Guinea Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Guinea Observing Site clear sky chart from 2005-11-06 to 2025-06-10.

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	14% 6% 2 6% 4 4 4 4 6% 8% 43%	119307
	Night	14% 6% 2 5% 4 4 4 3 5% 7% 45%	118899
Transparency	Day	39% 4 12% 23% 18% 5%	122954
	Night	38% 3 10% 23% 20% 6%	123388
Seeing	Day	20% 10% 26% 25% 14% 5%	15855
	Night	18% 9% 27% 31% 14% 2	25719

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	15% 5% 1 4 3 3 4 3 4 5% 53%	4056
	11th to 20th	Day	14% 7% 2 4 3 3 3 2 4 4 53%	4060
	21st to end	Day	16% 6% 2 6% 4 3 3 3 4 5% 47%	4466
February	1st to 10th	Day	13% 8% 2 6% 5% 5% 5% 4 6% 7% 41%	1800
	11th to 20th	Day	22% 7% 1 4 4 3 3 4 4 6% 42%	1774
	21st to end	Day	18% 7% 2 6% 4 5% 4 3 5% 7% 38%	1720
March	1st to 10th	Day	17% 6% 2 7% 5% 4 5% 4 5% 6% 39%	4935
	11th to 20th	Day	11% 5% 2 5% 3 3 4 3 5% 6% 52%	4980
	21st to end	Day	17% 6% 2 6% 5% 4 5% 4 5% 6% 42%	5465
April	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 5% 7% 50%	2370
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 5% 7% 49%	2374
	21st to end	Day	16% 5% 2 6% 5% 4 4 3 5% 8% 42%	2400
May	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 5% 7% 9% 34%	5817
	11th to 20th	Day	20% 7% 3 6% 5% 4 5% 4 6% 8% 31%	5861
	21st to end	Day	15% 5% 2 5% 4 4 4 3 6% 9% 44%	6703
June	1st to 10th	Day	10% 4 2 5% 4 4 4 4 7% 11% 45%	2786
	11th to 20th	Day	10% 4 1 5% 5% 5% 5% 5% 7% 10% 43%	2660
	21st to end	Day	8% 4 2 6% 4 5% 5% 6% 7% 10% 42%	2660
July	1st to 10th	Day	7% 5% 2 6% 4 5% 6% 6% 9% 12% 39%	4168
	11th to 20th	Day	11% 6% 2 6% 4 5% 6% 5% 8% 11% 36%	4120
	21st to end	Day	11% 7% 3 8% 6% 6% 6% 6% 8% 10% 32%	4466
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 11% 30%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 4 7% 10% 39%	3916
	21st to end	Day	8% 4 2 4 4 3 4 4 7% 10% 49%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 4 6% 47%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 3 4 5% 7% 45%	2221
	21st to end	Day	21% 6% 3 7% 4 4 3 3 5% 6% 38%	2013
October	1st to 10th	Day	16% 5% 2 5% 4 4 3 2 4 5% 49%	1900
	11th to 20th	Day	16% 4 1 4 3 3 3 3 4 6% 54%	1900
	21st to end	Day	13% 5% 2 5% 3 2 4 3 4 6% 55%	2090
November	1st to 10th	Day	13% 5% 1 5% 3 3 2 4 4 6% 54%	1957
	11th to 20th	Day	15% 6% 2 5% 3 4 3 2 5% 6% 49%	1835
	21st to end	Day	14% 5% 2 5% 3 3 3 3 5% 7% 52%	1600
December	1st to 10th	Day	12% 5% 2 5% 4 3 4 4 5% 5% 51%	2600
	11th to 20th	Day	20% 6% 2 5% 3 3 3 2 4 6% 47%	2990
	21st to end	Day	16% 6% 2 6% 4 4 4 4 5% 7% 43%	4080
January	1st to 10th	Night	13% 6% 2 4 3 3 3 3 4 5% 55%	5889
	11th to 20th	Night	14% 6% 2 4 2 3 3 2 4 5% 56%	5900
	21st to end	Night	17% 6% 2 5% 3 3 3 2 4 5% 50%	6490
February	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 6% 7% 43%	2600
	11th to 20th	Night	19% 7% 2 5% 4 3 3 3 4 7% 42%	2510
	21st to end	Night	15% 7% 2 5% 4 4 3 3 5% 6% 46%	1908
March	1st to 10th	Night	16% 5% 2 5% 4 4 4 3 5% 6% 47%	4918
	11th to 20th	Night	12% 4 2 4 3 2 3 3 5% 8% 53%	4980
	21st to end	Night	13% 6% 2 6% 4 4 3 4 5% 6% 47%	5467
April	1st to 10th	Night	15% 7% 2 6% 4 3 5% 3 5% 7% 44%	2029
	11th to 20th	Night	11% 6% 2 5% 4 3 4 4 5% 8% 50%	1975
	21st to end	Night	14% 7% 2 4 4 4 4 4 5% 7% 46%	2000
May	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 4 6% 8% 35%	4107
	11th to 20th	Night	22% 8% 3 6% 5% 4 5% 3 5% 7% 33%	4032
	21st to end	Night	15% 7% 2 6% 4 4 4 3 6% 9% 41%	4147
June	1st to 10th	Night	11% 5% 2 5% 4 5% 5% 4 7% 9% 44%	1598
	11th to 20th	Night	9% 6% 1 6% 5% 5% 5% 3 8% 9% 42%	1520
	21st to end	Night	8% 5% 2 5% 5% 4 5% 4 7% 11% 44%	1520
July	1st to 10th	Night	6% 4 3 7% 6% 5% 7% 6% 8% 10% 38%	2773
	11th to 20th	Night	8% 6% 2 7% 7% 6% 7% 5% 7% 11% 34%	2840
	21st to end	Night	11% 8% 4 9% 7% 6% 6% 6% 7% 7% 30%	3087
August	1st to 10th	Night	15% 8% 3 7% 5% 4 5% 5% 7% 9% 31%	2825
	11th to 20th	Night	9% 5% 3 7% 5% 5% 6% 6% 8% 10% 37%	2879
	21st to end	Night	9% 5% 2 7% 5% 4 5% 4 6% 9% 44%	3476
September	1st to 10th	Night	13% 6% 2 6% 5% 4 3 4 5% 7% 45%	1900
	11th to 20th	Night	13% 5% 2 5% 4 4 5% 4 5% 6% 46%	1955
	21st to end	Night	23% 8% 2 5% 4 3 5% 3 4 6% 36%	2166
October	1st to 10th	Night	16% 6% 2 6% 4 4 3 3 4 5% 47%	2280
	11th to 20th	Night	15% 5% 2 4 3 4 3 3 5% 6% 50%	2280
	21st to end	Night	13% 4 2 5% 3 3 4 3 4 6% 53%	2508
November	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 4 6% 51%	2341
	11th to 20th	Night	14% 6% 2 4 3 4 3 3 5% 6% 50%	2556
	21st to end	Night	13% 4 2 4 3 3 5% 3 6% 6% 52%	2800
December	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 5% 54%	4580
	11th to 20th	Night	20% 8% 2 6% 4 4 4 3 4 5% 40%	5205
	21st to end	Night	15% 7% 2 5% 3 4 4 3 6% 7% 44%	6858

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	36% 2 4 24% 25% 9%	4057
	11th to 20th	Day	35% 2 4 20% 27% 11%	4060
	21st to end	Day	42% 2 7% 27% 19% 4	4466
February	1st to 10th	Day	43% 3 9% 26% 15% 4	1800
	11th to 20th	Day	44% 3 5% 22% 21% 5%	1783
	21st to end	Day	47% 4 10% 15% 18% 6%	1720
March	1st to 10th	Day	45% 3 7% 19% 16% 9%	4935
	11th to 20th	Day	33% 2 8% 22% 25% 10%	4980
	21st to end	Day	45% 2 9% 19% 18% 6%	5465
April	1st to 10th	Day	35% 3 11% 22% 21% 8%	2370
	11th to 20th	Day	35% 2 11% 25% 21% 6%	2374
	21st to end	Day	41% 3 11% 24% 16% 5%	2400
May	1st to 10th	Day	45% 5% 16% 21% 11% 1	5851
	11th to 20th	Day	52% 4 10% 21% 12% 1	5865
	21st to end	Day	38% 3 15% 22% 19% 3	6718
June	1st to 10th	Day	34% 5% 16% 28% 16% 1	2786
	11th to 20th	Day	35% 6% 17% 24% 17% 1	2660
	21st to end	Day	34% 6% 16% 27% 15% 2	2660
July	1st to 10th	Day	33% 9% 23% 18% 11% 5%	4103
	11th to 20th	Day	38% 6% 22% 24% 8% 1	4051
	21st to end	Day	45% 7% 13% 20% 14%	4324
August	1st to 10th	Day	47% 6% 17% 23% 6% 1	4091
	11th to 20th	Day	37% 6% 19% 25% 13% 1	3955
	21st to end	Day	29% 5% 18% 29% 18% 1	4180
September	1st to 10th	Day	38% 4 13% 18% 22% 4	2280
	11th to 20th	Day	38% 4 8% 26% 20% 4	2221
	21st to end	Day	48% 3 8% 20% 17% 4	2013
October	1st to 10th	Day	36% 2 7% 20% 29% 6%	3160
	11th to 20th	Day	24% 2 5% 23% 32% 14%	3140
	21st to end	Day	20% 3 10% 28% 26% 13%	3428
November	1st to 10th	Day	32% 2 8% 25% 27% 5%	1957
	11th to 20th	Day	37% 2 9% 22% 23% 8%	1835
	21st to end	Day	34% 3 9% 24% 26% 5%	1600
December	1st to 10th	Day	34% 3 8% 26% 20% 8%	2600
	11th to 20th	Day	41% 2 11% 23% 17% 5%	2986
	21st to end	Day	42% 3 11% 26% 17% 1	4080
January	1st to 10th	Night	34% 2 4 21% 27% 12%	5889
	11th to 20th	Night	34% 2 5% 20% 30% 9%	5900
	21st to end	Night	38% 2 6% 28% 20% 6%	6490
February	1st to 10th	Night	40% 2 11% 25% 18% 3	2600
	11th to 20th	Night	44% 2 7% 20% 20% 7%	2512
	21st to end	Night	41% 2 7% 23% 19% 8%	1908
March	1st to 10th	Night	40% 2 6% 22% 21% 9%	4918
	11th to 20th	Night	31% 3 7% 19% 29% 12%	4980
	21st to end	Night	39% 3 8% 23% 21% 6%	5467
April	1st to 10th	Night	41% 3 10% 18% 22% 6%	2029
	11th to 20th	Night	34% 3 10% 24% 23% 6%	1975
	21st to end	Night	38% 4 11% 24% 18% 5%	2000
May	1st to 10th	Night	47% 5% 16% 20% 10% 1	4134
	11th to 20th	Night	52% 4 10% 23% 9% 2	4033
	21st to end	Night	41% 4 15% 25% 14% 2	4154
June	1st to 10th	Night	36% 5% 14% 27% 17% 1	1598
	11th to 20th	Night	37% 5% 19% 22% 15% 2	1520
	21st to end	Night	34% 6% 14% 24% 18% 3	1520
July	1st to 10th	Night	38% 9% 21% 17% 13% 3	2728
	11th to 20th	Night	42% 8% 20% 20% 8% 1	2786
	21st to end	Night	51% 7% 12% 19% 10%	2988
August	1st to 10th	Night	48% 6% 16% 23% 7%	2814
	11th to 20th	Night	39% 7% 17% 25% 12% 1	2906
	21st to end	Night	36% 5% 13% 32% 13% 2	3476
September	1st to 10th	Night	39% 6% 13% 19% 17% 6%	1900
	11th to 20th	Night	38% 5% 9% 23% 22% 2	1955
	21st to end	Night	50% 3 9% 18% 16% 4	2166
October	1st to 10th	Night	41% 4 9% 19% 23% 5%	3800
	11th to 20th	Night	25% 3 6% 22% 32% 12%	3779
	21st to end	Night	22% 2 5% 32% 26% 13%	4120
November	1st to 10th	Night	35% 3 8% 22% 26% 6%	2341
	11th to 20th	Night	36% 2 7% 21% 24% 9%	2556
	21st to end	Night	33% 2 8% 27% 24% 6%	2800
December	1st to 10th	Night	32% 2 7% 28% 25% 5%	4580
	11th to 20th	Night	47% 3 9% 18% 15% 7%	5208
	21st to end	Night	41% 2 10% 28% 17% 2	6858

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	31% 24% 26% 13% 6% 1	300
	11th to 20th	Day	28% 26% 33% 11% 2	300
	21st to end	Day	27% 21% 38% 11% 3	330
February	1st to 10th	Day	24% 25% 36% 12% 3	300
	11th to 20th	Day	39% 24% 27% 8% 2	321
	21st to end	Day	30% 16% 33% 18% 4	414
March	1st to 10th	Day	24% 20% 32% 17% 6%	500
	11th to 20th	Day	24% 20% 30% 20% 5% 1	500
	21st to end	Day	25% 18% 37% 15% 4 1	550
April	1st to 10th	Day	24% 19% 31% 18% 7% 1	500
	11th to 20th	Day	21% 14% 34% 20% 9% 3	492
	21st to end	Day	23% 10% 35% 22% 8% 2	500
May	1st to 10th	Day	23% 12% 34% 20% 9% 2	503
	11th to 20th	Day	24% 6% 29% 23% 16% 2	527
	21st to end	Day	21% 5% 21% 28% 18% 6%	573
June	1st to 10th	Day	10% 5% 27% 32% 20% 6%	526
	11th to 20th	Day	11% 6% 24% 34% 16% 10%	490
	21st to end	Day	11% 4 23% 33% 21% 6%	490
July	1st to 10th	Day	13% 1 14% 35% 27% 11%	485
	11th to 20th	Day	6% 3 15% 37% 28% 11%	484
	21st to end	Day	10% 3 22% 31% 25% 9%	532
August	1st to 10th	Day	15% 2 20% 27% 26% 9%	486
	11th to 20th	Day	13% 1 15% 33% 25% 13%	479
	21st to end	Day	11% 2 18% 29% 24% 17%	539
September	1st to 10th	Day	15% 5% 16% 29% 20% 16%	490
	11th to 20th	Day	16% 4 16% 31% 21% 12%	490
	21st to end	Day	28% 7% 20% 28% 12% 4	490
October	1st to 10th	Day	25% 4 20% 27% 18% 7%	490
	11th to 20th	Day	17% 11% 23% 27% 20% 3	490
	21st to end	Day	15% 12% 32% 27% 11% 3	539
November	1st to 10th	Day	17% 9% 28% 29% 13% 4	495
	11th to 20th	Day	20% 14% 30% 24% 11% 1	403
	21st to end	Day	22% 20% 28% 22% 6% 3	200
December	1st to 10th	Day	22% 19% 38% 17% 4 2	200
	11th to 20th	Day	30% 12% 28% 24% 6% 1	200
	21st to end	Day	28% 12% 31% 19% 9% 1	247
January	1st to 10th	Night	20% 18% 35% 24% 2	800
	11th to 20th	Night	21% 18% 31% 26% 4	800
	21st to end	Night	21% 16% 38% 24% 2	880
February	1st to 10th	Night	19% 16% 37% 25% 4	800
	11th to 20th	Night	26% 18% 37% 17% 1	783
	21st to end	Night	23% 15% 35% 25% 2	660
March	1st to 10th	Night	20% 17% 34% 26% 3	800
	11th to 20th	Night	21% 15% 36% 22% 5% 1	800
	21st to end	Night	19% 15% 38% 23% 5%	880
April	1st to 10th	Night	20% 16% 37% 22% 6%	800
	11th to 20th	Night	15% 12% 36% 29% 8% 1	791
	21st to end	Night	17% 9% 36% 31% 8%	800
May	1st to 10th	Night	18% 9% 30% 34% 9% 1	635
	11th to 20th	Night	18% 5% 25% 37% 14% 1	591
	21st to end	Night	16% 2 18% 38% 23% 3	531
June	1st to 10th	Night	11% 2 19% 45% 23% 1	400
	11th to 20th	Night	12% 4 17% 40% 25% 3	380
	21st to end	Night	9% 3 17% 47% 23% 1	380
July	1st to 10th	Night	11% 1 13% 39% 32% 4	514
	11th to 20th	Night	6% 1 10% 44% 34% 5%	552
	21st to end	Night	10% 1 16% 43% 27% 3	624
August	1st to 10th	Night	13% 2 11% 44% 27% 4	567
	11th to 20th	Night	14% 2 9% 43% 30% 2	619
	21st to end	Night	12% 1 13% 36% 32% 5%	836
September	1st to 10th	Night	15% 2 11% 34% 31% 6%	760
	11th to 20th	Night	15% 2 14% 34% 31% 4	760
	21st to end	Night	29% 4 14% 32% 20% 2	760
October	1st to 10th	Night	20% 3 19% 29% 22% 6%	760
	11th to 20th	Night	19% 7% 25% 31% 17% 1	760
	21st to end	Night	15% 8% 28% 33% 14% 2	836
November	1st to 10th	Night	16% 8% 27% 34% 13% 2	780
	11th to 20th	Night	17% 12% 29% 31% 10% 1	800
	21st to end	Night	15% 14% 29% 32% 10% 1	800
December	1st to 10th	Night	22% 10% 35% 25% 7% 1	800
	11th to 20th	Night	20% 10% 32% 33% 5%	800
	21st to end	Night	22% 13% 27% 34% 4	880

Page generated at 2025-06-07 10:28:17. Version ac07

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