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 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	5% 6% 2 4 3 3 4 3 5% 6% 59%	152915
	Night	6% 7% 2 5% 3 4 4 3 5% 7% 55%	146365
Transparency	Day	27% 5% 10% 23% 22% 13%	147768
	Night	31% 6% 12% 23% 19% 9%	142506
Seeing	Day	10% 14% 25% 28% 17% 6%	17236
	Night	10% 10% 23% 33% 20% 3	26294

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	9% 14% 5% 7% 5% 5% 6% 5% 7% 9% 30%	4722
	11th to 20th	Day	9% 8% 2 4 3 5% 5% 3 4 6% 51%	5058
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 7% 8% 49%	5843
February	1st to 10th	Day	4 9% 4 8% 5% 5% 5% 5% 8% 8% 39%	1890
	11th to 20th	Day	7% 10% 3 7% 5% 4 6% 4 7% 8% 38%	1845
	21st to end	Day	5% 14% 4 7% 5% 5% 5% 5% 6% 6% 38%	1728
March	1st to 10th	Day	8% 16% 4 9% 6% 5% 5% 4 5% 6% 33%	4888
	11th to 20th	Day	4 11% 2 7% 5% 5% 4 4 5% 7% 44%	5110
	21st to end	Day	7% 11% 3 8% 6% 5% 6% 4 6% 8% 36%	5713
April	1st to 10th	Day	6% 10% 4 8% 6% 5% 5% 4 7% 8% 38%	2520
	11th to 20th	Day	8% 11% 3 6% 5% 3 3 4 6% 8% 43%	2489
	21st to end	Day	7% 10% 3 6% 4 3 3 3 4 9% 48%	2567
May	1st to 10th	Day	5% 6% 2 3 2 2 3 2 4 7% 64%	7732
	11th to 20th	Day	4 4 1 3 2 2 3 3 5% 7% 65%	8160
	21st to end	Day	7% 5% 1 3 2 3 3 3 4 7% 62%	8992
June	1st to 10th	Day	8% 6% 2 5% 4 4 4 4 5% 7% 52%	2940
	11th to 20th	Day	5% 4 1 4 3 2 3 3 4 6% 65%	2940
	21st to end	Day	2 2 1 3 2 2 2 3 3 5% 74%	2940
July	1st to 10th	Day	1 1 2 1 2 2 2 3 4 83%	8219
	11th to 20th	Day	1 1 2 2 3 3 3 4 4 77%	8220
	21st to end	Day	1 1 2 2 2 3 3 4 4 77%	8477
August	1st to 10th	Day	2 1 1 2 2 2 3 3 4 5% 76%	5907
	11th to 20th	Day	2 1 1 2 1 2 2 2 4 5% 80%	5807
	21st to end	Day	2 1 2 1 1 3 2 4 5% 79%	5984
September	1st to 10th	Day	1 1 1 1 1 1 2 2 4 5% 81%	2400
	11th to 20th	Day	3 3 1 3 2 3 4 3 5% 6% 67%	2400
	21st to end	Day	3 3 1 3 2 2 3 3 4 6% 69%	2111
October	1st to 10th	Day	3 3 1 2 2 2 3 2 3 5% 73%	3280
	11th to 20th	Day	4 5% 2 5% 3 3 3 3 6% 7% 61%	3261
	21st to end	Day	6% 6% 2 7% 4 5% 5% 4 6% 9% 47%	3558
November	1st to 10th	Day	10% 9% 3 6% 5% 5% 3 4 6% 8% 41%	1894
	11th to 20th	Day	9% 10% 2 6% 5% 4 5% 5% 8% 11% 35%	1740
	21st to end	Day	5% 9% 2 6% 5% 4 4 3 6% 9% 45%	1680
December	1st to 10th	Day	4 5% 1 5% 4 5% 6% 4 7% 8% 51%	2700
	11th to 20th	Day	9% 9% 3 8% 5% 7% 7% 6% 8% 10% 28%	3108
	21st to end	Day	12% 14% 3 8% 6% 6% 6% 5% 7% 9% 24%	4092
January	1st to 10th	Night	10% 14% 4 8% 5% 5% 6% 4 6% 8% 30%	8172
	11th to 20th	Night	7% 7% 2 6% 5% 5% 4 3 4 5% 50%	7901
	21st to end	Night	9% 9% 3 6% 4 5% 5% 4 5% 7% 44%	8371
February	1st to 10th	Night	7% 10% 4 7% 5% 4 5% 3 7% 9% 40%	2730
	11th to 20th	Night	7% 11% 3 9% 5% 4 5% 5% 6% 8% 37%	2662
	21st to end	Night	6% 11% 4 7% 4 4 4 4 6% 10% 39%	2076
March	1st to 10th	Night	9% 15% 3 8% 5% 4 5% 3 6% 8% 33%	5212
	11th to 20th	Night	5% 11% 2 5% 4 4 4 4 6% 8% 47%	5110
	21st to end	Night	7% 12% 3 9% 6% 5% 6% 4 6% 8% 34%	5491
April	1st to 10th	Night	7% 11% 4 7% 4 4 5% 4 6% 8% 40%	2100
	11th to 20th	Night	7% 11% 3 5% 4 4 4 3 5% 7% 48%	2079
	21st to end	Night	10% 10% 2 5% 3 3 2 2 5% 8% 50%	2048
May	1st to 10th	Night	6% 7% 2 3 2 2 2 2 3 5% 66%	5208
	11th to 20th	Night	6% 7% 1 3 2 2 2 2 4 6% 64%	4700
	21st to end	Night	8% 6% 2 4 3 2 2 3 3 5% 62%	5181
June	1st to 10th	Night	8% 6% 2 4 3 3 5% 4 6% 7% 52%	1680
	11th to 20th	Night	6% 4 1 2 2 2 2 2 3 6% 69%	1680
	21st to end	Night	3 2 1 2 2 2 2 2 5% 4 76%	1680
July	1st to 10th	Night	1 1 1 1 1 1 1 1 2 3 86%	4740
	11th to 20th	Night	2 1 1 2 2 2 2 2 3 4 81%	4740
	21st to end	Night	1 1 2 1 2 2 2 3 4 82%	5619
August	1st to 10th	Night	1 2 1 1 1 2 2 4 5% 80%	4125
	11th to 20th	Night	2 1 1 2 1 1 1 1 2 3 84%	4130
	21st to end	Night	5% 2 1 2 2 2 2 2 3 4 78%	5015
September	1st to 10th	Night	2 1 1 1 1 1 1 3 5% 84%	2000
	11th to 20th	Night	4 4 1 2 2 3 2 2 4 6% 71%	2000
	21st to end	Night	4 4 1 3 2 2 2 2 4 6% 71%	2283
October	1st to 10th	Night	2 2 1 3 2 2 3 2 3 4 76%	3920
	11th to 20th	Night	6% 5% 1 3 3 2 3 2 4 6% 64%	3897
	21st to end	Night	5% 6% 1 4 3 4 4 4 6% 9% 53%	4253
November	1st to 10th	Night	8% 11% 3 6% 4 4 4 4 5% 8% 42%	2623
	11th to 20th	Night	12% 9% 3 5% 4 4 5% 4 7% 10% 38%	2877
	21st to end	Night	7% 9% 2 6% 4 5% 4 4 6% 8% 47%	2940
December	1st to 10th	Night	5% 5% 2 4 3 5% 5% 3 6% 8% 54%	4700
	11th to 20th	Night	9% 11% 3 8% 5% 7% 7% 5% 8% 9% 29%	5316
	21st to end	Night	14% 12% 3 6% 4 5% 5% 4 6% 8% 33%	7106

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	49% 9% 18% 19% 3	4723
	11th to 20th	Day	30% 11% 7% 24% 24% 4	5058
	21st to end	Day	35% 5% 14% 20% 19% 8%	5843
February	1st to 10th	Day	41% 10% 15% 19% 12% 3	1890
	11th to 20th	Day	43% 9% 15% 19% 12% 2	1854
	21st to end	Day	46% 8% 13% 18% 12% 3	1728
March	1st to 10th	Day	51% 7% 9% 22% 10% 1	4888
	11th to 20th	Day	41% 5% 14% 21% 18% 1	5110
	21st to end	Day	48% 8% 13% 22% 8% 1	5713
April	1st to 10th	Day	45% 8% 15% 20% 11% 2	2520
	11th to 20th	Day	40% 7% 14% 21% 14% 4	2492
	21st to end	Day	35% 7% 13% 26% 16% 3	2567
May	1st to 10th	Day	22% 4 10% 29% 31% 5%	7732
	11th to 20th	Day	20% 4 10% 25% 33% 7%	8163
	21st to end	Day	23% 5% 11% 42% 19% 1	8994
June	1st to 10th	Day	31% 6% 12% 29% 19% 2	2940
	11th to 20th	Day	22% 4 8% 30% 27% 8%	2940
	21st to end	Day	15% 3 7% 26% 32% 17%	2940
July	1st to 10th	Day	8% 2 4 19% 30% 37%	8151
	11th to 20th	Day	12% 3 2 12% 29% 43%	8145
	21st to end	Day	12% 2 4 20% 29% 32%	8288
August	1st to 10th	Day	13% 3 4 13% 24% 42%	4336
	11th to 20th	Day	9% 4 3 25% 40% 19%	4218
	21st to end	Day	10% 2 4 27% 38% 19%	4311
September	1st to 10th	Day	8% 3 4 17% 31% 37%	2400
	11th to 20th	Day	19% 5% 8% 21% 34% 13%	2400
	21st to end	Day	17% 4 9% 24% 28% 18%	2111
October	1st to 10th	Day	16% 3 10% 16% 24% 31%	3280
	11th to 20th	Day	23% 5% 12% 34% 20% 5%	3261
	21st to end	Day	33% 8% 12% 23% 17% 7%	3558
November	1st to 10th	Day	41% 6% 14% 21% 14% 4	1894
	11th to 20th	Day	42% 9% 17% 16% 12% 4	1740
	21st to end	Day	36% 8% 15% 20% 15% 6%	1680
December	1st to 10th	Day	29% 9% 11% 29% 20% 2	2700
	11th to 20th	Day	53% 8% 18% 13% 7% 1	3108
	21st to end	Day	57% 9% 15% 14% 5% 1	4092
January	1st to 10th	Night	52% 8% 18% 16% 5% 1	8172
	11th to 20th	Night	30% 13% 9% 19% 24% 4	7901
	21st to end	Night	42% 5% 10% 18% 19% 8%	8371
February	1st to 10th	Night	42% 8% 14% 17% 14% 5%	2730
	11th to 20th	Night	45% 8% 13% 19% 11% 3	2664
	21st to end	Night	41% 9% 17% 16% 14% 3	2076
March	1st to 10th	Night	50% 7% 11% 21% 10% 1	5212
	11th to 20th	Night	36% 6% 16% 21% 17% 4	5110
	21st to end	Night	47% 9% 16% 21% 7% 1	5491
April	1st to 10th	Night	42% 9% 18% 20% 9% 2	2100
	11th to 20th	Night	38% 7% 18% 20% 12% 5%	2079
	21st to end	Night	35% 6% 18% 29% 10% 1	2048
May	1st to 10th	Night	23% 3 11% 30% 29% 3	5206
	11th to 20th	Night	21% 6% 14% 33% 24% 3	4700
	21st to end	Night	23% 6% 15% 43% 12%	5182
June	1st to 10th	Night	31% 5% 16% 34% 11% 1	1680
	11th to 20th	Night	18% 4 12% 36% 24% 5%	1680
	21st to end	Night	13% 4 8% 34% 33% 9%	1680
July	1st to 10th	Night	7% 1 5% 24% 31% 31%	4700
	11th to 20th	Night	10% 2 3 13% 35% 38%	4692
	21st to end	Night	9% 2 6% 22% 34% 26%	5496
August	1st to 10th	Night	10% 2 5% 20% 23% 39%	3019
	11th to 20th	Night	6% 2 5% 35% 34% 17%	2994
	21st to end	Night	14% 3 5% 30% 30% 18%	3608
September	1st to 10th	Night	7% 2 6% 18% 31% 36%	2000
	11th to 20th	Night	16% 5% 8% 25% 33% 14%	2000
	21st to end	Night	17% 5% 10% 24% 24% 21%	2283
October	1st to 10th	Night	14% 4 8% 14% 30% 29%	3920
	11th to 20th	Night	23% 4 10% 39% 17% 6%	3897
	21st to end	Night	26% 7% 14% 26% 19% 7%	4253
November	1st to 10th	Night	42% 7% 14% 18% 14% 6%	2623
	11th to 20th	Night	42% 9% 15% 16% 13% 4	2877
	21st to end	Night	36% 9% 13% 17% 18% 7%	2940
December	1st to 10th	Night	26% 10% 10% 30% 22% 2	4700
	11th to 20th	Night	53% 8% 14% 16% 9% 1	5316
	21st to end	Night	51% 7% 17% 17% 7% 1	7106

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	16% 22% 32% 21% 6% 2	220
	11th to 20th	Day	18% 16% 20% 20% 18% 8%	330
	21st to end	Day	15% 14% 24% 25% 17% 5%	473
February	1st to 10th	Day	14% 18% 22% 32% 11% 3	430
	11th to 20th	Day	18% 22% 24% 24% 11% 1	425
	21st to end	Day	16% 19% 28% 26% 11% 1	446
March	1st to 10th	Day	17% 25% 27% 21% 9% 1	540
	11th to 20th	Day	17% 18% 25% 26% 12% 2	540
	21st to end	Day	18% 24% 28% 21% 8% 2	594
April	1st to 10th	Day	14% 23% 26% 23% 12% 2	540
	11th to 20th	Day	19% 18% 24% 23% 12% 4	532
	21st to end	Day	11% 19% 29% 21% 16% 5%	540
May	1st to 10th	Day	12% 21% 28% 23% 12% 3	543
	11th to 20th	Day	14% 19% 25% 23% 13% 5%	568
	21st to end	Day	13% 12% 25% 28% 16% 6%	617
June	1st to 10th	Day	9% 14% 23% 31% 18% 5%	570
	11th to 20th	Day	8% 16% 30% 25% 16% 5%	570
	21st to end	Day	2 10% 29% 32% 20% 7%	570
July	1st to 10th	Day	3 7% 28% 34% 20% 9%	566
	11th to 20th	Day	1 5% 27% 38% 20% 9%	564
	21st to end	Day	1 5% 22% 39% 23% 10%	619
August	1st to 10th	Day	2 4 23% 33% 26% 11%	567
	11th to 20th	Day	2 6% 23% 33% 23% 13%	534
	21st to end	Day	2 7% 22% 34% 24% 11%	583
September	1st to 10th	Day	2 7% 24% 38% 20% 10%	530
	11th to 20th	Day	6% 8% 23% 33% 23% 8%	530
	21st to end	Day	5% 14% 21% 29% 25% 6%	530
October	1st to 10th	Day	8% 13% 23% 25% 25% 7%	530
	11th to 20th	Day	11% 9% 18% 30% 25% 6%	530
	21st to end	Day	10% 13% 24% 29% 17% 7%	583
November	1st to 10th	Day	12% 15% 24% 26% 17% 5%	370
	11th to 20th	Day	12% 11% 24% 27% 21% 6%	250
	21st to end	Day	10% 9% 24% 30% 20% 7%	220
December	1st to 10th	Day	13% 11% 22% 27% 16% 12%	220
	11th to 20th	Day	22% 15% 20% 25% 10% 8%	220
	21st to end	Day	16% 15% 25% 28% 13% 3	242
January	1st to 10th	Night	15% 13% 31% 26% 12% 3	840
	11th to 20th	Night	12% 14% 26% 25% 19% 5%	840
	21st to end	Night	14% 11% 25% 30% 17% 4	924
February	1st to 10th	Night	13% 12% 28% 33% 12% 2	840
	11th to 20th	Night	14% 12% 28% 31% 14% 2	824
	21st to end	Night	12% 15% 29% 32% 10% 1	692
March	1st to 10th	Night	16% 21% 28% 23% 11% 2	840
	11th to 20th	Night	13% 15% 25% 29% 16% 2	840
	21st to end	Night	13% 19% 31% 27% 9% 1	924
April	1st to 10th	Night	13% 17% 29% 27% 13% 1	840
	11th to 20th	Night	11% 14% 30% 28% 15% 3	831
	21st to end	Night	14% 10% 25% 31% 18% 2	788
May	1st to 10th	Night	9% 9% 30% 29% 21% 2	593
	11th to 20th	Night	12% 7% 26% 33% 21% 1	414
	21st to end	Night	11% 8% 23% 34% 22% 1	455
June	1st to 10th	Night	11% 6% 20% 40% 22% 1	420
	11th to 20th	Night	6% 7% 23% 47% 16% 1	420
	21st to end	Night	4 4 20% 48% 24%	420
July	1st to 10th	Night	1 14% 50% 33% 1	410
	11th to 20th	Night	2 13% 53% 31% 1	408
	21st to end	Night	1 8% 42% 43% 5%	618
August	1st to 10th	Night	2 1 7% 44% 41% 5%	627
	11th to 20th	Night	2 1 11% 44% 35% 7%	622
	21st to end	Night	3 2 16% 41% 34% 4	880
September	1st to 10th	Night	2 3 17% 41% 33% 4	800
	11th to 20th	Night	5% 3 17% 35% 34% 6%	800
	21st to end	Night	6% 5% 17% 36% 30% 7%	800
October	1st to 10th	Night	4 5% 23% 36% 28% 4	800
	11th to 20th	Night	7% 8% 19% 36% 26% 5%	800
	21st to end	Night	8% 9% 20% 35% 20% 7%	880
November	1st to 10th	Night	13% 9% 25% 32% 15% 5%	820
	11th to 20th	Night	17% 11% 27% 30% 12% 3	840
	21st to end	Night	12% 10% 23% 33% 19% 3	840
December	1st to 10th	Night	11% 13% 22% 32% 17% 5%	840
	11th to 20th	Night	18% 14% 24% 28% 13% 4	840
	21st to end	Night	22% 16% 26% 24% 9% 2	924

Page generated at 2026-08-12 00:37:15. Version ac07

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