Santee
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santee clear sky chart from 2005-11-06 to 2026-08-15.

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	12% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	143505
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 43%	138392
Transparency	Day	39% 7% 13% 19% 17% 6%	147151
	Night	37% 6% 12% 18% 19% 7%	142818
Seeing	Day	13% 6% 21% 25% 22% 14%	17851
	Night	14% 6% 22% 33% 22% 3	27891

By Month

Percentage Cloud Cover SE (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	12% 5% 2 4 3 3 3 3 5% 6% 53%	5258
	11th to 20th	Day	12% 5% 2 5% 3 3 2 2 4 6% 56%	5280
	21st to end	Day	15% 8% 4 7% 4 4 4 3 5% 6% 40%	5780
February	1st to 10th	Day	14% 7% 2 5% 4 4 5% 4 6% 7% 42%	1890
	11th to 20th	Day	18% 7% 3 5% 3 3 3 3 4 6% 44%	2032
	21st to end	Day	16% 8% 2 5% 4 3 4 4 4 5% 45%	1845
March	1st to 10th	Day	19% 9% 3 7% 4 3 4 3 5% 6% 38%	5045
	11th to 20th	Day	8% 4 2 5% 4 3 4 4 5% 7% 54%	5090
	21st to end	Day	12% 6% 2 7% 5% 4 4 3 5% 5% 47%	5586
April	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 7% 7% 49%	2310
	11th to 20th	Day	9% 5% 2 6% 3 4 4 4 5% 7% 52%	2494
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 8% 50%	2560
May	1st to 10th	Day	13% 7% 3 7% 5% 4 5% 4 6% 9% 37%	7616
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 9% 40%	7626
	21st to end	Day	10% 6% 3 8% 6% 6% 6% 5% 7% 8% 34%	8391
June	1st to 10th	Day	9% 7% 3 8% 6% 6% 5% 5% 8% 9% 34%	2730
	11th to 20th	Day	8% 5% 1 5% 5% 5% 7% 5% 8% 11% 39%	2730
	21st to end	Day	5% 5% 1 6% 6% 7% 8% 6% 8% 11% 38%	2730
July	1st to 10th	Day	10% 6% 3 8% 7% 7% 7% 6% 9% 10% 27%	7680
	11th to 20th	Day	5% 4 2 8% 7% 7% 8% 7% 10% 13% 28%	7680
	21st to end	Day	7% 6% 3 8% 6% 6% 7% 6% 9% 13% 29%	8340
August	1st to 10th	Day	21% 7% 2 8% 6% 6% 7% 6% 8% 10% 20%	4364
	11th to 20th	Day	8% 6% 3 8% 6% 7% 6% 6% 9% 11% 32%	4175
	21st to end	Day	8% 5% 3 7% 5% 6% 6% 5% 8% 10% 38%	4312
September	1st to 10th	Day	9% 5% 2 6% 5% 6% 6% 4 7% 9% 40%	2243
	11th to 20th	Day	13% 6% 3 7% 5% 5% 6% 4 6% 7% 39%	2200
	21st to end	Day	15% 7% 3 6% 4 4 4 4 6% 7% 39%	2200
October	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 4 7% 46%	2060
	11th to 20th	Day	10% 5% 2 4 3 3 3 2 4 5% 58%	2000
	21st to end	Day	10% 5% 2 5% 3 3 3 3 4 5% 58%	2200
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 5% 6% 54%	2057
	11th to 20th	Day	13% 7% 2 5% 3 3 3 2 4 7% 51%	2063
	21st to end	Day	13% 5% 2 5% 4 4 3 3 5% 7% 49%	1890
December	1st to 10th	Day	10% 4 2 5% 3 4 5% 3 5% 7% 51%	3020
	11th to 20th	Day	15% 6% 2 6% 4 3 3 3 5% 6% 47%	3463
	21st to end	Day	19% 8% 2 5% 3 3 3 3 4 6% 45%	4565
January	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 4 5% 53%	7635
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 7% 49%	7680
	21st to end	Night	15% 8% 3 7% 5% 4 4 3 4 5% 43%	8401
February	1st to 10th	Night	16% 6% 2 5% 4 4 3 3 5% 7% 45%	2730
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 5% 5% 43%	2470
	21st to end	Night	12% 7% 3 6% 4 4 4 4 6% 6% 45%	1959
March	1st to 10th	Night	17% 9% 3 6% 4 4 4 3 5% 6% 38%	5028
	11th to 20th	Night	10% 4 2 4 3 3 4 3 5% 8% 54%	5090
	21st to end	Night	12% 4 2 5% 4 4 4 3 5% 7% 51%	5588
April	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 5% 7% 50%	2308
	11th to 20th	Night	10% 4 2 5% 3 4 3 4 5% 8% 53%	2075
	21st to end	Night	7% 5% 1 6% 4 3 4 4 6% 7% 52%	2076
May	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 4 7% 9% 40%	5237
	11th to 20th	Night	12% 5% 2 5% 4 4 4 4 6% 10% 44%	5234
	21st to end	Night	10% 6% 3 8% 5% 6% 6% 4 7% 9% 37%	5761
June	1st to 10th	Night	10% 6% 3 6% 5% 5% 6% 5% 8% 11% 35%	1890
	11th to 20th	Night	9% 5% 3 5% 7% 5% 6% 4 7% 12% 38%	1890
	21st to end	Night	6% 4 2 7% 5% 5% 7% 6% 9% 13% 37%	1890
July	1st to 10th	Night	9% 6% 2 8% 6% 6% 7% 6% 8% 12% 30%	5278
	11th to 20th	Night	7% 6% 3 8% 6% 6% 7% 6% 9% 14% 29%	5277
	21st to end	Night	9% 7% 3 9% 7% 6% 7% 5% 9% 12% 27%	5736
August	1st to 10th	Night	19% 7% 3 7% 5% 5% 7% 5% 8% 10% 24%	3005
	11th to 20th	Night	8% 5% 3 7% 6% 6% 6% 5% 8% 11% 35%	2927
	21st to end	Night	6% 4 2 5% 4 5% 5% 5% 7% 11% 46%	3586
September	1st to 10th	Night	9% 5% 2 7% 5% 5% 4 5% 7% 11% 40%	2151
	11th to 20th	Night	10% 6% 3 8% 7% 6% 5% 5% 5% 8% 38%	2200
	21st to end	Night	17% 7% 3 6% 4 4 4 3 6% 7% 39%	2200
October	1st to 10th	Night	13% 6% 2 6% 3 4 3 3 4 6% 51%	2340
	11th to 20th	Night	12% 4 2 4 3 3 3 3 4 6% 57%	2400
	21st to end	Night	10% 5% 2 4 3 3 3 3 5% 5% 57%	2640
November	1st to 10th	Night	12% 5% 2 4 3 3 3 3 5% 6% 54%	2461
	11th to 20th	Night	14% 7% 2 4 3 3 3 2 4 6% 52%	2554
	21st to end	Night	11% 6% 2 5% 4 4 4 4 5% 7% 49%	2730
December	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 53%	4380
	11th to 20th	Night	15% 8% 3 7% 4 3 3 3 4 5% 44%	4952
	21st to end	Night	17% 6% 2 6% 3 4 3 3 5% 6% 44%	6633

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	32% 4 8% 24% 27% 6%	5259
	11th to 20th	Day	32% 2 5% 16% 33% 12%	5280
	21st to end	Day	45% 4 5% 17% 18% 11%	5780
February	1st to 10th	Day	40% 4 9% 21% 20% 6%	1890
	11th to 20th	Day	42% 4 5% 19% 24% 7%	2042
	21st to end	Day	41% 4 6% 18% 20% 10%	1845
March	1st to 10th	Day	47% 4 7% 12% 21% 9%	5045
	11th to 20th	Day	29% 5% 8% 17% 24% 17%	5090
	21st to end	Day	39% 4 8% 17% 22% 10%	5586
April	1st to 10th	Day	32% 5% 11% 20% 25% 7%	2310
	11th to 20th	Day	33% 4 8% 23% 21% 12%	2494
	21st to end	Day	30% 6% 10% 27% 23% 5%	2560
May	1st to 10th	Day	43% 7% 13% 24% 12% 2	7651
	11th to 20th	Day	40% 6% 15% 22% 15% 2	7630
	21st to end	Day	44% 9% 14% 15% 17% 2	8405
June	1st to 10th	Day	43% 8% 16% 20% 11% 2	2730
	11th to 20th	Day	35% 8% 19% 26% 11% 1	2730
	21st to end	Day	36% 11% 19% 22% 10% 1	2730
July	1st to 10th	Day	46% 11% 20% 18% 4 1	7615
	11th to 20th	Day	42% 14% 30% 12% 2	7611
	21st to end	Day	42% 12% 21% 17% 7% 1	8156
August	1st to 10th	Day	56% 10% 20% 11% 3	4351
	11th to 20th	Day	41% 10% 19% 21% 9%	4214
	21st to end	Day	37% 8% 15% 28% 11% 1	4312
September	1st to 10th	Day	39% 9% 15% 17% 15% 5%	2243
	11th to 20th	Day	44% 6% 10% 18% 18% 4	2200
	21st to end	Day	43% 5% 12% 19% 16% 5%	2200
October	1st to 10th	Day	38% 5% 8% 17% 25% 8%	3359
	11th to 20th	Day	18% 2 5% 15% 32% 27%	3240
	21st to end	Day	24% 3 6% 17% 35% 15%	3538
November	1st to 10th	Day	31% 4 7% 20% 25% 13%	2057
	11th to 20th	Day	36% 3 6% 18% 26% 11%	2063
	21st to end	Day	35% 4 8% 22% 22% 9%	1890
December	1st to 10th	Day	33% 4 8% 18% 26% 11%	3020
	11th to 20th	Day	38% 4 8% 23% 21% 6%	3460
	21st to end	Day	43% 3 6% 22% 23% 3	4565
January	1st to 10th	Night	34% 4 6% 22% 28% 6%	7636
	11th to 20th	Night	35% 4 5% 15% 30% 11%	7680
	21st to end	Night	45% 4 5% 13% 24% 9%	8401
February	1st to 10th	Night	40% 3 7% 20% 22% 8%	2730
	11th to 20th	Night	43% 4 7% 17% 20% 8%	2471
	21st to end	Night	38% 5% 9% 16% 18% 13%	1959
March	1st to 10th	Night	46% 5% 7% 13% 20% 9%	5028
	11th to 20th	Night	29% 4 8% 13% 28% 19%	5090
	21st to end	Night	34% 4 9% 20% 20% 12%	5588
April	1st to 10th	Night	33% 5% 11% 21% 20% 9%	2308
	11th to 20th	Night	30% 4 8% 23% 23% 11%	2075
	21st to end	Night	29% 7% 11% 26% 22% 5%	2076
May	1st to 10th	Night	39% 7% 17% 24% 11% 2	5264
	11th to 20th	Night	35% 7% 20% 23% 14% 2	5235
	21st to end	Night	42% 10% 14% 18% 15% 1	5771
June	1st to 10th	Night	39% 10% 18% 21% 11% 2	1890
	11th to 20th	Night	37% 11% 20% 23% 9% 1	1890
	21st to end	Night	34% 13% 23% 21% 8% 1	1890
July	1st to 10th	Night	42% 10% 24% 19% 3 1	5235
	11th to 20th	Night	43% 13% 31% 11% 2	5226
	21st to end	Night	46% 11% 21% 15% 6% 1	5606
August	1st to 10th	Night	53% 10% 23% 12% 2	2994
	11th to 20th	Night	38% 12% 23% 20% 7%	2954
	21st to end	Night	30% 8% 18% 35% 8% 1	3586
September	1st to 10th	Night	36% 9% 18% 20% 12% 6%	2151
	11th to 20th	Night	42% 9% 12% 18% 16% 3	2200
	21st to end	Night	44% 7% 13% 19% 14% 3	2200
October	1st to 10th	Night	35% 4 8% 19% 27% 7%	3821
	11th to 20th	Night	18% 2 5% 13% 26% 35%	3899
	21st to end	Night	24% 4 6% 21% 28% 17%	4252
November	1st to 10th	Night	32% 4 9% 16% 26% 14%	2461
	11th to 20th	Night	35% 3 7% 17% 27% 12%	2554
	21st to end	Night	35% 4 8% 20% 22% 11%	2730
December	1st to 10th	Night	34% 4 8% 13% 30% 11%	4380
	11th to 20th	Night	43% 4 9% 17% 19% 8%	4954
	21st to end	Night	41% 5% 6% 21% 24% 3	6633

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	17% 11% 45% 21% 5% 1	330
	11th to 20th	Day	14% 13% 39% 24% 9% 1	330
	21st to end	Day	22% 15% 39% 21% 3 1	363
February	1st to 10th	Day	17% 10% 40% 24% 8% 1	330
	11th to 20th	Day	28% 11% 38% 18% 4	330
	21st to end	Day	19% 13% 38% 25% 5% 1	388
March	1st to 10th	Day	17% 10% 30% 26% 16% 2	540
	11th to 20th	Day	14% 9% 38% 26% 11% 1	540
	21st to end	Day	15% 9% 36% 27% 11% 2	594
April	1st to 10th	Day	13% 12% 29% 29% 13% 4	540
	11th to 20th	Day	10% 9% 26% 26% 22% 8%	532
	21st to end	Day	9% 5% 23% 29% 21% 14%	540
May	1st to 10th	Day	7% 9% 28% 28% 18% 10%	543
	11th to 20th	Day	15% 3 16% 25% 25% 16%	567
	21st to end	Day	12% 3 15% 22% 25% 22%	617
June	1st to 10th	Day	12% 3 11% 24% 31% 19%	570
	11th to 20th	Day	9% 1 13% 26% 26% 25%	570
	21st to end	Day	6% 1 8% 26% 32% 26%	570
July	1st to 10th	Day	9% 2 5% 18% 30% 36%	565
	11th to 20th	Day	9% 1 2 15% 36% 37%	564
	21st to end	Day	6% 3 5% 22% 37% 27%	620
August	1st to 10th	Day	15% 3 8% 17% 32% 26%	566
	11th to 20th	Day	10% 2 3 17% 36% 32%	535
	21st to end	Day	14% 3 7% 18% 32% 26%	583
September	1st to 10th	Day	10% 3 9% 24% 34% 20%	530
	11th to 20th	Day	16% 1 10% 27% 32% 15%	530
	21st to end	Day	20% 3 8% 26% 29% 14%	530
October	1st to 10th	Day	15% 3 18% 31% 23% 10%	530
	11th to 20th	Day	12% 3 20% 30% 26% 10%	530
	21st to end	Day	12% 4 22% 29% 24% 8%	583
November	1st to 10th	Day	15% 5% 24% 29% 19% 8%	535
	11th to 20th	Day	17% 6% 33% 29% 13% 3	503
	21st to end	Day	12% 8% 31% 31% 15% 3	330
December	1st to 10th	Day	21% 6% 34% 27% 10% 2	330
	11th to 20th	Day	18% 10% 32% 28% 8% 3	330
	21st to end	Day	20% 10% 34% 21% 12% 2	363
January	1st to 10th	Night	16% 11% 35% 32% 6%	840
	11th to 20th	Night	16% 12% 31% 33% 8%	840
	21st to end	Night	19% 10% 38% 30% 2	924
February	1st to 10th	Night	19% 8% 32% 34% 7%	840
	11th to 20th	Night	20% 12% 36% 29% 3	823
	21st to end	Night	16% 12% 37% 30% 5%	692
March	1st to 10th	Night	15% 8% 34% 34% 9%	840
	11th to 20th	Night	13% 9% 36% 33% 8%	840
	21st to end	Night	14% 9% 35% 34% 8%	924
April	1st to 10th	Night	13% 11% 30% 35% 11%	840
	11th to 20th	Night	12% 8% 27% 36% 16% 1	831
	21st to end	Night	10% 6% 28% 40% 15% 1	816
May	1st to 10th	Night	9% 5% 23% 46% 17% 1	630
	11th to 20th	Night	12% 4 23% 36% 22% 3	621
	21st to end	Night	9% 2 10% 37% 36% 5%	683
June	1st to 10th	Night	12% 2 9% 41% 30% 5%	630
	11th to 20th	Night	11% 1 9% 34% 34% 10%	630
	21st to end	Night	7% 2 7% 35% 40% 9%	630
July	1st to 10th	Night	9% 2 5% 29% 48% 7%	615
	11th to 20th	Night	8% 2 3 26% 50% 11%	612
	21st to end	Night	6% 2 4 34% 44% 9%	690
August	1st to 10th	Night	12% 2 4 29% 44% 10%	627
	11th to 20th	Night	9% 2 2 26% 50% 11%	609
	21st to end	Night	13% 3 6% 28% 40% 10%	880
September	1st to 10th	Night	11% 1 9% 29% 43% 7%	800
	11th to 20th	Night	12% 3 9% 32% 38% 7%	800
	21st to end	Night	20% 2 9% 33% 31% 4	800
October	1st to 10th	Night	16% 2 16% 33% 28% 5%	800
	11th to 20th	Night	14% 4 20% 34% 25% 3	800
	21st to end	Night	12% 5% 22% 33% 25% 3	880
November	1st to 10th	Night	15% 6% 22% 35% 19% 4	820
	11th to 20th	Night	18% 6% 26% 35% 14% 1	840
	21st to end	Night	13% 6% 30% 33% 16% 2	840
December	1st to 10th	Night	19% 7% 29% 32% 12%	840
	11th to 20th	Night	19% 7% 27% 35% 12% 1	840
	21st to end	Night	21% 9% 27% 33% 9% 1	924

Page generated at 2026-08-12 03:37:16. Version ac07

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