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 2026-07-01.

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% 8% 3 7% 4 4 5% 4 6% 8% 43%	146955
	Night	8% 10% 3 7% 4 4 4 4 6% 7% 43%	142830
Transparency	Day	38% 8% 13% 23% 15% 4	141666
	Night	39% 7% 13% 24% 14% 4	139128
Seeing	Day	13% 13% 28% 28% 14% 3	17850
	Night	14% 10% 31% 34% 11% 1	27300

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	6% 14% 4 9% 5% 4 5% 3 6% 9% 34%	4124
	11th to 20th	Day	6% 13% 5% 10% 6% 6% 7% 4 5% 5% 32%	4178
	21st to end	Day	2 10% 4 12% 5% 4 4 3 6% 7% 42%	5843
February	1st to 10th	Day	7% 17% 5% 11% 6% 5% 4 4 4 8% 29%	1890
	11th to 20th	Day	5% 19% 6% 11% 6% 5% 5% 3 5% 6% 30%	1845
	21st to end	Day	6% 15% 5% 10% 7% 5% 5% 3 6% 8% 31%	1557
March	1st to 10th	Day	6% 9% 3 8% 6% 5% 4 4 7% 8% 40%	4967
	11th to 20th	Day	5% 9% 4 10% 7% 6% 6% 5% 6% 7% 35%	5110
	21st to end	Day	9% 19% 6% 11% 6% 5% 5% 4 6% 8% 21%	5607
April	1st to 10th	Day	10% 14% 4 7% 6% 6% 5% 4 6% 7% 32%	2503
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 4 4 6% 6% 29%	2636
	21st to end	Day	16% 12% 3 8% 5% 4 4 4 5% 8% 31%	2730
May	1st to 10th	Day	16% 10% 2 5% 4 3 4 3 6% 7% 39%	7958
	11th to 20th	Day	14% 9% 3 8% 5% 5% 6% 4 7% 7% 32%	8191
	21st to end	Day	13% 5% 2 6% 4 4 5% 4 6% 9% 42%	9042
June	1st to 10th	Day	13% 6% 2 5% 4 4 5% 5% 8% 9% 37%	3150
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 4 8% 10% 36%	3150
	21st to end	Day	8% 3 2 4 4 4 5% 5% 7% 8% 49%	3150
July	1st to 10th	Day	4 2 1 4 4 5% 6% 5% 8% 9% 52%	6780
	11th to 20th	Day	6% 3 1 4 3 3 4 3 6% 7% 61%	6780
	21st to end	Day	3 2 1 4 4 5% 5% 5% 8% 9% 55%	6908
August	1st to 10th	Day	6% 3 2 5% 5% 6% 6% 6% 8% 9% 45%	5779
	11th to 20th	Day	4 2 1 3 3 4 4 4 7% 9% 58%	5798
	21st to end	Day	8% 5% 2 4 3 3 3 3 5% 7% 57%	6389
September	1st to 10th	Day	9% 4 1 4 3 3 3 3 4 7% 58%	2400
	11th to 20th	Day	10% 5% 2 5% 4 5% 4 3 5% 8% 49%	2295
	21st to end	Day	12% 3 1 3 3 3 4 3 5% 8% 54%	2170
October	1st to 10th	Day	10% 5% 1 4 3 3 3 2 3 6% 59%	3270
	11th to 20th	Day	9% 7% 2 5% 3 3 3 2 4 6% 55%	3250
	21st to end	Day	7% 7% 2 6% 4 4 4 3 6% 7% 48%	3432
November	1st to 10th	Day	11% 13% 3 6% 5% 4 4 4 6% 6% 39%	1648
	11th to 20th	Day	7% 13% 3 8% 5% 5% 5% 4 6% 7% 35%	1680
	21st to end	Day	6% 13% 4 7% 5% 6% 5% 4 5% 8% 38%	1680
December	1st to 10th	Day	4 14% 3 8% 5% 4 4 4 6% 7% 41%	2700
	11th to 20th	Day	5% 13% 4 9% 4 4 4 4 5% 8% 42%	2790
	21st to end	Day	6% 13% 5% 9% 5% 4 4 3 5% 5% 40%	3575
January	1st to 10th	Night	4 14% 5% 10% 5% 5% 5% 4 5% 7% 35%	8768
	11th to 20th	Night	6% 16% 4 9% 5% 4 5% 3 5% 6% 36%	8781
	21st to end	Night	4 11% 5% 10% 5% 4 4 4 5% 6% 43%	8430
February	1st to 10th	Night	8% 19% 5% 12% 7% 4 4 3 5% 6% 28%	2730
	11th to 20th	Night	5% 20% 5% 8% 6% 4 5% 4 5% 6% 31%	2662
	21st to end	Night	6% 16% 5% 10% 6% 5% 4 4 5% 7% 31%	2249
March	1st to 10th	Night	4 10% 3 6% 4 4 5% 4 8% 11% 42%	5140
	11th to 20th	Night	4 9% 4 9% 5% 5% 5% 4 6% 8% 41%	5110
	21st to end	Night	12% 18% 5% 10% 6% 5% 4 4 6% 7% 24%	5610
April	1st to 10th	Night	10% 13% 3 7% 5% 4 5% 4 6% 6% 36%	2116
	11th to 20th	Night	12% 14% 5% 8% 4 3 5% 4 6% 7% 31%	1928
	21st to end	Night	15% 11% 3 6% 4 4 5% 5% 5% 6% 37%	1890
May	1st to 10th	Night	14% 9% 2 5% 3 3 4 3 5% 7% 44%	4987
	11th to 20th	Night	15% 11% 3 7% 4 5% 5% 4 7% 7% 33%	4701
	21st to end	Night	11% 5% 1 5% 3 4 4 4 6% 8% 48%	5147
June	1st to 10th	Night	12% 5% 2 7% 6% 5% 4 4 6% 8% 41%	1470
	11th to 20th	Night	15% 6% 2 5% 4 4 5% 4 7% 7% 40%	1470
	21st to end	Night	8% 4 2 4 4 4 4 4 5% 7% 54%	1470
July	1st to 10th	Night	4 3 2 4 4 4 5% 4 7% 8% 55%	3180
	11th to 20th	Night	7% 2 1 3 3 3 3 3 5% 6% 64%	3180
	21st to end	Night	6% 4 2 6% 5% 5% 6% 4 7% 9% 45%	3957
August	1st to 10th	Night	7% 4 2 5% 4 5% 5% 5% 7% 10% 47%	4033
	11th to 20th	Night	5% 3 1 4 3 4 4 5% 8% 10% 53%	4051
	21st to end	Night	9% 5% 2 5% 3 3 4 3 6% 6% 54%	4587
September	1st to 10th	Night	10% 4 1 5% 4 3 4 3 4 7% 56%	2000
	11th to 20th	Night	11% 6% 2 4 3 4 5% 3 5% 8% 50%	2101
	21st to end	Night	12% 4 2 4 3 3 3 3 4 7% 54%	2229
October	1st to 10th	Night	11% 6% 2 4 2 3 3 2 3 5% 59%	3920
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 4 6% 51%	3898
	21st to end	Night	9% 9% 3 7% 4 3 4 3 4 6% 49%	4340
November	1st to 10th	Night	12% 11% 4 6% 4 4 5% 4 6% 7% 39%	2862
	11th to 20th	Night	8% 12% 4 6% 5% 4 5% 4 6% 7% 39%	2940
	21st to end	Night	6% 11% 3 7% 5% 4 4 4 7% 8% 41%	2940
December	1st to 10th	Night	4 15% 5% 7% 4 4 4 2 5% 6% 44%	4710
	11th to 20th	Night	5% 13% 4 9% 5% 5% 5% 5% 6% 7% 37%	5620
	21st to end	Night	5% 12% 4 7% 4 4 4 4 6% 8% 43%	7623

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	42% 9% 14% 27% 7%	4125
	11th to 20th	Day	48% 8% 14% 16% 12% 2	4178
	21st to end	Day	39% 7% 16% 24% 12% 1	5843
February	1st to 10th	Day	54% 7% 14% 15% 9% 2	1890
	11th to 20th	Day	53% 7% 13% 17% 7% 2	1854
	21st to end	Day	51% 9% 12% 15% 10% 3	1557
March	1st to 10th	Day	39% 8% 10% 20% 18% 5%	4967
	11th to 20th	Day	42% 11% 16% 22% 8% 1	5110
	21st to end	Day	57% 13% 11% 16% 3	5607
April	1st to 10th	Day	51% 9% 16% 19% 6% 1	2503
	11th to 20th	Day	55% 8% 13% 18% 6%	2639
	21st to end	Day	52% 8% 13% 19% 7%	2730
May	1st to 10th	Day	44% 6% 9% 28% 11% 1	7958
	11th to 20th	Day	46% 10% 12% 20% 9% 3	8195
	21st to end	Day	36% 9% 14% 27% 14%	9043
June	1st to 10th	Day	43% 12% 16% 21% 8%	3150
	11th to 20th	Day	43% 9% 15% 19% 11% 3	3150
	21st to end	Day	29% 10% 15% 27% 17% 1	3150
July	1st to 10th	Day	24% 8% 14% 27% 20% 7%	6707
	11th to 20th	Day	22% 5% 6% 28% 28% 12%	6699
	21st to end	Day	21% 8% 13% 19% 25% 13%	6709
August	1st to 10th	Day	30% 10% 11% 18% 22% 10%	4208
	11th to 20th	Day	26% 6% 11% 31% 22% 4	4197
	21st to end	Day	24% 6% 9% 28% 27% 7%	4608
September	1st to 10th	Day	28% 6% 10% 25% 22% 9%	2400
	11th to 20th	Day	33% 7% 11% 27% 17% 4	2295
	21st to end	Day	30% 6% 13% 27% 18% 6%	2170
October	1st to 10th	Day	29% 5% 8% 29% 23% 6%	3270
	11th to 20th	Day	31% 5% 12% 29% 19% 2	3250
	21st to end	Day	34% 7% 11% 24% 18% 6%	3432
November	1st to 10th	Day	45% 8% 10% 22% 12% 3	1648
	11th to 20th	Day	44% 9% 18% 19% 8% 2	1680
	21st to end	Day	43% 10% 16% 17% 11% 3	1680
December	1st to 10th	Day	41% 7% 18% 20% 11% 3	2700
	11th to 20th	Day	39% 9% 24% 20% 7% 1	2789
	21st to end	Day	46% 5% 8% 21% 13% 8%	3575
January	1st to 10th	Night	44% 9% 12% 25% 9% 1	8769
	11th to 20th	Night	47% 7% 16% 17% 9% 4	8781
	21st to end	Night	40% 8% 13% 24% 13% 3	8430
February	1st to 10th	Night	56% 7% 13% 15% 7% 2	2730
	11th to 20th	Night	51% 7% 14% 17% 9% 2	2663
	21st to end	Night	51% 8% 13% 17% 9% 3	2249
March	1st to 10th	Night	32% 7% 12% 29% 17% 3	5140
	11th to 20th	Night	36% 10% 19% 26% 8% 1	5110
	21st to end	Night	56% 10% 13% 16% 5%	5610
April	1st to 10th	Night	47% 9% 16% 20% 8% 1	2116
	11th to 20th	Night	51% 9% 12% 19% 7% 1	1928
	21st to end	Night	47% 8% 14% 22% 8%	1890
May	1st to 10th	Night	39% 6% 11% 24% 19% 1	4985
	11th to 20th	Night	45% 9% 10% 23% 12% 2	4702
	21st to end	Night	31% 7% 15% 32% 15%	5148
June	1st to 10th	Night	42% 11% 18% 21% 8% 1	1470
	11th to 20th	Night	41% 8% 15% 21% 13% 2	1470
	21st to end	Night	29% 7% 15% 30% 18% 1	1470
July	1st to 10th	Night	24% 5% 13% 28% 25% 4	3145
	11th to 20th	Night	22% 4 7% 30% 24% 13%	3138
	21st to end	Night	31% 7% 11% 18% 24% 10%	3845
August	1st to 10th	Night	29% 6% 12% 26% 18% 9%	2928
	11th to 20th	Night	26% 6% 10% 33% 21% 3	2928
	21st to end	Night	25% 6% 8% 33% 24% 4	3299
September	1st to 10th	Night	30% 6% 8% 24% 23% 10%	2000
	11th to 20th	Night	33% 7% 12% 28% 16% 4	2101
	21st to end	Night	31% 6% 12% 25% 21% 4	2229
October	1st to 10th	Night	29% 4 8% 28% 24% 7%	3920
	11th to 20th	Night	34% 6% 13% 23% 18% 5%	3898
	21st to end	Night	37% 5% 10% 24% 17% 6%	4340
November	1st to 10th	Night	43% 8% 15% 20% 11% 4	2862
	11th to 20th	Night	42% 9% 17% 20% 10% 1	2940
	21st to end	Night	38% 10% 18% 20% 10% 4	2940
December	1st to 10th	Night	40% 6% 18% 22% 11% 2	4710
	11th to 20th	Night	44% 8% 21% 20% 6% 1	5621
	21st to end	Night	36% 7% 10% 26% 13% 8%	7623

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	8% 22% 30% 21% 14% 4	220
	11th to 20th	Day	16% 19% 31% 23% 7% 4	227
	21st to end	Day	10% 17% 35% 28% 8% 1	363
February	1st to 10th	Day	15% 19% 40% 22% 4 1	330
	11th to 20th	Day	14% 16% 31% 28% 9% 3	330
	21st to end	Day	15% 17% 36% 26% 5% 1	273
March	1st to 10th	Day	15% 19% 32% 24% 8% 2	515
	11th to 20th	Day	14% 19% 33% 23% 9% 2	540
	21st to end	Day	16% 18% 31% 24% 9% 1	594
April	1st to 10th	Day	19% 18% 34% 20% 9% 1	540
	11th to 20th	Day	15% 24% 31% 22% 7% 1	532
	21st to end	Day	24% 14% 26% 24% 12% 1	540
May	1st to 10th	Day	18% 11% 23% 24% 19% 5%	656
	11th to 20th	Day	18% 10% 27% 27% 15% 3	775
	21st to end	Day	19% 9% 20% 27% 20% 5%	844
June	1st to 10th	Day	12% 10% 27% 28% 17% 5%	780
	11th to 20th	Day	17% 14% 30% 25% 12% 2	780
	21st to end	Day	10% 8% 26% 35% 18% 3	780
July	1st to 10th	Day	6% 6% 24% 37% 23% 4	722
	11th to 20th	Day	6% 6% 27% 41% 19% 2	718
	21st to end	Day	3 3 24% 41% 22% 6%	774
August	1st to 10th	Day	6% 7% 26% 38% 19% 5%	527
	11th to 20th	Day	8% 5% 23% 35% 22% 7%	517
	21st to end	Day	7% 8% 27% 33% 17% 8%	583
September	1st to 10th	Day	9% 9% 27% 32% 19% 4	530
	11th to 20th	Day	14% 8% 28% 28% 15% 7%	530
	21st to end	Day	16% 12% 24% 25% 17% 6%	500
October	1st to 10th	Day	15% 8% 25% 28% 18% 7%	330
	11th to 20th	Day	16% 12% 28% 27% 13% 5%	330
	21st to end	Day	14% 19% 28% 28% 9% 2	363
November	1st to 10th	Day	20% 17% 28% 23% 10% 3	330
	11th to 20th	Day	12% 20% 37% 20% 9% 2	330
	21st to end	Day	9% 19% 34% 27% 10% 1	330
December	1st to 10th	Day	15% 19% 33% 22% 10% 1	330
	11th to 20th	Day	18% 17% 33% 20% 11% 1	245
	21st to end	Day	15% 18% 29% 24% 12% 2	242
January	1st to 10th	Night	12% 15% 37% 27% 8% 1	1050
	11th to 20th	Night	16% 16% 39% 22% 6% 1	1050
	21st to end	Night	12% 17% 38% 26% 6% 1	945
February	1st to 10th	Night	15% 15% 34% 27% 9% 1	840
	11th to 20th	Night	14% 13% 36% 30% 6% 1	824
	21st to end	Night	12% 13% 35% 28% 9% 1	692
March	1st to 10th	Night	10% 9% 37% 34% 9% 1	840
	11th to 20th	Night	11% 8% 37% 35% 9% 1	840
	21st to end	Night	19% 8% 33% 30% 9% 1	924
April	1st to 10th	Night	14% 11% 33% 35% 7%	646
	11th to 20th	Night	19% 9% 31% 33% 8%	623
	21st to end	Night	21% 8% 26% 34% 9% 1	630
May	1st to 10th	Night	18% 7% 24% 37% 13% 1	630
	11th to 20th	Night	17% 7% 23% 37% 16% 1	621
	21st to end	Night	19% 7% 20% 36% 17% 1	675
June	1st to 10th	Night	14% 7% 22% 40% 16% 2	420
	11th to 20th	Night	16% 6% 33% 35% 9% 1	420
	21st to end	Night	9% 4 22% 49% 16% 1	420
July	1st to 10th	Night	8% 2 18% 50% 22% 1	390
	11th to 20th	Night	8% 4 19% 53% 16% 1	388
	21st to end	Night	6% 5% 21% 52% 17%	628
August	1st to 10th	Night	6% 5% 19% 49% 20% 1	597
	11th to 20th	Night	8% 4 17% 51% 19% 1	594
	21st to end	Night	10% 6% 21% 45% 17% 1	660
September	1st to 10th	Night	10% 4 21% 49% 16% 1	600
	11th to 20th	Night	13% 3 23% 40% 19% 2	701
	21st to end	Night	14% 5% 24% 37% 18% 3	800
October	1st to 10th	Night	17% 7% 25% 34% 16% 1	800
	11th to 20th	Night	17% 9% 29% 33% 11% 1	800
	21st to end	Night	14% 11% 33% 31% 9% 1	880
November	1st to 10th	Night	18% 11% 36% 26% 7% 1	1017
	11th to 20th	Night	14% 17% 38% 25% 6%	1050
	21st to end	Night	11% 14% 38% 32% 6%	1050
December	1st to 10th	Night	12% 16% 35% 28% 9%	1050
	11th to 20th	Night	12% 14% 40% 26% 6% 1	1050
	21st to end	Night	13% 14% 38% 27% 7% 1	1155

Page generated at 2026-06-28 00:10:44. Version ac07

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