Alcova
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alcova clear sky chart from 2005-11-06 to 2024-03-01.

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	5% 6% 2 4 4 3 4 5% 5% 8% 54%	78502
	Night	4 6% 3 5% 5% 3 4 5% 5% 8% 52%	80967
Transparency	Day	29% 7% 15% 25% 18% 7%	78208
	Night	30% 7% 16% 26% 16% 5%	80784
Seeing	Day	9% 13% 30% 28% 16% 4	14722
	Night	8% 12% 33% 34% 12% 1	24960

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 7% 3 8% 7% 4 4 4 5% 7% 50%	2538
	11th to 20th	Day	2 7% 4 8% 8% 4 6% 6% 7% 8% 41%	2581
	21st to end	Day	2 5% 2 4 3 3 4 3 4 7% 62%	3146
February	1st to 10th	Day	2 9% 5% 8% 6% 2 5% 6% 6% 8% 43%	1710
	11th to 20th	Day	4 9% 5% 7% 6% 2 4 4 5% 8% 46%	1678
	21st to end	Day	2 8% 4 5% 4 3 5% 5% 5% 8% 51%	1570
March	1st to 10th	Day	4 7% 3 6% 5% 2 4 5% 5% 9% 50%	1855
	11th to 20th	Day	3 7% 2 5% 4 3 5% 5% 6% 9% 50%	1980
	21st to end	Day	6% 10% 3 6% 4 3 6% 5% 6% 8% 42%	2250
April	1st to 10th	Day	6% 9% 2 4 5% 3 4 5% 6% 8% 48%	2160
	11th to 20th	Day	9% 10% 3 6% 5% 3 5% 5% 6% 7% 41%	2131
	21st to end	Day	10% 9% 3 5% 5% 3 4 5% 5% 6% 44%	2189
May	1st to 10th	Day	10% 7% 3 5% 5% 4 5% 6% 5% 9% 40%	2443
	11th to 20th	Day	12% 7% 2 4 5% 3 4 4 6% 9% 44%	2478
	21st to end	Day	9% 5% 2 4 5% 3 5% 6% 7% 10% 45%	2724
June	1st to 10th	Day	6% 3 2 4 4 3 4 6% 6% 10% 53%	2520
	11th to 20th	Day	5% 3 1 4 3 2 4 5% 6% 8% 59%	2520
	21st to end	Day	2 2 1 2 3 2 4 4 6% 8% 66%	2520
July	1st to 10th	Day	3 2 1 2 4 3 4 5% 6% 8% 61%	2520
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 9% 64%	2520
	21st to end	Day	4 3 1 3 3 3 4 5% 6% 9% 59%	2706
August	1st to 10th	Day	3 2 1 3 4 3 5% 6% 7% 9% 58%	2328
	11th to 20th	Day	3 3 1 3 4 2 3 5% 5% 8% 62%	2273
	21st to end	Day	3 2 1 2 4 2 3 4 5% 7% 66%	2376
September	1st to 10th	Day	6% 3 1 3 3 2 3 4 4 6% 65%	2160
	11th to 20th	Day	5% 2 1 3 3 3 3 4 4 7% 64%	2160
	21st to end	Day	6% 3 1 3 3 2 3 4 5% 6% 65%	1919
October	1st to 10th	Day	8% 5% 2 4 4 2 3 4 5% 6% 56%	1800
	11th to 20th	Day	8% 5% 2 3 3 3 3 4 4 8% 59%	1800
	21st to end	Day	5% 7% 2 4 4 2 3 4 5% 8% 55%	1937
November	1st to 10th	Day	5% 5% 2 4 4 3 4 4 6% 7% 55%	1673
	11th to 20th	Day	3 6% 2 5% 3 3 4 5% 5% 8% 55%	1577
	21st to end	Day	3 7% 3 6% 4 3 4 3 5% 7% 56%	1520
December	1st to 10th	Day	2 9% 5% 7% 6% 3 5% 5% 5% 6% 46%	1520
	11th to 20th	Day	3 7% 2 4 4 3 5% 3 4 8% 58%	1926
	21st to end	Day	3 9% 3 6% 5% 3 5% 5% 5% 7% 49%	2794
January	1st to 10th	Night	2 8% 4 7% 6% 3 6% 5% 7% 8% 44%	4417
	11th to 20th	Night	2 8% 4 9% 6% 4 6% 6% 6% 8% 41%	4416
	21st to end	Night	2 7% 3 6% 4 2 4 4 5% 9% 55%	4521
February	1st to 10th	Night	3 8% 3 8% 7% 3 5% 4 6% 8% 46%	2470
	11th to 20th	Night	4 8% 3 7% 6% 4 5% 5% 6% 8% 44%	2388
	21st to end	Night	2 8% 4 8% 6% 4 5% 6% 5% 7% 46%	1884
March	1st to 10th	Night	4 8% 3 6% 6% 3 4 4 6% 8% 49%	2108
	11th to 20th	Night	5% 8% 3 5% 5% 3 5% 4 5% 7% 50%	1980
	21st to end	Night	6% 10% 4 6% 5% 3 5% 5% 6% 9% 42%	2106
April	1st to 10th	Night	7% 9% 3 4 4 3 5% 6% 5% 8% 46%	1800
	11th to 20th	Night	10% 10% 3 8% 6% 3 5% 5% 6% 7% 39%	1777
	21st to end	Night	10% 8% 2 5% 4 4 4 5% 7% 7% 44%	1768
May	1st to 10th	Night	11% 6% 2 4 4 3 4 5% 5% 6% 49%	1515
	11th to 20th	Night	13% 4 2 4 4 4 3 5% 5% 10% 46%	1417
	21st to end	Night	8% 5% 2 4 4 3 4 6% 7% 8% 51%	1552
June	1st to 10th	Night	4 4 1 3 5% 3 4 5% 7% 9% 55%	1440
	11th to 20th	Night	6% 4 1 3 3 2 3 4 5% 8% 61%	1440
	21st to end	Night	3 2 3 3 2 3 5% 4 8% 67%	1440
July	1st to 10th	Night	4 3 1 3 4 3 5% 6% 7% 9% 57%	1440
	11th to 20th	Night	2 1 1 3 3 2 4 4 5% 9% 66%	1440
	21st to end	Night	3 2 1 3 3 2 4 5% 5% 8% 63%	1609
August	1st to 10th	Night	2 2 1 3 4 3 5% 6% 8% 10% 57%	1611
	11th to 20th	Night	4 2 1 2 3 2 4 5% 5% 8% 64%	1626
	21st to end	Night	2 2 1 3 3 2 4 4 7% 9% 63%	1980
September	1st to 10th	Night	4 3 1 2 3 3 3 4 4 7% 66%	1800
	11th to 20th	Night	5% 4 1 3 3 3 3 4 4 8% 64%	1800
	21st to end	Night	7% 3 1 3 3 2 2 2 3 5% 68%	2035
October	1st to 10th	Night	7% 7% 2 3 3 2 4 4 5% 6% 56%	2160
	11th to 20th	Night	8% 6% 2 3 3 2 4 3 4 6% 59%	2160
	21st to end	Night	6% 6% 2 4 4 2 3 4 4 7% 57%	2399
November	1st to 10th	Night	5% 7% 2 3 4 3 3 5% 5% 8% 55%	2405
	11th to 20th	Night	4 7% 3 6% 5% 3 4 5% 5% 7% 52%	2599
	21st to end	Night	3 9% 3 5% 4 3 3 4 5% 8% 54%	2660
December	1st to 10th	Night	3 8% 3 7% 5% 3 4 4 6% 6% 50%	2660
	11th to 20th	Night	3 7% 4 5% 5% 3 4 4 6% 9% 52%	3271
	21st to end	Night	4 9% 3 5% 4 4 5% 6% 7% 9% 44%	4873

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	35% 10% 14% 26% 14% 1	2539
	11th to 20th	Day	39% 10% 19% 19% 11% 1	2581
	21st to end	Day	25% 7% 30% 26% 11% 1	3146
February	1st to 10th	Day	38% 9% 17% 27% 8% 1	1710
	11th to 20th	Day	37% 9% 17% 24% 11% 3	1687
	21st to end	Day	30% 7% 21% 25% 14% 2	1570
March	1st to 10th	Day	31% 6% 18% 31% 12% 2	1855
	11th to 20th	Day	30% 7% 20% 28% 14% 1	1980
	21st to end	Day	39% 7% 17% 26% 10% 1	2250
April	1st to 10th	Day	35% 8% 20% 22% 12% 3	2160
	11th to 20th	Day	42% 7% 13% 24% 12% 2	2134
	21st to end	Day	39% 6% 13% 30% 11%	2189
May	1st to 10th	Day	40% 8% 14% 23% 14% 1	2443
	11th to 20th	Day	36% 7% 16% 27% 12% 1	2482
	21st to end	Day	34% 9% 17% 27% 12% 1	2724
June	1st to 10th	Day	26% 8% 14% 26% 20% 5%	2520
	11th to 20th	Day	22% 6% 13% 19% 26% 15%	2520
	21st to end	Day	16% 5% 10% 21% 31% 16%	2520
July	1st to 10th	Day	20% 6% 10% 21% 27% 16%	2451
	11th to 20th	Day	18% 5% 9% 21% 25% 22%	2445
	21st to end	Day	21% 6% 10% 20% 25% 17%	2556
August	1st to 10th	Day	21% 6% 10% 26% 22% 14%	2313
	11th to 20th	Day	20% 5% 10% 24% 28% 14%	2273
	21st to end	Day	18% 5% 9% 17% 35% 17%	2376
September	1st to 10th	Day	20% 4 8% 19% 29% 20%	2160
	11th to 20th	Day	20% 5% 10% 22% 27% 15%	2160
	21st to end	Day	22% 4 11% 27% 30% 7%	1919
October	1st to 10th	Day	29% 5% 13% 26% 21% 6%	1800
	11th to 20th	Day	27% 6% 15% 31% 18% 4	1800
	21st to end	Day	28% 6% 17% 29% 18% 2	1937
November	1st to 10th	Day	28% 6% 17% 26% 19% 3	1673
	11th to 20th	Day	27% 5% 19% 29% 17% 3	1577
	21st to end	Day	30% 6% 16% 30% 16% 3	1520
December	1st to 10th	Day	38% 8% 20% 19% 13% 2	1520
	11th to 20th	Day	27% 5% 24% 32% 11%	1924
	21st to end	Day	34% 7% 15% 29% 13% 2	2794
January	1st to 10th	Night	35% 8% 20% 26% 11% 1	4417
	11th to 20th	Night	39% 9% 19% 18% 11% 3	4416
	21st to end	Night	28% 7% 30% 25% 9% 1	4521
February	1st to 10th	Night	36% 8% 20% 25% 10% 1	2470
	11th to 20th	Night	37% 8% 16% 25% 11% 2	2389
	21st to end	Night	37% 6% 17% 22% 15% 2	1884
March	1st to 10th	Night	33% 6% 18% 28% 14% 1	2108
	11th to 20th	Night	33% 6% 16% 31% 12% 2	1980
	21st to end	Night	39% 8% 16% 25% 11% 1	2106
April	1st to 10th	Night	36% 7% 18% 23% 13% 3	1800
	11th to 20th	Night	44% 6% 13% 21% 15% 2	1777
	21st to end	Night	37% 9% 12% 27% 14% 1	1768
May	1st to 10th	Night	36% 7% 14% 27% 16% 1	1515
	11th to 20th	Night	34% 8% 16% 28% 13% 2	1418
	21st to end	Night	30% 7% 17% 28% 17% 2	1552
June	1st to 10th	Night	23% 7% 20% 27% 17% 6%	1440
	11th to 20th	Night	22% 5% 12% 21% 24% 16%	1440
	21st to end	Night	15% 5% 10% 22% 30% 18%	1440
July	1st to 10th	Night	22% 6% 12% 25% 21% 14%	1400
	11th to 20th	Night	16% 4 11% 22% 26% 22%	1392
	21st to end	Night	20% 5% 13% 20% 25% 17%	1520
August	1st to 10th	Night	18% 8% 14% 29% 19% 12%	1602
	11th to 20th	Night	18% 6% 9% 24% 26% 16%	1626
	21st to end	Night	17% 6% 10% 19% 31% 17%	1980
September	1st to 10th	Night	19% 4 9% 22% 28% 19%	1800
	11th to 20th	Night	21% 5% 11% 23% 27% 14%	1800
	21st to end	Night	21% 3 8% 27% 31% 10%	2035
October	1st to 10th	Night	29% 6% 12% 26% 19% 8%	2160
	11th to 20th	Night	27% 5% 12% 30% 19% 7%	2160
	21st to end	Night	26% 5% 17% 29% 18% 4	2399
November	1st to 10th	Night	28% 6% 16% 27% 21% 3	2405
	11th to 20th	Night	31% 7% 15% 30% 14% 3	2599
	21st to end	Night	30% 5% 15% 31% 17% 2	2660
December	1st to 10th	Night	34% 7% 20% 24% 14% 1	2660
	11th to 20th	Night	29% 7% 21% 34% 9% 1	3272
	21st to end	Night	34% 7% 17% 25% 13% 3	4873

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	10% 22% 29% 25% 11% 2	270
	11th to 20th	Day	7% 16% 43% 24% 8% 2	270
	21st to end	Day	9% 14% 39% 28% 8% 1	297
February	1st to 10th	Day	7% 24% 45% 22% 2	270
	11th to 20th	Day	3 25% 50% 15% 6%	270
	21st to end	Day	12% 21% 40% 20% 7%	225
March	1st to 10th	Day	6% 20% 39% 27% 8%	295
	11th to 20th	Day	7% 19% 35% 29% 8% 1	420
	21st to end	Day	13% 14% 38% 29% 5% 2	462
April	1st to 10th	Day	13% 19% 34% 28% 6%	420
	11th to 20th	Day	14% 19% 35% 25% 6%	412
	21st to end	Day	17% 11% 27% 26% 14% 5%	420
May	1st to 10th	Day	14% 13% 27% 28% 15% 3	526
	11th to 20th	Day	17% 8% 23% 28% 20% 4	625
	21st to end	Day	13% 12% 24% 27% 20% 5%	679
June	1st to 10th	Day	5% 10% 23% 27% 27% 8%	630
	11th to 20th	Day	8% 13% 32% 31% 15% 2	630
	21st to end	Day	4 6% 27% 35% 24% 4	630
July	1st to 10th	Day	3 5% 20% 36% 30% 6%	621
	11th to 20th	Day	2 5% 23% 36% 30% 4	618
	21st to end	Day	4 3 17% 37% 33% 6%	648
August	1st to 10th	Day	5% 6% 24% 37% 24% 5%	447
	11th to 20th	Day	4 5% 25% 31% 26% 9%	437
	21st to end	Day	4 8% 25% 33% 22% 8%	495
September	1st to 10th	Day	6% 11% 26% 27% 23% 8%	450
	11th to 20th	Day	5% 11% 32% 25% 20% 6%	450
	21st to end	Day	9% 13% 29% 28% 15% 7%	321
October	1st to 10th	Day	8% 14% 26% 29% 18% 5%	270
	11th to 20th	Day	11% 17% 29% 32% 9% 2	270
	21st to end	Day	11% 20% 40% 22% 7% 1	297
November	1st to 10th	Day	10% 24% 41% 19% 4 2	270
	11th to 20th	Day	14% 24% 39% 20% 4	270
	21st to end	Day	6% 24% 44% 21% 5%	270
December	1st to 10th	Day	10% 20% 39% 19% 9% 1	270
	11th to 20th	Day	9% 32% 36% 19% 4	270
	21st to end	Day	16% 20% 33% 22% 7% 1	297
January	1st to 10th	Night	6% 19% 34% 30% 9% 1	950
	11th to 20th	Night	7% 18% 42% 24% 8% 1	936
	21st to end	Night	9% 11% 42% 31% 7% 1	836
February	1st to 10th	Night	7% 13% 47% 25% 7% 1	760
	11th to 20th	Night	8% 15% 39% 28% 9%	744
	21st to end	Night	7% 21% 40% 25% 6%	628
March	1st to 10th	Night	7% 12% 40% 31% 9% 1	722
	11th to 20th	Night	8% 10% 33% 39% 10%	720
	21st to end	Night	11% 13% 33% 33% 10% 1	720
April	1st to 10th	Night	12% 11% 37% 35% 5%	540
	11th to 20th	Night	14% 12% 33% 35% 6%	533
	21st to end	Night	12% 10% 26% 39% 12% 1	540
May	1st to 10th	Night	14% 9% 26% 33% 16% 2	540
	11th to 20th	Night	15% 5% 25% 35% 20% 1	531
	21st to end	Night	11% 8% 23% 41% 16% 1	584
June	1st to 10th	Night	6% 7% 24% 38% 23% 1	540
	11th to 20th	Night	7% 8% 34% 43% 8% 1	540
	21st to end	Night	4 4 25% 47% 19% 1	540
July	1st to 10th	Night	5% 3 17% 46% 27% 1	525
	11th to 20th	Night	2 3 25% 48% 21% 1	522
	21st to end	Night	4 2 16% 54% 24% 1	591
August	1st to 10th	Night	3 2 18% 53% 24% 1	537
	11th to 20th	Night	3 2 16% 50% 26% 1	534
	21st to end	Night	3 3 22% 47% 23% 2	594
September	1st to 10th	Night	6% 3 22% 44% 23% 2	540
	11th to 20th	Night	5% 6% 26% 41% 19% 2	540
	21st to end	Night	8% 6% 24% 40% 20% 3	648
October	1st to 10th	Night	12% 8% 28% 33% 18% 1	720
	11th to 20th	Night	9% 9% 30% 38% 12% 1	720
	21st to end	Night	10% 10% 36% 33% 10% 2	815
November	1st to 10th	Night	9% 13% 41% 28% 9% 1	925
	11th to 20th	Night	8% 20% 43% 23% 6%	950
	21st to end	Night	7% 17% 41% 28% 6% 1	950
December	1st to 10th	Night	10% 18% 39% 25% 7%	950
	11th to 20th	Night	8% 21% 40% 27% 4	950
	21st to end	Night	11% 23% 37% 22% 7%	1045

Page generated at 2024-02-27 04:30:13. Version ac07

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