Lake Shastina
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Shastina clear sky chart from 2005-11-06 to 2025-04-11.

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	6% 7% 2 5% 4 3 4 3 5% 6% 55%	117647
	Night	7% 8% 2 5% 3 4 4 3 5% 7% 52%	119469
Transparency	Day	30% 6% 10% 21% 20% 13%	117398
	Night	33% 6% 12% 22% 17% 10%	119307
Seeing	Day	11% 15% 26% 28% 16% 5%	15445
	Night	11% 10% 23% 33% 20% 3	24706

By Month

Percentage Cloud Cover SW (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	10% 15% 5% 8% 5% 5% 5% 4 6% 8% 29%	3639
	11th to 20th	Day	11% 10% 2 6% 4 3 4 3 3 6% 48%	3888
	21st to end	Day	8% 6% 2 5% 4 4 4 3 5% 6% 52%	4510
February	1st to 10th	Day	5% 10% 4 8% 5% 5% 5% 5% 8% 8% 38%	1800
	11th to 20th	Day	7% 9% 3 6% 5% 4 6% 4 7% 8% 39%	1755
	21st to end	Day	5% 14% 4 6% 5% 5% 5% 4 7% 6% 38%	1648
March	1st to 10th	Day	8% 16% 4 10% 6% 5% 5% 4 5% 6% 32%	4782
	11th to 20th	Day	4 12% 2 7% 5% 5% 4 4 5% 7% 44%	5000
	21st to end	Day	7% 11% 3 8% 6% 5% 6% 4 6% 8% 35%	5590
April	1st to 10th	Day	7% 11% 4 8% 6% 5% 5% 4 7% 7% 37%	2400
	11th to 20th	Day	9% 12% 4 6% 5% 3 3 4 6% 8% 40%	2251
	21st to end	Day	7% 11% 3 7% 4 3 3 3 5% 9% 46%	2323
May	1st to 10th	Day	7% 9% 2 4 3 2 3 2 3 6% 58%	4165
	11th to 20th	Day	5% 5% 1 3 2 2 2 2 4 6% 66%	4377
	21st to end	Day	7% 7% 2 4 3 3 3 3 5% 8% 57%	4813
June	1st to 10th	Day	9% 6% 2 5% 4 4 4 5% 6% 8% 49%	2660
	11th to 20th	Day	5% 4 1 4 3 3 3 3 4 6% 65%	2660
	21st to end	Day	2 2 1 3 2 2 2 3 3 5% 74%	2660
July	1st to 10th	Day	1 1 2 1 1 2 1 2 3 85%	4420
	11th to 20th	Day	1 2 1 2 2 2 3 3 4 3 77%	4420
	21st to end	Day	1 1 1 1 2 2 2 3 3 83%	4552
August	1st to 10th	Day	2 1 1 2 2 2 3 3 4 5% 74%	4091
	11th to 20th	Day	1 1 2 1 2 2 3 4 6% 78%	3997
	21st to end	Day	2 1 1 2 1 1 2 2 3 4 81%	4180
September	1st to 10th	Day	1 1 1 1 1 1 2 2 3 4 82%	2280
	11th to 20th	Day	4 3 1 3 3 3 4 3 5% 6% 67%	2280
	21st to end	Day	3 3 1 3 2 2 3 3 4 6% 69%	2006
October	1st to 10th	Day	3 3 1 2 2 2 3 2 3 5% 74%	3180
	11th to 20th	Day	4 5% 2 5% 3 3 3 3 6% 7% 61%	3161
	21st to end	Day	6% 6% 2 7% 4 5% 5% 4 6% 9% 47%	3448
November	1st to 10th	Day	10% 9% 3 6% 5% 4 3 4 6% 8% 41%	1802
	11th to 20th	Day	9% 10% 2 6% 5% 4 5% 6% 8% 10% 34%	1657
	21st to end	Day	5% 10% 3 7% 5% 4 5% 3 7% 8% 44%	1600
December	1st to 10th	Day	4 5% 1 5% 4 5% 5% 4 7% 8% 51%	2620
	11th to 20th	Day	9% 10% 4 8% 5% 7% 7% 6% 8% 10% 27%	3028
	21st to end	Day	13% 14% 3 8% 6% 6% 6% 5% 7% 9% 24%	4004
January	1st to 10th	Night	12% 14% 5% 8% 5% 5% 6% 4 6% 8% 28%	6306
	11th to 20th	Night	9% 9% 3 8% 4 4 3 3 4 6% 48%	6079
	21st to end	Night	11% 10% 3 6% 4 4 4 3 4 6% 45%	6468
February	1st to 10th	Night	7% 10% 4 7% 5% 4 5% 4 7% 9% 39%	2600
	11th to 20th	Night	8% 11% 3 8% 5% 4 5% 5% 6% 8% 37%	2532
	21st to end	Night	6% 11% 4 7% 4 4 4 4 6% 10% 40%	1980
March	1st to 10th	Night	9% 15% 4 8% 5% 4 5% 3 6% 8% 33%	5098
	11th to 20th	Night	5% 11% 2 5% 4 5% 4 4 6% 8% 46%	5000
	21st to end	Night	8% 13% 4 9% 6% 5% 6% 4 6% 7% 33%	5372
April	1st to 10th	Night	7% 11% 4 7% 4 5% 5% 5% 7% 7% 39%	2000
	11th to 20th	Night	7% 11% 3 5% 4 3 4 3 5% 7% 47%	1883
	21st to end	Night	10% 10% 2 5% 3 3 2 2 5% 8% 49%	1853
May	1st to 10th	Night	8% 11% 3 4 2 2 2 2 3 5% 59%	2801
	11th to 20th	Night	5% 4 1 3 2 2 2 3 4 5% 69%	2516
	21st to end	Night	7% 8% 2 4 3 2 3 3 3 6% 58%	2762
June	1st to 10th	Night	9% 6% 2 5% 3 3 5% 4 6% 7% 49%	1520
	11th to 20th	Night	6% 5% 1 2 2 2 1 2 3 6% 68%	1520
	21st to end	Night	2 2 1 2 2 2 2 2 5% 4 77%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 88%	2540
	11th to 20th	Night	2 2 1 1 2 2 2 1 3 4 81%	2540
	21st to end	Night	1 1 1 1 1 1 1 2 3 88%	3004
August	1st to 10th	Night	2 2 2 1 1 2 2 4 5% 79%	2848
	11th to 20th	Night	1 1 1 1 1 2 2 3 4 85%	2840
	21st to end	Night	6% 3 2 1 1 1 1 2 3 79%	3498
September	1st to 10th	Night	2 1 1 1 1 1 1 3 5% 85%	1900
	11th to 20th	Night	4 4 1 2 2 3 3 2 4 6% 71%	1900
	21st to end	Night	4 4 1 3 2 2 2 2 4 6% 70%	2168
October	1st to 10th	Night	2 2 1 3 2 2 3 2 3 4 77%	3800
	11th to 20th	Night	6% 5% 1 3 3 2 3 2 4 6% 64%	3777
	21st to end	Night	5% 6% 1 4 3 4 4 4 6% 9% 53%	4121
November	1st to 10th	Night	8% 11% 3 6% 4 4 4 4 5% 8% 42%	2495
	11th to 20th	Night	12% 9% 3 5% 4 4 4 4 7% 10% 38%	2740
	21st to end	Night	7% 9% 2 6% 4 5% 4 4 5% 7% 46%	2800
December	1st to 10th	Night	5% 5% 2 4 3 5% 5% 3 6% 8% 54%	4560
	11th to 20th	Night	8% 11% 3 7% 5% 7% 7% 5% 8% 9% 29%	5176
	21st to end	Night	14% 12% 3 6% 4 5% 5% 4 6% 8% 33%	6952

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	52% 9% 14% 19% 4 1	3639
	11th to 20th	Day	38% 7% 9% 28% 15% 3	3888
	21st to end	Day	37% 5% 11% 17% 19% 10%	4510
February	1st to 10th	Day	42% 11% 15% 18% 11% 4	1800
	11th to 20th	Day	42% 9% 14% 19% 13% 2	1764
	21st to end	Day	45% 9% 13% 18% 12% 3	1648
March	1st to 10th	Day	52% 7% 9% 22% 10% 1	4782
	11th to 20th	Day	42% 5% 14% 21% 18% 1	5000
	21st to end	Day	48% 8% 13% 22% 8% 1	5590
April	1st to 10th	Day	47% 8% 15% 18% 11% 2	2400
	11th to 20th	Day	42% 7% 14% 21% 12% 4	2254
	21st to end	Day	37% 8% 14% 24% 14% 2	2323
May	1st to 10th	Day	29% 5% 11% 27% 24% 3	4165
	11th to 20th	Day	22% 5% 7% 20% 36% 10%	4380
	21st to end	Day	26% 7% 13% 39% 14% 1	4814
June	1st to 10th	Day	33% 7% 13% 28% 16% 2	2660
	11th to 20th	Day	22% 5% 8% 31% 27% 7%	2660
	21st to end	Day	15% 3 6% 25% 32% 18%	2660
July	1st to 10th	Day	7% 2 3 11% 21% 56%	4351
	11th to 20th	Day	12% 3 2 11% 22% 49%	4345
	21st to end	Day	8% 3 3 13% 34% 38%	4408
August	1st to 10th	Day	14% 4 4 12% 25% 42%	4076
	11th to 20th	Day	9% 4 3 25% 40% 19%	4036
	21st to end	Day	10% 2 4 27% 38% 19%	4179
September	1st to 10th	Day	8% 3 3 16% 31% 39%	2280
	11th to 20th	Day	19% 5% 8% 20% 34% 14%	2280
	21st to end	Day	17% 4 9% 25% 28% 17%	2006
October	1st to 10th	Day	16% 3 10% 16% 24% 32%	3180
	11th to 20th	Day	23% 5% 13% 33% 21% 6%	3161
	21st to end	Day	33% 8% 12% 23% 17% 8%	3448
November	1st to 10th	Day	42% 6% 13% 20% 14% 4	1802
	11th to 20th	Day	44% 9% 15% 16% 12% 4	1657
	21st to end	Day	38% 8% 14% 18% 16% 6%	1600
December	1st to 10th	Day	29% 9% 10% 29% 20% 2	2620
	11th to 20th	Day	53% 8% 18% 13% 7% 1	3028
	21st to end	Day	57% 9% 15% 13% 5% 1	4004
January	1st to 10th	Night	54% 8% 13% 18% 6% 1	6306
	11th to 20th	Night	37% 9% 11% 23% 16% 3	6079
	21st to end	Night	43% 5% 8% 14% 19% 10%	6468
February	1st to 10th	Night	43% 8% 14% 17% 14% 5%	2600
	11th to 20th	Night	45% 9% 13% 19% 11% 3	2534
	21st to end	Night	41% 9% 16% 17% 14% 4	1980
March	1st to 10th	Night	50% 7% 11% 21% 10% 1	5098
	11th to 20th	Night	37% 6% 16% 21% 17% 3	5000
	21st to end	Night	48% 9% 16% 20% 7% 1	5372
April	1st to 10th	Night	44% 9% 17% 20% 9% 2	2000
	11th to 20th	Night	39% 7% 19% 20% 11% 5%	1883
	21st to end	Night	35% 6% 19% 28% 10% 2	1853
May	1st to 10th	Night	30% 4 13% 32% 17% 4	2801
	11th to 20th	Night	19% 6% 10% 33% 27% 5%	2516
	21st to end	Night	24% 7% 23% 37% 8%	2762
June	1st to 10th	Night	33% 6% 17% 33% 9% 1	1520
	11th to 20th	Night	19% 5% 12% 38% 22% 5%	1520
	21st to end	Night	13% 4 8% 33% 34% 8%	1520
July	1st to 10th	Night	5% 2 6% 14% 21% 52%	2500
	11th to 20th	Night	10% 3 3 14% 24% 47%	2492
	21st to end	Night	6% 2 3 15% 44% 30%	2910
August	1st to 10th	Night	11% 2 4 19% 23% 40%	2839
	11th to 20th	Night	6% 2 5% 35% 34% 17%	2867
	21st to end	Night	14% 3 5% 30% 30% 18%	3498
September	1st to 10th	Night	6% 2 5% 17% 31% 38%	1900
	11th to 20th	Night	16% 5% 8% 25% 33% 14%	1900
	21st to end	Night	18% 5% 10% 23% 24% 20%	2168
October	1st to 10th	Night	14% 4 7% 14% 30% 30%	3800
	11th to 20th	Night	23% 4 10% 39% 17% 7%	3777
	21st to end	Night	27% 7% 14% 25% 20% 8%	4121
November	1st to 10th	Night	42% 7% 14% 17% 15% 6%	2495
	11th to 20th	Night	42% 9% 15% 16% 13% 4	2740
	21st to end	Night	37% 9% 13% 16% 18% 7%	2800
December	1st to 10th	Night	26% 10% 9% 30% 23% 2	4560
	11th to 20th	Night	53% 8% 14% 16% 8% 1	5176
	21st to end	Night	51% 7% 17% 17% 7% 1	6952

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% 22% 34% 20% 5% 3	200
	11th to 20th	Day	19% 17% 21% 21% 15% 6%	305
	21st to end	Day	16% 15% 25% 23% 16% 5%	440
February	1st to 10th	Day	14% 20% 23% 31% 10% 2	400
	11th to 20th	Day	18% 23% 24% 23% 11% 1	395
	21st to end	Day	16% 19% 28% 26% 10% 1	414
March	1st to 10th	Day	18% 27% 29% 18% 7% 1	500
	11th to 20th	Day	18% 19% 26% 23% 11% 3	500
	21st to end	Day	19% 26% 27% 20% 8% 1	550
April	1st to 10th	Day	15% 24% 27% 23% 10% 1	500
	11th to 20th	Day	21% 19% 24% 22% 11% 2	453
	21st to end	Day	12% 20% 32% 20% 12% 3	460
May	1st to 10th	Day	13% 24% 30% 20% 10% 3	463
	11th to 20th	Day	16% 20% 25% 22% 13% 5%	488
	21st to end	Day	14% 14% 27% 26% 14% 5%	529
June	1st to 10th	Day	10% 16% 24% 28% 16% 5%	490
	11th to 20th	Day	9% 18% 33% 24% 13% 3	490
	21st to end	Day	2 11% 31% 31% 18% 6%	490
July	1st to 10th	Day	3 8% 30% 33% 19% 7%	486
	11th to 20th	Day	1 6% 28% 39% 19% 7%	484
	21st to end	Day	1 5% 23% 40% 23% 9%	531
August	1st to 10th	Day	3 5% 26% 34% 23% 8%	487
	11th to 20th	Day	2 6% 25% 34% 22% 11%	477
	21st to end	Day	2 7% 23% 35% 23% 10%	539
September	1st to 10th	Day	2 7% 23% 39% 20% 8%	490
	11th to 20th	Day	6% 8% 24% 34% 22% 6%	490
	21st to end	Day	5% 15% 21% 31% 24% 4	490
October	1st to 10th	Day	8% 13% 23% 25% 25% 7%	490
	11th to 20th	Day	12% 10% 19% 29% 24% 6%	490
	21st to end	Day	10% 14% 26% 29% 16% 6%	539
November	1st to 10th	Day	14% 15% 24% 26% 16% 6%	338
	11th to 20th	Day	12% 11% 25% 26% 20% 6%	227
	21st to end	Day	12% 10% 26% 28% 19% 7%	200
December	1st to 10th	Day	14% 12% 23% 25% 14% 13%	200
	11th to 20th	Day	23% 16% 20% 26% 9% 8%	200
	21st to end	Day	16% 15% 25% 28% 14% 2	220
January	1st to 10th	Night	15% 13% 31% 26% 12% 3	800
	11th to 20th	Night	12% 14% 27% 25% 17% 5%	800
	21st to end	Night	15% 11% 25% 29% 16% 4	880
February	1st to 10th	Night	14% 13% 29% 31% 12% 2	800
	11th to 20th	Night	15% 13% 27% 29% 14% 2	784
	21st to end	Night	12% 14% 29% 33% 11% 1	660
March	1st to 10th	Night	16% 22% 28% 22% 11% 2	800
	11th to 20th	Night	14% 16% 24% 28% 17% 2	800
	21st to end	Night	13% 20% 31% 25% 10% 1	880
April	1st to 10th	Night	13% 18% 30% 27% 12% 1	800
	11th to 20th	Night	11% 14% 30% 26% 15% 3	753
	21st to end	Night	14% 11% 26% 29% 18% 2	713
May	1st to 10th	Night	10% 10% 31% 26% 20% 2	537
	11th to 20th	Night	12% 7% 25% 33% 23% 1	374
	21st to end	Night	11% 9% 24% 33% 22% 1	411
June	1st to 10th	Night	12% 7% 20% 38% 22% 1	380
	11th to 20th	Night	7% 7% 25% 45% 14% 1	380
	21st to end	Night	4 4 20% 48% 23%	380
July	1st to 10th	Night	2 1 15% 49% 33% 2	370
	11th to 20th	Night	2 13% 53% 32% 1	368
	21st to end	Night	1 1 8% 42% 44% 5%	558
August	1st to 10th	Night	3 1 8% 44% 39% 5%	567
	11th to 20th	Night	2 1 11% 45% 34% 7%	579
	21st to end	Night	3 2 16% 40% 34% 4	836
September	1st to 10th	Night	2 3 17% 41% 33% 4	760
	11th to 20th	Night	5% 3 18% 34% 34% 6%	760
	21st to end	Night	6% 5% 18% 35% 30% 7%	760
October	1st to 10th	Night	4 5% 22% 37% 28% 4	760
	11th to 20th	Night	7% 8% 18% 34% 27% 6%	760
	21st to end	Night	8% 9% 21% 35% 20% 7%	836
November	1st to 10th	Night	13% 9% 25% 32% 15% 5%	780
	11th to 20th	Night	17% 11% 27% 30% 11% 4	800
	21st to end	Night	13% 10% 23% 32% 19% 3	800
December	1st to 10th	Night	11% 14% 22% 30% 17% 5%	800
	11th to 20th	Night	18% 14% 24% 28% 13% 3	800
	21st to end	Night	23% 16% 26% 24% 9% 1	880

Page generated at 2025-04-08 06:17:24. Version ac07

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