Mitten Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mitten Lake Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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% 11% 4 9% 5% 5% 5% 4 5% 7% 32%	101997
	Night	13% 12% 4 10% 5% 5% 4 4 5% 6% 32%	98212
Transparency	Day	50% 6% 12% 22% 10% 1	105491
	Night	51% 6% 11% 22% 10% 1	102857
Seeing	Day	19% 13% 32% 22% 11% 3	16218
	Night	19% 11% 32% 27% 10% 1	26169

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	11% 18% 7% 22% 6% 5% 4 3 4 5% 16%	2527
	11th to 20th	Day	8% 16% 6% 17% 10% 8% 9% 4 5% 5% 12%	2530
	21st to end	Day	10% 17% 11% 18% 6% 4 4 3 4 5% 15%	2792
February	1st to 10th	Day	9% 13% 5% 10% 6% 6% 7% 6% 6% 6% 26%	1710
	11th to 20th	Day	9% 11% 5% 14% 7% 6% 7% 5% 6% 5% 26%	1697
	21st to end	Day	12% 12% 6% 12% 7% 7% 4 3 6% 6% 23%	1570
March	1st to 10th	Day	11% 12% 4 11% 6% 4 4 3 4 6% 37%	3120
	11th to 20th	Day	8% 13% 5% 13% 7% 5% 5% 4 5% 7% 29%	3402
	21st to end	Day	18% 14% 5% 13% 5% 4 4 3 4 5% 25%	4088
April	1st to 10th	Day	14% 15% 4 10% 6% 5% 4 4 5% 5% 28%	2280
	11th to 20th	Day	18% 13% 6% 9% 5% 3 3 3 5% 5% 30%	2254
	21st to end	Day	18% 11% 4 7% 6% 5% 4 4 4 6% 30%	2417
May	1st to 10th	Day	17% 9% 2 6% 4 4 4 3 5% 6% 39%	4399
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	4399
	21st to end	Day	16% 9% 3 8% 5% 4 4 4 5% 7% 34%	4824
June	1st to 10th	Day	14% 7% 2 5% 5% 5% 4 4 6% 9% 39%	2660
	11th to 20th	Day	14% 8% 2 6% 5% 5% 5% 5% 6% 6% 38%	2660
	21st to end	Day	13% 7% 3 6% 5% 5% 6% 5% 7% 8% 36%	2660
July	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 7% 9% 40%	4440
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 48%	4440
	21st to end	Day	8% 5% 3 6% 5% 4 5% 4 7% 8% 45%	4813
August	1st to 10th	Day	13% 7% 2 7% 4 6% 5% 4 6% 8% 38%	4423
	11th to 20th	Day	13% 6% 2 6% 3 4 4 3 5% 8% 46%	4026
	21st to end	Day	14% 8% 3 7% 5% 4 4 4 5% 8% 37%	4180
September	1st to 10th	Day	13% 8% 3 6% 3 4 5% 3 5% 8% 42%	2280
	11th to 20th	Day	12% 8% 2 6% 5% 3 4 4 6% 8% 39%	2249
	21st to end	Day	17% 9% 3 8% 4 4 4 3 5% 7% 35%	2073
October	1st to 10th	Day	18% 10% 3 6% 4 4 4 4 5% 7% 35%	1900
	11th to 20th	Day	20% 15% 5% 8% 5% 4 5% 3 6% 5% 25%	1900
	21st to end	Day	21% 16% 5% 9% 4 3 4 3 6% 6% 25%	1887
November	1st to 10th	Day	16% 15% 4 7% 5% 4 4 3 5% 6% 30%	1762
	11th to 20th	Day	15% 18% 6% 13% 7% 5% 4 3 4 5% 20%	1630
	21st to end	Day	13% 16% 7% 15% 9% 4 5% 3 5% 6% 17%	1600
December	1st to 10th	Day	10% 17% 7% 18% 9% 6% 5% 3 6% 4 14%	1600
	11th to 20th	Day	12% 15% 7% 16% 9% 6% 6% 4 4 4 15%	1998
	21st to end	Day	18% 25% 7% 14% 6% 5% 5% 2 3 3 12%	2807
January	1st to 10th	Night	11% 16% 7% 20% 7% 5% 4 3 4 5% 18%	4428
	11th to 20th	Night	8% 15% 6% 17% 9% 9% 6% 5% 6% 5% 14%	4440
	21st to end	Night	10% 19% 9% 18% 6% 4 4 3 4 4 18%	4872
February	1st to 10th	Night	7% 13% 6% 13% 7% 6% 5% 5% 5% 7% 27%	2470
	11th to 20th	Night	8% 11% 4 11% 7% 7% 6% 4 6% 8% 28%	2370
	21st to end	Night	11% 16% 5% 10% 6% 5% 5% 4 6% 5% 27%	1884
March	1st to 10th	Night	9% 7% 3 8% 4 5% 5% 4 7% 9% 40%	3733
	11th to 20th	Night	8% 10% 5% 13% 6% 5% 5% 3 5% 6% 33%	3587
	21st to end	Night	18% 14% 4 11% 5% 4 4 4 5% 5% 27%	3542
April	1st to 10th	Night	19% 11% 3 8% 5% 4 4 4 4 7% 29%	1900
	11th to 20th	Night	22% 10% 3 7% 4 4 3 3 5% 6% 34%	1875
	21st to end	Night	19% 10% 3 6% 4 4 5% 3 5% 5% 35%	1760
May	1st to 10th	Night	17% 9% 3 6% 4 5% 4 3 4 8% 36%	2506
	11th to 20th	Night	13% 8% 2 7% 5% 4 4 3 4 5% 45%	2506
	21st to end	Night	14% 9% 3 8% 5% 5% 4 4 5% 7% 37%	2743
June	1st to 10th	Night	12% 7% 2 6% 3 4 4 4 5% 7% 45%	1520
	11th to 20th	Night	12% 6% 3 7% 5% 5% 5% 5% 5% 7% 40%	1520
	21st to end	Night	12% 5% 2 7% 5% 4 5% 4 6% 9% 42%	1520
July	1st to 10th	Night	13% 6% 1 5% 3 3 3 4 5% 8% 48%	2530
	11th to 20th	Night	7% 4 2 5% 4 3 4 4 6% 9% 53%	2530
	21st to end	Night	8% 5% 2 5% 3 3 4 4 5% 8% 52%	2750
August	1st to 10th	Night	10% 7% 2 6% 4 5% 5% 4 6% 7% 43%	2517
	11th to 20th	Night	13% 6% 1 5% 3 3 3 3 5% 7% 52%	2795
	21st to end	Night	16% 9% 2 6% 4 3 3 2 4 6% 43%	3476
September	1st to 10th	Night	12% 5% 2 5% 3 4 4 4 5% 7% 49%	1900
	11th to 20th	Night	11% 6% 2 5% 3 4 4 4 5% 8% 47%	1911
	21st to end	Night	15% 8% 2 6% 5% 4 4 4 5% 7% 40%	2104
October	1st to 10th	Night	16% 7% 2 6% 4 4 3 3 4 8% 41%	2280
	11th to 20th	Night	16% 13% 4 7% 4 5% 4 4 6% 6% 31%	2280
	21st to end	Night	19% 14% 3 8% 5% 4 5% 4 6% 7% 25%	2710
November	1st to 10th	Night	15% 13% 4 7% 5% 4 4 3 5% 7% 33%	2536
	11th to 20th	Night	14% 16% 7% 12% 5% 5% 3 3 5% 5% 24%	2765
	21st to end	Night	14% 15% 6% 14% 7% 5% 4 3 5% 6% 21%	2800
December	1st to 10th	Night	10% 16% 6% 15% 8% 7% 5% 4 6% 5% 18%	2800
	11th to 20th	Night	11% 15% 8% 14% 8% 6% 5% 4 5% 5% 18%	3419
	21st to end	Night	23% 22% 6% 11% 5% 4 3 3 4 4 15%	4933

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	71% 4 5% 16% 3	2528
	11th to 20th	Day	73% 5% 8% 9% 5%	2530
	21st to end	Day	71% 4 10% 10% 4	2792
February	1st to 10th	Day	56% 5% 9% 18% 11%	1710
	11th to 20th	Day	57% 6% 9% 21% 6%	1706
	21st to end	Day	62% 5% 8% 15% 9% 1	1570
March	1st to 10th	Day	49% 4 14% 17% 16% 1	3120
	11th to 20th	Day	54% 5% 13% 18% 9% 1	3402
	21st to end	Day	62% 5% 9% 17% 6%	4088
April	1st to 10th	Day	58% 4 10% 17% 10% 1	2280
	11th to 20th	Day	56% 4 10% 20% 9% 1	2254
	21st to end	Day	54% 5% 9% 18% 13% 1	2417
May	1st to 10th	Day	46% 6% 9% 24% 14% 1	4440
	11th to 20th	Day	43% 7% 11% 26% 11% 1	4403
	21st to end	Day	49% 6% 10% 19% 15% 1	4837
June	1st to 10th	Day	40% 7% 13% 27% 12% 1	2660
	11th to 20th	Day	45% 7% 12% 22% 14% 1	2660
	21st to end	Day	42% 8% 15% 24% 9% 1	2660
July	1st to 10th	Day	38% 7% 14% 29% 11% 1	4371
	11th to 20th	Day	29% 7% 16% 33% 13% 2	4365
	21st to end	Day	34% 7% 12% 30% 16%	4662
August	1st to 10th	Day	42% 7% 15% 23% 11% 1	4408
	11th to 20th	Day	36% 7% 15% 30% 12%	4066
	21st to end	Day	44% 7% 15% 23% 11% 1	4179
September	1st to 10th	Day	40% 5% 14% 29% 12%	2280
	11th to 20th	Day	41% 7% 18% 26% 8%	2249
	21st to end	Day	48% 7% 11% 26% 9%	2073
October	1st to 10th	Day	37% 4 14% 29% 16%	3160
	11th to 20th	Day	53% 4 9% 20% 13%	3140
	21st to end	Day	53% 5% 16% 20% 5%	3087
November	1st to 10th	Day	55% 6% 10% 21% 8% 1	1762
	11th to 20th	Day	68% 4 9% 13% 6%	1630
	21st to end	Day	67% 7% 11% 11% 3 1	1600
December	1st to 10th	Day	71% 5% 9% 12% 3	1600
	11th to 20th	Day	71% 6% 9% 10% 4	1995
	21st to end	Day	79% 3 4 10% 3	2807
January	1st to 10th	Night	69% 5% 7% 15% 3	4428
	11th to 20th	Night	69% 6% 10% 12% 3	4440
	21st to end	Night	69% 5% 7% 15% 4	4872
February	1st to 10th	Night	57% 5% 7% 20% 11% 1	2470
	11th to 20th	Night	54% 6% 10% 20% 8% 1	2371
	21st to end	Night	58% 5% 10% 17% 9% 1	1884
March	1st to 10th	Night	39% 7% 17% 23% 13% 1	3733
	11th to 20th	Night	51% 5% 10% 24% 9% 1	3587
	21st to end	Night	60% 4 9% 18% 9% 1	3542
April	1st to 10th	Night	54% 5% 8% 18% 14% 1	1900
	11th to 20th	Night	51% 4 8% 22% 12% 2	1875
	21st to end	Night	50% 5% 10% 19% 15% 1	1760
May	1st to 10th	Night	46% 6% 13% 21% 13% 1	2530
	11th to 20th	Night	40% 8% 9% 25% 15% 3	2507
	21st to end	Night	45% 7% 15% 18% 14% 1	2751
June	1st to 10th	Night	37% 6% 16% 28% 13%	1520
	11th to 20th	Night	43% 7% 11% 23% 16% 1	1520
	21st to end	Night	37% 7% 15% 28% 10% 2	1520
July	1st to 10th	Night	34% 6% 18% 27% 12% 3	2490
	11th to 20th	Night	26% 6% 16% 38% 13% 1	2482
	21st to end	Night	29% 7% 12% 31% 18% 2	2662
August	1st to 10th	Night	38% 8% 13% 24% 15% 1	2508
	11th to 20th	Night	32% 7% 16% 31% 13% 1	2820
	21st to end	Night	42% 5% 14% 24% 13% 2	3476
September	1st to 10th	Night	34% 6% 14% 33% 13% 1	1900
	11th to 20th	Night	35% 6% 16% 35% 8%	1911
	21st to end	Night	43% 6% 13% 26% 11% 1	2104
October	1st to 10th	Night	33% 4 9% 33% 20% 2	3800
	11th to 20th	Night	43% 5% 11% 28% 12%	3779
	21st to end	Night	57% 5% 11% 20% 8%	4460
November	1st to 10th	Night	52% 5% 12% 22% 9%	2536
	11th to 20th	Night	62% 5% 12% 13% 8% 1	2765
	21st to end	Night	64% 5% 11% 14% 4 1	2800
December	1st to 10th	Night	66% 6% 11% 14% 3	2800
	11th to 20th	Night	67% 6% 9% 13% 4	3421
	21st to end	Night	74% 4 5% 13% 4	4933

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	19% 14% 33% 25% 7% 2	270
	11th to 20th	Day	22% 14% 35% 20% 8% 1	270
	21st to end	Day	20% 10% 42% 25% 4	297
February	1st to 10th	Day	18% 15% 41% 19% 6% 2	270
	11th to 20th	Day	15% 23% 41% 15% 6% 1	270
	21st to end	Day	19% 18% 50% 12% 1	225
March	1st to 10th	Day	16% 19% 42% 15% 7%	270
	11th to 20th	Day	20% 18% 36% 18% 8% 1	270
	21st to end	Day	24% 12% 36% 18% 7% 2	455
April	1st to 10th	Day	23% 16% 35% 20% 5% 1	460
	11th to 20th	Day	29% 12% 30% 20% 8% 1	452
	21st to end	Day	23% 15% 31% 20% 9% 2	493
May	1st to 10th	Day	22% 17% 31% 22% 6% 2	653
	11th to 20th	Day	19% 12% 32% 23% 11% 3	675
	21st to end	Day	21% 13% 30% 22% 12% 2	734
June	1st to 10th	Day	15% 14% 30% 25% 13% 3	680
	11th to 20th	Day	20% 10% 35% 22% 10% 3	680
	21st to end	Day	16% 12% 31% 23% 14% 4	680
July	1st to 10th	Day	10% 6% 30% 30% 16% 8%	671
	11th to 20th	Day	12% 9% 30% 26% 17% 6%	668
	21st to end	Day	9% 7% 32% 27% 15% 9%	739
August	1st to 10th	Day	14% 7% 26% 30% 18% 4	676
	11th to 20th	Day	17% 6% 21% 29% 22% 5%	632
	21st to end	Day	18% 10% 23% 25% 18% 5%	539
September	1st to 10th	Day	17% 12% 23% 25% 16% 6%	490
	11th to 20th	Day	14% 10% 28% 30% 14% 3	490
	21st to end	Day	23% 12% 24% 25% 10% 5%	473
October	1st to 10th	Day	22% 17% 28% 22% 10% 2	300
	11th to 20th	Day	25% 22% 35% 12% 6%	300
	21st to end	Day	32% 19% 35% 11% 3	330
November	1st to 10th	Day	26% 14% 36% 18% 5% 1	300
	11th to 20th	Day	25% 20% 38% 14% 2 1	300
	21st to end	Day	22% 18% 42% 13% 4	300
December	1st to 10th	Day	18% 14% 43% 20% 5%	300
	11th to 20th	Day	21% 18% 41% 17% 3	300
	21st to end	Day	25% 22% 33% 16% 3 1	306
January	1st to 10th	Night	16% 13% 42% 22% 6%	950
	11th to 20th	Night	18% 13% 41% 21% 6% 1	950
	21st to end	Night	20% 11% 37% 25% 6%	1045
February	1st to 10th	Night	15% 14% 40% 24% 7% 1	950
	11th to 20th	Night	15% 16% 40% 23% 6% 1	896
	21st to end	Night	19% 14% 39% 24% 4	628
March	1st to 10th	Night	17% 12% 35% 28% 7% 1	760
	11th to 20th	Night	17% 13% 40% 22% 8%	638
	21st to end	Night	20% 12% 28% 28% 10% 2	627
April	1st to 10th	Night	24% 9% 35% 24% 6% 1	570
	11th to 20th	Night	27% 10% 27% 29% 7%	563
	21st to end	Night	24% 8% 32% 26% 8% 1	570
May	1st to 10th	Night	21% 12% 29% 30% 6% 1	570
	11th to 20th	Night	20% 9% 29% 32% 9% 2	561
	21st to end	Night	16% 9% 28% 34% 13%	617
June	1st to 10th	Night	15% 7% 30% 35% 12% 1	570
	11th to 20th	Night	16% 10% 28% 36% 11%	570
	21st to end	Night	14% 7% 26% 37% 15% 2	570
July	1st to 10th	Night	10% 3 25% 38% 23% 2	555
	11th to 20th	Night	12% 6% 29% 31% 20% 1	552
	21st to end	Night	10% 2 24% 43% 18% 3	624
August	1st to 10th	Night	10% 4 26% 37% 22% 1	567
	11th to 20th	Night	15% 5% 19% 32% 26% 3	564
	21st to end	Night	17% 4 25% 30% 22% 1	627
September	1st to 10th	Night	16% 7% 25% 32% 17% 3	570
	11th to 20th	Night	14% 7% 27% 34% 16% 2	581
	21st to end	Night	20% 10% 28% 28% 13% 1	760
October	1st to 10th	Night	21% 11% 29% 26% 13% 1	760
	11th to 20th	Night	23% 15% 32% 24% 6%	760
	21st to end	Night	26% 11% 29% 26% 7%	836
November	1st to 10th	Night	24% 12% 36% 23% 6% 1	780
	11th to 20th	Night	24% 18% 33% 18% 6%	965
	21st to end	Night	23% 19% 33% 21% 4	1000
December	1st to 10th	Night	19% 18% 36% 22% 5% 1	1000
	11th to 20th	Night	20% 17% 36% 20% 6% 1	1000
	21st to end	Night	27% 15% 34% 19% 4	1063

Page generated at 2024-12-21 03:13:53. Version ac07

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