Fiddletown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fiddletown clear sky chart from 2005-11-06 to 2025-09-04.

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	8% 4 1 3 2 2 2 2 3 4 67%	134681
	Night	11% 5% 1 3 2 2 3 2 4 5% 62%	131441
Transparency	Day	22% 3 7% 17% 26% 25%	129644
	Night	26% 4 7% 18% 23% 22%	127464
Seeing	Day	12% 10% 27% 32% 15% 5%	16253
	Night	13% 4 14% 36% 27% 7%	25569

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	18% 8% 1 3 2 3 3 2 4 6% 50%	3639
	11th to 20th	Day	16% 5% 2 5% 3 3 3 2 3 3 54%	3944
	21st to end	Day	18% 7% 2 5% 4 4 3 3 4 6% 45%	4510
February	1st to 10th	Day	22% 7% 1 4 3 3 3 2 4 4 46%	1800
	11th to 20th	Day	17% 8% 2 5% 3 3 3 3 5% 6% 45%	1920
	21st to end	Day	20% 9% 2 4 3 2 3 3 4 4 45%	1650
March	1st to 10th	Day	17% 13% 2 7% 4 4 4 3 5% 6% 34%	4595
	11th to 20th	Day	18% 9% 2 4 2 3 3 3 4 6% 48%	5000
	21st to end	Day	19% 10% 2 5% 4 4 4 3 6% 6% 36%	5744
April	1st to 10th	Day	15% 8% 2 5% 3 3 3 3 5% 7% 47%	2400
	11th to 20th	Day	12% 5% 1 5% 3 3 3 3 5% 6% 54%	2369
	21st to end	Day	11% 4 1 3 2 2 3 3 5% 8% 57%	2400
May	1st to 10th	Day	6% 3 1 3 1 2 2 2 3 4 73%	5522
	11th to 20th	Day	4 2 1 2 1 1 2 2 3 5% 76%	6247
	21st to end	Day	3 1 1 2 1 1 2 2 3 4 79%	6902
June	1st to 10th	Day	5% 3 1 3 2 3 3 2 4 6% 68%	2800
	11th to 20th	Day	2 1 1 2 2 2 2 2 4 4 81%	2800
	21st to end	Day	2 2 1 2 1 1 1 2 2 2 84%	2800
July	1st to 10th	Day	1 1 1 1 1 1 94%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 89%	6320
	21st to end	Day	1 1 1 1 1 2 3 3 85%	6475
August	1st to 10th	Day	2 1 2 1 1 1 1 2 3 85%	5777
	11th to 20th	Day	1 1 1 1 2 2 92%	5364
	21st to end	Day	2 1 1 2 1 1 2 1 2 3 84%	5981
September	1st to 10th	Day	3 1 1 1 1 2 3 88%	2317
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 4 76%	2280
	21st to end	Day	3 2 1 2 1 1 2 2 2 3 79%	2069
October	1st to 10th	Day	3 2 1 3 2 2 3 3 4 4 74%	3180
	11th to 20th	Day	5% 2 1 2 1 2 2 2 3 3 77%	3161
	21st to end	Day	5% 3 1 4 3 3 3 3 4 6% 65%	3448
November	1st to 10th	Day	11% 6% 2 4 3 3 3 3 4 8% 54%	1781
	11th to 20th	Day	12% 5% 1 4 4 4 4 3 4 7% 53%	1800
	21st to end	Day	14% 6% 1 4 3 3 3 3 4 6% 54%	1715
December	1st to 10th	Day	9% 4 1 4 3 3 3 3 4 7% 59%	2620
	11th to 20th	Day	27% 9% 2 6% 3 3 3 3 4 5% 35%	3028
	21st to end	Day	23% 7% 2 6% 3 4 5% 4 6% 7% 31%	4004
January	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 5% 9% 48%	6306
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 3 4 53%	6013
	21st to end	Night	17% 7% 2 6% 4 4 4 3 3 5% 47%	6468
February	1st to 10th	Night	19% 8% 2 5% 3 3 3 2 3 5% 48%	2600
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 5% 6% 46%	2366
	21st to end	Night	17% 8% 2 4 3 2 3 3 4 4 49%	1980
March	1st to 10th	Night	20% 14% 2 5% 3 3 4 3 4 5% 36%	5296
	11th to 20th	Night	21% 10% 2 3 2 2 2 2 3 5% 48%	5000
	21st to end	Night	23% 9% 2 4 3 3 4 3 5% 7% 37%	5229
April	1st to 10th	Night	14% 6% 1 6% 3 3 3 3 4 7% 49%	2000
	11th to 20th	Night	12% 6% 1 4 4 3 4 3 4 6% 54%	1979
	21st to end	Night	9% 5% 1 3 2 3 3 3 5% 7% 59%	2000
May	1st to 10th	Night	3 4 1 2 2 2 2 2 4 5% 74%	4473
	11th to 20th	Night	4 2 1 2 2 2 2 2 3 5% 76%	3630
	21st to end	Night	3 1 1 2 1 2 2 2 2 4 81%	3972
June	1st to 10th	Night	5% 3 1 3 2 2 3 4 4 6% 68%	1600
	11th to 20th	Night	1 1 2 1 2 2 2 3 3 83%	1600
	21st to end	Night	2 2 2 1 1 2 1 2 3 85%	1600
July	1st to 10th	Night	1 1 1 1 1 94%	3640
	11th to 20th	Night	2 2 2 1 1 1 2 2 2 85%	3640
	21st to end	Night	2 1 1 2 2 2 2 2 3 5% 79%	4377
August	1st to 10th	Night	2 2 1 1 1 1 1 2 3 3 83%	4035
	11th to 20th	Night	1 1 1 1 1 2 3 91%	4505
	21st to end	Night	3 1 1 2 1 1 2 1 2 3 82%	5015
September	1st to 10th	Night	2 1 1 1 1 1 1 2 3 88%	1930
	11th to 20th	Night	3 2 1 2 1 1 2 2 3 3 80%	1900
	21st to end	Night	3 1 2 1 2 2 2 3 3 81%	2105
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 3 78%	3800
	11th to 20th	Night	3 2 1 1 1 2 2 3 5% 79%	3777
	21st to end	Night	8% 2 1 3 2 3 3 2 3 5% 66%	4121
November	1st to 10th	Night	13% 5% 1 3 2 3 3 2 4 7% 58%	2516
	11th to 20th	Night	11% 4 1 4 3 3 3 2 5% 7% 57%	2600
	21st to end	Night	13% 5% 1 4 3 3 3 2 4 6% 56%	2680
December	1st to 10th	Night	10% 4 1 3 2 3 3 3 4 6% 61%	4560
	11th to 20th	Night	25% 8% 2 5% 3 3 4 3 6% 9% 31%	5176
	21st to end	Night	23% 10% 3 7% 4 4 4 3 5% 6% 30%	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	37% 3 14% 22% 15% 8%	3639
	11th to 20th	Day	36% 4 6% 12% 25% 16%	3944
	21st to end	Day	40% 5% 9% 12% 22% 12%	4510
February	1st to 10th	Day	43% 3 8% 19% 17% 10%	1800
	11th to 20th	Day	40% 4 9% 20% 21% 6%	1930
	21st to end	Day	43% 4 8% 21% 17% 7%	1650
March	1st to 10th	Day	48% 7% 9% 15% 16% 5%	4595
	11th to 20th	Day	38% 4 13% 29% 9% 7%	5000
	21st to end	Day	43% 9% 15% 21% 11% 2	5744
April	1st to 10th	Day	37% 5% 13% 24% 17% 5%	2400
	11th to 20th	Day	31% 5% 13% 27% 18% 6%	2372
	21st to end	Day	25% 5% 13% 30% 24% 3	2400
May	1st to 10th	Day	15% 4 8% 28% 33% 13%	5522
	11th to 20th	Day	13% 3 6% 29% 42% 8%	6250
	21st to end	Day	10% 3 6% 25% 47% 8%	6904
June	1st to 10th	Day	19% 4 9% 25% 31% 12%	2800
	11th to 20th	Day	9% 3 7% 20% 36% 26%	2800
	21st to end	Day	9% 1 3 10% 33% 44%	2800
July	1st to 10th	Day	3 1 1 4 19% 73%	6251
	11th to 20th	Day	5% 1 2 5% 11% 75%	6245
	21st to end	Day	7% 1 2 12% 29% 48%	6288
August	1st to 10th	Day	10% 2 2 7% 22% 58%	4206
	11th to 20th	Day	4 1 2 6% 34% 54%	3880
	21st to end	Day	7% 1 2 7% 39% 44%	4311
September	1st to 10th	Day	6% 1 2 7% 29% 54%	2317
	11th to 20th	Day	12% 3 4 21% 38% 22%	2280
	21st to end	Day	12% 2 4 18% 36% 29%	2069
October	1st to 10th	Day	13% 3 4 11% 25% 44%	3180
	11th to 20th	Day	14% 2 4 20% 40% 21%	3161
	21st to end	Day	20% 3 6% 19% 37% 15%	3448
November	1st to 10th	Day	29% 4 10% 20% 22% 14%	1781
	11th to 20th	Day	31% 4 10% 21% 24% 11%	1800
	21st to end	Day	32% 4 8% 18% 25% 14%	1715
December	1st to 10th	Day	26% 3 7% 24% 26% 14%	2620
	11th to 20th	Day	51% 3 8% 14% 16% 8%	3028
	21st to end	Day	48% 6% 14% 17% 9% 4	4004
January	1st to 10th	Night	33% 5% 16% 23% 14% 10%	6306
	11th to 20th	Night	35% 4 8% 13% 25% 15%	6013
	21st to end	Night	40% 4 6% 12% 19% 18%	6468
February	1st to 10th	Night	40% 4 6% 17% 20% 12%	2600
	11th to 20th	Night	38% 5% 7% 22% 19% 9%	2367
	21st to end	Night	37% 4 9% 24% 18% 8%	1980
March	1st to 10th	Night	48% 6% 8% 17% 14% 7%	5296
	11th to 20th	Night	41% 4 9% 24% 15% 8%	5000
	21st to end	Night	45% 7% 12% 21% 12% 3	5229
April	1st to 10th	Night	35% 6% 13% 19% 21% 5%	2000
	11th to 20th	Night	30% 6% 12% 27% 15% 9%	1979
	21st to end	Night	24% 5% 12% 32% 21% 6%	2000
May	1st to 10th	Night	14% 3 11% 27% 27% 17%	4470
	11th to 20th	Night	13% 2 7% 30% 37% 10%	3630
	21st to end	Night	10% 3 6% 32% 42% 7%	3972
June	1st to 10th	Night	16% 6% 11% 26% 28% 12%	1600
	11th to 20th	Night	8% 2 6% 22% 33% 29%	1600
	21st to end	Night	8% 1 3 12% 34% 42%	1600
July	1st to 10th	Night	2 1 1 4 21% 71%	3600
	11th to 20th	Night	8% 1 2 4 13% 72%	3592
	21st to end	Night	10% 2 2 13% 24% 49%	4253
August	1st to 10th	Night	11% 2 2 8% 22% 55%	2929
	11th to 20th	Night	4 1 2 7% 31% 54%	3255
	21st to end	Night	8% 1 1 11% 36% 44%	3608
September	1st to 10th	Night	5% 1 3 8% 31% 52%	1930
	11th to 20th	Night	11% 2 5% 18% 41% 23%	1900
	21st to end	Night	10% 2 4 18% 35% 31%	2105
October	1st to 10th	Night	13% 2 3 10% 24% 47%	3800
	11th to 20th	Night	11% 2 4 25% 34% 23%	3777
	21st to end	Night	22% 3 4 17% 35% 20%	4121
November	1st to 10th	Night	27% 4 9% 21% 21% 18%	2516
	11th to 20th	Night	28% 4 10% 22% 25% 12%	2600
	21st to end	Night	32% 3 7% 19% 24% 15%	2680
December	1st to 10th	Night	26% 3 7% 21% 26% 17%	4560
	11th to 20th	Night	50% 4 8% 13% 19% 6%	5176
	21st to end	Night	53% 7% 12% 15% 9% 5%	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	36% 9% 23% 19% 11% 3	200
	11th to 20th	Day	21% 9% 22% 29% 15% 5%	335
	21st to end	Day	22% 8% 24% 24% 18% 4	440
February	1st to 10th	Day	29% 11% 21% 24% 12% 4	400
	11th to 20th	Day	25% 13% 28% 24% 10% 1	480
	21st to end	Day	21% 15% 27% 25% 11% 1	414
March	1st to 10th	Day	29% 19% 25% 19% 7% 2	500
	11th to 20th	Day	27% 17% 25% 18% 9% 3	500
	21st to end	Day	24% 18% 27% 22% 8% 1	550
April	1st to 10th	Day	19% 16% 31% 24% 9% 1	500
	11th to 20th	Day	14% 22% 24% 28% 9% 2	492
	21st to end	Day	11% 13% 30% 28% 16% 3	500
May	1st to 10th	Day	9% 16% 33% 26% 12% 3	503
	11th to 20th	Day	12% 14% 25% 29% 14% 6%	528
	21st to end	Day	10% 10% 25% 31% 18% 6%	573
June	1st to 10th	Day	6% 11% 27% 35% 12% 9%	530
	11th to 20th	Day	4 12% 31% 33% 14% 6%	530
	21st to end	Day	3 5% 31% 37% 16% 8%	530
July	1st to 10th	Day	5% 29% 43% 15% 8%	526
	11th to 20th	Day	2 1 27% 48% 15% 9%	524
	21st to end	Day	1 2 28% 44% 17% 8%	575
August	1st to 10th	Day	3 5% 30% 39% 16% 8%	527
	11th to 20th	Day	1 5% 30% 41% 15% 7%	517
	21st to end	Day	1 3 26% 47% 17% 5%	583
September	1st to 10th	Day	4 4 32% 40% 18% 3	503
	11th to 20th	Day	4 12% 28% 37% 17% 2	490
	21st to end	Day	3 8% 31% 40% 16% 2	490
October	1st to 10th	Day	4 11% 27% 36% 19% 3	490
	11th to 20th	Day	7% 7% 25% 34% 22% 5%	490
	21st to end	Day	7% 10% 27% 32% 19% 4	539
November	1st to 10th	Day	15% 8% 24% 22% 23% 7%	317
	11th to 20th	Day	13% 9% 22% 29% 19% 8%	300
	21st to end	Day	18% 7% 22% 27% 22% 4	257
December	1st to 10th	Day	20% 6% 22% 24% 20% 10%	200
	11th to 20th	Day	21% 12% 20% 27% 14% 8%	200
	21st to end	Day	25% 12% 21% 21% 18% 3	220
January	1st to 10th	Night	22% 6% 19% 28% 18% 8%	800
	11th to 20th	Night	16% 5% 20% 36% 17% 6%	800
	21st to end	Night	22% 3 20% 30% 19% 7%	880
February	1st to 10th	Night	21% 4 20% 32% 19% 5%	800
	11th to 20th	Night	19% 6% 20% 30% 19% 5%	784
	21st to end	Night	20% 7% 20% 36% 14% 2	660
March	1st to 10th	Night	25% 7% 17% 31% 15% 5%	800
	11th to 20th	Night	24% 6% 15% 29% 21% 5%	800
	21st to end	Night	22% 7% 18% 31% 20% 2	880
April	1st to 10th	Night	17% 4 18% 40% 19% 2	800
	11th to 20th	Night	13% 5% 20% 36% 21% 5%	791
	21st to end	Night	10% 3 17% 39% 25% 7%	800
May	1st to 10th	Night	10% 4 18% 38% 25% 5%	765
	11th to 20th	Night	10% 1 13% 40% 33% 4	408
	21st to end	Night	6% 3 11% 38% 38% 4	433
June	1st to 10th	Night	6% 2 10% 37% 38% 7%	400
	11th to 20th	Night	1 1 13% 41% 39% 5%	400
	21st to end	Night	2 1 7% 41% 44% 7%	400
July	1st to 10th	Night	1 4 41% 49% 5%	390
	11th to 20th	Night	2 1 3 43% 45% 6%	388
	21st to end	Night	2 2 4 30% 50% 11%	614
August	1st to 10th	Night	2 1 7% 36% 47% 7%	597
	11th to 20th	Night	1 8% 43% 39% 9%	791
	21st to end	Night	2 1 6% 40% 46% 6%	880
September	1st to 10th	Night	2 1 5% 42% 42% 7%	772
	11th to 20th	Night	4 1 10% 37% 37% 11%	760
	21st to end	Night	3 1 11% 42% 31% 12%	760
October	1st to 10th	Night	6% 3 11% 45% 26% 9%	760
	11th to 20th	Night	7% 3 13% 36% 34% 8%	760
	21st to end	Night	7% 4 15% 35% 25% 13%	836
November	1st to 10th	Night	15% 3 12% 34% 26% 10%	780
	11th to 20th	Night	14% 3 19% 37% 20% 7%	800
	21st to end	Night	15% 5% 19% 35% 18% 8%	800
December	1st to 10th	Night	19% 7% 15% 34% 19% 7%	800
	11th to 20th	Night	29% 3 17% 29% 17% 5%	800
	21st to end	Night	27% 6% 20% 27% 16% 3	880

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