Fred's Backyard Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fred's Backyard Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	131138
	Night	15% 10% 3 8% 5% 5% 5% 4 5% 7% 34%	129600
Transparency	Day	49% 4 12% 22% 12% 1	134732
	Night	49% 4 12% 22% 13% 1	134092
Seeing	Day	19% 10% 28% 25% 13% 5%	15962
	Night	19% 8% 28% 30% 13% 1	25510

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% 11% 4 12% 7% 5% 6% 4 7% 5% 23%	4661
	11th to 20th	Day	11% 18% 7% 17% 9% 6% 5% 3 5% 5% 15%	5141
	21st to end	Day	14% 14% 6% 12% 7% 5% 5% 4 6% 6% 21%	5780
February	1st to 10th	Day	15% 14% 3 13% 7% 6% 5% 4 4 6% 24%	1890
	11th to 20th	Day	12% 13% 6% 11% 9% 5% 4 4 5% 6% 25%	1798
	21st to end	Day	17% 12% 4 11% 6% 5% 5% 4 5% 5% 26%	1547
March	1st to 10th	Day	18% 9% 3 9% 5% 4 4 3 5% 6% 32%	4932
	11th to 20th	Day	12% 12% 4 9% 5% 4 5% 4 6% 8% 31%	4980
	21st to end	Day	18% 10% 4 9% 5% 5% 4 3 5% 5% 34%	5465
April	1st to 10th	Day	16% 12% 4 8% 5% 5% 4 4 6% 5% 30%	2355
	11th to 20th	Day	18% 10% 3 7% 5% 4 4 3 5% 6% 36%	2454
	21st to end	Day	19% 8% 3 7% 5% 5% 5% 3 5% 6% 34%	2600
May	1st to 10th	Day	19% 8% 3 8% 4 4 4 4 5% 7% 33%	5888
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 6% 8% 34%	6262
	21st to end	Day	18% 6% 2 7% 4 4 5% 4 6% 7% 39%	6949
June	1st to 10th	Day	14% 6% 2 6% 6% 5% 5% 4 7% 8% 39%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 8% 9% 39%	2800
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 4 7% 9% 40%	2800
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	6360
	11th to 20th	Day	8% 4 2 6% 4 4 5% 4 7% 9% 48%	6360
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 48%	6436
August	1st to 10th	Day	16% 6% 2 5% 4 4 4 4 6% 8% 39%	4234
	11th to 20th	Day	10% 6% 3 7% 6% 5% 5% 4 7% 9% 37%	4174
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 7% 9% 45%	4493
September	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 4 6% 8% 43%	2400
	11th to 20th	Day	10% 5% 3 5% 4 4 4 4 6% 9% 47%	2274
	21st to end	Day	13% 6% 3 7% 5% 5% 6% 4 5% 9% 37%	2164
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 4 6% 6% 38%	2000
	11th to 20th	Day	19% 8% 3 8% 6% 5% 5% 4 5% 7% 31%	2000
	21st to end	Day	23% 9% 4 7% 6% 5% 5% 5% 6% 6% 23%	2200
November	1st to 10th	Day	15% 9% 4 8% 5% 5% 4 3 6% 8% 34%	1787
	11th to 20th	Day	14% 13% 3 8% 6% 5% 5% 6% 5% 8% 27%	1680
	21st to end	Day	17% 14% 5% 8% 6% 6% 5% 3 6% 8% 22%	1680
December	1st to 10th	Day	18% 16% 4 10% 6% 7% 5% 5% 5% 6% 17%	2680
	11th to 20th	Day	21% 15% 4 10% 5% 4 4 4 4 5% 23%	3066
	21st to end	Day	27% 16% 5% 11% 5% 4 4 2 4 4 16%	4048
January	1st to 10th	Night	14% 13% 4 10% 6% 5% 5% 4 6% 7% 26%	8234
	11th to 20th	Night	12% 17% 5% 13% 9% 6% 5% 4 5% 5% 18%	7741
	21st to end	Night	14% 12% 5% 11% 7% 6% 5% 4 6% 6% 24%	8401
February	1st to 10th	Night	14% 14% 5% 9% 6% 5% 5% 4 5% 6% 27%	2730
	11th to 20th	Night	14% 14% 4 10% 7% 6% 5% 4 5% 5% 27%	2599
	21st to end	Night	14% 10% 5% 10% 6% 6% 5% 4 6% 6% 28%	2080
March	1st to 10th	Night	17% 9% 4 8% 6% 6% 5% 4 5% 6% 32%	4908
	11th to 20th	Night	10% 8% 3 7% 5% 4 5% 4 7% 8% 37%	4979
	21st to end	Night	20% 8% 3 6% 4 3 3 3 4 5% 40%	5467
April	1st to 10th	Night	18% 10% 3 8% 5% 5% 4 4 6% 5% 32%	2043
	11th to 20th	Night	16% 8% 3 7% 5% 5% 5% 3 5% 6% 38%	1912
	21st to end	Night	17% 8% 3 7% 5% 4 4 4 6% 7% 37%	1800
May	1st to 10th	Night	22% 8% 2 7% 4 4 4 3 5% 6% 35%	4053
	11th to 20th	Night	15% 7% 3 7% 4 5% 4 4 5% 8% 38%	3631
	21st to end	Night	17% 6% 2 6% 4 3 4 3 5% 7% 44%	3926
June	1st to 10th	Night	12% 5% 2 5% 5% 5% 5% 4 6% 8% 43%	1600
	11th to 20th	Night	10% 6% 2 6% 5% 4 4 5% 7% 9% 43%	1600
	21st to end	Night	10% 5% 3 6% 5% 4 4 5% 6% 8% 45%	1514
July	1st to 10th	Night	7% 5% 2 5% 4 4 4 4 7% 9% 48%	3600
	11th to 20th	Night	10% 4 2 4 4 4 4 4 6% 9% 50%	3600
	21st to end	Night	8% 4 2 5% 4 4 4 3 6% 8% 53%	4399
August	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 4 6% 7% 47%	2915
	11th to 20th	Night	11% 4 2 6% 3 3 4 3 5% 8% 50%	2875
	21st to end	Night	10% 5% 2 6% 3 4 4 4 6% 8% 47%	3371
September	1st to 10th	Night	9% 5% 2 6% 4 3 5% 4 7% 8% 48%	2000
	11th to 20th	Night	10% 4 1 5% 3 3 4 3 5% 7% 56%	2123
	21st to end	Night	15% 7% 3 7% 4 4 4 3 5% 7% 42%	2235
October	1st to 10th	Night	15% 6% 3 7% 4 3 4 4 5% 6% 42%	2400
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 3 4 6% 36%	2400
	21st to end	Night	20% 8% 3 8% 5% 4 5% 3 6% 6% 32%	2640
November	1st to 10th	Night	16% 8% 2 7% 5% 5% 4 3 5% 7% 39%	2726
	11th to 20th	Night	15% 11% 3 8% 5% 5% 6% 4 6% 7% 31%	2940
	21st to end	Night	20% 11% 3 8% 6% 5% 5% 4 6% 7% 26%	2940
December	1st to 10th	Night	18% 14% 5% 10% 6% 5% 5% 4 7% 6% 20%	4720
	11th to 20th	Night	17% 17% 4 10% 5% 5% 5% 4 5% 5% 23%	5348
	21st to end	Night	25% 15% 7% 10% 5% 4 4 3 4 5% 17%	7150

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	59% 5% 12% 14% 10%	4662
	11th to 20th	Day	71% 3 7% 12% 6%	5175
	21st to end	Day	63% 4 10% 15% 9%	5780
February	1st to 10th	Day	61% 3 12% 19% 5% 1	1890
	11th to 20th	Day	61% 3 9% 17% 8% 1	1807
	21st to end	Day	59% 3 10% 20% 8% 1	1547
March	1st to 10th	Day	54% 2 13% 17% 13% 1	4935
	11th to 20th	Day	51% 2 16% 19% 9% 3	4980
	21st to end	Day	54% 2 9% 21% 13% 1	5465
April	1st to 10th	Day	54% 3 10% 19% 13% 1	2355
	11th to 20th	Day	49% 2 10% 23% 15% 1	2454
	21st to end	Day	52% 3 10% 20% 13% 3	2600
May	1st to 10th	Day	50% 3 12% 19% 12% 5%	5897
	11th to 20th	Day	50% 4 12% 19% 14% 2	6266
	21st to end	Day	45% 3 12% 24% 14% 3	6949
June	1st to 10th	Day	42% 4 11% 25% 16% 2	2800
	11th to 20th	Day	39% 5% 13% 27% 16% 1	2800
	21st to end	Day	39% 4 14% 27% 15% 1	2800
July	1st to 10th	Day	36% 6% 14% 27% 15% 2	6290
	11th to 20th	Day	31% 5% 12% 35% 16% 1	6285
	21st to end	Day	31% 6% 14% 30% 18% 1	6251
August	1st to 10th	Day	43% 4 14% 24% 15% 1	4221
	11th to 20th	Day	42% 4 16% 26% 11% 1	4213
	21st to end	Day	34% 5% 12% 37% 11% 1	4493
September	1st to 10th	Day	38% 5% 13% 30% 12% 1	2400
	11th to 20th	Day	34% 3 14% 33% 15% 1	2274
	21st to end	Day	44% 4 14% 27% 10%	2164
October	1st to 10th	Day	37% 4 14% 30% 14% 1	3260
	11th to 20th	Day	39% 4 14% 28% 15%	3240
	21st to end	Day	53% 4 14% 22% 7%	3538
November	1st to 10th	Day	49% 4 13% 24% 10% 1	1787
	11th to 20th	Day	53% 5% 15% 17% 10% 1	1680
	21st to end	Day	60% 4 14% 18% 4	1680
December	1st to 10th	Day	67% 5% 14% 11% 4	2680
	11th to 20th	Day	63% 3 13% 11% 10%	3066
	21st to end	Day	73% 3 7% 11% 6%	4048
January	1st to 10th	Night	56% 4 11% 20% 7%	8234
	11th to 20th	Night	66% 4 8% 15% 6% 1	7782
	21st to end	Night	59% 4 9% 15% 12% 1	8401
February	1st to 10th	Night	57% 3 11% 22% 7% 1	2730
	11th to 20th	Night	59% 3 9% 18% 10% 1	2601
	21st to end	Night	56% 2 12% 21% 9%	2080
March	1st to 10th	Night	53% 3 10% 19% 12% 2	4918
	11th to 20th	Night	44% 2 19% 22% 11% 2	4980
	21st to end	Night	48% 2 8% 21% 19% 3	5467
April	1st to 10th	Night	53% 2 9% 19% 14% 2	2043
	11th to 20th	Night	49% 3 8% 21% 16% 2	1912
	21st to end	Night	47% 3 9% 21% 18% 2	1800
May	1st to 10th	Night	52% 2 11% 15% 14% 6%	4060
	11th to 20th	Night	48% 4 12% 20% 13% 3	3632
	21st to end	Night	41% 2 13% 24% 17% 2	3927
June	1st to 10th	Night	38% 4 10% 27% 18% 3	1600
	11th to 20th	Night	37% 3 11% 26% 21% 2	1600
	21st to end	Night	38% 3 14% 25% 18% 2	1514
July	1st to 10th	Night	32% 5% 15% 24% 22% 2	3560
	11th to 20th	Night	31% 5% 12% 31% 19% 1	3552
	21st to end	Night	30% 5% 13% 29% 22% 1	4269
August	1st to 10th	Night	37% 3 12% 29% 16% 3	2904
	11th to 20th	Night	34% 3 15% 34% 13% 1	2902
	21st to end	Night	35% 4 13% 32% 15% 1	3371
September	1st to 10th	Night	34% 4 14% 32% 15% 2	2000
	11th to 20th	Night	29% 3 11% 38% 19%	2123
	21st to end	Night	43% 3 12% 28% 13% 1	2235
October	1st to 10th	Night	33% 3 8% 30% 24% 1	3920
	11th to 20th	Night	43% 3 12% 29% 13%	3899
	21st to end	Night	41% 4 16% 27% 11% 1	4252
November	1st to 10th	Night	46% 4 11% 26% 13% 1	2726
	11th to 20th	Night	51% 4 14% 21% 10% 1	2940
	21st to end	Night	56% 4 16% 20% 4	2940
December	1st to 10th	Night	64% 4 14% 14% 5%	4720
	11th to 20th	Night	61% 5% 10% 14% 10% 1	5348
	21st to end	Night	71% 4 10% 10% 5%	7150

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	20% 20% 29% 22% 8% 1	220
	11th to 20th	Day	26% 21% 31% 13% 7% 1	310
	21st to end	Day	28% 13% 34% 20% 5%	363
February	1st to 10th	Day	25% 15% 38% 16% 5%	330
	11th to 20th	Day	24% 20% 37% 17% 2 1	315
	21st to end	Day	28% 20% 35% 15% 2	264
March	1st to 10th	Day	22% 13% 36% 22% 7%	500
	11th to 20th	Day	21% 17% 32% 22% 7% 1	500
	21st to end	Day	27% 11% 33% 22% 7% 1	550
April	1st to 10th	Day	22% 13% 33% 24% 7% 1	500
	11th to 20th	Day	26% 15% 29% 18% 9% 3	492
	21st to end	Day	24% 11% 32% 22% 9% 2	500
May	1st to 10th	Day	22% 8% 29% 24% 11% 5%	503
	11th to 20th	Day	17% 7% 28% 27% 15% 6%	527
	21st to end	Day	15% 6% 26% 29% 17% 7%	573
June	1st to 10th	Day	14% 8% 29% 31% 13% 4	530
	11th to 20th	Day	15% 7% 26% 29% 20% 3	530
	21st to end	Day	14% 7% 27% 28% 19% 5%	530
July	1st to 10th	Day	10% 4 20% 34% 23% 10%	525
	11th to 20th	Day	13% 4 21% 32% 20% 10%	524
	21st to end	Day	9% 3 23% 38% 19% 8%	576
August	1st to 10th	Day	13% 4 19% 28% 25% 11%	526
	11th to 20th	Day	9% 5% 20% 31% 21% 14%	519
	21st to end	Day	12% 5% 23% 29% 21% 10%	583
September	1st to 10th	Day	14% 5% 22% 29% 18% 12%	530
	11th to 20th	Day	8% 4 19% 26% 27% 16%	530
	21st to end	Day	15% 8% 28% 25% 16% 8%	530
October	1st to 10th	Day	20% 7% 26% 24% 15% 7%	530
	11th to 20th	Day	20% 11% 35% 23% 9% 2	530
	21st to end	Day	27% 11% 29% 25% 8% 1	583
November	1st to 10th	Day	22% 16% 26% 24% 10% 2	317
	11th to 20th	Day	25% 20% 29% 19% 7% 1	220
	21st to end	Day	24% 15% 39% 17% 5%	220
December	1st to 10th	Day	27% 15% 33% 20% 5%	220
	11th to 20th	Day	30% 19% 30% 16% 4	220
	21st to end	Day	29% 17% 34% 16% 3	242
January	1st to 10th	Night	23% 14% 35% 21% 5%	840
	11th to 20th	Night	28% 12% 31% 23% 5%	840
	21st to end	Night	20% 10% 37% 26% 6% 1	924
February	1st to 10th	Night	22% 13% 37% 25% 3	840
	11th to 20th	Night	22% 13% 36% 24% 5%	804
	21st to end	Night	19% 13% 40% 25% 3	660
March	1st to 10th	Night	19% 12% 35% 26% 7%	800
	11th to 20th	Night	21% 10% 36% 26% 7% 1	800
	21st to end	Night	21% 10% 30% 29% 9% 1	880
April	1st to 10th	Night	23% 9% 33% 30% 5%	800
	11th to 20th	Night	20% 9% 34% 25% 10% 2	728
	21st to end	Night	21% 6% 27% 35% 11%	600
May	1st to 10th	Night	19% 4 27% 33% 15% 2	600
	11th to 20th	Night	16% 4 22% 42% 14% 1	424
	21st to end	Night	13% 2 24% 36% 24% 1	433
June	1st to 10th	Night	13% 3 23% 42% 18% 1	400
	11th to 20th	Night	10% 4 27% 41% 18% 1	400
	21st to end	Night	11% 5% 20% 44% 20% 1	400
July	1st to 10th	Night	6% 1 21% 45% 24% 2	390
	11th to 20th	Night	12% 2 20% 41% 23% 3	388
	21st to end	Night	9% 2 16% 45% 25% 2	641
August	1st to 10th	Night	9% 2 12% 43% 30% 3	597
	11th to 20th	Night	9% 3 13% 41% 30% 4	594
	21st to end	Night	11% 2 18% 38% 27% 3	743
September	1st to 10th	Night	11% 6% 19% 35% 23% 6%	800
	11th to 20th	Night	12% 3 15% 33% 32% 6%	800
	21st to end	Night	18% 5% 20% 31% 23% 4	800
October	1st to 10th	Night	18% 4 25% 28% 23% 3	800
	11th to 20th	Night	21% 8% 29% 30% 10% 2	800
	21st to end	Night	25% 8% 30% 32% 6%	880
November	1st to 10th	Night	21% 10% 26% 31% 11% 1	820
	11th to 20th	Night	22% 11% 33% 24% 8% 2	840
	21st to end	Night	26% 10% 32% 25% 6%	840
December	1st to 10th	Night	27% 10% 35% 22% 6%	840
	11th to 20th	Night	25% 12% 37% 21% 5%	840
	21st to end	Night	31% 9% 34% 22% 3	924

Page generated at 2026-02-13 01:42:16. Version ac07

Copyright © 2026 Attilla Danko.