Alkali
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alkali clear sky chart from 2005-11-06 to 2024-11-03.

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	2 3 1 3 3 3 3 3 5% 6% 69%	100999
	Night	2 4 1 4 3 3 3 3 5% 7% 65%	98180
Transparency	Day	15% 3 7% 17% 26% 31%	100745
	Night	18% 4 8% 20% 26% 24%	98024
Seeing	Day	4 7% 19% 28% 25% 17%	15075
	Night	4 4 19% 42% 28% 3	24653

By Month

Percentage Cloud Cover SW (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	1 4 3 6% 3 4 4 5% 8% 9% 53%	2539
	11th to 20th	Day	1 5% 2 6% 4 5% 5% 5% 9% 9% 49%	2540
	21st to end	Day	4 7% 2 6% 4 4 4 5% 8% 12% 44%	3128
February	1st to 10th	Day	1 4 2 4 3 3 4 2 6% 10% 59%	1900
	11th to 20th	Day	1 4 1 5% 4 3 3 4 7% 10% 57%	1850
	21st to end	Day	1 5% 2 4 3 4 4 4 5% 7% 61%	1570
March	1st to 10th	Day	1 4 1 5% 4 3 4 4 6% 10% 56%	3138
	11th to 20th	Day	3 6% 2 4 3 3 3 3 5% 8% 60%	3293
	21st to end	Day	2 5% 2 6% 4 4 5% 5% 7% 9% 51%	4097
April	1st to 10th	Day	2 4 1 5% 3 3 4 4 5% 7% 62%	2280
	11th to 20th	Day	2 3 1 4 3 3 4 4 4 6% 67%	2249
	21st to end	Day	1 3 1 3 2 2 3 3 5% 9% 66%	2327
May	1st to 10th	Day	2 3 1 3 3 2 3 2 4 5% 72%	4110
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 6% 74%	4071
	21st to end	Day	1 2 1 3 2 3 3 3 4 5% 73%	4538
June	1st to 10th	Day	1 2 1 4 3 3 3 3 5% 7% 67%	2660
	11th to 20th	Day	2 1 3 2 2 3 2 4 5% 75%	2660
	21st to end	Day	1 1 2 2 2 2 2 3 4 80%	2660
July	1st to 10th	Day	1 1 2 1 1 2 1 2 3 85%	4420
	11th to 20th	Day	1 1 1 3 2 2 2 2 4 5% 76%	4420
	21st to end	Day	2 2 1 3 3 3 3 2 5% 6% 71%	4648
August	1st to 10th	Day	2 2 1 2 2 2 2 2 2 3 81%	3940
	11th to 20th	Day	1 1 1 1 1 1 2 4 87%	3724
	21st to end	Day	1 1 1 1 1 1 1 3 3 86%	4180
September	1st to 10th	Day	1 1 1 2 2 2 2 3 4 5% 78%	2280
	11th to 20th	Day	1 2 1 2 1 1 1 2 3 4 81%	2119
	21st to end	Day	1 1 1 1 1 1 2 1 3 5% 82%	2090
October	1st to 10th	Day	1 2 1 2 2 2 2 2 4 6% 76%	2090
	11th to 20th	Day	1 1 1 2 2 2 2 2 4 5% 78%	1967
	21st to end	Day	1 2 1 2 1 1 2 3 4 6% 76%	1914
November	1st to 10th	Day	1 3 1 3 3 3 3 3 4 8% 67%	1692
	11th to 20th	Day	1 2 1 2 2 2 2 2 5% 8% 73%	1710
	21st to end	Day	2 3 1 3 3 3 4 3 6% 7% 65%	1710
December	1st to 10th	Day	3 3 3 4 3 3 3 3 5% 7% 63%	1710
	11th to 20th	Day	3 7% 2 7% 5% 5% 4 5% 8% 9% 44%	1981
	21st to end	Day	2 5% 2 5% 4 5% 6% 6% 9% 11% 46%	2794
January	1st to 10th	Night	1 5% 3 7% 4 4 4 4 6% 9% 53%	4406
	11th to 20th	Night	1 5% 2 7% 4 5% 5% 5% 6% 9% 51%	4420
	21st to end	Night	5% 8% 2 6% 3 4 5% 4 7% 10% 47%	4521
February	1st to 10th	Night	2 5% 2 5% 3 3 3 4 5% 9% 61%	2280
	11th to 20th	Night	2 4 1 3 3 3 3 3 6% 9% 62%	2218
	21st to end	Night	1 5% 3 5% 4 3 3 3 6% 8% 61%	1884
March	1st to 10th	Night	1 3 1 5% 3 4 4 4 5% 7% 62%	3736
	11th to 20th	Night	3 7% 2 5% 4 3 4 4 6% 7% 55%	3686
	21st to end	Night	2 5% 2 4 3 3 4 3 6% 7% 59%	3553
April	1st to 10th	Night	2 4 1 4 3 3 3 3 4 7% 65%	1900
	11th to 20th	Night	2 3 1 4 3 2 3 3 4 6% 69%	1879
	21st to end	Night	4 4 1 4 3 2 2 3 4 6% 66%	1852
May	1st to 10th	Night	2 4 2 4 3 2 3 2 3 6% 69%	2860
	11th to 20th	Night	3 4 1 4 4 4 3 3 4 5% 65%	2834
	21st to end	Night	3 3 1 4 3 3 3 3 4 6% 67%	3029
June	1st to 10th	Night	2 2 1 3 3 4 3 3 5% 7% 68%	1520
	11th to 20th	Night	2 2 1 3 3 2 3 3 3 6% 73%	1520
	21st to end	Night	1 2 1 2 1 2 2 3 4 4 79%	1520
July	1st to 10th	Night	1 2 1 3 2 2 2 2 2 3 81%	2540
	11th to 20th	Night	2 2 1 4 3 4 4 4 6% 7% 64%	2540
	21st to end	Night	2 3 1 5% 4 4 4 3 5% 6% 64%	2906
August	1st to 10th	Night	3 2 1 3 3 3 3 3 4 6% 69%	3000
	11th to 20th	Night	1 1 1 1 2 2 2 3 4 83%	3126
	21st to end	Night	1 1 1 1 1 3 2 2 4 84%	3498
September	1st to 10th	Night	1 1 1 2 2 2 2 2 3 6% 79%	1900
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 5% 78%	2060
	21st to end	Night	2 1 1 2 2 2 2 1 3 4 82%	2090
October	1st to 10th	Night	3 2 1 2 2 2 2 2 4 5% 75%	2090
	11th to 20th	Night	1 1 1 3 2 1 2 2 3 5% 78%	2209
	21st to end	Night	1 1 1 2 2 2 3 3 3 4 79%	2681
November	1st to 10th	Night	1 2 1 3 3 2 2 2 4 7% 74%	2431
	11th to 20th	Night	1 2 1 3 2 3 2 2 4 7% 72%	2470
	21st to end	Night	2 3 1 4 3 3 4 3 5% 6% 67%	2470
December	1st to 10th	Night	2 3 2 5% 3 3 5% 3 6% 7% 61%	2470
	11th to 20th	Night	2 9% 2 6% 4 4 5% 4 6% 11% 46%	3219
	21st to end	Night	1 5% 2 7% 5% 6% 8% 6% 8% 10% 41%	4862

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	21% 5% 19% 33% 21% 1	2539
	11th to 20th	Day	25% 6% 18% 29% 16% 5%	2540
	21st to end	Day	27% 7% 17% 27% 19% 3	3128
February	1st to 10th	Day	21% 4 11% 29% 26% 9%	1900
	11th to 20th	Day	21% 4 10% 27% 31% 8%	1860
	21st to end	Day	22% 4 11% 28% 28% 8%	1570
March	1st to 10th	Day	19% 4 10% 28% 28% 11%	3138
	11th to 20th	Day	21% 3 11% 29% 27% 8%	3293
	21st to end	Day	25% 4 12% 29% 24% 6%	4097
April	1st to 10th	Day	20% 4 7% 26% 27% 16%	2280
	11th to 20th	Day	17% 4 7% 20% 32% 20%	2252
	21st to end	Day	15% 3 8% 24% 36% 15%	2327
May	1st to 10th	Day	13% 2 5% 20% 38% 21%	4110
	11th to 20th	Day	11% 2 6% 13% 40% 28%	4074
	21st to end	Day	13% 2 5% 15% 39% 25%	4538
June	1st to 10th	Day	15% 4 7% 13% 29% 32%	2660
	11th to 20th	Day	11% 2 5% 8% 28% 46%	2660
	21st to end	Day	9% 2 3 5% 19% 62%	2660
July	1st to 10th	Day	7% 1 2 4 8% 78%	4351
	11th to 20th	Day	10% 3 3 6% 15% 63%	4345
	21st to end	Day	14% 3 5% 13% 19% 45%	4501
August	1st to 10th	Day	11% 2 2 7% 24% 54%	3926
	11th to 20th	Day	5% 1 2 4 14% 73%	3760
	21st to end	Day	6% 1 1 5% 21% 65%	4179
September	1st to 10th	Day	9% 2 3 7% 23% 56%	2280
	11th to 20th	Day	8% 2 3 11% 30% 45%	2119
	21st to end	Day	8% 2 2 11% 34% 44%	2090
October	1st to 10th	Day	12% 2 5% 14% 35% 33%	2090
	11th to 20th	Day	11% 2 2 16% 37% 33%	1967
	21st to end	Day	9% 3 5% 21% 41% 21%	1914
November	1st to 10th	Day	16% 2 9% 24% 33% 15%	1692
	11th to 20th	Day	11% 3 9% 29% 38% 10%	1710
	21st to end	Day	18% 3 8% 26% 31% 13%	1710
December	1st to 10th	Day	20% 5% 12% 27% 26% 9%	1710
	11th to 20th	Day	32% 6% 10% 26% 20% 5%	1981
	21st to end	Day	27% 7% 20% 23% 20% 3	2794
January	1st to 10th	Night	23% 5% 16% 33% 21% 2	4406
	11th to 20th	Night	25% 6% 16% 29% 18% 6%	4420
	21st to end	Night	30% 6% 15% 29% 16% 4	4521
February	1st to 10th	Night	22% 3 11% 28% 25% 10%	2280
	11th to 20th	Night	18% 3 9% 26% 33% 10%	2219
	21st to end	Night	22% 4 10% 30% 27% 7%	1884
March	1st to 10th	Night	18% 5% 8% 26% 33% 11%	3736
	11th to 20th	Night	24% 5% 11% 26% 25% 9%	3686
	21st to end	Night	20% 4 12% 34% 25% 5%	3553
April	1st to 10th	Night	19% 4 8% 29% 27% 13%	1900
	11th to 20th	Night	17% 4 7% 24% 32% 17%	1879
	21st to end	Night	19% 3 7% 24% 35% 12%	1852
May	1st to 10th	Night	15% 3 7% 18% 42% 16%	2860
	11th to 20th	Night	18% 3 9% 12% 34% 24%	2835
	21st to end	Night	18% 3 9% 13% 40% 19%	3029
June	1st to 10th	Night	15% 4 8% 13% 32% 29%	1520
	11th to 20th	Night	14% 3 3 10% 26% 44%	1520
	21st to end	Night	9% 3 3 6% 22% 58%	1520
July	1st to 10th	Night	10% 2 3 4 7% 74%	2500
	11th to 20th	Night	16% 4 6% 9% 15% 50%	2492
	21st to end	Night	19% 5% 6% 13% 13% 44%	2815
August	1st to 10th	Night	15% 4 4 9% 25% 44%	2991
	11th to 20th	Night	7% 2 3 4 13% 71%	3156
	21st to end	Night	7% 2 2 7% 17% 65%	3498
September	1st to 10th	Night	10% 2 3 10% 22% 54%	1900
	11th to 20th	Night	11% 2 4 11% 27% 46%	2060
	21st to end	Night	9% 1 3 10% 31% 46%	2090
October	1st to 10th	Night	13% 2 5% 16% 31% 34%	2090
	11th to 20th	Night	11% 2 4 16% 33% 34%	2209
	21st to end	Night	10% 3 4 19% 40% 24%	2681
November	1st to 10th	Night	13% 2 7% 26% 35% 17%	2431
	11th to 20th	Night	14% 3 8% 26% 35% 15%	2470
	21st to end	Night	19% 3 6% 23% 36% 13%	2470
December	1st to 10th	Night	21% 5% 10% 26% 26% 10%	2470
	11th to 20th	Night	30% 5% 12% 27% 22% 4	3219
	21st to end	Night	30% 7% 14% 25% 20% 4	4862

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	7% 5% 25% 35% 22% 7%	180
	11th to 20th	Day	4 5% 23% 35% 21% 13%	180
	21st to end	Day	5% 7% 20% 28% 26% 14%	364
February	1st to 10th	Day	6% 11% 26% 29% 18% 10%	460
	11th to 20th	Day	5% 11% 30% 27% 18% 9%	455
	21st to end	Day	5% 11% 26% 34% 18% 5%	382
March	1st to 10th	Day	4 16% 29% 28% 17% 7%	460
	11th to 20th	Day	8% 11% 26% 29% 19% 7%	460
	21st to end	Day	8% 14% 33% 27% 13% 5%	506
April	1st to 10th	Day	6% 14% 25% 25% 19% 12%	460
	11th to 20th	Day	7% 14% 29% 27% 17% 6%	452
	21st to end	Day	6% 11% 28% 25% 17% 13%	460
May	1st to 10th	Day	5% 9% 29% 30% 16% 11%	463
	11th to 20th	Day	5% 10% 21% 26% 22% 15%	488
	21st to end	Day	4 8% 15% 29% 26% 19%	529
June	1st to 10th	Day	3 6% 17% 24% 28% 22%	490
	11th to 20th	Day	4 7% 18% 26% 26% 19%	490
	21st to end	Day	1 3 16% 25% 33% 21%	490
July	1st to 10th	Day	2 2 12% 29% 29% 26%	486
	11th to 20th	Day	1 2 8% 26% 35% 29%	484
	21st to end	Day	2 2 9% 28% 31% 28%	531
August	1st to 10th	Day	5% 2 10% 33% 31% 19%	487
	11th to 20th	Day	2 2 14% 25% 30% 28%	477
	21st to end	Day	3 1 13% 27% 29% 28%	539
September	1st to 10th	Day	3 3 13% 24% 28% 29%	490
	11th to 20th	Day	3 4 20% 29% 26% 18%	490
	21st to end	Day	2 4 14% 26% 34% 20%	490
October	1st to 10th	Day	2 7% 17% 24% 26% 23%	490
	11th to 20th	Day	2 6% 17% 27% 31% 17%	490
	21st to end	Day	3 6% 13% 29% 29% 20%	363
November	1st to 10th	Day	3 4 13% 32% 30% 18%	276
	11th to 20th	Day	3 5% 14% 32% 27% 19%	270
	21st to end	Day	5% 6% 16% 29% 30% 16%	270
December	1st to 10th	Day	4 4 16% 41% 25% 10%	270
	11th to 20th	Day	6% 5% 19% 34% 27% 9%	205
	21st to end	Day	4 9% 26% 27% 23% 12%	198
January	1st to 10th	Night	6% 4 20% 40% 25% 5%	760
	11th to 20th	Night	3 2 21% 49% 21% 4	760
	21st to end	Night	7% 4 22% 42% 22% 3	836
February	1st to 10th	Night	5% 4 26% 40% 23% 3	760
	11th to 20th	Night	4 6% 24% 42% 22% 3	744
	21st to end	Night	4 6% 26% 46% 16% 2	628
March	1st to 10th	Night	3 7% 26% 45% 17% 2	760
	11th to 20th	Night	4 7% 21% 42% 24% 2	760
	21st to end	Night	5% 8% 30% 39% 17% 1	836
April	1st to 10th	Night	3 10% 26% 39% 21% 1	760
	11th to 20th	Night	5% 9% 27% 39% 17% 2	751
	21st to end	Night	5% 8% 26% 38% 20% 3	712
May	1st to 10th	Night	4 10% 28% 40% 17% 1	570
	11th to 20th	Night	5% 9% 23% 37% 24% 2	561
	21st to end	Night	7% 9% 22% 36% 23% 2	575
June	1st to 10th	Night	1 5% 18% 44% 29% 3	380
	11th to 20th	Night	2 3 21% 48% 24% 1	380
	21st to end	Night	1 1 14% 52% 29% 2	380
July	1st to 10th	Night	4 1 6% 54% 35% 1	370
	11th to 20th	Night	3 1 7% 43% 42% 4	368
	21st to end	Night	2 2 5% 47% 42% 2	499
August	1st to 10th	Night	5% 2 11% 47% 34% 1	655
	11th to 20th	Night	2 1 9% 42% 43% 3	752
	21st to end	Night	2 1 8% 41% 44% 3	836
September	1st to 10th	Night	2 2 9% 36% 45% 6%	760
	11th to 20th	Night	2 2 12% 42% 37% 5%	760
	21st to end	Night	2 2 13% 37% 39% 6%	760
October	1st to 10th	Night	4 3 17% 38% 33% 6%	760
	11th to 20th	Night	1 3 15% 40% 35% 5%	760
	21st to end	Night	1 4 18% 37% 32% 8%	836
November	1st to 10th	Night	2 4 15% 38% 35% 6%	748
	11th to 20th	Night	2 2 16% 48% 27% 4	760
	21st to end	Night	3 2 18% 44% 29% 4	760
December	1st to 10th	Night	3 4 19% 49% 21% 4	760
	11th to 20th	Night	6% 4 18% 46% 22% 3	760
	21st to end	Night	4 4 25% 46% 19% 2	836

Page generated at 2024-10-31 00:39:26. Version ac07

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