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 2024-11-12.

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	5% 9% 4 9% 6% 6% 6% 5% 7% 8% 38%	106137
	Night	3 6% 3 7% 5% 5% 6% 5% 8% 8% 44%	101697
Transparency	Day	37% 7% 14% 23% 15% 4	105879
	Night	29% 8% 17% 26% 16% 4	101544
Seeing	Day	21% 30% 32% 14% 3	15843
	Night	17% 30% 30% 17% 5%	25365

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	2 2 10% 8% 9% 8% 7% 11% 10% 34%	2460
	11th to 20th	Day	3 2 6% 6% 8% 7% 7% 10% 11% 40%	2678
	21st to end	Day	5% 3 9% 5% 5% 5% 5% 7% 10% 46%	3146
February	1st to 10th	Day	6% 4 13% 9% 8% 8% 7% 10% 8% 28%	1710
	11th to 20th	Day	7% 4 13% 10% 8% 7% 5% 8% 6% 30%	1665
	21st to end	Day	8% 4 13% 10% 8% 7% 6% 9% 8% 26%	1423
March	1st to 10th	Day	5% 4 16% 9% 7% 7% 5% 7% 7% 32%	3444
	11th to 20th	Day	1 10% 5% 13% 6% 6% 6% 4 7% 7% 35%	3490
	21st to end	Day	2 17% 8% 17% 9% 8% 7% 5% 5% 6% 14%	3825
April	1st to 10th	Day	4 17% 7% 11% 7% 6% 5% 5% 6% 7% 26%	2251
	11th to 20th	Day	4 15% 5% 14% 8% 6% 6% 5% 6% 8% 24%	2333
	21st to end	Day	8% 21% 6% 11% 6% 5% 5% 3 5% 6% 24%	2470
May	1st to 10th	Day	8% 20% 6% 12% 7% 6% 5% 4 4 6% 22%	4166
	11th to 20th	Day	8% 10% 3 9% 6% 6% 6% 5% 7% 10% 31%	4388
	21st to end	Day	10% 13% 5% 10% 6% 6% 6% 5% 7% 8% 25%	4825
June	1st to 10th	Day	12% 10% 3 8% 6% 5% 5% 5% 8% 8% 30%	2660
	11th to 20th	Day	12% 9% 3 8% 5% 5% 5% 4 8% 8% 33%	2833
	21st to end	Day	6% 5% 2 6% 4 5% 5% 4 7% 8% 49%	2850
July	1st to 10th	Day	5% 5% 3 7% 6% 6% 6% 6% 7% 7% 40%	4740
	11th to 20th	Day	4 4 2 6% 4 5% 6% 6% 8% 9% 46%	4475
	21st to end	Day	4 5% 2 7% 6% 6% 6% 5% 7% 8% 45%	4595
August	1st to 10th	Day	8% 7% 3 7% 5% 6% 6% 6% 7% 7% 39%	4092
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 5% 6% 7% 46%	4028
	21st to end	Day	7% 5% 3 6% 4 4 4 3 5% 6% 53%	4409
September	1st to 10th	Day	9% 6% 2 5% 3 3 4 4 5% 7% 53%	2280
	11th to 20th	Day	9% 7% 3 6% 4 4 4 4 6% 8% 46%	2172
	21st to end	Day	7% 8% 2 4 4 5% 4 4 6% 6% 50%	2066
October	1st to 10th	Day	6% 9% 3 5% 3 3 3 2 3 5% 59%	3170
	11th to 20th	Day	4 10% 3 6% 3 3 3 3 4 6% 55%	3150
	21st to end	Day	2 10% 5% 8% 4 4 5% 5% 7% 8% 42%	3438
November	1st to 10th	Day	3 8% 4 8% 6% 7% 6% 5% 7% 9% 38%	1620
	11th to 20th	Day	1 7% 3 6% 5% 7% 5% 5% 8% 11% 42%	1528
	21st to end	Day	1 5% 4 8% 5% 6% 6% 4 9% 10% 43%	1520
December	1st to 10th	Day	1 3 3 9% 7% 6% 6% 7% 11% 9% 38%	1520
	11th to 20th	Day	4 3 8% 7% 7% 9% 6% 11% 10% 33%	1926
	21st to end	Day	6% 3 9% 6% 6% 5% 5% 7% 8% 45%	2791
January	1st to 10th	Night	2 1 7% 8% 8% 7% 6% 11% 9% 41%	4417
	11th to 20th	Night	2 2 6% 9% 9% 7% 6% 9% 10% 40%	4320
	21st to end	Night	1 6% 4 8% 5% 4 6% 5% 8% 10% 43%	4521
February	1st to 10th	Night	5% 3 9% 7% 7% 8% 7% 10% 10% 34%	2470
	11th to 20th	Night	1 5% 3 10% 8% 8% 7% 5% 11% 8% 33%	2402
	21st to end	Night	6% 4 11% 8% 7% 7% 6% 12% 9% 30%	2031
March	1st to 10th	Night	5% 5% 10% 6% 7% 7% 6% 9% 10% 35%	3430
	11th to 20th	Night	1 4 3 9% 5% 4 5% 5% 7% 9% 47%	3490
	21st to end	Night	1 7% 3 12% 7% 8% 8% 7% 10% 10% 26%	3828
April	1st to 10th	Night	3 10% 3 10% 7% 5% 5% 5% 6% 7% 38%	1928
	11th to 20th	Night	3 9% 3 10% 8% 5% 6% 6% 9% 7% 34%	1791
	21st to end	Night	4 14% 3 9% 6% 5% 5% 5% 6% 8% 36%	1710
May	1st to 10th	Night	6% 13% 5% 10% 7% 6% 5% 5% 6% 7% 31%	2801
	11th to 20th	Night	5% 10% 3 6% 4 4 4 4 7% 8% 46%	2517
	21st to end	Night	8% 11% 4 8% 5% 6% 5% 5% 7% 8% 32%	2762
June	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 5% 8% 10% 38%	1520
	11th to 20th	Night	9% 6% 2 7% 4 5% 5% 5% 6% 7% 44%	1341
	21st to end	Night	3 5% 2 4 3 4 4 4 6% 7% 58%	1330
July	1st to 10th	Night	4 3 1 4 3 4 5% 4 7% 7% 59%	2220
	11th to 20th	Night	3 3 1 5% 4 4 5% 4 8% 9% 54%	2476
	21st to end	Night	4 3 2 6% 4 4 4 4 6% 8% 57%	2965
August	1st to 10th	Night	7% 7% 2 5% 4 4 6% 4 7% 7% 45%	2847
	11th to 20th	Night	4 4 2 7% 6% 6% 6% 4 5% 7% 51%	2811
	21st to end	Night	4 4 2 4 3 3 3 3 4 5% 65%	3256
September	1st to 10th	Night	6% 5% 2 4 3 3 3 3 5% 7% 59%	1900
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 6% 7% 52%	2004
	21st to end	Night	8% 6% 2 5% 3 3 3 3 5% 6% 55%	2114
October	1st to 10th	Night	4 5% 2 6% 4 3 4 3 4 7% 58%	3800
	11th to 20th	Night	3 8% 3 6% 4 5% 4 4 4 6% 53%	3778
	21st to end	Night	3 7% 2 7% 5% 5% 5% 4 6% 7% 48%	4120
November	1st to 10th	Night	1 7% 2 7% 5% 5% 6% 7% 10% 10% 40%	2658
	11th to 20th	Night	1 5% 2 7% 6% 6% 6% 5% 9% 10% 42%	2675
	21st to end	Night	1 5% 2 8% 5% 5% 7% 5% 9% 10% 44%	2660
December	1st to 10th	Night	3 3 8% 6% 7% 7% 7% 12% 9% 39%	2660
	11th to 20th	Night	3 2 6% 6% 6% 7% 6% 11% 12% 41%	3271
	21st to end	Night	4 3 9% 6% 5% 5% 5% 8% 8% 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	30% 11% 20% 28% 11% 1	2460
	11th to 20th	Day	27% 13% 24% 18% 15% 3	2678
	21st to end	Day	27% 9% 24% 26% 13% 1	3146
February	1st to 10th	Day	41% 9% 20% 20% 8% 1	1710
	11th to 20th	Day	44% 9% 18% 20% 8% 2	1674
	21st to end	Day	44% 8% 16% 17% 13% 3	1423
March	1st to 10th	Day	34% 10% 14% 23% 16% 2	3444
	11th to 20th	Day	39% 7% 20% 26% 7% 1	3490
	21st to end	Day	58% 8% 18% 13% 2	3825
April	1st to 10th	Day	51% 7% 14% 20% 8% 1	2251
	11th to 20th	Day	53% 7% 17% 18% 4 1	2336
	21st to end	Day	57% 5% 15% 18% 5%	2470
May	1st to 10th	Day	59% 5% 8% 20% 7% 1	4166
	11th to 20th	Day	39% 9% 14% 24% 10% 3	4392
	21st to end	Day	47% 11% 12% 23% 7%	4825
June	1st to 10th	Day	45% 9% 16% 22% 8% 1	2660
	11th to 20th	Day	42% 7% 13% 18% 16% 3	2833
	21st to end	Day	28% 6% 12% 30% 17% 7%	2850
July	1st to 10th	Day	34% 8% 8% 22% 25% 4	4666
	11th to 20th	Day	27% 5% 7% 21% 25% 14%	4398
	21st to end	Day	31% 5% 7% 20% 25% 12%	4450
August	1st to 10th	Day	38% 6% 8% 20% 21% 7%	4078
	11th to 20th	Day	33% 5% 8% 25% 22% 8%	4067
	21st to end	Day	30% 4 7% 22% 27% 10%	4408
September	1st to 10th	Day	29% 3 8% 21% 31% 7%	2280
	11th to 20th	Day	32% 5% 12% 23% 24% 5%	2172
	21st to end	Day	30% 5% 12% 27% 20% 5%	2066
October	1st to 10th	Day	29% 2 7% 24% 33% 4	3170
	11th to 20th	Day	29% 4 14% 34% 16% 4	3150
	21st to end	Day	36% 6% 18% 26% 14% 1	3438
November	1st to 10th	Day	36% 8% 17% 23% 13% 3	1620
	11th to 20th	Day	30% 8% 23% 26% 11% 3	1528
	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	25% 11% 22% 26% 15% 1	4417
	11th to 20th	Night	28% 12% 24% 22% 10% 4	4320
	21st to end	Night	28% 10% 25% 26% 10% 1	4521
February	1st to 10th	Night	34% 10% 21% 25% 10% 1	2470
	11th to 20th	Night	35% 7% 21% 24% 11% 2	2403
	21st to end	Night	35% 8% 17% 22% 16% 3	2031
March	1st to 10th	Night	25% 12% 13% 26% 20% 3	3430
	11th to 20th	Night	27% 7% 24% 30% 10% 1	3490
	21st to end	Night	34% 11% 28% 24% 4 1	3828
April	1st to 10th	Night	39% 8% 20% 21% 11% 1	1928
	11th to 20th	Night	41% 9% 22% 22% 5% 1	1791
	21st to end	Night	41% 9% 22% 22% 7%	1710
May	1st to 10th	Night	47% 5% 12% 22% 11% 2	2801
	11th to 20th	Night	31% 6% 17% 34% 10% 2	2518
	21st to end	Night	38% 9% 19% 27% 7%	2762
June	1st to 10th	Night	35% 8% 23% 24% 8% 2	1520
	11th to 20th	Night	32% 7% 17% 24% 16% 4	1341
	21st to end	Night	22% 5% 15% 31% 20% 7%	1330
July	1st to 10th	Night	19% 7% 9% 30% 33% 3	2185
	11th to 20th	Night	22% 5% 8% 23% 33% 10%	2430
	21st to end	Night	24% 4 8% 25% 29% 10%	2872
August	1st to 10th	Night	34% 5% 10% 23% 19% 9%	2838
	11th to 20th	Night	32% 4 8% 26% 22% 8%	2838
	21st to end	Night	21% 4 7% 28% 32% 8%	3256
September	1st to 10th	Night	24% 4 9% 24% 31% 8%	1900
	11th to 20th	Night	27% 5% 14% 26% 22% 5%	2004
	21st to end	Night	27% 4 12% 30% 23% 3	2114
October	1st to 10th	Night	25% 3 9% 31% 29% 3	3800
	11th to 20th	Night	31% 3 13% 28% 22% 3	3778
	21st to end	Night	31% 5% 14% 30% 19% 1	4120
November	1st to 10th	Night	28% 11% 18% 26% 15% 2	2658
	11th to 20th	Night	27% 9% 26% 25% 11% 2	2675
	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	20% 45% 21% 9% 4	270
	21st to end	Day	17% 53% 22% 6% 2	297
February	1st to 10th	Day	30% 49% 17% 4	270
	11th to 20th	Day	36% 35% 19% 8% 3	270
	21st to end	Day	30% 40% 22% 7% 1	230
March	1st to 10th	Day	26% 40% 29% 5% 1	460
	11th to 20th	Day	20% 37% 36% 7% 1	460
	21st to end	Day	27% 33% 29% 9% 1	506
April	1st to 10th	Day	30% 39% 27% 4	460
	11th to 20th	Day	27% 38% 30% 4	452
	21st to end	Day	30% 27% 29% 11% 2 1	460
May	1st to 10th	Day	25% 26% 29% 17% 3 1	493
	11th to 20th	Day	25% 19% 33% 17% 5% 1	675
	21st to end	Day	25% 22% 27% 19% 5% 1	734
June	1st to 10th	Day	18% 24% 31% 21% 7%	680
	11th to 20th	Day	25% 29% 31% 11% 3	680
	21st to end	Day	12% 22% 39% 21% 6% 1	680
July	1st to 10th	Day	8% 19% 39% 25% 7% 1	671
	11th to 20th	Day	8% 22% 44% 20% 5%	668
	21st to end	Day	8% 17% 44% 24% 6% 1	620
August	1st to 10th	Day	14% 21% 43% 17% 5%	487
	11th to 20th	Day	12% 15% 43% 25% 5%	477
	21st to end	Day	14% 22% 41% 16% 6%	539
September	1st to 10th	Day	12% 27% 44% 15% 2	490
	11th to 20th	Day	20% 26% 33% 16% 4	490
	21st to end	Day	20% 28% 37% 11% 4	466
October	1st to 10th	Day	21% 28% 33% 14% 3	300
	11th to 20th	Day	23% 36% 27% 10% 3 1	300
	21st to end	Day	30% 41% 22% 7% 1	330
November	1st to 10th	Day	26% 44% 19% 8% 3	300
	11th to 20th	Day	27% 47% 23% 3 1	273
	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	22% 41% 25% 9% 4	879
	21st to end	Night	15% 48% 27% 8% 2	836
February	1st to 10th	Night	21% 42% 24% 11% 2	760
	11th to 20th	Night	22% 37% 27% 10% 3 1	744
	21st to end	Night	21% 37% 29% 9% 3	628
March	1st to 10th	Night	21% 34% 30% 13% 3	760
	11th to 20th	Night	17% 33% 33% 14% 3	760
	21st to end	Night	14% 32% 36% 15% 3	836
April	1st to 10th	Night	19% 31% 32% 15% 3	598
	11th to 20th	Night	17% 30% 34% 15% 4	563
	21st to end	Night	16% 25% 34% 19% 6%	570
May	1st to 10th	Night	20% 21% 30% 20% 8% 1	570
	11th to 20th	Night	19% 14% 31% 25% 10% 1	561
	21st to end	Night	20% 17% 31% 24% 7%	617
June	1st to 10th	Night	17% 18% 28% 29% 8% 1	570
	11th to 20th	Night	18% 23% 33% 22% 4	391
	21st to end	Night	8% 12% 35% 36% 9%	380
July	1st to 10th	Night	4 7% 35% 41% 13% 1	370
	11th to 20th	Night	6% 13% 39% 35% 6%	516
	21st to end	Night	8% 13% 31% 37% 11% 1	624
August	1st to 10th	Night	8% 10% 35% 39% 8%	567
	11th to 20th	Night	8% 9% 32% 39% 11% 1	564
	21st to end	Night	10% 13% 33% 33% 11%	627
September	1st to 10th	Night	11% 14% 34% 30% 9% 2	570
	11th to 20th	Night	13% 16% 34% 27% 8% 2	674
	21st to end	Night	17% 20% 30% 24% 8% 1	760
October	1st to 10th	Night	15% 24% 36% 19% 6% 1	760
	11th to 20th	Night	19% 29% 29% 18% 6%	760
	21st to end	Night	19% 36% 33% 8% 4	836
November	1st to 10th	Night	21% 41% 29% 8% 1	913
	11th to 20th	Night	22% 45% 27% 5% 1	956
	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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