Pine Bluff Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pine Bluff Observatory clear sky chart from 2005-11-06 to 2025-09-04.

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 8% 5% 4 4 4 6% 7% 38%	126457
	Night	12% 9% 4 8% 5% 4 4 4 5% 6% 39%	122520
Transparency	Day	44% 5% 12% 25% 14% 1	129939
	Night	44% 4 11% 23% 15% 2	127111
Seeing	Day	17% 11% 30% 25% 14% 4	17085
	Night	17% 10% 31% 30% 11% 1	26873

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	7% 10% 6% 18% 7% 6% 5% 4 5% 6% 26%	3617
	11th to 20th	Day	7% 10% 8% 12% 5% 4 5% 6% 7% 7% 30%	3620
	21st to end	Day	12% 14% 8% 9% 4 3 3 2 4 5% 35%	4212
February	1st to 10th	Day	12% 13% 6% 11% 5% 4 5% 4 5% 7% 30%	1800
	11th to 20th	Day	12% 11% 4 9% 5% 5% 5% 4 5% 6% 35%	1866
	21st to end	Day	12% 13% 4 11% 6% 5% 4 3 5% 5% 32%	1650
March	1st to 10th	Day	14% 8% 3 5% 4 3 3 3 4 6% 46%	4480
	11th to 20th	Day	11% 6% 2 8% 5% 4 5% 4 5% 7% 43%	4842
	21st to end	Day	21% 12% 4 10% 5% 4 4 3 4 5% 29%	5870
April	1st to 10th	Day	17% 13% 3 8% 4 5% 4 3 5% 6% 30%	2400
	11th to 20th	Day	17% 11% 3 8% 5% 4 4 4 5% 6% 33%	2374
	21st to end	Day	18% 10% 3 8% 5% 5% 4 3 5% 6% 32%	2451
May	1st to 10th	Day	14% 7% 2 6% 5% 4 4 3 6% 6% 40%	6124
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	6319
	21st to end	Day	15% 7% 3 6% 4 4 5% 4 6% 9% 38%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 4 7% 9% 44%	2800
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 4 6% 9% 41%	2800
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 6% 9% 39%	2800
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 39%	6360
	11th to 20th	Day	7% 6% 2 6% 4 4 5% 4 6% 9% 47%	6360
	21st to end	Day	10% 6% 2 7% 5% 4 6% 4 6% 9% 39%	6924
August	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 7% 10% 41%	4468
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 5% 8% 47%	3957
	21st to end	Day	9% 6% 2 6% 4 4 4 4 6% 10% 45%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 3 5% 7% 44%	2316
	11th to 20th	Day	12% 6% 2 4 3 3 3 3 6% 8% 49%	2231
	21st to end	Day	13% 7% 2 7% 4 5% 4 3 5% 6% 45%	2090
October	1st to 10th	Day	12% 7% 3 6% 4 3 3 4 4 7% 47%	1921
	11th to 20th	Day	18% 10% 3 7% 4 4 4 3 5% 7% 36%	1900
	21st to end	Day	18% 10% 3 6% 4 4 3 3 4 5% 40%	1926
November	1st to 10th	Day	11% 9% 3 7% 5% 4 5% 3 4 7% 43%	1762
	11th to 20th	Day	14% 12% 5% 9% 5% 5% 4 3 5% 6% 33%	1770
	21st to end	Day	13% 13% 4 10% 5% 3 3 3 4 6% 36%	1600
December	1st to 10th	Day	8% 9% 4 8% 5% 4 5% 4 6% 8% 38%	2610
	11th to 20th	Day	12% 14% 5% 11% 7% 5% 4 4 6% 6% 24%	3008
	21st to end	Day	17% 23% 9% 12% 5% 4 4 4 5% 4 14%	3982
January	1st to 10th	Night	8% 10% 6% 14% 7% 4 4 3 5% 5% 32%	6348
	11th to 20th	Night	10% 12% 6% 13% 7% 5% 5% 5% 7% 6% 24%	6360
	21st to end	Night	11% 14% 8% 10% 5% 5% 4 3 5% 5% 31%	6748
February	1st to 10th	Night	10% 14% 4 9% 6% 5% 5% 3 5% 6% 32%	2600
	11th to 20th	Night	11% 11% 3 8% 6% 4 5% 3 5% 6% 38%	2421
	21st to end	Night	15% 12% 4 8% 5% 3 3 3 5% 5% 36%	1980
March	1st to 10th	Night	15% 9% 3 7% 4 4 4 3 4 4 42%	5373
	11th to 20th	Night	9% 7% 2 6% 4 3 4 3 6% 8% 47%	5146
	21st to end	Night	22% 12% 4 10% 6% 4 4 3 4 5% 27%	5059
April	1st to 10th	Night	17% 9% 3 7% 5% 4 4 3 5% 6% 37%	2000
	11th to 20th	Night	18% 9% 3 7% 5% 4 3 3 5% 6% 38%	1975
	21st to end	Night	17% 8% 3 6% 4 4 5% 4 6% 7% 37%	1947
May	1st to 10th	Night	16% 7% 3 6% 3 4 4 4 6% 7% 40%	3779
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 5% 8% 47%	3596
	21st to end	Night	14% 8% 2 6% 5% 4 5% 4 5% 7% 39%	3942
June	1st to 10th	Night	8% 5% 2 6% 4 5% 4 4 8% 9% 45%	1600
	11th to 20th	Night	12% 7% 1 4 4 4 4 3 6% 10% 45%	1600
	21st to end	Night	9% 6% 2 6% 4 3 4 4 6% 7% 50%	1600
July	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 7% 8% 43%	3618
	11th to 20th	Night	5% 5% 2 6% 4 4 5% 3 5% 8% 53%	3617
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 50%	3947
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 49%	2689
	11th to 20th	Night	9% 7% 2 6% 3 4 4 3 6% 8% 48%	3094
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 6% 7% 50%	3586
September	1st to 10th	Night	9% 5% 2 5% 3 3 4 2 5% 7% 55%	1930
	11th to 20th	Night	11% 4 2 5% 4 4 3 3 5% 7% 51%	1929
	21st to end	Night	10% 6% 2 5% 4 3 4 4 5% 7% 50%	2090
October	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 4 6% 50%	2256
	11th to 20th	Night	16% 7% 2 6% 4 4 3 3 5% 6% 43%	2280
	21st to end	Night	17% 8% 3 6% 4 4 4 4 6% 7% 36%	2670
November	1st to 10th	Night	12% 8% 3 6% 4 4 4 4 4 6% 46%	2536
	11th to 20th	Night	13% 10% 4 9% 6% 5% 5% 4 5% 5% 34%	2629
	21st to end	Night	16% 11% 4 8% 4 3 4 3 4 6% 37%	2800
December	1st to 10th	Night	8% 9% 3 8% 5% 5% 4 4 5% 7% 42%	4580
	11th to 20th	Night	13% 17% 7% 10% 5% 5% 5% 3 4 5% 26%	5199
	21st to end	Night	18% 20% 6% 13% 6% 5% 4 3 4 4 17%	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	59% 3 12% 19% 7%	3618
	11th to 20th	Day	51% 4 10% 14% 19% 2	3620
	21st to end	Day	52% 3 12% 19% 13%	4212
February	1st to 10th	Day	54% 3 11% 18% 12% 1	1800
	11th to 20th	Day	49% 5% 11% 23% 10% 2	1875
	21st to end	Day	54% 4 8% 20% 11% 2	1650
March	1st to 10th	Day	40% 3 11% 29% 12% 4	4480
	11th to 20th	Day	39% 4 12% 30% 14% 2	4842
	21st to end	Day	58% 4 11% 15% 10% 2	5872
April	1st to 10th	Day	54% 4 9% 21% 12%	2400
	11th to 20th	Day	51% 4 9% 21% 12% 2	2374
	21st to end	Day	53% 5% 11% 19% 11% 2	2451
May	1st to 10th	Day	42% 5% 9% 25% 18% 1	6159
	11th to 20th	Day	40% 7% 9% 28% 15%	6323
	21st to end	Day	42% 5% 11% 27% 12% 2	6949
June	1st to 10th	Day	37% 5% 14% 28% 15% 2	2800
	11th to 20th	Day	38% 6% 13% 25% 17% 1	2800
	21st to end	Day	40% 6% 14% 24% 15% 1	2800
July	1st to 10th	Day	38% 6% 14% 30% 9% 1	6291
	11th to 20th	Day	34% 6% 14% 31% 14% 1	6285
	21st to end	Day	40% 7% 14% 22% 16% 1	6728
August	1st to 10th	Day	38% 6% 14% 29% 13% 1	4453
	11th to 20th	Day	35% 5% 14% 33% 13% 1	3995
	21st to end	Day	34% 5% 13% 30% 16% 1	4311
September	1st to 10th	Day	38% 6% 10% 26% 18% 2	2316
	11th to 20th	Day	32% 5% 11% 33% 17% 2	2231
	21st to end	Day	40% 5% 9% 29% 16% 1	2090
October	1st to 10th	Day	24% 3 6% 41% 26% 1	3194
	11th to 20th	Day	36% 3 9% 27% 23% 2	3140
	21st to end	Day	43% 2 10% 28% 14% 3	3151
November	1st to 10th	Day	41% 4 13% 26% 14% 2	1762
	11th to 20th	Day	51% 4 12% 21% 11% 1	1770
	21st to end	Day	51% 4 15% 23% 7% 1	1600
December	1st to 10th	Day	43% 3 21% 25% 7% 1	2610
	11th to 20th	Day	59% 3 12% 18% 6% 2	3005
	21st to end	Day	73% 3 7% 10% 6%	3982
January	1st to 10th	Night	52% 4 9% 23% 11% 1	6348
	11th to 20th	Night	58% 4 9% 12% 17% 1	6360
	21st to end	Night	55% 4 11% 18% 12%	6748
February	1st to 10th	Night	53% 3 11% 19% 13% 2	2600
	11th to 20th	Night	47% 4 10% 24% 14% 1	2422
	21st to end	Night	51% 3 11% 20% 12% 3	1980
March	1st to 10th	Night	45% 3 11% 23% 10% 7%	5373
	11th to 20th	Night	34% 5% 10% 33% 14% 4	5146
	21st to end	Night	60% 4 8% 16% 11% 1	5059
April	1st to 10th	Night	47% 5% 10% 22% 15% 2	2000
	11th to 20th	Night	48% 3 7% 21% 18% 3	1975
	21st to end	Night	44% 6% 12% 24% 12% 2	1947
May	1st to 10th	Night	42% 6% 11% 18% 21% 2	3806
	11th to 20th	Night	35% 7% 14% 23% 19% 2	3597
	21st to end	Night	41% 8% 9% 25% 15% 3	3950
June	1st to 10th	Night	32% 6% 13% 29% 19% 1	1600
	11th to 20th	Night	35% 5% 11% 25% 22% 2	1600
	21st to end	Night	33% 5% 17% 23% 19% 3	1600
July	1st to 10th	Night	37% 6% 14% 28% 13% 2	3580
	11th to 20th	Night	30% 5% 13% 32% 18% 2	3572
	21st to end	Night	31% 7% 16% 24% 20% 3	3832
August	1st to 10th	Night	32% 5% 14% 27% 20% 1	2680
	11th to 20th	Night	33% 4 13% 32% 16% 1	3122
	21st to end	Night	33% 5% 12% 28% 19% 3	3586
September	1st to 10th	Night	29% 5% 11% 29% 23% 2	1930
	11th to 20th	Night	31% 5% 11% 33% 19% 2	1929
	21st to end	Night	32% 5% 10% 31% 22% 1	2090
October	1st to 10th	Night	25% 3 5% 37% 28% 2	3763
	11th to 20th	Night	33% 3 11% 28% 24% 2	3779
	21st to end	Night	43% 4 9% 27% 15% 2	4395
November	1st to 10th	Night	39% 5% 10% 26% 16% 3	2536
	11th to 20th	Night	50% 4 12% 20% 12% 2	2629
	21st to end	Night	48% 4 13% 23% 10% 1	2800
December	1st to 10th	Night	41% 4 17% 29% 9% 1	4580
	11th to 20th	Night	60% 4 10% 16% 9% 1	5201
	21st to end	Night	70% 4 7% 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	16% 15% 34% 24% 10% 1	300
	11th to 20th	Day	15% 21% 40% 18% 6% 1	300
	21st to end	Day	23% 16% 35% 21% 5%	330
February	1st to 10th	Day	18% 20% 40% 17% 5%	300
	11th to 20th	Day	21% 20% 38% 17% 5%	300
	21st to end	Day	22% 19% 44% 14% 1	249
March	1st to 10th	Day	19% 19% 43% 14% 5%	300
	11th to 20th	Day	21% 20% 36% 17% 4 3	300
	21st to end	Day	29% 13% 32% 19% 6% 1	505
April	1st to 10th	Day	24% 17% 34% 19% 5%	500
	11th to 20th	Day	26% 19% 25% 18% 11% 1	492
	21st to end	Day	23% 15% 29% 22% 9% 2	500
May	1st to 10th	Day	21% 11% 32% 25% 9% 2	609
	11th to 20th	Day	18% 13% 29% 24% 13% 3	725
	21st to end	Day	19% 9% 27% 25% 16% 5%	789
June	1st to 10th	Day	11% 8% 29% 30% 18% 4	730
	11th to 20th	Day	14% 6% 33% 28% 15% 4	730
	21st to end	Day	13% 8% 31% 29% 15% 5%	730
July	1st to 10th	Day	8% 5% 19% 32% 25% 12%	721
	11th to 20th	Day	11% 6% 24% 30% 20% 9%	718
	21st to end	Day	9% 3 26% 34% 22% 7%	794
August	1st to 10th	Day	8% 4 20% 34% 24% 10%	726
	11th to 20th	Day	14% 4 19% 27% 23% 12%	591
	21st to end	Day	10% 7% 21% 31% 22% 9%	583
September	1st to 10th	Day	14% 8% 23% 26% 20% 8%	502
	11th to 20th	Day	12% 3 21% 31% 24% 8%	490
	21st to end	Day	15% 11% 27% 25% 18% 4	490
October	1st to 10th	Day	17% 10% 28% 26% 16% 3	321
	11th to 20th	Day	25% 16% 34% 17% 7%	300
	21st to end	Day	26% 17% 31% 20% 5% 2	330
November	1st to 10th	Day	17% 16% 37% 24% 6% 1	300
	11th to 20th	Day	21% 19% 36% 15% 9%	300
	21st to end	Day	23% 14% 40% 18% 4	300
December	1st to 10th	Day	17% 18% 41% 16% 6% 1	300
	11th to 20th	Day	20% 13% 40% 19% 8% 1	300
	21st to end	Day	27% 18% 35% 18% 2 1	330
January	1st to 10th	Night	16% 17% 36% 24% 7% 1	1000
	11th to 20th	Night	19% 13% 38% 24% 4 1	1000
	21st to end	Night	19% 13% 37% 25% 5% 1	1100
February	1st to 10th	Night	18% 14% 37% 25% 6%	1000
	11th to 20th	Night	16% 15% 39% 26% 4	866
	21st to end	Night	23% 14% 40% 20% 3	660
March	1st to 10th	Night	22% 12% 36% 23% 6% 1	800
	11th to 20th	Night	16% 12% 37% 28% 7%	675
	21st to end	Night	22% 11% 34% 27% 6% 1	660
April	1st to 10th	Night	20% 12% 39% 24% 4	600
	11th to 20th	Night	22% 13% 29% 28% 7%	593
	21st to end	Night	20% 10% 32% 29% 8% 1	600
May	1st to 10th	Night	20% 8% 33% 31% 7% 1	600
	11th to 20th	Night	18% 7% 30% 34% 10%	591
	21st to end	Night	14% 5% 27% 37% 15% 1	650
June	1st to 10th	Night	10% 4 29% 42% 15%	600
	11th to 20th	Night	15% 6% 29% 38% 13%	600
	21st to end	Night	10% 5% 28% 42% 16%	600
July	1st to 10th	Night	9% 3 12% 42% 30% 4	585
	11th to 20th	Night	8% 3 23% 42% 23% 2	582
	21st to end	Night	8% 1 18% 49% 22% 3	657
August	1st to 10th	Night	6% 2 15% 48% 25% 3	597
	11th to 20th	Night	10% 2 13% 43% 26% 5%	594
	21st to end	Night	10% 2 18% 43% 23% 3	660
September	1st to 10th	Night	9% 5% 23% 34% 22% 6%	579
	11th to 20th	Night	13% 3 22% 36% 23% 3	599
	21st to end	Night	13% 8% 24% 36% 18% 2	760
October	1st to 10th	Night	15% 5% 29% 32% 18% 1	760
	11th to 20th	Night	19% 12% 31% 29% 8%	760
	21st to end	Night	22% 11% 33% 27% 6% 1	836
November	1st to 10th	Night	15% 11% 39% 25% 9% 1	780
	11th to 20th	Night	19% 15% 38% 21% 6%	829
	21st to end	Night	21% 15% 34% 24% 6%	1000
December	1st to 10th	Night	19% 14% 39% 22% 5%	1000
	11th to 20th	Night	23% 12% 35% 23% 6% 1	1000
	21st to end	Night	27% 13% 33% 22% 4	1100

Page generated at 2025-09-01 00:51:04. Version ac07

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