Leitner Observatory and Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leitner Observatory and Planetarium clear sky chart from 2005-11-06 to 2025-09-19.

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	18% 7% 2 6% 4 4 4 4 5% 7% 40%	126121
	Night	19% 8% 2 6% 4 3 4 3 5% 6% 42%	122931
Transparency	Day	42% 6% 12% 22% 16% 3	129650
	Night	43% 5% 12% 22% 16% 3	127489
Seeing	Day	21% 16% 31% 22% 8% 2	16152
	Night	21% 13% 32% 25% 8% 1	25148

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	14% 6% 2 5% 4 5% 4 4 5% 5% 46%	3597
	11th to 20th	Day	15% 8% 3 6% 4 4 4 4 5% 5% 43%	3570
	21st to end	Day	18% 7% 3 8% 5% 4 4 3 4 5% 40%	4098
February	1st to 10th	Day	17% 7% 3 6% 5% 5% 5% 4 5% 6% 38%	1870
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 6% 7% 42%	1948
	21st to end	Day	21% 8% 3 5% 4 4 3 3 6% 6% 38%	1650
March	1st to 10th	Day	23% 8% 2 5% 3 3 3 3 4 5% 41%	4476
	11th to 20th	Day	15% 8% 2 5% 4 3 4 4 6% 7% 43%	4665
	21st to end	Day	20% 8% 2 6% 4 4 4 4 5% 6% 38%	5970
April	1st to 10th	Day	20% 8% 2 5% 4 4 4 3 5% 7% 38%	2400
	11th to 20th	Day	20% 6% 2 6% 3 4 4 3 3 7% 42%	2374
	21st to end	Day	20% 5% 2 5% 4 4 4 4 5% 6% 41%	2505
May	1st to 10th	Day	30% 8% 2 5% 3 3 3 3 6% 8% 28%	5886
	11th to 20th	Day	23% 8% 2 6% 4 4 4 3 5% 7% 35%	6124
	21st to end	Day	21% 6% 3 5% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	18% 5% 2 6% 4 4 5% 5% 6% 8% 37%	2800
	11th to 20th	Day	17% 6% 2 5% 4 4 4 4 6% 10% 37%	2800
	21st to end	Day	13% 7% 2 5% 5% 4 5% 4 6% 9% 40%	2800
July	1st to 10th	Day	15% 7% 2 7% 5% 4 5% 4 7% 10% 35%	6360
	11th to 20th	Day	14% 6% 2 7% 4 4 5% 4 7% 10% 36%	6360
	21st to end	Day	15% 7% 2 6% 4 4 4 3 5% 8% 42%	6926
August	1st to 10th	Day	19% 6% 2 6% 5% 5% 5% 4 6% 8% 34%	4382
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 9% 44%	3856
	21st to end	Day	8% 5% 2 6% 5% 4 4 4 6% 10% 47%	4312
September	1st to 10th	Day	14% 5% 2 5% 5% 4 4 4 5% 6% 46%	2400
	11th to 20th	Day	13% 5% 2 4 3 4 4 3 5% 6% 52%	2240
	21st to end	Day	20% 6% 2 5% 5% 4 4 3 4 6% 41%	2090
October	1st to 10th	Day	21% 7% 2 5% 4 3 3 3 4 6% 41%	2061
	11th to 20th	Day	15% 4 1 5% 4 3 3 4 5% 7% 48%	1889
	21st to end	Day	20% 6% 1 4 4 4 4 4 5% 7% 41%	1881
November	1st to 10th	Day	13% 7% 2 5% 4 4 2 3 4 6% 50%	1761
	11th to 20th	Day	19% 6% 2 4 2 3 3 2 5% 7% 48%	1800
	21st to end	Day	17% 6% 2 5% 4 3 4 3 6% 6% 44%	1775
December	1st to 10th	Day	16% 6% 2 5% 4 4 3 4 4 7% 46%	2600
	11th to 20th	Day	22% 7% 2 4 3 2 3 2 4 6% 46%	2986
	21st to end	Day	20% 9% 3 6% 4 3 3 3 4 6% 40%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 4 3 4 5% 6% 49%	6349
	11th to 20th	Night	15% 8% 3 7% 4 3 3 3 4 5% 46%	6315
	21st to end	Night	18% 9% 3 6% 4 4 4 4 4 5% 39%	6843
February	1st to 10th	Night	17% 9% 3 6% 4 3 3 3 4 5% 41%	2528
	11th to 20th	Night	18% 8% 3 5% 4 3 3 3 4 7% 42%	2338
	21st to end	Night	20% 8% 3 6% 4 3 4 3 3 6% 41%	1980
March	1st to 10th	Night	21% 10% 2 5% 3 3 3 3 4 5% 41%	5364
	11th to 20th	Night	17% 10% 3 5% 4 4 3 3 4 6% 42%	5288
	21st to end	Night	21% 9% 3 6% 4 3 3 3 5% 5% 39%	4962
April	1st to 10th	Night	20% 7% 2 6% 4 5% 4 4 6% 7% 37%	2000
	11th to 20th	Night	21% 6% 2 5% 4 3 3 3 5% 6% 42%	1975
	21st to end	Night	20% 7% 2 7% 4 3 4 3 4 5% 42%	1895
May	1st to 10th	Night	29% 11% 3 6% 4 3 4 3 5% 6% 27%	4054
	11th to 20th	Night	23% 9% 3 6% 4 4 4 4 5% 7% 33%	3810
	21st to end	Night	24% 9% 3 6% 4 4 4 3 4 6% 34%	3926
June	1st to 10th	Night	19% 6% 2 6% 5% 4 4 4 5% 6% 39%	1600
	11th to 20th	Night	17% 7% 2 5% 4 3 4 4 5% 9% 39%	1600
	21st to end	Night	14% 6% 2 6% 4 5% 4 3 5% 9% 43%	1600
July	1st to 10th	Night	17% 8% 2 7% 4 4 4 4 6% 8% 36%	3600
	11th to 20th	Night	20% 9% 2 6% 4 4 5% 4 6% 8% 32%	3600
	21st to end	Night	16% 6% 2 6% 4 4 4 3 6% 7% 43%	3926
August	1st to 10th	Night	23% 6% 2 7% 4 5% 5% 5% 6% 7% 30%	2734
	11th to 20th	Night	15% 6% 3 7% 4 4 6% 4 5% 7% 40%	3188
	21st to end	Night	10% 4 1 4 3 3 4 3 5% 8% 55%	3586
September	1st to 10th	Night	15% 5% 3 5% 4 4 4 3 4 8% 44%	2000
	11th to 20th	Night	15% 5% 2 4 3 3 4 3 4 6% 52%	2116
	21st to end	Night	18% 7% 3 5% 4 4 4 3 4 5% 43%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 4 4 2 4 6% 41%	2117
	11th to 20th	Night	15% 5% 2 6% 3 3 3 2 5% 6% 50%	2289
	21st to end	Night	22% 7% 2 5% 3 3 4 3 5% 5% 42%	2717
November	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 5% 6% 50%	2537
	11th to 20th	Night	19% 7% 2 4 3 3 3 3 4 6% 48%	2600
	21st to end	Night	16% 5% 1 5% 4 4 4 3 5% 7% 46%	2620
December	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 4 4 49%	4580
	11th to 20th	Night	26% 6% 2 4 3 3 4 2 3 4 42%	5208
	21st to end	Night	20% 10% 3 6% 3 3 3 3 3 5% 42%	6996

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	38% 5% 8% 28% 18% 3	3598
	11th to 20th	Day	41% 4 11% 22% 15% 7%	3600
	21st to end	Day	46% 6% 9% 22% 15% 2	4098
February	1st to 10th	Day	45% 6% 13% 20% 14% 2	1870
	11th to 20th	Day	41% 5% 11% 23% 16% 3	1957
	21st to end	Day	46% 6% 11% 19% 15% 3	1650
March	1st to 10th	Day	46% 4 12% 16% 13% 10%	4479
	11th to 20th	Day	40% 5% 16% 26% 12% 2	4665
	21st to end	Day	47% 4 8% 15% 20% 6%	5970
April	1st to 10th	Day	45% 6% 10% 19% 16% 4	2400
	11th to 20th	Day	43% 5% 11% 20% 18% 3	2374
	21st to end	Day	44% 5% 9% 21% 16% 4	2505
May	1st to 10th	Day	55% 7% 16% 13% 9% 1	5897
	11th to 20th	Day	48% 7% 13% 19% 12% 2	6128
	21st to end	Day	46% 7% 11% 22% 13% 1	6949
June	1st to 10th	Day	43% 8% 13% 23% 13% 1	2800
	11th to 20th	Day	41% 8% 15% 22% 13% 1	2800
	21st to end	Day	39% 9% 13% 23% 14% 1	2800
July	1st to 10th	Day	46% 8% 11% 20% 14% 1	6290
	11th to 20th	Day	42% 6% 18% 22% 11% 1	6285
	21st to end	Day	41% 5% 11% 23% 19% 1	6728
August	1st to 10th	Day	47% 7% 14% 22% 9% 1	4368
	11th to 20th	Day	37% 6% 14% 31% 11% 1	3892
	21st to end	Day	34% 7% 13% 27% 17% 2	4312
September	1st to 10th	Day	37% 7% 12% 23% 19% 2	2400
	11th to 20th	Day	33% 6% 12% 23% 24% 2	2240
	21st to end	Day	44% 6% 8% 20% 19% 3	2090
October	1st to 10th	Day	36% 5% 10% 20% 23% 6%	3425
	11th to 20th	Day	27% 4 10% 24% 32% 4	3117
	21st to end	Day	31% 5% 14% 25% 23% 3	3081
November	1st to 10th	Day	38% 4 14% 21% 21% 2	1761
	11th to 20th	Day	37% 4 12% 22% 22% 4	1800
	21st to end	Day	40% 5% 13% 27% 12% 3	1775
December	1st to 10th	Day	40% 4 15% 27% 13% 1	2600
	11th to 20th	Day	41% 3 15% 19% 19% 3	2986
	21st to end	Day	48% 4 8% 20% 16% 5%	3960
January	1st to 10th	Night	37% 4 9% 27% 20% 3	6349
	11th to 20th	Night	41% 4 13% 21% 16% 6%	6360
	21st to end	Night	48% 4 9% 19% 16% 4	6843
February	1st to 10th	Night	45% 5% 12% 24% 12% 2	2528
	11th to 20th	Night	43% 5% 10% 20% 18% 4	2340
	21st to end	Night	47% 3 9% 22% 15% 4	1980
March	1st to 10th	Night	47% 4 11% 18% 14% 7%	5374
	11th to 20th	Night	44% 5% 15% 21% 11% 4	5289
	21st to end	Night	49% 3 6% 12% 24% 5%	4962
April	1st to 10th	Night	47% 5% 10% 19% 15% 3	2000
	11th to 20th	Night	44% 5% 11% 19% 20% 2	1975
	21st to end	Night	45% 4 9% 22% 16% 4	1895
May	1st to 10th	Night	58% 6% 13% 12% 9% 1	4060
	11th to 20th	Night	51% 7% 13% 15% 11% 3	3811
	21st to end	Night	51% 5% 13% 21% 10% 1	3927
June	1st to 10th	Night	45% 6% 10% 20% 17% 2	1600
	11th to 20th	Night	41% 7% 14% 26% 12% 1	1600
	21st to end	Night	40% 7% 13% 25% 15% 1	1600
July	1st to 10th	Night	47% 8% 12% 20% 11% 1	3560
	11th to 20th	Night	50% 5% 16% 19% 9% 1	3552
	21st to end	Night	40% 5% 13% 25% 16% 1	3809
August	1st to 10th	Night	53% 7% 13% 16% 9% 1	2724
	11th to 20th	Night	43% 6% 14% 29% 9% 1	3218
	21st to end	Night	28% 5% 15% 32% 19% 1	3586
September	1st to 10th	Night	39% 6% 10% 26% 18% 2	2000
	11th to 20th	Night	34% 5% 10% 24% 25% 2	2116
	21st to end	Night	44% 5% 8% 20% 20% 3	2090
October	1st to 10th	Night	39% 4 12% 23% 19% 2	3533
	11th to 20th	Night	25% 4 9% 27% 31% 4	3800
	21st to end	Night	32% 4 13% 27% 21% 2	4467
November	1st to 10th	Night	36% 4 12% 22% 21% 4	2537
	11th to 20th	Night	40% 3 10% 23% 20% 4	2600
	21st to end	Night	39% 5% 12% 29% 13% 2	2620
December	1st to 10th	Night	41% 4 11% 29% 14% 1	4580
	11th to 20th	Night	48% 3 12% 17% 18% 2	5208
	21st to end	Night	46% 3 10% 19% 17% 4	6996

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	28% 26% 27% 19% 2	200
	11th to 20th	Day	24% 33% 29% 14% 1 1	200
	21st to end	Day	23% 28% 32% 11% 4 2	250
February	1st to 10th	Day	26% 26% 33% 14% 1	370
	11th to 20th	Day	25% 29% 33% 12% 1	496
	21st to end	Day	26% 25% 32% 14% 4	414
March	1st to 10th	Day	23% 25% 34% 15% 2	500
	11th to 20th	Day	21% 27% 34% 14% 3 1	500
	21st to end	Day	26% 24% 35% 10% 4 1	550
April	1st to 10th	Day	27% 25% 31% 12% 5% 1	500
	11th to 20th	Day	27% 21% 30% 15% 5% 1	492
	21st to end	Day	25% 18% 35% 16% 4 2	500
May	1st to 10th	Day	28% 20% 30% 15% 6% 1	503
	11th to 20th	Day	21% 16% 36% 21% 5% 1	527
	21st to end	Day	21% 10% 31% 26% 11% 2	573
June	1st to 10th	Day	18% 12% 33% 25% 11% 2	530
	11th to 20th	Day	18% 12% 33% 26% 9% 1	530
	21st to end	Day	16% 10% 33% 28% 12% 2	530
July	1st to 10th	Day	17% 7% 28% 31% 16% 2	525
	11th to 20th	Day	13% 6% 28% 34% 15% 4	524
	21st to end	Day	15% 7% 33% 33% 9% 2	576
August	1st to 10th	Day	13% 8% 28% 33% 13% 5%	526
	11th to 20th	Day	13% 5% 29% 32% 17% 5%	519
	21st to end	Day	10% 10% 32% 27% 14% 6%	583
September	1st to 10th	Day	18% 8% 29% 24% 16% 4	530
	11th to 20th	Day	14% 7% 31% 27% 13% 7%	522
	21st to end	Day	22% 11% 32% 22% 10% 3	490
October	1st to 10th	Day	27% 11% 24% 22% 12% 4	490
	11th to 20th	Day	16% 18% 29% 27% 9% 2	483
	21st to end	Day	25% 16% 32% 18% 8% 2	429
November	1st to 10th	Day	16% 18% 30% 23% 10% 3	395
	11th to 20th	Day	24% 24% 28% 20% 5%	400
	21st to end	Day	21% 22% 29% 20% 7%	375
December	1st to 10th	Day	22% 21% 36% 16% 6%	200
	11th to 20th	Day	29% 27% 31% 13% 2	200
	21st to end	Day	25% 20% 35% 15% 5%	220
January	1st to 10th	Night	21% 22% 36% 18% 3	800
	11th to 20th	Night	27% 19% 32% 20% 3	800
	21st to end	Night	20% 21% 37% 19% 3	880
February	1st to 10th	Night	22% 20% 34% 22% 2	800
	11th to 20th	Night	23% 21% 38% 16% 2	783
	21st to end	Night	25% 19% 36% 17% 3	660
March	1st to 10th	Night	24% 18% 36% 19% 3	800
	11th to 20th	Night	23% 15% 38% 21% 4 1	800
	21st to end	Night	23% 20% 36% 18% 3	880
April	1st to 10th	Night	24% 18% 35% 20% 3	800
	11th to 20th	Night	23% 14% 36% 23% 4	791
	21st to end	Night	22% 15% 36% 21% 5%	695
May	1st to 10th	Night	26% 12% 34% 22% 7%	600
	11th to 20th	Night	23% 12% 37% 22% 6%	499
	21st to end	Night	21% 5% 24% 39% 10%	433
June	1st to 10th	Night	22% 5% 29% 34% 10% 1	400
	11th to 20th	Night	20% 5% 29% 35% 12%	400
	21st to end	Night	16% 6% 27% 41% 10% 1	400
July	1st to 10th	Night	15% 5% 24% 41% 15% 1	390
	11th to 20th	Night	15% 2 21% 45% 17% 1	388
	21st to end	Night	15% 3 24% 44% 13% 1	438
August	1st to 10th	Night	13% 3 27% 41% 15% 1	481
	11th to 20th	Night	15% 3 20% 42% 17% 2	781
	21st to end	Night	14% 4 25% 36% 18% 3	880
September	1st to 10th	Night	17% 4 29% 33% 15% 3	800
	11th to 20th	Night	17% 5% 24% 31% 19% 3	793
	21st to end	Night	22% 6% 27% 29% 16% 1	760
October	1st to 10th	Night	23% 10% 26% 26% 13% 3	760
	11th to 20th	Night	19% 13% 31% 28% 9% 1	760
	21st to end	Night	26% 11% 34% 21% 8%	836
November	1st to 10th	Night	15% 14% 33% 25% 11% 1	780
	11th to 20th	Night	23% 17% 34% 20% 6% 1	800
	21st to end	Night	22% 17% 32% 24% 5% 1	800
December	1st to 10th	Night	26% 16% 32% 20% 5% 1	800
	11th to 20th	Night	26% 19% 31% 20% 3	800
	21st to end	Night	26% 17% 36% 18% 2	880

Page generated at 2025-09-16 01:49:11. Version ac07

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