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 2024-02-25.

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% 4 8% 6% 4 5% 5% 5% 7% 34%	78389
	Night	12% 10% 4 8% 6% 3 5% 5% 5% 7% 35%	80955
Transparency	Day	49% 6% 12% 22% 9% 1	78079
	Night	50% 5% 12% 22% 10% 1	80785
Seeing	Day	16% 9% 31% 27% 14% 4	15042
	Night	16% 8% 33% 31% 11% 1	25165

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% 16% 6% 15% 8% 4 5% 5% 5% 5% 22%	2218
	11th to 20th	Day	6% 8% 6% 13% 13% 8% 11% 9% 6% 6% 14%	2502
	21st to end	Day	6% 17% 11% 14% 8% 5% 5% 5% 5% 5% 19%	3048
February	1st to 10th	Day	8% 13% 5% 10% 8% 4 6% 5% 6% 6% 29%	1710
	11th to 20th	Day	7% 10% 5% 10% 7% 4 5% 4 6% 6% 35%	1664
	21st to end	Day	10% 10% 5% 11% 10% 3 4 4 6% 7% 30%	1393
March	1st to 10th	Day	13% 10% 5% 8% 7% 4 5% 5% 6% 7% 31%	1926
	11th to 20th	Day	14% 10% 4 8% 6% 4 5% 5% 5% 7% 34%	1980
	21st to end	Day	19% 10% 4 7% 6% 4 4 4 4 6% 32%	2200
April	1st to 10th	Day	16% 11% 4 7% 7% 4 4 4 5% 6% 32%	2160
	11th to 20th	Day	18% 13% 4 7% 6% 3 5% 5% 5% 6% 30%	2190
	21st to end	Day	21% 8% 4 6% 5% 3 5% 5% 4 5% 32%	2340
May	1st to 10th	Day	17% 8% 4 7% 6% 3 4 4 5% 7% 35%	2479
	11th to 20th	Day	16% 8% 3 5% 5% 3 5% 4 6% 7% 38%	2479
	21st to end	Day	16% 6% 3 5% 6% 3 5% 5% 6% 8% 38%	2725
June	1st to 10th	Day	12% 6% 2 5% 5% 3 5% 6% 6% 9% 40%	2574
	11th to 20th	Day	15% 6% 3 6% 5% 3 5% 4 6% 8% 39%	2700
	21st to end	Day	11% 5% 2 5% 6% 4 6% 6% 8% 10% 37%	2700
July	1st to 10th	Day	7% 4 2 4 4 3 4 5% 7% 9% 51%	2700
	11th to 20th	Day	9% 5% 3 6% 5% 3 4 4 6% 8% 46%	2608
	21st to end	Day	7% 4 2 5% 4 3 5% 5% 6% 10% 50%	2743
August	1st to 10th	Day	9% 5% 3 5% 5% 3 6% 6% 6% 10% 44%	2363
	11th to 20th	Day	12% 6% 3 5% 4 3 4 4 6% 8% 45%	2301
	21st to end	Day	11% 5% 2 5% 5% 3 4 5% 6% 7% 48%	2498
September	1st to 10th	Day	11% 6% 2 5% 5% 4 4 5% 5% 9% 44%	2160
	11th to 20th	Day	12% 7% 2 6% 5% 3 5% 5% 5% 7% 42%	2129
	21st to end	Day	17% 6% 3 5% 4 3 4 5% 5% 7% 40%	1899
October	1st to 10th	Day	18% 10% 2 5% 6% 4 4 5% 4 6% 35%	1800
	11th to 20th	Day	17% 12% 4 7% 5% 4 4 5% 4 6% 33%	1800
	21st to end	Day	19% 11% 4 7% 6% 3 4 5% 5% 6% 29%	1926
November	1st to 10th	Day	13% 12% 6% 7% 6% 4 5% 5% 4 6% 32%	1501
	11th to 20th	Day	15% 14% 7% 11% 7% 4 5% 4 4 4 24%	1520
	21st to end	Day	14% 11% 6% 9% 8% 4 5% 5% 6% 6% 27%	1520
December	1st to 10th	Day	11% 12% 7% 12% 10% 5% 5% 4 5% 6% 22%	1520
	11th to 20th	Day	10% 14% 7% 12% 9% 4 6% 6% 5% 5% 22%	1918
	21st to end	Day	22% 18% 6% 12% 8% 3 4 3 3 5% 16%	2495
January	1st to 10th	Night	10% 10% 6% 14% 9% 3 5% 5% 6% 6% 26%	4737
	11th to 20th	Night	6% 12% 5% 12% 11% 6% 9% 7% 6% 6% 20%	4463
	21st to end	Night	8% 18% 10% 14% 7% 3 5% 4 5% 5% 22%	4614
February	1st to 10th	Night	7% 11% 6% 9% 7% 4 6% 4 6% 6% 35%	2470
	11th to 20th	Night	6% 9% 5% 9% 7% 4 6% 6% 6% 7% 36%	2403
	21st to end	Night	12% 10% 5% 9% 8% 4 4 5% 5% 6% 31%	1957
March	1st to 10th	Night	10% 11% 4 8% 6% 4 5% 5% 4 7% 36%	2052
	11th to 20th	Night	11% 11% 4 7% 6% 4 4 4 4 5% 41%	1980
	21st to end	Night	16% 10% 4 8% 6% 3 5% 4 5% 6% 34%	2155
April	1st to 10th	Night	17% 9% 4 8% 5% 3 5% 4 5% 6% 34%	1800
	11th to 20th	Night	18% 11% 5% 6% 6% 2 4 4 4 6% 34%	1716
	21st to end	Night	18% 9% 4 7% 6% 2 4 5% 4 7% 34%	1620
May	1st to 10th	Night	15% 9% 4 7% 5% 3 4 4 5% 6% 38%	1481
	11th to 20th	Night	16% 6% 2 5% 5% 3 6% 4 6% 8% 40%	1416
	21st to end	Night	13% 5% 3 5% 5% 3 5% 5% 7% 9% 38%	1551
June	1st to 10th	Night	11% 5% 3 5% 5% 4 5% 6% 6% 10% 42%	1382
	11th to 20th	Night	10% 5% 2 5% 5% 3 5% 6% 5% 8% 45%	1260
	21st to end	Night	9% 4 3 6% 5% 3 4 6% 7% 9% 46%	1260
July	1st to 10th	Night	3 3 2 3 4 3 5% 5% 5% 10% 57%	1260
	11th to 20th	Night	8% 4 2 4 5% 2 3 5% 5% 8% 54%	1350
	21st to end	Night	5% 2 2 4 3 2 4 4 6% 9% 59%	1575
August	1st to 10th	Night	7% 4 1 5% 4 3 4 4 7% 8% 53%	1574
	11th to 20th	Night	11% 5% 2 4 4 3 3 4 4 6% 53%	1600
	21st to end	Night	10% 4 2 4 4 3 4 4 5% 8% 53%	1858
September	1st to 10th	Night	9% 4 3 5% 3 3 5% 5% 5% 7% 51%	1800
	11th to 20th	Night	9% 6% 2 5% 4 3 4 3 4 8% 51%	1829
	21st to end	Night	17% 5% 2 5% 5% 3 3 4 5% 7% 44%	2042
October	1st to 10th	Night	16% 8% 3 5% 5% 3 4 4 4 7% 41%	2160
	11th to 20th	Night	16% 10% 4 6% 5% 3 5% 4 4 6% 37%	2160
	21st to end	Night	19% 11% 4 7% 6% 3 4 5% 5% 6% 31%	2430
November	1st to 10th	Night	14% 11% 4 7% 6% 3 4 5% 5% 6% 36%	2574
	11th to 20th	Night	15% 11% 5% 10% 7% 3 5% 4 5% 6% 28%	2660
	21st to end	Night	12% 9% 4 8% 8% 4 4 5% 6% 8% 33%	2660
December	1st to 10th	Night	10% 12% 7% 12% 9% 4 6% 5% 5% 6% 23%	2660
	11th to 20th	Night	11% 14% 6% 10% 9% 5% 6% 6% 6% 6% 22%	3279
	21st to end	Night	23% 18% 6% 10% 7% 3 4 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	54% 4 10% 18% 12% 1	1393
March	1st to 10th	Day	53% 6% 14% 20% 8%	1926
	11th to 20th	Day	52% 5% 14% 20% 9% 1	1980
	21st to end	Day	55% 6% 10% 21% 8% 1	2200
April	1st to 10th	Day	54% 4 10% 18% 12% 2	2160
	11th to 20th	Day	56% 4 11% 17% 11% 1	2190
	21st to end	Day	54% 4 10% 20% 11%	2340
May	1st to 10th	Day	49% 6% 12% 23% 9% 2	2479
	11th to 20th	Day	46% 7% 12% 24% 9% 2	2483
	21st to end	Day	44% 6% 12% 25% 11% 1	2725
June	1st to 10th	Day	39% 7% 17% 27% 10% 1	2574
	11th to 20th	Day	43% 7% 14% 22% 13% 1	2700
	21st to end	Day	40% 9% 15% 26% 9% 1	2700
July	1st to 10th	Day	29% 8% 14% 33% 16% 1	2626
	11th to 20th	Day	36% 9% 13% 27% 15% 1	2528
	21st to end	Day	30% 9% 17% 28% 15% 1	2591
August	1st to 10th	Day	36% 8% 13% 32% 10% 2	2348
	11th to 20th	Day	37% 7% 18% 28% 10% 1	2301
	21st to end	Day	35% 6% 15% 29% 14% 1	2498
September	1st to 10th	Day	37% 6% 14% 32% 10%	2160
	11th to 20th	Day	41% 6% 18% 27% 7%	2129
	21st to end	Day	45% 5% 13% 31% 6%	1899
October	1st to 10th	Day	49% 5% 14% 25% 7%	1800
	11th to 20th	Day	53% 5% 12% 20% 10% 1	1800
	21st to end	Day	56% 6% 11% 20% 7%	1926
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% 5% 10% 20% 11% 1	1957
March	1st to 10th	Night	50% 4 15% 21% 10% 1	2052
	11th to 20th	Night	47% 4 12% 22% 14% 1	1980
	21st to end	Night	52% 5% 12% 21% 10% 1	2155
April	1st to 10th	Night	52% 4 10% 17% 16% 1	1800
	11th to 20th	Night	53% 4 8% 20% 14% 1	1716
	21st to end	Night	51% 4 8% 23% 13% 1	1620
May	1st to 10th	Night	46% 7% 11% 24% 11% 1	1481
	11th to 20th	Night	43% 5% 13% 23% 13% 2	1417
	21st to end	Night	41% 7% 12% 23% 15% 2	1552
June	1st to 10th	Night	38% 7% 18% 26% 10% 2	1382
	11th to 20th	Night	38% 6% 13% 23% 18% 1	1260
	21st to end	Night	35% 8% 15% 28% 13% 1	1260
July	1st to 10th	Night	23% 8% 18% 34% 17% 1	1225
	11th to 20th	Night	28% 8% 14% 30% 17% 4	1307
	21st to end	Night	22% 6% 18% 35% 18% 2	1487
August	1st to 10th	Night	28% 7% 16% 34% 11% 4	1565
	11th to 20th	Night	33% 6% 14% 31% 15% 1	1600
	21st to end	Night	31% 6% 13% 31% 17% 2	1858
September	1st to 10th	Night	31% 8% 15% 33% 13%	1800
	11th to 20th	Night	33% 5% 16% 33% 12%	1829
	21st to end	Night	41% 5% 11% 34% 9%	2042
October	1st to 10th	Night	44% 6% 11% 28% 10% 1	2160
	11th to 20th	Night	50% 4 11% 24% 10%	2160
	21st to end	Night	54% 6% 11% 20% 9%	2430
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% 10% 41% 29% 5%	210
March	1st to 10th	Day	18% 8% 35% 27% 11% 1	240
	11th to 20th	Day	20% 9% 31% 26% 11% 3	240
	21st to end	Day	23% 11% 29% 22% 14% 2	286
April	1st to 10th	Day	22% 12% 34% 22% 9% 1	420
	11th to 20th	Day	28% 9% 25% 25% 12% 1	468
	21st to end	Day	24% 10% 30% 22% 12% 2	600
May	1st to 10th	Day	19% 13% 30% 24% 10% 2	603
	11th to 20th	Day	20% 11% 29% 24% 12% 3	625
	21st to end	Day	18% 8% 27% 31% 13% 3	679
June	1st to 10th	Day	13% 6% 30% 31% 15% 4	630
	11th to 20th	Day	15% 10% 35% 27% 12% 2	630
	21st to end	Day	14% 8% 30% 26% 15% 7%	630
July	1st to 10th	Day	8% 5% 26% 29% 23% 9%	621
	11th to 20th	Day	10% 6% 32% 25% 19% 9%	618
	21st to end	Day	7% 3 26% 33% 22% 9%	684
August	1st to 10th	Day	10% 5% 24% 31% 24% 6%	626
	11th to 20th	Day	14% 5% 21% 32% 23% 6%	615
	21st to end	Day	14% 5% 24% 29% 22% 6%	617
September	1st to 10th	Day	12% 7% 26% 33% 19% 3	450
	11th to 20th	Day	13% 8% 27% 30% 17% 4	419
	21st to end	Day	21% 12% 31% 19% 11% 5%	270
October	1st to 10th	Day	23% 7% 30% 23% 11% 5%	270
	11th to 20th	Day	17% 13% 36% 27% 7% 1	270
	21st to end	Day	27% 11% 39% 15% 7% 1	297
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	737
March	1st to 10th	Night	14% 10% 38% 28% 9% 1	612
	11th to 20th	Night	16% 8% 41% 29% 6% 1	540
	21st to end	Night	20% 9% 28% 28% 11% 4	594
April	1st to 10th	Night	20% 9% 34% 29% 7% 1	540
	11th to 20th	Night	24% 7% 31% 29% 8% 1	533
	21st to end	Night	23% 9% 28% 28% 11% 1	540
May	1st to 10th	Night	17% 10% 34% 29% 8% 1	540
	11th to 20th	Night	19% 7% 30% 33% 11% 2	531
	21st to end	Night	16% 6% 30% 35% 13%	584
June	1st to 10th	Night	12% 5% 30% 37% 14% 1	540
	11th to 20th	Night	14% 4 33% 40% 10%	540
	21st to end	Night	10% 4 27% 39% 19% 1	540
July	1st to 10th	Night	6% 2 25% 40% 26% 2	525
	11th to 20th	Night	10% 3 27% 36% 21% 2	522
	21st to end	Night	7% 2 22% 45% 21% 3	591
August	1st to 10th	Night	8% 2 19% 49% 21% 1	537
	11th to 20th	Night	14% 3 21% 36% 24% 2	534
	21st to end	Night	11% 5% 24% 39% 20% 2	594
September	1st to 10th	Night	11% 4 24% 40% 20% 1	540
	11th to 20th	Night	12% 5% 31% 32% 17% 2	540
	21st to end	Night	18% 7% 33% 27% 13% 3	602
October	1st to 10th	Night	21% 9% 29% 29% 12% 1	720
	11th to 20th	Night	21% 10% 35% 27% 6%	720
	21st to end	Night	26% 9% 33% 26% 6%	792
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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