Ridgeway
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ridgeway 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	14% 6% 2 6% 4 4 4 4 6% 8% 42%	120443
	Night	14% 6% 2 5% 4 4 4 3 5% 7% 45%	118692
Transparency	Day	24% 41% 7% 14% 11% 4	124091
	Night	23% 40% 6% 14% 13% 4	123181
Seeing	Day	17% 10% 25% 25% 16% 7%	16295
	Night	17% 8% 25% 31% 17% 2	26388

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	16% 6% 2 4 2 2 2 3 4 6% 54%	4056
	11th to 20th	Day	13% 5% 2 4 2 3 3 2 3 5% 57%	4060
	21st to end	Day	17% 7% 2 5% 4 4 3 2 3 4 48%	4466
February	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 5% 7% 44%	1800
	11th to 20th	Day	20% 6% 2 5% 3 3 4 3 6% 6% 42%	1800
	21st to end	Day	19% 7% 2 5% 5% 4 3 3 5% 6% 41%	1750
March	1st to 10th	Day	19% 7% 3 5% 4 3 4 3 5% 7% 40%	4935
	11th to 20th	Day	10% 5% 2 4 3 3 3 4 5% 7% 53%	4980
	21st to end	Day	16% 7% 2 6% 3 4 4 3 5% 6% 44%	5465
April	1st to 10th	Day	11% 4 1 5% 5% 3 3 4 7% 7% 50%	2275
	11th to 20th	Day	13% 5% 2 6% 4 3 3 3 6% 8% 48%	2374
	21st to end	Day	14% 6% 3 6% 5% 5% 5% 4 5% 6% 43%	2495
May	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 10% 33%	5862
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 4 7% 8% 28%	5861
	21st to end	Day	13% 5% 2 7% 4 4 5% 4 7% 9% 40%	6433
June	1st to 10th	Day	9% 5% 2 5% 6% 5% 6% 5% 7% 10% 41%	2600
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	2600
	21st to end	Day	8% 5% 2 6% 5% 6% 5% 6% 7% 10% 42%	2600
July	1st to 10th	Day	7% 4 2 7% 5% 5% 7% 5% 8% 11% 37%	4250
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 6% 9% 14% 33%	4250
	21st to end	Day	13% 8% 3 8% 6% 7% 6% 5% 8% 9% 27%	4466
August	1st to 10th	Day	15% 7% 2 8% 5% 5% 6% 5% 8% 11% 28%	4104
	11th to 20th	Day	8% 5% 2 7% 6% 5% 7% 6% 8% 11% 35%	4044
	21st to end	Day	7% 4 2 5% 3 4 4 4 6% 11% 50%	4181
September	1st to 10th	Day	12% 4 2 5% 4 4 4 3 6% 7% 48%	2252
	11th to 20th	Day	16% 5% 2 6% 3 5% 5% 4 6% 8% 41%	2090
	21st to end	Day	23% 7% 2 6% 4 3 4 3 5% 6% 37%	2090
October	1st to 10th	Day	15% 5% 2 5% 3 2 4 3 4 6% 52%	1906
	11th to 20th	Day	15% 3 2 5% 3 3 3 3 4 6% 54%	1900
	21st to end	Day	14% 5% 2 5% 2 2 2 3 3 5% 56%	2090
November	1st to 10th	Day	14% 6% 2 4 3 3 3 3 3 6% 54%	1957
	11th to 20th	Day	14% 4 2 5% 3 2 3 3 4 6% 52%	1882
	21st to end	Day	14% 4 1 5% 3 4 4 3 5% 7% 50%	1800
December	1st to 10th	Day	13% 6% 2 4 3 3 4 3 4 5% 52%	2930
	11th to 20th	Day	20% 5% 2 4 3 3 4 3 5% 6% 45%	3373
	21st to end	Day	20% 6% 2 5% 3 3 4 4 5% 7% 40%	4466
January	1st to 10th	Night	13% 5% 1 4 3 3 3 3 3 5% 57%	5889
	11th to 20th	Night	13% 6% 2 4 3 2 3 2 4 4 56%	5900
	21st to end	Night	19% 6% 2 4 3 3 3 3 4 5% 50%	6490
February	1st to 10th	Night	17% 6% 2 5% 4 3 4 4 5% 5% 44%	2600
	11th to 20th	Night	20% 6% 2 5% 3 3 3 3 4 6% 44%	2483
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 6% 43%	1879
March	1st to 10th	Night	17% 5% 2 5% 3 4 4 3 4 5% 45%	4918
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 5% 6% 56%	4980
	21st to end	Night	15% 5% 2 5% 3 3 4 4 5% 7% 46%	5467
April	1st to 10th	Night	14% 7% 2 5% 5% 4 4 3 5% 6% 45%	2124
	11th to 20th	Night	13% 5% 2 4 4 4 3 3 5% 9% 48%	1975
	21st to end	Night	14% 5% 2 5% 4 4 4 4 6% 7% 46%	1921
May	1st to 10th	Night	14% 6% 2 8% 5% 4 4 4 6% 8% 39%	4033
	11th to 20th	Night	20% 8% 3 7% 5% 4 4 3 5% 7% 35%	4032
	21st to end	Night	16% 5% 2 5% 4 3 3 4 6% 10% 42%	4421
June	1st to 10th	Night	10% 5% 2 5% 4 5% 5% 5% 8% 11% 41%	1800
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 4 8% 11% 43%	1800
	21st to end	Night	7% 5% 1 5% 5% 5% 5% 5% 8% 12% 43%	1800
July	1st to 10th	Night	7% 6% 2 8% 6% 7% 5% 5% 8% 9% 36%	2930
	11th to 20th	Night	8% 6% 2 7% 5% 5% 6% 5% 8% 10% 37%	2930
	21st to end	Night	14% 8% 4 8% 5% 5% 5% 5% 8% 9% 29%	3087
August	1st to 10th	Night	17% 8% 3 6% 5% 5% 5% 6% 7% 11% 26%	2825
	11th to 20th	Night	7% 6% 2 7% 5% 5% 6% 5% 9% 10% 38%	2785
	21st to end	Night	6% 4 2 6% 5% 4 5% 4 6% 9% 50%	3441
September	1st to 10th	Night	12% 6% 2 5% 4 3 5% 4 6% 8% 45%	1924
	11th to 20th	Night	15% 6% 2 7% 4 4 5% 4 5% 7% 40%	2090
	21st to end	Night	22% 8% 3 6% 3 4 4 3 5% 4 38%	2090
October	1st to 10th	Night	15% 6% 1 5% 4 3 4 3 4 6% 48%	2272
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 5% 54%	2280
	21st to end	Night	13% 4 2 4 3 3 3 2 4 5% 56%	2508
November	1st to 10th	Night	15% 5% 2 5% 3 2 3 2 4 6% 53%	2341
	11th to 20th	Night	13% 5% 2 4 4 3 3 3 4 6% 53%	2515
	21st to end	Night	14% 4 1 5% 3 3 4 3 5% 6% 52%	2600
December	1st to 10th	Night	12% 5% 2 5% 3 3 4 3 5% 6% 52%	4250
	11th to 20th	Night	20% 8% 2 8% 4 4 3 3 4 4 40%	4822
	21st to end	Night	20% 4 1 4 3 3 3 4 5% 7% 44%	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	23% 26% 3 16% 24% 8%	4057
	11th to 20th	Day	20% 26% 4 15% 27% 9%	4060
	21st to end	Day	30% 28% 5% 17% 16% 3	4466
February	1st to 10th	Day	16% 62% 5% 8% 7% 2	1800
	11th to 20th	Day	18% 61% 3 8% 8% 2	1809
	21st to end	Day	18% 63% 3 6% 9% 2	1750
March	1st to 10th	Day	36% 30% 5% 11% 9% 10%	4935
	11th to 20th	Day	18% 29% 4 15% 22% 12%	4980
	21st to end	Day	29% 29% 6% 16% 15% 5%	5465
April	1st to 10th	Day	15% 63% 4 9% 8% 2	2275
	11th to 20th	Day	15% 62% 5% 10% 6% 2	2374
	21st to end	Day	16% 62% 5% 11% 5% 1	2495
May	1st to 10th	Day	30% 33% 13% 15% 7% 1	5897
	11th to 20th	Day	40% 31% 7% 15% 6%	5865
	21st to end	Day	27% 31% 11% 14% 14% 3	6447
June	1st to 10th	Day	14% 64% 6% 10% 5% 1	2600
	11th to 20th	Day	12% 65% 7% 9% 7%	2600
	21st to end	Day	14% 62% 7% 10% 5%	2600
July	1st to 10th	Day	23% 43% 14% 11% 6% 3	4185
	11th to 20th	Day	25% 39% 14% 19% 2	4181
	21st to end	Day	37% 40% 6% 11% 6%	4324
August	1st to 10th	Day	33% 40% 12% 12% 2	4091
	11th to 20th	Day	21% 41% 14% 17% 6% 1	4083
	21st to end	Day	13% 39% 12% 25% 11% 1	4181
September	1st to 10th	Day	14% 61% 7% 9% 7% 1	2252
	11th to 20th	Day	18% 60% 5% 8% 8% 1	2090
	21st to end	Day	23% 61% 6% 7% 4	2090
October	1st to 10th	Day	20% 38% 5% 11% 20% 8%	3166
	11th to 20th	Day	10% 37% 3 14% 21% 16%	3140
	21st to end	Day	12% 37% 6% 17% 15% 12%	3428
November	1st to 10th	Day	19% 55% 3 10% 9% 3	1957
	11th to 20th	Day	15% 57% 2 9% 13% 3	1882
	21st to end	Day	14% 57% 5% 10% 12% 1	1800
December	1st to 10th	Day	21% 36% 3 17% 17% 7%	2930
	11th to 20th	Day	29% 31% 7% 11% 17% 4	3370
	21st to end	Day	32% 29% 9% 18% 11% 1	4466
January	1st to 10th	Night	21% 27% 3 14% 24% 10%	5889
	11th to 20th	Night	21% 27% 3 12% 31% 6%	5900
	21st to end	Night	27% 28% 4 20% 17% 4	6490
February	1st to 10th	Night	17% 63% 4 8% 7% 1	2600
	11th to 20th	Night	19% 60% 4 7% 8% 2	2485
	21st to end	Night	15% 61% 3 10% 7% 4	1879
March	1st to 10th	Night	32% 31% 4 12% 14% 8%	4918
	11th to 20th	Night	17% 30% 3 13% 22% 14%	4980
	21st to end	Night	27% 29% 5% 18% 17% 4	5467
April	1st to 10th	Night	16% 62% 3 8% 8% 2	2124
	11th to 20th	Night	15% 62% 5% 10% 7% 2	1975
	21st to end	Night	13% 63% 6% 10% 7% 1	1921
May	1st to 10th	Night	33% 32% 12% 15% 8% 1	4060
	11th to 20th	Night	37% 32% 8% 13% 10% 1	4033
	21st to end	Night	26% 31% 10% 20% 9% 3	4429
June	1st to 10th	Night	13% 65% 6% 9% 6% 1	1800
	11th to 20th	Night	11% 64% 9% 10% 6% 1	1800
	21st to end	Night	13% 63% 7% 10% 6% 1	1800
July	1st to 10th	Night	29% 42% 9% 11% 7%	2885
	11th to 20th	Night	27% 39% 18% 14% 3	2876
	21st to end	Night	37% 38% 9% 11% 5%	2988
August	1st to 10th	Night	36% 40% 12% 10% 2	2814
	11th to 20th	Night	20% 42% 14% 18% 6%	2812
	21st to end	Night	16% 38% 8% 27% 10% 1	3441
September	1st to 10th	Night	15% 61% 7% 10% 5% 2	1924
	11th to 20th	Night	18% 62% 6% 7% 7% 1	2090
	21st to end	Night	24% 60% 5% 8% 2	2090
October	1st to 10th	Night	25% 37% 6% 10% 16% 6%	3792
	11th to 20th	Night	10% 36% 3 15% 23% 13%	3779
	21st to end	Night	11% 37% 3 19% 18% 11%	4120
November	1st to 10th	Night	19% 55% 4 10% 9% 3	2341
	11th to 20th	Night	15% 57% 3 8% 13% 5%	2515
	21st to end	Night	14% 57% 4 11% 13% 2	2600
December	1st to 10th	Night	21% 36% 4 17% 20% 2	4250
	11th to 20th	Night	36% 31% 5% 12% 10% 7%	4824
	21st to end	Night	28% 29% 11% 18% 14% 1	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	26% 24% 31% 14% 4 1	300
	11th to 20th	Day	26% 21% 36% 14% 3	300
	21st to end	Day	25% 20% 38% 16% 2	330
February	1st to 10th	Day	18% 22% 41% 15% 4	300
	11th to 20th	Day	35% 24% 31% 8% 2	300
	21st to end	Day	26% 20% 33% 18% 3	349
March	1st to 10th	Day	23% 15% 35% 21% 6% 1	500
	11th to 20th	Day	22% 17% 35% 20% 5% 1	500
	21st to end	Day	23% 15% 36% 20% 5%	550
April	1st to 10th	Day	21% 17% 33% 21% 6% 1	500
	11th to 20th	Day	18% 17% 28% 22% 12% 3	492
	21st to end	Day	18% 12% 33% 24% 11% 2	500
May	1st to 10th	Day	18% 16% 32% 23% 9% 3	503
	11th to 20th	Day	18% 7% 25% 25% 18% 8%	527
	21st to end	Day	17% 5% 19% 28% 21% 9%	573
June	1st to 10th	Day	11% 5% 23% 32% 20% 10%	530
	11th to 20th	Day	10% 4 20% 30% 22% 13%	530
	21st to end	Day	9% 5% 15% 36% 27% 8%	530
July	1st to 10th	Day	12% 2 13% 27% 34% 12%	525
	11th to 20th	Day	6% 2 11% 30% 35% 17%	524
	21st to end	Day	9% 3 12% 34% 26% 16%	532
August	1st to 10th	Day	14% 3 17% 25% 26% 15%	486
	11th to 20th	Day	10% 3 12% 31% 27% 17%	479
	21st to end	Day	10% 3 10% 30% 27% 20%	539
September	1st to 10th	Day	15% 3 17% 21% 26% 19%	490
	11th to 20th	Day	17% 3 13% 27% 26% 15%	490
	21st to end	Day	29% 7% 19% 24% 17% 3	490
October	1st to 10th	Day	19% 6% 20% 29% 20% 6%	490
	11th to 20th	Day	13% 9% 25% 27% 22% 4	490
	21st to end	Day	15% 9% 27% 32% 14% 3	539
November	1st to 10th	Day	20% 8% 27% 27% 16% 3	495
	11th to 20th	Day	17% 16% 30% 25% 12% 1	382
	21st to end	Day	16% 19% 29% 24% 11% 1	300
December	1st to 10th	Day	24% 16% 40% 16% 4 1	300
	11th to 20th	Day	19% 15% 36% 23% 5% 1	300
	21st to end	Day	28% 12% 31% 18% 10% 1	330
January	1st to 10th	Night	20% 14% 36% 26% 4 1	800
	11th to 20th	Night	19% 12% 37% 29% 3	800
	21st to end	Night	20% 10% 40% 28% 2	880
February	1st to 10th	Night	20% 13% 35% 29% 3	800
	11th to 20th	Night	24% 14% 39% 21% 2	783
	21st to end	Night	19% 13% 40% 25% 3	660
March	1st to 10th	Night	18% 15% 35% 28% 5%	800
	11th to 20th	Night	20% 13% 35% 26% 7% 1	800
	21st to end	Night	20% 11% 38% 26% 5%	880
April	1st to 10th	Night	18% 16% 33% 26% 7%	800
	11th to 20th	Night	16% 11% 34% 27% 11% 1	791
	21st to end	Night	17% 6% 33% 33% 10%	721
May	1st to 10th	Night	13% 8% 32% 34% 13% 1	600
	11th to 20th	Night	18% 5% 24% 32% 20% 1	591
	21st to end	Night	16% 3 12% 34% 31% 4	650
June	1st to 10th	Night	11% 3 16% 39% 29% 3	600
	11th to 20th	Night	12% 2 14% 32% 37% 4	600
	21st to end	Night	9% 3 14% 36% 36% 3	600
July	1st to 10th	Night	11% 2 8% 32% 43% 5%	585
	11th to 20th	Night	5% 2 8% 31% 47% 7%	582
	21st to end	Night	10% 1 10% 39% 36% 4	624
August	1st to 10th	Night	15% 2 7% 34% 36% 6%	567
	11th to 20th	Night	11% 2 8% 32% 42% 4	564
	21st to end	Night	11% 2 8% 32% 39% 8%	814
September	1st to 10th	Night	14% 2 9% 31% 36% 8%	760
	11th to 20th	Night	16% 3 12% 30% 34% 5%	760
	21st to end	Night	25% 4 16% 32% 22% 2	760
October	1st to 10th	Night	18% 5% 19% 28% 25% 5%	760
	11th to 20th	Night	15% 6% 25% 34% 18% 2	760
	21st to end	Night	16% 7% 25% 35% 16% 1	836
November	1st to 10th	Night	16% 7% 24% 35% 15% 2	780
	11th to 20th	Night	15% 9% 30% 34% 11%	800
	21st to end	Night	17% 7% 32% 33% 11% 1	800
December	1st to 10th	Night	21% 10% 33% 30% 6%	800
	11th to 20th	Night	20% 8% 33% 34% 6%	800
	21st to end	Night	25% 11% 27% 32% 6%	880

Page generated at 2025-07-18 01:10:02. Version ac07

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