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 2024-11-02.

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%	101532
	Night	18% 10% 3 8% 5% 4 4 3 5% 6% 32%	97454
Transparency	Day	49% 7% 12% 21% 10% 1	101293
	Night	52% 6% 12% 19% 10% 1	97313
Seeing	Day	21% 10% 27% 25% 13% 4	14562
	Night	23% 7% 28% 31% 11% 1	23501

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% 14% 5% 13% 6% 5% 5% 3 5% 5% 23%	2517
	11th to 20th	Day	15% 13% 6% 10% 6% 4 4 3 6% 7% 26%	2520
	21st to end	Day	15% 15% 4 10% 6% 5% 6% 4 5% 7% 24%	2772
February	1st to 10th	Day	14% 15% 4 11% 6% 4 5% 3 5% 5% 27%	1672
	11th to 20th	Day	13% 11% 5% 11% 6% 5% 5% 5% 6% 6% 28%	1757
	21st to end	Day	18% 16% 4 9% 5% 4 4 3 5% 6% 27%	1570
March	1st to 10th	Day	21% 12% 4 10% 6% 5% 4 3 4 5% 26%	3116
	11th to 20th	Day	13% 16% 4 11% 6% 5% 5% 4 4 5% 27%	3283
	21st to end	Day	15% 8% 3 8% 5% 4 4 3 5% 6% 39%	4160
April	1st to 10th	Day	21% 11% 3 7% 4 4 4 3 4 6% 32%	2280
	11th to 20th	Day	20% 9% 2 7% 5% 4 3 3 5% 5% 37%	2254
	21st to end	Day	21% 10% 3 7% 4 3 4 3 5% 5% 33%	2430
May	1st to 10th	Day	19% 8% 3 8% 6% 5% 5% 4 5% 7% 29%	4381
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	4398
	21st to end	Day	15% 6% 2 7% 5% 4 5% 4 6% 9% 37%	4837
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 7% 4 4 4 4 5% 6% 30%	1881
November	1st to 10th	Day	17% 9% 3 6% 4 4 6% 4 5% 7% 34%	1680
	11th to 20th	Day	18% 11% 4 8% 4 5% 4 4 6% 7% 29%	1629
	21st to end	Day	22% 11% 4 7% 5% 5% 6% 5% 6% 6% 25%	1520
December	1st to 10th	Day	24% 13% 6% 9% 6% 4 4 4 5% 5% 19%	1520
	11th to 20th	Day	21% 15% 4 8% 5% 3 5% 3 5% 5% 27%	1906
	21st to end	Day	28% 15% 4 10% 5% 4 4 3 3 3 20%	2772
January	1st to 10th	Night	17% 15% 6% 11% 5% 5% 5% 3 5% 5% 23%	4429
	11th to 20th	Night	12% 14% 4 13% 7% 6% 6% 4 5% 7% 23%	4440
	21st to end	Night	16% 17% 5% 11% 7% 5% 4 3 4 5% 24%	4884
February	1st to 10th	Night	14% 15% 5% 11% 7% 6% 4 4 5% 6% 23%	2507
	11th to 20th	Night	14% 11% 4 9% 6% 5% 5% 4 5% 7% 30%	2309
	21st to end	Night	15% 16% 3 9% 5% 4 4 3 4 5% 31%	1884
March	1st to 10th	Night	20% 11% 3 7% 5% 4 4 3 4 5% 33%	3724
	11th to 20th	Night	18% 18% 4 9% 5% 4 3 2 4 5% 27%	3671
	21st to end	Night	13% 10% 3 9% 5% 4 4 4 4 5% 39%	3471
April	1st to 10th	Night	23% 10% 3 6% 4 4 4 3 5% 6% 31%	1900
	11th to 20th	Night	23% 8% 3 7% 5% 3 4 3 4 6% 35%	1875
	21st to end	Night	22% 8% 3 7% 4 4 4 4 5% 5% 35%	1748
May	1st to 10th	Night	22% 9% 3 8% 4 4 4 4 5% 7% 31%	2588
	11th to 20th	Night	24% 7% 2 6% 4 4 4 4 5% 6% 36%	2495
	21st to end	Night	16% 7% 3 7% 5% 4 4 3 6% 8% 37%	2738
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% 10% 3 7% 5% 4 5% 4 5% 6% 32%	2421
	11th to 20th	Night	19% 10% 3 9% 4 4 4 4 5% 6% 33%	2550
	21st to end	Night	23% 14% 3 8% 5% 4 4 3 4 5% 28%	2660
December	1st to 10th	Night	21% 15% 5% 9% 6% 4 4 4 5% 5% 21%	2660
	11th to 20th	Night	23% 15% 5% 8% 5% 3 3 3 4 4 26%	3288
	21st to end	Night	29% 16% 5% 9% 3 3 3 3 4 4 22%	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	61% 10% 11% 13% 4 1	2518
	11th to 20th	Day	55% 7% 14% 15% 8%	2520
	21st to end	Day	59% 7% 13% 14% 5%	2772
February	1st to 10th	Day	59% 4 10% 20% 5% 2	1672
	11th to 20th	Day	55% 7% 11% 16% 9% 1	1766
	21st to end	Day	59% 4 10% 16% 10% 2	1570
March	1st to 10th	Day	60% 6% 8% 18% 8% 1	3119
	11th to 20th	Day	56% 7% 10% 13% 11% 2	3283
	21st to end	Day	45% 6% 9% 20% 18% 2	4160
April	1st to 10th	Day	55% 5% 8% 18% 13% 2	2280
	11th to 20th	Day	49% 6% 7% 22% 15% 2	2254
	21st to end	Day	53% 5% 9% 17% 13% 3	2430
May	1st to 10th	Day	51% 7% 9% 22% 10% 1	4395
	11th to 20th	Day	48% 9% 14% 18% 9% 2	4402
	21st to end	Day	42% 7% 12% 24% 14% 2	4837
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	49% 5% 12% 23% 11%	1956
	11th to 20th	Day	53% 7% 13% 21% 7%	1862
	21st to end	Day	55% 5% 13% 19% 8% 1	1881
November	1st to 10th	Day	48% 6% 15% 22% 8% 1	1680
	11th to 20th	Day	53% 6% 12% 17% 11% 1	1629
	21st to end	Day	57% 9% 14% 15% 6%	1520
December	1st to 10th	Day	67% 5% 11% 13% 4	1520
	11th to 20th	Day	60% 5% 13% 17% 5%	1906
	21st to end	Day	69% 6% 10% 10% 5%	2772
January	1st to 10th	Night	61% 7% 14% 12% 4	4429
	11th to 20th	Night	58% 7% 14% 14% 5% 1	4440
	21st to end	Night	62% 6% 12% 13% 6% 1	4884
February	1st to 10th	Night	62% 5% 11% 16% 6% 1	2507
	11th to 20th	Night	53% 5% 11% 21% 9% 1	2311
	21st to end	Night	56% 5% 8% 17% 13% 1	1884
March	1st to 10th	Night	54% 4 10% 19% 9% 3	3734
	11th to 20th	Night	59% 5% 9% 14% 12% 2	3672
	21st to end	Night	47% 5% 6% 23% 15% 3	3471
April	1st to 10th	Night	53% 4 8% 19% 14% 2	1900
	11th to 20th	Night	52% 4 7% 21% 14% 2	1875
	21st to end	Night	50% 4 9% 18% 14% 4	1748
May	1st to 10th	Night	52% 7% 10% 20% 9% 3	2594
	11th to 20th	Night	48% 7% 12% 19% 11% 2	2496
	21st to end	Night	45% 6% 9% 20% 18% 1	2739
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	46% 6% 10% 25% 12% 1	2221
	11th to 20th	Night	50% 5% 12% 25% 9%	2318
	21st to end	Night	55% 5% 13% 17% 9% 1	2717
November	1st to 10th	Night	52% 5% 12% 21% 9% 1	2421
	11th to 20th	Night	52% 5% 13% 19% 10% 1	2550
	21st to end	Night	59% 5% 12% 17% 6%	2660
December	1st to 10th	Night	65% 6% 11% 15% 4	2660
	11th to 20th	Night	62% 4 9% 18% 7%	3288
	21st to end	Night	67% 5% 9% 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	26% 11% 27% 26% 11%	180
	11th to 20th	Day	29% 13% 28% 22% 7% 1	180
	21st to end	Day	21% 12% 32% 26% 8% 2	198
February	1st to 10th	Day	29% 17% 35% 16% 3	252
	11th to 20th	Day	22% 12% 39% 23% 4	364
	21st to end	Day	28% 10% 32% 27% 2	382
March	1st to 10th	Day	25% 12% 30% 25% 8%	460
	11th to 20th	Day	22% 11% 35% 25% 6% 2	460
	21st to end	Day	26% 11% 31% 20% 9% 3	506
April	1st to 10th	Day	26% 14% 28% 20% 9% 2	460
	11th to 20th	Day	27% 15% 25% 20% 10% 3	452
	21st to end	Day	27% 12% 28% 20% 9% 3	460
May	1st to 10th	Day	22% 9% 31% 25% 10% 3	463
	11th to 20th	Day	19% 7% 30% 27% 12% 5%	487
	21st to end	Day	18% 9% 32% 25% 13% 3	529
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% 25% 22% 10%	429
November	1st to 10th	Day	28% 11% 24% 25% 11% 1	368
	11th to 20th	Day	22% 14% 34% 20% 8% 1	289
	21st to end	Day	28% 13% 28% 23% 7% 1	180
December	1st to 10th	Day	31% 9% 26% 26% 8% 2	180
	11th to 20th	Day	25% 13% 37% 19% 4 1	180
	21st to end	Day	31% 16% 29% 17% 7% 1	198
January	1st to 10th	Night	26% 10% 30% 28% 5%	760
	11th to 20th	Night	25% 9% 34% 26% 5%	760
	21st to end	Night	19% 7% 36% 29% 8%	836
February	1st to 10th	Night	21% 7% 36% 28% 6% 1	760
	11th to 20th	Night	21% 10% 36% 28% 5%	743
	21st to end	Night	24% 8% 32% 32% 4	628
March	1st to 10th	Night	25% 9% 31% 30% 6%	760
	11th to 20th	Night	27% 9% 31% 26% 7%	760
	21st to end	Night	22% 8% 29% 32% 8%	836
April	1st to 10th	Night	27% 8% 28% 31% 6%	760
	11th to 20th	Night	26% 9% 30% 27% 7% 1	751
	21st to end	Night	26% 8% 30% 26% 9%	608
May	1st to 10th	Night	23% 6% 32% 30% 8% 2	428
	11th to 20th	Night	23% 5% 26% 36% 9% 1	374
	21st to end	Night	17% 6% 33% 35% 9%	411
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	25% 9% 29% 28% 9%	745
	11th to 20th	Night	24% 9% 33% 24% 10% 1	760
	21st to end	Night	30% 10% 28% 24% 8% 1	760
December	1st to 10th	Night	30% 8% 31% 24% 6%	760
	11th to 20th	Night	29% 10% 33% 21% 6% 1	760
	21st to end	Night	33% 11% 30% 21% 5% 1	836

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