Tatum
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tatum clear sky chart from 2005-11-06 to 2024-11-03.

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	5% 4 1 4 3 3 3 3 5% 7% 62%	101157
	Night	4 4 1 3 3 3 3 3 5% 7% 64%	98002
Transparency	Day	22% 3 7% 19% 28% 21%	100922
	Night	21% 3 7% 19% 28% 21%	97827
Seeing	Day	6% 6% 21% 32% 26% 9%	15039
	Night	6% 5% 31% 40% 17% 1	25026

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	5% 8% 2 5% 3 3 3 2 3 5% 61%	2603
	11th to 20th	Day	3 2 1 1 1 2 2 3 4 6% 75%	3045
	21st to end	Day	6% 6% 2 5% 4 3 4 3 5% 7% 55%	3487
February	1st to 10th	Day	4 5% 2 4 3 3 3 3 5% 5% 65%	1900
	11th to 20th	Day	6% 5% 2 4 3 2 3 3 3 6% 62%	1849
	21st to end	Day	4 5% 2 4 3 3 3 3 4 6% 65%	1570
March	1st to 10th	Day	3 5% 2 4 2 3 3 3 5% 8% 64%	3130
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 4 6% 53%	3279
	21st to end	Day	3 5% 1 5% 4 4 4 4 6% 8% 57%	4165
April	1st to 10th	Day	4 3 1 3 2 3 3 3 4 5% 69%	2280
	11th to 20th	Day	5% 4 1 4 2 2 3 3 4 5% 66%	2251
	21st to end	Day	3 3 1 3 2 2 3 3 4 5% 72%	2280
May	1st to 10th	Day	5% 3 1 2 2 2 2 2 4 4 72%	3822
	11th to 20th	Day	8% 4 1 4 2 3 3 3 5% 6% 62%	4082
	21st to end	Day	5% 2 1 3 3 2 3 2 4 5% 68%	4489
June	1st to 10th	Day	3 3 1 4 4 3 3 3 5% 8% 62%	2470
	11th to 20th	Day	3 2 1 3 3 3 3 3 5% 8% 67%	2599
	21st to end	Day	3 3 1 4 4 4 4 4 6% 8% 59%	2660
July	1st to 10th	Day	8% 4 2 5% 5% 5% 5% 4 7% 9% 46%	4430
	11th to 20th	Day	4 2 1 3 4 4 4 3 5% 8% 62%	4200
	21st to end	Day	5% 3 1 5% 4 4 5% 4 6% 9% 53%	4118
August	1st to 10th	Day	2 2 3 2 3 3 3 5% 9% 68%	3784
	11th to 20th	Day	3 2 1 3 3 3 4 4 6% 8% 61%	3726
	21st to end	Day	6% 4 1 4 4 4 4 4 6% 8% 56%	4180
September	1st to 10th	Day	9% 4 1 5% 4 3 4 4 5% 8% 52%	2280
	11th to 20th	Day	10% 5% 2 6% 4 4 3 3 5% 6% 51%	2145
	21st to end	Day	8% 3 1 4 2 2 2 2 4 5% 66%	2090
October	1st to 10th	Day	7% 3 1 4 3 2 2 3 5% 6% 63%	2090
	11th to 20th	Day	8% 3 1 4 2 2 2 2 2 4 71%	1970
	21st to end	Day	5% 3 1 3 2 2 2 2 4 4 72%	2066
November	1st to 10th	Day	5% 3 1 3 2 2 3 2 3 6% 70%	1691
	11th to 20th	Day	3 4 2 4 2 2 2 2 4 6% 70%	1710
	21st to end	Day	8% 5% 2 3 2 2 3 3 4 6% 64%	1710
December	1st to 10th	Day	6% 4 2 4 2 3 4 3 4 6% 61%	1710
	11th to 20th	Day	3 4 2 4 3 4 4 5% 6% 7% 58%	2161
	21st to end	Day	5% 4 1 3 2 2 2 2 3 5% 71%	3135
January	1st to 10th	Night	3 5% 2 4 3 3 3 4 5% 6% 62%	4339
	11th to 20th	Night	3 3 1 2 2 2 3 3 5% 7% 70%	3912
	21st to end	Night	5% 3 1 5% 3 3 4 4 6% 8% 58%	4180
February	1st to 10th	Night	4 5% 2 4 2 2 3 3 4 6% 65%	2280
	11th to 20th	Night	5% 4 2 5% 3 3 3 3 5% 7% 60%	2218
	21st to end	Night	4 4 1 4 3 3 4 4 5% 6% 63%	1884
March	1st to 10th	Night	3 5% 2 3 2 2 2 2 4 4 69%	3734
	11th to 20th	Night	10% 6% 2 5% 3 3 3 3 5% 7% 54%	3687
	21st to end	Night	2 4 2 3 3 3 4 3 5% 7% 64%	3477
April	1st to 10th	Night	3 3 2 3 2 2 3 3 4 5% 68%	1900
	11th to 20th	Night	6% 3 1 4 3 3 3 2 5% 7% 63%	1877
	21st to end	Night	3 3 1 2 2 2 2 3 4 6% 71%	1900
May	1st to 10th	Night	5% 4 1 2 2 2 1 2 3 5% 73%	3148
	11th to 20th	Night	8% 3 1 3 3 2 3 2 5% 6% 63%	2823
	21st to end	Night	4 3 1 2 2 2 3 3 4 6% 72%	3098
June	1st to 10th	Night	2 3 1 3 3 3 4 5% 7% 11% 58%	1710
	11th to 20th	Night	2 1 3 3 3 3 5% 6% 8% 67%	1573
	21st to end	Night	3 3 1 3 2 3 4 4 7% 10% 60%	1520
July	1st to 10th	Night	3 3 1 4 4 4 5% 4 7% 10% 54%	2540
	11th to 20th	Night	2 2 1 4 4 4 4 4 6% 11% 59%	2762
	21st to end	Night	5% 3 1 4 3 3 4 4 7% 13% 52%	3445
August	1st to 10th	Night	2 2 1 3 3 3 4 3 7% 10% 63%	3155
	11th to 20th	Night	3 2 1 3 3 3 4 3 6% 10% 62%	3113
	21st to end	Night	4 3 1 4 4 3 5% 4 7% 11% 55%	3487
September	1st to 10th	Night	7% 5% 2 4 3 3 4 4 6% 8% 55%	1900
	11th to 20th	Night	8% 4 1 4 3 3 4 3 6% 7% 56%	2033
	21st to end	Night	8% 3 1 3 2 3 3 2 4 5% 66%	2090
October	1st to 10th	Night	6% 3 1 4 2 3 3 3 3 4 67%	2090
	11th to 20th	Night	8% 3 1 2 2 2 2 2 2 4 73%	2207
	21st to end	Night	6% 3 1 2 1 2 2 2 3 4 72%	2510
November	1st to 10th	Night	5% 3 1 2 1 1 3 2 4 5% 73%	2432
	11th to 20th	Night	2 2 1 3 2 3 3 3 4 7% 69%	2470
	21st to end	Night	7% 3 1 3 3 3 3 3 5% 7% 63%	2470
December	1st to 10th	Night	6% 5% 1 4 2 2 3 2 5% 7% 62%	2470
	11th to 20th	Night	4 4 2 4 3 3 4 4 5% 6% 61%	3036
	21st to end	Night	4 5% 1 4 3 3 2 3 3 5% 67%	4532

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	26% 3 3 15% 32% 20%	2604
	11th to 20th	Day	12% 2 7% 22% 40% 17%	3045
	21st to end	Day	28% 4 6% 20% 29% 14%	3487
February	1st to 10th	Day	22% 2 6% 17% 28% 25%	1900
	11th to 20th	Day	25% 3 4 18% 26% 24%	1859
	21st to end	Day	22% 4 2 11% 32% 30%	1570
March	1st to 10th	Day	21% 2 2 10% 32% 33%	3130
	11th to 20th	Day	32% 4 5% 14% 30% 15%	3279
	21st to end	Day	24% 4 4 13% 28% 27%	4165
April	1st to 10th	Day	18% 4 4 14% 30% 31%	2280
	11th to 20th	Day	20% 3 4 16% 24% 33%	2254
	21st to end	Day	16% 2 5% 19% 31% 28%	2280
May	1st to 10th	Day	17% 2 5% 13% 19% 44%	3822
	11th to 20th	Day	23% 4 6% 15% 23% 29%	4086
	21st to end	Day	18% 4 6% 14% 18% 40%	4489
June	1st to 10th	Day	21% 5% 11% 25% 23% 15%	2470
	11th to 20th	Day	16% 3 7% 17% 27% 29%	2599
	21st to end	Day	22% 5% 9% 22% 25% 17%	2660
July	1st to 10th	Day	34% 4 12% 24% 18% 9%	4361
	11th to 20th	Day	21% 3 12% 30% 28% 6%	4125
	21st to end	Day	26% 4 11% 28% 27% 4	3988
August	1st to 10th	Day	14% 3 9% 29% 33% 11%	3772
	11th to 20th	Day	20% 4 11% 20% 34% 11%	3762
	21st to end	Day	26% 4 11% 27% 26% 5%	4179
September	1st to 10th	Day	30% 6% 11% 17% 22% 13%	2280
	11th to 20th	Day	33% 5% 8% 20% 25% 10%	2145
	21st to end	Day	21% 3 5% 20% 33% 18%	2090
October	1st to 10th	Day	22% 4 8% 20% 24% 22%	2090
	11th to 20th	Day	21% 2 4 13% 30% 30%	1970
	21st to end	Day	17% 2 2 20% 33% 25%	2066
November	1st to 10th	Day	18% 2 5% 16% 32% 25%	1691
	11th to 20th	Day	18% 2 5% 19% 36% 20%	1710
	21st to end	Day	22% 3 5% 16% 30% 23%	1710
December	1st to 10th	Day	26% 3 5% 21% 31% 15%	1710
	11th to 20th	Day	25% 4 7% 20% 26% 18%	2159
	21st to end	Day	19% 2 3 20% 33% 23%	3135
January	1st to 10th	Night	21% 4 4 17% 40% 15%	4339
	11th to 20th	Night	15% 2 8% 20% 36% 18%	3912
	21st to end	Night	24% 4 6% 22% 31% 14%	4180
February	1st to 10th	Night	21% 3 5% 17% 26% 28%	2280
	11th to 20th	Night	25% 4 4 16% 27% 25%	2218
	21st to end	Night	22% 4 4 11% 25% 35%	1884
March	1st to 10th	Night	20% 3 2 10% 27% 39%	3734
	11th to 20th	Night	31% 3 6% 17% 24% 19%	3687
	21st to end	Night	20% 4 5% 15% 29% 27%	3477
April	1st to 10th	Night	18% 3 5% 14% 26% 34%	1900
	11th to 20th	Night	21% 4 6% 15% 23% 32%	1877
	21st to end	Night	15% 3 6% 21% 27% 29%	1900
May	1st to 10th	Night	16% 3 5% 15% 17% 44%	3148
	11th to 20th	Night	21% 4 9% 16% 21% 30%	2824
	21st to end	Night	15% 3 8% 14% 14% 46%	3099
June	1st to 10th	Night	19% 5% 13% 26% 21% 16%	1710
	11th to 20th	Night	13% 4 9% 19% 27% 28%	1573
	21st to end	Night	17% 6% 13% 23% 25% 16%	1520
July	1st to 10th	Night	26% 3 17% 33% 17% 4	2500
	11th to 20th	Night	20% 3 15% 26% 31% 5%	2714
	21st to end	Night	24% 3 12% 31% 26% 3	3336
August	1st to 10th	Night	17% 3 10% 29% 31% 10%	3144
	11th to 20th	Night	18% 4 11% 26% 33% 8%	3143
	21st to end	Night	23% 4 14% 28% 25% 5%	3487
September	1st to 10th	Night	28% 6% 12% 18% 25% 12%	1900
	11th to 20th	Night	27% 5% 12% 21% 23% 11%	2033
	21st to end	Night	22% 3 6% 18% 32% 19%	2090
October	1st to 10th	Night	22% 4 8% 20% 23% 24%	2090
	11th to 20th	Night	19% 1 5% 14% 30% 31%	2207
	21st to end	Night	18% 2 4 16% 33% 28%	2510
November	1st to 10th	Night	15% 3 5% 19% 33% 26%	2432
	11th to 20th	Night	16% 4 4 16% 36% 24%	2470
	21st to end	Night	23% 2 4 17% 32% 23%	2470
December	1st to 10th	Night	23% 2 4 20% 31% 20%	2470
	11th to 20th	Night	23% 3 5% 18% 32% 19%	3037
	21st to end	Night	21% 3 3 15% 38% 20%	4532

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	10% 7% 41% 29% 13% 1	270
	11th to 20th	Day	8% 12% 35% 29% 14% 2	270
	21st to end	Day	4 11% 33% 33% 16% 2	297
February	1st to 10th	Day	8% 10% 35% 34% 11% 1	270
	11th to 20th	Day	8% 11% 38% 30% 11% 1	270
	21st to end	Day	7% 17% 41% 31% 4	225
March	1st to 10th	Day	7% 9% 37% 37% 9% 1	270
	11th to 20th	Day	11% 13% 24% 36% 12% 3	313
	21st to end	Day	6% 15% 37% 31% 8% 2	506
April	1st to 10th	Day	7% 12% 36% 33% 12% 1	460
	11th to 20th	Day	7% 12% 43% 27% 10% 1	452
	21st to end	Day	5% 11% 36% 34% 13% 2	460
May	1st to 10th	Day	4 10% 34% 39% 12% 2	472
	11th to 20th	Day	7% 5% 27% 36% 21% 4	675
	21st to end	Day	5% 5% 29% 40% 19% 2	734
June	1st to 10th	Day	4 3 15% 41% 30% 7%	680
	11th to 20th	Day	4 1 17% 47% 26% 5%	680
	21st to end	Day	4 1 10% 36% 39% 10%	680
July	1st to 10th	Day	5% 6% 29% 42% 17%	671
	11th to 20th	Day	3 1 3 26% 47% 20%	622
	21st to end	Day	3 1 2 20% 46% 28%	531
August	1st to 10th	Day	3 1 5% 19% 45% 26%	487
	11th to 20th	Day	5% 1 6% 21% 45% 22%	477
	21st to end	Day	7% 1 4 22% 40% 27%	539
September	1st to 10th	Day	9% 4 27% 40% 20%	490
	11th to 20th	Day	5% 1 6% 26% 46% 17%	355
	21st to end	Day	12% 1 7% 22% 43% 15%	300
October	1st to 10th	Day	11% 2 14% 30% 33% 9%	300
	11th to 20th	Day	9% 2 22% 31% 24% 11%	300
	21st to end	Day	9% 5% 25% 26% 24% 11%	330
November	1st to 10th	Day	10% 5% 25% 32% 25% 4	276
	11th to 20th	Day	3 10% 21% 35% 23% 8%	270
	21st to end	Day	9% 13% 31% 27% 15% 4	270
December	1st to 10th	Day	9% 10% 30% 33% 17% 1	270
	11th to 20th	Day	5% 10% 34% 39% 12% 1	270
	21st to end	Day	8% 8% 42% 34% 8% 1	297
January	1st to 10th	Night	6% 7% 34% 40% 12% 1	932
	11th to 20th	Night	7% 6% 38% 35% 12% 2	760
	21st to end	Night	6% 7% 37% 40% 9%	836
February	1st to 10th	Night	7% 6% 45% 32% 9% 1	760
	11th to 20th	Night	8% 8% 45% 33% 6% 1	744
	21st to end	Night	6% 9% 52% 29% 3	628
March	1st to 10th	Night	7% 9% 43% 36% 5%	760
	11th to 20th	Night	10% 9% 36% 36% 7% 1	743
	21st to end	Night	4 11% 49% 31% 5%	627
April	1st to 10th	Night	5% 9% 47% 34% 5%	570
	11th to 20th	Night	7% 9% 51% 31% 2	563
	21st to end	Night	4 9% 46% 35% 5%	570
May	1st to 10th	Night	6% 7% 45% 38% 4	570
	11th to 20th	Night	7% 4 35% 43% 10% 1	561
	21st to end	Night	6% 4 40% 41% 9%	617
June	1st to 10th	Night	3 2 35% 51% 9%	570
	11th to 20th	Night	2 1 36% 52% 9%	570
	21st to end	Night	3 1 24% 49% 22%	570
July	1st to 10th	Night	5% 1 12% 49% 31% 2	555
	11th to 20th	Night	3 5% 49% 41% 2	552
	21st to end	Night	3 1 5% 44% 45% 2	624
August	1st to 10th	Night	2 1 5% 40% 50% 2	567
	11th to 20th	Night	4 1 6% 41% 47% 1	564
	21st to end	Night	5% 1 6% 40% 46% 2	627
September	1st to 10th	Night	7% 2 8% 46% 35% 3	570
	11th to 20th	Night	9% 1 12% 47% 29% 1	570
	21st to end	Night	9% 1 14% 47% 28% 1	570
October	1st to 10th	Night	7% 3 21% 48% 22%	570
	11th to 20th	Night	10% 3 25% 44% 17% 2	687
	21st to end	Night	8% 6% 25% 37% 22% 2	838
November	1st to 10th	Night	7% 3 24% 45% 20% 1	936
	11th to 20th	Night	2 5% 28% 45% 18% 1	950
	21st to end	Night	9% 7% 29% 37% 16% 1	950
December	1st to 10th	Night	9% 5% 33% 39% 13% 1	950
	11th to 20th	Night	8% 6% 39% 38% 9%	950
	21st to end	Night	8% 9% 38% 34% 9% 1	1045

Page generated at 2024-10-31 01:39:23. Version ac07

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