Christmas Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Christmas Valley clear sky chart from 2005-11-06 to 2024-03-08.

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	6% 7% 3 6% 6% 3 5% 5% 5% 7% 47%	78526
	Night	6% 8% 3 6% 6% 4 5% 5% 6% 7% 43%	81056
Transparency	Day	35% 7% 12% 20% 17% 9%	78229
	Night	37% 8% 13% 20% 15% 6%	80874
Seeing	Day	9% 12% 21% 26% 22% 10%	13756
	Night	9% 8% 23% 37% 21% 2	23044

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	8% 12% 4 9% 10% 6% 7% 7% 8% 8% 23%	2539
	11th to 20th	Day	11% 15% 5% 11% 9% 5% 6% 6% 5% 6% 21%	2540
	21st to end	Day	7% 12% 5% 10% 8% 5% 7% 5% 6% 8% 26%	3014
February	1st to 10th	Day	7% 10% 4 8% 8% 4 5% 7% 7% 9% 31%	1710
	11th to 20th	Day	6% 10% 5% 7% 7% 4 6% 6% 7% 8% 35%	1718
	21st to end	Day	4 9% 5% 8% 8% 4 8% 6% 8% 10% 32%	1570
March	1st to 10th	Day	4 11% 6% 10% 7% 5% 8% 7% 8% 6% 28%	1871
	11th to 20th	Day	5% 11% 4 8% 8% 4 7% 6% 6% 9% 33%	1968
	21st to end	Day	7% 11% 5% 9% 9% 5% 7% 6% 6% 6% 30%	2294
April	1st to 10th	Day	8% 12% 5% 9% 6% 4 6% 5% 5% 7% 34%	2160
	11th to 20th	Day	9% 9% 5% 6% 6% 3 4 4 5% 7% 40%	2129
	21st to end	Day	6% 9% 4 5% 6% 4 4 4 5% 7% 46%	2160
May	1st to 10th	Day	6% 8% 2 5% 5% 3 5% 4 4 7% 49%	2506
	11th to 20th	Day	10% 7% 3 6% 6% 3 4 5% 5% 6% 45%	2477
	21st to end	Day	11% 8% 4 6% 7% 4 5% 6% 5% 6% 40%	2723
June	1st to 10th	Day	10% 6% 3 6% 6% 3 5% 5% 6% 6% 44%	2520
	11th to 20th	Day	6% 4 2 4 4 2 5% 4 5% 7% 58%	2520
	21st to end	Day	4 3 1 3 3 3 3 4 4 5% 69%	2520
July	1st to 10th	Day	2 1 1 2 2 2 3 3 4 6% 74%	2520
	11th to 20th	Day	2 1 1 2 2 1 2 3 4 5% 77%	2520
	21st to end	Day	2 2 1 1 2 2 3 2 3 5% 77%	2741
August	1st to 10th	Day	2 2 1 3 3 3 4 5% 5% 6% 68%	2394
	11th to 20th	Day	2 2 1 2 3 1 2 2 4 4 77%	2238
	21st to end	Day	2 1 2 2 2 2 2 3 4 79%	2376
September	1st to 10th	Day	2 2 1 2 3 2 3 2 3 4 77%	2160
	11th to 20th	Day	4 3 2 4 3 3 4 4 5% 6% 61%	2160
	21st to end	Day	5% 5% 2 4 4 3 3 4 4 7% 61%	1945
October	1st to 10th	Day	8% 7% 3 4 5% 2 4 4 4 6% 54%	1800
	11th to 20th	Day	6% 6% 1 5% 5% 3 5% 5% 6% 8% 50%	1800
	21st to end	Day	7% 6% 2 6% 7% 4 4 5% 6% 6% 47%	1886
November	1st to 10th	Day	8% 9% 3 7% 6% 3 5% 5% 8% 8% 38%	1674
	11th to 20th	Day	7% 7% 4 8% 7% 5% 7% 7% 7% 8% 33%	1611
	21st to end	Day	6% 9% 4 7% 7% 5% 6% 6% 6% 11% 34%	1520
December	1st to 10th	Day	4 9% 4 9% 9% 5% 6% 6% 7% 10% 32%	1520
	11th to 20th	Day	9% 10% 4 10% 9% 5% 7% 8% 8% 10% 20%	1928
	21st to end	Day	7% 11% 6% 12% 11% 5% 7% 7% 7% 8% 18%	2794
January	1st to 10th	Night	4 11% 5% 10% 10% 5% 8% 8% 8% 10% 21%	4406
	11th to 20th	Night	8% 12% 5% 9% 12% 5% 5% 5% 6% 8% 24%	4420
	21st to end	Night	9% 13% 5% 9% 8% 5% 6% 6% 7% 7% 26%	4645
February	1st to 10th	Night	6% 11% 4 8% 6% 4 5% 6% 7% 8% 35%	2470
	11th to 20th	Night	5% 10% 5% 8% 6% 3 5% 5% 6% 7% 38%	2348
	21st to end	Night	4 6% 5% 8% 7% 4 8% 7% 7% 8% 35%	1884
March	1st to 10th	Night	7% 10% 4 8% 7% 4 6% 5% 7% 9% 33%	2249
	11th to 20th	Night	7% 10% 4 7% 7% 4 6% 6% 7% 9% 34%	1990
	21st to end	Night	5% 10% 5% 8% 7% 5% 6% 6% 7% 9% 32%	2061
April	1st to 10th	Night	8% 12% 3 8% 6% 4 5% 4 5% 7% 38%	1800
	11th to 20th	Night	6% 9% 4 6% 6% 4 6% 4 5% 7% 42%	1779
	21st to end	Night	7% 10% 3 5% 4 2 4 5% 5% 9% 47%	1798
May	1st to 10th	Night	6% 6% 3 5% 4 3 4 5% 6% 7% 52%	1450
	11th to 20th	Night	8% 6% 3 5% 4 2 5% 4 7% 9% 47%	1416
	21st to end	Night	10% 7% 4 6% 6% 3 5% 4 5% 7% 44%	1552
June	1st to 10th	Night	9% 7% 3 5% 5% 3 4 5% 5% 7% 48%	1440
	11th to 20th	Night	8% 5% 2 3 4 3 3 3 5% 6% 59%	1440
	21st to end	Night	3 3 1 3 3 2 2 3 3 6% 72%	1440
July	1st to 10th	Night	1 1 2 3 2 4 4 4 5% 71%	1440
	11th to 20th	Night	1 1 1 2 2 1 2 2 3 5% 79%	1440
	21st to end	Night	1 2 1 1 2 1 3 2 3 5% 79%	1576
August	1st to 10th	Night	1 1 1 3 2 2 3 4 5% 7% 68%	1542
	11th to 20th	Night	1 2 1 1 2 1 3 2 4 5% 78%	1660
	21st to end	Night	2 2 1 2 2 2 2 3 3 4 79%	1980
September	1st to 10th	Night	2 1 1 2 2 2 3 2 3 5% 79%	1800
	11th to 20th	Night	2 2 1 2 3 2 4 3 5% 5% 70%	1800
	21st to end	Night	5% 5% 1 3 3 2 3 3 4 6% 65%	2014
October	1st to 10th	Night	6% 4 3 4 3 2 4 3 4 6% 61%	2160
	11th to 20th	Night	6% 4 2 4 5% 2 5% 4 5% 6% 57%	2160
	21st to end	Night	7% 7% 2 6% 5% 3 4 4 5% 7% 50%	2468
November	1st to 10th	Night	10% 10% 3 5% 5% 4 5% 5% 6% 7% 40%	2405
	11th to 20th	Night	8% 8% 3 8% 6% 5% 6% 7% 7% 10% 32%	2565
	21st to end	Night	7% 8% 3 6% 5% 3 7% 7% 7% 10% 36%	2660
December	1st to 10th	Night	6% 8% 4 9% 7% 4 7% 6% 7% 9% 33%	2660
	11th to 20th	Night	6% 11% 5% 9% 9% 5% 7% 9% 9% 8% 21%	3276
	21st to end	Night	6% 11% 4 11% 10% 6% 7% 7% 8% 8% 20%	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	50% 11% 17% 18% 4	2539
	11th to 20th	Day	61% 11% 9% 13% 5% 2	2540
	21st to end	Day	50% 10% 17% 16% 6% 1	3014
February	1st to 10th	Day	45% 10% 16% 19% 9%	1710
	11th to 20th	Day	42% 9% 17% 19% 10% 2	1727
	21st to end	Day	43% 12% 15% 19% 9% 2	1570
March	1st to 10th	Day	49% 9% 15% 18% 9% 1	1871
	11th to 20th	Day	42% 11% 15% 22% 10%	1968
	21st to end	Day	52% 9% 16% 14% 8% 1	2294
April	1st to 10th	Day	48% 8% 13% 18% 10% 3	2160
	11th to 20th	Day	43% 6% 15% 19% 13% 4	2132
	21st to end	Day	36% 7% 15% 25% 15% 2	2160
May	1st to 10th	Day	34% 6% 13% 28% 17% 2	2506
	11th to 20th	Day	40% 5% 13% 23% 15% 3	2480
	21st to end	Day	42% 8% 15% 22% 12% 1	2724
June	1st to 10th	Day	37% 8% 12% 27% 15% 1	2520
	11th to 20th	Day	26% 5% 11% 29% 23% 5%	2520
	21st to end	Day	19% 3 8% 24% 31% 14%	2520
July	1st to 10th	Day	13% 3 8% 20% 27% 29%	2451
	11th to 20th	Day	11% 3 6% 17% 27% 36%	2445
	21st to end	Day	13% 2 4 12% 33% 36%	2589
August	1st to 10th	Day	16% 4 8% 21% 30% 21%	2377
	11th to 20th	Day	12% 3 7% 19% 32% 26%	2238
	21st to end	Day	11% 2 6% 20% 41% 20%	2376
September	1st to 10th	Day	13% 3 5% 18% 33% 28%	2160
	11th to 20th	Day	21% 5% 11% 21% 27% 16%	2160
	21st to end	Day	25% 4 9% 24% 24% 13%	1945
October	1st to 10th	Day	33% 5% 10% 17% 22% 12%	1800
	11th to 20th	Day	30% 6% 13% 24% 20% 8%	1800
	21st to end	Day	34% 7% 13% 21% 21% 4	1886
November	1st to 10th	Day	40% 7% 14% 23% 16% 1	1674
	11th to 20th	Day	45% 10% 19% 16% 10% 1	1611
	21st to end	Day	41% 8% 17% 17% 15% 2	1520
December	1st to 10th	Day	44% 11% 15% 21% 8% 1	1520
	11th to 20th	Day	51% 12% 14% 16% 7%	1928
	21st to end	Day	54% 15% 12% 15% 4	2794
January	1st to 10th	Night	50% 12% 17% 16% 4	4406
	11th to 20th	Night	53% 10% 13% 15% 7% 3	4420
	21st to end	Night	52% 10% 15% 16% 7%	4645
February	1st to 10th	Night	43% 9% 17% 18% 11% 1	2470
	11th to 20th	Night	41% 9% 16% 21% 11% 2	2350
	21st to end	Night	41% 11% 17% 20% 10% 1	1884
March	1st to 10th	Night	45% 9% 16% 17% 11% 2	2249
	11th to 20th	Night	43% 9% 15% 24% 9%	1990
	21st to end	Night	46% 11% 17% 19% 7%	2061
April	1st to 10th	Night	45% 8% 17% 18% 11% 1	1800
	11th to 20th	Night	40% 8% 15% 20% 14% 2	1779
	21st to end	Night	35% 8% 17% 25% 13% 2	1798
May	1st to 10th	Night	30% 8% 12% 33% 16% 2	1450
	11th to 20th	Night	33% 8% 14% 28% 13% 3	1416
	21st to end	Night	40% 8% 16% 24% 11% 1	1552
June	1st to 10th	Night	35% 8% 15% 27% 14%	1440
	11th to 20th	Night	27% 6% 10% 33% 18% 5%	1440
	21st to end	Night	16% 4 11% 30% 30% 9%	1440
July	1st to 10th	Night	14% 5% 8% 23% 25% 25%	1400
	11th to 20th	Night	8% 3 7% 19% 31% 32%	1392
	21st to end	Night	10% 2 5% 13% 35% 34%	1488
August	1st to 10th	Night	14% 4 8% 27% 31% 16%	1534
	11th to 20th	Night	10% 2 8% 23% 32% 24%	1660
	21st to end	Night	11% 3 6% 24% 34% 23%	1980
September	1st to 10th	Night	10% 3 5% 21% 33% 28%	1800
	11th to 20th	Night	17% 4 10% 24% 29% 17%	1800
	21st to end	Night	22% 4 9% 22% 24% 18%	2014
October	1st to 10th	Night	26% 5% 12% 21% 23% 13%	2160
	11th to 20th	Night	27% 6% 14% 23% 22% 9%	2160
	21st to end	Night	32% 7% 17% 19% 20% 5%	2468
November	1st to 10th	Night	42% 8% 12% 20% 16% 3	2405
	11th to 20th	Night	43% 8% 16% 22% 10% 1	2565
	21st to end	Night	37% 9% 16% 18% 17% 3	2660
December	1st to 10th	Night	43% 11% 15% 20% 10% 1	2660
	11th to 20th	Night	49% 11% 15% 17% 8%	3276
	21st to end	Night	51% 12% 13% 16% 8% 1	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	17% 19% 21% 26% 13% 3	180
	11th to 20th	Day	17% 14% 22% 27% 14% 6%	180
	21st to end	Day	10% 13% 24% 26% 20% 6%	327
February	1st to 10th	Day	9% 19% 25% 27% 18% 3	370
	11th to 20th	Day	16% 17% 24% 26% 13% 4	390
	21st to end	Day	9% 19% 28% 27% 15% 3	382
March	1st to 10th	Day	12% 19% 31% 28% 10% 1	449
	11th to 20th	Day	15% 16% 22% 29% 16% 3	420
	21st to end	Day	13% 18% 26% 27% 14% 2	462
April	1st to 10th	Day	14% 19% 24% 25% 13% 6%	420
	11th to 20th	Day	13% 20% 27% 23% 12% 6%	412
	21st to end	Day	9% 16% 28% 26% 15% 6%	420
May	1st to 10th	Day	9% 16% 24% 27% 17% 6%	423
	11th to 20th	Day	19% 13% 20% 21% 18% 9%	448
	21st to end	Day	13% 10% 18% 25% 23% 11%	485
June	1st to 10th	Day	9% 11% 20% 24% 22% 13%	450
	11th to 20th	Day	8% 17% 22% 25% 23% 5%	450
	21st to end	Day	3 5% 18% 29% 28% 16%	450
July	1st to 10th	Day	3 3 16% 34% 31% 12%	446
	11th to 20th	Day	2 3 18% 30% 32% 15%	444
	21st to end	Day	3 2 12% 29% 37% 17%	487
August	1st to 10th	Day	2 3 17% 27% 34% 18%	447
	11th to 20th	Day	1 3 13% 26% 30% 26%	437
	21st to end	Day	2 4 14% 25% 36% 19%	495
September	1st to 10th	Day	2 3 14% 28% 35% 18%	450
	11th to 20th	Day	5% 6% 16% 27% 28% 17%	450
	21st to end	Day	8% 8% 18% 24% 32% 11%	450
October	1st to 10th	Day	12% 9% 19% 25% 20% 15%	450
	11th to 20th	Day	10% 11% 20% 20% 25% 14%	450
	21st to end	Day	10% 14% 23% 23% 19% 11%	401
November	1st to 10th	Day	15% 13% 17% 31% 14% 9%	270
	11th to 20th	Day	7% 13% 20% 30% 22% 7%	223
	21st to end	Day	12% 14% 15% 23% 29% 6%	180
December	1st to 10th	Day	10% 10% 26% 24% 20% 11%	180
	11th to 20th	Day	13% 14% 26% 31% 16% 1	180
	21st to end	Day	10% 21% 22% 26% 18% 3	198
January	1st to 10th	Night	13% 11% 26% 32% 16% 2	760
	11th to 20th	Night	10% 13% 23% 29% 22% 3	760
	21st to end	Night	12% 7% 22% 34% 21% 3	836
February	1st to 10th	Night	10% 9% 30% 34% 16% 1	760
	11th to 20th	Night	10% 11% 26% 34% 17% 1	744
	21st to end	Night	7% 11% 29% 39% 14% 1	628
March	1st to 10th	Night	11% 12% 30% 32% 14% 2	750
	11th to 20th	Night	11% 10% 23% 37% 17% 2	720
	21st to end	Night	9% 12% 31% 34% 14%	792
April	1st to 10th	Night	13% 10% 25% 36% 14% 1	720
	11th to 20th	Night	8% 10% 31% 29% 17% 4	711
	21st to end	Night	11% 10% 27% 35% 16% 1	718
May	1st to 10th	Night	9% 7% 29% 37% 17% 1	370
	11th to 20th	Night	10% 6% 21% 38% 24% 1	354
	21st to end	Night	11% 7% 21% 39% 20% 2	389
June	1st to 10th	Night	11% 5% 23% 41% 20% 1	360
	11th to 20th	Night	8% 7% 31% 40% 13% 1	360
	21st to end	Night	3 1 25% 49% 20% 1	360
July	1st to 10th	Night	2 2 23% 49% 23%	350
	11th to 20th	Night	2 1 27% 53% 16%	348
	21st to end	Night	1 2 24% 51% 22%	394
August	1st to 10th	Night	3 1 16% 49% 30% 3	468
	11th to 20th	Night	2 1 13% 44% 38% 3	592
	21st to end	Night	3 2 15% 47% 31% 2	792
September	1st to 10th	Night	2 2 13% 45% 35% 3	720
	11th to 20th	Night	3 3 15% 35% 39% 5%	720
	21st to end	Night	6% 4 16% 34% 34% 5%	720
October	1st to 10th	Night	7% 3 20% 38% 28% 4	720
	11th to 20th	Night	8% 6% 18% 37% 28% 3	720
	21st to end	Night	10% 7% 19% 36% 21% 6%	792
November	1st to 10th	Night	12% 8% 22% 39% 17% 2	740
	11th to 20th	Night	11% 13% 22% 33% 19% 2	760
	21st to end	Night	11% 9% 20% 35% 21% 4	760
December	1st to 10th	Night	12% 9% 22% 35% 19% 4	760
	11th to 20th	Night	11% 11% 24% 33% 19% 1	760
	21st to end	Night	12% 14% 29% 31% 12% 1	836

Page generated at 2024-03-05 04:24:04. Version ac07

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