22)But then around 4 PM you can see the isobars balloon over the Belmont to Seal area. This means the pressure gradient drops over this area so the wind drop.

But Cabrillo, beyond the thermal trough (aka “heat bubble”) is more likely to stay windy.

To make things more complicated the cool air blowing past Cabrillo fights with the heat bubble so the winds at Belmont to Seal pump up and down. And if the Cabrillo winds are strong enough they could possibly overcome the Belmont to Seal heat bubble. But if the heat bubble is strong enough it will divert the wind from Belmont to Seal and deliver it to the Huntington Beach zone.

Hence my complex wind forecast for Long Beach area winds tomorrow Sunday.heat Bubble isobars

Incidentally this present heat producing 500 mb level upper high pressure is near the all time record level of strength. For the last 30 years the size, duration and strength of these 500 mb high pressure zones has been steadily increasing so California heat waves have become more common and of longer duration.

Posted in Los Angeles, San Diego



Today an eddy dominates Southern California and tomorrow the Bay Area winds. Why? Upper level winds!EddiesBay&SCallday

by Mike Godsey, mike AT

Imagery and text coming for Bay Area and Southern California.

Turbines will  be spinning to southerly winds in the interior of both the Bay Area and Southern California as upper level winds in the 5000′ to 18,000 ft. range keep the Golden Gate Eddy and the Catalina Eddy spinning all day creating southerly flow. This happens in Southern California today and for the Bay Area Sunday.

Catalina EddyAllDay+500mb.mp4GOLDEN GATEeddyAllDay

Posted in Los Angeles, San Diego, San Francisco

Please explain why/ how wind at 18,000 feet effects the ground wind..?


I was hoping no one would ask that question…

by Mike Godsey, mike at

Posted: 09 Jun 2016 17:35slide_36

U2U2U2 wrote: I’m not a meteorologist . Please explain why/ how wind at 18,000 feet effects the ground wind..?

Hi U2U2U2,

I was hoping no one would ask that question since a simplified answer would take pages and complex graphics. Which I will do one day in a blog. But for now here is an oversimplification using the Bay Area surface winds Friday June 10 as an example…

1. As the winds at ≈ 18,000 ft. flow over us there are areas where this wind flow converges. This acts to cause descending air that induces higher pressure towards the surface. Tomorrow for instance this happens over the North Pacific High so it grows and expands towards the Bay Area hence I am forecasting much stronger NW wind Friday.

2. By the same token winds at ≈ 18,000 ft. sometimes diverge so they cover a wider area. This tends to cause wind below to rise which deepens low pressure at the surface. I expect this to happen over the N. Great Basin tomorrow which should increase the SFO-Winnemucca pressure gradient which adds a few knots to our strong winds tomorrow.

Below are more reasons why the wind at ≈ 18,000 ft. are important but for now let’s focus on #1 & 2 above since they are the hardest to convergence & divvisualize. The top image shows the basic concept. When the 500 mb  winds at ≈ 18,000 ft. exit an upper ridge they converge some of the wind is forced downward towards the surface
packing more air into this region creating higher pressure. And tomorrow this happens over the North Pacific High as you can see comparing the second and third images. This makes the North Pacific High larger and means stronger wind on the California coast. But it also helps create the Southern California Catalina Eddy which you can just make out in the 2nd. image.

Looking at second  image again notice the low pressure in the Great Basin and the wind flow from the ocean over the Bay Area heading that way. The pressure gradient is strong tomorrow which enhances the Bay winds. Why? Compare the second and third image again. Notice the area where the winds at ≈ 18,000 ft. diverge. This causes surface winds to rise so less air is packed in the Great Basin which means lower pressure. Which turn means a stronger pressure gradient between the ocean and the Great Basin so we see stronger wind.

More reasons the wind at 18,000 feet effects the surface wind:

3. The most visible way the upper level winds impact the surface winds is the depth of the marine layer that are so critical in Bay Area surface winds. Basically when the upper level winds steer a upper ridge over the Bay Area the descending warm air creates an inversion with cool often foggy air near the surface and much warmer air just above the foggy air. If the upper ridge is strong this crushes the marine layer clouds so they barely extend to the coast to the Golden Gate. If the upper ridge is weaker the fog goes further into the bay.

On the other hand if the upper level winds steer an upper trough over the Bay Area the rising air allows inversion to lift so the marine layer deepens and the fog moves much further into the bay.

Either way the depth of the marine layer determines where the wind focus will be inside the bay. If an upper trough is above us then the wind focus will  be towards Sherman Island. If an upper ridge is aloft then sites near the coast are more likely to blow.

4. Winds at the 500mb level which averages at 18,000 ft. play a critical role in moving the North Pacific High around this part of the pacific making the NW ocean wind build if the NPH is closer or fade if it far away. So tomorrow they move the NPH closer to the Bay so I expect much stronger NW surface wind.

5. The upper troughs these 500 mb winds form also can make the NPH push a ridge into the Pacific Northwest which makes our ocean surface winds more NNW and creates NNW to NNE winds just over the Bay Area which in turn makes the pressure gradient focus west of Treasure Island so Sherman Island dies and the East Bay is weak as you will probably see Saturday.

6. Upper ridges formed by the 500mb winds cause heat waves when they are over the Central Valley causing stronger Bay winds. But if the upper ridges are too strong the Central Valley thermal low expands over the Bay killing first the East Bay winds then possibly all the wind.

7. Strong 500mb winds are typically accompanied by strong wind closer to the surface. When these winds at say 1000 feet hit the coast range they climb up those mountains where they pick up momentum from the even stronger winds above the mountains. So when they descend down the coast range they are much stronger and gustier than they were over the ocean surface. You will experience this tomorrow!

8. through 100… to be continued.


Posted in Columbia River Gorge, Los Angeles, San Diego, San Francisco

Water Footprints of TS Bonnie and TS Colin 2016

by WeatherFlow meteorologist Shea Gibson

Here is the NASA SPoRT Center Sea Surface Temperature loop that goes from May 20 to present. Notice the cool water up-welling eddies in the Gulf Stream off of the Southeast coast created by both Tropical Storm Bonnie and Tropical Storm Colin. We could say “footprints” over the water in this case.


Shea Gibson
WeatherFlow Meteorologist/Wind Forecaster
SE Coast/ EC
Outreach & New Station Projects
Twitter: @WeatherFlowCHAS

Posted in Coastal Georgia, Coastal South Carolina, Outer Banks of North Carolina, SouthEastern North Carolina

Rio Daze: The right stuff…


Add eddy, SW flow aloft, pressure gradient to N. Great Basin Sherman IslandDawnand the Central Valley and step back!

by Mike Godsey

Below is some imagery I will turn into a blog later. Right now I am preparing to hit the water!

But the imagery below should be enough for you to construct the probable blog text.

Posted in San Francisco

Tropics start out active. Invest 93L discussion w/ Florida in its sights.

By WeatherFlow meteorologist Shea Gibson

Here is the latest update for Invest 93L, which could become Tropical Storm Colin.

Be safe and have a plan this year!

~ Shea

Twitter: @WeatherFlowCHAS

Facebook: and “Shea Gibson – WeatherFlow”

Posted in Coastal Georgia, Coastal South Carolina, SouthEastern North Carolina

Now that is an Eddy!


Weighing at 10X the size of the Golden Gate eddy… EddyBodegameet the Bodega Eddy.

by Mike Godsey

On many recent days we have been cursed or blessed by the tiny Golden Gate just west of the Gate. Cursed if you ply the waters of the coast or much of the Peninsula, Blessed it your home waters are in the Central to East

Today we have a different type of eddy.

The Bodega Eddy is about 10X times as large as the Golden Gate Eddy and is well NW of the Golden Gate and just west of Bodega.

It is caused more by topography interacting with the NNW west of the ocean buoys while the Golden Gate Eddy is caused more by low pressure in the North Bay.

The top image shows the Bodega Eddy.

The bottom image shows the much smaller Golden Gate Eddy.GGeddySat

But despite the size and location differences the impact of the eddies is much the same:

  1. Southerly winds on the coast
  2. WSW winds in the north tower to TI to near Berkeley corridor.
  3. And a mix of SW-W-WNW winds for the Peninsula.

If you are a long time Bay water person you are probably wondering what is going in the last decade with all these eddies and spring and summer heatwaves.

I should do a blog about that sometime but it is largely beyond my very limited expertise so it would be more spec. than fact.

Posted in San Francisco

Will the building ridge spell stronger sea breezes for Southern California?

by Meteorologist, Kerry Challoner Anderson

With the marine layer clouds so well formed we have the perfect conditions to pick out wind patterns by viewing the satellite picture.  This morning a large eddy has developed centered northwest of Catalina Island.  The following satellite picture clearly shows the swirl of clouds moving west along the Santa Barbara coastline and then turning southward in the outer waters around the circulation center.

1pm clouds and winds

Visible Satellite picture and wind reports, May 31, 2016 10am to 1pm


Here is a look at how the Wf-Wrf model projected the circulation would look at that time.

11am wf=wrf

11am forecast Flowviz using Wf-Wrf


These eddies and thick marine layer clouds have been the star of the forecast for much of the past month and though they will linger we do have a change that should produce some stronger afternoon sea breezes. In fact the lingering marine clouds at the coast will help get these winds blowing. Currently the inversion that is capping these clouds is very strong and still quite high so the clouds have been able to penetrate the lower peaks and drive inland.  Today starts the development of a high pressure ridge over us. This will strengthen the inversion but will squash it down closer to the ground.


San Diego 12Z sounding showing more than 12C inversion at 2400 feet.

With the cap to the inversion closer to the ground the clouds won’t be able to penetrate quite as far inland and should burn off a little faster for the near valleys. They will be getting toasty warm.  Meanwhile, the beaches will be sitting under a shallower but strong inversion and the fog is likely to get soupy thick and the air will be cool.  This sets the stage for large local temperature contrasts in the afternoon.

So expect winds to be southerly and mild again in the morning as another eddy spins up, but then in the afternoon as the eddy dies we should see the sea breezes spring to life once the marine clouds clear enough so the local valleys can eat up.

Update:  Latest models show that the eddy will hang together for much of the day so most beaches won’t see the hoped for  gain in the wind on Wednesday.  Fingers crossed for Thursday.

Posted in Los Angeles, San Diego

Tropical Storm Bonnie Update

by WeatherFlow meteorologist Shea Gibson

Latest update from 9:30PM, Saturday May 28, 2016 (apologies clipped myself bottom right out due to resolution change in output).


Posted in Cape Cod