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 2024-09-14.

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	16% 13% 4 10% 6% 5% 5% 4 5% 6% 26%	100954
	Night	16% 15% 5% 12% 6% 4 4 3 4 5% 25%	96936
Transparency	Day	58% 5% 10% 19% 8% 1	100713
	Night	61% 4 10% 16% 8% 1	96797
Seeing	Day	28% 18% 28% 16% 7% 2	14468
	Night	26% 19% 25% 21% 8% 1	23458

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	11% 22% 9% 21% 9% 4 4 2 3 3 12%	2517
	11th to 20th	Day	9% 18% 9% 22% 16% 4 3 2 2 3 13%	2520
	21st to end	Day	11% 21% 10% 15% 7% 6% 6% 3 4 5% 12%	2804
February	1st to 10th	Day	11% 19% 7% 17% 11% 6% 4 3 3 3 16%	1710
	11th to 20th	Day	9% 16% 9% 18% 9% 6% 4 3 5% 4 17%	1767
	21st to end	Day	11% 19% 6% 16% 7% 7% 4 3 4 4 18%	1570
March	1st to 10th	Day	20% 17% 7% 12% 6% 4 4 3 4 5% 21%	3116
	11th to 20th	Day	10% 24% 8% 13% 6% 4 4 3 4 3 21%	3320
	21st to end	Day	14% 14% 5% 11% 7% 3 3 3 4 5% 32%	4134
April	1st to 10th	Day	18% 19% 5% 8% 5% 4 4 3 4 4 28%	2280
	11th to 20th	Day	17% 17% 4 7% 5% 4 4 3 4 5% 31%	2254
	21st to end	Day	22% 15% 3 9% 4 3 4 3 4 6% 27%	2387
May	1st to 10th	Day	22% 14% 4 8% 4 4 5% 4 5% 5% 26%	4329
	11th to 20th	Day	17% 12% 4 9% 6% 5% 5% 4 5% 7% 27%	4398
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4837
June	1st to 10th	Day	25% 9% 3 7% 5% 4 5% 4 5% 6% 26%	2660
	11th to 20th	Day	19% 9% 2 7% 5% 4 6% 4 6% 7% 30%	2660
	21st to end	Day	23% 9% 2 8% 6% 5% 5% 4 6% 6% 26%	2660
July	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	13% 7% 2 7% 6% 6% 6% 5% 7% 10% 30%	4440
	21st to end	Day	15% 7% 3 7% 6% 5% 5% 5% 6% 8% 34%	4814
August	1st to 10th	Day	18% 9% 3 7% 5% 5% 5% 4 6% 8% 29%	4423
	11th to 20th	Day	16% 8% 3 9% 5% 6% 6% 4 7% 8% 29%	3864
	21st to end	Day	17% 7% 2 6% 5% 5% 5% 5% 6% 8% 34%	4180
September	1st to 10th	Day	16% 7% 2 6% 4 4 5% 4 5% 8% 38%	2280
	11th to 20th	Day	17% 8% 2 5% 3 2 4 4 5% 7% 43%	2135
	21st to end	Day	17% 10% 2 5% 5% 4 4 5% 6% 7% 35%	1980
October	1st to 10th	Day	24% 11% 3 9% 5% 4 4 4 4 6% 27%	1846
	11th to 20th	Day	19% 15% 4 8% 5% 4 4 3 5% 6% 28%	1796
	21st to end	Day	24% 20% 5% 8% 4 4 3 3 3 5% 22%	1782
November	1st to 10th	Day	14% 17% 5% 9% 6% 6% 4 3 4 5% 26%	1671
	11th to 20th	Day	15% 19% 6% 11% 5% 6% 4 3 4 5% 23%	1662
	21st to end	Day	14% 20% 6% 14% 7% 5% 4 3 4 4 19%	1520
December	1st to 10th	Day	15% 24% 10% 15% 8% 3 3 2 4 3 12%	1520
	11th to 20th	Day	15% 19% 6% 18% 6% 4 5% 3 4 5% 14%	1906
	21st to end	Day	19% 20% 7% 13% 6% 5% 5% 3 4 4 15%	2772
January	1st to 10th	Night	12% 23% 8% 22% 6% 5% 3 2 3 3 12%	4429
	11th to 20th	Night	9% 18% 9% 23% 14% 6% 4 2 3 3 10%	4440
	21st to end	Night	14% 20% 9% 18% 8% 5% 5% 3 3 3 13%	4848
February	1st to 10th	Night	10% 18% 8% 19% 11% 5% 4 3 4 4 15%	2470
	11th to 20th	Night	9% 15% 9% 18% 10% 7% 6% 3 5% 3 16%	2297
	21st to end	Night	11% 18% 6% 17% 8% 6% 4 3 4 3 20%	1884
March	1st to 10th	Night	17% 13% 5% 10% 9% 5% 4 3 4 5% 25%	3724
	11th to 20th	Night	12% 21% 9% 11% 4 4 3 3 4 4 24%	3624
	21st to end	Night	14% 17% 6% 11% 6% 4 3 2 3 4 31%	3498
April	1st to 10th	Night	17% 19% 6% 9% 5% 3 3 3 4 5% 27%	1900
	11th to 20th	Night	18% 18% 4 8% 4 4 4 4 4 5% 27%	1875
	21st to end	Night	20% 13% 4 8% 5% 3 3 3 4 6% 32%	1792
May	1st to 10th	Night	23% 15% 3 7% 5% 4 4 4 5% 6% 24%	2627
	11th to 20th	Night	18% 12% 4 9% 5% 5% 5% 3 4 5% 31%	2495
	21st to end	Night	17% 9% 2 7% 4 4 4 4 5% 8% 36%	2738
June	1st to 10th	Night	23% 8% 2 6% 5% 4 5% 4 6% 7% 31%	1520
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 5% 7% 38%	1520
	21st to end	Night	21% 8% 3 7% 5% 3 5% 3 6% 7% 31%	1520
July	1st to 10th	Night	15% 7% 2 8% 6% 5% 6% 3 6% 7% 35%	2520
	11th to 20th	Night	16% 7% 2 6% 4 5% 4 4 6% 8% 39%	2520
	21st to end	Night	14% 8% 3 8% 4 4 4 4 6% 6% 39%	2739
August	1st to 10th	Night	22% 8% 3 6% 4 4 4 3 5% 7% 36%	2506
	11th to 20th	Night	18% 8% 3 8% 5% 4 4 4 5% 7% 34%	2928
	21st to end	Night	14% 8% 2 5% 3 4 4 4 7% 8% 40%	3476
September	1st to 10th	Night	16% 9% 2 6% 4 4 4 3 5% 7% 40%	1900
	11th to 20th	Night	15% 9% 2 5% 3 3 4 3 4 6% 47%	1902
	21st to end	Night	19% 9% 2 5% 3 3 4 3 6% 7% 39%	1980
October	1st to 10th	Night	21% 11% 3 7% 4 3 5% 4 6% 7% 29%	2112
	11th to 20th	Night	18% 16% 4 8% 4 4 5% 4 4 6% 28%	2162
	21st to end	Night	23% 20% 4 8% 5% 4 4 3 4 5% 20%	2574
November	1st to 10th	Night	16% 18% 5% 9% 5% 4 4 3 5% 5% 26%	2407
	11th to 20th	Night	15% 18% 7% 11% 6% 4 3 3 4 5% 24%	2517
	21st to end	Night	15% 20% 8% 14% 5% 4 4 2 4 5% 17%	2660
December	1st to 10th	Night	16% 27% 9% 16% 6% 4 3 3 3 3 11%	2660
	11th to 20th	Night	15% 22% 7% 16% 6% 3 4 3 4 4 16%	3288
	21st to end	Night	20% 19% 7% 18% 6% 3 4 3 4 3 13%	4884

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	74% 6% 6% 11% 3	2518
	11th to 20th	Day	78% 3 4 8% 5% 1	2520
	21st to end	Day	74% 3 9% 8% 5% 1	2804
February	1st to 10th	Day	73% 4 4 13% 4 2	1710
	11th to 20th	Day	68% 6% 7% 11% 8% 1	1776
	21st to end	Day	67% 5% 7% 11% 8% 2	1570
March	1st to 10th	Day	67% 3 9% 12% 8% 1	3119
	11th to 20th	Day	67% 5% 9% 11% 7% 2	3320
	21st to end	Day	54% 5% 6% 16% 17% 2	4134
April	1st to 10th	Day	60% 3 7% 18% 10% 2	2280
	11th to 20th	Day	56% 4 7% 19% 13% 1	2254
	21st to end	Day	60% 3 9% 15% 11% 3	2387
May	1st to 10th	Day	60% 4 9% 20% 7% 1	4343
	11th to 20th	Day	57% 4 12% 19% 7% 1	4402
	21st to end	Day	47% 4 12% 26% 10% 1	4837
June	1st to 10th	Day	59% 4 10% 17% 9%	2660
	11th to 20th	Day	52% 4 11% 23% 9% 2	2660
	21st to end	Day	58% 5% 10% 18% 8% 1	2660
July	1st to 10th	Day	46% 5% 14% 25% 10%	4370
	11th to 20th	Day	46% 7% 14% 28% 5%	4365
	21st to end	Day	47% 6% 12% 29% 6%	4661
August	1st to 10th	Day	53% 6% 13% 20% 8%	4409
	11th to 20th	Day	51% 7% 15% 22% 5%	3904
	21st to end	Day	46% 6% 16% 22% 10%	4180
September	1st to 10th	Day	45% 4 10% 28% 12% 1	2280
	11th to 20th	Day	41% 3 10% 30% 15% 1	2135
	21st to end	Day	46% 6% 13% 23% 10% 2	1980
October	1st to 10th	Day	59% 4 8% 18% 11%	1846
	11th to 20th	Day	57% 5% 13% 18% 8% 1	1796
	21st to end	Day	66% 3 9% 14% 7% 1	1782
November	1st to 10th	Day	59% 4 11% 17% 9%	1671
	11th to 20th	Day	63% 4 9% 13% 7% 3	1662
	21st to end	Day	66% 6% 11% 13% 5%	1520
December	1st to 10th	Day	77% 3 7% 9% 3	1520
	11th to 20th	Day	70% 5% 8% 10% 5%	1906
	21st to end	Day	73% 3 6% 10% 8%	2772
January	1st to 10th	Night	77% 4 7% 8% 4	4429
	11th to 20th	Night	79% 5% 5% 7% 3 1	4440
	21st to end	Night	77% 4 5% 9% 5% 1	4848
February	1st to 10th	Night	73% 3 7% 9% 6% 1	2470
	11th to 20th	Night	70% 5% 6% 11% 7%	2299
	21st to end	Night	67% 5% 7% 13% 8% 1	1884
March	1st to 10th	Night	62% 4 9% 14% 10% 1	3734
	11th to 20th	Night	63% 4 10% 14% 7% 1	3625
	21st to end	Night	57% 4 5% 17% 15% 2	3498
April	1st to 10th	Night	62% 3 7% 17% 11% 1	1900
	11th to 20th	Night	59% 4 9% 18% 10%	1875
	21st to end	Night	56% 3 10% 17% 12% 2	1792
May	1st to 10th	Night	62% 4 8% 17% 8% 1	2633
	11th to 20th	Night	55% 4 11% 21% 8% 1	2496
	21st to end	Night	47% 4 12% 22% 13% 1	2739
June	1st to 10th	Night	53% 6% 12% 21% 8% 1	1520
	11th to 20th	Night	45% 5% 16% 21% 13% 1	1520
	21st to end	Night	51% 5% 13% 23% 8%	1520
July	1st to 10th	Night	48% 5% 13% 23% 11% 1	2480
	11th to 20th	Night	44% 5% 15% 29% 7%	2472
	21st to end	Night	45% 7% 14% 25% 8%	2651
August	1st to 10th	Night	50% 4 15% 23% 8%	2496
	11th to 20th	Night	50% 6% 19% 19% 6%	2954
	21st to end	Night	40% 6% 16% 28% 9% 1	3476
September	1st to 10th	Night	43% 5% 14% 26% 11% 1	1900
	11th to 20th	Night	40% 2 14% 31% 11% 1	1902
	21st to end	Night	44% 5% 13% 25% 12% 2	1980
October	1st to 10th	Night	54% 4 12% 19% 10% 1	2112
	11th to 20th	Night	56% 5% 13% 17% 8% 1	2162
	21st to end	Night	67% 3 11% 12% 6% 2	2574
November	1st to 10th	Night	61% 3 12% 13% 9% 2	2407
	11th to 20th	Night	62% 5% 9% 14% 8% 3	2517
	21st to end	Night	69% 5% 9% 12% 5% 1	2660
December	1st to 10th	Night	78% 3 6% 9% 3	2660
	11th to 20th	Night	71% 5% 6% 11% 7%	3288
	21st to end	Night	75% 3 6% 11% 5%	4884

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	27% 21% 33% 13% 6% 1	180
	11th to 20th	Day	24% 27% 36% 10% 1 2	180
	21st to end	Day	22% 28% 36% 11% 3	207
February	1st to 10th	Day	40% 31% 21% 8% 1	270
	11th to 20th	Day	37% 25% 30% 7% 1	375
	21st to end	Day	34% 26% 26% 12% 3	382
March	1st to 10th	Day	31% 23% 28% 15% 3	460
	11th to 20th	Day	34% 21% 29% 12% 3 1	460
	21st to end	Day	32% 25% 25% 11% 6% 1	506
April	1st to 10th	Day	35% 18% 28% 12% 6% 1	460
	11th to 20th	Day	38% 18% 23% 13% 6% 2	452
	21st to end	Day	38% 16% 27% 11% 7% 2	460
May	1st to 10th	Day	35% 17% 27% 11% 6% 3	463
	11th to 20th	Day	26% 17% 29% 18% 7% 2	487
	21st to end	Day	25% 18% 28% 21% 7% 1	529
June	1st to 10th	Day	34% 15% 26% 16% 6% 2	490
	11th to 20th	Day	26% 13% 31% 20% 6% 2	490
	21st to end	Day	32% 14% 31% 16% 6% 2	490
July	1st to 10th	Day	18% 11% 35% 24% 11% 2	485
	11th to 20th	Day	17% 14% 36% 24% 7% 2	484
	21st to end	Day	18% 11% 43% 21% 6% 2	532
August	1st to 10th	Day	20% 14% 28% 23% 12% 4	486
	11th to 20th	Day	20% 10% 29% 23% 13% 5%	479
	21st to end	Day	19% 14% 27% 24% 11% 5%	539
September	1st to 10th	Day	19% 16% 29% 17% 12% 7%	490
	11th to 20th	Day	19% 15% 22% 19% 14% 10%	463
	21st to end	Day	19% 14% 30% 20% 11% 6%	450
October	1st to 10th	Day	30% 16% 21% 16% 12% 6%	450
	11th to 20th	Day	29% 22% 25% 15% 10% 1	448
	21st to end	Day	36% 18% 25% 16% 4	396
November	1st to 10th	Day	32% 17% 27% 16% 8%	365
	11th to 20th	Day	34% 24% 21% 13% 7% 1	322
	21st to end	Day	33% 22% 33% 11% 2	180
December	1st to 10th	Day	34% 21% 29% 12% 3 1	180
	11th to 20th	Day	36% 26% 28% 7% 2	180
	21st to end	Day	34% 28% 24% 11% 3 1	198
January	1st to 10th	Night	27% 28% 29% 13% 3	760
	11th to 20th	Night	25% 29% 29% 15% 3 1	760
	21st to end	Night	18% 29% 31% 18% 4	836
February	1st to 10th	Night	24% 30% 31% 14% 2	760
	11th to 20th	Night	26% 27% 30% 14% 2	743
	21st to end	Night	25% 27% 31% 15% 2	628
March	1st to 10th	Night	28% 23% 28% 18% 3	760
	11th to 20th	Night	29% 24% 26% 16% 4 1	760
	21st to end	Night	28% 21% 24% 20% 6% 1	836
April	1st to 10th	Night	30% 21% 29% 17% 4	760
	11th to 20th	Night	30% 23% 22% 19% 6%	751
	21st to end	Night	32% 17% 24% 20% 7%	652
May	1st to 10th	Night	34% 11% 24% 22% 8%	454
	11th to 20th	Night	21% 14% 28% 30% 7% 1	374
	21st to end	Night	18% 11% 29% 28% 12% 1	411
June	1st to 10th	Night	26% 8% 28% 26% 11%	380
	11th to 20th	Night	20% 7% 27% 36% 10%	380
	21st to end	Night	21% 10% 30% 28% 11%	380
July	1st to 10th	Night	16% 7% 27% 35% 15% 1	370
	11th to 20th	Night	13% 10% 24% 34% 18% 2	368
	21st to end	Night	15% 6% 31% 36% 12%	416
August	1st to 10th	Night	19% 7% 21% 38% 15% 1	378
	11th to 20th	Night	20% 6% 20% 33% 18% 3	641
	21st to end	Night	19% 9% 25% 27% 17% 2	836
September	1st to 10th	Night	21% 11% 21% 31% 15% 2	760
	11th to 20th	Night	18% 7% 22% 28% 20% 4	736
	21st to end	Night	22% 13% 23% 21% 19% 2	720
October	1st to 10th	Night	29% 15% 21% 20% 13% 2	720
	11th to 20th	Night	28% 16% 23% 22% 9% 1	720
	21st to end	Night	35% 20% 21% 19% 5%	792
November	1st to 10th	Night	29% 20% 25% 19% 7%	740
	11th to 20th	Night	30% 24% 22% 15% 8% 2	760
	21st to end	Night	29% 28% 21% 15% 6% 1	760
December	1st to 10th	Night	33% 30% 21% 12% 4	760
	11th to 20th	Night	30% 25% 26% 15% 4 1	760
	21st to end	Night	30% 26% 27% 14% 3	836

Page generated at 2024-09-11 10:00:02. Version ac07

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