Sisk Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sisk Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	12% 7% 2 6% 4 4 4 3 5% 7% 45%	100673
	Night	11% 7% 2 5% 4 3 3 3 5% 7% 50%	98420
Transparency	Day	36% 6% 12% 25% 17% 3	104323
	Night	33% 5% 11% 26% 20% 4	102910
Seeing	Day	14% 9% 26% 28% 18% 5%	15563
	Night	14% 8% 31% 33% 13% 1	25376

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% 10% 3 7% 4 4 4 3 4 6% 41%	2847
	11th to 20th	Day	10% 11% 4 8% 5% 3 3 2 4 7% 42%	2850
	21st to end	Day	18% 13% 3 7% 3 3 3 2 4 4 39%	3135
February	1st to 10th	Day	16% 10% 3 7% 5% 3 3 3 5% 4 40%	1710
	11th to 20th	Day	13% 10% 3 8% 4 4 3 2 4 5% 45%	1674
	21st to end	Day	13% 10% 3 6% 5% 4 4 4 5% 6% 40%	1662
March	1st to 10th	Day	14% 9% 3 5% 3 3 3 2 4 6% 49%	3436
	11th to 20th	Day	13% 7% 2 4 3 3 3 4 5% 7% 50%	3480
	21st to end	Day	16% 11% 4 7% 4 4 4 3 6% 6% 34%	3814
April	1st to 10th	Day	11% 8% 3 5% 5% 4 4 4 6% 7% 44%	2180
	11th to 20th	Day	15% 6% 2 8% 4 4 4 3 6% 6% 42%	2254
	21st to end	Day	20% 8% 3 6% 4 5% 4 3 5% 6% 36%	2366
May	1st to 10th	Day	19% 9% 3 7% 4 5% 4 3 5% 6% 35%	4082
	11th to 20th	Day	13% 6% 3 7% 4 5% 4 3 6% 8% 40%	4082
	21st to end	Day	13% 7% 2 7% 5% 4 5% 4 6% 9% 38%	4477
June	1st to 10th	Day	6% 4 2 5% 5% 4 4 5% 6% 11% 48%	2470
	11th to 20th	Day	7% 4 2 5% 5% 4 5% 4 7% 8% 48%	2470
	21st to end	Day	5% 2 1 4 4 4 3 4 7% 10% 57%	2470
July	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 5% 6% 9% 41%	4120
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 11% 51%	4120
	21st to end	Day	6% 4 2 5% 5% 5% 5% 5% 8% 11% 43%	4465
August	1st to 10th	Day	5% 4 1 4 3 5% 4 4 6% 9% 55%	4104
	11th to 20th	Day	8% 5% 2 7% 5% 5% 5% 4 6% 8% 45%	4041
	21st to end	Day	5% 4 2 4 3 4 4 4 5% 8% 56%	4222
September	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 5% 6% 54%	2280
	11th to 20th	Day	11% 4 2 6% 4 4 5% 3 5% 8% 48%	2091
	21st to end	Day	9% 4 2 5% 4 4 4 3 5% 7% 54%	2082
October	1st to 10th	Day	11% 4 2 5% 3 4 4 3 4 6% 55%	1900
	11th to 20th	Day	12% 6% 2 3 2 3 3 2 5% 5% 57%	1900
	21st to end	Day	18% 8% 2 5% 3 2 3 2 3 5% 50%	2090
November	1st to 10th	Day	9% 5% 2 5% 3 2 3 3 4 5% 58%	1888
	11th to 20th	Day	13% 7% 2 5% 3 3 3 2 4 5% 53%	1765
	21st to end	Day	15% 7% 2 6% 3 2 2 2 4 6% 51%	1559
December	1st to 10th	Day	12% 9% 3 6% 3 4 3 3 5% 7% 45%	1520
	11th to 20th	Day	13% 9% 4 8% 4 4 3 3 3 5% 44%	1932
	21st to end	Day	16% 16% 7% 7% 4 4 4 2 5% 6% 28%	3135
January	1st to 10th	Night	11% 10% 3 9% 4 3 3 2 3 5% 46%	4108
	11th to 20th	Night	10% 7% 3 7% 6% 5% 5% 4 5% 5% 44%	4120
	21st to end	Night	21% 11% 4 6% 2 2 2 2 4 5% 41%	4532
February	1st to 10th	Night	14% 10% 3 6% 4 4 4 3 4 5% 42%	2470
	11th to 20th	Night	14% 8% 3 6% 3 4 3 3 4 6% 46%	2403
	21st to end	Night	15% 8% 3 6% 3 4 3 3 3 6% 46%	1795
March	1st to 10th	Night	13% 7% 2 6% 3 3 3 3 4 6% 49%	3419
	11th to 20th	Night	11% 6% 2 5% 3 4 3 3 4 6% 53%	3480
	21st to end	Night	13% 7% 3 7% 5% 5% 4 3 4 5% 43%	3817
April	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 5% 6% 51%	1998
	11th to 20th	Night	14% 7% 3 5% 3 4 3 3 4 5% 49%	1875
	21st to end	Night	15% 7% 3 6% 4 5% 4 3 5% 5% 44%	1810
May	1st to 10th	Night	14% 9% 3 5% 4 4 4 4 4 7% 42%	2823
	11th to 20th	Night	13% 7% 3 7% 4 4 4 3 6% 7% 42%	2823
	21st to end	Night	11% 5% 2 6% 3 3 3 3 6% 9% 49%	3090
June	1st to 10th	Night	5% 4 2 4 4 3 5% 4 6% 10% 53%	1710
	11th to 20th	Night	4 3 2 4 3 4 5% 4 7% 10% 53%	1710
	21st to end	Night	4 3 1 4 4 3 5% 3 6% 9% 59%	1710
July	1st to 10th	Night	10% 6% 2 5% 4 3 4 4 6% 7% 49%	2850
	11th to 20th	Night	3 2 1 4 4 4 3 4 6% 10% 59%	2850
	21st to end	Night	6% 4 2 4 3 4 4 4 8% 11% 50%	3098
August	1st to 10th	Night	3 2 1 3 3 3 3 4 5% 8% 64%	2836
	11th to 20th	Night	7% 5% 2 6% 3 4 4 4 6% 8% 51%	2798
	21st to end	Night	3 3 1 4 3 3 3 3 5% 8% 64%	3435
September	1st to 10th	Night	9% 5% 2 4 3 3 4 3 4 6% 56%	1900
	11th to 20th	Night	10% 4 2 5% 5% 3 3 3 4 8% 53%	2085
	21st to end	Night	7% 5% 2 4 4 4 3 3 4 6% 59%	2090
October	1st to 10th	Night	8% 4 1 4 3 3 3 3 5% 6% 62%	2267
	11th to 20th	Night	13% 5% 1 4 3 2 2 3 4 5% 58%	2280
	21st to end	Night	15% 6% 1 5% 3 3 3 2 4 5% 53%	2508
November	1st to 10th	Night	11% 5% 1 3 2 3 2 2 3 5% 62%	2263
	11th to 20th	Night	10% 7% 3 5% 3 3 2 3 4 6% 53%	2413
	21st to end	Night	16% 7% 2 4 4 3 2 3 4 5% 52%	2615
December	1st to 10th	Night	13% 7% 3 5% 3 3 3 4 5% 6% 47%	2660
	11th to 20th	Night	13% 8% 3 6% 4 3 4 3 5% 6% 45%	3247
	21st to end	Night	16% 14% 5% 7% 4 4 4 3 4 5% 33%	4532

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	45% 3 9% 25% 17% 1	2848
	11th to 20th	Day	43% 3 13% 27% 11% 3	2850
	21st to end	Day	49% 4 9% 20% 16% 2	3135
February	1st to 10th	Day	47% 5% 9% 24% 11% 2	1710
	11th to 20th	Day	43% 4 10% 23% 16% 4	1683
	21st to end	Day	44% 4 8% 21% 15% 7%	1662
March	1st to 10th	Day	38% 4 7% 23% 22% 5%	3436
	11th to 20th	Day	34% 6% 11% 28% 17% 4	3480
	21st to end	Day	49% 8% 13% 21% 8% 1	3814
April	1st to 10th	Day	39% 7% 13% 22% 17% 3	2180
	11th to 20th	Day	42% 6% 14% 20% 15% 2	2254
	21st to end	Day	49% 5% 9% 24% 12% 1	2366
May	1st to 10th	Day	49% 8% 9% 19% 13% 2	4120
	11th to 20th	Day	40% 9% 13% 26% 12%	4086
	21st to end	Day	40% 9% 15% 23% 12% 1	4489
June	1st to 10th	Day	30% 9% 16% 27% 17% 2	2470
	11th to 20th	Day	29% 8% 15% 30% 17% 2	2470
	21st to end	Day	21% 7% 17% 31% 20% 4	2470
July	1st to 10th	Day	37% 8% 14% 21% 17% 3	4056
	11th to 20th	Day	27% 7% 12% 36% 17% 2	4051
	21st to end	Day	29% 9% 22% 30% 10% 1	4325
August	1st to 10th	Day	24% 6% 17% 25% 25% 3	4090
	11th to 20th	Day	36% 7% 15% 25% 15% 1	4080
	21st to end	Day	25% 7% 12% 40% 13% 4	4221
September	1st to 10th	Day	31% 5% 11% 26% 17% 9%	2280
	11th to 20th	Day	33% 6% 10% 25% 23% 2	2091
	21st to end	Day	29% 6% 10% 25% 25% 4	2082
October	1st to 10th	Day	19% 2 7% 18% 37% 17%	3160
	11th to 20th	Day	18% 2 4 27% 36% 12%	3140
	21st to end	Day	30% 3 7% 29% 26% 5%	3428
November	1st to 10th	Day	29% 5% 8% 30% 23% 5%	1888
	11th to 20th	Day	34% 4 9% 24% 24% 6%	1765
	21st to end	Day	38% 3 9% 25% 23% 2	1559
December	1st to 10th	Day	39% 5% 9% 31% 15% 1	1520
	11th to 20th	Day	44% 4 8% 21% 20% 3	1929
	21st to end	Day	57% 6% 9% 18% 9% 1	3135
January	1st to 10th	Night	41% 4 11% 28% 14% 2	4108
	11th to 20th	Night	40% 5% 13% 26% 14% 1	4120
	21st to end	Night	48% 4 12% 19% 15% 3	4532
February	1st to 10th	Night	43% 5% 11% 24% 14% 3	2470
	11th to 20th	Night	40% 5% 11% 25% 17% 3	2404
	21st to end	Night	39% 4 8% 23% 19% 7%	1795
March	1st to 10th	Night	37% 5% 11% 21% 20% 6%	3419
	11th to 20th	Night	32% 6% 9% 27% 23% 2	3480
	21st to end	Night	42% 6% 13% 27% 11% 1	3817
April	1st to 10th	Night	33% 5% 12% 23% 22% 6%	1998
	11th to 20th	Night	37% 5% 9% 23% 20% 5%	1875
	21st to end	Night	41% 7% 11% 24% 16% 2	1810
May	1st to 10th	Night	40% 8% 13% 20% 15% 4	2850
	11th to 20th	Night	39% 8% 13% 26% 13% 1	2824
	21st to end	Night	31% 9% 14% 30% 15% 1	3099
June	1st to 10th	Night	25% 9% 17% 28% 17% 3	1710
	11th to 20th	Night	22% 8% 17% 31% 20% 2	1710
	21st to end	Night	21% 5% 15% 33% 21% 5%	1710
July	1st to 10th	Night	32% 7% 14% 24% 17% 5%	2805
	11th to 20th	Night	20% 6% 11% 38% 22% 3	2796
	21st to end	Night	25% 7% 21% 33% 14%	2999
August	1st to 10th	Night	18% 6% 15% 34% 22% 5%	2826
	11th to 20th	Night	29% 7% 14% 29% 19% 1	2825
	21st to end	Night	18% 6% 13% 40% 19% 4	3435
September	1st to 10th	Night	28% 6% 10% 25% 22% 9%	1900
	11th to 20th	Night	30% 5% 10% 25% 26% 5%	2085
	21st to end	Night	27% 5% 9% 25% 29% 5%	2090
October	1st to 10th	Night	14% 3 7% 17% 42% 17%	3787
	11th to 20th	Night	21% 2 5% 20% 34% 17%	3779
	21st to end	Night	30% 4 7% 29% 26% 5%	4120
November	1st to 10th	Night	27% 4 10% 27% 25% 7%	2263
	11th to 20th	Night	33% 4 7% 25% 26% 5%	2413
	21st to end	Night	36% 4 8% 23% 24% 4	2615
December	1st to 10th	Night	38% 5% 13% 24% 19% 1	2660
	11th to 20th	Night	41% 5% 8% 24% 20% 2	3249
	21st to end	Night	53% 6% 9% 20% 10% 3	4532

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	22% 12% 35% 26% 5%	270
	11th to 20th	Day	23% 19% 37% 20% 1	270
	21st to end	Day	15% 14% 46% 18% 6%	297
February	1st to 10th	Day	24% 18% 34% 20% 3	270
	11th to 20th	Day	19% 20% 39% 17% 4	270
	21st to end	Day	23% 22% 40% 12% 4	225
March	1st to 10th	Day	21% 18% 36% 22% 3	270
	11th to 20th	Day	24% 18% 32% 23% 3	270
	21st to end	Day	31% 14% 38% 12% 4 1	297
April	1st to 10th	Day	18% 16% 41% 21% 5% 1	360
	11th to 20th	Day	18% 16% 39% 20% 7%	452
	21st to end	Day	24% 15% 29% 23% 8% 1	546
May	1st to 10th	Day	17% 14% 35% 24% 9% 1	653
	11th to 20th	Day	16% 9% 31% 26% 16% 3	675
	21st to end	Day	15% 7% 31% 24% 17% 7%	734
June	1st to 10th	Day	7% 3 19% 34% 29% 9%	680
	11th to 20th	Day	7% 3 21% 41% 22% 6%	680
	21st to end	Day	4 4 29% 39% 19% 5%	680
July	1st to 10th	Day	10% 3 15% 31% 28% 12%	671
	11th to 20th	Day	4 2 16% 38% 31% 9%	668
	21st to end	Day	7% 3 11% 33% 33% 12%	739
August	1st to 10th	Day	9% 2 13% 40% 31% 5%	676
	11th to 20th	Day	9% 3 16% 35% 31% 6%	665
	21st to end	Day	9% 1 9% 30% 40% 11%	568
September	1st to 10th	Day	10% 2 12% 32% 34% 10%	490
	11th to 20th	Day	5% 2 15% 39% 29% 11%	301
	21st to end	Day	12% 4 18% 37% 21% 8%	300
October	1st to 10th	Day	10% 9% 24% 27% 21% 9%	300
	11th to 20th	Day	12% 12% 38% 27% 9% 2	300
	21st to end	Day	27% 13% 31% 23% 5% 1	330
November	1st to 10th	Day	17% 11% 35% 24% 10% 2	279
	11th to 20th	Day	15% 17% 35% 22% 9% 3	270
	21st to end	Day	23% 16% 31% 23% 7% 1	270
December	1st to 10th	Day	16% 12% 43% 19% 8% 3	270
	11th to 20th	Day	18% 16% 37% 22% 6% 1	270
	21st to end	Day	21% 18% 42% 16% 2	297
January	1st to 10th	Night	16% 13% 39% 25% 6%	950
	11th to 20th	Night	17% 14% 40% 23% 5%	950
	21st to end	Night	15% 13% 39% 28% 4	1045
February	1st to 10th	Night	20% 13% 41% 23% 3	950
	11th to 20th	Night	18% 14% 41% 24% 3	929
	21st to end	Night	20% 16% 36% 25% 2	539
March	1st to 10th	Night	16% 12% 40% 26% 5%	570
	11th to 20th	Night	20% 11% 38% 25% 5%	570
	21st to end	Night	22% 12% 39% 22% 5%	627
April	1st to 10th	Night	14% 14% 37% 30% 6%	570
	11th to 20th	Night	18% 12% 35% 28% 6%	563
	21st to end	Night	18% 10% 39% 25% 8%	570
May	1st to 10th	Night	16% 5% 34% 36% 8% 1	570
	11th to 20th	Night	16% 4 28% 34% 17% 1	561
	21st to end	Night	13% 4 26% 37% 18% 2	617
June	1st to 10th	Night	6% 3 16% 44% 29% 1	570
	11th to 20th	Night	5% 1 24% 46% 22% 1	570
	21st to end	Night	3 3 23% 52% 18% 1	570
July	1st to 10th	Night	9% 1 12% 41% 34% 3	555
	11th to 20th	Night	4 1 12% 47% 33% 3	552
	21st to end	Night	7% 1 12% 42% 36% 3	624
August	1st to 10th	Night	5% 2 15% 44% 34% 1	567
	11th to 20th	Night	6% 2 10% 53% 26% 3	564
	21st to end	Night	5% 1 10% 39% 42% 4	627
September	1st to 10th	Night	10% 2 13% 43% 31% 1	570
	11th to 20th	Night	11% 2 15% 43% 25% 4	570
	21st to end	Night	9% 2 20% 41% 23% 3	570
October	1st to 10th	Night	8% 3 27% 37% 23% 3	747
	11th to 20th	Night	15% 6% 37% 32% 10% 1	760
	21st to end	Night	18% 9% 33% 29% 10%	836
November	1st to 10th	Night	14% 7% 37% 32% 10%	755
	11th to 20th	Night	14% 13% 34% 30% 8%	893
	21st to end	Night	19% 11% 36% 27% 7%	950
December	1st to 10th	Night	17% 11% 39% 28% 6%	950
	11th to 20th	Night	19% 11% 36% 29% 4	950
	21st to end	Night	18% 15% 38% 26% 3	1045

Page generated at 2024-11-01 21:47:34. Version ac07

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