Captains Way
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Captains Way clear sky chart from 2005-11-06 to 2024-12-02.

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	20% 9% 3 8% 5% 5% 5% 4 5% 7% 29%	102089
	Night	21% 10% 4 8% 5% 4 4 3 5% 6% 29%	97608
Transparency	Day	52% 8% 12% 18% 10% 1	105689
	Night	54% 7% 12% 17% 9% 1	102097
Seeing	Day	24% 12% 30% 24% 9% 1	17411
	Night	25% 12% 30% 24% 8% 1	24988

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	16% 10% 4 10% 8% 6% 5% 3 5% 6% 25%	2526
	11th to 20th	Day	16% 11% 5% 13% 7% 5% 7% 5% 6% 6% 18%	2654
	21st to end	Day	19% 9% 3 9% 6% 6% 6% 4 5% 7% 26%	3124
February	1st to 10th	Day	21% 12% 4 9% 7% 5% 5% 5% 5% 7% 20%	1710
	11th to 20th	Day	16% 11% 4 10% 8% 7% 5% 5% 5% 6% 24%	1663
	21st to end	Day	12% 10% 3 8% 7% 6% 5% 4 6% 8% 29%	1441
March	1st to 10th	Day	24% 12% 3 8% 5% 6% 4 3 4 5% 27%	3430
	11th to 20th	Day	16% 12% 3 7% 5% 5% 5% 5% 6% 7% 30%	3480
	21st to end	Day	31% 8% 3 9% 6% 5% 4 3 4 5% 22%	3816
April	1st to 10th	Day	24% 10% 3 7% 5% 4 4 4 5% 6% 27%	2266
	11th to 20th	Day	19% 9% 3 6% 5% 3 4 3 6% 7% 34%	2316
	21st to end	Day	22% 7% 2 7% 5% 4 4 3 6% 7% 33%	2470
May	1st to 10th	Day	23% 10% 4 8% 5% 5% 5% 4 6% 7% 22%	4185
	11th to 20th	Day	24% 9% 3 8% 5% 4 4 3 5% 7% 29%	4398
	21st to end	Day	18% 9% 3 7% 4 4 5% 5% 7% 9% 28%	4836
June	1st to 10th	Day	24% 10% 3 8% 5% 4 5% 4 6% 7% 25%	2660
	11th to 20th	Day	21% 9% 3 6% 4 4 4 3 5% 7% 33%	2689
	21st to end	Day	27% 10% 3 8% 6% 5% 4 4 4 6% 23%	2850
July	1st to 10th	Day	22% 10% 4 8% 5% 4 5% 4 6% 7% 24%	4536
	11th to 20th	Day	15% 11% 4 10% 6% 5% 4 4 6% 8% 26%	4440
	21st to end	Day	20% 9% 3 7% 5% 5% 4 4 6% 8% 28%	4635
August	1st to 10th	Day	22% 11% 3 9% 5% 5% 4 4 5% 6% 26%	4105
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 4 6% 9% 30%	4045
	21st to end	Day	9% 5% 2 6% 3 4 4 4 6% 7% 50%	4346
September	1st to 10th	Day	15% 6% 2 5% 4 3 5% 4 5% 8% 43%	2280
	11th to 20th	Day	18% 7% 2 5% 4 4 5% 3 4 6% 43%	2203
	21st to end	Day	17% 7% 2 6% 4 4 4 4 5% 6% 42%	2032
October	1st to 10th	Day	17% 6% 2 6% 4 4 4 3 5% 7% 41%	1900
	11th to 20th	Day	19% 7% 3 7% 4 3 4 4 6% 8% 36%	1900
	21st to end	Day	20% 10% 3 7% 4 4 5% 4 5% 7% 32%	2090
November	1st to 10th	Day	20% 10% 3 9% 5% 4 4 3 5% 6% 31%	1645
	11th to 20th	Day	23% 10% 4 8% 5% 5% 5% 4 5% 7% 26%	1600
	21st to end	Day	21% 11% 4 8% 7% 5% 5% 4 5% 5% 26%	1600
December	1st to 10th	Day	25% 12% 4 9% 6% 5% 5% 4 4 5% 20%	1529
	11th to 20th	Day	32% 10% 3 6% 5% 6% 5% 5% 5% 6% 17%	1906
	21st to end	Day	24% 10% 5% 10% 5% 5% 5% 4 4 7% 23%	2783
January	1st to 10th	Night	15% 11% 4 14% 7% 6% 5% 4 6% 5% 23%	4429
	11th to 20th	Night	19% 11% 4 14% 7% 6% 5% 4 5% 5% 18%	4308
	21st to end	Night	18% 13% 4 12% 6% 5% 5% 4 5% 7% 21%	4532
February	1st to 10th	Night	20% 14% 4 9% 7% 5% 5% 5% 5% 5% 20%	2470
	11th to 20th	Night	17% 9% 4 10% 7% 6% 5% 5% 7% 6% 22%	2403
	21st to end	Night	13% 12% 4 10% 7% 6% 6% 4 6% 6% 28%	2010
March	1st to 10th	Night	24% 11% 3 7% 6% 6% 4 3 4 6% 26%	3410
	11th to 20th	Night	19% 11% 4 9% 6% 5% 5% 4 6% 6% 23%	3479
	21st to end	Night	32% 10% 5% 10% 4 4 3 2 3 3 25%	3816
April	1st to 10th	Night	25% 11% 4 6% 4 4 4 4 5% 5% 29%	1913
	11th to 20th	Night	22% 9% 3 6% 5% 4 4 3 5% 7% 33%	1812
	21st to end	Night	25% 10% 3 7% 4 3 4 3 5% 5% 32%	1710
May	1st to 10th	Night	21% 12% 4 9% 6% 5% 5% 3 5% 6% 26%	2755
	11th to 20th	Night	26% 10% 3 6% 4 4 5% 3 5% 5% 28%	2506
	21st to end	Night	20% 13% 4 7% 4 4 4 3 5% 6% 30%	2749
June	1st to 10th	Night	28% 11% 2 7% 4 3 4 3 5% 5% 28%	1520
	11th to 20th	Night	22% 9% 3 7% 4 4 4 3 5% 6% 33%	1498
	21st to end	Night	29% 13% 3 7% 5% 4 4 2 4 6% 24%	1330
July	1st to 10th	Night	21% 13% 5% 9% 5% 4 5% 4 5% 6% 24%	2392
	11th to 20th	Night	17% 11% 5% 13% 7% 5% 4 3 5% 6% 23%	2530
	21st to end	Night	20% 9% 3 7% 4 4 4 3 4 6% 34%	2921
August	1st to 10th	Night	20% 10% 4 9% 5% 4 4 3 4 6% 32%	2825
	11th to 20th	Night	17% 9% 4 8% 4 4 4 3 6% 6% 35%	2782
	21st to end	Night	10% 6% 2 6% 2 4 3 3 4 7% 51%	3308
September	1st to 10th	Night	15% 7% 3 5% 3 3 4 4 6% 6% 43%	1900
	11th to 20th	Night	18% 8% 2 5% 4 3 3 3 5% 6% 44%	1975
	21st to end	Night	21% 8% 3 5% 4 3 4 3 4 6% 37%	2147
October	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 5% 7% 41%	2280
	11th to 20th	Night	20% 5% 2 5% 4 4 4 4 5% 7% 39%	2280
	21st to end	Night	24% 9% 2 5% 3 3 4 3 5% 6% 35%	2508
November	1st to 10th	Night	20% 9% 3 6% 5% 4 4 3 5% 6% 35%	2648
	11th to 20th	Night	20% 10% 4 8% 5% 4 4 4 5% 7% 28%	2800
	21st to end	Night	21% 11% 3 8% 5% 5% 5% 4 5% 7% 26%	2800
December	1st to 10th	Night	23% 13% 3 11% 6% 5% 5% 4 5% 6% 19%	2685
	11th to 20th	Night	31% 12% 3 8% 5% 4 5% 3 5% 6% 19%	3293
	21st to end	Night	25% 11% 3 10% 5% 4 4 3 5% 6% 24%	4884

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	57% 8% 18% 12% 4	2527
	11th to 20th	Day	60% 10% 14% 13% 4	2654
	21st to end	Day	56% 8% 13% 15% 8%	3124
February	1st to 10th	Day	63% 5% 12% 11% 7% 1	1710
	11th to 20th	Day	59% 7% 12% 14% 6% 1	1671
	21st to end	Day	50% 8% 13% 18% 9% 2	1441
March	1st to 10th	Day	59% 6% 9% 17% 7% 2	3434
	11th to 20th	Day	47% 12% 15% 17% 9% 1	3480
	21st to end	Day	62% 6% 8% 12% 10% 1	3816
April	1st to 10th	Day	54% 7% 10% 14% 13% 2	2266
	11th to 20th	Day	47% 7% 11% 21% 13% 2	2316
	21st to end	Day	47% 7% 13% 18% 13% 3	2470
May	1st to 10th	Day	56% 11% 13% 14% 5% 1	4199
	11th to 20th	Day	53% 10% 11% 18% 8%	4402
	21st to end	Day	45% 12% 16% 17% 9% 1	4836
June	1st to 10th	Day	55% 9% 10% 18% 7%	2660
	11th to 20th	Day	48% 8% 13% 17% 12% 2	2689
	21st to end	Day	60% 8% 8% 13% 9% 1	2850
July	1st to 10th	Day	58% 7% 10% 12% 12% 1	4466
	11th to 20th	Day	53% 8% 11% 20% 8%	4364
	21st to end	Day	51% 8% 12% 18% 9% 1	4487
August	1st to 10th	Day	57% 7% 11% 16% 8% 1	4092
	11th to 20th	Day	47% 7% 16% 23% 7%	4084
	21st to end	Day	32% 7% 12% 30% 19% 1	4346
September	1st to 10th	Day	38% 7% 14% 23% 16% 2	2280
	11th to 20th	Day	41% 7% 10% 25% 16% 2	2203
	21st to end	Day	41% 7% 10% 25% 17% 1	2032
October	1st to 10th	Day	42% 6% 12% 27% 13% 1	3160
	11th to 20th	Day	37% 5% 11% 25% 21% 1	3140
	21st to end	Day	44% 5% 15% 21% 12% 3	3428
November	1st to 10th	Day	53% 6% 11% 21% 9% 1	1645
	11th to 20th	Day	57% 7% 14% 15% 7% 1	1600
	21st to end	Day	60% 6% 13% 15% 6% 1	1600
December	1st to 10th	Day	64% 7% 10% 14% 4 1	1529
	11th to 20th	Day	67% 6% 10% 11% 6%	1905
	21st to end	Day	60% 7% 19% 9% 4 1	2783
January	1st to 10th	Night	58% 9% 13% 16% 3	4429
	11th to 20th	Night	62% 10% 13% 10% 5%	4308
	21st to end	Night	60% 8% 12% 12% 7%	4532
February	1st to 10th	Night	66% 6% 10% 10% 7% 1	2470
	11th to 20th	Night	61% 6% 13% 14% 6% 1	2406
	21st to end	Night	54% 7% 13% 17% 8% 1	2010
March	1st to 10th	Night	59% 5% 10% 15% 10% 1	3419
	11th to 20th	Night	56% 10% 12% 14% 8% 1	3480
	21st to end	Night	63% 5% 8% 14% 9% 1	3816
April	1st to 10th	Night	55% 6% 9% 15% 11% 3	1913
	11th to 20th	Night	50% 5% 10% 18% 14% 2	1812
	21st to end	Night	53% 4 11% 18% 11% 3	1710
May	1st to 10th	Night	57% 9% 13% 14% 6% 1	2761
	11th to 20th	Night	55% 8% 10% 18% 8%	2507
	21st to end	Night	54% 8% 12% 18% 7% 1	2750
June	1st to 10th	Night	56% 7% 10% 19% 7%	1520
	11th to 20th	Night	51% 7% 10% 20% 11% 1	1498
	21st to end	Night	62% 7% 10% 12% 9% 1	1330
July	1st to 10th	Night	62% 5% 11% 12% 9% 1	2353
	11th to 20th	Night	61% 6% 9% 14% 9% 1	2482
	21st to end	Night	51% 7% 11% 18% 12% 1	2829
August	1st to 10th	Night	54% 6% 12% 20% 8%	2813
	11th to 20th	Night	46% 8% 15% 23% 7%	2809
	21st to end	Night	32% 5% 15% 27% 21%	3307
September	1st to 10th	Night	38% 8% 10% 25% 16% 2	1900
	11th to 20th	Night	41% 5% 8% 28% 16% 1	1975
	21st to end	Night	48% 4 8% 24% 15% 1	2147
October	1st to 10th	Night	45% 5% 12% 25% 12% 1	3800
	11th to 20th	Night	36% 5% 13% 27% 20%	3779
	21st to end	Night	43% 4 12% 23% 17% 1	4120
November	1st to 10th	Night	50% 7% 13% 19% 11% 1	2648
	11th to 20th	Night	55% 7% 13% 16% 8%	2800
	21st to end	Night	57% 7% 16% 15% 5%	2800
December	1st to 10th	Night	66% 6% 11% 13% 3	2685
	11th to 20th	Night	69% 4 10% 11% 5%	3295
	21st to end	Night	59% 8% 13% 15% 5% 1	4884

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	26% 22% 37% 12% 3	370
	11th to 20th	Day	29% 19% 35% 13% 4	370
	21st to end	Day	21% 17% 39% 20% 3	407
February	1st to 10th	Day	29% 18% 34% 16% 3	370
	11th to 20th	Day	25% 24% 34% 15% 2	366
	21st to end	Day	18% 20% 38% 21% 4 1	307
March	1st to 10th	Day	25% 19% 35% 19% 2	460
	11th to 20th	Day	19% 23% 36% 17% 5% 1	460
	21st to end	Day	27% 16% 35% 15% 6% 1	506
April	1st to 10th	Day	30% 17% 32% 17% 4	460
	11th to 20th	Day	23% 10% 43% 18% 4 1	452
	21st to end	Day	24% 12% 30% 25% 9% 1	460
May	1st to 10th	Day	26% 12% 34% 22% 4 1	503
	11th to 20th	Day	21% 8% 33% 28% 8% 1	674
	21st to end	Day	27% 7% 30% 28% 6% 1	735
June	1st to 10th	Day	29% 7% 26% 28% 9% 1	680
	11th to 20th	Day	24% 6% 29% 29% 12% 1	680
	21st to end	Day	34% 4 23% 26% 11% 1	680
July	1st to 10th	Day	25% 4 24% 31% 14% 1	670
	11th to 20th	Day	23% 6% 21% 33% 15% 1	668
	21st to end	Day	25% 4 23% 34% 13% 1	635
August	1st to 10th	Day	19% 4 25% 37% 13% 2	486
	11th to 20th	Day	19% 6% 25% 28% 18% 4	479
	21st to end	Day	16% 6% 23% 32% 19% 4	539
September	1st to 10th	Day	17% 4 30% 34% 13% 2	490
	11th to 20th	Day	21% 9% 28% 24% 13% 5%	490
	21st to end	Day	21% 6% 31% 26% 14% 2	459
October	1st to 10th	Day	18% 9% 30% 26% 14% 3	390
	11th to 20th	Day	19% 14% 34% 22% 10% 3	390
	21st to end	Day	24% 14% 32% 21% 7% 1	429
November	1st to 10th	Day	22% 15% 31% 24% 8% 1	395
	11th to 20th	Day	27% 24% 27% 16% 6%	400
	21st to end	Day	29% 18% 37% 14% 3 1	400
December	1st to 10th	Day	31% 18% 31% 16% 3	374
	11th to 20th	Day	29% 28% 28% 13% 2	370
	21st to end	Day	28% 21% 32% 15% 3	407
January	1st to 10th	Night	26% 20% 35% 16% 3	850
	11th to 20th	Night	26% 19% 34% 17% 4	812
	21st to end	Night	23% 21% 36% 17% 3	836
February	1st to 10th	Night	29% 17% 32% 19% 2	760
	11th to 20th	Night	23% 22% 36% 15% 3	743
	21st to end	Night	18% 17% 38% 21% 5%	628
March	1st to 10th	Night	24% 16% 39% 17% 4	760
	11th to 20th	Night	23% 15% 30% 23% 8% 1	760
	21st to end	Night	25% 16% 32% 21% 6%	836
April	1st to 10th	Night	32% 11% 30% 21% 5%	583
	11th to 20th	Night	26% 7% 40% 20% 6% 1	564
	21st to end	Night	29% 8% 29% 24% 8% 1	570
May	1st to 10th	Night	30% 7% 29% 25% 7% 1	570
	11th to 20th	Night	28% 6% 25% 28% 10% 2	562
	21st to end	Night	22% 6% 28% 32% 9% 1	616
June	1st to 10th	Night	32% 6% 22% 30% 9%	570
	11th to 20th	Night	24% 5% 24% 35% 11% 1	548
	21st to end	Night	34% 4 16% 34% 11% 2	380
July	1st to 10th	Night	22% 4 21% 38% 14% 1	470
	11th to 20th	Night	23% 4 20% 33% 18% 2	552
	21st to end	Night	22% 4 18% 36% 20%	623
August	1st to 10th	Night	18% 3 19% 35% 22% 3	568
	11th to 20th	Night	20% 3 22% 31% 21% 3	562
	21st to end	Night	17% 4 22% 33% 20% 4	627
September	1st to 10th	Night	17% 5% 26% 34% 16% 2	570
	11th to 20th	Night	21% 7% 24% 29% 17% 3	645
	21st to end	Night	25% 7% 25% 29% 12% 2	760
October	1st to 10th	Night	22% 7% 28% 31% 11% 1	760
	11th to 20th	Night	21% 11% 34% 22% 11% 2	760
	21st to end	Night	27% 13% 32% 21% 6%	836
November	1st to 10th	Night	24% 13% 33% 23% 5% 2	863
	11th to 20th	Night	26% 20% 28% 19% 6%	900
	21st to end	Night	27% 19% 31% 18% 6%	900
December	1st to 10th	Night	31% 17% 34% 14% 4	859
	11th to 20th	Night	30% 23% 31% 14% 2	850
	21st to end	Night	29% 17% 34% 17% 3	935

Page generated at 2024-11-29 11:43:11. Version ac07

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