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 2025-04-11.

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	10% 9% 3 9% 6% 5% 5% 4 6% 7% 35%	116827
	Night	8% 9% 4 10% 6% 5% 5% 4 6% 7% 34%	120229
Transparency	Day	28% 43% 9% 15% 5%	116557
	Night	30% 41% 8% 15% 6%	120089
Seeing	Day	14% 9% 31% 28% 14% 3	16688
	Night	14% 8% 33% 32% 11% 1	26826

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	3 14% 5% 14% 9% 10% 8% 4 8% 6% 17%	3178
	11th to 20th	Day	4 7% 4 13% 10% 9% 12% 13% 11% 7% 12%	3530
	21st to end	Day	5% 10% 5% 16% 9% 7% 7% 5% 6% 6% 25%	4004
February	1st to 10th	Day	8% 13% 6% 12% 6% 7% 7% 6% 7% 6% 22%	1645
	11th to 20th	Day	5% 10% 4 11% 9% 7% 8% 7% 10% 5% 24%	1784
	21st to end	Day	7% 10% 4 12% 8% 8% 8% 7% 5% 7% 25%	1650
March	1st to 10th	Day	9% 10% 4 11% 6% 6% 4 4 7% 9% 28%	4500
	11th to 20th	Day	7% 12% 6% 14% 9% 6% 5% 4 6% 8% 23%	4931
	21st to end	Day	11% 13% 5% 15% 7% 7% 5% 4 5% 6% 23%	5527
April	1st to 10th	Day	9% 12% 4 9% 5% 4 4 4 6% 8% 35%	2420
	11th to 20th	Day	14% 11% 4 9% 6% 5% 4 4 5% 6% 31%	2440
	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	11% 8% 2 6% 4 4 4 3 4 5% 50%	3352
	11th to 20th	Day	9% 8% 2 6% 4 3 4 3 5% 8% 45%	2940
	21st to end	Day	12% 12% 4 7% 4 4 4 3 6% 8% 35%	3091
November	1st to 10th	Day	14% 14% 5% 10% 5% 3 4 3 4 5% 31%	1727
	11th to 20th	Day	8% 15% 7% 15% 7% 5% 5% 4 4 4 26%	1600
	21st to end	Day	10% 13% 5% 11% 9% 6% 5% 3 5% 6% 28%	1415
December	1st to 10th	Day	6% 13% 5% 16% 11% 9% 9% 5% 7% 6% 14%	2290
	11th to 20th	Day	9% 11% 5% 14% 10% 7% 6% 5% 7% 7% 19%	2643
	21st to end	Day	7% 10% 3 15% 8% 6% 5% 4 6% 5% 30%	3498
January	1st to 10th	Night	4 12% 6% 16% 9% 8% 8% 5% 7% 8% 18%	6787
	11th to 20th	Night	5% 9% 5% 13% 9% 8% 11% 8% 9% 7% 17%	6436
	21st to end	Night	6% 13% 8% 16% 8% 5% 5% 4 6% 6% 24%	6974
February	1st to 10th	Night	9% 11% 4 11% 7% 7% 7% 5% 7% 6% 25%	2755
	11th to 20th	Night	6% 9% 3 11% 8% 6% 8% 5% 7% 7% 32%	2522
	21st to end	Night	7% 10% 4 9% 6% 6% 6% 5% 7% 7% 33%	1980
March	1st to 10th	Night	7% 11% 4 10% 6% 6% 6% 5% 7% 8% 30%	5374
	11th to 20th	Night	8% 11% 4 11% 7% 5% 4 4 6% 7% 32%	5031
	21st to end	Night	8% 13% 6% 14% 6% 5% 5% 4 6% 5% 28%	5392
April	1st to 10th	Night	8% 8% 3 8% 6% 4 5% 3 7% 7% 40%	1980
	11th to 20th	Night	13% 12% 3 7% 5% 4 5% 4 5% 6% 35%	1694
	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	10% 7% 3 6% 4 4 4 3 5% 7% 48%	3576
	11th to 20th	Night	10% 8% 2 7% 4 4 5% 4 6% 8% 43%	3969
	21st to end	Night	7% 9% 3 8% 4 4 4 4 6% 7% 42%	4467
November	1st to 10th	Night	11% 10% 4 9% 5% 4 5% 4 5% 8% 34%	2570
	11th to 20th	Night	9% 14% 5% 13% 7% 5% 4 3 6% 6% 28%	2800
	21st to end	Night	10% 12% 4 11% 8% 6% 4 4 5% 6% 30%	2980
December	1st to 10th	Night	6% 12% 5% 14% 10% 8% 9% 5% 6% 6% 18%	4900
	11th to 20th	Night	8% 14% 5% 14% 9% 6% 6% 4 5% 7% 21%	5564
	21st to end	Night	7% 10% 4 15% 9% 7% 6% 5% 6% 6% 27%	7480

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	49% 28% 8% 12% 3	3179
	11th to 20th	Day	45% 29% 8% 12% 6%	3530
	21st to end	Day	41% 30% 12% 15% 2	4004
February	1st to 10th	Day	25% 62% 5% 4 3 1	1645
	11th to 20th	Day	21% 62% 4 10% 3	1793
	21st to end	Day	19% 62% 5% 9% 5%	1650
March	1st to 10th	Day	31% 30% 14% 16% 8%	4500
	11th to 20th	Day	45% 30% 10% 13% 3	4931
	21st to end	Day	46% 32% 7% 12% 4	5527
April	1st to 10th	Day	18% 63% 6% 10% 3	2420
	11th to 20th	Day	20% 65% 4 6% 4	2443
	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	22% 37% 5% 28% 7% 1	3352
	11th to 20th	Day	22% 37% 4 28% 9%	2940
	21st to end	Day	31% 36% 5% 20% 9%	3091
November	1st to 10th	Day	27% 56% 5% 9% 2	1727
	11th to 20th	Day	25% 57% 7% 8% 3	1600
	21st to end	Day	27% 57% 4 7% 4	1415
December	1st to 10th	Day	47% 36% 7% 7% 4	2290
	11th to 20th	Day	42% 33% 9% 12% 4	2640
	21st to end	Day	37% 27% 7% 17% 12%	3498
January	1st to 10th	Night	48% 29% 7% 13% 3	6787
	11th to 20th	Night	44% 29% 8% 14% 5%	6436
	21st to end	Night	44% 29% 8% 16% 2	6974
February	1st to 10th	Night	24% 62% 6% 5% 4	2755
	11th to 20th	Night	18% 61% 6% 10% 5%	2523
	21st to end	Night	16% 62% 4 12% 5%	1980
March	1st to 10th	Night	31% 32% 12% 15% 9%	5374
	11th to 20th	Night	35% 32% 9% 15% 9%	5031
	21st to end	Night	42% 31% 6% 15% 5%	5392
April	1st to 10th	Night	15% 63% 6% 11% 5% 1	1980
	11th to 20th	Night	17% 65% 4 9% 5% 1	1694
	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	23% 37% 7% 21% 11% 2	3576
	11th to 20th	Night	22% 37% 6% 21% 13%	3969
	21st to end	Night	24% 36% 7% 24% 8%	4467
November	1st to 10th	Night	24% 57% 7% 9% 3	2570
	11th to 20th	Night	23% 57% 7% 8% 4	2800
	21st to end	Night	26% 57% 5% 8% 4	2980
December	1st to 10th	Night	45% 37% 9% 7% 2	4900
	11th to 20th	Night	43% 32% 8% 13% 3 1	5566
	21st to end	Night	40% 27% 7% 16% 9% 1	7480

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	8% 10% 35% 31% 12% 4	300
	11th to 20th	Day	10% 13% 32% 33% 10% 1	300
	21st to end	Day	14% 9% 39% 26% 9% 3	330
February	1st to 10th	Day	12% 12% 38% 30% 5% 2	300
	11th to 20th	Day	10% 10% 38% 31% 10% 1	300
	21st to end	Day	5% 9% 38% 34% 12% 3	249
March	1st to 10th	Day	12% 13% 33% 32% 9% 1	300
	11th to 20th	Day	14% 12% 34% 26% 12% 2	300
	21st to end	Day	15% 10% 33% 26% 13% 3	355
April	1st to 10th	Day	13% 14% 33% 28% 10% 2	520
	11th to 20th	Day	19% 11% 33% 24% 11% 1	641
	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	25% 11% 36% 20% 6% 2	330
November	1st to 10th	Day	23% 12% 30% 24% 10%	300
	11th to 20th	Day	15% 11% 36% 29% 8%	300
	21st to end	Day	15% 12% 41% 23% 6% 2	300
December	1st to 10th	Day	12% 9% 36% 32% 10% 2	300
	11th to 20th	Day	16% 14% 40% 25% 5% 1	300
	21st to end	Day	13% 8% 39% 28% 9% 4	330
January	1st to 10th	Night	11% 10% 39% 29% 11% 1	1000
	11th to 20th	Night	14% 10% 40% 28% 8% 1	1000
	21st to end	Night	12% 12% 39% 28% 9% 1	1100
February	1st to 10th	Night	13% 11% 35% 32% 9% 1	1000
	11th to 20th	Night	10% 9% 36% 32% 11% 2	968
	21st to end	Night	11% 8% 34% 33% 11% 2	660
March	1st to 10th	Night	15% 9% 33% 29% 12% 2	800
	11th to 20th	Night	12% 8% 36% 32% 10% 1	625
	21st to end	Night	14% 7% 32% 31% 14% 2	660
April	1st to 10th	Night	12% 7% 36% 34% 10% 1	600
	11th to 20th	Night	18% 8% 30% 35% 8% 1	565
	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% 37% 27% 8% 1	1045
November	1st to 10th	Night	16% 11% 37% 28% 7% 1	975
	11th to 20th	Night	15% 11% 39% 25% 9% 2	1000
	21st to end	Night	16% 15% 38% 25% 5% 1	1000
December	1st to 10th	Night	11% 11% 38% 29% 10% 1	1000
	11th to 20th	Night	17% 12% 34% 29% 7% 2	1000
	21st to end	Night	19% 6% 34% 31% 9% 1	1100

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