Gorge: cut-Off Low slides down the California coast so….

GorgeBigWinds Cut-Off Low1

Big winds likely for the Gorge starting tomorrow.GorgeBigWinds Cut-Off Low2

by Mike Godsey, mike@iwindsurf.com

Video #1 Winds at ≈ 18,000 ft.

Today, Monday August 18: The Gorge has only low teen winds today . Looking at the video find the Gorge and notice the counter-clockwise spinning winds of the Cut-Off Low over Northern California. Then note the powerful WSW winds  north of the Gorge. There winds are from an upper trough over 3 miles aloft.

Video #2 & 3 Winds at ≈ 18,000 ft.

Tuesday August 19: Notice how overnight the Cut-Off Low you saw in the first video has dropped southward and is south of the S. F. Bay Area. This allow the powerful winds of the upper trough to come over the Gorge and the upper trough settles over the Pacific Northwest. 

 The Cut-Off Low  California should steer the upper trough over us. This:

a. enhances surface low pressure in the Columbia Basin.

b. Shoves the heat producing & gradient spoiling upper high eastward

c. Nudges the North Pacific High closer to the coast,

d. Increases brings clouds overhead and

e. Adds a major gust factor as the strong upper winds transfer momentum to the surface winds.

If all of this adds ups in the  wind equation parts to the Gorge should see upper 20′s wind tomorrow with gusts into the 30′s.

But remember…. this forecast all hinges on an unpredictable Cut-Off Low behaving!!!

GorgeBigWinds Cut-Off Low3

Posted in Columbia River Gorge

Cut-Off Low brings woe….

Weak Gorge winds.
Cut-Off LowGorge.gif

by Mike Godsey, mike@iwindsurf.com

There is an old saying in meteorology: A Cut-Off Low is a weatherman’s woe.
 This is because Cut-Off Lows are very unpredictable and tend to meander around since they are cut off from the main flow of weather. They and there counter-clockwise spinning flow or clouds can disrupt the surface pressure gradient and brings sudden switches from NW to SW flow aloft as the Cut-Off Low wobbles about. 

The imagery below of satellite and model output shows the counter-clockwise clouds and wind of the current Cut-Off Low parked over the Gorge that has brought woe to windsurfers and kiters for several days.

To see where this Cut-Off Low came from check out this blog:

http://blog.weatherflow.com/large-cut-off-low-anchors-off-bay-area/

 

 

Gorge Cut-Off Low Model.gif

GFS model animation

Posted in Columbia River Gorge

SAL-ty Atlantic: The Saharan Air Layer Part II

africandust_vir_2014175

by WeatherFlow meteorologist Shea Gibson

For SAL-ty Atlantic Part I of this series, please see http://wp.me/p4sVyF-4dz

So far, the Atlantic Season has seen two named storms: CAT 2 Hurricane Arthur -  which formed off the SE coast and made landfall over coastal NC… and Hurricane Bertha, which barely stumbled out the ITCZ (Intertropical Convergence Zone) gasping for moisture, crossed the Lesser Antilles/Puerto Rico/Dominican Republic/ Turks and Caicos, and curved up towards the SE coast and hooked away from land as it finally bombed out as a Category 1 and said its goodbye.

The ITCZ has continued to be heavily impacted this year by the Saharan Air Layer (or “SAL”), which sends dust off the western African coast to lower and mid levels of the atmosphere. This dry, dusty more stable air rides just along the northern ITCZ boundary and has been the downfall of many tropical waves coming off the coast by weakening cyclogenesis, or dissipating formation of convective storms around the centers of Low pressures.  Moisture contents have been low for feeding into potential candidates. This coupled with a few areas of mid/upper level shearing environments and below normal Tropical Atlantic sea surface temps, we just aren’t seeing much activity this year…yet.

This was taken by NASA (Earth Observatory) using Aqua MODIS on June 24, 2014 just to give you an overhead perspective of how far out the dust plume reaches – all the way to the South America, Caribbean and the Bahamas – and even into some parts of lower USA.  http://earthobservatory.nasa.gov/IOTD/view.php?id=83966

africandust_vir_2014175

You can view a nice animation of plumage here: http://youtu.be/F3Q8Sh2AjPo

Here is a neat little gif from the end of July to first couple of days into August , where you can see how the dust layer quickly suppresses clouding and convection:

sal gif

So as are getting more into the Cape Verde Season, we have seen a couple of tropical waves look very impressive coming off the African coast, but only to be blinked out of existence by wave after wave of dry air being swept off of Africa and bulging down from the north.

August 12:

12

3

August 14:

678

The most current wave looks to head NW directly into the SAL, so the NHC is giving it a very low 10% over the next 48hrs and 10% in the next 5 days.

All-in-all, we are waiting to see if the SAL weakens and/or lifts a bit farther north of the ITCZ so that some of these waves don’t have that initial stream of dry air to work through.  Even though next week is supposedly the talk right now with many meteorologists, the NHC seems fairly confident that we have an increased chance of a below-normal season at hand for the most part (updated August 7th).  http://www.noaanews.noaa.gov/stories2014/20140807_hurricaneoutlook_atlantic_update.html

Stay tuned for the next SAL-ty Atlantic part of this series as we get deeper into the peak season.

Posted in Coastal South Carolina

Large Cut-Off Low anchors off Bay Area…

Watch this Cut-Off Low trigger an atypical mild marine surge.Cut-Off Lowwinds.jpg

by Mike Godsey, mike@iwindsurf.com

As expected this Cut-Off Low triggered marine surge has been mild and very atypical. But overall the marine surge has been even weaker than expected. Anytime a Cut-Off Low is in the wind equation things get unpredictable.

Today, as Claire forecast, the SW marine surge flow is very modest. Let’s take a look at some imagery to see why this is happening.

Cut-Off LowToday.gifIn the first image we are seeing the GFS model output. Notice that there are very strong NNW winds from the North Pacific High far to the west. But the Cut-Off Low at about 18,000 ft. has induced a counter-clockwise low pressure at surface to our west. This is where our SW flow is coming from. But the low pressure is so far to the west that only a hint of those winds are reaching inside the Bay Area.

The second image shows the actual Cut-Off Low at about 18,000 ft. Note how powerful the winds are way above the Bay Area. You might expect that all that wind would stir up our surface wind. But today there is a strong inversion at about 2000 ft. so the cool dense surface air is barely moved by all that wind aloft.

The third image is an animation of the last 24 hours of the satellite imagery of the Bay Area. The long pause you see in the video is the END of the video. At the start of the video you see the Cut-Off Low stirring the surface clouds in a counter-clockwise fashion. Then the image goes gray as the sun went down last night. Then notice how the SW winds induced by the Cut-Off Low shove the marine layer clouds into the Bay Area. Then the image goes bright at dawn today and you can see the impact of the Cut-Off Low more clearly.

There is a corny old saying in meteorology. “Cut-Off Lows are a weatherman’s woe” And if the Cut-Off Low you see in this imagery were to suddenly shift eastward towards the Bay Area we could abruptly see Rio Daze this afternoon.

Posted in San Francisco

Eastern Long Island Sound- cloud induced compression zone?

Here is one of those days where I just bowed to mother nature and said, “You won this round”.     The setup here is a strong ridge of High pressure dominating the eastern seaboard which pretty much rules out much of a synoptic breeze (frontal generated).     I thought this would be a typical CT coastline sea breeze setup where due to the topography of the state of Connecticut, the sea breezes will tend to push inland then kill themselves.    However, a strong rule of thumb for forecasting CT waters is to watch the morning winds for a NW land breeze which can supply a return circulation and help the sea breeze mature and solidify.   This morning there was a NW flow early so I did up the numbers, but what I didn’t expect was for Great Gull Island to report upper teens solid all day long.

ggmap

Theory?  Checking obs, soundings, etc…  really didn’t come up with anything.   However, the satellite gave a great clue:sat315

 

See all that dense cumulus cloud?  It is streaming down from the north in almost a street of clouds and going over the coast.  However it erodes as it passes over Long Island Sound:

sat+wind

 

Note the persistent north winds on our new station on the Mystic River.     Also note the awesome dynamic coastal outline in the snapshot above!

Is it possible that the cumulus clouds are having an effect on the near shore winds and in some way forcing a type of compression zone where the clouds are eroding just north of Great Gull Island?   This zone could explain why GG Island is pushing gusts to 20 much of the afternoon, far stronger than any other values in the Northeast.

Another clue is that at 7pm you can see that the clouds were able to push further south once the sun was setting and all winds faded after that time:

7pm snap

 

What do you think caused this healthy surge of SW winds on the Eastern Sound today?   These blogs are meant to show lots of things we observe and sometimes we don’t have the answer either.   Tomorrow looks like a similar setup but not as much mid level moisture or early NW flow so it will be interesting to see if Great Gull repeats this performance.

Forecaster: Matt Corey

Navgen 12hr nam2.12hr avnsr2.12hr sat+wind 215

Posted in Connecticut, Rhode Island

Cut-Off Low heading towards Bay Area.

Then Cut-Off Low stops just west of Marin County creating a mild marine surge of SW wind and fog.Cut-Off LowHeadingBay

by Mike Godsey, mike@iwindsurf.com

Normally a marine surge of SW foggy cool air can happen to bring a sudden end to a heat wave. But today we have a less typical marine surge that is caused by a Cut-Off Low. What is a Cut-Off Low? Going around the earth at ≈ 18,000 ft. are 3-5 upper troughs and ridges moving from west to east. The upper troughs are southward extending loops in the upper level winds.

Sometimes one of these loops becomes so narrow that the most southward extending part of it pinches off and becomes a counter-clockwise spinning low pressure area. It is now called a Cut-Off Low because it has become disconnected from the main flow of upper level winds. Once you have a Cut-Off Low it becomes very hard to forecast its travel since it is disconnected form the main flow of weather around the globe.

Cut-Off LowWaterVaporIn this first satellite animation you can see the Cut-Off Low far to the west of California. Note the counter-clockwise flow spiraling out from the center of the Cut-Off Low.

In the second video you can see the Cut-Off Low from a different view. Note how it ends up stationary just west of Marin and Sonoma county on Sunday morning.

The third video takes you on a tour from the surface all the way up to ≈ 18,000 ft. In the first frames you are looking at the surface winds at 7AM today. Notice the strong NNW winds way to the west of the Bay Area. Look carefully in the almost calm area just west of the Golden Gate and you can see the weak Cut-Off Lowsurface2-500mbSW winds of the marine surge.

In the second set of frames you are seeing the counter-clockwise spinning winds of the Cut-Off Low at about 5000 feet above the Bay Area. These winds will stir some SW wind on the hilltops later today.

In the 3rd set of frames you are seeing the actual winds of the Cut-Off Low at about ≈ 18,000 ft. These winds are far stronger but do not directly impact the surface winds.

 

Posted in Los Angeles, San Diego, San Francisco

What to do when the models take a personal day???

What to do when the models take a personal day???

Regarding the SE Coast Saturday/Sunday July 5th and 6th

Tim Kent

 7/30/14

  • Preface this discussion with the fact that weather forecast models are a wonderful tool that at least on the East Coast are somewhat rarely so terribly wrong that you cannot even yield useful forecast information from them.
  • Enter my 7AM morning update for the 6th.  The models were fairly consistently showing mild E’rly flow veering to the SSE/S/SSW depending on which model you looked at in the image below.

Screen Shot 2014-07-06 at 7.15.11 AM

 

  • ENE at 19kts is well above any predictions from the 12z-18z runs from Saturday before or the early 00z-06z runs Sunday morning. WRF had a reasonable hold on the overnight flow but then craps out like the rest.
  • So the question is what do you do when none of your models are looking to be useful for the day??

We start where we should always start. Big to small analysis of observations and surface features.

Screen Shot 2014-07-06 at 7.15.41 AM

HPC MSLP CONUS map always a useful tool.  Depicting a kink of Low pressure along the old frontal boundary offshore.

Screen Shot 2014-07-30 at 2.04.57 PM

 

GOES 1450Z Infrared depicts heavy cloud cover

 

Screen Shot 2014-07-06 at 7.16.56 AM

SPC RUC Analysis with Radar Overlay depicts:

~ Frontal boundary draped across outer SC waters and into GA coast

~ RUC winds off as well with only one 15kt barb visible in the image

~ Scattered convection along convergence boundary offshore.

So, at this point I am scrambling at about 620AM trying to figure out whats going to happen through the day as I apparently have no good guidance to start with.  It appears that the kink of Low pressure was both stronger than modeled and closer to shore, allowing elevated NE/ENE flow to stay pinched along the lower SC coast.

Screen Shot 2014-07-30 at 1.49.26 PM

 

Screen Shot 2014-07-06 at 7.13.51 AM

I conveniently wasn’t able to find my actual forecast for the day but ended up going with steady ENE flow through the mid afternoon then fading it out into the evening.  Which ended up being pretty good, although the late afternoon did see some SE/S’rly flow pop in as the frontal boundary drifted further out.

Why did I hold on to the ENE flow and not just fade it out like the models showed???

  • Heavy cloud cover will limit any surface heating and the Sea Breeze will likely be none existent until clearing.
  • Rain in the area stabilizes things further complicating a Sea Breeze build, but not really effecting cool ENE flow.
  • Apparent stronger Low closer to the coast, really just a trend, but looking like a slower fade of the ENE flow.
  • Persistence of cool NE/ENE flow is often much longer than models suggest due to its cool stable nature.
  • SC/GA area generally favored for narrow pinched NE/ENE flow as High pressure builds in to the N and frontal boundaries drift SE.  Ask any of the NWS marine forecasters.

 

 

 

 

Posted in Cape Cod

Video: Nagging upper trough and upper high pressure bully the North Pacific High…

So weaker Gorge, Bay Area Peninsula & coast winds. 

by Mike Godsey, mike@iwindsurf.comNPHisobarsWeakNW

The Columbia River Gorge and the San Francisco Bay Area Peninsula and coast had a long spell of unusually weak winds the last 2 weak. Sometimes this was due to monsoonal clouds aloft and even sprinkles. Sometimes is was related to a weak pressure gradient in the area. And unbelievably sometimes the Hatch blew even through the middle of a heat wave.

Let’s explore some of the major causes of this weird wind drought. In a recent blog on monsoonal clouds I explained how these clouds weaken the wind. But normally monsoonal clouds are a 1-2 day event. Yet here we are a week later and there is still mention of these clouds in the forecasts! Meteorologist call this a stagnate pattern. But before we explore that stagnation let’s look at another issue

The North Pacific High, that giant clockwise spinning feature located between the west coast and Hawaii has been greatly distorted in recent weeks and has kept that distortion much of that time. This distortion has created an unfavorable focus of  it’s isobars for most of the Gorge and pars of the Bay Area.

Let’s look distribution of the NPH’s isobars yesterday July 29..

The Gorge: Looking at the top image find Portland and The Dalles area which roughly bracket the western Gorge. Note how the isobars of the North Pacific High are closest together out just west of the coast. In a normal summer pattern those isobars would be concentrated over the Gorge making for a strong pressure gradient and powerful wind in the Swell City to Doug’s zone. So while the Columbia Basin has been hot and has low pressure the pressure gradient is not concentrated over the Gorge. Hence modest winds.

The Bay Area: Now look at the 2nd image. Find San Francisco and note the Peninsula to the south and just north of Santa Cruz are the fabled wave sailing sites like Waddell. Note how the North Pacific High isobars are concentrated off of Cape Mendocino well north of the Bay Area. This positioning means  the ocean wind west of the Bay Area is NNW rather than the normal NW.

NNW rather than NW sounds like a subtle difference but give the orientation of the California coast it means only a bit of wind reaches the Bay Area coast. Moreover NNW winds favor the creation of a small eddy west of the Golden Gate that further weakens the coast and Waddell winds.

The next part of the weak wind mystery is the monsoonal clouds which never seem to depart. With these clouds over the Central Valley  and Columbia River Basin the pressure gradient has a hard time reaching its full sometime strength. So why are these clouds hanging around.

Let’s drop to the video at the bottom. This video starts with surface winds in GREEN. Then the video jumps to 18,000 feet Upper troughUpperHPdistortyNPHand shows the upper level winds in YELLOW. Looking at the green arrows locate the North Pacific High and the northerly winds along the west coast. Normally the NPH has an oval shape and extends from the west coast to past Hawaii. But in this case notice how it seems crushed against the coast.  Now look at the much stronger upper level winds in YELLOW. The loop you see in these winds is called an upper trough. Normally an upper trough tries to push the NPH eastward then at the upper trough passes to the east the North Pacific High pops back into position out in the Pacific. But this has not happened the last 2 weeks. Why?  Look at area east of the west coast and at the monsoonal clouds video and note the upper high pressure. This feature has been anchored over the desert west for almost 2 weeks. This in turn has locked the upper trough in position. So the North Pacific High has stayed in the crushed position causing the isobar distribution discussed above. Meanwhile the upper high pressure has continued to pump high clouds and humidity into much of the west coast. This stagnant pattern is beginning to break down so both the Gorge and the Peninsula are seeing improved winds.

 

 

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

Videos: Monsoonal clouds threaten Gorge, Bay Area and Southern California winds.

High pressure over the western USA sends moist air above the west coast.MonsoonalFlow

by Mike Godsey, mike@iwindsurf.com

Several times each summer the exotic phrase “Monsoonal Clouds” appears in the forecast. For some of you the phrase is just greek for others it triggers vague memories of something to do with India. If you are a Vietnam vet the phrase conjures up memories of sudden massive downpours that endure for months on end. But I bet all of you wonder what the hell monsoons have to do with your wind.

First some background.

Often times in the summer a large upper level high pressure develop over the western interior of the USA at ≈ 18,000 ft. feet. This normally heats up the California Central Valley, the Great Basin, Southern California deserts and the Columbia Basin that are one of the engines of west coast winds. This heating causes  the air at the surface to expand creating a  thermal low pressure area. Now if this low pressure stays put it enhances the wind at all the west coast windsurfing and  kiting venues since the pressure gradient deepens.

But if the upper high pressure is really strong and lingers the thermal low in these valleys begins to expands and since each of these valleys has a mountain range to the east the thermal low expands westward towards the coast. If it stops expanding before the coast there will still be good wend at more westward locations at each of these venires. So the Hatch, Crissy and Cabrillo can still blow during a moderate heat wave.

However if the upper high pressure is really intense the low pressure balloons completely over the  west coast so the pressure gradient fades away as does the wind. So Southern California, the Bay Area and the Gorge will be windless until the upper high pressure drifts away.

Where does Monsoonal Flow come from?

Video #1. We are looking at  the western USA from a satellite tuned to detect water vapor molecules above 10,000 feet. Notice the clockwise flow of clouds around the upper high pressure over the western USA. Occasionally, like today, this clockwise circulation pulls in  tropical moisture from Baja’s Sea of Cortez and the Gulf of Mexico. You can see this moisture as grayish clouds moving in form the SE over the west coast. This type of moist tropical air is known as monsoonal moisture. Notice how this  monsoonal moisture first hit Southern California, then Northern California and finally the Gorge.

MonsoonalCloudsWestCoast

These high clouds decrease the amount of sunlight hitting each of the valleys that are critical for generating the west coasts thermal winds. Cooler temps in these valleys mean weaker pressure gradients in Southern California, The Gorge and the Bay Area.  Most of this monsoonal moisture is in the form of invisible, to the human eye, water vapor. But when it hits a mountain range the air cools and forms clouds that may range from pearly high clouds to massive thunderstorms. Looking at the video you can see thunderstorms forming over Arizona and the Southern California deserts this morning. Now look at the Northern California part of the Central Valley and notice how it is blanketed by high clouds this morning. If these  persists this afternoon they will  spoilt the pressure gradient. Now look towards the Gorge and see how they  are moving into the Columbia Basin.  Once again if they linger the pressure gradient will be limited.

MonsoonalCloudsHitGorge

Video #2. Did you notice how much my forecast for the Bay Area changed in the last 24 hours. What happened to the promised 2nd. day of the marine surge? Here is the problem . Since it is almost impossible to determine exactly where monsoonal clouds will form and drop the pressure gradient forecasting becomes extremely difficult. This is why during monsoonal flow you may see the forecast change fast. And the winds may be much stronger that forecast if the clouds do not form or dissipate. Or the winds could be much weaker than forecast  if the clouds become more extensive.

Video #3 The Gorge was also impacted by these clouds. As they arrived and and made a t him high blanket over much of the region the pressure gradient ramp up was dulled and even the Hatch only saw 5.5 winds.

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

The North Pacific High’s surface NW winds return…

…as the battered old North Pacific High merges

LongSWflowEnds

with new North Pacific 

High.

by Mike Godsey, mike@iwindsurf.com

It has been a wild 9 days of unending SW flow and Sherman Island and East Bay winds such as we used to see a decade or two ago. And the Sherman Island wind distribution was much more like we used to see in the old Rio Daze. Meanwhile the coast and most of the Peninsula had a 9 day wind drought.

But by Thursday July 24 the NW winds should return. It will not be an epic or even major NW event rather it will be the resumption of the typical combo winds
NWflowReturnswith SW thermal winds combining with NW ocean wind.

But it is a pattern that will spread the wind focus much wider so it includes Crissy inside, Waddell and the Peninsula. Since we are moving into a warming pattern Thursday the winds may be late and modest but at least with a NW component.

The imagery below shows how the long absent old North Pacific High west of the Pacific Northwest will begin merging with a new North Pacific High west of Baja over the next 2 days to bring this switch from SW to NW flow.

And at the bottom is the interesting story about how we forecasted these SW winds in advance

SWtoNW. Monday July 14, following my lead, Claire issued a 7AM forecast for another hot day and modest Sherman Island winds. Early that morning, spurred by a graduate student which whom I had be talking to, I was doing some research on the Southern California Catalina Eddy.

The Catalina Eddy is a large counter-clockwise spinning eddy that often spins up in the zone from San Diego to just past Los Angeles and can be a wind killer for Southern California.  I noticed that the Catalina Eddy was huge that morning and extended way west of the Channel Islands and even north of Jalama and Point Conception. Curious as to what caused this expansion I noticed that there was a mid level (700mb) low pressure system just SW of the eddy. I quickly realized that this low pressure was venting the Catalina Eddy, that is sucking air from the center of the eddy causing it to turn into a surface low pressure.

I then followed the modeled trajectory of the 700mb low pressure and realized that it ran northward along the west coast. This meant that if the former Catalina Eddy followed the mid level low pressure we would have a giant eddy heading towards the Bay Area. And its  counter-clockwise spiraling winds would mean SW flow and a deeper marine layer for the Bay Area for a day or two.

So I shot Claire the following hedge to insert as a bullet at the bottom of her forecast: “Chance of atypical SW marine surge from a huge expanding Southern California Catalina Eddy late today. “

I knew that some of you hate such hedges so I posted the message on the forums titled 3 Videos: Weasel words in the forecast: marine surge. If you missed this blog check it out to see why we had the long stint of SW flow.

Now almost 10 days later the SW surge is poised to fade  and NW winds should begin to ramp up.

 

Posted in San Francisco