ICStars Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ICStars Ranch clear sky chart from 2005-11-06 to 2024-11-05.

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	12% 7% 2 6% 4 4 4 3 5% 7% 44%	101135
	Night	12% 7% 3 6% 4 4 4 3 5% 6% 47%	97975
Transparency	Day	37% 6% 12% 26% 17% 2	104785
	Night	36% 6% 11% 25% 18% 3	102466
Seeing	Day	15% 9% 27% 28% 17% 5%	15663
	Night	15% 8% 31% 32% 13% 1	25477

By Month

Percentage Cloud Cover SE (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	15% 9% 4 9% 5% 4 4 4 5% 6% 36%	2847
	11th to 20th	Day	11% 12% 4 9% 5% 7% 6% 2 3 4 37%	2850
	21st to end	Day	17% 17% 3 7% 4 3 4 2 3 4 35%	3135
February	1st to 10th	Day	15% 12% 4 8% 6% 4 3 3 4 6% 36%	1710
	11th to 20th	Day	14% 9% 3 8% 5% 5% 3 3 4 6% 41%	1664
	21st to end	Day	14% 9% 3 7% 5% 3 3 3 5% 6% 41%	1612
March	1st to 10th	Day	15% 12% 2 5% 4 3 3 2 3 5% 46%	3436
	11th to 20th	Day	13% 7% 2 4 3 2 3 3 5% 7% 50%	3480
	21st to end	Day	18% 12% 3 7% 4 4 4 3 4 7% 33%	3814
April	1st to 10th	Day	15% 8% 2 6% 4 4 3 3 5% 6% 44%	2237
	11th to 20th	Day	16% 8% 3 6% 4 4 4 4 5% 5% 42%	2254
	21st to end	Day	19% 7% 3 8% 6% 4 3 3 5% 7% 35%	2337
May	1st to 10th	Day	15% 8% 3 6% 6% 5% 4 4 6% 7% 37%	4082
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 5% 7% 39%	4082
	21st to end	Day	13% 6% 2 6% 4 4 4 4 5% 8% 44%	4757
June	1st to 10th	Day	7% 4 2 5% 4 4 4 6% 7% 10% 48%	2660
	11th to 20th	Day	7% 4 2 6% 4 5% 4 5% 6% 9% 48%	2660
	21st to end	Day	6% 4 1 5% 4 4 4 5% 8% 9% 50%	2660
July	1st to 10th	Day	12% 6% 2 7% 4 4 4 3 6% 9% 43%	4295
	11th to 20th	Day	4 5% 2 5% 4 4 4 4 6% 11% 52%	4120
	21st to end	Day	6% 5% 2 6% 5% 6% 6% 5% 9% 10% 41%	4465
August	1st to 10th	Day	5% 4 1 5% 4 4 4 4 6% 10% 54%	4104
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 6% 7% 47%	4041
	21st to end	Day	5% 4 1 4 4 4 4 4 7% 9% 55%	4184
September	1st to 10th	Day	11% 4 2 4 4 3 3 3 5% 7% 54%	2280
	11th to 20th	Day	10% 4 2 4 3 3 4 4 6% 8% 52%	2185
	21st to end	Day	8% 5% 2 5% 3 4 4 3 4 7% 55%	2033
October	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 4 6% 56%	1900
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 3 6% 55%	1900
	21st to end	Day	17% 8% 3 6% 3 3 3 2 4 5% 46%	2090
November	1st to 10th	Day	11% 7% 2 4 2 3 3 3 5% 7% 53%	1898
	11th to 20th	Day	15% 7% 2 5% 3 3 3 3 4 6% 49%	1622
	21st to end	Day	16% 9% 3 6% 3 3 3 3 4 5% 46%	1520
December	1st to 10th	Day	11% 9% 4 6% 4 3 3 3 4 6% 45%	1520
	11th to 20th	Day	13% 10% 4 8% 4 4 4 3 5% 5% 41%	1918
	21st to end	Day	17% 16% 6% 11% 4 4 4 3 3 5% 26%	2783
January	1st to 10th	Night	10% 11% 4 13% 5% 5% 3 3 3 4 39%	4108
	11th to 20th	Night	12% 10% 4 10% 5% 8% 4 4 4 5% 35%	4120
	21st to end	Night	19% 13% 5% 9% 4 3 3 2 4 5% 33%	4532
February	1st to 10th	Night	14% 10% 4 7% 6% 4 4 3 6% 5% 37%	2470
	11th to 20th	Night	12% 9% 3 8% 4 3 4 3 4 7% 42%	2403
	21st to end	Night	14% 10% 3 6% 3 3 3 3 4 5% 45%	1856
March	1st to 10th	Night	15% 10% 3 5% 3 3 4 2 4 4 46%	3419
	11th to 20th	Night	12% 6% 2 4 3 3 3 3 4 7% 54%	3480
	21st to end	Night	17% 9% 5% 8% 5% 5% 4 3 4 6% 34%	3817
April	1st to 10th	Night	11% 8% 2 4 3 4 4 3 5% 7% 50%	1941
	11th to 20th	Night	14% 8% 2 7% 3 3 3 3 5% 6% 47%	1875
	21st to end	Night	16% 7% 3 6% 4 3 3 3 5% 7% 42%	1839
May	1st to 10th	Night	15% 7% 2 7% 5% 4 4 3 5% 7% 40%	2823
	11th to 20th	Night	14% 7% 3 6% 4 3 4 3 6% 8% 41%	2823
	21st to end	Night	11% 5% 2 6% 4 3 4 3 6% 6% 51%	2805
June	1st to 10th	Night	7% 3 2 4 3 3 4 5% 7% 9% 54%	1520
	11th to 20th	Night	5% 4 2 4 4 4 4 4 7% 13% 49%	1520
	21st to end	Night	4 3 1 3 3 4 4 4 7% 9% 59%	1520
July	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 5% 8% 46%	2656
	11th to 20th	Night	3 3 1 4 3 3 4 3 6% 10% 59%	2850
	21st to end	Night	5% 3 2 5% 4 3 5% 5% 8% 11% 48%	3098
August	1st to 10th	Night	2 1 1 3 3 3 3 4 6% 9% 64%	2836
	11th to 20th	Night	12% 6% 2 5% 3 2 4 3 5% 6% 52%	2798
	21st to end	Night	4 3 1 5% 4 4 4 4 5% 7% 60%	3471
September	1st to 10th	Night	10% 4 2 4 3 3 3 2 5% 6% 57%	1900
	11th to 20th	Night	10% 4 2 4 3 4 3 3 5% 8% 55%	1991
	21st to end	Night	8% 4 2 4 4 4 3 3 4 7% 57%	2127
October	1st to 10th	Night	8% 5% 2 4 3 3 4 3 5% 5% 59%	2280
	11th to 20th	Night	13% 5% 1 4 3 2 3 3 4 5% 56%	2280
	21st to end	Night	16% 6% 2 5% 3 3 3 2 4 4 51%	2508
November	1st to 10th	Night	11% 5% 2 4 3 3 3 2 3 5% 58%	2280
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 5% 52%	2550
	21st to end	Night	16% 8% 2 5% 3 3 3 3 4 4 48%	2660
December	1st to 10th	Night	13% 8% 3 5% 4 4 3 4 5% 5% 45%	2660
	11th to 20th	Night	14% 9% 3 7% 3 3 4 3 4 6% 44%	3279
	21st to end	Night	19% 17% 5% 10% 4 3 3 2 3 4 28%	4880

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	47% 6% 10% 25% 11% 1	2848
	11th to 20th	Day	52% 4 10% 22% 10%	2850
	21st to end	Day	53% 5% 10% 17% 14% 1	3135
February	1st to 10th	Day	50% 4 12% 21% 11% 1	1710
	11th to 20th	Day	45% 5% 12% 21% 15% 2	1673
	21st to end	Day	43% 5% 11% 22% 16% 4	1612
March	1st to 10th	Day	42% 4 8% 24% 19% 2	3436
	11th to 20th	Day	34% 6% 12% 27% 17% 4	3480
	21st to end	Day	50% 8% 16% 20% 5% 1	3814
April	1st to 10th	Day	41% 6% 11% 24% 17% 2	2237
	11th to 20th	Day	43% 6% 13% 23% 15% 1	2254
	21st to end	Day	49% 6% 11% 23% 11% 1	2337
May	1st to 10th	Day	44% 9% 12% 22% 12% 1	4120
	11th to 20th	Day	43% 9% 12% 23% 13%	4086
	21st to end	Day	37% 8% 11% 30% 13% 1	4770
June	1st to 10th	Day	28% 10% 17% 30% 14% 1	2660
	11th to 20th	Day	32% 9% 14% 27% 16% 2	2660
	21st to end	Day	27% 9% 16% 30% 14% 4	2660
July	1st to 10th	Day	38% 7% 13% 24% 16% 3	4230
	11th to 20th	Day	26% 8% 13% 35% 17% 2	4051
	21st to end	Day	30% 11% 18% 29% 11% 1	4325
August	1st to 10th	Day	25% 7% 16% 29% 21% 1	4090
	11th to 20th	Day	35% 7% 16% 27% 15% 1	4080
	21st to end	Day	24% 7% 15% 36% 15% 4	4183
September	1st to 10th	Day	30% 6% 13% 26% 19% 6%	2280
	11th to 20th	Day	30% 6% 11% 26% 25% 3	2185
	21st to end	Day	29% 6% 10% 29% 22% 3	2033
October	1st to 10th	Day	18% 3 6% 22% 39% 11%	3160
	11th to 20th	Day	21% 3 5% 23% 40% 8%	3140
	21st to end	Day	36% 4 8% 24% 25% 3	3428
November	1st to 10th	Day	31% 5% 13% 26% 20% 5%	1898
	11th to 20th	Day	36% 5% 10% 24% 21% 3	1622
	21st to end	Day	43% 4 8% 27% 17% 1	1520
December	1st to 10th	Day	41% 5% 11% 29% 13% 1	1520
	11th to 20th	Day	45% 5% 13% 25% 10% 2	1915
	21st to end	Day	60% 6% 10% 15% 8% 1	2783
January	1st to 10th	Night	49% 6% 12% 22% 11% 1	4108
	11th to 20th	Night	53% 5% 11% 21% 10% 1	4120
	21st to end	Night	54% 4 12% 19% 10% 1	4532
February	1st to 10th	Night	47% 6% 11% 20% 13% 3	2470
	11th to 20th	Night	42% 5% 12% 21% 18% 3	2404
	21st to end	Night	41% 6% 10% 21% 18% 5%	1856
March	1st to 10th	Night	42% 5% 9% 23% 18% 4	3419
	11th to 20th	Night	31% 5% 9% 25% 25% 4	3480
	21st to end	Night	49% 8% 13% 22% 7% 1	3817
April	1st to 10th	Night	34% 5% 11% 25% 21% 4	1941
	11th to 20th	Night	38% 5% 9% 27% 17% 4	1875
	21st to end	Night	42% 5% 10% 26% 16% 1	1839
May	1st to 10th	Night	41% 10% 14% 20% 15% 1	2850
	11th to 20th	Night	39% 8% 14% 28% 11% 1	2824
	21st to end	Night	31% 8% 12% 25% 23% 1	2813
June	1st to 10th	Night	23% 9% 16% 31% 17% 4	1520
	11th to 20th	Night	26% 8% 14% 29% 20% 3	1520
	21st to end	Night	20% 7% 16% 33% 20% 5%	1520
July	1st to 10th	Night	35% 6% 12% 25% 18% 3	2613
	11th to 20th	Night	19% 7% 13% 39% 20% 2	2796
	21st to end	Night	25% 9% 22% 32% 12% 1	2999
August	1st to 10th	Night	16% 7% 21% 29% 24% 3	2826
	11th to 20th	Night	32% 5% 11% 29% 21% 1	2825
	21st to end	Night	23% 6% 12% 38% 17% 4	3471
September	1st to 10th	Night	28% 5% 11% 25% 23% 8%	1900
	11th to 20th	Night	27% 6% 11% 27% 24% 5%	1991
	21st to end	Night	28% 5% 8% 27% 28% 4	2127
October	1st to 10th	Night	17% 3 6% 22% 43% 10%	3800
	11th to 20th	Night	21% 3 7% 24% 30% 16%	3779
	21st to end	Night	33% 4 7% 29% 24% 3	4120
November	1st to 10th	Night	30% 5% 11% 26% 23% 5%	2280
	11th to 20th	Night	33% 4 8% 26% 24% 4	2550
	21st to end	Night	40% 4 8% 27% 17% 3	2660
December	1st to 10th	Night	40% 6% 12% 26% 15% 1	2660
	11th to 20th	Night	41% 5% 11% 29% 14% 1	3281
	21st to end	Night	59% 6% 8% 17% 8% 2	4880

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% 16% 36% 23% 6%	270
	11th to 20th	Day	29% 14% 41% 15% 2	270
	21st to end	Day	18% 16% 44% 19% 3 1	297
February	1st to 10th	Day	27% 15% 39% 16% 4	270
	11th to 20th	Day	21% 20% 38% 15% 6% 1	270
	21st to end	Day	23% 24% 37% 14% 2	225
March	1st to 10th	Day	17% 14% 47% 17% 3	270
	11th to 20th	Day	28% 13% 34% 21% 4	270
	21st to end	Day	34% 16% 30% 14% 5% 1	297
April	1st to 10th	Day	19% 16% 35% 22% 7%	417
	11th to 20th	Day	21% 14% 35% 22% 7% 1	452
	21st to end	Day	23% 14% 33% 22% 8% 1	517
May	1st to 10th	Day	17% 12% 35% 25% 9% 1	653
	11th to 20th	Day	18% 8% 29% 27% 15% 3	675
	21st to end	Day	17% 8% 27% 25% 18% 6%	734
June	1st to 10th	Day	6% 4 20% 35% 27% 9%	680
	11th to 20th	Day	9% 2 25% 36% 23% 5%	680
	21st to end	Day	6% 5% 31% 36% 18% 4	680
July	1st to 10th	Day	13% 2 14% 27% 30% 14%	671
	11th to 20th	Day	5% 2 17% 36% 30% 9%	668
	21st to end	Day	9% 2 16% 32% 31% 10%	739
August	1st to 10th	Day	7% 2 16% 40% 29% 6%	676
	11th to 20th	Day	8% 3 18% 34% 29% 7%	665
	21st to end	Day	9% 1 10% 32% 36% 12%	543
September	1st to 10th	Day	11% 3 13% 36% 28% 9%	490
	11th to 20th	Day	8% 3 13% 37% 31% 7%	395
	21st to end	Day	10% 7% 25% 32% 19% 7%	300
October	1st to 10th	Day	12% 6% 30% 28% 16% 8%	300
	11th to 20th	Day	12% 14% 41% 25% 7% 1	300
	21st to end	Day	25% 16% 32% 22% 5%	330
November	1st to 10th	Day	17% 7% 38% 24% 9% 5%	282
	11th to 20th	Day	17% 16% 31% 24% 9% 2	270
	21st to end	Day	25% 11% 32% 25% 7%	270
December	1st to 10th	Day	14% 14% 39% 23% 7% 2	270
	11th to 20th	Day	21% 14% 36% 22% 6% 1	270
	21st to end	Day	21% 22% 40% 16%	297
January	1st to 10th	Night	16% 11% 40% 26% 7%	950
	11th to 20th	Night	17% 14% 40% 23% 5% 1	950
	21st to end	Night	16% 12% 40% 28% 3	1045
February	1st to 10th	Night	18% 12% 43% 24% 3	950
	11th to 20th	Night	16% 15% 38% 28% 3	929
	21st to end	Night	21% 13% 44% 20% 3	600
March	1st to 10th	Night	17% 13% 41% 24% 5%	570
	11th to 20th	Night	19% 10% 34% 30% 6% 1	570
	21st to end	Night	27% 10% 34% 24% 4	627
April	1st to 10th	Night	16% 10% 38% 31% 5%	570
	11th to 20th	Night	19% 10% 31% 31% 8%	563
	21st to end	Night	18% 8% 37% 29% 8%	570
May	1st to 10th	Night	16% 6% 33% 37% 7%	570
	11th to 20th	Night	16% 6% 25% 35% 17% 1	561
	21st to end	Night	13% 5% 28% 33% 20% 2	617
June	1st to 10th	Night	8% 2 16% 44% 27% 2	570
	11th to 20th	Night	7% 1 25% 44% 21% 2	570
	21st to end	Night	4 3 25% 49% 18% 1	570
July	1st to 10th	Night	9% 2 12% 41% 31% 4	555
	11th to 20th	Night	5% 1 15% 44% 33% 2	552
	21st to end	Night	9% 1 12% 41% 35% 2	624
August	1st to 10th	Night	5% 1 12% 47% 34% 1	567
	11th to 20th	Night	6% 2 14% 45% 30% 3	564
	21st to end	Night	6% 1 11% 38% 39% 4	627
September	1st to 10th	Night	12% 2 14% 41% 27% 3	570
	11th to 20th	Night	10% 2 17% 38% 26% 6%	570
	21st to end	Night	8% 4 22% 41% 22% 4	607
October	1st to 10th	Night	10% 4 25% 37% 20% 3	760
	11th to 20th	Night	15% 7% 37% 31% 10%	760
	21st to end	Night	19% 11% 33% 27% 10%	836
November	1st to 10th	Night	14% 7% 34% 34% 11%	760
	11th to 20th	Night	15% 12% 36% 29% 9%	878
	21st to end	Night	19% 10% 37% 28% 6%	950
December	1st to 10th	Night	17% 10% 39% 27% 6% 1	950
	11th to 20th	Night	20% 10% 36% 30% 4	950
	21st to end	Night	20% 15% 37% 25% 3	1045

Page generated at 2024-11-03 01:11:07. Version ac07

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