Lassen National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lassen National Park clear sky chart from 2005-11-06 to 2024-11-04.

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 7% 3 6% 4 3 3 3 4 6% 59%	105267
	Night	3 7% 3 7% 4 4 4 3 5% 6% 55%	102456
Transparency	Day	27% 4 7% 19% 24% 18%	105017
	Night	30% 5% 8% 19% 22% 16%	102295
Seeing	Day	13% 17% 29% 25% 13% 3	15022
	Night	10% 12% 19% 32% 23% 4	24204

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	3 13% 6% 11% 7% 5% 5% 4 6% 6% 35%	2539
	11th to 20th	Day	3 12% 4 12% 7% 7% 5% 4 5% 6% 34%	2677
	21st to end	Day	4 14% 5% 12% 7% 5% 5% 4 5% 7% 34%	3146
February	1st to 10th	Day	4 9% 5% 9% 5% 6% 5% 4 6% 6% 41%	1710
	11th to 20th	Day	2 14% 5% 9% 5% 4 4 4 6% 7% 40%	1731
	21st to end	Day	4 14% 6% 9% 6% 5% 5% 4 4 7% 38%	1570
March	1st to 10th	Day	2 17% 8% 17% 7% 4 3 3 3 5% 29%	3250
	11th to 20th	Day	2 10% 4 7% 4 3 3 3 4 7% 52%	3490
	21st to end	Day	4 17% 6% 11% 7% 5% 6% 4 5% 7% 30%	3965
April	1st to 10th	Day	5% 14% 4 8% 5% 5% 5% 4 6% 8% 36%	2280
	11th to 20th	Day	5% 14% 3 7% 4 4 4 4 5% 7% 43%	2249
	21st to end	Day	5% 11% 3 5% 4 4 4 3 6% 7% 49%	2280
May	1st to 10th	Day	3 8% 2 5% 3 2 2 2 4 6% 63%	4103
	11th to 20th	Day	3 5% 1 3 3 2 2 2 4 5% 69%	4377
	21st to end	Day	6% 6% 2 4 3 2 3 3 4 7% 60%	4813
June	1st to 10th	Day	6% 6% 2 5% 5% 4 4 4 5% 6% 53%	2660
	11th to 20th	Day	3 4 1 3 2 2 3 3 4 6% 69%	2660
	21st to end	Day	2 2 1 2 3 2 3 2 3 4 76%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 3 88%	4420
	11th to 20th	Day	2 1 1 3 2 2 2 2 3 4 79%	4420
	21st to end	Day	1 1 1 2 1 1 2 2 3 4 83%	4584
August	1st to 10th	Day	2 2 1 3 2 2 2 2 5% 5% 74%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 87%	3879
	21st to end	Day	1 1 2 2 2 2 2 2 3 82%	4180
September	1st to 10th	Day	1 1 1 2 2 3 2 3 5% 81%	2280
	11th to 20th	Day	3 3 1 4 3 3 3 3 5% 7% 65%	2280
	21st to end	Day	3 3 1 3 2 1 2 2 4 6% 72%	2037
October	1st to 10th	Day	3 3 1 3 2 2 2 3 3 5% 72%	3180
	11th to 20th	Day	4 4 2 4 3 3 3 3 5% 7% 62%	3161
	21st to end	Day	3 5% 2 4 4 4 4 3 6% 8% 56%	3448
November	1st to 10th	Day	7% 9% 2 6% 6% 5% 5% 4 5% 8% 44%	1713
	11th to 20th	Day	4 7% 3 6% 5% 6% 6% 6% 8% 8% 41%	1672
	21st to end	Day	2 8% 3 8% 4 4 5% 5% 7% 8% 48%	1520
December	1st to 10th	Day	4 10% 3 8% 6% 5% 6% 4 5% 7% 41%	1520
	11th to 20th	Day	4 15% 5% 12% 7% 7% 5% 5% 6% 5% 26%	1928
	21st to end	Day	3 12% 5% 10% 6% 5% 5% 5% 7% 9% 35%	2794
January	1st to 10th	Night	2 8% 4 11% 6% 7% 6% 6% 8% 8% 34%	4406
	11th to 20th	Night	3 12% 4 11% 7% 6% 5% 5% 6% 7% 36%	4282
	21st to end	Night	4 13% 6% 13% 8% 6% 6% 4 5% 6% 29%	4521
February	1st to 10th	Night	4 8% 3 9% 6% 6% 5% 4 6% 8% 41%	2470
	11th to 20th	Night	2 9% 5% 10% 7% 5% 5% 4 5% 7% 41%	2335
	21st to end	Night	3 13% 4 10% 5% 4 5% 4 5% 6% 39%	1884
March	1st to 10th	Night	2 12% 7% 18% 9% 5% 4 3 4 5% 31%	3622
	11th to 20th	Night	2 8% 4 8% 6% 4 4 3 5% 6% 52%	3490
	21st to end	Night	2 14% 6% 10% 7% 5% 6% 5% 7% 8% 30%	3688
April	1st to 10th	Night	2 12% 4 8% 6% 5% 5% 4 5% 6% 42%	1900
	11th to 20th	Night	4 11% 3 6% 4 4 3 4 6% 8% 46%	1879
	21st to end	Night	4 11% 3 4 4 4 3 4 5% 8% 50%	1900
May	1st to 10th	Night	3 6% 3 5% 4 3 3 3 4 5% 61%	2846
	11th to 20th	Night	2 4 1 3 3 3 3 3 4 4 70%	2516
	21st to end	Night	6% 5% 1 3 3 3 3 2 4 5% 65%	2762
June	1st to 10th	Night	5% 7% 2 5% 4 3 4 3 6% 8% 53%	1520
	11th to 20th	Night	3 3 1 3 3 2 3 2 4 7% 69%	1520
	21st to end	Night	2 2 1 2 2 3 3 2 3 2 77%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 2 90%	2540
	11th to 20th	Night	1 2 1 2 1 2 2 1 2 2 83%	2540
	21st to end	Night	1 1 2 1 1 1 1 3 3 86%	2972
August	1st to 10th	Night	2 2 1 3 2 2 2 2 6% 5% 72%	2848
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 88%	2962
	21st to end	Night	1 1 1 1 1 1 1 1 2 87%	3498
September	1st to 10th	Night	2 1 1 1 2 2 1 2 3 84%	1900
	11th to 20th	Night	2 2 1 3 2 2 2 3 3 6% 74%	1900
	21st to end	Night	2 2 1 2 2 2 3 2 4 6% 73%	2140
October	1st to 10th	Night	3 3 1 2 2 3 2 2 2 3 77%	3800
	11th to 20th	Night	2 3 1 3 2 2 3 3 4 6% 69%	3777
	21st to end	Night	2 5% 2 5% 3 4 4 4 6% 9% 56%	4121
November	1st to 10th	Night	6% 7% 3 8% 6% 6% 5% 4 6% 7% 44%	2436
	11th to 20th	Night	4 7% 3 7% 6% 5% 6% 5% 8% 8% 42%	2503
	21st to end	Night	2 7% 4 7% 5% 4 4 4 7% 9% 47%	2660
December	1st to 10th	Night	4 8% 3 7% 5% 5% 5% 5% 6% 9% 44%	2660
	11th to 20th	Night	4 14% 4 12% 7% 6% 7% 5% 5% 7% 28%	3276
	21st to end	Night	3 13% 4 10% 7% 7% 6% 5% 6% 7% 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	49% 6% 12% 19% 12% 2	2539
	11th to 20th	Day	50% 6% 13% 13% 12% 6%	2677
	21st to end	Day	53% 4 12% 16% 11% 4	3146
February	1st to 10th	Day	42% 6% 11% 21% 13% 8%	1710
	11th to 20th	Day	45% 5% 8% 20% 18% 5%	1740
	21st to end	Day	46% 6% 10% 20% 13% 5%	1570
March	1st to 10th	Day	58% 7% 6% 11% 14% 3	3250
	11th to 20th	Day	34% 4 8% 31% 21% 3	3490
	21st to end	Day	53% 6% 10% 20% 9% 2	3965
April	1st to 10th	Day	45% 5% 13% 19% 15% 3	2280
	11th to 20th	Day	40% 5% 11% 24% 16% 4	2252
	21st to end	Day	33% 5% 14% 28% 17% 3	2280
May	1st to 10th	Day	24% 3 11% 26% 29% 7%	4103
	11th to 20th	Day	18% 4 6% 19% 45% 7%	4380
	21st to end	Day	23% 5% 9% 38% 23% 2	4814
June	1st to 10th	Day	31% 4 10% 26% 24% 4	2660
	11th to 20th	Day	17% 4 8% 24% 34% 13%	2660
	21st to end	Day	12% 3 4 19% 36% 26%	2660
July	1st to 10th	Day	6% 1 2 7% 18% 65%	4351
	11th to 20th	Day	10% 2 3 9% 19% 56%	4345
	21st to end	Day	7% 2 2 10% 31% 47%	4439
August	1st to 10th	Day	13% 3 3 11% 20% 50%	4076
	11th to 20th	Day	5% 2 2 11% 46% 34%	3918
	21st to end	Day	8% 3 2 20% 36% 31%	4179
September	1st to 10th	Day	8% 2 2 10% 33% 45%	2280
	11th to 20th	Day	18% 4 6% 20% 32% 20%	2280
	21st to end	Day	15% 3 6% 22% 33% 22%	2037
October	1st to 10th	Day	16% 3 4 15% 31% 31%	3180
	11th to 20th	Day	21% 5% 6% 25% 33% 11%	3161
	21st to end	Day	25% 6% 9% 24% 26% 10%	3448
November	1st to 10th	Day	38% 5% 10% 19% 17% 12%	1713
	11th to 20th	Day	36% 5% 12% 20% 18% 8%	1672
	21st to end	Day	35% 4 10% 20% 22% 9%	1520
December	1st to 10th	Day	43% 6% 8% 18% 20% 6%	1520
	11th to 20th	Day	58% 5% 9% 13% 12% 3	1928
	21st to end	Day	46% 6% 14% 15% 14% 4	2794
January	1st to 10th	Night	42% 6% 17% 21% 11% 3	4406
	11th to 20th	Night	48% 6% 12% 12% 15% 7%	4282
	21st to end	Night	57% 4 8% 15% 11% 5%	4521
February	1st to 10th	Night	40% 5% 9% 21% 17% 8%	2470
	11th to 20th	Night	41% 5% 10% 19% 19% 6%	2337
	21st to end	Night	43% 6% 11% 19% 15% 5%	1884
March	1st to 10th	Night	56% 8% 9% 13% 11% 4	3622
	11th to 20th	Night	33% 4 7% 28% 23% 4	3490
	21st to end	Night	48% 10% 14% 19% 8% 1	3688
April	1st to 10th	Night	41% 7% 12% 23% 12% 4	1900
	11th to 20th	Night	36% 5% 15% 24% 16% 5%	1879
	21st to end	Night	31% 5% 16% 28% 17% 3	1900
May	1st to 10th	Night	26% 5% 9% 29% 24% 6%	2846
	11th to 20th	Night	18% 3 8% 23% 35% 12%	2516
	21st to end	Night	22% 5% 12% 37% 22% 2	2762
June	1st to 10th	Night	28% 5% 12% 31% 21% 3	1520
	11th to 20th	Night	16% 5% 9% 25% 34% 10%	1520
	21st to end	Night	14% 3 5% 18% 34% 25%	1520
July	1st to 10th	Night	4 1 2 8% 17% 67%	2500
	11th to 20th	Night	10% 2 3 8% 16% 62%	2492
	21st to end	Night	7% 2 1 7% 36% 47%	2879
August	1st to 10th	Night	14% 3 3 10% 23% 48%	2839
	11th to 20th	Night	5% 2 1 11% 43% 38%	2989
	21st to end	Night	7% 2 3 17% 43% 28%	3498
September	1st to 10th	Night	7% 2 2 9% 31% 48%	1900
	11th to 20th	Night	13% 4 7% 21% 32% 23%	1900
	21st to end	Night	13% 2 6% 23% 33% 22%	2140
October	1st to 10th	Night	15% 2 4 13% 33% 32%	3800
	11th to 20th	Night	15% 4 7% 32% 31% 11%	3777
	21st to end	Night	21% 8% 9% 22% 28% 12%	4121
November	1st to 10th	Night	37% 6% 12% 17% 18% 10%	2436
	11th to 20th	Night	36% 6% 11% 21% 18% 7%	2503
	21st to end	Night	34% 5% 10% 22% 20% 11%	2660
December	1st to 10th	Night	39% 6% 9% 16% 21% 9%	2660
	11th to 20th	Night	56% 4 6% 13% 17% 4	3276
	21st to end	Night	49% 7% 11% 15% 14% 5%	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	32% 21% 23% 16% 7% 1	180
	11th to 20th	Day	20% 27% 23% 20% 8% 2	265
	21st to end	Day	18% 21% 29% 18% 12% 1	407
February	1st to 10th	Day	24% 21% 27% 18% 9% 1	370
	11th to 20th	Day	27% 20% 27% 18% 7% 1	396
	21st to end	Day	20% 24% 29% 22% 5%	382
March	1st to 10th	Day	30% 30% 23% 13% 4 1	460
	11th to 20th	Day	25% 19% 27% 18% 9% 2	460
	21st to end	Day	23% 30% 27% 15% 5%	506
April	1st to 10th	Day	20% 25% 30% 19% 6% 1	460
	11th to 20th	Day	24% 22% 25% 19% 9% 1	452
	21st to end	Day	17% 21% 29% 21% 10% 2	460
May	1st to 10th	Day	15% 24% 32% 19% 8% 2	463
	11th to 20th	Day	17% 16% 32% 20% 11% 4	488
	21st to end	Day	16% 17% 24% 26% 12% 4	529
June	1st to 10th	Day	11% 18% 27% 25% 16% 4	490
	11th to 20th	Day	10% 22% 30% 23% 12% 2	490
	21st to end	Day	3 13% 31% 31% 15% 5%	490
July	1st to 10th	Day	2 8% 40% 29% 16% 5%	486
	11th to 20th	Day	1 7% 35% 33% 16% 8%	484
	21st to end	Day	1 6% 33% 35% 17% 7%	531
August	1st to 10th	Day	4 9% 29% 34% 16% 8%	487
	11th to 20th	Day	2 12% 29% 30% 17% 9%	477
	21st to end	Day	3 8% 29% 35% 19% 5%	539
September	1st to 10th	Day	3 9% 34% 32% 18% 2	490
	11th to 20th	Day	6% 14% 30% 29% 18% 3	490
	21st to end	Day	7% 13% 32% 34% 12% 2	490
October	1st to 10th	Day	7% 16% 33% 25% 18% 1	490
	11th to 20th	Day	14% 15% 24% 28% 18% 2	490
	21st to end	Day	16% 19% 24% 25% 13% 3	539
November	1st to 10th	Day	18% 13% 23% 25% 18% 3	291
	11th to 20th	Day	11% 17% 27% 23% 19% 4	252
	21st to end	Day	14% 17% 29% 23% 12% 4	180
December	1st to 10th	Day	24% 16% 24% 17% 14% 6%	180
	11th to 20th	Day	19% 21% 23% 18% 14% 5%	180
	21st to end	Day	21% 19% 25% 22% 13% 1	198
January	1st to 10th	Night	14% 17% 25% 28% 12% 4	760
	11th to 20th	Night	13% 18% 25% 29% 13% 3	760
	21st to end	Night	13% 14% 27% 27% 16% 3	836
February	1st to 10th	Night	14% 16% 24% 29% 14% 2	760
	11th to 20th	Night	13% 17% 22% 30% 15% 3	744
	21st to end	Night	16% 14% 25% 32% 11% 1	628
March	1st to 10th	Night	19% 21% 22% 24% 11% 3	760
	11th to 20th	Night	16% 16% 19% 26% 21% 3	760
	21st to end	Night	14% 22% 24% 25% 13% 2	836
April	1st to 10th	Night	11% 18% 24% 33% 13% 1	760
	11th to 20th	Night	13% 15% 25% 29% 15% 3	751
	21st to end	Night	11% 11% 23% 33% 20% 3	760
May	1st to 10th	Night	10% 12% 29% 28% 18% 3	569
	11th to 20th	Night	10% 7% 18% 35% 26% 3	374
	21st to end	Night	13% 8% 17% 29% 30% 3	411
June	1st to 10th	Night	8% 6% 17% 37% 30% 2	380
	11th to 20th	Night	4 11% 20% 34% 28% 2	380
	21st to end	Night	3 4 14% 40% 36% 3	380
July	1st to 10th	Night	1 1 8% 39% 49% 2	370
	11th to 20th	Night	2 1 8% 42% 44% 3	368
	21st to end	Night	1 1 4 39% 48% 5%	539
August	1st to 10th	Night	3 1 7% 35% 48% 7%	567
	11th to 20th	Night	2 2 10% 41% 40% 6%	649
	21st to end	Night	3 2 8% 40% 44% 4	836
September	1st to 10th	Night	2 3 14% 41% 34% 4	760
	11th to 20th	Night	2 6% 12% 35% 36% 8%	760
	21st to end	Night	5% 6% 15% 37% 29% 9%	760
October	1st to 10th	Night	7% 9% 18% 34% 28% 5%	760
	11th to 20th	Night	9% 8% 16% 33% 29% 5%	760
	21st to end	Night	9% 13% 18% 30% 23% 7%	836
November	1st to 10th	Night	12% 12% 19% 31% 21% 5%	754
	11th to 20th	Night	10% 15% 23% 33% 16% 3	760
	21st to end	Night	8% 16% 24% 30% 18% 4	760
December	1st to 10th	Night	13% 16% 23% 29% 16% 3	760
	11th to 20th	Night	16% 15% 23% 29% 15% 3	760
	21st to end	Night	19% 18% 25% 28% 9% 1	836

Page generated at 2024-11-01 19:47:37. Version ac07

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