DON’T STOP!!! It feels soooo good! The demise of the North Pacific High.

bay10WCWBmovie

How can endless NW winds…end?ZZ55669365

Mike Godsey

You know the feeling. Your muscles ache from day after day on the water. Your blistered hands say “no more”. Yet you pray to the wind gods “DON’T STOP”

It seems that for endless days the North Pacific High’s surface NW winds have roared down the California coast and Baja Norte coasts.

Just take a look at this graphic and note all the recent days that Waddell just south of the Bay Area and Leo in Southern California had wind over 20 knots.

All this wind is largely due to NPH setting up a pressure gradient that has brought episodes of strong wind to the Gorge and Southern California’s Lake Isabella. Rarely have we seen so many strong days in a row.

Here are some typical forum posts and e-mails:

loop less: I can tell you PSC was <3.7 on Saturday as well!

ZZ7E7BEB8Bairwave: Sunday was a big day as well !  Keep it up !!!

Subs-rude: Hasn’t been this much wind I think since 1995 when I almost missed an entire semester of college!

Afriend: It was a real challenge to go downwind in the strong current.  Then when I got to Rufus the swells were huge and smooth.  Several times I got an a large swell riding downwind, upcurrent.  The sail had no apparent wind and I was just surfing down the face in the wind shadow of the big smoothie.

So why does the endless NW winds…end?

Looking at the next graphic check out the isobars. Isobars are useful forecast tools once you understand how use them. The lines represent locales where the  pressure will be the same.

Looking at the top image for Thursday April 28 notice all the roughly parallel isobar lines. The closer these lines are to each other the more greater the pressure gradient in that area.

In this case these isobars are from the North Pacific High far to the west. Notice that the isobars are especially tight over the Gorge, along the Northern and Central California coast, the Southern California coast and down into Baja Norte. This means that Thursday saw strong wind at many sites in all those venues.

Now look at the image for this Sunday May 1. Huge difference huh? To the upper left you can see the isobars around the counter-clockwise spinning low pressure which has helped distort the North Pacific High and moved it away from the coast. This means weaker NW wind along the coast.

In the same image notice how low pressure in the California Central Valley has expand over the coast and up into the Gorge. This low pressure spoils the pressure gradient so the winds fades even inside the Bay and Gorge.NPHpowerfulFadesMarineSurgeANIM

The next image is an animation of what happens to the NPH from Friday to Monday. Note how the winds turn an unfavorable NNW on the California coast Sunday which makes it very difficult for the wind to curve into the beach. At the same time this NNW flow heats up the Bay Area and the Central Valley thermal low expands over the coast so the pressure gradient fades away. The very last image in the animation is for Monday. It shows that the present NPH has faded away and the NW is absent.

Note that far to the west a new NPH  has formed but it will not help the west coast for a while.

The next factoid is subtle. Remember that low pressure from the Central Valley that extended over the Bay Area Sunday? Look back at that image above and note that it is mostly north of the Bay Area. Now go back to the animation and looking carefully you can see southerly flow along the Bay Area coast. Can you see the hint of a marine surge?

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

3PM, April 25, 2016: The West RIPS!

aKiteAnimWCWB

Southern California, Maui, S. F. Bay Area and the Columbia Gorge see winds in the 20-30 knot range at the same time.

by Mike GodseySoCalBayGorgeRIP

Winds in the Columbia River Gorge in the 20-30 knot range are common. But they are the exception in the S. F. Bay Area and are uncommon most of the season along the Southern California coast. So a dayisobars like April 25 when all three venues plus Maui are seeing winds in that range at exactly the same time is a rare event. So let’s look for the causes of this event.

In the next image look at the concentration of isobars around the North Pacific High and the Great Basin low pressure. The tighter the isobars the stronger the pressure gradient and the resulting wind.

The next image shows the overall wind flow resulting from these gradients.

Note the strong NW winds along the entire coast of California from the high. Also note how the NPH’s winds spiral to the SW heading to Maui creating powerful trade winds there April 25.SoCalBayGorgeHiLoRIP

So lets check out each venue in detail.

The Gorge: Note how the North Pacific High’s surface NW winds are relatively weak along the coast of the Pacific Northwest. So clearly the strong Gorge winds were not simply the NW ocean wind curving inland. Now check out the extension of high pressure extending up towards Oregon from the NPH. Such an extension is called a ridge and it produced a high pressure zone just west of the mouth of the Columbia. Meanwhile low pressure had formed in the strongWindaloftColumbia Basin and northern Great Basin and resulted in the wind flow indicated by the  red arrows. But notice that the wind lines over the Gorge pale in strength compared to the winds streaming down the California coast. So why were eastern Gorge sites blowing in the 30’s? The answer is that the Cascade mountains form a barrier to that mild wind flow between the high pressure and the low pressure. And the only low point in that barrier is the Gorge so most of the wind concentrates there and a venturi effect comes into play.

Bay Area: Why the Bay Area coast blew is obvious. But Great Basin pressure gradientwhy the strong W to NW winds inside the bay even at sites that normally have WSW/SW wind? Typically the Bay has a pressure gradient to the Central Valley. And that gradient is from SFO to Redding to the North to Bakersfield to the south so the wind coming into the Bay diverges with some wind curving WSW and some WNW. But April 25 almost the entire pressure gradient was focused towards Bakersfield which encouraged most of the wind flowing through gaps in the coast range stream from the NW over the Bay.

But why was the wind so unusually strong and so GUSTY?  The primary cause were the winds just aloft. In the next image notice the powerful gusts on the Bay Area hilltops. Such strong wind becomes turbulent as it collides with the hilltops and it transfers momentum to the surface wind making it stronger and gustier. The turbulence also makes the wind shift in unpredictable way as it winds its way around the ridge tops. If you were at the 3rd. Ave. launch site you got a taste of those shifts.

Now look at the pressure graphs to the left. Note that the pressure from the SFO airport to these points in the Great Basin  area are almost off the charts. So why didn’t the wind simply blow due east to the Great Basin. Simply put the towering Sierra Nevada act as a barrier to the wind so it has to flow (in yellow) down the state until in encounters the relative low pathway at the southern end of the Sierra. From there it flowed towards the Great Basin low pressure.

Southern California: The southland is a wind paradox. It is very common to see NW winds in the 20-30 knot range just offshore of NWbaySCgreatbasingPoint Conception where the California makes the kink defines Southern California. Unfortunately the North Pacific High’s surface NW winds don’t readily make a that turn at Point Conception and instead roar across the Southern California bight towards Baja Norte. And often when the NW wind does make the turn it helps form a wind killing Catalina Eddy. But on April 25 the pressure gradient to the Las Vegas and Great Basin region was so strong that the NW wind takes Point Conception like a Porsche 911 Carrera S and blasts into the Southern California coast as WNW wind on its way towards the Great Basin.

In the Gorge a perfect mid summer day is snowboarding at Timberline then kayaking on the White Salmon river then windsurfing or kiteboarding on the Columbia. Perhaps the perfect west coast sailing/kiting day would be doing the Gorge followed by the bay and then jetting to Southern California!

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

Sea Breezing from NC to Louisiana

gfs_mslp_wind_seus_2

by WeatherFlow meteorologist Shea Gibson

It’s getting warmer in the SE Region. which means our Sea Breezes are becoming more pronounced. Very visible on satellite imagery today!

Wanna see something “cool”? Check out the Sea Breeze lines showing all along the Carolina Coast and down in Florida this afternoon keeping air temps down a few degrees. Central High pressure over the Delmarva area has been driving down a Easterly flow from NC and all the way down the FL coast. Also, notice the Sea Breezes along the FL pan handle and all the way over to Louisiana pushing inland as well.

For the full effect, turn up the volume and sip on a Sea Breeze cocktail while watching.


gfs_mslp_wind_seus_2

 

Cheers!

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

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

Cold front sweeps across California…

bay7WCWBmovie

Post frontal NW clearing winds develop Saturday.

by Mike Godsey

Sunday: (updated Thursday April 21 at bottom of blog)

If you have lived east of the Rockies you were constantly hearing broadcast meteorologist talk about cold fronts and thunderstorms heading towards your locale.

cold_frontAnd on the TV  weather maps you were always seeing those blue lines with the ominous looking points that signify a cold front.Cold Front

But on the west coast the huge thermal mass of the pacific makes cold fronts
less common and often poorly defined.

But out in the pacific today there is a well defined cold front which will  bring a chance of rain Friday and, more importantly, NW post-frontal wind Saturday.

So exactly what is a cold front? The graphic above shows the basic concepts.

As a low pressure area approaches there is often a demarcation between the chilly air of the storm and the warmer air in its pathway. This is called a cold front and is represented on weather maps as the blue line with pints you see in the imagery.

Since the colder air in the front is heavier it pushes the warmer air aloft.

And if there is significant moisture vapor in the warmer air this moisture will condense as it rises and cools. This creates clouds that often clearly make the front. With all this moisture condensing there is  potential for rain. The cold front also brings southerly wind as it approaches and has northerly winds in its wake

Let’s take a look at the pacific cold front that will impact our weather and wind theColdFrontHittingBay next few days.

Thursday:

In the next image find the Bay Area and note the blue line outlining the Cold front.

Note the south winds in front to the cold front which hitting the Bay Area as weak storm winds Thursday.

Also note the small flattened North Pacific High way SW of the Bay Area.

Also note how the NPH is creating mild WNW winds for Southern California and easterly trade winds for Hawaii.

Friday:

The next image show the cold front and the wind patterns Friday afternoon. Check out how much the North Pacific High as enlarged. It now spans the waters from Hawaii to Southern California.

RainyColdFrontThenNWanimNow notice the cold front which is just 100 miles west of the S. F. Bay Area.ColdFrontHItBayanim

Also notice how there are weak southerly storm winds hitting the Northern California coast.

There is about a 60% chance of rain Friday from this cold front.

Next notice the WNW winds just west of the cold front. These are the clearing winds.

You are probably wondering why these clearing winds are WNW since you normally expect clearing winds to the NW.

The reason for the WNW winds is that the NPH is still a bit too far south for optimal clearing winds Friday.

Let’s zoom in on all this action in the wind animation to the right.

In this animation notice that off Northern California you can see a very well defined cold front with southerly winds in front of it and WNW/NW post frontal winds behind the front.

Also notice how ill-defined the cold front is off Southern California.

Now check out the left rain animation. This shows the area where rain might fall in BLUE. Looking at the days passing at the top of the graphic and you can see how the rainy cold front passes in the early AM predawn Saturday.

Saturday:

Now let’s get to the bottom line. Look at the last imagery
for Saturday April 23. Notice 4 developments:ZZ327FDB0F

  1. The North Pacific High has moved much further north so Friday’s WNW winds are more NW on Saturday.
  2. The NPH also has greatly expanded in size and now dominate the northern pacific.
  3. Also note how the NW winds are at the coast Saturday while Friday they were west of the ocean buoys.
  4. Lastly notice that while there is strong coast wind there is not much wind streaming over the California interior. This is because the pressure gradients to the Central Valley and the Great Basin looks like they will be modest.

If this is the case the Saturday NW blow will be mostly in the upper teens to barely modest low 20’s focused mostly near the coast. Let’s hope those pressure gradients go up over the next few days.

Sunday: (updated Thursday April 21)NWsurface&1000ftAnim

It now looks like the big NW blow for Sunday. Strong NW winds develop just aloft while the pressure gradients to Bakersfield, which favors NW flow goes up. At the same time the pressure gradient to the Great Basin ramps up which also accelerates the NW wind. So it could be a big blow.

You can  see part of the scenario in this animation. Notice the strong  4PM surface NW wind during the first half of the video. Then the video jumps to 1000 ft. above the surface. Notice how much stronger the winds are aloft as they come in from the Pacific.

Annotated graphics derived from windyty.com and  Null School

 

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

Never Forget the Short Wave!

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By WeatherFlow meteorologist Shea Gibson

In weather, the “Northeast Wedge” is no unfamiliar guest to us that live along the Eastern seaboard of the United States that see elongated periods of driving NE winds and beach erosional processes. We frequently see the wedge setup as High pressures position themselves to the north in a winter-like pattern and “wedge” cooler air down behind cold fronts as the boundaries exit the coast out into the Atlantic. There they become offshore troughs, where interaction between this troughing and High pressure tighten the gradient …and winds elevate.

This blog is about a feature that frequently occurs within the life cycle of the NE Wedge called a “short wave trough”.  According to NOAA, this is, “A disturbance in the mid or upper part of the atmosphere which induces upward motion ahead of it. If other conditions are favorable, the upward motion can contribute to thunderstorm development ahead of a shortwave trough.”  (also see my focused blog on what Short Waves are from June 2, 2015 here: http://blog.weatherflow.com/what-is-a-short-wave-and-how-can-it-affect-winds/ ).  These can occur where W’rly or SW’rly winds aloft move (lifting) moisture along frontal boundaries positioned to the south of these wedges.

The Sperry Charleston Race Week 2016 was this past week from Thursday, April 14 through Sunday, April 17.  I was on the forecasts through our SailFlow application and our other products (WindAlert, iKitesurf, iWindsurf and FishWeather) for those several days. Our NE Wedge began along South Carolina on Wednesday and lasted the entire time slot through Sunday, April 17.  Even though Thursday’s forecast went very well and morning clouds fizzled to a dry line at the coast and elevated ENE backdoor Sea Breezing occurred; however, things got a bit shaky on Friday with the forecast as rains/showers stuck around and a positively tilted shortwave trough developed just offshore.

In this case, an undulating front (stationary west-east cold front) laying across northern Florida and into the Atlantic was providing the Gulf moisture feed. Here is the video forecast where I explained the current setup and talked of the Gulf moisture push from the west…but never mentioned the short wave development. Doh!

 

This is a standard phrase you might see from us in our forecasts during these NE Wedges – this one from actually the day before that I mentioned as part of due diligence (and weariness from being tricked by it before):
d

So here was the Pro Forecast in our apps and products at 7AM..no mention of it as I had the day before. Confidence was (too) high for clouding/rains to break up and ENE Sea Breezing at the coast. Even though I did keep the mention of rains sticking around, the wind directions and speeds were the point of focus.
a

b

c

And here is what happened during race times from morning to early afternoon (SPC Mesoanalysis from ~2:00pm):

f
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A little after this post, the short wave started to loosen its grip offshore – but clouds and a few sprinkles did stick around. You can see where the winds turned side-side and started to crank up along the beaches once the Wedge paralleled the coast.
h

And here is what happened in the Charleston Harbor at our Fort Sumter Front Range Light sensor for the day:
iI fell well below forecast values and was off two entire cardinal directions (NNE vs ENE) through the morning and into the early afternoon hours until this situation was resolved by mid afternoon.  Pay close attention to the times between 2:45pm and 3:00pm once this began to straightened out. Notice the jumpiness due to an unstable gradient and lack of sunshine. With sunshine, this day was originally forecast to be the strongest in this period by the NAM5k and the GFS 0.5, to reach speeds of 30-32kts with gusts in the mid/upper 30’s, so we got lucky and topped out around 30kts later after the races. With the offshore gradient being so strong just a mile or two out near the jetties, the earlier offshore races were cancelled as winds/waves were too high for the racers to effectively compete in.

Bottom line is….even though the afternoon “straightened” out and met values, the morning forecast was mostly a bust due to letting the guard down on the short wave troughing feature that was already showing the night before.  Should have stayed with it. That is why we learn and move on with the knowledge…and take our whoppers at times in the process. A common these is that weather is uncertain; however, we are getting better and better with frequent and steadily increasing observation technologies. To my fellow forecasters and colleagues, and as the headline of this blog reads, “never forget the short wave!”

Until next time – stay safe out there.

Cheers!
Shea Gibson
WeatherFlow Forecasting Team
East Coast/ SE Region
Outreach/New Station Projects
Twitter: @WeatherFlowCHAS

 

 

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

Strong NNorthWesterlies Aimed at Southern California

by Meteorologist, Kerry Anderson

Springtime for Southern California is of course marked by flowers and blossoms like most locations but it also spells a return of the prevailing NorthWesterlies.  Mike Godsey detailed the formation of these winds a few weeks ago so I won’t go in more depth than to  say that as the SubTropical High strengthens off the coast the pressure gradient increases and the California coastline sees periods of strong NorthWesterly winds.  Depending on the location of the North Pacific High and the strength and track of inland Low pressure systems the NorthWesterlies will fizzle or potentially roar and for the next few days they will roar.

When the NorthWesterlies strengthen and turn more NNW we start to see eddies develop in the Bight.  Today we’ve seen an eddy spin up just North of San Nicholas island.  It is hard to find it on the surface observations but note the Southerly wind at Catalina and easterly direction at the buoy to the west.

12:30 pm Surface Wind Observations April 13,2016

12:30 pm Surface Wind Observations April 13,2016

It is a little easier to find this eddy on the high resolution models which are doing at great job at locating these eddies and forecasting how long they will last.

Eddy 10AM

WF-WRF 12Z Forecast for 10am April 13, 2016

We have big changes coming for the NorthWesterlies over the next 24 hours.   Low pressure moving inland to the North turns south and drops into the Great Basin tomorrow while the North Pacific High bulks up.  Southern California gets pinched between these two features and the isobars stack up.

Surface Pressure forecast for 5pm Thursday April 14, 2016 highlighting strong pressure gradient over Southern California.

Surface Pressure forecast for 5 pm Thursday April 14, 2016 highlighting strong pressure gradient over Southern California.

The gradient between San Francisco and Los Angeles drops to -10.3 mb.

Graph of Pressure Difference from Los Angeles to San Francisco

Graph of Pressure Difference from Los Angeles to San Francisco

As the gradient increases the NorthWesterlies will turn more NNorthWesterly and strong winds will extend down the coastline and fill into the Bight through Friday.  The winds may move too far inland for any large eddy to develop for the Bight but with this orientation it is likely that we will see an eddy develop south of Gaviota and is likely to be very powerful. Watch the daily forecasts for details on this developing weather pattern.

Wf 10am changing

Wind forecast for Wednesday to Friday showing extended period of strong NNorthWesterlies that will be blasting the Southern California coastline and filling into the Bight.

Posted in Los Angeles, San Diego, Weather Blog

Fast paced changes for the North Pacific High

bay3 marineLayer West Coast Wind Blo4

NW winds ramp up then down.

by Mike Godsey

NphRIdgefadesAnim

Posted in Los Angeles, San Diego, San Francisco

Wind Rivers: Can you relate?

Sullivan's Island Wind Rivers

by WeatherFlow meteorologist Shea Gibson

Ever been out on the water and notice there are systematically stronger areas than others? Why would the wind be higher near sandbars/shallow waters than right at the beach? Why would there be a strip of winds that seemingly follow the same tributaries or spit functions? Let’s take a good look into something I’d like to call “Wind Rivers” or even “Wind Streets”.

As kiteboarders, we have the ability to harness the raw power of the wind in our hands (as do many others who ride almost any time the winds come up). Part of the experience is learning when to power and de-power the bar as wind pulses up-and-down. This helps to control speed, balance and ability to go upwind. One thing many kiters have run into here in the Charleston area is a phenomena where winds are consistently higher in certain spots vs others. It’s where you always have to depower the bar as that extra “kick” pulses into the kite. Many factors control this – such as directions, sea surface temps, air temps and many of the complexities at the land-and-sea interface.  However, on a good solid wind day, we can find areas where there seems to be “rivers” of wind that are a few to several knots higher then other areas.

From my blog on ENE Seabreezes: We see that exposed sandbars help with accelerations. On several occasions, I (and others) have noticed that the winds are more onshore (Easterly) out beyond the sandbar..and become more side-shore (NE’rly) as we head in towards the beach. This makes it easier to get upwind on the outside, but harder to get upwind closer towards the beach. The tidal acceleration has a good bit to do with this as well, especially on an outgoing tide. However, there is absolutely a distinct shift..or “backing” of winds to the side-shore directions- and this could easily be due to the surface roughness guiding the surface winds in its direction.  It’s almost as if the deeper waters are host to a less frictional ENE/EAST wind than the shallower waters, which tend to gain surface friction from increased shallow water chop.

Breach-Inlet

Here is a good example of what we might experience on any given NE–>ENE event. Isle of Palms is the island at the top, Breach Inlet then Sullivan’s Island to the left. Then yellow arrows represent the directions winds are coming from.

Bacjdoor-Sea-Breeze-sandbars

**One important note: Once the sand bar becomes completely covered up by high tide, the wind direction pretty much becomes fairly uniform while the gradient weakens, resulting in the “drying up” of these wind rivers.
As we head into the Charleston Harbor during these directions, things get a bit more complex as land shadowing, river convergence and surface friction cause eddying and instability in the wind field. This divides the harbor into two sections – one for the main wind river pushing through in off the ocean…and a secondary wind river from the winds funneling down the Intracoastal Waterway.  Here is a map of what is occurring on an outgoing tide. The wind rivers widen just a bit on an incoming tide as surface friction calms down.

Chas-Harbor-Wind-Rivers

Here are the wind rivers during S–>SSW/SW Sea Breeze circulations (Coriolis shifting) and also applies to most instances of Low Level Jetting instigation where no Sea Breeze circulations exist…or the combination of both with coupling of the two.

Charleston Harbor – our Fort Sumter sensor regularly picks this one up as upwind warmer land masses allow for better surface mixing/instabilities.

Charleston Harbor Wind River

Sullivan’s Island beach and sand bar activity near Breach Inlet:

Sullivan's Island Wind Rivers

Breach Inlet Wind Rivers

UPDATE 4/11/16: This past Friday, April 8, we had a solid SW Sea Breeze at 20kts to the beaches. Great time to put this to the test once again. As I rode my kite between the sandbars, I felt the heat being generated and blown into me. The wind instantly got holes in it and was significantly lighter with lulls-to-gust being wider.  As soon as I made it just to the outside, it picked back up gradually, but not as strong as that area just inside the sandbar. Others riding with me in that area also confirmed their experience with this as well.
Wind River Thermal Imbalance

So what is causing this along our sandbars?

One theory involves dynamic mixing near these exposed surfaces at lower tides. The composition of the fine particle sand retains quartz and iron , which allow for rapid heating when the sun is out – especially when the ambient air temps rise to hotter temperatures. We all know too well the ‘ole RUN RUN! while walking these paths in the summer with bare feet- which I personally have experienced excruciating pain before reaching the beach. The focus is to run to the whiter piled up sand to cool the feet as the other lighter, coarser grains stay atop as winds blow it along into small bumps and dunes (wider granular profile and lighter weight for blowing).

Example of a cross section of what would be on a sandbar (pic from http://coastalcare.org/2015/05/what-the-sand-tell-us-a-look-back-at-southeastern-us-beaches-by-orrin-h-pilkey-william-j-neal/ )

Figure-4

And a better look at those irons and grains that retain heat- also from http://coastalcare.org/2015/05/what-the-sand-tell-us-a-look-back-at-southeastern-us-beaches-by-orrin-h-pilkey-william-j-neal/ – keep in mind that as sand bars dry, the whiter sands are stripped from the top and the darker colors are revealed (heat retaining).

Figure-8

Well – that very heating process helps create instability right along the sandbars – especially when the bars are directly upwind or side-side with the direction of the wind…or visa versa. This radiant mixing feature helps bring winds up in the immediate vicinity, where we experience anywhere from 2-5kts extra in those zones.

Another theory is that surface friction relaxes as waters ebb and overall swell height drops, thus leaving a cleaner surface to travel along.

We could even speculate that there is a compression of wind into the slightly elevated beaches along the dunes and homes all along the front line keeping winds pushed back, creating a highway of wind where the path of least resistance is- which is towards the coastal breaks and spits.

So should we call it “Wind Rivers”? Maybe Wind Streets or Wind Streeting? Does it need to be more technical to scientific terms such as “Thermally Induced Limited/Non-Limited Mixing Zones”?  Will be sharing with some in the weather community to see what their thoughts are.

**** For now as of 4/11/16, I’m leaving this blog open for additional information after speaking with our mets team and others (and likely coastal geology experts from the College of Charleston for their thoughts) *****

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

 

 

Posted in Coastal South Carolina

“The times they are a-changing”: Dylan

aBaywcwb

Record high temperatures then an early season marine surge.

by Mike Godsey

Working on text.AprilRecordTempMsurgeANIM

ZZ361A61DAToday in the Bay Area many all time record temperatures are likely to be broken as the temps move into the low to mid 90’s. Older windsurfing amongst you will remember that 40 years ago heat waves in the Bay Area were a Sept.-Oct phenomena as much of the bay was shrouded in fog most of the summer. Now we have heat waves in April!

Even more puzzling… for most of recorded California history marine surge blasts of SW cool air arrived at the earliest in June. Well as Ben mentioned this last weekend it looks like we will see a marine surge Thursday April 7 as the unseasonal heat wave ends with a chilly bang.

This looks like a big marine surge so expect strong winds in the north tower to Treasure Island to Pt. Isabel/Larkspur to Davis Pt. to Sherman Island corridor. Tigers and possibly Palo Alto have promise.

This is an atypical marine surge. Usually marine surges follow a heat wave. During a heat wave a combo of heating and NE flow causes the Central Valley thermal low to expand over the Bay Area coast. This causes the pressure gradient to the Central Valley to fade away and the winds are very weak over the water. Then as the heat wave fades the Central Valley thermal low retreats back to the valley. This retreat is especially fast right over the cool bay waters but the retreat is much slower over Napa and Sonoma in the North Bay. So a lobe of low pressure remains there after most of the low pressure is back in the Central Valley.

This creates a S. to N. pressure gradient so ocean wind begins sliding up the coast from Southern California. As this air comes into contact with the chilly Northern California waters its moisture condenses creating fog. Since this is now dense heavy air it tends to stick near the surface. So it slides up the coast “seeking” a near water level route to the Central Valley. And when it hits the Golden Gate it accelerates as it finds the low level route all the way to Sherman Island. This means strong wind at sites along that route.

Unfortunately for Coyote and 3rd. Ave. some of this southerly flow filters through the Hwy. 92 gap creating weak offshore winds in that area. Sometimes Palo Alto will paradoxically get NW wind in this pattern as the southerly wind turns towards the relatively warm low pressure air in the San Jose area.

So why is this an atypical marine surge? 

Take a look at the upper image to the right. Notice today there are weak NW winds over the Bay Area. Then note the storm system and cold front away out in the Pacific. By tomorrow that cold front will be close enough to the Bay Area to contribute to the southerly flow. And cold fronts often do not follow the model output exactly. So if this cold front slows overnight the marine surge could partially fizzle.

Posted in Los Angeles, San Diego, San Francisco

Leave the Meteorologist Home?

by Meteorologist, Kerry Anderson

When I was in college there was a running joke with the other departments with regard to when to schedule their annual picnic.  It was said that if you wanted to have the best chance to enjoy sunshine at the picnic then don’t schedule it on the same day as the meteorology department picnic.  The weather guys always seemed to pick the day with the rain.  There were no official statistics on this and likely this was more of the, hopefully, good-natured harassment that weather forecasters receive.  This tradition continues in my family. Any bad weather that is experienced when I am along is clearly to be blamed on the fact that I am part of the gathering.

Well maybe they are not entirely right but the current situation is not helping matters.  We are in the Riviera Maya in Yucatan, Mexico hoping to enjoy the crystal clear waters and lots of snorkeling.  Yes in my day job I hope to find higher winds for wind enthusiasts but not today for my vacation.  So guess what the weather maps look like.

Big winds

Weatherflow Flowviz map for April 1, 2016

Atlantic High

Surface map for the Atlantic Region April 1 2016.

An unusually large Atlantic High pressure system is dominating the weather for most of the Atlantic and around the southern edge the winds are being funneled toward the Yucatan.  The main topic of conversation with visitors and tour operators is the effects of these high winds on the tourist industry.  Boat tours are cancelled, currents are too strong for swimming and the visibility in the water is well lets just say it is not what you picture when you think of the Caribbean.

The good news is that with my Windalert data and my Windmeter I am ready to forecast anywhere in the world. The locals are surprised that I have more information on the local winds than they do.  And the wind meter has been great for taking observations.  It also becomes a great conversation starter. Especially when you are using it to read the winds at your table at a beach restaurant.

wind meter

So if you are interested in what the winds are doing in the Yucatan you can follow along on the WindAlert pages as I will recording and sharing my observations.  And if my family complains that I ruined another vacation I would appreciate if you would remind them that they aren’t at work or school and they are sitting at a beach restaurant in paradise.

Cheers.

 

 

Posted in Los Angeles, San Diego, Weather Blog