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 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	16% 13% 5% 11% 6% 5% 5% 4 5% 6% 26%	108565
	Night	15% 15% 6% 13% 6% 5% 4 3 4 5% 24%	109981
Transparency	Day	58% 5% 10% 18% 8% 1	112068
	Night	62% 4 9% 15% 8% 1	114642
Seeing	Day	28% 18% 28% 16% 7% 2	14915
	Night	26% 19% 25% 21% 8% 1	24095

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% 19% 9% 26% 10% 5% 4 2 3 3 11%	3597
	11th to 20th	Day	7% 16% 8% 25% 15% 5% 3 2 2 3 13%	3570
	21st to end	Day	10% 18% 9% 16% 8% 7% 6% 3 4 5% 14%	4006
February	1st to 10th	Day	11% 18% 7% 18% 11% 6% 5% 3 3 3 16%	1800
	11th to 20th	Day	9% 16% 9% 19% 9% 6% 4 4 5% 4 16%	1863
	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 3 4 4 5% 7% 43%	2213
	21st to end	Day	17% 10% 2 5% 5% 4 5% 5% 6% 7% 35%	2090
October	1st to 10th	Day	23% 11% 3 8% 5% 4 4 4 4 6% 28%	1948
	11th to 20th	Day	18% 16% 4 8% 4 4 4 3 5% 5% 29%	1895
	21st to end	Day	23% 20% 4 8% 4 4 3 3 3 6% 23%	1881
November	1st to 10th	Day	15% 17% 5% 9% 6% 5% 5% 3 4 5% 26%	1761
	11th to 20th	Day	14% 19% 6% 11% 5% 5% 4 3 4 5% 24%	1749
	21st to end	Day	15% 21% 7% 14% 6% 5% 4 3 4 4 18%	1600
December	1st to 10th	Day	11% 24% 10% 22% 10% 4 3 2 3 3 8%	2600
	11th to 20th	Day	14% 19% 6% 19% 5% 4 4 3 5% 5% 15%	2986
	21st to end	Day	15% 18% 7% 14% 6% 4 5% 4 4 5% 20%	3960
January	1st to 10th	Night	10% 20% 9% 27% 9% 6% 3 2 3 3 9%	6349
	11th to 20th	Night	7% 18% 10% 26% 14% 5% 4 2 3 3 7%	6315
	21st to end	Night	10% 16% 9% 21% 10% 8% 6% 4 3 3 11%	6932
February	1st to 10th	Night	11% 18% 8% 20% 11% 5% 4 3 3 4 15%	2600
	11th to 20th	Night	10% 15% 9% 18% 10% 7% 6% 3 5% 3 15%	2421
	21st to end	Night	11% 18% 6% 17% 8% 6% 4 3 4 3 20%	1885
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% 8% 2 5% 3 3 4 3 4 6% 46%	1966
	21st to end	Night	18% 8% 2 5% 3 3 4 4 6% 7% 39%	2090
October	1st to 10th	Night	21% 11% 3 7% 4 3 5% 3 6% 7% 30%	2230
	11th to 20th	Night	18% 16% 4 7% 4 4 5% 4 4 6% 29%	2283
	21st to end	Night	23% 19% 4 8% 5% 4 4 3 4 5% 21%	2717
November	1st to 10th	Night	17% 18% 5% 9% 5% 4 4 3 5% 5% 26%	2537
	11th to 20th	Night	15% 18% 7% 11% 6% 4 3 3 4 5% 25%	2650
	21st to end	Night	15% 21% 8% 14% 5% 4 4 2 4 5% 17%	2800
December	1st to 10th	Night	12% 24% 12% 25% 6% 3 2 2 3 3 7%	4580
	11th to 20th	Night	14% 22% 7% 17% 6% 4 4 3 3 3 16%	5208
	21st to end	Night	15% 18% 6% 16% 6% 5% 6% 3 4 3 18%	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	77% 4 5% 11% 3	3598
	11th to 20th	Day	78% 3 3 7% 7% 3	3600
	21st to end	Day	70% 4 9% 9% 6% 1	4006
February	1st to 10th	Day	74% 4 4 13% 4 2	1800
	11th to 20th	Day	68% 5% 7% 11% 8% 1	1872
	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	2213
	21st to end	Day	47% 6% 14% 22% 11% 2	2090
October	1st to 10th	Day	49% 5% 10% 24% 12%	3234
	11th to 20th	Day	51% 3 12% 20% 13% 1	3123
	21st to end	Day	50% 4 13% 26% 6% 1	3081
November	1st to 10th	Day	59% 5% 11% 17% 9%	1761
	11th to 20th	Day	62% 4 9% 12% 9% 4	1749
	21st to end	Day	67% 5% 10% 12% 5%	1600
December	1st to 10th	Day	82% 4 5% 6% 2	2600
	11th to 20th	Day	70% 6% 7% 11% 5%	2986
	21st to end	Day	66% 4 5% 12% 12% 1	3960
January	1st to 10th	Night	82% 3 6% 6% 3	6349
	11th to 20th	Night	82% 4 4 6% 3 1	6360
	21st to end	Night	77% 4 6% 7% 6% 1	6932
February	1st to 10th	Night	74% 3 7% 9% 6% 1	2600
	11th to 20th	Night	71% 5% 6% 10% 7%	2423
	21st to end	Night	67% 5% 7% 13% 8% 1	1885
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% 32% 12% 1	1966
	21st to end	Night	44% 5% 13% 24% 12% 1	2090
October	1st to 10th	Night	54% 5% 11% 21% 9%	3724
	11th to 20th	Night	54% 3 10% 20% 10% 3	3794
	21st to end	Night	57% 3 15% 19% 5% 1	4467
November	1st to 10th	Night	61% 3 11% 13% 9% 2	2537
	11th to 20th	Night	62% 5% 8% 13% 8% 3	2650
	21st to end	Night	69% 5% 9% 12% 5% 1	2800
December	1st to 10th	Night	84% 3 5% 6% 2	4580
	11th to 20th	Night	73% 5% 5% 9% 8%	5208
	21st to end	Night	72% 3 6% 9% 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	27% 25% 31% 12% 5% 1	200
	11th to 20th	Day	25% 29% 35% 9% 2 2	200
	21st to end	Day	27% 27% 33% 10% 3	230
February	1st to 10th	Day	42% 30% 20% 7% 1	300
	11th to 20th	Day	39% 24% 29% 6% 1	411
	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	18% 14% 21% 21% 15% 10%	490
	21st to end	Day	19% 14% 29% 20% 11% 6%	490
October	1st to 10th	Day	29% 16% 23% 16% 11% 5%	490
	11th to 20th	Day	29% 22% 25% 14% 10% 1	487
	21st to end	Day	35% 19% 25% 16% 4	429
November	1st to 10th	Day	33% 17% 27% 15% 7%	395
	11th to 20th	Day	34% 24% 21% 13% 7% 1	349
	21st to end	Day	37% 22% 31% 10% 2	200
December	1st to 10th	Day	34% 23% 29% 12% 3 1	200
	11th to 20th	Day	38% 25% 27% 8% 2	200
	21st to end	Day	33% 26% 25% 12% 3 1	220
January	1st to 10th	Night	27% 29% 28% 13% 3	800
	11th to 20th	Night	24% 30% 29% 14% 2 1	800
	21st to end	Night	18% 30% 30% 18% 4	880
February	1st to 10th	Night	26% 29% 30% 13% 2	800
	11th to 20th	Night	27% 28% 29% 14% 2	783
	21st to end	Night	25% 27% 31% 15% 2	629
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% 21% 28% 21% 4	760
	21st to end	Night	22% 12% 23% 22% 19% 2	760
October	1st to 10th	Night	29% 14% 21% 20% 13% 2	760
	11th to 20th	Night	29% 16% 23% 22% 9% 1	760
	21st to end	Night	35% 20% 21% 19% 5%	836
November	1st to 10th	Night	30% 20% 24% 19% 7%	780
	11th to 20th	Night	29% 24% 23% 15% 8% 2	800
	21st to end	Night	30% 28% 21% 14% 6% 1	800
December	1st to 10th	Night	33% 30% 21% 12% 4	800
	11th to 20th	Night	31% 24% 25% 15% 4 1	800
	21st to end	Night	30% 26% 26% 15% 3	880

Page generated at 2025-02-18 03:26:32. Version ac07

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