Distant Thunder Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Distant Thunder Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 40%	100507
	Night	12% 6% 2 5% 4 4 4 4 6% 8% 45%	98969
Transparency	Day	21% 48% 7% 10% 10% 4	104241
	Night	20% 47% 7% 10% 10% 5%	103374
Seeing	Day	13% 7% 19% 25% 24% 12%	14741
	Night	13% 5% 19% 31% 25% 7%	24343

By Month

Percentage Cloud Cover SE (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	16% 7% 2 6% 4 4 4 4 6% 7% 41%	2874
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 3 5% 55%	2941
	21st to end	Day	24% 7% 2 6% 4 3 4 3 4 5% 37%	3476
February	1st to 10th	Day	16% 9% 3 7% 4 4 4 4 5% 5% 39%	1900
	11th to 20th	Day	17% 8% 2 4 4 3 3 3 5% 7% 43%	1848
	21st to end	Day	16% 8% 3 8% 6% 3 4 3 5% 6% 38%	1570
March	1st to 10th	Day	23% 9% 3 7% 4 4 4 3 6% 8% 30%	3248
	11th to 20th	Day	14% 8% 3 7% 5% 5% 4 5% 7% 8% 35%	3480
	21st to end	Day	11% 6% 3 6% 5% 5% 5% 5% 6% 6% 42%	4021
April	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 8% 41%	2280
	11th to 20th	Day	13% 6% 3 7% 5% 4 5% 4 5% 8% 40%	2254
	21st to end	Day	9% 5% 2 4 4 5% 4 3 8% 7% 49%	2280
May	1st to 10th	Day	11% 5% 2 7% 4 6% 5% 6% 7% 10% 37%	3765
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 6% 8% 42%	3764
	21st to end	Day	5% 3 2 6% 4 4 5% 5% 8% 12% 46%	4129
June	1st to 10th	Day	9% 6% 3 6% 6% 6% 6% 6% 9% 10% 33%	2280
	11th to 20th	Day	4 5% 2 7% 6% 6% 7% 7% 8% 12% 35%	2393
	21st to end	Day	7% 6% 2 7% 6% 8% 8% 7% 9% 11% 28%	2470
July	1st to 10th	Day	6% 6% 3 8% 8% 8% 7% 7% 10% 14% 24%	4120
	11th to 20th	Day	5% 5% 2 7% 7% 7% 7% 7% 11% 14% 28%	4002
	21st to end	Day	7% 6% 3 9% 7% 7% 8% 7% 10% 13% 23%	4118
August	1st to 10th	Day	3 2 1 4 4 5% 5% 4 7% 11% 52%	3785
	11th to 20th	Day	5% 3 2 5% 5% 6% 7% 6% 9% 12% 39%	3729
	21st to end	Day	8% 6% 3 10% 6% 7% 7% 6% 8% 9% 32%	4180
September	1st to 10th	Day	10% 6% 2 7% 6% 5% 7% 5% 8% 10% 33%	2280
	11th to 20th	Day	10% 5% 3 6% 5% 6% 6% 5% 7% 9% 38%	2214
	21st to end	Day	8% 4 2 5% 4 5% 5% 4 7% 8% 48%	2090
October	1st to 10th	Day	6% 3 2 4 3 4 4 3 6% 8% 55%	2024
	11th to 20th	Day	6% 4 1 4 4 4 4 3 6% 7% 57%	1900
	21st to end	Day	10% 4 1 5% 3 3 3 3 4 6% 58%	2090
November	1st to 10th	Day	8% 5% 2 5% 3 4 4 5% 6% 6% 53%	1958
	11th to 20th	Day	11% 5% 1 4 3 3 3 3 5% 6% 55%	1900
	21st to end	Day	13% 5% 2 6% 4 4 4 3 5% 7% 46%	1773
December	1st to 10th	Day	15% 6% 3 5% 4 3 5% 3 5% 7% 43%	1710
	11th to 20th	Day	15% 9% 3 7% 4 5% 4 4 5% 7% 39%	2185
	21st to end	Day	18% 8% 2 7% 4 4 5% 4 5% 6% 38%	3476
January	1st to 10th	Night	17% 8% 2 4 3 3 4 3 5% 6% 47%	4053
	11th to 20th	Night	16% 6% 2 4 3 3 3 2 4 6% 53%	4015
	21st to end	Night	26% 7% 2 4 2 2 3 3 4 6% 40%	4180
February	1st to 10th	Night	17% 7% 2 6% 4 3 4 3 4 6% 43%	2280
	11th to 20th	Night	18% 8% 3 5% 4 3 3 3 5% 6% 42%	2218
	21st to end	Night	20% 8% 2 7% 4 3 3 4 5% 6% 39%	1884
March	1st to 10th	Night	24% 11% 3 7% 4 3 4 3 4 6% 30%	3619
	11th to 20th	Night	15% 7% 2 7% 5% 5% 5% 4 6% 8% 37%	3480
	21st to end	Night	14% 6% 2 5% 4 4 4 4 6% 7% 45%	3608
April	1st to 10th	Night	14% 8% 2 5% 4 4 4 3 5% 6% 46%	1900
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 5% 6% 45%	1875
	21st to end	Night	7% 5% 2 4 3 4 4 3 6% 7% 56%	1900
May	1st to 10th	Night	11% 6% 3 7% 4 4 4 3 6% 8% 45%	3130
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 43%	3129
	21st to end	Night	6% 4 2 4 3 4 5% 5% 8% 13% 47%	3426
June	1st to 10th	Night	7% 6% 2 5% 4 5% 5% 4 9% 11% 42%	1900
	11th to 20th	Night	3 3 2 5% 5% 5% 6% 7% 8% 12% 45%	1778
	21st to end	Night	6% 6% 2 6% 6% 5% 5% 6% 8% 10% 40%	1710
July	1st to 10th	Night	4 4 3 7% 5% 5% 7% 7% 9% 12% 37%	2850
	11th to 20th	Night	3 3 1 5% 5% 5% 6% 6% 9% 13% 42%	2956
	21st to end	Night	5% 5% 3 8% 7% 6% 7% 5% 9% 15% 30%	3435
August	1st to 10th	Night	2 2 1 3 4 4 5% 5% 8% 13% 55%	3144
	11th to 20th	Night	3 2 1 5% 4 5% 6% 5% 9% 15% 45%	3100
	21st to end	Night	5% 5% 2 8% 5% 5% 6% 6% 8% 9% 40%	3476
September	1st to 10th	Night	8% 5% 2 6% 5% 6% 6% 4 7% 11% 40%	1900
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 4 6% 10% 43%	1945
	21st to end	Night	6% 5% 2 5% 4 3 4 4 5% 9% 53%	2090
October	1st to 10th	Night	6% 4 1 5% 3 3 4 3 4 7% 60%	2152
	11th to 20th	Night	5% 4 1 4 3 3 3 3 5% 7% 61%	2280
	21st to end	Night	10% 4 2 5% 3 2 3 3 4 6% 57%	2508
November	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 6% 56%	2340
	11th to 20th	Night	12% 5% 1 4 4 3 3 2 4 7% 55%	2495
	21st to end	Night	12% 6% 2 5% 3 4 4 3 5% 7% 49%	2562
December	1st to 10th	Night	15% 7% 2 6% 4 3 3 3 5% 6% 46%	2470
	11th to 20th	Night	14% 8% 2 6% 4 4 5% 4 5% 6% 43%	3001
	21st to end	Night	18% 10% 3 6% 4 4 4 3 4 5% 40%	4180

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	27% 38% 5% 9% 15% 7%	2875
	11th to 20th	Day	18% 38% 3 11% 24% 6%	2941
	21st to end	Day	32% 40% 4 7% 13% 5%	3476
February	1st to 10th	Day	18% 65% 3 5% 6% 4	1900
	11th to 20th	Day	16% 65% 3 7% 7% 2	1858
	21st to end	Day	17% 65% 4 3 8% 3	1570
March	1st to 10th	Day	38% 43% 6% 9% 3 1	3248
	11th to 20th	Day	27% 44% 5% 12% 9% 1	3480
	21st to end	Day	25% 44% 6% 6% 12% 6%	4021
April	1st to 10th	Day	14% 66% 2 5% 8% 4	2280
	11th to 20th	Day	16% 66% 3 6% 5% 3	2254
	21st to end	Day	13% 66% 3 7% 8% 4	2280
May	1st to 10th	Day	23% 46% 10% 12% 6% 3	3800
	11th to 20th	Day	24% 42% 7% 11% 15% 1	3768
	21st to end	Day	15% 43% 11% 25% 5% 1	4141
June	1st to 10th	Day	15% 68% 5% 8% 4 1	2280
	11th to 20th	Day	16% 69% 5% 6% 4	2393
	21st to end	Day	16% 67% 6% 8% 3	2470
July	1st to 10th	Day	27% 39% 19% 13% 1	4056
	11th to 20th	Day	26% 40% 28% 5% 1	3933
	21st to end	Day	32% 42% 13% 11% 3	3987
August	1st to 10th	Day	10% 38% 8% 23% 21%	3773
	11th to 20th	Day	16% 39% 14% 22% 8% 1	3765
	21st to end	Day	30% 40% 7% 11% 10% 1	4179
September	1st to 10th	Day	17% 64% 7% 6% 5% 2	2280
	11th to 20th	Day	13% 62% 7% 8% 8% 3	2214
	21st to end	Day	12% 62% 4 13% 6% 2	2090
October	1st to 10th	Day	16% 38% 4 6% 14% 23%	3362
	11th to 20th	Day	6% 37% 2 13% 18% 24%	3140
	21st to end	Day	11% 36% 3 6% 31% 13%	3428
November	1st to 10th	Day	17% 58% 4 9% 8% 3	1958
	11th to 20th	Day	18% 57% 3 7% 10% 5%	1900
	21st to end	Day	15% 59% 4 9% 8% 5%	1773
December	1st to 10th	Day	18% 61% 4 7% 7% 3	1710
	11th to 20th	Day	22% 48% 3 6% 15% 6%	2182
	21st to end	Day	31% 39% 5% 9% 13% 3	3476
January	1st to 10th	Night	26% 37% 5% 9% 15% 8%	4053
	11th to 20th	Night	21% 37% 3 13% 19% 8%	4015
	21st to end	Night	30% 39% 3 10% 14% 4	4180
February	1st to 10th	Night	16% 65% 3 6% 7% 3	2280
	11th to 20th	Night	15% 64% 2 7% 8% 3	2219
	21st to end	Night	17% 65% 4 4 5% 4	1884
March	1st to 10th	Night	41% 43% 5% 6% 3 1	3619
	11th to 20th	Night	28% 43% 7% 10% 9% 3	3480
	21st to end	Night	24% 43% 5% 13% 10% 4	3608
April	1st to 10th	Night	15% 65% 3 5% 7% 5%	1900
	11th to 20th	Night	16% 66% 4 7% 5% 3	1875
	21st to end	Night	11% 65% 3 9% 9% 3	1900
May	1st to 10th	Night	23% 45% 9% 11% 9% 3	3160
	11th to 20th	Night	27% 41% 7% 12% 11% 1	3130
	21st to end	Night	15% 43% 15% 19% 6% 1	3435
June	1st to 10th	Night	12% 66% 6% 11% 5%	1900
	11th to 20th	Night	13% 68% 5% 11% 3	1778
	21st to end	Night	14% 66% 9% 8% 4	1710
July	1st to 10th	Night	22% 39% 25% 12% 2	2805
	11th to 20th	Night	18% 43% 33% 5% 1	2902
	21st to end	Night	27% 45% 13% 13% 2	3325
August	1st to 10th	Night	12% 38% 9% 20% 20% 1	3132
	11th to 20th	Night	14% 40% 18% 22% 7%	3130
	21st to end	Night	24% 41% 11% 14% 8% 3	3476
September	1st to 10th	Night	15% 61% 10% 7% 4 2	1900
	11th to 20th	Night	13% 62% 8% 9% 5% 3	1945
	21st to end	Night	12% 61% 5% 13% 6% 2	2090
October	1st to 10th	Night	20% 37% 4 6% 15% 18%	3594
	11th to 20th	Night	6% 36% 2 13% 20% 23%	3779
	21st to end	Night	10% 36% 4 4 29% 17%	4120
November	1st to 10th	Night	19% 56% 6% 9% 7% 3	2340
	11th to 20th	Night	18% 56% 3 7% 10% 6%	2495
	21st to end	Night	14% 58% 4 9% 10% 5%	2562
December	1st to 10th	Night	18% 60% 4 9% 7% 2	2470
	11th to 20th	Night	21% 49% 3 6% 11% 11%	3003
	21st to end	Night	33% 38% 4 10% 12% 4	4180

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	23% 11% 39% 19% 7% 1	270
	11th to 20th	Day	21% 14% 35% 23% 7%	270
	21st to end	Day	24% 18% 41% 14% 3	297
February	1st to 10th	Day	26% 18% 34% 17% 4 1	270
	11th to 20th	Day	28% 14% 34% 18% 5%	270
	21st to end	Day	16% 25% 44% 13% 1	225
March	1st to 10th	Day	18% 14% 43% 20% 5%	270
	11th to 20th	Day	19% 20% 36% 21% 4	270
	21st to end	Day	18% 13% 34% 25% 9%	414
April	1st to 10th	Day	16% 14% 33% 26% 11%	460
	11th to 20th	Day	17% 14% 31% 25% 12% 2	452
	21st to end	Day	11% 8% 29% 32% 16% 4	460
May	1st to 10th	Day	12% 7% 30% 27% 20% 4	463
	11th to 20th	Day	13% 3 18% 33% 24% 9%	487
	21st to end	Day	7% 2 14% 36% 27% 14%	529
June	1st to 10th	Day	13% 2 9% 31% 27% 17%	490
	11th to 20th	Day	7% 2 11% 29% 36% 15%	603
	21st to end	Day	9% 2 8% 27% 33% 21%	680
July	1st to 10th	Day	10% 2 4 24% 35% 25%	671
	11th to 20th	Day	8% 1 3 17% 42% 29%	602
	21st to end	Day	11% 2 3 18% 40% 27%	532
August	1st to 10th	Day	4 2 3 21% 39% 31%	486
	11th to 20th	Day	7% 2 2 15% 41% 32%	479
	21st to end	Day	13% 1 7% 20% 34% 25%	539
September	1st to 10th	Day	12% 2 4 22% 38% 22%	490
	11th to 20th	Day	12% 2 8% 24% 38% 15%	490
	21st to end	Day	8% 3 10% 30% 35% 14%	490
October	1st to 10th	Day	7% 4 16% 40% 26% 7%	424
	11th to 20th	Day	6% 6% 23% 36% 24% 5%	300
	21st to end	Day	17% 7% 18% 38% 15% 5%	330
November	1st to 10th	Day	16% 4 22% 37% 19% 2	300
	11th to 20th	Day	17% 11% 29% 29% 13% 2	300
	21st to end	Day	14% 9% 38% 26% 9% 3	291
December	1st to 10th	Day	21% 8% 29% 27% 11% 3	270
	11th to 20th	Day	23% 11% 37% 24% 6%	270
	21st to end	Day	25% 11% 33% 22% 8% 1	297
January	1st to 10th	Night	20% 9% 31% 33% 7% 1	921
	11th to 20th	Night	20% 8% 30% 33% 8% 1	884
	21st to end	Night	22% 10% 31% 31% 5%	836
February	1st to 10th	Night	21% 9% 36% 29% 6%	760
	11th to 20th	Night	22% 10% 30% 30% 7%	743
	21st to end	Night	22% 12% 36% 28% 2	628
March	1st to 10th	Night	18% 10% 35% 29% 8%	698
	11th to 20th	Night	16% 6% 29% 36% 12% 1	570
	21st to end	Night	16% 7% 30% 35% 12%	627
April	1st to 10th	Night	16% 10% 28% 33% 13%	570
	11th to 20th	Night	15% 8% 30% 31% 15% 1	563
	21st to end	Night	10% 3 24% 43% 18% 1	570
May	1st to 10th	Night	11% 3 22% 40% 23% 1	570
	11th to 20th	Night	9% 2 16% 41% 28% 4	561
	21st to end	Night	5% 2 12% 37% 36% 7%	617
June	1st to 10th	Night	9% 1 5% 36% 39% 9%	570
	11th to 20th	Night	4 1 7% 27% 48% 13%	570
	21st to end	Night	7% 2 5% 26% 43% 17%	570
July	1st to 10th	Night	6% 2 2 16% 52% 22%	555
	11th to 20th	Night	5% 1 1 10% 51% 32%	552
	21st to end	Night	6% 1 2 14% 54% 23%	624
August	1st to 10th	Night	3 1 1 17% 50% 29%	567
	11th to 20th	Night	4 1 1 12% 51% 30%	564
	21st to end	Night	8% 2 5% 17% 45% 24%	627
September	1st to 10th	Night	10% 1 4 19% 47% 19%	570
	11th to 20th	Night	12% 3 5% 24% 47% 10%	615
	21st to end	Night	9% 2 7% 34% 41% 8%	760
October	1st to 10th	Night	8% 2 14% 38% 33% 5%	760
	11th to 20th	Night	8% 4 18% 40% 27% 3	760
	21st to end	Night	12% 5% 19% 37% 25% 3	836
November	1st to 10th	Night	14% 4 16% 43% 20% 3	780
	11th to 20th	Night	15% 6% 25% 35% 17% 2	800
	21st to end	Night	15% 6% 26% 34% 17% 1	789
December	1st to 10th	Night	16% 8% 26% 33% 15% 1	760
	11th to 20th	Night	18% 7% 30% 35% 10% 1	760
	21st to end	Night	26% 8% 28% 30% 7%	836

Page generated at 2024-11-24 23:22:20. Version ac07

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