Tropics Update: Watching Invest 97L

By WeatherFlow meteorologist Shea Gibson.

My latest tropical update 9/26/16 at 10:00PM:

 

Stay safe!

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

Posted in Cape Cod, Chesapeake Bay, Coastal Georgia, Coastal South Carolina, Delmarva, Long Island/SE New York, Long Island/SE NY, Massachusetts North Coast, New Jersey, Outer Banks of North Carolina, Rhode Island, SouthEastern North Carolina, Tidewater Virginia, Weather Blog

Late September Canadian High first of the fall season NE/ENE wedges in the SE Region.

By WeatherFlow meteorologist Shea Gibson

Talk about unsettled weather in the SE Region…

You can easily see a temperature difference and cloud line in NC, but there is quite a bit going on here:
Screenshot of the GRE image by Daniel Cawley of the Foothills Weather Network in Burke County, NC.  You can see the warm air to the SW across GA and into Alabama – and also riding up into the higher elevations of the Appalachians.

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Here is the surface map from WSI that I edited to show the activity. High pressure to the north keeps the cooler sinking air wrapping clockwise into the coast, while warm air rides up over it inland. This setup tends to increase the ENE gradient at the coast to keep moderate winds going as that Northern High wedges down into the coastal troughing to the south.

9-26-16-analysis

Technical initial statement: Cool air advection at coast w/ pre-frontal ridge + isentropic lifting keeping the backdoor cold front in check … warm front bulging north.
Translation:  Sagging cold front in the SE region in being held back at the coast while warm air in injected from the SW up into it ahead of the next cold front.

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From this view using our Datascope viewer, we can see the weather station giving us a map of where the warm front/cold front is based on Southerly winds into the Piedmont, higher elevations and ENE winds at the coast.

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You can see at the higher elevations at Hogback Mtn, SC (3205.38ft) where the warmer SW wind is.

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If we look at the weather balloon in Greensboro, NC from this morning, we can see the warm air layer just aloft from the surface air (warm air inversion). Unfortunately, we do not have weather balloons in those spots where the profile would be more pronounced, but it gives an idea of what it looks like from a vertical standpoint.

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Tricky stuff for sure right now in the SE Region as we start to see signs of the seasonal shift to fall. For the coast, it makes forecasting that much trickier when we see this much activity and unsettled air patterns.

Stay safe!

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

Sources:
SPC NOAA, GREarth, The Weather Prediction, The Weather Company (WSI)

 

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

Southern California winds: Santa Ana winds continue into afternoon so…

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zz319459e7Typical wind reversal and strong beach winds may not happen.

by Mike Godsey, mike AT iwindsurf.com

UNDER CONSTRUCTION.

Check out all the weasel words in the Sept. 23 forecast and the extended forecast. Why was this and today’s forecast so iffy?

The short answer is in the animation below which shows the surface winds at 5PM then goes on to show the wind aloft at different levels from 1000 feet to 5000 feet.

Notice how the surface winds are a favorable westerly direction at the coast. But as we go aloft the wind becomes progressively more NE.

Why should you care about winds that far above your kite?

Because those NE winds interact with surface winds to a certain extent. As these NE winds come over the mountains they become turbulent with lots of southern-californiaoffshoreampmreversalup and down motion. So at times they transfer momentum to the surface winds. Given the NE direction of the winds aloft they will tend to “push” the surface winds away from the coast.

At the same time this NE flow aloft helps the thermal trough (aka “heat bubble”)  expand towards the coast spoiling the pressure gradient especially in the Belmont to Seal zone.

Posted in Los Angeles, San Diego

Omega Block Followed by Fall Temps to the East

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By WeatherFlow meteorologist Shea Gibson 9/20/2016

The Polar jet is starting to show a couple of strong dips from the north as we head into fall. Two Rossby waves (jet stream dips) are shown forming here that creates what is called an “Omega Block” Ω – this shows two upper Lows pinched off in the dips with High pressure in the middle.

This loop is from Sept 21- Sept 25

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Record warmth with a strong cold front drawn up behind the first dip are suggested, but not definite. This front could bring strong rains and storms up and down the line as moisture pulls from the Pacific and connects with the Gulf of Mexico.

Here is the GFS showing the cold front on Sept 25th – which this is likely to change over the next few days – my opinion is one of intensifying the front a bit more. This could bring severe weather to many spots.

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In its wake, a cold air mass pushes down behind the second dip and sweeps across the country as Canadian High pressure wedges down cooler air. Temps may be more significantly cooled along the northern tier, Midwest and NE United States, but temps should fall a few degrees across the SE region into FL with dew points also falling to help drier air filter in with it.

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In short, we could see our first real batch of widespread cooler fall air making its way across the midwest and eastern US by the end of the month. Of course, these Canadian air masses mean stronger N/NE winds for the East Coast and SE Regions, so heads up for the coastal water and offshore interests.

This 18z (6pm tonight) GFS forecast for Sept 29 shows a possible scenario with a NE wedge setup for the Mid Atlantic and SE region. This is 9 days out, so there again, we’ll need to watch for consistency ad verification of this model.

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Stay safe!

Shea Gibson
WeatherFlow Meteorologist/Wind Forecaster
SE Region/East Coast/Tropics
New Stations Projects & Outreach
Twitter: @WeatherFlowCHAS

 

Sources: California Regional Weather Server via San Francisco State University Dept of Meteorology, WeatherBELL Analytics, LLC , Tropical Tidbits 

Posted in Cape Cod, Chesapeake Bay, Coastal Georgia, Coastal South Carolina, Connecticut, Delmarva, Long Island/SE New York, Long Island/SE NY, Massachusetts North Coast, New Jersey, Ontario- Simcoe, Ontario: Lake Erie, Ontario: Lake Ontario, Outer Banks of North Carolina, Rhode Island, SouthEastern North Carolina, Tidewater Virginia

Bay Area Wind: Brown Skies and late local sea breezes mean…

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bayheatwaveairHigh pressure overhead crushing marine layer clouds.

by Mike Godsey, mike AT iwindsurf.com

I took the banner photography above while flying in a Coast Guard helicopter during a September heat wave day several years ago. Notice the brownish tint to the skies above San Francisco.

In recent  days this September we  have see a this same pattern. And it is a pattern that has become even more common in recent decades. Morning finds a beautiful reddish sunrises that give way to skies with a slight brownish tinge and very weak winds for most of the Bay Area.

Then in the late afternoon a few sites see a fast ramp up of very localized upper teens winds mostly far from shore. And all the while there is nary a trace of our typical summer marine layer clouds.

This pattern should begin to fade this afternoon and be mostly over by tomorrow Sept. 20.

So what brings on these events?

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The animation below of the western USA gives a part of the answer.

We are looking  at the wind patterns at about 10,000 feet. Notice the clockwise flow  over area and how the Bay Area is right on the edge of this flow today at 9AM Sept 19.

Yesterday this high pressure was completely over the west coast.

This upper high pressure zone is an area of descending warm air. And as it descends it compresses causing more surface heating.

So you would expect a heat wave to be impacting the areas below this high pressure zone.

In the next set of images you can see the how hot the valley portions of the western USA are under the upper high bayheatwavemlcrushedpressure.

The red color shows temps in the 90’s to over 100 degrees F. Notice how the Pacific Northwest is relatively cool. Looking the high pressure animation above you can see that this are is north of the high pressure hence it is cool.

This heat in turn produces a surface low pressure zone which can not expand upwards so it balloons outward.

Looking at the next image you can see the isobars of these low pressure zone. Especially note the Central Valley thermal low isobars.

During a heat wave pattern the Central Valley thermal low expands westward.

Looking at the next image note how those isobars are bulging out of the Central Valley and over the coast. With the Bay Area inside the Central Valley thermal low in the AM there is almost no pressure gradient in the AM hence only faint variable wind.

In the afternoon those isobars west of the Bay Area contract to about the East Bay hills. This allows a weak pressure gradient to develop between the cool dense air over the Pacific and the edge of the thermal low over the East Bay  hills. In this situation we have very local thermal winds aka as local sea breezes.

Now what happened to the marine layer clouds that were so prevalent in the days before the heat wave?

Remember that the air below the upper high pressure is descending air. That means it is falling from aloft towards the marine layer clouds. The days leading up to a heat wave this descending air acts to compress the marine layer.

From the hilltops you will notice that the top of the marine layer clouds look “harder” and they are thinner compared to preceding days as the inversion between the cool moist surface air and the hot dry air aloft becomes more marked. But as the heat wave matures the descending air crushes the marine layer clouds to the surface and the clouds are more confined to the coast. And once the heat wave matures the moisture in the clouds simply is not visible.

And the brownish skies? Natural and human made pollutants typically diffuse upward to the inversion and are blown inland by the afternoon winds. But during a heat wave all those pollutants are crushed closer to the surface giving the sky a brownish tinge. And with weak winds they tend to linger in the basin around the bay created by the coast range.

You can see what upper high pressure did to the marine layer clouds Sept 18 and 19 in the imagery at the bottom from the Bodega profiler. Note that time goes from right to left in this graph.

So why do we expect slightly cooler temps today and cooler yet tomorrow? And why are the winds forecast to improve Tuesday? Take a look at the animation of the high pressure above and remember that weather systems on the average move from west to east.

Posted in San Francisco

Tropics Update 9-18-16 with TD Julia, TS Karl and Invest 96L.

By WeatherFlow meteorologist Shea Gibson

Latest look at the tropics:

Stay safe out there!

Shea Gibson
WeatherFlow Meteorologist/Wind Forecaster
SE Region/East Coast/Tropics
New Stations Projects & Outreach
Twitter: @WeatherFlowCHAS

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

Bay Area Winds: Rare September Cut-Off Low brings…

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SE winds from ocean buoys the East Bay .bay-area-se

by Mike Godsey, mike AT iwindsurf.com

I got a text from Gorge sailor Greg M. at 2:30PM today Tuesday Sept. 13

Just landed at SFO after circling for an hour. And a westerly approach after being told the wind was easterly. Looked south to me. Wtf did you do to the wind here ?
Sent from my iPhone

Unless you have been following my and Ben’s extended forecasts for the last 4 days you are probably puzzled by these weird S to SSE winds.

Yea I know that we sometimes get SE winter storm winds. This usually happens when a Cut-Off Low at ≈ 18,000 ft. sets up in the right position near the Bay Area.cut-off-lowseptse-winds

So what is causing SE winds in Sept?

Good guess! Yes it is a Cut-Off Low. These critters do not occur in our waters in Sept. Welcome to Global Weirding!

This animation starts with the counter-clockwise spinning low pressure focused just west of the Bay Area as modeled at 3PM today. Sort of looks like a surface eddy huh?

But as we head aloft from the surface to 5500 meters you can see that the cause of the low pressure is a Cut-Off Low over the California and Nevada.  Why is the Cut-Off Low not centered over the Bay Area while the surface low pressure is just to the west of us? Think about friction from topography at the surface compared that 3 miles up.

Posted in San Francisco

S. F. Wind: Late season marine surge

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Part 1 : Rare Sept. marine surge could develop overnight.marine-surgetomonterey

by Mike Godsey, mike AT iwindsurf.com

Looking at Mark’s extended forecast for tomorrow Thursday Sept. 8 there is a mention of southerly flow along the coast. I have been watching the pressure gradients and the satellite imagery today and there is a chance this southerly flow could turn into a rare late season marine surge.

This is the first year in decades when we have not seen any marine surges. Instead there have been endless eddies. The eddies have little in common with a marine surge except they both create southerly wind mostly at sites North of the Bay Bridge. In fact for most kiters and windsurfers who only care about the wind strength and direction the different hardly matters.

The first hint of an impeding marine surge was in the satellite imagery early this morning.

Looking at this animation of the NRL satellite imagery notice how the marine layer clouds round Monterey an begin to head northward.

marine-surge-flowvizHowever this southerly flow slows as it feels the North Pacific High’s strong surface NW winds. Then as it lunges into Monterey Bay you can see it curve eastward. Why? Because the Salinas Valley is hot and this creates a pressure gradient that sucks the fog inland.

Forecasting this and all marine surges is tricky because both the NW wind and the Salinas Valley pressure gradient try to stall the marine surge before it reaches Santa Cruz much less the Golden Gate.

But overnight the pressure gradient to the Salinas Vally fades and typically the NW winds weaken near the coast. So there is a good chance that the marine surge will reach the Golden Gate by dawn.

The model output in the next animation goes from today at 7PM until 7AM Thursday Sept 8.

Looking at the bottom text note at 7PM today the weak southerly wind near Monterey. Also note the strong NW wind over the ocean.

The watch as the marine surge  works its way up the coast by dawn tomorrow.

Of course this model output is hypothetical and if the NW winds does not weaken we could have another hot day tomorrow. But give that the southerly winds in the satellite imagery in the first animation are about 4 hours early compared to the model output my bet is we see a marine surge tomorrow.

And just as I published this blog I noticed that the Waddell winds have turned southerly!!

Part 2 : Rare Sept. marine surge blasts to marine-surgeovernightSherman Island by dawn.

It is always nice when a challenging forecast turns out right. This marine surge is atypical in several ways. First marine surges don’t usually occur in Sept. Second this is marine surge has 2 causes. 1. The heat producing upper ridge at ≈ 18,000 ft. is departing but at the surface the Central Valley thermal low has left a lobe of low pressure over Napa creating a S. to N. pressure gradient. This is the typical cause of a marine surge. 2. But this marine surge was turbocharged by a counter-clockwise spinning low pressure near Southern California that sending southerly wind up the coast. You can see all of this happening from yesterday afternoon through the night to 8AM this morning.

Posted in San Francisco

Hurricanes: Friends and Foes.

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Warm water friend, Topography Foe.hurricanenewtondies

by Mike Godsey, mike AT iwindsurf.com

Hurricane Newton has been sliding up Baja’s Sea of Cortez the last few days and passed near La Ventana and Los Barriles will few reports of damage despite strong winds and heavy rain.

Recent years have seen unprecedented numbers of tropical storms and hurricanes curving off of coastal Mexico and passing towards Hawaii or Baja. All this hurricane action is fed by the unusually warm pacific waters in recent years. (you may be wondering why the Atlantic has had a hurricane drought the last decade. That is a complex but understood topic and maybe one of our east coast meteorologist will cover that in a blog.)

The genesis of hurricanes is a top far beyond the scope of this short blog but one face we know for sure. Warm ocean water is a major factor the creation of hurricanes and when a hurricane moves from the tropics to more temperate waters it usually fades fast.

And land is a major foe of hurricanes. It not as consistently warm are tropical waters so it provides less energy and hills and mountains create far more friction that the oceans surface. So topography quickly weakens the hurricanes winds.

In this model animation you can see how fast hurricane Newton si modeled to dies once it leaves the pacific and the Sea of Cortez.

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

Gorge winds: Autopsy of a “blown away” forecast.

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Why does a “good”GorgePressure forecast go “bad”?

by Mike Godsey, mike@ AT iwindsurf.com

So take a look at Ben’s forecast update for the Gorge yesterday at 11:30 for the corridor winds. And looking at the Swell City wind graph you can see his forecast for low to faint mid 20’s was right on.

But it was clear by mid afternoon that his and all the other computer and human forecasts were also blown away but solid upper 20’s wind.

The question is… why do these blown forecasts happen. I mean all forecasting really just looking  at the pressure gradients right? Wrong!

While the pressure gradient is an important variable the variables that shape the pressure gradients are incredible complex and sometime change dramatically in a few hours.

Moreover windsurfers and kiters often visualize winds at a 2D phenomenon. Since we only ply the surface with our boards we only focus on the variables like wind strength, gusts, lulls, direction, shifts etc. that directly impact our sail.

But often on the west coast where there is lot of topography the winds aloft can dramatically impact the surface wind in terms of wind velocity, gusts and wind shifts.

So in forecasting we do not simply look at the pressure gradient and the models surface winds but also at the winds aloft.

So yesterday at 7AM and 11:30AM the great majority of models showed a moderate pressure gradient from PDX to The Dalles. You can see this in the pressure graph above. In the graph the forecast pressure gradient is shown in the pink line while the red squares show the actual pressure gradient recorded from sensors.

Notice at 2PM yesterday the actual pressure gradient jumped significantly above the modeled pressure gradient. This is surprising since the pressure gradient largely reflects 2 variables: 1. the isobars from the North Pacific High off our coast and 2. The isobars from the heat induced low pressure in the Columbia Basin.

Since the Columbia Basin did not suddenly heat up in the afternoon and the NPH did not suddenly lurch towards the Gorge why did the pressure gradient and the Corridor winds ramp above the forecast levels?

The answer has to do with the winds aloft. Look at this animation of the modeled winds at 4PM yesterday.GorgeAutopsyNAM5

The first part of the animation shows the winds at about 2000-2500 feet as depicted GFS model. Note that it only has mild winds forecast just aloft in the Swell City to Dougs zone.

The second part of the animation shows the same winds as depicted by the famed european ECMWF that runs on the worlds fastest supercomputers devoted to modeling. Note the ECMWF only depicts mild winds aloft.

(It is not in my animation but the UofW MM5 also missed this blast aloft)

The third part of the animation shows the same winds as depicted by the NAM 5 model. Note the ECMWF only depicts strong WNW winds just aloft roaring over the Gorge in the afternoon. As this WNW wind hits the ridges up wind of the Hatch and Swell zone it becomes turbulent and transfers momentum to the surface winds as well as a direction shift.

This strong of wind also “moves” the isobars further east so the PDX-The Dalles pressure gradient jumps up and the winds at Dougs goes over forecast levels.

So why didn’t Ben notice this blast forecast by the NAM5? Probably because the NAM5 output only became available after the 11:30AM forecast had been issued.

Fortunately this is the type of blown forecast few complain about since it was a good day becoming a great day. It is on days we forecast weak winds and an epic day occurs that people get pissed.

Posted in Columbia River Gorge