Esparto
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Esparto clear sky chart from 2005-11-06 to 2026-04-17.

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	6% 3 1 3 2 2 3 2 4 5% 69%	140404
	Night	7% 3 1 3 2 2 3 2 4 6% 65%	139212
Transparency	Day	20% 3 8% 20% 25% 25%	135321
	Night	23% 3 9% 19% 23% 23%	135295
Seeing	Day	8% 5% 17% 26% 27% 16%	17083
	Night	8% 4 17% 37% 30% 4	26482

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	14% 7% 2 5% 4 4 4 3 5% 7% 45%	4820
	11th to 20th	Day	10% 5% 2 4 3 3 3 2 4 6% 59%	5340
	21st to end	Day	14% 5% 2 6% 4 4 4 3 5% 8% 46%	5843
February	1st to 10th	Day	14% 6% 1 5% 4 4 3 3 4 6% 50%	1890
	11th to 20th	Day	10% 6% 2 6% 5% 4 4 4 5% 7% 47%	1925
	21st to end	Day	11% 4 2 5% 4 4 4 4 5% 7% 50%	1730
March	1st to 10th	Day	9% 7% 3 7% 5% 5% 4 4 5% 7% 44%	4924
	11th to 20th	Day	10% 5% 1 5% 3 3 3 3 5% 6% 55%	5110
	21st to end	Day	11% 4 2 5% 5% 5% 5% 4 6% 8% 45%	5728
April	1st to 10th	Day	9% 6% 3 5% 4 4 4 4 5% 7% 50%	2520
	11th to 20th	Day	7% 3 1 4 3 4 4 3 5% 7% 59%	2442
	21st to end	Day	3 3 1 3 3 3 3 3 5% 7% 65%	2400
May	1st to 10th	Day	3 1 1 2 2 1 1 1 3 5% 80%	5693
	11th to 20th	Day	1 1 2 1 1 1 2 3 5% 82%	6135
	21st to end	Day	1 1 1 1 1 2 1 3 5% 83%	6902
June	1st to 10th	Day	4 2 1 2 2 2 2 3 4 7% 70%	2800
	11th to 20th	Day	1 1 1 1 2 2 3 4 83%	2800
	21st to end	Day	1 1 1 1 1 2 2 3 3 86%	2800
July	1st to 10th	Day	1 1 1 1 1 2 93%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 91%	6112
	21st to end	Day	1 1 1 1 1 2 3 88%	6402
August	1st to 10th	Day	1 1 1 1 1 2 2 3 4 84%	5777
	11th to 20th	Day	1 1 1 1 1 2 92%	5546
	21st to end	Day	1 1 1 1 1 1 1 2 3 87%	5984
September	1st to 10th	Day	1 1 1 1 2 1 2 3 89%	2400
	11th to 20th	Day	2 1 1 2 2 1 2 2 3 5% 78%	2400
	21st to end	Day	2 2 1 2 1 1 2 2 2 3 82%	2125
October	1st to 10th	Day	1 2 1 2 2 2 2 1 4 5% 79%	3280
	11th to 20th	Day	4 2 1 2 2 2 2 2 4 5% 75%	3261
	21st to end	Day	4 2 1 4 2 3 3 3 4 6% 68%	3558
November	1st to 10th	Day	7% 3 1 3 3 3 4 3 5% 7% 62%	1965
	11th to 20th	Day	9% 5% 2 5% 4 5% 4 3 5% 9% 51%	1890
	21st to end	Day	9% 4 1 4 4 3 3 3 5% 7% 57%	1683
December	1st to 10th	Day	7% 4 1 5% 3 2 3 3 5% 9% 57%	2700
	11th to 20th	Day	21% 8% 3 7% 5% 5% 5% 3 6% 6% 32%	3108
	21st to end	Day	19% 10% 3 7% 4 4 4 4 5% 7% 33%	4092
January	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 5% 8% 46%	8075
	11th to 20th	Night	9% 5% 2 4 3 2 3 2 4 5% 61%	7650
	21st to end	Night	12% 6% 2 6% 4 4 4 3 4 6% 48%	8371
February	1st to 10th	Night	14% 4 2 4 4 4 4 4 4 6% 52%	2730
	11th to 20th	Night	10% 4 2 6% 3 3 4 4 6% 7% 51%	2580
	21st to end	Night	11% 5% 1 5% 3 3 3 4 4 7% 55%	2076
March	1st to 10th	Night	8% 6% 2 6% 4 4 4 4 5% 8% 48%	5187
	11th to 20th	Night	11% 4 1 4 3 3 3 3 5% 6% 59%	5110
	21st to end	Night	11% 5% 2 6% 4 4 5% 3 6% 8% 48%	5488
April	1st to 10th	Night	6% 5% 1 4 3 4 5% 4 5% 7% 57%	2100
	11th to 20th	Night	7% 3 1 3 3 3 4 3 4 6% 64%	2039
	21st to end	Night	4 2 1 2 2 2 2 3 4 8% 70%	2000
May	1st to 10th	Night	2 1 1 2 2 2 1 1 3 5% 80%	4292
	11th to 20th	Night	1 1 1 2 2 3 2 4 5% 79%	3764
	21st to end	Night	1 1 1 1 1 1 3 4 87%	3972
June	1st to 10th	Night	3 2 1 2 3 2 3 2 4 7% 73%	1600
	11th to 20th	Night	1 1 1 1 2 2 3 4 85%	1600
	21st to end	Night	1 1 1 1 1 1 1 2 2 3 87%	1600
July	1st to 10th	Night	1 1 1 1 1 94%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 91%	3840
	21st to end	Night	1 1 1 1 1 3 4 86%	4472
August	1st to 10th	Night	2 1 1 1 1 1 1 3 4 85%	4035
	11th to 20th	Night	1 1 1 1 2 93%	4300
	21st to end	Night	1 1 2 1 1 2 1 2 3 86%	5015
September	1st to 10th	Night	1 1 1 1 1 1 2 3 90%	2000
	11th to 20th	Night	2 1 1 2 2 1 1 1 3 5% 81%	2000
	21st to end	Night	1 1 2 1 2 2 1 3 5% 83%	2270
October	1st to 10th	Night	2 1 1 2 2 2 2 2 3 4 80%	3920
	11th to 20th	Night	2 1 1 2 1 2 2 3 3 4 79%	3897
	21st to end	Night	4 2 1 3 2 2 3 3 5% 7% 68%	4253
November	1st to 10th	Night	6% 3 1 3 3 3 3 3 5% 8% 61%	2550
	11th to 20th	Night	9% 4 1 4 3 3 3 2 5% 7% 58%	2730
	21st to end	Night	8% 4 2 4 3 3 4 2 4 6% 60%	2934
December	1st to 10th	Night	7% 4 2 4 3 3 3 3 5% 7% 61%	4700
	11th to 20th	Night	19% 7% 2 5% 4 4 4 4 7% 9% 35%	5316
	21st to end	Night	19% 8% 3 7% 4 5% 4 3 5% 6% 35%	7106

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	40% 7% 16% 23% 11% 4	4821
	11th to 20th	Day	30% 2 8% 18% 23% 19%	5340
	21st to end	Day	40% 3 11% 18% 12% 16%	5843
February	1st to 10th	Day	37% 3 10% 22% 19% 9%	1890
	11th to 20th	Day	37% 5% 11% 20% 19% 7%	1934
	21st to end	Day	33% 5% 10% 25% 19% 8%	1730
March	1st to 10th	Day	39% 4 9% 21% 22% 4	4924
	11th to 20th	Day	30% 4 13% 25% 17% 10%	5110
	21st to end	Day	35% 6% 15% 27% 13% 3	5728
April	1st to 10th	Day	33% 5% 11% 23% 20% 7%	2520
	11th to 20th	Day	25% 4 13% 24% 23% 10%	2445
	21st to end	Day	19% 4 13% 29% 28% 8%	2400
May	1st to 10th	Day	10% 2 6% 25% 31% 26%	5693
	11th to 20th	Day	8% 2 4 28% 40% 18%	6138
	21st to end	Day	6% 2 7% 30% 40% 15%	6904
June	1st to 10th	Day	15% 4 9% 29% 30% 13%	2800
	11th to 20th	Day	7% 2 7% 20% 36% 28%	2800
	21st to end	Day	6% 1 2 13% 37% 41%	2800
July	1st to 10th	Day	3 1 1 6% 20% 68%	6251
	11th to 20th	Day	4 1 1 5% 15% 74%	6037
	21st to end	Day	4 1 4 16% 29% 46%	6217
August	1st to 10th	Day	9% 2 2 9% 28% 51%	4206
	11th to 20th	Day	3 1 1 10% 42% 42%	4017
	21st to end	Day	5% 1 2 11% 38% 42%	4311
September	1st to 10th	Day	5% 1 2 9% 30% 52%	2400
	11th to 20th	Day	12% 1 5% 24% 40% 19%	2400
	21st to end	Day	10% 2 5% 19% 32% 32%	2125
October	1st to 10th	Day	11% 2 4 12% 27% 44%	3280
	11th to 20th	Day	13% 3 6% 27% 29% 22%	3261
	21st to end	Day	18% 3 7% 24% 33% 15%	3558
November	1st to 10th	Day	23% 4 9% 29% 23% 11%	1965
	11th to 20th	Day	32% 4 14% 25% 19% 7%	1890
	21st to end	Day	27% 4 13% 22% 22% 11%	1683
December	1st to 10th	Day	25% 3 10% 29% 24% 8%	2700
	11th to 20th	Day	55% 5% 10% 15% 12% 2	3108
	21st to end	Day	52% 5% 13% 18% 11% 2	4092
January	1st to 10th	Night	37% 6% 20% 21% 13% 3	8075
	11th to 20th	Night	28% 3 8% 17% 29% 15%	7650
	21st to end	Night	38% 3 10% 17% 17% 15%	8371
February	1st to 10th	Night	35% 4 8% 21% 21% 11%	2730
	11th to 20th	Night	32% 4 11% 23% 21% 9%	2582
	21st to end	Night	30% 4 9% 25% 23% 9%	2076
March	1st to 10th	Night	35% 4 12% 21% 22% 5%	5187
	11th to 20th	Night	28% 3 15% 24% 21% 10%	5110
	21st to end	Night	34% 5% 14% 26% 17% 3	5488
April	1st to 10th	Night	27% 5% 12% 24% 22% 10%	2100
	11th to 20th	Night	23% 4 13% 28% 19% 13%	2039
	21st to end	Night	15% 3 12% 32% 30% 9%	2000
May	1st to 10th	Night	10% 2 6% 25% 32% 25%	4289
	11th to 20th	Night	9% 2 5% 26% 35% 23%	3764
	21st to end	Night	5% 1 6% 28% 38% 21%	3972
June	1st to 10th	Night	13% 3 10% 26% 32% 16%	1600
	11th to 20th	Night	7% 2 5% 20% 33% 33%	1600
	21st to end	Night	6% 1 3 11% 32% 47%	1600
July	1st to 10th	Night	3 1 1 5% 20% 71%	3600
	11th to 20th	Night	5% 1 1 4 10% 80%	3792
	21st to end	Night	5% 1 2 16% 25% 51%	4345
August	1st to 10th	Night	10% 1 1 8% 23% 57%	2929
	11th to 20th	Night	3 1 1 6% 34% 56%	3112
	21st to end	Night	7% 1 1 8% 34% 50%	3608
September	1st to 10th	Night	4 1 2 7% 29% 57%	2000
	11th to 20th	Night	10% 1 4 21% 37% 27%	2000
	21st to end	Night	8% 2 4 17% 31% 38%	2270
October	1st to 10th	Night	11% 2 4 11% 20% 52%	3920
	11th to 20th	Night	10% 3 7% 29% 28% 23%	3897
	21st to end	Night	18% 2 6% 22% 31% 22%	4253
November	1st to 10th	Night	22% 5% 9% 26% 22% 15%	2550
	11th to 20th	Night	27% 3 11% 27% 22% 9%	2730
	21st to end	Night	27% 4 9% 23% 24% 13%	2934
December	1st to 10th	Night	25% 3 8% 26% 26% 13%	4700
	11th to 20th	Night	46% 6% 12% 18% 15% 3	5316
	21st to end	Night	51% 5% 13% 17% 11% 3	7106

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	29% 5% 24% 25% 15% 2	253
	11th to 20th	Day	14% 7% 23% 30% 21% 5%	430
	21st to end	Day	16% 6% 22% 27% 23% 7%	473
February	1st to 10th	Day	18% 8% 21% 27% 20% 6%	430
	11th to 20th	Day	16% 14% 25% 26% 13% 6%	467
	21st to end	Day	13% 10% 27% 32% 15% 4	446
March	1st to 10th	Day	16% 11% 26% 29% 14% 5%	540
	11th to 20th	Day	16% 9% 19% 29% 19% 7%	540
	21st to end	Day	15% 11% 26% 27% 17% 5%	594
April	1st to 10th	Day	10% 9% 22% 28% 23% 8%	540
	11th to 20th	Day	8% 9% 25% 27% 18% 12%	517
	21st to end	Day	5% 7% 22% 26% 25% 15%	500
May	1st to 10th	Day	6% 7% 25% 27% 24% 11%	503
	11th to 20th	Day	5% 4 21% 25% 22% 22%	528
	21st to end	Day	4 5% 15% 28% 25% 23%	573
June	1st to 10th	Day	4 4 18% 24% 31% 20%	530
	11th to 20th	Day	1 5% 18% 28% 34% 14%	530
	21st to end	Day	3 12% 26% 32% 26%	530
July	1st to 10th	Day	1 1 7% 27% 36% 28%	526
	11th to 20th	Day	1 6% 23% 36% 35%	524
	21st to end	Day	1 1 5% 21% 41% 31%	575
August	1st to 10th	Day	3 1 7% 22% 39% 29%	527
	11th to 20th	Day	2 1 8% 26% 32% 32%	517
	21st to end	Day	1 1 5% 22% 38% 33%	583
September	1st to 10th	Day	8% 29% 38% 24%	530
	11th to 20th	Day	3 2 11% 25% 35% 25%	530
	21st to end	Day	3 3 15% 29% 32% 18%	530
October	1st to 10th	Day	3 6% 18% 26% 28% 19%	530
	11th to 20th	Day	7% 5% 16% 26% 30% 16%	530
	21st to end	Day	8% 5% 21% 27% 28% 11%	583
November	1st to 10th	Day	9% 5% 23% 23% 30% 10%	441
	11th to 20th	Day	11% 6% 22% 28% 23% 10%	330
	21st to end	Day	13% 4 22% 33% 22% 6%	221
December	1st to 10th	Day	19% 3 23% 27% 21% 7%	220
	11th to 20th	Day	17% 6% 22% 29% 18% 8%	220
	21st to end	Day	21% 11% 25% 23% 15% 5%	242
January	1st to 10th	Night	17% 6% 19% 35% 19% 5%	840
	11th to 20th	Night	13% 5% 18% 40% 20% 4	840
	21st to end	Night	15% 5% 17% 36% 22% 4	924
February	1st to 10th	Night	16% 7% 20% 35% 20% 2	840
	11th to 20th	Night	12% 7% 24% 35% 19% 4	824
	21st to end	Night	13% 7% 25% 38% 15% 2	692
March	1st to 10th	Night	15% 6% 24% 33% 20% 2	840
	11th to 20th	Night	13% 6% 19% 35% 25% 1	840
	21st to end	Night	13% 5% 26% 36% 18% 1	924
April	1st to 10th	Night	8% 7% 21% 42% 20% 2	840
	11th to 20th	Night	9% 5% 26% 35% 22% 3	815
	21st to end	Night	5% 6% 24% 38% 24% 3	800
May	1st to 10th	Night	5% 4 26% 36% 26% 3	688
	11th to 20th	Night	2 3 17% 38% 36% 4	464
	21st to end	Night	4 3 18% 37% 35% 3	433
June	1st to 10th	Night	3 2 16% 42% 35% 3	400
	11th to 20th	Night	1 3 18% 45% 32% 2	400
	21st to end	Night	1 1 9% 46% 41% 3	400
July	1st to 10th	Night	1 6% 41% 49% 3	390
	11th to 20th	Night	3 35% 57% 4	471
	21st to end	Night	2 3 32% 56% 8%	657
August	1st to 10th	Night	2 1 5% 32% 53% 7%	597
	11th to 20th	Night	1 1 5% 40% 46% 7%	699
	21st to end	Night	1 5% 35% 54% 5%	880
September	1st to 10th	Night	1 1 6% 41% 46% 6%	800
	11th to 20th	Night	3 9% 38% 44% 7%	800
	21st to end	Night	1 2 14% 37% 37% 9%	800
October	1st to 10th	Night	4 4 14% 40% 32% 7%	800
	11th to 20th	Night	5% 3 17% 36% 33% 6%	800
	21st to end	Night	7% 3 16% 35% 30% 9%	880
November	1st to 10th	Night	7% 4 19% 31% 34% 5%	820
	11th to 20th	Night	10% 4 18% 38% 26% 4	840
	21st to end	Night	10% 5% 19% 39% 23% 4	840
December	1st to 10th	Night	15% 5% 20% 34% 23% 5%	840
	11th to 20th	Night	20% 4 18% 33% 22% 3	840
	21st to end	Night	19% 8% 22% 33% 17% 1	924

Page generated at 2026-04-13 23:44:29. Version ac07

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