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 2024-11-02.

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% 7% 2 6% 5% 4 4 4 5% 6% 51%	101501
	Night	5% 8% 3 7% 5% 5% 5% 4 6% 7% 46%	97642
Transparency	Day	31% 7% 11% 20% 19% 13%	101244
	Night	34% 7% 13% 21% 17% 8%	97488
Seeing	Day	9% 11% 21% 26% 23% 10%	14704
	Night	9% 8% 23% 37% 21% 2	23798

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	7% 12% 3 10% 9% 7% 7% 6% 8% 8% 23%	2539
	11th to 20th	Day	10% 15% 5% 13% 8% 7% 5% 5% 5% 6% 21%	2540
	21st to end	Day	7% 13% 4 12% 6% 7% 6% 4 6% 8% 26%	3014
February	1st to 10th	Day	6% 10% 4 9% 7% 6% 5% 6% 8% 9% 31%	1710
	11th to 20th	Day	6% 12% 4 8% 6% 5% 5% 5% 7% 8% 35%	1718
	21st to end	Day	3 11% 4 9% 7% 6% 7% 5% 8% 9% 32%	1570
March	1st to 10th	Day	3 11% 4 11% 7% 7% 7% 7% 8% 8% 25%	3138
	11th to 20th	Day	3 8% 3 6% 5% 5% 5% 4 6% 8% 49%	3478
	21st to end	Day	5% 11% 4 11% 8% 7% 6% 5% 7% 7% 28%	4031
April	1st to 10th	Day	7% 13% 4 10% 5% 5% 5% 4 5% 7% 34%	2280
	11th to 20th	Day	8% 11% 4 7% 5% 5% 4 4 6% 7% 40%	2249
	21st to end	Day	6% 10% 3 6% 5% 5% 4 3 5% 8% 45%	2280
May	1st to 10th	Day	7% 10% 3 7% 5% 5% 4 4 5% 6% 44%	4406
	11th to 20th	Day	5% 4 2 4 3 3 3 3 4 5% 63%	4377
	21st to end	Day	6% 8% 2 6% 5% 4 5% 3 5% 6% 50%	4813
June	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 5% 6% 6% 44%	2660
	11th to 20th	Day	6% 4 2 4 4 3 4 3 5% 6% 58%	2660
	21st to end	Day	3 3 1 3 3 3 3 3 4 5% 69%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 2 3 3 84%	4420
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 5% 76%	4420
	21st to end	Day	1 1 1 2 2 2 3 2 3 4 80%	4790
August	1st to 10th	Day	3 3 1 4 2 3 3 3 5% 7% 65%	4196
	11th to 20th	Day	1 2 1 3 2 2 3 2 4 5% 74%	3914
	21st to end	Day	2 2 1 3 2 3 3 2 4 5% 75%	4180
September	1st to 10th	Day	2 2 1 3 2 2 3 2 3 5% 76%	2280
	11th to 20th	Day	4 4 2 5% 3 3 4 3 5% 6% 61%	2280
	21st to end	Day	5% 5% 2 5% 2 3 3 3 4 7% 62%	2052
October	1st to 10th	Day	8% 7% 2 5% 4 3 4 3 4 6% 55%	1900
	11th to 20th	Day	6% 6% 1 6% 4 5% 4 4 6% 8% 49%	1900
	21st to end	Day	7% 6% 2 7% 6% 5% 4 4 6% 6% 46%	1990
November	1st to 10th	Day	8% 10% 3 8% 5% 4 4 4 8% 8% 38%	1683
	11th to 20th	Day	6% 8% 3 10% 6% 7% 7% 6% 6% 8% 33%	1611
	21st to end	Day	6% 10% 3 8% 7% 5% 5% 5% 6% 11% 34%	1520
December	1st to 10th	Day	4 10% 3 11% 7% 7% 5% 5% 8% 9% 32%	1520
	11th to 20th	Day	9% 11% 3 12% 8% 6% 8% 6% 8% 10% 20%	1928
	21st to end	Day	6% 12% 6% 13% 9% 7% 8% 5% 7% 8% 18%	2794
January	1st to 10th	Night	4 11% 4 12% 9% 7% 7% 6% 8% 10% 21%	4406
	11th to 20th	Night	8% 13% 4 11% 10% 6% 5% 4 6% 8% 24%	4420
	21st to end	Night	9% 13% 5% 10% 6% 6% 6% 4 7% 7% 26%	4645
February	1st to 10th	Night	5% 11% 4 9% 5% 5% 6% 5% 7% 8% 35%	2470
	11th to 20th	Night	5% 11% 5% 9% 5% 5% 5% 4 6% 7% 38%	2348
	21st to end	Night	4 7% 5% 9% 7% 6% 6% 6% 8% 8% 35%	1884
March	1st to 10th	Night	4 13% 4 8% 7% 6% 7% 6% 8% 10% 26%	3736
	11th to 20th	Night	4 9% 2 6% 4 4 5% 5% 7% 8% 47%	3500
	21st to end	Night	4 10% 4 10% 6% 8% 7% 5% 8% 8% 29%	3621
April	1st to 10th	Night	7% 12% 3 8% 5% 5% 4 4 5% 7% 39%	1900
	11th to 20th	Night	6% 9% 3 7% 6% 6% 4 4 4 7% 44%	1879
	21st to end	Night	7% 10% 3 5% 3 3 4 4 6% 9% 46%	1897
May	1st to 10th	Night	8% 8% 2 6% 3 4 5% 4 6% 6% 49%	2550
	11th to 20th	Night	5% 4 2 4 2 2 3 2 5% 6% 66%	2516
	21st to end	Night	6% 6% 2 5% 4 3 4 3 4 6% 57%	2762
June	1st to 10th	Night	8% 7% 2 6% 4 4 5% 4 5% 7% 48%	1520
	11th to 20th	Night	7% 5% 2 3 3 4 3 3 5% 6% 59%	1520
	21st to end	Night	3 3 1 3 2 3 2 2 3 5% 73%	1520
July	1st to 10th	Night	1 1 1 2 2 2 2 3 3 83%	2540
	11th to 20th	Night	2 1 1 2 2 2 2 3 3 5% 77%	2540
	21st to end	Night	1 1 1 2 1 2 3 2 3 4 79%	2761
August	1st to 10th	Night	2 2 1 4 3 3 3 3 6% 6% 66%	2737
	11th to 20th	Night	1 2 1 3 3 2 3 2 4 4 74%	2926
	21st to end	Night	2 2 1 3 2 2 2 2 3 5% 77%	3498
September	1st to 10th	Night	2 1 1 2 2 2 2 2 3 5% 78%	1900
	11th to 20th	Night	2 3 2 3 3 3 4 2 5% 5% 69%	1900
	21st to end	Night	4 5% 1 3 3 3 3 2 4 6% 66%	2127
October	1st to 10th	Night	5% 5% 2 5% 3 3 3 2 4 6% 62%	2280
	11th to 20th	Night	6% 4 2 5% 4 4 4 3 5% 6% 58%	2280
	21st to end	Night	6% 7% 2 7% 4 4 4 3 5% 7% 50%	2606
November	1st to 10th	Night	9% 10% 3 6% 5% 5% 5% 4 6% 7% 40%	2430
	11th to 20th	Night	7% 9% 3 9% 5% 7% 6% 5% 7% 10% 32%	2565
	21st to end	Night	7% 9% 3 6% 5% 5% 7% 6% 7% 10% 36%	2660
December	1st to 10th	Night	6% 9% 4 10% 6% 6% 6% 5% 7% 8% 33%	2660
	11th to 20th	Night	6% 12% 5% 10% 8% 7% 7% 7% 9% 8% 21%	3276
	21st to end	Night	6% 12% 4 13% 9% 8% 7% 6% 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	44% 11% 15% 18% 12% 1	3138
	11th to 20th	Day	28% 9% 15% 36% 12%	3478
	21st to end	Day	48% 11% 15% 20% 6% 1	4031
April	1st to 10th	Day	47% 8% 13% 19% 10% 3	2280
	11th to 20th	Day	42% 6% 15% 19% 13% 3	2252
	21st to end	Day	36% 8% 15% 25% 15% 2	2280
May	1st to 10th	Day	35% 7% 13% 26% 17% 2	4406
	11th to 20th	Day	23% 4 10% 24% 32% 8%	4380
	21st to end	Day	32% 7% 16% 26% 17% 2	4814
June	1st to 10th	Day	37% 9% 12% 27% 15% 1	2660
	11th to 20th	Day	26% 5% 10% 29% 24% 6%	2660
	21st to end	Day	18% 3 8% 25% 32% 14%	2660
July	1st to 10th	Day	8% 2 5% 11% 17% 57%	4351
	11th to 20th	Day	13% 2 4 10% 20% 51%	4345
	21st to end	Day	10% 2 3 12% 35% 37%	4639
August	1st to 10th	Day	19% 3 5% 13% 27% 33%	4180
	11th to 20th	Day	13% 3 5% 20% 37% 23%	3953
	21st to end	Day	14% 2 5% 25% 29% 25%	4179
September	1st to 10th	Day	13% 3 5% 18% 34% 28%	2280
	11th to 20th	Day	22% 5% 11% 21% 26% 15%	2280
	21st to end	Day	24% 4 9% 24% 25% 13%	2052
October	1st to 10th	Day	31% 5% 10% 18% 23% 13%	1900
	11th to 20th	Day	30% 6% 13% 24% 20% 7%	1900
	21st to end	Day	35% 6% 13% 21% 21% 3	1990
November	1st to 10th	Day	40% 6% 14% 23% 16% 1	1683
	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	44% 9% 15% 20% 11% 1	3736
	11th to 20th	Night	30% 7% 12% 37% 14%	3500
	21st to end	Night	46% 12% 15% 19% 7% 1	3621
April	1st to 10th	Night	44% 8% 18% 19% 11% 1	1900
	11th to 20th	Night	39% 8% 16% 21% 14% 2	1879
	21st to end	Night	34% 8% 18% 26% 13% 2	1897
May	1st to 10th	Night	32% 7% 14% 28% 18% 1	2550
	11th to 20th	Night	19% 5% 10% 30% 33% 2	2516
	21st to end	Night	28% 6% 22% 31% 12% 1	2762
June	1st to 10th	Night	35% 8% 15% 27% 15%	1520
	11th to 20th	Night	26% 6% 10% 33% 19% 5%	1520
	21st to end	Night	16% 4 11% 29% 31% 10%	1520
July	1st to 10th	Night	8% 3 5% 13% 19% 52%	2500
	11th to 20th	Night	11% 2 4 12% 26% 44%	2492
	21st to end	Night	10% 2 4 14% 34% 36%	2674
August	1st to 10th	Night	18% 3 5% 17% 34% 23%	2729
	11th to 20th	Night	14% 2 5% 22% 39% 18%	2953
	21st to end	Night	12% 2 7% 28% 25% 25%	3498
September	1st to 10th	Night	10% 2 5% 21% 34% 28%	1900
	11th to 20th	Night	18% 4 10% 24% 27% 16%	1900
	21st to end	Night	21% 4 9% 22% 26% 17%	2127
October	1st to 10th	Night	25% 5% 11% 21% 23% 14%	2280
	11th to 20th	Night	27% 5% 14% 23% 22% 8%	2280
	21st to end	Night	32% 6% 16% 20% 20% 5%	2606
November	1st to 10th	Night	43% 7% 12% 20% 15% 3	2430
	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% 26% 11% 1	460
	11th to 20th	Day	14% 16% 22% 28% 16% 4	460
	21st to end	Day	13% 18% 27% 27% 13% 2	506
April	1st to 10th	Day	13% 18% 24% 27% 12% 6%	460
	11th to 20th	Day	12% 19% 27% 23% 13% 6%	452
	21st to end	Day	8% 17% 27% 26% 16% 6%	460
May	1st to 10th	Day	10% 17% 24% 27% 17% 6%	463
	11th to 20th	Day	17% 13% 20% 22% 18% 10%	488
	21st to end	Day	12% 10% 18% 24% 23% 12%	529
June	1st to 10th	Day	9% 11% 21% 23% 22% 13%	490
	11th to 20th	Day	7% 17% 23% 24% 23% 6%	490
	21st to end	Day	3 5% 19% 28% 28% 17%	490
July	1st to 10th	Day	3 3 16% 33% 32% 13%	486
	11th to 20th	Day	2 3 19% 30% 32% 15%	484
	21st to end	Day	2 2 12% 30% 37% 17%	531
August	1st to 10th	Day	3 3 17% 26% 34% 18%	487
	11th to 20th	Day	1 4 15% 25% 31% 25%	477
	21st to end	Day	2 5% 13% 25% 35% 20%	539
September	1st to 10th	Day	2 3 13% 28% 35% 19%	490
	11th to 20th	Day	6% 7% 17% 26% 28% 17%	490
	21st to end	Day	7% 7% 17% 24% 31% 13%	490
October	1st to 10th	Day	11% 8% 19% 26% 21% 15%	490
	11th to 20th	Day	10% 11% 19% 21% 26% 13%	490
	21st to end	Day	10% 15% 23% 25% 18% 10%	439
November	1st to 10th	Day	16% 14% 16% 31% 14% 9%	273
	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% 1	760
	11th to 20th	Night	11% 10% 23% 36% 18% 2	760
	21st to end	Night	9% 12% 31% 35% 13%	836
April	1st to 10th	Night	13% 10% 25% 36% 15% 1	760
	11th to 20th	Night	8% 11% 31% 30% 17% 3	751
	21st to end	Night	10% 10% 27% 35% 16% 1	757
May	1st to 10th	Night	10% 7% 29% 37% 16% 1	390
	11th to 20th	Night	10% 6% 22% 37% 24% 1	374
	21st to end	Night	10% 7% 22% 39% 20% 2	411
June	1st to 10th	Night	11% 4 23% 42% 19% 1	380
	11th to 20th	Night	8% 7% 31% 41% 13% 1	380
	21st to end	Night	3 2 25% 50% 20% 1	380
July	1st to 10th	Night	2 2 23% 51% 23%	370
	11th to 20th	Night	2 1 27% 53% 16%	368
	21st to end	Night	1 1 25% 52% 21%	416
August	1st to 10th	Night	3 1 15% 50% 28% 3	495
	11th to 20th	Night	2 1 13% 45% 36% 3	626
	21st to end	Night	3 3 14% 47% 31% 2	836
September	1st to 10th	Night	2 2 13% 46% 35% 3	760
	11th to 20th	Night	3 3 16% 36% 37% 5%	760
	21st to end	Night	6% 4 16% 35% 34% 5%	760
October	1st to 10th	Night	7% 3 20% 39% 29% 3	760
	11th to 20th	Night	8% 6% 18% 38% 28% 3	760
	21st to end	Night	10% 7% 20% 37% 21% 6%	836
November	1st to 10th	Night	12% 9% 22% 38% 17% 2	748
	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

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