Marshall
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marshall clear sky chart from 2005-11-06 to 2024-11-12.

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	9% 6% 2 5% 3 3 3 3 5% 8% 51%	105125
	Night	10% 8% 3 7% 4 3 3 3 4 6% 48%	102823
Transparency	Day	28% 7% 12% 19% 19% 15%	104887
	Night	34% 6% 9% 17% 19% 15%	102651
Seeing	Day	10% 9% 24% 30% 20% 7%	15459
	Night	12% 6% 17% 29% 28% 7%	24716

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	18% 8% 3 7% 4 3 4 2 5% 7% 39%	2766
	11th to 20th	Day	21% 10% 4 9% 5% 4 3 3 5% 5% 31%	2860
	21st to end	Day	23% 9% 3 8% 5% 4 4 3 5% 6% 30%	3146
February	1st to 10th	Day	18% 6% 3 5% 4 4 4 4 4 4 44%	1710
	11th to 20th	Day	13% 8% 3 7% 5% 5% 4 3 5% 9% 39%	1694
	21st to end	Day	16% 7% 2 4 3 4 3 3 5% 7% 46%	1579
March	1st to 10th	Day	17% 12% 3 9% 6% 4 4 3 5% 6% 31%	3442
	11th to 20th	Day	11% 5% 2 4 3 3 4 4 5% 8% 51%	3490
	21st to end	Day	17% 8% 3 6% 5% 4 4 4 7% 8% 35%	3825
April	1st to 10th	Day	13% 8% 3 6% 5% 5% 4 4 5% 6% 42%	2279
	11th to 20th	Day	8% 6% 3 5% 4 4 4 4 5% 7% 50%	2249
	21st to end	Day	7% 4 2 4 3 3 3 3 6% 12% 54%	2280
May	1st to 10th	Day	6% 4 2 3 2 2 2 2 3 6% 68%	4061
	11th to 20th	Day	4 3 1 4 3 2 3 3 5% 11% 60%	4091
	21st to end	Day	4 6% 2 3 2 2 2 2 4 5% 69%	4813
June	1st to 10th	Day	7% 7% 2 4 3 3 3 3 6% 9% 53%	2660
	11th to 20th	Day	2 4 2 3 2 2 3 3 5% 9% 66%	2660
	21st to end	Day	2 5% 2 5% 3 3 3 2 5% 8% 61%	2660
July	1st to 10th	Day	1 4 1 2 2 2 2 2 4 9% 70%	4365
	11th to 20th	Day	1 5% 2 4 3 3 3 3 7% 10% 59%	4110
	21st to end	Day	1 6% 4 7% 4 4 5% 3 6% 12% 49%	4455
August	1st to 10th	Day	2 5% 3 8% 4 4 5% 5% 9% 17% 37%	4091
	11th to 20th	Day	1 7% 2 4 3 3 4 3 5% 9% 60%	3916
	21st to end	Day	2 6% 3 6% 3 3 4 3 6% 12% 52%	4180
September	1st to 10th	Day	1 5% 1 4 3 3 3 3 6% 10% 61%	2280
	11th to 20th	Day	5% 7% 3 4 4 4 4 4 5% 9% 51%	2256
	21st to end	Day	4 4 1 3 2 3 3 3 4 7% 67%	2009
October	1st to 10th	Day	4 3 1 3 2 2 3 2 4 8% 68%	3180
	11th to 20th	Day	9% 6% 2 6% 3 3 3 3 5% 7% 54%	3161
	21st to end	Day	8% 6% 2 5% 3 3 4 4 6% 8% 51%	3448
November	1st to 10th	Day	9% 5% 1 5% 4 3 4 3 5% 9% 51%	1959
	11th to 20th	Day	13% 7% 3 6% 4 3 3 4 5% 7% 45%	1688
	21st to end	Day	11% 6% 2 5% 3 4 5% 2 5% 7% 51%	1520
December	1st to 10th	Day	16% 7% 2 6% 3 3 3 3 6% 6% 44%	1520
	11th to 20th	Day	27% 10% 4 6% 5% 4 3 3 4 5% 29%	1928
	21st to end	Day	24% 9% 3 6% 3 3 3 3 5% 7% 34%	2794
January	1st to 10th	Night	16% 8% 2 6% 4 4 4 4 5% 7% 39%	4185
	11th to 20th	Night	22% 9% 3 8% 6% 4 5% 4 5% 6% 29%	4110
	21st to end	Night	24% 13% 3 8% 4 3 4 3 4 5% 28%	4521
February	1st to 10th	Night	17% 7% 2 5% 3 4 3 2 5% 6% 46%	2470
	11th to 20th	Night	13% 7% 3 7% 5% 4 4 4 6% 7% 40%	2370
	21st to end	Night	14% 7% 2 4 3 4 3 3 5% 6% 50%	1874
March	1st to 10th	Night	18% 12% 4 8% 5% 4 4 3 4 6% 33%	3432
	11th to 20th	Night	13% 6% 4 5% 3 3 2 2 4 6% 52%	3490
	21st to end	Night	14% 13% 3 7% 4 4 3 3 4 7% 38%	3828
April	1st to 10th	Night	10% 9% 3 5% 5% 3 3 2 5% 8% 46%	1900
	11th to 20th	Night	9% 7% 3 5% 3 3 3 3 4 7% 53%	1879
	21st to end	Night	6% 6% 2 5% 3 3 3 3 5% 8% 57%	1900
May	1st to 10th	Night	6% 5% 1 4 3 2 2 2 2 4 69%	2906
	11th to 20th	Night	3 6% 4 10% 4 3 3 2 4 6% 56%	2809
	21st to end	Night	4 7% 2 3 2 2 2 1 3 4 71%	2762
June	1st to 10th	Night	6% 7% 2 5% 3 3 4 4 6% 10% 50%	1520
	11th to 20th	Night	2 5% 2 5% 3 2 4 3 4 6% 66%	1520
	21st to end	Night	4 8% 2 5% 2 2 3 2 3 7% 62%	1520
July	1st to 10th	Night	1 5% 4 4 3 2 2 2 2 6% 68%	2593
	11th to 20th	Night	2 12% 5% 7% 3 3 2 2 4 8% 52%	2860
	21st to end	Night	1 14% 7% 11% 4 4 4 3 5% 8% 38%	3109
August	1st to 10th	Night	3 11% 11% 16% 4 4 3 2 4 7% 34%	2848
	11th to 20th	Night	9% 4 7% 3 4 3 2 4 6% 58%	2926
	21st to end	Night	3 10% 5% 8% 4 4 3 3 5% 6% 49%	3498
September	1st to 10th	Night	6% 3 6% 4 4 3 3 4 7% 59%	1900
	11th to 20th	Night	6% 10% 3 7% 4 4 3 3 4 8% 50%	1921
	21st to end	Night	3 7% 2 6% 3 2 2 3 4 6% 61%	2170
October	1st to 10th	Night	4 4 2 5% 2 2 3 2 5% 6% 66%	3800
	11th to 20th	Night	5% 11% 5% 9% 3 3 3 2 3 4 52%	3777
	21st to end	Night	10% 5% 1 5% 3 3 3 3 5% 7% 55%	4121
November	1st to 10th	Night	10% 6% 2 6% 4 3 4 3 5% 7% 50%	2340
	11th to 20th	Night	11% 8% 3 5% 4 4 4 3 6% 7% 45%	2506
	21st to end	Night	10% 5% 1 6% 4 3 4 3 5% 6% 52%	2660
December	1st to 10th	Night	18% 7% 3 6% 4 3 3 2 5% 7% 42%	2660
	11th to 20th	Night	29% 8% 2 6% 4 3 3 3 5% 6% 30%	3276
	21st to end	Night	21% 8% 3 7% 5% 4 4 3 4 6% 35%	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	42% 7% 17% 24% 7% 3	2766
	11th to 20th	Day	54% 7% 11% 12% 10% 6%	2860
	21st to end	Day	53% 6% 11% 16% 10% 4	3146
February	1st to 10th	Day	41% 6% 8% 20% 19% 7%	1710
	11th to 20th	Day	41% 7% 10% 18% 18% 6%	1703
	21st to end	Day	37% 6% 9% 26% 15% 6%	1579
March	1st to 10th	Day	51% 9% 11% 15% 12% 2	3442
	11th to 20th	Day	28% 9% 14% 26% 11% 12%	3490
	21st to end	Day	41% 10% 17% 21% 9% 2	3825
April	1st to 10th	Day	40% 7% 13% 19% 16% 4	2279
	11th to 20th	Day	31% 7% 15% 23% 19% 4	2252
	21st to end	Day	24% 6% 18% 28% 21% 4	2280
May	1st to 10th	Day	18% 6% 13% 27% 24% 13%	4061
	11th to 20th	Day	18% 9% 17% 23% 24% 9%	4094
	21st to end	Day	18% 7% 10% 34% 29% 2	4814
June	1st to 10th	Day	27% 7% 13% 26% 22% 6%	2660
	11th to 20th	Day	15% 9% 11% 19% 33% 13%	2660
	21st to end	Day	18% 8% 11% 14% 27% 23%	2660
July	1st to 10th	Day	11% 4 7% 10% 11% 57%	4297
	11th to 20th	Day	16% 5% 10% 11% 12% 46%	4041
	21st to end	Day	18% 8% 16% 8% 18% 31%	4315
August	1st to 10th	Day	23% 5% 13% 12% 21% 26%	4076
	11th to 20th	Day	16% 7% 11% 12% 33% 21%	3955
	21st to end	Day	21% 7% 9% 15% 27% 21%	4179
September	1st to 10th	Day	17% 6% 8% 15% 23% 31%	2280
	11th to 20th	Day	26% 9% 11% 19% 25% 10%	2256
	21st to end	Day	16% 7% 9% 19% 29% 20%	2009
October	1st to 10th	Day	17% 3 7% 12% 25% 36%	3180
	11th to 20th	Day	27% 7% 7% 20% 25% 14%	3161
	21st to end	Day	28% 6% 11% 22% 23% 11%	3448
November	1st to 10th	Day	30% 6% 11% 26% 17% 10%	1959
	11th to 20th	Day	38% 6% 12% 22% 15% 7%	1688
	21st to end	Day	33% 6% 12% 20% 19% 10%	1520
December	1st to 10th	Day	41% 7% 10% 18% 17% 8%	1520
	11th to 20th	Day	58% 5% 9% 11% 14% 3	1928
	21st to end	Day	48% 6% 16% 19% 9% 3	2794
January	1st to 10th	Night	40% 9% 19% 22% 7% 3	4185
	11th to 20th	Night	52% 8% 12% 12% 8% 7%	4110
	21st to end	Night	54% 8% 10% 11% 11% 6%	4521
February	1st to 10th	Night	38% 5% 9% 20% 17% 10%	2470
	11th to 20th	Night	41% 6% 9% 19% 18% 7%	2372
	21st to end	Night	34% 5% 12% 26% 18% 5%	1874
March	1st to 10th	Night	48% 9% 11% 16% 13% 3	3432
	11th to 20th	Night	30% 8% 11% 21% 21% 10%	3490
	21st to end	Night	41% 11% 14% 21% 10% 3	3828
April	1st to 10th	Night	34% 8% 12% 22% 20% 5%	1900
	11th to 20th	Night	30% 6% 11% 25% 20% 7%	1879
	21st to end	Night	25% 5% 10% 30% 23% 6%	1900
May	1st to 10th	Night	20% 4 6% 27% 29% 14%	2906
	11th to 20th	Night	24% 9% 8% 18% 26% 16%	2810
	21st to end	Night	18% 4 8% 34% 33% 3	2762
June	1st to 10th	Night	27% 9% 10% 18% 29% 6%	1520
	11th to 20th	Night	18% 6% 8% 18% 32% 18%	1520
	21st to end	Night	20% 7% 5% 12% 28% 29%	1520
July	1st to 10th	Night	15% 4 4 4 14% 57%	2552
	11th to 20th	Night	28% 4 6% 7% 11% 43%	2806
	21st to end	Night	36% 5% 10% 5% 11% 33%	3011
August	1st to 10th	Night	43% 4 10% 8% 17% 18%	2839
	11th to 20th	Night	23% 5% 7% 6% 34% 24%	2953
	21st to end	Night	29% 5% 9% 10% 26% 21%	3498
September	1st to 10th	Night	20% 5% 6% 9% 27% 32%	1900
	11th to 20th	Night	30% 7% 7% 19% 25% 13%	1921
	21st to end	Night	21% 5% 6% 20% 25% 22%	2170
October	1st to 10th	Night	17% 3 6% 10% 22% 42%	3800
	11th to 20th	Night	32% 8% 5% 16% 19% 20%	3777
	21st to end	Night	28% 5% 5% 21% 24% 17%	4121
November	1st to 10th	Night	32% 6% 10% 25% 16% 11%	2340
	11th to 20th	Night	35% 7% 10% 24% 15% 8%	2506
	21st to end	Night	32% 5% 11% 19% 22% 11%	2660
December	1st to 10th	Night	41% 6% 8% 18% 17% 10%	2660
	11th to 20th	Night	55% 5% 10% 14% 14% 4	3276
	21st to end	Night	49% 7% 13% 17% 11% 3	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	27% 11% 25% 19% 15% 3	316
	11th to 20th	Day	22% 8% 22% 28% 17% 3	370
	21st to end	Day	17% 8% 24% 29% 19% 3	407
February	1st to 10th	Day	16% 11% 22% 26% 19% 5%	370
	11th to 20th	Day	17% 15% 26% 25% 14% 3	379
	21st to end	Day	17% 10% 27% 28% 16% 2	382
March	1st to 10th	Day	22% 14% 28% 23% 10% 2	460
	11th to 20th	Day	22% 12% 25% 23% 13% 5%	460
	21st to end	Day	17% 13% 35% 25% 8% 2	506
April	1st to 10th	Day	16% 16% 28% 24% 11% 5%	460
	11th to 20th	Day	13% 13% 32% 24% 12% 5%	452
	21st to end	Day	9% 16% 30% 26% 13% 5%	460
May	1st to 10th	Day	10% 15% 30% 29% 14% 3	463
	11th to 20th	Day	11% 13% 28% 27% 16% 5%	488
	21st to end	Day	11% 12% 26% 27% 17% 8%	529
June	1st to 10th	Day	7% 11% 27% 33% 14% 7%	490
	11th to 20th	Day	3 14% 28% 36% 15% 4	490
	21st to end	Day	2 5% 27% 34% 24% 7%	490
July	1st to 10th	Day	4 7% 20% 42% 22% 6%	486
	11th to 20th	Day	2 1 20% 41% 26% 11%	484
	21st to end	Day	2 4 15% 45% 24% 10%	531
August	1st to 10th	Day	3 5% 23% 38% 21% 9%	487
	11th to 20th	Day	4 5% 23% 33% 26% 9%	477
	21st to end	Day	6% 5% 16% 37% 27% 10%	539
September	1st to 10th	Day	3 4 18% 36% 28% 11%	490
	11th to 20th	Day	6% 8% 23% 33% 22% 9%	490
	21st to end	Day	4 8% 21% 32% 27% 10%	490
October	1st to 10th	Day	6% 6% 22% 28% 24% 13%	490
	11th to 20th	Day	8% 9% 18% 27% 26% 12%	490
	21st to end	Day	12% 9% 18% 29% 23% 10%	539
November	1st to 10th	Day	10% 9% 18% 27% 26% 9%	495
	11th to 20th	Day	11% 8% 14% 25% 25% 17%	261
	21st to end	Day	11% 7% 21% 28% 23% 11%	180
December	1st to 10th	Day	22% 10% 16% 19% 22% 11%	180
	11th to 20th	Day	22% 8% 21% 22% 21% 7%	180
	21st to end	Day	19% 14% 20% 27% 19% 2	198
January	1st to 10th	Night	19% 6% 16% 28% 24% 6%	760
	11th to 20th	Night	19% 6% 16% 29% 24% 5%	760
	21st to end	Night	19% 6% 14% 31% 26% 4	836
February	1st to 10th	Night	20% 6% 15% 30% 26% 4	760
	11th to 20th	Night	16% 8% 20% 27% 23% 6%	744
	21st to end	Night	16% 9% 19% 32% 20% 3	628
March	1st to 10th	Night	21% 10% 17% 28% 20% 4	760
	11th to 20th	Night	18% 7% 17% 33% 21% 3	760
	21st to end	Night	17% 10% 26% 29% 16% 2	836
April	1st to 10th	Night	13% 7% 27% 30% 18% 4	760
	11th to 20th	Night	11% 10% 27% 28% 19% 6%	751
	21st to end	Night	7% 10% 31% 25% 21% 6%	760
May	1st to 10th	Night	8% 7% 26% 31% 23% 6%	603
	11th to 20th	Night	7% 3 23% 33% 29% 5%	550
	21st to end	Night	9% 9% 24% 31% 22% 6%	411
June	1st to 10th	Night	9% 5% 24% 34% 26% 3	380
	11th to 20th	Night	2 5% 23% 42% 25% 3	380
	21st to end	Night	6% 3 15% 37% 33% 5%	380
July	1st to 10th	Night	3 3 17% 33% 36% 9%	396
	11th to 20th	Night	5% 1 11% 24% 40% 18%	552
	21st to end	Night	4 3 10% 26% 43% 13%	624
August	1st to 10th	Night	10% 4 14% 28% 34% 11%	567
	11th to 20th	Night	4 3 14% 29% 39% 12%	626
	21st to end	Night	7% 3 12% 26% 42% 10%	836
September	1st to 10th	Night	3 1 12% 28% 44% 12%	760
	11th to 20th	Night	9% 4 14% 29% 33% 10%	760
	21st to end	Night	5% 4 12% 28% 38% 12%	760
October	1st to 10th	Night	7% 4 15% 28% 34% 12%	760
	11th to 20th	Night	8% 5% 13% 25% 38% 11%	760
	21st to end	Night	11% 4 12% 26% 33% 14%	836
November	1st to 10th	Night	11% 4 15% 26% 33% 11%	780
	11th to 20th	Night	13% 4 11% 33% 31% 8%	764
	21st to end	Night	12% 4 16% 34% 28% 6%	760
December	1st to 10th	Night	20% 4 16% 30% 24% 6%	760
	11th to 20th	Night	25% 6% 15% 28% 22% 3	760
	21st to end	Night	21% 8% 21% 31% 18% 2	836

Page generated at 2024-11-08 19:45:34. Version ac07

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