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 2024-03-28.

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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	78697
	Night	13% 9% 4 7% 6% 3 4 4 5% 6% 37%	81353
Transparency	Day	47% 5% 12% 23% 12% 1	78397
	Night	47% 5% 11% 23% 13% 2	81173
Seeing	Day	17% 10% 29% 25% 14% 5%	14954
	Night	17% 10% 31% 30% 11% 1	25033

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	11% 13% 9% 15% 7% 3 4 4 4 5% 27%	2527
	11th to 20th	Day	9% 11% 6% 12% 9% 4 5% 9% 8% 7% 20%	2530
	21st to end	Day	16% 17% 11% 11% 6% 3 3 3 4 5% 21%	2943
February	1st to 10th	Day	12% 12% 6% 9% 5% 3 5% 5% 5% 7% 31%	1710
	11th to 20th	Day	13% 10% 4 8% 6% 3 5% 5% 5% 6% 35%	1770
	21st to end	Day	12% 12% 5% 9% 7% 4 5% 4 5% 6% 31%	1570
March	1st to 10th	Day	13% 9% 6% 7% 6% 3 5% 4 5% 6% 36%	1900
	11th to 20th	Day	12% 8% 3 7% 6% 3 4 5% 6% 7% 38%	2033
	21st to end	Day	20% 11% 4 8% 5% 3 5% 4 5% 7% 29%	2417
April	1st to 10th	Day	18% 12% 4 7% 5% 3 5% 4 5% 7% 30%	2160
	11th to 20th	Day	17% 10% 3 7% 6% 3 4 5% 5% 6% 34%	2134
	21st to end	Day	19% 10% 4 8% 5% 4 4 4 5% 6% 32%	2205
May	1st to 10th	Day	17% 8% 3 6% 7% 3 6% 5% 6% 7% 31%	2434
	11th to 20th	Day	17% 7% 3 7% 6% 3 5% 5% 5% 7% 34%	2479
	21st to end	Day	15% 7% 3 5% 6% 3 6% 5% 6% 8% 37%	2725
June	1st to 10th	Day	10% 5% 2 5% 6% 3 4 5% 6% 9% 44%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 6% 9% 42%	2520
	21st to end	Day	11% 6% 3 6% 5% 4 5% 6% 6% 10% 39%	2520
July	1st to 10th	Day	7% 5% 2 4 5% 3 5% 5% 7% 10% 47%	2520
	11th to 20th	Day	7% 4 2 5% 5% 3 5% 6% 7% 9% 45%	2520
	21st to end	Day	8% 4 2 5% 5% 3 6% 5% 6% 11% 46%	2743
August	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 6% 8% 12% 41%	2457
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 4 5% 8% 43%	2190
	21st to end	Day	10% 5% 2 6% 5% 3 5% 5% 5% 9% 46%	2376
September	1st to 10th	Day	13% 6% 2 5% 6% 3 5% 4 5% 7% 43%	2160
	11th to 20th	Day	13% 5% 3 4 4 2 4 4 6% 7% 49%	2114
	21st to end	Day	13% 7% 3 6% 5% 4 4 4 5% 6% 44%	1980
October	1st to 10th	Day	13% 7% 3 6% 5% 3 4 4 4 7% 46%	1820
	11th to 20th	Day	19% 10% 3 7% 5% 3 4 4 5% 7% 35%	1800
	21st to end	Day	19% 10% 4 6% 4 3 3 4 4 5% 39%	1825
November	1st to 10th	Day	10% 8% 3 6% 6% 3 4 4 5% 7% 44%	1672
	11th to 20th	Day	14% 10% 5% 8% 6% 4 5% 4 5% 6% 34%	1682
	21st to end	Day	14% 11% 4 8% 6% 3 4 3 4 6% 37%	1520
December	1st to 10th	Day	14% 14% 5% 8% 7% 3 4 4 5% 7% 30%	1520
	11th to 20th	Day	13% 14% 5% 9% 7% 3 4 5% 6% 6% 28%	1918
	21st to end	Day	18% 20% 10% 11% 6% 3 4 4 4 4 16%	2783
January	1st to 10th	Night	11% 12% 8% 11% 7% 3 4 4 4 5% 30%	4428
	11th to 20th	Night	11% 13% 8% 12% 8% 3 4 6% 7% 6% 21%	4440
	21st to end	Night	15% 17% 9% 10% 6% 4 4 3 4 4 23%	4720
February	1st to 10th	Night	10% 13% 5% 8% 6% 4 5% 5% 4 7% 33%	2470
	11th to 20th	Night	11% 9% 4 6% 7% 3 5% 4 5% 6% 39%	2297
	21st to end	Night	16% 11% 4 8% 6% 3 3 3 5% 5% 36%	1884
March	1st to 10th	Night	17% 9% 4 6% 6% 3 5% 4 5% 6% 36%	2280
	11th to 20th	Night	12% 6% 3 5% 5% 4 5% 5% 6% 8% 40%	2161
	21st to end	Night	19% 10% 4 8% 6% 3 5% 4 5% 6% 30%	2093
April	1st to 10th	Night	17% 8% 4 6% 6% 3 4 4 5% 7% 36%	1800
	11th to 20th	Night	19% 9% 2 6% 5% 3 4 4 5% 6% 37%	1775
	21st to end	Night	18% 7% 3 5% 5% 3 5% 5% 5% 7% 37%	1753
May	1st to 10th	Night	17% 6% 3 7% 5% 3 5% 5% 7% 9% 34%	1522
	11th to 20th	Night	17% 7% 3 6% 5% 3 5% 5% 4 7% 37%	1416
	21st to end	Night	12% 6% 2 5% 6% 2 4 5% 6% 9% 43%	1551
June	1st to 10th	Night	8% 4 2 5% 5% 4 5% 5% 8% 9% 45%	1440
	11th to 20th	Night	12% 6% 1 4 4 2 4 4 6% 10% 46%	1440
	21st to end	Night	8% 5% 2 4 5% 2 3 5% 6% 7% 52%	1440
July	1st to 10th	Night	6% 3 1 3 4 3 4 5% 6% 9% 56%	1440
	11th to 20th	Night	6% 4 3 5% 4 2 3 4 5% 7% 55%	1440
	21st to end	Night	6% 3 2 3 4 3 4 5% 7% 10% 52%	1575
August	1st to 10th	Night	5% 4 3 4 5% 3 5% 6% 6% 9% 49%	1479
	11th to 20th	Night	8% 5% 2 5% 4 2 4 4 6% 9% 51%	1710
	21st to end	Night	9% 4 2 4 4 3 5% 4 5% 6% 53%	1980
September	1st to 10th	Night	10% 5% 2 5% 4 2 4 3 5% 7% 53%	1800
	11th to 20th	Night	11% 4 2 4 4 2 3 4 5% 7% 52%	1827
	21st to end	Night	10% 6% 2 4 4 3 4 4 5% 7% 50%	1980
October	1st to 10th	Night	12% 6% 2 5% 5% 3 3 5% 4 7% 49%	2137
	11th to 20th	Night	17% 7% 3 5% 5% 3 3 4 5% 6% 42%	2160
	21st to end	Night	18% 8% 3 6% 4 3 5% 4 6% 7% 36%	2529
November	1st to 10th	Night	11% 8% 3 5% 4 3 5% 5% 4 6% 47%	2406
	11th to 20th	Night	13% 9% 4 8% 6% 4 5% 5% 5% 6% 34%	2497
	21st to end	Night	17% 9% 4 6% 5% 3 4 4 4 6% 38%	2660
December	1st to 10th	Night	13% 13% 4 9% 6% 4 5% 5% 5% 6% 30%	2660
	11th to 20th	Night	14% 13% 7% 9% 6% 3 5% 4 5% 5% 28%	3279
	21st to end	Night	20% 17% 6% 10% 6% 4 5% 5% 4 4 20%	4884

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	62% 3 12% 16% 6%	2528
	11th to 20th	Day	59% 6% 10% 18% 8%	2530
	21st to end	Day	66% 3 10% 15% 5%	2943
February	1st to 10th	Day	54% 4 12% 19% 12% 1	1710
	11th to 20th	Day	49% 5% 11% 23% 11% 2	1779
	21st to end	Day	54% 4 8% 20% 11% 3	1570
March	1st to 10th	Day	49% 5% 12% 23% 10% 1	1900
	11th to 20th	Day	45% 4 12% 24% 13% 1	2033
	21st to end	Day	56% 4 10% 21% 8% 1	2417
April	1st to 10th	Day	54% 5% 10% 20% 11%	2160
	11th to 20th	Day	51% 4 9% 21% 12% 2	2134
	21st to end	Day	53% 5% 10% 19% 11% 2	2205
May	1st to 10th	Day	51% 6% 13% 22% 8% 1	2434
	11th to 20th	Day	49% 5% 11% 22% 12%	2483
	21st to end	Day	46% 6% 12% 21% 14% 2	2725
June	1st to 10th	Day	37% 5% 14% 28% 15% 2	2520
	11th to 20th	Day	37% 6% 13% 25% 17% 2	2520
	21st to end	Day	40% 6% 14% 24% 14% 1	2520
July	1st to 10th	Day	32% 6% 15% 30% 14% 2	2451
	11th to 20th	Day	34% 6% 16% 25% 17% 2	2445
	21st to end	Day	32% 5% 17% 29% 15% 3	2591
August	1st to 10th	Day	34% 7% 16% 30% 12% 1	2442
	11th to 20th	Day	40% 4 14% 28% 13% 1	2190
	21st to end	Day	34% 6% 12% 27% 19% 2	2376
September	1st to 10th	Day	40% 6% 10% 25% 17% 2	2160
	11th to 20th	Day	33% 5% 12% 32% 16% 2	2114
	21st to end	Day	41% 5% 9% 30% 14% 1	1980
October	1st to 10th	Day	40% 4 9% 30% 16% 1	1820
	11th to 20th	Day	50% 4 10% 23% 12% 1	1800
	21st to end	Day	49% 3 11% 23% 13% 1	1825
November	1st to 10th	Day	41% 4 13% 26% 14% 2	1672
	11th to 20th	Day	51% 4 12% 21% 11% 1	1682
	21st to end	Day	49% 4 16% 23% 8% 1	1520
December	1st to 10th	Day	55% 3 14% 18% 8% 1	1520
	11th to 20th	Day	55% 3 15% 16% 8% 3	1915
	21st to end	Day	72% 4 8% 10% 6%	2783
January	1st to 10th	Night	56% 5% 9% 21% 9%	4428
	11th to 20th	Night	62% 4 9% 16% 9%	4440
	21st to end	Night	66% 3 8% 16% 6% 1	4720
February	1st to 10th	Night	53% 3 10% 20% 13% 2	2470
	11th to 20th	Night	46% 4 10% 24% 14% 1	2298
	21st to end	Night	51% 3 10% 21% 12% 3	1884
March	1st to 10th	Night	49% 4 12% 22% 10% 3	2280
	11th to 20th	Night	40% 5% 12% 24% 17% 2	2161
	21st to end	Night	56% 3 9% 20% 10% 2	2093
April	1st to 10th	Night	48% 5% 10% 21% 14% 2	1800
	11th to 20th	Night	49% 3 7% 19% 18% 3	1775
	21st to end	Night	44% 6% 12% 23% 13% 2	1753
May	1st to 10th	Night	45% 7% 13% 21% 14%	1522
	11th to 20th	Night	47% 5% 10% 22% 15% 1	1417
	21st to end	Night	37% 6% 13% 26% 16% 2	1552
June	1st to 10th	Night	33% 6% 13% 28% 19% 1	1440
	11th to 20th	Night	34% 5% 10% 26% 23% 2	1440
	21st to end	Night	31% 5% 18% 25% 18% 3	1440
July	1st to 10th	Night	25% 6% 13% 34% 19% 4	1400
	11th to 20th	Night	29% 5% 11% 30% 21% 3	1392
	21st to end	Night	25% 7% 17% 30% 17% 5%	1487
August	1st to 10th	Night	30% 7% 16% 29% 16% 3	1470
	11th to 20th	Night	30% 5% 15% 32% 17% 1	1710
	21st to end	Night	31% 5% 11% 28% 21% 4	1980
September	1st to 10th	Night	31% 5% 12% 27% 22% 3	1800
	11th to 20th	Night	31% 5% 11% 33% 18% 2	1827
	21st to end	Night	33% 5% 10% 31% 20% 1	1980
October	1st to 10th	Night	36% 5% 8% 30% 20% 2	2137
	11th to 20th	Night	43% 3 12% 24% 18% 1	2160
	21st to end	Night	47% 5% 11% 24% 13% 1	2529
November	1st to 10th	Night	38% 5% 10% 27% 17% 3	2406
	11th to 20th	Night	50% 4 12% 20% 12% 1	2497
	21st to end	Night	47% 4 13% 24% 10% 1	2660
December	1st to 10th	Night	54% 5% 12% 20% 8% 1	2660
	11th to 20th	Night	57% 5% 11% 18% 8% 1	3281
	21st to end	Night	67% 5% 8% 15% 5%	4884

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% 33% 23% 10% 1	270
	11th to 20th	Day	17% 19% 39% 19% 6% 1	270
	21st to end	Day	24% 14% 34% 22% 5%	297
February	1st to 10th	Day	16% 20% 40% 18% 5%	270
	11th to 20th	Day	21% 21% 37% 16% 5%	270
	21st to end	Day	21% 17% 45% 15% 1	225
March	1st to 10th	Day	19% 19% 43% 14% 5%	270
	11th to 20th	Day	19% 19% 37% 17% 5% 3	270
	21st to end	Day	29% 11% 31% 20% 7% 2	447
April	1st to 10th	Day	24% 15% 35% 20% 6%	420
	11th to 20th	Day	26% 17% 25% 20% 11% 2	412
	21st to end	Day	23% 13% 28% 23% 10% 2	420
May	1st to 10th	Day	21% 11% 34% 25% 8% 2	517
	11th to 20th	Day	20% 12% 30% 24% 12% 2	625
	21st to end	Day	19% 7% 26% 24% 18% 6%	679
June	1st to 10th	Day	10% 7% 29% 31% 19% 5%	630
	11th to 20th	Day	15% 6% 29% 29% 17% 5%	630
	21st to end	Day	13% 7% 29% 30% 16% 5%	630
July	1st to 10th	Day	8% 4 17% 32% 26% 13%	621
	11th to 20th	Day	10% 5% 25% 31% 20% 9%	618
	21st to end	Day	9% 3 27% 33% 22% 6%	684
August	1st to 10th	Day	8% 3 18% 35% 25% 11%	626
	11th to 20th	Day	13% 5% 18% 27% 24% 14%	504
	21st to end	Day	11% 6% 22% 30% 22% 10%	495
September	1st to 10th	Day	15% 8% 23% 27% 20% 7%	450
	11th to 20th	Day	14% 3 21% 31% 22% 9%	450
	21st to end	Day	16% 12% 26% 24% 18% 5%	450
October	1st to 10th	Day	19% 9% 26% 27% 17% 4	290
	11th to 20th	Day	26% 16% 35% 16% 7%	270
	21st to end	Day	27% 16% 30% 21% 5% 2	297
November	1st to 10th	Day	15% 15% 38% 24% 6% 1	270
	11th to 20th	Day	20% 18% 37% 16% 9%	270
	21st to end	Day	23% 14% 40% 19% 5%	270
December	1st to 10th	Day	18% 18% 40% 16% 6% 1	270
	11th to 20th	Day	20% 12% 39% 20% 9% 1	270
	21st to end	Day	27% 18% 36% 17% 2	297
January	1st to 10th	Night	16% 17% 36% 23% 7% 1	950
	11th to 20th	Night	20% 13% 38% 24% 5% 1	950
	21st to end	Night	20% 12% 37% 26% 5% 1	1045
February	1st to 10th	Night	18% 13% 37% 26% 6%	950
	11th to 20th	Night	16% 14% 39% 26% 4	822
	21st to end	Night	23% 14% 39% 20% 3	628
March	1st to 10th	Night	22% 12% 36% 23% 6% 1	760
	11th to 20th	Night	16% 11% 37% 28% 7%	641
	21st to end	Night	22% 10% 33% 27% 6% 1	615
April	1st to 10th	Night	20% 12% 39% 25% 4	540
	11th to 20th	Night	23% 12% 29% 29% 8%	533
	21st to end	Night	20% 9% 32% 29% 9% 1	540
May	1st to 10th	Night	20% 8% 34% 29% 7% 1	540
	11th to 20th	Night	18% 7% 31% 34% 9%	531
	21st to end	Night	14% 5% 27% 36% 17% 1	584
June	1st to 10th	Night	10% 4 29% 42% 16%	540
	11th to 20th	Night	15% 6% 27% 38% 14%	540
	21st to end	Night	10% 3 26% 43% 17%	540
July	1st to 10th	Night	8% 3 11% 42% 32% 5%	525
	11th to 20th	Night	7% 3 23% 42% 23% 2	522
	21st to end	Night	8% 1 18% 49% 22% 2	591
August	1st to 10th	Night	6% 2 15% 48% 25% 4	537
	11th to 20th	Night	10% 2 13% 43% 27% 5%	534
	21st to end	Night	10% 3 18% 43% 23% 3	594
September	1st to 10th	Night	9% 5% 24% 34% 21% 6%	540
	11th to 20th	Night	13% 3 23% 35% 23% 3	567
	21st to end	Night	13% 8% 25% 34% 18% 2	720
October	1st to 10th	Night	16% 5% 28% 32% 18% 1	720
	11th to 20th	Night	20% 12% 30% 30% 8%	720
	21st to end	Night	22% 11% 33% 27% 7% 1	792
November	1st to 10th	Night	14% 11% 39% 25% 10% 1	740
	11th to 20th	Night	19% 15% 39% 21% 6%	787
	21st to end	Night	21% 14% 35% 24% 6%	950
December	1st to 10th	Night	20% 14% 39% 21% 5%	950
	11th to 20th	Night	23% 12% 35% 23% 6% 1	950
	21st to end	Night	27% 13% 34% 22% 3	1045

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