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 2025-04-11.

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%	113617
	Night	12% 7% 3 7% 4 4 4 3 5% 6% 46%	114872
Transparency	Day	39% 4 12% 26% 16% 3	117265
	Night	38% 4 11% 25% 18% 3	119366
Seeing	Day	14% 9% 26% 28% 18% 5%	16167
	Night	15% 8% 31% 33% 13% 1	26185

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	15% 11% 4 10% 4 5% 4 3 4 6% 33%	3961
	11th to 20th	Day	8% 9% 4 9% 6% 7% 7% 3 4 5% 39%	4080
	21st to end	Day	15% 13% 4 9% 5% 4 4 2 3 4 35%	4488
February	1st to 10th	Day	16% 12% 4 9% 5% 4 4 2 5% 7% 34%	1800
	11th to 20th	Day	14% 11% 4 7% 5% 3 3 3 5% 6% 38%	1754
	21st to end	Day	12% 8% 3 8% 5% 3 4 3 5% 6% 43%	1678
March	1st to 10th	Day	15% 9% 3 5% 3 3 2 2 3 4 51%	4936
	11th to 20th	Day	10% 6% 2 5% 4 3 4 3 4 6% 53%	4980
	21st to end	Day	15% 11% 3 8% 5% 4 5% 4 6% 7% 33%	5462
April	1st to 10th	Day	15% 7% 2 7% 5% 3 4 3 5% 6% 43%	2372
	11th to 20th	Day	15% 9% 2 6% 4 3 4 4 5% 7% 40%	2254
	21st to end	Day	21% 8% 2 7% 4 5% 4 4 5% 6% 34%	2329
May	1st to 10th	Day	13% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	4082
	11th to 20th	Day	16% 9% 3 7% 5% 4 3 3 5% 7% 38%	4104
	21st to end	Day	12% 6% 2 6% 5% 4 4 4 6% 7% 45%	4824
June	1st to 10th	Day	7% 4 2 5% 4 5% 5% 5% 7% 10% 47%	2660
	11th to 20th	Day	7% 6% 2 6% 4 5% 5% 4 6% 9% 46%	2660
	21st to end	Day	6% 5% 1 7% 5% 4 5% 4 7% 10% 47%	2660
July	1st to 10th	Day	12% 6% 2 7% 4 4 4 4 7% 8% 41%	4412
	11th to 20th	Day	6% 4 2 5% 3 3 4 4 6% 9% 54%	4120
	21st to end	Day	6% 4 2 6% 4 5% 5% 5% 7% 11% 45%	4465
August	1st to 10th	Day	4 4 1 5% 4 4 4 4 7% 11% 53%	4104
	11th to 20th	Day	12% 4 2 6% 4 3 4 3 6% 8% 46%	4024
	21st to end	Day	5% 4 2 5% 4 4 5% 4 6% 9% 54%	4180
September	1st to 10th	Day	11% 4 1 4 3 3 4 3 5% 7% 54%	2280
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 6% 8% 52%	2209
	21st to end	Day	8% 5% 1 5% 4 3 4 3 5% 6% 55%	2021
October	1st to 10th	Day	12% 4 2 4 4 3 3 3 5% 7% 54%	1900
	11th to 20th	Day	13% 6% 2 4 3 3 2 2 4 6% 54%	1900
	21st to end	Day	16% 8% 2 6% 4 2 3 2 4 5% 46%	2090
November	1st to 10th	Day	12% 6% 2 5% 3 3 4 3 4 6% 53%	1953
	11th to 20th	Day	14% 7% 2 6% 3 3 3 2 4 6% 49%	1675
	21st to end	Day	17% 9% 3 7% 4 3 2 3 4 5% 44%	1600
December	1st to 10th	Day	6% 7% 3 6% 4 3 4 3 4 7% 53%	2610
	11th to 20th	Day	11% 8% 4 8% 4 3 4 3 4 5% 46%	3008
	21st to end	Day	18% 19% 8% 12% 4 4 4 2 4 4 22%	3982
January	1st to 10th	Night	13% 10% 5% 15% 5% 5% 3 2 3 4 34%	6000
	11th to 20th	Night	11% 9% 4 10% 4 6% 4 4 5% 4 39%	5900
	21st to end	Night	14% 10% 5% 9% 5% 4 4 3 4 5% 37%	6490
February	1st to 10th	Night	14% 10% 4 7% 5% 5% 4 4 4 6% 37%	2600
	11th to 20th	Night	13% 9% 3 8% 5% 4 4 3 4 6% 41%	2533
	21st to end	Night	13% 8% 3 7% 3 3 3 3 5% 6% 45%	1966
March	1st to 10th	Night	16% 10% 2 6% 3 3 3 2 4 5% 46%	4919
	11th to 20th	Night	10% 6% 2 4 3 3 3 2 4 6% 55%	4980
	21st to end	Night	14% 9% 3 9% 5% 5% 5% 4 6% 7% 34%	5467
April	1st to 10th	Night	11% 7% 2 6% 4 3 4 3 6% 6% 49%	2027
	11th to 20th	Night	14% 6% 3 7% 4 3 3 3 4 5% 48%	1881
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 6% 41%	1848
May	1st to 10th	Night	15% 6% 3 7% 5% 4 4 4 6% 8% 38%	2823
	11th to 20th	Night	14% 8% 3 5% 4 4 3 4 5% 9% 41%	2796
	21st to end	Night	11% 5% 2 5% 4 3 5% 3 6% 7% 50%	2743
June	1st to 10th	Night	6% 4 1 4 3 4 3 4 7% 10% 54%	1520
	11th to 20th	Night	6% 3 2 5% 4 4 5% 4 7% 10% 51%	1520
	21st to end	Night	4 3 1 5% 2 4 5% 3 7% 9% 57%	1520
July	1st to 10th	Night	13% 6% 2 7% 3 4 4 3 5% 8% 47%	2552
	11th to 20th	Night	3 2 1 4 3 3 4 3 6% 9% 61%	2850
	21st to end	Night	5% 4 2 5% 4 5% 6% 5% 7% 10% 48%	3098
August	1st to 10th	Night	3 2 1 3 2 3 4 4 6% 10% 62%	2836
	11th to 20th	Night	11% 6% 1 4 3 3 3 3 5% 7% 52%	2812
	21st to end	Night	4 3 2 5% 4 4 5% 4 5% 8% 58%	3476
September	1st to 10th	Night	9% 4 2 5% 3 3 3 3 4 6% 58%	1900
	11th to 20th	Night	10% 4 2 3 3 3 4 4 5% 7% 55%	1967
	21st to end	Night	8% 5% 2 4 3 3 4 3 5% 6% 57%	2139
October	1st to 10th	Night	10% 5% 2 4 3 2 4 3 5% 5% 58%	2280
	11th to 20th	Night	13% 5% 1 5% 4 2 3 2 4 5% 56%	2280
	21st to end	Night	15% 8% 2 4 3 3 3 3 4 4 52%	2508
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 6% 58%	2343
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 4 6% 52%	2723
	21st to end	Night	16% 8% 2 4 3 3 3 3 4 5% 48%	2800
December	1st to 10th	Night	8% 6% 3 5% 4 3 4 3 5% 6% 52%	4580
	11th to 20th	Night	13% 8% 4 7% 4 4 4 3 5% 6% 43%	5199
	21st to end	Night	22% 15% 5% 10% 4 3 3 3 4 4 27%	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	52% 3 11% 22% 10% 1	3962
	11th to 20th	Day	50% 3 10% 21% 13% 4	4080
	21st to end	Day	54% 3 11% 14% 16% 3	4488
February	1st to 10th	Day	51% 4 12% 21% 10% 1	1800
	11th to 20th	Day	46% 5% 12% 21% 13% 3	1763
	21st to end	Day	42% 4 12% 23% 17% 2	1678
March	1st to 10th	Day	39% 3 7% 25% 22% 3	4936
	11th to 20th	Day	33% 3 9% 23% 25% 6%	4980
	21st to end	Day	50% 4 17% 23% 5%	5464
April	1st to 10th	Day	42% 5% 12% 26% 14% 2	2372
	11th to 20th	Day	44% 5% 12% 24% 14% 2	2254
	21st to end	Day	50% 5% 11% 22% 11%	2329
May	1st to 10th	Day	44% 7% 12% 23% 12% 1	4120
	11th to 20th	Day	46% 6% 13% 24% 11%	4108
	21st to end	Day	37% 6% 10% 31% 14% 1	4837
June	1st to 10th	Day	29% 8% 17% 31% 14% 1	2660
	11th to 20th	Day	33% 8% 13% 29% 16% 2	2660
	21st to end	Day	30% 6% 17% 30% 14% 4	2660
July	1st to 10th	Day	40% 5% 13% 24% 15% 3	4343
	11th to 20th	Day	28% 5% 13% 35% 17% 2	4051
	21st to end	Day	31% 5% 20% 30% 13% 1	4325
August	1st to 10th	Day	26% 6% 18% 31% 19% 1	4090
	11th to 20th	Day	36% 4 15% 29% 16% 1	4063
	21st to end	Day	27% 4 16% 35% 14% 5%	4179
September	1st to 10th	Day	30% 5% 12% 27% 20% 7%	2280
	11th to 20th	Day	30% 5% 13% 25% 24% 3	2209
	21st to end	Day	30% 5% 10% 29% 23% 3	2021
October	1st to 10th	Day	19% 2 6% 21% 39% 11%	3160
	11th to 20th	Day	22% 2 4 23% 41% 8%	3140
	21st to end	Day	36% 3 8% 25% 26% 2	3428
November	1st to 10th	Day	34% 3 13% 26% 19% 4	1953
	11th to 20th	Day	38% 3 10% 26% 20% 3	1675
	21st to end	Day	44% 3 10% 28% 16% 1	1600
December	1st to 10th	Day	33% 3 16% 31% 17% 1	2610
	11th to 20th	Day	42% 3 14% 29% 11% 1	3005
	21st to end	Day	67% 3 11% 12% 5% 1	3982
January	1st to 10th	Night	55% 2 10% 22% 10% 1	6000
	11th to 20th	Night	48% 3 10% 21% 14% 4	5900
	21st to end	Night	50% 3 10% 17% 16% 4	6490
February	1st to 10th	Night	48% 4 12% 20% 13% 3	2600
	11th to 20th	Night	45% 4 11% 20% 17% 2	2534
	21st to end	Night	40% 4 10% 23% 19% 4	1966
March	1st to 10th	Night	43% 3 7% 21% 22% 4	4919
	11th to 20th	Night	31% 3 6% 26% 28% 6%	4980
	21st to end	Night	49% 4 14% 23% 8% 2	5467
April	1st to 10th	Night	35% 5% 10% 26% 19% 4	2027
	11th to 20th	Night	38% 4 9% 28% 17% 4	1881
	21st to end	Night	43% 4 10% 24% 17% 1	1848
May	1st to 10th	Night	42% 8% 14% 20% 15% 1	2850
	11th to 20th	Night	40% 6% 13% 28% 12% 1	2797
	21st to end	Night	33% 6% 11% 25% 24% 2	2751
June	1st to 10th	Night	25% 6% 16% 31% 18% 4	1520
	11th to 20th	Night	26% 8% 12% 29% 20% 5%	1520
	21st to end	Night	23% 5% 15% 32% 19% 5%	1520
July	1st to 10th	Night	37% 4 11% 25% 19% 3	2512
	11th to 20th	Night	21% 5% 15% 37% 21% 2	2796
	21st to end	Night	29% 4 22% 32% 12% 1	2999
August	1st to 10th	Night	18% 4 23% 28% 25% 2	2826
	11th to 20th	Night	34% 3 11% 29% 22% 1	2839
	21st to end	Night	25% 4 14% 36% 17% 4	3476
September	1st to 10th	Night	28% 5% 10% 24% 25% 7%	1900
	11th to 20th	Night	28% 5% 10% 27% 25% 5%	1967
	21st to end	Night	28% 5% 9% 28% 27% 4	2139
October	1st to 10th	Night	17% 3 6% 20% 45% 9%	3800
	11th to 20th	Night	23% 2 5% 24% 31% 15%	3779
	21st to end	Night	34% 2 7% 29% 25% 3	4120
November	1st to 10th	Night	30% 4 12% 27% 22% 6%	2343
	11th to 20th	Night	35% 3 8% 26% 24% 4	2723
	21st to end	Night	41% 3 10% 27% 17% 2	2800
December	1st to 10th	Night	33% 3 14% 35% 15% 1	4580
	11th to 20th	Night	43% 2 14% 26% 14% 1	5201
	21st to end	Night	62% 3 12% 16% 6% 1	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	19% 14% 36% 24% 7% 1	300
	11th to 20th	Day	27% 16% 37% 18% 2	300
	21st to end	Day	16% 15% 42% 23% 5%	330
February	1st to 10th	Day	24% 12% 43% 17% 3	300
	11th to 20th	Day	19% 18% 38% 18% 7%	300
	21st to end	Day	14% 20% 42% 20% 4	249
March	1st to 10th	Day	18% 16% 42% 20% 4	300
	11th to 20th	Day	27% 11% 32% 24% 6%	300
	21st to end	Day	31% 22% 31% 13% 4	330
April	1st to 10th	Day	22% 17% 31% 23% 7% 1	472
	11th to 20th	Day	19% 15% 34% 23% 8% 1	452
	21st to end	Day	22% 12% 33% 23% 10% 1	509
May	1st to 10th	Day	16% 13% 34% 26% 9% 1	653
	11th to 20th	Day	19% 8% 27% 28% 15% 3	675
	21st to end	Day	14% 8% 25% 29% 18% 5%	734
June	1st to 10th	Day	7% 5% 19% 33% 28% 10%	680
	11th to 20th	Day	9% 2 25% 34% 26% 5%	680
	21st to end	Day	5% 6% 29% 38% 18% 4	680
July	1st to 10th	Day	12% 3 12% 28% 30% 15%	671
	11th to 20th	Day	6% 2 18% 33% 32% 10%	668
	21st to end	Day	8% 2 13% 32% 34% 11%	739
August	1st to 10th	Day	5% 2 16% 38% 32% 7%	676
	11th to 20th	Day	10% 3 16% 35% 29% 8%	661
	21st to end	Day	9% 1 12% 29% 35% 14%	539
September	1st to 10th	Day	12% 2 13% 33% 31% 9%	490
	11th to 20th	Day	9% 2 15% 33% 31% 11%	419
	21st to end	Day	11% 5% 23% 31% 23% 7%	300
October	1st to 10th	Day	13% 5% 27% 28% 17% 9%	300
	11th to 20th	Day	10% 15% 38% 25% 12% 1	300
	21st to end	Day	25% 16% 31% 22% 7%	330
November	1st to 10th	Day	19% 6% 35% 26% 9% 5%	300
	11th to 20th	Day	16% 17% 31% 23% 11% 2	300
	21st to end	Day	24% 14% 30% 25% 7%	300
December	1st to 10th	Day	11% 16% 38% 25% 8% 3	300
	11th to 20th	Day	20% 13% 38% 20% 9% 1	300
	21st to end	Day	25% 18% 36% 20% 2	330
January	1st to 10th	Night	15% 10% 40% 27% 8%	1000
	11th to 20th	Night	17% 13% 40% 24% 5% 1	1000
	21st to end	Night	16% 12% 40% 29% 4	1100
February	1st to 10th	Night	17% 11% 43% 25% 4	1000
	11th to 20th	Night	18% 13% 36% 30% 3	979
	21st to end	Night	18% 12% 46% 20% 3	646
March	1st to 10th	Night	17% 12% 41% 26% 4	600
	11th to 20th	Night	18% 11% 36% 29% 6% 1	600
	21st to end	Night	27% 12% 35% 21% 5%	660
April	1st to 10th	Night	15% 14% 36% 31% 5%	600
	11th to 20th	Night	17% 12% 34% 29% 8%	565
	21st to end	Night	19% 8% 37% 28% 8%	570
May	1st to 10th	Night	17% 8% 31% 36% 7% 1	570
	11th to 20th	Night	15% 6% 27% 36% 15% 1	561
	21st to end	Night	12% 6% 26% 34% 19% 2	617
June	1st to 10th	Night	7% 3 19% 45% 22% 4	570
	11th to 20th	Night	6% 3 23% 46% 20% 2	570
	21st to end	Night	5% 3 26% 47% 19% 1	570
July	1st to 10th	Night	10% 3 10% 40% 34% 4	555
	11th to 20th	Night	5% 2 14% 43% 34% 2	552
	21st to end	Night	7% 1 12% 43% 36% 2	624
August	1st to 10th	Night	5% 2 11% 46% 34% 2	567
	11th to 20th	Night	8% 2 12% 42% 32% 3	564
	21st to end	Night	7% 1 10% 42% 37% 3	627
September	1st to 10th	Night	11% 2 14% 41% 29% 4	570
	11th to 20th	Night	12% 1 16% 38% 27% 5%	570
	21st to end	Night	8% 4 23% 40% 22% 3	619
October	1st to 10th	Night	12% 4 28% 34% 19% 3	760
	11th to 20th	Night	16% 9% 35% 32% 9%	760
	21st to end	Night	19% 11% 33% 28% 8%	836
November	1st to 10th	Night	14% 8% 32% 36% 10%	780
	11th to 20th	Night	15% 11% 36% 29% 9%	923
	21st to end	Night	20% 11% 36% 28% 5%	1000
December	1st to 10th	Night	17% 10% 39% 29% 5% 1	1000
	11th to 20th	Night	20% 9% 35% 32% 5%	1000
	21st to end	Night	22% 13% 35% 27% 3	1100

Page generated at 2025-04-08 08:17:30. Version ac07

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