Joseph
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph clear sky chart from 2005-11-06 to 2025-10-04.

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	4 7% 3 7% 5% 5% 5% 4 6% 8% 47%	135363
	Night	3 6% 2 6% 5% 5% 5% 5% 7% 8% 47%	131330
Transparency	Day	33% 8% 13% 22% 17% 7%	130079
	Night	33% 9% 14% 23% 16% 5%	127616
Seeing	Day	8% 12% 29% 30% 16% 5%	15529
	Night	7% 7% 26% 37% 19% 3	24659

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 8% 5% 12% 7% 8% 8% 6% 10% 9% 25%	3639
	11th to 20th	Day	1 7% 4 11% 8% 7% 6% 5% 6% 7% 37%	3640
	21st to end	Day	1 6% 3 8% 6% 6% 7% 4 7% 9% 43%	4004
February	1st to 10th	Day	2 11% 7% 11% 7% 6% 6% 5% 8% 9% 29%	1663
	11th to 20th	Day	1 13% 6% 12% 7% 7% 7% 6% 7% 7% 26%	1941
	21st to end	Day	2 8% 5% 13% 8% 8% 7% 7% 8% 8% 25%	1650
March	1st to 10th	Day	2 9% 4 10% 7% 6% 7% 6% 8% 9% 32%	4518
	11th to 20th	Day	1 9% 4 9% 6% 6% 7% 6% 8% 8% 37%	4708
	21st to end	Day	3 14% 5% 14% 9% 8% 8% 6% 7% 8% 18%	5895
April	1st to 10th	Day	6% 14% 5% 11% 8% 5% 6% 6% 7% 7% 26%	2400
	11th to 20th	Day	6% 13% 4 9% 6% 6% 5% 5% 6% 7% 34%	2399
	21st to end	Day	9% 15% 4 9% 6% 4 4 4 6% 7% 32%	2600
May	1st to 10th	Day	5% 9% 3 7% 4 4 4 4 5% 7% 47%	5965
	11th to 20th	Day	9% 9% 3 7% 4 4 5% 4 6% 8% 41%	6277
	21st to end	Day	8% 9% 2 7% 5% 4 4 3 5% 7% 46%	6902
June	1st to 10th	Day	11% 10% 3 8% 6% 5% 5% 5% 7% 9% 33%	2800
	11th to 20th	Day	10% 9% 3 6% 6% 5% 5% 3 6% 7% 40%	2800
	21st to end	Day	4 3 1 4 3 3 5% 4 6% 8% 58%	2800
July	1st to 10th	Day	2 2 1 2 2 3 3 3 5% 6% 73%	6319
	11th to 20th	Day	1 1 1 1 2 2 3 2 4 4 80%	6320
	21st to end	Day	2 1 1 2 2 3 4 4 6% 8% 67%	6880
August	1st to 10th	Day	3 2 1 4 3 4 6% 5% 7% 9% 56%	6210
	11th to 20th	Day	2 2 1 3 2 3 3 3 5% 7% 69%	5790
	21st to end	Day	4 3 1 3 2 3 4 4 6% 7% 62%	5984
September	1st to 10th	Day	3 3 1 4 2 3 3 3 5% 6% 67%	2400
	11th to 20th	Day	5% 5% 2 5% 3 5% 5% 4 6% 7% 53%	2270
	21st to end	Day	7% 6% 2 5% 4 3 5% 4 6% 5% 55%	2200
October	1st to 10th	Day	5% 5% 2 4 3 3 3 3 4 4 63%	3447
	11th to 20th	Day	5% 6% 2 5% 4 4 5% 4 6% 8% 50%	3010
	21st to end	Day	5% 9% 4 9% 6% 6% 5% 6% 7% 8% 37%	3101
November	1st to 10th	Day	4 11% 3 8% 7% 7% 7% 5% 7% 9% 33%	1764
	11th to 20th	Day	3 8% 4 9% 6% 6% 7% 6% 10% 12% 31%	1800
	21st to end	Day	2 7% 4 8% 6% 6% 7% 6% 9% 9% 36%	1615
December	1st to 10th	Day	1 6% 2 8% 5% 5% 4 5% 5% 7% 53%	2620
	11th to 20th	Day	2 9% 3 9% 6% 8% 8% 7% 10% 11% 27%	3028
	21st to end	Day	3 9% 3 9% 7% 8% 8% 6% 8% 10% 30%	4004
January	1st to 10th	Night	2 9% 4 10% 8% 7% 9% 8% 9% 10% 25%	6306
	11th to 20th	Night	2 9% 4 12% 7% 6% 6% 5% 7% 9% 33%	6320
	21st to end	Night	1 5% 2 7% 6% 6% 6% 5% 8% 10% 44%	6952
February	1st to 10th	Night	3 10% 5% 11% 8% 7% 7% 6% 8% 7% 27%	2735
	11th to 20th	Night	2 9% 5% 10% 7% 7% 7% 6% 8% 9% 30%	2345
	21st to end	Night	2 7% 3 11% 8% 7% 7% 7% 10% 8% 29%	1980
March	1st to 10th	Night	2 7% 3 7% 5% 5% 6% 5% 9% 11% 40%	5376
	11th to 20th	Night	1 7% 3 7% 5% 6% 7% 6% 8% 9% 41%	5291
	21st to end	Night	3 9% 3 9% 7% 9% 8% 6% 9% 10% 27%	5077
April	1st to 10th	Night	4 10% 4 8% 6% 7% 6% 5% 8% 9% 33%	2000
	11th to 20th	Night	5% 9% 3 7% 7% 5% 6% 4 6% 7% 42%	1948
	21st to end	Night	7% 9% 2 7% 6% 5% 6% 4 6% 8% 39%	1800
May	1st to 10th	Night	9% 6% 2 5% 3 3 5% 3 5% 7% 53%	4008
	11th to 20th	Night	7% 8% 2 6% 3 3 4 3 6% 7% 51%	3616
	21st to end	Night	8% 8% 2 6% 4 3 3 2 4 5% 55%	3972
June	1st to 10th	Night	8% 6% 2 5% 6% 4 5% 4 7% 9% 44%	1600
	11th to 20th	Night	9% 5% 2 5% 4 3 5% 3 6% 8% 49%	1600
	21st to end	Night	4 3 1 3 3 3 4 4 6% 6% 64%	1600
July	1st to 10th	Night	1 1 1 2 2 2 3 4 6% 79%	3640
	11th to 20th	Night	1 1 1 1 2 1 1 2 4 85%	3640
	21st to end	Night	2 1 1 1 1 2 3 2 4 7% 75%	3970
August	1st to 10th	Night	2 1 1 3 2 3 3 3 6% 8% 68%	3582
	11th to 20th	Night	1 1 1 2 2 2 3 3 3 6% 78%	4056
	21st to end	Night	4 3 1 4 3 3 3 2 5% 6% 67%	5015
September	1st to 10th	Night	3 2 1 3 2 3 2 3 5% 6% 71%	2000
	11th to 20th	Night	4 4 2 4 3 4 5% 4 5% 7% 58%	2130
	21st to end	Night	5% 5% 2 4 3 4 3 3 4 6% 60%	2200
October	1st to 10th	Night	5% 4 1 4 2 2 3 3 5% 6% 65%	3585
	11th to 20th	Night	3 6% 2 5% 4 4 5% 4 6% 9% 53%	3922
	21st to end	Night	3 7% 3 8% 4 5% 6% 6% 7% 9% 42%	4457
November	1st to 10th	Night	4 9% 3 8% 7% 6% 6% 6% 7% 9% 36%	2535
	11th to 20th	Night	3 8% 3 8% 7% 7% 7% 6% 8% 11% 33%	2600
	21st to end	Night	3 6% 3 7% 6% 7% 7% 5% 8% 9% 40%	2784
December	1st to 10th	Night	1 4 2 6% 4 5% 5% 5% 7% 8% 53%	4560
	11th to 20th	Night	2 8% 3 8% 7% 7% 9% 7% 10% 12% 27%	5176
	21st to end	Night	2 9% 4 9% 6% 7% 8% 6% 8% 9% 31%	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	47% 15% 16% 18% 3	3639
	11th to 20th	Day	43% 8% 17% 22% 9% 1	3640
	21st to end	Day	38% 12% 11% 18% 19% 2	4004
February	1st to 10th	Day	52% 13% 14% 16% 4 1	1663
	11th to 20th	Day	53% 12% 14% 13% 7% 1	1951
	21st to end	Day	54% 11% 14% 13% 7% 1	1650
March	1st to 10th	Day	46% 6% 16% 19% 10% 3	4518
	11th to 20th	Day	37% 10% 15% 30% 9%	4708
	21st to end	Day	56% 14% 13% 14% 4	5895
April	1st to 10th	Day	54% 8% 17% 16% 4	2400
	11th to 20th	Day	46% 8% 16% 16% 11% 1	2402
	21st to end	Day	50% 9% 11% 20% 9%	2600
May	1st to 10th	Day	33% 7% 15% 27% 17% 2	5965
	11th to 20th	Day	37% 6% 18% 25% 11% 3	6280
	21st to end	Day	34% 7% 19% 28% 11% 2	6904
June	1st to 10th	Day	46% 9% 13% 23% 9%	2800
	11th to 20th	Day	41% 7% 13% 23% 13% 3	2800
	21st to end	Day	21% 7% 13% 30% 23% 5%	2800
July	1st to 10th	Day	12% 2 8% 19% 28% 29%	6251
	11th to 20th	Day	9% 2 6% 11% 33% 39%	6245
	21st to end	Day	12% 4 7% 28% 33% 16%	6681
August	1st to 10th	Day	19% 4 9% 16% 35% 17%	4524
	11th to 20th	Day	16% 4 9% 29% 31% 12%	4189
	21st to end	Day	16% 4 10% 30% 25% 14%	4311
September	1st to 10th	Day	17% 5% 11% 23% 29% 14%	2400
	11th to 20th	Day	28% 6% 13% 21% 24% 8%	2270
	21st to end	Day	29% 6% 11% 28% 22% 4	2200
October	1st to 10th	Day	24% 5% 11% 22% 31% 6%	3447
	11th to 20th	Day	30% 5% 17% 29% 17% 1	3010
	21st to end	Day	41% 9% 11% 27% 12%	3101
November	1st to 10th	Day	46% 9% 18% 19% 7% 1	1764
	11th to 20th	Day	44% 13% 19% 19% 6%	1800
	21st to end	Day	41% 12% 18% 16% 11% 2	1615
December	1st to 10th	Day	31% 9% 21% 28% 10% 1	2620
	11th to 20th	Day	48% 16% 18% 14% 4	3028
	21st to end	Day	45% 10% 19% 18% 6% 1	4004
January	1st to 10th	Night	50% 13% 13% 20% 3	6306
	11th to 20th	Night	44% 10% 17% 19% 10% 1	6320
	21st to end	Night	36% 15% 12% 21% 16% 1	6952
February	1st to 10th	Night	53% 12% 14% 14% 5% 1	2735
	11th to 20th	Night	47% 14% 14% 16% 8% 1	2346
	21st to end	Night	50% 13% 14% 14% 8% 1	1980
March	1st to 10th	Night	35% 9% 18% 18% 16% 3	5376
	11th to 20th	Night	36% 10% 13% 31% 10%	5291
	21st to end	Night	46% 15% 16% 18% 5%	5077
April	1st to 10th	Night	45% 11% 18% 21% 6%	2000
	11th to 20th	Night	41% 8% 15% 23% 11% 2	1948
	21st to end	Night	42% 12% 13% 21% 12%	1800
May	1st to 10th	Night	30% 8% 11% 28% 19% 4	4005
	11th to 20th	Night	32% 5% 15% 32% 16%	3616
	21st to end	Night	30% 6% 18% 32% 14%	3972
June	1st to 10th	Night	36% 11% 14% 27% 10% 1	1600
	11th to 20th	Night	32% 8% 16% 26% 15% 2	1600
	21st to end	Night	21% 7% 13% 29% 25% 4	1600
July	1st to 10th	Night	9% 3 7% 19% 30% 33%	3600
	11th to 20th	Night	6% 2 5% 16% 29% 41%	3592
	21st to end	Night	9% 2 7% 33% 31% 17%	3857
August	1st to 10th	Night	13% 3 9% 18% 44% 12%	2601
	11th to 20th	Night	10% 5% 7% 32% 35% 11%	2933
	21st to end	Night	15% 3 8% 32% 29% 13%	3608
September	1st to 10th	Night	15% 4 10% 26% 29% 16%	2000
	11th to 20th	Night	24% 7% 12% 24% 23% 10%	2130
	21st to end	Night	27% 6% 11% 27% 22% 8%	2200
October	1st to 10th	Night	23% 6% 8% 25% 30% 9%	3585
	11th to 20th	Night	27% 7% 22% 23% 20% 2	3922
	21st to end	Night	34% 9% 13% 29% 14% 1	4457
November	1st to 10th	Night	42% 11% 16% 18% 11% 2	2535
	11th to 20th	Night	43% 13% 16% 20% 7%	2600
	21st to end	Night	40% 12% 14% 19% 14% 2	2784
December	1st to 10th	Night	28% 9% 24% 27% 11% 1	4560
	11th to 20th	Night	46% 16% 17% 17% 3 1	5176
	21st to end	Night	44% 12% 18% 18% 8% 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	5% 16% 36% 26% 15% 3	200
	11th to 20th	Day	7% 11% 36% 30% 11% 7%	200
	21st to end	Day	9% 12% 35% 26% 17% 2	220
February	1st to 10th	Day	10% 18% 39% 24% 7% 1	263
	11th to 20th	Day	7% 19% 38% 24% 10% 1	491
	21st to end	Day	8% 23% 29% 30% 10%	414
March	1st to 10th	Day	8% 20% 37% 26% 8% 1	500
	11th to 20th	Day	9% 20% 29% 29% 10% 3	500
	21st to end	Day	16% 20% 31% 25% 6% 2	550
April	1st to 10th	Day	11% 21% 31% 23% 12% 3	500
	11th to 20th	Day	10% 20% 32% 23% 10% 4	492
	21st to end	Day	14% 15% 30% 27% 11% 3	500
May	1st to 10th	Day	11% 13% 28% 31% 13% 4	503
	11th to 20th	Day	19% 13% 23% 25% 14% 5%	528
	21st to end	Day	18% 9% 21% 25% 20% 8%	573
June	1st to 10th	Day	11% 11% 26% 27% 18% 8%	530
	11th to 20th	Day	12% 16% 33% 24% 12% 3	530
	21st to end	Day	5% 8% 28% 33% 21% 5%	530
July	1st to 10th	Day	3 7% 28% 36% 21% 6%	526
	11th to 20th	Day	1 7% 32% 35% 19% 5%	524
	21st to end	Day	1 5% 28% 36% 23% 8%	575
August	1st to 10th	Day	4 7% 23% 35% 22% 9%	527
	11th to 20th	Day	2 5% 22% 36% 24% 10%	517
	21st to end	Day	5% 8% 22% 35% 22% 9%	583
September	1st to 10th	Day	5% 6% 22% 32% 25% 11%	530
	11th to 20th	Day	8% 7% 25% 31% 21% 8%	530
	21st to end	Day	8% 9% 24% 34% 19% 6%	530
October	1st to 10th	Day	12% 10% 25% 28% 18% 6%	503
	11th to 20th	Day	6% 12% 28% 30% 18% 6%	403
	21st to end	Day	11% 11% 32% 28% 16% 3	330
November	1st to 10th	Day	9% 15% 30% 33% 11% 1	300
	11th to 20th	Day	7% 12% 33% 32% 12% 3	300
	21st to end	Day	4 11% 30% 37% 15% 2	207
December	1st to 10th	Day	6% 12% 26% 31% 16% 11%	200
	11th to 20th	Day	8% 13% 42% 27% 10% 1	200
	21st to end	Day	6% 15% 39% 27% 11% 2	220
January	1st to 10th	Night	8% 12% 35% 30% 14% 2	800
	11th to 20th	Night	7% 12% 33% 31% 15% 3	800
	21st to end	Night	6% 7% 31% 35% 19% 2	880
February	1st to 10th	Night	8% 12% 37% 34% 9% 2	800
	11th to 20th	Night	7% 7% 38% 33% 13% 2	784
	21st to end	Night	6% 13% 34% 32% 12% 3	660
March	1st to 10th	Night	6% 9% 36% 32% 15% 2	800
	11th to 20th	Night	7% 8% 33% 33% 15% 3	800
	21st to end	Night	10% 11% 31% 35% 12% 1	880
April	1st to 10th	Night	8% 8% 31% 35% 16% 2	800
	11th to 20th	Night	9% 9% 31% 32% 16% 3	760
	21st to end	Night	11% 9% 25% 37% 17% 2	600
May	1st to 10th	Night	11% 6% 25% 39% 16% 2	560
	11th to 20th	Night	10% 5% 19% 34% 27% 5%	394
	21st to end	Night	12% 6% 14% 34% 28% 5%	433
June	1st to 10th	Night	10% 6% 19% 41% 23% 3	400
	11th to 20th	Night	12% 6% 19% 43% 18% 3	400
	21st to end	Night	6% 1 13% 47% 32% 1	400
July	1st to 10th	Night	1 2 12% 48% 35% 3	390
	11th to 20th	Night	2 1 10% 59% 28% 1	388
	21st to end	Night	2 1 8% 54% 33% 3	438
August	1st to 10th	Night	2 1 8% 48% 36% 4	398
	11th to 20th	Night	1 1 11% 47% 33% 6%	586
	21st to end	Night	4 2 15% 42% 33% 5%	880
September	1st to 10th	Night	4 2 12% 43% 33% 7%	800
	11th to 20th	Night	5% 2 14% 36% 35% 9%	800
	21st to end	Night	9% 3 19% 35% 27% 7%	800
October	1st to 10th	Night	11% 4 19% 39% 22% 5%	772
	11th to 20th	Night	6% 6% 24% 37% 20% 7%	760
	21st to end	Night	8% 6% 28% 38% 15% 5%	836
November	1st to 10th	Night	9% 7% 31% 40% 12% 1	780
	11th to 20th	Night	8% 12% 34% 33% 11% 2	800
	21st to end	Night	6% 10% 31% 34% 16% 4	800
December	1st to 10th	Night	7% 7% 32% 35% 16% 3	800
	11th to 20th	Night	7% 9% 37% 34% 11% 2	800
	21st to end	Night	7% 12% 40% 33% 8% 1	880

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