Wadsworth Observatory
Clear Sky Chart
History

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

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	15% 11% 4 8% 5% 5% 5% 4 5% 7% 31%	100959
	Night	16% 12% 4 8% 5% 4 4 3 5% 6% 32%	98041
Transparency	Day	51% 6% 11% 20% 11% 1	104635
	Night	51% 5% 11% 20% 12% 1	102504
Seeing	Day	20% 13% 27% 22% 13% 5%	14638
	Night	20% 10% 27% 28% 12% 2	24549

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	19% 20% 8% 14% 5% 4 4 3 4 4 15%	2836
	11th to 20th	Day	15% 24% 8% 11% 6% 6% 5% 2 3 5% 15%	2840
	21st to end	Day	27% 20% 10% 12% 6% 5% 3 3 3 4 9%	3124
February	1st to 10th	Day	18% 18% 5% 13% 7% 5% 3 2 4 5% 22%	1710
	11th to 20th	Day	15% 14% 6% 14% 7% 6% 4 4 4 4 22%	1733
	21st to end	Day	18% 15% 4 11% 5% 5% 4 4 4 5% 25%	1570
March	1st to 10th	Day	22% 13% 5% 9% 5% 4 3 3 4 6% 25%	3342
	11th to 20th	Day	12% 13% 5% 10% 5% 5% 4 4 4 5% 34%	3480
	21st to end	Day	21% 11% 4 9% 5% 4 4 3 4 7% 29%	3815
April	1st to 10th	Day	14% 13% 4 8% 6% 6% 4 4 5% 7% 30%	2115
	11th to 20th	Day	18% 10% 3 8% 6% 4 4 3 5% 6% 33%	2418
	21st to end	Day	19% 11% 3 8% 5% 5% 4 4 4 6% 33%	2470
May	1st to 10th	Day	20% 9% 3 8% 5% 5% 4 4 5% 7% 29%	4082
	11th to 20th	Day	20% 8% 3 7% 4 4 5% 4 6% 8% 33%	4081
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 9% 39%	4476
June	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	2627
	11th to 20th	Day	12% 7% 3 8% 5% 4 5% 4 7% 8% 37%	2660
	21st to end	Day	11% 6% 2 5% 6% 5% 5% 5% 7% 10% 39%	2576
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 6% 10% 38%	4120
	11th to 20th	Day	9% 4 2 6% 4 5% 6% 4 8% 10% 42%	4120
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 5% 7% 8% 38%	4466
August	1st to 10th	Day	13% 7% 3 8% 5% 5% 6% 4 6% 8% 34%	4104
	11th to 20th	Day	11% 7% 3 7% 5% 5% 6% 5% 8% 10% 35%	4044
	21st to end	Day	8% 6% 2 8% 5% 6% 6% 4 7% 9% 39%	4468
September	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 5% 8% 43%	2161
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 3 7% 9% 43%	2090
	21st to end	Day	20% 8% 3 6% 4 4 4 3 5% 6% 38%	2090
October	1st to 10th	Day	14% 7% 2 7% 4 5% 4 3 7% 8% 39%	1972
	11th to 20th	Day	18% 10% 3 7% 4 4 4 3 5% 5% 36%	1900
	21st to end	Day	20% 11% 3 8% 5% 4 4 3 5% 6% 30%	2081
November	1st to 10th	Day	11% 11% 3 7% 4 5% 4 5% 5% 6% 40%	1717
	11th to 20th	Day	18% 14% 3 7% 5% 4 4 3 5% 5% 31%	1710
	21st to end	Day	17% 16% 6% 9% 6% 5% 4 4 5% 6% 23%	1535
December	1st to 10th	Day	18% 20% 8% 12% 5% 5% 3 3 3 4 19%	1520
	11th to 20th	Day	18% 17% 7% 15% 5% 4 4 3 5% 6% 17%	1910
	21st to end	Day	26% 23% 7% 11% 5% 3 4 3 4 4 10%	2996
January	1st to 10th	Night	16% 22% 7% 14% 6% 4 3 3 4 5% 16%	4109
	11th to 20th	Night	14% 22% 9% 16% 6% 4 5% 4 4 4 11%	4120
	21st to end	Night	27% 19% 7% 13% 5% 3 3 2 3 4 14%	4532
February	1st to 10th	Night	20% 15% 5% 11% 6% 5% 3 3 4 5% 22%	2470
	11th to 20th	Night	17% 14% 5% 11% 7% 5% 5% 4 5% 5% 23%	2331
	21st to end	Night	20% 13% 4 11% 7% 4 4 3 4 5% 24%	1884
March	1st to 10th	Night	22% 13% 4 7% 4 3 3 2 3 5% 33%	3509
	11th to 20th	Night	15% 10% 3 8% 4 4 4 4 5% 7% 36%	3480
	21st to end	Night	18% 10% 4 8% 5% 4 4 3 5% 6% 34%	3817
April	1st to 10th	Night	16% 12% 3 7% 5% 5% 4 3 5% 7% 33%	2063
	11th to 20th	Night	17% 10% 3 8% 5% 4 4 4 6% 7% 35%	1725
	21st to end	Night	15% 9% 3 6% 5% 5% 5% 4 5% 7% 36%	1710
May	1st to 10th	Night	24% 10% 3 8% 5% 4 4 4 5% 6% 28%	2813
	11th to 20th	Night	17% 8% 3 5% 3 4 4 3 5% 8% 39%	2812
	21st to end	Night	10% 5% 2 5% 4 3 4 4 7% 10% 46%	3079
June	1st to 10th	Night	10% 6% 2 7% 4 5% 5% 4 7% 7% 44%	1549
	11th to 20th	Night	9% 5% 3 6% 5% 5% 5% 4 7% 9% 42%	1520
	21st to end	Night	11% 5% 2 5% 5% 4 5% 5% 6% 10% 43%	1596
July	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 8% 45%	2840
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 6% 10% 48%	2840
	21st to end	Night	7% 6% 2 7% 5% 4 5% 5% 6% 8% 44%	3087
August	1st to 10th	Night	11% 8% 3 7% 5% 5% 4 3 6% 8% 39%	2825
	11th to 20th	Night	11% 8% 3 8% 5% 5% 3 3 5% 7% 43%	2785
	21st to end	Night	7% 5% 2 6% 5% 5% 6% 4 6% 9% 45%	3154
September	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 5% 6% 48%	2015
	11th to 20th	Night	10% 4 2 5% 4 3 4 3 5% 7% 54%	2090
	21st to end	Night	16% 7% 3 6% 4 4 4 3 5% 6% 42%	2090
October	1st to 10th	Night	14% 6% 2 6% 3 4 4 4 7% 8% 43%	2206
	11th to 20th	Night	17% 9% 3 8% 4 5% 4 3 5% 5% 37%	2280
	21st to end	Night	22% 10% 3 6% 4 5% 4 4 5% 6% 31%	2514
November	1st to 10th	Night	14% 9% 3 6% 4 3 4 4 5% 7% 41%	2483
	11th to 20th	Night	17% 14% 4 8% 4 4 4 3 5% 5% 30%	2470
	21st to end	Night	20% 15% 5% 7% 6% 4 4 4 4 6% 25%	2642
December	1st to 10th	Night	21% 19% 6% 10% 5% 4 3 3 5% 5% 21%	2660
	11th to 20th	Night	17% 16% 7% 12% 5% 4 3 3 5% 5% 23%	3285
	21st to end	Night	25% 20% 8% 10% 5% 4 4 3 4 5% 13%	4656

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	73% 4 9% 11% 3	2837
	11th to 20th	Day	74% 3 8% 10% 4	2840
	21st to end	Day	82% 3 7% 6% 2	3124
February	1st to 10th	Day	67% 3 9% 14% 7%	1710
	11th to 20th	Day	66% 4 8% 14% 7% 1	1742
	21st to end	Day	61% 4 12% 15% 7% 2	1570
March	1st to 10th	Day	61% 5% 9% 21% 5%	3342
	11th to 20th	Day	53% 5% 10% 23% 8% 1	3480
	21st to end	Day	55% 6% 8% 18% 12% 1	3815
April	1st to 10th	Day	53% 6% 11% 17% 12% 1	2115
	11th to 20th	Day	52% 6% 11% 17% 13% 2	2418
	21st to end	Day	53% 5% 10% 20% 10% 2	2470
May	1st to 10th	Day	54% 6% 9% 21% 8% 1	4120
	11th to 20th	Day	49% 7% 11% 22% 10% 1	4085
	21st to end	Day	39% 8% 13% 21% 15% 4	4489
June	1st to 10th	Day	44% 7% 11% 24% 13% 1	2627
	11th to 20th	Day	43% 7% 12% 22% 15% 1	2660
	21st to end	Day	39% 7% 13% 23% 16% 2	2576
July	1st to 10th	Day	41% 6% 12% 23% 17% 2	4055
	11th to 20th	Day	35% 7% 14% 25% 19% 1	4051
	21st to end	Day	41% 6% 14% 18% 19% 2	4324
August	1st to 10th	Day	46% 6% 13% 23% 12%	4091
	11th to 20th	Day	40% 8% 11% 29% 11% 1	4083
	21st to end	Day	38% 7% 13% 29% 10% 2	4468
September	1st to 10th	Day	39% 5% 13% 22% 17% 4	2161
	11th to 20th	Day	37% 6% 14% 24% 17% 2	2090
	21st to end	Day	48% 5% 9% 21% 16% 1	2090
October	1st to 10th	Day	32% 4 13% 30% 19% 1	3271
	11th to 20th	Day	46% 4 10% 20% 16% 4	3140
	21st to end	Day	42% 3 13% 25% 16% 1	3407
November	1st to 10th	Day	45% 5% 12% 23% 15% 1	1717
	11th to 20th	Day	55% 4 10% 20% 9% 2	1710
	21st to end	Day	63% 5% 11% 14% 6% 1	1535
December	1st to 10th	Day	71% 4 8% 12% 4	1520
	11th to 20th	Day	69% 4 9% 14% 4	1906
	21st to end	Day	78% 4 10% 6% 2	2996
January	1st to 10th	Night	72% 4 9% 11% 4	4109
	11th to 20th	Night	76% 4 8% 9% 2	4120
	21st to end	Night	77% 3 7% 11% 2	4532
February	1st to 10th	Night	66% 4 9% 14% 6%	2470
	11th to 20th	Night	63% 4 10% 16% 7%	2333
	21st to end	Night	64% 4 8% 14% 9% 2	1884
March	1st to 10th	Night	56% 3 9% 22% 9%	3509
	11th to 20th	Night	47% 6% 15% 21% 9% 2	3480
	21st to end	Night	50% 5% 9% 24% 10% 1	3817
April	1st to 10th	Night	52% 5% 10% 18% 14% 2	2063
	11th to 20th	Night	48% 5% 12% 16% 15% 3	1725
	21st to end	Night	47% 5% 12% 19% 15% 2	1710
May	1st to 10th	Night	56% 5% 8% 20% 9% 2	2840
	11th to 20th	Night	44% 7% 11% 24% 13% 2	2813
	21st to end	Night	32% 8% 13% 27% 16% 4	3087
June	1st to 10th	Night	39% 7% 9% 25% 16% 3	1549
	11th to 20th	Night	38% 7% 13% 22% 17% 3	1520
	21st to end	Night	36% 8% 11% 26% 16% 2	1596
July	1st to 10th	Night	36% 6% 12% 24% 18% 5%	2795
	11th to 20th	Night	32% 6% 13% 30% 18% 1	2786
	21st to end	Night	35% 7% 12% 19% 24% 2	2988
August	1st to 10th	Night	43% 6% 12% 23% 15% 1	2814
	11th to 20th	Night	40% 6% 10% 28% 14% 1	2812
	21st to end	Night	35% 7% 14% 28% 14% 2	3154
September	1st to 10th	Night	35% 7% 11% 25% 18% 4	2015
	11th to 20th	Night	30% 5% 12% 26% 24% 2	2090
	21st to end	Night	43% 6% 11% 21% 19% 1	2090
October	1st to 10th	Night	31% 5% 9% 30% 25% 1	3687
	11th to 20th	Night	43% 5% 10% 21% 18% 3	3779
	21st to end	Night	39% 4 10% 28% 16% 2	4138
November	1st to 10th	Night	42% 5% 12% 22% 15% 3	2483
	11th to 20th	Night	55% 3 10% 18% 11% 2	2470
	21st to end	Night	59% 5% 13% 17% 6%	2642
December	1st to 10th	Night	67% 5% 10% 12% 6%	2660
	11th to 20th	Night	63% 5% 12% 16% 3	3288
	21st to end	Night	75% 5% 10% 8% 2	4656

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	28% 23% 33% 11% 4 1	270
	11th to 20th	Day	30% 23% 34% 9% 3	270
	21st to end	Day	28% 24% 32% 13% 2	297
February	1st to 10th	Day	27% 22% 37% 11% 2 1	270
	11th to 20th	Day	26% 30% 33% 9% 2	270
	21st to end	Day	27% 31% 33% 8%	225
March	1st to 10th	Day	25% 20% 31% 19% 4	401
	11th to 20th	Day	27% 17% 31% 18% 6%	460
	21st to end	Day	31% 17% 28% 19% 4 1	506
April	1st to 10th	Day	21% 21% 31% 18% 8% 2	460
	11th to 20th	Day	26% 19% 25% 17% 8% 4	452
	21st to end	Day	24% 17% 30% 20% 8% 1	460
May	1st to 10th	Day	25% 16% 28% 19% 10% 3	463
	11th to 20th	Day	20% 10% 33% 20% 12% 6%	487
	21st to end	Day	16% 7% 24% 27% 20% 6%	529
June	1st to 10th	Day	14% 8% 27% 31% 15% 4	490
	11th to 20th	Day	15% 10% 22% 34% 14% 5%	490
	21st to end	Day	14% 9% 29% 28% 14% 6%	490
July	1st to 10th	Day	13% 4 19% 29% 23% 13%	485
	11th to 20th	Day	11% 7% 21% 29% 22% 10%	484
	21st to end	Day	12% 4 23% 27% 25% 10%	532
August	1st to 10th	Day	13% 5% 20% 28% 24% 11%	486
	11th to 20th	Day	15% 5% 22% 26% 21% 11%	479
	21st to end	Day	8% 5% 19% 30% 23% 14%	539
September	1st to 10th	Day	15% 5% 22% 24% 22% 12%	490
	11th to 20th	Day	10% 3 17% 26% 30% 14%	490
	21st to end	Day	24% 10% 20% 22% 16% 7%	490
October	1st to 10th	Day	12% 10% 27% 25% 22% 5%	490
	11th to 20th	Day	20% 16% 33% 18% 10% 3	490
	21st to end	Day	27% 17% 29% 21% 5% 1	530
November	1st to 10th	Day	15% 22% 33% 18% 11% 1	285
	11th to 20th	Day	29% 18% 32% 14% 6% 1	270
	21st to end	Day	25% 21% 41% 11% 2	187
December	1st to 10th	Day	27% 20% 36% 12% 4 2	180
	11th to 20th	Day	24% 22% 38% 14% 2	180
	21st to end	Day	33% 22% 31% 12% 2	261
January	1st to 10th	Night	25% 21% 33% 17% 4	760
	11th to 20th	Night	31% 16% 33% 16% 3	760
	21st to end	Night	28% 17% 30% 22% 3	836
February	1st to 10th	Night	28% 15% 32% 21% 3	760
	11th to 20th	Night	25% 16% 36% 21% 2	743
	21st to end	Night	29% 16% 36% 17% 2	628
March	1st to 10th	Night	24% 14% 34% 24% 5%	760
	11th to 20th	Night	22% 14% 33% 24% 6% 1	760
	21st to end	Night	23% 12% 33% 25% 7% 1	836
April	1st to 10th	Night	22% 12% 35% 24% 6% 1	760
	11th to 20th	Night	23% 10% 35% 21% 9% 1	601
	21st to end	Night	18% 9% 34% 31% 7% 1	570
May	1st to 10th	Night	19% 8% 30% 31% 10% 1	570
	11th to 20th	Night	20% 7% 24% 37% 11% 2	561
	21st to end	Night	12% 2 21% 39% 23% 3	617
June	1st to 10th	Night	10% 3 27% 40% 18% 1	409
	11th to 20th	Night	10% 4 25% 45% 15% 1	380
	21st to end	Night	13% 5% 22% 41% 19% 1	456
July	1st to 10th	Night	9% 2 13% 42% 29% 4	555
	11th to 20th	Night	9% 2 19% 40% 27% 3	552
	21st to end	Night	8% 2 15% 43% 29% 3	624
August	1st to 10th	Night	10% 2 16% 41% 28% 3	567
	11th to 20th	Night	11% 3 12% 41% 28% 4	564
	21st to end	Night	10% 2 17% 34% 31% 5%	644
September	1st to 10th	Night	14% 4 16% 34% 27% 5%	760
	11th to 20th	Night	10% 2 15% 36% 33% 4	760
	21st to end	Night	19% 5% 22% 30% 20% 4	760
October	1st to 10th	Night	16% 8% 21% 33% 19% 3	760
	11th to 20th	Night	23% 11% 28% 27% 10% 2	760
	21st to end	Night	26% 12% 28% 27% 7%	836
November	1st to 10th	Night	21% 10% 29% 28% 11% 1	764
	11th to 20th	Night	24% 15% 31% 22% 7% 1	760
	21st to end	Night	29% 15% 31% 19% 6%	760
December	1st to 10th	Night	31% 15% 32% 18% 4	760
	11th to 20th	Night	26% 16% 33% 21% 3 1	760
	21st to end	Night	29% 15% 33% 21% 2	836

Page generated at 2024-11-03 13:18:59. Version ac07

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