Santa Maria
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santa Maria clear sky chart from 2005-11-06 to 2024-03-28.

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% 4 2 4 3 2 3 4 5% 7% 59%	78965
	Night	7% 6% 3 5% 4 2 4 4 5% 7% 53%	81054
Transparency	Day	24% 5% 9% 19% 26% 18%	78685
	Night	29% 7% 9% 16% 22% 18%	80855
Seeing	Day	8% 8% 25% 35% 19% 5%	14728
	Night	8% 3 14% 35% 33% 8%	24466

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	8% 3 2 4 4 3 3 4 4 6% 60%	2713
	11th to 20th	Day	12% 5% 2 4 4 3 4 5% 6% 8% 47%	2860
	21st to end	Day	13% 6% 2 4 5% 3 4 6% 6% 9% 42%	3146
February	1st to 10th	Day	13% 5% 2 4 2 2 3 3 4 6% 56%	1809
	11th to 20th	Day	8% 5% 2 5% 4 3 3 4 4 8% 54%	1850
	21st to end	Day	11% 4 2 5% 3 2 4 5% 5% 6% 52%	1570
March	1st to 10th	Day	11% 5% 3 6% 5% 4 4 5% 6% 8% 45%	1943
	11th to 20th	Day	10% 5% 2 4 5% 3 3 4 4 8% 50%	2090
	21st to end	Day	7% 5% 2 4 3 3 4 4 5% 7% 56%	2361
April	1st to 10th	Day	8% 3 2 4 4 3 4 4 6% 7% 56%	2160
	11th to 20th	Day	6% 4 2 4 3 2 3 4 5% 7% 61%	2129
	21st to end	Day	8% 5% 1 3 2 1 3 3 4 7% 64%	2160
May	1st to 10th	Day	5% 4 2 3 3 2 3 3 4 8% 63%	2160
	11th to 20th	Day	2 4 2 4 3 1 4 4 4 7% 65%	2190
	21st to end	Day	5% 6% 2 4 3 2 3 3 4 7% 59%	2690
June	1st to 10th	Day	4 5% 2 4 4 2 3 3 5% 8% 60%	2520
	11th to 20th	Day	1 4 1 3 2 2 3 3 3 7% 69%	2520
	21st to end	Day	1 3 2 4 3 2 3 4 4 7% 67%	2520
July	1st to 10th	Day	1 4 2 5% 3 2 3 4 5% 8% 62%	2520
	11th to 20th	Day	2 4 2 3 3 2 4 4 4 8% 65%	2347
	21st to end	Day	2 3 2 5% 4 2 4 5% 6% 9% 57%	2546
August	1st to 10th	Day	2 6% 2 5% 3 2 3 4 5% 8% 59%	2199
	11th to 20th	Day	2 4 2 4 3 2 2 4 5% 7% 66%	2122
	21st to end	Day	1 3 2 4 3 1 4 4 6% 8% 63%	2376
September	1st to 10th	Day	2 3 1 3 2 1 3 4 5% 7% 67%	2160
	11th to 20th	Day	2 4 2 4 3 1 3 4 4 8% 66%	2147
	21st to end	Day	1 3 2 2 3 1 2 3 5% 6% 72%	1980
October	1st to 10th	Day	3 2 1 2 3 1 3 4 5% 7% 69%	1823
	11th to 20th	Day	3 3 2 3 3 2 3 3 3 4 72%	1800
	21st to end	Day	4 3 1 3 3 2 3 4 4 7% 68%	1980
November	1st to 10th	Day	6% 3 1 3 3 1 2 3 5% 6% 66%	1783
	11th to 20th	Day	5% 3 1 2 3 1 3 4 3 6% 67%	1710
	21st to end	Day	8% 3 1 3 3 2 3 3 5% 7% 61%	1710
December	1st to 10th	Day	8% 5% 3 4 5% 3 3 4 4 7% 55%	1649
	11th to 20th	Day	18% 8% 3 5% 5% 2 4 3 5% 6% 41%	1928
	21st to end	Day	14% 6% 2 5% 5% 3 4 4 5% 7% 45%	2794
January	1st to 10th	Night	9% 6% 2 4 4 2 3 4 4 5% 58%	4220
	11th to 20th	Night	11% 8% 3 5% 5% 3 4 5% 5% 7% 44%	4110
	21st to end	Night	17% 8% 2 5% 4 3 4 5% 5% 7% 42%	4521
February	1st to 10th	Night	11% 6% 2 4 3 2 3 3 4 6% 56%	2369
	11th to 20th	Night	8% 6% 2 3 4 2 3 4 4 8% 56%	2218
	21st to end	Night	12% 6% 2 4 4 2 3 3 3 6% 54%	1884
March	1st to 10th	Night	10% 7% 3 5% 4 3 5% 4 6% 8% 44%	2233
	11th to 20th	Night	9% 6% 3 5% 4 2 5% 5% 6% 8% 47%	2090
	21st to end	Night	9% 7% 2 4 3 2 3 3 5% 7% 54%	2148
April	1st to 10th	Night	7% 5% 2 5% 5% 3 4 4 5% 7% 54%	1800
	11th to 20th	Night	6% 6% 2 5% 3 2 3 4 4 6% 59%	1779
	21st to end	Night	6% 7% 2 3 3 2 3 4 4 9% 57%	1800
May	1st to 10th	Night	4 8% 3 4 4 2 4 3 5% 9% 54%	1800
	11th to 20th	Night	4 9% 4 8% 5% 2 3 4 5% 8% 48%	1701
	21st to end	Night	5% 11% 3 6% 3 2 4 4 4 8% 50%	1581
June	1st to 10th	Night	3 8% 4 6% 3 3 4 4 5% 8% 51%	1440
	11th to 20th	Night	2 6% 4 6% 3 2 3 4 4 8% 56%	1440
	21st to end	Night	1 6% 3 7% 4 2 4 6% 5% 10% 52%	1440
July	1st to 10th	Night	1 5% 4 7% 3 2 4 5% 6% 11% 51%	1440
	11th to 20th	Night	2 4 3 6% 4 2 4 7% 7% 10% 51%	1608
	21st to end	Night	1 3 4 10% 5% 3 6% 7% 8% 10% 43%	1773
August	1st to 10th	Night	1 7% 5% 9% 4 3 5% 5% 6% 9% 47%	1740
	11th to 20th	Night	1 4 2 6% 4 3 4 5% 8% 11% 52%	1780
	21st to end	Night	1 5% 3 5% 4 2 4 4 6% 9% 57%	1980
September	1st to 10th	Night	2 4 2 5% 2 2 4 6% 5% 7% 61%	1800
	11th to 20th	Night	3 5% 2 5% 4 2 4 4 5% 8% 57%	1813
	21st to end	Night	3 4 1 3 3 1 3 3 4 6% 69%	1980
October	1st to 10th	Night	4 4 2 3 2 2 3 3 4 6% 67%	2133
	11th to 20th	Night	5% 5% 3 5% 3 2 3 4 5% 5% 61%	2160
	21st to end	Night	4 6% 2 3 2 2 2 3 4 5% 65%	2376
November	1st to 10th	Night	4 5% 2 4 3 2 3 4 5% 8% 61%	2292
	11th to 20th	Night	4 3 2 4 3 2 3 3 5% 8% 64%	2470
	21st to end	Night	5% 5% 2 3 3 2 4 4 5% 6% 61%	2470
December	1st to 10th	Night	10% 5% 2 4 4 2 3 3 5% 7% 55%	2527
	11th to 20th	Night	17% 8% 3 6% 4 2 4 5% 5% 6% 40%	3276
	21st to end	Night	13% 7% 3 6% 5% 3 5% 4 5% 7% 41%	4862

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	25% 4 10% 35% 21% 6%	2713
	11th to 20th	Day	35% 5% 12% 18% 18% 11%	2860
	21st to end	Day	38% 6% 9% 23% 14% 10%	3146
February	1st to 10th	Day	31% 3 6% 19% 21% 19%	1809
	11th to 20th	Day	29% 5% 8% 23% 23% 11%	1860
	21st to end	Day	32% 5% 11% 20% 25% 8%	1570
March	1st to 10th	Day	37% 5% 12% 18% 18% 10%	1943
	11th to 20th	Day	33% 5% 13% 20% 19% 10%	2090
	21st to end	Day	27% 6% 13% 28% 20% 7%	2361
April	1st to 10th	Day	27% 6% 13% 26% 19% 9%	2160
	11th to 20th	Day	24% 4 14% 26% 24% 9%	2132
	21st to end	Day	21% 5% 11% 26% 28% 8%	2160
May	1st to 10th	Day	22% 5% 12% 23% 31% 9%	2160
	11th to 20th	Day	18% 6% 9% 29% 28% 10%	2193
	21st to end	Day	24% 6% 11% 30% 25% 4	2690
June	1st to 10th	Day	23% 6% 10% 22% 28% 12%	2520
	11th to 20th	Day	17% 5% 7% 13% 38% 21%	2520
	21st to end	Day	16% 6% 6% 8% 31% 32%	2520
July	1st to 10th	Day	18% 5% 6% 11% 26% 34%	2451
	11th to 20th	Day	17% 5% 8% 14% 30% 26%	2277
	21st to end	Day	20% 8% 8% 13% 30% 21%	2405
August	1st to 10th	Day	23% 5% 5% 9% 27% 30%	2183
	11th to 20th	Day	17% 5% 5% 12% 32% 29%	2122
	21st to end	Day	17% 6% 5% 11% 32% 29%	2376
September	1st to 10th	Day	15% 5% 5% 11% 27% 37%	2160
	11th to 20th	Day	17% 6% 4 17% 33% 23%	2147
	21st to end	Day	13% 4 5% 17% 36% 25%	1980
October	1st to 10th	Day	15% 4 9% 19% 25% 29%	1823
	11th to 20th	Day	18% 3 6% 16% 29% 28%	1800
	21st to end	Day	19% 4 6% 14% 28% 29%	1980
November	1st to 10th	Day	20% 4 6% 17% 29% 23%	1783
	11th to 20th	Day	19% 4 8% 18% 27% 23%	1710
	21st to end	Day	24% 4 7% 15% 26% 24%	1710
December	1st to 10th	Day	29% 5% 8% 17% 24% 17%	1649
	11th to 20th	Day	45% 5% 8% 15% 17% 10%	1928
	21st to end	Day	38% 7% 10% 24% 14% 8%	2794
January	1st to 10th	Night	28% 5% 9% 25% 24% 8%	4220
	11th to 20th	Night	38% 9% 8% 18% 15% 13%	4110
	21st to end	Night	41% 6% 8% 16% 18% 10%	4521
February	1st to 10th	Night	32% 4 7% 16% 24% 17%	2369
	11th to 20th	Night	28% 5% 9% 20% 24% 15%	2219
	21st to end	Night	32% 5% 8% 20% 24% 10%	1884
March	1st to 10th	Night	38% 7% 11% 19% 16% 9%	2233
	11th to 20th	Night	34% 8% 9% 18% 21% 10%	2090
	21st to end	Night	29% 6% 13% 21% 23% 8%	2148
April	1st to 10th	Night	30% 8% 13% 23% 17% 9%	1800
	11th to 20th	Night	26% 7% 9% 25% 21% 10%	1779
	21st to end	Night	26% 7% 9% 23% 27% 10%	1800
May	1st to 10th	Night	27% 7% 10% 20% 24% 12%	1800
	11th to 20th	Night	31% 8% 9% 19% 22% 11%	1702
	21st to end	Night	32% 8% 11% 21% 22% 6%	1581
June	1st to 10th	Night	30% 7% 9% 18% 23% 12%	1440
	11th to 20th	Night	26% 6% 6% 11% 28% 23%	1440
	21st to end	Night	24% 7% 8% 8% 23% 30%	1440
July	1st to 10th	Night	21% 12% 10% 8% 19% 31%	1400
	11th to 20th	Night	23% 10% 10% 10% 19% 29%	1555
	21st to end	Night	28% 10% 9% 12% 21% 20%	1674
August	1st to 10th	Night	30% 8% 8% 9% 16% 29%	1731
	11th to 20th	Night	20% 9% 8% 10% 24% 29%	1780
	21st to end	Night	20% 8% 9% 7% 27% 30%	1980
September	1st to 10th	Night	19% 6% 9% 8% 20% 39%	1800
	11th to 20th	Night	23% 7% 8% 11% 26% 25%	1813
	21st to end	Night	16% 7% 4 13% 33% 27%	1980
October	1st to 10th	Night	17% 6% 6% 17% 24% 29%	2133
	11th to 20th	Night	25% 6% 7% 12% 23% 26%	2160
	21st to end	Night	22% 5% 5% 11% 27% 30%	2376
November	1st to 10th	Night	23% 6% 6% 16% 25% 24%	2292
	11th to 20th	Night	20% 5% 9% 16% 25% 25%	2470
	21st to end	Night	25% 4 9% 16% 22% 24%	2470
December	1st to 10th	Night	30% 5% 7% 15% 24% 19%	2527
	11th to 20th	Night	44% 6% 9% 15% 17% 10%	3276
	21st to end	Night	41% 6% 11% 19% 15% 8%	4862

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% 11% 28% 25% 13% 1	289
	11th to 20th	Day	12% 12% 31% 28% 16% 2	370
	21st to end	Day	12% 11% 32% 28% 14% 2	407
February	1st to 10th	Day	12% 13% 27% 28% 16% 4	417
	11th to 20th	Day	13% 11% 32% 28% 13% 3	455
	21st to end	Day	10% 14% 36% 27% 10% 2	382
March	1st to 10th	Day	17% 17% 31% 25% 9% 1	460
	11th to 20th	Day	12% 15% 31% 31% 8% 2	460
	21st to end	Day	12% 18% 36% 24% 8% 2	491
April	1st to 10th	Day	9% 16% 36% 22% 13% 4	420
	11th to 20th	Day	10% 15% 35% 29% 9% 3	412
	21st to end	Day	7% 14% 33% 29% 12% 5%	420
May	1st to 10th	Day	10% 10% 33% 30% 13% 4	423
	11th to 20th	Day	5% 11% 31% 37% 12% 3	448
	21st to end	Day	13% 10% 28% 33% 13% 4	485
June	1st to 10th	Day	8% 6% 22% 37% 21% 6%	450
	11th to 20th	Day	4 4 28% 38% 20% 6%	450
	21st to end	Day	3 3 21% 40% 24% 8%	450
July	1st to 10th	Day	3 1 14% 44% 30% 8%	446
	11th to 20th	Day	4 1 8% 45% 31% 11%	444
	21st to end	Day	2 10% 44% 32% 12%	487
August	1st to 10th	Day	6% 2 16% 48% 21% 7%	447
	11th to 20th	Day	5% 11% 42% 31% 11%	437
	21st to end	Day	3 2 14% 44% 29% 8%	495
September	1st to 10th	Day	3 2 15% 42% 28% 9%	450
	11th to 20th	Day	4 5% 21% 43% 21% 6%	450
	21st to end	Day	2 6% 20% 36% 28% 8%	450
October	1st to 10th	Day	2 8% 25% 36% 23% 6%	450
	11th to 20th	Day	4 8% 26% 36% 20% 6%	450
	21st to end	Day	5% 5% 26% 38% 21% 6%	495
November	1st to 10th	Day	6% 8% 22% 35% 23% 6%	379
	11th to 20th	Day	8% 6% 23% 32% 24% 7%	270
	21st to end	Day	9% 6% 23% 30% 26% 6%	270
December	1st to 10th	Day	10% 9% 27% 32% 19% 2	241
	11th to 20th	Day	11% 11% 21% 31% 20% 7%	180
	21st to end	Day	17% 11% 29% 26% 14% 4	198
January	1st to 10th	Night	14% 4 20% 34% 20% 8%	760
	11th to 20th	Night	9% 4 20% 39% 22% 7%	760
	21st to end	Night	16% 3 19% 40% 16% 5%	836
February	1st to 10th	Night	13% 6% 16% 35% 24% 6%	760
	11th to 20th	Night	11% 6% 20% 37% 21% 5%	744
	21st to end	Night	13% 5% 20% 42% 16% 3	628
March	1st to 10th	Night	13% 5% 20% 41% 19% 3	760
	11th to 20th	Night	11% 3 18% 39% 24% 5%	760
	21st to end	Night	11% 5% 21% 39% 21% 3	820
April	1st to 10th	Night	8% 3 20% 41% 25% 4	720
	11th to 20th	Night	8% 6% 21% 34% 27% 4	711
	21st to end	Night	8% 4 21% 33% 28% 7%	720
May	1st to 10th	Night	7% 3 14% 39% 30% 6%	720
	11th to 20th	Night	7% 4 12% 37% 33% 6%	638
	21st to end	Night	6% 5% 14% 37% 32% 5%	419
June	1st to 10th	Night	6% 3 9% 32% 45% 6%	360
	11th to 20th	Night	5% 2 7% 32% 48% 6%	360
	21st to end	Night	3 2 2 33% 53% 8%	360
July	1st to 10th	Night	2 2 1 22% 62% 11%	350
	11th to 20th	Night	3 1 12% 58% 25%	511
	21st to end	Night	3 1 2 13% 56% 26%	591
August	1st to 10th	Night	3 1 4 30% 48% 13%	666
	11th to 20th	Night	2 1 3 22% 56% 16%	712
	21st to end	Night	2 1 3 22% 56% 17%	792
September	1st to 10th	Night	3 2 4 23% 55% 13%	720
	11th to 20th	Night	4 3 6% 34% 43% 10%	720
	21st to end	Night	3 1 9% 28% 48% 11%	720
October	1st to 10th	Night	5% 3 9% 39% 39% 6%	720
	11th to 20th	Night	6% 3 12% 37% 36% 7%	720
	21st to end	Night	6% 2 13% 36% 33% 9%	792
November	1st to 10th	Night	6% 3 13% 39% 29% 10%	740
	11th to 20th	Night	5% 2 16% 41% 28% 8%	760
	21st to end	Night	6% 3 18% 41% 25% 6%	760
December	1st to 10th	Night	11% 3 18% 39% 24% 5%	760
	11th to 20th	Night	14% 3 20% 39% 20% 4	760
	21st to end	Night	14% 6% 22% 38% 17% 4	836

Page generated at 2024-03-24 20:37:03. Version ac07

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