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Old 02-26-2019, 04:29 PM
 
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Going through wiki climate tables of various Southern cities leads me to the conclusion that the diurnal temperature is quite large. I'm not surprised that this is the case for Southern cities in Appalachia where higher elevation would be the major factor. However, in cities such as Macon, GA which is near sea level, humid year-round and not too far from the ocean, why is there a 25 degrees difference in some months? For example, April sees the average high at around 77 degrees but the low at 50 degrees. This is the same temperature variation seen in April in San Bernadino, CA, which is highly arid and at a higher elevation.

This isn't just Macon, GA. All over the South, you see a similar pattern: Jackson, MS, Birmingham AL, Columbia SC etc. Why is it that these humid sub-tropical climates in this region of the world experience such temperature fluctuations that you wouldn't see in other similar climate zones in other countries?

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Old 02-27-2019, 06:50 AM
 
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I think it is because the high pressure/monsoon systems are less strong than in say, Eastern China.
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Old 02-27-2019, 07:15 AM
 
Location: Live:Downtown Phoenix, AZ/Work:Greater Los Angeles, CA
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Two reasons:

Extreme lows in certain years dragging down the averages

Less Urban Heat Island in the cities you listed (like Macon) compared to an Atlanta or Dallas
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Old 02-27-2019, 06:50 PM
 
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Quote:
Originally Posted by FirebirdCamaro1220 View Post
Extreme lows in certain years dragging down the averages
In April?
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Old 02-27-2019, 06:57 PM
 
Location: Bemidji, Minnesota
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Quote:
Originally Posted by ScrappyJoe View Post
In April?
Near Houston, Texas there were always a share of mornings from late September to early May that had a huge difference between the low and the high. There would be mornings at freezing that would suddenly warm up to room temperature or higher. Then a few warm to toasty days with very dry conditions that would suddenly drop to freezing at night. So a few of those days go throughout the month, and then a few average days would indeed cause the larger than expected diurnal range.


That's my guess anyways.
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Old 02-27-2019, 10:01 PM
 
Location: Austin, TX
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Quote:
Originally Posted by seanow View Post
Going through wiki climate tables of various Southern cities leads me to the conclusion that the diurnal temperature is quite large. I'm not surprised that this is the case for Southern cities in Appalachia where higher elevation would be the major factor. However, in cities such as Macon, GA which is near sea level, humid year-round and not too far from the ocean, why is there a 25 degrees difference in some months? For example, April sees the average high at around 77 degrees but the low at 50 degrees. This is the same temperature variation seen in April in San Bernadino, CA, which is highly arid and at a higher elevation.

This isn't just Macon, GA. All over the South, you see a similar pattern: Jackson, MS, Birmingham AL, Columbia SC etc. Why is it that these humid sub-tropical climates in this region of the world experience such temperature fluctuations that you wouldn't see in other similar climate zones in other countries?

April is one of those drier months in the Southeast. April is one of the wetter months in San Bernardino.

During the late Spring in the South there is no convective thunderstorms but cold fronts can't reach the region or if they do it's the very southern part of the cold front (they say a cold front is a comma shaped, basically a large circular low pressure region with a trailing portion to the south).

The south in the fall and late spring gets the lower portion of the cold front so there is a small line of thunderstorms associated with that and then clearing. The wind is from the north so it's dry and cools off quickly at night but the strong sun angle at being 30-35 degrees latitude means that it can warm up fast.

This pattern continues unabated until the summer when the tropics can heat up and convective thunderstorms can play a role. The South Central portion of the country is different, it gets a dome of high pressure in the summer and that dominates for weeks at a time.

For a fairer comparison check the diurnal ranges of San Bernardino in the August versus Macon in April. That would be comparing the dry times of year for the two places.
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Old 02-27-2019, 11:44 PM
 
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Originally Posted by cBach View Post
The South Central portion of the country is different, it gets a dome of high pressure in the summer and that dominates for weeks at a time.
It's actually the warm air aloft (an inversion dragged from the high elevations out West) that is responsible for limiting summer rain in that part of the country, not the high pressure by itself.
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Old 02-28-2019, 11:55 AM
 
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Quote:
Originally Posted by cBach View Post
April is one of those drier months in the Southeast. April is one of the wetter months in San Bernardino.

During the late Spring in the South there is no convective thunderstorms but cold fronts can't reach the region or if they do it's the very southern part of the cold front (they say a cold front is a comma shaped, basically a large circular low pressure region with a trailing portion to the south).

The south in the fall and late spring gets the lower portion of the cold front so there is a small line of thunderstorms associated with that and then clearing. The wind is from the north so it's dry and cools off quickly at night but the strong sun angle at being 30-35 degrees latitude means that it can warm up fast.

This pattern continues unabated until the summer when the tropics can heat up and convective thunderstorms can play a role. The South Central portion of the country is different, it gets a dome of high pressure in the summer and that dominates for weeks at a time.

For a fairer comparison check the diurnal ranges of San Bernardino in the August versus Macon in April. That would be comparing the dry times of year for the two places.
San Bernardino still gets half the amount of rainfall in April than Macon. It makes sense that the extremely dry summer in SB warrants such large diurnal ranges but there is no typically dry month in Macon, just less wet than the summer but still fairly rainy.
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Old 02-28-2019, 06:57 PM
 
Location: Austin, TX
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Quote:
Originally Posted by seanow View Post
San Bernardino still gets half the amount of rainfall in April than Macon. It makes sense that the extremely dry summer in SB warrants such large diurnal ranges but there is no typically dry month in Macon, just less wet than the summer but still fairly rainy.
Take New Orleans because I know it better. There is a summer maximum but also a winter maximum. Summer maximum is around 6", winter maximum is around 5". October and April are around 2". That is a substantial difference.

San Bernardino in the summer gets a trace of rain but it gets some rain in April and also a lot more cloud cover. Not enough to not have a diurnal range but enough that it can be comparable to some places in the Southeast in that limited timeframe.
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