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July Obs Thread 2015


mackerel_sky

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How dry are the valleys in Antarctica?

 

verage rainfall: 0

Though Antarctica summons a mental picture of snow-covered terrain, it's Dry Valleys are actually the world's driest spot. The valleys have extremely low humidity and almost no ice or snow cover the largest ice-free region on the continent. Nearby mountains are high enough that they block seaward flowing ice from reaching the valleys. The unique conditions are caused, in part, by powerful katabatic winds these occur when cold, dense air is pulled downhill by the force of gravity. The winds can reach speeds of 200 mph (322 kph), heating as they descend, and evaporating all water, ice and snow. The valleys are considered theclosest of any of Earth's environments to the planet Mars, and scientists are studying the ecosystem to better understand the surface of the Red Planet.

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I was kidding. lol. Parts of the Atacama can go 100 years without seeing a single drop of rain.

And it's right on the ocean, correct? Hard to believe an ocean climate could be so dry.

 

I found this on wikipedia:   Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971.[5]

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verage rainfall: 0

Though Antarctica summons a mental picture of snow-covered terrain, it's Dry Valleys are actually the world's driest spot. The valleys have extremely low humidity and almost no ice or snow cover the largest ice-free region on the continent. Nearby mountains are high enough that they block seaward flowing ice from reaching the valleys. The unique conditions are caused, in part, by powerful katabatic winds these occur when cold, dense air is pulled downhill by the force of gravity. The winds can reach speeds of 200 mph (322 kph), heating as they descend, and evaporating all water, ice and snow. The valleys are considered theclosest of any of Earth's environments to the planet Mars, and scientists are studying the ecosystem to better understand the surface of the Red Planet.

 

Wow, thats incredible especially the winds. Thats nearly EF 5 tornado wind speeds.

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And it's right on the ocean, correct? Hard to believe an ocean climate could be so dry.

 

I found this on wikipedia:   Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971.[5]

Ive heard that a big reason in part is the very cold ocean current that lies just offshore. The Mountains also block anything coming from the east. Cold ocean currents are also the reason that the coast of Namibia is so extremely dry.

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Aren't there cold ocean currents off the California coast also ?

There are probably some other factors, but thats what i heard a long time ago.

 

It seems that a rain shadowing effect caused by the Andes would be a bigger cause. Same reason the Amazon is so wet. Also mentioned is high pressure drags cold, dry air down from the upper altitudes into the Atacama.

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Aren't there cold ocean currents off the California coast also ?

 

Cold ocean currents hinder any type of storm development.  Where the Humboldt Current flows in orientation to Chile, those areas are so dry that they use fog harvesting techniques in order to supplement rainfall (30% or more of annual water).  Opposite of say the gulf stream, a cold current tends to weaken an approaching ocean storm and will provide a marine fog layer that socks everything in with advection fog.  If you bring mountains into play, then a desert is likely on the other side due to none other than this new crazy phenomenon called downsloping.  Adiabatic warming creates very high temps and extremely dry conditions that are associated with wicked winds.  If you look at most desert and their locations, they typically are orientated close to a cold ocean current and in the lee of an extremely high mountain chain.  This is why you see such dry conditions in the 4 corners region and the best way for that area to receive rainfall is with season monsoon(reversal from dominate H to L pressure) as it is able to provide southerly flow and build storms.  Much like the Jonesville desert, which needs its seasonal reversal of pressure to get rainfall.  No worries Shet, monsoon season will arrive.  Just be grateful you don't have a cold current close by or you would never get any rain seeing as how downsloping is a killa.  Maybe you guys in the Upstate should look into some large nylon mesh nets and do as the Chileans do.  Just a thought. 

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Cold ocean currents hinder any type of storm development.  Where the Humboldt Current flows in orientation to Chile, those areas are so dry that they use fog harvesting techniques in order to supplement rainfall (30% or more of annual water).  Opposite of say the gulf stream, a cold current tends to weaken an approaching ocean storm and will provide a marine fog layer that socks everything in with advection fog.  If you bring mountains into play, then a desert is likely on the other side due to none other than this new crazy phenomenon called downsloping.  Adiabatic warming creates very high temps and extremely dry conditions that are associated with wicked winds.  If you look at most desert and their locations, they typically are orientated close to a cold ocean current and in the lee of an extremely high mountain chain.  This is why you see such dry conditions in the 4 corners region and the best way for that area to receive rainfall is with season monsoon(reversal from dominate H to L pressure) as it is able to provide southerly flow and build storms.  Much like the Jonesville desert, which needs its seasonal reversal of pressure to get rainfall.  No worries Shet, monsoon season will arrive.  Just be grateful you don't have a cold current close by or you would never get any rain seeing as how downsloping is a killa.  Maybe you guys in the Upstate should look into some large nylon mesh nets and do as the Chileans do.  Just a thought. 

 

That's good stuff right there.  :lmao::clap:

 

The first part was truly very informative.  And then you applied it so well to our Jonesville situation.  Post of the day here.

 

Downsloping is a killa...

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That's good stuff right there.  :lmao::clap:

 

The first part was truly very informative.  And then you applied it so well to our Jonesville situation.  Post of the day here.

 

Downsloping is a killa...

 

 

Haha thanks man, just trying to lighten the mood!  Ha happy 4th!

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On a visit to St. Simons Island, GA, I encountered steady ~35-40 mph winds coming off the water ahead of thunderstorms. It was like a tropical storm. then, on my drive from St. Simons Island to SAV, I encountered nearly endless heavy thunderstorms. It was quite worrisome at times with blinding rain and hydroplaning dangers. I was sometimes going only 40. It got quite windy at times.

Once in SAV, I encountered very heavy thunderstorms, widespread CTG lightning, and a flooded surface street.

So, driving wx back to SAV was downright awful and very dangerous. I was soooo happy to get home!

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All week long they played up today(Sunday) as the wettest/best chance of showers and storms in this current pattern. As late as last night, we were in the 60% likely for today, tonight, Monday, Monday night. Now we're back to the typical summer forecast of 30-40% chance for the week. Summer doldrums...

 

Ended up with .20" Saturday from 3 showers. No thunder.

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With that low pressure close in the Tennessee valley I feel like once we get some decent heating and instability up a lot of us should see some decent storms, we were under just a general outlook for thunderstorms today but they have added us back in the marginal risk.

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With that low pressure close in the Tennessee valley I feel like once we get some decent heating and instability up a lot of us should see some decent storms, we were under just a general outlook for thunderstorms today but they have added us back in the marginal risk.

Yep - they're painting us with the really broad brush this morning...

...ARKLATEX/LWR MS VLY/SOUTHEAST THIS AFTN...   AFTN HEATING OF MOIST AIR ON SW AND SE FLANKS OF TN VLY/SRN   APPALACHIANS UPR TROUGH SHOULD LEAD TO ANOTHER ROUND OF DIURNALLY   ENHANCED STORMS FROM THE ARKLATEX...E/SE ACROSS THE CNTRL GULF CST   REGION INTO GA/FL...THE ERN CAROLINAS...AND TIDEWATER VA. ASSOCIATED   BAND OF STRONGER LOW TO MID-TROPOSPHERIC FLOW WILL BE SOMEWHAT   RELAXED COMPARED TO THE PAST TWO DAYS. NEVERTHELESS...COMBINATION OF   1.75 INCH PW WITH 25-30 KT 700-500 MB UNIDIRECTIONAL SW FLOW COULD   YIELD BROKEN LINES/SMALL CLUSTERS OF STORMS CAPABLE OF LOCALLY DMGG   WIND FROM AL/GA NE INTO THE CAROLINAS/SE VA. FARTHER W...GREATER   DIRECTIONAL SHEAR AND STEEPER MID-LVL LAPSE RATES WILL EXIST ACROSS   E TX...SRN AR...AND LA/MS...WHERE A FEW TRANSIENT SUPERCELLS WITH   SVR WIND/MARGINALLY SVR HAIL AND PERHAPS A TORNADO MAY OCCUR.
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All week long they played up today(Sunday) as the wettest/best chance of showers and storms in this current pattern. As late as last night, we were in the 60% likely for today, tonight, Monday, Monday night. Now we're back to the typical summer forecast of 30-40% chance for the week. Summer doldrums...

 

Ended up with .20" Saturday from 3 showers. No thunder.

 

That storm yesterday that we had was one of the more windy ones, saw several trees down or broken mostly Bradford Pears etc nothing to stout but still I am guessing some localized 50+ winds just to the south of my house where most of that damage was. MHX still has us at 60% for today.

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