by Meteorologist, Kerry Challoner Anderson

As we start to move into the heart of fall we expect the North Pacific High to slide further south and that is exactly what we are seeing this weekend and the reason the Central Coast is enjoying such strong winds.  Saturday’s pressure maps showed a 1028mb High centered to the west of the Southern California coast resulting in strong coastal gradients.

Jalama’s waters were busy as winds topped 30 knots for much of the afternoon.

Though Jalama can receive strong days in the fall, it is also tricky to forecast at this time of the year due to the High-pressure systems that move into the Great Basin behind eastward-moving cold fronts. This sets up NNE/E winds that battle against the coastal winds.  The offshore winds are channeled through the East- West oriented canyons of the Santa Ynez range and can become very strong.  We begin to see these winds set up later this weekend.

As the Pacific High strengthens and moves a little closer to the coast, the Los Angeles to San Francisco gradient increases on Sunday to -8.5mb.  This will keep the coastal winds working. That will bring another strong day on Sunday for Jalama. But then the Great Basin High starts to exert its influence as the E/NE gradients start to climb.  By Sunday the Los Angeles to Daggett gradient starts to increase and  by Monday is at -5.1mb.  So we start to watch the NE winds increase and the battle begins at the coast.

Sunday sees the coastal winds win out so expect another solid day but then forecast is not so certain.






by Kate Looney with imagery by Kate Looney and Mike Godsey

The first major coastal storm of the fall season took shape over the Chesapeake Bay on October 16th with a swath of moderate to strong E/SE winds building ahead of the storm and a powerful W/SW blast shaping up on the backside of the system.  Tens of thousands of people lost power and new surface low pressure records were set for October in several locations across Rhode Island, Massachusetts (including Boston), New Hampshire, and Maine (more on this later).

Let’s take a look at how the system evolved.

Looking at the surface analysis progression (courtesy of NOAA’s WPC), we see the beginning of a nice double-barreled low pressure system building at the surface at 2PM EDT the 16th across the Chesapeake Bay. This was in response to a splitting southern branch of the jet stream high above the surface (top left image).

By 00Z (8PM EDT, top right), the surface cold front has caught the warm front across the Delmarva region and a second occlusion has formed along the deepening coastal low. Moderate to strong SE to E winds were building from the Delmarva region all the way up into Massachusetts in response to the continued strengthening of this low.

The low continued tracking up the New Jersey coastline and up into the Rhode Island/Cape Cod area by 6Z (2AM EDT, bottom right) before rotating back northwestward just west of Boston as it rapidly “bombed out”, or strengthened quickly over a short period of time. The two different areas of surface low pressure eventually evolved into one exceptionally strong October surface low, hence the records set for minimum surface pressure.

Here’s a look at the water vapor imagery overlaid with surface pressure as the coastal low continues deepening from about 2AM EDT to 7:30 EDT the 17th:

WeatherFlow’s Carson Beach sensor reported a surface low pressure of 973mb just after 3am local time on the 17th as the low passed between Boston and Worcester, Massachusetts. 

As this low moved up west of Boston, the occlusion eventually began to choke the system. Eventually, the low slowed down and began to weaken across New Hampshire/southern Maine.

As a result, a large swath of very strong W to SW winds pummeled much of the Mid-Atlantic and especially the Northeast this morning, only finally easing up late this afternoon. The image below is an areal snapshot of WeatherFlow sensors across Rhode Island and Massachusetts about 10:30EDT with many sites maintaining near or above tropical storm force averages a good portion of the day and even stronger gusts well into the afternoon hours.

Another areal view of strong W/WSW winds with gusts noted as of 3:30 EDT.  Notice the gusts into the 50s/60s through eastern Long Island Sound, coastal Rhode Island, and southern Cape Cod waters.

The images below show the dramatic drop in surface pressure from WeatherFlow’s Carson Beach sensor in the Boston area from Wednesday to Thursday, hence the meteorological distinction of a “bombing” low (greater than 24mb drop in 24 hour period):

WeatherFlow’s Flow Map product nicely shows the cyclonic spiraling of surface winds into this low overlaid with surface wind observations. The surface low tracked right across the Concord, New Hampshire area around 8AM EDT, which also set a new record October low pressure of 973mb pending NWS verification.

Also of note about this storm-this post has thus far avoided the term “Nor’Easter” in association with this system. Although it did maintain a northeastern track as coastal lows often do during the fall and winter seasons, a classic Nor’Easter is named because of the strong NE winds that develop ahead of the system across the Mid-Atlantic and Northeastern US. In this case, due to the track of the coastal low much closer in to the coastline, winds ahead of the system remained out of the SE to E.  Really it’s a moot point though as no matter what you call it, it was definitely a record-setting system for October.

Bottom line, the track of the low plays a big role in how the wind field evolves for a very large area.

Because of the necessity in an accurate forecast track and it’s implications on the wind field, these systems can be quite tricky to forecast on days when adventurous sailors, surfers, and kiters may want to take advantage of strong winds. WeatherFlow meteorologists may include a statement like “forecast remains subject to change/highly dependent on track of the low/winds may drop quickly” to convey the uncertainty in these situations until a more clear track is known.  Large swings in speed and direction can happen over the course of an hour or two for areas where the surface low passes overhead or close by, somewhat like the calmer winds in an eye of a hurricane.

This image below from WeatherFlow’s Kalmus sensor in Cape Cod highlights the potential for rapid changes in winds:  You can see around 1AM that winds begin to drop out to mid 20s briefly after building to nearly 50mph. This is followed by a steady build and almost 180 degree reversal in direction from ESE to WSW due to proximity of the surface low swinging by just the west. Quite the variety in speed/direction over a few hours!











A more dramatic example can be seen below at Weatherflow’s Pt. Judith, Rhode Island sensor, where winds went from 50mph to near 10mph in about an hour! Steady veering to the SW/WSW ensued with a quick build back to very strong upper 40s/low 50s with passage of the low.


by Meteorologist, Kerry Challoner Anderson


Thousand Oaks Hillsides May 2019

The much anticipated first major Santa Ana wind event has begun.  Strong offshore winds are typical at this time each year when cold Arctic High-pressure systems move into the Great Basin.  This event is very strong.  The Tonopah to Los Angeles gradients dropped this morning to -15mb and stays this low through Friday morning.  However, this event is getting more media attention due to the anticipated pre-planned power outages to lower the risk of wildfires.  Last year’s wetter than normal winter brought stunningly green and lush foliage to the area in May. But that beauty has now turned to be a potential fire hazard after our long dry summer. Adding to the concern is just how low the relative humidity falls when the air descends from the Great Basin and dries due to compressional heating.  Overnight the dewpoint at Opal Mountain sunk from 30 F to – 19 F leaving the relative humidity at an ultra-low 3%.  

While we usually focus the attention of our models on the interaction with the ocean you will find that you can use Weatherflow’s Wf-Wrf model to help follow the winds.  We watch how this model performs carefully to see how it responds to different weather scenarios and our modeling team dials in the forecasting parameters to fine-tune the model for the area.  The Wf-Wrf is run on both a 3 km and a smaller version on a 1 km grid.  The smaller grid allows us to forecast finer features which is vital in an area with such varied topography.  It is interesting to see how vital this finer grid is when forecasting events such as this.  The 12km Nam model (below) gives the general location of the strongest winds beginning first through Palmdale and finding their way through the Oxnard Plain.

12 km NAM forecast for 10 October, 2019

Wf-Wrf forecast for 10 October, 2019

But you can see that the Wf-Wrf forecast (above) for the same time gives greater detail of the location timing and speed of the winds. It also shows the response at the beaches.  These offshore events are particularly difficult to forecast.  You will find us using the phrase “battle between the offshore wind and the ocean winds”.  Due to the topography of the mountains coming right to the shoreline and the canyons that funnel and speed up the offshore winds we can see the winds curve back onshore.  We also find that the valleys warm and sea breezes set up where the mountains shelter the beaches.  Consequently the beach winds will have extreme Up and Down conditions that can be hazardous. Surfer’s Point in Ventura is just one example.  You can see that despite 30 – 40 kt winds driving down the Oxnard Plain, Surfer’s still had an onshore wind in the model, though the model predicts that won’t last.  We will be keeping close tabs on all the beaches and also the valleys and canyons through this event.  You can use the Wf-Wrf and our network of observations to keep track of this event. Stay safe!

by Mike Godsey,

Here is the story of this massive wind event in imagery and animations.


by Mike Godsey,

Did you get wildly excited early this morning when you saw San Francisco’s Point Blunt winds averaging 28 and Berkeley already 22 while Crissy was 23? It looked like the classic Bay Area marine surge end of a heatwave. But by 8AM the wind had faded away at most sites. I forecast a major fade mid morning but not to this extent. What happened?

Watch the animation above from 6:30AM to 9:14 AM. Focus on Crissy and note the amazing drop off of wind from dawn’s 23 knots to 3 knots at 9:14 AM.

Now study this satellite animation and you can see the problem. A normal marine surge after a heatwave is comprised of fog and wind running parallel to the coast due to a N.-S. pressure gradient. And when the surge nears the Bay it is sucked through the Golden Gate and we have strong southerly winds all day.

But today’s marine surge is largely caused by a counter-clockwise spinning low pressure just NW of the Golden Gate and that is promoting large scale SSW to SSE winds. And as you can see in this satellite animation the wind in the morning became too SSE mid-morning to curve into the Bay. So the winds dropped fast at Crissy.

I expect the fog and winds to pick up later today as the pressure gradient becomes strong enough to curve even SSW winds into the Bay Area.



by Mike Godsey,


Pismo Beach saw strong winds today but Isla Vista to Ledbetter only had weak winds as 3 different wind masses battled over the area this afternoon.

This animation shows the story and an upcoming blog will fill in the details


by Mike Godsey,

The forecast was for scattered showers as a wintry cold front moved over the Bay Area and then broke up. While the afternoon saw upper-teens to maybe 2o clearing winds.

But the actual winds barely reached the upper-teens at some sites and the Waddell did not even reach the mid-teens forecast.

This satellite animation shows the problem.

Notice the well organized cold front in most of the images as is slides over the Bay Area.

Then in the last frames notice how the cold front breaks up and then stalls over the Bay. This stopped the WNW clearing winds from fully reaching many sites.

by Mike Godsey

Hurricane Dorian is bearing down on our hundred+ hardened weather stations along the eastern seaboard. As you can see in the attached photos these stations are massive and designed to survive at least 140 mph winds.

This sensor mesonet will be providing critical information for the NWS/NOAA during the landfall.

Here is the live link so you can watch our HurrNet sensors that we make public in real-time as Dorian hits the coast. (Some of our critical sensors are not on this page)

by Meteorologist, Kerry Challoner Anderson

For days the Southland has been sitting under a late summer upper-level ridge that has been steadily heating the Los Angeles Basin.  When this happens we watch carefully to see how close that heat comes to the beaches.  Forecasting sea breeze activity is tricky.  The strongest winds develop where we have the steepest temperature gradients.  Due to the topography of the Basin, we have very warm air move close to the shoreline and so we see some of our strongest and most consistent sea breeze activity at Cabrillo beach.  Below is the temperature profile this afternoon.  You can see the heat right up to the beach.  If the heat moves offshore the winds shut down but if we can get a little cooling then we have a steep temperature gradient and strong winds.  I will admit it is a tough forecast because it is either feast or famine.

Today as the I prepared the Midday Update the coast had spent the morning in full sunshine due to a lack of marine clouds.  The temperature profile showed the heat approaching the beach, which will shut down the sea breeze activity.  I backed off from the original forecast of Low 20 winds.  Just after I posted the sea breezes kicked in just enough to start to cool the beach and once that starts unless there is a strong offshore flow this will strengthen the temperature gradients which in turn strengthens the winds, resulting in these low 20s that we are now experiencing.  Enjoy!


By WeatherFlow Meteorologist Shea Gibson

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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