Hidden Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hidden Lake Observatory clear sky chart from 2005-11-06 to 2024-07-16.

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	17% 9% 3 7% 5% 4 5% 4 5% 7% 35%	89631
	Night	17% 9% 3 7% 4 4 4 4 5% 6% 36%	89856
Transparency	Day	46% 7% 12% 21% 12% 2	89350
	Night	45% 6% 13% 22% 12% 2	89691
Seeing	Day	25% 19% 29% 17% 7% 2	14504
	Night	24% 18% 29% 22% 7% 1	23559

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% 9% 3 6% 4 5% 5% 4 6% 6% 38%	2517
	11th to 20th	Day	16% 11% 5% 10% 6% 4 5% 4 4 6% 30%	2520
	21st to end	Day	21% 14% 7% 8% 4 4 3 3 3 4 27%	2842
February	1st to 10th	Day	16% 10% 3 8% 6% 5% 5% 5% 5% 6% 30%	1736
	11th to 20th	Day	13% 9% 3 7% 7% 6% 5% 4 5% 6% 35%	1848
	21st to end	Day	17% 12% 3 8% 5% 4 4 3 5% 6% 32%	1570
March	1st to 10th	Day	22% 14% 4 8% 5% 3 3 2 3 5% 30%	3116
	11th to 20th	Day	11% 10% 5% 8% 5% 5% 5% 5% 6% 7% 33%	3256
	21st to end	Day	20% 8% 3 7% 5% 5% 4 3 5% 6% 35%	4166
April	1st to 10th	Day	17% 11% 4 6% 4 5% 4 4 4 6% 34%	2280
	11th to 20th	Day	17% 8% 2 7% 5% 4 4 4 4 6% 39%	2254
	21st to end	Day	19% 9% 3 7% 5% 5% 4 3 6% 6% 34%	2382
May	1st to 10th	Day	26% 9% 3 7% 4 4 4 3 4 7% 28%	4106
	11th to 20th	Day	21% 8% 3 8% 5% 4 4 3 5% 7% 32%	4356
	21st to end	Day	14% 5% 2 5% 5% 4 5% 5% 7% 8% 40%	4837
June	1st to 10th	Day	17% 8% 2 5% 5% 6% 6% 5% 6% 9% 32%	2660
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 5% 6% 9% 35%	2660
	21st to end	Day	16% 8% 2 7% 5% 6% 5% 4 6% 9% 33%	2660
July	1st to 10th	Day	13% 7% 3 6% 5% 5% 4 5% 7% 8% 38%	2660
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 9% 40%	2593
	21st to end	Day	13% 7% 2 6% 6% 5% 5% 5% 7% 8% 36%	2744
August	1st to 10th	Day	12% 6% 2 7% 5% 5% 6% 5% 7% 9% 36%	2453
	11th to 20th	Day	14% 6% 3 7% 5% 5% 6% 5% 6% 9% 35%	2139
	21st to end	Day	14% 6% 2 7% 5% 4 5% 4 6% 8% 40%	2376
September	1st to 10th	Day	12% 6% 2 7% 6% 5% 5% 4 6% 7% 39%	2160
	11th to 20th	Day	15% 6% 2 5% 4 3 4 3 5% 6% 47%	2051
	21st to end	Day	17% 6% 2 5% 3 4 5% 3 6% 7% 41%	1980
October	1st to 10th	Day	23% 8% 3 6% 4 4 4 3 5% 4 37%	1926
	11th to 20th	Day	15% 8% 2 5% 4 4 4 3 6% 8% 41%	1792
	21st to end	Day	23% 9% 3 7% 5% 4 5% 3 5% 6% 31%	1782
November	1st to 10th	Day	13% 9% 3 6% 4 3 3 3 4 6% 45%	1671
	11th to 20th	Day	18% 8% 2 4 4 4 5% 4 5% 7% 38%	1710
	21st to end	Day	17% 9% 3 8% 4 3 4 4 5% 6% 37%	1630
December	1st to 10th	Day	19% 10% 3 8% 6% 5% 4 4 4 6% 31%	1520
	11th to 20th	Day	21% 9% 3 5% 4 4 3 4 5% 6% 36%	1906
	21st to end	Day	21% 12% 5% 8% 5% 4 4 4 5% 7% 25%	2772
January	1st to 10th	Night	16% 8% 3 7% 4 4 4 4 6% 6% 39%	4429
	11th to 20th	Night	14% 10% 4 9% 5% 4 4 4 6% 6% 34%	4440
	21st to end	Night	21% 14% 4 7% 4 5% 4 3 4 6% 27%	4811
February	1st to 10th	Night	16% 10% 3 6% 4 5% 5% 5% 5% 7% 34%	2442
	11th to 20th	Night	13% 10% 3 7% 5% 5% 5% 4 7% 7% 34%	2218
	21st to end	Night	18% 9% 3 8% 5% 4 4 3 5% 6% 35%	1884
March	1st to 10th	Night	23% 12% 3 7% 5% 4 4 3 4 5% 31%	3724
	11th to 20th	Night	12% 10% 3 7% 6% 5% 4 4 6% 8% 36%	3671
	21st to end	Night	19% 12% 2 8% 5% 3 3 3 5% 4 35%	3466
April	1st to 10th	Night	16% 10% 3 8% 5% 4 4 4 6% 7% 32%	1900
	11th to 20th	Night	19% 9% 2 6% 4 5% 4 3 4 6% 37%	1875
	21st to end	Night	20% 9% 3 7% 4 3 3 2 5% 6% 38%	1796
May	1st to 10th	Night	25% 10% 3 7% 5% 4 3 3 5% 6% 29%	2834
	11th to 20th	Night	19% 10% 3 8% 6% 5% 5% 3 5% 6% 30%	2564
	21st to end	Night	16% 6% 2 6% 4 4 4 4 5% 8% 40%	2738
June	1st to 10th	Night	17% 8% 2 5% 4 3 4 3 6% 8% 40%	1520
	11th to 20th	Night	16% 7% 3 6% 4 5% 4 5% 7% 8% 36%	1520
	21st to end	Night	15% 7% 2 6% 4 3 5% 4 6% 8% 41%	1520
July	1st to 10th	Night	14% 6% 1 5% 3 4 4 4 5% 8% 45%	1520
	11th to 20th	Night	15% 5% 3 5% 4 4 4 5% 6% 8% 41%	1488
	21st to end	Night	10% 6% 2 6% 4 5% 5% 4 6% 8% 44%	1574
August	1st to 10th	Night	10% 5% 2 6% 4 5% 3 4 6% 8% 46%	1468
	11th to 20th	Night	12% 7% 3 6% 5% 5% 5% 4 6% 9% 39%	1757
	21st to end	Night	14% 6% 3 5% 4 4 3 3 5% 8% 46%	1980
September	1st to 10th	Night	14% 6% 2 6% 5% 3 4 4 5% 7% 44%	1800
	11th to 20th	Night	14% 6% 2 5% 3 2 2 2 4 6% 52%	1908
	21st to end	Night	17% 7% 3 5% 3 3 4 3 5% 6% 45%	1980
October	1st to 10th	Night	21% 7% 2 6% 5% 3 4 3 5% 5% 40%	2032
	11th to 20th	Night	14% 8% 2 7% 4 4 4 4 5% 7% 42%	2168
	21st to end	Night	22% 9% 2 6% 4 4 3 3 5% 6% 34%	2574
November	1st to 10th	Night	15% 7% 3 6% 4 4 4 3 5% 5% 46%	2407
	11th to 20th	Night	18% 7% 2 5% 4 4 4 4 6% 6% 39%	2470
	21st to end	Night	14% 8% 3 6% 5% 5% 5% 4 6% 7% 39%	2546
December	1st to 10th	Night	19% 10% 3 7% 5% 5% 4 4 6% 7% 30%	2660
	11th to 20th	Night	19% 9% 4 5% 5% 5% 5% 4 6% 6% 32%	3288
	21st to end	Night	21% 11% 5% 8% 5% 4 4 4 5% 6% 27%	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	41% 6% 13% 32% 7% 1	2518
	11th to 20th	Day	53% 6% 12% 21% 7% 1	2520
	21st to end	Day	60% 4 10% 18% 8% 1	2842
February	1st to 10th	Day	51% 5% 14% 18% 10% 1	1736
	11th to 20th	Day	45% 6% 10% 23% 13% 2	1857
	21st to end	Day	51% 5% 12% 18% 12% 2	1570
March	1st to 10th	Day	57% 4 12% 15% 11% 2	3119
	11th to 20th	Day	42% 10% 15% 23% 8% 1	3256
	21st to end	Day	48% 5% 6% 18% 19% 4	4166
April	1st to 10th	Day	49% 6% 10% 20% 12% 3	2280
	11th to 20th	Day	46% 5% 10% 21% 16% 2	2254
	21st to end	Day	48% 6% 9% 19% 14% 4	2382
May	1st to 10th	Day	56% 6% 12% 14% 11% 1	4120
	11th to 20th	Day	50% 6% 15% 20% 8% 1	4360
	21st to end	Day	36% 9% 14% 26% 15% 1	4837
June	1st to 10th	Day	45% 9% 13% 22% 10% 1	2660
	11th to 20th	Day	44% 7% 14% 22% 11% 1	2660
	21st to end	Day	46% 7% 14% 20% 12% 1	2660
July	1st to 10th	Day	42% 8% 12% 22% 15% 1	2590
	11th to 20th	Day	38% 8% 15% 26% 11% 1	2518
	21st to end	Day	42% 8% 15% 19% 14% 2	2591
August	1st to 10th	Day	41% 9% 14% 23% 12% 1	2439
	11th to 20th	Day	43% 8% 15% 23% 10% 1	2139
	21st to end	Day	39% 7% 12% 24% 16% 1	2376
September	1st to 10th	Day	42% 7% 12% 24% 14% 1	2160
	11th to 20th	Day	36% 5% 10% 25% 22% 2	2051
	21st to end	Day	41% 5% 11% 23% 17% 3	1980
October	1st to 10th	Day	50% 5% 8% 21% 13% 3	1926
	11th to 20th	Day	39% 7% 13% 26% 13% 2	1792
	21st to end	Day	51% 5% 12% 18% 11% 3	1782
November	1st to 10th	Day	39% 5% 14% 25% 14% 3	1671
	11th to 20th	Day	42% 5% 12% 23% 16% 2	1710
	21st to end	Day	45% 5% 14% 24% 10% 2	1630
December	1st to 10th	Day	52% 6% 14% 17% 11% 1	1520
	11th to 20th	Day	44% 6% 16% 21% 11% 1	1906
	21st to end	Day	55% 7% 12% 15% 10%	2772
January	1st to 10th	Night	42% 4 15% 26% 10% 3	4429
	11th to 20th	Night	47% 5% 14% 21% 10% 2	4440
	21st to end	Night	57% 5% 11% 17% 9% 1	4811
February	1st to 10th	Night	46% 6% 15% 21% 10% 2	2442
	11th to 20th	Night	44% 7% 12% 20% 14% 2	2220
	21st to end	Night	47% 5% 12% 22% 10% 3	1884
March	1st to 10th	Night	54% 6% 11% 19% 10% 1	3734
	11th to 20th	Night	41% 7% 16% 25% 10% 2	3672
	21st to end	Night	47% 6% 7% 15% 20% 4	3466
April	1st to 10th	Night	49% 6% 10% 21% 12% 2	1900
	11th to 20th	Night	48% 6% 9% 20% 17% 1	1875
	21st to end	Night	46% 5% 10% 21% 15% 4	1796
May	1st to 10th	Night	55% 6% 12% 15% 9% 2	2840
	11th to 20th	Night	53% 8% 13% 16% 9% 2	2565
	21st to end	Night	39% 8% 17% 22% 13% 1	2739
June	1st to 10th	Night	42% 7% 13% 26% 12% 1	1520
	11th to 20th	Night	42% 7% 17% 22% 11%	1520
	21st to end	Night	39% 8% 15% 24% 13% 1	1520
July	1st to 10th	Night	38% 6% 15% 25% 15% 2	1480
	11th to 20th	Night	38% 8% 16% 28% 9%	1440
	21st to end	Night	35% 9% 16% 23% 14% 3	1486
August	1st to 10th	Night	34% 9% 17% 28% 12% 1	1458
	11th to 20th	Night	40% 9% 16% 25% 10% 1	1757
	21st to end	Night	37% 7% 12% 26% 17% 1	1980
September	1st to 10th	Night	40% 6% 13% 25% 16% 1	1800
	11th to 20th	Night	33% 6% 12% 24% 23% 2	1908
	21st to end	Night	38% 5% 10% 26% 19% 2	1980
October	1st to 10th	Night	45% 5% 12% 22% 13% 3	2032
	11th to 20th	Night	40% 6% 14% 27% 12% 1	2168
	21st to end	Night	48% 5% 14% 20% 11% 1	2574
November	1st to 10th	Night	38% 5% 13% 21% 19% 3	2407
	11th to 20th	Night	43% 5% 12% 21% 15% 3	2470
	21st to end	Night	41% 6% 16% 26% 9% 1	2546
December	1st to 10th	Night	47% 7% 15% 20% 10%	2660
	11th to 20th	Night	45% 7% 16% 18% 12% 2	3288
	21st to end	Night	53% 6% 11% 20% 10%	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	31% 26% 33% 8% 2	180
	11th to 20th	Day	33% 29% 29% 8% 1 1	180
	21st to end	Day	26% 29% 34% 8% 3 1	220
February	1st to 10th	Day	35% 32% 26% 5% 1	296
	11th to 20th	Day	36% 28% 27% 8% 2	456
	21st to end	Day	33% 26% 27% 12% 2	382
March	1st to 10th	Day	33% 23% 30% 12% 2	460
	11th to 20th	Day	33% 26% 30% 9% 1 1	460
	21st to end	Day	36% 24% 25% 9% 3 2	506
April	1st to 10th	Day	32% 24% 28% 10% 5% 1	460
	11th to 20th	Day	32% 25% 26% 12% 4 2	452
	21st to end	Day	29% 23% 29% 13% 5% 1	460
May	1st to 10th	Day	33% 22% 25% 13% 5% 2	463
	11th to 20th	Day	22% 22% 32% 18% 5% 1	487
	21st to end	Day	21% 14% 32% 20% 10% 3	529
June	1st to 10th	Day	18% 17% 33% 21% 9% 2	490
	11th to 20th	Day	19% 15% 34% 21% 9% 2	490
	21st to end	Day	18% 19% 31% 22% 8% 2	490
July	1st to 10th	Day	13% 11% 36% 25% 12% 2	485
	11th to 20th	Day	14% 8% 34% 30% 12% 3	465
	21st to end	Day	14% 11% 39% 25% 9% 2	488
August	1st to 10th	Day	15% 9% 28% 32% 11% 5%	446
	11th to 20th	Day	16% 10% 31% 25% 12% 7%	439
	21st to end	Day	14% 13% 29% 26% 14% 5%	495
September	1st to 10th	Day	20% 11% 25% 23% 16% 5%	450
	11th to 20th	Day	17% 15% 26% 21% 14% 8%	450
	21st to end	Day	21% 15% 30% 18% 12% 4	450
October	1st to 10th	Day	29% 14% 25% 17% 10% 5%	450
	11th to 20th	Day	20% 21% 29% 23% 6% 1	446
	21st to end	Day	34% 16% 28% 15% 7% 1	396
November	1st to 10th	Day	25% 21% 23% 22% 8% 1	365
	11th to 20th	Day	32% 24% 25% 15% 3 1	370
	21st to end	Day	30% 23% 27% 16% 3 1	290
December	1st to 10th	Day	28% 31% 26% 11% 4	180
	11th to 20th	Day	42% 22% 29% 4 2	180
	21st to end	Day	29% 29% 30% 10% 1 1	198
January	1st to 10th	Night	24% 28% 31% 15% 2	760
	11th to 20th	Night	31% 22% 30% 15% 2	760
	21st to end	Night	23% 26% 32% 16% 2	836
February	1st to 10th	Night	27% 23% 32% 17% 2	760
	11th to 20th	Night	26% 27% 35% 11% 1	743
	21st to end	Night	32% 25% 27% 14% 2	628
March	1st to 10th	Night	28% 23% 32% 14% 3	760
	11th to 20th	Night	25% 27% 31% 15% 3	760
	21st to end	Night	28% 23% 29% 16% 4 1	836
April	1st to 10th	Night	27% 20% 34% 15% 3	760
	11th to 20th	Night	26% 22% 30% 17% 6%	751
	21st to end	Night	27% 21% 30% 18% 4	656
May	1st to 10th	Night	29% 16% 31% 18% 6%	570
	11th to 20th	Night	22% 16% 35% 24% 4	417
	21st to end	Night	19% 10% 30% 31% 9%	411
June	1st to 10th	Night	20% 11% 33% 27% 9%	380
	11th to 20th	Night	17% 9% 29% 35% 9% 1	380
	21st to end	Night	17% 11% 27% 34% 10% 1	380
July	1st to 10th	Night	15% 5% 28% 35% 16% 1	370
	11th to 20th	Night	16% 4 26% 39% 14% 1	360
	21st to end	Night	10% 8% 27% 41% 14%	394
August	1st to 10th	Night	12% 5% 25% 44% 13% 1	394
	11th to 20th	Night	15% 5% 26% 33% 17% 2	693
	21st to end	Night	16% 8% 23% 34% 17% 2	792
September	1st to 10th	Night	15% 8% 30% 31% 14% 2	720
	11th to 20th	Night	17% 10% 25% 28% 17% 4	720
	21st to end	Night	21% 9% 26% 29% 12% 3	720
October	1st to 10th	Night	26% 11% 26% 25% 11% 2	720
	11th to 20th	Night	21% 17% 28% 26% 7%	720
	21st to end	Night	29% 19% 28% 20% 5%	792
November	1st to 10th	Night	19% 20% 30% 22% 7% 1	740
	11th to 20th	Night	26% 22% 27% 18% 6% 1	760
	21st to end	Night	24% 21% 29% 21% 4 1	760
December	1st to 10th	Night	28% 25% 29% 15% 3	760
	11th to 20th	Night	30% 22% 30% 16% 2	760
	21st to end	Night	30% 26% 30% 12% 2	836

Page generated at 2024-07-13 10:19:52. Version ac07

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