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 2026-06-16.

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	18% 13% 4 10% 6% 5% 4 3 5% 6% 26%	137858
	Night	17% 14% 6% 12% 6% 5% 4 3 4 5% 24%	134170
Transparency	Day	57% 6% 10% 17% 8% 1	141313
	Night	62% 6% 9% 15% 7% 1	138792
Seeing	Day	28% 19% 27% 16% 7% 3	16661
	Night	26% 18% 25% 21% 8% 1	25755

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% 17% 7% 27% 11% 5% 4 2 2 2 12%	4661
	11th to 20th	Day	9% 19% 10% 21% 13% 6% 3 2 2 2 13%	4650
	21st to end	Day	10% 16% 8% 16% 10% 9% 8% 3 4 4 14%	5282
February	1st to 10th	Day	12% 16% 8% 15% 9% 7% 5% 3 4 3 16%	1890
	11th to 20th	Day	10% 16% 8% 17% 10% 5% 4 3 3 4 18%	1951
	21st to end	Day	14% 18% 7% 15% 8% 6% 3 2 4 5% 18%	1730
March	1st to 10th	Day	19% 15% 8% 16% 5% 3 4 2 3 3 20%	4576
	11th to 20th	Day	13% 20% 7% 9% 5% 4 4 3 4 5% 26%	4902
	21st to end	Day	19% 15% 5% 11% 5% 3 3 2 3 4 29%	6026
April	1st to 10th	Day	20% 17% 5% 9% 5% 3 3 3 3 4 28%	2520
	11th to 20th	Day	18% 16% 4 8% 4 4 4 3 4 4 31%	2494
	21st to end	Day	22% 15% 3 7% 4 4 3 3 4 5% 29%	2611
May	1st to 10th	Day	30% 13% 3 7% 4 5% 4 3 4 5% 22%	8090
	11th to 20th	Day	19% 11% 3 8% 5% 5% 5% 4 5% 7% 28%	8221
	21st to end	Day	23% 10% 3 7% 4 4 5% 4 5% 6% 28%	9060
June	1st to 10th	Day	22% 9% 3 7% 6% 5% 4 4 6% 7% 29%	2940
	11th to 20th	Day	21% 7% 2 7% 5% 4 5% 5% 6% 7% 29%	2870
	21st to end	Day	22% 9% 3 7% 5% 5% 5% 4 6% 7% 28%	2800
July	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 5% 7% 10% 34%	6360
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 5% 7% 9% 33%	6360
	21st to end	Day	16% 6% 2 7% 4 4 5% 4 6% 9% 37%	6926
August	1st to 10th	Day	19% 8% 2 6% 4 5% 5% 4 6% 8% 32%	4547
	11th to 20th	Day	18% 9% 2 8% 5% 5% 5% 5% 6% 7% 30%	3954
	21st to end	Day	19% 6% 2 6% 4 5% 5% 4 7% 9% 34%	4312
September	1st to 10th	Day	18% 7% 2 6% 4 4 5% 4 4 9% 38%	2400
	11th to 20th	Day	16% 7% 2 6% 4 3 3 3 6% 6% 44%	2340
	21st to end	Day	19% 10% 2 6% 4 3 5% 4 6% 8% 35%	2200
October	1st to 10th	Day	24% 11% 3 7% 4 4 4 3 4 5% 32%	2030
	11th to 20th	Day	20% 15% 3 7% 3 4 4 3 5% 6% 29%	2000
	21st to end	Day	24% 17% 4 7% 5% 4 4 3 4 4 24%	1999
November	1st to 10th	Day	15% 18% 5% 9% 6% 4 4 3 4 5% 27%	1851
	11th to 20th	Day	14% 20% 6% 10% 5% 3 4 3 4 5% 25%	1831
	21st to end	Day	16% 23% 6% 11% 5% 5% 4 3 4 5% 18%	1680
December	1st to 10th	Day	15% 26% 9% 20% 8% 3 2 2 2 3 10%	2680
	11th to 20th	Day	16% 19% 8% 20% 6% 3 3 2 4 3 15%	3066
	21st to end	Day	17% 18% 8% 13% 6% 4 3 4 4 5% 19%	4048
January	1st to 10th	Night	11% 19% 9% 25% 9% 6% 3 2 3 3 12%	8234
	11th to 20th	Night	9% 18% 11% 25% 14% 6% 4 2 2 2 7%	8235
	21st to end	Night	10% 13% 7% 19% 10% 11% 8% 4 3 3 10%	8895
February	1st to 10th	Night	12% 17% 7% 17% 10% 8% 4 3 4 3 15%	2730
	11th to 20th	Night	11% 14% 7% 18% 9% 7% 5% 3 4 5% 16%	2554
	21st to end	Night	12% 17% 6% 15% 9% 6% 4 3 4 5% 19%	2076
March	1st to 10th	Night	19% 15% 5% 14% 8% 6% 4 2 3 4 20%	5484
	11th to 20th	Night	13% 16% 7% 10% 4 3 3 2 5% 6% 30%	5259
	21st to end	Night	20% 16% 7% 12% 5% 3 3 2 3 4 24%	5148
April	1st to 10th	Night	20% 16% 6% 8% 4 4 3 3 4 5% 28%	2100
	11th to 20th	Night	21% 17% 4 6% 5% 4 3 2 4 5% 29%	2075
	21st to end	Night	20% 12% 4 8% 4 3 4 4 4 5% 32%	2007
May	1st to 10th	Night	31% 15% 3 7% 4 3 3 3 4 5% 21%	4864
	11th to 20th	Night	22% 12% 3 6% 4 4 4 3 5% 7% 30%	4639
	21st to end	Night	21% 12% 2 6% 4 5% 5% 3 6% 7% 29%	5114
June	1st to 10th	Night	22% 7% 2 6% 4 4 4 5% 4 7% 34%	1680
	11th to 20th	Night	21% 6% 2 6% 4 4 4 4 4 7% 36%	1640
	21st to end	Night	20% 7% 3 7% 5% 4 5% 3 6% 8% 33%	1600
July	1st to 10th	Night	15% 6% 2 7% 5% 5% 5% 4 6% 9% 36%	3600
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 5% 7% 39%	3600
	21st to end	Night	12% 7% 2 6% 4 4 3 3 5% 8% 45%	3926
August	1st to 10th	Night	23% 8% 2 6% 3 3 3 2 4 7% 38%	2586
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 5% 5% 35%	3062
	21st to end	Night	15% 9% 2 5% 3 4 5% 4 5% 8% 40%	3586
September	1st to 10th	Night	15% 8% 2 5% 4 4 4 3 5% 7% 42%	2000
	11th to 20th	Night	14% 8% 2 5% 3 3 3 3 5% 7% 47%	2059
	21st to end	Night	19% 9% 2 6% 3 3 3 3 6% 7% 39%	2200
October	1st to 10th	Night	23% 11% 3 5% 4 3 5% 3 5% 6% 31%	2365
	11th to 20th	Night	18% 14% 3 8% 4 4 4 4 5% 6% 30%	2400
	21st to end	Night	23% 19% 4 7% 4 4 4 3 4 5% 22%	2840
November	1st to 10th	Night	17% 17% 7% 8% 4 4 4 3 5% 4 27%	2667
	11th to 20th	Night	16% 17% 7% 10% 5% 4 3 4 4 6% 24%	2787
	21st to end	Night	16% 20% 8% 14% 5% 3 4 3 5% 5% 17%	2940
December	1st to 10th	Night	16% 23% 11% 22% 6% 3 2 2 3 3 9%	4720
	11th to 20th	Night	19% 21% 8% 15% 6% 4 3 2 3 3 16%	5348
	21st to end	Night	18% 20% 6% 16% 6% 5% 4 3 4 4 16%	7150

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	80% 3 5% 9% 3	4662
	11th to 20th	Day	80% 3 3 5% 8% 2	4680
	21st to end	Day	74% 5% 7% 8% 5% 1	5282
February	1st to 10th	Day	72% 5% 7% 11% 4 1	1890
	11th to 20th	Day	69% 4 8% 10% 8% 1	1960
	21st to end	Day	69% 5% 8% 10% 8% 1	1730
March	1st to 10th	Day	68% 5% 7% 9% 9% 3	4579
	11th to 20th	Day	61% 4 13% 12% 7% 3	4902
	21st to end	Day	60% 3 6% 12% 16% 2	6026
April	1st to 10th	Day	61% 4 8% 15% 10% 2	2520
	11th to 20th	Day	56% 5% 7% 17% 13% 1	2494
	21st to end	Day	58% 5% 8% 15% 11% 3	2611
May	1st to 10th	Day	63% 6% 8% 14% 8% 1	8102
	11th to 20th	Day	55% 7% 11% 20% 7%	8225
	21st to end	Day	55% 7% 9% 22% 7%	9061
June	1st to 10th	Day	54% 7% 12% 16% 10% 1	2940
	11th to 20th	Day	51% 8% 11% 21% 9% 1	2870
	21st to end	Day	55% 7% 11% 18% 8% 1	2800
July	1st to 10th	Day	43% 8% 16% 23% 10%	6290
	11th to 20th	Day	43% 10% 14% 24% 9%	6285
	21st to end	Day	42% 8% 12% 33% 6%	6728
August	1st to 10th	Day	48% 8% 15% 20% 9%	4533
	11th to 20th	Day	49% 8% 16% 22% 5%	3993
	21st to end	Day	43% 9% 16% 23% 9%	4312
September	1st to 10th	Day	44% 6% 11% 28% 11% 1	2400
	11th to 20th	Day	39% 6% 10% 28% 17% 1	2340
	21st to end	Day	47% 6% 13% 21% 12% 1	2200
October	1st to 10th	Day	49% 6% 11% 24% 10%	3303
	11th to 20th	Day	50% 5% 13% 18% 14% 1	3240
	21st to end	Day	51% 5% 13% 24% 6% 1	3199
November	1st to 10th	Day	59% 6% 11% 15% 9%	1851
	11th to 20th	Day	61% 6% 9% 13% 9% 3	1831
	21st to end	Day	68% 7% 11% 9% 5%	1680
December	1st to 10th	Day	82% 4 5% 7% 2	2680
	11th to 20th	Day	74% 4 6% 11% 4	3066
	21st to end	Day	67% 5% 6% 9% 12% 1	4048
January	1st to 10th	Night	79% 4 6% 7% 3	8234
	11th to 20th	Night	85% 4 3 4 3 1	8280
	21st to end	Night	78% 4 6% 7% 5% 1	8895
February	1st to 10th	Night	73% 5% 7% 9% 5% 1	2730
	11th to 20th	Night	70% 6% 8% 9% 7%	2556
	21st to end	Night	67% 5% 8% 11% 7% 1	2076
March	1st to 10th	Night	67% 5% 7% 11% 9% 1	5494
	11th to 20th	Night	57% 5% 15% 14% 7% 3	5260
	21st to end	Night	65% 4 5% 14% 11% 1	5148
April	1st to 10th	Night	60% 5% 9% 15% 10% 1	2100
	11th to 20th	Night	57% 6% 9% 17% 11%	2075
	21st to end	Night	54% 5% 9% 17% 12% 2	2007
May	1st to 10th	Night	64% 6% 8% 13% 9% 1	4870
	11th to 20th	Night	53% 7% 10% 21% 8% 1	4640
	21st to end	Night	54% 7% 10% 20% 8% 1	5115
June	1st to 10th	Night	49% 7% 13% 21% 10% 1	1680
	11th to 20th	Night	46% 7% 13% 21% 11% 1	1640
	21st to end	Night	49% 9% 13% 21% 9%	1600
July	1st to 10th	Night	43% 8% 17% 20% 11%	3560
	11th to 20th	Night	44% 8% 13% 25% 11%	3552
	21st to end	Night	38% 7% 14% 32% 8%	3809
August	1st to 10th	Night	47% 6% 16% 23% 8%	2576
	11th to 20th	Night	49% 7% 16% 21% 7%	3089
	21st to end	Night	41% 8% 15% 27% 8% 1	3586
September	1st to 10th	Night	42% 7% 13% 28% 10% 1	2000
	11th to 20th	Night	37% 5% 13% 32% 12%	2059
	21st to end	Night	44% 7% 12% 24% 12% 2	2200
October	1st to 10th	Night	52% 7% 11% 21% 9% 1	3872
	11th to 20th	Night	50% 6% 12% 18% 10% 4	3899
	21st to end	Night	56% 5% 13% 19% 5% 1	4578
November	1st to 10th	Night	60% 6% 10% 14% 8% 2	2667
	11th to 20th	Night	62% 5% 9% 13% 8% 3	2787
	21st to end	Night	68% 7% 9% 11% 5% 1	2940
December	1st to 10th	Night	83% 4 5% 5% 2	4720
	11th to 20th	Night	74% 4 5% 9% 7%	5348
	21st to end	Night	73% 5% 5% 6% 8% 3	7150

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% 25% 34% 8% 6%	220
	11th to 20th	Day	33% 27% 32% 6% 1 1	220
	21st to end	Day	26% 27% 35% 10% 3	271
February	1st to 10th	Day	38% 30% 27% 5%	330
	11th to 20th	Day	35% 26% 31% 7% 1	438
	21st to end	Day	35% 25% 29% 9% 2	446
March	1st to 10th	Day	34% 23% 28% 13% 3	540
	11th to 20th	Day	34% 24% 29% 10% 3 1	540
	21st to end	Day	36% 27% 21% 11% 5% 1	594
April	1st to 10th	Day	39% 23% 21% 12% 5% 1	540
	11th to 20th	Day	37% 21% 21% 14% 5% 2	532
	21st to end	Day	35% 20% 28% 9% 5% 2	540
May	1st to 10th	Day	35% 21% 25% 10% 6% 3	543
	11th to 20th	Day	25% 18% 29% 20% 6% 2	567
	21st to end	Day	25% 19% 29% 15% 10% 2	617
June	1st to 10th	Day	27% 18% 28% 20% 5% 2	570
	11th to 20th	Day	26% 15% 28% 20% 8% 3	550
	21st to end	Day	28% 18% 28% 17% 7% 2	530
July	1st to 10th	Day	16% 12% 33% 24% 12% 3	525
	11th to 20th	Day	15% 12% 32% 26% 11% 2	524
	21st to end	Day	17% 12% 36% 25% 9% 2	576
August	1st to 10th	Day	18% 10% 25% 27% 15% 5%	526
	11th to 20th	Day	19% 10% 28% 23% 14% 7%	519
	21st to end	Day	16% 16% 29% 23% 10% 6%	583
September	1st to 10th	Day	19% 12% 28% 18% 14% 8%	530
	11th to 20th	Day	16% 13% 23% 21% 15% 13%	530
	21st to end	Day	19% 15% 28% 20% 13% 5%	530
October	1st to 10th	Day	30% 14% 23% 15% 13% 5%	530
	11th to 20th	Day	29% 21% 24% 18% 7% 2	530
	21st to end	Day	33% 21% 25% 17% 4	472
November	1st to 10th	Day	34% 19% 24% 17% 6%	425
	11th to 20th	Day	32% 23% 25% 14% 5% 1	371
	21st to end	Day	36% 27% 25% 10% 1	220
December	1st to 10th	Day	34% 23% 31% 11% 2	220
	11th to 20th	Day	36% 27% 30% 6% 1	220
	21st to end	Day	35% 21% 31% 10% 2 1	242
January	1st to 10th	Night	27% 29% 28% 13% 2	840
	11th to 20th	Night	30% 25% 29% 12% 3	840
	21st to end	Night	21% 26% 32% 18% 4	924
February	1st to 10th	Night	26% 26% 32% 15% 2	840
	11th to 20th	Night	25% 29% 30% 14% 2	823
	21st to end	Night	26% 24% 33% 14% 2	692
March	1st to 10th	Night	30% 21% 30% 17% 2	840
	11th to 20th	Night	31% 24% 24% 16% 4 1	840
	21st to end	Night	30% 19% 28% 17% 5% 1	924
April	1st to 10th	Night	31% 21% 26% 19% 3	840
	11th to 20th	Night	32% 21% 23% 17% 6%	831
	21st to end	Night	29% 19% 24% 20% 7%	747
May	1st to 10th	Night	35% 11% 25% 19% 10%	494
	11th to 20th	Night	21% 13% 27% 31% 7%	414
	21st to end	Night	18% 13% 29% 28% 12% 1	455
June	1st to 10th	Night	24% 10% 24% 30% 11% 1	420
	11th to 20th	Night	24% 7% 21% 34% 13%	410
	21st to end	Night	22% 9% 27% 32% 9% 1	400
July	1st to 10th	Night	14% 5% 26% 37% 17% 1	390
	11th to 20th	Night	13% 6% 25% 38% 16% 2	388
	21st to end	Night	12% 9% 23% 42% 12% 1	438
August	1st to 10th	Night	18% 6% 18% 40% 17% 1	398
	11th to 20th	Night	18% 7% 20% 29% 22% 3	703
	21st to end	Night	18% 9% 22% 33% 18% 1	880
September	1st to 10th	Night	18% 10% 23% 30% 17% 3	800
	11th to 20th	Night	18% 8% 19% 29% 23% 4	800
	21st to end	Night	25% 11% 23% 21% 19% 2	800
October	1st to 10th	Night	29% 14% 20% 20% 15% 2	800
	11th to 20th	Night	26% 17% 23% 25% 8% 1	800
	21st to end	Night	35% 19% 22% 19% 4	880
November	1st to 10th	Night	30% 19% 25% 19% 6%	820
	11th to 20th	Night	30% 20% 26% 15% 8% 1	840
	21st to end	Night	31% 23% 25% 16% 5% 1	840
December	1st to 10th	Night	33% 26% 23% 14% 3	840
	11th to 20th	Night	30% 26% 24% 16% 3 1	840
	21st to end	Night	32% 26% 25% 14% 3	924

Page generated at 2026-06-13 02:31:38. Version ac07

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