Stargazer's Field Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargazer's Field Observatory 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	13% 7% 3 6% 5% 4 5% 4 6% 8% 40%	100861
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 44%	98092
Transparency	Day	41% 7% 11% 22% 17% 3	100670
	Night	39% 6% 10% 21% 19% 5%	97952
Seeing	Day	18% 10% 22% 23% 18% 8%	14550
	Night	17% 8% 20% 29% 21% 4	24530

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	18% 13% 3 6% 3 3 3 3 6% 6% 34%	2836
	11th to 20th	Day	21% 7% 4 10% 4 3 2 2 3 4 40%	2844
	21st to end	Day	24% 10% 4 5% 3 3 3 2 4 5% 37%	3476
February	1st to 10th	Day	19% 10% 3 6% 4 3 3 3 5% 5% 38%	1900
	11th to 20th	Day	22% 8% 2 8% 4 4 3 3 4 4 37%	1848
	21st to end	Day	24% 8% 3 6% 5% 3 3 4 4 5% 36%	1570
March	1st to 10th	Day	24% 10% 3 6% 4 4 4 3 5% 5% 31%	3120
	11th to 20th	Day	15% 7% 3 6% 4 3 4 3 5% 7% 44%	3370
	21st to end	Day	15% 6% 3 8% 5% 5% 4 4 6% 7% 38%	3963
April	1st to 10th	Day	14% 7% 2 5% 4 4 5% 3 6% 6% 44%	2280
	11th to 20th	Day	13% 7% 2 7% 4 3 4 3 5% 7% 44%	2254
	21st to end	Day	10% 6% 2 6% 4 4 5% 3 5% 8% 45%	2299
May	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 6% 8% 39%	4082
	11th to 20th	Day	16% 8% 3 7% 4 4 5% 4 6% 8% 36%	4081
	21st to end	Day	11% 6% 3 6% 4 4 5% 4 7% 9% 42%	4476
June	1st to 10th	Day	9% 6% 2 7% 5% 6% 7% 6% 8% 10% 34%	2470
	11th to 20th	Day	5% 5% 1 5% 5% 4 6% 5% 8% 10% 45%	2470
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 6% 7% 9% 41%	2470
July	1st to 10th	Day	7% 5% 2 8% 6% 7% 7% 6% 10% 12% 29%	4120
	11th to 20th	Day	9% 5% 3 6% 6% 6% 7% 6% 9% 11% 32%	4120
	21st to end	Day	14% 11% 4 10% 7% 6% 6% 5% 7% 8% 22%	4466
August	1st to 10th	Day	4 3 1 5% 5% 5% 5% 4 7% 11% 48%	3831
	11th to 20th	Day	5% 4 2 6% 6% 5% 6% 6% 8% 9% 43%	3729
	21st to end	Day	7% 4 2 5% 4 5% 6% 4 5% 7% 51%	4180
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 6% 5% 6% 10% 39%	2223
	11th to 20th	Day	11% 5% 3 6% 5% 4 5% 4 6% 9% 41%	2090
	21st to end	Day	11% 6% 2 6% 4 4 4 4 5% 7% 48%	2090
October	1st to 10th	Day	10% 5% 1 5% 4 4 4 3 3 5% 56%	2090
	11th to 20th	Day	10% 4 2 5% 3 4 4 3 5% 6% 54%	2090
	21st to end	Day	14% 5% 1 5% 4 4 3 3 4 5% 52%	1926
November	1st to 10th	Day	12% 5% 1 5% 2 3 4 3 4 6% 54%	1690
	11th to 20th	Day	12% 6% 2 5% 4 3 4 3 5% 6% 50%	1710
	21st to end	Day	17% 7% 2 5% 3 3 4 4 5% 7% 43%	1710
December	1st to 10th	Day	21% 8% 3 6% 5% 4 4 4 6% 5% 34%	1710
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 3 4 6% 39%	2153
	21st to end	Day	17% 10% 5% 8% 5% 4 5% 3 5% 7% 31%	3124
January	1st to 10th	Night	19% 12% 3 5% 3 3 3 2 4 5% 39%	4109
	11th to 20th	Night	20% 8% 4 7% 3 3 3 3 3 4 41%	4111
	21st to end	Night	22% 14% 3 5% 3 3 3 2 3 4 38%	4180
February	1st to 10th	Night	19% 9% 3 6% 4 3 3 3 4 6% 41%	2280
	11th to 20th	Night	22% 7% 3 5% 4 4 3 3 4 4 40%	2218
	21st to end	Night	23% 7% 2 6% 4 4 5% 3 5% 5% 36%	1884
March	1st to 10th	Night	26% 9% 3 7% 4 4 4 3 4 6% 32%	3733
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 6% 7% 47%	3590
	21st to end	Night	16% 7% 3 8% 5% 5% 4 3 4 4 40%	3695
April	1st to 10th	Night	11% 5% 2 6% 5% 4 4 3 6% 8% 46%	1900
	11th to 20th	Night	14% 6% 2 5% 3 4 3 3 5% 8% 48%	1875
	21st to end	Night	11% 6% 2 5% 4 4 3 3 6% 6% 50%	1880
May	1st to 10th	Night	12% 6% 2 6% 5% 4 4 4 7% 8% 43%	2813
	11th to 20th	Night	15% 7% 3 7% 4 3 4 4 5% 8% 38%	2812
	21st to end	Night	7% 5% 2 6% 4 4 5% 5% 7% 10% 44%	3079
June	1st to 10th	Night	7% 6% 3 7% 6% 4 5% 5% 7% 11% 39%	1710
	11th to 20th	Night	5% 3 1 3 4 4 5% 5% 7% 12% 52%	1710
	21st to end	Night	6% 5% 2 5% 4 4 5% 5% 7% 11% 46%	1710
July	1st to 10th	Night	7% 6% 3 8% 7% 6% 6% 5% 8% 10% 35%	2840
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 5% 8% 11% 39%	2840
	21st to end	Night	10% 9% 5% 11% 7% 6% 6% 5% 7% 9% 25%	3087
August	1st to 10th	Night	2 3 1 4 3 3 4 4 7% 12% 57%	3080
	11th to 20th	Night	6% 4 2 5% 4 4 5% 4 7% 9% 51%	3100
	21st to end	Night	6% 4 1 4 3 3 4 3 6% 7% 59%	3476
September	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 6% 8% 49%	1937
	11th to 20th	Night	10% 6% 3 6% 5% 4 4 3 6% 9% 44%	2090
	21st to end	Night	9% 6% 2 6% 4 3 3 3 5% 7% 52%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 3 2 4 6% 60%	2090
	11th to 20th	Night	12% 6% 2 6% 4 4 3 2 4 5% 53%	2090
	21st to end	Night	14% 6% 1 5% 3 2 3 3 4 6% 53%	2666
November	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 5% 53%	2433
	11th to 20th	Night	11% 6% 3 5% 4 4 3 3 5% 5% 52%	2470
	21st to end	Night	16% 8% 2 6% 4 3 3 3 5% 6% 45%	2470
December	1st to 10th	Night	20% 8% 2 6% 4 4 4 4 5% 6% 38%	2470
	11th to 20th	Night	17% 7% 3 5% 3 3 3 3 4 6% 45%	3042
	21st to end	Night	18% 11% 4 8% 5% 4 5% 4 5% 7% 29%	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	49% 4 6% 18% 21% 2	2837
	11th to 20th	Day	48% 5% 6% 18% 21% 2	2844
	21st to end	Day	50% 4 7% 20% 17% 2	3476
February	1st to 10th	Day	48% 4 7% 20% 18% 3	1900
	11th to 20th	Day	51% 4 6% 19% 16% 5%	1858
	21st to end	Day	51% 4 7% 14% 19% 6%	1570
March	1st to 10th	Day	54% 5% 8% 10% 14% 8%	3120
	11th to 20th	Day	40% 5% 7% 23% 19% 7%	3370
	21st to end	Day	44% 5% 12% 20% 16% 3	3963
April	1st to 10th	Day	39% 5% 11% 23% 17% 5%	2280
	11th to 20th	Day	39% 5% 7% 21% 23% 6%	2254
	21st to end	Day	37% 5% 9% 28% 18% 3	2299
May	1st to 10th	Day	39% 9% 11% 24% 14% 2	4120
	11th to 20th	Day	44% 7% 12% 25% 11%	4085
	21st to end	Day	37% 7% 10% 25% 18% 1	4489
June	1st to 10th	Day	41% 9% 13% 21% 14% 1	2470
	11th to 20th	Day	30% 8% 18% 25% 17% 2	2470
	21st to end	Day	35% 10% 18% 20% 14% 3	2470
July	1st to 10th	Day	40% 12% 19% 22% 5% 1	4055
	11th to 20th	Day	39% 11% 21% 22% 6% 1	4051
	21st to end	Day	57% 9% 13% 16% 5%	4324
August	1st to 10th	Day	27% 8% 13% 36% 16% 1	3818
	11th to 20th	Day	32% 9% 15% 26% 15% 3	3765
	21st to end	Day	29% 8% 13% 25% 23% 2	4179
September	1st to 10th	Day	38% 8% 15% 18% 17% 5%	2223
	11th to 20th	Day	38% 8% 11% 20% 21% 3	2090
	21st to end	Day	35% 5% 11% 22% 20% 7%	2090
October	1st to 10th	Day	31% 5% 6% 21% 28% 9%	2090
	11th to 20th	Day	31% 4 8% 22% 25% 11%	2090
	21st to end	Day	35% 5% 5% 19% 29% 8%	1926
November	1st to 10th	Day	33% 3 8% 19% 29% 8%	1690
	11th to 20th	Day	36% 3 6% 21% 25% 8%	1710
	21st to end	Day	41% 5% 5% 20% 24% 5%	1710
December	1st to 10th	Day	50% 5% 5% 17% 19% 4	1710
	11th to 20th	Day	47% 4 6% 20% 19% 4	2150
	21st to end	Day	52% 5% 8% 20% 12% 3	3124
January	1st to 10th	Night	48% 3 6% 19% 23% 2	4109
	11th to 20th	Night	46% 5% 6% 19% 18% 6%	4111
	21st to end	Night	52% 3 4 19% 18% 3	4180
February	1st to 10th	Night	46% 3 8% 20% 20% 4	2280
	11th to 20th	Night	48% 4 6% 18% 16% 7%	2219
	21st to end	Night	50% 5% 6% 16% 17% 7%	1884
March	1st to 10th	Night	53% 5% 7% 13% 16% 6%	3733
	11th to 20th	Night	36% 5% 8% 21% 21% 9%	3590
	21st to end	Night	48% 4 8% 20% 19% 2	3695
April	1st to 10th	Night	35% 6% 12% 23% 20% 5%	1900
	11th to 20th	Night	35% 4 7% 20% 22% 11%	1875
	21st to end	Night	34% 5% 11% 28% 19% 4	1880
May	1st to 10th	Night	37% 9% 12% 24% 17% 2	2840
	11th to 20th	Night	42% 8% 14% 23% 13% 1	2813
	21st to end	Night	30% 10% 14% 25% 19% 2	3087
June	1st to 10th	Night	37% 8% 14% 22% 17% 2	1710
	11th to 20th	Night	24% 8% 18% 29% 20% 2	1710
	21st to end	Night	29% 9% 18% 23% 17% 5%	1710
July	1st to 10th	Night	41% 9% 21% 21% 7% 2	2795
	11th to 20th	Night	34% 10% 24% 23% 7% 2	2786
	21st to end	Night	54% 10% 14% 15% 7% 1	2988
August	1st to 10th	Night	18% 8% 14% 37% 21% 1	3069
	11th to 20th	Night	27% 8% 19% 28% 16% 2	3130
	21st to end	Night	24% 6% 14% 25% 28% 3	3476
September	1st to 10th	Night	31% 8% 18% 21% 17% 6%	1937
	11th to 20th	Night	35% 8% 14% 17% 23% 3	2090
	21st to end	Night	32% 5% 9% 22% 22% 9%	2090
October	1st to 10th	Night	28% 4 7% 24% 28% 10%	2090
	11th to 20th	Night	34% 4 6% 21% 23% 12%	2090
	21st to end	Night	34% 4 5% 20% 28% 10%	2666
November	1st to 10th	Night	33% 5% 7% 21% 24% 10%	2433
	11th to 20th	Night	34% 4 6% 18% 28% 10%	2470
	21st to end	Night	41% 3 6% 21% 23% 6%	2470
December	1st to 10th	Night	46% 5% 8% 19% 18% 4	2470
	11th to 20th	Night	40% 4 6% 19% 26% 5%	3044
	21st to end	Night	52% 6% 7% 19% 14% 2	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	31% 25% 28% 14% 3	270
	11th to 20th	Day	32% 23% 28% 11% 6%	270
	21st to end	Day	25% 28% 31% 14% 2	297
February	1st to 10th	Day	29% 24% 30% 13% 3	270
	11th to 20th	Day	37% 20% 31% 9% 1 1	270
	21st to end	Day	42% 20% 31% 6% 1	225
March	1st to 10th	Day	30% 22% 30% 13% 4 1	270
	11th to 20th	Day	25% 20% 29% 20% 5% 1	389
	21st to end	Day	25% 19% 31% 18% 6% 1	506
April	1st to 10th	Day	26% 15% 27% 20% 11% 2	460
	11th to 20th	Day	23% 14% 30% 22% 10% 1	452
	21st to end	Day	18% 13% 29% 26% 11% 1	460
May	1st to 10th	Day	17% 10% 30% 25% 12% 5%	463
	11th to 20th	Day	12% 8% 27% 28% 16% 9%	487
	21st to end	Day	13% 7% 19% 32% 17% 13%	529
June	1st to 10th	Day	14% 7% 17% 26% 26% 10%	490
	11th to 20th	Day	6% 4 18% 26% 26% 21%	490
	21st to end	Day	11% 4 16% 24% 29% 15%	490
July	1st to 10th	Day	12% 2 12% 23% 31% 20%	485
	11th to 20th	Day	9% 2 11% 23% 30% 25%	484
	21st to end	Day	12% 2 9% 25% 31% 21%	532
August	1st to 10th	Day	12% 2 9% 25% 33% 19%	486
	11th to 20th	Day	11% 3 11% 28% 34% 12%	479
	21st to end	Day	14% 3 10% 22% 34% 17%	539
September	1st to 10th	Day	11% 3 12% 31% 31% 12%	490
	11th to 20th	Day	11% 4 15% 26% 30% 14%	490
	21st to end	Day	17% 4 15% 28% 31% 6%	490
October	1st to 10th	Day	12% 4 25% 29% 21% 9%	490
	11th to 20th	Day	13% 10% 28% 30% 18% 2	490
	21st to end	Day	20% 11% 23% 30% 14% 2	354
November	1st to 10th	Day	18% 8% 34% 24% 13% 3	276
	11th to 20th	Day	16% 18% 39% 21% 6%	270
	21st to end	Day	20% 19% 31% 17% 11% 1	270
December	1st to 10th	Day	34% 16% 27% 16% 6%	270
	11th to 20th	Day	23% 24% 31% 13% 9%	270
	21st to end	Day	31% 18% 32% 16% 4	297
January	1st to 10th	Night	28% 16% 29% 22% 5%	760
	11th to 20th	Night	27% 18% 27% 21% 7%	760
	21st to end	Night	22% 15% 31% 28% 4	836
February	1st to 10th	Night	23% 14% 29% 29% 5%	760
	11th to 20th	Night	28% 16% 27% 26% 2	743
	21st to end	Night	31% 16% 27% 24% 2	628
March	1st to 10th	Night	23% 15% 26% 31% 5%	760
	11th to 20th	Night	20% 13% 29% 30% 8% 1	760
	21st to end	Night	21% 12% 28% 28% 11%	765
April	1st to 10th	Night	15% 12% 29% 31% 13%	570
	11th to 20th	Night	17% 10% 30% 29% 13% 1	563
	21st to end	Night	15% 8% 24% 36% 15% 1	570
May	1st to 10th	Night	14% 5% 24% 33% 21% 3	570
	11th to 20th	Night	14% 4 20% 33% 26% 4	561
	21st to end	Night	8% 2 14% 38% 32% 6%	617
June	1st to 10th	Night	9% 3 15% 32% 36% 6%	570
	11th to 20th	Night	5% 2 8% 33% 42% 11%	570
	21st to end	Night	8% 1 8% 32% 43% 9%	570
July	1st to 10th	Night	10% 2 8% 27% 39% 15%	555
	11th to 20th	Night	10% 1 6% 25% 41% 18%	552
	21st to end	Night	10% 1 6% 24% 46% 13%	624
August	1st to 10th	Night	5% 1 4 25% 54% 11%	567
	11th to 20th	Night	10% 3 7% 29% 43% 7%	564
	21st to end	Night	11% 2 7% 27% 43% 9%	627
September	1st to 10th	Night	11% 3 9% 26% 43% 8%	607
	11th to 20th	Night	12% 3 14% 29% 36% 6%	760
	21st to end	Night	11% 3 13% 31% 39% 2	760
October	1st to 10th	Night	11% 5% 18% 32% 29% 6%	760
	11th to 20th	Night	16% 6% 24% 32% 21% 1	760
	21st to end	Night	18% 8% 18% 35% 19% 2	836
November	1st to 10th	Night	15% 8% 20% 34% 20% 3	749
	11th to 20th	Night	16% 10% 27% 32% 14% 1	760
	21st to end	Night	21% 11% 24% 30% 13% 1	760
December	1st to 10th	Night	25% 14% 25% 29% 8%	760
	11th to 20th	Night	23% 12% 26% 29% 9%	760
	21st to end	Night	29% 11% 25% 29% 5%	836

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