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Old 02-26-2011, 03:57 AM
 
Location: Yorkshire, England
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Default When the nights are warmer than the days

I just saw the local weather forecast which mentioned our mild overnight temperatures falling through the day as a cold front comes through so I got thinking about how normal it is to get daily high temperatures outside when you'd expect them, i.e. in the afternoon. Looking through the archives I found that between 23rd December 2010 and 22nd January 2011 (cherry-picking the dates a little) of those 31 days only 13 had a daily high recorded between midday and sunset, three had a high recorded in the morning, and 15 had daily maxima recorded at times almost randomly distributed during darkness hours.

Most of those days were mostly or fully overcast and the sun then has little heating power compared to the many fronts we get passing over us at that time of the year, and to be fair the nights are about twice as long as the days in mid-winter, but I was surprised that over a whole month roughly half the nights were milder than the days. This may be relatively common around the winter solstice, but not so the rest of the year even on completely overcast days - I looked up the data for 23rd June to 23rd July 2010 (31 days again) and adjusted for daylight savings time 29 of those days had a high between midday and 6pm, and the other two between 11am and noon. The diurnal range in midsummer is also noticeably bigger than in winter.

Is there anywhere else where the warmest part of the day can regularly be during the middle of the night?
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Old 02-26-2011, 09:12 AM
 
Location: Ann Arbor, MI
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It's not uncommon here (and likely the rest of North America east of the Rockies) because cold fronts come barreling through regardless of the time of day. The time of year in which this is more common probably differs by region; in the Southeast, it seems this is most common during late fall, winter, and early spring when cold fronts are most active.

I'll make a post later today giving some stats on how often this has occurred in my area in the last year.
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Old 02-26-2011, 03:00 PM
 
Location: Ann Arbor, MI
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Looked from January 2010 to now:
4 times in Jan '10
3 times in Feb '10
3 times in Mar '10
1 time in Apr '10
The last time this happened before the summer hit was May 8th; the next time was on October 28th.
4 times in Nov
4 times in Dec
3 times in Jan '11
2 times this month

Only one or two of these days had sunny conditions during the day; otherwise, it was overcast, sometimes with rain or snow.
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Old 02-26-2011, 05:57 PM
 
Location: Toronto
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It's not uncommon where I am as well. I don't have statistics but off the top of my head, I recall around 3-4 times where it was distinctly getting cooler by day (probably there were more) this winter.
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Old 02-26-2011, 07:53 PM
 
Location: motueka nz
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Very rare here. Our worst winter days here will be about 10 C with a northerly and grey. Night temps will be only a degree or two cooler, but I can't remember ever seeing them warmer. The one time I can remember, was 24C at 4 am following a 21C day, and that was in early October- a freak event.

The situation where you are sounds very different to here. Places in NZ with a lower winter diurnal range might experience it more often.
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Old 02-27-2011, 03:19 AM
 
Location: Yorkshire, England
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Hmm, it seems what we have is not unique by a long shot but I can't see anywhere represented on this board apart from Seattle/Vancouver and the west coast of Ireland being capable of 15 nights in a month being warmer than the days. From the little I know of some of the Scottish island climates their winter temperatures are much more at the mercy of fronts/wind than sun so they'd probably have an even more random distribution of times of day when high temps were recorded than us. Also, does anybody know anything about how diurnal ranges work in Arctic climates during the dark period when there is no day? I'd imagine somewhere like Tromso in a maritime climate it would be all about the timing of the (many) fronts, but for somewhere like Alert or Verkhoyansk?
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Old 02-27-2011, 01:17 PM
 
Location: Newcastle NSW Australia
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Not overly common here, but more likely to occur the further you go south and the stronger the cold southerly fronts are.
The most likely event is that the southerly hits just before daybreak, and the temp does not rise, hence the maximum temperature is the same as the minimum temperature. (eg 20C -20C daily range).
Have seen that happen in Sydney a number of times!
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Old 02-27-2011, 11:33 PM
 
Location: Paris
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Very common in Hong Kong when the city is regularly affected by cold northeast winds in winter. Last time I experienced it was when I was there for a week end this Feburary, 19C at midnight and around 12-13C in the afternoon the next day
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Old 02-28-2011, 05:03 PM
 
Location: Western Massachusetts
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I've remember it happening here, but not very often. Most often when a strong cold front comes through.
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Old 02-28-2011, 07:32 PM
 
Location: Western Massachusetts
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Hmm. Today might be an exception. Warmest temperature (39F) was at 7:00 pm and again the same temperature at 8:30 pm. It just dropped slightly as the clouds cleared.
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