Waverly
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waverly clear sky chart from 2005-11-06 to 2026-08-15.

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% 7% 3 7% 4 4 4 3 5% 7% 44%	143719
	Night	12% 7% 3 7% 4 4 4 3 5% 7% 46%	138524
Transparency	Day	39% 4 13% 26% 16% 2	147326
	Night	38% 4 12% 25% 18% 3	142996
Seeing	Day	14% 9% 27% 28% 18% 5%	18159
	Night	15% 8% 31% 33% 13% 1	27907

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% 11% 3 10% 4 5% 4 3 4 6% 37%	5147
	11th to 20th	Day	6% 7% 3 9% 6% 7% 6% 4 5% 6% 41%	5310
	21st to end	Day	14% 13% 4 9% 5% 4 4 2 3 4 38%	5812
February	1st to 10th	Day	15% 11% 3 9% 4 4 4 2 5% 7% 35%	1890
	11th to 20th	Day	14% 10% 4 7% 5% 3 3 3 5% 6% 39%	1844
	21st to end	Day	12% 8% 3 8% 5% 3 4 3 5% 6% 44%	1760
March	1st to 10th	Day	15% 9% 3 5% 3 3 2 2 3 4 50%	5046
	11th to 20th	Day	10% 6% 2 5% 4 3 4 3 4 6% 53%	5090
	21st to end	Day	14% 11% 3 8% 5% 4 5% 4 6% 7% 33%	5583
April	1st to 10th	Day	15% 7% 2 7% 5% 3 4 3 5% 6% 42%	2491
	11th to 20th	Day	16% 9% 2 6% 4 3 4 4 5% 7% 41%	2494
	21st to end	Day	20% 8% 2 7% 5% 5% 5% 4 6% 7% 33%	2575
May	1st to 10th	Day	14% 7% 3 6% 4 4 5% 4 6% 8% 41%	7617
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 6% 8% 44%	7677
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 6% 37%	9047
June	1st to 10th	Day	7% 4 2 5% 4 5% 5% 5% 7% 9% 46%	2940
	11th to 20th	Day	8% 6% 2 6% 4 5% 5% 5% 6% 9% 45%	2940
	21st to end	Day	7% 5% 2 6% 5% 4 5% 4 7% 9% 46%	2940
July	1st to 10th	Day	9% 5% 2 7% 4 4 4 4 6% 8% 47%	8224
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 6% 9% 51%	7680
	21st to end	Day	10% 5% 2 6% 4 5% 5% 4 7% 11% 40%	8337
August	1st to 10th	Day	4 4 1 5% 4 4 4 4 6% 11% 52%	4364
	11th to 20th	Day	11% 4 2 6% 4 3 5% 3 6% 9% 47%	4207
	21st to end	Day	5% 4 2 5% 4 4 5% 4 6% 9% 54%	4312
September	1st to 10th	Day	11% 4 2 4 3 3 4 3 5% 7% 53%	2400
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 6% 8% 51%	2325
	21st to end	Day	9% 5% 1 5% 4 3 4 3 5% 6% 55%	2127
October	1st to 10th	Day	12% 4 2 4 4 3 3 3 5% 7% 54%	2000
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 4 6% 53%	2000
	21st to end	Day	17% 8% 2 6% 4 2 3 2 4 5% 45%	2200
November	1st to 10th	Day	11% 6% 2 5% 3 3 4 3 4 6% 53%	2053
	11th to 20th	Day	14% 7% 2 6% 3 3 3 2 4 6% 49%	1759
	21st to end	Day	17% 9% 3 7% 4 3 2 3 4 5% 43%	1680
December	1st to 10th	Day	6% 7% 3 7% 4 3 4 3 4 7% 52%	2690
	11th to 20th	Day	11% 8% 4 8% 4 3 4 3 4 5% 46%	3088
	21st to end	Day	18% 19% 7% 12% 4 4 4 2 4 4 22%	4070
January	1st to 10th	Night	12% 11% 5% 13% 5% 5% 3 2 3 4 37%	7772
	11th to 20th	Night	9% 8% 3 9% 4 5% 4 4 5% 4 45%	7680
	21st to end	Night	12% 11% 5% 9% 5% 5% 4 3 4 5% 37%	8402
February	1st to 10th	Night	13% 10% 4 7% 5% 5% 4 4 5% 6% 38%	2730
	11th to 20th	Night	13% 9% 3 8% 5% 4 4 3 4 6% 41%	2663
	21st to end	Night	13% 8% 3 7% 3 3 3 3 5% 6% 46%	2061
March	1st to 10th	Night	17% 10% 3 6% 3 3 3 2 4 5% 46%	5029
	11th to 20th	Night	10% 6% 2 5% 3 3 3 2 4 6% 55%	5090
	21st to end	Night	14% 9% 3 8% 5% 5% 4 4 6% 7% 35%	5588
April	1st to 10th	Night	12% 7% 2 6% 4 3 4 3 5% 6% 48%	2128
	11th to 20th	Night	14% 6% 3 7% 4 4 3 3 5% 6% 47%	2075
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 6% 40%	2042
May	1st to 10th	Night	15% 6% 3 6% 4 4 4 4 5% 8% 42%	5266
	11th to 20th	Night	12% 6% 2 5% 3 4 4 3 6% 9% 46%	5210
	21st to end	Night	15% 7% 3 7% 4 4 5% 3 6% 7% 40%	5139
June	1st to 10th	Night	6% 4 1 4 3 4 3 4 7% 10% 53%	1680
	11th to 20th	Night	6% 3 2 5% 4 4 4 4 6% 10% 51%	1680
	21st to end	Night	5% 3 1 5% 3 4 5% 3 6% 9% 56%	1680
July	1st to 10th	Night	8% 4 2 5% 3 3 4 3 6% 10% 50%	4758
	11th to 20th	Night	6% 4 2 5% 4 4 5% 4 6% 8% 54%	5307
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 8% 12% 44%	5770
August	1st to 10th	Night	4 3 1 3 2 3 4 4 6% 10% 62%	3016
	11th to 20th	Night	11% 6% 1 4 3 3 3 3 5% 7% 53%	2938
	21st to end	Night	4 3 2 5% 4 4 5% 4 6% 8% 58%	3586
September	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 6% 57%	2000
	11th to 20th	Night	9% 4 2 4 3 3 4 4 6% 7% 54%	2071
	21st to end	Night	8% 5% 2 5% 3 3 4 3 5% 6% 57%	2252
October	1st to 10th	Night	9% 4 2 4 3 3 4 3 5% 5% 58%	2400
	11th to 20th	Night	13% 5% 2 6% 4 2 3 2 4 5% 55%	2400
	21st to end	Night	16% 8% 2 4 3 3 3 3 4 4 51%	2640
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 6% 57%	2463
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 4 6% 53%	2859
	21st to end	Night	17% 8% 3 5% 3 3 3 3 4 5% 47%	2940
December	1st to 10th	Night	8% 6% 3 6% 4 4 4 4 5% 6% 51%	4720
	11th to 20th	Night	13% 8% 4 7% 4 4 4 3 5% 6% 43%	5339
	21st to end	Night	22% 15% 5% 9% 4 3 3 3 4 4 28%	7150

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	50% 3 11% 24% 11% 2	5148
	11th to 20th	Day	45% 3 10% 24% 14% 4	5310
	21st to end	Day	52% 2 12% 17% 15% 2	5812
February	1st to 10th	Day	49% 4 13% 23% 10% 1	1890
	11th to 20th	Day	46% 5% 12% 21% 13% 3	1853
	21st to end	Day	41% 4 12% 23% 17% 2	1760
March	1st to 10th	Day	40% 3 7% 25% 22% 3	5046
	11th to 20th	Day	33% 3 9% 23% 25% 6%	5090
	21st to end	Day	50% 4 17% 24% 5% 1	5585
April	1st to 10th	Day	43% 4 12% 25% 14% 1	2491
	11th to 20th	Day	44% 5% 12% 23% 14% 2	2494
	21st to end	Day	51% 4 12% 22% 10%	2575
May	1st to 10th	Day	42% 5% 13% 27% 13%	7655
	11th to 20th	Day	39% 4 14% 25% 16% 2	7681
	21st to end	Day	47% 4 9% 26% 13% 1	9061
June	1st to 10th	Day	31% 7% 17% 30% 14% 1	2940
	11th to 20th	Day	34% 7% 13% 28% 16% 2	2940
	21st to end	Day	31% 6% 17% 29% 14% 4	2940
July	1st to 10th	Day	36% 3 14% 28% 17% 2	8155
	11th to 20th	Day	31% 4 17% 28% 16% 4	7611
	21st to end	Day	37% 4 20% 31% 8%	8155
August	1st to 10th	Day	26% 5% 18% 31% 18% 1	4350
	11th to 20th	Day	35% 4 15% 30% 15% 1	4246
	21st to end	Day	27% 4 15% 34% 14% 5%	4311
September	1st to 10th	Day	31% 5% 12% 27% 19% 6%	2400
	11th to 20th	Day	31% 5% 13% 25% 23% 3	2325
	21st to end	Day	31% 5% 9% 28% 24% 3	2127
October	1st to 10th	Day	20% 2 6% 21% 39% 11%	3260
	11th to 20th	Day	22% 2 4 23% 40% 8%	3240
	21st to end	Day	37% 3 8% 25% 25% 2	3538
November	1st to 10th	Day	33% 3 13% 27% 19% 4	2053
	11th to 20th	Day	37% 3 10% 27% 20% 3	1759
	21st to end	Day	45% 3 9% 28% 15% 1	1680
December	1st to 10th	Day	33% 3 16% 30% 17% 1	2690
	11th to 20th	Day	42% 3 14% 30% 10% 1	3085
	21st to end	Day	67% 3 12% 13% 5% 1	4070
January	1st to 10th	Night	53% 2 12% 23% 10% 1	7773
	11th to 20th	Night	42% 3 8% 25% 17% 4	7680
	21st to end	Night	50% 3 12% 18% 14% 3	8402
February	1st to 10th	Night	47% 4 12% 21% 13% 2	2730
	11th to 20th	Night	45% 4 10% 22% 16% 2	2664
	21st to end	Night	39% 4 9% 23% 20% 4	2061
March	1st to 10th	Night	43% 3 7% 21% 22% 3	5029
	11th to 20th	Night	31% 3 6% 26% 27% 6%	5090
	21st to end	Night	48% 4 14% 24% 8% 2	5588
April	1st to 10th	Night	37% 5% 9% 26% 19% 4	2128
	11th to 20th	Night	38% 4 10% 27% 17% 4	2075
	21st to end	Night	44% 4 11% 24% 16% 1	2042
May	1st to 10th	Night	41% 5% 12% 25% 15% 1	5293
	11th to 20th	Night	36% 4 13% 24% 19% 5%	5211
	21st to end	Night	44% 5% 9% 21% 19% 1	5149
June	1st to 10th	Night	26% 6% 16% 31% 17% 3	1680
	11th to 20th	Night	27% 7% 12% 29% 20% 4	1680
	21st to end	Night	24% 5% 15% 32% 19% 5%	1680
July	1st to 10th	Night	30% 3 15% 28% 23% 2	4720
	11th to 20th	Night	28% 4 16% 28% 18% 5%	5256
	21st to end	Night	33% 3 20% 36% 8%	5641
August	1st to 10th	Night	19% 4 23% 28% 25% 2	3006
	11th to 20th	Night	33% 3 11% 30% 22% 1	2965
	21st to end	Night	25% 4 14% 36% 17% 4	3586
September	1st to 10th	Night	29% 5% 10% 24% 25% 7%	2000
	11th to 20th	Night	29% 5% 11% 27% 24% 5%	2071
	21st to end	Night	28% 5% 9% 27% 27% 4	2252
October	1st to 10th	Night	17% 3 6% 20% 45% 9%	3920
	11th to 20th	Night	24% 2 6% 24% 30% 14%	3899
	21st to end	Night	35% 2 7% 29% 25% 3	4252
November	1st to 10th	Night	30% 4 11% 28% 22% 5%	2463
	11th to 20th	Night	34% 3 9% 26% 23% 4	2859
	21st to end	Night	42% 3 10% 27% 16% 2	2940
December	1st to 10th	Night	33% 3 14% 34% 15% 1	4720
	11th to 20th	Night	42% 2 13% 27% 15% 1	5341
	21st to end	Night	62% 3 12% 17% 6% 1	7150

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	19% 13% 38% 24% 6% 1	330
	11th to 20th	Day	25% 18% 38% 18% 2	330
	21st to end	Day	15% 15% 43% 23% 5%	363
February	1st to 10th	Day	22% 13% 43% 18% 4	330
	11th to 20th	Day	19% 18% 38% 18% 7%	330
	21st to end	Day	14% 20% 43% 19% 4	273
March	1st to 10th	Day	20% 15% 42% 19% 3	330
	11th to 20th	Day	27% 12% 32% 22% 6%	330
	21st to end	Day	30% 22% 31% 13% 4	363
April	1st to 10th	Day	23% 16% 32% 22% 6% 1	511
	11th to 20th	Day	20% 16% 36% 21% 7% 1	532
	21st to end	Day	22% 12% 35% 22% 9% 1	595
May	1st to 10th	Day	16% 13% 34% 27% 10% 1	753
	11th to 20th	Day	18% 9% 28% 27% 15% 2	775
	21st to end	Day	16% 9% 24% 29% 17% 5%	844
June	1st to 10th	Day	8% 5% 20% 32% 26% 9%	780
	11th to 20th	Day	10% 3 24% 32% 25% 4	780
	21st to end	Day	7% 5% 29% 38% 18% 3	780
July	1st to 10th	Day	11% 3 13% 28% 31% 15%	771
	11th to 20th	Day	6% 1 18% 33% 32% 11%	768
	21st to end	Day	8% 3 14% 32% 33% 10%	849
August	1st to 10th	Day	6% 2 17% 37% 32% 7%	776
	11th to 20th	Day	9% 3 16% 34% 30% 8%	732
	21st to end	Day	8% 1 12% 31% 34% 14%	583
September	1st to 10th	Day	11% 2 14% 33% 31% 8%	530
	11th to 20th	Day	9% 2 14% 33% 32% 11%	455
	21st to end	Day	12% 5% 22% 30% 24% 8%	330
October	1st to 10th	Day	13% 5% 26% 30% 18% 9%	330
	11th to 20th	Day	10% 16% 37% 25% 12% 1	330
	21st to end	Day	28% 15% 30% 21% 7%	363
November	1st to 10th	Day	18% 7% 37% 25% 8% 5%	330
	11th to 20th	Day	15% 16% 31% 25% 11% 2	330
	21st to end	Day	24% 14% 29% 25% 8% 1	330
December	1st to 10th	Day	11% 15% 38% 25% 8% 2	330
	11th to 20th	Day	19% 13% 38% 19% 8% 1	330
	21st to end	Day	24% 16% 37% 20% 2	363
January	1st to 10th	Night	15% 10% 40% 27% 7%	1050
	11th to 20th	Night	17% 13% 41% 23% 5% 1	1050
	21st to end	Night	16% 12% 40% 28% 4	1155
February	1st to 10th	Night	16% 11% 43% 25% 4	1050
	11th to 20th	Night	18% 13% 36% 30% 3	1029
	21st to end	Night	18% 13% 46% 20% 3	677
March	1st to 10th	Night	18% 12% 41% 25% 3	630
	11th to 20th	Night	18% 11% 36% 29% 5% 1	630
	21st to end	Night	26% 12% 36% 21% 4	693
April	1st to 10th	Night	16% 14% 37% 30% 4	630
	11th to 20th	Night	17% 13% 35% 28% 7%	623
	21st to end	Night	20% 8% 37% 28% 7%	630
May	1st to 10th	Night	17% 7% 31% 36% 7% 1	630
	11th to 20th	Night	15% 6% 27% 35% 15% 1	621
	21st to end	Night	13% 6% 26% 35% 18% 2	683
June	1st to 10th	Night	7% 3 20% 45% 22% 3	630
	11th to 20th	Night	7% 3 24% 44% 20% 2	630
	21st to end	Night	6% 3 27% 46% 19% 1	630
July	1st to 10th	Night	9% 3 10% 41% 34% 4	615
	11th to 20th	Night	6% 2 13% 42% 34% 3	612
	21st to end	Night	7% 1 12% 43% 35% 2	690
August	1st to 10th	Night	7% 2 12% 46% 32% 2	627
	11th to 20th	Night	8% 2 12% 41% 33% 3	606
	21st to end	Night	7% 1 9% 43% 37% 3	660
September	1st to 10th	Night	11% 2 15% 41% 28% 3	600
	11th to 20th	Night	12% 1 16% 39% 28% 5%	600
	21st to end	Night	8% 4 22% 41% 23% 3	652
October	1st to 10th	Night	12% 4 28% 35% 19% 2	800
	11th to 20th	Night	15% 9% 34% 33% 9%	800
	21st to end	Night	20% 11% 34% 27% 8%	880
November	1st to 10th	Night	14% 8% 33% 35% 9%	820
	11th to 20th	Night	15% 10% 37% 30% 8%	969
	21st to end	Night	21% 11% 35% 28% 5%	1050
December	1st to 10th	Night	17% 10% 39% 29% 5% 1	1050
	11th to 20th	Night	19% 9% 36% 31% 4	1050
	21st to end	Night	22% 13% 35% 27% 3	1155

Page generated at 2026-08-12 02:37:15. Version ac07

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