Optiques Fullum
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Optiques Fullum clear sky chart from 2005-11-06 to 2026-05-17.

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	16% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	131996
	Night	17% 11% 4 9% 5% 5% 5% 4 5% 6% 29%	130832
Transparency	Day	50% 6% 13% 21% 9% 1	135441
	Night	55% 6% 11% 18% 9% 1	135474
Seeing	Day	20% 11% 29% 24% 13% 4	16428
	Night	22% 10% 30% 28% 10% 1	25513

By Month

Percentage Cloud Cover NE (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% 18% 6% 12% 5% 5% 5% 4 5% 5% 21%	4661
	11th to 20th	Day	11% 14% 6% 13% 7% 6% 6% 4 5% 6% 22%	4650
	21st to end	Day	10% 13% 5% 11% 9% 8% 6% 4 6% 6% 22%	5124
February	1st to 10th	Day	14% 14% 4 10% 7% 6% 5% 4 5% 5% 26%	1869
	11th to 20th	Day	14% 11% 4 10% 6% 6% 5% 4 6% 6% 27%	1940
	21st to end	Day	17% 15% 4 10% 6% 5% 4 4 4 6% 26%	1730
March	1st to 10th	Day	17% 12% 4 10% 6% 5% 5% 4 5% 6% 26%	4576
	11th to 20th	Day	10% 11% 4 11% 6% 4 5% 4 6% 6% 31%	4844
	21st to end	Day	18% 8% 3 9% 6% 4 4 3 5% 5% 35%	6073
April	1st to 10th	Day	21% 9% 4 7% 5% 4 4 4 5% 6% 31%	2520
	11th to 20th	Day	19% 8% 3 7% 5% 4 4 4 5% 5% 35%	2494
	21st to end	Day	21% 9% 3 7% 6% 5% 4 3 5% 5% 33%	2669
May	1st to 10th	Day	24% 10% 3 9% 6% 5% 5% 4 5% 6% 23%	6433
	11th to 20th	Day	19% 8% 3 8% 5% 4 5% 3 5% 7% 32%	6402
	21st to end	Day	21% 8% 3 6% 4 4 5% 4 6% 7% 32%	6949
June	1st to 10th	Day	19% 8% 3 7% 5% 4 5% 4 6% 7% 32%	2800
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 4 6% 8% 39%	2800
	21st to end	Day	19% 7% 2 7% 5% 5% 5% 4 6% 7% 33%	2800
July	1st to 10th	Day	11% 6% 3 8% 6% 5% 6% 5% 6% 8% 35%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 7% 8% 42%	6360
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 6% 10% 45%	6926
August	1st to 10th	Day	14% 6% 3 8% 5% 4 5% 4 7% 9% 35%	4563
	11th to 20th	Day	12% 6% 3 7% 5% 4 5% 3 6% 8% 40%	4094
	21st to end	Day	16% 5% 2 5% 4 4 4 4 7% 8% 41%	4312
September	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 5% 8% 45%	2400
	11th to 20th	Day	12% 5% 2 5% 4 4 3 3 5% 7% 50%	2329
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 6% 7% 41%	2200
October	1st to 10th	Day	18% 7% 3 6% 5% 4 4 4 5% 6% 38%	2045
	11th to 20th	Day	17% 9% 3 8% 5% 6% 5% 5% 5% 6% 32%	1974
	21st to end	Day	24% 10% 3 8% 4 4 4 3 6% 6% 28%	1980
November	1st to 10th	Day	16% 11% 3 7% 4 4 5% 3 6% 8% 32%	1851
	11th to 20th	Day	16% 11% 3 9% 6% 5% 5% 4 6% 6% 29%	1794
	21st to end	Day	20% 14% 3 9% 6% 5% 6% 4 5% 7% 22%	1680
December	1st to 10th	Day	20% 19% 6% 10% 5% 5% 5% 4 5% 5% 16%	2680
	11th to 20th	Day	17% 13% 5% 10% 6% 5% 5% 4 6% 5% 24%	3066
	21st to end	Day	23% 13% 4 10% 5% 5% 5% 4 6% 6% 19%	4048
January	1st to 10th	Night	14% 19% 8% 14% 5% 4 4 3 4 5% 20%	8234
	11th to 20th	Night	12% 16% 6% 17% 8% 6% 5% 4 5% 6% 15%	8235
	21st to end	Night	11% 15% 5% 12% 8% 6% 5% 3 4 6% 25%	9057
February	1st to 10th	Night	13% 15% 6% 12% 7% 6% 5% 4 5% 6% 22%	2750
	11th to 20th	Night	14% 12% 3 11% 6% 5% 5% 4 6% 5% 28%	2564
	21st to end	Night	15% 14% 5% 10% 5% 5% 4 3 4 5% 31%	2076
March	1st to 10th	Night	20% 13% 3 9% 5% 4 4 3 4 5% 29%	5484
	11th to 20th	Night	16% 12% 4 8% 5% 4 5% 4 6% 7% 29%	5329
	21st to end	Night	16% 11% 3 9% 6% 5% 5% 3 4 5% 32%	5101
April	1st to 10th	Night	23% 9% 3 7% 5% 5% 4 3 5% 6% 30%	2100
	11th to 20th	Night	22% 9% 3 7% 4 4 4 3 3 6% 33%	2075
	21st to end	Night	21% 9% 3 7% 4 4 3 3 5% 6% 35%	1949
May	1st to 10th	Night	25% 11% 3 8% 5% 4 5% 3 5% 7% 24%	3771
	11th to 20th	Night	21% 8% 3 7% 5% 5% 4 3 5% 7% 32%	3623
	21st to end	Night	17% 9% 4 9% 5% 5% 5% 3 5% 7% 32%	3926
June	1st to 10th	Night	20% 7% 3 8% 5% 5% 5% 4 6% 8% 29%	1600
	11th to 20th	Night	15% 7% 3 6% 3 4 5% 4 6% 7% 40%	1600
	21st to end	Night	18% 7% 3 7% 5% 4 5% 4 6% 6% 35%	1600
July	1st to 10th	Night	12% 7% 2 8% 6% 5% 6% 5% 7% 9% 34%	3600
	11th to 20th	Night	13% 5% 2 7% 5% 5% 5% 4 6% 8% 41%	3600
	21st to end	Night	10% 6% 2 7% 4 4 5% 4 6% 8% 44%	3926
August	1st to 10th	Night	14% 7% 3 7% 5% 4 4 4 5% 7% 39%	2586
	11th to 20th	Night	15% 7% 2 8% 5% 4 5% 3 5% 7% 39%	2905
	21st to end	Night	16% 5% 2 7% 4 5% 5% 3 6% 7% 40%	3586
September	1st to 10th	Night	11% 6% 3 7% 5% 4 5% 4 5% 7% 44%	2000
	11th to 20th	Night	15% 6% 2 4 4 3 3 2 5% 6% 50%	2070
	21st to end	Night	17% 7% 2 5% 4 4 4 4 5% 7% 41%	2200
October	1st to 10th	Night	17% 7% 2 7% 5% 4 5% 4 5% 6% 38%	2350
	11th to 20th	Night	19% 7% 3 7% 5% 4 5% 3 5% 5% 35%	2425
	21st to end	Night	23% 7% 3 8% 6% 6% 4 3 5% 6% 30%	2860
November	1st to 10th	Night	19% 9% 4 8% 5% 4 4 4 5% 7% 31%	2667
	11th to 20th	Night	18% 11% 3 8% 5% 5% 5% 3 4 5% 32%	2825
	21st to end	Night	21% 12% 4 10% 6% 5% 5% 3 5% 5% 24%	2940
December	1st to 10th	Night	18% 18% 6% 12% 6% 5% 5% 4 5% 4 17%	4720
	11th to 20th	Night	22% 14% 4 10% 5% 4 4 3 5% 5% 22%	5348
	21st to end	Night	25% 15% 4 10% 4 4 4 4 5% 5% 20%	7150

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	65% 6% 13% 13% 2	4662
	11th to 20th	Day	61% 6% 10% 13% 9% 1	4680
	21st to end	Day	60% 7% 11% 11% 10% 1	5124
February	1st to 10th	Day	60% 5% 11% 17% 5% 1	1869
	11th to 20th	Day	56% 6% 14% 17% 7% 1	1949
	21st to end	Day	59% 5% 11% 15% 8% 1	1730
March	1st to 10th	Day	57% 5% 9% 15% 10% 3	4579
	11th to 20th	Day	51% 6% 17% 15% 10% 1	4844
	21st to end	Day	51% 4 8% 18% 16% 2	6073
April	1st to 10th	Day	53% 6% 8% 20% 12% 2	2520
	11th to 20th	Day	49% 5% 9% 20% 15% 1	2494
	21st to end	Day	51% 5% 10% 18% 12% 3	2669
May	1st to 10th	Day	60% 7% 10% 16% 7% 1	6444
	11th to 20th	Day	51% 7% 14% 18% 9% 1	6406
	21st to end	Day	49% 7% 13% 20% 11% 1	6949
June	1st to 10th	Day	49% 8% 11% 18% 13% 1	2800
	11th to 20th	Day	43% 6% 11% 23% 14% 2	2800
	21st to end	Day	49% 8% 12% 20% 10% 1	2800
July	1st to 10th	Day	45% 6% 13% 26% 9%	6290
	11th to 20th	Day	37% 7% 14% 29% 13%	6285
	21st to end	Day	34% 7% 13% 37% 8%	6728
August	1st to 10th	Day	45% 7% 17% 23% 8%	4549
	11th to 20th	Day	41% 7% 17% 28% 7%	4136
	21st to end	Day	39% 6% 19% 22% 14%	4312
September	1st to 10th	Day	36% 8% 14% 30% 13%	2400
	11th to 20th	Day	34% 6% 13% 31% 15% 1	2329
	21st to end	Day	41% 7% 14% 25% 11% 1	2200
October	1st to 10th	Day	44% 7% 14% 27% 9%	3331
	11th to 20th	Day	43% 6% 18% 26% 7%	3190
	21st to end	Day	46% 5% 19% 22% 7%	3180
November	1st to 10th	Day	51% 7% 14% 20% 8% 1	1851
	11th to 20th	Day	56% 6% 12% 16% 10% 1	1794
	21st to end	Day	63% 8% 13% 13% 4	1680
December	1st to 10th	Day	70% 5% 11% 13% 1	2680
	11th to 20th	Day	60% 8% 10% 15% 7%	3066
	21st to end	Day	65% 6% 9% 15% 5%	4048
January	1st to 10th	Night	68% 5% 10% 12% 4	8234
	11th to 20th	Night	69% 7% 9% 10% 6%	8280
	21st to end	Night	61% 5% 9% 14% 11% 1	9057
February	1st to 10th	Night	64% 5% 9% 15% 6% 1	2750
	11th to 20th	Night	56% 6% 12% 19% 7%	2566
	21st to end	Night	56% 5% 9% 17% 12% 1	2076
March	1st to 10th	Night	57% 5% 7% 16% 11% 4	5494
	11th to 20th	Night	52% 7% 14% 16% 10% 2	5330
	21st to end	Night	54% 4 7% 21% 11% 2	5101
April	1st to 10th	Night	55% 4 9% 18% 13% 1	2100
	11th to 20th	Night	54% 5% 9% 19% 12% 1	2075
	21st to end	Night	51% 4 8% 18% 14% 4	1949
May	1st to 10th	Night	60% 6% 10% 16% 7% 2	3777
	11th to 20th	Night	51% 6% 11% 19% 11% 1	3624
	21st to end	Night	51% 7% 10% 18% 14% 1	3927
June	1st to 10th	Night	50% 8% 11% 18% 12% 1	1600
	11th to 20th	Night	43% 6% 12% 21% 15% 2	1600
	21st to end	Night	47% 7% 13% 20% 12% 1	1600
July	1st to 10th	Night	44% 6% 17% 22% 10%	3560
	11th to 20th	Night	39% 6% 16% 27% 11%	3552
	21st to end	Night	38% 7% 15% 28% 12%	3809
August	1st to 10th	Night	45% 6% 14% 27% 8%	2576
	11th to 20th	Night	44% 6% 18% 22% 9%	2929
	21st to end	Night	41% 7% 15% 23% 13% 1	3586
September	1st to 10th	Night	39% 7% 12% 28% 14% 1	2000
	11th to 20th	Night	36% 6% 13% 32% 13%	2070
	21st to end	Night	42% 7% 12% 24% 15% 1	2200
October	1st to 10th	Night	44% 6% 14% 26% 10% 1	3844
	11th to 20th	Night	45% 5% 13% 28% 9%	3948
	21st to end	Night	49% 5% 15% 20% 11% 1	4610
November	1st to 10th	Night	53% 6% 12% 20% 8% 1	2667
	11th to 20th	Night	54% 5% 12% 19% 9% 1	2825
	21st to end	Night	62% 7% 12% 15% 5%	2940
December	1st to 10th	Night	71% 5% 11% 10% 3	4720
	11th to 20th	Night	64% 4 8% 14% 9%	5348
	21st to end	Night	65% 5% 9% 14% 7%	7150

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	26% 11% 32% 23% 7% 1	220
	11th to 20th	Day	25% 17% 34% 19% 4 1	220
	21st to end	Day	19% 14% 36% 24% 7% 1	242
February	1st to 10th	Day	24% 19% 34% 16% 6%	319
	11th to 20th	Day	20% 14% 42% 20% 4	427
	21st to end	Day	25% 13% 31% 28% 3	446
March	1st to 10th	Day	21% 14% 35% 23% 6%	540
	11th to 20th	Day	20% 17% 34% 21% 7% 1	540
	21st to end	Day	25% 13% 31% 19% 10% 2	594
April	1st to 10th	Day	28% 15% 29% 19% 9% 1	540
	11th to 20th	Day	24% 16% 28% 19% 10% 3	532
	21st to end	Day	24% 12% 32% 20% 10% 2	540
May	1st to 10th	Day	24% 11% 32% 22% 9% 3	543
	11th to 20th	Day	17% 10% 32% 23% 14% 4	551
	21st to end	Day	18% 11% 27% 25% 15% 3	573
June	1st to 10th	Day	22% 10% 23% 29% 12% 4	530
	11th to 20th	Day	13% 10% 28% 28% 18% 2	530
	21st to end	Day	22% 8% 29% 24% 13% 4	530
July	1st to 10th	Day	11% 7% 27% 28% 20% 6%	525
	11th to 20th	Day	13% 7% 27% 28% 19% 5%	524
	21st to end	Day	12% 7% 24% 34% 19% 5%	576
August	1st to 10th	Day	15% 6% 19% 33% 21% 8%	526
	11th to 20th	Day	13% 4 22% 32% 20% 9%	519
	21st to end	Day	14% 9% 24% 26% 19% 8%	583
September	1st to 10th	Day	12% 10% 26% 23% 20% 9%	530
	11th to 20th	Day	13% 8% 19% 22% 25% 14%	530
	21st to end	Day	16% 7% 28% 24% 18% 6%	530
October	1st to 10th	Day	21% 10% 25% 23% 16% 6%	530
	11th to 20th	Day	20% 12% 30% 24% 12% 2	515
	21st to end	Day	31% 12% 25% 24% 8%	462
November	1st to 10th	Day	26% 16% 28% 22% 8% 1	425
	11th to 20th	Day	25% 18% 29% 19% 7% 2	334
	21st to end	Day	25% 20% 29% 20% 5%	220
December	1st to 10th	Day	29% 12% 29% 22% 7% 2	220
	11th to 20th	Day	23% 17% 38% 19% 3 1	220
	21st to end	Day	29% 14% 29% 20% 5% 2	242
January	1st to 10th	Night	25% 14% 32% 25% 4	840
	11th to 20th	Night	27% 12% 33% 22% 5%	840
	21st to end	Night	19% 11% 36% 26% 7% 1	924
February	1st to 10th	Night	20% 13% 36% 25% 5% 1	840
	11th to 20th	Night	20% 13% 37% 26% 4	823
	21st to end	Night	21% 11% 36% 29% 4	692
March	1st to 10th	Night	23% 13% 34% 25% 5%	840
	11th to 20th	Night	25% 12% 33% 24% 5%	840
	21st to end	Night	24% 10% 31% 27% 8% 1	924
April	1st to 10th	Night	27% 13% 28% 26% 5%	840
	11th to 20th	Night	27% 11% 31% 24% 6%	831
	21st to end	Night	25% 10% 31% 26% 8%	689
May	1st to 10th	Night	28% 7% 29% 26% 9% 1	465
	11th to 20th	Night	20% 7% 31% 31% 10% 1	406
	21st to end	Night	17% 6% 33% 34% 10%	433
June	1st to 10th	Night	22% 7% 28% 33% 9% 1	400
	11th to 20th	Night	19% 6% 27% 34% 14% 1	400
	21st to end	Night	18% 8% 29% 28% 18% 1	400
July	1st to 10th	Night	12% 4 25% 41% 18% 1	390
	11th to 20th	Night	10% 5% 24% 41% 18% 2	388
	21st to end	Night	13% 3 24% 42% 16% 2	438
August	1st to 10th	Night	15% 3 17% 44% 20% 1	398
	11th to 20th	Night	15% 3 21% 34% 24% 3	608
	21st to end	Night	17% 3 23% 36% 19% 2	880
September	1st to 10th	Night	13% 5% 26% 36% 18% 1	800
	11th to 20th	Night	17% 5% 16% 36% 22% 4	800
	21st to end	Night	18% 6% 25% 29% 19% 2	800
October	1st to 10th	Night	20% 8% 26% 29% 16% 1	800
	11th to 20th	Night	22% 10% 29% 28% 10%	800
	21st to end	Night	25% 11% 31% 27% 5%	880
November	1st to 10th	Night	25% 15% 28% 24% 8%	820
	11th to 20th	Night	25% 14% 32% 20% 9% 1	840
	21st to end	Night	26% 14% 32% 19% 8%	840
December	1st to 10th	Night	30% 13% 31% 21% 5%	840
	11th to 20th	Night	28% 16% 30% 20% 5% 1	840
	21st to end	Night	34% 13% 29% 20% 4 1	924

Page generated at 2026-05-14 01:58:56. Version ac07

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