Sarles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sarles clear sky chart from 2005-11-06 to 2024-10-24.

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	11% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	101695
	Night	9% 9% 4 9% 6% 5% 5% 4 6% 7% 36%	97263
Transparency	Day	24% 49% 9% 14% 4	101425
	Night	23% 50% 8% 14% 5%	97123
Seeing	Day	14% 9% 31% 29% 14% 4	16168
	Night	14% 8% 33% 32% 12% 1	26060

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	4 18% 5% 13% 7% 9% 6% 4 7% 6% 21%	2218
	11th to 20th	Day	4 8% 4 15% 12% 10% 13% 10% 8% 7% 11%	2458
	21st to end	Day	7% 12% 4 15% 9% 6% 5% 4 6% 6% 25%	2794
February	1st to 10th	Day	8% 13% 6% 12% 6% 7% 7% 6% 7% 7% 21%	1562
	11th to 20th	Day	5% 11% 4 11% 9% 7% 9% 7% 9% 5% 22%	1692
	21st to end	Day	7% 11% 5% 12% 8% 7% 8% 6% 5% 6% 25%	1570
March	1st to 10th	Day	12% 11% 4 11% 6% 6% 4 4 5% 8% 28%	3130
	11th to 20th	Day	7% 12% 5% 13% 9% 5% 5% 4 6% 8% 25%	3444
	21st to end	Day	11% 11% 6% 13% 8% 6% 5% 4 5% 7% 25%	3863
April	1st to 10th	Day	9% 12% 4 9% 5% 4 4 4 6% 8% 34%	2299
	11th to 20th	Day	14% 11% 4 9% 6% 5% 4 4 5% 6% 31%	2439
	21st to end	Day	16% 11% 3 8% 5% 4 4 3 6% 6% 34%	2470
May	1st to 10th	Day	19% 11% 3 6% 4 4 4 3 5% 7% 33%	4141
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 7% 34%	4600
	21st to end	Day	18% 7% 3 7% 5% 4 5% 4 5% 7% 35%	5173
June	1st to 10th	Day	13% 6% 2 6% 4 4 4 5% 7% 8% 40%	2850
	11th to 20th	Day	15% 6% 3 6% 5% 5% 4 4 6% 8% 37%	2850
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 39%	2850
July	1st to 10th	Day	9% 4 2 5% 5% 5% 5% 4 8% 11% 44%	4750
	11th to 20th	Day	7% 4 1 5% 4 4 5% 4 7% 9% 51%	4750
	21st to end	Day	5% 4 2 4 4 4 4 4 7% 10% 51%	4811
August	1st to 10th	Day	10% 6% 2 6% 4 4 4 3 6% 9% 47%	4360
	11th to 20th	Day	12% 4 2 5% 3 3 4 4 6% 9% 48%	4041
	21st to end	Day	10% 5% 2 6% 3 3 3 4 6% 8% 50%	4532
September	1st to 10th	Day	11% 5% 1 5% 4 4 4 3 5% 7% 52%	2304
	11th to 20th	Day	15% 6% 2 5% 4 4 4 4 5% 7% 45%	2090
	21st to end	Day	13% 7% 2 6% 3 4 5% 3 6% 9% 43%	2090
October	1st to 10th	Day	16% 11% 3 7% 3 4 4 3 4 5% 39%	2014
	11th to 20th	Day	12% 11% 3 7% 5% 3 5% 4 6% 7% 38%	1782
	21st to end	Day	14% 13% 4 9% 5% 5% 4 3 6% 8% 30%	1809
November	1st to 10th	Day	15% 14% 5% 10% 5% 4 4 3 4 5% 31%	1639
	11th to 20th	Day	7% 15% 7% 15% 8% 5% 5% 4 4 4 26%	1520
	21st to end	Day	10% 14% 5% 12% 8% 5% 5% 3 4 6% 29%	1345
December	1st to 10th	Day	7% 14% 5% 13% 9% 6% 7% 6% 7% 7% 19%	1330
	11th to 20th	Day	9% 13% 7% 15% 8% 6% 5% 4 6% 7% 19%	1683
	21st to end	Day	8% 10% 3 12% 6% 6% 4 4 7% 6% 33%	2442
January	1st to 10th	Night	6% 15% 6% 14% 6% 6% 6% 5% 6% 7% 22%	4737
	11th to 20th	Night	5% 9% 5% 15% 10% 8% 10% 7% 7% 7% 17%	4498
	21st to end	Night	7% 13% 6% 17% 8% 5% 5% 4 5% 5% 25%	4873
February	1st to 10th	Night	9% 11% 4 11% 7% 7% 6% 5% 7% 6% 25%	2618
	11th to 20th	Night	6% 9% 3 11% 8% 6% 8% 5% 6% 6% 31%	2393
	21st to end	Night	7% 11% 4 9% 6% 6% 7% 5% 7% 7% 32%	1884
March	1st to 10th	Night	9% 12% 4 10% 7% 6% 5% 4 5% 7% 31%	3734
	11th to 20th	Night	7% 11% 4 10% 6% 5% 4 4 6% 8% 37%	3517
	21st to end	Night	7% 12% 6% 13% 7% 5% 5% 4 6% 5% 31%	3768
April	1st to 10th	Night	8% 8% 2 7% 6% 5% 5% 3 7% 7% 40%	1881
	11th to 20th	Night	13% 12% 3 7% 6% 4 5% 4 5% 7% 35%	1689
	21st to end	Night	15% 9% 2 6% 5% 5% 4 4 6% 7% 37%	1710
May	1st to 10th	Night	18% 9% 2 8% 6% 4 4 4 5% 7% 34%	2828
	11th to 20th	Night	14% 7% 2 5% 4 4 4 5% 6% 7% 41%	2302
	21st to end	Night	16% 7% 2 5% 4 3 3 3 6% 7% 44%	2414
June	1st to 10th	Night	11% 4 2 4 4 3 4 4 6% 8% 50%	1330
	11th to 20th	Night	12% 6% 2 6% 6% 5% 5% 4 6% 8% 41%	1330
	21st to end	Night	9% 4 2 4 3 4 4 4 8% 10% 47%	1330
July	1st to 10th	Night	8% 3 1 4 3 4 4 3 7% 8% 54%	2220
	11th to 20th	Night	6% 2 1 4 3 3 4 3 5% 9% 60%	2220
	21st to end	Night	4 3 1 5% 3 4 6% 4 8% 8% 52%	2750
August	1st to 10th	Night	6% 4 2 5% 3 4 4 3 5% 7% 56%	2578
	11th to 20th	Night	7% 4 1 4 4 4 4 4 6% 10% 52%	2798
	21st to end	Night	11% 4 2 5% 3 3 4 2 4 7% 56%	3135
September	1st to 10th	Night	8% 4 2 4 4 4 4 3 5% 7% 55%	1873
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 6% 7% 50%	2090
	21st to end	Night	13% 6% 2 6% 4 4 4 4 5% 7% 45%	2090
October	1st to 10th	Night	13% 9% 3 6% 5% 4 4 3 4 6% 42%	2147
	11th to 20th	Night	14% 9% 2 7% 4 4 4 4 5% 8% 39%	2394
	21st to end	Night	11% 11% 4 9% 5% 4 4 4 7% 6% 35%	2614
November	1st to 10th	Night	11% 10% 5% 9% 5% 4 5% 4 5% 8% 34%	2438
	11th to 20th	Night	9% 14% 5% 13% 7% 5% 4 3 6% 6% 28%	2660
	21st to end	Night	10% 13% 4 11% 7% 5% 4 3 5% 6% 31%	2831
December	1st to 10th	Night	7% 11% 5% 12% 9% 7% 7% 5% 6% 6% 25%	2850
	11th to 20th	Night	9% 14% 6% 15% 7% 6% 6% 4 5% 7% 22%	3514
	21st to end	Night	9% 11% 4 12% 6% 5% 4 4 5% 6% 33%	5225

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	39% 39% 11% 9% 2 1	2219
	11th to 20th	Day	42% 41% 8% 7% 2	2458
	21st to end	Day	33% 41% 6% 17% 3	2794
February	1st to 10th	Day	23% 65% 5% 5% 2	1562
	11th to 20th	Day	20% 65% 5% 8% 2	1701
	21st to end	Day	17% 65% 5% 8% 5%	1570
March	1st to 10th	Day	25% 43% 9% 16% 7%	3130
	11th to 20th	Day	36% 43% 8% 11% 2	3444
	21st to end	Day	34% 44% 7% 10% 5%	3863
April	1st to 10th	Day	17% 66% 6% 10% 2	2299
	11th to 20th	Day	20% 66% 4 6% 4	2442
	21st to end	Day	16% 65% 5% 9% 4 1	2470
May	1st to 10th	Day	29% 43% 10% 12% 6%	4141
	11th to 20th	Day	30% 44% 8% 12% 5% 1	4604
	21st to end	Day	27% 43% 8% 16% 6%	5173
June	1st to 10th	Day	12% 65% 8% 9% 5% 1	2850
	11th to 20th	Day	18% 66% 5% 8% 4	2850
	21st to end	Day	16% 65% 6% 10% 3	2850
July	1st to 10th	Day	23% 39% 20% 16% 2	4676
	11th to 20th	Day	18% 36% 15% 27% 4	4669
	21st to end	Day	17% 36% 19% 23% 5%	4659
August	1st to 10th	Day	22% 37% 13% 19% 9%	4345
	11th to 20th	Day	21% 37% 14% 24% 4	4080
	21st to end	Day	22% 37% 15% 23% 3	4531
September	1st to 10th	Day	12% 61% 7% 15% 4	2304
	11th to 20th	Day	17% 60% 8% 11% 4 1	2090
	21st to end	Day	20% 60% 7% 9% 4	2090
October	1st to 10th	Day	21% 61% 4 11% 3	2014
	11th to 20th	Day	17% 60% 5% 13% 5%	1782
	21st to end	Day	23% 61% 5% 8% 3	1809
November	1st to 10th	Day	26% 59% 5% 8% 2	1639
	11th to 20th	Day	23% 60% 7% 6% 3	1520
	21st to end	Day	24% 60% 4 7% 4	1345
December	1st to 10th	Day	24% 60% 5% 8% 3	1330
	11th to 20th	Day	29% 51% 6% 9% 4 1	1680
	21st to end	Day	25% 37% 9% 15% 14%	2442
January	1st to 10th	Night	37% 41% 8% 10% 3	4737
	11th to 20th	Night	39% 40% 8% 10% 3	4498
	21st to end	Night	36% 41% 5% 16% 2	4873
February	1st to 10th	Night	22% 65% 6% 5% 3	2618
	11th to 20th	Night	17% 65% 6% 9% 3	2394
	21st to end	Night	16% 65% 3 10% 5%	1884
March	1st to 10th	Night	25% 45% 9% 15% 6%	3734
	11th to 20th	Night	21% 46% 11% 15% 6%	3517
	21st to end	Night	32% 44% 7% 13% 5%	3768
April	1st to 10th	Night	13% 66% 5% 10% 5%	1881
	11th to 20th	Night	17% 65% 4 9% 5% 1	1689
	21st to end	Night	15% 66% 3 11% 5% 1	1710
May	1st to 10th	Night	30% 44% 6% 14% 5%	2828
	11th to 20th	Night	25% 42% 9% 16% 6% 2	2303
	21st to end	Night	23% 42% 8% 21% 6%	2414
June	1st to 10th	Night	9% 65% 8% 14% 4 1	1330
	11th to 20th	Night	17% 66% 4 8% 5%	1330
	21st to end	Night	13% 64% 8% 13% 2	1330
July	1st to 10th	Night	20% 40% 20% 17% 3	2185
	11th to 20th	Night	15% 36% 12% 32% 5%	2178
	21st to end	Night	18% 35% 17% 24% 5% 1	2664
August	1st to 10th	Night	19% 37% 11% 23% 10% 1	2570
	11th to 20th	Night	19% 38% 14% 23% 6%	2825
	21st to end	Night	22% 36% 13% 23% 6%	3135
September	1st to 10th	Night	12% 59% 7% 15% 5% 1	1873
	11th to 20th	Night	15% 61% 10% 10% 4	2090
	21st to end	Night	17% 60% 4 12% 6% 1	2090
October	1st to 10th	Night	19% 60% 6% 11% 3	2147
	11th to 20th	Night	16% 60% 4 13% 7%	2394
	21st to end	Night	18% 61% 7% 9% 4	2614
November	1st to 10th	Night	23% 60% 6% 8% 2	2438
	11th to 20th	Night	21% 60% 7% 7% 4	2660
	21st to end	Night	23% 60% 5% 7% 4	2831
December	1st to 10th	Night	23% 60% 5% 9% 3	2850
	11th to 20th	Night	29% 50% 9% 7% 3 1	3516
	21st to end	Night	27% 38% 8% 15% 12% 1	5225

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	9% 11% 34% 32% 11% 4	270
	11th to 20th	Day	10% 13% 31% 34% 11% 1	270
	21st to end	Day	13% 9% 37% 27% 10% 3	297
February	1st to 10th	Day	12% 10% 39% 32% 5% 2	270
	11th to 20th	Day	11% 11% 38% 30% 10% 1	270
	21st to end	Day	5% 7% 39% 34% 12% 3	225
March	1st to 10th	Day	13% 14% 33% 31% 8% 1	270
	11th to 20th	Day	12% 13% 34% 26% 13% 2	270
	21st to end	Day	14% 10% 32% 27% 13% 4	321
April	1st to 10th	Day	13% 15% 33% 27% 10% 2	479
	11th to 20th	Day	19% 11% 33% 24% 11% 1	640
	21st to end	Day	18% 10% 32% 25% 12% 2	650
May	1st to 10th	Day	16% 11% 25% 29% 16% 2	653
	11th to 20th	Day	20% 8% 31% 25% 13% 3	675
	21st to end	Day	19% 9% 24% 29% 15% 3	734
June	1st to 10th	Day	14% 11% 30% 26% 14% 5%	680
	11th to 20th	Day	15% 10% 35% 26% 10% 4	680
	21st to end	Day	13% 8% 29% 29% 17% 4	680
July	1st to 10th	Day	8% 5% 27% 32% 20% 8%	671
	11th to 20th	Day	11% 6% 29% 29% 18% 7%	668
	21st to end	Day	5% 4 27% 36% 20% 7%	739
August	1st to 10th	Day	10% 5% 23% 34% 21% 7%	676
	11th to 20th	Day	13% 5% 23% 30% 22% 7%	665
	21st to end	Day	11% 7% 25% 32% 20% 4	748
September	1st to 10th	Day	14% 9% 33% 27% 14% 4	514
	11th to 20th	Day	19% 9% 26% 33% 12% 1	300
	21st to end	Day	21% 10% 33% 25% 10% 2	300
October	1st to 10th	Day	23% 12% 27% 25% 12% 2	300
	11th to 20th	Day	19% 9% 38% 22% 9% 2	300
	21st to end	Day	26% 11% 35% 20% 5% 2	306
November	1st to 10th	Day	24% 13% 29% 23% 11%	270
	11th to 20th	Day	13% 12% 37% 30% 9%	270
	21st to end	Day	17% 12% 39% 26% 5% 1	270
December	1st to 10th	Day	11% 9% 35% 32% 10% 2	270
	11th to 20th	Day	16% 14% 40% 24% 5% 1	270
	21st to end	Day	13% 8% 39% 29% 7% 3	297
January	1st to 10th	Night	11% 10% 38% 29% 11% 1	950
	11th to 20th	Night	14% 10% 39% 29% 8% 1	950
	21st to end	Night	12% 11% 37% 30% 9% 1	1045
February	1st to 10th	Night	13% 10% 35% 32% 9% 1	950
	11th to 20th	Night	10% 9% 36% 32% 10% 3	919
	21st to end	Night	11% 7% 34% 34% 11% 2	628
March	1st to 10th	Night	15% 9% 32% 29% 12% 2	760
	11th to 20th	Night	12% 9% 35% 32% 11% 1	594
	21st to end	Night	14% 7% 31% 32% 15% 2	627
April	1st to 10th	Night	11% 7% 37% 34% 10% 1	570
	11th to 20th	Night	18% 8% 30% 34% 8% 1	563
	21st to end	Night	17% 8% 30% 31% 14% 1	570
May	1st to 10th	Night	18% 7% 30% 30% 14% 1	570
	11th to 20th	Night	18% 6% 28% 34% 14%	561
	21st to end	Night	20% 7% 28% 31% 13% 1	617
June	1st to 10th	Night	12% 8% 33% 32% 13% 1	570
	11th to 20th	Night	15% 6% 33% 32% 14% 1	570
	21st to end	Night	10% 6% 26% 40% 18%	570
July	1st to 10th	Night	8% 1 25% 41% 23% 2	555
	11th to 20th	Night	8% 5% 26% 44% 16% 1	552
	21st to end	Night	6% 3 22% 47% 19% 3	624
August	1st to 10th	Night	9% 3 22% 46% 19% 2	567
	11th to 20th	Night	7% 4 25% 43% 20% 2	564
	21st to end	Night	11% 4 28% 40% 16% 1	627
September	1st to 10th	Night	10% 4 31% 35% 18% 3	570
	11th to 20th	Night	13% 7% 31% 37% 11% 1	570
	21st to end	Night	17% 9% 32% 29% 13% 1	570
October	1st to 10th	Night	17% 10% 32% 32% 9%	627
	11th to 20th	Night	19% 10% 32% 31% 9%	874
	21st to end	Night	17% 10% 36% 27% 8% 1	1006
November	1st to 10th	Night	16% 11% 37% 28% 7% 1	925
	11th to 20th	Night	14% 11% 39% 25% 9% 2	950
	21st to end	Night	16% 14% 37% 26% 5% 1	950
December	1st to 10th	Night	11% 11% 37% 29% 10% 1	950
	11th to 20th	Night	17% 12% 33% 29% 7% 2	950
	21st to end	Night	20% 6% 34% 31% 9% 1	1045

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