Zones of Wind Shear

[Richard]

Hypothesis: There are zones more inclined to experience wind shear than other areas. These zones may be non-mountainous areas.

Physical observation: Ground based observer views SCT022 layer hauling ass from the north-north east. Simultaneously a BKN layer at 050 is hauling out of the SSW. Similar observations have been made each day for the previous two week period. Sightings include morning, noon, and twilight observations.

Example: Cape Cod, Massachusetts

KHYA 040956Z 04012G31KT 10SM SCT022 OVC065 14/11 A3011 RMK AO2 PK WND 05031/0953 RAB11E34 SLP198 P0000 T01390106
KHYA 040532Z 0406/0506 05017G28KT P6SM SCT020 OVC050 FM041200 05019G31KT P6SM OVC020 FM041500 07017G31KT P6SM -RA OVC010 FM042100 06015G29KT 5SM -RA OVC010 FM050000 06013KT 2SM -RA BR OVC003 FM050300 06010KT 1SM -RA BR OVC003

KACK 040953Z 03021G32KT 6SM -RA BR FEW018 BKN024 OVC036 13/12 A3008 RMK AO2 PK WND 02032/0947 SLP186 P0001 T01330117
KACK 040532Z 0406/0506 05022G31KT P6SM SCT020 OVC050 FM041200 06025G35KT P6SM -RA OVC020 FM041400 06024G37KT P6SM -RA OVC010 FM042100 06019G30KT 5SM -RA OVC003 FM050000 06018KT 3SM -RA BR OVC003 FM050300 07014KT 1SM -RA BR OVC003

Winds aloft for Boston and Nantuckett, the two closest wx stations 52 nm and 27 nm respectively.

DATA BASED ON 040600Z
ACK 0730 1215+11 2011+06 2219+02 2246-10 2270-21 720334 721341 721352
BOS 0729 0821+07 1620+05 2019-01 2139-13 2266-24 720935 721741 721450

 

[Richard]

Opinions expressed by various pilots including local experienced CFIs support the hypothesis that over Cape Cod there exists a fairly permanent zone of shear. The layer of shear may exist between 020 and 060.

 

[DutchessFlier]

Shear over coastal environments usually the result of land-breeze/sea-breeze components near the surface and upper air components above. Can happen anytime of the year, and sometimes is a pretty localized event, sometimes enhanced by an approaching frontal system.

 

[JohnSBA]

So in flight is this experienced as an abrupt shear or a layer of turbulence? I've flown through layers of less dramatic shear and not even noticed anything other than a gradual but dramatic change in ground speed.

 

[Richard]

So in flight is this experienced as an abrupt shear or a layer of turbulence?

Both. Usually the latter.

As yet, I'm uncertain if this is mechanical due to landforms or caused by the confluence of water on three sides of the peninsula which is Cape Cod. I suspect the latter given the upper altitudes of the layer and the absence of significant elevation changes of the terrain.

Being in Santa Barbara perhaps you are familiar with the coastline from Pt Conception to Avila/Port San Luis (Pt Buchon) in the north. There there are coastal range and the venturi effect most notably at Pt Sal and Pt Buchon. This occurs with winds 260 to approx 030. The venturi is more pronounced as the winds veer more north of the prevailing 330 winds. Even with the prevailing winds, the wind is onshore/offshore/onshore as they pass the prominence of the points. The turb layer ranges from 1,400 to 5,000.

 

[Richard]

Scott, as always, your input is highly appreciated. Your responses are like candy to a child.

However, I should say there were a couple days several weeks ago that cloud observations were similar to the conditions which were the basis of this thread. That was before the recent period of high humidity and temps.

I will be watching how the next few days develop. It looks very interesting.

 

[Richard]

Scott, nothing personal but I'm going to be looking for observations to prove your synoptic picture incorrect (as reason for local observations).

I'll be looking to define if this "shear" is a result of geography and not short-term weather patterns, seasonal wx inclusive.

EDIT: This reminds me of the convergence zone in the PNW and a similar zone in the mid-eastern region of the Los Angeles basin. These zones exist throughout the year (although seasonally pronounced) and are a result of geography.

 

[JohnSBA]

Both. Usually the latter.

Thanks for the reply. Glad I didn't encounter that while flying in that area!

perhaps you are familiar with the coastline from Pt Conception to Avila/Port San Luis

Wish you could see my enigmatic smile. Actually though most of my encounters with wind shear and mountain wave have been on the East-West portion of coast between Carpinteria and Pt. Conception. Sometimes just making the 10 minute hop from SBA to IZA can be a bit harrowing. Several times I've returned from a long, placid flight elsewhere to be greeted by hot air crossing the mountains into SBA, and cool air two minutes later on the ground. Needless to say, those two minutes can be interesting. Often the shear layers are gradual, and sometimes there's not even much turbulence. Worst I've commonly encountered is between El Capitan and Point Conception, and when I see lenticular clouds out there my flight plans on local scenic flights are elsewhere. The coast from the point to VBG is on pretty much permanent restricted status, so I've never been closer than two miles of shore. Seems to me the stretch of East-West coast and mountains has the worst shear issues due to the upper level winds commonly being North and sometimes South, while lower level are more West and sometimes East.

 

[Richard]

FYI: that moisture sucked up last week from the disturbance off FLA warmed the local water in Nantucket Sound and Cape Cod Bay. The surface temps rose from 60 to 65 in two days.

In coastal central California, of which I am most familiar, such a rise in sea surface temps while rare would deepen the marine layer. The marine layer is stratus therefore as smooth as butter.

How such a rise in sea surface temps surrounding Cape Cod would impact winds aloft I haven't a clue.

 

[Richard]

John, it is not uncommon to see an air temp difference of 50*F in the summer months 'tween IZA and SBA. Or Morro Bay and Atascadero, which I am most familiar with.