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 2026-02-01.

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% 3 6% 4 4 4 3 5% 7% 37%	126795
	Night	19% 9% 3 7% 4 4 4 3 5% 6% 36%	125199
Transparency	Day	46% 5% 12% 22% 13% 2	130316
	Night	48% 4 11% 21% 14% 2	129766
Seeing	Day	23% 16% 32% 20% 7% 2	17237
	Night	24% 14% 29% 25% 8% 1	25742

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% 8% 3 8% 5% 5% 5% 3 5% 6% 36%	3677
	11th to 20th	Day	15% 9% 3 5% 3 3 3 4 5% 6% 43%	3650
	21st to end	Day	12% 10% 4 7% 4 4 3 3 5% 5% 44%	4124
February	1st to 10th	Day	17% 10% 3 6% 4 4 5% 4 5% 7% 36%	1800
	11th to 20th	Day	14% 9% 2 7% 4 4 6% 4 6% 6% 38%	1867
	21st to end	Day	13% 11% 3 7% 5% 5% 4 5% 4 6% 37%	1650
March	1st to 10th	Day	25% 10% 3 7% 5% 5% 4 3 4 5% 30%	4512
	11th to 20th	Day	20% 10% 3 6% 5% 4 4 3 5% 7% 33%	4980
	21st to end	Day	29% 8% 3 6% 4 3 3 3 5% 6% 29%	5466
April	1st to 10th	Day	21% 9% 4 7% 5% 4 4 3 4 6% 33%	2380
	11th to 20th	Day	19% 8% 2 6% 6% 4 4 2 5% 6% 38%	2542
	21st to end	Day	21% 8% 3 7% 5% 4 3 3 4 5% 36%	2600
May	1st to 10th	Day	29% 10% 3 8% 4 3 4 3 4 5% 26%	5886
	11th to 20th	Day	19% 8% 3 8% 6% 5% 5% 4 5% 6% 32%	5861
	21st to end	Day	19% 8% 3 6% 4 4 5% 4 6% 8% 32%	7032
June	1st to 10th	Day	22% 7% 3 7% 5% 4 5% 4 5% 7% 31%	3000
	11th to 20th	Day	18% 8% 2 6% 5% 4 4 3 5% 7% 38%	3000
	21st to end	Day	25% 7% 3 6% 5% 4 5% 4 6% 6% 31%	3000
July	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 5% 6% 9% 31%	6482
	11th to 20th	Day	16% 9% 3 5% 4 4 4 3 6% 9% 36%	6360
	21st to end	Day	16% 6% 2 5% 3 3 4 4 6% 9% 42%	6805
August	1st to 10th	Day	17% 7% 2 7% 4 5% 4 4 6% 8% 36%	4235
	11th to 20th	Day	17% 8% 3 7% 4 4 5% 4 6% 7% 35%	4175
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 8% 48%	4647
September	1st to 10th	Day	11% 5% 2 6% 4 3 4 3 5% 8% 50%	2300
	11th to 20th	Day	13% 5% 1 4 3 4 3 3 5% 5% 53%	2200
	21st to end	Day	17% 6% 2 5% 3 3 3 4 6% 7% 44%	2200
October	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 4 7% 42%	2149
	11th to 20th	Day	19% 6% 2 6% 5% 3 3 3 5% 7% 41%	1985
	21st to end	Day	22% 8% 2 6% 4 4 4 3 5% 5% 37%	1980
November	1st to 10th	Day	18% 6% 2 6% 3 4 4 3 5% 7% 41%	1851
	11th to 20th	Day	20% 6% 2 5% 3 4 4 3 6% 6% 42%	1869
	21st to end	Day	22% 8% 2 5% 3 4 2 3 4 6% 41%	1680
December	1st to 10th	Day	16% 12% 1 5% 3 3 3 2 5% 7% 43%	2502
	11th to 20th	Day	20% 9% 2 5% 3 2 4 3 4 5% 44%	2688
	21st to end	Day	21% 12% 3 5% 3 4 3 3 5% 5% 36%	3660
January	1st to 10th	Night	13% 10% 3 8% 5% 4 4 3 5% 7% 39%	6489
	11th to 20th	Night	14% 10% 3 9% 6% 4 5% 3 5% 6% 34%	6455
	21st to end	Night	12% 11% 3 7% 4 4 4 4 5% 6% 39%	7060
February	1st to 10th	Night	17% 10% 3 7% 5% 5% 5% 4 5% 5% 34%	2601
	11th to 20th	Night	13% 9% 3 7% 5% 5% 4 4 5% 6% 38%	2415
	21st to end	Night	15% 9% 3 7% 5% 4 4 3 4 6% 39%	1980
March	1st to 10th	Night	27% 10% 3 7% 4 3 4 3 4 5% 31%	5327
	11th to 20th	Night	18% 10% 4 7% 4 5% 5% 4 6% 6% 31%	4979
	21st to end	Night	26% 8% 2 6% 4 4 4 4 6% 6% 29%	5466
April	1st to 10th	Night	23% 11% 3 7% 4 3 3 3 4 5% 33%	2017
	11th to 20th	Night	19% 7% 3 6% 4 4 4 4 6% 7% 34%	1807
	21st to end	Night	24% 9% 2 7% 4 3 4 3 4 5% 35%	1800
May	1st to 10th	Night	30% 10% 4 7% 4 3 3 3 4 6% 26%	4054
	11th to 20th	Night	22% 9% 3 6% 4 5% 4 4 5% 7% 30%	4033
	21st to end	Night	16% 9% 4 7% 5% 5% 4 4 5% 7% 33%	3860
June	1st to 10th	Night	22% 9% 3 7% 5% 4 4 4 6% 8% 31%	1400
	11th to 20th	Night	17% 9% 3 6% 3 4 4 4 4 8% 38%	1400
	21st to end	Night	24% 11% 3 6% 4 4 4 3 5% 6% 30%	1400
July	1st to 10th	Night	15% 9% 3 8% 5% 5% 6% 5% 6% 8% 30%	3465
	11th to 20th	Night	18% 11% 3 7% 5% 4 4 3 6% 7% 32%	3600
	21st to end	Night	12% 6% 2 5% 3 4 5% 4 6% 10% 42%	3988
August	1st to 10th	Night	22% 9% 3 8% 5% 5% 5% 4 5% 7% 30%	2915
	11th to 20th	Night	18% 11% 3 7% 4 5% 5% 3 5% 8% 31%	2872
	21st to end	Night	10% 6% 2 6% 5% 4 4 3 7% 8% 44%	3247
September	1st to 10th	Night	14% 6% 1 4 4 3 4 4 5% 7% 49%	2098
	11th to 20th	Night	15% 6% 2 4 2 3 3 3 5% 7% 51%	2200
	21st to end	Night	18% 6% 2 4 4 3 3 4 5% 7% 44%	2200
October	1st to 10th	Night	18% 7% 2 5% 4 4 4 3 4 6% 43%	2250
	11th to 20th	Night	18% 6% 2 6% 3 3 4 3 5% 6% 43%	2411
	21st to end	Night	24% 8% 2 5% 4 4 4 3 5% 5% 38%	2860
November	1st to 10th	Night	19% 6% 2 6% 4 4 4 4 5% 5% 43%	2667
	11th to 20th	Night	18% 7% 2 6% 3 4 5% 4 5% 6% 42%	2747
	21st to end	Night	19% 7% 2 6% 3 4 4 3 5% 6% 40%	2940
December	1st to 10th	Night	18% 9% 2 6% 4 4 4 3 6% 7% 37%	4904
	11th to 20th	Night	23% 9% 2 4 3 3 3 3 4 5% 42%	5741
	21st to end	Night	22% 10% 3 5% 3 3 4 3 4 6% 38%	7551

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	49% 4 10% 26% 10% 1	3678
	11th to 20th	Day	42% 4 11% 29% 12% 2	3680
	21st to end	Day	43% 4 10% 19% 18% 6%	4124
February	1st to 10th	Day	48% 5% 11% 18% 15% 3	1800
	11th to 20th	Day	46% 5% 11% 20% 15% 2	1875
	21st to end	Day	49% 4 9% 21% 12% 5%	1650
March	1st to 10th	Day	57% 5% 7% 10% 15% 6%	4515
	11th to 20th	Day	51% 5% 15% 17% 10% 2	4980
	21st to end	Day	55% 3 6% 17% 15% 3	5466
April	1st to 10th	Day	51% 5% 7% 17% 16% 4	2380
	11th to 20th	Day	47% 5% 9% 22% 15% 3	2542
	21st to end	Day	50% 4 8% 19% 16% 4	2600
May	1st to 10th	Day	59% 8% 9% 16% 7% 1	5897
	11th to 20th	Day	50% 8% 11% 21% 7% 3	5865
	21st to end	Day	48% 7% 13% 19% 12% 1	7032
June	1st to 10th	Day	51% 7% 11% 20% 10% 1	3000
	11th to 20th	Day	46% 6% 10% 21% 16% 2	3000
	21st to end	Day	53% 7% 10% 18% 10% 2	3000
July	1st to 10th	Day	49% 5% 14% 21% 10%	6412
	11th to 20th	Day	45% 5% 15% 21% 12% 1	6285
	21st to end	Day	40% 6% 13% 27% 14% 1	6609
August	1st to 10th	Day	46% 7% 14% 26% 6%	4222
	11th to 20th	Day	47% 6% 18% 20% 9%	4214
	21st to end	Day	32% 6% 13% 28% 20% 1	4647
September	1st to 10th	Day	34% 4 14% 28% 19% 1	2300
	11th to 20th	Day	33% 5% 11% 28% 21% 3	2200
	21st to end	Day	39% 6% 11% 26% 17% 1	2200
October	1st to 10th	Day	48% 5% 11% 23% 12% 1	3500
	11th to 20th	Day	34% 4 9% 32% 21%	3213
	21st to end	Day	36% 3 16% 24% 19% 3	3180
November	1st to 10th	Day	43% 5% 13% 23% 15% 2	1851
	11th to 20th	Day	42% 5% 10% 23% 18% 3	1869
	21st to end	Day	46% 4 14% 23% 11% 1	1680
December	1st to 10th	Day	43% 3 15% 25% 13% 1	2502
	11th to 20th	Day	44% 3 12% 17% 17% 7%	2688
	21st to end	Day	50% 4 11% 19% 13% 3	3660
January	1st to 10th	Night	45% 4 12% 26% 11% 1	6489
	11th to 20th	Night	52% 4 12% 21% 10% 2	6500
	21st to end	Night	46% 3 8% 21% 17% 5%	7060
February	1st to 10th	Night	51% 4 10% 18% 13% 2	2601
	11th to 20th	Night	47% 5% 10% 20% 16% 3	2418
	21st to end	Night	47% 3 10% 20% 15% 4	1980
March	1st to 10th	Night	57% 3 6% 13% 14% 7%	5337
	11th to 20th	Night	49% 7% 18% 16% 8% 1	4980
	21st to end	Night	55% 3 6% 16% 18% 2	5466
April	1st to 10th	Night	54% 4 7% 14% 17% 3	2017
	11th to 20th	Night	48% 4 10% 21% 15% 2	1807
	21st to end	Night	52% 3 11% 16% 15% 3	1800
May	1st to 10th	Night	59% 5% 12% 15% 7%	4060
	11th to 20th	Night	53% 6% 13% 19% 8% 1	4034
	21st to end	Night	50% 6% 13% 21% 10% 1	3861
June	1st to 10th	Night	52% 6% 10% 21% 9% 1	1400
	11th to 20th	Night	46% 5% 15% 20% 12% 2	1400
	21st to end	Night	55% 5% 9% 19% 10% 2	1400
July	1st to 10th	Night	52% 5% 13% 21% 9%	3425
	11th to 20th	Night	53% 4 13% 20% 10%	3552
	21st to end	Night	40% 4 18% 28% 9% 1	3870
August	1st to 10th	Night	56% 4 12% 20% 8%	2903
	11th to 20th	Night	51% 6% 14% 20% 9%	2899
	21st to end	Night	36% 6% 12% 25% 20% 1	3247
September	1st to 10th	Night	35% 5% 13% 30% 17% 1	2098
	11th to 20th	Night	35% 4 11% 28% 21% 2	2200
	21st to end	Night	40% 5% 8% 29% 16% 1	2200
October	1st to 10th	Night	42% 4 13% 25% 15% 1	3679
	11th to 20th	Night	34% 4 9% 30% 23% 1	3922
	21st to end	Night	40% 3 11% 29% 15% 2	4610
November	1st to 10th	Night	43% 5% 11% 24% 16% 1	2667
	11th to 20th	Night	43% 4 11% 22% 18% 2	2747
	21st to end	Night	46% 4 14% 20% 15% 2	2940
December	1st to 10th	Night	47% 3 9% 28% 13%	4904
	11th to 20th	Night	46% 3 11% 20% 18% 2	5742
	21st to end	Night	49% 4 10% 18% 17% 1	7551

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	25% 26% 28% 16% 4	220
	11th to 20th	Day	29% 26% 29% 13% 3	220
	21st to end	Day	20% 24% 34% 19% 2	279
February	1st to 10th	Day	25% 21% 34% 16% 4	400
	11th to 20th	Day	24% 29% 35% 10% 2	454
	21st to end	Day	22% 23% 36% 15% 4	414
March	1st to 10th	Day	26% 23% 33% 16% 2	500
	11th to 20th	Day	23% 25% 32% 16% 3 1	500
	21st to end	Day	31% 21% 29% 14% 4 1	550
April	1st to 10th	Day	32% 22% 30% 10% 4 1	500
	11th to 20th	Day	30% 23% 30% 12% 4 1	492
	21st to end	Day	25% 21% 34% 15% 4 1	500
May	1st to 10th	Day	29% 21% 33% 12% 4 1	503
	11th to 20th	Day	19% 20% 34% 21% 5% 2	527
	21st to end	Day	23% 16% 34% 19% 7%	638
June	1st to 10th	Day	23% 15% 29% 22% 10% 2	730
	11th to 20th	Day	22% 12% 31% 22% 11% 2	730
	21st to end	Day	28% 8% 29% 26% 9% 1	730
July	1st to 10th	Day	24% 8% 33% 25% 9% 2	582
	11th to 20th	Day	20% 8% 35% 25% 10% 2	524
	21st to end	Day	18% 7% 37% 25% 10% 3	576
August	1st to 10th	Day	17% 7% 30% 31% 12% 2	526
	11th to 20th	Day	18% 9% 28% 29% 14% 3	519
	21st to end	Day	16% 11% 31% 27% 12% 3	583
September	1st to 10th	Day	16% 8% 36% 25% 12% 3	530
	11th to 20th	Day	17% 11% 30% 23% 12% 7%	530
	21st to end	Day	19% 11% 33% 21% 12% 4	530
October	1st to 10th	Day	19% 13% 27% 24% 15% 2	501
	11th to 20th	Day	21% 15% 33% 20% 8% 3	420
	21st to end	Day	29% 17% 30% 19% 5% 1	462
November	1st to 10th	Day	23% 19% 29% 22% 6% 2	425
	11th to 20th	Day	25% 19% 35% 17% 4 1	430
	21st to end	Day	29% 22% 28% 15% 6%	430
December	1st to 10th	Day	25% 19% 33% 18% 3 1	320
	11th to 20th	Day	30% 29% 29% 9% 3	220
	21st to end	Day	28% 27% 26% 15% 3	242
January	1st to 10th	Night	23% 22% 32% 18% 4	840
	11th to 20th	Night	26% 22% 31% 17% 4	840
	21st to end	Night	19% 24% 34% 20% 4	924
February	1st to 10th	Night	25% 22% 29% 21% 2	801
	11th to 20th	Night	21% 23% 36% 17% 3 1	783
	21st to end	Night	23% 17% 34% 22% 3	660
March	1st to 10th	Night	26% 18% 35% 19% 2	800
	11th to 20th	Night	22% 17% 33% 22% 6%	800
	21st to end	Night	25% 17% 30% 22% 5% 1	880
April	1st to 10th	Night	31% 15% 34% 17% 3 1	800
	11th to 20th	Night	25% 11% 32% 26% 6%	623
	21st to end	Night	30% 11% 30% 23% 6%	600
May	1st to 10th	Night	27% 7% 33% 26% 7% 1	600
	11th to 20th	Night	26% 7% 33% 27% 6% 1	592
	21st to end	Night	24% 6% 28% 31% 10% 1	481
June	1st to 10th	Night	27% 7% 22% 34% 11% 1	400
	11th to 20th	Night	21% 8% 22% 33% 15% 1	400
	21st to end	Night	31% 4 18% 37% 10%	400
July	1st to 10th	Night	22% 4 19% 41% 14% 1	390
	11th to 20th	Night	23% 1 19% 39% 15% 1	388
	21st to end	Night	20% 2 22% 37% 16% 1	463
August	1st to 10th	Night	20% 3 23% 39% 15% 1	598
	11th to 20th	Night	21% 5% 21% 36% 16% 1	592
	21st to end	Night	18% 4 24% 35% 18% 2	671
September	1st to 10th	Night	18% 4 28% 32% 17% 2	800
	11th to 20th	Night	19% 8% 24% 27% 18% 5%	800
	21st to end	Night	22% 7% 26% 29% 15% 2	800
October	1st to 10th	Night	22% 9% 23% 28% 17% 1	800
	11th to 20th	Night	21% 12% 29% 25% 10% 2	800
	21st to end	Night	28% 15% 28% 24% 5%	880
November	1st to 10th	Night	25% 14% 28% 25% 7% 1	820
	11th to 20th	Night	23% 17% 31% 20% 8%	849
	21st to end	Night	25% 22% 27% 19% 6%	950
December	1st to 10th	Night	29% 15% 34% 17% 5%	950
	11th to 20th	Night	27% 24% 30% 15% 3	950
	21st to end	Night	28% 21% 30% 18% 3	1017

Page generated at 2026-01-29 01:21:44. Version ac07

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