Sandi South Woodridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sandi South Woodridge clear sky chart from 2005-11-06 to 2025-12-18.

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	11% 10% 4 9% 6% 5% 5% 4 6% 7% 34%	127615
	Night	10% 11% 4 11% 6% 5% 5% 4 6% 6% 30%	123679
Transparency	Day	48% 6% 14% 23% 9% 1	131034
	Night	51% 5% 13% 21% 9% 1	128357
Seeing	Day	18% 16% 35% 22% 8% 2	17767
	Night	16% 13% 35% 26% 9% 1	27726

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	4 13% 8% 16% 6% 6% 7% 6% 6% 5% 23%	3178
	11th to 20th	Day	4 9% 6% 16% 9% 9% 10% 7% 10% 8% 12%	3152
	21st to end	Day	5% 17% 10% 18% 7% 7% 6% 3 5% 6% 16%	3928
February	1st to 10th	Day	6% 12% 5% 12% 8% 6% 8% 6% 7% 7% 21%	1798
	11th to 20th	Day	6% 9% 4 10% 8% 7% 6% 6% 8% 7% 28%	1754
	21st to end	Day	4 13% 3 13% 9% 8% 6% 5% 5% 6% 27%	1515
March	1st to 10th	Day	9% 12% 3 9% 9% 5% 4 3 5% 6% 35%	4713
	11th to 20th	Day	9% 9% 4 12% 8% 5% 5% 5% 5% 9% 30%	4980
	21st to end	Day	12% 15% 5% 10% 5% 5% 4 3 5% 6% 31%	5464
April	1st to 10th	Day	11% 13% 4 8% 6% 4 4 4 5% 6% 33%	2409
	11th to 20th	Day	13% 12% 4 9% 6% 5% 4 4 6% 6% 31%	2572
	21st to end	Day	19% 10% 3 8% 5% 4 4 4 6% 6% 30%	2600
May	1st to 10th	Day	13% 8% 3 6% 3 4 4 3 5% 6% 45%	6165
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 5% 8% 34%	6421
	21st to end	Day	14% 9% 2 6% 4 4 4 3 5% 6% 42%	7428
June	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 8% 35%	3000
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	3000
	21st to end	Day	14% 7% 3 7% 6% 5% 6% 6% 7% 9% 31%	3000
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	6799
	11th to 20th	Day	11% 5% 3 6% 4 4 5% 4 6% 8% 43%	6800
	21st to end	Day	10% 6% 3 6% 5% 5% 5% 5% 7% 8% 41%	7406
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 9% 44%	4282
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 4 7% 9% 41%	4171
	21st to end	Day	14% 6% 2 6% 4 4 5% 3 6% 9% 42%	4675
September	1st to 10th	Day	11% 6% 2 7% 4 3 5% 4 7% 7% 45%	2456
	11th to 20th	Day	15% 8% 3 7% 5% 4 5% 4 6% 8% 36%	2235
	21st to end	Day	17% 8% 3 6% 4 3 3 3 5% 7% 40%	2196
October	1st to 10th	Day	17% 12% 4 7% 5% 5% 5% 3 4 6% 33%	2000
	11th to 20th	Day	15% 16% 4 7% 4 4 3 3 4 6% 32%	2000
	21st to end	Day	16% 17% 5% 11% 5% 4 4 3 5% 5% 25%	1997
November	1st to 10th	Day	13% 19% 4 10% 5% 4 4 4 3 5% 26%	1647
	11th to 20th	Day	12% 16% 6% 14% 7% 5% 4 3 4 5% 24%	1680
	21st to end	Day	11% 15% 6% 15% 10% 7% 5% 3 5% 5% 19%	1648
December	1st to 10th	Day	11% 15% 5% 16% 12% 8% 4 4 6% 6% 13%	2360
	11th to 20th	Day	8% 16% 6% 15% 7% 4 4 5% 7% 6% 22%	2688
	21st to end	Day	10% 15% 7% 19% 8% 6% 4 3 5% 5% 18%	3498
January	1st to 10th	Night	4 12% 6% 17% 9% 10% 7% 6% 6% 6% 16%	6787
	11th to 20th	Night	4 14% 6% 13% 9% 9% 10% 9% 11% 5% 9%	6753
	21st to end	Night	7% 20% 7% 15% 7% 6% 5% 4 7% 6% 17%	7048
February	1st to 10th	Night	7% 12% 4 11% 8% 7% 7% 5% 8% 7% 23%	2601
	11th to 20th	Night	7% 9% 3 9% 6% 6% 7% 6% 8% 8% 30%	2533
	21st to end	Night	6% 10% 5% 14% 9% 7% 7% 4 6% 7% 27%	2132
March	1st to 10th	Night	7% 11% 4 10% 8% 6% 6% 4 6% 6% 31%	5138
	11th to 20th	Night	6% 11% 5% 11% 7% 5% 6% 4 6% 8% 31%	4979
	21st to end	Night	13% 14% 5% 11% 5% 4 4 3 5% 5% 31%	5467
April	1st to 10th	Night	12% 10% 3 8% 6% 5% 4 4 5% 6% 37%	1986
	11th to 20th	Night	14% 12% 3 8% 5% 4 3 3 5% 6% 36%	1779
	21st to end	Night	13% 10% 4 9% 5% 4 4 4 7% 6% 36%	1800
May	1st to 10th	Night	15% 8% 3 6% 3 3 3 3 4 6% 46%	3781
	11th to 20th	Night	16% 9% 2 7% 5% 5% 4 3 5% 7% 37%	3492
	21st to end	Night	14% 7% 2 5% 3 3 4 3 6% 6% 47%	3470
June	1st to 10th	Night	12% 7% 3 6% 5% 4 4 3 6% 8% 42%	1400
	11th to 20th	Night	12% 6% 2 7% 5% 4 4 4 6% 7% 43%	1400
	21st to end	Night	11% 7% 3 5% 4 4 5% 4 6% 9% 42%	1400
July	1st to 10th	Night	9% 4 2 5% 3 4 4 4 6% 9% 50%	3180
	11th to 20th	Night	7% 3 2 4 3 4 4 4 7% 10% 51%	3180
	21st to end	Night	7% 5% 2 6% 4 4 4 4 7% 9% 47%	3469
August	1st to 10th	Night	5% 4 2 5% 5% 5% 5% 4 7% 9% 48%	2874
	11th to 20th	Night	12% 5% 1 4 3 3 4 4 5% 7% 51%	2888
	21st to end	Night	10% 6% 3 6% 4 4 4 4 6% 8% 45%	3234
September	1st to 10th	Night	11% 5% 2 6% 4 3 3 4 4 7% 52%	1943
	11th to 20th	Night	13% 8% 2 6% 3 4 4 4 6% 8% 42%	2162
	21st to end	Night	17% 7% 2 5% 3 3 4 4 4 6% 43%	2200
October	1st to 10th	Night	15% 9% 3 6% 4 5% 5% 3 5% 6% 37%	2384
	11th to 20th	Night	16% 12% 4 9% 4 4 4 3 4 7% 32%	2400
	21st to end	Night	16% 15% 5% 9% 4 4 4 4 5% 6% 28%	2838
November	1st to 10th	Night	13% 15% 6% 11% 6% 4 4 3 4 6% 27%	2871
	11th to 20th	Night	11% 15% 7% 14% 7% 5% 4 3 5% 6% 24%	2940
	21st to end	Night	11% 14% 6% 16% 9% 5% 6% 3 5% 5% 20%	2966
December	1st to 10th	Night	8% 16% 6% 18% 13% 8% 5% 4 5% 4 12%	5050
	11th to 20th	Night	7% 14% 6% 16% 9% 6% 6% 6% 7% 5% 19%	5674
	21st to end	Night	9% 13% 8% 21% 9% 7% 5% 4 5% 5% 16%	7480

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	62% 5% 8% 16% 9%	3179
	11th to 20th	Day	64% 5% 9% 17% 5%	3180
	21st to end	Day	69% 5% 9% 13% 4	3928
February	1st to 10th	Day	58% 7% 11% 15% 9% 1	1798
	11th to 20th	Day	50% 6% 14% 20% 9%	1763
	21st to end	Day	55% 7% 12% 16% 9% 1	1515
March	1st to 10th	Day	50% 3 16% 16% 12% 2	4715
	11th to 20th	Day	50% 6% 15% 19% 10%	4980
	21st to end	Day	54% 4 8% 22% 11% 1	5464
April	1st to 10th	Day	50% 4 9% 23% 12% 1	2409
	11th to 20th	Day	51% 4 11% 21% 11% 1	2572
	21st to end	Day	53% 6% 12% 20% 9% 1	2600
May	1st to 10th	Day	39% 5% 10% 26% 19% 1	6176
	11th to 20th	Day	47% 6% 10% 23% 14%	6425
	21st to end	Day	41% 5% 8% 25% 17% 3	7428
June	1st to 10th	Day	45% 7% 16% 22% 10% 1	3000
	11th to 20th	Day	46% 7% 14% 24% 9% 1	3000
	21st to end	Day	46% 8% 17% 22% 7%	3000
July	1st to 10th	Day	34% 8% 23% 29% 6%	6726
	11th to 20th	Day	37% 6% 20% 31% 6%	6719
	21st to end	Day	39% 7% 19% 29% 6%	7193
August	1st to 10th	Day	35% 7% 18% 30% 10% 1	4265
	11th to 20th	Day	37% 7% 22% 29% 5%	4210
	21st to end	Day	38% 5% 22% 28% 6%	4674
September	1st to 10th	Day	37% 7% 16% 31% 9% 1	2456
	11th to 20th	Day	46% 6% 20% 23% 5%	2235
	21st to end	Day	44% 5% 13% 31% 6%	2196
October	1st to 10th	Day	41% 3 15% 29% 11%	3260
	11th to 20th	Day	45% 4 14% 23% 14%	3240
	21st to end	Day	53% 5% 15% 22% 5%	3206
November	1st to 10th	Day	60% 5% 12% 17% 5% 1	1647
	11th to 20th	Day	63% 5% 15% 12% 5% 1	1680
	21st to end	Day	67% 5% 14% 11% 3	1648
December	1st to 10th	Day	71% 7% 11% 8% 2	2360
	11th to 20th	Day	60% 4 12% 16% 8%	2689
	21st to end	Day	69% 3 8% 16% 4	3498
January	1st to 10th	Night	66% 6% 10% 10% 8%	6787
	11th to 20th	Night	68% 5% 7% 16% 4	6800
	21st to end	Night	67% 5% 11% 12% 5%	7048
February	1st to 10th	Night	55% 6% 12% 17% 9% 1	2601
	11th to 20th	Night	47% 7% 16% 20% 10%	2534
	21st to end	Night	54% 6% 11% 19% 10%	2132
March	1st to 10th	Night	51% 6% 15% 16% 10% 3	5149
	11th to 20th	Night	48% 7% 15% 20% 10%	4980
	21st to end	Night	55% 5% 8% 20% 11% 1	5467
April	1st to 10th	Night	45% 5% 10% 23% 15% 2	1986
	11th to 20th	Night	49% 3 8% 22% 15% 2	1779
	21st to end	Night	46% 5% 11% 27% 10% 2	1800
May	1st to 10th	Night	38% 5% 10% 26% 21% 1	3789
	11th to 20th	Night	45% 6% 9% 23% 16% 1	3493
	21st to end	Night	36% 5% 9% 26% 20% 4	3470
June	1st to 10th	Night	40% 6% 16% 25% 13% 1	1400
	11th to 20th	Night	39% 7% 15% 25% 13% 1	1400
	21st to end	Night	37% 7% 21% 26% 8% 1	1400
July	1st to 10th	Night	29% 8% 23% 31% 5% 3	3145
	11th to 20th	Night	28% 5% 20% 39% 7%	3138
	21st to end	Night	32% 7% 21% 31% 7% 1	3368
August	1st to 10th	Night	31% 6% 17% 35% 11% 1	2867
	11th to 20th	Night	31% 6% 25% 31% 7%	2915
	21st to end	Night	35% 5% 21% 30% 8%	3234
September	1st to 10th	Night	32% 6% 15% 34% 13%	1943
	11th to 20th	Night	39% 7% 19% 26% 9%	2162
	21st to end	Night	41% 6% 13% 29% 10%	2200
October	1st to 10th	Night	41% 4 11% 33% 11%	3904
	11th to 20th	Night	45% 4 13% 30% 8%	3899
	21st to end	Night	51% 5% 12% 26% 6%	4588
November	1st to 10th	Night	58% 4 13% 17% 6% 1	2871
	11th to 20th	Night	63% 5% 12% 15% 5% 1	2940
	21st to end	Night	66% 6% 13% 11% 5%	2966
December	1st to 10th	Night	75% 5% 9% 9% 2	5050
	11th to 20th	Night	63% 5% 11% 11% 10%	5672
	21st to end	Night	70% 5% 7% 14% 4	7480

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	11% 18% 40% 23% 7% 2	300
	11th to 20th	Day	12% 17% 39% 26% 6%	300
	21st to end	Day	17% 18% 37% 21% 6% 2	330
February	1st to 10th	Day	16% 19% 40% 22% 2 1	300
	11th to 20th	Day	12% 21% 41% 18% 6% 2	300
	21st to end	Day	14% 26% 39% 14% 5% 1	249
March	1st to 10th	Day	17% 19% 41% 17% 5% 1	300
	11th to 20th	Day	16% 20% 40% 17% 5% 1	300
	21st to end	Day	18% 20% 39% 16% 6% 1	330
April	1st to 10th	Day	16% 19% 38% 19% 6% 1	509
	11th to 20th	Day	21% 21% 33% 20% 4	690
	21st to end	Day	23% 18% 32% 20% 6% 1	700
May	1st to 10th	Day	21% 18% 35% 20% 5% 1	703
	11th to 20th	Day	23% 16% 34% 18% 7% 2	725
	21st to end	Day	20% 14% 34% 24% 7% 1	789
June	1st to 10th	Day	18% 16% 32% 23% 9% 2	730
	11th to 20th	Day	21% 14% 39% 20% 5% 2	730
	21st to end	Day	16% 14% 32% 25% 9% 3	730
July	1st to 10th	Day	10% 12% 35% 25% 14% 5%	721
	11th to 20th	Day	14% 15% 30% 27% 11% 3	718
	21st to end	Day	10% 9% 37% 26% 13% 5%	794
August	1st to 10th	Day	11% 10% 33% 28% 15% 3	726
	11th to 20th	Day	13% 9% 31% 27% 14% 5%	715
	21st to end	Day	16% 11% 33% 26% 12% 1	803
September	1st to 10th	Day	14% 12% 37% 25% 10% 2	586
	11th to 20th	Day	21% 16% 38% 19% 6%	365
	21st to end	Day	23% 15% 39% 17% 5% 2	330
October	1st to 10th	Day	22% 16% 38% 15% 7% 2	330
	11th to 20th	Day	22% 20% 38% 18% 3	330
	21st to end	Day	29% 18% 33% 17% 4	363
November	1st to 10th	Day	25% 19% 34% 16% 5% 1	330
	11th to 20th	Day	25% 20% 34% 17% 3	330
	21st to end	Day	22% 25% 35% 15% 2	330
December	1st to 10th	Day	17% 19% 38% 20% 5% 1	330
	11th to 20th	Day	19% 18% 47% 13% 3	321
	21st to end	Day	16% 16% 38% 18% 10% 2	330
January	1st to 10th	Night	11% 17% 37% 24% 10% 2	1000
	11th to 20th	Night	14% 13% 43% 24% 6% 1	1000
	21st to end	Night	14% 16% 39% 24% 6%	1100
February	1st to 10th	Night	13% 15% 37% 27% 8%	1000
	11th to 20th	Night	12% 14% 38% 26% 9% 2	979
	21st to end	Night	11% 17% 40% 23% 8% 1	812
March	1st to 10th	Night	16% 14% 33% 26% 9% 1	705
	11th to 20th	Night	12% 16% 43% 21% 7% 1	600
	21st to end	Night	19% 14% 30% 26% 10% 2	660
April	1st to 10th	Night	16% 13% 35% 27% 8% 1	600
	11th to 20th	Night	21% 11% 33% 25% 9%	593
	21st to end	Night	17% 13% 34% 27% 9%	600
May	1st to 10th	Night	19% 10% 38% 24% 8%	600
	11th to 20th	Night	20% 11% 33% 27% 8% 1	591
	21st to end	Night	21% 9% 34% 28% 7% 1	650
June	1st to 10th	Night	16% 11% 31% 31% 12% 1	600
	11th to 20th	Night	14% 8% 35% 32% 11%	600
	21st to end	Night	15% 6% 29% 35% 14% 2	600
July	1st to 10th	Night	7% 5% 31% 36% 20% 1	585
	11th to 20th	Night	9% 8% 30% 37% 15% 2	582
	21st to end	Night	8% 5% 29% 38% 18% 2	657
August	1st to 10th	Night	9% 4 30% 39% 16% 2	597
	11th to 20th	Night	13% 6% 28% 30% 19% 4	594
	21st to end	Night	15% 7% 28% 35% 15%	660
September	1st to 10th	Night	14% 6% 35% 31% 12% 2	600
	11th to 20th	Night	18% 10% 33% 29% 11%	600
	21st to end	Night	21% 12% 33% 24% 10% 1	600
October	1st to 10th	Night	22% 14% 37% 21% 6%	784
	11th to 20th	Night	24% 11% 36% 22% 7% 1	800
	21st to end	Night	25% 14% 33% 22% 6% 1	1066
November	1st to 10th	Night	21% 16% 34% 20% 8% 1	1025
	11th to 20th	Night	19% 16% 36% 21% 7% 1	1050
	21st to end	Night	19% 20% 38% 17% 5% 1	1050
December	1st to 10th	Night	14% 14% 40% 24% 7% 1	1050
	11th to 20th	Night	17% 18% 40% 18% 5% 1	1036
	21st to end	Night	19% 13% 37% 22% 7% 1	1100

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