Wellington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wellington clear sky chart from 2005-11-06 to 2025-12-03.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	2 3 1 4 3 3 3 3 5% 6% 66%	135522
	Night	2 4 2 4 3 3 3 3 5% 6% 66%	132569
Transparency	Day	17% 4 10% 18% 27% 24%	130516
	Night	17% 5% 11% 23% 27% 18%	128554
Seeing	Day	7% 14% 26% 30% 17% 6%	16464
	Night	4 5% 22% 41% 23% 5%	25864

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	1 3 1 4 4 4 5% 4 7% 8% 58%	3639
	11th to 20th	Day	1 4 2 4 3 3 4 3 5% 6% 64%	3704
	21st to end	Day	2 7% 4 7% 4 4 5% 4 6% 8% 49%	4510
February	1st to 10th	Day	1 5% 2 4 4 3 4 4 7% 8% 57%	1855
	11th to 20th	Day	1 6% 2 6% 4 4 5% 3 5% 10% 54%	1950
	21st to end	Day	1 4 2 6% 4 4 3 4 5% 8% 60%	1650
March	1st to 10th	Day	2 9% 3 7% 5% 5% 5% 5% 7% 10% 43%	4518
	11th to 20th	Day	1 3 1 4 3 3 4 4 5% 9% 63%	4838
	21st to end	Day	2 6% 2 5% 4 4 5% 4 6% 8% 56%	5896
April	1st to 10th	Day	3 4 2 5% 4 4 5% 3 6% 7% 57%	2400
	11th to 20th	Day	3 4 1 4 3 3 4 3 5% 7% 63%	2369
	21st to end	Day	4 5% 1 4 3 3 4 3 4 7% 61%	2400
May	1st to 10th	Day	4 4 1 3 2 2 3 2 3 5% 69%	5748
	11th to 20th	Day	2 3 1 3 2 3 3 3 4 5% 72%	6014
	21st to end	Day	3 3 1 4 2 3 3 3 4 5% 69%	6902
June	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 7% 63%	2800
	11th to 20th	Day	2 2 1 2 2 2 3 2 5% 5% 75%	2800
	21st to end	Day	2 2 1 3 2 3 3 2 4 4 74%	2800
July	1st to 10th	Day	1 1 1 2 2 2 2 2 2 2 84%	6319
	11th to 20th	Day	2 2 1 3 3 3 3 3 4 5% 70%	6320
	21st to end	Day	2 1 1 3 3 4 5% 4 5% 6% 66%	6781
August	1st to 10th	Day	2 2 1 3 2 2 3 2 4 4 77%	5606
	11th to 20th	Day	1 1 1 2 2 2 2 2 2 3 83%	5364
	21st to end	Day	2 3 1 4 3 3 3 3 4 4 71%	5984
September	1st to 10th	Day	2 1 1 2 2 2 2 3 4 5% 77%	2400
	11th to 20th	Day	2 2 1 3 3 3 2 2 4 6% 72%	2340
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 79%	2200
October	1st to 10th	Day	2 2 1 3 2 2 2 2 4 5% 74%	3413
	11th to 20th	Day	2 2 1 2 2 1 1 2 2 4 80%	3261
	21st to end	Day	1 2 1 2 2 3 4 3 5% 8% 70%	3434
November	1st to 10th	Day	2 3 1 3 3 3 3 4 4 8% 66%	1854
	11th to 20th	Day	3 3 1 3 3 3 3 3 6% 8% 65%	1890
	21st to end	Day	2 3 1 3 3 3 5% 4 5% 9% 63%	1890
December	1st to 10th	Day	1 3 1 3 2 2 3 3 5% 8% 69%	2641
	11th to 20th	Day	2 6% 2 6% 4 4 6% 5% 7% 10% 48%	3028
	21st to end	Day	1 5% 3 7% 4 4 5% 5% 7% 13% 46%	4004
January	1st to 10th	Night	1 5% 2 5% 3 3 3 3 5% 9% 59%	6306
	11th to 20th	Night	1 5% 3 5% 3 3 4 3 5% 6% 62%	6254
	21st to end	Night	2 8% 3 6% 4 3 4 3 5% 7% 54%	6468
February	1st to 10th	Night	2 5% 3 5% 4 4 5% 4 5% 8% 57%	2543
	11th to 20th	Night	1 6% 2 5% 3 4 5% 3 5% 9% 56%	2338
	21st to end	Night	1 4 2 5% 3 3 4 3 6% 8% 61%	1980
March	1st to 10th	Night	2 8% 3 6% 4 4 5% 4 6% 8% 50%	5376
	11th to 20th	Night	1 4 3 4 3 4 5% 4 5% 8% 60%	5159
	21st to end	Night	2 5% 2 6% 4 4 4 4 6% 8% 54%	5077
April	1st to 10th	Night	3 4 2 4 3 4 4 4 6% 8% 59%	2000
	11th to 20th	Night	2 5% 1 3 3 4 3 3 6% 7% 63%	1979
	21st to end	Night	4 5% 2 4 4 2 3 2 4 6% 64%	2000
May	1st to 10th	Night	5% 3 1 3 1 1 3 2 3 5% 74%	4224
	11th to 20th	Night	2 3 1 3 2 3 3 2 3 6% 71%	3873
	21st to end	Night	2 2 1 3 2 2 2 2 3 5% 76%	3972
June	1st to 10th	Night	5% 3 1 2 2 2 3 4 4 6% 68%	1600
	11th to 20th	Night	1 2 1 2 1 2 2 2 3 4 82%	1600
	21st to end	Night	2 1 1 2 2 2 2 3 3 3 80%	1600
July	1st to 10th	Night	1 1 1 1 1 1 1 2 2 89%	3640
	11th to 20th	Night	1 2 1 3 2 2 2 2 4 4 76%	3640
	21st to end	Night	1 1 1 2 2 2 3 3 4 6% 75%	4057
August	1st to 10th	Night	1 1 2 1 2 2 1 3 4 83%	4214
	11th to 20th	Night	1 1 2 1 1 2 2 3 3 83%	4506
	21st to end	Night	2 2 1 3 2 2 2 2 3 4 76%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 5% 85%	2000
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 5% 75%	2060
	21st to end	Night	2 2 1 3 2 2 2 2 3 4 78%	2200
October	1st to 10th	Night	2 2 1 3 2 2 3 2 3 5% 76%	3784
	11th to 20th	Night	2 2 2 1 1 3 2 3 5% 79%	3897
	21st to end	Night	2 4 1 3 2 2 3 2 3 6% 72%	4373
November	1st to 10th	Night	2 3 1 2 2 2 3 3 6% 8% 68%	2665
	11th to 20th	Night	2 3 1 3 3 3 3 3 5% 7% 66%	2730
	21st to end	Night	2 4 2 3 3 2 4 2 5% 7% 66%	2730
December	1st to 10th	Night	1 3 1 3 2 3 4 3 5% 7% 68%	4581
	11th to 20th	Night	2 5% 2 5% 3 5% 5% 5% 7% 13% 48%	5176
	21st to end	Night	1 6% 3 8% 6% 5% 6% 5% 8% 10% 42%	6952

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	18% 7% 23% 31% 20% 1	3639
	11th to 20th	Day	20% 6% 12% 22% 33% 7%	3704
	21st to end	Day	30% 6% 14% 18% 25% 8%	4510
February	1st to 10th	Day	22% 5% 14% 27% 24% 9%	1855
	11th to 20th	Day	24% 5% 13% 26% 25% 8%	1960
	21st to end	Day	22% 5% 14% 29% 22% 8%	1650
March	1st to 10th	Day	30% 6% 13% 23% 23% 6%	4518
	11th to 20th	Day	16% 5% 13% 31% 30% 5%	4838
	21st to end	Day	23% 7% 15% 23% 28% 5%	5896
April	1st to 10th	Day	25% 6% 12% 25% 24% 8%	2400
	11th to 20th	Day	20% 5% 11% 26% 28% 10%	2372
	21st to end	Day	22% 5% 13% 27% 26% 7%	2400
May	1st to 10th	Day	18% 4 6% 20% 42% 9%	5748
	11th to 20th	Day	14% 3 8% 19% 39% 16%	6017
	21st to end	Day	16% 3 8% 15% 41% 17%	6904
June	1st to 10th	Day	19% 6% 10% 19% 31% 15%	2800
	11th to 20th	Day	10% 3 8% 16% 32% 31%	2800
	21st to end	Day	13% 2 6% 8% 27% 43%	2800
July	1st to 10th	Day	8% 2 3 4 11% 72%	6251
	11th to 20th	Day	14% 3 5% 6% 11% 60%	6245
	21st to end	Day	14% 6% 6% 10% 22% 42%	6584
August	1st to 10th	Day	15% 3 5% 7% 20% 49%	4079
	11th to 20th	Day	8% 1 4 4 16% 66%	3880
	21st to end	Day	10% 1 3 7% 28% 51%	4311
September	1st to 10th	Day	11% 2 6% 8% 26% 47%	2400
	11th to 20th	Day	14% 2 8% 14% 33% 29%	2340
	21st to end	Day	12% 2 4 14% 36% 32%	2200
October	1st to 10th	Day	13% 3 6% 11% 29% 39%	3413
	11th to 20th	Day	11% 2 4 15% 47% 21%	3261
	21st to end	Day	12% 4 6% 25% 39% 15%	3434
November	1st to 10th	Day	17% 4 12% 26% 29% 12%	1854
	11th to 20th	Day	16% 5% 13% 25% 32% 8%	1890
	21st to end	Day	18% 5% 14% 26% 29% 9%	1890
December	1st to 10th	Day	14% 5% 14% 28% 33% 6%	2641
	11th to 20th	Day	27% 8% 18% 23% 20% 5%	3028
	21st to end	Day	25% 9% 22% 26% 16% 2	4004
January	1st to 10th	Night	21% 5% 23% 31% 17% 2	6306
	11th to 20th	Night	22% 5% 12% 28% 29% 4	6254
	21st to end	Night	28% 7% 11% 22% 28% 4	6468
February	1st to 10th	Night	25% 5% 14% 26% 20% 10%	2543
	11th to 20th	Night	23% 5% 12% 30% 24% 5%	2339
	21st to end	Night	19% 6% 16% 30% 22% 7%	1980
March	1st to 10th	Night	27% 5% 12% 25% 25% 6%	5376
	11th to 20th	Night	18% 7% 12% 42% 18% 3	5159
	21st to end	Night	23% 6% 21% 29% 16% 4	5077
April	1st to 10th	Night	22% 7% 14% 31% 20% 7%	2000
	11th to 20th	Night	20% 6% 13% 29% 22% 10%	1979
	21st to end	Night	22% 5% 12% 31% 26% 4	2000
May	1st to 10th	Night	14% 4 7% 27% 41% 7%	4221
	11th to 20th	Night	14% 5% 8% 19% 41% 12%	3873
	21st to end	Night	12% 3 7% 19% 47% 11%	3972
June	1st to 10th	Night	16% 6% 10% 24% 32% 12%	1600
	11th to 20th	Night	8% 2 7% 18% 36% 29%	1600
	21st to end	Night	10% 2 5% 11% 30% 42%	1600
July	1st to 10th	Night	4 1 2 4 15% 73%	3600
	11th to 20th	Night	11% 2 4 5% 14% 64%	3592
	21st to end	Night	9% 3 6% 17% 22% 43%	3943
August	1st to 10th	Night	11% 2 5% 10% 25% 47%	3060
	11th to 20th	Night	6% 1 4 6% 18% 65%	3256
	21st to end	Night	7% 1 3 8% 34% 46%	3608
September	1st to 10th	Night	6% 1 5% 10% 32% 45%	2000
	11th to 20th	Night	12% 3 8% 16% 34% 28%	2060
	21st to end	Night	12% 2 5% 15% 36% 30%	2200
October	1st to 10th	Night	12% 3 5% 12% 32% 35%	3784
	11th to 20th	Night	9% 2 6% 17% 49% 17%	3897
	21st to end	Night	14% 3 6% 23% 38% 16%	4373
November	1st to 10th	Night	14% 5% 12% 30% 27% 12%	2665
	11th to 20th	Night	17% 5% 11% 29% 31% 6%	2730
	21st to end	Night	17% 4 12% 30% 28% 8%	2730
December	1st to 10th	Night	16% 4 15% 27% 29% 8%	4581
	11th to 20th	Night	24% 8% 17% 30% 18% 3	5176
	21st to end	Night	31% 9% 18% 23% 16% 3	6952

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	11% 14% 28% 27% 18% 4	200
	11th to 20th	Day	6% 14% 23% 33% 16% 7%	225
	21st to end	Day	5% 10% 28% 32% 19% 6%	440
February	1st to 10th	Day	11% 17% 26% 26% 15% 6%	427
	11th to 20th	Day	7% 16% 28% 32% 14% 3	495
	21st to end	Day	7% 17% 32% 30% 13% 2	414
March	1st to 10th	Day	9% 22% 27% 30% 10% 2	500
	11th to 20th	Day	9% 23% 25% 26% 12% 4	500
	21st to end	Day	12% 22% 25% 28% 12% 1	550
April	1st to 10th	Day	9% 21% 30% 24% 13% 3	500
	11th to 20th	Day	12% 23% 27% 25% 9% 4	492
	21st to end	Day	10% 20% 27% 25% 14% 4	500
May	1st to 10th	Day	13% 17% 30% 25% 10% 5%	503
	11th to 20th	Day	10% 21% 25% 25% 13% 6%	528
	21st to end	Day	9% 15% 23% 28% 17% 8%	573
June	1st to 10th	Day	6% 16% 25% 27% 17% 9%	530
	11th to 20th	Day	8% 16% 32% 23% 15% 5%	530
	21st to end	Day	3 13% 29% 33% 15% 8%	530
July	1st to 10th	Day	3 13% 26% 31% 19% 8%	526
	11th to 20th	Day	3 8% 25% 32% 21% 10%	524
	21st to end	Day	3 7% 25% 31% 22% 11%	575
August	1st to 10th	Day	3 10% 28% 29% 20% 9%	527
	11th to 20th	Day	3 9% 29% 28% 20% 10%	517
	21st to end	Day	3 8% 29% 32% 20% 8%	583
September	1st to 10th	Day	4 7% 26% 31% 24% 8%	530
	11th to 20th	Day	5% 12% 26% 33% 18% 6%	530
	21st to end	Day	3 10% 27% 38% 17% 4	530
October	1st to 10th	Day	4 12% 26% 31% 22% 5%	530
	11th to 20th	Day	5% 11% 25% 34% 19% 7%	530
	21st to end	Day	5% 11% 25% 33% 19% 7%	508
November	1st to 10th	Day	7% 10% 22% 28% 23% 10%	330
	11th to 20th	Day	5% 9% 22% 35% 19% 10%	330
	21st to end	Day	5% 8% 23% 30% 25% 9%	330
December	1st to 10th	Day	7% 9% 21% 25% 25% 13%	207
	11th to 20th	Day	7% 14% 24% 30% 19% 8%	200
	21st to end	Day	15% 10% 20% 33% 16% 5%	220
January	1st to 10th	Night	4 7% 29% 34% 17% 10%	800
	11th to 20th	Night	2 6% 24% 43% 19% 7%	800
	21st to end	Night	5% 4 24% 41% 18% 7%	880
February	1st to 10th	Night	6% 7% 26% 38% 20% 4	800
	11th to 20th	Night	4 6% 31% 36% 17% 6%	784
	21st to end	Night	2 9% 30% 42% 14% 3	660
March	1st to 10th	Night	6% 8% 30% 39% 15% 3	800
	11th to 20th	Night	3 10% 28% 34% 19% 5%	800
	21st to end	Night	4 11% 31% 37% 15% 1	880
April	1st to 10th	Night	5% 8% 28% 39% 18% 2	800
	11th to 20th	Night	5% 9% 29% 35% 17% 5%	791
	21st to end	Night	6% 10% 25% 36% 19% 5%	800
May	1st to 10th	Night	6% 10% 25% 39% 17% 4	659
	11th to 20th	Night	4 6% 25% 45% 20% 1	508
	21st to end	Night	5% 4 19% 43% 26% 3	433
June	1st to 10th	Night	5% 3 19% 45% 26% 3	400
	11th to 20th	Night	2 2 23% 49% 22% 3	400
	21st to end	Night	2 1 14% 56% 25% 2	400
July	1st to 10th	Night	1 12% 54% 31% 2	390
	11th to 20th	Night	1 1 13% 52% 33%	388
	21st to end	Night	2 1 8% 47% 37% 4	475
August	1st to 10th	Night	3 1 11% 43% 38% 4	676
	11th to 20th	Night	2 2 18% 42% 32% 5%	792
	21st to end	Night	2 2 14% 46% 32% 4	880
September	1st to 10th	Night	1 2 13% 44% 35% 6%	800
	11th to 20th	Night	3 3 16% 41% 32% 6%	800
	21st to end	Night	2 4 16% 41% 29% 9%	800
October	1st to 10th	Night	5% 3 16% 43% 25% 9%	800
	11th to 20th	Night	3 4 17% 39% 30% 7%	800
	21st to end	Night	3 5% 16% 39% 25% 12%	880
November	1st to 10th	Night	3 4 20% 36% 27% 9%	820
	11th to 20th	Night	4 5% 22% 44% 18% 7%	840
	21st to end	Night	4 6% 21% 39% 24% 6%	840
December	1st to 10th	Night	4 5% 24% 41% 20% 7%	808
	11th to 20th	Night	5% 6% 25% 40% 17% 7%	800
	21st to end	Night	6% 9% 28% 40% 14% 3	880

Page generated at 2025-11-29 22:00:56. Version ac07

Copyright © 2025 Attilla Danko.