Great Basin College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Basin College 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	3 5% 2 6% 5% 4 4 4 6% 7% 53%	101098
	Night	4 7% 2 7% 5% 5% 5% 4 6% 7% 47%	98063
Transparency	Day	27% 8% 11% 17% 19% 19%	100846
	Night	30% 9% 13% 18% 17% 14%	97905
Seeing	Day	6% 9% 22% 30% 23% 10%	14698
	Night	7% 4 18% 41% 26% 3	24180

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	4 11% 6% 16% 7% 6% 6% 5% 7% 8% 23%	2539
	11th to 20th	Day	3 12% 5% 11% 9% 9% 8% 6% 7% 6% 23%	2540
	21st to end	Day	5% 10% 4 14% 14% 10% 7% 6% 7% 8% 15%	2891
February	1st to 10th	Day	4 7% 5% 10% 7% 6% 7% 5% 8% 11% 30%	1824
	11th to 20th	Day	3 8% 4 9% 7% 5% 7% 6% 9% 8% 33%	1850
	21st to end	Day	1 6% 2 9% 6% 6% 7% 5% 8% 10% 39%	1570
March	1st to 10th	Day	2 10% 4 11% 7% 7% 7% 7% 11% 11% 23%	3138
	11th to 20th	Day	2 6% 2 6% 4 4 5% 4 10% 9% 49%	3397
	21st to end	Day	4 11% 4 12% 9% 7% 6% 5% 7% 7% 28%	3931
April	1st to 10th	Day	4 9% 2 8% 6% 5% 5% 5% 7% 9% 40%	2280
	11th to 20th	Day	4 6% 2 6% 5% 5% 6% 5% 6% 8% 46%	2263
	21st to end	Day	6% 7% 2 6% 4 5% 4 4 6% 8% 49%	2470
May	1st to 10th	Day	4 8% 2 6% 5% 5% 5% 4 6% 7% 49%	4110
	11th to 20th	Day	3 4 1 4 3 3 3 3 5% 7% 64%	4071
	21st to end	Day	3 4 2 4 4 3 4 4 5% 6% 60%	4626
June	1st to 10th	Day	3 4 2 5% 4 4 5% 4 6% 7% 55%	2660
	11th to 20th	Day	3 3 1 3 3 3 3 3 5% 6% 66%	2660
	21st to end	Day	2 2 1 2 2 2 3 2 4 5% 75%	2660
July	1st to 10th	Day	1 1 2 1 2 2 2 3 4 81%	4420
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 6% 67%	4420
	21st to end	Day	2 2 1 4 3 3 4 4 5% 7% 65%	4683
August	1st to 10th	Day	3 2 1 4 2 3 3 3 4 7% 68%	4092
	11th to 20th	Day	1 1 1 3 2 2 3 2 3 4 78%	3966
	21st to end	Day	2 2 1 2 2 2 2 2 3 5% 78%	4180
September	1st to 10th	Day	2 1 1 3 2 2 3 2 4 5% 76%	2256
	11th to 20th	Day	2 2 1 4 3 3 4 2 4 6% 69%	2090
	21st to end	Day	3 3 1 4 3 3 2 2 3 4 72%	2090
October	1st to 10th	Day	4 4 2 6% 3 3 3 4 4 5% 62%	2090
	11th to 20th	Day	3 5% 1 4 3 3 3 3 5% 7% 64%	1929
	21st to end	Day	4 3 1 4 3 3 4 3 6% 7% 63%	1881
November	1st to 10th	Day	4 5% 4 8% 5% 5% 5% 4 7% 8% 45%	1683
	11th to 20th	Day	5% 7% 3 5% 4 4 5% 4 8% 8% 46%	1710
	21st to end	Day	4 7% 3 10% 5% 5% 5% 4 5% 8% 43%	1710
December	1st to 10th	Day	5% 8% 3 8% 8% 6% 5% 4 6% 8% 39%	1696
	11th to 20th	Day	5% 10% 4 10% 6% 5% 7% 5% 9% 11% 29%	1928
	21st to end	Day	5% 8% 4 9% 7% 7% 8% 6% 8% 9% 29%	2794
January	1st to 10th	Night	3 12% 4 12% 7% 7% 8% 6% 8% 9% 23%	4406
	11th to 20th	Night	4 15% 5% 13% 9% 8% 7% 5% 6% 7% 21%	4420
	21st to end	Night	6% 13% 5% 15% 11% 7% 7% 5% 5% 7% 19%	4765
February	1st to 10th	Night	4 8% 3 9% 7% 5% 6% 5% 8% 10% 35%	2352
	11th to 20th	Night	3 8% 3 8% 5% 5% 6% 6% 8% 10% 38%	2218
	21st to end	Night	2 9% 4 9% 7% 8% 7% 6% 7% 8% 33%	1884
March	1st to 10th	Night	3 9% 5% 11% 7% 7% 6% 6% 11% 11% 25%	3736
	11th to 20th	Night	3 7% 2 6% 5% 4 6% 5% 9% 9% 44%	3570
	21st to end	Night	5% 9% 3 9% 6% 5% 5% 5% 8% 10% 34%	3719
April	1st to 10th	Night	5% 6% 3 7% 6% 5% 6% 6% 8% 9% 40%	1900
	11th to 20th	Night	5% 7% 2 5% 4 5% 5% 5% 6% 6% 50%	1864
	21st to end	Night	7% 8% 2 5% 4 4 4 4 6% 5% 52%	1710
May	1st to 10th	Night	7% 8% 2 5% 4 3 4 3 5% 7% 52%	2860
	11th to 20th	Night	4 3 2 4 3 3 4 3 5% 7% 63%	2834
	21st to end	Night	5% 5% 2 5% 4 4 5% 4 5% 7% 53%	2950
June	1st to 10th	Night	3 4 1 4 4 4 5% 3 5% 8% 60%	1520
	11th to 20th	Night	5% 4 1 3 3 3 4 3 5% 6% 65%	1520
	21st to end	Night	3 2 1 3 3 3 3 3 5% 5% 70%	1520
July	1st to 10th	Night	2 1 1 3 2 2 3 2 4 5% 75%	2540
	11th to 20th	Night	3 3 2 6% 4 4 5% 4 6% 8% 55%	2540
	21st to end	Night	3 3 2 5% 4 4 6% 4 7% 6% 55%	2872
August	1st to 10th	Night	2 3 1 4 3 4 5% 4 6% 6% 61%	2847
	11th to 20th	Night	2 2 1 4 2 3 3 3 4 4 72%	2871
	21st to end	Night	3 2 1 3 2 2 3 2 3 4 75%	3498
September	1st to 10th	Night	4 1 1 3 2 2 3 3 5% 6% 71%	1924
	11th to 20th	Night	4 3 2 3 2 3 3 3 4 6% 68%	2090
	21st to end	Night	4 3 1 3 2 2 2 2 3 4 74%	2090
October	1st to 10th	Night	4 5% 1 4 3 3 4 2 4 5% 64%	2090
	11th to 20th	Night	4 4 1 5% 3 3 3 3 5% 5% 64%	2247
	21st to end	Night	4 4 1 3 2 3 3 3 4 7% 65%	2717
November	1st to 10th	Night	6% 6% 2 6% 4 4 5% 4 6% 7% 49%	2430
	11th to 20th	Night	4 6% 2 6% 4 4 4 4 7% 8% 52%	2470
	21st to end	Night	3 6% 2 7% 6% 6% 5% 5% 8% 10% 42%	2470
December	1st to 10th	Night	5% 9% 3 9% 5% 5% 5% 5% 6% 8% 40%	2481
	11th to 20th	Night	6% 10% 3 9% 7% 6% 7% 6% 7% 11% 26%	3276
	21st to end	Night	5% 10% 3 11% 8% 7% 7% 6% 10% 9% 23%	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	53% 12% 16% 16% 3	2539
	11th to 20th	Day	52% 15% 15% 10% 6% 1	2540
	21st to end	Day	48% 21% 16% 10% 4 1	2891
February	1st to 10th	Day	42% 12% 18% 20% 6% 2	1824
	11th to 20th	Day	39% 11% 17% 20% 11% 2	1860
	21st to end	Day	34% 11% 21% 24% 9% 2	1570
March	1st to 10th	Day	42% 14% 18% 17% 8% 1	3138
	11th to 20th	Day	26% 9% 19% 31% 13% 1	3397
	21st to end	Day	49% 13% 17% 14% 5% 1	3931
April	1st to 10th	Day	38% 9% 16% 21% 13% 3	2280
	11th to 20th	Day	32% 9% 14% 23% 19% 3	2266
	21st to end	Day	32% 7% 14% 26% 18% 3	2470
May	1st to 10th	Day	26% 10% 15% 25% 18% 5%	4110
	11th to 20th	Day	19% 6% 8% 22% 37% 9%	4074
	21st to end	Day	22% 7% 11% 27% 29% 4	4626
June	1st to 10th	Day	25% 6% 12% 20% 28% 8%	2660
	11th to 20th	Day	19% 5% 8% 17% 30% 22%	2660
	21st to end	Day	12% 3 5% 14% 29% 37%	2660
July	1st to 10th	Day	9% 2 3 7% 13% 66%	4351
	11th to 20th	Day	14% 4 4 7% 17% 53%	4345
	21st to end	Day	15% 5% 6% 9% 25% 41%	4535
August	1st to 10th	Day	16% 3 5% 8% 19% 49%	4078
	11th to 20th	Day	11% 3 4 7% 21% 55%	4005
	21st to end	Day	11% 2 4 10% 26% 47%	4179
September	1st to 10th	Day	12% 3 6% 10% 28% 41%	2256
	11th to 20th	Day	16% 5% 7% 16% 29% 27%	2090
	21st to end	Day	17% 3 5% 16% 31% 26%	2090
October	1st to 10th	Day	24% 5% 8% 18% 28% 17%	2090
	11th to 20th	Day	21% 5% 8% 24% 32% 11%	1929
	21st to end	Day	20% 6% 13% 32% 23% 7%	1881
November	1st to 10th	Day	34% 9% 11% 22% 19% 5%	1683
	11th to 20th	Day	31% 9% 12% 31% 15% 2	1710
	21st to end	Day	38% 6% 15% 22% 15% 3	1710
December	1st to 10th	Day	40% 11% 16% 21% 8% 3	1696
	11th to 20th	Day	43% 14% 17% 16% 10% 1	1928
	21st to end	Day	43% 14% 15% 16% 12%	2794
January	1st to 10th	Night	47% 13% 20% 15% 5% 1	4406
	11th to 20th	Night	54% 15% 14% 8% 6% 2	4420
	21st to end	Night	46% 22% 15% 11% 5% 2	4765
February	1st to 10th	Night	38% 11% 20% 22% 7% 2	2352
	11th to 20th	Night	36% 10% 17% 23% 13% 2	2219
	21st to end	Night	38% 10% 20% 22% 9% 2	1884
March	1st to 10th	Night	42% 10% 19% 20% 8% 2	3736
	11th to 20th	Night	26% 10% 19% 29% 14% 1	3570
	21st to end	Night	35% 13% 19% 23% 8% 1	3719
April	1st to 10th	Night	35% 10% 16% 23% 13% 3	1900
	11th to 20th	Night	29% 8% 13% 28% 17% 4	1864
	21st to end	Night	30% 8% 14% 23% 23% 3	1710
May	1st to 10th	Night	28% 7% 13% 26% 22% 4	2860
	11th to 20th	Night	19% 6% 8% 23% 35% 9%	2835
	21st to end	Night	25% 9% 11% 23% 27% 5%	2950
June	1st to 10th	Night	21% 7% 14% 21% 30% 7%	1520
	11th to 20th	Night	20% 5% 7% 18% 29% 21%	1520
	21st to end	Night	14% 4 7% 11% 29% 35%	1520
July	1st to 10th	Night	12% 3 5% 6% 12% 62%	2500
	11th to 20th	Night	23% 5% 6% 8% 17% 41%	2492
	21st to end	Night	24% 5% 5% 10% 17% 39%	2782
August	1st to 10th	Night	19% 5% 6% 11% 18% 42%	2838
	11th to 20th	Night	15% 3 5% 7% 20% 49%	2898
	21st to end	Night	14% 2 4 9% 20% 51%	3498
September	1st to 10th	Night	14% 3 6% 10% 26% 40%	1924
	11th to 20th	Night	18% 4 7% 14% 27% 31%	2090
	21st to end	Night	15% 3 5% 14% 32% 30%	2090
October	1st to 10th	Night	21% 6% 8% 18% 29% 19%	2090
	11th to 20th	Night	22% 5% 6% 21% 33% 13%	2247
	21st to end	Night	19% 5% 11% 30% 28% 8%	2717
November	1st to 10th	Night	33% 8% 12% 20% 20% 8%	2430
	11th to 20th	Night	27% 7% 14% 25% 23% 3	2470
	21st to end	Night	32% 8% 15% 26% 15% 3	2470
December	1st to 10th	Night	38% 10% 16% 23% 9% 4	2481
	11th to 20th	Night	44% 11% 18% 18% 8% 1	3276
	21st to end	Night	42% 16% 20% 15% 6% 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% 9% 22% 31% 21% 5%	180
	11th to 20th	Day	9% 8% 13% 34% 25% 11%	180
	21st to end	Day	7% 8% 17% 30% 25% 15%	226
February	1st to 10th	Day	7% 7% 32% 28% 20% 6%	384
	11th to 20th	Day	6% 10% 27% 33% 18% 5%	455
	21st to end	Day	3 11% 30% 34% 19% 3	382
March	1st to 10th	Day	7% 9% 23% 36% 22% 3	460
	11th to 20th	Day	3 11% 24% 32% 24% 6%	460
	21st to end	Day	8% 12% 25% 36% 16% 3	506
April	1st to 10th	Day	10% 13% 22% 28% 21% 6%	460
	11th to 20th	Day	6% 12% 28% 35% 14% 5%	452
	21st to end	Day	10% 10% 23% 31% 21% 5%	460
May	1st to 10th	Day	5% 14% 25% 32% 16% 8%	463
	11th to 20th	Day	10% 7% 27% 31% 16% 9%	488
	21st to end	Day	10% 12% 20% 26% 22% 10%	529
June	1st to 10th	Day	5% 11% 22% 25% 26% 10%	490
	11th to 20th	Day	7% 13% 26% 30% 18% 6%	490
	21st to end	Day	3 7% 25% 34% 20% 12%	490
July	1st to 10th	Day	3 5% 24% 33% 26% 8%	486
	11th to 20th	Day	2 4 22% 35% 26% 11%	484
	21st to end	Day	3 2 19% 30% 32% 13%	531
August	1st to 10th	Day	6% 4 22% 29% 29% 11%	487
	11th to 20th	Day	3 4 23% 27% 29% 15%	477
	21st to end	Day	2 4 21% 29% 29% 15%	539
September	1st to 10th	Day	2 6% 18% 28% 27% 20%	490
	11th to 20th	Day	4 10% 19% 28% 25% 14%	490
	21st to end	Day	6% 6% 20% 29% 27% 12%	490
October	1st to 10th	Day	3 9% 22% 23% 27% 16%	490
	11th to 20th	Day	5% 10% 19% 22% 29% 15%	394
	21st to end	Day	7% 8% 18% 33% 26% 8%	330
November	1st to 10th	Day	6% 11% 21% 29% 26% 7%	273
	11th to 20th	Day	9% 5% 20% 34% 24% 9%	270
	21st to end	Day	9% 9% 14% 33% 26% 8%	270
December	1st to 10th	Day	7% 9% 19% 33% 22% 11%	264
	11th to 20th	Day	4 8% 21% 28% 29% 9%	180
	21st to end	Day	11% 10% 18% 33% 23% 6%	198
January	1st to 10th	Night	9% 7% 19% 35% 25% 5%	760
	11th to 20th	Night	6% 7% 22% 36% 25% 4	760
	21st to end	Night	10% 5% 17% 39% 24% 6%	836
February	1st to 10th	Night	6% 7% 21% 42% 21% 3	760
	11th to 20th	Night	6% 3 22% 48% 18% 2	744
	21st to end	Night	5% 6% 26% 43% 19% 2	628
March	1st to 10th	Night	7% 5% 24% 43% 18% 3	760
	11th to 20th	Night	6% 5% 21% 42% 25% 2	760
	21st to end	Night	10% 6% 22% 43% 17% 1	836
April	1st to 10th	Night	8% 5% 24% 41% 20% 2	760
	11th to 20th	Night	8% 7% 23% 40% 19% 3	736
	21st to end	Night	10% 4 23% 36% 24% 3	570
May	1st to 10th	Night	6% 7% 26% 39% 19% 3	570
	11th to 20th	Night	9% 4 21% 34% 28% 4	561
	21st to end	Night	10% 5% 20% 36% 27% 3	522
June	1st to 10th	Night	4 3 22% 39% 29% 3	380
	11th to 20th	Night	6% 3 22% 42% 26% 1	380
	21st to end	Night	3 2 16% 52% 26% 1	380
July	1st to 10th	Night	4 1 10% 52% 32% 1	370
	11th to 20th	Night	3 1 13% 54% 29% 1	368
	21st to end	Night	3 1 9% 50% 35% 1	478
August	1st to 10th	Night	5% 2 13% 47% 32% 1	567
	11th to 20th	Night	3 2 11% 51% 31% 2	598
	21st to end	Night	2 2 11% 44% 37% 3	836
September	1st to 10th	Night	4 2 8% 43% 37% 4	760
	11th to 20th	Night	5% 2 12% 38% 36% 7%	760
	21st to end	Night	5% 2 11% 37% 36% 8%	760
October	1st to 10th	Night	6% 2 17% 39% 33% 4	760
	11th to 20th	Night	4 6% 15% 40% 32% 4	760
	21st to end	Night	6% 3 19% 40% 26% 6%	836
November	1st to 10th	Night	10% 3 15% 39% 29% 4	748
	11th to 20th	Night	7% 4 19% 46% 21% 4	760
	21st to end	Night	5% 4 21% 39% 26% 5%	760
December	1st to 10th	Night	8% 6% 22% 40% 20% 4	760
	11th to 20th	Night	11% 6% 18% 41% 21% 2	760
	21st to end	Night	13% 9% 23% 38% 15% 2	836

Page generated at 2024-10-30 10:19:20. Version ac07

Copyright © 2024 Attilla Danko.