Fabreville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fabreville clear sky chart from 2005-11-06 to 2025-05-26.

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	17% 9% 3 8% 5% 4 5% 4 5% 7% 33%	114004
	Night	18% 11% 4 9% 5% 4 4 3 5% 6% 31%	115275
Transparency	Day	50% 6% 12% 21% 10% 1	117497
	Night	53% 5% 11% 19% 10% 1	119933
Seeing	Day	21% 10% 28% 25% 13% 4	15197
	Night	23% 7% 28% 31% 10% 1	24266

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	16% 18% 6% 14% 5% 4 4 2 4 4 22%	3597
	11th to 20th	Day	13% 15% 6% 12% 6% 5% 4 3 5% 6% 25%	3570
	21st to end	Day	12% 15% 4 10% 5% 5% 6% 4 5% 6% 27%	3960
February	1st to 10th	Day	14% 15% 4 11% 6% 5% 5% 3 5% 5% 27%	1760
	11th to 20th	Day	14% 11% 5% 11% 6% 5% 5% 4 6% 6% 27%	1852
	21st to end	Day	17% 16% 4 9% 5% 4 4 3 5% 6% 27%	1650
March	1st to 10th	Day	20% 12% 5% 11% 6% 5% 5% 3 4 5% 26%	4476
	11th to 20th	Day	11% 13% 3 10% 6% 5% 5% 4 6% 6% 32%	4699
	21st to end	Day	19% 9% 3 8% 5% 4 4 3 4 5% 35%	5964
April	1st to 10th	Day	21% 11% 3 7% 4 4 4 3 4 6% 32%	2400
	11th to 20th	Day	20% 10% 2 7% 5% 4 3 3 4 5% 37%	2374
	21st to end	Day	21% 10% 3 7% 5% 3 4 4 5% 5% 33%	2558
May	1st to 10th	Day	20% 8% 3 8% 6% 5% 5% 4 5% 7% 28%	4520
	11th to 20th	Day	18% 8% 3 8% 4 5% 5% 4 6% 7% 33%	4538
	21st to end	Day	16% 6% 2 7% 5% 4 5% 4 6% 9% 36%	4907
June	1st to 10th	Day	21% 9% 2 6% 5% 4 5% 4 6% 8% 30%	2660
	11th to 20th	Day	14% 6% 2 6% 6% 4 5% 4 6% 9% 38%	2660
	21st to end	Day	20% 7% 3 7% 6% 5% 4 4 6% 7% 31%	2660
July	1st to 10th	Day	12% 5% 2 7% 6% 5% 5% 4 6% 8% 38%	4440
	11th to 20th	Day	14% 5% 2 6% 4 5% 6% 4 7% 9% 39%	4440
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 8% 46%	4814
August	1st to 10th	Day	14% 5% 3 8% 5% 5% 6% 4 6% 9% 34%	4423
	11th to 20th	Day	14% 5% 3 7% 5% 4 4 3 6% 8% 40%	4008
	21st to end	Day	16% 5% 2 6% 4 5% 5% 3 7% 8% 40%	4180
September	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 6% 9% 42%	2280
	11th to 20th	Day	13% 5% 2 4 4 4 4 4 5% 7% 49%	2204
	21st to end	Day	17% 6% 2 6% 4 4 4 3 5% 7% 41%	2090
October	1st to 10th	Day	20% 7% 3 7% 4 5% 5% 3 5% 6% 36%	1956
	11th to 20th	Day	18% 8% 2 7% 6% 6% 6% 4 5% 6% 30%	1862
	21st to end	Day	24% 10% 3 6% 4 4 4 3 5% 6% 31%	1881
November	1st to 10th	Day	17% 10% 3 6% 4 4 6% 4 5% 7% 34%	1761
	11th to 20th	Day	17% 10% 4 8% 4 5% 4 4 6% 7% 31%	1714
	21st to end	Day	22% 12% 4 7% 5% 5% 5% 5% 5% 6% 25%	1600
December	1st to 10th	Day	21% 18% 7% 10% 5% 4 4 4 5% 5% 18%	2600
	11th to 20th	Day	18% 14% 4 9% 5% 4 5% 4 5% 4 27%	2986
	21st to end	Day	24% 13% 3 10% 6% 4 5% 4 5% 5% 22%	3960
January	1st to 10th	Night	14% 20% 8% 14% 5% 4 4 3 4 4 21%	6349
	11th to 20th	Night	10% 15% 6% 16% 7% 6% 6% 3 5% 6% 20%	6315
	21st to end	Night	13% 15% 5% 11% 7% 5% 5% 3 4 6% 25%	6996
February	1st to 10th	Night	14% 15% 5% 11% 6% 6% 4 4 5% 6% 24%	2638
	11th to 20th	Night	14% 12% 4 9% 6% 5% 5% 4 5% 7% 29%	2433
	21st to end	Night	15% 16% 4 9% 5% 4 4 3 4 5% 31%	1980
March	1st to 10th	Night	21% 13% 4 8% 5% 4 4 3 3 5% 30%	5364
	11th to 20th	Night	15% 13% 3 8% 4 5% 4 3 6% 8% 30%	5255
	21st to end	Night	16% 10% 3 9% 5% 5% 5% 4 4 5% 33%	4967
April	1st to 10th	Night	23% 10% 3 6% 4 4 4 3 5% 6% 31%	2000
	11th to 20th	Night	23% 8% 3 7% 5% 4 4 3 4 6% 34%	1975
	21st to end	Night	22% 8% 3 7% 4 4 4 3 5% 5% 35%	1840
May	1st to 10th	Night	23% 9% 3 8% 4 4 4 4 5% 7% 30%	2670
	11th to 20th	Night	24% 6% 2 6% 4 5% 4 4 5% 6% 35%	2575
	21st to end	Night	16% 7% 3 7% 5% 4 4 3 5% 8% 36%	2784
June	1st to 10th	Night	21% 8% 2 7% 5% 5% 5% 3 6% 7% 32%	1520
	11th to 20th	Night	15% 7% 2 7% 4 3 3 4 6% 7% 40%	1520
	21st to end	Night	19% 6% 3 9% 5% 4 5% 4 6% 6% 34%	1520
July	1st to 10th	Night	15% 6% 2 8% 4 5% 6% 4 6% 8% 35%	2520
	11th to 20th	Night	15% 5% 2 7% 4 5% 4 4 5% 9% 41%	2520
	21st to end	Night	12% 5% 2 6% 4 5% 4 4 6% 8% 44%	2739
August	1st to 10th	Night	16% 6% 3 7% 5% 4 5% 3 5% 7% 39%	2506
	11th to 20th	Night	16% 6% 3 8% 4 5% 4 3 5% 6% 39%	2785
	21st to end	Night	17% 5% 2 7% 5% 4 5% 4 5% 7% 39%	3476
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 4 5% 8% 45%	1900
	11th to 20th	Night	15% 6% 2 5% 4 2 3 2 4 8% 49%	1976
	21st to end	Night	16% 5% 2 6% 4 4 4 4 4 7% 43%	2090
October	1st to 10th	Night	18% 6% 3 7% 4 4 5% 4 5% 6% 38%	2221
	11th to 20th	Night	20% 8% 3 7% 5% 5% 4 3 5% 6% 36%	2318
	21st to end	Night	22% 9% 3 8% 4 5% 4 3 5% 4 32%	2717
November	1st to 10th	Night	19% 9% 3 7% 5% 4 5% 4 5% 6% 32%	2537
	11th to 20th	Night	18% 10% 3 8% 4 4 4 4 5% 6% 33%	2685
	21st to end	Night	22% 14% 3 8% 5% 4 4 3 4 5% 28%	2800
December	1st to 10th	Night	18% 17% 6% 11% 6% 5% 5% 4 5% 5% 19%	4580
	11th to 20th	Night	24% 13% 4 9% 5% 4 4 3 6% 4 25%	5208
	21st to end	Night	26% 15% 4 8% 4 3 4 3 5% 5% 22%	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	64% 7% 9% 16% 3	3598
	11th to 20th	Day	59% 6% 11% 15% 7% 1	3600
	21st to end	Day	57% 6% 12% 15% 10% 1	3960
February	1st to 10th	Day	59% 4 9% 19% 6% 2	1760
	11th to 20th	Day	57% 7% 11% 15% 9% 1	1861
	21st to end	Day	59% 4 10% 16% 10% 2	1650
March	1st to 10th	Day	60% 5% 7% 14% 11% 3	4479
	11th to 20th	Day	50% 7% 16% 14% 11% 2	4699
	21st to end	Day	52% 5% 7% 16% 18% 2	5964
April	1st to 10th	Day	54% 5% 7% 19% 13% 2	2400
	11th to 20th	Day	49% 5% 7% 21% 16% 2	2374
	21st to end	Day	53% 5% 9% 17% 13% 3	2558
May	1st to 10th	Day	52% 7% 9% 21% 10% 1	4534
	11th to 20th	Day	48% 9% 14% 18% 9% 2	4542
	21st to end	Day	43% 7% 12% 24% 14% 2	4907
June	1st to 10th	Day	50% 7% 11% 19% 12% 2	2660
	11th to 20th	Day	43% 7% 11% 23% 14% 3	2660
	21st to end	Day	51% 7% 11% 20% 10% 1	2660
July	1st to 10th	Day	42% 7% 13% 27% 11% 1	4370
	11th to 20th	Day	39% 7% 15% 30% 8%	4365
	21st to end	Day	36% 6% 14% 34% 10%	4661
August	1st to 10th	Day	45% 7% 17% 22% 9%	4409
	11th to 20th	Day	42% 6% 17% 28% 7%	4050
	21st to end	Day	40% 6% 17% 21% 15% 1	4180
September	1st to 10th	Day	37% 7% 15% 28% 13% 1	2280
	11th to 20th	Day	34% 6% 13% 31% 15% 1	2204
	21st to end	Day	41% 6% 14% 27% 11% 1	2090
October	1st to 10th	Day	45% 5% 13% 28% 9%	3242
	11th to 20th	Day	44% 5% 17% 27% 7%	3078
	21st to end	Day	44% 4 20% 23% 9% 1	3081
November	1st to 10th	Day	48% 5% 14% 23% 8% 1	1761
	11th to 20th	Day	52% 6% 12% 18% 12% 1	1714
	21st to end	Day	58% 8% 13% 15% 5%	1600
December	1st to 10th	Day	69% 4 9% 15% 3	2600
	11th to 20th	Day	59% 5% 10% 17% 9%	2986
	21st to end	Day	64% 5% 11% 13% 6%	3960
January	1st to 10th	Night	67% 5% 11% 13% 4	6349
	11th to 20th	Night	64% 6% 12% 14% 4	6360
	21st to end	Night	61% 5% 10% 12% 13% 1	6996
February	1st to 10th	Night	61% 5% 10% 16% 7% 1	2638
	11th to 20th	Night	54% 5% 12% 20% 9%	2435
	21st to end	Night	56% 5% 8% 18% 12% 1	1980
March	1st to 10th	Night	58% 4 7% 15% 12% 4	5374
	11th to 20th	Night	52% 5% 14% 16% 12% 2	5256
	21st to end	Night	53% 4 6% 21% 13% 2	4967
April	1st to 10th	Night	54% 4 8% 19% 14% 2	2000
	11th to 20th	Night	53% 3 7% 21% 14% 2	1975
	21st to end	Night	50% 4 9% 18% 14% 4	1840
May	1st to 10th	Night	53% 7% 10% 19% 8% 3	2676
	11th to 20th	Night	48% 7% 12% 19% 11% 2	2576
	21st to end	Night	46% 6% 9% 20% 18% 1	2785
June	1st to 10th	Night	50% 7% 10% 21% 12% 1	1520
	11th to 20th	Night	42% 6% 12% 22% 15% 3	1520
	21st to end	Night	48% 8% 11% 19% 13% 1	1520
July	1st to 10th	Night	46% 6% 14% 20% 13%	2480
	11th to 20th	Night	39% 7% 18% 27% 9%	2472
	21st to end	Night	37% 7% 18% 25% 13%	2651
August	1st to 10th	Night	46% 6% 13% 26% 9%	2496
	11th to 20th	Night	44% 7% 18% 23% 8%	2809
	21st to end	Night	43% 7% 14% 21% 14% 1	3476
September	1st to 10th	Night	38% 6% 13% 26% 16% 1	1900
	11th to 20th	Night	36% 4 14% 32% 13% 1	1976
	21st to end	Night	41% 6% 12% 26% 15%	2090
October	1st to 10th	Night	44% 5% 14% 27% 10%	3702
	11th to 20th	Night	44% 4 13% 31% 9%	3841
	21st to end	Night	47% 4 17% 19% 12% 1	4467
November	1st to 10th	Night	52% 5% 12% 22% 8% 1	2537
	11th to 20th	Night	52% 5% 13% 19% 11% 1	2685
	21st to end	Night	60% 5% 12% 17% 6%	2800
December	1st to 10th	Night	68% 5% 12% 12% 4	4580
	11th to 20th	Night	62% 4 8% 16% 11%	5208
	21st to end	Night	63% 4 8% 14% 10%	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	26% 12% 29% 24% 10%	200
	11th to 20th	Day	28% 15% 29% 22% 6% 2	200
	21st to end	Day	21% 13% 33% 25% 7% 1	220
February	1st to 10th	Day	29% 18% 35% 16% 3	280
	11th to 20th	Day	22% 15% 38% 22% 3	399
	21st to end	Day	27% 11% 32% 27% 2	414
March	1st to 10th	Day	25% 12% 31% 24% 8%	500
	11th to 20th	Day	21% 11% 36% 24% 6% 1	500
	21st to end	Day	26% 13% 31% 20% 8% 3	550
April	1st to 10th	Day	26% 16% 28% 20% 8% 2	500
	11th to 20th	Day	27% 16% 25% 19% 10% 2	492
	21st to end	Day	27% 12% 30% 19% 9% 2	500
May	1st to 10th	Day	24% 9% 31% 25% 9% 3	503
	11th to 20th	Day	20% 7% 30% 26% 13% 5%	527
	21st to end	Day	20% 9% 31% 24% 13% 3	549
June	1st to 10th	Day	23% 10% 25% 28% 12% 3	490
	11th to 20th	Day	16% 9% 23% 33% 15% 3	490
	21st to end	Day	21% 7% 25% 27% 16% 4	490
July	1st to 10th	Day	11% 7% 24% 33% 19% 6%	485
	11th to 20th	Day	13% 6% 27% 32% 18% 5%	484
	21st to end	Day	13% 5% 21% 35% 21% 5%	532
August	1st to 10th	Day	15% 3 21% 33% 21% 7%	486
	11th to 20th	Day	11% 6% 19% 29% 23% 11%	479
	21st to end	Day	14% 7% 24% 25% 21% 9%	539
September	1st to 10th	Day	12% 7% 24% 29% 18% 10%	490
	11th to 20th	Day	14% 7% 20% 25% 21% 14%	490
	21st to end	Day	18% 7% 25% 24% 19% 6%	490
October	1st to 10th	Day	21% 9% 28% 22% 14% 6%	490
	11th to 20th	Day	21% 11% 31% 22% 13% 2	470
	21st to end	Day	32% 11% 24% 22% 10%	429
November	1st to 10th	Day	28% 11% 25% 24% 11% 1	395
	11th to 20th	Day	21% 15% 35% 21% 7% 1	314
	21st to end	Day	30% 14% 28% 22% 6% 1	200
December	1st to 10th	Day	29% 10% 26% 27% 8% 2	200
	11th to 20th	Day	25% 15% 37% 19% 4 1	200
	21st to end	Day	29% 15% 28% 20% 7% 1	220
January	1st to 10th	Night	25% 11% 31% 28% 5%	800
	11th to 20th	Night	25% 10% 33% 27% 6%	800
	21st to end	Night	19% 7% 36% 30% 8%	880
February	1st to 10th	Night	21% 8% 37% 28% 6% 1	800
	11th to 20th	Night	22% 10% 37% 27% 4	783
	21st to end	Night	23% 8% 32% 32% 4	660
March	1st to 10th	Night	25% 10% 31% 29% 6%	800
	11th to 20th	Night	26% 9% 31% 26% 7%	800
	21st to end	Night	23% 9% 28% 32% 8%	880
April	1st to 10th	Night	28% 9% 28% 30% 5%	800
	11th to 20th	Night	26% 10% 30% 27% 7% 1	791
	21st to end	Night	27% 8% 30% 26% 9%	640
May	1st to 10th	Night	24% 7% 31% 29% 7% 2	450
	11th to 20th	Night	24% 5% 26% 36% 9% 1	394
	21st to end	Night	18% 6% 32% 34% 10%	423
June	1st to 10th	Night	24% 5% 22% 36% 12% 1	380
	11th to 20th	Night	18% 4 26% 37% 14% 1	380
	21st to end	Night	19% 6% 23% 36% 16% 1	380
July	1st to 10th	Night	12% 4 25% 42% 17% 1	370
	11th to 20th	Night	12% 3 20% 48% 17% 1	368
	21st to end	Night	13% 3 18% 45% 20% 1	416
August	1st to 10th	Night	17% 2 12% 45% 23% 1	378
	11th to 20th	Night	15% 2 19% 36% 26% 2	561
	21st to end	Night	16% 3 20% 37% 23% 2	836
September	1st to 10th	Night	14% 4 23% 42% 17% 1	760
	11th to 20th	Night	18% 4 17% 36% 23% 3	760
	21st to end	Night	19% 3 25% 33% 19% 2	760
October	1st to 10th	Night	21% 6% 26% 33% 13% 1	760
	11th to 20th	Night	23% 7% 27% 31% 11% 1	760
	21st to end	Night	27% 8% 30% 29% 6%	836
November	1st to 10th	Night	24% 10% 29% 28% 9%	780
	11th to 20th	Night	24% 9% 33% 25% 10% 1	800
	21st to end	Night	30% 11% 28% 23% 8% 1	800
December	1st to 10th	Night	30% 8% 31% 24% 7%	800
	11th to 20th	Night	29% 10% 32% 22% 6% 1	800
	21st to end	Night	32% 11% 29% 22% 5% 1	880

Page generated at 2025-05-23 09:20:58. Version ac07

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