Gower Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gower Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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	19% 10% 3 7% 5% 4 4 3 5% 6% 33%	101986
	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 33%	98201
Transparency	Day	50% 7% 13% 20% 10% 1	105514
	Night	51% 7% 12% 20% 9% 1	102762
Seeing	Day	27% 18% 30% 18% 6% 1	16652
	Night	26% 16% 31% 22% 5%	24482

By Month

Percentage Cloud Cover NE (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	14% 14% 5% 9% 5% 3 4 2 4 6% 33%	2207
	11th to 20th	Day	15% 14% 5% 10% 6% 4 4 3 3 3 35%	2379
	21st to end	Day	12% 10% 3 9% 5% 3 5% 5% 6% 6% 35%	3064
February	1st to 10th	Day	16% 13% 4 6% 6% 4 5% 3 5% 6% 31%	1710
	11th to 20th	Day	16% 13% 3 9% 4 5% 4 3 6% 7% 30%	1663
	21st to end	Day	12% 13% 3 7% 5% 5% 4 3 5% 5% 37%	1488
March	1st to 10th	Day	23% 15% 5% 8% 4 3 3 3 4 5% 27%	3329
	11th to 20th	Day	19% 17% 4 10% 6% 5% 4 3 4 5% 24%	3480
	21st to end	Day	30% 12% 4 8% 5% 3 3 2 4 5% 23%	3816
April	1st to 10th	Day	23% 15% 3 7% 5% 4 4 3 4 5% 27%	2219
	11th to 20th	Day	20% 11% 2 6% 4 4 4 3 5% 7% 33%	2442
	21st to end	Day	25% 10% 3 7% 3 3 3 2 5% 6% 32%	2470
May	1st to 10th	Day	21% 14% 3 7% 5% 4 4 3 5% 6% 27%	4106
	11th to 20th	Day	19% 8% 3 7% 5% 5% 4 4 4 7% 34%	4393
	21st to end	Day	18% 7% 3 7% 5% 5% 6% 4 7% 8% 30%	4923
June	1st to 10th	Day	26% 9% 3 7% 5% 5% 5% 3 5% 6% 27%	2850
	11th to 20th	Day	21% 7% 3 7% 4 4 5% 4 6% 7% 33%	2850
	21st to end	Day	28% 8% 3 6% 4 4 4 3 4 6% 29%	2850
July	1st to 10th	Day	15% 6% 3 7% 5% 6% 5% 5% 6% 9% 33%	4760
	11th to 20th	Day	20% 6% 2 6% 4 4 5% 4 6% 8% 35%	4760
	21st to end	Day	16% 7% 2 7% 4 5% 5% 4 6% 7% 36%	4632
August	1st to 10th	Day	21% 8% 2 6% 5% 5% 5% 4 6% 7% 32%	4105
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	4045
	21st to end	Day	16% 4 2 5% 4 4 4 3 6% 7% 45%	4510
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 4 5% 7% 45%	2280
	11th to 20th	Day	18% 6% 2 5% 4 3 4 3 4 6% 45%	2100
	21st to end	Day	20% 6% 2 5% 4 4 3 3 4 5% 43%	2090
October	1st to 10th	Day	18% 6% 4 7% 4 4 4 3 5% 6% 40%	1909
	11th to 20th	Day	20% 7% 2 6% 4 3 4 3 4 7% 37%	1900
	21st to end	Day	21% 10% 3 7% 5% 4 4 3 4 6% 33%	1998
November	1st to 10th	Day	22% 9% 3 7% 5% 4 4 3 4 5% 34%	1648
	11th to 20th	Day	21% 10% 3 8% 5% 4 3 3 5% 5% 34%	1600
	21st to end	Day	21% 14% 3 7% 5% 4 3 3 5% 4 30%	1600
December	1st to 10th	Day	24% 12% 4 8% 4 3 4 3 4 5% 29%	1600
	11th to 20th	Day	20% 15% 5% 10% 6% 4 3 2 3 4 28%	1758
	21st to end	Day	21% 13% 4 7% 4 3 3 2 4 4 34%	2452
January	1st to 10th	Night	14% 11% 4 8% 4 4 5% 4 5% 7% 34%	4748
	11th to 20th	Night	18% 12% 4 10% 7% 4 4 3 5% 5% 28%	4570
	21st to end	Night	14% 13% 4 8% 6% 4 4 4 6% 6% 31%	4590
February	1st to 10th	Night	16% 13% 3 9% 5% 4 4 3 6% 6% 31%	2470
	11th to 20th	Night	17% 13% 4 9% 6% 5% 4 3 5% 4 29%	2403
	21st to end	Night	15% 13% 4 8% 4 5% 4 3 5% 5% 34%	1965
March	1st to 10th	Night	24% 15% 4 8% 5% 6% 4 2 3 4 26%	3511
	11th to 20th	Night	22% 16% 4 9% 5% 4 5% 4 5% 6% 21%	3479
	21st to end	Night	31% 12% 3 7% 4 3 3 3 5% 4 25%	3816
April	1st to 10th	Night	24% 13% 3 7% 5% 4 4 4 4 4 28%	1957
	11th to 20th	Night	22% 10% 2 8% 4 4 4 3 5% 5% 33%	1688
	21st to end	Night	24% 11% 3 6% 5% 4 4 2 5% 6% 30%	1710
May	1st to 10th	Night	23% 12% 2 6% 4 4 4 3 5% 6% 30%	2834
	11th to 20th	Night	21% 8% 2 5% 4 4 5% 4 4 7% 36%	2511
	21st to end	Night	16% 9% 3 8% 5% 4 5% 4 5% 7% 33%	2690
June	1st to 10th	Night	26% 10% 2 5% 5% 5% 4 4 5% 6% 28%	1330
	11th to 20th	Night	20% 8% 2 7% 4 4 5% 4 5% 5% 35%	1330
	21st to end	Night	27% 8% 3 6% 5% 3 4 4 5% 4 31%	1330
July	1st to 10th	Night	16% 7% 2 7% 4 5% 6% 5% 6% 8% 34%	2210
	11th to 20th	Night	21% 7% 2 7% 4 5% 5% 3 6% 8% 32%	2210
	21st to end	Night	19% 7% 3 6% 6% 4 4 4 6% 7% 35%	2889
August	1st to 10th	Night	19% 8% 4 8% 5% 5% 6% 4 6% 7% 29%	2825
	11th to 20th	Night	12% 8% 3 8% 5% 4 5% 4 7% 8% 36%	2782
	21st to end	Night	16% 4 2 5% 4 4 4 2 5% 8% 47%	3146
September	1st to 10th	Night	17% 6% 2 6% 4 4 4 4 5% 7% 43%	1900
	11th to 20th	Night	17% 6% 3 5% 3 3 3 3 4 6% 47%	2076
	21st to end	Night	21% 6% 2 5% 3 4 3 3 5% 6% 43%	2090
October	1st to 10th	Night	20% 7% 3 6% 3 3 4 3 5% 6% 40%	2270
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 5% 7% 38%	2280
	21st to end	Night	24% 8% 2 7% 4 3 4 3 4 5% 35%	2598
November	1st to 10th	Night	22% 9% 2 6% 4 3 4 3 4 5% 36%	2649
	11th to 20th	Night	22% 10% 3 7% 4 4 4 3 5% 6% 32%	2800
	21st to end	Night	24% 11% 4 7% 4 4 4 2 5% 5% 30%	2800
December	1st to 10th	Night	25% 13% 3 7% 5% 4 4 2 4 4 29%	2800
	11th to 20th	Night	25% 13% 4 8% 4 4 3 3 3 4 29%	3656
	21st to end	Night	21% 14% 5% 8% 4 3 3 3 3 4 31%	5288

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	53% 7% 15% 15% 10%	2208
	11th to 20th	Day	53% 6% 8% 21% 11% 1	2379
	21st to end	Day	45% 10% 14% 18% 13% 1	3064
February	1st to 10th	Day	52% 7% 12% 18% 10% 1	1710
	11th to 20th	Day	53% 6% 12% 17% 11% 1	1671
	21st to end	Day	49% 5% 11% 21% 11% 3	1488
March	1st to 10th	Day	59% 5% 11% 16% 6% 3	3333
	11th to 20th	Day	61% 8% 10% 13% 7% 2	3480
	21st to end	Day	63% 4 7% 15% 8% 2	3816
April	1st to 10th	Day	60% 5% 8% 14% 10% 2	2219
	11th to 20th	Day	51% 5% 11% 19% 12% 1	2442
	21st to end	Day	54% 5% 10% 16% 12% 4	2470
May	1st to 10th	Day	55% 8% 9% 19% 8% 1	4120
	11th to 20th	Day	47% 9% 15% 20% 7% 1	4397
	21st to end	Day	46% 12% 13% 17% 11%	4923
June	1st to 10th	Day	57% 7% 11% 16% 8%	2850
	11th to 20th	Day	49% 7% 12% 18% 12% 1	2850
	21st to end	Day	55% 8% 11% 16% 9% 1	2850
July	1st to 10th	Day	45% 9% 17% 19% 10%	4685
	11th to 20th	Day	45% 8% 15% 23% 8%	4679
	21st to end	Day	45% 9% 14% 24% 8%	4483
August	1st to 10th	Day	51% 8% 13% 22% 6%	4092
	11th to 20th	Day	44% 10% 15% 24% 7%	4084
	21st to end	Day	36% 8% 15% 25% 15%	4510
September	1st to 10th	Day	37% 9% 16% 25% 13%	2280
	11th to 20th	Day	40% 5% 13% 25% 15% 2	2100
	21st to end	Day	42% 7% 10% 26% 14% 1	2090
October	1st to 10th	Day	46% 7% 13% 25% 10%	3169
	11th to 20th	Day	45% 6% 11% 31% 7%	3140
	21st to end	Day	40% 6% 16% 21% 17%	3274
November	1st to 10th	Day	51% 7% 10% 21% 10% 1	1648
	11th to 20th	Day	52% 6% 12% 16% 13% 1	1600
	21st to end	Day	57% 6% 15% 16% 6%	1600
December	1st to 10th	Day	59% 6% 13% 17% 5%	1600
	11th to 20th	Day	62% 4 8% 16% 8% 1	1758
	21st to end	Day	53% 6% 15% 17% 8% 2	2452
January	1st to 10th	Night	48% 7% 15% 22% 7% 1	4748
	11th to 20th	Night	53% 8% 11% 19% 8% 1	4570
	21st to end	Night	50% 8% 11% 21% 10% 1	4590
February	1st to 10th	Night	53% 6% 12% 17% 12% 2	2470
	11th to 20th	Night	56% 7% 10% 15% 11% 2	2406
	21st to end	Night	52% 5% 10% 20% 12% 2	1965
March	1st to 10th	Night	62% 6% 8% 15% 8% 2	3520
	11th to 20th	Night	61% 10% 10% 11% 7% 1	3480
	21st to end	Night	62% 4 7% 15% 10% 2	3816
April	1st to 10th	Night	58% 6% 7% 14% 10% 4	1957
	11th to 20th	Night	52% 6% 10% 19% 13% 1	1688
	21st to end	Night	54% 6% 11% 14% 13% 2	1710
May	1st to 10th	Night	52% 9% 15% 15% 7% 1	2840
	11th to 20th	Night	45% 9% 14% 23% 8% 1	2512
	21st to end	Night	46% 12% 18% 17% 7% 1	2691
June	1st to 10th	Night	54% 9% 12% 17% 8% 1	1330
	11th to 20th	Night	50% 7% 12% 22% 8% 2	1330
	21st to end	Night	55% 7% 12% 16% 8% 1	1330
July	1st to 10th	Night	45% 9% 16% 19% 11%	2175
	11th to 20th	Night	49% 7% 16% 20% 7%	2168
	21st to end	Night	46% 10% 12% 22% 9% 1	2798
August	1st to 10th	Night	54% 8% 13% 19% 6%	2813
	11th to 20th	Night	42% 10% 18% 23% 7%	2809
	21st to end	Night	35% 7% 17% 24% 13% 3	3145
September	1st to 10th	Night	40% 7% 13% 27% 12% 1	1900
	11th to 20th	Night	38% 6% 14% 27% 14%	2076
	21st to end	Night	42% 7% 9% 27% 14% 1	2090
October	1st to 10th	Night	49% 5% 12% 24% 10%	3790
	11th to 20th	Night	39% 6% 12% 30% 12%	3779
	21st to end	Night	44% 5% 16% 22% 13%	4272
November	1st to 10th	Night	50% 6% 13% 20% 10% 1	2649
	11th to 20th	Night	53% 6% 13% 18% 10% 1	2800
	21st to end	Night	56% 7% 14% 15% 9%	2800
December	1st to 10th	Night	59% 5% 11% 18% 6%	2800
	11th to 20th	Night	60% 3 10% 18% 9%	3657
	21st to end	Night	58% 5% 11% 18% 7% 2	5288

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	32% 17% 36% 15% 1	180
	11th to 20th	Day	38% 22% 27% 9% 3	180
	21st to end	Day	21% 18% 37% 19% 5% 1	373
February	1st to 10th	Day	30% 19% 31% 14% 5% 1	370
	11th to 20th	Day	30% 26% 28% 12% 2 1	366
	21st to end	Day	27% 23% 31% 14% 5%	343
March	1st to 10th	Day	31% 25% 28% 12% 3 1	460
	11th to 20th	Day	29% 23% 30% 14% 3 1	460
	21st to end	Day	34% 22% 27% 12% 4 1	506
April	1st to 10th	Day	38% 23% 25% 10% 3	460
	11th to 20th	Day	31% 25% 25% 13% 4 1	452
	21st to end	Day	34% 22% 25% 12% 5% 1	460
May	1st to 10th	Day	33% 22% 25% 14% 5% 1	463
	11th to 20th	Day	28% 16% 29% 20% 6% 1	669
	21st to end	Day	28% 18% 32% 18% 4	735
June	1st to 10th	Day	31% 18% 28% 18% 5% 1	680
	11th to 20th	Day	27% 16% 29% 21% 6% 1	680
	21st to end	Day	30% 14% 29% 21% 6%	680
July	1st to 10th	Day	23% 13% 35% 21% 8%	670
	11th to 20th	Day	19% 11% 35% 24% 10% 1	668
	21st to end	Day	20% 11% 36% 24% 9% 1	591
August	1st to 10th	Day	18% 13% 37% 23% 8% 1	486
	11th to 20th	Day	20% 11% 32% 25% 10% 1	479
	21st to end	Day	19% 12% 29% 26% 10% 3	539
September	1st to 10th	Day	13% 17% 34% 26% 8% 2	490
	11th to 20th	Day	24% 11% 31% 20% 10% 3	490
	21st to end	Day	21% 17% 32% 17% 9% 3	490
October	1st to 10th	Day	22% 15% 25% 21% 14% 2	394
	11th to 20th	Day	25% 19% 27% 18% 9% 2	390
	21st to end	Day	27% 21% 32% 14% 5%	429
November	1st to 10th	Day	33% 16% 33% 13% 5% 1	395
	11th to 20th	Day	35% 19% 26% 15% 5% 1	400
	21st to end	Day	33% 22% 30% 14% 2	400
December	1st to 10th	Day	34% 15% 31% 15% 5%	400
	11th to 20th	Day	38% 25% 26% 10% 1	220
	21st to end	Day	32% 24% 31% 11% 2	204
January	1st to 10th	Night	27% 19% 31% 19% 3	850
	11th to 20th	Night	27% 19% 29% 20% 4	796
	21st to end	Night	20% 19% 35% 21% 5%	836
February	1st to 10th	Night	27% 19% 31% 19% 4	760
	11th to 20th	Night	24% 25% 32% 15% 4	743
	21st to end	Night	24% 18% 31% 23% 4	628
March	1st to 10th	Night	28% 17% 34% 18% 2	760
	11th to 20th	Night	25% 20% 30% 20% 5%	760
	21st to end	Night	27% 18% 34% 17% 5%	836
April	1st to 10th	Night	31% 18% 30% 18% 3	644
	11th to 20th	Night	30% 17% 33% 17% 4	564
	21st to end	Night	30% 18% 30% 18% 5%	570
May	1st to 10th	Night	31% 15% 29% 21% 4	570
	11th to 20th	Night	28% 14% 33% 22% 3	562
	21st to end	Night	19% 18% 42% 18% 3	583
June	1st to 10th	Night	26% 11% 34% 26% 3	380
	11th to 20th	Night	23% 12% 32% 28% 5%	380
	21st to end	Night	30% 7% 29% 29% 4 1	380
July	1st to 10th	Night	19% 7% 41% 27% 5%	370
	11th to 20th	Night	19% 7% 32% 33% 9%	368
	21st to end	Night	21% 9% 33% 31% 6% 1	563
August	1st to 10th	Night	18% 6% 35% 33% 8% 1	568
	11th to 20th	Night	18% 8% 29% 35% 9%	562
	21st to end	Night	16% 10% 29% 32% 13% 1	627
September	1st to 10th	Night	20% 9% 39% 25% 7%	570
	11th to 20th	Night	21% 10% 25% 31% 12% 1	746
	21st to end	Night	23% 13% 29% 26% 9%	760
October	1st to 10th	Night	25% 11% 29% 27% 8% 1	760
	11th to 20th	Night	22% 14% 34% 21% 8% 1	760
	21st to end	Night	29% 18% 29% 19% 4	836
November	1st to 10th	Night	29% 16% 27% 21% 5%	837
	11th to 20th	Night	29% 19% 29% 17% 6% 1	900
	21st to end	Night	31% 19% 29% 18% 3	900
December	1st to 10th	Night	32% 15% 31% 18% 4	900
	11th to 20th	Night	31% 21% 28% 17% 3	900
	21st to end	Night	31% 19% 28% 19% 3 1	953

Page generated at 2024-12-21 05:13:50. Version ac07

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