Wever
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wever clear sky chart from 2005-11-06 to 2025-04-26.

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	12% 8% 3 7% 5% 4 4 4 5% 7% 40%	113832
	Night	13% 9% 3 8% 4 4 4 3 5% 6% 41%	115016
Transparency	Day	26% 41% 7% 15% 10% 1	117442
	Night	27% 40% 7% 14% 10% 1	119549
Seeing	Day	16% 9% 28% 27% 15% 5%	16324
	Night	17% 8% 30% 31% 12% 1	26324

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	11% 12% 6% 16% 7% 6% 5% 3 4 6% 26%	3617
	11th to 20th	Day	9% 9% 4 11% 7% 6% 7% 4 6% 6% 32%	3822
	21st to end	Day	14% 14% 7% 11% 6% 5% 4 3 4 5% 28%	4488
February	1st to 10th	Day	14% 12% 5% 10% 7% 4 5% 4 5% 6% 29%	1800
	11th to 20th	Day	13% 11% 3 8% 5% 4 5% 4 5% 6% 35%	1832
	21st to end	Day	13% 12% 3 9% 5% 4 3 4 4 6% 37%	1650
March	1st to 10th	Day	18% 10% 3 5% 3 3 3 2 3 5% 45%	4651
	11th to 20th	Day	8% 6% 2 6% 4 4 5% 4 6% 9% 46%	4980
	21st to end	Day	18% 11% 3 9% 5% 4 5% 3 6% 6% 29%	5686
April	1st to 10th	Day	16% 11% 3 7% 5% 3 4 3 4 7% 37%	2400
	11th to 20th	Day	15% 9% 2 7% 5% 4 4 3 4 6% 39%	2374
	21st to end	Day	20% 8% 3 7% 5% 4 4 3 6% 6% 34%	2340
May	1st to 10th	Day	15% 7% 3 7% 4 5% 5% 4 6% 9% 35%	4102
	11th to 20th	Day	17% 7% 3 6% 4 4 4 3 5% 7% 40%	4399
	21st to end	Day	12% 6% 2 6% 4 4 5% 3 5% 6% 46%	4824
June	1st to 10th	Day	7% 5% 3 6% 5% 4 5% 4 7% 8% 46%	2660
	11th to 20th	Day	6% 6% 2 7% 5% 5% 5% 4 6% 8% 48%	2660
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 8% 9% 41%	2660
July	1st to 10th	Day	9% 7% 2 7% 5% 6% 6% 5% 7% 10% 37%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 7% 9% 49%	4440
	21st to end	Day	6% 5% 2 6% 4 5% 6% 5% 8% 12% 42%	4656
August	1st to 10th	Day	6% 4 2 6% 4 4 6% 5% 8% 10% 45%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 4 4 7% 9% 40%	3882
	21st to end	Day	6% 5% 2 6% 4 4 4 4 5% 9% 51%	4180
September	1st to 10th	Day	11% 4 2 5% 4 3 4 4 6% 7% 50%	2280
	11th to 20th	Day	9% 4 1 5% 3 4 3 4 6% 8% 53%	2280
	21st to end	Day	9% 6% 2 5% 4 4 5% 5% 5% 8% 49%	2027
October	1st to 10th	Day	13% 6% 2 5% 3 3 4 3 4 5% 51%	1900
	11th to 20th	Day	15% 8% 2 6% 3 3 4 2 4 6% 46%	1900
	21st to end	Day	19% 9% 3 6% 3 3 4 3 4 6% 42%	2066
November	1st to 10th	Day	12% 7% 2 6% 4 3 4 3 5% 8% 47%	1762
	11th to 20th	Day	16% 10% 3 7% 4 3 4 3 4 6% 40%	1770
	21st to end	Day	16% 12% 4 8% 5% 3 3 3 4 7% 37%	1600
December	1st to 10th	Day	8% 8% 3 8% 4 4 3 2 5% 6% 49%	2610
	11th to 20th	Day	14% 11% 4 14% 5% 4 5% 3 5% 6% 28%	3008
	21st to end	Day	23% 21% 7% 12% 4 4 3 2 3 4 16%	3982
January	1st to 10th	Night	13% 12% 7% 12% 5% 4 3 3 4 5% 31%	6348
	11th to 20th	Night	11% 13% 5% 12% 7% 6% 6% 3 6% 4 28%	6156
	21st to end	Night	15% 14% 5% 11% 5% 4 4 3 4 6% 31%	6490
February	1st to 10th	Night	14% 12% 4 8% 6% 4 4 3 4 6% 35%	2600
	11th to 20th	Night	13% 11% 4 7% 4 4 4 4 5% 6% 38%	2453
	21st to end	Night	14% 10% 3 8% 4 3 3 2 4 5% 43%	1980
March	1st to 10th	Night	18% 9% 3 6% 4 3 4 2 3 5% 43%	5245
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 4 7% 52%	4980
	21st to end	Night	16% 12% 5% 9% 5% 4 4 4 5% 6% 31%	5243
April	1st to 10th	Night	14% 9% 3 6% 5% 4 3 4 5% 7% 41%	2000
	11th to 20th	Night	15% 8% 2 7% 4 3 3 4 5% 6% 43%	1975
	21st to end	Night	18% 7% 2 7% 5% 4 4 4 4 6% 39%	1956
May	1st to 10th	Night	18% 7% 2 7% 4 4 4 4 7% 8% 34%	2796
	11th to 20th	Night	12% 5% 2 7% 3 4 4 4 5% 8% 45%	2506
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 8% 50%	2743
June	1st to 10th	Night	8% 4 1 5% 4 4 4 4 6% 8% 51%	1520
	11th to 20th	Night	8% 6% 2 4 3 4 3 4 7% 10% 50%	1520
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 9% 48%	1520
July	1st to 10th	Night	13% 5% 2 6% 5% 4 4 4 7% 8% 43%	2530
	11th to 20th	Night	3 4 2 5% 3 3 4 4 6% 9% 58%	2530
	21st to end	Night	6% 5% 2 5% 4 3 4 4 6% 9% 50%	2903
August	1st to 10th	Night	4 3 1 4 2 3 4 4 6% 9% 58%	2836
	11th to 20th	Night	7% 5% 1 5% 4 4 4 3 5% 7% 54%	2951
	21st to end	Night	4 4 1 5% 4 4 4 4 6% 9% 55%	3476
September	1st to 10th	Night	11% 4 2 4 2 3 3 3 5% 7% 57%	1900
	11th to 20th	Night	9% 4 1 6% 3 4 4 3 4 7% 54%	1900
	21st to end	Night	8% 4 2 6% 4 4 4 4 5% 8% 52%	2131
October	1st to 10th	Night	10% 5% 2 5% 3 4 3 2 5% 6% 55%	2280
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 5% 6% 51%	2280
	21st to end	Night	16% 8% 3 6% 4 4 3 3 5% 5% 42%	2532
November	1st to 10th	Night	12% 6% 2 5% 2 3 4 3 4 6% 54%	2536
	11th to 20th	Night	13% 9% 3 6% 3 4 4 4 6% 7% 42%	2625
	21st to end	Night	16% 10% 3 8% 4 4 4 3 4 5% 39%	2800
December	1st to 10th	Night	8% 9% 4 7% 4 3 3 3 5% 6% 48%	4580
	11th to 20th	Night	15% 9% 4 11% 5% 4 4 3 5% 6% 34%	5199
	21st to end	Night	23% 18% 7% 10% 5% 4 4 3 4 3 19%	6996

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	46% 28% 8% 12% 5%	3618
	11th to 20th	Day	37% 27% 6% 13% 13% 4	3822
	21st to end	Day	44% 28% 7% 15% 5% 1	4488
February	1st to 10th	Day	23% 61% 5% 7% 4	1800
	11th to 20th	Day	20% 61% 4 9% 5% 1	1841
	21st to end	Day	17% 62% 4 9% 7% 1	1650
March	1st to 10th	Day	32% 28% 5% 17% 16% 2	4651
	11th to 20th	Day	21% 29% 7% 26% 16% 1	4980
	21st to end	Day	39% 29% 11% 16% 4	5688
April	1st to 10th	Day	22% 62% 4 8% 4	2400
	11th to 20th	Day	18% 62% 5% 9% 5% 1	2374
	21st to end	Day	19% 63% 3 8% 6% 1	2340
May	1st to 10th	Day	26% 42% 7% 12% 13%	4138
	11th to 20th	Day	27% 40% 7% 21% 5%	4403
	21st to end	Day	20% 41% 5% 18% 15% 1	4837
June	1st to 10th	Day	9% 66% 6% 10% 7% 2	2660
	11th to 20th	Day	13% 65% 5% 9% 6% 1	2660
	21st to end	Day	13% 65% 8% 10% 4	2660
July	1st to 10th	Day	31% 36% 8% 16% 7% 1	4371
	11th to 20th	Day	20% 36% 11% 21% 12%	4365
	21st to end	Day	22% 36% 17% 16% 9%	4510
August	1st to 10th	Day	21% 38% 12% 22% 8%	4090
	11th to 20th	Day	28% 37% 8% 19% 7%	3921
	21st to end	Day	21% 37% 12% 21% 7% 1	4179
September	1st to 10th	Day	12% 60% 6% 11% 10% 1	2280
	11th to 20th	Day	11% 60% 5% 12% 8% 3	2280
	21st to end	Day	15% 61% 5% 12% 7%	2027
October	1st to 10th	Day	13% 36% 2 8% 38% 2	3160
	11th to 20th	Day	11% 36% 6% 15% 27% 6%	3140
	21st to end	Day	25% 36% 4 19% 14% 2	3380
November	1st to 10th	Day	17% 57% 8% 9% 7% 1	1762
	11th to 20th	Day	19% 56% 4 11% 9% 1	1770
	21st to end	Day	24% 56% 6% 11% 3	1600
December	1st to 10th	Day	20% 35% 11% 25% 9%	2610
	11th to 20th	Day	39% 31% 8% 13% 8% 1	3005
	21st to end	Day	59% 26% 6% 5% 2	3982
January	1st to 10th	Night	44% 26% 10% 15% 4	6348
	11th to 20th	Night	45% 26% 7% 8% 11% 2	6156
	21st to end	Night	41% 28% 5% 14% 10% 1	6490
February	1st to 10th	Night	20% 61% 5% 8% 5%	2600
	11th to 20th	Night	19% 61% 4 10% 6%	2454
	21st to end	Night	16% 61% 3 9% 9% 1	1980
March	1st to 10th	Night	35% 29% 3 18% 13% 2	5245
	11th to 20th	Night	22% 28% 5% 25% 16% 5%	4980
	21st to end	Night	38% 30% 11% 14% 5% 1	5243
April	1st to 10th	Night	18% 62% 4 10% 4 1	2000
	11th to 20th	Night	15% 63% 6% 10% 6% 1	1975
	21st to end	Night	17% 63% 4 6% 6% 2	1956
May	1st to 10th	Night	30% 42% 8% 11% 9%	2825
	11th to 20th	Night	21% 42% 11% 21% 5%	2507
	21st to end	Night	16% 41% 8% 16% 18% 1	2751
June	1st to 10th	Night	9% 65% 6% 10% 8% 2	1520
	11th to 20th	Night	11% 65% 4 11% 8% 1	1520
	21st to end	Night	11% 65% 7% 11% 6% 1	1520
July	1st to 10th	Night	30% 35% 10% 15% 10% 1	2490
	11th to 20th	Night	14% 36% 9% 24% 16%	2482
	21st to end	Night	20% 35% 16% 14% 14% 1	2811
August	1st to 10th	Night	14% 37% 14% 21% 13% 1	2826
	11th to 20th	Night	20% 37% 10% 22% 10% 1	2978
	21st to end	Night	20% 37% 12% 22% 7% 1	3476
September	1st to 10th	Night	10% 60% 5% 12% 11% 2	1900
	11th to 20th	Night	11% 61% 5% 11% 9% 4	1900
	21st to end	Night	15% 60% 5% 11% 9% 1	2131
October	1st to 10th	Night	14% 36% 2 14% 32% 2	3800
	11th to 20th	Night	11% 36% 6% 15% 28% 4	3779
	21st to end	Night	28% 36% 4 14% 15% 3	4168
November	1st to 10th	Night	17% 56% 6% 11% 8% 2	2536
	11th to 20th	Night	18% 57% 4 10% 10% 1	2625
	21st to end	Night	22% 57% 4 10% 6% 1	2800
December	1st to 10th	Night	22% 35% 7% 27% 9%	4580
	11th to 20th	Night	35% 32% 8% 17% 8%	5201
	21st to end	Night	56% 26% 7% 8% 3	6996

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	22% 13% 33% 22% 9%	300
	11th to 20th	Day	21% 20% 40% 17% 2	300
	21st to end	Day	24% 14% 36% 22% 5%	330
February	1st to 10th	Day	22% 14% 39% 22% 3	300
	11th to 20th	Day	24% 18% 31% 19% 6% 1	300
	21st to end	Day	21% 13% 44% 18% 3	249
March	1st to 10th	Day	18% 20% 39% 20% 3	300
	11th to 20th	Day	22% 17% 33% 22% 5% 1	300
	21st to end	Day	35% 13% 31% 16% 4 1	425
April	1st to 10th	Day	22% 15% 35% 20% 6% 1	500
	11th to 20th	Day	20% 15% 34% 19% 10% 1	492
	21st to end	Day	26% 9% 33% 22% 9% 1	480
May	1st to 10th	Day	21% 8% 34% 27% 8% 2	582
	11th to 20th	Day	20% 11% 29% 26% 13% 3	675
	21st to end	Day	16% 6% 29% 28% 15% 6%	734
June	1st to 10th	Day	8% 5% 25% 32% 23% 8%	680
	11th to 20th	Day	8% 3 28% 37% 20% 4	680
	21st to end	Day	11% 9% 31% 30% 14% 4	680
July	1st to 10th	Day	12% 2 16% 30% 27% 13%	671
	11th to 20th	Day	9% 3 21% 34% 25% 7%	668
	21st to end	Day	8% 1 17% 39% 28% 8%	739
August	1st to 10th	Day	8% 2 18% 36% 26% 10%	676
	11th to 20th	Day	9% 4 15% 31% 30% 11%	571
	21st to end	Day	8% 1 15% 30% 33% 12%	539
September	1st to 10th	Day	13% 4 16% 31% 27% 9%	490
	11th to 20th	Day	9% 2 16% 38% 25% 10%	490
	21st to end	Day	12% 7% 26% 24% 23% 7%	413
October	1st to 10th	Day	19% 5% 27% 29% 13% 8%	300
	11th to 20th	Day	18% 18% 31% 22% 10% 1	300
	21st to end	Day	30% 12% 32% 19% 6% 1	330
November	1st to 10th	Day	16% 9% 38% 26% 9% 3	300
	11th to 20th	Day	22% 13% 32% 22% 9% 2	300
	21st to end	Day	26% 10% 36% 23% 5%	300
December	1st to 10th	Day	17% 13% 40% 22% 6% 3	300
	11th to 20th	Day	21% 13% 38% 21% 7%	300
	21st to end	Day	28% 18% 35% 15% 3	330
January	1st to 10th	Night	17% 12% 40% 25% 6%	1000
	11th to 20th	Night	19% 14% 39% 23% 6%	1000
	21st to end	Night	20% 13% 36% 27% 4	1100
February	1st to 10th	Night	21% 11% 39% 25% 4	1000
	11th to 20th	Night	19% 14% 35% 28% 4	899
	21st to end	Night	19% 13% 41% 23% 3	660
March	1st to 10th	Night	19% 12% 38% 26% 5%	750
	11th to 20th	Night	19% 11% 35% 29% 7%	600
	21st to end	Night	23% 12% 34% 25% 5%	660
April	1st to 10th	Night	20% 12% 38% 25% 5%	600
	11th to 20th	Night	19% 11% 34% 29% 7%	593
	21st to end	Night	22% 9% 31% 30% 8%	587
May	1st to 10th	Night	19% 6% 37% 29% 8% 1	570
	11th to 20th	Night	17% 6% 27% 38% 12% 1	561
	21st to end	Night	13% 5% 26% 36% 19% 1	617
June	1st to 10th	Night	10% 3 21% 45% 18% 2	570
	11th to 20th	Night	9% 3 24% 42% 21% 1	570
	21st to end	Night	10% 3 27% 39% 20% 1	570
July	1st to 10th	Night	9% 1 12% 41% 33% 4	555
	11th to 20th	Night	5% 2 17% 45% 28% 2	552
	21st to end	Night	8% 3 11% 46% 31% 1	624
August	1st to 10th	Night	7% 2 12% 44% 31% 4	567
	11th to 20th	Night	8% 3 11% 40% 33% 5%	564
	21st to end	Night	8% 1 12% 42% 35% 2	627
September	1st to 10th	Night	14% 2 16% 39% 26% 3	570
	11th to 20th	Night	11% 2 18% 35% 29% 5%	570
	21st to end	Night	9% 6% 25% 34% 24% 3	727
October	1st to 10th	Night	13% 6% 26% 33% 21% 2	760
	11th to 20th	Night	17% 9% 32% 31% 11%	760
	21st to end	Night	21% 10% 35% 27% 7%	836
November	1st to 10th	Night	14% 9% 38% 29% 8% 1	780
	11th to 20th	Night	18% 12% 38% 25% 6% 1	825
	21st to end	Night	21% 10% 36% 25% 7%	1000
December	1st to 10th	Night	19% 11% 38% 27% 4 1	1000
	11th to 20th	Night	23% 8% 34% 28% 7%	1000
	21st to end	Night	29% 13% 31% 24% 3	1100

Page generated at 2025-04-23 08:25:05. Version ac07

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