Kelly's Chapel
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kelly's Chapel 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	15% 9% 3 7% 5% 5% 5% 4 6% 7% 34%	101455
	Night	15% 10% 3 7% 4 4 4 4 5% 7% 36%	98133
Transparency	Day	45% 9% 12% 19% 12% 3	105171
	Night	44% 8% 11% 19% 13% 3	102556
Seeing	Day	22% 16% 24% 21% 13% 5%	15194
	Night	20% 13% 22% 27% 16% 2	25280

By Month

Percentage Cloud Cover SE (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	15% 14% 7% 13% 5% 3 3 2 4 5% 28%	2836
	11th to 20th	Day	14% 17% 8% 14% 6% 5% 3 3 3 4 23%	2840
	21st to end	Day	15% 18% 6% 9% 4 4 4 3 3 4 29%	3124
February	1st to 10th	Day	16% 14% 4 8% 5% 5% 4 3 5% 4 30%	1710
	11th to 20th	Day	21% 12% 5% 9% 3 3 3 3 4 5% 30%	1833
	21st to end	Day	22% 12% 4 8% 4 3 4 3 5% 6% 31%	1570
March	1st to 10th	Day	20% 14% 4 6% 3 3 4 3 4 6% 33%	3421
	11th to 20th	Day	13% 9% 3 7% 4 3 3 3 5% 5% 44%	3480
	21st to end	Day	18% 10% 2 6% 4 3 4 4 5% 7% 37%	3815
April	1st to 10th	Day	14% 9% 4 6% 5% 4 4 4 5% 7% 38%	2090
	11th to 20th	Day	15% 10% 3 6% 4 3 4 4 5% 5% 41%	2290
	21st to end	Day	17% 8% 2 7% 5% 5% 5% 4 5% 6% 37%	2470
May	1st to 10th	Day	21% 9% 3 8% 6% 5% 5% 4 6% 6% 27%	4082
	11th to 20th	Day	19% 9% 3 7% 6% 5% 6% 4 6% 7% 28%	4081
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 9% 11% 33%	4476
June	1st to 10th	Day	13% 6% 2 7% 6% 5% 6% 5% 7% 9% 34%	2470
	11th to 20th	Day	9% 6% 3 8% 5% 6% 6% 6% 8% 10% 33%	2470
	21st to end	Day	12% 7% 2 7% 6% 6% 5% 5% 7% 9% 34%	2470
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 7% 6% 8% 11% 35%	4120
	11th to 20th	Day	12% 7% 3 6% 4 5% 6% 4 8% 9% 35%	4120
	21st to end	Day	19% 9% 4 9% 7% 7% 7% 5% 6% 7% 21%	4466
August	1st to 10th	Day	12% 7% 3 8% 7% 6% 7% 5% 9% 11% 25%	4104
	11th to 20th	Day	13% 6% 2 7% 6% 6% 5% 5% 8% 9% 33%	4044
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 51%	4327
September	1st to 10th	Day	12% 7% 2 5% 4 5% 6% 4 6% 9% 40%	2090
	11th to 20th	Day	14% 7% 2 7% 4 5% 6% 4 5% 8% 37%	2090
	21st to end	Day	16% 7% 2 6% 5% 5% 5% 4 6% 7% 37%	2090
October	1st to 10th	Day	15% 5% 1 6% 5% 4 4 3 4 6% 47%	2003
	11th to 20th	Day	17% 7% 2 5% 3 3 4 3 3 5% 48%	1900
	21st to end	Day	16% 10% 2 5% 3 4 3 3 4 6% 45%	2090
November	1st to 10th	Day	12% 7% 2 5% 4 3 4 4 5% 6% 48%	1887
	11th to 20th	Day	11% 10% 3 6% 5% 5% 4 4 6% 7% 40%	1800
	21st to end	Day	14% 11% 3 8% 4 4 3 3 4 5% 41%	1800
December	1st to 10th	Day	20% 15% 5% 8% 4 3 3 3 5% 5% 29%	1719
	11th to 20th	Day	17% 16% 3 7% 3 3 3 3 6% 7% 33%	2153
	21st to end	Day	14% 15% 7% 11% 5% 5% 6% 4 6% 5% 23%	3124
January	1st to 10th	Night	16% 19% 8% 11% 5% 4 3 2 4 4 24%	4109
	11th to 20th	Night	18% 13% 4 9% 5% 6% 4 3 4 4 30%	4120
	21st to end	Night	20% 11% 5% 9% 5% 5% 4 3 4 5% 29%	4532
February	1st to 10th	Night	16% 12% 4 8% 5% 4 4 3 5% 6% 34%	2470
	11th to 20th	Night	20% 14% 4 9% 5% 4 4 3 4 5% 28%	2228
	21st to end	Night	20% 15% 3 8% 3 3 4 3 5% 5% 30%	1884
March	1st to 10th	Night	23% 13% 4 6% 4 3 3 3 3 5% 33%	3432
	11th to 20th	Night	14% 8% 4 7% 3 2 3 3 4 6% 43%	3480
	21st to end	Night	15% 9% 2 6% 4 4 4 4 5% 7% 41%	3817
April	1st to 10th	Night	14% 11% 2 7% 4 3 5% 4 6% 7% 38%	2090
	11th to 20th	Night	14% 10% 2 4 4 4 4 4 6% 6% 43%	1852
	21st to end	Night	14% 7% 3 5% 6% 3 5% 3 6% 7% 40%	1710
May	1st to 10th	Night	20% 10% 3 8% 4 4 4 4 6% 7% 30%	2813
	11th to 20th	Night	18% 9% 3 7% 5% 4 5% 4 5% 7% 34%	2812
	21st to end	Night	11% 7% 3 6% 4 5% 5% 5% 7% 9% 37%	3079
June	1st to 10th	Night	11% 6% 2 5% 5% 5% 5% 5% 7% 11% 39%	1710
	11th to 20th	Night	7% 6% 3 6% 5% 4 6% 5% 7% 10% 42%	1710
	21st to end	Night	11% 5% 2 7% 5% 4 5% 4 7% 11% 40%	1710
July	1st to 10th	Night	11% 5% 2 5% 4 5% 6% 5% 9% 13% 35%	2840
	11th to 20th	Night	10% 6% 3 6% 3 4 5% 4 6% 11% 41%	2840
	21st to end	Night	17% 11% 4 8% 6% 5% 5% 4 7% 9% 24%	3087
August	1st to 10th	Night	13% 7% 2 7% 5% 5% 6% 5% 7% 11% 32%	2825
	11th to 20th	Night	13% 7% 3 7% 5% 5% 6% 4 7% 8% 35%	2785
	21st to end	Night	5% 4 2 4 4 4 4 4 6% 10% 54%	3290
September	1st to 10th	Night	12% 7% 2 6% 5% 4 4 4 5% 7% 44%	2090
	11th to 20th	Night	13% 8% 2 6% 4 4 3 3 5% 7% 45%	2090
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 8% 45%	2090
October	1st to 10th	Night	16% 6% 2 4 3 3 3 3 4 6% 50%	2175
	11th to 20th	Night	16% 8% 2 4 3 3 3 4 5% 5% 47%	2280
	21st to end	Night	15% 10% 2 4 4 3 3 3 4 6% 47%	2508
November	1st to 10th	Night	12% 7% 3 6% 4 3 3 3 5% 5% 49%	2406
	11th to 20th	Night	13% 11% 3 6% 4 3 4 3 5% 7% 42%	2600
	21st to end	Night	13% 11% 3 7% 3 3 4 3 5% 6% 42%	2600
December	1st to 10th	Night	19% 14% 4 9% 5% 3 4 3 4 6% 28%	2495
	11th to 20th	Night	17% 14% 5% 11% 4 3 4 3 4 5% 32%	3042
	21st to end	Night	14% 16% 8% 9% 5% 4 5% 3 5% 7% 23%	4532

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% 6% 6% 13% 14% 4	2837
	11th to 20th	Day	61% 7% 6% 13% 11% 2	2840
	21st to end	Day	59% 5% 6% 14% 15% 1	3124
February	1st to 10th	Day	55% 5% 8% 16% 14% 2	1710
	11th to 20th	Day	57% 4 7% 15% 14% 3	1843
	21st to end	Day	54% 6% 8% 13% 15% 5%	1570
March	1st to 10th	Day	50% 6% 10% 17% 14% 3	3421
	11th to 20th	Day	40% 8% 8% 23% 15% 6%	3480
	21st to end	Day	46% 7% 10% 23% 12% 4	3815
April	1st to 10th	Day	45% 7% 10% 21% 14% 3	2090
	11th to 20th	Day	43% 6% 10% 20% 17% 4	2290
	21st to end	Day	48% 8% 12% 20% 10% 2	2470
May	1st to 10th	Day	55% 10% 10% 17% 8% 1	4120
	11th to 20th	Day	51% 12% 12% 20% 5% 1	4085
	21st to end	Day	38% 14% 17% 20% 9% 2	4489
June	1st to 10th	Day	44% 12% 14% 19% 11%	2470
	11th to 20th	Day	43% 14% 14% 16% 12% 2	2470
	21st to end	Day	43% 10% 15% 18% 13% 1	2470
July	1st to 10th	Day	39% 14% 19% 17% 10% 1	4055
	11th to 20th	Day	42% 11% 18% 23% 5% 1	4051
	21st to end	Day	60% 10% 10% 13% 6%	4324
August	1st to 10th	Day	47% 13% 17% 17% 5%	4091
	11th to 20th	Day	43% 11% 17% 20% 8% 1	4083
	21st to end	Day	29% 9% 21% 29% 11% 1	4327
September	1st to 10th	Day	40% 12% 11% 19% 12% 6%	2090
	11th to 20th	Day	43% 11% 9% 20% 16% 1	2090
	21st to end	Day	44% 10% 12% 18% 14% 3	2090
October	1st to 10th	Day	30% 6% 9% 18% 29% 7%	3328
	11th to 20th	Day	31% 4 9% 23% 15% 19%	3140
	21st to end	Day	30% 4 5% 31% 15% 14%	3428
November	1st to 10th	Day	36% 6% 9% 19% 25% 5%	1887
	11th to 20th	Day	42% 5% 8% 18% 21% 6%	1800
	21st to end	Day	45% 5% 7% 20% 19% 4	1800
December	1st to 10th	Day	57% 6% 7% 16% 10% 2	1719
	11th to 20th	Day	49% 6% 8% 15% 19% 3	2150
	21st to end	Day	56% 7% 11% 17% 8% 1	3124
January	1st to 10th	Night	63% 7% 6% 11% 10% 4	4109
	11th to 20th	Night	54% 6% 7% 14% 16% 3	4120
	21st to end	Night	56% 7% 9% 15% 13% 1	4532
February	1st to 10th	Night	51% 5% 10% 18% 14% 2	2470
	11th to 20th	Night	58% 6% 6% 15% 11% 4	2229
	21st to end	Night	55% 6% 8% 17% 10% 4	1884
March	1st to 10th	Night	55% 6% 8% 15% 13% 2	3432
	11th to 20th	Night	40% 8% 9% 24% 13% 7%	3480
	21st to end	Night	41% 7% 11% 22% 15% 3	3817
April	1st to 10th	Night	44% 8% 12% 20% 13% 3	2090
	11th to 20th	Night	40% 8% 12% 20% 16% 5%	1852
	21st to end	Night	42% 9% 13% 24% 11% 1	1710
May	1st to 10th	Night	52% 12% 11% 19% 6%	2840
	11th to 20th	Night	48% 13% 14% 21% 4	2813
	21st to end	Night	36% 16% 17% 21% 8% 2	3087
June	1st to 10th	Night	37% 13% 18% 19% 13%	1710
	11th to 20th	Night	34% 14% 20% 21% 10% 1	1710
	21st to end	Night	37% 11% 16% 20% 13% 2	1710
July	1st to 10th	Night	37% 13% 21% 19% 9% 1	2795
	11th to 20th	Night	34% 12% 23% 24% 5% 2	2786
	21st to end	Night	55% 11% 14% 16% 5%	2988
August	1st to 10th	Night	44% 12% 20% 19% 6%	2814
	11th to 20th	Night	43% 11% 17% 22% 7%	2812
	21st to end	Night	25% 8% 18% 36% 12% 1	3290
September	1st to 10th	Night	37% 10% 15% 19% 14% 4	2090
	11th to 20th	Night	38% 10% 12% 22% 16% 2	2090
	21st to end	Night	38% 11% 12% 23% 15% 1	2090
October	1st to 10th	Night	34% 7% 9% 19% 27% 5%	3630
	11th to 20th	Night	33% 5% 7% 20% 18% 17%	3779
	21st to end	Night	26% 4 7% 29% 19% 14%	4120
November	1st to 10th	Night	37% 7% 9% 19% 22% 5%	2406
	11th to 20th	Night	42% 5% 8% 17% 21% 7%	2600
	21st to end	Night	43% 6% 8% 21% 19% 4	2600
December	1st to 10th	Night	57% 8% 7% 16% 10% 3	2495
	11th to 20th	Night	56% 4 7% 13% 17% 3	3044
	21st to end	Night	57% 9% 9% 13% 10% 1	4532

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	36% 31% 24% 7% 1 1	270
	11th to 20th	Day	39% 28% 24% 8% 1	270
	21st to end	Day	36% 29% 24% 9% 1	297
February	1st to 10th	Day	34% 30% 25% 9% 2	270
	11th to 20th	Day	50% 26% 18% 6% 1	270
	21st to end	Day	43% 27% 25% 4	225
March	1st to 10th	Day	27% 26% 26% 16% 4	446
	11th to 20th	Day	32% 29% 24% 12% 4 1	460
	21st to end	Day	31% 25% 24% 16% 4	506
April	1st to 10th	Day	29% 21% 27% 14% 8% 1	460
	11th to 20th	Day	26% 19% 26% 17% 10% 2	452
	21st to end	Day	27% 20% 24% 17% 9% 3	460
May	1st to 10th	Day	26% 21% 26% 16% 6% 5%	463
	11th to 20th	Day	20% 15% 26% 24% 10% 5%	487
	21st to end	Day	15% 11% 25% 22% 18% 9%	529
June	1st to 10th	Day	14% 8% 28% 26% 17% 7%	490
	11th to 20th	Day	9% 9% 24% 30% 20% 7%	490
	21st to end	Day	13% 11% 29% 25% 15% 7%	490
July	1st to 10th	Day	15% 4 21% 28% 21% 11%	485
	11th to 20th	Day	14% 5% 19% 33% 19% 10%	484
	21st to end	Day	15% 5% 23% 29% 19% 9%	532
August	1st to 10th	Day	14% 7% 24% 24% 19% 12%	486
	11th to 20th	Day	15% 4 23% 27% 21% 11%	479
	21st to end	Day	10% 5% 15% 29% 24% 17%	539
September	1st to 10th	Day	12% 4 19% 27% 26% 12%	490
	11th to 20th	Day	14% 7% 17% 28% 25% 9%	490
	21st to end	Day	20% 11% 22% 24% 18% 5%	490
October	1st to 10th	Day	17% 10% 22% 27% 19% 5%	490
	11th to 20th	Day	19% 19% 20% 24% 16% 2	490
	21st to end	Day	21% 15% 25% 23% 12% 4	539
November	1st to 10th	Day	20% 14% 28% 24% 10% 3	425
	11th to 20th	Day	26% 24% 23% 21% 6%	300
	21st to end	Day	27% 25% 29% 14% 5% 1	300
December	1st to 10th	Day	34% 23% 30% 11% 2	273
	11th to 20th	Day	29% 27% 26% 14% 4	270
	21st to end	Day	29% 28% 27% 11% 6%	297
January	1st to 10th	Night	28% 26% 26% 17% 3	760
	11th to 20th	Night	31% 21% 28% 19% 2	760
	21st to end	Night	23% 28% 30% 17% 2	836
February	1st to 10th	Night	24% 21% 31% 22% 2	760
	11th to 20th	Night	32% 28% 27% 13% 1	743
	21st to end	Night	32% 24% 27% 15% 2	628
March	1st to 10th	Night	23% 20% 31% 22% 4	760
	11th to 20th	Night	29% 17% 28% 19% 6% 1	760
	21st to end	Night	24% 17% 32% 21% 6%	836
April	1st to 10th	Night	22% 19% 27% 24% 7%	760
	11th to 20th	Night	21% 16% 26% 27% 9% 1	701
	21st to end	Night	17% 13% 27% 34% 7% 1	570
May	1st to 10th	Night	18% 13% 28% 27% 14% 1	570
	11th to 20th	Night	16% 7% 25% 33% 18% 1	561
	21st to end	Night	12% 6% 18% 32% 28% 6%	617
June	1st to 10th	Night	10% 4 16% 41% 25% 4	570
	11th to 20th	Night	7% 4 17% 34% 33% 4	570
	21st to end	Night	11% 5% 13% 40% 28% 3	570
July	1st to 10th	Night	14% 2 10% 32% 37% 4	555
	11th to 20th	Night	11% 3 9% 36% 37% 5%	552
	21st to end	Night	11% 2 12% 32% 36% 7%	624
August	1st to 10th	Night	13% 2 11% 33% 39% 3	567
	11th to 20th	Night	12% 4 9% 33% 35% 6%	564
	21st to end	Night	10% 2 10% 31% 39% 8%	706
September	1st to 10th	Night	12% 3 14% 32% 33% 6%	760
	11th to 20th	Night	15% 5% 15% 28% 32% 5%	760
	21st to end	Night	16% 7% 18% 32% 24% 3	760
October	1st to 10th	Night	17% 8% 18% 26% 25% 5%	760
	11th to 20th	Night	20% 11% 23% 28% 15% 2	760
	21st to end	Night	20% 11% 23% 31% 12% 1	836
November	1st to 10th	Night	16% 10% 28% 28% 16% 2	780
	11th to 20th	Night	21% 15% 24% 29% 9% 1	800
	21st to end	Night	20% 16% 28% 27% 9%	800
December	1st to 10th	Night	27% 21% 25% 22% 5%	768
	11th to 20th	Night	24% 20% 27% 24% 4	760
	21st to end	Night	27% 18% 28% 22% 4	836

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