Saranac Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saranac Lake Observatory 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	16% 13% 5% 11% 6% 5% 5% 4 5% 6% 26%	137784
	Night	15% 15% 6% 13% 7% 5% 4 3 4 5% 23%	134233
Transparency	Day	58% 5% 9% 18% 9% 1	141241
	Night	63% 4 9% 15% 8% 1	138865
Seeing	Day	29% 19% 28% 15% 7% 2	16644
	Night	26% 19% 25% 20% 8% 1	25708

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	9% 18% 9% 26% 10% 6% 4 2 3 3 10%	4661
	11th to 20th	Day	6% 16% 10% 25% 14% 7% 3 2 2 3 13%	4650
	21st to end	Day	8% 16% 8% 16% 10% 11% 6% 3 4 4 13%	5184
February	1st to 10th	Day	10% 17% 7% 18% 11% 7% 5% 3 3 3 16%	1890
	11th to 20th	Day	8% 16% 9% 19% 9% 6% 4 4 5% 4 17%	1959
	21st to end	Day	11% 20% 7% 16% 7% 8% 4 3 4 4 17%	1730
March	1st to 10th	Day	16% 17% 8% 17% 6% 3 4 2 3 4 21%	4576
	11th to 20th	Day	10% 20% 6% 12% 6% 4 4 3 5% 5% 25%	4855
	21st to end	Day	16% 14% 5% 11% 6% 4 4 3 4 5% 28%	6055
April	1st to 10th	Day	18% 19% 5% 9% 5% 4 4 3 4 4 26%	2520
	11th to 20th	Day	17% 17% 4 8% 5% 4 4 3 4 5% 30%	2494
	21st to end	Day	21% 15% 3 9% 4 4 4 3 4 6% 28%	2639
May	1st to 10th	Day	25% 13% 4 9% 5% 5% 5% 4 5% 5% 21%	8056
	11th to 20th	Day	18% 11% 3 8% 6% 5% 5% 4 5% 7% 28%	8221
	21st to end	Day	22% 11% 3 7% 5% 4 5% 4 5% 6% 27%	9060
June	1st to 10th	Day	24% 9% 3 7% 5% 4 5% 4 5% 6% 27%	2940
	11th to 20th	Day	18% 9% 2 7% 5% 4 6% 5% 6% 8% 30%	2870
	21st to end	Day	22% 9% 2 8% 6% 5% 5% 4 6% 7% 27%	2800
July	1st to 10th	Day	13% 7% 3 7% 5% 6% 6% 5% 7% 9% 32%	6360
	11th to 20th	Day	12% 7% 2 7% 5% 5% 6% 5% 7% 9% 34%	6360
	21st to end	Day	15% 6% 2 6% 5% 4 5% 5% 6% 9% 38%	6926
August	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 8% 30%	4563
	11th to 20th	Day	16% 8% 3 9% 5% 5% 6% 4 7% 7% 30%	3988
	21st to end	Day	17% 7% 2 6% 5% 5% 5% 5% 6% 8% 34%	4312
September	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 5% 8% 39%	2400
	11th to 20th	Day	16% 8% 2 5% 3 3 4 4 5% 7% 44%	2329
	21st to end	Day	17% 9% 2 6% 5% 4 4 5% 6% 7% 35%	2200
October	1st to 10th	Day	21% 10% 3 8% 5% 4 4 4 4 6% 31%	2050
	11th to 20th	Day	18% 15% 4 8% 4 4 4 3 5% 6% 30%	1995
	21st to end	Day	23% 19% 5% 8% 4 4 3 3 3 6% 23%	1980
November	1st to 10th	Day	15% 18% 5% 9% 6% 5% 5% 3 4 5% 25%	1851
	11th to 20th	Day	14% 20% 6% 11% 5% 5% 4 3 4 5% 24%	1836
	21st to end	Day	14% 21% 7% 14% 6% 5% 4 3 4 4 17%	1680
December	1st to 10th	Day	11% 23% 10% 21% 10% 4 3 2 3 3 9%	2680
	11th to 20th	Day	14% 19% 6% 19% 5% 4 4 3 5% 5% 15%	3066
	21st to end	Day	15% 18% 7% 14% 6% 4 5% 4 4 5% 19%	4048
January	1st to 10th	Night	10% 20% 8% 24% 10% 6% 3 2 3 3 10%	8234
	11th to 20th	Night	7% 18% 10% 26% 15% 6% 4 2 3 2 7%	8235
	21st to end	Night	8% 13% 7% 19% 12% 12% 8% 4 3 3 10%	8979
February	1st to 10th	Night	10% 18% 7% 19% 11% 5% 5% 3 4 4 15%	2730
	11th to 20th	Night	9% 15% 9% 18% 10% 7% 6% 3 4 3 15%	2545
	21st to end	Night	10% 18% 7% 17% 9% 6% 4 3 4 4 19%	2076
March	1st to 10th	Night	15% 13% 5% 14% 10% 7% 4 3 4 4 21%	5484
	11th to 20th	Night	11% 17% 7% 10% 5% 4 4 4 5% 6% 27%	5309
	21st to end	Night	16% 18% 7% 12% 6% 4 3 2 3 4 25%	5119
April	1st to 10th	Night	18% 18% 5% 10% 5% 3 3 3 4 5% 27%	2100
	11th to 20th	Night	19% 18% 4 8% 4 4 4 4 4 4 27%	2075
	21st to end	Night	19% 13% 4 8% 5% 3 3 3 4 5% 33%	1980
May	1st to 10th	Night	26% 16% 4 8% 5% 4 4 3 4 6% 20%	4885
	11th to 20th	Night	18% 12% 3 8% 4 5% 5% 3 5% 7% 28%	4639
	21st to end	Night	21% 13% 3 7% 4 5% 4 4 5% 7% 27%	5114
June	1st to 10th	Night	23% 7% 2 7% 5% 4 4 4 6% 7% 32%	1680
	11th to 20th	Night	19% 7% 2 7% 5% 4 4 4 5% 7% 37%	1640
	21st to end	Night	21% 7% 3 7% 5% 4 5% 4 6% 7% 32%	1600
July	1st to 10th	Night	14% 6% 2 7% 5% 5% 6% 4 6% 9% 35%	3600
	11th to 20th	Night	17% 7% 2 6% 4 5% 4 4 5% 7% 40%	3600
	21st to end	Night	12% 7% 3 7% 4 4 4 3 6% 7% 43%	3926
August	1st to 10th	Night	21% 8% 2 6% 4 3 4 3 5% 7% 37%	2586
	11th to 20th	Night	18% 8% 3 8% 5% 4 4 4 5% 7% 35%	3022
	21st to end	Night	14% 8% 2 6% 3 4 4 4 7% 8% 40%	3586
September	1st to 10th	Night	16% 9% 2 6% 4 4 4 3 5% 7% 41%	2000
	11th to 20th	Night	14% 8% 2 5% 3 3 4 3 4 6% 47%	2070
	21st to end	Night	19% 9% 2 5% 3 3 4 3 6% 7% 39%	2200
October	1st to 10th	Night	21% 11% 3 7% 4 3 4 4 6% 7% 32%	2348
	11th to 20th	Night	18% 16% 3 7% 4 4 5% 4 4 6% 30%	2403
	21st to end	Night	22% 19% 4 8% 5% 4 4 3 4 5% 21%	2860
November	1st to 10th	Night	17% 19% 5% 9% 5% 4 4 3 5% 5% 25%	2667
	11th to 20th	Night	15% 18% 8% 11% 6% 4 3 3 4 5% 24%	2783
	21st to end	Night	15% 21% 8% 14% 5% 4 4 3 4 5% 17%	2940
December	1st to 10th	Night	12% 24% 12% 24% 6% 3 3 2 3 3 8%	4720
	11th to 20th	Night	14% 22% 8% 17% 7% 4 4 3 3 3 15%	5348
	21st to end	Night	15% 18% 6% 16% 6% 5% 5% 3 4 3 18%	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	78% 4 5% 11% 2	4662
	11th to 20th	Day	79% 2 3 6% 8% 2	4680
	21st to end	Day	73% 4 7% 8% 7% 1	5184
February	1st to 10th	Day	73% 4 4 13% 4 2	1890
	11th to 20th	Day	68% 5% 7% 12% 8% 1	1968
	21st to end	Day	68% 5% 7% 10% 8% 2	1730
March	1st to 10th	Day	69% 3 8% 10% 8% 3	4579
	11th to 20th	Day	61% 5% 11% 13% 7% 3	4855
	21st to end	Day	59% 4 5% 13% 17% 2	6055
April	1st to 10th	Day	61% 3 7% 17% 10% 2	2520
	11th to 20th	Day	57% 4 7% 18% 13% 1	2494
	21st to end	Day	59% 3 8% 16% 11% 2	2639
May	1st to 10th	Day	65% 4 7% 15% 8% 1	8068
	11th to 20th	Day	56% 4 12% 19% 7% 1	8225
	21st to end	Day	58% 4 8% 22% 7%	9061
June	1st to 10th	Day	58% 4 10% 18% 10%	2940
	11th to 20th	Day	51% 5% 11% 23% 9% 2	2870
	21st to end	Day	57% 5% 10% 18% 9% 1	2800
July	1st to 10th	Day	47% 6% 15% 23% 10%	6290
	11th to 20th	Day	44% 7% 12% 26% 9%	6285
	21st to end	Day	43% 6% 12% 34% 6%	6728
August	1st to 10th	Day	52% 6% 13% 21% 8%	4549
	11th to 20th	Day	51% 7% 15% 22% 5%	4028
	21st to end	Day	46% 6% 16% 22% 10%	4312
September	1st to 10th	Day	44% 4 10% 30% 12% 1	2400
	11th to 20th	Day	40% 3 10% 30% 16% 1	2329
	21st to end	Day	47% 5% 13% 22% 11% 1	2200
October	1st to 10th	Day	48% 5% 10% 24% 13%	3336
	11th to 20th	Day	51% 3 11% 20% 14% 1	3223
	21st to end	Day	51% 4 13% 26% 6% 1	3180
November	1st to 10th	Day	60% 4 11% 16% 9%	1851
	11th to 20th	Day	63% 4 9% 12% 9% 3	1836
	21st to end	Day	68% 5% 10% 12% 4	1680
December	1st to 10th	Day	82% 4 5% 7% 3	2680
	11th to 20th	Day	70% 6% 7% 11% 6%	3066
	21st to end	Day	67% 4 5% 12% 12% 1	4048
January	1st to 10th	Night	80% 4 6% 7% 3	8234
	11th to 20th	Night	83% 4 4 5% 4 1	8280
	21st to end	Night	78% 5% 5% 6% 6% 1	8979
February	1st to 10th	Night	73% 3 7% 9% 6% 1	2730
	11th to 20th	Night	71% 5% 6% 11% 7%	2547
	21st to end	Night	68% 5% 7% 13% 7% 1	2076
March	1st to 10th	Night	68% 4 7% 11% 10% 1	5494
	11th to 20th	Night	57% 5% 14% 14% 7% 3	5310
	21st to end	Night	63% 4 4 15% 13% 1	5119
April	1st to 10th	Night	61% 3 7% 16% 11% 1	2100
	11th to 20th	Night	60% 4 8% 17% 10%	2075
	21st to end	Night	55% 3 9% 18% 12% 2	1980
May	1st to 10th	Night	66% 4 8% 15% 7% 1	4891
	11th to 20th	Night	55% 5% 10% 22% 7% 1	4640
	21st to end	Night	57% 4 9% 20% 9%	5115
June	1st to 10th	Night	52% 5% 11% 22% 9% 1	1680
	11th to 20th	Night	46% 5% 15% 21% 12% 1	1640
	21st to end	Night	51% 6% 12% 23% 8%	1600
July	1st to 10th	Night	46% 5% 17% 23% 9%	3560
	11th to 20th	Night	44% 5% 14% 27% 10%	3552
	21st to end	Night	41% 6% 14% 31% 8%	3809
August	1st to 10th	Night	49% 4 15% 23% 8%	2576
	11th to 20th	Night	49% 6% 18% 20% 7%	3048
	21st to end	Night	40% 6% 16% 28% 9% 1	3586
September	1st to 10th	Night	43% 5% 14% 28% 11% 1	2000
	11th to 20th	Night	40% 3 13% 32% 12% 1	2070
	21st to end	Night	44% 5% 13% 24% 13% 1	2200
October	1st to 10th	Night	53% 5% 11% 21% 10%	3842
	11th to 20th	Night	53% 3 10% 20% 11% 3	3914
	21st to end	Night	57% 3 15% 19% 5% 1	4610
November	1st to 10th	Night	62% 3 11% 14% 8% 2	2667
	11th to 20th	Night	62% 5% 8% 13% 8% 3	2783
	21st to end	Night	69% 5% 9% 12% 5% 1	2940
December	1st to 10th	Night	83% 3 5% 7% 2	4720
	11th to 20th	Night	74% 5% 5% 9% 8%	5348
	21st to end	Night	72% 3 5% 9% 7% 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	28% 26% 30% 11% 5%	220
	11th to 20th	Day	30% 27% 32% 8% 1 1	220
	21st to end	Day	30% 25% 32% 9% 3	253
February	1st to 10th	Day	39% 29% 23% 8% 1	330
	11th to 20th	Day	38% 24% 30% 7% 1	447
	21st to end	Day	33% 27% 27% 10% 2	446
March	1st to 10th	Day	33% 24% 27% 13% 3	540
	11th to 20th	Day	37% 21% 27% 12% 2 1	540
	21st to end	Day	35% 27% 23% 9% 5% 1	594
April	1st to 10th	Day	39% 19% 26% 10% 6% 1	540
	11th to 20th	Day	40% 18% 23% 12% 5% 2	532
	21st to end	Day	37% 17% 27% 10% 6% 2	540
May	1st to 10th	Day	38% 17% 27% 10% 5% 3	543
	11th to 20th	Day	28% 18% 28% 17% 7% 2	567
	21st to end	Day	26% 20% 27% 20% 6% 1	617
June	1st to 10th	Day	33% 15% 29% 15% 6% 2	570
	11th to 20th	Day	26% 17% 31% 18% 6% 2	550
	21st to end	Day	31% 15% 31% 15% 5% 2	530
July	1st to 10th	Day	18% 13% 35% 22% 10% 2	525
	11th to 20th	Day	17% 14% 36% 25% 7% 2	524
	21st to end	Day	18% 12% 43% 20% 6% 2	576
August	1st to 10th	Day	18% 13% 28% 24% 12% 4	526
	11th to 20th	Day	19% 10% 29% 22% 13% 5%	519
	21st to end	Day	19% 15% 27% 23% 11% 5%	583
September	1st to 10th	Day	19% 16% 29% 16% 13% 7%	530
	11th to 20th	Day	17% 14% 22% 21% 15% 10%	530
	21st to end	Day	20% 15% 29% 20% 11% 6%	530
October	1st to 10th	Day	28% 16% 24% 16% 11% 5%	530
	11th to 20th	Day	29% 22% 25% 14% 9% 1	527
	21st to end	Day	35% 19% 25% 16% 4	462
November	1st to 10th	Day	33% 19% 26% 14% 7%	425
	11th to 20th	Day	33% 24% 23% 12% 6% 1	376
	21st to end	Day	38% 23% 29% 9% 1	220
December	1st to 10th	Day	35% 22% 29% 11% 2	220
	11th to 20th	Day	39% 27% 25% 7% 2	220
	21st to end	Day	34% 25% 25% 12% 3 1	242
January	1st to 10th	Night	28% 29% 28% 12% 3	840
	11th to 20th	Night	26% 29% 28% 14% 2	840
	21st to end	Night	20% 30% 29% 17% 4	924
February	1st to 10th	Night	25% 28% 30% 15% 1	840
	11th to 20th	Night	27% 28% 30% 13% 2	823
	21st to end	Night	25% 27% 32% 14% 2	692
March	1st to 10th	Night	29% 24% 27% 17% 3	840
	11th to 20th	Night	31% 24% 26% 15% 4 1	840
	21st to end	Night	30% 21% 24% 19% 6% 1	924
April	1st to 10th	Night	31% 22% 27% 16% 4	840
	11th to 20th	Night	32% 22% 22% 19% 5%	831
	21st to end	Night	32% 18% 24% 20% 6%	720
May	1st to 10th	Night	36% 12% 24% 21% 8%	502
	11th to 20th	Night	21% 15% 28% 28% 7%	414
	21st to end	Night	20% 13% 29% 26% 11% 1	455
June	1st to 10th	Night	26% 8% 28% 26% 11%	420
	11th to 20th	Night	22% 8% 27% 34% 10%	410
	21st to end	Night	21% 11% 30% 27% 11%	400
July	1st to 10th	Night	16% 8% 27% 35% 14% 1	390
	11th to 20th	Night	13% 10% 24% 35% 18% 2	388
	21st to end	Night	15% 7% 30% 36% 12%	438
August	1st to 10th	Night	18% 6% 22% 38% 15% 1	398
	11th to 20th	Night	20% 6% 20% 32% 18% 3	675
	21st to end	Night	19% 10% 25% 27% 17% 2	880
September	1st to 10th	Night	20% 11% 21% 31% 15% 2	800
	11th to 20th	Night	18% 7% 21% 29% 21% 5%	800
	21st to end	Night	23% 13% 23% 21% 19% 2	800
October	1st to 10th	Night	28% 14% 22% 21% 13% 2	800
	11th to 20th	Night	28% 16% 25% 22% 9% 1	800
	21st to end	Night	35% 20% 21% 19% 5%	880
November	1st to 10th	Night	31% 20% 24% 18% 6%	820
	11th to 20th	Night	30% 24% 23% 14% 8% 2	840
	21st to end	Night	30% 28% 21% 14% 5% 1	840
December	1st to 10th	Night	33% 29% 22% 12% 3	840
	11th to 20th	Night	32% 25% 25% 14% 4 1	840
	21st to end	Night	31% 26% 25% 14% 3	924

Page generated at 2026-06-13 02:31:42. Version ac07

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