Loon Call Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Loon Call Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	16% 11% 4 9% 5% 4 4 3 5% 6% 32%	127665
	Night	16% 12% 4 9% 5% 5% 4 3 5% 6% 30%	123664
Transparency	Day	52% 5% 10% 20% 11% 1	131207
	Night	52% 6% 11% 19% 11% 1	128208
Seeing	Day	24% 16% 31% 18% 8% 3	15808
	Night	22% 14% 31% 23% 9% 1	25112

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	12% 16% 5% 12% 6% 4 5% 4 6% 6% 25%	3605
	11th to 20th	Day	10% 20% 9% 17% 7% 6% 5% 3 3 4 15%	3570
	21st to end	Day	14% 18% 7% 17% 6% 5% 4 3 4 4 18%	4447
February	1st to 10th	Day	13% 17% 5% 15% 7% 5% 4 4 5% 4 21%	1800
	11th to 20th	Day	13% 15% 6% 13% 6% 5% 4 3 4 5% 26%	1753
	21st to end	Day	17% 17% 5% 10% 7% 5% 4 3 4 5% 24%	1567
March	1st to 10th	Day	19% 14% 5% 10% 5% 4 4 2 4 6% 27%	4770
	11th to 20th	Day	11% 15% 5% 9% 5% 5% 5% 4 6% 7% 28%	4980
	21st to end	Day	19% 13% 4 7% 4 3 3 2 3 4 38%	5570
April	1st to 10th	Day	20% 14% 4 8% 5% 4 4 3 4 6% 29%	2400
	11th to 20th	Day	21% 12% 2 6% 5% 4 3 2 5% 5% 36%	2374
	21st to end	Day	22% 11% 3 8% 5% 3 4 3 4 5% 33%	2599
May	1st to 10th	Day	22% 9% 3 7% 5% 4 4 3 5% 6% 32%	6197
	11th to 20th	Day	18% 10% 3 7% 4 5% 4 3 4 7% 33%	6318
	21st to end	Day	19% 9% 3 7% 4 4 4 4 5% 7% 34%	6949
June	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 4 5% 7% 31%	2800
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 8% 36%	2800
	21st to end	Day	17% 8% 2 6% 5% 5% 5% 4 6% 8% 35%	2800
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 9% 37%	6360
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 45%	6360
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 7% 9% 46%	6895
August	1st to 10th	Day	15% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	4234
	11th to 20th	Day	17% 7% 3 7% 5% 5% 5% 4 6% 9% 32%	4174
	21st to end	Day	11% 6% 2 7% 4 5% 5% 5% 7% 9% 40%	4393
September	1st to 10th	Day	15% 7% 2 6% 5% 4 4 4 6% 8% 40%	2400
	11th to 20th	Day	12% 5% 2 6% 5% 4 3 4 5% 7% 48%	2400
	21st to end	Day	19% 6% 2 7% 5% 5% 4 4 5% 7% 36%	2085
October	1st to 10th	Day	20% 9% 3 6% 5% 4 4 3 4 7% 35%	2000
	11th to 20th	Day	23% 11% 3 9% 6% 4 4 3 6% 6% 27%	2000
	21st to end	Day	27% 13% 3 8% 5% 4 4 3 3 6% 24%	2155
November	1st to 10th	Day	17% 11% 4 7% 5% 4 5% 3 5% 7% 31%	1756
	11th to 20th	Day	16% 15% 5% 9% 5% 4 4 4 6% 6% 26%	1680
	21st to end	Day	20% 20% 7% 9% 5% 4 4 3 4 4 19%	1680
December	1st to 10th	Day	18% 24% 7% 12% 6% 5% 3 3 4 5% 14%	2680
	11th to 20th	Day	17% 21% 7% 13% 5% 4 3 3 3 4 22%	3066
	21st to end	Day	22% 21% 6% 11% 5% 4 2 2 2 5% 20%	4048
January	1st to 10th	Night	15% 16% 8% 13% 6% 5% 4 3 5% 6% 21%	6364
	11th to 20th	Night	11% 16% 7% 17% 10% 7% 6% 4 4 5% 14%	6315
	21st to end	Night	13% 16% 8% 15% 6% 5% 4 3 4 5% 19%	6508
February	1st to 10th	Night	12% 17% 5% 11% 7% 5% 5% 4 6% 7% 21%	2600
	11th to 20th	Night	12% 15% 6% 11% 6% 5% 5% 3 5% 4 28%	2533
	21st to end	Night	13% 16% 4 9% 6% 5% 4 4 6% 7% 27%	2062
March	1st to 10th	Night	18% 14% 4 11% 5% 4 3 3 4 5% 29%	5055
	11th to 20th	Night	10% 13% 5% 9% 5% 6% 5% 4 7% 7% 29%	4979
	21st to end	Night	19% 10% 4 8% 5% 4 4 3 5% 6% 32%	5361
April	1st to 10th	Night	19% 12% 3 8% 5% 4 4 3 5% 6% 31%	2000
	11th to 20th	Night	18% 9% 3 8% 5% 3 4 3 4 6% 37%	1975
	21st to end	Night	19% 10% 3 7% 4 5% 5% 4 6% 6% 33%	1818
May	1st to 10th	Night	24% 8% 2 6% 5% 4 5% 4 5% 6% 32%	3742
	11th to 20th	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	3575
	21st to end	Night	18% 8% 3 7% 5% 5% 4 3 5% 6% 37%	3926
June	1st to 10th	Night	16% 7% 3 8% 4 4 5% 5% 6% 7% 36%	1600
	11th to 20th	Night	12% 6% 2 4 5% 5% 5% 4 6% 8% 43%	1600
	21st to end	Night	15% 7% 3 6% 5% 5% 5% 3 5% 7% 38%	1600
July	1st to 10th	Night	11% 6% 2 7% 5% 6% 6% 4 6% 8% 39%	3600
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 4 7% 49%	3600
	21st to end	Night	9% 6% 2 5% 3 4 4 4 5% 8% 51%	3940
August	1st to 10th	Night	12% 5% 2 6% 3 4 4 5% 6% 8% 46%	2915
	11th to 20th	Night	14% 7% 2 5% 4 4 5% 4 5% 7% 44%	2875
	21st to end	Night	11% 5% 2 6% 4 5% 4 3 6% 9% 45%	3472
September	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 9% 46%	2000
	11th to 20th	Night	12% 4 2 4 3 4 4 4 5% 7% 52%	2000
	21st to end	Night	20% 6% 2 6% 4 3 4 3 5% 5% 41%	2309
October	1st to 10th	Night	18% 6% 3 7% 4 4 4 3 5% 7% 39%	2400
	11th to 20th	Night	20% 10% 3 8% 6% 4 4 4 5% 5% 31%	2400
	21st to end	Night	21% 13% 3 7% 5% 5% 4 4 6% 6% 27%	2685
November	1st to 10th	Night	17% 11% 3 8% 5% 5% 4 3 5% 6% 33%	2757
	11th to 20th	Night	17% 14% 4 9% 5% 4 4 3 5% 6% 29%	2940
	21st to end	Night	19% 17% 5% 10% 5% 5% 4 4 5% 6% 20%	2940
December	1st to 10th	Night	19% 19% 7% 11% 5% 5% 4 3 5% 5% 16%	4720
	11th to 20th	Night	18% 19% 7% 14% 5% 4 4 3 4 4 19%	5348
	21st to end	Night	24% 19% 5% 12% 5% 4 3 3 3 4 17%	7150

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	58% 4 9% 19% 9% 1	3606
	11th to 20th	Day	72% 5% 8% 8% 6% 1	3600
	21st to end	Day	70% 4 6% 10% 9% 1	4447
February	1st to 10th	Day	65% 6% 9% 14% 6% 1	1800
	11th to 20th	Day	61% 5% 9% 13% 11% 2	1762
	21st to end	Day	63% 4 9% 12% 10% 1	1567
March	1st to 10th	Day	58% 4 11% 10% 14% 1	4773
	11th to 20th	Day	55% 5% 14% 15% 8% 2	4980
	21st to end	Day	51% 4 6% 20% 16% 3	5570
April	1st to 10th	Day	57% 4 7% 18% 12% 3	2400
	11th to 20th	Day	52% 4 7% 20% 16% 1	2374
	21st to end	Day	55% 5% 7% 18% 13% 3	2599
May	1st to 10th	Day	52% 5% 8% 20% 11% 4	6207
	11th to 20th	Day	50% 7% 8% 17% 17% 1	6322
	21st to end	Day	50% 6% 11% 20% 12% 2	6949
June	1st to 10th	Day	52% 6% 9% 19% 13% 1	2800
	11th to 20th	Day	43% 7% 10% 24% 13% 2	2800
	21st to end	Day	46% 7% 14% 20% 12% 1	2800
July	1st to 10th	Day	42% 6% 14% 26% 12% 1	6290
	11th to 20th	Day	36% 6% 12% 29% 17%	6285
	21st to end	Day	33% 7% 12% 36% 12%	6697
August	1st to 10th	Day	47% 7% 12% 23% 11%	4221
	11th to 20th	Day	46% 6% 13% 26% 8%	4213
	21st to end	Day	38% 6% 12% 33% 10% 1	4393
September	1st to 10th	Day	41% 7% 11% 29% 12% 1	2400
	11th to 20th	Day	36% 7% 11% 31% 15% 1	2400
	21st to end	Day	47% 7% 12% 23% 11%	2085
October	1st to 10th	Day	45% 5% 10% 28% 11% 1	3260
	11th to 20th	Day	49% 5% 12% 20% 12% 1	3240
	21st to end	Day	58% 5% 11% 19% 7%	3457
November	1st to 10th	Day	53% 6% 13% 20% 7% 1	1756
	11th to 20th	Day	57% 6% 12% 15% 10% 2	1680
	21st to end	Day	68% 6% 9% 10% 7% 1	1680
December	1st to 10th	Day	73% 4 11% 8% 4	2680
	11th to 20th	Day	67% 5% 7% 13% 6%	3066
	21st to end	Day	69% 3 6% 14% 8%	4048
January	1st to 10th	Night	64% 4 9% 15% 8%	6364
	11th to 20th	Night	70% 7% 8% 9% 6% 1	6360
	21st to end	Night	67% 5% 8% 8% 12% 1	6508
February	1st to 10th	Night	61% 5% 11% 15% 7% 1	2600
	11th to 20th	Night	58% 4 11% 18% 9% 1	2535
	21st to end	Night	55% 6% 10% 19% 9% 1	2062
March	1st to 10th	Night	58% 3 8% 15% 11% 5%	5065
	11th to 20th	Night	51% 6% 17% 17% 8% 2	4980
	21st to end	Night	50% 5% 11% 18% 14% 2	5361
April	1st to 10th	Night	55% 4 7% 19% 12% 2	2000
	11th to 20th	Night	48% 5% 8% 23% 15% 1	1975
	21st to end	Night	50% 6% 9% 16% 16% 2	1818
May	1st to 10th	Night	52% 5% 9% 17% 12% 5%	3748
	11th to 20th	Night	40% 8% 13% 20% 16% 2	3576
	21st to end	Night	47% 7% 11% 20% 14% 1	3927
June	1st to 10th	Night	45% 7% 12% 21% 14% 1	1600
	11th to 20th	Night	38% 7% 11% 24% 18% 1	1600
	21st to end	Night	44% 7% 13% 22% 12% 2	1600
July	1st to 10th	Night	41% 6% 15% 21% 15% 1	3560
	11th to 20th	Night	35% 5% 12% 32% 15%	3552
	21st to end	Night	31% 7% 12% 36% 14%	3823
August	1st to 10th	Night	35% 7% 14% 26% 16% 1	2904
	11th to 20th	Night	39% 7% 17% 25% 11% 1	2902
	21st to end	Night	35% 6% 13% 32% 12% 2	3472
September	1st to 10th	Night	34% 8% 15% 28% 14% 1	2000
	11th to 20th	Night	31% 6% 15% 33% 14% 1	2000
	21st to end	Night	44% 6% 9% 28% 12%	2309
October	1st to 10th	Night	37% 5% 9% 29% 19%	3920
	11th to 20th	Night	46% 5% 15% 24% 10%	3899
	21st to end	Night	51% 6% 13% 22% 8%	4333
November	1st to 10th	Night	50% 5% 13% 22% 9%	2757
	11th to 20th	Night	55% 6% 11% 18% 9% 1	2940
	21st to end	Night	63% 6% 12% 14% 5%	2940
December	1st to 10th	Night	68% 6% 11% 12% 3	4720
	11th to 20th	Night	69% 4 8% 12% 7%	5348
	21st to end	Night	71% 4 6% 10% 8%	7150

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	22% 23% 34% 17% 3	202
	11th to 20th	Day	31% 17% 34% 16% 3 1	200
	21st to end	Day	29% 20% 34% 13% 3	327
February	1st to 10th	Day	32% 24% 32% 10% 2	300
	11th to 20th	Day	33% 27% 33% 6% 1	300
	21st to end	Day	36% 18% 35% 10% 1	331
March	1st to 10th	Day	26% 21% 36% 14% 3	500
	11th to 20th	Day	27% 20% 35% 13% 4 1	500
	21st to end	Day	34% 18% 29% 13% 5% 1	550
April	1st to 10th	Day	30% 20% 32% 12% 6%	500
	11th to 20th	Day	34% 22% 22% 12% 8% 2	492
	21st to end	Day	30% 20% 30% 13% 5% 1	500
May	1st to 10th	Day	27% 16% 32% 17% 4 4	503
	11th to 20th	Day	23% 15% 35% 17% 7% 3	527
	21st to end	Day	20% 18% 32% 18% 9% 3	573
June	1st to 10th	Day	24% 15% 32% 22% 7% 1	530
	11th to 20th	Day	17% 13% 37% 22% 9% 2	530
	21st to end	Day	25% 11% 35% 18% 9% 2	530
July	1st to 10th	Day	14% 10% 33% 28% 14% 2	525
	11th to 20th	Day	14% 13% 32% 23% 14% 3	524
	21st to end	Day	12% 12% 34% 26% 11% 3	576
August	1st to 10th	Day	14% 8% 30% 31% 13% 5%	526
	11th to 20th	Day	15% 7% 26% 32% 13% 6%	519
	21st to end	Day	15% 10% 33% 23% 13% 6%	583
September	1st to 10th	Day	16% 12% 31% 21% 13% 7%	530
	11th to 20th	Day	11% 11% 25% 21% 19% 13%	530
	21st to end	Day	21% 13% 25% 24% 12% 5%	530
October	1st to 10th	Day	26% 15% 24% 19% 13% 3	530
	11th to 20th	Day	27% 22% 29% 14% 5% 2	530
	21st to end	Day	33% 19% 29% 16% 3 1	558
November	1st to 10th	Day	31% 16% 31% 16% 6%	330
	11th to 20th	Day	30% 25% 30% 10% 4 2	220
	21st to end	Day	32% 20% 35% 9% 3	220
December	1st to 10th	Day	30% 21% 31% 15% 2	220
	11th to 20th	Day	37% 23% 28% 10% 1 1	220
	21st to end	Day	37% 19% 28% 11% 4 1	242
January	1st to 10th	Night	28% 20% 32% 16% 4	805
	11th to 20th	Night	29% 17% 30% 19% 5%	800
	21st to end	Night	21% 16% 34% 22% 6% 1	880
February	1st to 10th	Night	23% 21% 34% 20% 2	800
	11th to 20th	Night	24% 19% 36% 18% 3	783
	21st to end	Night	24% 20% 34% 18% 3	660
March	1st to 10th	Night	26% 18% 35% 18% 3	800
	11th to 20th	Night	23% 20% 33% 19% 4 1	800
	21st to end	Night	23% 15% 33% 20% 8% 1	880
April	1st to 10th	Night	27% 15% 32% 22% 5%	800
	11th to 20th	Night	25% 18% 29% 20% 8% 1	791
	21st to end	Night	24% 11% 32% 22% 11%	618
May	1st to 10th	Night	24% 10% 29% 26% 11% 1	470
	11th to 20th	Night	16% 12% 32% 30% 9%	394
	21st to end	Night	15% 8% 35% 29% 12% 1	433
June	1st to 10th	Night	18% 8% 34% 31% 10%	400
	11th to 20th	Night	15% 12% 29% 33% 11% 1	400
	21st to end	Night	18% 8% 29% 34% 11%	400
July	1st to 10th	Night	7% 6% 33% 40% 14% 1	390
	11th to 20th	Night	11% 6% 29% 37% 16% 1	388
	21st to end	Night	13% 4 30% 38% 14% 1	440
August	1st to 10th	Night	12% 4 23% 35% 25% 2	597
	11th to 20th	Night	12% 4 21% 34% 25% 3	594
	21st to end	Night	12% 6% 30% 30% 19% 2	805
September	1st to 10th	Night	13% 7% 32% 29% 16% 3	800
	11th to 20th	Night	12% 5% 25% 30% 23% 4	800
	21st to end	Night	23% 9% 22% 26% 16% 3	800
October	1st to 10th	Night	21% 11% 29% 23% 15% 2	800
	11th to 20th	Night	27% 14% 30% 20% 8% 1	800
	21st to end	Night	29% 15% 30% 20% 5%	880
November	1st to 10th	Night	25% 13% 30% 23% 8%	820
	11th to 20th	Night	25% 16% 33% 17% 7% 1	840
	21st to end	Night	31% 16% 29% 19% 5%	840
December	1st to 10th	Night	30% 19% 32% 15% 4	840
	11th to 20th	Night	27% 20% 34% 16% 3 1	840
	21st to end	Night	34% 14% 32% 17% 3	924

Page generated at 2025-12-30 01:14:05. Version ac07

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