Lake Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Sky Observatory clear sky chart from 2005-11-06 to 2024-11-30.

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% 8% 2 6% 4 4 4 4 5% 7% 38%	101445
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 39%	98143
Transparency	Day	25% 47% 6% 13% 9% 1	104983
	Night	24% 47% 6% 13% 9% 1	102668
Seeing	Day	24% 18% 32% 18% 7% 2	15127
	Night	22% 17% 34% 21% 6%	24079

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	14% 8% 3 6% 5% 4 3 3 4 5% 45%	2517
	11th to 20th	Day	16% 9% 3 7% 5% 4 5% 4 4 5% 38%	2520
	21st to end	Day	21% 13% 3 7% 4 4 3 3 5% 5% 34%	2772
February	1st to 10th	Day	18% 8% 3 6% 4 5% 5% 4 6% 6% 36%	1791
	11th to 20th	Day	13% 8% 3 6% 5% 4 5% 4 5% 6% 40%	1848
	21st to end	Day	20% 11% 3 6% 4 4 3 3 4 6% 37%	1570
March	1st to 10th	Day	23% 14% 3 8% 4 3 3 2 4 4 32%	3116
	11th to 20th	Day	11% 6% 1 6% 5% 5% 6% 4 6% 9% 41%	3306
	21st to end	Day	21% 10% 3 5% 4 3 4 3 6% 6% 36%	4088
April	1st to 10th	Day	18% 10% 3 6% 5% 4 4 3 5% 6% 37%	2280
	11th to 20th	Day	18% 5% 2 5% 5% 4 4 4 5% 8% 40%	2254
	21st to end	Day	22% 6% 2 7% 5% 4 4 4 5% 6% 36%	2451
May	1st to 10th	Day	25% 11% 3 7% 4 4 3 3 5% 7% 27%	4106
	11th to 20th	Day	23% 9% 3 7% 4 4 4 2 5% 6% 33%	4176
	21st to end	Day	15% 5% 2 5% 3 4 4 3 6% 8% 45%	4837
June	1st to 10th	Day	18% 7% 3 6% 4 4 5% 4 6% 8% 35%	2660
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 5% 6% 8% 37%	2660
	21st to end	Day	16% 6% 2 7% 5% 5% 5% 4 6% 8% 35%	2660
July	1st to 10th	Day	13% 6% 2 7% 6% 6% 5% 5% 7% 8% 34%	4440
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 9% 39%	4440
	21st to end	Day	19% 8% 2 6% 5% 4 5% 4 5% 7% 34%	4814
August	1st to 10th	Day	18% 7% 2 8% 5% 5% 6% 4 6% 9% 31%	4179
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 4 5% 7% 40%	3903
	21st to end	Day	7% 4 2 6% 5% 5% 5% 5% 7% 8% 46%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 5% 4 3 5% 6% 45%	2280
	11th to 20th	Day	15% 5% 2 5% 3 3 4 3 4 6% 51%	2104
	21st to end	Day	18% 7% 2 5% 4 5% 4 3 4 7% 42%	2090
October	1st to 10th	Day	22% 6% 2 5% 5% 3 4 3 4 6% 41%	2090
	11th to 20th	Day	14% 7% 2 4 4 3 4 3 5% 7% 47%	1856
	21st to end	Day	19% 7% 3 6% 4 4 3 3 5% 6% 41%	1881
November	1st to 10th	Day	13% 8% 2 6% 4 4 4 3 4 5% 49%	1761
	11th to 20th	Day	18% 7% 1 4 3 3 3 3 6% 5% 47%	1800
	21st to end	Day	17% 8% 3 5% 4 4 4 3 5% 6% 43%	1798
December	1st to 10th	Day	19% 8% 2 6% 4 3 5% 3 5% 5% 38%	1539
	11th to 20th	Day	22% 7% 1 4 3 3 3 3 4 6% 44%	1906
	21st to end	Day	20% 11% 3 7% 4 3 4 3 4 6% 34%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 4 3 4 7% 46%	4429
	11th to 20th	Night	15% 10% 3 8% 4 4 3 3 4 5% 40%	4440
	21st to end	Night	22% 12% 4 7% 5% 3 4 3 4 5% 31%	4884
February	1st to 10th	Night	16% 10% 3 6% 4 4 4 4 5% 6% 39%	2384
	11th to 20th	Night	14% 9% 3 7% 5% 4 4 4 5% 6% 40%	2218
	21st to end	Night	17% 10% 2 7% 5% 4 3 3 4 6% 40%	1884
March	1st to 10th	Night	26% 12% 1 5% 4 3 3 3 4 6% 33%	3724
	11th to 20th	Night	11% 9% 3 6% 5% 4 5% 3 6% 8% 42%	3653
	21st to end	Night	22% 9% 2 6% 4 3 4 4 6% 6% 34%	3542
April	1st to 10th	Night	17% 9% 2 7% 5% 5% 4 4 6% 5% 36%	1900
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 5% 6% 38%	1875
	21st to end	Night	21% 8% 3 5% 4 3 4 3 4 6% 40%	1728
May	1st to 10th	Night	25% 10% 2 6% 4 5% 5% 4 5% 7% 28%	2834
	11th to 20th	Night	22% 8% 3 8% 5% 5% 5% 4 6% 7% 27%	2731
	21st to end	Night	17% 7% 2 5% 3 4 4 3 7% 8% 41%	2738
June	1st to 10th	Night	15% 9% 2 6% 5% 4 4 3 5% 7% 39%	1520
	11th to 20th	Night	18% 7% 2 5% 6% 4 5% 3 5% 7% 38%	1520
	21st to end	Night	14% 6% 2 6% 4 4 3 4 7% 8% 41%	1520
July	1st to 10th	Night	14% 6% 3 7% 6% 4 5% 4 7% 10% 33%	2520
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 6% 8% 38%	2520
	21st to end	Night	18% 9% 3 8% 5% 4 5% 3 5% 5% 35%	2739
August	1st to 10th	Night	22% 7% 3 8% 5% 5% 5% 4 5% 6% 30%	2719
	11th to 20th	Night	12% 8% 3 8% 5% 6% 6% 5% 6% 7% 35%	2907
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 7% 57%	3476
September	1st to 10th	Night	13% 7% 3 7% 4 4 4 4 5% 6% 44%	1900
	11th to 20th	Night	13% 8% 2 4 3 3 3 3 4 6% 52%	2076
	21st to end	Night	17% 7% 3 7% 4 3 4 4 5% 5% 42%	2090
October	1st to 10th	Night	20% 8% 2 5% 3 3 3 3 5% 7% 41%	2090
	11th to 20th	Night	15% 6% 2 4 4 3 4 3 5% 5% 48%	2318
	21st to end	Night	20% 9% 2 6% 4 3 4 3 4 5% 39%	2717
November	1st to 10th	Night	13% 6% 2 5% 4 4 3 3 6% 6% 48%	2537
	11th to 20th	Night	17% 8% 2 5% 3 3 3 3 4 5% 47%	2600
	21st to end	Night	16% 8% 2 4 4 4 5% 3 5% 6% 45%	2598
December	1st to 10th	Night	19% 9% 2 6% 4 3 4 3 4 6% 40%	2640
	11th to 20th	Night	20% 6% 2 5% 4 3 4 4 5% 6% 40%	3288
	21st to end	Night	20% 11% 3 7% 4 3 4 3 4 6% 36%	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	26% 38% 4 22% 8% 2	2518
	11th to 20th	Day	30% 37% 4 19% 8% 1	2520
	21st to end	Day	39% 40% 3 11% 6% 1	2772
February	1st to 10th	Day	17% 65% 6% 8% 4 1	1791
	11th to 20th	Day	18% 64% 2 7% 9% 1	1857
	21st to end	Day	15% 65% 5% 9% 4 1	1570
March	1st to 10th	Day	41% 40% 5% 7% 6% 1	3119
	11th to 20th	Day	19% 43% 9% 19% 9% 1	3306
	21st to end	Day	32% 41% 3 10% 9% 4	4088
April	1st to 10th	Day	20% 65% 3 6% 5% 1	2280
	11th to 20th	Day	15% 66% 4 7% 8% 1	2254
	21st to end	Day	19% 65% 2 7% 6% 1	2451
May	1st to 10th	Day	36% 43% 9% 6% 6%	4120
	11th to 20th	Day	35% 42% 10% 9% 3	4180
	21st to end	Day	22% 42% 5% 16% 13% 1	4837
June	1st to 10th	Day	15% 65% 4 10% 6%	2660
	11th to 20th	Day	14% 65% 6% 9% 5% 1	2660
	21st to end	Day	15% 64% 4 9% 8%	2660
July	1st to 10th	Day	30% 38% 7% 14% 11% 1	4370
	11th to 20th	Day	28% 36% 11% 15% 8% 1	4365
	21st to end	Day	35% 36% 7% 13% 9% 1	4661
August	1st to 10th	Day	34% 37% 11% 13% 4	4165
	11th to 20th	Day	27% 38% 10% 21% 5%	3942
	21st to end	Day	20% 38% 9% 22% 11% 1	4180
September	1st to 10th	Day	15% 60% 5% 11% 8% 1	2280
	11th to 20th	Day	17% 60% 3 9% 10% 2	2104
	21st to end	Day	19% 60% 5% 9% 8% 1	2090
October	1st to 10th	Day	26% 37% 4 15% 15% 3	3480
	11th to 20th	Day	18% 37% 3 16% 23% 4	3046
	21st to end	Day	18% 37% 8% 22% 14% 2	3081
November	1st to 10th	Day	18% 56% 6% 10% 8% 1	1761
	11th to 20th	Day	16% 56% 4 8% 14% 2	1800
	21st to end	Day	17% 57% 5% 13% 6% 2	1798
December	1st to 10th	Day	19% 61% 6% 6% 9%	1539
	11th to 20th	Day	23% 48% 6% 8% 10% 4	1906
	21st to end	Day	34% 38% 5% 15% 8%	2772
January	1st to 10th	Night	24% 37% 6% 23% 7% 3	4429
	11th to 20th	Night	29% 38% 7% 17% 8% 2	4440
	21st to end	Night	41% 40% 5% 8% 5% 1	4884
February	1st to 10th	Night	16% 66% 5% 7% 5% 1	2384
	11th to 20th	Night	16% 64% 3 6% 10% 2	2220
	21st to end	Night	16% 65% 2 8% 6% 2	1884
March	1st to 10th	Night	38% 41% 4 10% 5% 1	3734
	11th to 20th	Night	21% 43% 10% 13% 11% 2	3654
	21st to end	Night	33% 41% 3 6% 13% 4	3542
April	1st to 10th	Night	20% 65% 3 7% 5% 1	1900
	11th to 20th	Night	15% 67% 5% 6% 7% 1	1875
	21st to end	Night	16% 65% 3 8% 6% 1	1728
May	1st to 10th	Night	34% 44% 9% 9% 4	2840
	11th to 20th	Night	38% 45% 8% 7% 2	2732
	21st to end	Night	25% 42% 7% 16% 9%	2739
June	1st to 10th	Night	14% 66% 3 9% 7%	1520
	11th to 20th	Night	14% 65% 6% 9% 5%	1520
	21st to end	Night	14% 63% 4 12% 7% 1	1520
July	1st to 10th	Night	30% 38% 9% 14% 10%	2480
	11th to 20th	Night	28% 37% 11% 15% 9%	2472
	21st to end	Night	36% 36% 7% 9% 11% 1	2651
August	1st to 10th	Night	38% 39% 7% 10% 5% 1	2709
	11th to 20th	Night	32% 39% 8% 16% 4	2934
	21st to end	Night	13% 37% 11% 22% 16% 1	3476
September	1st to 10th	Night	15% 61% 4 12% 8% 1	1900
	11th to 20th	Night	15% 60% 3 9% 11% 1	2076
	21st to end	Night	19% 60% 4 9% 8%	2090
October	1st to 10th	Night	26% 37% 8% 15% 11% 2	3480
	11th to 20th	Night	11% 37% 5% 18% 27% 3	3841
	21st to end	Night	19% 36% 7% 23% 14% 2	4467
November	1st to 10th	Night	17% 57% 4 10% 10% 2	2537
	11th to 20th	Night	16% 57% 4 8% 12% 3	2600
	21st to end	Night	15% 57% 6% 13% 7% 1	2598
December	1st to 10th	Night	20% 60% 5% 9% 7%	2640
	11th to 20th	Night	23% 50% 5% 9% 10% 2	3288
	21st to end	Night	33% 38% 5% 15% 8%	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	28% 28% 26% 17% 2	180
	11th to 20th	Day	31% 30% 28% 8% 3	180
	21st to end	Day	26% 27% 34% 10% 3 1	198
February	1st to 10th	Day	35% 23% 31% 9% 1	369
	11th to 20th	Day	31% 31% 29% 9%	456
	21st to end	Day	35% 22% 30% 10% 4	382
March	1st to 10th	Day	32% 22% 32% 11% 3	460
	11th to 20th	Day	31% 26% 29% 11% 3	460
	21st to end	Day	30% 23% 32% 10% 4 2	506
April	1st to 10th	Day	33% 24% 26% 11% 5% 1	460
	11th to 20th	Day	29% 21% 35% 11% 3 1	452
	21st to end	Day	30% 19% 32% 14% 3 2	460
May	1st to 10th	Day	33% 21% 28% 13% 4 1	463
	11th to 20th	Day	23% 17% 40% 14% 5% 1	487
	21st to end	Day	20% 15% 35% 22% 7% 2	529
June	1st to 10th	Day	20% 15% 34% 21% 8% 2	490
	11th to 20th	Day	16% 14% 40% 22% 7% 1	490
	21st to end	Day	19% 15% 35% 21% 8% 2	490
July	1st to 10th	Day	16% 10% 32% 27% 13% 2	485
	11th to 20th	Day	16% 8% 33% 28% 12% 2	484
	21st to end	Day	15% 9% 39% 28% 8% 1	532
August	1st to 10th	Day	13% 10% 34% 31% 10% 2	486
	11th to 20th	Day	16% 10% 32% 30% 10% 4	479
	21st to end	Day	12% 10% 36% 24% 14% 4	539
September	1st to 10th	Day	19% 11% 29% 21% 16% 4	490
	11th to 20th	Day	19% 11% 29% 21% 12% 8%	490
	21st to end	Day	23% 11% 33% 20% 8% 4	490
October	1st to 10th	Day	26% 15% 25% 22% 8% 4	490
	11th to 20th	Day	20% 18% 34% 18% 7% 3	449
	21st to end	Day	26% 17% 32% 17% 6% 1	429
November	1st to 10th	Day	22% 19% 33% 15% 9% 2	395
	11th to 20th	Day	30% 23% 29% 16% 4 1	400
	21st to end	Day	29% 22% 31% 15% 4	400
December	1st to 10th	Day	28% 28% 27% 12% 5%	199
	11th to 20th	Day	39% 24% 29% 6% 2	180
	21st to end	Day	28% 26% 32% 9% 3 2	198
January	1st to 10th	Night	24% 22% 39% 13% 2	760
	11th to 20th	Night	30% 21% 34% 14% 2	760
	21st to end	Night	22% 24% 34% 17% 2	836
February	1st to 10th	Night	26% 20% 37% 16% 2	760
	11th to 20th	Night	24% 28% 36% 11% 1	743
	21st to end	Night	30% 21% 32% 14% 2	628
March	1st to 10th	Night	26% 23% 33% 14% 3	760
	11th to 20th	Night	22% 26% 37% 14% 2	760
	21st to end	Night	28% 21% 33% 14% 3	836
April	1st to 10th	Night	25% 21% 36% 16% 2	760
	11th to 20th	Night	23% 22% 34% 18% 3	751
	21st to end	Night	24% 20% 37% 16% 2	588
May	1st to 10th	Night	32% 14% 32% 18% 4	570
	11th to 20th	Night	22% 17% 39% 18% 4	519
	21st to end	Night	19% 9% 41% 26% 5%	411
June	1st to 10th	Night	18% 9% 39% 27% 7%	380
	11th to 20th	Night	19% 9% 40% 26% 5% 1	380
	21st to end	Night	14% 8% 40% 33% 6%	380
July	1st to 10th	Night	14% 6% 34% 36% 10% 1	370
	11th to 20th	Night	16% 4 30% 39% 11%	368
	21st to end	Night	15% 6% 36% 37% 6%	416
August	1st to 10th	Night	13% 5% 37% 36% 8%	500
	11th to 20th	Night	15% 6% 31% 35% 12%	635
	21st to end	Night	15% 6% 28% 34% 15% 2	836
September	1st to 10th	Night	17% 7% 35% 30% 11% 1	760
	11th to 20th	Night	16% 9% 28% 28% 17% 2	760
	21st to end	Night	22% 9% 31% 26% 10% 2	760
October	1st to 10th	Night	25% 11% 29% 23% 11% 1	760
	11th to 20th	Night	19% 15% 33% 22% 11% 1	760
	21st to end	Night	26% 17% 32% 18% 6%	836
November	1st to 10th	Night	17% 17% 34% 23% 7% 1	780
	11th to 20th	Night	24% 22% 33% 16% 5% 1	800
	21st to end	Night	26% 19% 34% 16% 5%	800
December	1st to 10th	Night	27% 20% 34% 15% 4	760
	11th to 20th	Night	25% 23% 33% 18% 2	760
	21st to end	Night	27% 21% 37% 14% 2	836

Page generated at 2024-11-27 17:30:49. Version ac07

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