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 2026-06-16.

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	3 5% 2 5% 4 4 4 3 5% 7% 57%	145538
	Night	4 6% 2 5% 4 4 4 4 5% 8% 56%	143816
Transparency	Day	25% 5% 10% 22% 23% 14%	140309
	Night	27% 5% 12% 24% 21% 11%	140046
Seeing	Day	7% 11% 27% 30% 19% 6%	16459
	Night	8% 5% 22% 41% 21% 4	26120

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% 5% 5% 4 7% 10% 38%	4722
	11th to 20th	Day	1 6% 3 6% 3 3 4 3 5% 8% 58%	4740
	21st to end	Day	5% 7% 2 6% 3 4 4 4 6% 8% 50%	5246
February	1st to 10th	Day	5% 8% 2 7% 5% 5% 5% 4 6% 8% 45%	1890
	11th to 20th	Day	4 9% 3 9% 6% 6% 4 5% 7% 11% 37%	2034
	21st to end	Day	3 9% 4 9% 7% 5% 5% 4 7% 9% 38%	1730
March	1st to 10th	Day	3 9% 3 7% 5% 5% 5% 4 7% 9% 42%	4618
	11th to 20th	Day	3 8% 3 7% 4 3 4 3 5% 7% 52%	5060
	21st to end	Day	4 8% 3 8% 6% 6% 6% 5% 8% 9% 37%	5644
April	1st to 10th	Day	5% 7% 3 7% 5% 5% 5% 5% 7% 8% 43%	2520
	11th to 20th	Day	3 8% 3 7% 5% 5% 4 5% 5% 8% 47%	2603
	21st to end	Day	5% 6% 3 6% 5% 4 5% 4 7% 9% 46%	2730
May	1st to 10th	Day	3 5% 1 5% 4 4 4 4 6% 8% 56%	7626
	11th to 20th	Day	3 5% 2 6% 4 4 4 3 5% 6% 57%	7596
	21st to end	Day	3 3 1 5% 4 4 5% 4 7% 9% 56%	8875
June	1st to 10th	Day	5% 4 2 5% 4 4 5% 4 7% 9% 50%	2940
	11th to 20th	Day	5% 3 1 4 3 4 3 3 6% 8% 60%	2871
	21st to end	Day	2 2 1 3 2 2 3 3 5% 6% 72%	2800
July	1st to 10th	Day	1 1 2 2 2 3 2 4 5% 79%	6319
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 5% 79%	6320
	21st to end	Day	2 2 1 3 2 3 3 3 5% 8% 68%	6842
August	1st to 10th	Day	2 3 1 3 2 4 4 3 6% 7% 65%	5779
	11th to 20th	Day	1 1 1 2 2 2 2 2 4 5% 79%	5798
	21st to end	Day	3 4 1 4 3 3 3 2 4 4 68%	6214
September	1st to 10th	Day	2 2 1 3 3 2 3 2 4 6% 73%	2350
	11th to 20th	Day	4 4 2 4 3 3 3 2 4 7% 64%	2200
	21st to end	Day	5% 4 1 3 3 3 3 2 4 6% 66%	2200
October	1st to 10th	Day	4 3 1 4 3 3 3 2 4 5% 68%	3600
	11th to 20th	Day	3 4 1 5% 3 3 3 3 6% 8% 62%	3195
	21st to end	Day	3 5% 2 4 3 3 4 4 7% 8% 58%	3200
November	1st to 10th	Day	5% 6% 3 7% 4 4 5% 4 6% 8% 50%	1854
	11th to 20th	Day	5% 6% 2 6% 5% 5% 5% 4 7% 9% 46%	1890
	21st to end	Day	4 7% 2 5% 4 4 4 3 7% 9% 52%	1890
December	1st to 10th	Day	4 5% 2 4 3 3 3 2 4 5% 65%	2584
	11th to 20th	Day	6% 12% 3 7% 5% 5% 5% 4 7% 9% 37%	2966
	21st to end	Day	6% 10% 3 8% 5% 5% 5% 4 5% 7% 41%	4092
January	1st to 10th	Night	4 10% 4 9% 6% 6% 6% 5% 8% 8% 36%	8172
	11th to 20th	Night	3 6% 3 5% 3 4 4 3 4 7% 57%	8220
	21st to end	Night	4 9% 2 5% 3 4 4 4 6% 9% 49%	8937
February	1st to 10th	Night	5% 10% 3 6% 5% 5% 4 4 7% 8% 43%	2730
	11th to 20th	Night	4 10% 3 6% 5% 4 4 4 7% 8% 46%	2471
	21st to end	Night	4 9% 4 6% 5% 4 5% 4 6% 8% 44%	2076
March	1st to 10th	Night	3 12% 4 7% 4 4 4 3 5% 8% 48%	5496
	11th to 20th	Night	4 9% 2 5% 4 4 4 4 6% 7% 52%	5159
	21st to end	Night	4 6% 2 5% 4 5% 5% 5% 8% 10% 46%	5570
April	1st to 10th	Night	4 6% 2 5% 5% 4 5% 4 6% 8% 50%	2100
	11th to 20th	Night	4 6% 2 6% 4 4 5% 3 6% 7% 53%	1963
	21st to end	Night	3 5% 2 6% 5% 4 4 5% 5% 9% 53%	1890
May	1st to 10th	Night	3 4 1 3 2 3 4 3 5% 8% 64%	5321
	11th to 20th	Night	3 4 1 3 3 3 4 4 5% 7% 62%	5296
	21st to end	Night	2 4 1 3 3 3 4 4 6% 9% 60%	5300
June	1st to 10th	Night	5% 4 2 4 5% 4 4 4 7% 8% 53%	1680
	11th to 20th	Night	5% 3 1 4 3 3 3 3 5% 7% 63%	1640
	21st to end	Night	1 2 1 3 2 3 3 3 5% 6% 73%	1600
July	1st to 10th	Night	1 1 1 2 2 2 2 3 4 4 78%	3640
	11th to 20th	Night	1 1 1 1 2 2 3 2 4 4 80%	3640
	21st to end	Night	1 3 1 3 3 3 3 3 6% 10% 63%	4010
August	1st to 10th	Night	3 3 1 3 3 4 3 3 5% 8% 65%	4033
	11th to 20th	Night	1 1 1 1 2 2 3 4 6% 78%	4051
	21st to end	Night	3 2 1 4 2 3 3 3 4 5% 69%	4773
September	1st to 10th	Night	2 2 2 3 2 2 3 2 3 5% 73%	2050
	11th to 20th	Night	4 3 1 4 3 2 3 3 5% 7% 66%	2200
	21st to end	Night	5% 3 1 3 2 3 3 2 3 5% 69%	2200
October	1st to 10th	Night	3 2 1 3 2 2 3 2 3 5% 74%	3600
	11th to 20th	Night	4 3 1 5% 3 4 4 3 4 7% 61%	3950
	21st to end	Night	3 4 2 4 3 3 5% 4 7% 8% 56%	4600
November	1st to 10th	Night	7% 7% 2 5% 4 4 4 4 6% 8% 51%	2665
	11th to 20th	Night	5% 6% 2 5% 4 5% 6% 5% 7% 9% 46%	2730
	21st to end	Night	4 7% 2 6% 4 4 5% 3 6% 9% 50%	2730
December	1st to 10th	Night	3 5% 2 4 2 2 3 3 5% 7% 64%	4755
	11th to 20th	Night	6% 13% 3 8% 5% 5% 5% 4 7% 9% 34%	5462
	21st to end	Night	6% 9% 3 7% 5% 5% 6% 4 6% 6% 41%	7106

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	39% 7% 20% 21% 12%	4723
	11th to 20th	Day	26% 6% 17% 33% 15% 4	4740
	21st to end	Day	31% 7% 15% 30% 13% 4	5246
February	1st to 10th	Day	34% 9% 22% 24% 9% 2	1890
	11th to 20th	Day	40% 9% 18% 20% 11% 1	2044
	21st to end	Day	41% 9% 16% 22% 10% 3	1730
March	1st to 10th	Day	36% 5% 14% 27% 14% 4	4618
	11th to 20th	Day	31% 5% 11% 32% 19% 2	5060
	21st to end	Day	37% 8% 19% 25% 10% 1	5644
April	1st to 10th	Day	36% 6% 18% 22% 16% 3	2520
	11th to 20th	Day	33% 4 14% 26% 19% 3	2606
	21st to end	Day	33% 5% 12% 27% 21% 1	2730
May	1st to 10th	Day	23% 3 10% 25% 32% 7%	7626
	11th to 20th	Day	26% 5% 6% 22% 30% 11%	7599
	21st to end	Day	22% 6% 7% 30% 29% 7%	8876
June	1st to 10th	Day	29% 6% 13% 26% 23% 4	2940
	11th to 20th	Day	22% 4 9% 21% 30% 14%	2871
	21st to end	Day	14% 3 5% 18% 36% 23%	2800
July	1st to 10th	Day	10% 2 2 8% 24% 54%	6251
	11th to 20th	Day	10% 2 1 6% 24% 56%	6245
	21st to end	Day	14% 3 2 8% 38% 35%	6643
August	1st to 10th	Day	21% 3 4 11% 31% 30%	4208
	11th to 20th	Day	11% 2 3 15% 39% 30%	4197
	21st to end	Day	16% 2 4 15% 33% 30%	4481
September	1st to 10th	Day	14% 2 6% 16% 32% 29%	2350
	11th to 20th	Day	22% 3 8% 25% 27% 16%	2200
	21st to end	Day	20% 3 7% 25% 32% 13%	2200
October	1st to 10th	Day	21% 3 7% 17% 38% 14%	3600
	11th to 20th	Day	21% 3 10% 31% 23% 11%	3195
	21st to end	Day	23% 5% 13% 31% 26% 2	3200
November	1st to 10th	Day	33% 6% 15% 25% 18% 3	1854
	11th to 20th	Day	31% 7% 21% 28% 11% 1	1890
	21st to end	Day	28% 7% 19% 28% 15% 3	1890
December	1st to 10th	Day	23% 5% 22% 33% 16% 1	2584
	11th to 20th	Day	43% 7% 22% 22% 5% 1	2966
	21st to end	Day	41% 6% 14% 22% 14% 2	4092
January	1st to 10th	Night	43% 7% 16% 24% 10%	8172
	11th to 20th	Night	28% 4 15% 31% 18% 4	8220
	21st to end	Night	31% 6% 14% 32% 13% 3	8937
February	1st to 10th	Night	37% 9% 19% 24% 9% 2	2730
	11th to 20th	Night	34% 7% 18% 26% 13% 2	2472
	21st to end	Night	35% 8% 18% 25% 13% 2	2076
March	1st to 10th	Night	36% 5% 11% 24% 20% 5%	5496
	11th to 20th	Night	31% 5% 11% 26% 24% 3	5159
	21st to end	Night	29% 8% 19% 29% 13% 1	5570
April	1st to 10th	Night	30% 6% 15% 29% 17% 4	2100
	11th to 20th	Night	31% 4 13% 27% 23% 2	1963
	21st to end	Night	29% 5% 14% 28% 23% 1	1890
May	1st to 10th	Night	19% 3 8% 30% 29% 10%	5319
	11th to 20th	Night	22% 4 7% 25% 33% 11%	5297
	21st to end	Night	20% 4 8% 27% 36% 6%	5301
June	1st to 10th	Night	28% 5% 13% 27% 22% 5%	1680
	11th to 20th	Night	21% 4 9% 22% 31% 12%	1640
	21st to end	Night	13% 2 6% 18% 33% 27%	1600
July	1st to 10th	Night	11% 2 3 8% 23% 55%	3600
	11th to 20th	Night	9% 1 1 6% 24% 58%	3592
	21st to end	Night	17% 2 2 7% 38% 33%	3897
August	1st to 10th	Night	22% 2 4 10% 23% 38%	2928
	11th to 20th	Night	11% 3 3 15% 32% 37%	2928
	21st to end	Night	14% 2 4 15% 35% 31%	3431
September	1st to 10th	Night	15% 3 5% 12% 33% 32%	2050
	11th to 20th	Night	20% 3 6% 25% 27% 19%	2200
	21st to end	Night	20% 3 5% 23% 31% 18%	2200
October	1st to 10th	Night	16% 3 6% 19% 34% 23%	3600
	11th to 20th	Night	24% 3 7% 28% 27% 10%	3950
	21st to end	Night	25% 4 12% 31% 24% 4	4600
November	1st to 10th	Night	32% 5% 14% 23% 23% 3	2665
	11th to 20th	Night	33% 7% 17% 29% 11% 2	2730
	21st to end	Night	31% 5% 17% 28% 16% 3	2730
December	1st to 10th	Night	22% 5% 23% 34% 15% 1	4755
	11th to 20th	Night	46% 7% 19% 22% 6% 1	5462
	21st to end	Night	41% 6% 17% 21% 13% 2	7106

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% 11% 25% 27% 20% 5%	220
	11th to 20th	Day	7% 7% 23% 29% 25% 9%	220
	21st to end	Day	10% 5% 21% 33% 21% 10%	253
February	1st to 10th	Day	13% 15% 30% 24% 13% 5%	330
	11th to 20th	Day	10% 14% 32% 29% 12% 3	519
	21st to end	Day	8% 14% 33% 31% 12% 2	446
March	1st to 10th	Day	8% 13% 34% 30% 12% 2	540
	11th to 20th	Day	9% 14% 29% 29% 16% 3	540
	21st to end	Day	10% 16% 30% 31% 12% 1	594
April	1st to 10th	Day	9% 18% 27% 26% 14% 5%	540
	11th to 20th	Day	8% 20% 33% 25% 11% 3	532
	21st to end	Day	8% 17% 29% 27% 14% 4	540
May	1st to 10th	Day	6% 14% 29% 30% 16% 5%	543
	11th to 20th	Day	13% 14% 29% 25% 14% 5%	568
	21st to end	Day	10% 11% 25% 27% 17% 10%	617
June	1st to 10th	Day	7% 14% 28% 25% 20% 7%	570
	11th to 20th	Day	7% 17% 36% 23% 15% 3	551
	21st to end	Day	4 9% 28% 30% 22% 6%	530
July	1st to 10th	Day	2 8% 28% 33% 21% 7%	526
	11th to 20th	Day	2 7% 33% 31% 21% 5%	524
	21st to end	Day	3 4 25% 35% 24% 9%	575
August	1st to 10th	Day	6% 5% 29% 32% 23% 6%	527
	11th to 20th	Day	2 4 26% 31% 24% 13%	517
	21st to end	Day	3 9% 25% 29% 25% 9%	583
September	1st to 10th	Day	3 6% 21% 32% 27% 11%	530
	11th to 20th	Day	9% 6% 23% 30% 23% 10%	530
	21st to end	Day	5% 8% 24% 32% 24% 7%	530
October	1st to 10th	Day	8% 8% 25% 28% 23% 8%	530
	11th to 20th	Day	7% 13% 22% 25% 21% 12%	350
	21st to end	Day	7% 10% 26% 35% 18% 4	363
November	1st to 10th	Day	13% 10% 25% 31% 18% 3	330
	11th to 20th	Day	8% 8% 26% 34% 20% 4	330
	21st to end	Day	9% 5% 23% 35% 24% 5%	330
December	1st to 10th	Day	9% 11% 20% 34% 16% 10%	269
	11th to 20th	Day	14% 9% 23% 30% 20% 5%	220
	21st to end	Day	17% 12% 17% 31% 17% 6%	242
January	1st to 10th	Night	10% 5% 24% 39% 18% 4	840
	11th to 20th	Night	9% 7% 21% 39% 19% 6%	840
	21st to end	Night	10% 3 21% 42% 21% 4	924
February	1st to 10th	Night	13% 5% 28% 37% 14% 3	840
	11th to 20th	Night	9% 5% 27% 40% 15% 3	824
	21st to end	Night	10% 5% 29% 37% 16% 3	692
March	1st to 10th	Night	8% 6% 28% 40% 15% 3	840
	11th to 20th	Night	8% 6% 29% 36% 19% 2	840
	21st to end	Night	10% 6% 29% 39% 13% 2	924
April	1st to 10th	Night	8% 9% 24% 40% 17% 3	840
	11th to 20th	Night	7% 7% 30% 41% 12% 2	715
	21st to end	Night	5% 8% 28% 39% 19% 2	630
May	1st to 10th	Night	6% 7% 26% 41% 19% 2	630
	11th to 20th	Night	8% 5% 24% 36% 23% 4	621
	21st to end	Night	8% 6% 18% 37% 26% 5%	497
June	1st to 10th	Night	7% 4 18% 42% 27% 2	420
	11th to 20th	Night	5% 4 26% 43% 20% 1	410
	21st to end	Night	4 1 16% 49% 29% 2	400
July	1st to 10th	Night	1 1 10% 55% 30% 3	390
	11th to 20th	Night	2 1 13% 57% 26% 1	388
	21st to end	Night	2 1 9% 49% 35% 5%	453
August	1st to 10th	Night	5% 2 13% 49% 28% 3	597
	11th to 20th	Night	2 2 12% 51% 32% 2	594
	21st to end	Night	3 2 15% 46% 30% 4	768
September	1st to 10th	Night	3 2 11% 44% 34% 6%	800
	11th to 20th	Night	5% 1 11% 41% 33% 9%	800
	21st to end	Night	6% 2 17% 38% 27% 11%	800
October	1st to 10th	Night	8% 3 17% 39% 28% 6%	800
	11th to 20th	Night	7% 5% 19% 38% 25% 6%	800
	21st to end	Night	5% 5% 25% 40% 20% 6%	880
November	1st to 10th	Night	11% 4 23% 38% 21% 4	820
	11th to 20th	Night	10% 5% 23% 43% 16% 3	840
	21st to end	Night	8% 5% 20% 39% 21% 7%	840
December	1st to 10th	Night	9% 6% 24% 41% 17% 3	965
	11th to 20th	Night	14% 5% 21% 41% 15% 4	934
	21st to end	Night	13% 7% 26% 39% 12% 3	924

Page generated at 2026-06-13 00:31:42. Version ac07

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