High Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High Mountain Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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% 7% 2 6% 4 4 4 4 5% 7% 39%	101536
	Night	18% 7% 2 6% 4 4 4 3 5% 6% 42%	98009
Transparency	Day	43% 4 11% 24% 16% 2	105068
	Night	43% 3 11% 24% 17% 3	102553
Seeing	Day	22% 13% 30% 22% 10% 3	15050
	Night	21% 10% 30% 29% 9% 1	24207

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	15% 7% 2 5% 3 4 3 3 5% 6% 47%	2517
	11th to 20th	Day	15% 9% 3 7% 6% 6% 5% 4 4 6% 36%	2520
	21st to end	Day	22% 12% 4 7% 4 3 3 3 4 5% 33%	3024
February	1st to 10th	Day	18% 7% 2 7% 4 4 4 4 4 7% 39%	1710
	11th to 20th	Day	15% 7% 3 6% 4 3 4 3 5% 5% 45%	1846
	21st to end	Day	20% 8% 2 6% 4 4 4 4 6% 4 39%	1570
March	1st to 10th	Day	26% 8% 2 6% 4 3 4 3 4 5% 35%	3116
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 7% 8% 44%	3347
	21st to end	Day	21% 7% 2 5% 3 3 3 3 4 5% 43%	4125
April	1st to 10th	Day	18% 8% 3 7% 3 4 4 3 5% 6% 39%	2280
	11th to 20th	Day	17% 6% 2 6% 4 4 3 3 5% 7% 41%	2254
	21st to end	Day	20% 6% 2 5% 4 4 4 3 5% 7% 40%	2296
May	1st to 10th	Day	29% 8% 2 5% 4 3 4 3 5% 7% 30%	4106
	11th to 20th	Day	23% 8% 3 7% 5% 4 4 4 5% 6% 30%	4393
	21st to end	Day	14% 5% 2 5% 3 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	16% 6% 2 5% 5% 5% 5% 4 7% 9% 37%	2660
	11th to 20th	Day	15% 7% 2 6% 5% 5% 6% 4 7% 8% 36%	2660
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2660
July	1st to 10th	Day	9% 7% 3 7% 6% 5% 6% 5% 6% 10% 36%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 4 6% 5% 8% 9% 38%	4440
	21st to end	Day	14% 8% 3 7% 6% 6% 5% 4 6% 7% 33%	4814
August	1st to 10th	Day	21% 5% 3 7% 4 5% 6% 4 6% 8% 31%	4180
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 6% 8% 43%	3730
	21st to end	Day	11% 5% 2 5% 4 4 5% 3 5% 8% 46%	4180
September	1st to 10th	Day	15% 4 3 6% 5% 4 5% 3 5% 7% 43%	2280
	11th to 20th	Day	13% 5% 2 4 4 3 3 3 5% 7% 50%	2204
	21st to end	Day	18% 6% 2 6% 5% 5% 4 4 5% 5% 40%	2090
October	1st to 10th	Day	20% 6% 2 5% 3 4 3 3 5% 6% 42%	1972
	11th to 20th	Day	16% 5% 2 5% 3 4 3 3 5% 7% 48%	1900
	21st to end	Day	21% 5% 1 4 3 4 3 3 4 7% 43%	1945
November	1st to 10th	Day	14% 6% 2 5% 3 3 3 2 5% 5% 53%	1761
	11th to 20th	Day	18% 6% 1 4 3 3 3 4 4 6% 48%	1800
	21st to end	Day	16% 7% 1 5% 4 3 4 4 6% 7% 44%	1681
December	1st to 10th	Day	19% 8% 2 5% 4 4 4 3 5% 7% 38%	1520
	11th to 20th	Day	23% 5% 2 4 3 3 3 3 5% 6% 44%	1906
	21st to end	Day	18% 8% 4 8% 5% 5% 4 4 5% 7% 31%	2772
January	1st to 10th	Night	17% 6% 2 5% 3 3 3 3 5% 6% 47%	4429
	11th to 20th	Night	16% 8% 3 7% 4 4 4 3 4 5% 41%	4440
	21st to end	Night	25% 11% 2 5% 3 3 3 3 4 5% 35%	4628
February	1st to 10th	Night	17% 9% 3 5% 3 4 4 3 5% 5% 43%	2470
	11th to 20th	Night	16% 8% 2 7% 4 4 4 3 5% 5% 42%	2218
	21st to end	Night	19% 8% 2 6% 4 5% 3 3 4 5% 41%	1884
March	1st to 10th	Night	24% 10% 2 5% 4 3 3 2 4 5% 37%	3724
	11th to 20th	Night	12% 7% 2 6% 4 3 3 3 5% 6% 48%	3607
	21st to end	Night	18% 10% 3 6% 4 3 3 3 4 5% 43%	3505
April	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 6% 39%	1900
	11th to 20th	Night	19% 7% 2 5% 4 3 4 3 6% 7% 40%	1875
	21st to end	Night	19% 8% 2 6% 4 4 3 3 5% 6% 42%	1881
May	1st to 10th	Night	27% 10% 3 7% 4 4 3 3 4 6% 30%	2834
	11th to 20th	Night	25% 8% 3 7% 4 4 3 3 4 5% 34%	2529
	21st to end	Night	16% 6% 2 6% 4 3 4 3 6% 8% 42%	2738
June	1st to 10th	Night	16% 6% 2 5% 4 3 5% 4 5% 9% 42%	1520
	11th to 20th	Night	13% 7% 2 4 5% 4 4 3 6% 9% 42%	1520
	21st to end	Night	11% 5% 2 5% 4 3 5% 4 6% 10% 43%	1520
July	1st to 10th	Night	9% 6% 3 7% 5% 6% 5% 5% 7% 10% 39%	2520
	11th to 20th	Night	13% 7% 2 7% 4 5% 5% 5% 7% 9% 37%	2520
	21st to end	Night	17% 8% 2 6% 4 4 5% 5% 6% 8% 36%	2739
August	1st to 10th	Night	22% 7% 2 7% 4 4 4 4 5% 7% 34%	2714
	11th to 20th	Night	14% 6% 3 7% 5% 5% 5% 4 6% 6% 39%	3097
	21st to end	Night	11% 5% 2 5% 3 3 4 3 5% 7% 52%	3476
September	1st to 10th	Night	15% 6% 2 6% 4 4 3 4 5% 7% 44%	1900
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 6% 53%	1975
	21st to end	Night	19% 6% 3 5% 3 3 3 2 5% 6% 44%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 4 3 3 4 7% 41%	2204
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 5% 6% 50%	2280
	21st to end	Night	21% 6% 2 4 3 3 3 3 4 6% 45%	2651
November	1st to 10th	Night	13% 5% 2 5% 3 3 4 3 5% 6% 52%	2537
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 4 5% 48%	2600
	21st to end	Night	15% 5% 2 5% 5% 3 4 3 5% 6% 46%	2652
December	1st to 10th	Night	19% 7% 2 6% 4 4 4 4 5% 6% 40%	2660
	11th to 20th	Night	19% 7% 1 5% 4 4 4 3 5% 6% 42%	3288
	21st to end	Night	20% 9% 3 6% 4 4 4 3 5% 5% 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	39% 2 8% 34% 14% 3	2518
	11th to 20th	Day	50% 3 10% 22% 13% 2	2520
	21st to end	Day	56% 2 8% 22% 11% 2	3024
February	1st to 10th	Day	46% 4 12% 24% 13% 2	1710
	11th to 20th	Day	42% 3 8% 25% 18% 3	1855
	21st to end	Day	47% 3 10% 22% 15% 4	1570
March	1st to 10th	Day	53% 2 9% 24% 10% 2	3119
	11th to 20th	Day	38% 3 9% 32% 16% 2	3347
	21st to end	Day	45% 2 6% 18% 24% 5%	4125
April	1st to 10th	Day	46% 3 9% 21% 16% 5%	2280
	11th to 20th	Day	43% 3 11% 22% 18% 4	2254
	21st to end	Day	44% 3 9% 23% 18% 4	2296
May	1st to 10th	Day	55% 2 12% 16% 13% 2	4120
	11th to 20th	Day	55% 2 12% 20% 9% 2	4397
	21st to end	Day	38% 3 10% 28% 20% 2	4837
June	1st to 10th	Day	42% 5% 13% 22% 16% 2	2660
	11th to 20th	Day	45% 4 11% 25% 12% 2	2660
	21st to end	Day	40% 5% 14% 24% 16% 1	2660
July	1st to 10th	Day	42% 8% 11% 23% 15% 1	4370
	11th to 20th	Day	39% 7% 15% 24% 14% 1	4365
	21st to end	Day	48% 6% 10% 17% 16% 2	4661
August	1st to 10th	Day	50% 5% 13% 22% 10%	4166
	11th to 20th	Day	38% 4 14% 29% 13% 1	3766
	21st to end	Day	35% 5% 9% 30% 19% 2	4180
September	1st to 10th	Day	41% 4 9% 23% 20% 3	2280
	11th to 20th	Day	35% 3 10% 25% 25% 3	2204
	21st to end	Day	46% 4 8% 21% 18% 3	2090
October	1st to 10th	Day	39% 4 8% 20% 24% 6%	3271
	11th to 20th	Day	27% 3 9% 25% 32% 4	3140
	21st to end	Day	28% 3 13% 26% 26% 4	3183
November	1st to 10th	Day	35% 2 11% 25% 24% 3	1761
	11th to 20th	Day	38% 3 9% 25% 21% 4	1800
	21st to end	Day	40% 3 13% 30% 12% 2	1681
December	1st to 10th	Day	46% 3 14% 21% 14% 2	1520
	11th to 20th	Day	42% 3 15% 24% 13% 3	1906
	21st to end	Day	54% 3 9% 25% 9% 1	2772
January	1st to 10th	Night	40% 2 10% 32% 12% 4	4429
	11th to 20th	Night	46% 3 12% 24% 13% 2	4440
	21st to end	Night	54% 1 7% 24% 12% 2	4628
February	1st to 10th	Night	45% 3 12% 25% 13% 2	2470
	11th to 20th	Night	44% 3 9% 20% 19% 5%	2220
	21st to end	Night	46% 2 6% 25% 17% 4	1884
March	1st to 10th	Night	52% 2 8% 23% 12% 3	3734
	11th to 20th	Night	38% 2 13% 26% 18% 3	3608
	21st to end	Night	46% 2 6% 17% 22% 7%	3505
April	1st to 10th	Night	46% 3 9% 22% 17% 4	1900
	11th to 20th	Night	44% 4 9% 22% 20% 2	1875
	21st to end	Night	44% 2 8% 22% 19% 4	1881
May	1st to 10th	Night	58% 3 9% 18% 11% 1	2840
	11th to 20th	Night	55% 3 14% 16% 11% 2	2530
	21st to end	Night	41% 4 14% 25% 13% 3	2739
June	1st to 10th	Night	41% 4 11% 22% 20% 2	1520
	11th to 20th	Night	40% 4 14% 30% 12% 1	1520
	21st to end	Night	35% 6% 14% 27% 16% 1	1520
July	1st to 10th	Night	40% 9% 14% 20% 15% 3	2480
	11th to 20th	Night	42% 7% 13% 24% 13% 1	2472
	21st to end	Night	44% 6% 14% 15% 19% 2	2651
August	1st to 10th	Night	51% 5% 15% 18% 10% 1	2704
	11th to 20th	Night	43% 6% 11% 29% 11% 1	3127
	21st to end	Night	32% 5% 10% 32% 20% 1	3476
September	1st to 10th	Night	40% 4 10% 26% 19% 1	1900
	11th to 20th	Night	34% 3 9% 25% 25% 3	1975
	21st to end	Night	42% 3 8% 23% 23% 2	2090
October	1st to 10th	Night	39% 4 10% 24% 21% 2	3672
	11th to 20th	Night	26% 3 9% 29% 30% 4	3779
	21st to end	Night	31% 2 11% 31% 22% 2	4363
November	1st to 10th	Night	34% 4 10% 25% 22% 4	2537
	11th to 20th	Night	40% 2 8% 24% 21% 5%	2600
	21st to end	Night	39% 3 13% 29% 15% 2	2652
December	1st to 10th	Night	44% 3 13% 24% 14% 2	2660
	11th to 20th	Night	44% 2 12% 21% 17% 4	3288
	21st to end	Night	52% 2 10% 23% 12% 1	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	22% 27% 33% 16% 3	180
	11th to 20th	Day	30% 23% 33% 11% 3	180
	21st to end	Day	22% 21% 38% 12% 5% 2	268
February	1st to 10th	Day	30% 17% 39% 11% 2	270
	11th to 20th	Day	25% 19% 37% 16% 2	454
	21st to end	Day	28% 18% 34% 17% 4	382
March	1st to 10th	Day	25% 22% 30% 18% 5%	460
	11th to 20th	Day	22% 22% 33% 17% 5% 1	460
	21st to end	Day	29% 19% 31% 14% 7% 1	506
April	1st to 10th	Day	26% 20% 31% 14% 7% 2	460
	11th to 20th	Day	25% 20% 32% 15% 6% 2	452
	21st to end	Day	30% 16% 32% 16% 4 2	460
May	1st to 10th	Day	33% 17% 27% 16% 6% 2	463
	11th to 20th	Day	25% 12% 33% 21% 8% 1	487
	21st to end	Day	20% 8% 28% 28% 14% 2	529
June	1st to 10th	Day	18% 11% 33% 24% 13% 3	490
	11th to 20th	Day	20% 10% 29% 28% 12% 1	490
	21st to end	Day	16% 11% 31% 26% 14% 2	490
July	1st to 10th	Day	15% 6% 24% 32% 18% 5%	485
	11th to 20th	Day	11% 5% 27% 33% 20% 3	484
	21st to end	Day	13% 8% 29% 33% 15% 2	532
August	1st to 10th	Day	15% 4 25% 34% 16% 6%	486
	11th to 20th	Day	16% 5% 23% 32% 19% 5%	479
	21st to end	Day	14% 6% 29% 27% 16% 7%	539
September	1st to 10th	Day	18% 9% 25% 25% 16% 7%	490
	11th to 20th	Day	16% 6% 27% 24% 16% 11%	490
	21st to end	Day	23% 8% 30% 23% 10% 6%	490
October	1st to 10th	Day	26% 9% 27% 20% 14% 5%	490
	11th to 20th	Day	18% 17% 30% 21% 12% 2	490
	21st to end	Day	26% 12% 31% 19% 11% 2	462
November	1st to 10th	Day	18% 13% 32% 24% 10% 4	395
	11th to 20th	Day	25% 16% 33% 22% 5% 1	400
	21st to end	Day	21% 19% 34% 19% 5% 2	299
December	1st to 10th	Day	24% 23% 31% 16% 7%	180
	11th to 20th	Day	31% 20% 33% 14% 2	180
	21st to end	Day	29% 15% 37% 13% 6% 1	198
January	1st to 10th	Night	20% 15% 39% 22% 4	760
	11th to 20th	Night	25% 14% 32% 25% 4	760
	21st to end	Night	21% 15% 36% 24% 3	836
February	1st to 10th	Night	23% 11% 36% 28% 2	760
	11th to 20th	Night	22% 17% 41% 19% 1	743
	21st to end	Night	25% 15% 34% 21% 4	628
March	1st to 10th	Night	24% 15% 35% 21% 5%	760
	11th to 20th	Night	23% 14% 36% 22% 4 1	760
	21st to end	Night	23% 15% 36% 21% 5%	836
April	1st to 10th	Night	23% 17% 34% 21% 5%	760
	11th to 20th	Night	23% 14% 34% 24% 5%	751
	21st to end	Night	23% 13% 33% 24% 6%	741
May	1st to 10th	Night	25% 13% 32% 22% 8%	570
	11th to 20th	Night	24% 11% 29% 30% 7%	395
	21st to end	Night	21% 5% 19% 40% 13% 1	411
June	1st to 10th	Night	20% 4 27% 36% 12% 1	380
	11th to 20th	Night	15% 5% 28% 38% 13%	380
	21st to end	Night	12% 4 26% 47% 12%	380
July	1st to 10th	Night	13% 4 23% 39% 21% 1	370
	11th to 20th	Night	13% 4 19% 43% 19% 1	368
	21st to end	Night	16% 2 20% 45% 15% 1	416
August	1st to 10th	Night	13% 2 20% 42% 20% 2	495
	11th to 20th	Night	14% 4 19% 37% 24% 1	750
	21st to end	Night	16% 4 18% 38% 23% 2	836
September	1st to 10th	Night	17% 3 24% 36% 18% 2	760
	11th to 20th	Night	18% 4 19% 35% 20% 4	760
	21st to end	Night	22% 4 24% 34% 15% 2	760
October	1st to 10th	Night	24% 7% 27% 24% 15% 3	760
	11th to 20th	Night	18% 10% 29% 31% 12%	760
	21st to end	Night	24% 8% 33% 25% 8%	836
November	1st to 10th	Night	16% 11% 31% 28% 13% 1	780
	11th to 20th	Night	22% 11% 33% 25% 7% 1	800
	21st to end	Night	20% 14% 33% 25% 7% 1	789
December	1st to 10th	Night	24% 13% 31% 26% 5% 1	760
	11th to 20th	Night	23% 12% 34% 27% 4	760
	21st to end	Night	24% 13% 34% 27% 2	836

Page generated at 2024-11-25 00:22:17. Version ac07

Copyright © 2024 Attilla Danko.