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Driest month here is on our still used longterm average (1961-1990) February with 36.1 mm (1.42 inch) but in the past two decades this has shifted considerably towards April, so according to the new 1981-2010 longterm average gives an rainfall average for April of only 38.0 mm (1.5 in), while February now gets 42 mm (1.65 in).
Since i started recording data myself in 2006 this even became more pronounced with April only averaging 27 mm, while the remaining months all average at least over 40 mm. Late winter and spring were already the driest time here before, but it looks like there seem to be some changes in the atmosphere patterns, so that High pressure systems here last longer and due to the North Sea being almost at their coldest, we can sometimes receive no drop of rain for several weeks.
Our wettest month is July, closely followed by June and with some gap- August. The longterm values from 1961-1990 show the following numbers for June, July and August: 73.1 mm (2.88 in), 78.7 mm (3.10 in), 71.7 mm (2.82 in). According to the 1981-2010 it didn't changed much over this period, now June has 78 mm (3.07 in), July 80 mm (3.15 in), August 76 mm (2.99 in).
Only September has become much wetter now with a new average of 75 mm (2.95 in), the "old" longterm average was just 67 mm (2.64 in), which was due to some heavier rainfall events occuring in September, including our alltime wettest month overall in September 2001 with no less than 259 mm (10.2 in) of rain.
Driest month = April (32mm)
Wettest month = August (80mm)
Most precipitation days: November (13)
Least precipitation days: April, May (7)
Hottest month (max, min, and mean) = July at 22.3°C, 12.6°C, and 17.5°C
Coldest month (max, min, and mean) = February at -2.1°C, -8.3°C, and -5.2°C
Month with the most bright sunshine = July 287 hours
Month with the least bright sunshine = December at 27 hours
Windiest month = November, December, January at 13.3 km/h (8.3 mph)
Least windy month = August at 11.2 km/h (6.9 mph)
Month with the highest median daily snow depth = March at around 25 cm
Month with the highest end-of-month snow depth = February at around 20 cm
Wettest month: August - 164 mm
Driest month: February- 89mm
A classic Oceanic rainfall pattern, with the last month of winter as the wettest and the last month of summer as the driest.
Most rain days:September - 9.4
Least rain days: February- 5.4
Most sunshine: February- 267 hours
Least sunshine: June - 155 hours
Warmest max temp: Feb- 23.9C
Coldest max temp: July - 13.4C
Warmest minimum temp: February - 11.5C
Coldest minimum temp: July - 1.1C
Warmest average temp: February- 17.3C
Coldest average temp: July- 7.4C
Wettest month: August - 164 mm
Driest month: February- 89mm
A classic Oceanic rainfall pattern, with the last month of winter as the wettest and the last month of summer as the driest.
Most rain days:September - 9.4
Least rain days: February- 5.0
Most sunshine: February- 267 hours
Least sunshine: June - 155 hours
Warmest max temp: Feb- 23.9C
Coldest max temp: July - 13.6C
Bit unusual actually for an oceanic climate. Normally its the autumn months that are the wettest or maybe the first month of winter.
Driest month = August (81mm)
Wettest month = March (116mm)
Most precipitation days: January (17)
Least precipitation days: August, September (12)
Hottest month (max, min, and mean) = July at 24.7°C, 12.9°C, and 18.8°C
Coldest month (max, min, and mean) = January at -3.7°C, -14°C, and -8.9°C
Month with the most bright sunshine = July 256 hours
Month with the least bright sunshine = November at 95 hours
Ask Tom Why: Is August Chicago's wettest month?
July 16, 2010
Dear Tom,
Is August Chicago's wettest month?
—Peggy Gilmore, Chicago
Dear Peggy,
You've asked a straightforward question, but the answer is complex. Identifying Chicago's wettest month depends upon the observation site and the period of years from which monthly precipitation totals are calculated. To be sure, August is a strong contender for "wettest," but it does not lead the pack at all locations and in all precipitation data sets.
In officially published data from the National Climatic Data Center in Asheville, N.C., August ranks wettest (4.62 inches) followed by April (3.68 inches). That's based on O'Hare International Airport data for the 30-year period 1971-2000. However, at Midway Airport during the same period, June is the wettest (4.16 inches) followed by August (3.92 inches). And in the 139 years of official data, 1871-2009, June (3.65 inches) is Chicago's wettest month, barely beating out August (3.64 inches).
Then it gets even more complex as the new 1981-2010 data shows May wetter than June for Midway. Though August is still the wettest at O'Hare, but now July and May are both wetter then April.
Springburn weather station (in the north-east of the city at 82m above sea level), closest station to where I live:
Wettest: October (129.4mm)
Driest: May (61.4mm)
Most days of rainfall >=1mm: January (17)
Least days of rainfall >=1mm: June (11.7)
Sunniest: May (173.3hours)
Gloomiest: December (32.9 hours)
Warmest: July (19.2C/11.1C)
Coldest: January (6.0C/1.0C)
Frostiest: January (11.0 days)
Paisley (just to the west of the city boundary, in a built up area):
Wettest: January (148.2mm)
Driest: April (63.6mm)
Most days of rainfall >=1mm: January (17.3)
Least days """"""""""""""""": June (11.1)
Sunniest: May (180.1 hours)
Gloomiest: December (33.1 hours)
Warmest: July (19.7C/12C)
Coolest: December (6.9C/1.7C)
Frostiest: December (9.3 days)
Windiest: February (mean wind speed of 6.8 knots)
Bishopton (in the countryside, just to the west of the city):
Wettest: January (153mm)
Driest: May (65.3mm)
Most days >=1mm rainfall: January (18.1)
Fewest days """"""""""""": May (11.3)
Sunniest: May (189.5 hours)
Gloomiest: December (44.2hours)
Warmest: July (19.2C/11.1C)
Coolest: December (6.4C/1.1C)
Frostiest: December (10.9 days)
Windiest: March (average windspeed 9.4 knots)
October is the wettest (4.72"), January is the driest (3.23"). But the difference isn't that big, it's definitely possible for January to be wetter than October. Interestingly, early fall has the highest standard deviation in monthly precipitation. It has the potential to be either very wet or dry. Autumn weather tends to have long, settled stretches, but perhaps fronts + tropical moisture influxes can boost the totals. September 2011 (8.5"), September 2009 (1.3"), September 2010 (2.3"), September 2008 (8.9").
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