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 2025-02-21.

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	17% 13% 5% 10% 6% 4 4 3 5% 6% 26%	108601
	Night	16% 15% 6% 13% 6% 5% 4 3 4 5% 24%	109956
Transparency	Day	57% 6% 10% 17% 8% 1	112102
	Night	62% 6% 9% 15% 7% 1	114607
Seeing	Day	27% 18% 28% 17% 7% 3	14930
	Night	26% 18% 25% 21% 8% 1	24138

By Month

Percentage Cloud Cover NE (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	10% 16% 8% 27% 11% 5% 4 2 3 2 13%	3597
	11th to 20th	Day	10% 19% 8% 22% 15% 4 3 2 2 3 13%	3570
	21st to end	Day	12% 18% 9% 16% 8% 5% 7% 3 4 4 14%	4076
February	1st to 10th	Day	13% 17% 8% 15% 9% 7% 4 3 4 3 16%	1800
	11th to 20th	Day	10% 16% 7% 17% 10% 6% 5% 4 3 4 18%	1856
	21st to end	Day	14% 18% 5% 15% 7% 6% 3 2 4 5% 20%	1570
March	1st to 10th	Day	22% 15% 7% 12% 6% 3 4 3 4 4 20%	3116
	11th to 20th	Day	11% 25% 8% 11% 5% 4 4 3 4 4 22%	3352
	21st to end	Day	15% 14% 6% 11% 6% 3 3 2 3 4 32%	4120
April	1st to 10th	Day	20% 18% 5% 7% 4 3 3 3 4 5% 29%	2280
	11th to 20th	Day	17% 16% 4 7% 4 4 4 3 4 4 32%	2254
	21st to end	Day	22% 15% 3 7% 4 4 3 3 4 6% 28%	2362
May	1st to 10th	Day	24% 12% 3 7% 4 5% 4 3 4 6% 27%	4349
	11th to 20th	Day	18% 10% 3 9% 6% 5% 5% 4 5% 8% 28%	4398
	21st to end	Day	16% 8% 3 7% 4 4 5% 4 6% 8% 34%	4837
June	1st to 10th	Day	23% 9% 3 7% 6% 5% 5% 4 6% 7% 27%	2660
	11th to 20th	Day	21% 8% 2 7% 5% 4 5% 5% 6% 7% 30%	2660
	21st to end	Day	22% 9% 3 7% 5% 5% 5% 4 6% 7% 27%	2660
July	1st to 10th	Day	15% 7% 2 6% 5% 5% 5% 5% 7% 9% 34%	4440
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 6% 7% 10% 31%	4440
	21st to end	Day	16% 7% 2 7% 5% 5% 6% 4 7% 8% 33%	4814
August	1st to 10th	Day	19% 8% 2 6% 4 5% 5% 4 6% 8% 31%	4407
	11th to 20th	Day	18% 9% 2 8% 5% 5% 5% 5% 6% 7% 29%	3831
	21st to end	Day	19% 6% 2 6% 4 5% 5% 4 7% 9% 34%	4180
September	1st to 10th	Day	18% 7% 2 6% 4 4 5% 4 4 9% 37%	2280
	11th to 20th	Day	17% 7% 2 6% 3 3 3 3 6% 6% 43%	2223
	21st to end	Day	19% 10% 2 6% 4 3 5% 4 6% 8% 35%	2090
October	1st to 10th	Day	25% 11% 2 7% 4 4 4 3 4 5% 30%	1929
	11th to 20th	Day	20% 15% 3 7% 4 5% 4 3 5% 6% 29%	1900
	21st to end	Day	24% 18% 4 7% 5% 4 4 3 4 5% 23%	1899
November	1st to 10th	Day	14% 17% 5% 8% 6% 4 4 3 4 5% 27%	1761
	11th to 20th	Day	15% 19% 6% 10% 5% 3 4 3 4 5% 26%	1744
	21st to end	Day	17% 22% 6% 11% 5% 5% 4 3 4 5% 19%	1600
December	1st to 10th	Day	15% 27% 9% 20% 8% 3 2 2 2 2 10%	2600
	11th to 20th	Day	16% 20% 8% 20% 6% 3 3 2 4 3 15%	2986
	21st to end	Day	17% 19% 8% 12% 6% 4 3 4 4 5% 19%	3960
January	1st to 10th	Night	11% 18% 9% 27% 9% 6% 3 2 3 3 11%	6349
	11th to 20th	Night	8% 18% 10% 26% 14% 5% 4 2 3 2 8%	6315
	21st to end	Night	12% 15% 8% 20% 9% 8% 6% 3 4 3 11%	6876
February	1st to 10th	Night	13% 17% 8% 17% 10% 7% 4 3 4 4 15%	2600
	11th to 20th	Night	11% 14% 7% 17% 9% 8% 5% 3 4 5% 16%	2429
	21st to end	Night	13% 16% 6% 15% 9% 6% 4 3 4 5% 20%	1885
March	1st to 10th	Night	19% 15% 5% 10% 8% 5% 4 3 4 5% 23%	3724
	11th to 20th	Night	13% 20% 9% 11% 4 3 3 2 3 4 26%	3589
	21st to end	Night	16% 16% 6% 11% 5% 3 3 2 3 4 31%	3512
April	1st to 10th	Night	19% 16% 6% 8% 4 4 3 3 4 5% 27%	1900
	11th to 20th	Night	20% 16% 3 6% 5% 4 3 2 4 5% 30%	1875
	21st to end	Night	21% 12% 4 8% 4 3 4 4 4 5% 31%	1816
May	1st to 10th	Night	25% 12% 3 7% 5% 4 4 3 5% 5% 26%	2620
	11th to 20th	Night	20% 14% 3 8% 4 3 4 3 4 6% 31%	2495
	21st to end	Night	16% 8% 2 6% 4 4 5% 4 7% 8% 36%	2738
June	1st to 10th	Night	21% 7% 2 6% 4 5% 4 5% 5% 7% 33%	1520
	11th to 20th	Night	20% 6% 2 6% 4 4 4 4 5% 8% 37%	1520
	21st to end	Night	20% 7% 3 7% 5% 4 5% 3 6% 8% 33%	1520
July	1st to 10th	Night	15% 6% 2 8% 5% 5% 6% 4 5% 7% 36%	2520
	11th to 20th	Night	17% 7% 2 5% 4 4 4 4 5% 8% 39%	2520
	21st to end	Night	14% 7% 3 7% 4 5% 4 3 5% 8% 40%	2739
August	1st to 10th	Night	23% 8% 2 6% 3 3 3 2 4 7% 37%	2506
	11th to 20th	Night	20% 10% 3 7% 4 4 4 3 5% 6% 34%	2966
	21st to end	Night	15% 9% 2 5% 3 4 5% 4 5% 8% 40%	3476
September	1st to 10th	Night	15% 8% 2 5% 4 4 4 3 5% 7% 42%	1900
	11th to 20th	Night	14% 8% 2 5% 4 3 3 3 5% 7% 47%	1956
	21st to end	Night	19% 8% 2 6% 3 3 3 3 6% 7% 39%	2090
October	1st to 10th	Night	24% 11% 3 6% 4 3 5% 4 5% 6% 29%	2247
	11th to 20th	Night	18% 14% 3 8% 4 4 4 4 5% 6% 29%	2280
	21st to end	Night	24% 19% 4 7% 4 4 4 3 4 5% 21%	2698
November	1st to 10th	Night	16% 17% 7% 8% 4 4 4 3 5% 5% 27%	2537
	11th to 20th	Night	16% 17% 6% 9% 5% 4 3 4 4 6% 25%	2654
	21st to end	Night	16% 20% 7% 14% 5% 4 4 3 5% 5% 18%	2800
December	1st to 10th	Night	17% 23% 11% 22% 6% 3 2 2 3 3 8%	4580
	11th to 20th	Night	19% 21% 8% 15% 6% 4 3 2 3 3 17%	5208
	21st to end	Night	18% 20% 6% 16% 5% 5% 4 3 3 4 16%	6996

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	79% 3 5% 9% 4	3598
	11th to 20th	Day	79% 3 4 5% 7% 2	3600
	21st to end	Day	72% 5% 8% 8% 5% 1	4076
February	1st to 10th	Day	72% 5% 7% 11% 4 2	1800
	11th to 20th	Day	69% 5% 8% 9% 8% 1	1865
	21st to end	Day	68% 4 8% 10% 9% 1	1570
March	1st to 10th	Day	67% 6% 7% 10% 9% 1	3119
	11th to 20th	Day	67% 5% 10% 10% 7% 1	3352
	21st to end	Day	56% 3 8% 15% 16% 2	4120
April	1st to 10th	Day	59% 4 9% 16% 10% 2	2280
	11th to 20th	Day	55% 5% 8% 17% 13% 1	2254
	21st to end	Day	59% 5% 9% 14% 10% 3	2362
May	1st to 10th	Day	58% 6% 9% 18% 7% 1	4363
	11th to 20th	Day	54% 8% 11% 20% 7% 1	4402
	21st to end	Day	46% 8% 11% 25% 10% 1	4837
June	1st to 10th	Day	56% 7% 12% 15% 10% 1	2660
	11th to 20th	Day	51% 8% 10% 21% 9% 1	2660
	21st to end	Day	55% 7% 11% 18% 8% 1	2660
July	1st to 10th	Day	43% 8% 15% 24% 10%	4370
	11th to 20th	Day	43% 10% 16% 26% 5%	4365
	21st to end	Day	46% 9% 12% 26% 7%	4661
August	1st to 10th	Day	49% 8% 15% 19% 9%	4393
	11th to 20th	Day	50% 8% 16% 21% 5%	3870
	21st to end	Day	43% 9% 16% 23% 9%	4180
September	1st to 10th	Day	45% 6% 10% 27% 11% 1	2280
	11th to 20th	Day	40% 6% 10% 27% 16% 1	2223
	21st to end	Day	47% 6% 13% 21% 12% 1	2090
October	1st to 10th	Day	50% 6% 11% 23% 9%	3202
	11th to 20th	Day	50% 4 13% 18% 14% 1	3140
	21st to end	Day	50% 5% 13% 24% 6% 1	3099
November	1st to 10th	Day	58% 6% 11% 15% 9%	1761
	11th to 20th	Day	60% 6% 9% 13% 9% 3	1744
	21st to end	Day	68% 7% 11% 9% 5%	1600
December	1st to 10th	Day	82% 4 5% 7% 1	2600
	11th to 20th	Day	74% 4 6% 11% 4	2986
	21st to end	Day	67% 5% 6% 9% 12% 1	3960
January	1st to 10th	Night	81% 4 5% 6% 3	6349
	11th to 20th	Night	84% 4 4 4 3 1	6360
	21st to end	Night	77% 4 6% 7% 5% 1	6876
February	1st to 10th	Night	74% 5% 7% 9% 5% 1	2600
	11th to 20th	Night	70% 6% 8% 9% 7%	2431
	21st to end	Night	66% 6% 8% 12% 7% 1	1885
March	1st to 10th	Night	63% 5% 8% 13% 9% 1	3734
	11th to 20th	Night	63% 4 10% 14% 7% 1	3590
	21st to end	Night	59% 4 6% 16% 13% 2	3512
April	1st to 10th	Night	60% 5% 9% 16% 9% 1	1900
	11th to 20th	Night	56% 6% 10% 17% 11%	1875
	21st to end	Night	55% 6% 10% 16% 12% 2	1816
May	1st to 10th	Night	58% 7% 10% 15% 9% 1	2626
	11th to 20th	Night	54% 7% 10% 19% 8% 1	2496
	21st to end	Night	44% 8% 13% 21% 13% 1	2739
June	1st to 10th	Night	50% 8% 13% 20% 8% 1	1520
	11th to 20th	Night	45% 7% 14% 21% 11% 1	1520
	21st to end	Night	49% 9% 13% 20% 9%	1520
July	1st to 10th	Night	45% 8% 15% 19% 13% 1	2480
	11th to 20th	Night	42% 8% 16% 27% 7%	2472
	21st to end	Night	43% 8% 14% 28% 7% 1	2651
August	1st to 10th	Night	48% 6% 16% 23% 7%	2496
	11th to 20th	Night	49% 8% 16% 21% 6%	2993
	21st to end	Night	41% 8% 15% 28% 8% 1	3476
September	1st to 10th	Night	42% 7% 13% 28% 10% 1	1900
	11th to 20th	Night	38% 6% 13% 32% 11%	1956
	21st to end	Night	43% 7% 12% 24% 12% 2	2090
October	1st to 10th	Night	53% 7% 11% 21% 8% 1	3754
	11th to 20th	Night	50% 6% 12% 18% 10% 4	3779
	21st to end	Night	56% 5% 13% 20% 5% 1	4436
November	1st to 10th	Night	59% 6% 10% 14% 9% 2	2537
	11th to 20th	Night	61% 6% 9% 13% 8% 3	2654
	21st to end	Night	68% 7% 9% 11% 5% 1	2800
December	1st to 10th	Night	83% 4 5% 5% 2	4580
	11th to 20th	Night	74% 4 5% 9% 7%	5208
	21st to end	Night	73% 5% 5% 6% 8% 3	6996

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	26% 26% 33% 9% 7% 1	200
	11th to 20th	Day	32% 26% 34% 7% 1 1	200
	21st to end	Day	26% 26% 35% 10% 3	246
February	1st to 10th	Day	40% 31% 25% 4	300
	11th to 20th	Day	36% 26% 31% 7% 1	403
	21st to end	Day	35% 25% 28% 10% 3	382
March	1st to 10th	Day	32% 22% 29% 14% 3	460
	11th to 20th	Day	31% 23% 30% 11% 4 1	460
	21st to end	Day	34% 26% 22% 12% 6% 1	506
April	1st to 10th	Day	36% 22% 23% 13% 5% 1	460
	11th to 20th	Day	35% 21% 20% 16% 5% 2	452
	21st to end	Day	35% 18% 28% 11% 6% 2	460
May	1st to 10th	Day	32% 20% 25% 11% 6% 4	463
	11th to 20th	Day	24% 17% 29% 22% 6% 2	487
	21st to end	Day	23% 19% 29% 16% 11% 2	529
June	1st to 10th	Day	27% 18% 28% 19% 6% 2	490
	11th to 20th	Day	24% 14% 28% 21% 9% 3	490
	21st to end	Day	29% 18% 27% 17% 7% 2	490
July	1st to 10th	Day	17% 11% 32% 25% 13% 4	485
	11th to 20th	Day	16% 12% 33% 26% 11% 2	484
	21st to end	Day	17% 11% 36% 26% 8% 2	532
August	1st to 10th	Day	19% 10% 26% 25% 14% 5%	486
	11th to 20th	Day	19% 11% 28% 22% 13% 7%	479
	21st to end	Day	17% 15% 28% 23% 11% 6%	539
September	1st to 10th	Day	19% 13% 29% 18% 13% 8%	490
	11th to 20th	Day	17% 13% 22% 20% 15% 13%	490
	21st to end	Day	19% 15% 27% 21% 13% 5%	490
October	1st to 10th	Day	31% 15% 23% 14% 12% 5%	490
	11th to 20th	Day	28% 22% 23% 18% 7% 2	490
	21st to end	Day	33% 20% 25% 17% 5%	438
November	1st to 10th	Day	33% 17% 25% 18% 6% 1	395
	11th to 20th	Day	33% 23% 24% 14% 5% 1	344
	21st to end	Day	37% 25% 26% 12% 1	200
December	1st to 10th	Day	34% 22% 31% 12% 2	200
	11th to 20th	Day	37% 26% 30% 7% 1 1	200
	21st to end	Day	34% 22% 30% 11% 3 1	220
January	1st to 10th	Night	27% 29% 28% 13% 2	800
	11th to 20th	Night	29% 25% 30% 13% 3	800
	21st to end	Night	20% 25% 33% 18% 4	880
February	1st to 10th	Night	28% 26% 31% 14% 2	800
	11th to 20th	Night	26% 29% 29% 14% 2	783
	21st to end	Night	27% 24% 32% 15% 3	629
March	1st to 10th	Night	28% 21% 30% 18% 3	760
	11th to 20th	Night	30% 24% 24% 16% 4 1	760
	21st to end	Night	28% 19% 28% 18% 6% 1	836
April	1st to 10th	Night	28% 22% 26% 20% 4	760
	11th to 20th	Night	30% 21% 25% 17% 7%	751
	21st to end	Night	30% 19% 23% 21% 7%	676
May	1st to 10th	Night	32% 11% 26% 20% 11%	447
	11th to 20th	Night	20% 13% 26% 33% 7%	374
	21st to end	Night	16% 13% 28% 29% 13% 1	411
June	1st to 10th	Night	23% 10% 24% 30% 11% 1	380
	11th to 20th	Night	23% 6% 20% 36% 14%	380
	21st to end	Night	22% 8% 27% 33% 9% 1	380
July	1st to 10th	Night	14% 5% 25% 37% 18% 1	370
	11th to 20th	Night	13% 6% 25% 38% 16% 2	368
	21st to end	Night	13% 8% 22% 43% 13% 1	416
August	1st to 10th	Night	19% 7% 18% 39% 17% 1	378
	11th to 20th	Night	18% 8% 20% 29% 21% 3	667
	21st to end	Night	18% 8% 22% 33% 19% 1	836
September	1st to 10th	Night	18% 10% 23% 30% 16% 3	760
	11th to 20th	Night	18% 8% 19% 28% 22% 4	760
	21st to end	Night	25% 11% 23% 20% 19% 3	760
October	1st to 10th	Night	29% 15% 21% 19% 14% 2	760
	11th to 20th	Night	27% 16% 23% 25% 8% 1	760
	21st to end	Night	35% 19% 22% 19% 5%	836
November	1st to 10th	Night	29% 19% 26% 19% 7% 1	780
	11th to 20th	Night	30% 20% 26% 16% 8% 1	800
	21st to end	Night	31% 24% 25% 16% 5% 1	800
December	1st to 10th	Night	33% 26% 23% 14% 4	800
	11th to 20th	Night	30% 26% 24% 17% 3 1	800
	21st to end	Night	31% 26% 26% 14% 3	880

Page generated at 2025-02-18 03:26:27. Version ac07

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