Little Rock Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Rock Creek Observatory clear sky chart from 2005-11-06 to 2025-02-25.

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	8% 9% 3 7% 5% 4 4 4 6% 7% 43%	112421
	Night	8% 11% 3 7% 4 4 4 4 5% 7% 43%	115030
Transparency	Day	38% 8% 13% 21% 15% 4	112153
	Night	39% 8% 13% 23% 14% 4	114889
Seeing	Day	13% 13% 29% 28% 14% 3	15939
	Night	14% 10% 31% 33% 11% 1	25595

By Month

Percentage Cloud Cover SW (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	8% 18% 5% 11% 5% 5% 5% 3 6% 8% 28%	3179
	11th to 20th	Day	5% 14% 4 12% 7% 7% 8% 4 4 5% 30%	3204
	21st to end	Day	3 10% 4 9% 4 3 4 3 6% 6% 47%	4509
February	1st to 10th	Day	7% 17% 5% 11% 6% 5% 4 4 4 8% 28%	1800
	11th to 20th	Day	5% 19% 6% 11% 6% 4 5% 3 5% 5% 29%	1755
	21st to end	Day	6% 16% 5% 10% 7% 5% 5% 3 6% 8% 29%	1449
March	1st to 10th	Day	4 9% 4 8% 6% 5% 4 4 7% 9% 38%	3376
	11th to 20th	Day	4 9% 4 8% 5% 4 5% 4 6% 8% 43%	3490
	21st to end	Day	10% 19% 6% 11% 6% 5% 5% 4 6% 8% 20%	3825
April	1st to 10th	Day	11% 15% 4 7% 6% 6% 5% 4 6% 7% 30%	2265
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 4 4 5% 6% 28%	2382
	21st to end	Day	18% 11% 3 8% 5% 4 4 3 5% 8% 31%	2470
May	1st to 10th	Day	23% 14% 3 7% 5% 4 4 3 4 5% 28%	4290
	11th to 20th	Day	11% 8% 3 7% 5% 5% 5% 4 8% 8% 34%	4388
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 5% 7% 9% 32%	4841
June	1st to 10th	Day	14% 6% 2 5% 4 4 6% 6% 8% 9% 37%	2850
	11th to 20th	Day	16% 6% 2 6% 5% 4 4 4 7% 9% 37%	2850
	21st to end	Day	6% 3 2 4 4 4 5% 5% 7% 9% 50%	2850
July	1st to 10th	Day	5% 3 1 4 4 5% 5% 5% 7% 8% 52%	4740
	11th to 20th	Day	3 2 1 3 3 3 4 3 6% 8% 65%	4740
	21st to end	Day	3 2 1 3 3 4 4 4 6% 8% 63%	4808
August	1st to 10th	Day	7% 3 2 6% 5% 6% 4 5% 7% 7% 48%	4092
	11th to 20th	Day	5% 3 1 4 4 5% 5% 5% 7% 9% 52%	4028
	21st to end	Day	7% 3 1 3 3 3 3 4 6% 8% 59%	4468
September	1st to 10th	Day	9% 4 1 4 3 3 3 3 4 7% 58%	2280
	11th to 20th	Day	10% 5% 2 5% 4 5% 4 4 5% 8% 49%	2180
	21st to end	Day	13% 4 1 4 3 3 4 3 5% 8% 53%	2062
October	1st to 10th	Day	10% 5% 2 4 3 3 3 2 3 6% 59%	3170
	11th to 20th	Day	8% 6% 2 5% 3 3 3 2 4 6% 57%	3150
	21st to end	Day	7% 7% 2 7% 4 4 4 3 7% 7% 47%	3326
November	1st to 10th	Day	11% 13% 3 6% 5% 4 4 4 6% 6% 39%	1568
	11th to 20th	Day	7% 13% 3 8% 6% 5% 5% 4 6% 7% 35%	1600
	21st to end	Day	7% 12% 4 7% 5% 6% 5% 4 5% 8% 38%	1600
December	1st to 10th	Day	4 13% 3 8% 5% 4 4 4 6% 7% 42%	2620
	11th to 20th	Day	4 13% 4 9% 4 4 4 4 5% 8% 42%	2718
	21st to end	Day	6% 13% 5% 9% 5% 4 4 3 5% 5% 40%	3498
January	1st to 10th	Night	6% 16% 6% 9% 4 4 4 3 5% 7% 35%	6766
	11th to 20th	Night	5% 19% 5% 10% 6% 4 5% 3 5% 5% 33%	6754
	21st to end	Night	4 10% 5% 8% 4 4 4 4 5% 7% 46%	6514
February	1st to 10th	Night	8% 19% 5% 12% 7% 5% 4 4 5% 6% 27%	2600
	11th to 20th	Night	6% 20% 6% 8% 6% 4 5% 4 5% 6% 31%	2532
	21st to end	Night	6% 16% 6% 10% 6% 5% 4 4 5% 7% 30%	2099
March	1st to 10th	Night	4 11% 4 7% 4 5% 5% 4 6% 9% 41%	3492
	11th to 20th	Night	4 8% 3 6% 5% 5% 4 4 6% 8% 47%	3490
	21st to end	Night	11% 19% 5% 11% 6% 5% 4 4 6% 7% 23%	3828
April	1st to 10th	Night	10% 13% 4 7% 6% 4 5% 5% 6% 5% 35%	1914
	11th to 20th	Night	12% 15% 6% 8% 4 3 5% 4 6% 7% 29%	1742
	21st to end	Night	16% 11% 3 6% 4 4 5% 4 5% 6% 37%	1710
May	1st to 10th	Night	21% 13% 2 6% 3 3 4 3 5% 7% 33%	2678
	11th to 20th	Night	11% 8% 3 7% 4 4 5% 4 6% 8% 39%	2517
	21st to end	Night	14% 6% 2 6% 4 4 4 4 6% 8% 42%	2742
June	1st to 10th	Night	12% 5% 2 6% 6% 5% 4 4 6% 8% 40%	1330
	11th to 20th	Night	15% 6% 2 4 4 3 5% 4 7% 8% 41%	1330
	21st to end	Night	7% 4 2 3 4 4 4 3 5% 7% 56%	1330
July	1st to 10th	Night	5% 3 2 3 3 3 4 4 7% 9% 56%	2220
	11th to 20th	Night	3 2 1 2 3 2 3 3 5% 6% 69%	2220
	21st to end	Night	4 3 1 5% 4 4 6% 4 7% 8% 53%	2748
August	1st to 10th	Night	7% 4 2 5% 4 4 4 5% 6% 8% 50%	2847
	11th to 20th	Night	6% 3 1 5% 3 4 4 5% 9% 10% 49%	2811
	21st to end	Night	8% 3 2 3 3 3 5% 3 7% 6% 57%	3198
September	1st to 10th	Night	10% 4 1 5% 4 3 3 3 4 7% 55%	1900
	11th to 20th	Night	12% 6% 2 4 2 4 5% 3 5% 8% 49%	1996
	21st to end	Night	13% 4 2 4 3 3 4 3 4 7% 53%	2117
October	1st to 10th	Night	11% 6% 2 4 2 3 3 2 3 5% 59%	3800
	11th to 20th	Night	9% 7% 2 5% 4 4 4 3 4 6% 51%	3778
	21st to end	Night	9% 9% 3 7% 4 3 4 3 4 6% 48%	4205
November	1st to 10th	Night	12% 12% 4 6% 4 3 4 4 5% 7% 38%	2722
	11th to 20th	Night	9% 12% 4 6% 5% 4 5% 4 5% 7% 39%	2800
	21st to end	Night	6% 11% 3 7% 5% 4 4 4 7% 8% 41%	2800
December	1st to 10th	Night	4 15% 5% 7% 4 4 4 2 5% 6% 45%	4570
	11th to 20th	Night	5% 13% 4 9% 5% 5% 5% 5% 6% 7% 37%	5472
	21st to end	Night	5% 12% 4 7% 4 4 4 3 6% 8% 43%	7458

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	50% 10% 13% 22% 6%	3179
	11th to 20th	Day	51% 8% 14% 13% 12% 2	3204
	21st to end	Day	34% 8% 16% 27% 14% 1	4509
February	1st to 10th	Day	56% 7% 14% 15% 8% 2	1800
	11th to 20th	Day	55% 7% 13% 17% 7% 2	1764
	21st to end	Day	53% 10% 12% 14% 9% 3	1449
March	1st to 10th	Day	37% 11% 13% 21% 18%	3376
	11th to 20th	Day	35% 12% 22% 23% 7% 1	3490
	21st to end	Day	58% 15% 12% 11% 3 1	3825
April	1st to 10th	Day	53% 9% 16% 16% 5% 1	2265
	11th to 20th	Day	57% 8% 13% 16% 6%	2385
	21st to end	Day	53% 8% 14% 17% 7%	2470
May	1st to 10th	Day	59% 7% 9% 19% 6% 1	4290
	11th to 20th	Day	42% 13% 14% 21% 9% 1	4392
	21st to end	Day	45% 12% 17% 19% 7%	4841
June	1st to 10th	Day	43% 13% 17% 20% 7%	2850
	11th to 20th	Day	43% 10% 15% 18% 11% 3	2850
	21st to end	Day	28% 10% 15% 27% 17% 2	2850
July	1st to 10th	Day	26% 8% 11% 28% 17% 9%	4666
	11th to 20th	Day	17% 5% 7% 21% 33% 16%	4659
	21st to end	Day	17% 6% 7% 19% 31% 19%	4656
August	1st to 10th	Day	30% 9% 10% 18% 22% 10%	4078
	11th to 20th	Day	26% 6% 11% 31% 22% 4	4067
	21st to end	Day	23% 6% 9% 28% 27% 7%	4467
September	1st to 10th	Day	28% 6% 10% 24% 23% 9%	2280
	11th to 20th	Day	33% 8% 12% 26% 17% 4	2180
	21st to end	Day	31% 6% 14% 27% 17% 6%	2062
October	1st to 10th	Day	29% 5% 8% 29% 23% 6%	3170
	11th to 20th	Day	30% 5% 13% 30% 20% 2	3150
	21st to end	Day	35% 7% 11% 24% 17% 6%	3326
November	1st to 10th	Day	46% 8% 10% 21% 12% 3	1568
	11th to 20th	Day	45% 9% 17% 18% 8% 3	1600
	21st to end	Day	43% 10% 16% 18% 11% 2	1600
December	1st to 10th	Day	40% 7% 18% 21% 11% 3	2620
	11th to 20th	Day	39% 9% 25% 20% 6% 1	2717
	21st to end	Day	46% 5% 8% 20% 13% 8%	3498
January	1st to 10th	Night	45% 9% 12% 24% 9% 1	6766
	11th to 20th	Night	51% 7% 13% 14% 11% 3	6754
	21st to end	Night	34% 10% 13% 25% 14% 4	6514
February	1st to 10th	Night	57% 7% 13% 14% 7% 2	2600
	11th to 20th	Night	52% 7% 15% 17% 7% 2	2533
	21st to end	Night	51% 8% 13% 15% 9% 3	2099
March	1st to 10th	Night	35% 8% 15% 23% 17% 1	3492
	11th to 20th	Night	29% 12% 25% 26% 7% 1	3490
	21st to end	Night	57% 11% 14% 14% 3 1	3828
April	1st to 10th	Night	48% 9% 16% 19% 8% 1	1914
	11th to 20th	Night	53% 10% 12% 17% 7% 1	1742
	21st to end	Night	48% 8% 14% 21% 8%	1710
May	1st to 10th	Night	50% 8% 11% 18% 12% 2	2678
	11th to 20th	Night	37% 12% 13% 27% 10% 1	2518
	21st to end	Night	37% 9% 17% 28% 9%	2742
June	1st to 10th	Night	42% 11% 19% 22% 6% 1	1330
	11th to 20th	Night	40% 9% 16% 21% 12% 2	1330
	21st to end	Night	27% 8% 15% 31% 18% 2	1330
July	1st to 10th	Night	23% 6% 12% 29% 26% 3	2185
	11th to 20th	Night	16% 4 7% 25% 30% 19%	2178
	21st to end	Night	24% 5% 8% 18% 30% 14%	2663
August	1st to 10th	Night	29% 6% 11% 26% 18% 9%	2838
	11th to 20th	Night	27% 7% 10% 32% 21% 3	2838
	21st to end	Night	25% 7% 8% 33% 24% 4	3198
September	1st to 10th	Night	31% 6% 8% 23% 23% 10%	1900
	11th to 20th	Night	34% 7% 12% 27% 16% 4	1996
	21st to end	Night	32% 6% 13% 26% 20% 4	2117
October	1st to 10th	Night	29% 5% 8% 28% 23% 7%	3800
	11th to 20th	Night	34% 6% 13% 24% 19% 5%	3778
	21st to end	Night	38% 5% 10% 23% 18% 6%	4205
November	1st to 10th	Night	43% 8% 15% 19% 11% 4	2722
	11th to 20th	Night	43% 9% 17% 20% 11% 1	2800
	21st to end	Night	38% 10% 18% 20% 9% 4	2800
December	1st to 10th	Night	39% 6% 18% 23% 11% 3	4570
	11th to 20th	Night	44% 8% 21% 20% 6% 1	5473
	21st to end	Night	37% 7% 10% 26% 13% 8%	7458

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	9% 21% 29% 23% 14% 5%	200
	11th to 20th	Day	16% 15% 33% 25% 7% 4	206
	21st to end	Day	11% 17% 35% 28% 9% 1	330
February	1st to 10th	Day	15% 19% 40% 21% 4 1	300
	11th to 20th	Day	15% 18% 30% 28% 7% 3	300
	21st to end	Day	16% 14% 36% 27% 5% 1	237
March	1st to 10th	Day	15% 20% 34% 23% 6% 1	437
	11th to 20th	Day	12% 18% 35% 23% 10% 2	460
	21st to end	Day	17% 17% 32% 23% 10% 1	506
April	1st to 10th	Day	19% 19% 36% 20% 6%	460
	11th to 20th	Day	15% 27% 31% 21% 5%	452
	21st to end	Day	25% 13% 26% 24% 11% 1	460
May	1st to 10th	Day	19% 12% 23% 24% 18% 4	565
	11th to 20th	Day	17% 8% 27% 27% 17% 4	675
	21st to end	Day	20% 10% 21% 26% 18% 4	734
June	1st to 10th	Day	11% 11% 27% 29% 17% 5%	680
	11th to 20th	Day	18% 14% 31% 24% 10% 2	680
	21st to end	Day	8% 8% 28% 35% 19% 3	680
July	1st to 10th	Day	6% 7% 25% 37% 22% 4	671
	11th to 20th	Day	4 6% 28% 41% 18% 2	668
	21st to end	Day	3 4 25% 42% 21% 6%	720
August	1st to 10th	Day	5% 7% 27% 38% 18% 4	487
	11th to 20th	Day	8% 5% 24% 35% 20% 6%	477
	21st to end	Day	6% 8% 29% 35% 16% 6%	539
September	1st to 10th	Day	9% 9% 28% 32% 18% 3	490
	11th to 20th	Day	15% 9% 30% 27% 13% 5%	490
	21st to end	Day	17% 13% 25% 24% 17% 4	462
October	1st to 10th	Day	15% 8% 26% 27% 17% 6%	300
	11th to 20th	Day	15% 12% 28% 27% 13% 5%	300
	21st to end	Day	15% 20% 28% 26% 9% 2	330
November	1st to 10th	Day	21% 16% 27% 23% 10% 3	300
	11th to 20th	Day	13% 21% 38% 20% 8% 1	300
	21st to end	Day	10% 21% 35% 25% 9% 1	300
December	1st to 10th	Day	12% 20% 32% 23% 11% 1	300
	11th to 20th	Day	17% 15% 34% 22% 12% 1	223
	21st to end	Day	16% 17% 30% 24% 11% 3	220
January	1st to 10th	Night	13% 16% 36% 27% 8% 1	1000
	11th to 20th	Night	16% 16% 38% 23% 7% 1	1000
	21st to end	Night	12% 17% 38% 25% 7% 1	900
February	1st to 10th	Night	15% 15% 34% 26% 9% 1	800
	11th to 20th	Night	14% 14% 36% 29% 6% 1	784
	21st to end	Night	12% 14% 34% 28% 10% 2	646
March	1st to 10th	Night	11% 10% 37% 33% 8% 1	760
	11th to 20th	Night	10% 8% 35% 37% 10% 1	760
	21st to end	Night	19% 8% 32% 30% 10% 1	836
April	1st to 10th	Night	15% 10% 34% 34% 7%	584
	11th to 20th	Night	19% 10% 31% 32% 8%	563
	21st to end	Night	22% 8% 26% 33% 9% 1	570
May	1st to 10th	Night	19% 7% 25% 35% 12% 1	570
	11th to 20th	Night	15% 6% 23% 37% 17% 1	561
	21st to end	Night	20% 8% 21% 34% 17% 1	610
June	1st to 10th	Night	13% 7% 22% 39% 16% 2	380
	11th to 20th	Night	16% 7% 33% 34% 9% 1	380
	21st to end	Night	8% 4 23% 49% 16% 1	380
July	1st to 10th	Night	8% 2 17% 50% 22% 1	370
	11th to 20th	Night	7% 4 20% 54% 16% 1	368
	21st to end	Night	6% 5% 21% 52% 17%	596
August	1st to 10th	Night	6% 5% 19% 49% 20% 1	567
	11th to 20th	Night	8% 4 18% 50% 19% 1	564
	21st to end	Night	10% 6% 21% 44% 17% 1	627
September	1st to 10th	Night	10% 4 22% 48% 16% 1	570
	11th to 20th	Night	14% 3 24% 39% 18% 2	666
	21st to end	Night	15% 5% 25% 36% 17% 3	760
October	1st to 10th	Night	18% 7% 26% 33% 15% 1	760
	11th to 20th	Night	16% 9% 29% 33% 12% 1	760
	21st to end	Night	15% 12% 32% 31% 9% 1	836
November	1st to 10th	Night	18% 11% 35% 27% 8% 1	967
	11th to 20th	Night	15% 18% 38% 24% 5%	1000
	21st to end	Night	11% 14% 38% 32% 5%	1000
December	1st to 10th	Night	12% 16% 34% 28% 10%	1000
	11th to 20th	Night	12% 14% 40% 27% 6% 1	1000
	21st to end	Night	13% 14% 37% 27% 7% 1	1100

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