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 2024-11-12.

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% 10% 4 9% 6% 5% 5% 4 6% 7% 33%	101907
	Night	10% 11% 4 10% 6% 5% 5% 4 6% 7% 31%	97425
Transparency	Day	48% 6% 15% 23% 8%	105347
	Night	50% 6% 14% 22% 8% 1	102080
Seeing	Day	17% 16% 35% 22% 8% 2	16252
	Night	16% 12% 35% 26% 9% 1	26167

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	6% 15% 7% 15% 6% 6% 6% 5% 6% 6% 22%	2218
	11th to 20th	Day	4 8% 6% 16% 10% 11% 11% 6% 7% 8% 13%	2220
	21st to end	Day	8% 19% 10% 18% 6% 5% 4 2 5% 6% 17%	2732
February	1st to 10th	Day	6% 13% 6% 13% 8% 5% 8% 5% 7% 8% 22%	1708
	11th to 20th	Day	7% 10% 4 10% 8% 7% 7% 6% 7% 7% 28%	1664
	21st to end	Day	5% 13% 4 13% 9% 8% 6% 5% 5% 6% 27%	1441
March	1st to 10th	Day	11% 12% 3 9% 11% 6% 4 3 5% 5% 29%	3278
	11th to 20th	Day	6% 9% 4 13% 9% 5% 5% 5% 5% 8% 31%	3480
	21st to end	Day	11% 17% 5% 9% 5% 4 4 3 4 6% 30%	3814
April	1st to 10th	Day	11% 13% 4 8% 6% 4 4 3 5% 6% 34%	2288
	11th to 20th	Day	13% 12% 4 8% 6% 5% 4 4 6% 6% 31%	2442
	21st to end	Day	18% 10% 3 8% 6% 4 4 4 7% 6% 30%	2470
May	1st to 10th	Day	17% 10% 4 7% 4 5% 4 3 5% 7% 35%	4301
	11th to 20th	Day	18% 9% 3 7% 5% 5% 5% 4 5% 7% 32%	4475
	21st to end	Day	19% 12% 3 6% 5% 4 4 3 5% 6% 33%	5173
June	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 8% 34%	2850
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 5% 6% 7% 34%	2850
	21st to end	Day	14% 7% 3 7% 6% 5% 6% 6% 7% 9% 31%	2850
July	1st to 10th	Day	8% 4 2 6% 6% 5% 6% 5% 7% 10% 41%	4750
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 9% 49%	4750
	21st to end	Day	8% 6% 3 5% 5% 5% 5% 5% 7% 8% 44%	5151
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 9% 44%	4151
	11th to 20th	Day	11% 5% 2 5% 5% 5% 5% 4 7% 9% 42%	4041
	21st to end	Day	14% 5% 2 6% 4 4 5% 3 6% 9% 42%	4532
September	1st to 10th	Day	11% 6% 2 6% 3 3 5% 4 7% 7% 45%	2333
	11th to 20th	Day	14% 7% 3 7% 5% 4 5% 4 6% 8% 37%	2123
	21st to end	Day	18% 9% 3 6% 4 3 3 3 5% 7% 39%	2086
October	1st to 10th	Day	17% 12% 4 7% 5% 5% 5% 3 4 6% 32%	1900
	11th to 20th	Day	14% 16% 4 8% 4 4 3 3 4 6% 32%	1900
	21st to end	Day	16% 17% 5% 11% 5% 4 5% 3 5% 5% 25%	1898
November	1st to 10th	Day	13% 19% 4 10% 5% 4 5% 4 4 6% 26%	1567
	11th to 20th	Day	11% 16% 7% 15% 8% 5% 4 3 4 6% 22%	1528
	21st to end	Day	12% 15% 5% 13% 10% 7% 4 3 5% 5% 20%	1492
December	1st to 10th	Day	7% 14% 5% 16% 9% 6% 5% 5% 7% 7% 18%	1330
	11th to 20th	Day	8% 16% 8% 16% 7% 5% 5% 3 6% 6% 19%	1679
	21st to end	Day	12% 14% 5% 14% 6% 6% 5% 4 6% 6% 22%	2442
January	1st to 10th	Night	5% 13% 6% 16% 9% 10% 8% 5% 6% 6% 17%	4737
	11th to 20th	Night	5% 13% 6% 15% 11% 11% 9% 6% 8% 6% 10%	4750
	21st to end	Night	8% 20% 8% 15% 6% 6% 5% 5% 6% 5% 16%	4933
February	1st to 10th	Night	7% 12% 4 12% 8% 6% 7% 5% 8% 7% 23%	2471
	11th to 20th	Night	7% 9% 4 10% 6% 6% 7% 6% 7% 7% 31%	2403
	21st to end	Night	6% 9% 5% 14% 9% 7% 6% 4 6% 7% 27%	2029
March	1st to 10th	Night	10% 11% 3 10% 8% 6% 5% 3 6% 6% 31%	3568
	11th to 20th	Night	5% 10% 5% 11% 7% 5% 6% 4 6% 8% 34%	3479
	21st to end	Night	13% 14% 5% 10% 6% 5% 4 3 5% 6% 29%	3817
April	1st to 10th	Night	12% 9% 3 7% 6% 5% 4 4 6% 6% 37%	1887
	11th to 20th	Night	14% 12% 3 7% 5% 4 3 3 5% 6% 36%	1689
	21st to end	Night	13% 10% 3 9% 5% 4 4 4 7% 6% 36%	1710
May	1st to 10th	Night	20% 9% 3 7% 4 4 4 3 5% 6% 36%	2635
	11th to 20th	Night	17% 9% 2 7% 4 4 5% 3 5% 7% 37%	2428
	21st to end	Night	19% 9% 2 6% 4 3 4 3 5% 5% 41%	2414
June	1st to 10th	Night	13% 7% 3 6% 5% 4 4 3 6% 8% 41%	1330
	11th to 20th	Night	12% 6% 2 7% 5% 4 4 4 6% 7% 43%	1330
	21st to end	Night	11% 7% 3 4 4 4 4 4 6% 9% 43%	1330
July	1st to 10th	Night	8% 3 1 4 3 3 4 4 7% 11% 51%	2220
	11th to 20th	Night	5% 2 1 4 3 3 4 3 7% 10% 57%	2220
	21st to end	Night	7% 4 2 5% 4 4 4 5% 7% 9% 50%	2414
August	1st to 10th	Night	5% 4 2 6% 5% 5% 5% 4 7% 9% 48%	2786
	11th to 20th	Night	12% 5% 1 4 3 3 4 4 5% 7% 51%	2798
	21st to end	Night	10% 6% 3 6% 4 4 4 4 6% 9% 45%	3135
September	1st to 10th	Night	11% 5% 2 6% 4 3 3 4 4 7% 52%	1846
	11th to 20th	Night	12% 7% 2 6% 3 4 4 4 6% 8% 43%	2054
	21st to end	Night	17% 8% 2 5% 3 4 4 4 5% 6% 42%	2090
October	1st to 10th	Night	16% 10% 3 6% 4 5% 5% 3 5% 6% 36%	2265
	11th to 20th	Night	16% 12% 4 9% 4 4 4 4 4 7% 32%	2280
	21st to end	Night	15% 15% 5% 9% 4 4 4 4 5% 6% 28%	2695
November	1st to 10th	Night	13% 16% 6% 10% 6% 4 4 3 4 6% 27%	2731
	11th to 20th	Night	10% 15% 7% 15% 8% 5% 4 3 5% 5% 22%	2675
	21st to end	Night	11% 14% 6% 14% 8% 5% 6% 4 5% 5% 21%	2683
December	1st to 10th	Night	7% 14% 5% 16% 10% 8% 7% 5% 6% 6% 16%	2850
	11th to 20th	Night	9% 15% 6% 16% 9% 6% 6% 5% 6% 6% 17%	3518
	21st to end	Night	11% 13% 5% 16% 8% 7% 6% 4 6% 6% 20%	5225

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	60% 7% 11% 17% 4	2219
	11th to 20th	Day	67% 7% 11% 13% 3	2220
	21st to end	Day	67% 5% 9% 14% 5%	2732
February	1st to 10th	Day	57% 7% 11% 15% 9% 1	1708
	11th to 20th	Day	51% 7% 14% 19% 9%	1673
	21st to end	Day	55% 7% 11% 16% 9% 1	1441
March	1st to 10th	Day	56% 4 14% 19% 7%	3280
	11th to 20th	Day	49% 7% 15% 20% 9%	3480
	21st to end	Day	55% 5% 9% 22% 9%	3814
April	1st to 10th	Day	50% 4 9% 24% 12% 1	2288
	11th to 20th	Day	51% 4 12% 21% 11% 1	2442
	21st to end	Day	52% 6% 12% 20% 8% 1	2470
May	1st to 10th	Day	48% 6% 11% 23% 11% 1	4312
	11th to 20th	Day	50% 7% 11% 20% 12% 1	4479
	21st to end	Day	51% 6% 10% 23% 9% 1	5173
June	1st to 10th	Day	45% 7% 16% 21% 10% 1	2850
	11th to 20th	Day	47% 7% 13% 23% 9% 1	2850
	21st to end	Day	46% 9% 17% 22% 7%	2850
July	1st to 10th	Day	35% 9% 22% 28% 6%	4676
	11th to 20th	Day	30% 7% 22% 34% 8%	4669
	21st to end	Day	36% 7% 18% 33% 6%	4988
August	1st to 10th	Day	35% 7% 18% 30% 10% 1	4134
	11th to 20th	Day	36% 7% 22% 29% 5%	4080
	21st to end	Day	38% 5% 22% 28% 6%	4531
September	1st to 10th	Day	36% 7% 16% 32% 9% 1	2333
	11th to 20th	Day	44% 6% 20% 24% 5%	2123
	21st to end	Day	45% 5% 13% 30% 6%	2086
October	1st to 10th	Day	42% 3 15% 29% 11%	3160
	11th to 20th	Day	45% 4 14% 23% 14%	3140
	21st to end	Day	52% 5% 15% 23% 5%	3107
November	1st to 10th	Day	60% 5% 12% 17% 4 1	1567
	11th to 20th	Day	64% 5% 15% 12% 4	1528
	21st to end	Day	66% 5% 14% 11% 3	1492
December	1st to 10th	Day	63% 7% 12% 13% 4	1330
	11th to 20th	Day	64% 5% 14% 14% 3	1680
	21st to end	Day	62% 4 10% 19% 5%	2442
January	1st to 10th	Night	64% 8% 12% 12% 3	4737
	11th to 20th	Night	70% 7% 7% 13% 3	4750
	21st to end	Night	68% 6% 12% 11% 3	4933
February	1st to 10th	Night	54% 6% 13% 17% 9% 1	2471
	11th to 20th	Night	47% 7% 16% 19% 10%	2404
	21st to end	Night	54% 6% 11% 19% 10%	2029
March	1st to 10th	Night	52% 6% 13% 19% 11% 1	3579
	11th to 20th	Night	43% 9% 17% 22% 9%	3480
	21st to end	Night	56% 5% 10% 19% 10% 1	3817
April	1st to 10th	Night	45% 5% 10% 23% 16% 2	1887
	11th to 20th	Night	49% 3 8% 21% 16% 2	1689
	21st to end	Night	46% 5% 11% 26% 10% 1	1710
May	1st to 10th	Night	47% 6% 10% 24% 13% 1	2643
	11th to 20th	Night	45% 7% 10% 25% 11% 1	2429
	21st to end	Night	44% 6% 10% 27% 12% 1	2414
June	1st to 10th	Night	40% 6% 16% 24% 12% 1	1330
	11th to 20th	Night	39% 7% 15% 24% 14% 1	1330
	21st to end	Night	36% 7% 21% 27% 8% 1	1330
July	1st to 10th	Night	25% 9% 24% 34% 6% 1	2185
	11th to 20th	Night	21% 6% 22% 41% 9%	2178
	21st to end	Night	29% 8% 21% 34% 8% 1	2337
August	1st to 10th	Night	31% 6% 17% 35% 11% 1	2779
	11th to 20th	Night	31% 6% 25% 31% 7%	2825
	21st to end	Night	35% 5% 21% 30% 8%	3135
September	1st to 10th	Night	33% 5% 15% 34% 13%	1846
	11th to 20th	Night	38% 6% 19% 27% 9%	2054
	21st to end	Night	42% 6% 13% 29% 10%	2090
October	1st to 10th	Night	41% 4 10% 33% 11%	3785
	11th to 20th	Night	44% 4 13% 31% 8%	3779
	21st to end	Night	50% 5% 12% 26% 7%	4445
November	1st to 10th	Night	58% 4 14% 17% 6% 1	2731
	11th to 20th	Night	64% 5% 12% 14% 5% 1	2675
	21st to end	Night	64% 7% 13% 11% 5%	2683
December	1st to 10th	Night	65% 8% 13% 11% 4	2850
	11th to 20th	Night	65% 6% 11% 13% 4	3516
	21st to end	Night	63% 6% 9% 15% 6%	5225

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% 22% 7% 2	270
	11th to 20th	Day	12% 18% 39% 26% 6%	270
	21st to end	Day	16% 14% 38% 23% 7% 2	297
February	1st to 10th	Day	15% 18% 41% 23% 2 1	270
	11th to 20th	Day	14% 23% 39% 17% 6% 1	270
	21st to end	Day	14% 25% 39% 16% 6% 1	225
March	1st to 10th	Day	18% 18% 41% 17% 4 1	270
	11th to 20th	Day	16% 19% 41% 17% 6% 1	270
	21st to end	Day	17% 19% 40% 17% 6% 1	297
April	1st to 10th	Day	14% 20% 38% 20% 7% 1	468
	11th to 20th	Day	21% 21% 33% 21% 5%	640
	21st to end	Day	21% 19% 33% 19% 6% 1	650
May	1st to 10th	Day	22% 18% 34% 20% 5% 2	653
	11th to 20th	Day	23% 15% 33% 20% 7% 2	675
	21st to end	Day	22% 14% 33% 24% 6% 1	734
June	1st to 10th	Day	18% 16% 31% 23% 9% 3	680
	11th to 20th	Day	22% 14% 39% 19% 5% 2	680
	21st to end	Day	15% 14% 32% 26% 10% 3	680
July	1st to 10th	Day	10% 12% 33% 25% 14% 5%	671
	11th to 20th	Day	13% 15% 29% 28% 11% 3	668
	21st to end	Day	10% 9% 36% 27% 13% 5%	739
August	1st to 10th	Day	11% 9% 34% 28% 15% 3	676
	11th to 20th	Day	14% 9% 30% 29% 14% 6%	665
	21st to end	Day	16% 11% 33% 26% 12% 1	748
September	1st to 10th	Day	13% 12% 38% 25% 10% 2	543
	11th to 20th	Day	18% 16% 39% 20% 6%	333
	21st to end	Day	25% 16% 39% 17% 4	300
October	1st to 10th	Day	23% 17% 36% 15% 7% 2	300
	11th to 20th	Day	19% 19% 39% 19% 4	300
	21st to end	Day	28% 18% 33% 17% 4	330
November	1st to 10th	Day	23% 18% 36% 17% 6% 1	300
	11th to 20th	Day	22% 22% 35% 18% 3	273
	21st to end	Day	24% 24% 34% 14% 3	270
December	1st to 10th	Day	15% 17% 39% 22% 6% 1	270
	11th to 20th	Day	17% 20% 46% 13% 4	270
	21st to end	Day	15% 16% 38% 19% 9% 2	297
January	1st to 10th	Night	11% 16% 37% 24% 11% 1	950
	11th to 20th	Night	14% 13% 43% 23% 7% 1	950
	21st to end	Night	14% 16% 39% 24% 6%	1045
February	1st to 10th	Night	13% 14% 37% 28% 9%	950
	11th to 20th	Night	13% 14% 37% 25% 9% 2	929
	21st to end	Night	10% 17% 40% 24% 8% 1	773
March	1st to 10th	Night	16% 13% 33% 27% 9% 1	670
	11th to 20th	Night	12% 15% 43% 21% 8% 1	570
	21st to end	Night	19% 13% 30% 26% 10% 2	627
April	1st to 10th	Night	16% 13% 36% 26% 9% 1	570
	11th to 20th	Night	21% 11% 33% 26% 9%	563
	21st to end	Night	17% 12% 34% 27% 9%	570
May	1st to 10th	Night	20% 10% 38% 24% 8%	570
	11th to 20th	Night	20% 11% 33% 28% 8% 1	561
	21st to end	Night	22% 10% 34% 27% 6% 1	617
June	1st to 10th	Night	16% 10% 30% 31% 12% 1	570
	11th to 20th	Night	15% 8% 35% 30% 12%	570
	21st to end	Night	14% 6% 28% 35% 15% 2	570
July	1st to 10th	Night	7% 5% 31% 36% 20% 1	555
	11th to 20th	Night	9% 8% 30% 37% 16% 2	552
	21st to end	Night	8% 5% 29% 37% 18% 3	624
August	1st to 10th	Night	9% 4 31% 39% 16% 2	567
	11th to 20th	Night	13% 7% 27% 30% 20% 4	564
	21st to end	Night	14% 7% 29% 34% 15%	627
September	1st to 10th	Night	14% 6% 35% 31% 12% 2	570
	11th to 20th	Night	17% 10% 32% 29% 11%	570
	21st to end	Night	22% 12% 33% 24% 9% 1	570
October	1st to 10th	Night	23% 13% 36% 21% 6%	745
	11th to 20th	Night	23% 11% 37% 21% 7% 1	760
	21st to end	Night	25% 13% 33% 22% 6% 1	1012
November	1st to 10th	Night	21% 16% 34% 21% 8% 1	975
	11th to 20th	Night	19% 16% 36% 22% 7% 1	956
	21st to end	Night	20% 20% 38% 16% 5% 1	950
December	1st to 10th	Night	14% 13% 40% 24% 7% 1	950
	11th to 20th	Night	18% 17% 39% 19% 5% 1	950
	21st to end	Night	19% 14% 37% 22% 7% 1	1045

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