Cape Jellison
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cape Jellison clear sky chart from 2005-11-06 to 2024-11-28.

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	19% 8% 2 6% 4 4 4 4 5% 7% 37%	101354
	Night	19% 9% 3 6% 4 4 4 3 5% 6% 36%	98174
Transparency	Day	46% 6% 12% 22% 13% 2	104893
	Night	47% 5% 12% 21% 13% 2	102725
Seeing	Day	23% 16% 32% 20% 7% 2	15787
	Night	24% 14% 29% 24% 8% 1	24162

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	17% 8% 3 6% 4 4 4 3 4 6% 40%	2517
	11th to 20th	Day	18% 7% 2 5% 3 3 3 4 5% 6% 44%	2520
	21st to end	Day	16% 10% 4 7% 4 4 3 4 5% 6% 37%	2818
February	1st to 10th	Day	18% 10% 3 6% 4 4 4 4 5% 7% 35%	1710
	11th to 20th	Day	14% 9% 2 7% 4 4 5% 4 6% 6% 37%	1771
	21st to end	Day	13% 11% 3 8% 5% 5% 4 5% 4 6% 36%	1570
March	1st to 10th	Day	26% 10% 3 6% 4 4 4 3 4 5% 30%	3138
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 7% 34%	3480
	21st to end	Day	27% 9% 3 5% 4 4 3 4 6% 6% 29%	3816
April	1st to 10th	Day	21% 9% 4 7% 5% 4 4 3 4 6% 33%	2261
	11th to 20th	Day	18% 8% 2 6% 6% 4 4 3 5% 6% 39%	2413
	21st to end	Day	21% 8% 3 7% 5% 4 4 3 4 6% 36%	2470
May	1st to 10th	Day	20% 8% 2 7% 5% 4 5% 4 6% 7% 33%	4106
	11th to 20th	Day	19% 8% 2 7% 5% 4 5% 4 6% 7% 34%	4081
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 7% 9% 35%	4906
June	1st to 10th	Day	22% 7% 3 7% 5% 4 5% 4 5% 7% 31%	2850
	11th to 20th	Day	17% 8% 2 6% 5% 4 4 3 5% 7% 37%	2850
	21st to end	Day	25% 7% 3 6% 5% 4 5% 4 6% 6% 30%	2850
July	1st to 10th	Day	15% 7% 3 6% 5% 4 5% 4 6% 8% 36%	4520
	11th to 20th	Day	15% 6% 2 5% 4 4 4 4 7% 10% 38%	4440
	21st to end	Day	21% 7% 2 5% 3 4 4 3 6% 8% 36%	4735
August	1st to 10th	Day	18% 7% 2 7% 4 5% 4 4 6% 8% 34%	4105
	11th to 20th	Day	17% 8% 3 7% 4 4 5% 4 6% 7% 34%	4045
	21st to end	Day	10% 5% 2 6% 4 5% 4 4 6% 8% 47%	4505
September	1st to 10th	Day	11% 5% 2 6% 4 3 4 3 5% 8% 50%	2185
	11th to 20th	Day	13% 5% 1 4 3 4 3 3 5% 5% 53%	2090
	21st to end	Day	18% 6% 2 5% 3 3 3 4 7% 7% 43%	2090
October	1st to 10th	Day	16% 7% 2 6% 5% 4 4 4 4 7% 40%	2042
	11th to 20th	Day	19% 6% 2 5% 5% 3 3 3 5% 7% 42%	1886
	21st to end	Day	22% 9% 2 5% 4 4 4 3 5% 5% 37%	1881
November	1st to 10th	Day	18% 6% 2 6% 3 4 4 3 5% 7% 42%	1761
	11th to 20th	Day	20% 6% 2 4 3 4 4 3 6% 7% 42%	1780
	21st to end	Day	22% 8% 2 5% 3 3 2 3 4 6% 42%	1576
December	1st to 10th	Day	23% 10% 2 7% 4 4 3 2 5% 6% 35%	1421
	11th to 20th	Day	23% 10% 2 5% 4 2 4 3 4 5% 38%	1668
	21st to end	Day	25% 10% 3 5% 4 4 3 4 4 5% 33%	2497
January	1st to 10th	Night	15% 10% 3 7% 5% 4 4 3 5% 6% 40%	4429
	11th to 20th	Night	14% 9% 3 9% 5% 4 5% 3 5% 6% 38%	4440
	21st to end	Night	17% 12% 4 8% 4 4 4 3 4 6% 34%	4824
February	1st to 10th	Night	17% 10% 3 7% 5% 6% 5% 4 5% 5% 34%	2470
	11th to 20th	Night	14% 9% 3 7% 5% 5% 4 4 5% 6% 38%	2291
	21st to end	Night	15% 9% 3 7% 5% 4 4 3 4 6% 39%	1884
March	1st to 10th	Night	28% 12% 3 6% 4 3 3 2 3 5% 31%	3701
	11th to 20th	Night	16% 9% 3 8% 5% 6% 6% 5% 7% 6% 29%	3479
	21st to end	Night	28% 9% 2 6% 4 4 5% 4 6% 5% 28%	3816
April	1st to 10th	Night	22% 11% 3 7% 4 4 3 3 4 5% 34%	1916
	11th to 20th	Night	19% 7% 3 6% 4 4 4 4 6% 7% 35%	1716
	21st to end	Night	23% 9% 2 7% 4 3 4 3 4 6% 35%	1710
May	1st to 10th	Night	24% 8% 3 7% 3 3 4 3 5% 7% 33%	2834
	11th to 20th	Night	19% 7% 2 8% 5% 6% 5% 5% 6% 9% 29%	2813
	21st to end	Night	16% 8% 4 6% 5% 5% 4 4 5% 8% 36%	2696
June	1st to 10th	Night	22% 9% 3 7% 5% 4 3 4 6% 7% 31%	1330
	11th to 20th	Night	17% 9% 3 6% 3 4 4 4 4 8% 38%	1330
	21st to end	Night	25% 11% 3 6% 4 4 5% 3 4 6% 29%	1330
July	1st to 10th	Night	16% 8% 2 8% 5% 5% 6% 5% 6% 8% 30%	2424
	11th to 20th	Night	18% 7% 3 7% 5% 4 5% 4 6% 8% 35%	2520
	21st to end	Night	17% 8% 2 5% 4 4 5% 4 5% 8% 37%	2787
August	1st to 10th	Night	22% 9% 3 8% 5% 5% 5% 4 5% 7% 29%	2825
	11th to 20th	Night	19% 11% 3 7% 4 5% 4 3 5% 8% 30%	2782
	21st to end	Night	10% 6% 2 6% 5% 4 4 3 6% 8% 44%	3147
September	1st to 10th	Night	14% 6% 1 4 4 3 4 4 5% 7% 49%	1993
	11th to 20th	Night	16% 6% 1 4 2 3 3 3 4 7% 50%	2090
	21st to end	Night	19% 6% 2 4 4 3 3 4 5% 7% 44%	2090
October	1st to 10th	Night	19% 7% 2 5% 4 4 4 3 4 6% 41%	2137
	11th to 20th	Night	18% 6% 2 6% 3 4 4 3 5% 6% 43%	2290
	21st to end	Night	24% 8% 2 5% 4 3 4 3 4 5% 38%	2717
November	1st to 10th	Night	18% 6% 2 6% 4 4 4 4 5% 6% 43%	2537
	11th to 20th	Night	18% 6% 2 6% 3 4 5% 4 5% 6% 42%	2616
	21st to end	Night	19% 7% 2 6% 3 4 4 3 5% 7% 40%	2759
December	1st to 10th	Night	23% 10% 3 6% 4 4 4 3 5% 6% 33%	2755
	11th to 20th	Night	23% 8% 2 5% 4 3 3 3 5% 5% 39%	3531
	21st to end	Night	25% 9% 3 5% 3 3 4 3 4 6% 36%	5165

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	46% 4 13% 26% 10% 1	2518
	11th to 20th	Day	42% 4 12% 27% 13% 2	2520
	21st to end	Day	48% 4 14% 20% 14% 1	2818
February	1st to 10th	Day	49% 5% 11% 18% 14% 3	1710
	11th to 20th	Day	47% 5% 10% 20% 15% 2	1779
	21st to end	Day	49% 4 10% 21% 11% 5%	1570
March	1st to 10th	Day	57% 5% 9% 13% 14% 3	3141
	11th to 20th	Day	47% 6% 13% 18% 13% 3	3480
	21st to end	Day	56% 3 7% 14% 15% 5%	3816
April	1st to 10th	Day	51% 5% 7% 17% 16% 4	2261
	11th to 20th	Day	46% 4 10% 22% 15% 2	2413
	21st to end	Day	50% 4 8% 18% 16% 4	2470
May	1st to 10th	Day	47% 10% 12% 20% 10% 2	4120
	11th to 20th	Day	46% 9% 13% 21% 9% 1	4085
	21st to end	Day	44% 8% 15% 18% 14% 1	4906
June	1st to 10th	Day	52% 7% 11% 20% 9% 1	2850
	11th to 20th	Day	46% 6% 10% 20% 15% 2	2850
	21st to end	Day	54% 7% 10% 17% 10% 2	2850
July	1st to 10th	Day	46% 6% 12% 24% 11%	4450
	11th to 20th	Day	40% 6% 18% 25% 11% 1	4365
	21st to end	Day	47% 6% 12% 22% 13% 1	4584
August	1st to 10th	Day	47% 7% 14% 26% 6%	4092
	11th to 20th	Day	48% 6% 18% 20% 9%	4084
	21st to end	Day	33% 6% 13% 28% 20% 1	4505
September	1st to 10th	Day	34% 5% 14% 27% 19% 1	2185
	11th to 20th	Day	33% 5% 12% 28% 20% 3	2090
	21st to end	Day	40% 6% 11% 26% 17% 1	2090
October	1st to 10th	Day	49% 5% 11% 22% 12% 1	3393
	11th to 20th	Day	33% 4 9% 32% 21%	3114
	21st to end	Day	36% 3 16% 24% 19% 3	3081
November	1st to 10th	Day	42% 5% 13% 23% 15% 2	1761
	11th to 20th	Day	42% 5% 10% 23% 18% 3	1780
	21st to end	Day	46% 4 15% 22% 11% 1	1576
December	1st to 10th	Day	52% 4 10% 21% 11% 1	1421
	11th to 20th	Day	50% 4 10% 19% 14% 2	1668
	21st to end	Day	53% 6% 12% 18% 9% 3	2497
January	1st to 10th	Night	45% 4 14% 25% 10% 2	4429
	11th to 20th	Night	48% 4 13% 21% 11% 3	4440
	21st to end	Night	53% 3 10% 21% 12% 1	4824
February	1st to 10th	Night	51% 5% 11% 19% 12% 2	2470
	11th to 20th	Night	47% 5% 9% 21% 16% 2	2294
	21st to end	Night	47% 3 10% 20% 15% 4	1884
March	1st to 10th	Night	58% 3 8% 16% 11% 4	3711
	11th to 20th	Night	48% 9% 14% 16% 10% 2	3480
	21st to end	Night	58% 3 7% 14% 16% 2	3816
April	1st to 10th	Night	53% 4 8% 14% 18% 3	1916
	11th to 20th	Night	47% 5% 9% 22% 15% 2	1716
	21st to end	Night	51% 3 11% 16% 15% 3	1710
May	1st to 10th	Night	48% 7% 17% 20% 8% 1	2840
	11th to 20th	Night	50% 9% 15% 18% 7% 1	2814
	21st to end	Night	46% 7% 15% 20% 11% 1	2697
June	1st to 10th	Night	52% 6% 10% 21% 9% 1	1330
	11th to 20th	Night	46% 5% 15% 20% 12% 2	1330
	21st to end	Night	57% 5% 9% 18% 9% 2	1330
July	1st to 10th	Night	52% 6% 13% 18% 12%	2384
	11th to 20th	Night	48% 5% 15% 24% 9%	2472
	21st to end	Night	46% 5% 14% 24% 11% 1	2698
August	1st to 10th	Night	57% 4 12% 19% 7%	2813
	11th to 20th	Night	51% 6% 14% 19% 10%	2809
	21st to end	Night	36% 6% 12% 25% 20% 1	3147
September	1st to 10th	Night	34% 5% 13% 30% 17% 1	1993
	11th to 20th	Night	36% 4 11% 27% 20% 2	2090
	21st to end	Night	40% 5% 8% 30% 16% 1	2090
October	1st to 10th	Night	43% 4 14% 25% 14% 1	3566
	11th to 20th	Night	34% 4 9% 30% 23% 1	3801
	21st to end	Night	39% 3 11% 29% 16% 2	4467
November	1st to 10th	Night	43% 5% 11% 25% 15% 1	2537
	11th to 20th	Night	43% 4 10% 22% 18% 3	2616
	21st to end	Night	45% 4 13% 20% 15% 2	2759
December	1st to 10th	Night	53% 4 9% 21% 12%	2755
	11th to 20th	Night	47% 4 11% 21% 17% 1	3532
	21st to end	Night	49% 5% 13% 18% 12% 2	5165

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% 26% 25% 19% 4	180
	11th to 20th	Day	29% 25% 29% 13% 3 1	180
	21st to end	Day	22% 23% 32% 21% 2	231
February	1st to 10th	Day	25% 20% 34% 17% 4	370
	11th to 20th	Day	24% 29% 34% 11% 2	418
	21st to end	Day	23% 24% 34% 16% 4	382
March	1st to 10th	Day	25% 23% 34% 16% 2	460
	11th to 20th	Day	22% 26% 32% 17% 3 1	460
	21st to end	Day	30% 21% 29% 14% 5% 1	506
April	1st to 10th	Day	31% 23% 30% 10% 4 2	460
	11th to 20th	Day	29% 22% 31% 13% 4 1	452
	21st to end	Day	24% 22% 34% 15% 4 1	460
May	1st to 10th	Day	26% 23% 34% 13% 4 1	463
	11th to 20th	Day	18% 21% 34% 21% 5% 1	487
	21st to end	Day	22% 17% 35% 19% 7% 1	591
June	1st to 10th	Day	23% 15% 29% 22% 10% 2	680
	11th to 20th	Day	21% 12% 30% 24% 11% 2	680
	21st to end	Day	28% 8% 28% 25% 9% 1	680
July	1st to 10th	Day	23% 8% 33% 25% 9% 2	539
	11th to 20th	Day	18% 7% 37% 26% 10% 2	484
	21st to end	Day	19% 8% 36% 25% 10% 3	532
August	1st to 10th	Day	18% 8% 30% 30% 12% 2	486
	11th to 20th	Day	19% 8% 28% 30% 13% 3	479
	21st to end	Day	16% 11% 30% 27% 12% 3	539
September	1st to 10th	Day	16% 8% 37% 26% 11% 3	490
	11th to 20th	Day	18% 11% 29% 22% 12% 7%	490
	21st to end	Day	19% 12% 31% 21% 12% 4	490
October	1st to 10th	Day	20% 13% 27% 23% 14% 2	464
	11th to 20th	Day	21% 15% 32% 21% 8% 3	390
	21st to end	Day	28% 17% 30% 19% 5% 1	429
November	1st to 10th	Day	22% 18% 29% 23% 6% 2	395
	11th to 20th	Day	26% 19% 34% 17% 3 1	400
	21st to end	Day	29% 21% 27% 15% 7%	391
December	1st to 10th	Day	26% 19% 35% 16% 3 1	271
	11th to 20th	Day	32% 28% 29% 7% 3	180
	21st to end	Day	28% 29% 25% 14% 4	198
January	1st to 10th	Night	24% 23% 31% 19% 4	760
	11th to 20th	Night	26% 23% 31% 16% 4	760
	21st to end	Night	19% 24% 34% 19% 4	836
February	1st to 10th	Night	25% 22% 30% 21% 3	760
	11th to 20th	Night	20% 22% 36% 18% 3 1	743
	21st to end	Night	23% 18% 35% 22% 3	628
March	1st to 10th	Night	26% 18% 35% 19% 2	760
	11th to 20th	Night	22% 18% 33% 21% 6%	760
	21st to end	Night	25% 17% 30% 22% 6% 1	836
April	1st to 10th	Night	30% 14% 34% 18% 3 1	760
	11th to 20th	Night	25% 12% 31% 26% 6%	592
	21st to end	Night	30% 11% 31% 23% 6%	570
May	1st to 10th	Night	26% 7% 33% 25% 7% 1	570
	11th to 20th	Night	26% 7% 33% 28% 6% 1	562
	21st to end	Night	24% 6% 28% 30% 11% 1	457
June	1st to 10th	Night	27% 7% 21% 34% 11% 1	380
	11th to 20th	Night	21% 8% 22% 32% 16% 1	380
	21st to end	Night	32% 3 17% 37% 9%	380
July	1st to 10th	Night	23% 4 20% 39% 14% 1	370
	11th to 20th	Night	23% 1 20% 39% 16% 1	368
	21st to end	Night	21% 2 22% 37% 17% 1	440
August	1st to 10th	Night	20% 3 23% 39% 15% 1	568
	11th to 20th	Night	22% 4 21% 35% 16% 1	562
	21st to end	Night	18% 4 24% 35% 18% 2	637
September	1st to 10th	Night	18% 4 29% 32% 16% 2	760
	11th to 20th	Night	19% 8% 24% 27% 17% 5%	760
	21st to end	Night	22% 7% 26% 28% 15% 2	760
October	1st to 10th	Night	23% 8% 24% 28% 17% 1	760
	11th to 20th	Night	21% 12% 30% 25% 11% 2	760
	21st to end	Night	28% 16% 27% 23% 5%	836
November	1st to 10th	Night	25% 13% 29% 25% 7% 1	780
	11th to 20th	Night	23% 18% 31% 20% 8%	808
	21st to end	Night	26% 22% 26% 20% 6%	886
December	1st to 10th	Night	29% 16% 34% 16% 5%	850
	11th to 20th	Night	27% 24% 30% 16% 3	850
	21st to end	Night	28% 21% 29% 18% 3	913

Page generated at 2024-11-25 00:22:21. Version ac07

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