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 2026-10-14.

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	14% 10% 3 7% 4 4 4 3 5% 8% 37%	158564
	Night	19% 15% 4 7% 4 4 4 3 4 6% 31%	150663
Transparency	Day	45% 4 14% 21% 12% 4	153337
	Night	55% 3 11% 16% 10% 4	146891
Seeing	Day	22% 11% 30% 26% 10% 2	17445
	Night	27% 6% 17% 27% 19% 3	26343

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	31% 15% 5% 10% 6% 4 5% 3 4 5% 13%	4722
	11th to 20th	Day	20% 7% 2 4 3 3 3 3 4 6% 46%	5236
	21st to end	Day	21% 10% 3 8% 5% 4 4 3 4 5% 31%	5843
February	1st to 10th	Day	25% 12% 3 8% 6% 4 5% 4 5% 5% 22%	1890
	11th to 20th	Day	24% 13% 4 9% 6% 5% 4 3 4 5% 23%	1845
	21st to end	Day	26% 14% 4 9% 5% 4 4 3 4 5% 22%	1622
March	1st to 10th	Day	19% 15% 3 8% 5% 6% 6% 5% 5% 8% 21%	5062
	11th to 20th	Day	25% 13% 4 8% 5% 4 4 3 4 5% 24%	5110
	21st to end	Day	25% 13% 3 10% 6% 7% 6% 4 7% 6% 13%	5607
April	1st to 10th	Day	25% 14% 4 8% 6% 5% 3 4 5% 7% 20%	2479
	11th to 20th	Day	21% 13% 3 8% 6% 3 4 3 5% 7% 27%	2529
	21st to end	Day	20% 9% 3 7% 5% 4 5% 4 8% 8% 29%	2730
May	1st to 10th	Day	12% 8% 2 7% 4 4 4 3 5% 9% 41%	7627
	11th to 20th	Day	11% 9% 2 7% 4 4 4 4 6% 8% 41%	8046
	21st to end	Day	10% 9% 2 6% 4 4 5% 3 6% 9% 42%	8992
June	1st to 10th	Day	17% 11% 3 7% 6% 4 4 3 5% 8% 33%	2940
	11th to 20th	Day	12% 10% 3 7% 4 3 4 4 6% 8% 39%	2940
	21st to end	Day	10% 8% 2 6% 4 4 3 4 6% 8% 46%	2940
July	1st to 10th	Day	2 9% 3 5% 3 3 3 3 5% 9% 56%	8219
	11th to 20th	Day	3 7% 2 5% 4 4 4 3 6% 9% 53%	8172
	21st to end	Day	5% 10% 3 6% 4 4 3 3 5% 10% 47%	8304
August	1st to 10th	Day	4 9% 3 7% 4 4 4 3 6% 9% 48%	7547
	11th to 20th	Day	6% 10% 3 7% 4 4 4 3 6% 10% 42%	7563
	21st to end	Day	4 7% 3 6% 3 3 4 4 6% 10% 50%	8073
September	1st to 10th	Day	4 6% 2 5% 2 3 3 3 6% 9% 56%	2520
	11th to 20th	Day	9% 8% 3 6% 4 3 4 3 6% 8% 45%	2393
	21st to end	Day	10% 5% 2 5% 3 3 4 3 6% 8% 50%	2284
October	1st to 10th	Day	11% 7% 2 6% 3 3 3 3 4 6% 50%	3380
	11th to 20th	Day	17% 7% 4 8% 5% 5% 5% 4 6% 8% 31%	3292
	21st to end	Day	20% 9% 3 8% 5% 4 4 4 6% 8% 29%	3558
November	1st to 10th	Day	26% 11% 3 8% 5% 4 5% 3 6% 6% 23%	1839
	11th to 20th	Day	25% 11% 5% 9% 6% 4 5% 4 5% 7% 20%	1680
	21st to end	Day	22% 12% 3 7% 5% 4 4 3 5% 6% 30%	1680
December	1st to 10th	Day	18% 7% 2 7% 4 4 4 4 5% 7% 37%	2700
	11th to 20th	Day	30% 14% 4 10% 6% 4 4 3 5% 4 15%	3108
	21st to end	Day	34% 15% 5% 11% 6% 4 4 3 4 4 11%	4092
January	1st to 10th	Night	35% 14% 4 9% 5% 5% 4 3 4 4 13%	8172
	11th to 20th	Night	20% 9% 3 6% 3 3 3 3 4 8% 39%	7747
	21st to end	Night	25% 10% 3 8% 4 4 4 3 4 5% 30%	8371
February	1st to 10th	Night	23% 13% 4 7% 7% 4 4 4 5% 7% 21%	2730
	11th to 20th	Night	25% 14% 4 8% 5% 4 3 3 4 5% 24%	2662
	21st to end	Night	28% 13% 4 8% 6% 4 4 3 5% 5% 21%	2180
March	1st to 10th	Night	20% 18% 5% 11% 6% 5% 6% 4 5% 6% 15%	5052
	11th to 20th	Night	22% 15% 5% 9% 5% 4 4 3 4 5% 24%	5110
	21st to end	Night	28% 17% 5% 11% 6% 4 4 3 4 4 14%	5610
April	1st to 10th	Night	26% 13% 3 8% 5% 5% 4 4 5% 6% 23%	2139
	11th to 20th	Night	20% 14% 4 7% 4 4 4 3 4 6% 30%	2034
	21st to end	Night	22% 14% 4 6% 5% 4 3 4 5% 5% 27%	1890
May	1st to 10th	Night	15% 15% 3 6% 4 4 4 2 4 6% 38%	5321
	11th to 20th	Night	15% 15% 4 9% 4 4 3 3 5% 6% 32%	4818
	21st to end	Night	13% 13% 3 6% 3 4 4 3 5% 7% 40%	5181
June	1st to 10th	Night	17% 13% 4 7% 4 3 5% 3 4 7% 33%	1680
	11th to 20th	Night	12% 10% 3 6% 4 3 3 3 6% 7% 42%	1680
	21st to end	Night	11% 12% 2 6% 4 3 2 3 5% 7% 44%	1680
July	1st to 10th	Night	6% 24% 2 4 3 2 2 2 3 5% 48%	4740
	11th to 20th	Night	4 23% 5% 8% 4 3 2 2 3 5% 41%	4773
	21st to end	Night	10% 29% 4 6% 4 3 3 2 3 4 32%	5806
August	1st to 10th	Night	10% 29% 4 6% 3 2 2 2 2 4 36%	5275
	11th to 20th	Night	14% 26% 3 5% 4 3 3 3 3 5% 32%	5292
	21st to end	Night	7% 17% 3 7% 3 3 4 2 3 5% 46%	6158
September	1st to 10th	Night	6% 9% 2 5% 3 3 4 3 5% 6% 54%	2100
	11th to 20th	Night	8% 10% 2 6% 4 3 3 3 5% 7% 49%	2224
	21st to end	Night	12% 9% 3 6% 4 4 3 3 4 6% 47%	2335
October	1st to 10th	Night	9% 9% 3 7% 4 3 3 2 4 5% 51%	4040
	11th to 20th	Night	13% 12% 4 9% 4 5% 4 3 5% 7% 33%	3933
	21st to end	Night	22% 11% 4 8% 5% 4 4 3 5% 6% 27%	4253
November	1st to 10th	Night	24% 10% 4 8% 5% 4 4 4 5% 7% 25%	2675
	11th to 20th	Night	26% 12% 4 9% 5% 5% 4 4 4 5% 22%	2940
	21st to end	Night	19% 10% 3 8% 5% 5% 4 4 5% 6% 30%	2940
December	1st to 10th	Night	18% 9% 2 6% 4 4 3 4 5% 8% 37%	4700
	11th to 20th	Night	33% 12% 4 9% 5% 4 4 3 4 6% 14%	5316
	21st to end	Night	33% 12% 4 9% 5% 5% 4 3 4 5% 17%	7106

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% 3 8% 9% 5% 1	4723
	11th to 20th	Day	41% 2 7% 18% 17% 14%	5236
	21st to end	Day	56% 2 7% 11% 10% 13%	5843
February	1st to 10th	Day	64% 3 12% 15% 4 2	1890
	11th to 20th	Day	65% 3 12% 13% 5% 2	1854
	21st to end	Day	66% 3 9% 13% 7% 1	1622
March	1st to 10th	Day	61% 4 13% 18% 3	5062
	11th to 20th	Day	63% 4 7% 16% 9% 1	5110
	21st to end	Day	69% 4 13% 11% 2	5607
April	1st to 10th	Day	64% 3 14% 14% 5%	2479
	11th to 20th	Day	58% 3 13% 17% 8% 1	2532
	21st to end	Day	52% 5% 15% 20% 6% 1	2730
May	1st to 10th	Day	40% 3 16% 28% 11% 2	7627
	11th to 20th	Day	39% 6% 22% 24% 8% 1	8049
	21st to end	Day	38% 5% 28% 26% 2	8994
June	1st to 10th	Day	51% 4 14% 26% 6%	2940
	11th to 20th	Day	44% 3 18% 26% 8% 1	2940
	21st to end	Day	36% 4 16% 30% 12% 2	2940
July	1st to 10th	Day	24% 3 14% 26% 16% 16%	8151
	11th to 20th	Day	24% 3 10% 15% 36% 12%	8097
	21st to end	Day	30% 4 15% 31% 18% 3	8119
August	1st to 10th	Day	29% 2 13% 20% 27% 10%	5976
	11th to 20th	Day	35% 5% 18% 30% 10% 1	5962
	21st to end	Day	26% 5% 16% 34% 17% 2	6328
September	1st to 10th	Day	26% 2 10% 33% 20% 9%	2520
	11th to 20th	Day	35% 4 14% 29% 14% 4	2393
	21st to end	Day	32% 4 14% 29% 17% 5%	2284
October	1st to 10th	Day	35% 3 8% 21% 19% 14%	3380
	11th to 20th	Day	46% 7% 15% 20% 11% 2	3292
	21st to end	Day	52% 4 11% 19% 11% 3	3558
November	1st to 10th	Day	61% 4 9% 16% 8% 1	1839
	11th to 20th	Day	64% 3 11% 11% 7% 4	1680
	21st to end	Day	55% 3 12% 12% 11% 7%	1680
December	1st to 10th	Day	46% 3 11% 15% 18% 7%	2700
	11th to 20th	Day	72% 3 11% 9% 4 1	3108
	21st to end	Day	78% 3 6% 9% 3 1	4092
January	1st to 10th	Night	75% 3 8% 9% 3 2	8172
	11th to 20th	Night	45% 2 8% 15% 18% 12%	7747
	21st to end	Night	58% 2 6% 9% 13% 11%	8371
February	1st to 10th	Night	63% 4 12% 13% 6% 2	2730
	11th to 20th	Night	63% 3 11% 16% 6% 1	2664
	21st to end	Night	66% 4 9% 12% 7% 2	2180
March	1st to 10th	Night	69% 4 10% 14% 3	5052
	11th to 20th	Night	64% 4 11% 12% 7% 2	5110
	21st to end	Night	74% 4 12% 9% 2	5610
April	1st to 10th	Night	63% 3 15% 14% 4	2139
	11th to 20th	Night	57% 5% 13% 17% 6% 2	2034
	21st to end	Night	59% 3 12% 19% 6% 1	1890
May	1st to 10th	Night	48% 3 12% 27% 9% 1	5319
	11th to 20th	Night	53% 5% 15% 19% 6% 1	4818
	21st to end	Night	44% 4 29% 21% 2	5182
June	1st to 10th	Night	52% 3 17% 25% 3	1680
	11th to 20th	Night	41% 4 18% 28% 7% 1	1680
	21st to end	Night	40% 2 16% 31% 8% 2	1680
July	1st to 10th	Night	40% 4 10% 17% 14% 15%	4700
	11th to 20th	Night	44% 2 8% 13% 27% 6%	4725
	21st to end	Night	54% 3 12% 15% 15% 2	5679
August	1st to 10th	Night	51% 2 8% 15% 17% 7%	4169
	11th to 20th	Night	56% 4 11% 19% 8% 2	4169
	21st to end	Night	35% 3 11% 32% 16% 2	4829
September	1st to 10th	Night	30% 4 9% 29% 19% 10%	2100
	11th to 20th	Night	35% 4 15% 27% 17% 3	2224
	21st to end	Night	38% 3 13% 22% 16% 7%	2335
October	1st to 10th	Night	35% 4 8% 19% 26% 9%	4040
	11th to 20th	Night	49% 5% 17% 17% 10% 2	3933
	21st to end	Night	58% 3 10% 16% 8% 4	4253
November	1st to 10th	Night	59% 4 13% 15% 9% 1	2675
	11th to 20th	Night	64% 3 9% 13% 6% 4	2940
	21st to end	Night	55% 3 11% 13% 11% 7%	2940
December	1st to 10th	Night	45% 3 9% 18% 20% 4	4700
	11th to 20th	Night	72% 4 10% 8% 5% 1	5316
	21st to end	Night	70% 4 9% 13% 3 1	7106

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	41% 16% 18% 15% 6% 4	220
	11th to 20th	Day	35% 9% 19% 17% 14% 6%	391
	21st to end	Day	30% 11% 23% 19% 11% 4	473
February	1st to 10th	Day	32% 11% 24% 23% 9% 1	430
	11th to 20th	Day	38% 12% 28% 16% 4 2	425
	21st to end	Day	33% 15% 27% 20% 4 1	375
March	1st to 10th	Day	36% 15% 24% 19% 6% 1	540
	11th to 20th	Day	32% 11% 27% 20% 8% 2	540
	21st to end	Day	32% 19% 24% 20% 5% 1	594
April	1st to 10th	Day	31% 16% 25% 20% 7% 2	540
	11th to 20th	Day	28% 16% 29% 18% 5% 3	532
	21st to end	Day	24% 16% 33% 20% 7% 1	540
May	1st to 10th	Day	19% 16% 36% 21% 7% 1	543
	11th to 20th	Day	27% 12% 29% 23% 8% 1	568
	21st to end	Day	21% 12% 36% 25% 6% 1	617
June	1st to 10th	Day	18% 12% 36% 25% 9% 1	570
	11th to 20th	Day	16% 16% 42% 22% 4	570
	21st to end	Day	10% 10% 39% 34% 6% 1	570
July	1st to 10th	Day	8% 7% 42% 33% 10%	566
	11th to 20th	Day	6% 8% 44% 33% 7% 1	564
	21st to end	Day	8% 5% 38% 37% 10% 1	619
August	1st to 10th	Day	9% 4 30% 38% 15% 3	567
	11th to 20th	Day	9% 5% 31% 38% 14% 3	557
	21st to end	Day	9% 5% 35% 36% 11% 4	627
September	1st to 10th	Day	7% 5% 34% 35% 17% 3	570
	11th to 20th	Day	16% 9% 28% 31% 15% 2	570
	21st to end	Day	15% 11% 28% 31% 12% 3	570
October	1st to 10th	Day	18% 9% 26% 29% 13% 4	570
	11th to 20th	Day	17% 14% 25% 25% 14% 5%	543
	21st to end	Day	26% 15% 22% 25% 8% 3	583
November	1st to 10th	Day	32% 11% 25% 20% 10% 2	379
	11th to 20th	Day	28% 17% 20% 17% 13% 5%	220
	21st to end	Day	31% 10% 20% 18% 17% 4	220
December	1st to 10th	Day	31% 9% 16% 20% 15% 9%	220
	11th to 20th	Day	42% 10% 15% 20% 10% 3	220
	21st to end	Day	39% 14% 15% 20% 11% 1	242
January	1st to 10th	Night	41% 9% 17% 19% 10% 3	840
	11th to 20th	Night	35% 6% 19% 18% 18% 5%	840
	21st to end	Night	30% 6% 15% 25% 20% 4	924
February	1st to 10th	Night	32% 8% 14% 28% 17% 2	840
	11th to 20th	Night	33% 8% 20% 25% 13% 2	824
	21st to end	Night	37% 8% 17% 25% 12% 1	692
March	1st to 10th	Night	37% 8% 19% 23% 12% 1	840
	11th to 20th	Night	30% 8% 18% 27% 14% 2	840
	21st to end	Night	39% 7% 18% 23% 12% 1	924
April	1st to 10th	Night	35% 7% 16% 23% 16% 2	840
	11th to 20th	Night	31% 7% 20% 25% 15% 3	786
	21st to end	Night	31% 4 16% 28% 19% 2	630
May	1st to 10th	Night	25% 6% 18% 30% 18% 1	630
	11th to 20th	Night	26% 4 15% 27% 24% 4	456
	21st to end	Night	29% 5% 15% 31% 17% 3	455
June	1st to 10th	Night	25% 4 19% 32% 18% 2	420
	11th to 20th	Night	17% 4 26% 38% 14% 2	420
	21st to end	Night	20% 2 16% 37% 23% 2	420
July	1st to 10th	Night	17% 2 14% 37% 27% 2	410
	11th to 20th	Night	17% 3 22% 37% 18% 2	415
	21st to end	Night	21% 3 13% 35% 25% 3	690
August	1st to 10th	Night	24% 2 9% 28% 30% 7%	627
	11th to 20th	Night	17% 3 7% 29% 37% 6%	624
	21st to end	Night	15% 2 15% 36% 27% 5%	800
September	1st to 10th	Night	10% 3 16% 38% 30% 4	840
	11th to 20th	Night	13% 4 14% 31% 29% 9%	840
	21st to end	Night	17% 5% 19% 30% 23% 6%	840
October	1st to 10th	Night	16% 4 21% 29% 24% 5%	840
	11th to 20th	Night	20% 7% 18% 28% 21% 6%	812
	21st to end	Night	26% 8% 21% 26% 15% 4	880
November	1st to 10th	Night	30% 8% 19% 26% 15% 2	820
	11th to 20th	Night	34% 9% 16% 25% 14% 2	840
	21st to end	Night	25% 9% 18% 29% 17% 3	840
December	1st to 10th	Night	28% 8% 16% 28% 18% 3	840
	11th to 20th	Night	39% 7% 17% 21% 14% 2	840
	21st to end	Night	42% 10% 16% 21% 10% 1	924

Page generated at 2026-10-11 02:06:28. Version ac07

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