Urban heat islands.

[chicagogeorge]

Originally Posted by alex985

All I can say is, Atlanta's UHI is HUGE. I know car thermometers are crap, but I noticed once you got outside the I-285 loop the temperature would almost immediately start dropping on most nights.

Same case with Chicago. Get 15 miles outside the city and Lake Michigan's insulation temps can easily be 5-10F cooler at night.

[Cambium]

Originally Posted by Shalop

Speaking of UHI, check out some of the major nighttime differences between some of the places in or near the NYC metro area:


Here's Danbury CT (DXR), approximately 75 miles NE of the city and not very affected by UHI. It's similar to Westhampton, although it's a bit inland.

Yup.. I see this everyday while looking at the current temps. Plus driving there I can feel the difference.

Take a look right now 8:30am. Mid 70s NYC. Mid 60s Danbury. I'm in middle of Bridgeport and Danbury as usual at 70F

But notice it's warmer around NYC/Newark areas than outside it by couple degrees.

White Plains (suburb north of NYC) is at 72F.

[ischyros]

Originally Posted by It is 57 below zero

What if the big city had a very low population density and was very spacious? Would that make it less likely to have warmer nighttime temps?

I haven't looked through to see if anyone else answered this. Indianapolis is a big city that is very spread out and pretty low density. It often tends to be 5 degrees or so warmer than rural areas away from the metro are. This obviously is more common on nights following sunny, hot days. But even in winter it's not uncommon for an overnight temperature to be, say, 43 degrees in the city while farmland outside the city drops into the upper 30s with frost.

[chicagogeorge]

UHI's mainly effect the nightly minimums. For us particularly in the winter. An example of this from Feb 2011.

This sations are within 30 miles of each other. ORD and MDW have UHI's, Waukegan has a station right on the lakefront. Joilet and Aurora are "inland" suburbs

[sloguy1496]

Originally Posted by It is 57 below zero

What if the big city had a very low population density and was very spacious? Would that make it less likely to have warmer nighttime temps?

You just described Phoenix and Las Vegas, which are some of the best and most extreme examples of the UHI in North America. Phoenix low temps can be up to 20 degrees warmer than the surrounding rural deserts, while Las Vegas low temps can be up to 27 degrees warmer. Las Vegas averages about 7 degrees warmer than the surrounding areas, making it the worst UHI of major North American cities.

There ARE some major cities that don't experience an urban heat island. The first one that comes to mind would be San Francisco. BUT, this is because of outside factors (moderation of temperatures by cold Pacific). Same concept holds true for Central Chicago but to a lesser extent...Lake Michigan moderates the temps of areas immediately adjacent to the lake, making summer nights slightly cooler (despite Downtown Chicago being very dense) and winter nights slightly warmer than the surrounding cities and rural countryside of metro Chicago.

Heres a fun link to check out if you want to compare cities' UHI effects. Scroll down in the article slightly.

Seattle among nation's 10 hottest 'urban islands'

Take note that 9 of the top 10 (in yellow) are traditionally considered to be big, sprawled, spacious cities with low population densities (the exception being Washington DC).

[chicagogeorge]

Originally Posted by sloguy1496

Same concept holds true for Central Chicago but to a lesser extent...Lake Michigan moderates the temps of areas immediately adjacent to the lake, making summer nights slightly cooler (despite Downtown Chicago being very dense) and winter nights slightly warmer than the surrounding cities and rural countryside of metro Chicago..

Don't know if that is accurate.

Northerly Island right on the lake just to the east of the CBD (aka Loop) has summer nights warmer than other inland stations.




UofC: strong UHI about 1.5 miles from Lake Michigan. Albeit closer to the lake, it seems to have more in common with MDW than Northerly Island.




MDW: strong urban heat island 9 miles from Lake Michigan





and Streamwood: Little of no UHI, 15 miles west of city limits, also in a river valley which would skew winter minimums colder, and summer maximum higher

[Cambium]

Urban Heat Islands..

Are you guys surprised NYC Central Park hit 50s more recently than the UHI's and CT Coast?

[Wildcat15]

Jacksonville seems to have a pronounced heat island. I believe the river also has an effect.

The International Airport averages 17 frosts per year compared to 9 at the Naval Air Station.

[sloguy1496]

For those interested, here is a thorough and very informative article about the UHI effect, particularly as it relates to the Phoenix Area. Interesting read.

https://borderpusher.wordpress.com/c...island-effect/