Long Lake Conservation Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Lake Conservation Center clear sky chart from 2005-11-06 to 2024-10-25.

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 8% 5% 5% 5% 4 6% 7% 35%	101804
	Night	12% 10% 4 9% 5% 4 4 4 5% 6% 36%	97065
Transparency	Day	48% 6% 13% 24% 10% 1	101586
	Night	48% 5% 12% 23% 10% 1	96954
Seeing	Day	16% 9% 31% 27% 14% 4	16078
	Night	16% 8% 33% 31% 11% 1	25934

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% 17% 6% 17% 7% 6% 4 4 5% 5% 21%	2218
	11th to 20th	Day	6% 10% 5% 15% 11% 10% 11% 6% 6% 6% 14%	2502
	21st to end	Day	6% 18% 10% 17% 7% 6% 5% 4 5% 5% 18%	3048
February	1st to 10th	Day	8% 14% 4 11% 7% 6% 5% 5% 6% 6% 29%	1710
	11th to 20th	Day	7% 11% 5% 11% 6% 5% 5% 3 6% 6% 35%	1664
	21st to end	Day	9% 12% 5% 13% 7% 4 4 3 6% 7% 31%	1440
March	1st to 10th	Day	11% 10% 3 9% 6% 5% 5% 4 6% 6% 35%	3344
	11th to 20th	Day	9% 10% 4 11% 5% 4 4 3 5% 6% 37%	3480
	21st to end	Day	20% 12% 4 10% 5% 4 4 3 4 6% 27%	3863
April	1st to 10th	Day	16% 12% 4 9% 6% 5% 4 3 5% 6% 32%	2280
	11th to 20th	Day	17% 13% 3 8% 5% 5% 5% 4 5% 6% 30%	2314
	21st to end	Day	22% 9% 4 7% 5% 5% 4 4 4 5% 32%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 3 3 5% 7% 37%	4331
	11th to 20th	Day	15% 8% 3 5% 4 4 4 3 6% 7% 41%	4399
	21st to end	Day	18% 7% 3 6% 5% 5% 5% 4 6% 7% 33%	4824
June	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 41%	2717
	11th to 20th	Day	15% 7% 3 7% 4 4 5% 3 6% 7% 38%	2850
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 8% 9% 37%	2850
July	1st to 10th	Day	9% 5% 2 7% 5% 6% 6% 5% 8% 9% 39%	4750
	11th to 20th	Day	6% 4 2 6% 4 4 4 4 7% 9% 51%	4580
	21st to end	Day	7% 4 2 5% 4 4 4 4 6% 9% 49%	4813
August	1st to 10th	Day	11% 5% 2 5% 4 5% 5% 4 7% 9% 42%	4153
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 6% 9% 42%	4041
	21st to end	Day	14% 7% 3 6% 4 4 4 4 6% 6% 42%	4386
September	1st to 10th	Day	10% 6% 2 6% 4 4 4 4 5% 9% 45%	2280
	11th to 20th	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 43%	2247
	21st to end	Day	16% 6% 3 6% 4 4 4 3 5% 7% 42%	2004
October	1st to 10th	Day	17% 10% 2 7% 5% 4 4 4 5% 7% 36%	1900
	11th to 20th	Day	16% 12% 3 8% 4 4 4 4 4 6% 34%	1900
	21st to end	Day	19% 13% 3 8% 5% 4 4 4 5% 6% 29%	1972
November	1st to 10th	Day	13% 13% 4 8% 6% 6% 5% 4 4 6% 32%	1501
	11th to 20th	Day	14% 15% 6% 13% 6% 6% 4 3 4 4 24%	1520
	21st to end	Day	14% 11% 6% 11% 6% 5% 5% 4 6% 6% 27%	1520
December	1st to 10th	Day	11% 13% 7% 13% 10% 6% 4 4 5% 6% 22%	1520
	11th to 20th	Day	10% 15% 7% 13% 7% 5% 6% 5% 5% 5% 22%	1918
	21st to end	Day	22% 19% 6% 14% 5% 4 4 3 3 5% 16%	2495
January	1st to 10th	Night	10% 12% 5% 16% 8% 5% 5% 4 6% 6% 25%	4737
	11th to 20th	Night	6% 13% 5% 14% 9% 8% 9% 5% 6% 6% 20%	4463
	21st to end	Night	8% 19% 9% 15% 6% 5% 4 3 5% 5% 22%	4614
February	1st to 10th	Night	6% 11% 5% 10% 6% 6% 5% 4 6% 6% 35%	2470
	11th to 20th	Night	6% 9% 4 10% 7% 5% 6% 4 7% 6% 35%	2403
	21st to end	Night	12% 11% 5% 10% 7% 5% 4 4 5% 6% 31%	2013
March	1st to 10th	Night	8% 9% 3 7% 5% 4 4 3 4 7% 44%	3528
	11th to 20th	Night	9% 10% 4 11% 6% 6% 4 3 5% 5% 37%	3480
	21st to end	Night	20% 14% 5% 10% 5% 3 3 2 3 4 28%	3767
April	1st to 10th	Night	16% 10% 4 9% 4 5% 4 3 5% 5% 35%	1900
	11th to 20th	Night	17% 12% 4 7% 5% 4 4 3 4 6% 35%	1812
	21st to end	Night	18% 9% 3 8% 5% 3 4 4 4 6% 35%	1710
May	1st to 10th	Night	15% 9% 3 7% 4 5% 4 3 5% 6% 39%	2574
	11th to 20th	Night	15% 6% 2 5% 4 4 4 3 5% 7% 44%	2506
	21st to end	Night	17% 8% 3 7% 5% 4 5% 4 5% 7% 35%	2743
June	1st to 10th	Night	11% 6% 2 6% 4 5% 4 5% 6% 10% 41%	1458
	11th to 20th	Night	10% 6% 2 5% 5% 5% 5% 4 5% 7% 44%	1330
	21st to end	Night	9% 4 3 7% 4 4 4 5% 7% 8% 45%	1330
July	1st to 10th	Night	8% 4 2 5% 4 4 5% 5% 7% 11% 46%	2220
	11th to 20th	Night	5% 3 1 4 4 3 4 3 5% 8% 60%	2375
	21st to end	Night	5% 4 2 5% 3 4 4 3 6% 9% 55%	2750
August	1st to 10th	Night	10% 5% 2 5% 4 3 3 4 6% 8% 50%	2771
	11th to 20th	Night	14% 5% 2 4 3 3 4 4 5% 6% 50%	2798
	21st to end	Night	12% 5% 2 6% 4 4 4 3 6% 9% 44%	3276
September	1st to 10th	Night	9% 4 2 5% 3 4 5% 4 5% 7% 52%	1900
	11th to 20th	Night	9% 6% 2 6% 3 4 4 3 5% 8% 51%	1931
	21st to end	Night	16% 5% 2 6% 4 3 3 3 5% 7% 46%	2156
October	1st to 10th	Night	15% 7% 3 5% 5% 3 4 3 4 6% 43%	2280
	11th to 20th	Night	15% 11% 4 7% 4 4 5% 3 4 6% 38%	2280
	21st to end	Night	18% 12% 4 8% 5% 4 4 4 5% 6% 31%	2490
November	1st to 10th	Night	13% 12% 3 8% 5% 4 5% 4 5% 6% 36%	2574
	11th to 20th	Night	15% 12% 5% 11% 6% 4 5% 3 5% 6% 28%	2660
	21st to end	Night	12% 9% 4 10% 6% 5% 4 4 6% 8% 32%	2660
December	1st to 10th	Night	9% 13% 6% 13% 8% 6% 5% 4 5% 6% 23%	2660
	11th to 20th	Night	11% 14% 5% 12% 8% 6% 5% 5% 6% 6% 22%	3279
	21st to end	Night	22% 19% 5% 11% 6% 4 3 3 4 5% 18%	5167

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% 5% 9% 16% 6%	2219
	11th to 20th	Day	69% 6% 8% 13% 4	2502
	21st to end	Day	67% 6% 7% 15% 5%	3048
February	1st to 10th	Day	55% 4 10% 20% 11% 1	1710
	11th to 20th	Day	49% 5% 13% 22% 10% 2	1673
	21st to end	Day	53% 5% 10% 18% 13% 1	1440
March	1st to 10th	Day	49% 6% 11% 23% 10%	3344
	11th to 20th	Day	46% 4 14% 26% 10%	3480
	21st to end	Day	59% 6% 10% 20% 5% 1	3863
April	1st to 10th	Day	53% 4 10% 18% 13% 2	2280
	11th to 20th	Day	55% 4 11% 17% 11% 1	2314
	21st to end	Day	54% 4 10% 21% 10%	2470
May	1st to 10th	Day	46% 5% 13% 21% 13% 1	4371
	11th to 20th	Day	42% 7% 13% 26% 10% 3	4403
	21st to end	Day	47% 8% 13% 23% 9% 1	4837
June	1st to 10th	Day	38% 7% 17% 27% 10% 1	2717
	11th to 20th	Day	44% 7% 13% 22% 13% 1	2850
	21st to end	Day	40% 8% 15% 27% 9% 1	2850
July	1st to 10th	Day	39% 7% 17% 24% 13%	4676
	11th to 20th	Day	29% 6% 15% 36% 13% 1	4500
	21st to end	Day	31% 6% 17% 32% 13% 1	4662
August	1st to 10th	Day	38% 5% 15% 29% 12% 1	4138
	11th to 20th	Day	38% 6% 17% 32% 7%	4080
	21st to end	Day	43% 5% 15% 26% 11% 1	4385
September	1st to 10th	Day	36% 6% 15% 33% 10%	2280
	11th to 20th	Day	40% 6% 19% 27% 8%	2247
	21st to end	Day	43% 5% 13% 32% 7% 1	2004
October	1st to 10th	Day	47% 5% 14% 26% 8%	1900
	11th to 20th	Day	52% 5% 12% 20% 10% 1	1900
	21st to end	Day	55% 6% 12% 20% 7%	1972
November	1st to 10th	Day	54% 5% 11% 18% 10% 1	1501
	11th to 20th	Day	63% 5% 12% 12% 7% 1	1520
	21st to end	Day	57% 5% 13% 17% 5% 2	1520
December	1st to 10th	Day	63% 5% 11% 16% 4	1520
	11th to 20th	Day	64% 6% 10% 16% 4	1915
	21st to end	Day	73% 4 5% 11% 6% 1	2495
January	1st to 10th	Night	59% 5% 10% 20% 6% 1	4737
	11th to 20th	Night	63% 6% 12% 14% 5% 1	4463
	21st to end	Night	65% 4 8% 17% 5%	4614
February	1st to 10th	Night	50% 4 10% 23% 12% 1	2470
	11th to 20th	Night	46% 6% 12% 23% 11% 1	2404
	21st to end	Night	53% 4 11% 20% 11% 1	2013
March	1st to 10th	Night	39% 4 15% 23% 16% 2	3528
	11th to 20th	Night	48% 4 10% 23% 14% 1	3480
	21st to end	Night	61% 4 8% 17% 9% 1	3767
April	1st to 10th	Night	51% 4 9% 18% 16% 1	1900
	11th to 20th	Night	51% 4 8% 20% 15% 1	1812
	21st to end	Night	50% 5% 8% 23% 13% 1	1710
May	1st to 10th	Night	44% 7% 11% 25% 11% 1	2599
	11th to 20th	Night	39% 5% 11% 25% 17% 3	2507
	21st to end	Night	47% 8% 12% 21% 11% 1	2751
June	1st to 10th	Night	38% 6% 18% 26% 11% 2	1458
	11th to 20th	Night	38% 6% 13% 23% 18% 1	1330
	21st to end	Night	35% 7% 15% 29% 13% 1	1330
July	1st to 10th	Night	31% 7% 21% 26% 15%	2185
	11th to 20th	Night	23% 5% 12% 42% 15% 2	2332
	21st to end	Night	26% 5% 17% 36% 15% 1	2662
August	1st to 10th	Night	33% 5% 18% 26% 16% 2	2762
	11th to 20th	Night	35% 5% 13% 36% 10% 1	2825
	21st to end	Night	38% 6% 17% 28% 10% 1	3276
September	1st to 10th	Night	30% 7% 16% 34% 12%	1900
	11th to 20th	Night	33% 5% 17% 33% 12%	1931
	21st to end	Night	39% 5% 11% 34% 11%	2156
October	1st to 10th	Night	42% 5% 11% 29% 11% 2	2280
	11th to 20th	Night	49% 4 11% 24% 11%	2280
	21st to end	Night	53% 6% 12% 20% 9%	2490
November	1st to 10th	Night	49% 6% 12% 23% 9% 1	2574
	11th to 20th	Night	56% 5% 14% 16% 8% 1	2660
	21st to end	Night	50% 6% 16% 21% 5% 2	2660
December	1st to 10th	Night	61% 5% 14% 15% 4 1	2660
	11th to 20th	Night	60% 6% 12% 15% 6% 1	3281
	21st to end	Night	70% 4 9% 13% 6%	5167

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	12% 12% 33% 29% 12% 3	270
	11th to 20th	Day	17% 9% 30% 35% 9% 1	270
	21st to end	Day	12% 7% 36% 26% 17% 2	297
February	1st to 10th	Day	18% 11% 43% 20% 7% 1	270
	11th to 20th	Day	13% 16% 37% 23% 9% 2	270
	21st to end	Day	15% 13% 42% 26% 4	225
March	1st to 10th	Day	17% 9% 37% 26% 10% 1	270
	11th to 20th	Day	18% 9% 33% 26% 10% 3	270
	21st to end	Day	22% 12% 29% 21% 13% 2	321
April	1st to 10th	Day	22% 12% 33% 24% 8% 1	460
	11th to 20th	Day	27% 10% 26% 25% 11% 1	512
	21st to end	Day	24% 10% 30% 22% 12% 2	650
May	1st to 10th	Day	19% 15% 30% 24% 10% 2	653
	11th to 20th	Day	20% 11% 30% 24% 12% 3	675
	21st to end	Day	19% 8% 27% 31% 12% 3	734
June	1st to 10th	Day	13% 8% 31% 31% 14% 4	680
	11th to 20th	Day	16% 10% 35% 26% 11% 2	680
	21st to end	Day	15% 8% 30% 25% 15% 6%	680
July	1st to 10th	Day	8% 6% 25% 28% 23% 10%	671
	11th to 20th	Day	9% 6% 31% 24% 19% 10%	668
	21st to end	Day	7% 3 27% 33% 22% 9%	739
August	1st to 10th	Day	11% 5% 25% 31% 23% 6%	676
	11th to 20th	Day	13% 5% 21% 33% 22% 6%	665
	21st to end	Day	15% 5% 25% 29% 21% 6%	667
September	1st to 10th	Day	11% 7% 27% 32% 18% 4	490
	11th to 20th	Day	13% 7% 28% 30% 17% 5%	457
	21st to end	Day	19% 12% 31% 21% 11% 6%	300
October	1st to 10th	Day	23% 8% 31% 22% 11% 5%	300
	11th to 20th	Day	17% 14% 36% 26% 6% 1	300
	21st to end	Day	27% 11% 39% 16% 6% 1	311
November	1st to 10th	Day	19% 13% 35% 23% 9% 1	270
	11th to 20th	Day	19% 14% 40% 21% 6%	270
	21st to end	Day	19% 10% 43% 24% 4	270
December	1st to 10th	Day	16% 13% 36% 26% 8% 1	270
	11th to 20th	Day	19% 14% 34% 25% 8%	270
	21st to end	Day	27% 10% 37% 21% 5%	297
January	1st to 10th	Night	14% 9% 35% 30% 10% 1	950
	11th to 20th	Night	15% 8% 38% 29% 9% 1	950
	21st to end	Night	17% 8% 36% 29% 8% 1	1045
February	1st to 10th	Night	13% 8% 37% 31% 10% 1	950
	11th to 20th	Night	10% 10% 42% 26% 10% 1	929
	21st to end	Night	17% 8% 34% 30% 10% 1	757
March	1st to 10th	Night	13% 10% 39% 27% 9% 1	645
	11th to 20th	Night	15% 9% 40% 29% 5% 1	570
	21st to end	Night	21% 9% 28% 29% 11% 3	627
April	1st to 10th	Night	19% 10% 35% 29% 7% 1	570
	11th to 20th	Night	23% 7% 32% 29% 8% 1	563
	21st to end	Night	23% 9% 29% 29% 10% 1	570
May	1st to 10th	Night	17% 11% 34% 29% 8% 1	570
	11th to 20th	Night	19% 6% 30% 33% 10% 1	561
	21st to end	Night	16% 7% 29% 35% 13%	617
June	1st to 10th	Night	13% 5% 30% 37% 14% 1	570
	11th to 20th	Night	14% 4 33% 39% 9%	570
	21st to end	Night	10% 4 28% 39% 18% 1	570
July	1st to 10th	Night	6% 2 24% 40% 26% 1	555
	11th to 20th	Night	10% 3 26% 37% 22% 2	552
	21st to end	Night	7% 2 22% 45% 22% 3	624
August	1st to 10th	Night	8% 2 19% 49% 21% 1	567
	11th to 20th	Night	14% 3 21% 37% 24% 2	564
	21st to end	Night	11% 5% 24% 38% 20% 2	627
September	1st to 10th	Night	11% 4 24% 41% 19% 2	570
	11th to 20th	Night	12% 5% 31% 33% 17% 2	570
	21st to end	Night	17% 6% 32% 27% 14% 3	636
October	1st to 10th	Night	20% 9% 30% 29% 11% 1	760
	11th to 20th	Night	21% 11% 35% 27% 6%	760
	21st to end	Night	25% 9% 33% 26% 6%	812
November	1st to 10th	Night	19% 9% 33% 29% 10%	908
	11th to 20th	Night	21% 11% 34% 25% 9% 1	950
	21st to end	Night	18% 11% 39% 26% 6%	950
December	1st to 10th	Night	15% 11% 34% 30% 9% 1	950
	11th to 20th	Night	19% 9% 38% 25% 7% 1	950
	21st to end	Night	26% 9% 34% 24% 7% 1	1045

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