Dog-Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dog-Star Observatory clear sky chart from 2005-11-06 to 2024-10-24.

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	16% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	101216
	Night	16% 9% 3 8% 5% 4 4 4 5% 7% 35%	97498
Transparency	Day	49% 7% 12% 21% 11% 1	101017
	Night	47% 7% 12% 21% 11% 1	97367
Seeing	Day	23% 14% 27% 21% 11% 4	14733
	Night	21% 12% 25% 29% 11% 1	24170

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	15% 17% 6% 10% 5% 5% 4 4 4 4 27%	2521
	11th to 20th	Day	11% 17% 9% 15% 7% 6% 4 3 4 4 19%	2840
	21st to end	Day	21% 18% 8% 12% 7% 4 3 3 4 4 17%	3124
February	1st to 10th	Day	15% 16% 5% 10% 7% 5% 4 3 4 6% 24%	1710
	11th to 20th	Day	14% 11% 5% 12% 6% 5% 5% 4 6% 5% 27%	1663
	21st to end	Day	18% 12% 4 11% 5% 4 4 4 4 6% 29%	1549
March	1st to 10th	Day	22% 11% 3 8% 5% 4 4 3 4 7% 29%	3424
	11th to 20th	Day	12% 12% 4 9% 5% 5% 5% 3 5% 6% 34%	3480
	21st to end	Day	15% 10% 3 7% 6% 5% 4 3 5% 5% 37%	3836
April	1st to 10th	Day	16% 11% 3 8% 5% 5% 5% 4 5% 6% 32%	2280
	11th to 20th	Day	16% 11% 3 7% 4 4 4 3 6% 6% 35%	2254
	21st to end	Day	20% 8% 4 7% 5% 5% 4 3 5% 6% 33%	2356
May	1st to 10th	Day	28% 8% 3 7% 5% 4 4 3 5% 6% 29%	4082
	11th to 20th	Day	23% 8% 3 8% 5% 5% 4 3 5% 7% 28%	4324
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 7% 9% 40%	4823
June	1st to 10th	Day	13% 7% 3 6% 6% 6% 5% 4 6% 8% 35%	2660
	11th to 20th	Day	14% 6% 2 7% 5% 6% 5% 4 6% 9% 35%	2660
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 9% 39%	2660
July	1st to 10th	Day	7% 6% 3 8% 6% 5% 5% 5% 7% 9% 37%	4440
	11th to 20th	Day	7% 6% 3 7% 6% 6% 6% 5% 8% 10% 38%	4381
	21st to end	Day	10% 8% 3 8% 6% 5% 5% 5% 6% 7% 37%	4466
August	1st to 10th	Day	18% 7% 3 7% 5% 5% 6% 4 7% 9% 29%	4104
	11th to 20th	Day	13% 6% 3 7% 5% 6% 7% 5% 7% 7% 34%	4012
	21st to end	Day	13% 7% 2 5% 4 4 5% 4 6% 9% 42%	4180
September	1st to 10th	Day	16% 6% 2 6% 5% 3 4 4 4 6% 44%	2280
	11th to 20th	Day	14% 5% 2 4 4 3 4 3 5% 8% 48%	2261
	21st to end	Day	22% 8% 2 6% 4 4 3 3 7% 6% 36%	1991
October	1st to 10th	Day	17% 7% 3 6% 5% 4 4 4 4 7% 39%	1900
	11th to 20th	Day	17% 8% 3 7% 5% 4 4 4 6% 6% 36%	1900
	21st to end	Day	18% 9% 3 6% 5% 4 5% 4 5% 6% 36%	2010
November	1st to 10th	Day	12% 7% 3 6% 5% 4 5% 5% 5% 6% 42%	1752
	11th to 20th	Day	16% 13% 3 7% 6% 5% 5% 4 5% 6% 31%	1571
	21st to end	Day	17% 11% 3 8% 6% 5% 5% 4 6% 6% 29%	1520
December	1st to 10th	Day	18% 15% 4 11% 6% 5% 4 4 5% 6% 21%	1520
	11th to 20th	Day	18% 15% 6% 9% 4 4 4 4 4 6% 26%	1910
	21st to end	Day	22% 17% 7% 10% 7% 5% 5% 4 4 4 17%	2772
January	1st to 10th	Night	14% 14% 6% 11% 6% 5% 4 3 5% 7% 25%	4420
	11th to 20th	Night	15% 15% 6% 13% 5% 4 4 3 6% 6% 22%	4120
	21st to end	Night	23% 14% 6% 12% 5% 4 4 3 4 4 21%	4532
February	1st to 10th	Night	15% 12% 4 9% 6% 5% 4 4 5% 7% 30%	2470
	11th to 20th	Night	16% 10% 4 9% 6% 5% 7% 4 5% 5% 30%	2403
	21st to end	Night	16% 11% 4 10% 5% 6% 4 3 4 5% 32%	1904
March	1st to 10th	Night	22% 13% 3 6% 4 4 4 3 4 5% 32%	3428
	11th to 20th	Night	11% 10% 6% 8% 4 5% 4 4 6% 6% 36%	3480
	21st to end	Night	15% 9% 3 6% 5% 4 3 3 4 6% 43%	3795
April	1st to 10th	Night	17% 12% 4 9% 5% 4 4 4 4 6% 32%	1900
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 4 5% 6% 38%	1875
	21st to end	Night	17% 6% 3 6% 5% 5% 4 4 5% 8% 37%	1839
May	1st to 10th	Night	27% 9% 3 6% 5% 4 4 3 4 5% 29%	2813
	11th to 20th	Night	26% 10% 3 7% 3 4 4 3 5% 6% 30%	2565
	21st to end	Night	13% 6% 2 7% 5% 5% 5% 4 7% 10% 39%	2732
June	1st to 10th	Night	12% 6% 2 7% 4 4 4 3 6% 9% 44%	1520
	11th to 20th	Night	11% 6% 3 7% 5% 3 5% 5% 7% 9% 40%	1520
	21st to end	Night	11% 6% 1 5% 4 5% 5% 4 8% 11% 42%	1520
July	1st to 10th	Night	8% 6% 3 8% 6% 5% 5% 4 6% 9% 41%	2520
	11th to 20th	Night	6% 5% 3 6% 4 5% 5% 5% 7% 10% 44%	2574
	21st to end	Night	12% 7% 2 7% 5% 5% 5% 4 5% 7% 42%	3087
August	1st to 10th	Night	16% 7% 3 6% 4 4 5% 4 6% 8% 36%	2825
	11th to 20th	Night	14% 8% 3 6% 4 4 5% 4 6% 7% 40%	2785
	21st to end	Night	14% 5% 2 5% 4 4 5% 4 5% 8% 46%	3476
September	1st to 10th	Night	16% 5% 2 4 5% 4 4 3 5% 7% 46%	1900
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 5% 8% 51%	1914
	21st to end	Night	20% 6% 2 6% 4 4 4 3 4 7% 40%	2187
October	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 4 7% 44%	2280
	11th to 20th	Night	15% 8% 2 6% 5% 3 4 3 5% 6% 43%	2280
	21st to end	Night	20% 9% 3 5% 3 4 4 3 5% 6% 38%	2413
November	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 4 6% 49%	2325
	11th to 20th	Night	16% 10% 3 6% 5% 5% 4 3 5% 6% 35%	2607
	21st to end	Night	17% 10% 4 7% 5% 4 5% 4 5% 6% 33%	2660
December	1st to 10th	Night	18% 11% 3 10% 5% 5% 5% 4 6% 8% 25%	2660
	11th to 20th	Night	18% 11% 4 10% 5% 5% 5% 4 5% 6% 29%	3285
	21st to end	Night	19% 13% 5% 10% 6% 6% 5% 4 6% 6% 21%	4884

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	57% 8% 12% 17% 5% 2	2522
	11th to 20th	Day	67% 5% 8% 11% 7% 1	2840
	21st to end	Day	70% 6% 8% 12% 4 1	3124
February	1st to 10th	Day	60% 6% 12% 15% 7% 1	1710
	11th to 20th	Day	56% 6% 10% 21% 7% 1	1672
	21st to end	Day	56% 6% 10% 18% 7% 3	1549
March	1st to 10th	Day	54% 6% 12% 21% 6%	3424
	11th to 20th	Day	47% 8% 15% 21% 8% 2	3480
	21st to end	Day	47% 6% 13% 20% 13% 2	3836
April	1st to 10th	Day	51% 6% 11% 19% 12% 2	2280
	11th to 20th	Day	47% 6% 10% 18% 15% 3	2254
	21st to end	Day	50% 6% 10% 20% 13% 2	2356
May	1st to 10th	Day	55% 7% 9% 19% 10% 1	4120
	11th to 20th	Day	53% 8% 14% 16% 7% 1	4328
	21st to end	Day	37% 10% 14% 24% 13% 2	4837
June	1st to 10th	Day	44% 8% 12% 22% 14% 1	2660
	11th to 20th	Day	43% 8% 14% 20% 13% 2	2660
	21st to end	Day	39% 7% 14% 26% 13% 1	2660
July	1st to 10th	Day	42% 7% 15% 24% 11% 2	4370
	11th to 20th	Day	40% 6% 14% 24% 15% 1	4306
	21st to end	Day	44% 5% 11% 23% 16% 1	4324
August	1st to 10th	Day	50% 7% 15% 20% 9%	4091
	11th to 20th	Day	46% 5% 10% 27% 10% 1	4051
	21st to end	Day	39% 5% 11% 28% 15% 2	4180
September	1st to 10th	Day	41% 6% 10% 23% 18% 3	2280
	11th to 20th	Day	34% 6% 11% 27% 19% 2	2261
	21st to end	Day	47% 6% 12% 18% 16% 1	1991
October	1st to 10th	Day	45% 6% 10% 22% 15% 2	1900
	11th to 20th	Day	46% 7% 11% 23% 11% 1	1900
	21st to end	Day	47% 6% 12% 22% 12% 1	2010
November	1st to 10th	Day	40% 6% 14% 21% 16% 3	1752
	11th to 20th	Day	53% 6% 10% 20% 9% 3	1571
	21st to end	Day	53% 7% 12% 21% 7%	1520
December	1st to 10th	Day	61% 7% 12% 13% 6%	1520
	11th to 20th	Day	57% 6% 13% 19% 5%	1906
	21st to end	Day	69% 7% 10% 11% 3	2772
January	1st to 10th	Night	56% 7% 12% 18% 6% 1	4420
	11th to 20th	Night	59% 7% 14% 13% 6% 1	4120
	21st to end	Night	65% 5% 9% 15% 5% 1	4532
February	1st to 10th	Night	53% 6% 12% 21% 8% 1	2470
	11th to 20th	Night	53% 6% 11% 19% 11%	2405
	21st to end	Night	53% 7% 9% 19% 10% 2	1904
March	1st to 10th	Night	53% 6% 11% 21% 8% 1	3428
	11th to 20th	Night	43% 9% 13% 25% 9% 1	3480
	21st to end	Night	42% 5% 9% 23% 19% 3	3795
April	1st to 10th	Night	52% 5% 10% 18% 13% 1	1900
	11th to 20th	Night	44% 7% 11% 20% 15% 2	1875
	21st to end	Night	44% 6% 11% 22% 14% 3	1839
May	1st to 10th	Night	55% 7% 8% 17% 10% 2	2840
	11th to 20th	Night	52% 9% 14% 15% 9% 1	2566
	21st to end	Night	37% 9% 17% 21% 12% 4	2739
June	1st to 10th	Night	38% 7% 13% 25% 15% 2	1520
	11th to 20th	Night	37% 9% 14% 23% 14% 2	1520
	21st to end	Night	35% 8% 14% 27% 15%	1520
July	1st to 10th	Night	41% 6% 13% 20% 16% 3	2480
	11th to 20th	Night	35% 6% 15% 26% 16% 1	2526
	21st to end	Night	41% 6% 13% 18% 21% 2	2988
August	1st to 10th	Night	46% 7% 15% 23% 9%	2814
	11th to 20th	Night	43% 4 11% 27% 13% 1	2812
	21st to end	Night	37% 5% 12% 32% 13% 2	3476
September	1st to 10th	Night	38% 7% 11% 23% 18% 3	1900
	11th to 20th	Night	31% 6% 11% 30% 20% 2	1914
	21st to end	Night	44% 6% 11% 22% 17% 1	2187
October	1st to 10th	Night	39% 6% 14% 25% 15% 1	2280
	11th to 20th	Night	41% 6% 12% 25% 15% 2	2280
	21st to end	Night	46% 5% 11% 23% 14% 1	2413
November	1st to 10th	Night	36% 6% 14% 24% 18% 3	2325
	11th to 20th	Night	47% 6% 10% 21% 13% 3	2607
	21st to end	Night	49% 6% 13% 22% 9% 1	2660
December	1st to 10th	Night	55% 8% 14% 17% 6%	2660
	11th to 20th	Night	55% 6% 12% 20% 7%	3288
	21st to end	Night	60% 8% 14% 15% 3	4884

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% 27% 28% 11% 5% 1	182
	11th to 20th	Day	37% 22% 29% 11% 1	270
	21st to end	Day	28% 24% 35% 9% 3 1	297
February	1st to 10th	Day	29% 23% 32% 13% 3	270
	11th to 20th	Day	36% 25% 32% 6% 1	270
	21st to end	Day	34% 21% 26% 17% 1	361
March	1st to 10th	Day	30% 20% 28% 18% 4	460
	11th to 20th	Day	30% 22% 28% 15% 4 1	460
	21st to end	Day	28% 21% 29% 15% 5% 2	506
April	1st to 10th	Day	27% 21% 26% 19% 5% 1	460
	11th to 20th	Day	23% 22% 24% 18% 9% 4	452
	21st to end	Day	29% 16% 32% 15% 7% 2	460
May	1st to 10th	Day	31% 17% 27% 13% 10% 3	463
	11th to 20th	Day	25% 16% 25% 18% 12% 4	487
	21st to end	Day	20% 9% 26% 23% 16% 5%	529
June	1st to 10th	Day	18% 14% 26% 26% 12% 4	490
	11th to 20th	Day	19% 10% 26% 27% 14% 4	490
	21st to end	Day	16% 11% 29% 27% 13% 3	490
July	1st to 10th	Day	15% 7% 24% 27% 17% 10%	485
	11th to 20th	Day	10% 6% 28% 30% 20% 6%	484
	21st to end	Day	15% 7% 29% 28% 16% 5%	532
August	1st to 10th	Day	15% 6% 24% 26% 22% 8%	486
	11th to 20th	Day	15% 5% 24% 25% 20% 10%	479
	21st to end	Day	14% 8% 24% 27% 15% 12%	539
September	1st to 10th	Day	19% 8% 19% 28% 18% 8%	490
	11th to 20th	Day	17% 4 20% 27% 23% 9%	490
	21st to end	Day	29% 10% 21% 21% 14% 5%	490
October	1st to 10th	Day	24% 10% 19% 24% 19% 4	490
	11th to 20th	Day	22% 15% 28% 22% 11% 2	490
	21st to end	Day	25% 14% 31% 22% 7% 1	507
November	1st to 10th	Day	19% 15% 29% 24% 12% 2	405
	11th to 20th	Day	25% 22% 28% 17% 7% 1	231
	21st to end	Day	22% 22% 36% 16% 3 1	180
December	1st to 10th	Day	31% 23% 32% 9% 4 1	180
	11th to 20th	Day	30% 23% 28% 17% 2	180
	21st to end	Day	30% 21% 28% 17% 5%	198
January	1st to 10th	Night	25% 19% 34% 18% 4	760
	11th to 20th	Night	28% 16% 30% 23% 3	760
	21st to end	Night	23% 20% 32% 23% 3	836
February	1st to 10th	Night	26% 18% 28% 26% 2	760
	11th to 20th	Night	28% 23% 31% 17% 1	743
	21st to end	Night	28% 18% 31% 21% 2	628
March	1st to 10th	Night	25% 16% 32% 24% 3	760
	11th to 20th	Night	26% 19% 29% 22% 5%	760
	21st to end	Night	25% 15% 32% 21% 6% 1	836
April	1st to 10th	Night	26% 17% 30% 22% 5%	760
	11th to 20th	Night	21% 13% 31% 26% 7% 1	751
	21st to end	Night	23% 12% 28% 30% 7%	699
May	1st to 10th	Night	25% 9% 24% 31% 11% 1	570
	11th to 20th	Night	20% 8% 29% 33% 10%	418
	21st to end	Night	14% 6% 20% 38% 20% 1	411
June	1st to 10th	Night	13% 7% 22% 39% 19% 1	380
	11th to 20th	Night	13% 6% 23% 39% 18%	380
	21st to end	Night	11% 6% 21% 44% 17%	380
July	1st to 10th	Night	12% 6% 18% 41% 22% 3	370
	11th to 20th	Night	6% 3 18% 41% 30% 2	396
	21st to end	Night	12% 3 17% 45% 22% 1	624
August	1st to 10th	Night	10% 1 15% 43% 29% 2	567
	11th to 20th	Night	15% 4 13% 37% 27% 4	564
	21st to end	Night	14% 3 17% 34% 29% 3	836
September	1st to 10th	Night	18% 4 17% 34% 24% 3	760
	11th to 20th	Night	14% 4 17% 32% 28% 5%	760
	21st to end	Night	23% 8% 18% 29% 19% 3	760
October	1st to 10th	Night	22% 7% 20% 28% 20% 3	760
	11th to 20th	Night	20% 13% 24% 31% 11% 1	760
	21st to end	Night	25% 13% 23% 31% 7% 1	805
November	1st to 10th	Night	16% 11% 27% 34% 11% 1	740
	11th to 20th	Night	25% 18% 23% 25% 8% 1	760
	21st to end	Night	23% 17% 27% 27% 5% 1	760
December	1st to 10th	Night	29% 16% 29% 21% 5%	760
	11th to 20th	Night	26% 16% 28% 26% 4	760
	21st to end	Night	26% 16% 28% 27% 3	836

Page generated at 2024-10-21 02:20:04. Version ac07

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