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 2026-02-01.

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	10% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	126438
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	125565
Transparency	Day	24% 39% 9% 13% 11% 5%	130136
	Night	24% 38% 8% 12% 12% 5%	129941
Seeing	Day	13% 7% 20% 25% 23% 12%	16258
	Night	13% 5% 20% 31% 24% 7%	25899

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% 5% 2 5% 4 4 4 4 6% 7% 44%	4195
	11th to 20th	Day	13% 6% 2 6% 4 3 4 3 3 5% 50%	4303
	21st to end	Day	21% 7% 3 7% 4 4 5% 4 5% 5% 36%	5082
February	1st to 10th	Day	16% 9% 3 7% 4 4 4 4 5% 5% 39%	2000
	11th to 20th	Day	17% 8% 2 4 4 3 4 3 5% 7% 43%	1948
	21st to end	Day	16% 8% 3 8% 6% 3 4 3 5% 6% 38%	1650
March	1st to 10th	Day	18% 8% 3 7% 4 4 4 3 5% 7% 37%	4664
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 45%	4980
	21st to end	Day	13% 8% 3 7% 5% 4 5% 4 5% 6% 41%	5753
April	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 5% 7% 8% 40%	2400
	11th to 20th	Day	13% 6% 3 7% 5% 4 5% 3 5% 8% 41%	2374
	21st to end	Day	9% 5% 2 4 4 5% 4 4 8% 7% 48%	2400
May	1st to 10th	Day	15% 6% 2 7% 4 5% 5% 5% 7% 9% 34%	5405
	11th to 20th	Day	9% 4 2 4 4 4 5% 4 7% 9% 46%	5404
	21st to end	Day	6% 4 2 6% 4 4 5% 5% 8% 13% 42%	5932
June	1st to 10th	Day	9% 6% 2 6% 6% 6% 6% 6% 9% 10% 34%	2400
	11th to 20th	Day	4 5% 2 7% 6% 6% 6% 7% 8% 12% 35%	2519
	21st to end	Day	7% 6% 2 7% 6% 8% 8% 7% 10% 11% 28%	2600
July	1st to 10th	Day	5% 5% 2 7% 7% 7% 7% 7% 10% 14% 30%	5900
	11th to 20th	Day	4 4 2 7% 6% 6% 7% 6% 10% 14% 34%	5726
	21st to end	Day	5% 5% 2 8% 6% 7% 8% 7% 10% 13% 28%	5922
August	1st to 10th	Day	3 2 1 4 4 5% 6% 4 7% 11% 51%	3905
	11th to 20th	Day	5% 3 2 5% 5% 6% 7% 6% 9% 12% 39%	3849
	21st to end	Day	8% 6% 3 10% 6% 7% 7% 6% 8% 9% 32%	4312
September	1st to 10th	Day	10% 6% 2 7% 6% 5% 7% 5% 8% 10% 34%	2400
	11th to 20th	Day	10% 5% 3 6% 5% 6% 6% 5% 7% 9% 39%	2330
	21st to end	Day	8% 4 2 5% 4 5% 5% 4 7% 8% 48%	2200
October	1st to 10th	Day	6% 3 2 4 3 4 5% 3 6% 8% 54%	2130
	11th to 20th	Day	6% 4 1 4 4 4 4 4 6% 7% 58%	2000
	21st to end	Day	9% 4 1 5% 3 3 3 3 4 7% 58%	2200
November	1st to 10th	Day	8% 5% 2 5% 3 4 4 4 5% 6% 54%	2058
	11th to 20th	Day	11% 5% 1 4 3 3 3 3 5% 6% 56%	1995
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 7% 46%	1890
December	1st to 10th	Day	18% 7% 3 6% 4 4 5% 3 5% 5% 41%	3020
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 7% 48%	3510
	21st to end	Day	17% 8% 2 6% 4 4 4 3 4 5% 43%	5082
January	1st to 10th	Night	18% 7% 2 4 3 3 3 3 5% 6% 47%	5948
	11th to 20th	Night	19% 7% 2 5% 3 3 3 2 4 6% 48%	5865
	21st to end	Night	22% 7% 2 6% 3 4 4 3 5% 7% 37%	6116
February	1st to 10th	Night	16% 8% 2 6% 4 3 4 3 4 6% 42%	2401
	11th to 20th	Night	19% 8% 3 5% 4 3 4 3 5% 6% 41%	2338
	21st to end	Night	20% 8% 2 7% 3 3 3 4 5% 6% 39%	1980
March	1st to 10th	Night	19% 9% 3 7% 4 3 4 3 5% 6% 38%	5217
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 4 6% 49%	4980
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 6% 46%	5174
April	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 5% 6% 45%	2000
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 5% 6% 47%	1975
	21st to end	Night	7% 5% 2 4 3 4 3 3 6% 7% 56%	2000
May	1st to 10th	Night	14% 7% 3 7% 5% 4 4 4 6% 8% 38%	4490
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 5% 7% 45%	4489
	21st to end	Night	6% 5% 2 6% 4 4 5% 5% 7% 12% 45%	4922
June	1st to 10th	Night	7% 6% 2 5% 4 5% 5% 4 8% 11% 43%	2000
	11th to 20th	Night	3 3 1 5% 5% 5% 6% 7% 8% 12% 44%	1871
	21st to end	Night	6% 6% 2 6% 6% 6% 5% 6% 8% 10% 40%	1800
July	1st to 10th	Night	3 3 2 6% 4 6% 7% 7% 9% 12% 39%	4078
	11th to 20th	Night	3 3 1 5% 5% 5% 6% 5% 9% 13% 45%	4222
	21st to end	Night	4 4 2 7% 6% 6% 6% 5% 9% 15% 35%	4929
August	1st to 10th	Night	2 2 1 3 4 4 5% 5% 8% 13% 55%	3244
	11th to 20th	Night	3 2 1 5% 4 5% 6% 5% 9% 15% 45%	3200
	21st to end	Night	5% 5% 2 8% 5% 5% 6% 6% 8% 9% 40%	3586
September	1st to 10th	Night	8% 5% 2 5% 5% 6% 6% 4 8% 11% 41%	2000
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 4 6% 10% 44%	2048
	21st to end	Night	6% 5% 2 5% 4 4 4 4 5% 9% 53%	2200
October	1st to 10th	Night	6% 5% 2 5% 3 3 4 3 4 6% 59%	2265
	11th to 20th	Night	5% 4 1 4 3 3 3 3 5% 7% 62%	2400
	21st to end	Night	10% 4 2 5% 3 2 3 3 4 6% 57%	2640
November	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 3 6% 57%	2460
	11th to 20th	Night	11% 4 1 4 4 3 3 2 4 6% 56%	2620
	21st to end	Night	11% 6% 2 6% 4 4 4 3 5% 7% 48%	2730
December	1st to 10th	Night	15% 7% 2 7% 5% 4 4 3 4 5% 44%	4380
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 5% 6% 49%	4881
	21st to end	Night	18% 10% 3 6% 4 3 3 3 3 4 43%	6116

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	31% 26% 5% 15% 19% 5%	4196
	11th to 20th	Day	28% 26% 3 11% 25% 7%	4303
	21st to end	Day	39% 28% 6% 8% 12% 9%	5082
February	1st to 10th	Day	19% 62% 3 5% 7% 4	2000
	11th to 20th	Day	17% 62% 4 7% 8% 2	1958
	21st to end	Day	19% 62% 4 3 9% 3	1650
March	1st to 10th	Day	37% 30% 5% 11% 9% 8%	4664
	11th to 20th	Day	25% 31% 5% 12% 14% 14%	4980
	21st to end	Day	33% 31% 7% 11% 11% 7%	5755
April	1st to 10th	Day	17% 63% 2 6% 8% 4	2400
	11th to 20th	Day	16% 63% 3 7% 7% 4	2374
	21st to end	Day	14% 63% 4 9% 7% 3	2400
May	1st to 10th	Day	34% 32% 10% 15% 6% 2	5440
	11th to 20th	Day	23% 29% 13% 21% 14% 1	5408
	21st to end	Day	23% 31% 13% 24% 8% 1	5945
June	1st to 10th	Day	15% 64% 5% 9% 5% 1	2400
	11th to 20th	Day	17% 65% 6% 7% 5%	2519
	21st to end	Day	17% 64% 8% 8% 3	2600
July	1st to 10th	Day	28% 28% 25% 16% 3	5836
	11th to 20th	Day	26% 30% 35% 8% 1	5657
	21st to end	Day	31% 31% 16% 19% 2	5752
August	1st to 10th	Day	11% 37% 8% 23% 21%	3893
	11th to 20th	Day	17% 37% 15% 22% 8% 1	3885
	21st to end	Day	31% 39% 8% 11% 10% 1	4311
September	1st to 10th	Day	16% 61% 8% 8% 5% 2	2400
	11th to 20th	Day	13% 59% 7% 10% 9% 3	2330
	21st to end	Day	13% 59% 5% 14% 7% 2	2200
October	1st to 10th	Day	17% 37% 4 6% 14% 22%	3468
	11th to 20th	Day	6% 36% 2 13% 19% 24%	3240
	21st to end	Day	11% 35% 3 6% 31% 13%	3538
November	1st to 10th	Day	17% 55% 4 10% 8% 5%	2058
	11th to 20th	Day	18% 55% 3 8% 11% 5%	1995
	21st to end	Day	17% 55% 4 10% 9% 5%	1890
December	1st to 10th	Day	33% 35% 4 9% 17% 4	3020
	11th to 20th	Day	22% 30% 6% 15% 18% 9%	3507
	21st to end	Day	33% 27% 4 12% 19% 4	5082
January	1st to 10th	Night	31% 25% 5% 15% 18% 6%	5948
	11th to 20th	Night	32% 25% 2 12% 22% 7%	5865
	21st to end	Night	37% 27% 5% 10% 14% 7%	6116
February	1st to 10th	Night	18% 62% 3 6% 8% 3	2401
	11th to 20th	Night	18% 61% 2 8% 8% 3	2339
	21st to end	Night	18% 62% 4 5% 6% 5%	1980
March	1st to 10th	Night	39% 30% 6% 8% 11% 7%	5217
	11th to 20th	Night	26% 30% 5% 10% 15% 13%	4980
	21st to end	Night	29% 30% 7% 17% 11% 6%	5174
April	1st to 10th	Night	18% 62% 3 5% 7% 5%	2000
	11th to 20th	Night	16% 63% 3 7% 7% 4	1975
	21st to end	Night	12% 62% 5% 10% 9% 3	2000
May	1st to 10th	Night	34% 32% 10% 13% 9% 2	4520
	11th to 20th	Night	28% 29% 12% 20% 11% 1	4490
	21st to end	Night	24% 30% 16% 23% 6% 1	4931
June	1st to 10th	Night	13% 63% 7% 11% 6%	2000
	11th to 20th	Night	15% 65% 7% 11% 3	1871
	21st to end	Night	15% 63% 10% 8% 4	1800
July	1st to 10th	Night	24% 30% 27% 16% 3	4035
	11th to 20th	Night	21% 34% 38% 6% 1	4171
	21st to end	Night	27% 34% 15% 21% 2	4785
August	1st to 10th	Night	12% 37% 9% 21% 20% 1	3232
	11th to 20th	Night	15% 38% 19% 22% 6%	3230
	21st to end	Night	24% 39% 12% 14% 8% 3	3586
September	1st to 10th	Night	15% 58% 11% 8% 5% 2	2000
	11th to 20th	Night	13% 58% 9% 10% 7% 3	2048
	21st to end	Night	13% 58% 6% 14% 6% 3	2200
October	1st to 10th	Night	21% 36% 4 7% 15% 17%	3707
	11th to 20th	Night	6% 35% 2 13% 20% 23%	3899
	21st to end	Night	11% 35% 4 5% 29% 17%	4252
November	1st to 10th	Night	20% 53% 5% 9% 9% 4	2460
	11th to 20th	Night	18% 54% 3 9% 11% 6%	2620
	21st to end	Night	16% 55% 5% 9% 10% 5%	2730
December	1st to 10th	Night	32% 34% 3 10% 16% 5%	4380
	11th to 20th	Night	24% 30% 7% 14% 15% 9%	4883
	21st to end	Night	36% 26% 4 11% 17% 6%	6116

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	22% 12% 41% 18% 6% 1	330
	11th to 20th	Day	20% 15% 38% 21% 6% 1	330
	21st to end	Day	25% 17% 40% 15% 3	363
February	1st to 10th	Day	25% 16% 34% 18% 6% 1	300
	11th to 20th	Day	26% 17% 35% 17% 5%	300
	21st to end	Day	16% 23% 44% 14% 3	249
March	1st to 10th	Day	19% 15% 42% 20% 5%	300
	11th to 20th	Day	20% 21% 35% 20% 4	300
	21st to end	Day	19% 13% 34% 24% 9%	453
April	1st to 10th	Day	17% 14% 33% 25% 11%	500
	11th to 20th	Day	16% 14% 32% 24% 12% 2	492
	21st to end	Day	10% 8% 29% 32% 16% 4	500
May	1st to 10th	Day	14% 7% 29% 26% 20% 4	503
	11th to 20th	Day	13% 3 20% 33% 22% 9%	527
	21st to end	Day	7% 2 16% 36% 26% 14%	573
June	1st to 10th	Day	13% 2 10% 32% 28% 16%	530
	11th to 20th	Day	7% 2 10% 29% 35% 16%	649
	21st to end	Day	9% 2 8% 27% 33% 22%	730
July	1st to 10th	Day	10% 2 4 25% 36% 25%	721
	11th to 20th	Day	8% 1 3 18% 41% 29%	648
	21st to end	Day	10% 1 3 18% 41% 26%	576
August	1st to 10th	Day	4 2 2 20% 40% 31%	526
	11th to 20th	Day	7% 2 2 14% 42% 34%	519
	21st to end	Day	13% 1 7% 20% 34% 26%	583
September	1st to 10th	Day	12% 2 4 24% 38% 21%	530
	11th to 20th	Day	11% 2 8% 24% 38% 17%	530
	21st to end	Day	8% 3 10% 31% 35% 14%	530
October	1st to 10th	Day	8% 3 17% 39% 26% 7%	460
	11th to 20th	Day	5% 5% 24% 35% 24% 5%	330
	21st to end	Day	17% 7% 19% 38% 13% 5%	363
November	1st to 10th	Day	15% 5% 22% 36% 18% 3	330
	11th to 20th	Day	15% 10% 28% 29% 14% 2	330
	21st to end	Day	13% 11% 40% 25% 9% 3	330
December	1st to 10th	Day	23% 8% 32% 24% 10% 2	330
	11th to 20th	Day	21% 10% 37% 24% 7%	330
	21st to end	Day	23% 11% 33% 21% 11% 1	363
January	1st to 10th	Night	20% 9% 32% 33% 6%	1019
	11th to 20th	Night	20% 9% 30% 33% 8% 1	976
	21st to end	Night	23% 10% 31% 31% 5%	924
February	1st to 10th	Night	21% 8% 35% 29% 6%	801
	11th to 20th	Night	24% 11% 29% 29% 7%	783
	21st to end	Night	23% 11% 37% 27% 3	660
March	1st to 10th	Night	17% 10% 35% 29% 8%	735
	11th to 20th	Night	16% 6% 30% 36% 12% 1	600
	21st to end	Night	15% 7% 30% 36% 12%	660
April	1st to 10th	Night	18% 10% 27% 34% 12%	600
	11th to 20th	Night	15% 8% 30% 32% 15% 1	593
	21st to end	Night	11% 3 23% 43% 19% 1	600
May	1st to 10th	Night	12% 3 21% 41% 22% 1	600
	11th to 20th	Night	9% 2 17% 41% 27% 4	591
	21st to end	Night	6% 2 13% 37% 36% 7%	650
June	1st to 10th	Night	10% 1 6% 36% 38% 9%	600
	11th to 20th	Night	3 1 6% 26% 50% 13%	600
	21st to end	Night	7% 2 5% 26% 44% 17%	600
July	1st to 10th	Night	6% 2 2 17% 52% 22%	585
	11th to 20th	Night	5% 1 1 10% 50% 33%	582
	21st to end	Night	6% 1 2 14% 55% 23%	657
August	1st to 10th	Night	3 1 1 16% 51% 29%	597
	11th to 20th	Night	4 1 1 12% 50% 32%	594
	21st to end	Night	8% 2 5% 17% 45% 24%	660
September	1st to 10th	Night	10% 1 4 20% 46% 19%	600
	11th to 20th	Night	11% 3 4 24% 48% 10%	648
	21st to end	Night	9% 2 7% 34% 41% 8%	800
October	1st to 10th	Night	9% 2 14% 38% 33% 5%	800
	11th to 20th	Night	7% 4 18% 40% 28% 4	800
	21st to end	Night	12% 5% 19% 37% 24% 3	880
November	1st to 10th	Night	13% 5% 16% 43% 21% 3	820
	11th to 20th	Night	15% 5% 25% 36% 18% 2	840
	21st to end	Night	15% 7% 27% 34% 16% 1	840
December	1st to 10th	Night	18% 8% 27% 33% 14% 1	840
	11th to 20th	Night	18% 7% 29% 35% 11% 1	840
	21st to end	Night	25% 8% 27% 31% 8% 1	924

Page generated at 2026-01-29 00:21:41. Version ac07

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