Long Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Lake clear sky chart from 2005-11-06 to 2024-01-14.

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	6% 8% 4 7% 7% 4 6% 6% 7% 8% 37%	75214
	Night	3 5% 3 6% 6% 4 6% 6% 8% 9% 43%	74503
Transparency	Day	39% 7% 16% 21% 13% 4	74916
	Night	30% 8% 20% 25% 14% 4	74322
Seeing	Day	20% 30% 32% 14% 4	14644
	Night	17% 30% 30% 17% 5%	24341

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	3 3 8% 7% 5% 8% 7% 11% 11% 36%	1466
	11th to 20th	Day	3 4 6% 7% 6% 7% 7% 10% 10% 41%	1546
	21st to end	Day	6% 3 8% 8% 5% 6% 7% 9% 11% 38%	1782
February	1st to 10th	Day	5% 5% 10% 10% 6% 9% 8% 10% 9% 29%	1620
	11th to 20th	Day	1 6% 5% 11% 11% 6% 8% 7% 9% 6% 31%	1575
	21st to end	Day	8% 5% 12% 11% 6% 8% 6% 8% 9% 26%	1340
March	1st to 10th	Day	1 7% 4 11% 11% 6% 8% 8% 8% 8% 30%	1980
	11th to 20th	Day	2 10% 4 10% 8% 4 7% 6% 8% 10% 30%	1980
	21st to end	Day	3 15% 8% 13% 9% 5% 7% 6% 6% 7% 21%	2178
April	1st to 10th	Day	5% 16% 7% 11% 8% 4 5% 5% 5% 7% 26%	2132
	11th to 20th	Day	5% 15% 6% 12% 9% 4 6% 6% 5% 8% 23%	2208
	21st to end	Day	9% 19% 7% 9% 7% 4 6% 4 5% 6% 24%	2340
May	1st to 10th	Day	10% 17% 5% 8% 7% 4 5% 6% 5% 7% 24%	2368
	11th to 20th	Day	13% 14% 5% 9% 7% 4 6% 5% 6% 9% 24%	2478
	21st to end	Day	17% 15% 4 7% 6% 4 6% 5% 7% 8% 19%	2724
June	1st to 10th	Day	13% 9% 3 7% 7% 4 5% 7% 8% 8% 29%	2520
	11th to 20th	Day	12% 8% 4 7% 6% 3 6% 5% 7% 8% 33%	2683
	21st to end	Day	6% 4 2 5% 5% 4 6% 6% 6% 8% 49%	2700
July	1st to 10th	Day	6% 3 2 4 6% 4 6% 7% 8% 9% 46%	2700
	11th to 20th	Day	5% 3 2 5% 4 3 6% 5% 7% 8% 51%	2552
	21st to end	Day	5% 4 2 5% 6% 3 6% 6% 6% 8% 50%	2630
August	1st to 10th	Day	10% 5% 3 5% 6% 4 6% 6% 7% 8% 42%	2328
	11th to 20th	Day	7% 5% 2 4 7% 4 5% 6% 6% 7% 48%	2299
	21st to end	Day	8% 5% 3 5% 5% 3 5% 5% 5% 7% 49%	2514
September	1st to 10th	Day	9% 6% 3 4 4 2 4 5% 4 7% 53%	2160
	11th to 20th	Day	9% 7% 3 5% 4 3 4 5% 6% 8% 48%	2058
	21st to end	Day	8% 8% 2 4 4 3 4 5% 6% 6% 49%	1958
October	1st to 10th	Day	10% 13% 4 7% 5% 3 5% 4 4 7% 39%	1800
	11th to 20th	Day	5% 11% 3 6% 5% 3 4 5% 5% 7% 47%	1800
	21st to end	Day	4 8% 4 6% 5% 3 6% 6% 8% 10% 41%	1980
November	1st to 10th	Day	3 8% 4 7% 7% 5% 7% 6% 7% 9% 37%	1538
	11th to 20th	Day	1 6% 3 5% 6% 5% 7% 6% 7% 11% 43%	1520
	21st to end	Day	1 4 4 7% 5% 4 7% 5% 9% 10% 43%	1520
December	1st to 10th	Day	1 3 3 8% 8% 4 8% 8% 10% 9% 39%	1520
	11th to 20th	Day	4 3 7% 8% 5% 9% 8% 11% 10% 34%	1926
	21st to end	Day	1 5% 3 7% 7% 4 6% 6% 7% 8% 45%	2791
January	1st to 10th	Night	2 2 7% 9% 5% 7% 8% 12% 10% 40%	2647
	11th to 20th	Night	1 2 2 6% 7% 5% 6% 8% 9% 10% 43%	2501
	21st to end	Night	1 4 4 6% 6% 4 6% 6% 8% 11% 44%	2574
February	1st to 10th	Night	4 3 8% 8% 5% 8% 9% 10% 10% 36%	2340
	11th to 20th	Night	1 4 3 9% 9% 6% 8% 7% 11% 8% 33%	2272
	21st to end	Night	1 5% 5% 9% 10% 5% 7% 7% 11% 9% 31%	1916
March	1st to 10th	Night	1 7% 3 8% 7% 3 8% 9% 8% 10% 38%	1980
	11th to 20th	Night	1 5% 3 6% 6% 3 7% 7% 9% 11% 42%	1980
	21st to end	Night	2 8% 4 9% 8% 5% 8% 8% 9% 10% 29%	2178
April	1st to 10th	Night	4 9% 4 9% 7% 4 6% 6% 6% 7% 38%	1827
	11th to 20th	Night	3 8% 4 9% 9% 4 7% 7% 8% 8% 34%	1696
	21st to end	Night	5% 13% 3 8% 6% 3 5% 6% 6% 8% 36%	1620
May	1st to 10th	Night	6% 12% 4 7% 7% 3 4 6% 6% 8% 36%	1589
	11th to 20th	Night	8% 11% 4 7% 6% 3 5% 5% 7% 8% 36%	1417
	21st to end	Night	13% 10% 4 7% 6% 4 6% 6% 7% 9% 27%	1552
June	1st to 10th	Night	10% 5% 3 4 6% 4 6% 6% 8% 10% 39%	1440
	11th to 20th	Night	10% 5% 2 6% 5% 4 6% 6% 5% 9% 43%	1271
	21st to end	Night	3 5% 2 3 4 3 4 5% 6% 7% 58%	1260
July	1st to 10th	Night	3 2 1 3 3 4 5% 6% 7% 7% 58%	1260
	11th to 20th	Night	3 2 1 3 4 2 5% 4 7% 8% 59%	1404
	21st to end	Night	5% 2 2 3 4 2 5% 5% 6% 7% 60%	1685
August	1st to 10th	Night	6% 5% 2 4 5% 3 5% 6% 8% 8% 48%	1611
	11th to 20th	Night	5% 4 2 4 4 2 4 5% 5% 8% 57%	1602
	21st to end	Night	5% 5% 2 4 4 2 4 5% 5% 7% 56%	1840
September	1st to 10th	Night	7% 5% 2 4 4 2 3 4 5% 7% 58%	1800
	11th to 20th	Night	6% 4 2 5% 4 3 5% 5% 6% 8% 53%	1898
	21st to end	Night	8% 6% 2 4 4 2 3 4 5% 6% 54%	2002
October	1st to 10th	Night	8% 9% 3 6% 5% 3 6% 5% 6% 8% 42%	2160
	11th to 20th	Night	4 7% 3 6% 5% 4 6% 6% 5% 7% 48%	2160
	21st to end	Night	2 5% 2 6% 6% 5% 6% 5% 8% 7% 48%	2376
November	1st to 10th	Night	2 7% 3 6% 5% 4 6% 8% 9% 10% 41%	2521
	11th to 20th	Night	1 4 2 6% 7% 5% 7% 7% 8% 11% 42%	2660
	21st to end	Night	2 4 2 7% 6% 3 7% 7% 8% 10% 44%	2660
December	1st to 10th	Night	3 3 7% 7% 4 8% 8% 12% 9% 40%	2660
	11th to 20th	Night	3 2 5% 6% 5% 6% 7% 11% 12% 41%	3271
	21st to end	Night	3 3 8% 7% 4 6% 6% 8% 9% 46%	4873

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	29% 11% 27% 22% 11% 1	1466
	11th to 20th	Day	27% 11% 26% 21% 13% 3	1546
	21st to end	Day	32% 9% 24% 22% 11% 2	1782
February	1st to 10th	Day	40% 9% 21% 21% 7% 1	1620
	11th to 20th	Day	44% 8% 19% 20% 8% 1	1584
	21st to end	Day	46% 7% 15% 16% 13% 3	1340
March	1st to 10th	Day	40% 8% 23% 20% 8% 1	1980
	11th to 20th	Day	41% 7% 22% 20% 8% 2	1980
	21st to end	Day	57% 7% 17% 15% 4	2178
April	1st to 10th	Day	52% 7% 14% 19% 7% 1	2132
	11th to 20th	Day	54% 7% 17% 18% 4	2211
	21st to end	Day	57% 4 15% 19% 5%	2340
May	1st to 10th	Day	55% 5% 11% 21% 7%	2368
	11th to 20th	Day	54% 7% 17% 19% 3	2482
	21st to end	Day	57% 9% 16% 14% 4	2724
June	1st to 10th	Day	46% 9% 16% 21% 7% 1	2520
	11th to 20th	Day	43% 7% 14% 18% 15% 3	2683
	21st to end	Day	29% 6% 13% 29% 16% 7%	2700
July	1st to 10th	Day	29% 7% 12% 24% 22% 7%	2626
	11th to 20th	Day	26% 6% 9% 20% 25% 15%	2475
	21st to end	Day	29% 5% 8% 20% 25% 14%	2484
August	1st to 10th	Day	36% 5% 10% 22% 19% 8%	2313
	11th to 20th	Day	32% 5% 9% 26% 20% 8%	2299
	21st to end	Day	32% 5% 9% 20% 23% 11%	2514
September	1st to 10th	Day	30% 3 8% 20% 31% 8%	2160
	11th to 20th	Day	30% 5% 12% 23% 25% 6%	2058
	21st to end	Day	31% 5% 13% 28% 19% 4	1958
October	1st to 10th	Day	43% 4 13% 22% 15% 3	1800
	11th to 20th	Day	34% 5% 19% 27% 12% 3	1800
	21st to end	Day	32% 8% 21% 23% 15% 1	1980
November	1st to 10th	Day	36% 8% 18% 22% 13% 3	1538
	11th to 20th	Day	30% 8% 23% 26% 11% 3	1520
	21st to end	Day	30% 8% 22% 25% 14% 1	1520
December	1st to 10th	Day	29% 10% 23% 22% 12% 4	1520
	11th to 20th	Day	31% 10% 29% 23% 6% 1	1924
	21st to end	Day	29% 7% 13% 25% 14% 12%	2791
January	1st to 10th	Night	26% 12% 26% 24% 10% 2	2647
	11th to 20th	Night	27% 10% 25% 23% 11% 4	2501
	21st to end	Night	28% 10% 25% 23% 12% 2	2574
February	1st to 10th	Night	34% 10% 22% 25% 10%	2340
	11th to 20th	Night	36% 7% 22% 23% 10% 2	2273
	21st to end	Night	36% 8% 17% 20% 16% 3	1916
March	1st to 10th	Night	31% 10% 22% 24% 11% 2	1980
	11th to 20th	Night	26% 8% 26% 27% 10% 2	1980
	21st to end	Night	41% 7% 24% 22% 5% 1	2178
April	1st to 10th	Night	39% 8% 21% 20% 11% 1	1827
	11th to 20th	Night	41% 9% 22% 22% 5% 1	1696
	21st to end	Night	41% 8% 23% 22% 7%	1620
May	1st to 10th	Night	42% 6% 18% 27% 7% 1	1589
	11th to 20th	Night	42% 7% 21% 24% 6%	1418
	21st to end	Night	46% 9% 23% 16% 6%	1552
June	1st to 10th	Night	36% 8% 23% 24% 8% 2	1440
	11th to 20th	Night	33% 7% 18% 24% 14% 4	1271
	21st to end	Night	22% 5% 16% 32% 19% 7%	1260
July	1st to 10th	Night	19% 8% 13% 32% 23% 5%	1225
	11th to 20th	Night	18% 5% 12% 25% 27% 13%	1358
	21st to end	Night	19% 5% 11% 22% 31% 12%	1591
August	1st to 10th	Night	28% 6% 14% 26% 18% 8%	1602
	11th to 20th	Night	25% 5% 10% 30% 23% 7%	1602
	21st to end	Night	24% 6% 10% 25% 27% 8%	1840
September	1st to 10th	Night	25% 4 9% 24% 30% 8%	1800
	11th to 20th	Night	26% 5% 15% 26% 22% 5%	1898
	21st to end	Night	28% 4 12% 31% 22% 2	2002
October	1st to 10th	Night	37% 4 16% 27% 15% 2	2160
	11th to 20th	Night	32% 5% 17% 27% 15% 3	2160
	21st to end	Night	28% 8% 20% 27% 15% 2	2376
November	1st to 10th	Night	27% 11% 19% 26% 14% 2	2521
	11th to 20th	Night	27% 9% 26% 25% 11% 2	2660
	21st to end	Night	28% 9% 21% 24% 14% 3	2660
December	1st to 10th	Night	26% 11% 27% 21% 13% 2	2660
	11th to 20th	Night	23% 9% 29% 30% 9% 1	3272
	21st to end	Night	28% 8% 16% 27% 12% 10%	4873

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	25% 39% 24% 10% 2	248
	11th to 20th	Day	18% 46% 21% 9% 5%	249
	21st to end	Day	16% 56% 22% 5% 2	264
February	1st to 10th	Day	32% 52% 15% 2	240
	11th to 20th	Day	36% 34% 20% 7% 3	240
	21st to end	Day	28% 41% 23% 7% 1	202
March	1st to 10th	Day	26% 40% 28% 5% 1	420
	11th to 20th	Day	21% 37% 34% 7% 1	420
	21st to end	Day	27% 32% 30% 10% 1	462
April	1st to 10th	Day	31% 39% 26% 4	420
	11th to 20th	Day	28% 39% 28% 5%	412
	21st to end	Day	30% 27% 29% 11% 3 1	420
May	1st to 10th	Day	23% 26% 29% 18% 3 1	451
	11th to 20th	Day	25% 19% 33% 17% 5% 1	625
	21st to end	Day	26% 21% 27% 19% 6% 1	679
June	1st to 10th	Day	17% 23% 30% 22% 7%	630
	11th to 20th	Day	23% 29% 31% 12% 3	630
	21st to end	Day	9% 21% 40% 22% 6% 1	630
July	1st to 10th	Day	8% 18% 40% 27% 7% 1	621
	11th to 20th	Day	7% 22% 45% 20% 5%	618
	21st to end	Day	7% 16% 45% 25% 6% 1	572
August	1st to 10th	Day	13% 21% 43% 18% 5%	447
	11th to 20th	Day	11% 13% 44% 27% 5%	437
	21st to end	Day	13% 22% 42% 17% 6%	495
September	1st to 10th	Day	13% 27% 45% 14% 2	450
	11th to 20th	Day	18% 26% 35% 17% 4	450
	21st to end	Day	18% 29% 37% 11% 4	428
October	1st to 10th	Day	20% 28% 33% 16% 3	270
	11th to 20th	Day	24% 36% 27% 9% 3 1	270
	21st to end	Day	27% 42% 23% 7% 1	297
November	1st to 10th	Day	26% 46% 18% 7% 3	270
	11th to 20th	Day	26% 47% 23% 3 1	270
	21st to end	Day	21% 41% 33% 4 1	270
December	1st to 10th	Day	28% 45% 16% 9% 3	270
	11th to 20th	Day	31% 44% 19% 6% 1	270
	21st to end	Day	23% 41% 24% 10% 2	297
January	1st to 10th	Night	21% 40% 29% 9% 1	950
	11th to 20th	Night	21% 42% 25% 9% 4	850
	21st to end	Night	15% 48% 26% 9% 2	792
February	1st to 10th	Night	22% 44% 22% 10% 2	720
	11th to 20th	Night	22% 36% 28% 10% 4 1	704
	21st to end	Night	19% 38% 30% 10% 3	592
March	1st to 10th	Night	19% 34% 31% 13% 3	720
	11th to 20th	Night	18% 33% 32% 14% 3	720
	21st to end	Night	14% 32% 35% 16% 3	792
April	1st to 10th	Night	19% 31% 31% 15% 3	567
	11th to 20th	Night	17% 30% 33% 15% 4	533
	21st to end	Night	15% 25% 34% 19% 6%	540
May	1st to 10th	Night	19% 21% 30% 21% 9% 1	540
	11th to 20th	Night	19% 14% 31% 25% 10% 1	531
	21st to end	Night	21% 16% 31% 25% 8%	584
June	1st to 10th	Night	16% 17% 28% 29% 8% 1	540
	11th to 20th	Night	17% 23% 33% 23% 4	371
	21st to end	Night	7% 12% 34% 37% 9%	360
July	1st to 10th	Night	4 6% 35% 41% 14% 1	350
	11th to 20th	Night	6% 14% 39% 35% 6%	488
	21st to end	Night	7% 11% 32% 37% 11% 1	591
August	1st to 10th	Night	7% 10% 36% 39% 8%	537
	11th to 20th	Night	7% 8% 32% 40% 12% 1	534
	21st to end	Night	9% 13% 32% 34% 11%	594
September	1st to 10th	Night	11% 14% 35% 29% 9% 2	540
	11th to 20th	Night	11% 16% 35% 27% 8% 2	638
	21st to end	Night	16% 20% 30% 24% 8% 1	720
October	1st to 10th	Night	15% 23% 36% 19% 7% 1	720
	11th to 20th	Night	19% 30% 28% 17% 6%	720
	21st to end	Night	16% 37% 34% 9% 4	792
November	1st to 10th	Night	21% 41% 30% 7% 1	866
	11th to 20th	Night	22% 45% 27% 5% 1	950
	21st to end	Night	20% 38% 33% 8% 1	950
December	1st to 10th	Night	20% 42% 25% 11% 2	950
	11th to 20th	Night	18% 45% 26% 8% 2 1	950
	21st to end	Night	21% 41% 25% 10% 3	1045

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