Stake Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stake Lake Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	7% 10% 4 9% 6% 6% 6% 5% 6% 7% 34%	105335
	Night	6% 10% 4 10% 6% 6% 6% 4 7% 8% 34%	102277
Transparency	Day	44% 8% 15% 21% 10% 3	105090
	Night	45% 7% 16% 21% 9% 2	102168
Seeing	Day	16% 17% 26% 23% 14% 4	15624
	Night	13% 16% 26% 27% 15% 3	23919

By Month

Percentage Cloud Cover NW (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% 14% 6% 16% 9% 7% 6% 6% 6% 7% 16%	2219
	11th to 20th	Day	5% 15% 5% 10% 7% 5% 5% 4 7% 9% 27%	2332
	21st to end	Day	3 16% 6% 12% 7% 7% 7% 6% 8% 9% 20%	2794
February	1st to 10th	Day	6% 18% 6% 11% 7% 6% 7% 5% 6% 6% 22%	1578
	11th to 20th	Day	4 15% 6% 11% 6% 5% 6% 6% 6% 7% 29%	1665
	21st to end	Day	3 14% 7% 13% 9% 8% 5% 5% 7% 6% 23%	1505
March	1st to 10th	Day	2 10% 4 12% 8% 8% 8% 6% 9% 8% 23%	3138
	11th to 20th	Day	3 8% 3 8% 6% 6% 6% 5% 6% 7% 39%	3387
	21st to end	Day	4 15% 5% 12% 9% 7% 7% 5% 7% 7% 24%	4072
April	1st to 10th	Day	7% 13% 6% 13% 9% 7% 8% 4 6% 7% 19%	2280
	11th to 20th	Day	7% 15% 5% 11% 8% 6% 6% 5% 5% 7% 23%	2256
	21st to end	Day	8% 15% 4 12% 7% 6% 6% 5% 6% 7% 24%	2657
May	1st to 10th	Day	6% 12% 4 8% 6% 5% 5% 4 5% 7% 38%	4420
	11th to 20th	Day	9% 10% 4 11% 6% 6% 6% 5% 7% 11% 26%	4377
	21st to end	Day	13% 16% 6% 14% 7% 6% 5% 4 5% 5% 18%	4813
June	1st to 10th	Day	18% 10% 3 9% 6% 6% 5% 5% 6% 7% 25%	3011
	11th to 20th	Day	16% 12% 4 11% 8% 6% 6% 4 5% 6% 22%	3040
	21st to end	Day	11% 7% 2 9% 5% 5% 5% 5% 7% 7% 34%	3040
July	1st to 10th	Day	5% 5% 2 6% 4 4 4 4 5% 6% 55%	4785
	11th to 20th	Day	4 3 1 4 3 4 4 3 5% 6% 60%	4688
	21st to end	Day	6% 5% 2 5% 4 4 4 4 7% 8% 51%	4790
August	1st to 10th	Day	3 3 2 5% 4 5% 6% 4 7% 6% 56%	4401
	11th to 20th	Day	4 4 2 8% 6% 7% 7% 6% 7% 9% 41%	4270
	21st to end	Day	9% 5% 2 7% 4 5% 5% 5% 7% 8% 42%	4305
September	1st to 10th	Day	9% 6% 3 7% 4 4 4 3 5% 6% 49%	2280
	11th to 20th	Day	12% 9% 3 7% 5% 5% 5% 3 5% 6% 40%	2280
	21st to end	Day	12% 8% 3 8% 5% 5% 5% 4 7% 8% 35%	2036
October	1st to 10th	Day	6% 7% 3 8% 6% 5% 5% 4 6% 8% 41%	3180
	11th to 20th	Day	13% 13% 3 7% 5% 5% 5% 4 6% 8% 33%	3103
	21st to end	Day	7% 13% 4 11% 6% 5% 6% 4 6% 9% 30%	3101
November	1st to 10th	Day	10% 14% 5% 13% 7% 6% 6% 4 5% 6% 26%	1559
	11th to 20th	Day	6% 14% 4 9% 7% 7% 6% 5% 7% 6% 29%	1520
	21st to end	Day	8% 15% 3 10% 7% 7% 6% 6% 7% 8% 24%	1425
December	1st to 10th	Day	4 11% 5% 13% 8% 9% 8% 5% 6% 7% 24%	1330
	11th to 20th	Day	3 13% 6% 13% 8% 8% 6% 6% 7% 8% 22%	1503
	21st to end	Day	4 12% 5% 12% 8% 8% 8% 6% 8% 8% 22%	2195
January	1st to 10th	Night	6% 15% 6% 14% 9% 8% 7% 5% 6% 7% 17%	4726
	11th to 20th	Night	5% 13% 6% 13% 8% 6% 5% 4 9% 8% 24%	4563
	21st to end	Night	4 11% 5% 12% 8% 8% 7% 6% 9% 9% 22%	4862
February	1st to 10th	Night	7% 16% 5% 12% 7% 7% 6% 5% 6% 6% 24%	2599
	11th to 20th	Night	4 12% 4 12% 6% 5% 6% 4 6% 7% 32%	2402
	21st to end	Night	3 12% 6% 15% 9% 6% 6% 4 6% 9% 26%	1948
March	1st to 10th	Night	2 10% 3 9% 6% 6% 8% 6% 9% 11% 29%	3736
	11th to 20th	Night	2 6% 2 7% 6% 4 6% 5% 8% 9% 45%	3588
	21st to end	Night	5% 13% 5% 9% 7% 6% 7% 6% 6% 7% 29%	3581
April	1st to 10th	Night	4 11% 4 11% 8% 6% 6% 5% 7% 8% 31%	1900
	11th to 20th	Night	3 12% 5% 10% 8% 7% 6% 6% 6% 6% 30%	1874
	21st to end	Night	4 11% 3 8% 6% 6% 5% 5% 7% 8% 36%	1522
May	1st to 10th	Night	6% 13% 4 9% 5% 6% 5% 3 6% 6% 38%	2540
	11th to 20th	Night	5% 10% 3 10% 6% 6% 5% 5% 8% 9% 32%	2516
	21st to end	Night	9% 10% 4 9% 6% 6% 6% 4 6% 8% 31%	2762
June	1st to 10th	Night	13% 7% 3 9% 5% 5% 5% 5% 8% 7% 32%	1160
	11th to 20th	Night	11% 8% 3 9% 8% 4 7% 5% 8% 8% 30%	1140
	21st to end	Night	6% 7% 4 8% 5% 5% 4 3 7% 7% 44%	1140
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 3 5% 6% 54%	2171
	11th to 20th	Night	3 2 1 3 3 3 3 4 5% 7% 66%	2270
	21st to end	Night	5% 3 2 5% 4 4 4 4 5% 7% 58%	2762
August	1st to 10th	Night	4 5% 2 5% 4 5% 4 4 5% 7% 55%	2529
	11th to 20th	Night	5% 4 2 6% 6% 5% 5% 4 8% 10% 45%	2556
	21st to end	Night	8% 6% 2 6% 5% 5% 5% 4 6% 8% 45%	3368
September	1st to 10th	Night	6% 5% 2 6% 3 3 5% 2 6% 7% 54%	1900
	11th to 20th	Night	8% 6% 3 6% 4 4 6% 3 6% 8% 46%	1900
	21st to end	Night	9% 9% 3 7% 4 5% 4 4 5% 9% 42%	2139
October	1st to 10th	Night	8% 8% 3 7% 5% 5% 5% 4 6% 7% 42%	3800
	11th to 20th	Night	11% 11% 3 7% 5% 5% 5% 4 6% 8% 34%	3832
	21st to end	Night	7% 10% 4 11% 6% 5% 5% 4 6% 7% 36%	4457
November	1st to 10th	Night	9% 14% 4 10% 7% 7% 6% 5% 6% 6% 26%	2615
	11th to 20th	Night	5% 13% 4 11% 8% 7% 6% 4 6% 7% 29%	2660
	21st to end	Night	7% 16% 4 10% 8% 6% 7% 5% 6% 7% 24%	2734
December	1st to 10th	Night	5% 12% 5% 10% 7% 7% 7% 5% 7% 7% 27%	2850
	11th to 20th	Night	6% 16% 7% 15% 9% 7% 6% 4 5% 5% 19%	3686
	21st to end	Night	4 13% 5% 12% 8% 7% 7% 6% 7% 7% 25%	5489

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	63% 8% 14% 13% 2	2219
	11th to 20th	Day	52% 7% 19% 13% 4 5%	2354
	21st to end	Day	57% 12% 17% 11% 3	2794
February	1st to 10th	Day	58% 8% 12% 13% 6% 1	1578
	11th to 20th	Day	52% 7% 16% 16% 8% 1	1674
	21st to end	Day	57% 7% 14% 16% 6%	1505
March	1st to 10th	Day	49% 10% 13% 20% 7%	3138
	11th to 20th	Day	40% 7% 19% 28% 6%	3387
	21st to end	Day	55% 7% 15% 14% 8%	4072
April	1st to 10th	Day	58% 10% 12% 15% 5%	2280
	11th to 20th	Day	53% 10% 9% 16% 10% 1	2256
	21st to end	Day	53% 9% 13% 16% 9%	2657
May	1st to 10th	Day	42% 7% 11% 29% 10% 1	4420
	11th to 20th	Day	43% 12% 14% 25% 6%	4380
	21st to end	Day	60% 10% 12% 14% 4	4814
June	1st to 10th	Day	52% 9% 11% 16% 9% 4	3011
	11th to 20th	Day	59% 8% 10% 16% 7%	3040
	21st to end	Day	43% 8% 14% 22% 12% 2	3040
July	1st to 10th	Day	26% 5% 9% 21% 21% 16%	4711
	11th to 20th	Day	20% 5% 11% 25% 28% 12%	4607
	21st to end	Day	26% 5% 16% 27% 18% 8%	4639
August	1st to 10th	Day	23% 6% 12% 31% 25% 3	4384
	11th to 20th	Day	32% 10% 22% 25% 10% 2	4312
	21st to end	Day	35% 7% 19% 30% 8% 1	4304
September	1st to 10th	Day	34% 6% 14% 29% 14% 3	2280
	11th to 20th	Day	42% 6% 12% 25% 12% 3	2280
	21st to end	Day	43% 9% 18% 20% 10% 1	2036
October	1st to 10th	Day	38% 6% 21% 26% 8%	3180
	11th to 20th	Day	47% 6% 15% 27% 6%	3103
	21st to end	Day	47% 10% 19% 20% 4	3101
November	1st to 10th	Day	57% 8% 13% 17% 5% 1	1559
	11th to 20th	Day	51% 8% 17% 18% 6% 1	1520
	21st to end	Day	53% 9% 16% 16% 6%	1425
December	1st to 10th	Day	54% 12% 16% 15% 3	1330
	11th to 20th	Day	57% 10% 16% 12% 4	1505
	21st to end	Day	55% 10% 17% 17% 2	2195
January	1st to 10th	Night	63% 7% 16% 11% 4	4726
	11th to 20th	Night	55% 6% 16% 13% 5% 4	4603
	21st to end	Night	55% 12% 18% 11% 3	4862
February	1st to 10th	Night	58% 7% 14% 14% 6% 1	2599
	11th to 20th	Night	49% 7% 16% 18% 8% 1	2404
	21st to end	Night	53% 7% 15% 17% 7%	1948
March	1st to 10th	Night	42% 11% 15% 23% 10%	3736
	11th to 20th	Night	31% 7% 21% 31% 10%	3589
	21st to end	Night	50% 7% 14% 18% 10%	3581
April	1st to 10th	Night	47% 8% 19% 19% 6%	1900
	11th to 20th	Night	48% 9% 13% 19% 11%	1874
	21st to end	Night	41% 8% 15% 25% 10% 1	1522
May	1st to 10th	Night	43% 8% 10% 26% 12% 1	2540
	11th to 20th	Night	41% 11% 15% 26% 7%	2516
	21st to end	Night	49% 6% 18% 21% 6%	2762
June	1st to 10th	Night	45% 8% 13% 22% 8% 4	1160
	11th to 20th	Night	46% 10% 15% 22% 7%	1140
	21st to end	Night	37% 5% 19% 24% 13% 2	1140
July	1st to 10th	Night	29% 5% 10% 18% 24% 14%	2136
	11th to 20th	Night	16% 4 9% 30% 32% 8%	2228
	21st to end	Night	23% 6% 14% 28% 16% 14%	2674
August	1st to 10th	Night	25% 6% 12% 26% 28% 3	2521
	11th to 20th	Night	30% 7% 20% 29% 12% 2	2580
	21st to end	Night	32% 8% 22% 27% 10% 1	3368
September	1st to 10th	Night	27% 6% 16% 31% 16% 3	1900
	11th to 20th	Night	34% 6% 16% 25% 14% 5%	1900
	21st to end	Night	39% 6% 21% 20% 12% 2	2139
October	1st to 10th	Night	38% 6% 21% 27% 9%	3800
	11th to 20th	Night	45% 6% 14% 27% 7%	3832
	21st to end	Night	45% 6% 16% 28% 5%	4457
November	1st to 10th	Night	55% 8% 15% 15% 7%	2615
	11th to 20th	Night	53% 8% 16% 15% 7% 1	2660
	21st to end	Night	56% 8% 17% 13% 6%	2734
December	1st to 10th	Night	52% 9% 17% 17% 5%	2850
	11th to 20th	Night	66% 8% 12% 11% 3	3683
	21st to end	Night	55% 8% 18% 15% 4	5489

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	13% 27% 27% 18% 8% 7%	180
	11th to 20th	Day	13% 19% 29% 22% 13% 4	180
	21st to end	Day	14% 23% 28% 20% 12% 2	198
February	1st to 10th	Day	19% 24% 32% 18% 5% 1	238
	11th to 20th	Day	16% 24% 28% 22% 8% 2	365
	21st to end	Day	15% 21% 32% 18% 11% 2	352
March	1st to 10th	Day	20% 25% 25% 18% 11% 1	460
	11th to 20th	Day	19% 24% 25% 18% 10% 3	460
	21st to end	Day	19% 27% 25% 16% 10% 3	506
April	1st to 10th	Day	22% 21% 28% 21% 6% 2	460
	11th to 20th	Day	17% 26% 24% 19% 11% 2	452
	21st to end	Day	19% 21% 30% 17% 9% 3	460
May	1st to 10th	Day	17% 21% 23% 28% 8% 3	463
	11th to 20th	Day	17% 13% 20% 28% 16% 5%	488
	21st to end	Day	17% 15% 25% 24% 15% 4	529
June	1st to 10th	Day	21% 21% 25% 21% 10% 1	841
	11th to 20th	Day	19% 15% 28% 24% 12% 3	870
	21st to end	Day	15% 12% 26% 26% 17% 4	870
July	1st to 10th	Day	11% 13% 26% 31% 15% 4	703
	11th to 20th	Day	10% 14% 28% 28% 16% 5%	642
	21st to end	Day	7% 7% 22% 38% 20% 6%	531
August	1st to 10th	Day	7% 6% 22% 29% 28% 8%	487
	11th to 20th	Day	7% 11% 23% 31% 21% 7%	477
	21st to end	Day	12% 12% 28% 28% 14% 6%	539
September	1st to 10th	Day	13% 14% 26% 25% 17% 5%	490
	11th to 20th	Day	18% 17% 23% 22% 17% 4	490
	21st to end	Day	20% 17% 27% 22% 12% 2	490
October	1st to 10th	Day	21% 14% 24% 21% 16% 3	490
	11th to 20th	Day	23% 19% 23% 18% 14% 2	457
	21st to end	Day	22% 17% 26% 23% 10% 2	330
November	1st to 10th	Day	22% 22% 27% 19% 10% 1	208
	11th to 20th	Day	22% 21% 27% 12% 14% 4	180
	21st to end	Day	20% 19% 29% 15% 11% 6%	180
December	1st to 10th	Day	13% 14% 24% 24% 18% 7%	180
	11th to 20th	Day	12% 27% 29% 15% 12% 5%	180
	21st to end	Day	16% 13% 32% 27% 9% 3	198
January	1st to 10th	Night	22% 20% 24% 23% 10% 1	850
	11th to 20th	Night	13% 15% 27% 31% 13% 2	810
	21st to end	Night	11% 17% 28% 28% 14% 2	836
February	1st to 10th	Night	16% 17% 25% 29% 11% 3	760
	11th to 20th	Night	12% 17% 24% 32% 14% 1	744
	21st to end	Night	13% 15% 28% 24% 18% 2	628
March	1st to 10th	Night	12% 22% 23% 25% 15% 3	760
	11th to 20th	Night	13% 23% 27% 22% 14% 2	760
	21st to end	Night	13% 19% 29% 22% 13% 4	836
April	1st to 10th	Night	13% 18% 25% 26% 15% 3	760
	11th to 20th	Night	12% 20% 27% 25% 15% 1	746
	21st to end	Night	10% 21% 31% 26% 10% 2	382
May	1st to 10th	Night	14% 13% 28% 27% 15% 3	380
	11th to 20th	Night	11% 10% 25% 36% 15% 3	374
	21st to end	Night	14% 9% 28% 26% 20% 2	411
June	1st to 10th	Night	16% 14% 30% 28% 9% 2	380
	11th to 20th	Night	14% 13% 32% 26% 13% 3	380
	21st to end	Night	7% 13% 30% 27% 19% 3	380
July	1st to 10th	Night	8% 9% 28% 37% 17% 2	370
	11th to 20th	Night	7% 9% 30% 32% 21% 1	368
	21st to end	Night	5% 5% 28% 35% 23% 4	416
August	1st to 10th	Night	8% 4 20% 32% 30% 6%	378
	11th to 20th	Night	6% 5% 25% 29% 29% 5%	409
	21st to end	Night	11% 9% 25% 30% 21% 4	758
September	1st to 10th	Night	11% 9% 21% 28% 26% 5%	760
	11th to 20th	Night	12% 10% 19% 25% 27% 7%	760
	21st to end	Night	17% 16% 23% 23% 17% 4	760
October	1st to 10th	Night	12% 15% 23% 27% 20% 4	760
	11th to 20th	Night	17% 17% 21% 25% 17% 3	760
	21st to end	Night	17% 18% 28% 22% 12% 2	836
November	1st to 10th	Night	20% 18% 28% 26% 8% 1	760
	11th to 20th	Night	17% 24% 24% 21% 13% 1	760
	21st to end	Night	16% 19% 25% 25% 12% 3	834
December	1st to 10th	Night	14% 14% 27% 28% 15% 2	950
	11th to 20th	Night	14% 21% 27% 27% 10% 1	1010
	21st to end	Night	16% 18% 28% 27% 10% 2	1093

Page generated at 2024-11-02 23:11:28. Version ac07

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