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 2024-11-04.

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	5% 4 2 4 3 3 3 3 5% 7% 63%	104718
	Night	6% 7% 3 6% 3 3 3 3 5% 7% 53%	103070
Transparency	Day	21% 5% 8% 19% 26% 22%	104475
	Night	28% 7% 8% 16% 22% 20%	102902
Seeing	Day	7% 8% 25% 35% 19% 6%	15612
	Night	8% 3 14% 35% 33% 8%	25224

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 5% 3 3 4 3 4 6% 60%	2713
	11th to 20th	Day	12% 6% 2 5% 3 4 5% 3 6% 8% 47%	2860
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 6% 9% 42%	3146
February	1st to 10th	Day	13% 5% 2 4 2 2 3 2 4 5% 56%	1809
	11th to 20th	Day	7% 6% 1 5% 4 4 3 3 5% 7% 54%	1850
	21st to end	Day	11% 5% 2 5% 3 4 4 4 5% 6% 52%	1570
March	1st to 10th	Day	12% 7% 2 7% 4 4 3 4 6% 7% 43%	3217
	11th to 20th	Day	6% 3 1 3 3 2 3 2 4 7% 64%	3490
	21st to end	Day	7% 7% 2 6% 4 5% 4 5% 6% 8% 45%	4005
April	1st to 10th	Day	8% 4 1 4 4 3 4 3 6% 6% 57%	2280
	11th to 20th	Day	6% 4 2 4 3 2 3 3 5% 7% 60%	2249
	21st to end	Day	7% 5% 1 3 2 2 3 3 4 6% 63%	2280
May	1st to 10th	Day	4 4 1 3 2 2 2 1 3 5% 74%	3800
	11th to 20th	Day	1 5% 2 6% 3 2 3 3 4 8% 61%	3882
	21st to end	Day	3 5% 2 6% 3 3 3 3 4 6% 64%	4767
June	1st to 10th	Day	4 5% 1 4 4 3 3 3 5% 8% 60%	2660
	11th to 20th	Day	1 4 1 4 2 2 3 3 4 7% 68%	2660
	21st to end	Day	1 3 1 4 3 2 4 3 4 7% 67%	2660
July	1st to 10th	Day	1 2 1 3 2 2 2 3 4 6% 73%	4420
	11th to 20th	Day	1 3 2 4 3 2 3 3 4 7% 68%	4117
	21st to end	Day	1 2 1 5% 3 2 3 3 5% 7% 67%	4455
August	1st to 10th	Day	2 4 1 4 2 2 3 2 5% 7% 68%	3858
	11th to 20th	Day	1 3 1 2 1 2 2 3 4 5% 77%	3724
	21st to end	Day	1 2 1 4 2 2 2 2 4 6% 74%	4180
September	1st to 10th	Day	2 3 1 3 2 2 3 3 6% 6% 68%	2280
	11th to 20th	Day	2 4 2 4 2 2 3 3 4 8% 66%	2266
	21st to end	Day	1 3 1 3 2 1 2 3 5% 6% 73%	2090
October	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 76%	3216
	11th to 20th	Day	2 2 1 3 2 3 3 2 4 4 74%	3161
	21st to end	Day	3 2 1 3 2 3 4 3 4 6% 68%	3448
November	1st to 10th	Day	6% 4 1 3 3 2 2 3 5% 6% 65%	1814
	11th to 20th	Day	5% 4 1 3 3 2 3 3 4 6% 67%	1710
	21st to end	Day	8% 4 1 3 3 3 2 3 5% 7% 60%	1710
December	1st to 10th	Day	8% 5% 2 5% 4 3 3 3 4 7% 55%	1649
	11th to 20th	Day	18% 8% 3 6% 4 3 3 3 5% 5% 41%	1928
	21st to end	Day	14% 6% 2 6% 4 4 4 3 5% 7% 44%	2794
January	1st to 10th	Night	9% 6% 2 5% 3 3 3 3 4 5% 58%	4220
	11th to 20th	Night	11% 8% 3 6% 4 4 4 4 5% 7% 44%	4110
	21st to end	Night	17% 8% 2 5% 3 4 4 4 5% 7% 41%	4521
February	1st to 10th	Night	11% 6% 2 5% 3 3 3 2 5% 5% 56%	2369
	11th to 20th	Night	8% 7% 1 4 4 3 3 3 5% 8% 56%	2218
	21st to end	Night	11% 6% 2 5% 3 3 3 2 3 6% 54%	1884
March	1st to 10th	Night	11% 10% 3 6% 4 5% 4 3 6% 8% 39%	3653
	11th to 20th	Night	6% 5% 2 4 3 3 4 3 5% 7% 59%	3490
	21st to end	Night	11% 10% 2 7% 3 3 3 3 5% 7% 46%	3646
April	1st to 10th	Night	6% 6% 2 6% 4 4 4 3 5% 6% 54%	1900
	11th to 20th	Night	6% 7% 2 5% 3 3 4 3 4 6% 59%	1879
	21st to end	Night	5% 9% 2 4 3 2 3 3 5% 9% 56%	1900
May	1st to 10th	Night	3 5% 2 3 3 2 2 2 5% 6% 67%	3180
	11th to 20th	Night	2 14% 8% 10% 3 3 2 2 5% 7% 43%	3025
	21st to end	Night	3 13% 6% 9% 2 3 3 2 4 5% 50%	2805
June	1st to 10th	Night	2 9% 3 7% 3 4 4 3 6% 9% 49%	1520
	11th to 20th	Night	2 8% 3 6% 3 3 3 3 5% 8% 56%	1520
	21st to end	Night	1 5% 3 8% 3 2 4 5% 6% 10% 52%	1520
July	1st to 10th	Night	3 2 5% 3 3 2 4 6% 9% 62%	2540
	11th to 20th	Night	1 3 4 10% 3 3 4 5% 8% 9% 49%	2848
	21st to end	Night	1 6% 5% 16% 6% 4 5% 4 6% 9% 38%	3109
August	1st to 10th	Night	1 5% 3 9% 4 4 4 3 7% 11% 49%	3089
	11th to 20th	Night	1 3 2 7% 5% 3 4 4 6% 9% 58%	3126
	21st to end	Night	6% 4 9% 5% 3 3 3 5% 8% 55%	3498
September	1st to 10th	Night	2 5% 2 5% 2 3 3 4 5% 7% 62%	1900
	11th to 20th	Night	3 6% 3 6% 3 3 4 4 5% 8% 55%	1914
	21st to end	Night	2 4 1 5% 3 1 3 3 4 6% 68%	2090
October	1st to 10th	Night	2 3 1 3 1 2 2 2 5% 7% 72%	3760
	11th to 20th	Night	3 6% 5% 6% 2 3 5% 4 7% 5% 55%	3777
	21st to end	Night	3 6% 2 3 2 2 2 2 3 6% 68%	4121
November	1st to 10th	Night	4 5% 2 4 3 3 3 3 4 8% 61%	2333
	11th to 20th	Night	4 3 2 4 3 3 3 3 5% 7% 64%	2470
	21st to end	Night	5% 6% 2 4 3 3 4 3 5% 6% 60%	2470
December	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 5% 7% 54%	2527
	11th to 20th	Night	17% 8% 2 7% 3 3 4 4 6% 5% 39%	3276
	21st to end	Night	13% 8% 3 7% 4 4 5% 3 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% 6% 14% 20% 17% 6%	3217
	11th to 20th	Day	21% 4 15% 29% 17% 13%	3490
	21st to end	Day	32% 8% 16% 26% 14% 4	4005
April	1st to 10th	Day	26% 6% 13% 27% 20% 8%	2280
	11th to 20th	Day	23% 5% 14% 26% 24% 8%	2252
	21st to end	Day	21% 5% 11% 27% 28% 8%	2280
May	1st to 10th	Day	16% 3 7% 26% 36% 11%	3800
	11th to 20th	Day	15% 11% 6% 26% 32% 10%	3885
	21st to end	Day	16% 9% 9% 29% 33% 5%	4767
June	1st to 10th	Day	22% 7% 10% 23% 27% 11%	2660
	11th to 20th	Day	16% 5% 7% 14% 38% 21%	2660
	21st to end	Day	16% 6% 6% 8% 31% 34%	2660
July	1st to 10th	Day	11% 3 4 8% 16% 58%	4351
	11th to 20th	Day	15% 4 6% 9% 21% 46%	4047
	21st to end	Day	15% 5% 5% 13% 28% 34%	4315
August	1st to 10th	Day	16% 4 4 13% 33% 30%	3843
	11th to 20th	Day	10% 4 3 8% 33% 42%	3760
	21st to end	Day	12% 4 4 12% 32% 37%	4179
September	1st to 10th	Day	15% 5% 5% 10% 28% 38%	2280
	11th to 20th	Day	17% 6% 5% 17% 34% 21%	2266
	21st to end	Day	13% 4 4 17% 35% 26%	2090
October	1st to 10th	Day	11% 2 5% 14% 25% 42%	3216
	11th to 20th	Day	14% 4 6% 20% 33% 23%	3161
	21st to end	Day	18% 3 5% 13% 34% 27%	3448
November	1st to 10th	Day	21% 4 6% 18% 29% 23%	1814
	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	39% 9% 10% 20% 15% 7%	3653
	11th to 20th	Night	25% 7% 10% 26% 21% 11%	3490
	21st to end	Night	36% 7% 16% 21% 16% 5%	3646
April	1st to 10th	Night	30% 8% 12% 23% 18% 9%	1900
	11th to 20th	Night	26% 8% 9% 25% 22% 10%	1879
	21st to end	Night	26% 7% 9% 22% 27% 9%	1900
May	1st to 10th	Night	17% 6% 10% 22% 25% 19%	3180
	11th to 20th	Night	30% 17% 8% 14% 19% 12%	3026
	21st to end	Night	27% 13% 10% 17% 28% 5%	2805
June	1st to 10th	Night	30% 9% 9% 18% 23% 12%	1520
	11th to 20th	Night	26% 6% 6% 11% 28% 23%	1520
	21st to end	Night	24% 7% 8% 7% 23% 31%	1520
July	1st to 10th	Night	13% 7% 7% 8% 13% 52%	2500
	11th to 20th	Night	25% 6% 8% 9% 16% 37%	2795
	21st to end	Night	38% 7% 6% 10% 21% 18%	3011
August	1st to 10th	Night	26% 7% 7% 13% 20% 27%	3080
	11th to 20th	Night	19% 7% 5% 9% 20% 40%	3156
	21st to end	Night	25% 6% 6% 8% 24% 31%	3498
September	1st to 10th	Night	18% 6% 8% 8% 20% 39%	1900
	11th to 20th	Night	25% 8% 7% 11% 26% 24%	1914
	21st to end	Night	16% 6% 4 13% 33% 27%	2090
October	1st to 10th	Night	11% 4 4 13% 26% 41%	3760
	11th to 20th	Night	25% 9% 7% 15% 20% 25%	3777
	21st to end	Night	20% 4 3 11% 33% 28%	4121
November	1st to 10th	Night	23% 6% 6% 16% 25% 24%	2333
	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	13% 18% 37% 23% 8% 2	506
April	1st to 10th	Day	9% 16% 35% 22% 13% 4	460
	11th to 20th	Day	10% 14% 34% 29% 9% 4	452
	21st to end	Day	7% 13% 33% 30% 12% 5%	460
May	1st to 10th	Day	10% 10% 33% 29% 14% 3	463
	11th to 20th	Day	4 11% 30% 39% 14% 3	488
	21st to end	Day	12% 9% 27% 34% 14% 4	529
June	1st to 10th	Day	7% 6% 21% 38% 21% 6%	490
	11th to 20th	Day	3 4 30% 38% 19% 6%	490
	21st to end	Day	3 3 20% 41% 23% 9%	490
July	1st to 10th	Day	3 1 14% 44% 30% 9%	486
	11th to 20th	Day	4 1 10% 45% 30% 11%	484
	21st to end	Day	2 10% 45% 30% 13%	531
August	1st to 10th	Day	5% 2 15% 48% 21% 9%	487
	11th to 20th	Day	4 13% 42% 30% 12%	477
	21st to end	Day	3 3 14% 43% 28% 9%	539
September	1st to 10th	Day	3 2 15% 41% 29% 10%	490
	11th to 20th	Day	4 7% 22% 41% 20% 6%	490
	21st to end	Day	2 6% 21% 36% 27% 9%	490
October	1st to 10th	Day	2 7% 23% 37% 24% 6%	490
	11th to 20th	Day	3 8% 26% 36% 21% 6%	490
	21st to end	Day	5% 5% 26% 37% 21% 6%	539
November	1st to 10th	Day	6% 8% 23% 35% 23% 5%	392
	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	12% 5% 21% 38% 21% 3	836
April	1st to 10th	Night	8% 4 21% 40% 24% 3	760
	11th to 20th	Night	8% 6% 20% 34% 27% 4	751
	21st to end	Night	8% 4 21% 33% 28% 7%	760
May	1st to 10th	Night	7% 3 14% 41% 29% 6%	760
	11th to 20th	Night	7% 4 13% 37% 33% 6%	674
	21st to end	Night	6% 5% 14% 37% 33% 6%	442
June	1st to 10th	Night	5% 3 9% 32% 46% 6%	380
	11th to 20th	Night	4 2 7% 34% 47% 6%	380
	21st to end	Night	3 2 3 32% 54% 8%	380
July	1st to 10th	Night	2 2 1 22% 62% 11%	370
	11th to 20th	Night	3 1 1 13% 59% 24%	541
	21st to end	Night	3 1 2 13% 56% 25%	624
August	1st to 10th	Night	3 1 4 30% 48% 14%	704
	11th to 20th	Night	2 1 3 23% 56% 15%	752
	21st to end	Night	2 1 3 23% 55% 16%	836
September	1st to 10th	Night	3 2 4 24% 55% 13%	760
	11th to 20th	Night	4 3 6% 35% 42% 9%	760
	21st to end	Night	3 1 8% 29% 48% 10%	760
October	1st to 10th	Night	4 2 9% 38% 40% 6%	760
	11th to 20th	Night	5% 3 11% 37% 36% 7%	760
	21st to end	Night	7% 2 12% 37% 33% 8%	836
November	1st to 10th	Night	6% 3 13% 39% 29% 9%	754
	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 2024-11-01 19:47:46. Version ac07

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