Richard Bong State Recreation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Richard Bong State Recreation Area clear sky chart from 2005-11-06 to 2025-08-05.

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	12% 9% 3 7% 5% 4 5% 4 6% 7% 37%	125779
	Night	13% 10% 4 8% 5% 4 4 4 5% 6% 39%	122517
Transparency	Day	44% 5% 12% 24% 14% 1	129277
	Night	45% 5% 11% 23% 15% 2	127092
Seeing	Day	17% 10% 30% 25% 13% 5%	16906
	Night	18% 9% 30% 29% 12% 1	26731

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	9% 11% 7% 14% 6% 5% 6% 4 6% 6% 26%	3617
	11th to 20th	Day	9% 11% 6% 12% 4 4 3 6% 6% 7% 32%	3620
	21st to end	Day	13% 15% 8% 9% 3 3 3 3 4 6% 33%	4046
February	1st to 10th	Day	11% 16% 5% 10% 6% 5% 5% 4 5% 7% 28%	1814
	11th to 20th	Day	13% 12% 3 8% 4 4 5% 4 5% 5% 36%	1948
	21st to end	Day	12% 14% 5% 10% 6% 4 4 3 6% 6% 31%	1650
March	1st to 10th	Day	14% 10% 3 6% 4 3 4 3 5% 6% 42%	4480
	11th to 20th	Day	10% 6% 3 7% 5% 4 5% 4 6% 8% 42%	4673
	21st to end	Day	19% 12% 5% 12% 5% 5% 5% 4 4 5% 24%	5967
April	1st to 10th	Day	17% 13% 3 8% 5% 5% 4 4 5% 6% 30%	2400
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 4 6% 5% 35%	2374
	21st to end	Day	18% 9% 3 7% 6% 5% 4 3 5% 6% 35%	2524
May	1st to 10th	Day	15% 9% 3 7% 4 4 5% 4 6% 7% 37%	5862
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 7% 7% 40%	6269
	21st to end	Day	15% 6% 2 6% 4 4 4 4 6% 9% 39%	6935
June	1st to 10th	Day	9% 6% 2 7% 5% 5% 4 4 6% 9% 45%	2800
	11th to 20th	Day	11% 5% 2 5% 5% 4 4 4 6% 10% 44%	2800
	21st to end	Day	10% 7% 2 6% 5% 5% 5% 4 6% 8% 41%	2800
July	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 5% 8% 10% 37%	6360
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 4 7% 10% 43%	6360
	21st to end	Day	9% 7% 2 7% 5% 5% 5% 4 6% 9% 42%	6924
August	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 7% 9% 42%	4430
	11th to 20th	Day	10% 4 2 6% 5% 5% 5% 4 7% 8% 44%	3775
	21st to end	Day	8% 6% 2 7% 4 5% 4 4 6% 8% 47%	4180
September	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 5% 8% 46%	2280
	11th to 20th	Day	12% 4 2 4 4 3 4 3 6% 8% 51%	2165
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 5% 8% 43%	2090
October	1st to 10th	Day	13% 7% 3 6% 4 3 4 3 4 7% 47%	2026
	11th to 20th	Day	18% 8% 3 7% 4 5% 5% 4 4 8% 34%	1877
	21st to end	Day	19% 8% 4 7% 5% 4 3 3 4 6% 38%	1881
November	1st to 10th	Day	11% 11% 3 7% 4 2 4 3 5% 6% 43%	1762
	11th to 20th	Day	13% 12% 4 10% 5% 5% 4 4 5% 7% 31%	1800
	21st to end	Day	18% 11% 3 8% 5% 3 3 3 4 6% 36%	1690
December	1st to 10th	Day	9% 8% 4 7% 5% 5% 4 4 6% 9% 39%	2610
	11th to 20th	Day	12% 15% 5% 10% 6% 5% 5% 4 6% 7% 26%	3008
	21st to end	Day	21% 21% 9% 11% 6% 4 3 2 4 4 15%	3982
January	1st to 10th	Night	10% 12% 6% 12% 5% 5% 4 3 4 5% 33%	6348
	11th to 20th	Night	12% 13% 6% 13% 6% 6% 5% 5% 6% 5% 23%	6360
	21st to end	Night	14% 15% 6% 9% 4 4 3 3 4 5% 32%	6927
February	1st to 10th	Night	13% 14% 4 10% 6% 5% 3 3 4 5% 33%	2585
	11th to 20th	Night	13% 10% 3 7% 5% 4 4 4 5% 6% 38%	2338
	21st to end	Night	18% 11% 3 8% 4 4 3 3 4 6% 36%	1980
March	1st to 10th	Night	16% 9% 3 8% 4 3 4 3 4 5% 42%	5373
	11th to 20th	Night	9% 7% 2 5% 4 4 4 4 5% 9% 47%	5314
	21st to end	Night	20% 12% 5% 10% 5% 4 4 3 4 4 28%	4962
April	1st to 10th	Night	16% 8% 4 6% 4 5% 4 5% 5% 6% 38%	2000
	11th to 20th	Night	18% 9% 4 7% 4 4 4 2 4 6% 37%	1975
	21st to end	Night	17% 8% 3 6% 5% 4 4 4 5% 6% 39%	1875
May	1st to 10th	Night	17% 9% 3 6% 4 4 4 3 5% 8% 37%	4033
	11th to 20th	Night	12% 6% 3 7% 4 4 5% 4 5% 8% 42%	3640
	21st to end	Night	15% 8% 3 7% 5% 4 4 3 4 6% 40%	3942
June	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 48%	1600
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 10% 44%	1600
	21st to end	Night	8% 7% 2 6% 4 5% 3 4 7% 9% 44%	1600
July	1st to 10th	Night	10% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	3618
	11th to 20th	Night	6% 6% 2 6% 4 4 4 4 6% 8% 51%	3617
	21st to end	Night	7% 6% 2 5% 4 4 5% 4 6% 8% 48%	3947
August	1st to 10th	Night	8% 5% 2 5% 3 3 4 4 6% 9% 51%	2594
	11th to 20th	Night	8% 5% 3 6% 3 4 4 3 5% 9% 49%	3039
	21st to end	Night	7% 4 2 6% 4 3 4 4 6% 9% 51%	3476
September	1st to 10th	Night	8% 6% 2 6% 4 4 3 3 4 5% 54%	1900
	11th to 20th	Night	9% 5% 2 4 3 4 5% 3 5% 6% 54%	1995
	21st to end	Night	11% 6% 2 6% 4 4 4 3 4 7% 48%	2090
October	1st to 10th	Night	12% 5% 2 6% 3 3 4 3 4 6% 52%	2152
	11th to 20th	Night	17% 8% 2 5% 3 3 4 3 5% 7% 43%	2301
	21st to end	Night	19% 8% 2 6% 4 4 4 3 6% 7% 37%	2717
November	1st to 10th	Night	12% 8% 3 6% 4 3 4 4 4 6% 47%	2536
	11th to 20th	Night	13% 11% 4 8% 5% 4 4 3 5% 6% 36%	2600
	21st to end	Night	16% 10% 4 7% 4 5% 4 3 6% 6% 36%	2708
December	1st to 10th	Night	9% 9% 3 7% 5% 5% 5% 4 5% 6% 42%	4580
	11th to 20th	Night	16% 15% 5% 9% 5% 5% 4 3 5% 5% 27%	5199
	21st to end	Night	21% 18% 6% 10% 5% 5% 4 3 4 5% 18%	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	57% 4 12% 18% 8%	3618
	11th to 20th	Day	51% 4 11% 14% 17% 3	3620
	21st to end	Day	53% 3 10% 21% 13%	4046
February	1st to 10th	Day	55% 4 12% 17% 10% 1	1814
	11th to 20th	Day	49% 4 9% 24% 11% 2	1958
	21st to end	Day	54% 5% 8% 20% 11% 2	1650
March	1st to 10th	Day	43% 5% 9% 26% 12% 5%	4480
	11th to 20th	Day	40% 5% 12% 30% 12% 1	4673
	21st to end	Day	61% 6% 10% 14% 8% 1	5969
April	1st to 10th	Day	55% 6% 10% 20% 10%	2400
	11th to 20th	Day	49% 6% 9% 21% 12% 3	2374
	21st to end	Day	50% 5% 12% 18% 13% 1	2524
May	1st to 10th	Day	44% 6% 10% 23% 15% 1	5897
	11th to 20th	Day	40% 8% 11% 25% 15%	6273
	21st to end	Day	40% 6% 11% 26% 13% 2	6949
June	1st to 10th	Day	36% 5% 13% 27% 17% 2	2800
	11th to 20th	Day	35% 6% 14% 24% 19% 2	2800
	21st to end	Day	39% 7% 13% 23% 16% 2	2800
July	1st to 10th	Day	39% 7% 12% 28% 13% 1	6291
	11th to 20th	Day	34% 7% 14% 28% 15% 1	6285
	21st to end	Day	37% 7% 15% 22% 17% 2	6728
August	1st to 10th	Day	36% 7% 14% 29% 13% 1	4415
	11th to 20th	Day	34% 7% 12% 33% 13% 1	3812
	21st to end	Day	34% 7% 12% 24% 22% 2	4179
September	1st to 10th	Day	36% 5% 12% 28% 17% 2	2280
	11th to 20th	Day	31% 5% 11% 32% 18% 2	2165
	21st to end	Day	39% 4 10% 30% 16% 1	2090
October	1st to 10th	Day	25% 3 7% 40% 24% 1	3364
	11th to 20th	Day	34% 4 11% 29% 22% 1	3093
	21st to end	Day	43% 3 8% 29% 13% 4	3081
November	1st to 10th	Day	41% 5% 13% 24% 16% 1	1762
	11th to 20th	Day	53% 5% 11% 20% 10% 1	1800
	21st to end	Day	51% 3 12% 25% 8%	1690
December	1st to 10th	Day	42% 4 20% 27% 7%	2610
	11th to 20th	Day	57% 4 12% 18% 8% 1	3005
	21st to end	Day	74% 3 6% 11% 6%	3982
January	1st to 10th	Night	54% 4 8% 22% 12% 1	6348
	11th to 20th	Night	62% 4 8% 11% 15% 1	6360
	21st to end	Night	55% 3 14% 16% 11% 1	6927
February	1st to 10th	Night	54% 4 9% 19% 13% 2	2585
	11th to 20th	Night	47% 4 10% 23% 14% 1	2339
	21st to end	Night	51% 4 9% 21% 11% 4	1980
March	1st to 10th	Night	45% 4 12% 23% 12% 4	5373
	11th to 20th	Night	34% 5% 11% 32% 14% 4	5314
	21st to end	Night	59% 5% 8% 16% 11% 1	4962
April	1st to 10th	Night	47% 5% 9% 23% 14% 1	2000
	11th to 20th	Night	49% 4 7% 20% 17% 4	1975
	21st to end	Night	45% 4 11% 22% 16% 2	1875
May	1st to 10th	Night	46% 5% 13% 18% 17% 2	4060
	11th to 20th	Night	39% 7% 13% 23% 14% 4	3641
	21st to end	Night	44% 6% 8% 22% 14% 5%	3950
June	1st to 10th	Night	32% 6% 12% 28% 19% 3	1600
	11th to 20th	Night	35% 7% 9% 25% 22% 2	1600
	21st to end	Night	35% 6% 15% 24% 17% 2	1600
July	1st to 10th	Night	38% 7% 11% 29% 11% 3	3580
	11th to 20th	Night	28% 6% 14% 32% 18% 2	3572
	21st to end	Night	31% 8% 13% 24% 22% 2	3832
August	1st to 10th	Night	29% 6% 15% 28% 20% 2	2585
	11th to 20th	Night	31% 7% 13% 33% 16% 1	3067
	21st to end	Night	28% 6% 13% 30% 19% 4	3476
September	1st to 10th	Night	32% 5% 10% 26% 24% 3	1900
	11th to 20th	Night	31% 4 9% 33% 21% 2	1995
	21st to end	Night	37% 5% 8% 32% 17% 1	2090
October	1st to 10th	Night	24% 3 7% 39% 26% 1	3594
	11th to 20th	Night	34% 5% 9% 26% 24% 2	3824
	21st to end	Night	42% 4 9% 26% 18% 2	4467
November	1st to 10th	Night	39% 4 9% 27% 18% 3	2536
	11th to 20th	Night	49% 4 11% 22% 12% 2	2600
	21st to end	Night	49% 5% 13% 22% 11% 1	2708
December	1st to 10th	Night	43% 5% 15% 26% 9% 2	4580
	11th to 20th	Night	58% 5% 10% 16% 10% 1	5201
	21st to end	Night	69% 4 8% 13% 6%	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	18% 15% 35% 26% 6%	300
	11th to 20th	Day	18% 16% 39% 22% 3 1	300
	21st to end	Day	23% 13% 39% 17% 7% 1	330
February	1st to 10th	Day	15% 22% 41% 18% 4 1	300
	11th to 20th	Day	20% 23% 36% 16% 5%	300
	21st to end	Day	22% 19% 45% 12% 2 1	249
March	1st to 10th	Day	17% 22% 43% 15% 2	300
	11th to 20th	Day	25% 17% 34% 18% 4 2	322
	21st to end	Day	26% 12% 31% 21% 7% 2	550
April	1st to 10th	Day	24% 12% 34% 23% 6%	500
	11th to 20th	Day	23% 19% 27% 21% 8% 2	492
	21st to end	Day	23% 11% 30% 22% 11% 2	500
May	1st to 10th	Day	22% 11% 32% 23% 9% 2	503
	11th to 20th	Day	21% 9% 31% 26% 9% 4	701
	21st to end	Day	17% 7% 32% 22% 16% 6%	789
June	1st to 10th	Day	10% 8% 33% 28% 15% 5%	730
	11th to 20th	Day	14% 6% 31% 30% 15% 5%	730
	21st to end	Day	13% 6% 32% 30% 15% 5%	730
July	1st to 10th	Day	8% 3 23% 31% 24% 11%	721
	11th to 20th	Day	9% 4 28% 32% 17% 10%	718
	21st to end	Day	8% 3 25% 38% 19% 7%	794
August	1st to 10th	Day	9% 4 21% 33% 22% 11%	673
	11th to 20th	Day	11% 3 21% 26% 26% 14%	479
	21st to end	Day	9% 3 17% 32% 27% 11%	539
September	1st to 10th	Day	14% 5% 24% 26% 22% 9%	490
	11th to 20th	Day	11% 1 19% 32% 25% 12%	490
	21st to end	Day	15% 9% 26% 27% 16% 8%	490
October	1st to 10th	Day	16% 8% 27% 27% 18% 5%	426
	11th to 20th	Day	24% 18% 29% 21% 8% 1	300
	21st to end	Day	29% 12% 34% 18% 5% 1	330
November	1st to 10th	Day	16% 16% 35% 24% 7% 2	300
	11th to 20th	Day	23% 16% 39% 13% 9%	300
	21st to end	Day	26% 9% 42% 19% 4	300
December	1st to 10th	Day	17% 18% 39% 20% 5% 1	300
	11th to 20th	Day	20% 17% 36% 21% 5% 1	300
	21st to end	Day	26% 20% 32% 18% 2 1	330
January	1st to 10th	Night	18% 17% 36% 24% 5%	1000
	11th to 20th	Night	21% 15% 36% 22% 6% 1	1000
	21st to end	Night	21% 10% 38% 25% 5%	1100
February	1st to 10th	Night	20% 14% 37% 23% 6%	985
	11th to 20th	Night	20% 16% 35% 25% 4	783
	21st to end	Night	24% 12% 39% 20% 4	660
March	1st to 10th	Night	20% 11% 38% 23% 8% 1	800
	11th to 20th	Night	17% 13% 37% 25% 8% 1	776
	21st to end	Night	23% 8% 30% 29% 9% 1	660
April	1st to 10th	Night	20% 11% 36% 28% 6%	600
	11th to 20th	Night	24% 10% 32% 25% 7% 2	593
	21st to end	Night	20% 7% 31% 32% 9% 1	600
May	1st to 10th	Night	20% 7% 32% 33% 8% 1	600
	11th to 20th	Night	18% 5% 27% 34% 14% 2	591
	21st to end	Night	16% 4 24% 34% 20% 2	650
June	1st to 10th	Night	11% 4 24% 44% 17% 1	600
	11th to 20th	Night	14% 3 30% 38% 15% 1	600
	21st to end	Night	10% 4 27% 42% 17% 1	600
July	1st to 10th	Night	10% 1 16% 39% 31% 3	585
	11th to 20th	Night	9% 2 20% 40% 25% 4	582
	21st to end	Night	6% 2 16% 49% 25% 3	657
August	1st to 10th	Night	6% 2 13% 46% 28% 4	579
	11th to 20th	Night	11% 2 13% 39% 30% 5%	564
	21st to end	Night	9% 2 15% 40% 32% 2	627
September	1st to 10th	Night	10% 2 21% 34% 26% 6%	570
	11th to 20th	Night	12% 3 18% 34% 29% 5%	665
	21st to end	Night	14% 8% 22% 31% 21% 4	760
October	1st to 10th	Night	15% 6% 26% 32% 20% 2	760
	11th to 20th	Night	22% 8% 32% 27% 10%	760
	21st to end	Night	24% 9% 33% 26% 8%	836
November	1st to 10th	Night	16% 11% 36% 25% 11% 1	780
	11th to 20th	Night	20% 15% 34% 25% 6% 1	800
	21st to end	Night	21% 13% 36% 23% 7%	908
December	1st to 10th	Night	21% 14% 37% 23% 5%	1000
	11th to 20th	Night	23% 13% 36% 24% 5%	1000
	21st to end	Night	29% 12% 37% 19% 3	1100

Page generated at 2025-08-02 00:32:29. Version ac07

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