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I live in the Pacific Northwest. We and those living in the Alaskan Panhandle, Aleutian Chain and in Coastal British Columbia can and have endured 30 to 40 consecutive days with no trace of sunshine at all. It's rare but it has happened.
The worst I have experienced personally was March, 2011 where my hometown saw - maybe - 25 hours of sunshine, nine of them on the last day. The remainder of the month was cloudy and gloomy and there was measurable rainfall on 30 of 31 days.
I wish I had enough data to properly find out. We had a freakishly long period of 78 consecutive rainy days here this winter if we're going by a 1800-1800 recording period and including trace rainfall, but we had enough sunny spells between rain bands to get a roughly average amount of sunshine. Even though it's sunnier on average, I actually think the south of England is more prone to long completely sunless stretches than us because it is more prone to anticyclonic gloom in winter.
December 2010 - January 2011 in Hampstead had three streaks of either eight or nine days with no more than a few minutes of sun in any one day, and up here we had a succession of really dull (<20 hours) winter months in the early / mid-1990s, but usually sooner or later there's enough energy in our weather to blow one system away and replace it with another, giving a sunny interlude of a few hours in between. It's possible I've never gone much more than about a week seeing no sun at all.
Our dullest summers on record are more impressive than our dullest winters, though an honourable mention must go to Cape Wrath on the northwest coast on Scotland for only getting 36 minutes of sun in the whole of January 1983, given how vigorous the weather usually is up there.
If we're talking about extended periods of non-stop rain, then the most I've seen was 30 hours in London on 28-29 April 2012. I've only got the Hampstead data for this since 2000, but while there have been other 24 hour+ efforts the day with the most wet hours only had 23, because of the timing of when it started raining.
More or less all of November 2009 was wet, but this was the worst period around here:
The most I've personally experienced was 22 consecutive rainy days in November 2009 (out of 25 days of rain total that month, for a total of 332mm) here in Vancouver.
The lightest two days of rain featured only 0.2mm each while the heaviest day was 43.4mm. Out of those 22 consecutive days, 18 of them had over 5mm of rain and 14 of them had over 10mm.
42 consecutive days with measurable rain (0.2mm or more) from Jan 5th to Feb 15th this year. Many places in the UK had something similar this "winter" just gone.
The longest completely sunless spell I can remember was about 15 days: the dullest month was January 1996 with 16 hours of sunshine.
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