Salvador Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salvador Observatory 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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	131839
	Night	15% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	130288
Transparency	Day	46% 8% 14% 20% 11% 1	135431
	Night	47% 7% 13% 20% 12% 1	134783
Seeing	Day	17% 10% 28% 28% 14% 4	16191
	Night	18% 9% 30% 29% 13% 1	25707

By Month

Percentage Cloud Cover NE (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	16% 10% 4 9% 5% 5% 6% 3 5% 7% 30%	4661
	11th to 20th	Day	10% 17% 7% 17% 8% 6% 5% 4 5% 5% 16%	5024
	21st to end	Day	14% 14% 5% 13% 6% 6% 6% 4 5% 6% 21%	5780
February	1st to 10th	Day	14% 15% 4 12% 7% 6% 5% 4 4 6% 24%	1890
	11th to 20th	Day	13% 13% 6% 13% 7% 5% 5% 4 4 6% 26%	1843
	21st to end	Day	17% 12% 4 9% 7% 5% 5% 4 4 6% 27%	1612
March	1st to 10th	Day	19% 9% 4 8% 5% 5% 5% 3 5% 6% 32%	5042
	11th to 20th	Day	11% 10% 4 10% 6% 5% 6% 4 6% 7% 31%	5090
	21st to end	Day	17% 9% 3 8% 5% 5% 4 3 5% 6% 34%	5586
April	1st to 10th	Day	17% 12% 4 8% 5% 5% 5% 4 5% 6% 30%	2495
	11th to 20th	Day	19% 10% 3 7% 5% 4 4 4 6% 6% 35%	2502
	21st to end	Day	18% 9% 2 8% 6% 5% 5% 3 5% 6% 34%	2600
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 4 4 6% 6% 33%	5920
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 5% 7% 35%	6318
	21st to end	Day	17% 6% 2 6% 4 4 5% 3 5% 8% 39%	6949
June	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 4 7% 9% 36%	2800
	11th to 20th	Day	11% 5% 2 7% 4 6% 5% 5% 6% 9% 40%	2800
	21st to end	Day	13% 5% 2 6% 5% 5% 5% 4 7% 9% 39%	2800
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	6360
	11th to 20th	Day	8% 4 2 6% 4 4 5% 4 6% 9% 48%	6360
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 7% 9% 47%	6546
August	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 6% 8% 39%	4234
	11th to 20th	Day	10% 6% 3 8% 4 5% 4 5% 8% 10% 38%	4174
	21st to end	Day	8% 5% 2 6% 4 5% 4 5% 7% 8% 45%	4477
September	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 4 6% 7% 45%	2400
	11th to 20th	Day	10% 5% 2 5% 4 4 4 3 6% 7% 49%	2305
	21st to end	Day	13% 5% 3 7% 5% 5% 6% 4 6% 8% 39%	2145
October	1st to 10th	Day	16% 7% 3 7% 4 5% 4 4 5% 6% 39%	2000
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 5% 6% 33%	2000
	21st to end	Day	22% 9% 4 9% 5% 5% 5% 3 6% 6% 26%	2200
November	1st to 10th	Day	14% 8% 4 8% 6% 5% 5% 4 6% 8% 33%	1772
	11th to 20th	Day	15% 11% 3 9% 6% 6% 5% 5% 8% 7% 26%	1680
	21st to end	Day	18% 11% 4 11% 6% 5% 4 4 5% 8% 23%	1680
December	1st to 10th	Day	18% 14% 5% 11% 7% 7% 6% 5% 6% 6% 16%	2680
	11th to 20th	Day	20% 14% 4 9% 5% 5% 5% 4 5% 6% 24%	3066
	21st to end	Day	27% 15% 5% 12% 6% 5% 4 3 4 4 15%	4048
January	1st to 10th	Night	15% 11% 4 9% 5% 5% 5% 4 6% 7% 28%	8234
	11th to 20th	Night	12% 14% 5% 12% 9% 6% 7% 4 6% 6% 19%	7845
	21st to end	Night	13% 12% 4 10% 7% 6% 6% 5% 6% 7% 26%	8401
February	1st to 10th	Night	13% 15% 4 8% 6% 6% 5% 4 6% 6% 27%	2730
	11th to 20th	Night	15% 11% 5% 9% 7% 5% 5% 4 5% 7% 27%	2663
	21st to end	Night	14% 12% 3 9% 6% 6% 5% 4 6% 7% 29%	2191
March	1st to 10th	Night	16% 9% 4 8% 6% 5% 5% 4 5% 6% 33%	5018
	11th to 20th	Night	11% 7% 3 8% 6% 5% 5% 4 7% 8% 37%	5089
	21st to end	Night	20% 7% 2 7% 4 4 4 3 4 5% 39%	5588
April	1st to 10th	Night	18% 10% 3 7% 5% 4 4 3 6% 6% 32%	2123
	11th to 20th	Night	15% 8% 3 6% 6% 5% 5% 3 5% 6% 38%	1997
	21st to end	Night	15% 8% 2 7% 6% 4 4 5% 6% 7% 36%	1800
May	1st to 10th	Night	23% 8% 2 6% 4 4 4 4 5% 5% 35%	4018
	11th to 20th	Night	15% 7% 3 7% 4 5% 5% 4 6% 7% 36%	3575
	21st to end	Night	17% 5% 2 6% 3 4 4 3 5% 7% 43%	3926
June	1st to 10th	Night	12% 5% 2 6% 4 5% 5% 4 6% 7% 44%	1600
	11th to 20th	Night	8% 6% 2 6% 6% 5% 5% 4 6% 8% 44%	1600
	21st to end	Night	13% 5% 2 5% 4 4 5% 4 6% 8% 44%	1600
July	1st to 10th	Night	7% 5% 3 6% 5% 4 5% 4 6% 9% 47%	3600
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 6% 8% 50%	3600
	21st to end	Night	9% 4 2 4 3 4 4 4 6% 8% 53%	4289
August	1st to 10th	Night	9% 5% 2 5% 4 4 5% 4 6% 8% 48%	2915
	11th to 20th	Night	12% 5% 2 5% 3 4 3 4 5% 7% 51%	2875
	21st to end	Night	10% 5% 2 6% 4 5% 4 3 6% 8% 47%	3388
September	1st to 10th	Night	9% 5% 2 6% 4 4 5% 5% 7% 6% 48%	2000
	11th to 20th	Night	10% 4 2 4 4 3 3 3 5% 7% 56%	2090
	21st to end	Night	16% 6% 2 7% 4 3 4 3 5% 7% 42%	2255
October	1st to 10th	Night	15% 6% 2 8% 4 4 4 4 5% 7% 41%	2400
	11th to 20th	Night	19% 7% 3 7% 5% 4 5% 4 5% 7% 34%	2400
	21st to end	Night	20% 9% 3 7% 4 5% 5% 4 6% 6% 32%	2640
November	1st to 10th	Night	16% 7% 2 6% 5% 4 5% 4 6% 7% 38%	2740
	11th to 20th	Night	16% 9% 3 8% 6% 5% 5% 4 6% 8% 31%	2940
	21st to end	Night	19% 10% 3 7% 6% 5% 5% 4 7% 7% 25%	2940
December	1st to 10th	Night	17% 13% 4 10% 6% 6% 6% 5% 6% 6% 21%	4720
	11th to 20th	Night	17% 15% 4 8% 5% 5% 5% 3 6% 6% 25%	5348
	21st to end	Night	26% 13% 6% 10% 6% 5% 5% 4 4 5% 15%	7150

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	52% 8% 15% 14% 10%	4662
	11th to 20th	Day	69% 6% 10% 9% 5%	5058
	21st to end	Day	60% 7% 13% 11% 9%	5780
February	1st to 10th	Day	61% 8% 11% 15% 5% 1	1890
	11th to 20th	Day	58% 8% 12% 15% 6% 1	1852
	21st to end	Day	57% 7% 13% 16% 6%	1612
March	1st to 10th	Day	51% 6% 15% 14% 13% 1	5045
	11th to 20th	Day	49% 7% 18% 17% 7% 2	5090
	21st to end	Day	49% 6% 11% 20% 14% 1	5586
April	1st to 10th	Day	53% 7% 11% 18% 10% 1	2495
	11th to 20th	Day	48% 7% 11% 20% 13% 1	2502
	21st to end	Day	49% 8% 11% 17% 12% 3	2600
May	1st to 10th	Day	48% 8% 13% 16% 12% 4	5929
	11th to 20th	Day	46% 12% 11% 15% 16% 1	6322
	21st to end	Day	42% 7% 13% 23% 12% 3	6949
June	1st to 10th	Day	41% 9% 14% 20% 15% 1	2800
	11th to 20th	Day	37% 9% 14% 24% 15% 1	2800
	21st to end	Day	38% 9% 16% 23% 14% 1	2800
July	1st to 10th	Day	36% 7% 15% 25% 15% 2	6290
	11th to 20th	Day	31% 7% 14% 32% 15% 1	6285
	21st to end	Day	31% 9% 14% 30% 16%	6359
August	1st to 10th	Day	41% 8% 15% 22% 13% 1	4221
	11th to 20th	Day	38% 8% 16% 27% 10% 1	4213
	21st to end	Day	34% 7% 15% 35% 9% 1	4477
September	1st to 10th	Day	35% 9% 15% 29% 11% 1	2400
	11th to 20th	Day	32% 9% 15% 30% 14% 1	2305
	21st to end	Day	41% 10% 14% 25% 9%	2145
October	1st to 10th	Day	35% 6% 17% 27% 14% 1	3260
	11th to 20th	Day	38% 6% 18% 24% 14%	3240
	21st to end	Day	50% 7% 15% 21% 6%	3538
November	1st to 10th	Day	47% 9% 15% 20% 8% 1	1772
	11th to 20th	Day	53% 10% 15% 13% 8%	1680
	21st to end	Day	58% 9% 15% 15% 3	1680
December	1st to 10th	Day	65% 9% 14% 8% 3	2680
	11th to 20th	Day	59% 10% 13% 10% 9%	3066
	21st to end	Day	70% 9% 7% 8% 5%	4048
January	1st to 10th	Night	53% 8% 15% 19% 5%	8234
	11th to 20th	Night	63% 9% 11% 11% 6% 1	7886
	21st to end	Night	55% 8% 12% 12% 12% 1	8401
February	1st to 10th	Night	56% 8% 12% 18% 5% 1	2730
	11th to 20th	Night	56% 8% 12% 17% 8%	2665
	21st to end	Night	53% 7% 13% 19% 8%	2191
March	1st to 10th	Night	51% 6% 11% 18% 12% 2	5028
	11th to 20th	Night	42% 7% 19% 21% 10% 2	5090
	21st to end	Night	46% 4 11% 20% 17% 2	5588
April	1st to 10th	Night	50% 6% 12% 18% 13% 1	2123
	11th to 20th	Night	47% 7% 9% 20% 15% 2	1997
	21st to end	Night	44% 9% 12% 18% 16% 2	1800
May	1st to 10th	Night	50% 7% 12% 14% 13% 6%	4025
	11th to 20th	Night	43% 9% 14% 18% 13% 2	3576
	21st to end	Night	39% 7% 14% 23% 15% 2	3927
June	1st to 10th	Night	38% 7% 13% 24% 16% 3	1600
	11th to 20th	Night	36% 7% 14% 22% 20% 2	1600
	21st to end	Night	38% 7% 13% 23% 17% 1	1600
July	1st to 10th	Night	33% 6% 15% 25% 19% 2	3560
	11th to 20th	Night	30% 7% 13% 31% 17% 1	3552
	21st to end	Night	28% 8% 12% 29% 22% 1	4162
August	1st to 10th	Night	34% 6% 15% 28% 15% 2	2904
	11th to 20th	Night	32% 6% 16% 32% 13% 1	2902
	21st to end	Night	33% 6% 14% 32% 13% 1	3388
September	1st to 10th	Night	33% 9% 15% 28% 14% 1	2000
	11th to 20th	Night	27% 7% 13% 34% 18%	2090
	21st to end	Night	41% 8% 12% 26% 12% 1	2255
October	1st to 10th	Night	33% 6% 10% 27% 23% 1	3920
	11th to 20th	Night	41% 7% 15% 27% 10%	3899
	21st to end	Night	39% 7% 16% 26% 11% 1	4252
November	1st to 10th	Night	44% 8% 13% 22% 12% 1	2740
	11th to 20th	Night	51% 8% 15% 16% 9% 1	2940
	21st to end	Night	55% 11% 16% 15% 3	2940
December	1st to 10th	Night	60% 9% 13% 14% 4	4720
	11th to 20th	Night	58% 9% 11% 12% 9% 1	5348
	21st to end	Night	70% 9% 10% 7% 5%	7150

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	21% 18% 33% 21% 6%	220
	11th to 20th	Day	22% 24% 33% 15% 5% 1	289
	21st to end	Day	23% 15% 36% 21% 4	363
February	1st to 10th	Day	21% 18% 38% 19% 4 1	330
	11th to 20th	Day	20% 20% 41% 16% 3	330
	21st to end	Day	25% 21% 33% 19% 2	309
March	1st to 10th	Day	19% 15% 39% 22% 5%	540
	11th to 20th	Day	20% 17% 34% 22% 6% 1	540
	21st to end	Day	24% 13% 34% 22% 6% 1	594
April	1st to 10th	Day	19% 17% 33% 25% 6%	540
	11th to 20th	Day	24% 11% 31% 22% 9% 2	516
	21st to end	Day	22% 9% 34% 24% 10% 2	500
May	1st to 10th	Day	20% 8% 27% 30% 11% 4	503
	11th to 20th	Day	15% 5% 24% 35% 17% 4	527
	21st to end	Day	14% 3 23% 34% 21% 6%	573
June	1st to 10th	Day	12% 6% 26% 38% 15% 2	530
	11th to 20th	Day	12% 5% 25% 36% 18% 3	530
	21st to end	Day	16% 5% 22% 37% 17% 4	530
July	1st to 10th	Day	8% 2 20% 37% 26% 7%	525
	11th to 20th	Day	12% 2 19% 34% 23% 8%	524
	21st to end	Day	7% 3 20% 42% 22% 6%	576
August	1st to 10th	Day	10% 3 17% 34% 26% 9%	526
	11th to 20th	Day	7% 4 20% 31% 29% 9%	519
	21st to end	Day	11% 4 18% 36% 22% 8%	583
September	1st to 10th	Day	10% 6% 21% 32% 22% 10%	530
	11th to 20th	Day	8% 3 15% 31% 26% 17%	530
	21st to end	Day	14% 6% 26% 30% 16% 7%	530
October	1st to 10th	Day	18% 8% 26% 26% 16% 6%	530
	11th to 20th	Day	17% 12% 37% 24% 9% 2	530
	21st to end	Day	24% 11% 33% 23% 8% 1	583
November	1st to 10th	Day	20% 15% 29% 27% 9% 1	319
	11th to 20th	Day	17% 20% 35% 23% 6%	220
	21st to end	Day	21% 16% 43% 16% 5%	220
December	1st to 10th	Day	24% 14% 35% 21% 6%	220
	11th to 20th	Day	25% 24% 30% 17% 5%	220
	21st to end	Day	27% 17% 39% 14% 2	242
January	1st to 10th	Night	22% 15% 39% 18% 6%	840
	11th to 20th	Night	25% 15% 33% 22% 4	840
	21st to end	Night	18% 11% 39% 26% 6%	924
February	1st to 10th	Night	20% 15% 39% 23% 3	840
	11th to 20th	Night	21% 14% 37% 24% 4	823
	21st to end	Night	20% 13% 42% 21% 4	692
March	1st to 10th	Night	19% 12% 37% 27% 5%	840
	11th to 20th	Night	21% 13% 36% 25% 5% 1	840
	21st to end	Night	19% 10% 32% 28% 9% 1	924
April	1st to 10th	Night	23% 11% 32% 28% 6%	840
	11th to 20th	Night	17% 9% 33% 30% 10% 1	777
	21st to end	Night	19% 7% 31% 32% 11%	600
May	1st to 10th	Night	18% 4 25% 35% 16% 2	591
	11th to 20th	Night	15% 2 26% 39% 17% 1	394
	21st to end	Night	11% 3 20% 42% 22% 2	433
June	1st to 10th	Night	13% 3 24% 42% 18% 1	400
	11th to 20th	Night	11% 4 23% 39% 23% 1	400
	21st to end	Night	12% 4 21% 43% 21% 1	400
July	1st to 10th	Night	5% 3 14% 48% 28% 2	390
	11th to 20th	Night	11% 4 15% 40% 27% 3	388
	21st to end	Night	8% 3 15% 45% 26% 3	596
August	1st to 10th	Night	9% 2 13% 38% 34% 3	597
	11th to 20th	Night	8% 3 14% 37% 34% 4	594
	21st to end	Night	10% 3 21% 36% 27% 3	760
September	1st to 10th	Night	10% 5% 21% 36% 22% 6%	800
	11th to 20th	Night	12% 4 18% 30% 29% 8%	800
	21st to end	Night	18% 5% 18% 33% 22% 4	800
October	1st to 10th	Night	19% 4 27% 27% 22% 2	800
	11th to 20th	Night	21% 9% 31% 29% 10% 1	800
	21st to end	Night	24% 9% 31% 31% 6%	880
November	1st to 10th	Night	20% 11% 28% 30% 10% 1	820
	11th to 20th	Night	20% 12% 34% 25% 6% 2	840
	21st to end	Night	23% 12% 33% 25% 5%	840
December	1st to 10th	Night	26% 12% 36% 21% 5%	840
	11th to 20th	Night	21% 13% 41% 20% 4	840
	21st to end	Night	30% 11% 36% 21% 2	924

Page generated at 2026-04-14 02:44:26. Version ac07

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