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 2024-02-20.

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% 4 7% 6% 4 5% 5% 5% 7% 32%	78385
	Night	16% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	80805
Transparency	Day	50% 7% 12% 19% 11% 2	78095
	Night	47% 7% 12% 21% 11% 1	80614
Seeing	Day	23% 14% 27% 21% 11% 4	13747
	Night	21% 12% 25% 29% 11% 1	23367

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% 16% 6% 9% 6% 4 4 5% 4 5% 27%	2521
	11th to 20th	Day	11% 17% 9% 14% 9% 4 5% 4 4 4 20%	2840
	21st to end	Day	21% 18% 8% 10% 8% 3 3 4 4 4 17%	3124
February	1st to 10th	Day	16% 15% 6% 8% 8% 4 5% 4 4 6% 24%	1710
	11th to 20th	Day	14% 10% 6% 11% 8% 4 5% 5% 6% 5% 26%	1654
	21st to end	Day	18% 11% 4 10% 6% 3 4 4 4 5% 29%	1460
March	1st to 10th	Day	14% 10% 4 8% 6% 4 4 4 4 7% 35%	1969
	11th to 20th	Day	18% 12% 4 7% 6% 3 6% 4 4 6% 29%	1980
	21st to end	Day	19% 10% 3 7% 6% 3 4 4 4 5% 33%	2186
April	1st to 10th	Day	16% 9% 5% 7% 6% 3 5% 4 4 7% 33%	2160
	11th to 20th	Day	16% 10% 3 6% 6% 3 4 4 6% 6% 35%	2134
	21st to end	Day	21% 7% 4 6% 6% 3 5% 4 4 7% 33%	2232
May	1st to 10th	Day	19% 8% 3 6% 6% 3 5% 5% 6% 8% 30%	2340
	11th to 20th	Day	21% 7% 2 6% 6% 4 5% 4 5% 7% 32%	2432
	21st to end	Day	14% 7% 3 6% 5% 4 5% 6% 6% 8% 38%	2725
June	1st to 10th	Day	14% 6% 3 6% 6% 5% 6% 5% 6% 8% 35%	2520
	11th to 20th	Day	15% 6% 2 6% 6% 4 6% 5% 6% 8% 35%	2520
	21st to end	Day	12% 5% 2 5% 5% 4 5% 6% 6% 9% 39%	2520
July	1st to 10th	Day	10% 6% 3 6% 7% 4 5% 6% 7% 9% 37%	2520
	11th to 20th	Day	8% 6% 3 6% 6% 4 6% 6% 7% 9% 38%	2489
	21st to end	Day	10% 6% 3 6% 7% 4 6% 6% 7% 8% 36%	2547
August	1st to 10th	Day	11% 4 2 7% 7% 4 8% 7% 8% 10% 32%	2327
	11th to 20th	Day	13% 6% 3 6% 7% 4 7% 6% 7% 8% 34%	2285
	21st to end	Day	14% 6% 3 5% 6% 4 6% 6% 6% 9% 36%	2376
September	1st to 10th	Day	17% 6% 2 6% 5% 3 5% 4 5% 6% 42%	2160
	11th to 20th	Day	15% 5% 2 4 4 2 4 4 5% 8% 47%	2142
	21st to end	Day	19% 7% 3 5% 5% 3 4 4 7% 6% 38%	1887
October	1st to 10th	Day	17% 7% 3 6% 6% 4 4 4 4 7% 38%	1800
	11th to 20th	Day	18% 8% 3 6% 6% 3 5% 5% 6% 6% 35%	1800
	21st to end	Day	19% 9% 3 5% 6% 3 5% 5% 4 6% 35%	1980
November	1st to 10th	Day	12% 7% 3 6% 5% 3 5% 6% 5% 7% 42%	1752
	11th to 20th	Day	16% 12% 4 6% 6% 4 6% 5% 5% 7% 31%	1571
	21st to end	Day	17% 11% 3 7% 7% 4 5% 5% 6% 6% 29%	1520
December	1st to 10th	Day	18% 14% 5% 9% 7% 4 4 5% 5% 6% 22%	1520
	11th to 20th	Day	18% 15% 6% 9% 4 3 4 5% 4 6% 27%	1910
	21st to end	Day	22% 16% 7% 8% 8% 3 5% 5% 4 4 17%	2772
January	1st to 10th	Night	14% 13% 6% 10% 8% 4 5% 4 5% 7% 25%	4420
	11th to 20th	Night	15% 15% 7% 12% 7% 3 4 4 5% 6% 22%	4120
	21st to end	Night	23% 14% 6% 11% 6% 3 4 4 4 4 21%	4532
February	1st to 10th	Night	15% 11% 5% 8% 6% 4 5% 5% 5% 7% 30%	2470
	11th to 20th	Night	16% 9% 4 8% 7% 4 7% 5% 5% 6% 30%	2397
	21st to end	Night	16% 11% 4 10% 5% 4 5% 4 4 5% 32%	1795
March	1st to 10th	Night	14% 7% 3 6% 5% 4 5% 5% 6% 6% 39%	1990
	11th to 20th	Night	17% 10% 4 6% 6% 3 4 4 5% 5% 37%	1980
	21st to end	Night	18% 9% 3 6% 6% 3 4 4 4 6% 37%	2169
April	1st to 10th	Night	17% 11% 5% 9% 5% 2 4 5% 4 6% 32%	1800
	11th to 20th	Night	16% 7% 3 5% 6% 3 5% 5% 5% 6% 38%	1775
	21st to end	Night	18% 6% 3 5% 6% 4 5% 5% 4 8% 37%	1743
May	1st to 10th	Night	19% 7% 3 6% 6% 3 5% 5% 5% 6% 35%	1620
	11th to 20th	Night	18% 7% 3 6% 4 3 4 5% 5% 7% 38%	1457
	21st to end	Night	12% 6% 3 5% 5% 3 4 4 6% 9% 42%	1550
June	1st to 10th	Night	12% 5% 3 6% 5% 3 4 4 5% 8% 44%	1440
	11th to 20th	Night	12% 5% 4 6% 5% 3 5% 5% 7% 9% 38%	1440
	21st to end	Night	11% 5% 2 5% 4 3 5% 5% 7% 11% 43%	1440
July	1st to 10th	Night	11% 5% 3 5% 6% 3 5% 4 6% 8% 45%	1440
	11th to 20th	Night	7% 4 2 5% 5% 3 3 6% 7% 9% 49%	1466
	21st to end	Night	10% 4 2 5% 6% 4 5% 6% 6% 10% 43%	1771
August	1st to 10th	Night	7% 6% 3 5% 5% 3 5% 6% 6% 9% 45%	1611
	11th to 20th	Night	12% 7% 2 5% 6% 3 5% 5% 6% 7% 42%	1598
	21st to end	Night	12% 6% 3 5% 5% 2 5% 5% 6% 9% 44%	1980
September	1st to 10th	Night	17% 4 2 4 5% 2 5% 4 5% 7% 45%	1800
	11th to 20th	Night	12% 5% 2 4 4 2 4 4 6% 8% 51%	1813
	21st to end	Night	16% 6% 3 5% 5% 3 4 4 4 7% 42%	2071
October	1st to 10th	Night	17% 6% 2 5% 4 2 4 4 4 7% 43%	2160
	11th to 20th	Night	16% 7% 2 6% 5% 2 4 4 5% 7% 42%	2160
	21st to end	Night	20% 9% 3 5% 4 2 4 4 5% 6% 37%	2376
November	1st to 10th	Night	11% 6% 3 5% 5% 3 4 4 4 6% 49%	2325
	11th to 20th	Night	17% 10% 4 5% 5% 3 5% 4 5% 6% 35%	2607
	21st to end	Night	17% 9% 5% 7% 5% 4 5% 5% 5% 6% 34%	2660
December	1st to 10th	Night	19% 10% 3 9% 6% 3 5% 6% 5% 8% 26%	2660
	11th to 20th	Night	18% 11% 4 9% 5% 4 5% 4 5% 6% 29%	3285
	21st to end	Night	19% 12% 5% 8% 7% 4 5% 5% 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	57% 6% 10% 20% 7% 1	1663
	21st to end	Day	56% 6% 10% 17% 7% 3	1460
March	1st to 10th	Day	49% 6% 12% 22% 9% 1	1969
	11th to 20th	Day	56% 5% 10% 17% 9% 3	1980
	21st to end	Day	53% 4 9% 19% 13% 2	2186
April	1st to 10th	Day	50% 6% 11% 19% 12% 2	2160
	11th to 20th	Day	48% 6% 10% 18% 16% 3	2134
	21st to end	Day	51% 5% 9% 20% 13% 2	2232
May	1st to 10th	Day	51% 7% 10% 18% 12% 2	2340
	11th to 20th	Day	50% 7% 12% 16% 12% 3	2436
	21st to end	Day	43% 9% 15% 20% 10% 2	2725
June	1st to 10th	Day	45% 8% 12% 21% 13% 1	2520
	11th to 20th	Day	44% 8% 14% 19% 13% 2	2520
	21st to end	Day	39% 8% 15% 26% 13% 1	2520
July	1st to 10th	Day	42% 10% 13% 19% 13% 3	2450
	11th to 20th	Day	37% 10% 13% 24% 14% 1	2414
	21st to end	Day	41% 9% 13% 21% 16% 1	2405
August	1st to 10th	Day	41% 11% 16% 21% 11%	2314
	11th to 20th	Day	44% 9% 12% 21% 12% 1	2285
	21st to end	Day	42% 8% 12% 21% 14% 3	2376
September	1st to 10th	Day	43% 6% 10% 22% 16% 3	2160
	11th to 20th	Day	35% 6% 11% 27% 18% 2	2142
	21st to end	Day	44% 6% 12% 19% 17% 1	1887
October	1st to 10th	Day	46% 7% 11% 21% 14% 2	1800
	11th to 20th	Day	47% 7% 11% 23% 11%	1800
	21st to end	Day	48% 7% 12% 22% 11% 1	1980
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% 10% 19% 11% 1	2399
	21st to end	Night	54% 6% 8% 19% 11% 1	1795
March	1st to 10th	Night	43% 6% 12% 25% 13% 1	1990
	11th to 20th	Night	48% 6% 10% 21% 13% 2	1980
	21st to end	Night	48% 5% 9% 19% 16% 3	2169
April	1st to 10th	Night	52% 5% 10% 18% 14% 1	1800
	11th to 20th	Night	44% 7% 11% 21% 15% 2	1775
	21st to end	Night	45% 5% 11% 21% 14% 4	1743
May	1st to 10th	Night	48% 8% 10% 19% 12% 4	1620
	11th to 20th	Night	44% 8% 13% 18% 16% 2	1458
	21st to end	Night	38% 8% 16% 23% 13% 3	1551
June	1st to 10th	Night	38% 7% 13% 25% 15% 2	1440
	11th to 20th	Night	39% 9% 13% 22% 15% 2	1440
	21st to end	Night	34% 9% 14% 27% 15%	1440
July	1st to 10th	Night	37% 10% 13% 23% 15% 3	1400
	11th to 20th	Night	29% 9% 16% 26% 18% 2	1418
	21st to end	Night	34% 9% 17% 22% 16% 2	1672
August	1st to 10th	Night	34% 9% 17% 26% 14% 1	1600
	11th to 20th	Night	40% 7% 16% 21% 16% 1	1598
	21st to end	Night	36% 8% 14% 24% 15% 3	1980
September	1st to 10th	Night	38% 7% 11% 23% 17% 4	1800
	11th to 20th	Night	31% 7% 12% 30% 19% 2	1813
	21st to end	Night	41% 6% 11% 22% 18% 1	2071
October	1st to 10th	Night	40% 7% 14% 24% 14% 1	2160
	11th to 20th	Night	41% 6% 13% 25% 14% 1	2160
	21st to end	Night	47% 5% 11% 23% 13% 1	2376
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	37% 25% 33% 6%	267
	21st to end	Day	35% 21% 25% 17% 1	326
March	1st to 10th	Day	30% 20% 28% 19% 3	420
	11th to 20th	Day	29% 21% 29% 15% 4 1	420
	21st to end	Day	29% 20% 29% 15% 5% 2	462
April	1st to 10th	Day	26% 22% 27% 19% 5% 1	420
	11th to 20th	Day	23% 21% 25% 18% 10% 4	412
	21st to end	Day	30% 15% 31% 15% 6% 2	420
May	1st to 10th	Day	29% 18% 27% 13% 10% 3	423
	11th to 20th	Day	25% 17% 25% 18% 11% 4	447
	21st to end	Day	21% 8% 26% 22% 17% 6%	485
June	1st to 10th	Day	17% 15% 26% 27% 11% 4	450
	11th to 20th	Day	20% 11% 26% 26% 14% 4	450
	21st to end	Day	16% 10% 30% 28% 13% 4	450
July	1st to 10th	Day	16% 7% 22% 27% 18% 11%	445
	11th to 20th	Day	9% 5% 28% 31% 21% 7%	444
	21st to end	Day	15% 7% 29% 27% 17% 5%	488
August	1st to 10th	Day	13% 6% 24% 26% 23% 8%	446
	11th to 20th	Day	15% 4 23% 26% 21% 11%	439
	21st to end	Day	14% 8% 23% 27% 15% 12%	495
September	1st to 10th	Day	19% 7% 19% 28% 18% 9%	450
	11th to 20th	Day	17% 4 20% 27% 22% 9%	450
	21st to end	Day	24% 10% 23% 22% 15% 6%	450
October	1st to 10th	Day	23% 10% 18% 24% 20% 4	450
	11th to 20th	Day	22% 16% 28% 24% 10% 1	450
	21st to end	Day	25% 14% 31% 22% 7% 1	495
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	742
	21st to end	Night	29% 18% 31% 20% 2	592
March	1st to 10th	Night	24% 17% 33% 23% 3	720
	11th to 20th	Night	26% 17% 29% 23% 5%	720
	21st to end	Night	25% 15% 32% 22% 6% 1	792
April	1st to 10th	Night	26% 18% 29% 22% 5%	720
	11th to 20th	Night	21% 13% 31% 26% 8% 1	711
	21st to end	Night	24% 12% 28% 30% 6%	663
May	1st to 10th	Night	24% 9% 24% 32% 11% 1	540
	11th to 20th	Night	19% 9% 30% 32% 9%	396
	21st to end	Night	15% 6% 20% 38% 21% 1	389
June	1st to 10th	Night	13% 6% 22% 39% 19% 1	360
	11th to 20th	Night	14% 7% 24% 37% 19%	360
	21st to end	Night	11% 6% 21% 45% 16%	360
July	1st to 10th	Night	11% 6% 17% 40% 22% 3	350
	11th to 20th	Night	7% 3 18% 40% 30% 2	374
	21st to end	Night	11% 3 18% 45% 22% 1	591
August	1st to 10th	Night	9% 1 16% 43% 29% 2	537
	11th to 20th	Night	15% 4 13% 37% 27% 4	534
	21st to end	Night	15% 3 17% 34% 29% 3	792
September	1st to 10th	Night	18% 3 17% 34% 24% 3	720
	11th to 20th	Night	14% 4 18% 31% 27% 5%	720
	21st to end	Night	19% 8% 19% 30% 20% 3	720
October	1st to 10th	Night	21% 7% 20% 29% 20% 3	720
	11th to 20th	Night	20% 13% 24% 32% 10% 1	720
	21st to end	Night	25% 14% 23% 31% 6% 1	792
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 2024-02-17 06:28:37. Version ac07

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