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 2026-03-03.

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	14% 10% 4 8% 5% 5% 5% 4 6% 7% 34%	131328
	Night	14% 10% 4 8% 5% 4 4 3 5% 7% 36%	129853
Transparency	Day	46% 8% 12% 19% 13% 3	135000
	Night	45% 8% 11% 19% 13% 3	134251
Seeing	Day	23% 16% 24% 21% 12% 5%	16813
	Night	20% 13% 23% 26% 16% 2	26969

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% 17% 6% 11% 5% 3 3 2 4 4 30%	5258
	11th to 20th	Day	10% 17% 8% 13% 5% 4 3 2 3 3 33%	5280
	21st to end	Day	14% 14% 5% 11% 5% 3 3 2 3 4 35%	5780
February	1st to 10th	Day	16% 14% 4 9% 5% 5% 4 3 5% 4 31%	1890
	11th to 20th	Day	22% 12% 5% 9% 3 3 3 3 4 5% 30%	2033
	21st to end	Day	21% 11% 4 8% 4 3 3 3 5% 5% 33%	1730
March	1st to 10th	Day	16% 16% 4 6% 4 4 4 3 4 5% 33%	4928
	11th to 20th	Day	11% 10% 3 7% 4 3 3 3 5% 6% 45%	4980
	21st to end	Day	16% 9% 2 7% 4 3 4 3 5% 7% 39%	5465
April	1st to 10th	Day	15% 9% 4 7% 4 4 4 3 5% 7% 37%	2200
	11th to 20th	Day	15% 9% 3 6% 4 3 4 4 5% 6% 41%	2413
	21st to end	Day	17% 8% 2 7% 5% 5% 5% 4 5% 6% 36%	2600
May	1st to 10th	Day	17% 9% 3 9% 6% 6% 6% 5% 7% 8% 25%	5862
	11th to 20th	Day	17% 9% 3 9% 6% 5% 6% 5% 7% 8% 25%	5861
	21st to end	Day	15% 8% 3 8% 5% 5% 6% 5% 8% 10% 28%	6433
June	1st to 10th	Day	13% 6% 2 7% 6% 5% 6% 5% 7% 9% 34%	2600
	11th to 20th	Day	10% 7% 3 8% 5% 6% 6% 6% 8% 10% 33%	2600
	21st to end	Day	11% 6% 2 6% 6% 6% 5% 5% 7% 9% 36%	2600
July	1st to 10th	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 11% 37%	5900
	11th to 20th	Day	12% 8% 3 7% 5% 5% 6% 5% 9% 11% 30%	5900
	21st to end	Day	16% 8% 4 9% 6% 6% 7% 5% 7% 8% 25%	6424
August	1st to 10th	Day	12% 7% 3 8% 7% 6% 7% 5% 9% 11% 25%	4234
	11th to 20th	Day	13% 6% 2 7% 6% 6% 5% 5% 7% 10% 33%	4174
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 51%	4464
September	1st to 10th	Day	12% 7% 2 5% 4 5% 6% 4 6% 9% 41%	2200
	11th to 20th	Day	14% 7% 2 7% 4 5% 6% 4 5% 8% 38%	2200
	21st to end	Day	16% 7% 3 6% 5% 5% 5% 4 6% 7% 36%	2200
October	1st to 10th	Day	14% 5% 1 6% 5% 4 4 3 4 6% 49%	2108
	11th to 20th	Day	16% 7% 2 5% 3 3 4 3 4 5% 49%	2000
	21st to end	Day	16% 10% 2 5% 3 4 3 3 4 6% 44%	2200
November	1st to 10th	Day	12% 7% 2 6% 4 3 3 4 5% 6% 48%	1983
	11th to 20th	Day	11% 10% 3 6% 5% 5% 3 4 6% 7% 41%	1890
	21st to end	Day	14% 11% 3 8% 4 4 3 3 4 6% 40%	1890
December	1st to 10th	Day	15% 14% 4 11% 4 3 3 3 4 4 35%	3020
	11th to 20th	Day	19% 15% 4 7% 3 4 4 4 6% 6% 28%	3463
	21st to end	Day	12% 13% 7% 10% 5% 5% 6% 5% 6% 7% 25%	4565
January	1st to 10th	Night	15% 18% 7% 13% 6% 4 3 2 3 4 26%	7635
	11th to 20th	Night	15% 13% 4 11% 5% 5% 4 2 3 4 35%	7680
	21st to end	Night	17% 10% 4 11% 5% 4 4 3 4 5% 34%	8401
February	1st to 10th	Night	16% 13% 4 8% 4 4 4 3 5% 6% 34%	2730
	11th to 20th	Night	20% 13% 4 9% 5% 4 4 3 4 5% 29%	2468
	21st to end	Night	19% 14% 3 9% 4 3 4 3 5% 4 31%	2076
March	1st to 10th	Night	18% 13% 4 7% 4 3 3 3 3 5% 39%	4970
	11th to 20th	Night	12% 7% 3 6% 3 3 3 3 4 6% 49%	4980
	21st to end	Night	12% 9% 3 7% 4 4 5% 4 6% 7% 40%	5467
April	1st to 10th	Night	14% 11% 2 7% 5% 3 5% 4 6% 7% 37%	2200
	11th to 20th	Night	13% 10% 2 4 4 4 4 4 6% 6% 43%	1950
	21st to end	Night	14% 7% 3 6% 6% 3 6% 3 6% 7% 39%	1800
May	1st to 10th	Night	18% 11% 3 8% 4 4 5% 4 7% 8% 28%	4033
	11th to 20th	Night	16% 9% 3 9% 6% 5% 5% 4 6% 8% 29%	4032
	21st to end	Night	20% 9% 3 7% 4 4 5% 4 6% 7% 31%	4421
June	1st to 10th	Night	11% 6% 2 5% 5% 5% 5% 5% 7% 10% 39%	1800
	11th to 20th	Night	7% 6% 3 6% 5% 4 6% 5% 7% 10% 41%	1800
	21st to end	Night	10% 5% 2 7% 5% 4 5% 4 7% 11% 40%	1800
July	1st to 10th	Night	12% 5% 2 5% 4 4 5% 5% 8% 12% 37%	4058
	11th to 20th	Night	12% 7% 3 7% 4 5% 5% 5% 7% 11% 32%	4057
	21st to end	Night	15% 10% 4 9% 7% 5% 6% 4 7% 9% 25%	4427
August	1st to 10th	Night	13% 7% 2 7% 5% 5% 6% 5% 7% 10% 32%	2915
	11th to 20th	Night	13% 7% 3 6% 5% 5% 6% 4 7% 9% 35%	2875
	21st to end	Night	5% 4 2 4 4 4 4 4 6% 9% 53%	3394
September	1st to 10th	Night	12% 6% 2 6% 5% 4 4 4 5% 8% 45%	2200
	11th to 20th	Night	12% 8% 2 5% 4 4 3 3 4 7% 46%	2200
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 8% 43%	2200
October	1st to 10th	Night	16% 6% 1 4 3 3 3 3 4 6% 51%	2290
	11th to 20th	Night	15% 8% 2 4 3 3 3 4 5% 5% 47%	2400
	21st to end	Night	15% 10% 2 4 4 3 3 2 4 6% 46%	2640
November	1st to 10th	Night	12% 7% 3 6% 4 3 3 3 5% 5% 49%	2529
	11th to 20th	Night	13% 11% 3 7% 3 3 4 3 5% 6% 43%	2730
	21st to end	Night	13% 11% 3 7% 3 3 4 3 5% 6% 41%	2730
December	1st to 10th	Night	15% 13% 4 10% 5% 3 4 3 4 5% 33%	4380
	11th to 20th	Night	19% 13% 7% 11% 4 4 4 3 4 5% 27%	4952
	21st to end	Night	13% 14% 7% 9% 5% 4 4 3 5% 8% 28%	6633

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	56% 5% 10% 13% 14% 2	5259
	11th to 20th	Day	54% 5% 5% 13% 19% 4	5280
	21st to end	Day	53% 4 8% 20% 13% 2	5780
February	1st to 10th	Day	55% 5% 8% 16% 14% 2	1890
	11th to 20th	Day	57% 4 7% 16% 13% 3	2043
	21st to end	Day	53% 5% 8% 14% 15% 5%	1730
March	1st to 10th	Day	50% 5% 9% 14% 16% 6%	4928
	11th to 20th	Day	38% 6% 7% 19% 22% 8%	4980
	21st to end	Day	45% 6% 9% 25% 13% 3	5465
April	1st to 10th	Day	46% 7% 10% 21% 14% 3	2200
	11th to 20th	Day	43% 6% 10% 20% 17% 4	2413
	21st to end	Day	48% 8% 12% 21% 10% 2	2600
May	1st to 10th	Day	53% 10% 12% 17% 7%	5897
	11th to 20th	Day	53% 12% 13% 18% 4 1	5865
	21st to end	Day	45% 12% 16% 16% 9% 2	6447
June	1st to 10th	Day	44% 12% 14% 19% 11%	2600
	11th to 20th	Day	44% 14% 14% 16% 12% 2	2600
	21st to end	Day	41% 10% 16% 19% 13% 1	2600
July	1st to 10th	Day	37% 12% 19% 20% 11% 1	5835
	11th to 20th	Day	44% 13% 21% 18% 4 1	5831
	21st to end	Day	53% 11% 12% 15% 8%	6240
August	1st to 10th	Day	47% 13% 17% 18% 5%	4221
	11th to 20th	Day	43% 11% 17% 20% 8% 1	4213
	21st to end	Day	29% 9% 21% 29% 12% 1	4464
September	1st to 10th	Day	39% 12% 12% 19% 14% 5%	2200
	11th to 20th	Day	43% 11% 9% 21% 15% 1	2200
	21st to end	Day	45% 10% 12% 17% 14% 3	2200
October	1st to 10th	Day	29% 6% 9% 18% 30% 7%	3433
	11th to 20th	Day	30% 4 9% 23% 16% 18%	3240
	21st to end	Day	31% 4 5% 31% 15% 13%	3538
November	1st to 10th	Day	36% 6% 9% 19% 24% 5%	1983
	11th to 20th	Day	41% 5% 9% 19% 20% 6%	1890
	21st to end	Day	46% 5% 7% 21% 18% 4	1890
December	1st to 10th	Day	52% 5% 7% 17% 17% 2	3020
	11th to 20th	Day	54% 7% 8% 15% 14% 2	3460
	21st to end	Day	52% 8% 13% 17% 8% 1	4565
January	1st to 10th	Night	61% 5% 9% 15% 7% 2	7636
	11th to 20th	Night	51% 5% 6% 15% 20% 4	7680
	21st to end	Night	51% 5% 8% 20% 13% 2	8401
February	1st to 10th	Night	51% 5% 11% 18% 14% 2	2730
	11th to 20th	Night	59% 6% 6% 16% 10% 3	2469
	21st to end	Night	55% 6% 8% 17% 10% 4	2076
March	1st to 10th	Night	49% 5% 7% 19% 14% 5%	4970
	11th to 20th	Night	35% 6% 8% 22% 22% 8%	4980
	21st to end	Night	43% 7% 12% 23% 13% 2	5467
April	1st to 10th	Night	45% 8% 12% 20% 13% 3	2200
	11th to 20th	Night	39% 8% 12% 21% 16% 4	1950
	21st to end	Night	43% 9% 13% 24% 10% 1	1800
May	1st to 10th	Night	51% 12% 13% 17% 7%	4060
	11th to 20th	Night	51% 13% 15% 17% 4	4033
	21st to end	Night	47% 13% 15% 18% 6% 1	4429
June	1st to 10th	Night	38% 13% 18% 18% 13%	1800
	11th to 20th	Night	35% 14% 19% 21% 10% 1	1800
	21st to end	Night	37% 11% 16% 21% 13% 2	1800
July	1st to 10th	Night	36% 11% 20% 23% 9% 1	4015
	11th to 20th	Night	42% 13% 23% 17% 4 1	4006
	21st to end	Night	53% 12% 13% 14% 8%	4297
August	1st to 10th	Night	44% 12% 20% 19% 5%	2904
	11th to 20th	Night	42% 12% 18% 22% 7%	2902
	21st to end	Night	25% 8% 18% 36% 11% 1	3394
September	1st to 10th	Night	37% 10% 16% 19% 15% 3	2200
	11th to 20th	Night	37% 10% 13% 23% 16% 1	2200
	21st to end	Night	39% 11% 12% 22% 15% 1	2200
October	1st to 10th	Night	33% 7% 9% 19% 27% 5%	3745
	11th to 20th	Night	33% 5% 7% 20% 18% 16%	3899
	21st to end	Night	27% 4 7% 29% 19% 14%	4252
November	1st to 10th	Night	37% 6% 9% 20% 22% 5%	2529
	11th to 20th	Night	42% 5% 8% 18% 21% 6%	2730
	21st to end	Night	44% 5% 7% 21% 18% 4	2730
December	1st to 10th	Night	51% 6% 8% 20% 13% 2	4380
	11th to 20th	Night	59% 5% 9% 14% 12% 2	4954
	21st to end	Night	53% 8% 12% 15% 11% 1	6633

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	38% 30% 23% 7% 2 1	330
	11th to 20th	Day	42% 28% 22% 7% 1	330
	21st to end	Day	39% 29% 23% 8% 1	363
February	1st to 10th	Day	33% 30% 27% 8% 2	330
	11th to 20th	Day	53% 23% 17% 6% 1	330
	21st to end	Day	40% 27% 27% 6%	273
March	1st to 10th	Day	29% 25% 26% 15% 4	492
	11th to 20th	Day	31% 28% 25% 12% 3 1	500
	21st to end	Day	31% 25% 25% 15% 3	550
April	1st to 10th	Day	30% 22% 26% 13% 8% 1	500
	11th to 20th	Day	26% 20% 27% 17% 9% 1	492
	21st to end	Day	27% 19% 23% 18% 10% 3	500
May	1st to 10th	Day	24% 23% 26% 16% 6% 4	503
	11th to 20th	Day	21% 16% 25% 24% 9% 5%	527
	21st to end	Day	17% 11% 25% 21% 17% 9%	573
June	1st to 10th	Day	14% 9% 28% 26% 17% 7%	530
	11th to 20th	Day	9% 9% 24% 30% 20% 7%	530
	21st to end	Day	12% 10% 28% 26% 17% 7%	530
July	1st to 10th	Day	14% 4 20% 30% 20% 11%	525
	11th to 20th	Day	13% 5% 19% 33% 19% 10%	524
	21st to end	Day	14% 5% 22% 29% 21% 9%	576
August	1st to 10th	Day	15% 7% 23% 24% 19% 12%	526
	11th to 20th	Day	15% 4 21% 27% 22% 11%	519
	21st to end	Day	10% 5% 16% 29% 23% 16%	583
September	1st to 10th	Day	12% 4 20% 27% 25% 12%	530
	11th to 20th	Day	13% 6% 17% 28% 26% 9%	530
	21st to end	Day	20% 11% 23% 24% 17% 5%	530
October	1st to 10th	Day	17% 9% 21% 27% 21% 6%	530
	11th to 20th	Day	18% 17% 22% 25% 15% 2	530
	21st to end	Day	24% 15% 25% 22% 11% 3	583
November	1st to 10th	Day	20% 15% 30% 23% 9% 3	461
	11th to 20th	Day	27% 25% 23% 20% 5%	330
	21st to end	Day	29% 25% 28% 13% 4 1	330
December	1st to 10th	Day	36% 23% 31% 9% 2	330
	11th to 20th	Day	29% 27% 27% 14% 3	330
	21st to end	Day	29% 27% 27% 11% 6%	363
January	1st to 10th	Night	29% 25% 26% 16% 3	840
	11th to 20th	Night	31% 21% 28% 17% 2	840
	21st to end	Night	23% 27% 31% 16% 2	924
February	1st to 10th	Night	25% 20% 32% 22% 2	840
	11th to 20th	Night	32% 26% 29% 12% 1	823
	21st to end	Night	30% 24% 29% 15% 2	692
March	1st to 10th	Night	23% 19% 32% 22% 4	809
	11th to 20th	Night	28% 18% 28% 20% 6% 1	800
	21st to end	Night	24% 18% 32% 20% 6%	880
April	1st to 10th	Night	22% 20% 27% 24% 7%	800
	11th to 20th	Night	21% 16% 27% 27% 9% 1	738
	21st to end	Night	17% 13% 28% 34% 7% 1	600
May	1st to 10th	Night	17% 13% 29% 27% 14% 1	600
	11th to 20th	Night	16% 8% 25% 33% 17% 1	591
	21st to end	Night	14% 6% 18% 31% 27% 5%	650
June	1st to 10th	Night	10% 5% 17% 40% 25% 4	600
	11th to 20th	Night	9% 5% 16% 34% 32% 4	600
	21st to end	Night	11% 5% 13% 39% 30% 3	600
July	1st to 10th	Night	14% 2 10% 32% 38% 4	585
	11th to 20th	Night	11% 3 9% 35% 37% 5%	582
	21st to end	Night	11% 3 12% 31% 36% 7%	657
August	1st to 10th	Night	13% 2 11% 33% 39% 3	597
	11th to 20th	Night	12% 4 9% 32% 37% 6%	594
	21st to end	Night	10% 2 10% 32% 37% 8%	743
September	1st to 10th	Night	12% 3 14% 34% 33% 5%	800
	11th to 20th	Night	14% 5% 15% 29% 33% 5%	800
	21st to end	Night	16% 8% 18% 33% 24% 3	800
October	1st to 10th	Night	17% 8% 17% 28% 25% 5%	800
	11th to 20th	Night	20% 11% 23% 30% 15% 2	800
	21st to end	Night	21% 12% 24% 30% 12% 1	880
November	1st to 10th	Night	16% 10% 28% 29% 16% 2	820
	11th to 20th	Night	22% 15% 25% 28% 9% 1	840
	21st to end	Night	20% 16% 28% 26% 9%	840
December	1st to 10th	Night	27% 21% 27% 21% 4	840
	11th to 20th	Night	25% 19% 28% 23% 4	840
	21st to end	Night	27% 18% 28% 23% 4	924

Page generated at 2026-02-28 01:40:25. Version ac07

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