Rummy's Stargazing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rummy's Stargazing Site clear sky chart from 2005-11-06 to 2025-07-21.

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% 7% 3 6% 4 4 4 4 5% 7% 38%	120220
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	118869
Transparency	Day	44% 6% 12% 21% 14% 2	123767
	Night	43% 6% 13% 22% 15% 2	123483
Seeing	Day	24% 18% 29% 18% 8% 2	15761
	Night	22% 17% 29% 23% 8% 1	24965

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% 10% 3 7% 4 4 4 3 5% 6% 42%	3597
	11th to 20th	Day	12% 10% 5% 12% 7% 4 4 3 4 6% 32%	3570
	21st to end	Day	16% 11% 4 8% 4 4 4 3 4 5% 38%	4443
February	1st to 10th	Day	15% 9% 3 8% 5% 5% 6% 4 5% 5% 35%	1800
	11th to 20th	Day	13% 10% 3 7% 5% 5% 5% 4 5% 6% 38%	1879
	21st to end	Day	19% 10% 3 7% 5% 3 4 4 4 5% 36%	1650
March	1st to 10th	Day	21% 8% 2 6% 4 4 3 3 4 5% 40%	4476
	11th to 20th	Day	12% 7% 4 7% 4 4 4 3 4 7% 42%	4952
	21st to end	Day	19% 8% 2 5% 4 3 4 3 5% 6% 41%	5819
April	1st to 10th	Day	18% 9% 2 6% 5% 5% 4 5% 5% 6% 35%	2400
	11th to 20th	Day	17% 9% 2 6% 4 4 4 3 4 6% 39%	2374
	21st to end	Day	16% 6% 2 5% 5% 6% 5% 3 6% 6% 39%	2400
May	1st to 10th	Day	28% 7% 2 6% 4 4 4 4 5% 7% 29%	6011
	11th to 20th	Day	24% 8% 3 7% 5% 4 5% 3 5% 6% 31%	6318
	21st to end	Day	21% 5% 2 5% 4 4 5% 4 7% 8% 34%	6949
June	1st to 10th	Day	15% 5% 3 7% 6% 5% 5% 4 6% 8% 36%	2800
	11th to 20th	Day	17% 6% 2 6% 4 5% 5% 4 6% 9% 34%	2800
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 6% 8% 39%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 9% 39%	4580
	11th to 20th	Day	11% 6% 2 6% 5% 4 6% 4 7% 11% 38%	4580
	21st to end	Day	16% 7% 3 7% 6% 5% 5% 4 6% 7% 35%	4814
August	1st to 10th	Day	22% 5% 3 7% 4 5% 6% 4 7% 6% 31%	4120
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 4 6% 9% 39%	3769
	21st to end	Day	16% 5% 2 4 3 3 4 3 6% 8% 45%	4180
September	1st to 10th	Day	16% 6% 3 5% 3 4 5% 4 5% 8% 41%	2280
	11th to 20th	Day	14% 4 2 5% 3 3 4 4 5% 6% 50%	2247
	21st to end	Day	20% 7% 3 6% 4 4 4 3 5% 5% 39%	2090
October	1st to 10th	Day	20% 7% 2 6% 4 4 4 4 5% 6% 40%	1900
	11th to 20th	Day	16% 4 2 6% 4 4 5% 3 4 7% 45%	1900
	21st to end	Day	21% 6% 2 6% 4 3 4 4 6% 6% 39%	1991
November	1st to 10th	Day	14% 7% 2 5% 3 3 2 3 4 6% 52%	1761
	11th to 20th	Day	18% 8% 2 4 4 3 3 4 6% 5% 44%	1800
	21st to end	Day	17% 7% 2 6% 5% 5% 4 4 5% 7% 38%	1624
December	1st to 10th	Day	17% 8% 3 6% 4 4 5% 4 4 6% 40%	2600
	11th to 20th	Day	23% 8% 3 5% 3 3 4 3 5% 5% 38%	2986
	21st to end	Day	18% 10% 4 9% 4 4 4 3 5% 6% 32%	3960
January	1st to 10th	Night	13% 6% 3 8% 5% 4 5% 4 6% 7% 41%	6349
	11th to 20th	Night	13% 9% 4 9% 5% 4 4 3 5% 6% 37%	6315
	21st to end	Night	16% 9% 3 6% 5% 5% 4 4 5% 5% 39%	6511
February	1st to 10th	Night	16% 10% 3 5% 4 4 4 4 4 6% 40%	2600
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 5% 5% 6% 39%	2406
	21st to end	Night	17% 8% 3 6% 4 5% 4 4 5% 6% 38%	1980
March	1st to 10th	Night	18% 9% 2 6% 4 3 3 3 5% 5% 40%	5364
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 5% 6% 47%	4990
	21st to end	Night	16% 9% 3 7% 4 4 4 3 4 5% 42%	5112
April	1st to 10th	Night	17% 8% 3 7% 5% 5% 5% 4 6% 6% 34%	2000
	11th to 20th	Night	19% 7% 2 5% 3 5% 4 4 6% 7% 39%	1975
	21st to end	Night	20% 6% 2 5% 3 3 4 3 6% 7% 41%	2000
May	1st to 10th	Night	31% 7% 2 6% 3 3 4 3 5% 6% 28%	3957
	11th to 20th	Night	24% 9% 3 6% 4 3 4 3 5% 5% 34%	3575
	21st to end	Night	22% 6% 2 5% 4 4 4 3 6% 7% 37%	3926
June	1st to 10th	Night	17% 5% 2 5% 4 4 4 4 5% 8% 42%	1600
	11th to 20th	Night	17% 5% 1 5% 3 5% 5% 5% 6% 9% 41%	1600
	21st to end	Night	13% 4 1 4 5% 4 4 4 8% 10% 45%	1600
July	1st to 10th	Night	11% 4 2 6% 5% 5% 5% 4 7% 9% 41%	2600
	11th to 20th	Night	13% 5% 2 5% 4 4 5% 5% 7% 11% 39%	2600
	21st to end	Night	18% 6% 2 4 3 5% 5% 4 6% 6% 41%	2739
August	1st to 10th	Night	22% 5% 2 6% 4 4 4 4 5% 9% 35%	2792
	11th to 20th	Night	16% 7% 2 6% 4 5% 4 3 5% 6% 43%	3026
	21st to end	Night	14% 4 2 4 3 2 3 4 5% 7% 52%	3476
September	1st to 10th	Night	16% 6% 2 5% 4 4 3 2 5% 6% 47%	1900
	11th to 20th	Night	12% 6% 2 5% 3 3 3 2 4 7% 53%	1931
	21st to end	Night	19% 6% 2 6% 3 3 4 3 5% 6% 43%	2090
October	1st to 10th	Night	23% 5% 2 5% 3 3 3 3 4 6% 43%	2275
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 5% 6% 48%	2280
	21st to end	Night	22% 7% 2 4 2 3 3 3 5% 7% 42%	2605
November	1st to 10th	Night	13% 5% 1 5% 2 4 4 4 5% 5% 51%	2537
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 4 5% 45%	2600
	21st to end	Night	15% 6% 2 5% 4 4 4 4 6% 7% 43%	2774
December	1st to 10th	Night	13% 7% 3 7% 4 4 4 3 5% 6% 43%	4580
	11th to 20th	Night	24% 8% 2 5% 3 4 4 3 5% 5% 39%	5208
	21st to end	Night	20% 12% 4 7% 4 4 4 3 4 5% 35%	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	43% 5% 9% 26% 14% 2	3598
	11th to 20th	Day	52% 5% 9% 19% 10% 4	3600
	21st to end	Day	50% 5% 9% 22% 13% 1	4443
February	1st to 10th	Day	49% 7% 12% 18% 12% 1	1800
	11th to 20th	Day	47% 7% 9% 21% 14% 2	1888
	21st to end	Day	49% 6% 10% 22% 11% 2	1650
March	1st to 10th	Day	47% 4 10% 19% 13% 7%	4479
	11th to 20th	Day	40% 7% 14% 27% 8% 4	4952
	21st to end	Day	44% 5% 11% 12% 23% 5%	5819
April	1st to 10th	Day	48% 7% 10% 19% 13% 4	2400
	11th to 20th	Day	46% 6% 11% 21% 15% 2	2374
	21st to end	Day	44% 6% 11% 20% 14% 4	2400
May	1st to 10th	Day	54% 7% 13% 16% 9% 1	6022
	11th to 20th	Day	53% 7% 9% 19% 11% 1	6322
	21st to end	Day	45% 8% 12% 22% 12% 2	6949
June	1st to 10th	Day	44% 8% 14% 20% 13% 1	2800
	11th to 20th	Day	45% 8% 14% 21% 10% 2	2800
	21st to end	Day	41% 9% 13% 25% 12% 1	2800
July	1st to 10th	Day	40% 10% 13% 22% 14% 2	4510
	11th to 20th	Day	38% 9% 18% 23% 12% 1	4505
	21st to end	Day	48% 7% 11% 18% 15% 1	4661
August	1st to 10th	Day	51% 8% 13% 19% 9%	4106
	11th to 20th	Day	40% 7% 14% 28% 11%	3806
	21st to end	Day	36% 6% 12% 31% 14% 1	4180
September	1st to 10th	Day	41% 7% 13% 21% 17% 2	2280
	11th to 20th	Day	34% 7% 11% 22% 24% 2	2247
	21st to end	Day	45% 7% 10% 17% 19% 2	2090
October	1st to 10th	Day	42% 5% 10% 18% 22% 3	3160
	11th to 20th	Day	32% 5% 9% 28% 22% 4	3140
	21st to end	Day	30% 5% 17% 26% 20% 3	3255
November	1st to 10th	Day	36% 5% 14% 25% 18% 3	1761
	11th to 20th	Day	41% 6% 11% 23% 16% 3	1800
	21st to end	Day	45% 7% 15% 24% 9% 1	1624
December	1st to 10th	Day	46% 5% 14% 25% 9% 2	2600
	11th to 20th	Day	48% 5% 14% 21% 11% 1	2986
	21st to end	Day	52% 6% 10% 17% 13% 1	3960
January	1st to 10th	Night	42% 6% 11% 23% 16% 3	6349
	11th to 20th	Night	45% 5% 15% 19% 12% 4	6360
	21st to end	Night	45% 7% 11% 17% 17% 4	6511
February	1st to 10th	Night	45% 6% 15% 22% 11% 1	2600
	11th to 20th	Night	45% 6% 11% 20% 15% 3	2408
	21st to end	Night	46% 6% 10% 22% 14% 3	1980
March	1st to 10th	Night	46% 5% 13% 19% 12% 6%	5374
	11th to 20th	Night	37% 6% 18% 24% 11% 4	4991
	21st to end	Night	45% 5% 8% 16% 23% 4	5112
April	1st to 10th	Night	49% 6% 11% 19% 12% 3	2000
	11th to 20th	Night	43% 7% 11% 21% 17% 1	1975
	21st to end	Night	42% 7% 11% 21% 16% 4	2000
May	1st to 10th	Night	56% 6% 11% 16% 9% 2	3963
	11th to 20th	Night	52% 8% 11% 15% 13% 2	3576
	21st to end	Night	45% 7% 14% 22% 11% 1	3927
June	1st to 10th	Night	40% 8% 11% 24% 18% 1	1600
	11th to 20th	Night	38% 8% 18% 24% 11% 1	1600
	21st to end	Night	33% 10% 15% 28% 13% 1	1600
July	1st to 10th	Night	39% 9% 16% 18% 16% 1	2560
	11th to 20th	Night	38% 9% 16% 25% 12% 1	2552
	21st to end	Night	41% 8% 14% 17% 19% 1	2651
August	1st to 10th	Night	46% 9% 17% 20% 8%	2782
	11th to 20th	Night	42% 7% 14% 26% 11%	3055
	21st to end	Night	31% 7% 12% 32% 17% 1	3476
September	1st to 10th	Night	38% 6% 12% 25% 18% 1	1900
	11th to 20th	Night	33% 6% 10% 24% 25% 2	1931
	21st to end	Night	41% 6% 11% 21% 20% 1	2090
October	1st to 10th	Night	41% 5% 11% 23% 19% 1	3795
	11th to 20th	Night	29% 4 10% 28% 24% 4	3779
	21st to end	Night	30% 5% 15% 29% 19% 2	4291
November	1st to 10th	Night	35% 6% 14% 23% 20% 3	2537
	11th to 20th	Night	41% 4 12% 22% 18% 3	2600
	21st to end	Night	39% 7% 16% 26% 11% 1	2774
December	1st to 10th	Night	42% 5% 13% 30% 8% 1	4580
	11th to 20th	Night	49% 4 13% 20% 13% 1	5208
	21st to end	Night	52% 5% 11% 17% 14% 2	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	39% 26% 25% 10% 2	200
	11th to 20th	Day	39% 27% 25% 8% 2	200
	21st to end	Day	25% 34% 29% 8% 3 1	325
February	1st to 10th	Day	33% 33% 26% 7% 1	300
	11th to 20th	Day	38% 28% 28% 6%	427
	21st to end	Day	36% 24% 30% 9% 2	414
March	1st to 10th	Day	33% 21% 34% 11% 2	500
	11th to 20th	Day	29% 26% 28% 13% 3 1	500
	21st to end	Day	33% 27% 27% 10% 3 1	550
April	1st to 10th	Day	32% 25% 27% 11% 4	500
	11th to 20th	Day	29% 26% 25% 12% 5% 1	492
	21st to end	Day	27% 22% 34% 12% 4 2	500
May	1st to 10th	Day	32% 21% 27% 11% 7% 1	503
	11th to 20th	Day	26% 19% 31% 17% 7% 1	527
	21st to end	Day	21% 12% 29% 25% 11% 2	573
June	1st to 10th	Day	20% 15% 30% 23% 10% 2	530
	11th to 20th	Day	22% 16% 26% 25% 11% 1	530
	21st to end	Day	15% 15% 32% 27% 9% 2	530
July	1st to 10th	Day	13% 10% 28% 27% 18% 4	525
	11th to 20th	Day	11% 6% 29% 31% 19% 3	524
	21st to end	Day	16% 9% 35% 25% 12% 3	532
August	1st to 10th	Day	14% 7% 29% 28% 15% 6%	486
	11th to 20th	Day	14% 8% 26% 33% 15% 5%	479
	21st to end	Day	14% 11% 29% 26% 12% 7%	539
September	1st to 10th	Day	20% 12% 24% 22% 15% 7%	490
	11th to 20th	Day	12% 10% 29% 23% 16% 10%	490
	21st to end	Day	24% 13% 27% 21% 10% 4	490
October	1st to 10th	Day	28% 12% 22% 22% 12% 4	490
	11th to 20th	Day	20% 19% 31% 21% 7% 2	490
	21st to end	Day	27% 18% 29% 20% 6% 1	486
November	1st to 10th	Day	21% 19% 30% 20% 8% 2	395
	11th to 20th	Day	28% 24% 28% 16% 4 1	400
	21st to end	Day	29% 24% 32% 13% 2	224
December	1st to 10th	Day	29% 31% 26% 11% 4 1	200
	11th to 20th	Day	40% 24% 26% 9% 3	200
	21st to end	Day	29% 24% 32% 10% 5%	220
January	1st to 10th	Night	24% 26% 35% 13% 2	800
	11th to 20th	Night	28% 23% 31% 17% 1	800
	21st to end	Night	20% 26% 36% 16% 1	880
February	1st to 10th	Night	25% 23% 36% 15% 1	800
	11th to 20th	Night	27% 29% 34% 9% 1	783
	21st to end	Night	30% 23% 31% 14% 2	660
March	1st to 10th	Night	27% 24% 33% 14% 3	800
	11th to 20th	Night	25% 24% 29% 18% 4	800
	21st to end	Night	23% 26% 33% 14% 4 1	880
April	1st to 10th	Night	25% 24% 32% 17% 2	800
	11th to 20th	Night	24% 20% 31% 20% 5%	791
	21st to end	Night	25% 18% 30% 23% 4	800
May	1st to 10th	Night	28% 13% 29% 24% 5% 1	568
	11th to 20th	Night	21% 12% 35% 26% 6% 1	394
	21st to end	Night	19% 6% 27% 36% 11%	433
June	1st to 10th	Night	17% 8% 25% 36% 14%	400
	11th to 20th	Night	18% 7% 30% 34% 12%	400
	21st to end	Night	14% 7% 25% 43% 11%	400
July	1st to 10th	Night	14% 5% 22% 39% 18% 1	390
	11th to 20th	Night	12% 4 22% 43% 16% 2	388
	21st to end	Night	12% 5% 24% 42% 15% 1	416
August	1st to 10th	Night	14% 2 22% 38% 22% 2	547
	11th to 20th	Night	16% 5% 18% 37% 22% 2	703
	21st to end	Night	18% 5% 21% 33% 21% 1	836
September	1st to 10th	Night	18% 7% 27% 31% 16% 2	760
	11th to 20th	Night	16% 6% 25% 28% 20% 5%	760
	21st to end	Night	22% 8% 25% 29% 15% 2	760
October	1st to 10th	Night	26% 11% 23% 24% 15% 1	760
	11th to 20th	Night	20% 14% 30% 29% 7% 1	760
	21st to end	Night	27% 16% 30% 21% 7%	836
November	1st to 10th	Night	19% 18% 30% 25% 8%	780
	11th to 20th	Night	27% 18% 28% 20% 5% 1	800
	21st to end	Night	22% 22% 32% 19% 5%	800
December	1st to 10th	Night	26% 20% 33% 16% 4	800
	11th to 20th	Night	27% 21% 33% 18% 2	800
	21st to end	Night	27% 21% 32% 17% 3	880

Page generated at 2025-07-18 01:10:00. Version ac07

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