Wishing Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wishing Star Observatory 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	18% 8% 2 6% 4 4 4 3 5% 7% 39%	143320
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 40%	138551
Transparency	Day	44% 6% 12% 21% 15% 3	146855
	Night	44% 5% 11% 21% 16% 3	143092
Seeing	Day	24% 19% 33% 17% 6% 2	17398
	Night	23% 16% 33% 22% 6%	26236

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	11% 10% 3 6% 4 4 4 3 5% 5% 45%	4661
	11th to 20th	Day	16% 9% 3 6% 3 3 3 3 4 4 47%	4650
	21st to end	Day	15% 9% 2 5% 3 3 4 3 4 6% 47%	5124
February	1st to 10th	Day	18% 8% 2 5% 4 4 5% 4 5% 7% 37%	2008
	11th to 20th	Day	14% 8% 2 6% 5% 4 4 4 4 6% 43%	2048
	21st to end	Day	19% 9% 3 5% 4 4 4 3 4 6% 39%	1730
March	1st to 10th	Day	22% 11% 3 5% 3 3 3 2 4 6% 37%	4576
	11th to 20th	Day	17% 9% 2 5% 3 4 4 3 6% 6% 42%	4891
	21st to end	Day	25% 9% 2 6% 4 4 4 3 5% 5% 32%	5885
April	1st to 10th	Day	21% 8% 3 6% 4 3 3 4 5% 7% 38%	2520
	11th to 20th	Day	18% 7% 2 6% 3 4 4 4 5% 6% 40%	2498
	21st to end	Day	20% 7% 3 5% 4 4 4 4 5% 5% 39%	2730
May	1st to 10th	Day	26% 10% 3 7% 4 3 4 3 5% 7% 29%	7639
	11th to 20th	Day	20% 9% 3 6% 4 4 4 3 4 6% 37%	7625
	21st to end	Day	22% 8% 3 6% 5% 4 5% 4 6% 8% 31%	9060
June	1st to 10th	Day	18% 7% 2 6% 3 5% 5% 4 7% 8% 36%	2940
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 5% 6% 9% 37%	2940
	21st to end	Day	15% 6% 2 5% 4 4 5% 4 6% 9% 39%	2940
July	1st to 10th	Day	18% 7% 2 6% 4 4 5% 4 6% 9% 34%	8280
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 11% 40%	8280
	21st to end	Day	16% 7% 2 6% 3 4 4 3 5% 8% 41%	8993
August	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 9% 31%	4366
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 4 6% 8% 37%	4138
	21st to end	Day	7% 4 2 5% 4 5% 6% 5% 6% 9% 47%	4312
September	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 6% 5% 46%	2390
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 5% 6% 51%	2200
	21st to end	Day	20% 6% 2 6% 4 4 5% 3 4 6% 42%	2200
October	1st to 10th	Day	22% 7% 2 4 4 3 4 3 3 5% 44%	2200
	11th to 20th	Day	17% 6% 2 5% 3 3 3 3 5% 7% 47%	1973
	21st to end	Day	18% 5% 2 5% 4 4 4 3 4 6% 44%	1980
November	1st to 10th	Day	16% 7% 2 4 4 3 3 4 4 5% 47%	1851
	11th to 20th	Day	17% 6% 1 5% 4 3 3 3 4 7% 47%	1890
	21st to end	Day	18% 7% 2 5% 4 4 3 3 4 6% 44%	1890
December	1st to 10th	Day	15% 8% 3 5% 3 3 3 2 4 6% 48%	2798
	11th to 20th	Day	19% 7% 2 4 3 2 3 2 4 5% 49%	3066
	21st to end	Day	20% 10% 3 8% 3 3 3 2 4 5% 38%	4048
January	1st to 10th	Night	15% 7% 2 5% 3 3 4 3 4 6% 49%	8234
	11th to 20th	Night	15% 10% 3 8% 4 4 3 3 4 5% 40%	8235
	21st to end	Night	14% 9% 3 7% 4 5% 4 3 4 4 41%	9057
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 4 6% 40%	2605
	11th to 20th	Night	18% 8% 3 5% 4 4 3 4 5% 5% 41%	2458
	21st to end	Night	19% 9% 2 6% 4 4 4 3 4 5% 41%	2076
March	1st to 10th	Night	24% 8% 2 5% 4 3 4 3 4 6% 38%	5484
	11th to 20th	Night	18% 10% 3 6% 4 4 3 3 4 5% 39%	5288
	21st to end	Night	24% 10% 2 6% 4 4 4 3 5% 4 33%	5272
April	1st to 10th	Night	20% 8% 3 6% 4 4 4 3 4 7% 36%	2100
	11th to 20th	Night	19% 9% 2 6% 4 4 4 3 5% 6% 38%	2070
	21st to end	Night	21% 7% 2 7% 4 3 3 4 4 5% 40%	1890
May	1st to 10th	Night	27% 9% 2 6% 4 3 4 3 4 6% 31%	5259
	11th to 20th	Night	19% 9% 2 8% 4 5% 4 3 6% 7% 32%	5235
	21st to end	Night	23% 8% 3 8% 5% 4 5% 4 6% 6% 28%	5155
June	1st to 10th	Night	16% 8% 3 6% 5% 4 4 4 6% 6% 38%	1680
	11th to 20th	Night	18% 7% 3 6% 4 4 4 4 5% 9% 36%	1680
	21st to end	Night	18% 7% 2 5% 4 3 4 4 6% 8% 39%	1680
July	1st to 10th	Night	20% 8% 2 7% 4 4 4 4 6% 9% 32%	4680
	11th to 20th	Night	15% 7% 2 5% 4 4 4 4 6% 8% 40%	4680
	21st to end	Night	15% 7% 2 6% 4 4 4 3 6% 7% 41%	5084
August	1st to 10th	Night	22% 8% 3 6% 4 4 5% 4 6% 8% 30%	2967
	11th to 20th	Night	9% 7% 3 7% 5% 6% 6% 5% 7% 9% 36%	2994
	21st to end	Night	9% 4 1 5% 4 3 3 3 5% 8% 54%	3586
September	1st to 10th	Night	14% 6% 3 7% 4 4 4 4 5% 6% 43%	2010
	11th to 20th	Night	15% 6% 2 6% 3 2 4 2 4 6% 51%	2200
	21st to end	Night	19% 8% 3 5% 4 4 4 3 4 5% 41%	2200
October	1st to 10th	Night	20% 7% 2 6% 4 3 3 3 3 6% 44%	2200
	11th to 20th	Night	16% 5% 2 4 3 4 3 3 5% 7% 47%	2423
	21st to end	Night	20% 8% 2 6% 4 3 4 3 4 6% 41%	2860
November	1st to 10th	Night	15% 5% 2 6% 3 4 4 3 5% 5% 48%	2667
	11th to 20th	Night	17% 7% 2 5% 4 3 3 3 4 6% 47%	2730
	21st to end	Night	16% 6% 2 5% 3 3 4 3 5% 7% 45%	2730
December	1st to 10th	Night	19% 8% 2 4 3 3 3 2 4 5% 47%	4584
	11th to 20th	Night	22% 9% 3 5% 3 3 3 3 4 5% 42%	5348
	21st to end	Night	17% 11% 3 7% 3 3 3 3 4 5% 40%	7150

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	41% 4 9% 24% 19% 3	4662
	11th to 20th	Day	41% 4 9% 20% 18% 8%	4680
	21st to end	Day	40% 3 10% 23% 21% 2	5124
February	1st to 10th	Day	46% 6% 14% 16% 15% 3	2008
	11th to 20th	Day	42% 6% 11% 22% 16% 3	2057
	21st to end	Day	47% 5% 11% 19% 15% 3	1730
March	1st to 10th	Day	49% 4 11% 13% 12% 11%	4579
	11th to 20th	Day	40% 8% 14% 26% 10% 2	4891
	21st to end	Day	54% 4 7% 14% 14% 7%	5885
April	1st to 10th	Day	46% 5% 11% 18% 16% 3	2520
	11th to 20th	Day	43% 6% 10% 20% 17% 3	2498
	21st to end	Day	45% 6% 10% 18% 17% 4	2730
May	1st to 10th	Day	55% 6% 13% 14% 10% 1	7651
	11th to 20th	Day	49% 6% 14% 18% 11% 1	7629
	21st to end	Day	51% 7% 11% 19% 12% 1	9061
June	1st to 10th	Day	44% 8% 12% 22% 13% 1	2940
	11th to 20th	Day	42% 8% 13% 21% 13% 2	2940
	21st to end	Day	41% 9% 15% 21% 14% 1	2940
July	1st to 10th	Day	46% 7% 14% 20% 11% 1	8210
	11th to 20th	Day	36% 7% 16% 27% 13% 1	8205
	21st to end	Day	42% 5% 11% 23% 17% 1	8795
August	1st to 10th	Day	49% 8% 16% 19% 8% 1	4352
	11th to 20th	Day	42% 8% 14% 26% 10% 1	4177
	21st to end	Day	32% 7% 15% 26% 18% 2	4312
September	1st to 10th	Day	39% 7% 11% 22% 21% 1	2390
	11th to 20th	Day	34% 5% 10% 24% 24% 3	2200
	21st to end	Day	44% 5% 9% 20% 21% 2	2200
October	1st to 10th	Day	38% 5% 10% 22% 20% 4	3590
	11th to 20th	Day	32% 4 7% 27% 27% 3	3176
	21st to end	Day	31% 4 14% 27% 21% 3	3180
November	1st to 10th	Day	40% 5% 13% 21% 19% 2	1851
	11th to 20th	Day	39% 4 10% 22% 21% 4	1890
	21st to end	Day	42% 5% 12% 26% 12% 3	1890
December	1st to 10th	Day	39% 4 14% 27% 16% 1	2798
	11th to 20th	Day	39% 3 14% 17% 19% 7%	3066
	21st to end	Day	49% 4 9% 20% 13% 4	4048
January	1st to 10th	Night	38% 3 11% 30% 17% 2	8234
	11th to 20th	Night	47% 3 10% 19% 15% 5%	8280
	21st to end	Night	47% 4 8% 18% 20% 4	9057
February	1st to 10th	Night	45% 5% 12% 21% 14% 2	2605
	11th to 20th	Night	45% 5% 9% 20% 17% 4	2460
	21st to end	Night	46% 4 8% 23% 15% 4	2076
March	1st to 10th	Night	48% 4 10% 16% 15% 7%	5494
	11th to 20th	Night	45% 7% 16% 18% 12% 3	5289
	21st to end	Night	54% 4 6% 11% 18% 6%	5272
April	1st to 10th	Night	48% 6% 10% 18% 15% 3	2100
	11th to 20th	Night	46% 6% 9% 18% 18% 3	2070
	21st to end	Night	47% 6% 9% 19% 15% 4	1890
May	1st to 10th	Night	53% 7% 15% 13% 11% 1	5265
	11th to 20th	Night	50% 7% 15% 18% 9% 2	5236
	21st to end	Night	54% 7% 13% 18% 8%	5156
June	1st to 10th	Night	44% 8% 12% 22% 14% 1	1680
	11th to 20th	Night	45% 7% 13% 22% 13% 1	1680
	21st to end	Night	41% 8% 16% 23% 12% 1	1680
July	1st to 10th	Night	49% 6% 12% 19% 13%	4640
	11th to 20th	Night	40% 6% 15% 24% 14% 1	4632
	21st to end	Night	42% 5% 12% 24% 16% 1	4967
August	1st to 10th	Night	51% 9% 12% 18% 9% 1	2957
	11th to 20th	Night	42% 9% 15% 26% 8%	3021
	21st to end	Night	28% 6% 16% 27% 22% 1	3586
September	1st to 10th	Night	40% 7% 11% 23% 17% 2	2010
	11th to 20th	Night	35% 6% 11% 23% 25% 2	2200
	21st to end	Night	46% 6% 9% 19% 18% 3	2200
October	1st to 10th	Night	39% 5% 12% 24% 16% 3	3590
	11th to 20th	Night	27% 4 9% 26% 31% 3	3946
	21st to end	Night	34% 4 11% 28% 21% 2	4610
November	1st to 10th	Night	37% 6% 12% 22% 19% 3	2667
	11th to 20th	Night	40% 4 10% 22% 20% 4	2730
	21st to end	Night	39% 5% 13% 27% 13% 2	2730
December	1st to 10th	Night	42% 4 12% 27% 15% 1	4584
	11th to 20th	Night	46% 4 14% 15% 20% 2	5348
	21st to end	Night	46% 5% 9% 20% 17% 3	7150

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	28% 28% 27% 15% 2	220
	11th to 20th	Day	32% 29% 31% 6% 2	220
	21st to end	Day	28% 28% 32% 10% 2 1	242
February	1st to 10th	Day	31% 24% 31% 13% 1	478
	11th to 20th	Day	30% 31% 30% 7% 1	536
	21st to end	Day	29% 26% 32% 11% 3	446
March	1st to 10th	Day	33% 21% 31% 13% 2	540
	11th to 20th	Day	31% 26% 28% 11% 3	540
	21st to end	Day	32% 25% 29% 9% 4 1	594
April	1st to 10th	Day	35% 23% 27% 9% 4 1	540
	11th to 20th	Day	30% 26% 31% 11% 2 1	532
	21st to end	Day	27% 23% 33% 14% 2 2	540
May	1st to 10th	Day	34% 24% 29% 11% 2 1	543
	11th to 20th	Day	25% 20% 40% 12% 4 1	567
	21st to end	Day	22% 17% 36% 19% 5% 1	617
June	1st to 10th	Day	20% 16% 37% 21% 6% 1	570
	11th to 20th	Day	17% 20% 39% 19% 4 1	570
	21st to end	Day	19% 15% 36% 23% 6% 1	570
July	1st to 10th	Day	18% 10% 34% 28% 9% 2	565
	11th to 20th	Day	15% 10% 36% 26% 11% 2	564
	21st to end	Day	14% 12% 39% 25% 7% 1	620
August	1st to 10th	Day	13% 11% 36% 29% 10% 1	566
	11th to 20th	Day	14% 11% 35% 26% 11% 3	535
	21st to end	Day	12% 13% 36% 23% 12% 5%	583
September	1st to 10th	Day	20% 12% 30% 22% 12% 4	530
	11th to 20th	Day	16% 12% 29% 26% 10% 6%	530
	21st to end	Day	25% 12% 32% 20% 6% 4	530
October	1st to 10th	Day	27% 13% 27% 20% 9% 5%	530
	11th to 20th	Day	21% 18% 33% 16% 10% 1	472
	21st to end	Day	26% 19% 29% 17% 7% 2	462
November	1st to 10th	Day	24% 16% 34% 16% 8% 2	425
	11th to 20th	Day	26% 24% 32% 14% 4	430
	21st to end	Day	27% 23% 30% 13% 6%	430
December	1st to 10th	Day	24% 29% 31% 12% 4	299
	11th to 20th	Day	35% 25% 31% 6% 2	220
	21st to end	Day	30% 24% 31% 10% 2 2	242
January	1st to 10th	Night	23% 23% 35% 16% 3	840
	11th to 20th	Night	30% 22% 32% 14% 2	840
	21st to end	Night	22% 24% 34% 16% 3	924
February	1st to 10th	Night	24% 21% 36% 18% 1	840
	11th to 20th	Night	27% 23% 35% 13% 1	823
	21st to end	Night	25% 23% 33% 16% 3	692
March	1st to 10th	Night	26% 19% 35% 16% 3	840
	11th to 20th	Night	23% 23% 35% 17% 3	840
	21st to end	Night	27% 22% 32% 16% 3	924
April	1st to 10th	Night	25% 22% 33% 16% 3	840
	11th to 20th	Night	24% 21% 35% 18% 3	826
	21st to end	Night	24% 17% 38% 17% 3	630
May	1st to 10th	Night	30% 14% 34% 19% 3	630
	11th to 20th	Night	21% 17% 40% 19% 3	622
	21st to end	Night	22% 9% 36% 27% 5%	470
June	1st to 10th	Night	17% 10% 32% 33% 8%	420
	11th to 20th	Night	20% 8% 35% 30% 7%	420
	21st to end	Night	20% 7% 32% 36% 5%	420
July	1st to 10th	Night	19% 5% 33% 35% 8%	410
	11th to 20th	Night	16% 5% 33% 36% 9%	408
	21st to end	Night	15% 5% 31% 40% 8%	460
August	1st to 10th	Night	14% 6% 36% 36% 7%	602
	11th to 20th	Night	13% 6% 31% 38% 12%	651
	21st to end	Night	14% 6% 28% 36% 15% 1	880
September	1st to 10th	Night	17% 5% 33% 32% 12% 1	800
	11th to 20th	Night	17% 8% 28% 28% 16% 3	800
	21st to end	Night	25% 8% 27% 26% 12% 2	800
October	1st to 10th	Night	23% 12% 27% 25% 12% 2	800
	11th to 20th	Night	20% 11% 34% 22% 11% 1	800
	21st to end	Night	25% 16% 33% 19% 7%	880
November	1st to 10th	Night	19% 16% 33% 22% 9% 1	820
	11th to 20th	Night	23% 20% 33% 16% 6%	840
	21st to end	Night	23% 19% 33% 20% 4 1	840
December	1st to 10th	Night	26% 19% 34% 16% 4	840
	11th to 20th	Night	29% 19% 32% 18% 2	840
	21st to end	Night	27% 21% 33% 17% 2	924

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

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