Chrysalis Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chrysalis Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	126465
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	122930
Transparency	Day	37% 7% 12% 22% 17% 5%	130071
	Night	37% 6% 10% 21% 20% 6%	127393
Seeing	Day	16% 8% 23% 25% 19% 9%	16603
	Night	16% 7% 25% 32% 18% 2	26665

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% 5% 2 5% 2 2 2 2 3 4 56%	4056
	11th to 20th	Day	13% 6% 2 4 2 2 3 3 3 4 58%	4060
	21st to end	Day	16% 7% 3 6% 4 4 3 3 3 4 48%	4466
February	1st to 10th	Day	14% 6% 2 5% 5% 4 4 3 6% 7% 43%	1800
	11th to 20th	Day	20% 7% 2 5% 4 3 4 3 5% 5% 44%	1816
	21st to end	Day	17% 8% 3 6% 4 4 3 3 5% 6% 41%	1750
March	1st to 10th	Day	19% 7% 2 6% 3 4 4 3 5% 7% 41%	4935
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 5% 7% 54%	4980
	21st to end	Day	16% 7% 2 6% 4 3 4 3 4 5% 46%	5465
April	1st to 10th	Day	11% 4 2 4 3 3 4 4 5% 8% 52%	2267
	11th to 20th	Day	13% 6% 2 5% 4 3 3 4 5% 7% 49%	2374
	21st to end	Day	14% 5% 2 5% 4 5% 4 4 6% 6% 44%	2490
May	1st to 10th	Day	10% 6% 3 7% 5% 6% 6% 5% 8% 11% 34%	5862
	11th to 20th	Day	20% 7% 3 7% 4 5% 6% 5% 6% 8% 29%	5861
	21st to end	Day	13% 5% 2 6% 4 5% 5% 4 6% 9% 40%	6433
June	1st to 10th	Day	8% 6% 2 7% 5% 5% 4 5% 7% 11% 41%	2600
	11th to 20th	Day	7% 6% 2 6% 5% 5% 5% 4 8% 11% 40%	2600
	21st to end	Day	7% 4 2 5% 5% 5% 6% 5% 7% 11% 42%	2600
July	1st to 10th	Day	8% 5% 3 7% 5% 6% 6% 5% 7% 10% 39%	5900
	11th to 20th	Day	7% 5% 3 8% 6% 6% 7% 6% 9% 13% 31%	5900
	21st to end	Day	9% 7% 3 8% 6% 6% 6% 5% 7% 10% 33%	6424
August	1st to 10th	Day	17% 8% 2 7% 5% 5% 5% 5% 8% 11% 26%	4234
	11th to 20th	Day	8% 6% 3 7% 6% 6% 6% 5% 8% 11% 35%	4174
	21st to end	Day	6% 4 2 5% 4 4 5% 3 7% 9% 52%	4312
September	1st to 10th	Day	11% 4 2 5% 4 5% 5% 4 6% 7% 48%	2357
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 4 5% 8% 43%	2200
	21st to end	Day	21% 6% 2 7% 3 4 4 4 4 6% 39%	2200
October	1st to 10th	Day	14% 6% 1 5% 3 2 3 2 4 6% 54%	1943
	11th to 20th	Day	13% 5% 2 5% 3 2 3 3 4 5% 55%	1900
	21st to end	Day	12% 5% 2 5% 3 3 3 2 3 6% 56%	2090
November	1st to 10th	Day	12% 6% 2 6% 3 4 3 3 4 4 54%	1957
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 4 7% 52%	1890
	21st to end	Day	13% 5% 2 5% 4 4 4 4 5% 5% 50%	1800
December	1st to 10th	Day	13% 5% 2 4 3 3 4 3 5% 6% 53%	2930
	11th to 20th	Day	17% 6% 2 6% 4 4 4 3 5% 5% 45%	3373
	21st to end	Day	19% 6% 2 5% 3 3 4 4 5% 8% 42%	4466
January	1st to 10th	Night	12% 6% 2 4 2 2 3 2 4 5% 57%	5889
	11th to 20th	Night	12% 6% 2 5% 3 3 3 2 3 4 58%	5900
	21st to end	Night	16% 6% 2 5% 3 3 3 3 4 5% 48%	6490
February	1st to 10th	Night	15% 8% 2 5% 4 4 4 4 5% 6% 44%	2600
	11th to 20th	Night	20% 6% 2 4 3 3 4 3 5% 5% 44%	2468
	21st to end	Night	14% 7% 3 6% 4 3 4 4 5% 6% 45%	1878
March	1st to 10th	Night	17% 7% 2 6% 4 4 4 3 4 5% 45%	4918
	11th to 20th	Night	10% 4 1 5% 3 3 3 3 5% 7% 56%	4980
	21st to end	Night	15% 5% 2 5% 4 4 4 3 5% 7% 48%	5467
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 6% 7% 48%	2131
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 5% 8% 49%	1975
	21st to end	Night	14% 6% 1 5% 4 4 5% 4 5% 7% 45%	1926
May	1st to 10th	Night	13% 6% 3 8% 5% 5% 5% 4 6% 9% 37%	4033
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 5% 8% 36%	4032
	21st to end	Night	16% 5% 2 5% 4 3 4 3 6% 10% 43%	4421
June	1st to 10th	Night	9% 5% 3 6% 5% 4 6% 5% 7% 11% 40%	1800
	11th to 20th	Night	8% 5% 2 6% 5% 5% 6% 5% 7% 11% 41%	1800
	21st to end	Night	7% 5% 2 4 4 5% 6% 4 8% 11% 43%	1800
July	1st to 10th	Night	10% 7% 3 9% 5% 6% 6% 5% 8% 9% 33%	4058
	11th to 20th	Night	9% 8% 3 9% 6% 7% 7% 5% 8% 10% 27%	4057
	21st to end	Night	11% 7% 3 7% 6% 6% 6% 5% 8% 10% 32%	4427
August	1st to 10th	Night	20% 7% 3 8% 5% 5% 6% 4 7% 9% 25%	2915
	11th to 20th	Night	8% 6% 2 7% 5% 5% 5% 6% 8% 11% 38%	2875
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 6% 8% 50%	3553
September	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 6% 7% 48%	2038
	11th to 20th	Night	14% 6% 2 6% 4 5% 4 4 5% 7% 43%	2200
	21st to end	Night	19% 8% 2 6% 4 4 5% 4 5% 5% 37%	2200
October	1st to 10th	Night	15% 6% 2 6% 4 4 3 2 4 6% 49%	2303
	11th to 20th	Night	13% 6% 1 4 3 3 3 3 4 5% 55%	2280
	21st to end	Night	13% 5% 2 4 4 3 2 2 3 5% 57%	2508
November	1st to 10th	Night	14% 6% 2 5% 4 2 2 2 4 4 54%	2341
	11th to 20th	Night	13% 5% 2 5% 4 4 4 3 4 5% 52%	2505
	21st to end	Night	13% 5% 2 4 3 3 4 3 5% 6% 52%	2600
December	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 4 6% 52%	4250
	11th to 20th	Night	20% 8% 3 6% 4 4 4 3 3 4 40%	4822
	21st to end	Night	19% 5% 2 4 3 3 4 4 5% 7% 45%	6490

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	33% 2 5% 22% 29% 9%	4057
	11th to 20th	Day	31% 3 4 19% 35% 9%	4060
	21st to end	Day	41% 3 5% 23% 23% 5%	4466
February	1st to 10th	Day	39% 5% 11% 21% 19% 4	1800
	11th to 20th	Day	42% 4 7% 23% 19% 6%	1825
	21st to end	Day	43% 4 11% 15% 20% 7%	1750
March	1st to 10th	Day	43% 4 7% 18% 17% 11%	4935
	11th to 20th	Day	30% 5% 6% 20% 23% 16%	4980
	21st to end	Day	41% 4 8% 22% 20% 6%	5465
April	1st to 10th	Day	30% 4 12% 23% 23% 7%	2267
	11th to 20th	Day	35% 5% 11% 21% 21% 7%	2374
	21st to end	Day	39% 7% 11% 25% 15% 3	2490
May	1st to 10th	Day	41% 9% 17% 20% 11% 2	5897
	11th to 20th	Day	51% 9% 11% 21% 8% 1	5865
	21st to end	Day	38% 8% 13% 21% 17% 3	6447
June	1st to 10th	Day	35% 8% 17% 26% 14% 1	2600
	11th to 20th	Day	35% 9% 18% 22% 14% 2	2600
	21st to end	Day	33% 9% 19% 23% 15% 1	2600
July	1st to 10th	Day	37% 12% 16% 20% 13% 2	5835
	11th to 20th	Day	39% 13% 24% 18% 4 1	5831
	21st to end	Day	43% 11% 16% 21% 9%	6240
August	1st to 10th	Day	49% 9% 18% 19% 5%	4221
	11th to 20th	Day	38% 11% 21% 21% 9% 1	4213
	21st to end	Day	26% 8% 16% 34% 14% 2	4312
September	1st to 10th	Day	34% 8% 14% 22% 18% 5%	2357
	11th to 20th	Day	38% 6% 12% 22% 20% 2	2200
	21st to end	Day	46% 6% 10% 18% 17% 3	2200
October	1st to 10th	Day	31% 5% 7% 20% 27% 10%	3203
	11th to 20th	Day	21% 3 5% 22% 25% 23%	3140
	21st to end	Day	24% 4 8% 26% 23% 15%	3428
November	1st to 10th	Day	34% 3 8% 22% 25% 8%	1957
	11th to 20th	Day	33% 3 8% 24% 25% 7%	1890
	21st to end	Day	35% 4 9% 22% 26% 4	1800
December	1st to 10th	Day	32% 5% 7% 22% 27% 8%	2930
	11th to 20th	Day	41% 4 10% 17% 23% 5%	3370
	21st to end	Day	40% 5% 11% 26% 17% 1	4466
January	1st to 10th	Night	31% 2 6% 19% 31% 11%	5889
	11th to 20th	Night	32% 3 5% 17% 35% 8%	5900
	21st to end	Night	38% 3 6% 23% 25% 5%	6490
February	1st to 10th	Night	41% 4 9% 22% 20% 4	2600
	11th to 20th	Night	43% 3 8% 18% 21% 7%	2470
	21st to end	Night	39% 5% 9% 20% 20% 7%	1878
March	1st to 10th	Night	42% 4 6% 16% 23% 10%	4918
	11th to 20th	Night	29% 4 6% 18% 25% 17%	4980
	21st to end	Night	37% 4 7% 26% 21% 4	5467
April	1st to 10th	Night	36% 4 11% 19% 24% 5%	2131
	11th to 20th	Night	34% 4 10% 22% 22% 8%	1975
	21st to end	Night	37% 5% 12% 24% 18% 4	1926
May	1st to 10th	Night	42% 8% 15% 20% 13% 1	4060
	11th to 20th	Night	48% 8% 11% 20% 13% 1	4033
	21st to end	Night	36% 7% 14% 27% 13% 3	4429
June	1st to 10th	Night	36% 10% 15% 23% 15% 2	1800
	11th to 20th	Night	35% 9% 17% 23% 14% 2	1800
	21st to end	Night	33% 10% 18% 22% 15% 3	1800
July	1st to 10th	Night	43% 13% 14% 16% 12% 1	4015
	11th to 20th	Night	48% 15% 19% 13% 4 1	4006
	21st to end	Night	44% 10% 16% 21% 7%	4297
August	1st to 10th	Night	52% 9% 17% 16% 6%	2904
	11th to 20th	Night	35% 10% 22% 22% 10% 1	2902
	21st to end	Night	30% 8% 12% 33% 15% 2	3553
September	1st to 10th	Night	33% 9% 14% 21% 16% 5%	2038
	11th to 20th	Night	40% 7% 11% 19% 21% 2	2200
	21st to end	Night	48% 6% 10% 17% 15% 3	2200
October	1st to 10th	Night	38% 5% 8% 18% 24% 7%	3823
	11th to 20th	Night	23% 3 6% 23% 29% 17%	3779
	21st to end	Night	24% 3 6% 26% 25% 16%	4120
November	1st to 10th	Night	35% 4 7% 20% 25% 9%	2341
	11th to 20th	Night	35% 4 7% 19% 25% 10%	2505
	21st to end	Night	33% 4 6% 24% 26% 6%	2600
December	1st to 10th	Night	34% 4 7% 21% 30% 4	4250
	11th to 20th	Night	48% 4 7% 17% 15% 9%	4824
	21st to end	Night	38% 5% 13% 22% 21% 2	6490

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% 18% 34% 15% 7% 1	300
	11th to 20th	Day	21% 20% 36% 18% 5%	300
	21st to end	Day	18% 18% 42% 18% 4	330
February	1st to 10th	Day	16% 18% 42% 16% 8% 1	300
	11th to 20th	Day	35% 17% 33% 11% 4	300
	21st to end	Day	24% 19% 34% 20% 3	349
March	1st to 10th	Day	22% 14% 32% 25% 6% 1	500
	11th to 20th	Day	21% 12% 40% 21% 6% 1	500
	21st to end	Day	22% 14% 35% 23% 5% 1	550
April	1st to 10th	Day	19% 16% 31% 22% 11% 1	500
	11th to 20th	Day	14% 14% 30% 24% 14% 3	492
	21st to end	Day	18% 12% 26% 26% 16% 2	500
May	1st to 10th	Day	17% 13% 27% 26% 13% 4	503
	11th to 20th	Day	17% 5% 20% 27% 22% 9%	527
	21st to end	Day	17% 5% 16% 27% 22% 13%	573
June	1st to 10th	Day	10% 4 18% 32% 24% 12%	530
	11th to 20th	Day	10% 3 16% 29% 23% 19%	530
	21st to end	Day	8% 2 12% 30% 33% 14%	530
July	1st to 10th	Day	10% 2 9% 26% 33% 20%	525
	11th to 20th	Day	5% 1 8% 26% 35% 25%	524
	21st to end	Day	8% 2 9% 26% 36% 19%	576
August	1st to 10th	Day	17% 2 13% 23% 28% 16%	526
	11th to 20th	Day	9% 1 11% 27% 31% 20%	519
	21st to end	Day	10% 3 9% 25% 33% 21%	583
September	1st to 10th	Day	13% 2 13% 23% 28% 21%	530
	11th to 20th	Day	16% 3 13% 23% 26% 20%	530
	21st to end	Day	26% 4 19% 26% 19% 6%	530
October	1st to 10th	Day	18% 4 15% 31% 22% 10%	502
	11th to 20th	Day	14% 7% 22% 28% 23% 6%	490
	21st to end	Day	14% 7% 23% 32% 19% 5%	539
November	1st to 10th	Day	18% 7% 28% 26% 17% 4	495
	11th to 20th	Day	17% 11% 33% 22% 14% 3	390
	21st to end	Day	13% 15% 29% 26% 12% 4	300
December	1st to 10th	Day	21% 13% 37% 24% 5% 1	300
	11th to 20th	Day	17% 11% 33% 28% 9% 2	300
	21st to end	Day	25% 15% 27% 20% 11% 2	330
January	1st to 10th	Night	19% 12% 38% 27% 5%	800
	11th to 20th	Night	19% 11% 39% 28% 4	800
	21st to end	Night	17% 9% 42% 30% 3	880
February	1st to 10th	Night	19% 12% 39% 28% 3	800
	11th to 20th	Night	25% 12% 39% 21% 2	783
	21st to end	Night	18% 14% 37% 27% 4	660
March	1st to 10th	Night	17% 13% 36% 29% 5%	800
	11th to 20th	Night	20% 12% 37% 25% 6% 1	800
	21st to end	Night	18% 8% 38% 30% 5%	880
April	1st to 10th	Night	16% 14% 34% 29% 7%	800
	11th to 20th	Night	15% 10% 34% 29% 12%	791
	21st to end	Night	15% 6% 31% 37% 10%	726
May	1st to 10th	Night	11% 8% 30% 35% 15% 1	600
	11th to 20th	Night	14% 6% 23% 33% 22% 2	591
	21st to end	Night	15% 2 12% 36% 32% 3	650
June	1st to 10th	Night	11% 2 15% 40% 30% 3	600
	11th to 20th	Night	11% 1 13% 36% 33% 6%	600
	21st to end	Night	10% 1 11% 37% 39% 3	600
July	1st to 10th	Night	11% 3 6% 33% 41% 6%	585
	11th to 20th	Night	7% 2 7% 32% 46% 7%	582
	21st to end	Night	9% 3 6% 38% 36% 8%	657
August	1st to 10th	Night	16% 3 7% 32% 36% 7%	597
	11th to 20th	Night	13% 2 7% 31% 41% 7%	594
	21st to end	Night	11% 2 7% 31% 40% 9%	860
September	1st to 10th	Night	13% 2 8% 34% 36% 8%	800
	11th to 20th	Night	17% 2 9% 31% 35% 7%	800
	21st to end	Night	22% 3 15% 33% 25% 3	800
October	1st to 10th	Night	16% 3 16% 32% 27% 6%	773
	11th to 20th	Night	15% 6% 26% 32% 19% 2	760
	21st to end	Night	14% 6% 25% 35% 19% 1	836
November	1st to 10th	Night	17% 6% 22% 38% 16% 2	780
	11th to 20th	Night	15% 7% 31% 36% 11%	800
	21st to end	Night	15% 7% 31% 34% 12% 1	800
December	1st to 10th	Night	21% 9% 32% 31% 7%	800
	11th to 20th	Night	20% 6% 34% 32% 7%	800
	21st to end	Night	22% 9% 27% 34% 8%	880

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