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 2024-10-25.

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 6% 7% 40%	101332
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 42%	97574
Transparency	Day	23% 48% 7% 13% 8% 1	101126
	Night	23% 49% 7% 13% 8% 1	97452
Seeing	Day	16% 8% 27% 27% 16% 5%	15747
	Night	16% 8% 30% 31% 13% 1	25553

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	12% 12% 6% 16% 7% 5% 4 3 4 6% 26%	2527
	11th to 20th	Day	12% 11% 4 12% 8% 6% 8% 4 6% 6% 23%	2662
	21st to end	Day	16% 17% 9% 13% 7% 4 4 3 3 4 20%	3135
February	1st to 10th	Day	14% 12% 5% 10% 7% 4 4 4 4 6% 30%	1710
	11th to 20th	Day	13% 11% 3 8% 5% 4 5% 4 5% 6% 36%	1738
	21st to end	Day	13% 13% 3 10% 5% 4 3 4 5% 6% 35%	1570
March	1st to 10th	Day	16% 11% 4 7% 4 4 3 3 3 5% 39%	3235
	11th to 20th	Day	9% 7% 3 6% 4 4 4 4 6% 7% 46%	3480
	21st to end	Day	20% 13% 3 9% 5% 4 4 3 5% 6% 28%	3968
April	1st to 10th	Day	16% 11% 3 6% 5% 3 3 3 4 8% 37%	2280
	11th to 20th	Day	15% 10% 2 7% 5% 4 4 3 4 6% 39%	2254
	21st to end	Day	20% 8% 3 7% 6% 4 4 3 5% 5% 35%	2280
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% 2 6% 3 3 4 3 4 6% 41%	2004
November	1st to 10th	Day	11% 7% 2 6% 4 3 4 3 5% 8% 48%	1672
	11th to 20th	Day	16% 10% 3 7% 3 3 4 3 5% 6% 40%	1682
	21st to end	Day	16% 12% 3 7% 5% 3 3 3 4 7% 38%	1520
December	1st to 10th	Day	14% 12% 4 9% 6% 4 4 2 5% 6% 35%	1520
	11th to 20th	Day	14% 11% 3 8% 5% 4 5% 3 5% 7% 35%	1918
	21st to end	Day	23% 17% 7% 12% 5% 4 4 3 4 4 18%	2783
January	1st to 10th	Night	13% 12% 7% 12% 5% 4 4 3 4 5% 30%	4428
	11th to 20th	Night	13% 16% 6% 11% 5% 5% 6% 4 7% 4 24%	4306
	21st to end	Night	18% 18% 6% 12% 5% 4 3 2 4 6% 22%	4532
February	1st to 10th	Night	14% 12% 4 8% 6% 4 4 3 4 6% 35%	2470
	11th to 20th	Night	13% 10% 3 7% 4 4 4 4 5% 7% 38%	2327
	21st to end	Night	14% 10% 4 8% 4 4 3 2 4 5% 42%	1884
March	1st to 10th	Night	18% 10% 3 6% 4 4 4 2 3 5% 41%	3647
	11th to 20th	Night	12% 7% 3 5% 3 3 3 2 4 6% 52%	3480
	21st to end	Night	20% 13% 5% 9% 6% 4 4 3 4 6% 27%	3663
April	1st to 10th	Night	14% 9% 3 6% 5% 4 3 4 5% 7% 41%	1900
	11th to 20th	Night	15% 8% 2 6% 4 3 3 4 5% 6% 43%	1875
	21st to end	Night	18% 7% 2 7% 5% 4 3 4 4 6% 39%	1900
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%	2458
November	1st to 10th	Night	11% 6% 2 5% 2 3 4 3 4 6% 55%	2406
	11th to 20th	Night	13% 9% 2 6% 3 3 4 4 6% 7% 43%	2493
	21st to end	Night	16% 9% 3 8% 4 4 4 3 4 5% 40%	2660
December	1st to 10th	Night	13% 11% 5% 8% 5% 4 4 3 5% 6% 37%	2660
	11th to 20th	Night	15% 9% 4 9% 5% 4 4 3 5% 5% 38%	3279
	21st to end	Night	21% 17% 7% 11% 5% 4 4 3 4 4 21%	4884

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	39% 39% 7% 11% 3	2528
	11th to 20th	Day	40% 38% 5% 12% 5%	2662
	21st to end	Day	45% 40% 5% 6% 4	3135
February	1st to 10th	Day	21% 64% 4 7% 4	1710
	11th to 20th	Day	17% 65% 4 9% 5%	1747
	21st to end	Day	17% 65% 3 8% 6% 1	1570
March	1st to 10th	Day	30% 41% 6% 11% 11% 1	3235
	11th to 20th	Day	16% 41% 9% 17% 15% 1	3480
	21st to end	Day	34% 42% 10% 12% 2	3968
April	1st to 10th	Day	20% 65% 4 8% 3	2280
	11th to 20th	Day	16% 65% 5% 8% 5% 1	2254
	21st to end	Day	18% 65% 3 8% 6% 1	2280
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	18% 60% 3 8% 10%	1900
	11th to 20th	Day	14% 59% 4 10% 11% 2	1900
	21st to end	Day	19% 60% 5% 8% 7% 1	2004
November	1st to 10th	Day	16% 60% 7% 9% 7% 1	1672
	11th to 20th	Day	17% 59% 4 11% 9% 1	1682
	21st to end	Day	22% 59% 5% 10% 4	1520
December	1st to 10th	Day	22% 60% 5% 8% 5%	1520
	11th to 20th	Day	22% 48% 6% 16% 7% 2	1915
	21st to end	Day	50% 38% 4 5% 3	2783
January	1st to 10th	Night	40% 38% 6% 11% 5%	4428
	11th to 20th	Night	41% 37% 6% 8% 6% 1	4306
	21st to end	Night	43% 39% 5% 10% 3	4532
February	1st to 10th	Night	18% 65% 4 8% 5%	2470
	11th to 20th	Night	16% 64% 4 10% 6%	2328
	21st to end	Night	15% 64% 2 9% 8% 2	1884
March	1st to 10th	Night	30% 42% 4 14% 9% 1	3647
	11th to 20th	Night	17% 40% 5% 22% 12% 4	3480
	21st to end	Night	35% 43% 11% 9% 3	3663
April	1st to 10th	Night	17% 65% 4 9% 3 1	1900
	11th to 20th	Night	13% 66% 5% 9% 6% 1	1875
	21st to end	Night	16% 65% 4 6% 7% 2	1900
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	18% 60% 3 8% 9% 1	2280
	11th to 20th	Night	12% 60% 4 11% 11% 2	2280
	21st to end	Night	17% 61% 4 9% 8% 1	2458
November	1st to 10th	Night	15% 59% 6% 10% 8% 2	2406
	11th to 20th	Night	15% 60% 4 9% 10% 1	2493
	21st to end	Night	20% 60% 4 10% 6%	2660
December	1st to 10th	Night	20% 60% 5% 9% 6% 1	2660
	11th to 20th	Night	21% 50% 6% 16% 7% 1	3281
	21st to end	Night	48% 37% 5% 6% 4	4884

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	23% 13% 33% 21% 9%	270
	11th to 20th	Day	23% 19% 38% 18% 2	270
	21st to end	Day	24% 14% 33% 23% 5%	297
February	1st to 10th	Day	23% 14% 38% 21% 4	270
	11th to 20th	Day	24% 18% 29% 21% 7% 1	270
	21st to end	Day	23% 12% 44% 18% 3	225
March	1st to 10th	Day	17% 20% 39% 21% 3	270
	11th to 20th	Day	23% 15% 34% 21% 6% 1	270
	21st to end	Day	35% 13% 31% 16% 4 1	387
April	1st to 10th	Day	22% 14% 36% 21% 6% 1	460
	11th to 20th	Day	20% 14% 34% 20% 11% 2	452
	21st to end	Day	25% 9% 32% 22% 10% 2	460
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% 31% 20% 6% 1	311
November	1st to 10th	Day	14% 8% 40% 26% 9% 3	270
	11th to 20th	Day	21% 14% 32% 22% 9% 2	270
	21st to end	Day	27% 9% 35% 23% 6%	270
December	1st to 10th	Day	18% 12% 38% 23% 7% 3	270
	11th to 20th	Day	20% 13% 37% 22% 7%	270
	21st to end	Day	26% 20% 36% 15% 3	297
January	1st to 10th	Night	17% 12% 40% 24% 7%	950
	11th to 20th	Night	19% 13% 38% 23% 6%	950
	21st to end	Night	20% 13% 35% 27% 4	1045
February	1st to 10th	Night	21% 11% 38% 25% 4	950
	11th to 20th	Night	18% 13% 36% 29% 4	853
	21st to end	Night	20% 13% 40% 23% 3	628
March	1st to 10th	Night	19% 12% 40% 25% 5%	713
	11th to 20th	Night	19% 11% 34% 29% 7%	570
	21st to end	Night	24% 11% 33% 26% 5%	627
April	1st to 10th	Night	19% 12% 38% 25% 5%	570
	11th to 20th	Night	19% 11% 33% 29% 7%	563
	21st to end	Night	22% 9% 32% 29% 8%	570
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% 9% 35% 27% 7%	812
November	1st to 10th	Night	13% 10% 39% 29% 8% 1	740
	11th to 20th	Night	17% 12% 38% 25% 6% 1	783
	21st to end	Night	21% 10% 36% 25% 7%	950
December	1st to 10th	Night	19% 11% 38% 27% 4 1	950
	11th to 20th	Night	23% 8% 33% 28% 7%	950
	21st to end	Night	27% 14% 31% 24% 3	1045

Page generated at 2024-10-22 19:21:02. Version ac07

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