Fairfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fairfield clear sky chart from 2005-11-06 to 2025-02-21.

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	4 6% 2 5% 4 4 4 3 5% 7% 56%	112021
	Night	4 6% 2 5% 4 4 4 4 5% 7% 55%	115268
Transparency	Day	27% 5% 11% 22% 21% 14%	111766
	Night	28% 5% 12% 23% 20% 11%	115113
Seeing	Day	8% 11% 27% 30% 19% 6%	14719
	Night	8% 5% 21% 41% 21% 4	24478

By Month

Percentage Cloud Cover SW (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	3 9% 4 9% 5% 6% 6% 4 7% 10% 38%	3639
	11th to 20th	Day	2 8% 3 8% 4 4 4 4 5% 8% 49%	3640
	21st to end	Day	6% 9% 3 6% 3 4 3 3 5% 7% 50%	4049
February	1st to 10th	Day	5% 8% 3 7% 5% 5% 5% 4 6% 9% 44%	1800
	11th to 20th	Day	4 10% 3 9% 6% 7% 4 4 7% 11% 37%	1935
	21st to end	Day	3 9% 4 10% 7% 5% 5% 4 7% 9% 37%	1571
March	1st to 10th	Day	3 10% 4 8% 5% 5% 6% 5% 7% 9% 37%	3138
	11th to 20th	Day	4 7% 2 6% 3 3 3 3 5% 6% 57%	3454
	21st to end	Day	5% 9% 3 9% 7% 6% 6% 5% 8% 9% 32%	3848
April	1st to 10th	Day	6% 8% 3 7% 5% 5% 5% 5% 7% 7% 42%	2280
	11th to 20th	Day	3 8% 3 7% 5% 5% 5% 5% 5% 8% 47%	2351
	21st to end	Day	6% 6% 3 6% 5% 4 5% 4 7% 8% 46%	2470
May	1st to 10th	Day	5% 8% 2 7% 5% 5% 6% 4 6% 8% 44%	4110
	11th to 20th	Day	3 4 2 6% 4 4 4 3 5% 6% 59%	4071
	21st to end	Day	5% 5% 2 6% 4 4 4 4 6% 8% 52%	4748
June	1st to 10th	Day	6% 5% 2 6% 5% 4 5% 4 7% 8% 48%	2660
	11th to 20th	Day	5% 4 1 4 3 4 4 3 6% 8% 59%	2660
	21st to end	Day	2 2 1 3 2 2 3 3 5% 6% 72%	2660
July	1st to 10th	Day	1 1 2 1 1 2 2 3 4 81%	4420
	11th to 20th	Day	2 2 1 3 2 3 3 3 4 6% 73%	4420
	21st to end	Day	2 3 1 3 2 2 3 3 5% 7% 68%	4765
August	1st to 10th	Day	3 4 1 4 3 4 4 3 6% 7% 61%	4092
	11th to 20th	Day	1 1 1 2 2 2 2 2 4 6% 76%	4028
	21st to end	Day	2 3 1 3 2 2 2 2 3 4 75%	4345
September	1st to 10th	Day	2 2 1 3 3 2 2 2 4 5% 74%	2233
	11th to 20th	Day	5% 4 2 4 3 3 3 2 4 7% 64%	2090
	21st to end	Day	5% 4 1 3 3 3 3 2 4 6% 66%	2090
October	1st to 10th	Day	4 3 1 4 3 3 3 2 4 5% 68%	3490
	11th to 20th	Day	3 4 1 4 3 3 3 3 6% 8% 62%	3097
	21st to end	Day	2 5% 2 4 3 3 4 4 7% 8% 57%	3101
November	1st to 10th	Day	5% 7% 3 7% 4 4 5% 4 5% 7% 49%	1764
	11th to 20th	Day	5% 6% 2 6% 5% 5% 5% 4 7% 9% 47%	1800
	21st to end	Day	5% 7% 2 6% 4 3 4 3 7% 9% 51%	1800
December	1st to 10th	Day	4 5% 2 4 3 3 3 2 4 5% 65%	2508
	11th to 20th	Day	7% 12% 3 7% 5% 5% 5% 4 7% 9% 37%	2890
	21st to end	Day	6% 10% 3 8% 5% 5% 5% 4 5% 7% 41%	4004
January	1st to 10th	Night	3 10% 3 8% 6% 5% 6% 5% 7% 9% 38%	6306
	11th to 20th	Night	4 8% 4 7% 4 5% 5% 4 5% 7% 48%	6320
	21st to end	Night	5% 11% 3 6% 4 4 4 4 5% 8% 46%	6908
February	1st to 10th	Night	5% 11% 3 6% 5% 5% 4 4 7% 8% 43%	2600
	11th to 20th	Night	4 9% 2 6% 5% 3 4 4 7% 8% 47%	2351
	21st to end	Night	4 10% 4 7% 5% 4 5% 4 7% 9% 43%	1884
March	1st to 10th	Night	4 13% 4 8% 4 4 4 3 5% 7% 43%	3736
	11th to 20th	Night	4 7% 2 4 3 3 4 4 5% 6% 59%	3525
	21st to end	Night	6% 7% 3 7% 5% 5% 5% 5% 8% 10% 41%	3802
April	1st to 10th	Night	5% 6% 2 5% 5% 4 5% 4 6% 8% 49%	1900
	11th to 20th	Night	5% 6% 2 6% 4 4 5% 3 6% 7% 52%	1775
	21st to end	Night	4 5% 2 6% 4 4 4 5% 5% 9% 52%	1710
May	1st to 10th	Night	6% 6% 2 4 3 4 4 3 6% 9% 53%	2860
	11th to 20th	Night	3 3 1 3 3 3 3 3 4 8% 65%	2834
	21st to end	Night	4 5% 2 4 4 4 4 4 5% 8% 57%	2825
June	1st to 10th	Night	5% 4 2 5% 5% 4 4 4 7% 9% 52%	1520
	11th to 20th	Night	5% 3 1 4 3 3 3 3 5% 7% 63%	1520
	21st to end	Night	1 2 1 3 2 3 3 3 5% 6% 72%	1520
July	1st to 10th	Night	1 1 1 2 2 2 2 4 4 81%	2540
	11th to 20th	Night	1 1 1 2 2 3 3 3 4 5% 75%	2540
	21st to end	Night	1 2 1 4 3 3 4 3 5% 7% 67%	2787
August	1st to 10th	Night	4 4 1 4 3 4 4 3 5% 7% 61%	2847
	11th to 20th	Night	1 2 1 1 1 2 2 3 4 6% 76%	2811
	21st to end	Night	1 2 1 3 2 2 2 3 4 4 76%	3326
September	1st to 10th	Night	2 2 1 3 2 2 3 2 3 5% 74%	1947
	11th to 20th	Night	4 3 1 4 3 2 3 3 5% 6% 66%	2090
	21st to end	Night	5% 3 1 3 2 3 3 2 3 5% 69%	2090
October	1st to 10th	Night	4 2 1 3 2 2 2 2 3 5% 74%	3490
	11th to 20th	Night	4 3 1 5% 3 4 4 3 4 7% 62%	3828
	21st to end	Night	3 4 1 4 3 4 5% 4 7% 9% 56%	4457
November	1st to 10th	Night	7% 7% 2 4 4 4 4 4 6% 7% 51%	2535
	11th to 20th	Night	5% 6% 2 5% 4 5% 5% 4 6% 9% 47%	2600
	21st to end	Night	4 7% 2 6% 4 4 5% 3 6% 9% 51%	2600
December	1st to 10th	Night	3 5% 2 4 2 2 3 3 4 6% 65%	4614
	11th to 20th	Night	6% 13% 4 8% 5% 5% 5% 4 7% 9% 34%	5318
	21st to end	Night	6% 9% 3 7% 5% 5% 5% 4 6% 6% 41%	6952

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	40% 8% 16% 23% 13% 1	3639
	11th to 20th	Day	33% 7% 18% 24% 15% 2	3640
	21st to end	Day	34% 6% 14% 30% 11% 5%	4049
February	1st to 10th	Day	35% 10% 22% 23% 8% 2	1800
	11th to 20th	Day	41% 9% 19% 19% 11% 1	1945
	21st to end	Day	42% 9% 17% 21% 8% 3	1571
March	1st to 10th	Day	38% 7% 17% 23% 14% 1	3138
	11th to 20th	Day	26% 4 14% 35% 19% 2	3454
	21st to end	Day	41% 9% 18% 22% 9% 1	3848
April	1st to 10th	Day	38% 7% 18% 19% 15% 3	2280
	11th to 20th	Day	33% 5% 16% 27% 17% 2	2354
	21st to end	Day	33% 5% 13% 28% 20% 1	2470
May	1st to 10th	Day	34% 4 14% 22% 23% 4	4110
	11th to 20th	Day	23% 4 10% 28% 24% 11%	4074
	21st to end	Day	27% 7% 11% 32% 20% 4	4748
June	1st to 10th	Day	30% 7% 14% 27% 20% 3	2660
	11th to 20th	Day	23% 4 9% 21% 28% 14%	2660
	21st to end	Day	14% 3 5% 18% 36% 23%	2660
July	1st to 10th	Day	9% 2 3 8% 19% 59%	4351
	11th to 20th	Day	13% 3 2 7% 20% 55%	4345
	21st to end	Day	15% 3 3 8% 31% 40%	4614
August	1st to 10th	Day	22% 3 5% 10% 31% 31%	4078
	11th to 20th	Day	12% 2 3 14% 39% 30%	4067
	21st to end	Day	15% 2 4 15% 34% 31%	4344
September	1st to 10th	Day	14% 2 6% 15% 33% 30%	2233
	11th to 20th	Day	22% 3 9% 24% 26% 16%	2090
	21st to end	Day	20% 3 7% 25% 31% 13%	2090
October	1st to 10th	Day	21% 3 7% 17% 38% 14%	3490
	11th to 20th	Day	21% 3 11% 31% 24% 11%	3097
	21st to end	Day	23% 5% 13% 30% 27% 2	3101
November	1st to 10th	Day	34% 6% 15% 23% 18% 4	1764
	11th to 20th	Day	31% 8% 21% 27% 12% 1	1800
	21st to end	Day	30% 7% 18% 27% 15% 3	1800
December	1st to 10th	Day	23% 5% 22% 34% 16% 1	2508
	11th to 20th	Day	43% 7% 22% 22% 4	2890
	21st to end	Day	41% 6% 14% 22% 14% 2	4004
January	1st to 10th	Night	40% 8% 14% 27% 11% 1	6306
	11th to 20th	Night	36% 5% 15% 21% 19% 4	6320
	21st to end	Night	36% 6% 12% 29% 13% 4	6908
February	1st to 10th	Night	38% 10% 18% 23% 9% 2	2600
	11th to 20th	Night	33% 8% 18% 26% 13% 2	2352
	21st to end	Night	36% 8% 18% 25% 11% 2	1884
March	1st to 10th	Night	39% 6% 15% 19% 19% 2	3736
	11th to 20th	Night	26% 5% 13% 29% 23% 3	3525
	21st to end	Night	35% 9% 17% 29% 10% 1	3802
April	1st to 10th	Night	31% 6% 15% 27% 16% 4	1900
	11th to 20th	Night	31% 5% 14% 27% 21% 2	1775
	21st to end	Night	28% 5% 14% 28% 23% 1	1710
May	1st to 10th	Night	27% 4 10% 29% 23% 7%	2860
	11th to 20th	Night	18% 4 10% 31% 27% 10%	2835
	21st to end	Night	25% 5% 11% 30% 25% 5%	2825
June	1st to 10th	Night	28% 6% 15% 29% 20% 2	1520
	11th to 20th	Night	22% 5% 10% 22% 30% 11%	1520
	21st to end	Night	13% 3 6% 17% 33% 27%	1520
July	1st to 10th	Night	9% 1 3 8% 20% 59%	2500
	11th to 20th	Night	13% 2 1 6% 19% 59%	2492
	21st to end	Night	17% 3 3 7% 33% 38%	2700
August	1st to 10th	Night	23% 2 4 10% 22% 39%	2838
	11th to 20th	Night	11% 3 3 15% 32% 37%	2838
	21st to end	Night	13% 2 4 14% 35% 31%	3326
September	1st to 10th	Night	15% 3 5% 11% 33% 34%	1947
	11th to 20th	Night	20% 3 7% 24% 26% 20%	2090
	21st to end	Night	20% 3 5% 23% 30% 19%	2090
October	1st to 10th	Night	15% 3 5% 19% 34% 24%	3490
	11th to 20th	Night	24% 3 7% 28% 27% 11%	3828
	21st to end	Night	25% 4 12% 31% 24% 4	4457
November	1st to 10th	Night	33% 5% 14% 22% 23% 3	2535
	11th to 20th	Night	33% 7% 17% 30% 11% 2	2600
	21st to end	Night	31% 6% 17% 27% 16% 3	2600
December	1st to 10th	Night	22% 5% 24% 34% 15% 1	4614
	11th to 20th	Night	46% 7% 19% 22% 6%	5318
	21st to end	Night	41% 6% 17% 21% 14% 2	6952

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	13% 9% 25% 28% 20% 6%	200
	11th to 20th	Day	8% 8% 24% 27% 24% 10%	200
	21st to end	Day	11% 5% 20% 34% 19% 11%	230
February	1st to 10th	Day	14% 15% 30% 24% 12% 4	300
	11th to 20th	Day	10% 14% 32% 29% 12% 3	480
	21st to end	Day	8% 13% 34% 32% 12% 2	383
March	1st to 10th	Day	8% 12% 36% 32% 11% 2	460
	11th to 20th	Day	8% 12% 29% 30% 17% 4	460
	21st to end	Day	11% 13% 31% 32% 12% 1	506
April	1st to 10th	Day	11% 18% 26% 27% 14% 4	460
	11th to 20th	Day	7% 20% 34% 26% 10% 3	452
	21st to end	Day	8% 17% 30% 27% 14% 4	460
May	1st to 10th	Day	7% 15% 30% 28% 16% 4	463
	11th to 20th	Day	12% 13% 27% 26% 15% 6%	488
	21st to end	Day	10% 9% 24% 28% 17% 11%	529
June	1st to 10th	Day	7% 13% 26% 25% 22% 7%	490
	11th to 20th	Day	8% 18% 34% 23% 14% 3	490
	21st to end	Day	4 9% 28% 30% 22% 7%	490
July	1st to 10th	Day	2 8% 26% 34% 22% 7%	486
	11th to 20th	Day	2 7% 32% 32% 22% 5%	484
	21st to end	Day	3 4 25% 35% 24% 8%	531
August	1st to 10th	Day	6% 4 29% 32% 23% 6%	487
	11th to 20th	Day	2 4 26% 31% 24% 13%	477
	21st to end	Day	2 9% 26% 29% 25% 9%	539
September	1st to 10th	Day	3 7% 22% 32% 27% 10%	490
	11th to 20th	Day	10% 7% 23% 30% 22% 9%	490
	21st to end	Day	5% 9% 25% 31% 23% 7%	490
October	1st to 10th	Day	8% 9% 24% 27% 23% 8%	490
	11th to 20th	Day	7% 12% 20% 26% 23% 13%	319
	21st to end	Day	6% 11% 27% 35% 17% 3	330
November	1st to 10th	Day	14% 10% 24% 32% 17% 3	300
	11th to 20th	Day	8% 8% 27% 34% 19% 4	300
	21st to end	Day	9% 6% 23% 33% 24% 5%	300
December	1st to 10th	Day	10% 9% 19% 34% 16% 11%	245
	11th to 20th	Day	13% 9% 22% 32% 20% 5%	200
	21st to end	Day	15% 11% 17% 33% 16% 7%	220
January	1st to 10th	Night	9% 6% 24% 38% 19% 5%	800
	11th to 20th	Night	10% 7% 21% 38% 18% 6%	800
	21st to end	Night	10% 3 21% 40% 22% 4	880
February	1st to 10th	Night	13% 6% 28% 37% 14% 2	800
	11th to 20th	Night	9% 5% 27% 41% 16% 3	784
	21st to end	Night	10% 5% 28% 38% 16% 3	628
March	1st to 10th	Night	8% 6% 27% 41% 15% 3	760
	11th to 20th	Night	8% 6% 27% 37% 21% 3	760
	21st to end	Night	11% 6% 27% 39% 14% 2	836
April	1st to 10th	Night	8% 10% 24% 39% 16% 3	760
	11th to 20th	Night	7% 8% 28% 41% 12% 3	647
	21st to end	Night	5% 8% 27% 39% 19% 2	570
May	1st to 10th	Night	6% 8% 26% 40% 18% 2	570
	11th to 20th	Night	8% 4 23% 36% 25% 5%	561
	21st to end	Night	9% 6% 17% 37% 26% 6%	449
June	1st to 10th	Night	7% 4 18% 41% 28% 2	380
	11th to 20th	Night	6% 4 26% 42% 21% 2	380
	21st to end	Night	4 1 16% 48% 31% 2	380
July	1st to 10th	Night	1 1 9% 55% 31% 3	370
	11th to 20th	Night	2 1 14% 57% 26% 1	368
	21st to end	Night	2 1 9% 49% 34% 5%	430
August	1st to 10th	Night	5% 2 13% 49% 29% 3	567
	11th to 20th	Night	2 2 12% 50% 32% 2	564
	21st to end	Night	2 2 15% 46% 31% 4	729
September	1st to 10th	Night	3 2 12% 44% 33% 6%	760
	11th to 20th	Night	6% 1 12% 40% 32% 9%	760
	21st to end	Night	6% 1 17% 37% 27% 11%	760
October	1st to 10th	Night	8% 3 17% 38% 28% 6%	760
	11th to 20th	Night	7% 4 17% 39% 26% 6%	760
	21st to end	Night	5% 5% 25% 40% 19% 6%	836
November	1st to 10th	Night	12% 4 22% 38% 21% 4	780
	11th to 20th	Night	10% 5% 24% 43% 16% 3	800
	21st to end	Night	9% 5% 21% 38% 21% 7%	800
December	1st to 10th	Night	9% 5% 23% 41% 18% 3	919
	11th to 20th	Night	14% 5% 20% 40% 16% 4	890
	21st to end	Night	13% 7% 26% 40% 12% 3	880

Page generated at 2025-02-18 01:26:32. Version ac07

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