Sideroad 10D
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sideroad 10D clear sky chart from 2005-11-06 to 2025-09-19.

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	14% 12% 5% 11% 6% 5% 4 3 5% 6% 29%	126693
	Night	13% 13% 5% 12% 6% 5% 4 3 5% 6% 27%	122367
Transparency	Day	55% 6% 10% 18% 10% 1	130255
	Night	58% 6% 10% 16% 9% 1	126893
Seeing	Day	20% 17% 30% 21% 9% 3	16178
	Night	20% 17% 30% 24% 9% 1	25219

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	10% 16% 10% 23% 14% 6% 5% 3 3 3 7%	3158
	11th to 20th	Day	7% 17% 10% 28% 12% 9% 4 2 4 3 4	3927
	21st to end	Day	12% 18% 8% 23% 8% 6% 6% 3 4 3 9%	4466
February	1st to 10th	Day	12% 17% 8% 20% 10% 6% 5% 4 4 4 11%	1800
	11th to 20th	Day	11% 13% 8% 21% 10% 6% 5% 4 4 5% 13%	1753
	21st to end	Day	12% 20% 7% 15% 8% 6% 4 3 4 4 16%	1575
March	1st to 10th	Day	13% 13% 6% 14% 7% 6% 4 3 4 5% 25%	4857
	11th to 20th	Day	9% 14% 10% 14% 6% 5% 4 3 6% 5% 24%	4980
	21st to end	Day	15% 17% 8% 11% 5% 4 4 3 4 5% 26%	5465
April	1st to 10th	Day	16% 17% 5% 10% 5% 4 4 3 4 6% 25%	2320
	11th to 20th	Day	16% 14% 3 7% 4 4 3 3 4 5% 35%	2534
	21st to end	Day	18% 13% 4 8% 4 4 3 3 5% 6% 32%	2600
May	1st to 10th	Day	14% 11% 3 8% 4 4 4 3 5% 7% 36%	5888
	11th to 20th	Day	14% 11% 3 8% 5% 4 4 3 5% 6% 35%	6180
	21st to end	Day	20% 9% 3 6% 4 4 4 3 4 7% 37%	6949
June	1st to 10th	Day	16% 8% 2 6% 4 4 5% 4 6% 9% 35%	2849
	11th to 20th	Day	12% 7% 2 6% 4 4 5% 5% 7% 9% 39%	3000
	21st to end	Day	17% 7% 2 6% 5% 4 5% 4 5% 7% 37%	3000
July	1st to 10th	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 37%	6819
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 8% 46%	6553
	21st to end	Day	10% 5% 2 6% 4 4 4 3 6% 8% 48%	6424
August	1st to 10th	Day	13% 7% 3 7% 4 4 6% 4 6% 8% 37%	4234
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 5% 6% 8% 33%	4174
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 6% 9% 42%	4587
September	1st to 10th	Day	16% 8% 2 8% 5% 4 5% 3 5% 7% 38%	2400
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 6% 8% 43%	2193
	21st to end	Day	16% 8% 3 10% 5% 6% 4 4 5% 7% 33%	2090
October	1st to 10th	Day	20% 11% 3 7% 5% 4 4 3 5% 7% 31%	1901
	11th to 20th	Day	19% 16% 4 10% 6% 6% 5% 3 5% 5% 22%	1900
	21st to end	Day	25% 20% 3 9% 4 4 4 3 6% 4 17%	2058
November	1st to 10th	Day	14% 21% 4 10% 5% 4 5% 4 4 6% 24%	1687
	11th to 20th	Day	14% 19% 6% 12% 6% 6% 6% 3 5% 7% 17%	1600
	21st to end	Day	15% 22% 7% 14% 7% 6% 5% 4 4 5% 11%	1600
December	1st to 10th	Day	14% 26% 12% 18% 6% 4 3 3 3 4 7%	2600
	11th to 20th	Day	15% 23% 8% 19% 6% 4 3 2 3 3 13%	2986
	21st to end	Day	20% 18% 7% 16% 8% 6% 4 3 4 4 11%	3586
January	1st to 10th	Night	10% 17% 9% 24% 14% 5% 4 3 4 3 8%	6808
	11th to 20th	Night	8% 14% 10% 27% 12% 8% 5% 3 4 3 6%	5953
	21st to end	Night	10% 15% 9% 20% 10% 6% 5% 3 4 5% 12%	6490
February	1st to 10th	Night	9% 18% 8% 17% 10% 7% 6% 4 4 4 12%	2600
	11th to 20th	Night	11% 14% 8% 17% 10% 7% 5% 4 4 5% 15%	2533
	21st to end	Night	11% 14% 5% 15% 10% 6% 5% 4 5% 5% 20%	2052
March	1st to 10th	Night	12% 14% 6% 11% 5% 5% 6% 4 5% 7% 25%	4981
	11th to 20th	Night	7% 13% 7% 10% 5% 5% 6% 5% 7% 7% 30%	4979
	21st to end	Night	15% 13% 5% 11% 5% 4 5% 4 4 5% 29%	5467
April	1st to 10th	Night	17% 14% 4 10% 5% 4 4 4 5% 6% 28%	2078
	11th to 20th	Night	16% 12% 4 8% 5% 4 3 3 3 7% 36%	1832
	21st to end	Night	16% 14% 4 9% 5% 4 4 3 5% 6% 31%	1800
May	1st to 10th	Night	15% 9% 2 7% 4 5% 5% 3 6% 7% 37%	4053
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 6% 7% 44%	3699
	21st to end	Night	19% 8% 2 6% 3 3 3 3 5% 6% 42%	3926
June	1st to 10th	Night	14% 7% 3 6% 5% 5% 5% 4 5% 9% 39%	1547
	11th to 20th	Night	11% 5% 2 5% 5% 5% 5% 5% 6% 10% 41%	1400
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 8% 42%	1400
July	1st to 10th	Night	13% 8% 3 5% 4 3 4 3 5% 8% 45%	3160
	11th to 20th	Night	14% 6% 1 5% 4 3 3 2 5% 6% 50%	3408
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 8% 49%	4428
August	1st to 10th	Night	10% 7% 3 6% 4 4 5% 3 6% 6% 45%	2915
	11th to 20th	Night	14% 6% 3 6% 4 4 4 4 5% 8% 41%	2875
	21st to end	Night	14% 6% 2 6% 4 4 5% 3 5% 7% 45%	3277
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 6% 8% 46%	2000
	11th to 20th	Night	12% 6% 2 4 3 3 4 4 6% 7% 49%	2161
	21st to end	Night	18% 9% 2 7% 4 4 5% 3 4 7% 37%	2090
October	1st to 10th	Night	19% 8% 3 7% 4 5% 4 3 4 7% 36%	2278
	11th to 20th	Night	20% 14% 3 9% 5% 5% 4 3 5% 6% 26%	2280
	21st to end	Night	20% 19% 4 8% 6% 5% 4 3 5% 6% 20%	2536
November	1st to 10th	Night	15% 20% 5% 9% 5% 4 4 3 4 5% 26%	2609
	11th to 20th	Night	13% 19% 6% 12% 6% 5% 5% 4 6% 6% 19%	2800
	21st to end	Night	16% 19% 10% 13% 6% 5% 5% 3 5% 5% 15%	2800
December	1st to 10th	Night	13% 25% 10% 17% 5% 4 4 3 4 4 9%	4580
	11th to 20th	Night	9% 21% 10% 19% 8% 6% 5% 3 3 3 11%	5208
	21st to end	Night	17% 21% 8% 20% 7% 7% 4 3 3 3 9%	7364

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	82% 5% 7% 5% 1	3159
	11th to 20th	Day	85% 6% 4 3 1	3961
	21st to end	Day	78% 6% 8% 6% 3	4466
February	1st to 10th	Day	76% 6% 6% 9% 2	1800
	11th to 20th	Day	74% 5% 7% 9% 4 1	1762
	21st to end	Day	71% 6% 7% 11% 5%	1575
March	1st to 10th	Day	62% 5% 12% 11% 9%	4860
	11th to 20th	Day	59% 5% 10% 17% 5% 2	4980
	21st to end	Day	60% 5% 8% 17% 8% 1	5465
April	1st to 10th	Day	61% 5% 8% 18% 8% 1	2320
	11th to 20th	Day	52% 5% 7% 21% 14% 1	2534
	21st to end	Day	54% 5% 9% 17% 12% 2	2600
May	1st to 10th	Day	47% 6% 11% 19% 12% 6%	5897
	11th to 20th	Day	49% 7% 9% 17% 17% 1	6184
	21st to end	Day	47% 5% 10% 19% 15% 4	6949
June	1st to 10th	Day	45% 7% 10% 21% 15% 1	2849
	11th to 20th	Day	40% 7% 11% 24% 16% 1	3000
	21st to end	Day	44% 7% 12% 23% 13% 1	3000
July	1st to 10th	Day	44% 6% 13% 22% 14% 1	6746
	11th to 20th	Day	35% 6% 11% 32% 15% 1	6472
	21st to end	Day	34% 6% 11% 31% 17% 1	6240
August	1st to 10th	Day	43% 8% 13% 23% 12% 1	4221
	11th to 20th	Day	46% 8% 15% 22% 8%	4213
	21st to end	Day	38% 7% 13% 31% 10% 1	4587
September	1st to 10th	Day	46% 6% 12% 25% 10% 2	2400
	11th to 20th	Day	39% 5% 14% 29% 12% 1	2193
	21st to end	Day	51% 7% 11% 23% 8% 1	2090
October	1st to 10th	Day	47% 6% 12% 23% 11% 1	3161
	11th to 20th	Day	55% 5% 10% 18% 12% 1	3140
	21st to end	Day	63% 6% 11% 16% 4	3372
November	1st to 10th	Day	62% 5% 11% 15% 7%	1687
	11th to 20th	Day	67% 7% 10% 10% 6% 1	1600
	21st to end	Day	75% 6% 9% 8% 1	1600
December	1st to 10th	Day	83% 6% 6% 4 1	2600
	11th to 20th	Day	78% 4 7% 8% 3	2986
	21st to end	Day	79% 5% 6% 6% 4	3586
January	1st to 10th	Night	82% 4 7% 5% 2	6808
	11th to 20th	Night	83% 7% 5% 4 1	5994
	21st to end	Night	73% 5% 9% 6% 6%	6490
February	1st to 10th	Night	74% 6% 8% 10% 2	2600
	11th to 20th	Night	70% 6% 9% 12% 3	2535
	21st to end	Night	64% 8% 9% 12% 7%	2052
March	1st to 10th	Night	57% 7% 12% 15% 8% 1	4991
	11th to 20th	Night	51% 8% 15% 17% 8% 1	4980
	21st to end	Night	57% 5% 9% 18% 10% 1	5467
April	1st to 10th	Night	58% 4 7% 19% 11%	2078
	11th to 20th	Night	50% 5% 7% 20% 16% 1	1832
	21st to end	Night	55% 5% 8% 15% 15% 2	1800
May	1st to 10th	Night	46% 5% 12% 16% 13% 8%	4060
	11th to 20th	Night	39% 7% 12% 24% 15% 2	3700
	21st to end	Night	42% 5% 12% 25% 14% 2	3927
June	1st to 10th	Night	43% 5% 12% 21% 18% 2	1547
	11th to 20th	Night	38% 7% 12% 25% 18% 1	1400
	21st to end	Night	40% 5% 14% 26% 14% 1	1400
July	1st to 10th	Night	38% 5% 14% 25% 16% 3	3125
	11th to 20th	Night	36% 5% 11% 30% 18% 1	3366
	21st to end	Night	33% 7% 11% 33% 16% 1	4297
August	1st to 10th	Night	37% 6% 13% 28% 15% 1	2904
	11th to 20th	Night	40% 7% 16% 24% 12% 1	2902
	21st to end	Night	38% 7% 13% 30% 11% 1	3277
September	1st to 10th	Night	35% 8% 14% 30% 13% 1	2000
	11th to 20th	Night	33% 6% 15% 28% 17% 1	2161
	21st to end	Night	47% 7% 12% 25% 9% 1	2090
October	1st to 10th	Night	42% 6% 10% 24% 17% 1	3798
	11th to 20th	Night	51% 5% 12% 18% 14%	3779
	21st to end	Night	55% 7% 13% 19% 5%	4172
November	1st to 10th	Night	60% 6% 10% 17% 7% 1	2609
	11th to 20th	Night	65% 6% 12% 11% 4 2	2800
	21st to end	Night	71% 7% 12% 8% 2	2800
December	1st to 10th	Night	79% 7% 9% 4 1	4580
	11th to 20th	Night	77% 5% 8% 9% 2	5208
	21st to end	Night	82% 4 5% 7% 2	7364

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	18% 30% 34% 14% 5% 1	200
	11th to 20th	Day	18% 33% 35% 11% 3	293
	21st to end	Day	24% 24% 33% 17% 2	330
February	1st to 10th	Day	26% 31% 32% 9% 2	300
	11th to 20th	Day	24% 30% 36% 8% 2	300
	21st to end	Day	27% 30% 34% 9%	249
March	1st to 10th	Day	21% 24% 36% 14% 4	462
	11th to 20th	Day	22% 21% 36% 17% 4	500
	21st to end	Day	28% 16% 33% 17% 5%	550
April	1st to 10th	Day	25% 21% 33% 16% 5%	500
	11th to 20th	Day	29% 21% 24% 14% 8% 4	492
	21st to end	Day	28% 17% 29% 19% 6% 1	500
May	1st to 10th	Day	20% 17% 32% 21% 8% 2	503
	11th to 20th	Day	20% 9% 30% 24% 13% 3	527
	21st to end	Day	20% 11% 27% 25% 14% 3	573
June	1st to 10th	Day	18% 15% 28% 26% 11% 1	579
	11th to 20th	Day	15% 13% 32% 28% 10% 2	730
	21st to end	Day	20% 10% 31% 26% 10% 2	730
July	1st to 10th	Day	13% 10% 28% 30% 16% 3	721
	11th to 20th	Day	13% 9% 30% 28% 13% 6%	623
	21st to end	Day	10% 8% 31% 31% 16% 4	576
August	1st to 10th	Day	12% 7% 25% 33% 16% 7%	526
	11th to 20th	Day	16% 7% 22% 30% 18% 7%	519
	21st to end	Day	14% 10% 26% 30% 16% 5%	583
September	1st to 10th	Day	16% 13% 24% 25% 15% 6%	530
	11th to 20th	Day	12% 7% 22% 27% 21% 10%	522
	21st to end	Day	15% 15% 28% 24% 14% 4	490
October	1st to 10th	Day	24% 16% 24% 20% 12% 3	490
	11th to 20th	Day	24% 24% 32% 16% 4	490
	21st to end	Day	33% 26% 25% 13% 3	507
November	1st to 10th	Day	26% 27% 29% 13% 5%	263
	11th to 20th	Day	26% 29% 33% 10% 2 1	200
	21st to end	Day	25% 28% 38% 9% 1	200
December	1st to 10th	Day	22% 35% 31% 12% 1	200
	11th to 20th	Day	25% 36% 30% 9% 2	200
	21st to end	Day	28% 32% 31% 6% 3	220
January	1st to 10th	Night	19% 27% 34% 16% 4	1000
	11th to 20th	Night	22% 24% 33% 17% 4	827
	21st to end	Night	16% 19% 39% 20% 5% 1	880
February	1st to 10th	Night	19% 26% 35% 18% 2	800
	11th to 20th	Night	20% 22% 35% 20% 4	783
	21st to end	Night	21% 24% 33% 18% 3	660
March	1st to 10th	Night	18% 21% 36% 20% 5%	800
	11th to 20th	Night	18% 22% 37% 19% 4 1	800
	21st to end	Night	20% 16% 30% 26% 7% 1	880
April	1st to 10th	Night	23% 17% 33% 23% 3	800
	11th to 20th	Night	21% 15% 30% 23% 9% 1	648
	21st to end	Night	23% 14% 28% 25% 10%	600
May	1st to 10th	Night	19% 8% 27% 33% 11% 2	600
	11th to 20th	Night	17% 8% 28% 35% 11% 1	453
	21st to end	Night	15% 6% 27% 39% 14%	433
June	1st to 10th	Night	16% 10% 30% 34% 10% 1	400
	11th to 20th	Night	11% 11% 23% 40% 16%	400
	21st to end	Night	17% 6% 25% 34% 16% 1	400
July	1st to 10th	Night	10% 5% 19% 46% 19% 1	390
	11th to 20th	Night	11% 5% 28% 34% 21% 1	400
	21st to end	Night	10% 4 25% 42% 18% 1	657
August	1st to 10th	Night	12% 5% 21% 37% 24% 1	597
	11th to 20th	Night	10% 5% 20% 36% 26% 4	594
	21st to end	Night	16% 7% 23% 31% 22% 2	688
September	1st to 10th	Night	14% 9% 24% 32% 17% 5%	800
	11th to 20th	Night	15% 5% 21% 35% 19% 4	793
	21st to end	Night	19% 11% 22% 30% 14% 4	760
October	1st to 10th	Night	24% 10% 29% 22% 13% 1	760
	11th to 20th	Night	27% 18% 27% 21% 6% 1	760
	21st to end	Night	32% 20% 28% 16% 3	836
November	1st to 10th	Night	28% 18% 31% 16% 7%	780
	11th to 20th	Night	22% 27% 28% 17% 4 1	800
	21st to end	Night	26% 24% 33% 15% 2	800
December	1st to 10th	Night	27% 25% 33% 12% 4	800
	11th to 20th	Night	21% 28% 35% 13% 2 1	800
	21st to end	Night	27% 24% 34% 13% 2	1040

Page generated at 2025-09-16 01:49:12. Version ac07

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