Yanna Research Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yanna Research Station clear sky chart from 2005-11-06 to 2025-07-06.

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	13% 9% 3 7% 5% 4 4 4 5% 7% 38%	120081
	Night	13% 10% 4 8% 4 4 4 3 5% 6% 39%	118931
Transparency	Day	45% 4 12% 25% 14% 1	123620
	Night	46% 3 11% 24% 15% 2	123532
Seeing	Day	17% 11% 29% 25% 14% 5%	16785
	Night	17% 9% 31% 30% 11% 1	26673

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	8% 10% 8% 15% 6% 6% 6% 4 5% 5% 27%	3617
	11th to 20th	Day	8% 11% 7% 11% 5% 4 5% 6% 6% 7% 31%	3620
	21st to end	Day	12% 14% 8% 9% 4 2 3 3 4 6% 35%	4210
February	1st to 10th	Day	12% 14% 5% 10% 5% 5% 5% 4 5% 5% 31%	1800
	11th to 20th	Day	13% 12% 4 8% 5% 4 5% 3 5% 6% 36%	1884
	21st to end	Day	12% 14% 4 11% 6% 4 3 3 4 6% 33%	1650
March	1st to 10th	Day	15% 7% 3 5% 3 3 3 3 4 7% 46%	4480
	11th to 20th	Day	12% 6% 3 7% 4 4 4 3 5% 8% 44%	4814
	21st to end	Day	23% 12% 4 9% 5% 4 4 3 4 5% 29%	5893
April	1st to 10th	Day	18% 13% 4 7% 5% 4 5% 3 5% 6% 31%	2400
	11th to 20th	Day	17% 11% 3 7% 5% 4 4 4 5% 7% 34%	2374
	21st to end	Day	18% 10% 3 8% 5% 4 4 3 4 6% 33%	2457
May	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 6% 7% 39%	6043
	11th to 20th	Day	15% 5% 2 6% 5% 5% 5% 3 5% 7% 42%	6319
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 6% 8% 38%	6935
June	1st to 10th	Day	11% 4 2 6% 5% 5% 5% 4 7% 8% 43%	2800
	11th to 20th	Day	12% 5% 2 6% 4 4 4 5% 7% 9% 41%	2800
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 5% 6% 9% 39%	2800
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 4 7% 10% 35%	4511
	11th to 20th	Day	5% 4 2 4 4 4 6% 4 6% 9% 52%	4440
	21st to end	Day	10% 6% 2 7% 4 5% 5% 4 6% 9% 42%	4813
August	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	4337
	11th to 20th	Day	12% 5% 2 5% 4 5% 4 3 5% 7% 48%	3802
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 9% 46%	4180
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 6% 7% 46%	2280
	11th to 20th	Day	12% 4 2 5% 3 3 3 3 5% 8% 51%	2218
	21st to end	Day	12% 6% 3 7% 4 4 4 3 5% 7% 45%	2090
October	1st to 10th	Day	12% 6% 3 7% 3 3 3 3 4 7% 48%	1938
	11th to 20th	Day	19% 9% 3 7% 5% 4 3 3 4 6% 37%	1900
	21st to end	Day	19% 10% 2 7% 4 3 3 3 5% 5% 39%	1919
November	1st to 10th	Day	12% 9% 3 6% 4 3 4 3 4 7% 44%	1762
	11th to 20th	Day	14% 12% 4 9% 4 5% 4 3 6% 7% 32%	1795
	21st to end	Day	15% 13% 4 9% 5% 4 3 2 4 6% 36%	1600
December	1st to 10th	Day	8% 10% 5% 7% 5% 5% 5% 3 5% 7% 40%	2610
	11th to 20th	Day	13% 15% 5% 11% 5% 5% 4 4 6% 7% 25%	3008
	21st to end	Day	20% 23% 9% 11% 5% 4 3 4 4 4 14%	3982
January	1st to 10th	Night	9% 11% 7% 14% 6% 4 3 3 4 5% 34%	6348
	11th to 20th	Night	11% 14% 7% 13% 6% 5% 5% 5% 6% 5% 24%	6360
	21st to end	Night	12% 15% 7% 10% 4 4 4 3 4 5% 31%	6766
February	1st to 10th	Night	12% 13% 4 10% 5% 5% 4 3 4 5% 34%	2600
	11th to 20th	Night	11% 11% 4 7% 6% 4 4 3 4 6% 39%	2402
	21st to end	Night	16% 11% 3 7% 5% 4 3 3 5% 6% 36%	1980
March	1st to 10th	Night	16% 9% 3 7% 4 3 4 3 4 4 43%	5373
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 5% 8% 49%	5174
	21st to end	Night	23% 13% 4 10% 5% 4 4 3 4 5% 27%	5036
April	1st to 10th	Night	18% 10% 3 6% 4 3 4 4 4 8% 37%	2000
	11th to 20th	Night	19% 10% 3 6% 4 4 4 3 4 6% 37%	1975
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 5% 7% 38%	1941
May	1st to 10th	Night	17% 7% 3 7% 4 3 4 3 5% 7% 40%	3844
	11th to 20th	Night	11% 6% 2 6% 4 5% 4 4 5% 7% 45%	3596
	21st to end	Night	15% 7% 2 6% 4 5% 4 4 5% 7% 40%	3942
June	1st to 10th	Night	9% 5% 2 6% 4 5% 3 5% 6% 9% 48%	1600
	11th to 20th	Night	13% 5% 2 5% 4 3 4 4 6% 9% 45%	1600
	21st to end	Night	10% 6% 2 6% 4 4 4 4 4 6% 49%	1600
July	1st to 10th	Night	15% 6% 2 5% 4 4 5% 4 6% 8% 41%	2570
	11th to 20th	Night	5% 3 1 5% 4 3 4 4 6% 9% 56%	2530
	21st to end	Night	7% 4 2 6% 4 4 5% 4 7% 8% 48%	2750
August	1st to 10th	Night	9% 4 2 5% 4 4 4 4 6% 8% 50%	2601
	11th to 20th	Night	10% 5% 2 4 4 3 4 4 5% 7% 51%	3029
	21st to end	Night	11% 4 2 5% 3 4 4 4 6% 7% 51%	3476
September	1st to 10th	Night	9% 4 2 5% 3 4 4 2 5% 7% 54%	1900
	11th to 20th	Night	12% 4 2 4 3 3 4 3 5% 7% 53%	1942
	21st to end	Night	11% 5% 2 5% 4 4 4 3 5% 6% 50%	2090
October	1st to 10th	Night	12% 6% 2 6% 4 3 4 3 5% 6% 51%	2237
	11th to 20th	Night	17% 7% 2 5% 4 4 3 3 4 5% 45%	2280
	21st to end	Night	18% 8% 3 6% 4 4 4 4 5% 7% 37%	2678
November	1st to 10th	Night	12% 8% 3 6% 4 3 4 2 4 5% 48%	2536
	11th to 20th	Night	14% 11% 3 9% 5% 5% 4 3 5% 5% 36%	2600
	21st to end	Night	17% 11% 3 7% 5% 3 3 3 5% 6% 37%	2800
December	1st to 10th	Night	9% 9% 3 7% 4 4 5% 4 5% 7% 43%	4580
	11th to 20th	Night	16% 18% 5% 9% 5% 4 4 3 4 4 28%	5199
	21st to end	Night	20% 20% 6% 11% 5% 5% 4 3 4 4 18%	6996

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% 3 11% 19% 7%	3618
	11th to 20th	Day	51% 3 12% 12% 19% 2	3620
	21st to end	Day	53% 2 13% 20% 12%	4210
February	1st to 10th	Day	55% 3 11% 19% 12% 1	1800
	11th to 20th	Day	50% 3 11% 24% 10% 2	1893
	21st to end	Day	53% 3 10% 20% 12% 2	1650
March	1st to 10th	Day	41% 2 12% 30% 11% 4	4480
	11th to 20th	Day	40% 3 12% 31% 13% 2	4814
	21st to end	Day	60% 3 11% 15% 9% 1	5895
April	1st to 10th	Day	55% 4 10% 20% 11% 1	2400
	11th to 20th	Day	51% 3 10% 21% 12% 2	2374
	21st to end	Day	52% 4 12% 19% 12% 2	2457
May	1st to 10th	Day	44% 3 9% 24% 19% 1	6078
	11th to 20th	Day	43% 4 10% 28% 15% 1	6323
	21st to end	Day	43% 4 10% 29% 12% 2	6949
June	1st to 10th	Day	36% 6% 14% 27% 16% 1	2800
	11th to 20th	Day	37% 6% 14% 25% 17% 2	2800
	21st to end	Day	41% 6% 13% 24% 14% 2	2800
July	1st to 10th	Day	44% 5% 14% 27% 9% 1	4442
	11th to 20th	Day	28% 5% 17% 31% 18% 1	4365
	21st to end	Day	39% 5% 14% 21% 18% 2	4662
August	1st to 10th	Day	38% 5% 14% 29% 12% 1	4322
	11th to 20th	Day	36% 3 14% 32% 13% 1	3839
	21st to end	Day	35% 4 13% 30% 16% 1	4179
September	1st to 10th	Day	38% 4 11% 27% 20% 1	2280
	11th to 20th	Day	33% 4 11% 34% 17% 2	2218
	21st to end	Day	40% 3 9% 30% 16% 1	2090
October	1st to 10th	Day	24% 3 6% 40% 26% 1	3224
	11th to 20th	Day	36% 3 8% 28% 23% 1	3140
	21st to end	Day	43% 3 9% 29% 14% 3	3144
November	1st to 10th	Day	43% 3 14% 25% 13% 2	1762
	11th to 20th	Day	52% 3 13% 21% 10% 1	1795
	21st to end	Day	51% 4 14% 23% 7%	1600
December	1st to 10th	Day	44% 3 21% 24% 7% 1	2610
	11th to 20th	Day	60% 2 12% 17% 7% 2	3005
	21st to end	Day	75% 2 7% 9% 6%	3982
January	1st to 10th	Night	55% 2 9% 22% 11% 1	6348
	11th to 20th	Night	60% 3 8% 12% 16% 1	6360
	21st to end	Night	57% 2 11% 18% 11%	6766
February	1st to 10th	Night	54% 4 10% 19% 12% 2	2600
	11th to 20th	Night	48% 4 10% 23% 14% 1	2403
	21st to end	Night	49% 3 12% 21% 12% 3	1980
March	1st to 10th	Night	46% 2 11% 23% 10% 7%	5373
	11th to 20th	Night	35% 3 11% 35% 14% 3	5174
	21st to end	Night	61% 3 8% 17% 10% 1	5036
April	1st to 10th	Night	47% 4 10% 23% 15% 2	2000
	11th to 20th	Night	49% 3 6% 21% 18% 3	1975
	21st to end	Night	46% 4 12% 24% 12% 2	1941
May	1st to 10th	Night	45% 3 11% 19% 20% 2	3871
	11th to 20th	Night	39% 4 14% 24% 17% 2	3597
	21st to end	Night	43% 4 11% 24% 16% 3	3950
June	1st to 10th	Night	33% 6% 13% 28% 20% 1	1600
	11th to 20th	Night	35% 4 11% 25% 23% 2	1600
	21st to end	Night	36% 5% 14% 23% 19% 3	1600
July	1st to 10th	Night	42% 4 15% 23% 13% 3	2530
	11th to 20th	Night	26% 4 15% 35% 18% 2	2482
	21st to end	Night	31% 6% 17% 22% 20% 3	2662
August	1st to 10th	Night	33% 4 15% 28% 20% 2	2592
	11th to 20th	Night	33% 4 12% 33% 17% 1	3058
	21st to end	Night	33% 5% 13% 29% 18% 3	3476
September	1st to 10th	Night	30% 5% 11% 28% 24% 3	1900
	11th to 20th	Night	31% 4 11% 34% 19% 2	1942
	21st to end	Night	35% 3 10% 31% 20% 1	2090
October	1st to 10th	Night	26% 2 5% 37% 28% 1	3731
	11th to 20th	Night	34% 3 9% 29% 23% 2	3779
	21st to end	Night	43% 3 9% 28% 15% 2	4403
November	1st to 10th	Night	40% 3 10% 28% 17% 2	2536
	11th to 20th	Night	51% 3 12% 22% 11% 2	2600
	21st to end	Night	50% 3 13% 23% 10% 1	2800
December	1st to 10th	Night	42% 3 16% 28% 10% 1	4580
	11th to 20th	Night	60% 3 10% 16% 10% 1	5201
	21st to end	Night	71% 2 7% 14% 5%	6996

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% 15% 31% 29% 8% 1	300
	11th to 20th	Day	20% 17% 36% 22% 5% 1	300
	21st to end	Day	22% 16% 34% 22% 5%	330
February	1st to 10th	Day	15% 20% 41% 17% 6% 1	300
	11th to 20th	Day	22% 21% 35% 19% 3	300
	21st to end	Day	24% 17% 43% 13% 2	249
March	1st to 10th	Day	17% 20% 43% 15% 5%	300
	11th to 20th	Day	22% 20% 34% 16% 6% 2	300
	21st to end	Day	29% 13% 30% 19% 6% 2	515
April	1st to 10th	Day	25% 16% 33% 21% 5%	500
	11th to 20th	Day	26% 18% 26% 18% 10% 2	492
	21st to end	Day	24% 14% 30% 20% 10% 2	500
May	1st to 10th	Day	20% 11% 32% 27% 8% 3	580
	11th to 20th	Day	20% 10% 30% 22% 14% 4	725
	21st to end	Day	17% 9% 29% 23% 16% 7%	789
June	1st to 10th	Day	9% 8% 31% 30% 17% 5%	730
	11th to 20th	Day	13% 5% 30% 30% 15% 6%	730
	21st to end	Day	14% 8% 28% 30% 16% 4	730
July	1st to 10th	Day	9% 3 17% 33% 25% 13%	697
	11th to 20th	Day	9% 5% 25% 30% 22% 9%	668
	21st to end	Day	7% 4 22% 35% 22% 9%	739
August	1st to 10th	Day	8% 5% 17% 35% 25% 11%	676
	11th to 20th	Day	13% 4 20% 26% 23% 14%	528
	21st to end	Day	13% 6% 18% 30% 24% 9%	539
September	1st to 10th	Day	14% 6% 23% 26% 23% 8%	490
	11th to 20th	Day	11% 4 19% 31% 23% 10%	490
	21st to end	Day	14% 12% 26% 24% 16% 7%	490
October	1st to 10th	Day	16% 11% 28% 27% 16% 2	338
	11th to 20th	Day	24% 17% 33% 20% 7% 1	300
	21st to end	Day	27% 16% 31% 21% 5% 1	330
November	1st to 10th	Day	16% 16% 36% 22% 9% 1	300
	11th to 20th	Day	21% 18% 34% 16% 10%	300
	21st to end	Day	26% 11% 41% 18% 4	300
December	1st to 10th	Day	18% 19% 37% 17% 8% 1	300
	11th to 20th	Day	19% 15% 39% 19% 7% 1	300
	21st to end	Day	25% 18% 36% 18% 3	330
January	1st to 10th	Night	16% 15% 37% 25% 7% 1	1000
	11th to 20th	Night	19% 13% 38% 25% 4 1	1000
	21st to end	Night	19% 13% 36% 27% 5%	1100
February	1st to 10th	Night	19% 12% 38% 25% 6%	1000
	11th to 20th	Night	17% 17% 37% 25% 4	847
	21st to end	Night	22% 14% 39% 22% 3	660
March	1st to 10th	Night	23% 11% 37% 24% 5% 1	800
	11th to 20th	Night	17% 13% 34% 28% 8%	690
	21st to end	Night	24% 11% 30% 27% 7% 1	660
April	1st to 10th	Night	23% 12% 37% 24% 4	600
	11th to 20th	Night	23% 14% 29% 28% 6%	593
	21st to end	Night	21% 9% 33% 29% 8% 1	600
May	1st to 10th	Night	19% 8% 34% 32% 8%	600
	11th to 20th	Night	19% 7% 30% 32% 12%	591
	21st to end	Night	14% 4 28% 39% 15% 1	650
June	1st to 10th	Night	9% 5% 25% 46% 15% 1	600
	11th to 20th	Night	15% 4 30% 37% 12% 1	600
	21st to end	Night	13% 4 25% 42% 16% 1	600
July	1st to 10th	Night	8% 2 16% 38% 31% 4	570
	11th to 20th	Night	8% 3 21% 43% 23% 3	552
	21st to end	Night	7% 2 19% 45% 25% 2	624
August	1st to 10th	Night	6% 1 16% 47% 26% 3	567
	11th to 20th	Night	9% 2 14% 40% 29% 6%	564
	21st to end	Night	11% 2 16% 42% 27% 2	627
September	1st to 10th	Night	9% 3 23% 36% 24% 5%	570
	11th to 20th	Night	12% 3 22% 34% 26% 3	612
	21st to end	Night	13% 7% 24% 34% 20% 2	760
October	1st to 10th	Night	14% 6% 29% 32% 17% 1	760
	11th to 20th	Night	20% 11% 31% 27% 10% 1	760
	21st to end	Night	22% 12% 32% 27% 7% 1	836
November	1st to 10th	Night	16% 10% 37% 27% 9% 1	780
	11th to 20th	Night	21% 14% 36% 23% 7%	800
	21st to end	Night	22% 13% 34% 24% 7%	1000
December	1st to 10th	Night	21% 13% 37% 23% 6%	1000
	11th to 20th	Night	24% 12% 34% 25% 5% 1	1000
	21st to end	Night	29% 13% 32% 23% 3	1100

Page generated at 2025-07-03 00:30:15. Version ac07

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