Sunset Field
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunset Field clear sky chart from 2005-11-06 to 2024-11-04.

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	14% 6% 2 6% 4 5% 5% 4 6% 8% 40%	100697
	Night	15% 6% 2 6% 4 4 4 3 6% 7% 43%	98219
Transparency	Day	39% 6% 12% 23% 16% 4	104346
	Night	38% 5% 11% 23% 18% 5%	102709
Seeing	Day	19% 11% 23% 25% 16% 6%	15087
	Night	17% 8% 23% 33% 17% 2	25251

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	17% 4 1 5% 5% 4 3 3 5% 7% 45%	2836
	11th to 20th	Day	15% 8% 2 7% 4 4 5% 4 5% 5% 41%	2840
	21st to end	Day	21% 8% 3 6% 4 4 4 3 4 5% 39%	3124
February	1st to 10th	Day	12% 6% 3 7% 5% 5% 6% 4 5% 7% 39%	1710
	11th to 20th	Day	18% 6% 3 5% 5% 5% 4 3 5% 6% 40%	1663
	21st to end	Day	20% 7% 3 6% 4 4 4 3 5% 5% 38%	1670
March	1st to 10th	Day	20% 9% 2 6% 3 4 4 4 6% 7% 35%	3435
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 6% 50%	3480
	21st to end	Day	18% 8% 2 8% 4 4 4 4 5% 6% 37%	3815
April	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 6% 8% 47%	2189
	11th to 20th	Day	15% 5% 2 5% 4 4 5% 4 6% 7% 44%	2254
	21st to end	Day	16% 6% 2 7% 5% 4 4 4 5% 6% 41%	2372
May	1st to 10th	Day	16% 6% 2 7% 5% 6% 6% 5% 7% 9% 30%	4082
	11th to 20th	Day	21% 7% 2 6% 5% 5% 5% 3 6% 8% 32%	4081
	21st to end	Day	9% 4 2 5% 5% 5% 6% 5% 7% 10% 43%	4476
June	1st to 10th	Day	10% 5% 2 5% 5% 5% 5% 5% 7% 10% 42%	2492
	11th to 20th	Day	10% 5% 2 7% 4 5% 5% 5% 8% 11% 39%	2590
	21st to end	Day	7% 5% 2 6% 6% 5% 5% 6% 7% 11% 40%	2470
July	1st to 10th	Day	7% 4 2 6% 5% 5% 7% 6% 9% 11% 39%	4120
	11th to 20th	Day	9% 5% 2 6% 5% 6% 6% 5% 8% 12% 35%	4120
	21st to end	Day	13% 8% 3 9% 7% 7% 6% 5% 7% 8% 26%	4466
August	1st to 10th	Day	14% 7% 2 7% 5% 5% 5% 5% 8% 11% 30%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 6% 6% 5% 8% 11% 36%	4044
	21st to end	Day	8% 4 2 5% 4 4 5% 4 7% 9% 47%	4180
September	1st to 10th	Day	13% 5% 2 5% 3 5% 5% 4 5% 7% 46%	2280
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 6% 7% 41%	2105
	21st to end	Day	24% 7% 2 6% 4 3 4 3 5% 5% 36%	2076
October	1st to 10th	Day	16% 6% 2 4 3 4 3 3 4 6% 49%	1900
	11th to 20th	Day	15% 5% 2 4 2 3 3 3 5% 6% 51%	1900
	21st to end	Day	14% 6% 2 5% 3 3 3 3 5% 5% 50%	2090
November	1st to 10th	Day	12% 5% 1 5% 4 3 4 2 4 6% 55%	1887
	11th to 20th	Day	15% 5% 1 4 3 3 4 2 5% 6% 50%	1777
	21st to end	Day	14% 5% 2 5% 4 3 3 3 4 8% 48%	1538
December	1st to 10th	Day	17% 7% 3 8% 4 4 4 4 6% 7% 36%	1520
	11th to 20th	Day	16% 5% 2 4 3 3 4 2 4 6% 52%	1910
	21st to end	Day	20% 6% 3 6% 4 4 5% 5% 7% 8% 33%	3101
January	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 6% 48%	4109
	11th to 20th	Night	16% 7% 2 5% 3 4 4 3 4 5% 46%	4120
	21st to end	Night	22% 7% 2 5% 4 4 4 3 4 5% 40%	4532
February	1st to 10th	Night	13% 7% 2 7% 4 4 4 3 7% 6% 43%	2470
	11th to 20th	Night	19% 7% 2 6% 4 3 4 3 4 6% 41%	2399
	21st to end	Night	15% 8% 3 6% 4 4 4 4 5% 7% 40%	1783
March	1st to 10th	Night	22% 9% 2 7% 4 4 5% 4 5% 5% 33%	3418
	11th to 20th	Night	11% 4 1 5% 3 4 4 4 5% 7% 51%	3480
	21st to end	Night	16% 6% 2 5% 4 3 4 2 5% 5% 47%	3817
April	1st to 10th	Night	14% 7% 2 6% 4 3 4 3 6% 7% 44%	1990
	11th to 20th	Night	14% 5% 2 5% 3 3 4 4 5% 8% 48%	1875
	21st to end	Night	15% 6% 2 6% 4 4 4 4 6% 7% 44%	1823
May	1st to 10th	Night	18% 8% 3 6% 4 4 4 3 6% 9% 34%	2813
	11th to 20th	Night	24% 8% 3 6% 4 4 4 3 4 6% 35%	2812
	21st to end	Night	10% 4 2 6% 4 4 5% 4 7% 10% 45%	3079
June	1st to 10th	Night	9% 5% 2 5% 4 5% 4 4 8% 11% 44%	1666
	11th to 20th	Night	10% 5% 2 7% 4 4 5% 4 8% 9% 43%	1566
	21st to end	Night	8% 4 1 5% 5% 5% 5% 4 7% 10% 45%	1710
July	1st to 10th	Night	7% 5% 2 5% 5% 5% 6% 5% 8% 11% 42%	2840
	11th to 20th	Night	9% 5% 3 6% 5% 5% 6% 5% 8% 11% 38%	2840
	21st to end	Night	11% 8% 3 8% 6% 6% 5% 4 7% 9% 31%	3087
August	1st to 10th	Night	17% 7% 2 7% 5% 4 4 4 7% 10% 33%	2825
	11th to 20th	Night	10% 6% 2 6% 5% 5% 6% 5% 7% 9% 38%	2785
	21st to end	Night	9% 5% 3 6% 4 4 4 4 7% 8% 47%	3442
September	1st to 10th	Night	11% 6% 3 6% 4 4 5% 4 5% 7% 47%	1900
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 3 5% 6% 42%	2071
	21st to end	Night	24% 7% 3 7% 4 3 3 3 5% 5% 37%	2104
October	1st to 10th	Night	16% 7% 2 6% 3 3 3 2 5% 6% 48%	2280
	11th to 20th	Night	14% 6% 2 4 4 3 3 2 4 6% 51%	2280
	21st to end	Night	14% 3 1 4 3 3 3 2 6% 6% 55%	2508
November	1st to 10th	Night	14% 6% 2 5% 3 2 3 3 4 4 54%	2264
	11th to 20th	Night	14% 4 2 4 4 3 4 4 5% 6% 51%	2398
	21st to end	Night	13% 5% 2 5% 4 3 4 3 5% 6% 49%	2638
December	1st to 10th	Night	18% 9% 2 6% 4 3 3 2 5% 6% 42%	2660
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 45%	3285
	21st to end	Night	17% 5% 2 6% 5% 4 5% 4 7% 8% 37%	4550

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	36% 5% 7% 30% 17% 6%	2837
	11th to 20th	Day	42% 4 7% 19% 23% 5%	2840
	21st to end	Day	48% 3 7% 22% 17% 3	3124
February	1st to 10th	Day	41% 5% 12% 23% 16% 3	1710
	11th to 20th	Day	44% 4 8% 22% 18% 4	1672
	21st to end	Day	48% 4 10% 17% 17% 5%	1670
March	1st to 10th	Day	47% 4 8% 20% 14% 6%	3435
	11th to 20th	Day	32% 5% 8% 25% 20% 9%	3480
	21st to end	Day	47% 5% 9% 20% 16% 3	3815
April	1st to 10th	Day	34% 5% 11% 24% 19% 8%	2189
	11th to 20th	Day	37% 4 11% 23% 19% 5%	2254
	21st to end	Day	42% 5% 12% 23% 14% 4	2372
May	1st to 10th	Day	47% 7% 13% 20% 12% 2	4120
	11th to 20th	Day	49% 6% 11% 22% 10% 1	4085
	21st to end	Day	33% 7% 17% 22% 18% 3	4489
June	1st to 10th	Day	34% 8% 17% 26% 14% 1	2492
	11th to 20th	Day	35% 8% 17% 22% 16% 1	2590
	21st to end	Day	34% 10% 15% 25% 14% 2	2470
July	1st to 10th	Day	34% 11% 22% 19% 9% 5%	4055
	11th to 20th	Day	37% 9% 20% 24% 10% 1	4051
	21st to end	Day	50% 9% 13% 20% 8%	4324
August	1st to 10th	Day	44% 8% 18% 24% 6%	4091
	11th to 20th	Day	36% 9% 15% 28% 11% 1	4083
	21st to end	Day	30% 6% 21% 28% 13% 1	4180
September	1st to 10th	Day	35% 7% 13% 20% 21% 4	2280
	11th to 20th	Day	41% 5% 9% 26% 17% 3	2105
	21st to end	Day	49% 4 8% 18% 18% 2	2076
October	1st to 10th	Day	33% 3 8% 20% 28% 8%	3160
	11th to 20th	Day	24% 3 9% 23% 28% 13%	3140
	21st to end	Day	22% 3 12% 29% 23% 12%	3428
November	1st to 10th	Day	31% 4 9% 23% 28% 5%	1887
	11th to 20th	Day	34% 4 8% 24% 22% 8%	1777
	21st to end	Day	34% 5% 9% 25% 24% 4	1538
December	1st to 10th	Day	45% 5% 11% 20% 16% 4	1520
	11th to 20th	Day	33% 5% 8% 25% 22% 7%	1906
	21st to end	Day	45% 4 10% 27% 13% 2	3101
January	1st to 10th	Night	35% 4 7% 26% 24% 4	4109
	11th to 20th	Night	39% 4 7% 21% 24% 5%	4120
	21st to end	Night	46% 4 6% 25% 15% 5%	4532
February	1st to 10th	Night	39% 4 11% 24% 19% 2	2470
	11th to 20th	Night	44% 3 9% 20% 18% 6%	2401
	21st to end	Night	42% 5% 10% 23% 15% 5%	1783
March	1st to 10th	Night	50% 5% 8% 19% 15% 4	3418
	11th to 20th	Night	30% 5% 7% 21% 28% 8%	3480
	21st to end	Night	38% 4 10% 23% 19% 5%	3817
April	1st to 10th	Night	38% 5% 11% 20% 21% 5%	1990
	11th to 20th	Night	34% 5% 13% 22% 21% 6%	1875
	21st to end	Night	38% 6% 11% 24% 17% 4	1823
May	1st to 10th	Night	46% 6% 15% 19% 12% 2	2840
	11th to 20th	Night	50% 6% 10% 22% 12% 1	2813
	21st to end	Night	33% 7% 17% 26% 13% 4	3087
June	1st to 10th	Night	33% 9% 15% 27% 15% 1	1666
	11th to 20th	Night	35% 7% 18% 22% 16% 2	1566
	21st to end	Night	31% 10% 16% 23% 16% 4	1710
July	1st to 10th	Night	34% 10% 22% 18% 13% 3	2795
	11th to 20th	Night	38% 8% 21% 24% 8% 1	2786
	21st to end	Night	47% 8% 15% 22% 8%	2988
August	1st to 10th	Night	45% 7% 18% 22% 7%	2814
	11th to 20th	Night	37% 8% 17% 26% 11% 1	2812
	21st to end	Night	33% 7% 16% 33% 9% 2	3442
September	1st to 10th	Night	36% 8% 13% 19% 18% 6%	1900
	11th to 20th	Night	41% 7% 8% 23% 18% 3	2071
	21st to end	Night	50% 5% 7% 20% 15% 3	2104
October	1st to 10th	Night	37% 4 9% 19% 25% 6%	3800
	11th to 20th	Night	25% 3 9% 22% 28% 14%	3779
	21st to end	Night	19% 2 9% 30% 28% 11%	4120
November	1st to 10th	Night	34% 3 8% 23% 25% 7%	2264
	11th to 20th	Night	34% 4 9% 22% 24% 7%	2398
	21st to end	Night	34% 4 9% 27% 21% 6%	2638
December	1st to 10th	Night	44% 3 8% 25% 16% 3	2660
	11th to 20th	Night	39% 4 8% 22% 21% 6%	3288
	21st to end	Night	42% 5% 10% 22% 19% 2	4550

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% 24% 17% 3 1	270
	11th to 20th	Day	37% 16% 30% 16%	270
	21st to end	Day	30% 23% 29% 14% 4	297
February	1st to 10th	Day	23% 21% 37% 13% 6%	270
	11th to 20th	Day	40% 18% 32% 7% 3	270
	21st to end	Day	30% 23% 27% 18% 3	325
March	1st to 10th	Day	26% 17% 28% 24% 5%	460
	11th to 20th	Day	23% 22% 28% 22% 5% 1	460
	21st to end	Day	23% 17% 31% 22% 7%	506
April	1st to 10th	Day	22% 22% 26% 21% 9% 1	460
	11th to 20th	Day	21% 14% 29% 22% 11% 4	452
	21st to end	Day	24% 13% 27% 22% 12% 3	460
May	1st to 10th	Day	20% 14% 32% 21% 10% 3	463
	11th to 20th	Day	21% 11% 23% 25% 16% 5%	487
	21st to end	Day	18% 6% 19% 28% 19% 9%	529
June	1st to 10th	Day	10% 6% 28% 31% 18% 8%	490
	11th to 20th	Day	11% 6% 21% 31% 20% 10%	490
	21st to end	Day	10% 7% 24% 31% 21% 7%	490
July	1st to 10th	Day	11% 2 17% 28% 28% 14%	485
	11th to 20th	Day	6% 2 15% 33% 31% 13%	484
	21st to end	Day	14% 2 19% 29% 23% 13%	532
August	1st to 10th	Day	16% 3 18% 24% 24% 14%	486
	11th to 20th	Day	12% 5% 18% 27% 24% 14%	479
	21st to end	Day	10% 3 12% 29% 26% 20%	539
September	1st to 10th	Day	13% 3 15% 25% 26% 17%	490
	11th to 20th	Day	19% 3 14% 24% 28% 11%	490
	21st to end	Day	27% 9% 19% 24% 17% 5%	490
October	1st to 10th	Day	22% 5% 20% 28% 20% 5%	490
	11th to 20th	Day	16% 13% 21% 28% 18% 3	490
	21st to end	Day	17% 12% 28% 29% 12% 2	539
November	1st to 10th	Day	17% 10% 25% 31% 13% 3	467
	11th to 20th	Day	22% 17% 23% 24% 12% 1	337
	21st to end	Day	22% 16% 27% 23% 10% 2	188
December	1st to 10th	Day	24% 19% 32% 19% 6%	180
	11th to 20th	Day	24% 16% 28% 19% 10% 2	180
	21st to end	Day	28% 15% 28% 20% 9% 1	292
January	1st to 10th	Night	21% 15% 33% 27% 3	760
	11th to 20th	Night	20% 15% 31% 32% 3	760
	21st to end	Night	20% 13% 37% 27% 3	836
February	1st to 10th	Night	17% 13% 36% 31% 3	760
	11th to 20th	Night	27% 16% 33% 23% 1	743
	21st to end	Night	21% 15% 34% 27% 3	628
March	1st to 10th	Night	17% 15% 31% 33% 4	760
	11th to 20th	Night	23% 12% 30% 26% 7% 1	760
	21st to end	Night	18% 12% 31% 33% 6%	836
April	1st to 10th	Night	17% 18% 31% 29% 6%	760
	11th to 20th	Night	16% 13% 27% 31% 12% 1	751
	21st to end	Night	18% 5% 28% 38% 11%	683
May	1st to 10th	Night	16% 7% 25% 36% 14% 1	570
	11th to 20th	Night	19% 6% 19% 38% 17% 2	561
	21st to end	Night	16% 2 10% 34% 33% 5%	617
June	1st to 10th	Night	10% 1 12% 43% 31% 2	526
	11th to 20th	Night	9% 2 14% 39% 34% 2	426
	21st to end	Night	9% 2 10% 44% 30% 4	570
July	1st to 10th	Night	11% 1 8% 33% 41% 6%	555
	11th to 20th	Night	7% 1 7% 31% 47% 7%	552
	21st to end	Night	9% 2 8% 39% 37% 5%	624
August	1st to 10th	Night	14% 1 10% 35% 36% 4	567
	11th to 20th	Night	13% 2 10% 34% 37% 4	564
	21st to end	Night	12% 1 9% 34% 37% 7%	815
September	1st to 10th	Night	14% 2 11% 32% 35% 7%	760
	11th to 20th	Night	19% 3 10% 30% 33% 5%	760
	21st to end	Night	25% 4 17% 31% 21% 2	760
October	1st to 10th	Night	18% 7% 18% 28% 26% 4	760
	11th to 20th	Night	16% 9% 23% 34% 17% 1	760
	21st to end	Night	16% 7% 21% 40% 14% 2	836
November	1st to 10th	Night	18% 7% 21% 37% 14% 2	755
	11th to 20th	Night	17% 11% 24% 35% 12% 1	760
	21st to end	Night	16% 11% 25% 37% 11% 1	760
December	1st to 10th	Night	23% 12% 29% 29% 6%	760
	11th to 20th	Night	18% 10% 31% 36% 5%	760
	21st to end	Night	20% 13% 28% 35% 3	836

Page generated at 2024-11-01 22:47:50. Version ac07

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