Mount Shasta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Shasta clear sky chart from 2005-11-06 to 2024-10-25.

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	8% 8% 2 4 3 3 3 3 4 6% 55%	101310
	Night	10% 9% 2 4 3 3 3 3 4 6% 52%	97676
Transparency	Day	28% 6% 10% 18% 21% 17%	101062
	Night	31% 7% 12% 20% 19% 12%	97514
Seeing	Day	16% 18% 29% 25% 11% 2	14966
	Night	15% 10% 24% 32% 17% 2	24070

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	13% 18% 4 6% 5% 5% 6% 4 5% 6% 27%	2539
	11th to 20th	Day	20% 20% 3 6% 3 4 2 3 3 4 31%	2709
	21st to end	Day	20% 18% 3 6% 4 3 3 3 4 6% 29%	3146
February	1st to 10th	Day	16% 11% 3 4 4 3 4 4 6% 7% 37%	1710
	11th to 20th	Day	11% 15% 4 5% 4 4 3 4 5% 6% 39%	1669
	21st to end	Day	11% 14% 4 6% 4 4 5% 3 6% 7% 36%	1570
March	1st to 10th	Day	13% 28% 9% 8% 3 2 2 2 3 4 26%	3322
	11th to 20th	Day	10% 13% 2 5% 2 2 3 2 4 5% 52%	3490
	21st to end	Day	13% 24% 4 6% 4 3 4 3 5% 7% 26%	3905
April	1st to 10th	Day	14% 14% 2 7% 5% 4 3 4 5% 7% 35%	2280
	11th to 20th	Day	12% 11% 3 5% 4 4 4 4 6% 8% 41%	2249
	21st to end	Day	6% 8% 2 6% 4 3 4 4 6% 9% 47%	2311
May	1st to 10th	Day	6% 6% 2 4 3 3 4 3 5% 6% 59%	4162
	11th to 20th	Day	6% 4 1 3 2 3 3 3 5% 6% 65%	4377
	21st to end	Day	7% 5% 2 4 3 3 3 3 5% 8% 57%	4813
June	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 7% 8% 49%	2660
	11th to 20th	Day	5% 3 2 3 3 3 3 3 5% 6% 64%	2660
	21st to end	Day	5% 2 1 2 2 1 2 3 4 4 74%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 2 3 86%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 77%	4420
	21st to end	Day	1 1 1 1 1 2 2 3 4 83%	4532
August	1st to 10th	Day	3 2 1 3 2 2 3 3 4 6% 72%	4091
	11th to 20th	Day	1 1 1 2 1 2 3 2 5% 5% 77%	3978
	21st to end	Day	3 2 1 3 1 1 2 2 3 4 78%	4180
September	1st to 10th	Day	1 1 1 1 2 2 2 2 3 4 80%	2280
	11th to 20th	Day	4 3 1 3 3 3 3 4 4 6% 66%	2280
	21st to end	Day	4 3 1 3 2 2 2 3 4 7% 70%	2009
October	1st to 10th	Day	7% 3 1 3 2 2 3 2 5% 5% 66%	1900
	11th to 20th	Day	10% 4 1 3 3 2 3 3 5% 6% 59%	1900
	21st to end	Day	12% 6% 2 3 3 4 4 3 5% 7% 52%	2025
November	1st to 10th	Day	14% 8% 2 5% 5% 4 3 5% 5% 8% 41%	1714
	11th to 20th	Day	15% 8% 2 6% 3 3 4 4 6% 10% 38%	1587
	21st to end	Day	10% 8% 3 6% 4 4 4 3 5% 9% 45%	1520
December	1st to 10th	Day	15% 13% 2 4 3 3 3 4 6% 5% 41%	1520
	11th to 20th	Day	23% 15% 2 6% 4 4 4 5% 5% 6% 26%	1928
	21st to end	Day	20% 16% 3 6% 4 4 4 3 6% 6% 28%	2794
January	1st to 10th	Night	10% 16% 4 8% 5% 5% 6% 7% 6% 6% 27%	4406
	11th to 20th	Night	18% 16% 4 8% 3 4 3 4 5% 6% 29%	4251
	21st to end	Night	21% 19% 4 7% 4 4 3 3 4 4 26%	4521
February	1st to 10th	Night	15% 10% 3 6% 3 3 4 4 5% 8% 39%	2470
	11th to 20th	Night	12% 16% 2 5% 4 4 3 3 6% 7% 38%	2397
	21st to end	Night	12% 11% 4 5% 4 4 4 3 6% 8% 39%	1884
March	1st to 10th	Night	13% 25% 7% 9% 4 3 3 2 4 5% 27%	3550
	11th to 20th	Night	9% 13% 3 4 3 3 3 2 4 5% 51%	3490
	21st to end	Night	11% 17% 4 7% 4 5% 5% 5% 7% 7% 27%	3747
April	1st to 10th	Night	13% 12% 2 5% 4 4 4 4 5% 8% 37%	1900
	11th to 20th	Night	9% 10% 2 4 4 3 4 3 5% 7% 48%	1879
	21st to end	Night	9% 7% 1 4 3 4 3 3 6% 10% 51%	1865
May	1st to 10th	Night	8% 3 2 4 3 3 3 3 4 5% 63%	2806
	11th to 20th	Night	5% 3 1 3 2 2 3 2 5% 5% 69%	2516
	21st to end	Night	6% 3 1 3 2 2 2 3 4 9% 64%	2762
June	1st to 10th	Night	7% 6% 2 5% 3 4 3 4 6% 7% 52%	1520
	11th to 20th	Night	4 3 1 3 2 2 2 2 4 6% 71%	1520
	21st to end	Night	3 3 1 2 1 2 2 2 3 5% 76%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 1 2 3 88%	2540
	11th to 20th	Night	2 3 1 3 2 2 2 2 3 4 77%	2540
	21st to end	Night	1 1 1 2 1 1 1 2 3 87%	3012
August	1st to 10th	Night	3 2 1 2 2 2 2 3 3 4 76%	2848
	11th to 20th	Night	1 1 2 1 2 2 2 3 4 82%	2862
	21st to end	Night	6% 2 1 1 1 1 1 1 2 3 80%	3498
September	1st to 10th	Night	1 1 1 1 1 1 2 3 3 86%	1900
	11th to 20th	Night	4 2 1 3 2 2 2 2 5% 7% 71%	1900
	21st to end	Night	4 2 1 3 2 3 3 2 4 6% 71%	2166
October	1st to 10th	Night	5% 3 1 3 3 3 2 2 4 5% 69%	2280
	11th to 20th	Night	9% 4 1 3 2 2 3 2 5% 6% 62%	2280
	21st to end	Night	11% 5% 1 3 2 3 3 3 5% 8% 58%	2436
November	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 7% 42%	2364
	11th to 20th	Night	15% 9% 1 5% 4 3 4 5% 6% 8% 40%	2588
	21st to end	Night	9% 9% 2 6% 5% 4 5% 4 5% 7% 45%	2660
December	1st to 10th	Night	16% 13% 2 4 2 2 3 3 5% 7% 42%	2660
	11th to 20th	Night	25% 14% 3 5% 3 3 3 4 5% 7% 29%	3276
	21st to end	Night	19% 17% 4 6% 3 3 4 3 5% 6% 31%	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% 13% 13% 17% 7% 1	2539
	11th to 20th	Day	55% 9% 10% 13% 8% 5%	2709
	21st to end	Day	52% 10% 13% 13% 9% 4	3146
February	1st to 10th	Day	43% 6% 15% 19% 12% 5%	1710
	11th to 20th	Day	42% 6% 13% 20% 15% 3	1678
	21st to end	Day	44% 7% 14% 19% 12% 4	1570
March	1st to 10th	Day	61% 7% 8% 12% 11% 1	3322
	11th to 20th	Day	34% 6% 13% 21% 25% 1	3490
	21st to end	Day	53% 9% 14% 17% 6% 1	3905
April	1st to 10th	Day	46% 6% 15% 18% 13% 2	2280
	11th to 20th	Day	38% 6% 14% 25% 12% 4	2252
	21st to end	Day	31% 7% 16% 26% 17% 3	2311
May	1st to 10th	Day	24% 7% 10% 25% 26% 7%	4162
	11th to 20th	Day	18% 4 9% 19% 34% 17%	4380
	21st to end	Day	21% 6% 16% 30% 25% 2	4814
June	1st to 10th	Day	30% 6% 14% 24% 22% 4	2660
	11th to 20th	Day	19% 5% 10% 25% 31% 10%	2660
	21st to end	Day	14% 2 7% 20% 32% 25%	2660
July	1st to 10th	Day	6% 2 3 9% 16% 63%	4351
	11th to 20th	Day	11% 2 5% 9% 21% 51%	4345
	21st to end	Day	6% 2 5% 14% 28% 45%	4389
August	1st to 10th	Day	13% 3 5% 11% 22% 46%	4076
	11th to 20th	Day	8% 3 7% 21% 38% 23%	4017
	21st to end	Day	11% 3 6% 20% 36% 24%	4179
September	1st to 10th	Day	8% 2 5% 14% 28% 44%	2280
	11th to 20th	Day	18% 5% 8% 19% 33% 17%	2280
	21st to end	Day	16% 3 8% 22% 29% 22%	2009
October	1st to 10th	Day	20% 3 10% 22% 24% 21%	1900
	11th to 20th	Day	25% 4 11% 22% 26% 12%	1900
	21st to end	Day	28% 7% 12% 20% 18% 15%	2025
November	1st to 10th	Day	39% 6% 13% 20% 17% 6%	1714
	11th to 20th	Day	40% 8% 14% 18% 14% 7%	1587
	21st to end	Day	38% 6% 13% 19% 16% 9%	1520
December	1st to 10th	Day	42% 7% 11% 17% 19% 5%	1520
	11th to 20th	Day	55% 9% 10% 15% 10% 2	1928
	21st to end	Day	48% 14% 13% 15% 8% 2	2794
January	1st to 10th	Night	48% 12% 16% 17% 5% 2	4406
	11th to 20th	Night	49% 11% 11% 15% 8% 6%	4251
	21st to end	Night	57% 8% 9% 12% 11% 3	4521
February	1st to 10th	Night	41% 6% 15% 19% 13% 6%	2470
	11th to 20th	Night	43% 6% 14% 20% 14% 3	2399
	21st to end	Night	40% 7% 16% 19% 14% 4	1884
March	1st to 10th	Night	54% 9% 11% 17% 8% 1	3550
	11th to 20th	Night	33% 8% 11% 24% 23% 2	3490
	21st to end	Night	45% 14% 18% 15% 7% 1	3747
April	1st to 10th	Night	42% 8% 18% 19% 10% 2	1900
	11th to 20th	Night	34% 8% 19% 23% 13% 4	1879
	21st to end	Night	26% 9% 22% 27% 14% 2	1865
May	1st to 10th	Night	20% 5% 15% 33% 20% 6%	2806
	11th to 20th	Night	16% 5% 11% 22% 33% 13%	2516
	21st to end	Night	17% 9% 22% 34% 18% 1	2762
June	1st to 10th	Night	29% 7% 16% 29% 18% 1	1520
	11th to 20th	Night	15% 5% 12% 32% 30% 8%	1520
	21st to end	Night	13% 2 8% 25% 39% 14%	1520
July	1st to 10th	Night	5% 2 4 12% 18% 59%	2500
	11th to 20th	Night	11% 3 4 11% 21% 50%	2492
	21st to end	Night	6% 1 4 15% 35% 38%	2918
August	1st to 10th	Night	12% 2 4 15% 26% 41%	2839
	11th to 20th	Night	6% 2 6% 28% 37% 21%	2889
	21st to end	Night	11% 3 5% 28% 33% 19%	3498
September	1st to 10th	Night	6% 1 5% 14% 29% 44%	1900
	11th to 20th	Night	14% 5% 8% 22% 34% 17%	1900
	21st to end	Night	15% 4 11% 22% 26% 23%	2166
October	1st to 10th	Night	19% 4 11% 19% 29% 19%	2280
	11th to 20th	Night	22% 5% 10% 25% 26% 13%	2280
	21st to end	Night	24% 6% 14% 21% 19% 14%	2436
November	1st to 10th	Night	37% 8% 15% 17% 16% 7%	2364
	11th to 20th	Night	39% 9% 15% 18% 14% 5%	2588
	21st to end	Night	37% 6% 14% 16% 18% 9%	2660
December	1st to 10th	Night	40% 6% 11% 18% 19% 6%	2660
	11th to 20th	Night	53% 6% 9% 16% 14% 1	3276
	21st to end	Night	50% 10% 12% 15% 11% 2	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	35% 24% 24% 11% 4 2	180
	11th to 20th	Day	29% 21% 23% 17% 8% 2	284
	21st to end	Day	26% 18% 26% 17% 11% 1	407
February	1st to 10th	Day	24% 20% 29% 21% 6%	370
	11th to 20th	Day	28% 23% 26% 16% 6%	367
	21st to end	Day	21% 23% 32% 19% 4	382
March	1st to 10th	Day	35% 25% 25% 10% 5%	460
	11th to 20th	Day	26% 23% 25% 16% 8% 1	460
	21st to end	Day	29% 29% 22% 16% 4	506
April	1st to 10th	Day	29% 23% 29% 15% 4 1	460
	11th to 20th	Day	29% 19% 26% 19% 5% 2	452
	21st to end	Day	15% 27% 27% 21% 8% 2	460
May	1st to 10th	Day	16% 27% 32% 16% 7% 1	463
	11th to 20th	Day	22% 21% 27% 18% 9% 3	488
	21st to end	Day	16% 19% 27% 25% 12% 3	529
June	1st to 10th	Day	13% 17% 28% 27% 12% 2	490
	11th to 20th	Day	15% 23% 29% 23% 8% 1	490
	21st to end	Day	5% 14% 33% 31% 13% 3	490
July	1st to 10th	Day	3 12% 36% 34% 12% 3	486
	11th to 20th	Day	1 11% 35% 35% 14% 3	484
	21st to end	Day	1 7% 32% 38% 18% 4	531
August	1st to 10th	Day	2 8% 38% 33% 15% 5%	487
	11th to 20th	Day	4 12% 27% 33% 17% 6%	477
	21st to end	Day	5% 9% 35% 30% 17% 3	539
September	1st to 10th	Day	3 13% 32% 36% 13% 3	490
	11th to 20th	Day	7% 15% 33% 30% 13% 2	490
	21st to end	Day	8% 19% 29% 30% 12% 1	490
October	1st to 10th	Day	10% 18% 27% 28% 14% 2	490
	11th to 20th	Day	15% 14% 25% 29% 15% 2	490
	21st to end	Day	16% 18% 27% 26% 11% 3	514
November	1st to 10th	Day	21% 15% 26% 23% 13% 2	310
	11th to 20th	Day	18% 12% 27% 25% 14% 4	212
	21st to end	Day	18% 13% 27% 28% 12% 1	180
December	1st to 10th	Day	27% 15% 23% 19% 10% 6%	180
	11th to 20th	Day	27% 17% 24% 17% 10% 4	180
	21st to end	Day	21% 19% 27% 19% 12% 2	198
January	1st to 10th	Night	24% 10% 27% 24% 12% 3	760
	11th to 20th	Night	23% 11% 26% 24% 13% 3	760
	21st to end	Night	20% 12% 24% 27% 13% 3	836
February	1st to 10th	Night	20% 12% 28% 28% 11% 1	760
	11th to 20th	Night	24% 11% 22% 30% 12% 1	744
	21st to end	Night	18% 15% 28% 31% 8%	628
March	1st to 10th	Night	30% 16% 24% 20% 8% 2	760
	11th to 20th	Night	22% 14% 22% 26% 15% 1	760
	21st to end	Night	25% 17% 26% 22% 8% 1	836
April	1st to 10th	Night	22% 16% 27% 25% 10%	760
	11th to 20th	Night	16% 15% 31% 24% 12% 2	751
	21st to end	Night	14% 13% 30% 30% 13% 1	725
May	1st to 10th	Night	11% 14% 33% 25% 16%	542
	11th to 20th	Night	13% 10% 24% 32% 20% 1	374
	21st to end	Night	14% 11% 26% 32% 16% 1	411
June	1st to 10th	Night	10% 8% 24% 37% 20% 1	380
	11th to 20th	Night	7% 13% 30% 39% 9% 1	380
	21st to end	Night	5% 4 27% 49% 15%	380
July	1st to 10th	Night	2 5% 19% 48% 26%	370
	11th to 20th	Night	3 2 18% 51% 25% 1	368
	21st to end	Night	1 1 11% 50% 35% 2	566
August	1st to 10th	Night	3 1 12% 49% 32% 3	567
	11th to 20th	Night	3 1 17% 45% 31% 3	588
	21st to end	Night	3 3 19% 44% 29% 2	836
September	1st to 10th	Night	2 4 21% 43% 27% 3	760
	11th to 20th	Night	5% 6% 19% 34% 32% 4	760
	21st to end	Night	5% 8% 21% 37% 25% 5%	760
October	1st to 10th	Night	7% 7% 26% 36% 21% 3	760
	11th to 20th	Night	12% 7% 19% 36% 22% 4	760
	21st to end	Night	15% 7% 20% 34% 18% 5%	812
November	1st to 10th	Night	16% 10% 23% 34% 13% 4	740
	11th to 20th	Night	20% 8% 29% 30% 11% 3	760
	21st to end	Night	14% 10% 29% 31% 14% 2	760
December	1st to 10th	Night	24% 8% 25% 28% 13% 3	760
	11th to 20th	Night	28% 9% 25% 24% 12% 2	760
	21st to end	Night	25% 15% 28% 24% 7% 1	836

Page generated at 2024-10-22 17:21:05. Version ac07

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