Many Worlds Cross Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Many Worlds Cross Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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% 4 9% 5% 5% 5% 4 5% 7% 32%	137469
	Night	17% 11% 4 9% 5% 5% 4 3 5% 6% 31%	134556
Transparency	Day	51% 4 11% 21% 12% 1	140975
	Night	50% 5% 11% 20% 12% 2	139139
Seeing	Day	27% 20% 28% 17% 7% 2	16897
	Night	25% 18% 27% 21% 7% 1	25963

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	9% 14% 6% 21% 10% 5% 5% 3 4 5% 19%	4661
	11th to 20th	Day	13% 11% 4 14% 8% 6% 4 4 4 5% 26%	4650
	21st to end	Day	13% 14% 6% 9% 6% 5% 4 3 4 5% 31%	5226
February	1st to 10th	Day	15% 12% 4 11% 7% 6% 6% 4 6% 5% 25%	1903
	11th to 20th	Day	13% 11% 6% 13% 8% 5% 4 4 4 6% 26%	2048
	21st to end	Day	17% 13% 4 12% 6% 4 4 3 4 4 28%	1730
March	1st to 10th	Day	19% 13% 6% 10% 5% 4 4 3 4 5% 28%	4576
	11th to 20th	Day	13% 11% 5% 10% 5% 5% 4 3 5% 5% 33%	4777
	21st to end	Day	21% 9% 4 10% 5% 4 4 3 4 5% 31%	6102
April	1st to 10th	Day	18% 13% 3 9% 5% 4 4 3 5% 5% 31%	2520
	11th to 20th	Day	16% 10% 3 7% 4 5% 6% 4 5% 6% 34%	2494
	21st to end	Day	18% 9% 4 7% 6% 5% 4 4 5% 5% 33%	2641
May	1st to 10th	Day	26% 12% 3 7% 4 4 4 3 5% 6% 25%	7639
	11th to 20th	Day	17% 10% 3 8% 5% 5% 4 4 6% 6% 32%	8216
	21st to end	Day	21% 9% 3 7% 5% 5% 5% 4 6% 7% 27%	9060
June	1st to 10th	Day	17% 7% 2 7% 5% 6% 5% 5% 7% 9% 30%	2940
	11th to 20th	Day	19% 6% 2 6% 5% 5% 4 5% 6% 9% 33%	2870
	21st to end	Day	17% 7% 3 8% 5% 5% 5% 4 5% 8% 31%	2800
July	1st to 10th	Day	13% 7% 3 7% 6% 5% 5% 5% 7% 9% 33%	6360
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 11% 34%	6360
	21st to end	Day	15% 7% 2 7% 4 4 5% 4 5% 7% 40%	6926
August	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 8% 31%	4483
	11th to 20th	Day	14% 8% 3 7% 5% 5% 6% 4 8% 8% 33%	3889
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 8% 38%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 5% 7% 42%	2400
	11th to 20th	Day	15% 6% 2 6% 4 3 4 3 5% 7% 46%	2282
	21st to end	Day	17% 6% 3 6% 4 4 4 4 6% 7% 39%	2200
October	1st to 10th	Day	21% 9% 2 7% 4 3 4 2 5% 5% 37%	2130
	11th to 20th	Day	18% 8% 3 6% 5% 3 4 4 5% 6% 38%	1985
	21st to end	Day	21% 13% 4 8% 4 4 3 3 4 5% 30%	1980
November	1st to 10th	Day	12% 10% 4 7% 5% 3 3 3 4 6% 43%	1851
	11th to 20th	Day	16% 12% 3 7% 6% 3 5% 3 6% 6% 34%	1890
	21st to end	Day	17% 14% 5% 8% 5% 4 4 3 4 5% 30%	1774
December	1st to 10th	Day	15% 13% 5% 12% 6% 5% 5% 3 5% 5% 25%	2680
	11th to 20th	Day	18% 15% 6% 8% 5% 3 3 3 3 4 32%	3066
	21st to end	Day	17% 14% 5% 12% 4 4 3 3 5% 5% 28%	4048
January	1st to 10th	Night	12% 13% 7% 19% 8% 5% 4 3 4 5% 21%	8234
	11th to 20th	Night	12% 12% 4 17% 9% 7% 6% 4 5% 5% 18%	8235
	21st to end	Night	12% 12% 4 8% 6% 7% 7% 4 6% 6% 29%	8938
February	1st to 10th	Night	14% 11% 4 9% 7% 7% 5% 5% 6% 6% 26%	2715
	11th to 20th	Night	12% 10% 6% 12% 7% 6% 6% 5% 6% 5% 25%	2458
	21st to end	Night	15% 13% 4 10% 6% 4 5% 4 5% 5% 28%	2076
March	1st to 10th	Night	19% 10% 4 12% 6% 5% 5% 3 5% 5% 27%	5484
	11th to 20th	Night	15% 10% 4 8% 6% 5% 4 3 5% 6% 32%	5385
	21st to end	Night	20% 14% 5% 10% 5% 4 4 3 4 4 29%	5072
April	1st to 10th	Night	19% 12% 3 8% 5% 4 5% 4 5% 6% 29%	2100
	11th to 20th	Night	18% 12% 3 7% 5% 4 4 3 4 6% 34%	2075
	21st to end	Night	20% 10% 3 6% 4 3 4 4 5% 5% 37%	1979
May	1st to 10th	Night	27% 14% 3 6% 3 4 4 3 5% 6% 26%	5259
	11th to 20th	Night	17% 12% 3 7% 5% 4 5% 3 5% 8% 30%	4698
	21st to end	Night	24% 11% 3 6% 4 4 4 3 5% 7% 29%	5114
June	1st to 10th	Night	19% 7% 2 7% 4 4 4 3 5% 7% 39%	1680
	11th to 20th	Night	18% 7% 3 6% 4 4 5% 3 5% 8% 36%	1640
	21st to end	Night	15% 6% 2 5% 4 5% 5% 5% 6% 7% 41%	1600
July	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 6% 9% 38%	3600
	11th to 20th	Night	17% 8% 3 6% 4 4 4 5% 6% 8% 35%	3600
	21st to end	Night	13% 8% 2 6% 4 4 4 3 4 6% 47%	3926
August	1st to 10th	Night	25% 8% 2 6% 3 4 4 3 5% 6% 34%	2633
	11th to 20th	Night	14% 7% 3 7% 5% 4 5% 4 5% 7% 40%	3156
	21st to end	Night	9% 8% 2 6% 3 4 4 3 5% 8% 47%	3586
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 5% 6% 45%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 4 7% 52%	2116
	21st to end	Night	17% 7% 3 7% 4 4 3 3 4 6% 43%	2200
October	1st to 10th	Night	20% 8% 2 6% 4 4 3 3 5% 6% 39%	2267
	11th to 20th	Night	16% 8% 3 6% 5% 3 4 3 5% 5% 41%	2415
	21st to end	Night	20% 12% 3 7% 5% 3 4 3 5% 6% 32%	2860
November	1st to 10th	Night	14% 10% 2 6% 4 3 4 3 5% 6% 41%	2667
	11th to 20th	Night	17% 10% 4 9% 5% 4 5% 3 4 5% 34%	2730
	21st to end	Night	13% 13% 3 9% 4 5% 5% 4 6% 6% 32%	2840
December	1st to 10th	Night	17% 14% 5% 13% 6% 5% 4 4 5% 6% 22%	4720
	11th to 20th	Night	23% 13% 5% 9% 5% 4 3 3 3 4 29%	5348
	21st to end	Night	18% 14% 6% 12% 5% 4 4 3 4 4 26%	7150

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	63% 6% 8% 18% 5%	4662
	11th to 20th	Day	58% 4 8% 13% 14% 2	4680
	21st to end	Day	52% 6% 7% 22% 12% 1	5226
February	1st to 10th	Day	56% 6% 11% 16% 10% 1	1903
	11th to 20th	Day	55% 6% 8% 19% 11% 1	2057
	21st to end	Day	57% 4 9% 18% 10% 1	1730
March	1st to 10th	Day	57% 5% 10% 14% 11% 4	4579
	11th to 20th	Day	52% 2 15% 20% 8% 3	4777
	21st to end	Day	55% 3 5% 14% 19% 3	6102
April	1st to 10th	Day	55% 3 8% 20% 11% 2	2520
	11th to 20th	Day	50% 5% 10% 20% 14% 1	2494
	21st to end	Day	52% 4 8% 19% 13% 3	2641
May	1st to 10th	Day	60% 4 10% 16% 9% 1	7651
	11th to 20th	Day	53% 3 13% 21% 9% 1	8220
	21st to end	Day	55% 4 10% 21% 9% 1	9061
June	1st to 10th	Day	49% 6% 12% 23% 10%	2940
	11th to 20th	Day	47% 5% 15% 21% 11% 1	2870
	21st to end	Day	50% 5% 13% 20% 11% 1	2800
July	1st to 10th	Day	47% 6% 13% 23% 11% 1	6290
	11th to 20th	Day	42% 6% 16% 24% 12% 1	6285
	21st to end	Day	43% 4 12% 26% 14%	6728
August	1st to 10th	Day	50% 5% 14% 21% 9% 1	4469
	11th to 20th	Day	46% 5% 16% 26% 7% 1	3926
	21st to end	Day	40% 6% 13% 29% 11% 1	4312
September	1st to 10th	Day	41% 5% 11% 28% 15% 1	2400
	11th to 20th	Day	40% 4 9% 25% 21% 2	2282
	21st to end	Day	44% 4 11% 23% 15% 3	2200
October	1st to 10th	Day	48% 5% 7% 20% 19% 2	3468
	11th to 20th	Day	42% 3 10% 24% 16% 4	3213
	21st to end	Day	41% 5% 12% 26% 14% 3	3180
November	1st to 10th	Day	41% 5% 14% 24% 14% 2	1851
	11th to 20th	Day	49% 5% 8% 20% 16% 2	1890
	21st to end	Day	53% 4 13% 20% 8% 1	1774
December	1st to 10th	Day	54% 6% 13% 20% 7%	2680
	11th to 20th	Day	56% 3 11% 17% 13% 1	3066
	21st to end	Day	58% 3 7% 14% 14% 4	4048
January	1st to 10th	Night	60% 7% 9% 16% 7% 1	8234
	11th to 20th	Night	61% 6% 9% 12% 9% 2	8280
	21st to end	Night	50% 5% 9% 17% 16% 2	8938
February	1st to 10th	Night	53% 5% 11% 20% 9% 2	2715
	11th to 20th	Night	54% 6% 10% 17% 12% 1	2460
	21st to end	Night	54% 4 10% 21% 8% 2	2076
March	1st to 10th	Night	55% 5% 11% 15% 13% 1	5494
	11th to 20th	Night	50% 4 16% 20% 8% 3	5386
	21st to end	Night	57% 4 4 13% 19% 3	5072
April	1st to 10th	Night	53% 4 10% 19% 12% 2	2100
	11th to 20th	Night	51% 4 9% 21% 15% 1	2075
	21st to end	Night	48% 4 10% 19% 16% 3	1979
May	1st to 10th	Night	59% 4 11% 15% 10% 1	5265
	11th to 20th	Night	53% 4 14% 20% 8% 1	4699
	21st to end	Night	56% 4 11% 20% 8% 1	5115
June	1st to 10th	Night	45% 5% 11% 26% 12% 1	1680
	11th to 20th	Night	46% 5% 15% 23% 10%	1640
	21st to end	Night	41% 6% 15% 25% 13% 1	1600
July	1st to 10th	Night	41% 6% 16% 22% 15% 1	3560
	11th to 20th	Night	46% 6% 13% 21% 13% 1	3552
	21st to end	Night	37% 5% 14% 28% 15% 1	3809
August	1st to 10th	Night	51% 4 14% 23% 8%	2623
	11th to 20th	Night	43% 5% 18% 26% 8%	3185
	21st to end	Night	32% 7% 15% 34% 13% 1	3586
September	1st to 10th	Night	39% 5% 12% 27% 16% 1	2000
	11th to 20th	Night	36% 3 10% 28% 22% 1	2116
	21st to end	Night	43% 4 10% 25% 16% 2	2200
October	1st to 10th	Night	45% 5% 12% 22% 15% 2	3709
	11th to 20th	Night	37% 4 11% 23% 19% 5%	3926
	21st to end	Night	39% 4 14% 30% 12% 1	4610
November	1st to 10th	Night	42% 5% 11% 22% 17% 2	2667
	11th to 20th	Night	50% 5% 9% 19% 15% 2	2730
	21st to end	Night	50% 5% 14% 23% 8%	2840
December	1st to 10th	Night	55% 8% 10% 22% 5%	4720
	11th to 20th	Night	58% 5% 11% 11% 14% 1	5348
	21st to end	Night	59% 4 6% 14% 13% 4	7150

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	34% 31% 25% 6% 3	220
	11th to 20th	Day	35% 31% 26% 6% 1	220
	21st to end	Day	28% 33% 26% 10% 3	261
February	1st to 10th	Day	38% 31% 24% 4 2	343
	11th to 20th	Day	38% 27% 26% 9% 1	536
	21st to end	Day	33% 29% 28% 10% 1	446
March	1st to 10th	Day	34% 27% 26% 11% 1	540
	11th to 20th	Day	34% 27% 27% 9% 3	540
	21st to end	Day	37% 26% 23% 9% 4 2	594
April	1st to 10th	Day	41% 21% 22% 10% 5% 1	540
	11th to 20th	Day	34% 25% 26% 10% 4 1	532
	21st to end	Day	29% 22% 31% 12% 4 1	540
May	1st to 10th	Day	36% 22% 25% 11% 4 1	543
	11th to 20th	Day	24% 22% 33% 16% 4 1	567
	21st to end	Day	24% 15% 30% 21% 8% 2	617
June	1st to 10th	Day	19% 17% 32% 22% 10% 1	570
	11th to 20th	Day	23% 15% 31% 20% 11% 1	550
	21st to end	Day	20% 18% 33% 19% 9% 2	530
July	1st to 10th	Day	16% 12% 34% 25% 11% 2	525
	11th to 20th	Day	13% 9% 34% 31% 11% 2	524
	21st to end	Day	15% 12% 38% 24% 9% 2	576
August	1st to 10th	Day	13% 11% 28% 31% 11% 5%	526
	11th to 20th	Day	16% 8% 32% 24% 13% 6%	519
	21st to end	Day	14% 14% 29% 26% 11% 6%	583
September	1st to 10th	Day	19% 11% 28% 23% 13% 6%	530
	11th to 20th	Day	16% 13% 24% 20% 17% 10%	530
	21st to end	Day	21% 12% 30% 21% 10% 6%	530
October	1st to 10th	Day	27% 14% 24% 20% 12% 4	530
	11th to 20th	Day	26% 19% 28% 18% 7% 2	522
	21st to end	Day	32% 20% 26% 17% 5% 1	462
November	1st to 10th	Day	27% 23% 24% 18% 7%	425
	11th to 20th	Day	31% 25% 26% 14% 4 1	430
	21st to end	Day	37% 24% 23% 13% 2 1	314
December	1st to 10th	Day	35% 28% 24% 10% 3	220
	11th to 20th	Day	41% 26% 23% 9% 1	220
	21st to end	Day	36% 21% 31% 10% 2	242
January	1st to 10th	Night	27% 30% 30% 11% 2	840
	11th to 20th	Night	29% 26% 28% 15% 2	840
	21st to end	Night	25% 26% 32% 15% 2	924
February	1st to 10th	Night	27% 25% 32% 14% 2	840
	11th to 20th	Night	27% 28% 32% 13% 1	823
	21st to end	Night	29% 27% 27% 14% 2	692
March	1st to 10th	Night	30% 24% 29% 15% 2	840
	11th to 20th	Night	27% 27% 28% 16% 2	840
	21st to end	Night	31% 22% 26% 16% 5%	924
April	1st to 10th	Night	31% 20% 29% 17% 3	840
	11th to 20th	Night	28% 23% 27% 16% 6%	831
	21st to end	Night	29% 20% 27% 19% 4	719
May	1st to 10th	Night	32% 13% 30% 19% 6% 1	630
	11th to 20th	Night	21% 16% 31% 28% 4	435
	21st to end	Night	21% 8% 29% 29% 12% 1	455
June	1st to 10th	Night	20% 9% 30% 29% 12%	420
	11th to 20th	Night	17% 11% 29% 32% 10%	410
	21st to end	Night	17% 9% 27% 35% 12% 1	400
July	1st to 10th	Night	17% 5% 24% 41% 13% 1	390
	11th to 20th	Night	16% 5% 23% 40% 15% 1	388
	21st to end	Night	12% 7% 24% 43% 14%	438
August	1st to 10th	Night	15% 4 23% 40% 17% 1	419
	11th to 20th	Night	16% 5% 22% 33% 21% 2	761
	21st to end	Night	16% 8% 23% 32% 19% 2	880
September	1st to 10th	Night	17% 8% 29% 29% 16% 2	800
	11th to 20th	Night	16% 9% 22% 27% 21% 5%	800
	21st to end	Night	20% 12% 24% 28% 14% 3	800
October	1st to 10th	Night	27% 10% 24% 25% 12% 2	800
	11th to 20th	Night	22% 16% 29% 24% 9%	800
	21st to end	Night	28% 18% 29% 22% 4	880
November	1st to 10th	Night	23% 21% 28% 21% 6%	820
	11th to 20th	Night	27% 23% 26% 17% 6% 1	840
	21st to end	Night	28% 22% 28% 18% 4 1	840
December	1st to 10th	Night	30% 26% 25% 14% 4	840
	11th to 20th	Night	33% 23% 26% 15% 3	840
	21st to end	Night	31% 28% 25% 14% 2	924

Page generated at 2026-06-13 02:31:43. Version ac07

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