Wells Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wells Observing Site clear sky chart from 2005-11-06 to 2024-11-12.

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	10% 6% 2 6% 5% 5% 5% 4 7% 8% 40%	100824
	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	98286
Transparency	Day	38% 8% 13% 17% 17% 8%	104748
	Night	35% 7% 13% 17% 19% 9%	102500
Seeing	Day	13% 8% 21% 25% 21% 12%	14771
	Night	12% 7% 21% 31% 23% 5%	24720

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	14% 6% 1 6% 4 4 4 3 6% 7% 45%	2836
	11th to 20th	Day	11% 7% 2 4 3 2 3 3 6% 6% 53%	3046
	21st to end	Day	21% 7% 2 5% 3 4 4 3 5% 6% 39%	3476
February	1st to 10th	Day	15% 8% 2 7% 4 4 4 3 4 6% 42%	1900
	11th to 20th	Day	17% 6% 2 5% 3 3 3 3 5% 7% 45%	1848
	21st to end	Day	15% 7% 2 6% 3 5% 5% 4 6% 6% 40%	1570
March	1st to 10th	Day	18% 8% 3 7% 4 4 5% 4 5% 7% 35%	3120
	11th to 20th	Day	9% 6% 2 7% 5% 4 5% 4 6% 8% 44%	3438
	21st to end	Day	14% 5% 2 5% 4 4 4 4 5% 7% 44%	3815
April	1st to 10th	Day	12% 6% 2 7% 4 4 4 3 5% 6% 46%	2273
	11th to 20th	Day	11% 7% 2 6% 4 6% 5% 4 5% 6% 45%	2254
	21st to end	Day	6% 5% 2 5% 4 4 4 3 5% 6% 54%	2280
May	1st to 10th	Day	8% 5% 2 5% 5% 5% 6% 4 6% 9% 46%	3988
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	4081
	21st to end	Day	5% 4 2 6% 6% 5% 5% 4 7% 10% 45%	4476
June	1st to 10th	Day	8% 7% 3 9% 7% 7% 6% 6% 7% 9% 31%	2470
	11th to 20th	Day	6% 4 2 6% 6% 7% 8% 6% 9% 12% 33%	2470
	21st to end	Day	7% 6% 2 8% 8% 7% 7% 7% 9% 9% 30%	2470
July	1st to 10th	Day	7% 7% 3 9% 8% 9% 8% 8% 11% 11% 19%	4120
	11th to 20th	Day	5% 4 3 8% 6% 7% 8% 7% 10% 11% 31%	4120
	21st to end	Day	6% 6% 3 9% 8% 9% 8% 8% 11% 14% 19%	4263
August	1st to 10th	Day	6% 4 2 5% 6% 6% 8% 7% 10% 12% 34%	3785
	11th to 20th	Day	6% 5% 2 7% 4 5% 5% 5% 7% 9% 44%	3729
	21st to end	Day	7% 6% 2 8% 6% 7% 8% 6% 9% 10% 29%	4180
September	1st to 10th	Day	12% 7% 3 8% 6% 6% 7% 5% 7% 8% 32%	2161
	11th to 20th	Day	13% 7% 3 8% 5% 5% 6% 5% 6% 7% 34%	2090
	21st to end	Day	11% 5% 3 6% 4 3 4 4 5% 7% 50%	2090
October	1st to 10th	Day	10% 6% 1 6% 4 4 5% 3 5% 6% 51%	2090
	11th to 20th	Day	10% 3 1 3 3 3 4 2 5% 7% 60%	2090
	21st to end	Day	8% 5% 2 5% 4 3 3 3 4 6% 57%	2117
November	1st to 10th	Day	10% 5% 1 4 3 3 4 3 4 7% 55%	1762
	11th to 20th	Day	10% 5% 2 4 4 3 4 3 5% 7% 54%	1719
	21st to end	Day	12% 5% 2 6% 5% 3 4 3 4 7% 48%	1710
December	1st to 10th	Day	14% 6% 2 5% 4 4 4 3 4 6% 47%	1710
	11th to 20th	Day	15% 8% 3 6% 4 4 3 5% 5% 6% 41%	2153
	21st to end	Day	18% 9% 2 6% 4 3 3 3 3 5% 42%	3124
January	1st to 10th	Night	16% 6% 2 6% 4 5% 4 3 5% 6% 45%	4109
	11th to 20th	Night	9% 7% 2 6% 5% 4 4 4 5% 7% 48%	3896
	21st to end	Night	21% 10% 3 6% 4 3 3 3 4 5% 39%	4180
February	1st to 10th	Night	13% 8% 3 6% 4 3 4 3 5% 6% 45%	2280
	11th to 20th	Night	17% 8% 2 6% 3 3 3 2 3 5% 47%	2218
	21st to end	Night	15% 7% 2 5% 5% 4 4 3 5% 6% 45%	1884
March	1st to 10th	Night	21% 11% 3 7% 4 4 4 3 4 6% 33%	3733
	11th to 20th	Night	10% 7% 2 5% 4 4 4 4 6% 9% 45%	3521
	21st to end	Night	13% 7% 2 5% 4 4 4 3 5% 7% 46%	3817
April	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 7% 46%	1920
	11th to 20th	Night	11% 6% 2 7% 5% 3 4 3 6% 7% 47%	1875
	21st to end	Night	7% 3 1 4 5% 3 4 4 5% 8% 57%	1900
May	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 6% 9% 45%	2893
	11th to 20th	Night	12% 6% 3 7% 5% 4 4 4 5% 7% 44%	2812
	21st to end	Night	5% 4 1 5% 4 4 5% 4 6% 12% 50%	3079
June	1st to 10th	Night	8% 5% 2 8% 5% 4 5% 5% 9% 11% 36%	1710
	11th to 20th	Night	3 5% 1 4 5% 4 6% 5% 10% 14% 41%	1710
	21st to end	Night	5% 5% 2 6% 5% 4 6% 6% 10% 13% 39%	1710
July	1st to 10th	Night	7% 6% 3 7% 6% 6% 7% 7% 11% 13% 25%	2840
	11th to 20th	Night	3 3 1 5% 5% 5% 6% 5% 10% 13% 42%	2840
	21st to end	Night	3 4 2 8% 7% 6% 7% 6% 11% 15% 30%	3271
August	1st to 10th	Night	5% 4 2 7% 5% 5% 6% 6% 9% 14% 37%	3144
	11th to 20th	Night	5% 4 2 6% 5% 5% 5% 5% 8% 12% 44%	3100
	21st to end	Night	6% 5% 2 8% 5% 6% 7% 6% 10% 11% 33%	3476
September	1st to 10th	Night	10% 7% 3 7% 5% 6% 7% 5% 8% 9% 33%	2000
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 4 7% 9% 40%	2090
	21st to end	Night	10% 6% 2 5% 4 5% 4 3 6% 8% 49%	2090
October	1st to 10th	Night	9% 4 2 5% 3 4 4 3 5% 8% 52%	2090
	11th to 20th	Night	7% 4 2 3 3 2 3 3 4 7% 63%	2090
	21st to end	Night	9% 5% 2 5% 3 4 4 3 4 5% 55%	2474
November	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 5% 6% 56%	2536
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 4 6% 55%	2484
	21st to end	Night	13% 6% 1 5% 3 4 4 3 5% 7% 49%	2470
December	1st to 10th	Night	13% 6% 2 5% 4 4 5% 4 5% 7% 47%	2470
	11th to 20th	Night	15% 7% 2 6% 3 3 4 3 4 5% 46%	3042
	21st to end	Night	16% 10% 3 7% 3 3 4 3 5% 5% 41%	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	38% 5% 6% 17% 24% 11%	2837
	11th to 20th	Day	30% 5% 6% 17% 30% 13%	3046
	21st to end	Day	45% 4 6% 14% 19% 11%	3476
February	1st to 10th	Day	42% 4 8% 15% 20% 10%	1900
	11th to 20th	Day	39% 4 6% 16% 23% 13%	1858
	21st to end	Day	43% 6% 8% 15% 18% 11%	1570
March	1st to 10th	Day	47% 6% 9% 17% 15% 7%	3120
	11th to 20th	Day	35% 7% 12% 16% 20% 12%	3438
	21st to end	Day	37% 6% 11% 18% 17% 11%	3815
April	1st to 10th	Day	37% 6% 10% 17% 18% 13%	2273
	11th to 20th	Day	38% 5% 8% 16% 22% 11%	2254
	21st to end	Day	29% 6% 8% 23% 23% 11%	2280
May	1st to 10th	Day	32% 9% 11% 22% 21% 6%	4024
	11th to 20th	Day	42% 7% 11% 20% 16% 3	4085
	21st to end	Day	30% 10% 14% 26% 19% 2	4489
June	1st to 10th	Day	45% 10% 14% 21% 9% 2	2470
	11th to 20th	Day	36% 13% 17% 22% 10% 2	2470
	21st to end	Day	45% 11% 18% 15% 9% 2	2470
July	1st to 10th	Day	50% 15% 24% 8% 2	4055
	11th to 20th	Day	41% 14% 31% 11% 2 1	4051
	21st to end	Day	47% 17% 22% 11% 3	4127
August	1st to 10th	Day	34% 13% 20% 20% 11% 2	3773
	11th to 20th	Day	33% 9% 17% 23% 16% 1	3765
	21st to end	Day	43% 10% 22% 15% 9% 1	4179
September	1st to 10th	Day	46% 11% 16% 13% 10% 4	2161
	11th to 20th	Day	46% 7% 13% 15% 12% 6%	2090
	21st to end	Day	34% 6% 10% 20% 21% 9%	2090
October	1st to 10th	Day	37% 4 6% 11% 16% 26%	3480
	11th to 20th	Day	16% 3 5% 17% 24% 34%	3458
	21st to end	Day	20% 3 4 14% 39% 20%	3469
November	1st to 10th	Day	29% 4 9% 20% 23% 15%	1762
	11th to 20th	Day	30% 5% 7% 18% 27% 13%	1719
	21st to end	Day	36% 4 7% 20% 20% 12%	1710
December	1st to 10th	Day	38% 5% 12% 16% 21% 8%	1710
	11th to 20th	Day	44% 4 6% 15% 23% 8%	2150
	21st to end	Day	45% 3 5% 17% 23% 6%	3124
January	1st to 10th	Night	40% 4 6% 11% 24% 14%	4109
	11th to 20th	Night	35% 5% 7% 14% 28% 12%	3896
	21st to end	Night	48% 4 5% 13% 23% 7%	4180
February	1st to 10th	Night	40% 4 7% 16% 21% 11%	2280
	11th to 20th	Night	42% 4 6% 13% 20% 16%	2219
	21st to end	Night	41% 4 7% 17% 17% 14%	1884
March	1st to 10th	Night	53% 5% 8% 14% 13% 7%	3733
	11th to 20th	Night	35% 6% 13% 16% 21% 10%	3521
	21st to end	Night	38% 6% 10% 18% 18% 11%	3817
April	1st to 10th	Night	35% 7% 10% 15% 19% 14%	1920
	11th to 20th	Night	36% 5% 7% 18% 23% 11%	1875
	21st to end	Night	25% 5% 10% 26% 24% 9%	1900
May	1st to 10th	Night	32% 11% 17% 18% 17% 6%	2921
	11th to 20th	Night	38% 8% 13% 21% 17% 3	2813
	21st to end	Night	24% 9% 18% 30% 15% 3	3087
June	1st to 10th	Night	36% 11% 19% 22% 9% 2	1710
	11th to 20th	Night	26% 15% 22% 24% 10% 3	1710
	21st to end	Night	30% 14% 27% 18% 9% 2	1710
July	1st to 10th	Night	43% 15% 29% 11% 1 1	2795
	11th to 20th	Night	27% 15% 42% 13% 3	2786
	21st to end	Night	37% 21% 26% 13% 3	3167
August	1st to 10th	Night	31% 12% 24% 24% 8% 1	3132
	11th to 20th	Night	29% 11% 24% 21% 14% 1	3130
	21st to end	Night	37% 11% 26% 15% 9% 1	3476
September	1st to 10th	Night	42% 13% 18% 14% 10% 4	2000
	11th to 20th	Night	39% 10% 15% 17% 14% 5%	2090
	21st to end	Night	33% 7% 13% 19% 21% 8%	2090
October	1st to 10th	Night	35% 5% 8% 11% 19% 21%	3480
	11th to 20th	Night	14% 2 5% 16% 31% 32%	3461
	21st to end	Night	21% 4 4 13% 40% 18%	4072
November	1st to 10th	Night	28% 4 7% 18% 25% 17%	2536
	11th to 20th	Night	31% 4 6% 15% 29% 15%	2484
	21st to end	Night	34% 5% 8% 18% 22% 13%	2470
December	1st to 10th	Night	36% 6% 10% 17% 23% 8%	2470
	11th to 20th	Night	40% 4 7% 12% 25% 12%	3044
	21st to end	Night	45% 5% 6% 18% 22% 5%	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	17% 18% 41% 17% 6%	270
	11th to 20th	Day	15% 20% 35% 20% 9% 1	270
	21st to end	Day	19% 23% 44% 10% 5%	297
February	1st to 10th	Day	21% 19% 40% 15% 6%	270
	11th to 20th	Day	30% 16% 33% 19% 3	270
	21st to end	Day	18% 29% 32% 17% 4	225
March	1st to 10th	Day	14% 26% 37% 16% 5% 1	270
	11th to 20th	Day	16% 18% 32% 21% 12% 1	431
	21st to end	Day	15% 17% 33% 23% 12% 1	506
April	1st to 10th	Day	17% 18% 27% 22% 13% 2	460
	11th to 20th	Day	12% 13% 32% 23% 16% 3	452
	21st to end	Day	9% 11% 27% 29% 19% 4	460
May	1st to 10th	Day	7% 10% 26% 30% 21% 7%	463
	11th to 20th	Day	8% 3 24% 30% 21% 14%	487
	21st to end	Day	9% 4 17% 32% 22% 16%	529
June	1st to 10th	Day	12% 2 15% 30% 24% 17%	490
	11th to 20th	Day	9% 2 12% 29% 29% 20%	490
	21st to end	Day	9% 2 9% 29% 26% 24%	490
July	1st to 10th	Day	8% 2 6% 20% 34% 30%	485
	11th to 20th	Day	6% 2 4 18% 34% 36%	484
	21st to end	Day	5% 1 6% 24% 36% 28%	532
August	1st to 10th	Day	7% 1 6% 20% 34% 31%	486
	11th to 20th	Day	9% 2 4 18% 38% 29%	479
	21st to end	Day	10% 3 9% 27% 31% 20%	539
September	1st to 10th	Day	16% 3 7% 22% 30% 21%	490
	11th to 20th	Day	18% 2 9% 29% 28% 12%	490
	21st to end	Day	12% 4 11% 27% 30% 16%	490
October	1st to 10th	Day	12% 4 27% 33% 19% 5%	490
	11th to 20th	Day	9% 5% 19% 32% 26% 9%	490
	21st to end	Day	11% 8% 25% 31% 20% 4	506
November	1st to 10th	Day	18% 4 31% 27% 14% 5%	300
	11th to 20th	Day	11% 11% 41% 26% 9% 1	273
	21st to end	Day	14% 14% 35% 26% 10% 2	270
December	1st to 10th	Day	20% 13% 29% 26% 10% 2	270
	11th to 20th	Day	26% 14% 35% 19% 7%	270
	21st to end	Day	23% 12% 33% 21% 9% 2	297
January	1st to 10th	Night	18% 14% 33% 27% 6% 1	760
	11th to 20th	Night	14% 16% 28% 33% 9% 1	760
	21st to end	Night	22% 14% 33% 27% 4	836
February	1st to 10th	Night	17% 13% 31% 33% 7%	760
	11th to 20th	Night	21% 13% 31% 27% 8%	743
	21st to end	Night	17% 14% 34% 32% 3	628
March	1st to 10th	Night	15% 12% 33% 34% 7%	760
	11th to 20th	Night	14% 13% 30% 31% 11% 1	760
	21st to end	Night	12% 14% 31% 32% 10%	836
April	1st to 10th	Night	14% 10% 28% 36% 12% 1	590
	11th to 20th	Night	15% 8% 27% 31% 18% 1	563
	21st to end	Night	7% 6% 24% 41% 21% 1	570
May	1st to 10th	Night	9% 4 27% 35% 23% 3	570
	11th to 20th	Night	8% 3 18% 37% 29% 5%	561
	21st to end	Night	7% 2 11% 39% 37% 5%	617
June	1st to 10th	Night	9% 2 9% 35% 39% 7%	570
	11th to 20th	Night	5% 2 10% 32% 40% 12%	570
	21st to end	Night	7% 2 8% 32% 39% 12%	570
July	1st to 10th	Night	6% 2 4 25% 46% 18%	555
	11th to 20th	Night	5% 1 4 19% 45% 26%	552
	21st to end	Night	4 3 24% 50% 19%	624
August	1st to 10th	Night	6% 1 4 17% 47% 26%	567
	11th to 20th	Night	8% 2 3 17% 48% 22%	564
	21st to end	Night	10% 3 7% 22% 42% 16%	627
September	1st to 10th	Night	11% 2 8% 24% 42% 13%	670
	11th to 20th	Night	13% 4 11% 33% 32% 7%	760
	21st to end	Night	13% 2 15% 26% 38% 7%	760
October	1st to 10th	Night	11% 3 25% 33% 25% 4	760
	11th to 20th	Night	9% 6% 21% 33% 27% 3	760
	21st to end	Night	10% 8% 22% 36% 22% 2	836
November	1st to 10th	Night	10% 6% 26% 37% 19% 2	780
	11th to 20th	Night	12% 11% 30% 32% 13% 1	765
	21st to end	Night	13% 8% 30% 33% 15% 1	760
December	1st to 10th	Night	16% 9% 26% 33% 14% 2	760
	11th to 20th	Night	18% 9% 29% 32% 12% 1	760
	21st to end	Night	24% 11% 27% 28% 10%	836

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