DaltonSkyGazer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DaltonSkyGazer Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	17% 9% 4 8% 5% 4 5% 4 5% 7% 32%	126827
	Night	17% 10% 4 9% 5% 4 4 3 5% 6% 33%	123551
Transparency	Day	51% 4 11% 21% 12% 2	130331
	Night	50% 5% 11% 20% 12% 2	128121
Seeing	Day	27% 19% 28% 17% 7% 2	16217
	Night	25% 18% 26% 22% 8% 1	25215

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	10% 11% 6% 20% 10% 4 4 3 5% 5% 23%	3597
	11th to 20th	Day	13% 11% 5% 15% 9% 5% 4 3 4 5% 26%	3570
	21st to end	Day	15% 14% 7% 9% 5% 4 5% 3 4 5% 30%	4029
February	1st to 10th	Day	14% 12% 4 11% 7% 5% 6% 4 6% 6% 25%	1819
	11th to 20th	Day	12% 10% 5% 12% 7% 5% 6% 4 6% 5% 27%	1948
	21st to end	Day	18% 12% 4 10% 6% 5% 4 3 4 4 29%	1650
March	1st to 10th	Day	19% 13% 5% 11% 4 4 4 3 4 5% 29%	4476
	11th to 20th	Day	13% 10% 5% 10% 6% 5% 4 3 5% 6% 33%	4672
	21st to end	Day	21% 8% 4 9% 5% 5% 4 3 4 5% 31%	5970
April	1st to 10th	Day	17% 13% 3 9% 6% 4 4 3 4 6% 31%	2400
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 4 5% 6% 34%	2374
	21st to end	Day	17% 9% 4 9% 5% 5% 4 4 5% 5% 32%	2520
May	1st to 10th	Day	32% 11% 3 7% 4 4 4 3 4 6% 22%	5886
	11th to 20th	Day	19% 11% 3 8% 5% 5% 5% 4 5% 6% 29%	6307
	21st to end	Day	21% 9% 3 7% 5% 4 4 4 6% 7% 30%	6949
June	1st to 10th	Day	17% 7% 3 7% 5% 6% 5% 4 7% 9% 30%	2800
	11th to 20th	Day	19% 7% 2 6% 5% 4 4 5% 6% 9% 33%	2800
	21st to end	Day	17% 7% 3 7% 6% 6% 5% 4 6% 8% 31%	2800
July	1st to 10th	Day	14% 7% 3 8% 5% 5% 6% 5% 6% 9% 33%	6360
	11th to 20th	Day	12% 5% 2 7% 5% 5% 6% 5% 8% 11% 34%	6360
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 5% 7% 40%	6926
August	1st to 10th	Day	20% 7% 3 8% 5% 4 5% 4 6% 7% 32%	4476
	11th to 20th	Day	14% 7% 3 7% 4 6% 6% 4 7% 8% 33%	3894
	21st to end	Day	12% 6% 2 7% 4 5% 6% 4 7% 9% 38%	4312
September	1st to 10th	Day	13% 7% 2 6% 5% 4 5% 3 5% 7% 43%	2400
	11th to 20th	Day	15% 5% 2 6% 4 3 4 3 4 7% 46%	2279
	21st to end	Day	16% 7% 3 7% 4 4 4 4 6% 7% 39%	2200
October	1st to 10th	Day	22% 9% 2 7% 4 4 4 3 4 4 37%	2135
	11th to 20th	Day	17% 8% 2 7% 5% 4 4 3 5% 6% 38%	1980
	21st to end	Day	21% 13% 3 8% 4 3 4 2 5% 5% 30%	1980
November	1st to 10th	Day	12% 10% 3 6% 4 3 4 2 5% 7% 42%	1851
	11th to 20th	Day	16% 11% 3 7% 5% 4 4 4 5% 6% 35%	1863
	21st to end	Day	17% 12% 3 6% 5% 5% 4 3 4 6% 32%	1698
December	1st to 10th	Day	15% 12% 5% 12% 5% 4 4 4 5% 7% 26%	2600
	11th to 20th	Day	18% 15% 6% 8% 4 4 3 2 3 5% 32%	2986
	21st to end	Day	17% 14% 4 11% 6% 3 3 3 5% 6% 29%	3960
January	1st to 10th	Night	12% 10% 6% 19% 8% 5% 4 3 4 5% 24%	6349
	11th to 20th	Night	11% 11% 5% 18% 9% 5% 5% 4 5% 5% 22%	6315
	21st to end	Night	13% 12% 4 8% 6% 5% 5% 4 5% 6% 31%	6923
February	1st to 10th	Night	14% 10% 4 10% 6% 7% 7% 4 7% 6% 26%	2580
	11th to 20th	Night	12% 10% 5% 11% 7% 6% 5% 5% 6% 6% 27%	2338
	21st to end	Night	15% 14% 4 9% 6% 5% 4 4 6% 5% 29%	1980
March	1st to 10th	Night	19% 10% 4 11% 6% 4 5% 4 5% 5% 28%	5364
	11th to 20th	Night	15% 9% 4 7% 5% 5% 5% 4 5% 7% 33%	5271
	21st to end	Night	20% 13% 4 10% 5% 4 3 3 4 4 29%	4962
April	1st to 10th	Night	17% 12% 4 7% 5% 5% 4 4 6% 6% 30%	2000
	11th to 20th	Night	18% 12% 3 7% 4 3 4 3 5% 6% 35%	1975
	21st to end	Night	20% 10% 2 6% 4 3 3 3 5% 6% 36%	1880
May	1st to 10th	Night	33% 13% 2 6% 4 3 4 3 4 5% 24%	4054
	11th to 20th	Night	19% 13% 3 7% 5% 4 4 4 4 7% 29%	3630
	21st to end	Night	24% 11% 3 7% 4 3 4 3 5% 7% 30%	3926
June	1st to 10th	Night	19% 8% 2 7% 5% 4 4 3 5% 6% 38%	1600
	11th to 20th	Night	17% 6% 2 7% 4 4 5% 4 5% 8% 36%	1600
	21st to end	Night	16% 6% 1 6% 5% 4 4 4 5% 8% 41%	1600
July	1st to 10th	Night	14% 8% 2 7% 4 4 4 4 6% 9% 39%	3600
	11th to 20th	Night	18% 8% 2 7% 4 4 4 4 6% 8% 36%	3600
	21st to end	Night	14% 8% 2 6% 4 3 4 3 4 6% 48%	3926
August	1st to 10th	Night	26% 6% 2 6% 3 4 4 3 5% 6% 35%	2639
	11th to 20th	Night	16% 7% 2 6% 5% 4 5% 4 5% 7% 39%	3150
	21st to end	Night	10% 8% 2 5% 4 3 4 3 5% 8% 49%	3586
September	1st to 10th	Night	14% 7% 2 7% 4 4 4 4 5% 6% 45%	2000
	11th to 20th	Night	13% 6% 2 5% 2 4 4 3 3 7% 51%	2120
	21st to end	Night	18% 7% 2 6% 4 4 4 3 5% 6% 42%	2200
October	1st to 10th	Night	21% 8% 3 5% 3 4 4 3 5% 5% 40%	2260
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 3 5% 6% 41%	2420
	21st to end	Night	20% 11% 3 7% 4 4 3 3 5% 6% 33%	2860
November	1st to 10th	Night	14% 10% 3 6% 4 3 3 3 5% 6% 42%	2667
	11th to 20th	Night	16% 10% 3 8% 6% 5% 4 4 4 5% 35%	2692
	21st to end	Night	13% 12% 4 8% 4 5% 4 4 6% 5% 34%	2700
December	1st to 10th	Night	17% 13% 5% 12% 5% 5% 4 4 5% 6% 24%	4580
	11th to 20th	Night	24% 12% 5% 8% 4 4 3 3 4 4 30%	5208
	21st to end	Night	17% 13% 6% 12% 6% 4 4 3 4 4 27%	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	60% 6% 7% 21% 5%	3598
	11th to 20th	Day	60% 4 9% 13% 12% 3	3600
	21st to end	Day	55% 5% 6% 21% 12% 1	4029
February	1st to 10th	Day	58% 5% 11% 15% 10% 1	1819
	11th to 20th	Day	55% 6% 8% 19% 11% 1	1957
	21st to end	Day	57% 4 9% 18% 11% 1	1650
March	1st to 10th	Day	57% 5% 10% 13% 11% 4	4479
	11th to 20th	Day	52% 2 15% 21% 8% 3	4672
	21st to end	Day	56% 3 5% 14% 19% 3	5970
April	1st to 10th	Day	55% 4 7% 21% 11% 2	2400
	11th to 20th	Day	50% 5% 9% 20% 14% 1	2374
	21st to end	Day	53% 4 8% 19% 13% 3	2520
May	1st to 10th	Day	64% 4 9% 14% 8% 1	5897
	11th to 20th	Day	56% 3 13% 19% 8% 1	6311
	21st to end	Day	53% 5% 11% 22% 10% 1	6949
June	1st to 10th	Day	50% 5% 12% 22% 10%	2800
	11th to 20th	Day	48% 5% 15% 21% 11% 1	2800
	21st to end	Day	50% 5% 13% 20% 11% 1	2800
July	1st to 10th	Day	47% 6% 13% 23% 11% 1	6290
	11th to 20th	Day	42% 6% 16% 24% 12% 1	6285
	21st to end	Day	43% 4 12% 26% 14%	6728
August	1st to 10th	Day	50% 5% 14% 21% 9% 1	4462
	11th to 20th	Day	46% 5% 16% 26% 7% 1	3931
	21st to end	Day	40% 6% 13% 29% 11% 1	4312
September	1st to 10th	Day	41% 5% 11% 28% 15% 1	2400
	11th to 20th	Day	40% 4 9% 25% 21% 2	2279
	21st to end	Day	44% 4 11% 23% 15% 3	2200
October	1st to 10th	Day	48% 5% 7% 20% 19% 2	3473
	11th to 20th	Day	42% 3 10% 24% 16% 4	3208
	21st to end	Day	41% 5% 12% 26% 14% 3	3180
November	1st to 10th	Day	41% 5% 14% 24% 14% 2	1851
	11th to 20th	Day	49% 5% 9% 19% 16% 2	1863
	21st to end	Day	52% 4 14% 21% 8% 2	1698
December	1st to 10th	Day	54% 6% 13% 20% 6%	2600
	11th to 20th	Day	56% 3 11% 16% 13% 1	2986
	21st to end	Day	58% 3 7% 14% 14% 4	3960
January	1st to 10th	Night	58% 7% 9% 17% 7% 1	6349
	11th to 20th	Night	59% 6% 11% 13% 8% 2	6360
	21st to end	Night	52% 4 10% 16% 16% 3	6923
February	1st to 10th	Night	54% 5% 12% 19% 8% 2	2580
	11th to 20th	Night	53% 6% 10% 17% 12% 1	2340
	21st to end	Night	54% 5% 10% 20% 8% 3	1980
March	1st to 10th	Night	55% 5% 11% 15% 13% 2	5374
	11th to 20th	Night	49% 3 16% 20% 8% 3	5272
	21st to end	Night	57% 4 4 13% 19% 3	4962
April	1st to 10th	Night	53% 4 10% 20% 11% 2	2000
	11th to 20th	Night	50% 4 9% 21% 15% 1	1975
	21st to end	Night	49% 4 10% 19% 16% 3	1880
May	1st to 10th	Night	64% 3 10% 13% 8% 1	4060
	11th to 20th	Night	57% 4 13% 17% 8% 2	3631
	21st to end	Night	55% 4 12% 18% 10% 1	3927
June	1st to 10th	Night	46% 5% 12% 25% 12% 1	1600
	11th to 20th	Night	46% 5% 15% 23% 11%	1600
	21st to end	Night	41% 6% 15% 25% 13% 1	1600
July	1st to 10th	Night	41% 6% 16% 22% 15% 1	3560
	11th to 20th	Night	46% 6% 13% 21% 13% 1	3552
	21st to end	Night	37% 5% 14% 28% 15% 1	3809
August	1st to 10th	Night	51% 4 14% 23% 8% 1	2629
	11th to 20th	Night	43% 5% 18% 26% 8%	3179
	21st to end	Night	32% 7% 15% 34% 13% 1	3586
September	1st to 10th	Night	39% 5% 12% 27% 16% 1	2000
	11th to 20th	Night	36% 3 10% 28% 22% 1	2120
	21st to end	Night	43% 4 10% 25% 16% 2	2200
October	1st to 10th	Night	45% 5% 12% 22% 15% 2	3689
	11th to 20th	Night	37% 4 11% 23% 19% 5%	3931
	21st to end	Night	39% 4 14% 30% 12% 1	4610
November	1st to 10th	Night	42% 5% 11% 22% 17% 2	2667
	11th to 20th	Night	50% 5% 9% 19% 16% 2	2692
	21st to end	Night	49% 5% 14% 23% 8% 1	2700
December	1st to 10th	Night	56% 8% 10% 22% 5%	4580
	11th to 20th	Night	58% 4 11% 11% 15% 1	5208
	21st to end	Night	59% 4 6% 13% 13% 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	34% 30% 26% 7% 3 1	200
	11th to 20th	Day	34% 31% 27% 7% 1 1	200
	21st to end	Day	29% 29% 29% 11% 2 1	235
February	1st to 10th	Day	40% 30% 22% 5% 1	319
	11th to 20th	Day	38% 28% 24% 9% 1	496
	21st to end	Day	32% 27% 29% 10% 1	414
March	1st to 10th	Day	32% 28% 26% 12% 2	500
	11th to 20th	Day	33% 27% 27% 9% 3 1	500
	21st to end	Day	36% 25% 24% 8% 4 3	550
April	1st to 10th	Day	39% 22% 22% 11% 5% 1	500
	11th to 20th	Day	34% 24% 25% 11% 4 2	492
	21st to end	Day	30% 22% 31% 12% 4 2	500
May	1st to 10th	Day	37% 21% 24% 11% 5% 2	503
	11th to 20th	Day	24% 21% 33% 17% 5% 1	527
	21st to end	Day	23% 13% 30% 23% 8% 2	573
June	1st to 10th	Day	20% 17% 31% 20% 11% 2	530
	11th to 20th	Day	24% 14% 30% 20% 10% 1	530
	21st to end	Day	20% 18% 33% 19% 8% 2	530
July	1st to 10th	Day	17% 11% 35% 24% 11% 2	525
	11th to 20th	Day	14% 8% 34% 32% 10% 2	524
	21st to end	Day	15% 11% 39% 23% 9% 2	576
August	1st to 10th	Day	14% 11% 28% 31% 11% 5%	526
	11th to 20th	Day	15% 10% 29% 26% 13% 7%	519
	21st to end	Day	15% 13% 29% 25% 12% 6%	583
September	1st to 10th	Day	20% 11% 27% 22% 14% 6%	530
	11th to 20th	Day	17% 12% 24% 22% 15% 10%	530
	21st to end	Day	22% 12% 29% 21% 10% 6%	530
October	1st to 10th	Day	27% 14% 25% 17% 12% 4	530
	11th to 20th	Day	25% 19% 29% 18% 8% 2	519
	21st to end	Day	32% 19% 27% 16% 5% 1	462
November	1st to 10th	Day	28% 23% 23% 19% 7%	425
	11th to 20th	Day	30% 26% 26% 14% 4 1	421
	21st to end	Day	38% 21% 24% 14% 2 1	298
December	1st to 10th	Day	36% 27% 24% 11% 3	200
	11th to 20th	Day	42% 25% 25% 9% 1	200
	21st to end	Day	34% 23% 29% 11% 3	220
January	1st to 10th	Night	26% 29% 31% 12% 2	800
	11th to 20th	Night	30% 25% 27% 16% 2	800
	21st to end	Night	23% 27% 31% 16% 2	880
February	1st to 10th	Night	29% 26% 30% 14% 2	800
	11th to 20th	Night	28% 30% 28% 13% 1	783
	21st to end	Night	31% 27% 26% 14% 2	660
March	1st to 10th	Night	30% 26% 25% 16% 3	800
	11th to 20th	Night	26% 25% 27% 18% 3 1	800
	21st to end	Night	30% 21% 26% 18% 5% 1	880
April	1st to 10th	Night	30% 19% 30% 16% 4	800
	11th to 20th	Night	29% 21% 26% 18% 5% 1	791
	21st to end	Night	30% 20% 26% 20% 4	680
May	1st to 10th	Night	33% 14% 26% 19% 7% 1	600
	11th to 20th	Night	22% 15% 32% 27% 4	423
	21st to end	Night	22% 7% 29% 28% 13%	433
June	1st to 10th	Night	20% 10% 30% 29% 11%	400
	11th to 20th	Night	18% 9% 28% 35% 10% 1	400
	21st to end	Night	19% 8% 26% 35% 13% 1	400
July	1st to 10th	Night	16% 6% 24% 39% 13% 1	390
	11th to 20th	Night	18% 4 22% 39% 16% 1	388
	21st to end	Night	11% 7% 25% 42% 16%	438
August	1st to 10th	Night	15% 3 21% 40% 19% 1	425
	11th to 20th	Night	17% 6% 22% 31% 21% 3	755
	21st to end	Night	17% 7% 23% 32% 19% 2	880
September	1st to 10th	Night	17% 10% 26% 29% 16% 2	800
	11th to 20th	Night	16% 8% 22% 27% 21% 6%	800
	21st to end	Night	23% 10% 23% 28% 14% 3	800
October	1st to 10th	Night	26% 12% 24% 24% 12% 3	800
	11th to 20th	Night	23% 17% 27% 23% 9% 1	800
	21st to end	Night	28% 18% 29% 20% 4	880
November	1st to 10th	Night	23% 21% 27% 21% 7%	820
	11th to 20th	Night	28% 23% 24% 17% 7% 1	829
	21st to end	Night	27% 22% 28% 18% 4 1	800
December	1st to 10th	Night	30% 27% 24% 15% 4	800
	11th to 20th	Night	32% 23% 25% 17% 3	800
	21st to end	Night	30% 28% 25% 14% 3	880

Page generated at 2025-11-15 00:55:54. Version ac07

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