Bandon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bandon clear sky chart from 2005-11-06 to 2025-06-10.

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	17% 10% 3 7% 4 4 4 3 5% 7% 35%	123803
	Night	21% 13% 3 7% 4 4 4 3 4 6% 31%	123300
Transparency	Day	48% 3 13% 19% 11% 4	123559
	Night	55% 3 11% 16% 10% 4	123131
Seeing	Day	22% 11% 29% 26% 10% 2	15663
	Night	28% 6% 17% 27% 19% 3	24697

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	32% 16% 4 10% 5% 4 4 2 4 5% 14%	3639
	11th to 20th	Day	26% 9% 2 5% 3 3 3 3 4 5% 37%	4024
	21st to end	Day	24% 10% 3 6% 5% 3 4 3 4 5% 34%	4510
February	1st to 10th	Day	26% 12% 4 8% 6% 4 5% 4 5% 5% 21%	1800
	11th to 20th	Day	24% 13% 4 9% 5% 5% 4 3 4 5% 23%	1755
	21st to end	Day	25% 14% 4 9% 5% 5% 4 3 4 5% 22%	1547
March	1st to 10th	Day	19% 15% 3 8% 5% 6% 6% 4 5% 7% 21%	4952
	11th to 20th	Day	25% 13% 4 8% 5% 4 4 3 4 5% 24%	5000
	21st to end	Day	26% 13% 3 10% 6% 6% 5% 4 7% 6% 13%	5486
April	1st to 10th	Day	26% 14% 4 8% 6% 4 3 4 5% 6% 20%	2361
	11th to 20th	Day	20% 13% 3 8% 6% 3 4 3 5% 7% 28%	2407
	21st to end	Day	20% 9% 3 7% 5% 4 5% 5% 8% 8% 28%	2600
May	1st to 10th	Day	14% 8% 2 6% 4 4 4 3 4 7% 43%	5880
	11th to 20th	Day	13% 10% 3 7% 4 4 4 3 5% 8% 37%	6188
	21st to end	Day	11% 8% 2 6% 4 4 5% 3 6% 10% 42%	6902
June	1st to 10th	Day	17% 11% 3 7% 6% 4 4 3 5% 8% 33%	2789
	11th to 20th	Day	13% 11% 3 7% 4 3 4 3 6% 9% 37%	2660
	21st to end	Day	9% 7% 2 5% 5% 3 3 4 6% 8% 48%	2660
July	1st to 10th	Day	3 6% 2 4 3 2 2 2 4 7% 65%	4420
	11th to 20th	Day	5% 8% 3 5% 4 4 3 3 6% 8% 52%	4398
	21st to end	Day	6% 11% 3 5% 3 3 3 4 5% 9% 48%	4455
August	1st to 10th	Day	5% 12% 4 8% 5% 4 5% 4 7% 10% 36%	4091
	11th to 20th	Day	7% 8% 3 6% 4 3 4 4 6% 10% 47%	4026
	21st to end	Day	6% 6% 2 6% 3 3 3 2 5% 9% 54%	4351
September	1st to 10th	Day	3 5% 2 5% 2 3 3 3 6% 9% 58%	2280
	11th to 20th	Day	10% 8% 3 6% 5% 3 4 3 6% 8% 44%	2165
	21st to end	Day	10% 5% 2 5% 3 3 4 3 6% 9% 49%	2066
October	1st to 10th	Day	11% 7% 2 6% 4 3 3 3 4 6% 50%	3180
	11th to 20th	Day	17% 7% 4 8% 5% 6% 5% 4 6% 8% 30%	3161
	21st to end	Day	20% 9% 3 8% 5% 4 4 4 6% 8% 29%	3448
November	1st to 10th	Day	26% 12% 3 8% 4 4 5% 3 6% 6% 23%	1750
	11th to 20th	Day	24% 11% 5% 8% 6% 4 5% 4 6% 7% 21%	1600
	21st to end	Day	22% 12% 3 7% 5% 4 4 3 5% 6% 30%	1600
December	1st to 10th	Day	18% 7% 2 7% 4 4 4 4 5% 7% 38%	2620
	11th to 20th	Day	30% 14% 4 10% 6% 4 4 3 5% 4 15%	3028
	21st to end	Day	34% 15% 5% 11% 6% 4 4 3 4 4 10%	4004
January	1st to 10th	Night	36% 14% 4 8% 5% 5% 4 3 4 4 13%	6306
	11th to 20th	Night	26% 12% 3 6% 3 3 3 2 4 6% 33%	5951
	21st to end	Night	30% 10% 3 6% 3 3 3 2 3 4 33%	6468
February	1st to 10th	Night	24% 14% 4 7% 7% 4 4 4 5% 7% 20%	2600
	11th to 20th	Night	26% 14% 4 8% 5% 4 3 3 4 5% 24%	2532
	21st to end	Night	27% 13% 4 8% 6% 4 3 3 5% 5% 22%	2080
March	1st to 10th	Night	20% 18% 5% 11% 6% 5% 6% 4 5% 6% 15%	4942
	11th to 20th	Night	22% 16% 5% 9% 5% 4 4 3 4 5% 24%	5000
	21st to end	Night	28% 17% 5% 11% 6% 4 4 3 4 4 13%	5489
April	1st to 10th	Night	27% 13% 3 8% 5% 5% 4 4 5% 6% 22%	2037
	11th to 20th	Night	20% 14% 4 7% 4 4 4 3 4 6% 30%	1936
	21st to end	Night	23% 13% 4 6% 5% 5% 4 4 6% 5% 26%	1800
May	1st to 10th	Night	16% 8% 3 6% 4 4 4 2 4 5% 44%	4100
	11th to 20th	Night	17% 15% 5% 9% 4 3 3 3 4 5% 32%	3708
	21st to end	Night	14% 11% 2 6% 3 4 4 3 5% 7% 43%	3972
June	1st to 10th	Night	18% 13% 4 7% 4 3 5% 3 4 7% 33%	1595
	11th to 20th	Night	12% 10% 4 7% 4 3 3 3 6% 8% 40%	1520
	21st to end	Night	11% 11% 2 6% 4 3 2 3 5% 7% 45%	1520
July	1st to 10th	Night	5% 10% 1 3 2 2 2 2 4 5% 65%	2540
	11th to 20th	Night	5% 19% 4 7% 4 3 3 3 3 6% 44%	2559
	21st to end	Night	12% 22% 3 5% 3 2 3 2 3 5% 40%	3109
August	1st to 10th	Night	8% 35% 5% 7% 3 3 2 2 3 5% 27%	2848
	11th to 20th	Night	11% 18% 3 6% 3 3 3 3 4 7% 39%	2812
	21st to end	Night	8% 8% 2 6% 3 2 4 2 3 5% 57%	3321
September	1st to 10th	Night	5% 8% 2 5% 3 3 4 3 5% 6% 56%	1900
	11th to 20th	Night	8% 9% 2 6% 4 3 3 3 5% 7% 48%	2012
	21st to end	Night	12% 8% 3 6% 4 4 3 3 4 7% 46%	2113
October	1st to 10th	Night	10% 8% 3 7% 4 3 3 2 4 5% 52%	3800
	11th to 20th	Night	13% 13% 4 9% 4 5% 4 3 5% 7% 33%	3777
	21st to end	Night	22% 11% 4 9% 5% 4 4 3 5% 6% 27%	4121
November	1st to 10th	Night	24% 10% 4 8% 5% 4 4 3 5% 6% 25%	2544
	11th to 20th	Night	26% 11% 4 9% 5% 5% 4 4 4 5% 22%	2800
	21st to end	Night	20% 10% 3 8% 5% 5% 4 4 5% 6% 30%	2800
December	1st to 10th	Night	17% 9% 2 6% 4 4 3 4 5% 8% 37%	4560
	11th to 20th	Night	33% 12% 4 9% 5% 5% 4 3 4 6% 14%	5176
	21st to end	Night	33% 12% 4 9% 5% 5% 4 3 4 5% 17%	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	74% 2 9% 9% 5% 1	3639
	11th to 20th	Day	51% 3 7% 19% 15% 5%	4024
	21st to end	Day	53% 2 8% 11% 12% 14%	4510
February	1st to 10th	Day	65% 3 12% 15% 4 2	1800
	11th to 20th	Day	65% 3 12% 13% 5% 2	1764
	21st to end	Day	65% 3 10% 14% 7% 1	1547
March	1st to 10th	Day	61% 4 13% 18% 3	4952
	11th to 20th	Day	63% 4 7% 16% 9% 1	5000
	21st to end	Day	70% 4 13% 11% 2	5486
April	1st to 10th	Day	66% 3 13% 14% 5%	2361
	11th to 20th	Day	58% 3 13% 16% 8% 1	2410
	21st to end	Day	53% 5% 15% 20% 6% 1	2600
May	1st to 10th	Day	42% 2 14% 27% 12% 2	5880
	11th to 20th	Day	44% 5% 18% 21% 10% 1	6191
	21st to end	Day	39% 5% 32% 22% 1	6904
June	1st to 10th	Day	52% 3 14% 25% 6%	2789
	11th to 20th	Day	45% 3 20% 26% 6%	2660
	21st to end	Day	35% 3 17% 31% 12% 2	2660
July	1st to 10th	Day	20% 2 9% 16% 22% 31%	4351
	11th to 20th	Day	27% 2 9% 19% 29% 13%	4323
	21st to end	Day	31% 3 11% 25% 25% 5%	4315
August	1st to 10th	Day	37% 2 16% 24% 16% 5%	4076
	11th to 20th	Day	31% 5% 17% 33% 13% 2	4065
	21st to end	Day	27% 4 16% 27% 23% 2	4350
September	1st to 10th	Day	24% 2 9% 34% 22% 9%	2280
	11th to 20th	Day	36% 4 14% 27% 15% 4	2165
	21st to end	Day	32% 3 14% 29% 16% 5%	2066
October	1st to 10th	Day	35% 3 8% 21% 18% 14%	3180
	11th to 20th	Day	47% 7% 15% 19% 10% 2	3161
	21st to end	Day	52% 4 11% 19% 12% 3	3448
November	1st to 10th	Day	61% 4 9% 15% 9% 1	1750
	11th to 20th	Day	63% 3 12% 11% 7% 4	1600
	21st to end	Day	55% 3 11% 11% 12% 7%	1600
December	1st to 10th	Day	45% 3 11% 15% 18% 7%	2620
	11th to 20th	Day	73% 3 11% 9% 4	3028
	21st to end	Day	79% 3 6% 8% 3 1	4004
January	1st to 10th	Night	76% 2 6% 9% 4 2	6306
	11th to 20th	Night	55% 2 8% 15% 16% 4	5951
	21st to end	Night	57% 1 5% 9% 14% 13%	6468
February	1st to 10th	Night	64% 4 12% 14% 5% 2	2600
	11th to 20th	Night	63% 3 11% 16% 6% 2	2534
	21st to end	Night	65% 3 10% 13% 7% 2	2080
March	1st to 10th	Night	69% 3 10% 15% 3	4942
	11th to 20th	Night	64% 4 11% 12% 7% 2	5000
	21st to end	Night	74% 4 12% 9% 1	5489
April	1st to 10th	Night	63% 3 14% 14% 5%	2037
	11th to 20th	Night	56% 5% 13% 18% 6% 2	1936
	21st to end	Night	59% 3 13% 18% 6% 1	1800
May	1st to 10th	Night	44% 3 11% 30% 11% 1	4097
	11th to 20th	Night	55% 4 14% 18% 8% 2	3708
	21st to end	Night	42% 4 33% 19% 2	3972
June	1st to 10th	Night	52% 3 18% 24% 3	1595
	11th to 20th	Night	43% 4 19% 27% 6%	1520
	21st to end	Night	39% 2 17% 33% 8% 3	1520
July	1st to 10th	Night	24% 2 7% 16% 22% 29%	2500
	11th to 20th	Night	40% 2 8% 16% 25% 9%	2511
	21st to end	Night	46% 3 6% 20% 22% 3	3011
August	1st to 10th	Night	61% 2 9% 18% 9% 2	2839
	11th to 20th	Night	45% 5% 13% 24% 11% 2	2839
	21st to end	Night	29% 3 12% 31% 22% 3	3321
September	1st to 10th	Night	27% 3 9% 30% 21% 10%	1900
	11th to 20th	Night	35% 4 15% 26% 17% 3	2012
	21st to end	Night	38% 3 13% 22% 16% 7%	2113
October	1st to 10th	Night	35% 4 8% 19% 26% 9%	3800
	11th to 20th	Night	50% 5% 17% 17% 9% 2	3777
	21st to end	Night	58% 3 10% 15% 9% 4	4121
November	1st to 10th	Night	59% 4 12% 15% 9% 1	2544
	11th to 20th	Night	64% 4 9% 13% 7% 4	2800
	21st to end	Night	55% 3 11% 13% 11% 7%	2800
December	1st to 10th	Night	45% 3 9% 19% 20% 4	4560
	11th to 20th	Night	72% 4 10% 8% 5% 1	5176
	21st to end	Night	71% 4 9% 13% 3 1	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	42% 15% 18% 15% 6% 4	200
	11th to 20th	Day	37% 10% 19% 16% 12% 5%	363
	21st to end	Day	31% 11% 23% 20% 11% 5%	440
February	1st to 10th	Day	33% 11% 24% 22% 9% 1	400
	11th to 20th	Day	39% 12% 28% 16% 4 2	395
	21st to end	Day	32% 15% 27% 21% 4 1	349
March	1st to 10th	Day	37% 14% 23% 19% 6%	500
	11th to 20th	Day	34% 10% 27% 19% 9% 2	500
	21st to end	Day	33% 18% 23% 20% 5% 1	550
April	1st to 10th	Day	32% 17% 25% 19% 6% 1	500
	11th to 20th	Day	27% 17% 29% 18% 5% 3	492
	21st to end	Day	24% 16% 32% 19% 7% 1	500
May	1st to 10th	Day	19% 17% 35% 20% 7% 1	503
	11th to 20th	Day	28% 11% 28% 24% 8% 1	528
	21st to end	Day	20% 12% 36% 25% 6% 1	573
June	1st to 10th	Day	18% 12% 35% 25% 9% 1	527
	11th to 20th	Day	17% 17% 41% 21% 4	490
	21st to end	Day	9% 9% 39% 36% 6% 1	490
July	1st to 10th	Day	9% 7% 42% 32% 10%	486
	11th to 20th	Day	6% 7% 44% 35% 8% 1	484
	21st to end	Day	9% 4 39% 38% 9% 1	531
August	1st to 10th	Day	10% 4 29% 39% 16% 3	487
	11th to 20th	Day	8% 4 30% 41% 14% 3	477
	21st to end	Day	10% 5% 35% 36% 10% 4	539
September	1st to 10th	Day	6% 4 32% 37% 18% 3	490
	11th to 20th	Day	17% 8% 26% 32% 15% 2	490
	21st to end	Day	14% 11% 29% 30% 12% 3	490
October	1st to 10th	Day	19% 10% 25% 29% 14% 4	490
	11th to 20th	Day	18% 12% 24% 25% 15% 6%	490
	21st to end	Day	27% 15% 21% 25% 9% 3	539
November	1st to 10th	Day	30% 11% 26% 21% 10% 3	350
	11th to 20th	Day	28% 15% 21% 18% 14% 5%	200
	21st to end	Day	31% 10% 20% 17% 18% 5%	200
December	1st to 10th	Day	31% 7% 15% 22% 16% 10%	200
	11th to 20th	Day	44% 9% 15% 21% 9% 3	200
	21st to end	Day	40% 14% 14% 21% 11% 1	220
January	1st to 10th	Night	41% 9% 17% 19% 11% 3	800
	11th to 20th	Night	36% 6% 19% 18% 17% 5%	800
	21st to end	Night	31% 6% 14% 25% 20% 4	880
February	1st to 10th	Night	33% 8% 14% 27% 17% 2	800
	11th to 20th	Night	33% 8% 19% 24% 13% 2	784
	21st to end	Night	36% 8% 17% 25% 13% 1	660
March	1st to 10th	Night	38% 8% 18% 23% 12% 1	800
	11th to 20th	Night	30% 8% 18% 26% 15% 2	800
	21st to end	Night	39% 6% 18% 23% 13% 1	880
April	1st to 10th	Night	36% 7% 16% 23% 15% 3	800
	11th to 20th	Night	30% 7% 20% 25% 15% 3	748
	21st to end	Night	30% 5% 15% 29% 20% 2	600
May	1st to 10th	Night	24% 6% 19% 30% 19% 1	600
	11th to 20th	Night	26% 4 15% 27% 26% 4	434
	21st to end	Night	29% 5% 15% 30% 18% 3	433
June	1st to 10th	Night	25% 3 20% 31% 19% 3	399
	11th to 20th	Night	17% 4 26% 37% 14% 2	380
	21st to end	Night	20% 1 17% 37% 23% 2	380
July	1st to 10th	Night	15% 2 15% 37% 28% 3	370
	11th to 20th	Night	17% 3 21% 38% 19% 2	374
	21st to end	Night	21% 3 13% 36% 25% 3	624
August	1st to 10th	Night	24% 2 8% 29% 31% 7%	567
	11th to 20th	Night	15% 3 7% 30% 38% 7%	564
	21st to end	Night	15% 2 14% 36% 27% 6%	724
September	1st to 10th	Night	9% 2 15% 39% 31% 4	760
	11th to 20th	Night	13% 4 13% 29% 31% 10%	760
	21st to end	Night	16% 5% 18% 31% 23% 7%	760
October	1st to 10th	Night	17% 4 21% 28% 25% 6%	760
	11th to 20th	Night	21% 6% 16% 28% 22% 6%	760
	21st to end	Night	27% 7% 20% 26% 16% 5%	836
November	1st to 10th	Night	30% 8% 19% 26% 16% 2	780
	11th to 20th	Night	34% 9% 16% 25% 14% 2	800
	21st to end	Night	25% 9% 17% 28% 18% 3	800
December	1st to 10th	Night	28% 7% 16% 28% 18% 4	800
	11th to 20th	Night	38% 7% 17% 22% 14% 2	800
	21st to end	Night	42% 10% 16% 21% 11% 1	880

Page generated at 2025-06-07 07:28:20. Version ac07

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