WYA Eastern Lassen Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WYA Eastern Lassen Site clear sky chart from 2005-11-06 to 2024-11-08.

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	3 5% 2 5% 4 4 4 3 5% 7% 58%	105231
	Night	3 6% 2 6% 4 4 4 3 5% 7% 55%	102572
Transparency	Day	24% 5% 8% 20% 23% 19%	104972
	Night	27% 5% 10% 21% 22% 15%	102420
Seeing	Day	6% 9% 21% 28% 25% 10%	14906
	Night	6% 6% 20% 39% 25% 5%	24145

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	2 11% 5% 12% 8% 7% 6% 5% 6% 10% 30%	2539
	11th to 20th	Day	4 10% 6% 13% 8% 6% 6% 5% 6% 9% 28%	2540
	21st to end	Day	4 14% 6% 13% 7% 5% 5% 4 5% 9% 28%	3110
February	1st to 10th	Day	4 7% 4 8% 5% 6% 5% 5% 6% 9% 42%	1710
	11th to 20th	Day	2 6% 3 8% 6% 5% 6% 6% 6% 12% 42%	1800
	21st to end	Day	2 7% 3 7% 7% 6% 5% 5% 6% 9% 41%	1570
March	1st to 10th	Day	3 8% 5% 11% 8% 7% 7% 5% 7% 7% 31%	3138
	11th to 20th	Day	2 5% 2 6% 4 4 4 3 5% 10% 55%	3428
	21st to end	Day	2 8% 4 8% 6% 6% 6% 5% 8% 10% 38%	4066
April	1st to 10th	Day	3 8% 3 8% 6% 5% 4 5% 6% 8% 44%	2280
	11th to 20th	Day	4 6% 2 6% 4 5% 5% 4 6% 8% 50%	2249
	21st to end	Day	3 6% 2 5% 4 4 4 4 7% 9% 52%	2280
May	1st to 10th	Day	2 6% 3 5% 3 2 3 3 4 8% 61%	4141
	11th to 20th	Day	3 3 1 3 3 2 2 2 4 7% 70%	4377
	21st to end	Day	3 4 2 5% 4 3 3 3 5% 7% 61%	4813
June	1st to 10th	Day	3 4 2 6% 5% 4 5% 5% 6% 8% 52%	2660
	11th to 20th	Day	3 3 1 4 3 3 3 3 4 6% 68%	2660
	21st to end	Day	2 2 1 3 3 3 3 3 3 4 74%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 3 3 86%	4420
	11th to 20th	Day	2 2 1 3 2 2 3 2 3 4 76%	4420
	21st to end	Day	1 1 1 3 2 2 3 3 4 6% 73%	4790
August	1st to 10th	Day	2 2 1 3 3 2 3 3 5% 6% 68%	4101
	11th to 20th	Day	1 1 1 2 2 2 3 2 2 4 81%	3765
	21st to end	Day	2 1 1 2 1 2 1 2 2 3 83%	4180
September	1st to 10th	Day	2 1 2 1 2 2 2 2 4 81%	2280
	11th to 20th	Day	3 3 1 3 2 2 3 3 4 5% 71%	2258
	21st to end	Day	2 3 1 3 2 2 2 2 4 6% 72%	2090
October	1st to 10th	Day	3 3 1 2 3 3 3 2 4 6% 70%	3190
	11th to 20th	Day	5% 3 2 4 3 3 3 3 4 6% 64%	3161
	21st to end	Day	2 3 2 5% 3 4 4 4 6% 9% 57%	3305
November	1st to 10th	Day	6% 7% 2 6% 5% 3 5% 5% 6% 8% 48%	1737
	11th to 20th	Day	3 7% 2 6% 5% 5% 7% 7% 7% 8% 43%	1710
	21st to end	Day	2 6% 3 7% 5% 5% 5% 4 7% 10% 47%	1561
December	1st to 10th	Day	4 9% 4 9% 5% 4 6% 4 6% 7% 42%	1520
	11th to 20th	Day	6% 10% 4 11% 7% 6% 6% 6% 8% 8% 28%	1928
	21st to end	Day	3 10% 3 10% 7% 6% 6% 5% 6% 12% 32%	2794
January	1st to 10th	Night	3 9% 4 10% 6% 6% 6% 5% 8% 9% 33%	4406
	11th to 20th	Night	2 11% 6% 12% 7% 6% 5% 5% 6% 9% 30%	4420
	21st to end	Night	5% 13% 5% 11% 7% 6% 5% 4 6% 8% 29%	4552
February	1st to 10th	Night	3 7% 3 9% 5% 5% 5% 5% 7% 8% 44%	2470
	11th to 20th	Night	2 8% 2 8% 6% 5% 5% 5% 6% 9% 44%	2267
	21st to end	Night	2 9% 3 6% 6% 5% 5% 4 7% 9% 43%	1884
March	1st to 10th	Night	2 9% 6% 12% 7% 7% 6% 4 6% 8% 33%	3736
	11th to 20th	Night	2 7% 3 7% 4 3 4 4 5% 6% 56%	3535
	21st to end	Night	3 8% 3 8% 7% 7% 6% 5% 7% 10% 35%	3586
April	1st to 10th	Night	3 8% 3 6% 4 5% 6% 4 7% 8% 46%	1900
	11th to 20th	Night	3 7% 3 6% 4 5% 4 3 5% 7% 53%	1879
	21st to end	Night	4 5% 1 4 3 4 4 4 6% 8% 56%	1900
May	1st to 10th	Night	3 5% 2 6% 4 3 3 3 4 5% 62%	2822
	11th to 20th	Night	2 3 1 4 2 2 3 2 4 5% 71%	2516
	21st to end	Night	3 4 1 4 3 3 4 3 5% 7% 63%	2762
June	1st to 10th	Night	3 6% 2 5% 4 4 3 4 6% 7% 56%	1520
	11th to 20th	Night	3 3 1 3 1 2 3 3 4 6% 70%	1520
	21st to end	Night	2 2 1 3 3 3 3 3 4 5% 72%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 1 3 3 86%	2540
	11th to 20th	Night	3 2 1 3 2 2 2 2 3 4 76%	2540
	21st to end	Night	2 1 1 2 3 2 3 2 4 4 76%	2761
August	1st to 10th	Night	3 4 1 3 2 2 3 3 5% 6% 69%	2835
	11th to 20th	Night	2 1 2 1 2 2 1 3 3 84%	3083
	21st to end	Night	1 2 1 2 1 1 1 1 2 3 85%	3498
September	1st to 10th	Night	2 1 1 2 1 2 2 1 3 3 81%	1900
	11th to 20th	Night	2 3 1 3 2 2 2 2 3 6% 74%	1920
	21st to end	Night	2 2 1 3 2 2 2 2 4 6% 74%	2090
October	1st to 10th	Night	2 3 1 3 3 2 2 1 2 4 76%	3787
	11th to 20th	Night	1 3 1 4 2 2 2 3 4 6% 72%	3777
	21st to end	Night	3 4 2 5% 3 4 3 3 5% 7% 59%	4259
November	1st to 10th	Night	5% 6% 2 6% 5% 3 4 5% 8% 8% 47%	2502
	11th to 20th	Night	3 6% 2 6% 4 4 4 5% 8% 8% 48%	2470
	21st to end	Night	2 6% 3 7% 5% 5% 4 4 6% 9% 49%	2617
December	1st to 10th	Night	5% 8% 4 9% 4 4 5% 4 5% 9% 44%	2660
	11th to 20th	Night	6% 10% 5% 11% 6% 6% 5% 5% 8% 10% 28%	3276
	21st to end	Night	4 9% 4 10% 7% 6% 6% 5% 7% 10% 32%	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	43% 10% 16% 24% 6% 1	2539
	11th to 20th	Day	49% 11% 16% 14% 9% 2	2540
	21st to end	Day	51% 9% 11% 21% 8% 1	3110
February	1st to 10th	Day	34% 8% 14% 27% 12% 5%	1710
	11th to 20th	Day	32% 7% 17% 25% 17% 3	1810
	21st to end	Day	34% 9% 15% 23% 14% 3	1570
March	1st to 10th	Day	41% 11% 13% 19% 15% 1	3138
	11th to 20th	Day	23% 6% 10% 40% 19% 2	3428
	21st to end	Day	35% 10% 16% 28% 10% 2	4066
April	1st to 10th	Day	34% 8% 15% 26% 16% 2	2280
	11th to 20th	Day	29% 7% 13% 30% 19% 4	2252
	21st to end	Day	26% 5% 15% 32% 20% 2	2280
May	1st to 10th	Day	21% 5% 10% 34% 27% 3	4141
	11th to 20th	Day	15% 3 6% 20% 48% 8%	4380
	21st to end	Day	21% 5% 9% 40% 21% 3	4814
June	1st to 10th	Day	27% 6% 8% 25% 28% 5%	2660
	11th to 20th	Day	17% 4 6% 22% 35% 16%	2660
	21st to end	Day	14% 3 3 14% 34% 32%	2660
July	1st to 10th	Day	6% 2 2 6% 15% 70%	4351
	11th to 20th	Day	14% 2 1 5% 16% 63%	4345
	21st to end	Day	13% 2 1 7% 27% 50%	4639
August	1st to 10th	Day	17% 2 1 7% 20% 53%	4085
	11th to 20th	Day	10% 2 1 6% 33% 47%	3801
	21st to end	Day	9% 1 1 11% 39% 39%	4179
September	1st to 10th	Day	9% 1 1 10% 32% 46%	2280
	11th to 20th	Day	15% 3 5% 18% 32% 26%	2258
	21st to end	Day	14% 3 4 23% 32% 24%	2090
October	1st to 10th	Day	17% 2 4 14% 34% 30%	3190
	11th to 20th	Day	21% 3 4 25% 38% 10%	3161
	21st to end	Day	24% 3 7% 31% 27% 9%	3305
November	1st to 10th	Day	30% 7% 12% 24% 21% 6%	1737
	11th to 20th	Day	31% 10% 13% 25% 17% 3	1710
	21st to end	Day	29% 6% 13% 26% 22% 4	1561
December	1st to 10th	Day	38% 8% 12% 23% 16% 3	1520
	11th to 20th	Day	49% 8% 12% 19% 10% 1	1928
	21st to end	Day	42% 8% 18% 21% 12% 1	2794
January	1st to 10th	Night	40% 9% 19% 23% 8% 1	4406
	11th to 20th	Night	47% 9% 13% 17% 11% 3	4420
	21st to end	Night	50% 8% 12% 18% 10% 2	4552
February	1st to 10th	Night	32% 7% 14% 25% 18% 3	2470
	11th to 20th	Night	33% 7% 15% 24% 18% 3	2268
	21st to end	Night	35% 7% 15% 25% 15% 4	1884
March	1st to 10th	Night	43% 9% 14% 18% 14% 2	3736
	11th to 20th	Night	26% 6% 9% 39% 19% 2	3535
	21st to end	Night	38% 9% 17% 25% 9% 1	3586
April	1st to 10th	Night	32% 8% 14% 29% 13% 4	1900
	11th to 20th	Night	29% 7% 15% 25% 20% 5%	1879
	21st to end	Night	24% 5% 15% 34% 18% 3	1900
May	1st to 10th	Night	21% 7% 9% 35% 23% 6%	2822
	11th to 20th	Night	16% 3 7% 22% 44% 9%	2516
	21st to end	Night	20% 4 13% 38% 23% 3	2762
June	1st to 10th	Night	26% 6% 11% 31% 22% 4	1520
	11th to 20th	Night	15% 4 8% 23% 38% 12%	1520
	21st to end	Night	16% 3 4 16% 30% 30%	1520
July	1st to 10th	Night	6% 2 2 8% 15% 67%	2500
	11th to 20th	Night	16% 1 1 5% 18% 58%	2492
	21st to end	Night	13% 2 2 7% 33% 43%	2674
August	1st to 10th	Night	17% 2 2 8% 24% 48%	2827
	11th to 20th	Night	9% 1 1 7% 37% 44%	3113
	21st to end	Night	9% 1 1 14% 42% 33%	3498
September	1st to 10th	Night	10% 2 1 9% 29% 49%	1900
	11th to 20th	Night	15% 2 5% 19% 31% 28%	1920
	21st to end	Night	13% 3 3 23% 32% 26%	2090
October	1st to 10th	Night	16% 1 4 13% 35% 31%	3787
	11th to 20th	Night	16% 2 5% 31% 35% 11%	3777
	21st to end	Night	22% 2 7% 31% 27% 10%	4259
November	1st to 10th	Night	29% 8% 12% 24% 20% 7%	2502
	11th to 20th	Night	29% 8% 16% 24% 21% 3	2470
	21st to end	Night	29% 5% 14% 25% 20% 6%	2617
December	1st to 10th	Night	35% 7% 12% 23% 19% 4	2660
	11th to 20th	Night	46% 8% 11% 19% 14% 2	3276
	21st to end	Night	45% 8% 14% 17% 15% 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	12% 17% 20% 26% 21% 5%	180
	11th to 20th	Day	6% 12% 22% 26% 26% 9%	180
	21st to end	Day	8% 6% 19% 31% 25% 11%	384
February	1st to 10th	Day	6% 11% 23% 28% 25% 8%	370
	11th to 20th	Day	8% 14% 22% 28% 22% 6%	432
	21st to end	Day	4 14% 24% 33% 19% 6%	382
March	1st to 10th	Day	10% 13% 27% 28% 17% 5%	460
	11th to 20th	Day	8% 8% 23% 30% 22% 8%	460
	21st to end	Day	8% 13% 27% 29% 19% 4	506
April	1st to 10th	Day	10% 10% 23% 30% 22% 7%	460
	11th to 20th	Day	8% 13% 21% 28% 21% 9%	452
	21st to end	Day	6% 13% 18% 27% 23% 12%	460
May	1st to 10th	Day	8% 11% 21% 32% 19% 10%	463
	11th to 20th	Day	10% 12% 22% 24% 20% 13%	488
	21st to end	Day	10% 8% 19% 23% 22% 17%	529
June	1st to 10th	Day	6% 11% 20% 24% 26% 13%	490
	11th to 20th	Day	8% 12% 26% 27% 20% 7%	490
	21st to end	Day	3 7% 19% 30% 28% 13%	490
July	1st to 10th	Day	2 5% 18% 31% 33% 10%	486
	11th to 20th	Day	2 4 21% 31% 30% 12%	484
	21st to end	Day	2 4 18% 32% 31% 13%	531
August	1st to 10th	Day	3 3 17% 31% 31% 15%	487
	11th to 20th	Day	2 5% 18% 27% 32% 16%	477
	21st to end	Day	3 5% 19% 32% 27% 14%	539
September	1st to 10th	Day	3 3 17% 31% 32% 13%	490
	11th to 20th	Day	5% 7% 21% 26% 29% 12%	490
	21st to end	Day	5% 7% 20% 32% 27% 8%	490
October	1st to 10th	Day	6% 10% 22% 26% 27% 10%	490
	11th to 20th	Day	8% 12% 17% 27% 27% 9%	490
	21st to end	Day	7% 13% 25% 28% 21% 7%	458
November	1st to 10th	Day	12% 9% 21% 25% 23% 10%	291
	11th to 20th	Day	3 10% 23% 25% 27% 12%	270
	21st to end	Day	6% 13% 17% 29% 25% 11%	199
December	1st to 10th	Day	9% 12% 19% 22% 24% 13%	180
	11th to 20th	Day	7% 5% 27% 24% 23% 13%	180
	21st to end	Day	11% 8% 19% 27% 27% 8%	198
January	1st to 10th	Night	9% 8% 21% 33% 23% 6%	760
	11th to 20th	Night	5% 9% 20% 37% 23% 5%	760
	21st to end	Night	10% 4 19% 37% 24% 6%	836
February	1st to 10th	Night	6% 8% 23% 38% 23% 3	760
	11th to 20th	Night	6% 8% 21% 40% 22% 3	744
	21st to end	Night	5% 11% 23% 41% 18% 3	628
March	1st to 10th	Night	7% 9% 27% 36% 17% 4	760
	11th to 20th	Night	7% 8% 22% 35% 25% 4	760
	21st to end	Night	8% 11% 27% 35% 18% 2	836
April	1st to 10th	Night	6% 9% 24% 38% 21% 2	760
	11th to 20th	Night	6% 11% 25% 33% 21% 5%	751
	21st to end	Night	8% 7% 18% 38% 23% 5%	760
May	1st to 10th	Night	8% 8% 26% 36% 20% 2	558
	11th to 20th	Night	5% 5% 23% 35% 26% 6%	374
	21st to end	Night	7% 6% 18% 35% 30% 3	411
June	1st to 10th	Night	6% 5% 21% 40% 26% 3	380
	11th to 20th	Night	4 4 27% 41% 21% 2	380
	21st to end	Night	3 2 19% 49% 26% 2	380
July	1st to 10th	Night	2 1 17% 53% 26% 1	370
	11th to 20th	Night	2 1 17% 57% 21% 1	368
	21st to end	Night	3 1 11% 53% 31% 2	416
August	1st to 10th	Night	7% 12% 47% 30% 4	554
	11th to 20th	Night	4 1 11% 45% 35% 4	721
	21st to end	Night	2 1 13% 46% 34% 3	836
September	1st to 10th	Night	3 1 12% 42% 37% 5%	760
	11th to 20th	Night	3 3 14% 36% 36% 9%	760
	21st to end	Night	3 4 15% 35% 32% 10%	760
October	1st to 10th	Night	6% 4 17% 38% 29% 7%	760
	11th to 20th	Night	4 7% 15% 35% 32% 6%	760
	21st to end	Night	5% 6% 18% 35% 26% 9%	836
November	1st to 10th	Night	6% 6% 22% 34% 25% 6%	770
	11th to 20th	Night	7% 6% 20% 42% 20% 5%	760
	21st to end	Night	5% 10% 18% 36% 25% 5%	760
December	1st to 10th	Night	8% 9% 20% 39% 21% 4	760
	11th to 20th	Night	9% 6% 22% 36% 23% 4	760
	21st to end	Night	10% 9% 25% 39% 15% 2	836

Page generated at 2024-11-05 05:15:50. Version ac07

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