Wayside Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wayside Observatory clear sky chart from 2005-11-06 to 2024-11-03.

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	15% 6% 2 6% 4 4 4 4 6% 7% 40%	101285
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	97699
Transparency	Day	41% 6% 11% 24% 15% 3	101046
	Night	42% 5% 11% 24% 16% 3	97558
Seeing	Day	20% 15% 29% 22% 11% 3	14985
	Night	19% 13% 29% 27% 10% 1	24306

By Month

Percentage Cloud Cover NE (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% 6% 2 5% 5% 4 3 3 4 5% 45%	2517
	11th to 20th	Day	14% 11% 3 10% 6% 4 4 3 4 5% 36%	2684
	21st to end	Day	20% 8% 3 6% 5% 4 4 4 5% 5% 36%	3124
February	1st to 10th	Day	15% 7% 2 7% 5% 4 4 3 6% 6% 39%	1710
	11th to 20th	Day	16% 8% 2 6% 4 5% 4 3 5% 6% 40%	1775
	21st to end	Day	19% 11% 3 6% 4 3 3 2 4 5% 39%	1570
March	1st to 10th	Day	24% 6% 2 5% 4 3 4 3 4 6% 39%	3202
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 4 6% 6% 47%	3480
	21st to end	Day	22% 6% 3 5% 4 3 3 2 4 4 44%	3995
April	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 5% 7% 41%	2280
	11th to 20th	Day	13% 6% 2 6% 5% 5% 4 4 5% 7% 44%	2254
	21st to end	Day	17% 5% 2 6% 4 4 5% 4 5% 7% 40%	2280
May	1st to 10th	Day	28% 8% 2 6% 4 4 4 3 5% 7% 29%	4026
	11th to 20th	Day	24% 8% 3 8% 5% 4 5% 4 5% 7% 27%	4398
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 6% 8% 45%	4837
June	1st to 10th	Day	11% 6% 2 5% 5% 5% 5% 5% 6% 10% 39%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 5% 8% 9% 37%	2660
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 6% 10% 43%	2660
July	1st to 10th	Day	7% 4 2 6% 5% 6% 7% 5% 9% 11% 39%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 11% 39%	4440
	21st to end	Day	12% 7% 3 8% 6% 6% 5% 5% 7% 8% 33%	4610
August	1st to 10th	Day	19% 5% 2 6% 4 5% 6% 4 7% 8% 33%	4104
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 5% 6% 9% 42%	3772
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 8% 47%	4180
September	1st to 10th	Day	14% 6% 2 6% 5% 4 4 3 6% 6% 44%	2280
	11th to 20th	Day	13% 4 2 6% 3 3 4 3 4 8% 50%	2277
	21st to end	Day	19% 8% 3 7% 4 4 3 4 4 7% 37%	2046
October	1st to 10th	Day	16% 7% 2 5% 4 3 4 4 4 7% 44%	1900
	11th to 20th	Day	15% 6% 2 5% 4 3 4 3 4 6% 49%	1900
	21st to end	Day	17% 6% 2 5% 4 3 3 4 4 5% 47%	2069
November	1st to 10th	Day	14% 6% 2 5% 2 3 3 3 5% 6% 52%	1689
	11th to 20th	Day	16% 5% 2 5% 3 3 3 4 5% 6% 48%	1710
	21st to end	Day	15% 6% 2 5% 4 4 5% 3 5% 6% 45%	1558
December	1st to 10th	Day	18% 6% 2 6% 5% 4 4 3 6% 6% 39%	1520
	11th to 20th	Day	19% 7% 3 4 4 4 4 3 5% 6% 42%	1906
	21st to end	Day	16% 6% 3 7% 6% 5% 5% 5% 6% 6% 35%	2772
January	1st to 10th	Night	17% 7% 2 4 4 4 3 3 5% 6% 44%	4429
	11th to 20th	Night	19% 8% 2 5% 3 3 4 3 4 5% 43%	4274
	21st to end	Night	22% 8% 2 7% 4 4 3 3 4 5% 39%	4532
February	1st to 10th	Night	16% 8% 2 6% 5% 4 4 3 5% 6% 40%	2470
	11th to 20th	Night	18% 8% 2 6% 4 3 4 3 5% 5% 42%	2289
	21st to end	Night	18% 7% 2 5% 5% 4 4 4 4 7% 40%	1884
March	1st to 10th	Night	21% 8% 3 7% 4 3 3 2 4 6% 38%	3635
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 4 6% 51%	3479
	21st to end	Night	16% 9% 2 6% 4 3 3 2 4 4 46%	3636
April	1st to 10th	Night	15% 7% 2 7% 5% 4 4 3 5% 6% 41%	1900
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 6% 7% 43%	1875
	21st to end	Night	18% 6% 2 5% 4 3 4 3 5% 6% 43%	1900
May	1st to 10th	Night	23% 9% 3 7% 4 5% 3 3 5% 7% 30%	2939
	11th to 20th	Night	25% 9% 3 7% 4 4 4 5% 5% 6% 28%	2495
	21st to end	Night	13% 6% 3 6% 4 3 4 3 6% 9% 43%	2738
June	1st to 10th	Night	13% 6% 2 6% 4 4 3 4 6% 8% 45%	1520
	11th to 20th	Night	11% 6% 3 8% 4 4 5% 3 6% 10% 40%	1520
	21st to end	Night	10% 4 2 5% 5% 4 4 5% 6% 12% 42%	1520
July	1st to 10th	Night	7% 6% 3 7% 6% 5% 5% 5% 7% 10% 39%	2520
	11th to 20th	Night	11% 7% 2 6% 4 5% 6% 5% 8% 9% 37%	2520
	21st to end	Night	15% 6% 3 7% 5% 5% 5% 4 7% 8% 37%	2925
August	1st to 10th	Night	21% 5% 2 7% 4 5% 4 4 6% 8% 34%	2825
	11th to 20th	Night	14% 6% 2 6% 5% 5% 4 3 5% 7% 42%	3024
	21st to end	Night	11% 5% 2 5% 4 4 4 3 5% 7% 50%	3476
September	1st to 10th	Night	14% 6% 2 6% 4 3 4 2 5% 6% 47%	1900
	11th to 20th	Night	13% 6% 2 4 3 2 3 3 5% 7% 53%	1902
	21st to end	Night	20% 6% 2 6% 5% 3 3 3 5% 7% 39%	2132
October	1st to 10th	Night	19% 7% 2 6% 5% 3 4 2 4 5% 43%	2280
	11th to 20th	Night	16% 4 2 4 3 3 3 3 5% 6% 51%	2280
	21st to end	Night	17% 5% 2 5% 3 3 3 2 5% 6% 50%	2527
November	1st to 10th	Night	11% 5% 2 6% 3 3 3 4 6% 5% 53%	2434
	11th to 20th	Night	16% 6% 2 6% 3 3 3 3 4 6% 47%	2470
	21st to end	Night	13% 5% 1 5% 4 4 5% 4 6% 7% 46%	2617
December	1st to 10th	Night	18% 8% 2 6% 5% 4 4 3 5% 6% 39%	2660
	11th to 20th	Night	18% 5% 2 5% 4 4 4 3 6% 7% 42%	3288
	21st to end	Night	16% 7% 3 6% 4 4 5% 4 6% 7% 37%	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% 5% 12% 26% 15% 4	2518
	11th to 20th	Day	49% 4 9% 21% 13% 3	2684
	21st to end	Day	47% 6% 12% 22% 11% 2	3124
February	1st to 10th	Day	44% 4 13% 25% 12% 2	1710
	11th to 20th	Day	44% 4 8% 26% 15% 3	1784
	21st to end	Day	47% 4 9% 22% 14% 4	1570
March	1st to 10th	Day	45% 4 9% 28% 11% 3	3205
	11th to 20th	Day	34% 6% 8% 29% 19% 4	3480
	21st to end	Day	45% 4 8% 20% 19% 4	3995
April	1st to 10th	Day	41% 5% 11% 20% 17% 5%	2280
	11th to 20th	Day	38% 6% 11% 23% 17% 5%	2254
	21st to end	Day	41% 6% 11% 20% 19% 4	2280
May	1st to 10th	Day	53% 6% 9% 18% 11% 2	4038
	11th to 20th	Day	52% 7% 13% 18% 8% 2	4402
	21st to end	Day	34% 7% 12% 26% 18% 2	4837
June	1st to 10th	Day	38% 7% 12% 25% 16% 2	2660
	11th to 20th	Day	39% 7% 13% 25% 13% 3	2660
	21st to end	Day	33% 9% 14% 24% 19% 1	2660
July	1st to 10th	Day	36% 9% 16% 22% 13% 4	4370
	11th to 20th	Day	38% 5% 17% 26% 12% 2	4365
	21st to end	Day	46% 6% 11% 20% 16% 2	4463
August	1st to 10th	Day	47% 6% 15% 23% 9%	4091
	11th to 20th	Day	38% 5% 11% 31% 14% 1	3809
	21st to end	Day	34% 4 11% 30% 19% 2	4180
September	1st to 10th	Day	39% 5% 11% 20% 21% 4	2280
	11th to 20th	Day	33% 5% 9% 27% 23% 4	2277
	21st to end	Day	47% 4 8% 19% 19% 2	2046
October	1st to 10th	Day	40% 6% 9% 23% 20% 2	1900
	11th to 20th	Day	36% 4 11% 22% 24% 3	1900
	21st to end	Day	39% 4 7% 28% 20% 2	2069
November	1st to 10th	Day	34% 3 12% 25% 21% 4	1689
	11th to 20th	Day	38% 4 10% 24% 22% 3	1710
	21st to end	Day	38% 5% 10% 31% 13% 3	1558
December	1st to 10th	Day	43% 5% 14% 23% 13% 1	1520
	11th to 20th	Day	42% 4 10% 30% 10% 2	1906
	21st to end	Day	45% 7% 13% 22% 13% 1	2772
January	1st to 10th	Night	42% 4 10% 27% 14% 3	4429
	11th to 20th	Night	43% 3 10% 26% 14% 3	4274
	21st to end	Night	49% 3 7% 28% 11% 1	4532
February	1st to 10th	Night	44% 3 13% 25% 13% 2	2470
	11th to 20th	Night	44% 3 9% 21% 19% 4	2291
	21st to end	Night	45% 3 10% 21% 16% 6%	1884
March	1st to 10th	Night	47% 5% 8% 25% 14% 2	3645
	11th to 20th	Night	34% 5% 12% 30% 16% 3	3480
	21st to end	Night	43% 4 7% 18% 23% 5%	3636
April	1st to 10th	Night	43% 4 10% 19% 20% 4	1900
	11th to 20th	Night	39% 5% 11% 21% 19% 5%	1875
	21st to end	Night	41% 5% 10% 20% 18% 6%	1900
May	1st to 10th	Night	52% 7% 9% 19% 12% 2	2946
	11th to 20th	Night	54% 8% 12% 14% 10% 2	2496
	21st to end	Night	36% 8% 15% 22% 15% 4	2739
June	1st to 10th	Night	37% 7% 11% 24% 18% 2	1520
	11th to 20th	Night	39% 7% 13% 25% 15% 1	1520
	21st to end	Night	34% 7% 14% 26% 16% 3	1520
July	1st to 10th	Night	41% 7% 18% 18% 13% 4	2480
	11th to 20th	Night	42% 5% 18% 24% 10% 1	2472
	21st to end	Night	44% 7% 13% 19% 17% 1	2832
August	1st to 10th	Night	47% 7% 18% 19% 9% 1	2814
	11th to 20th	Night	42% 5% 11% 28% 14% 1	3053
	21st to end	Night	35% 4 10% 30% 19% 2	3476
September	1st to 10th	Night	38% 5% 10% 21% 21% 4	1900
	11th to 20th	Night	31% 5% 9% 25% 25% 5%	1902
	21st to end	Night	45% 5% 7% 21% 19% 3	2132
October	1st to 10th	Night	45% 3 10% 22% 18% 2	2280
	11th to 20th	Night	35% 4 10% 28% 19% 4	2280
	21st to end	Night	36% 4 9% 28% 19% 3	2527
November	1st to 10th	Night	33% 5% 10% 27% 19% 6%	2434
	11th to 20th	Night	38% 4 9% 23% 20% 5%	2470
	21st to end	Night	37% 4 11% 28% 17% 2	2617
December	1st to 10th	Night	46% 3 11% 24% 14% 1	2660
	11th to 20th	Night	41% 4 12% 22% 17% 4	3288
	21st to end	Night	43% 7% 14% 24% 10% 1	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	25% 27% 33% 12% 2 1	180
	11th to 20th	Day	33% 29% 27% 11% 1	227
	21st to end	Day	22% 33% 28% 13% 4	297
February	1st to 10th	Day	26% 30% 30% 11% 3	270
	11th to 20th	Day	33% 25% 34% 8% 1	383
	21st to end	Day	32% 23% 30% 13% 2	382
March	1st to 10th	Day	26% 25% 30% 15% 4	460
	11th to 20th	Day	27% 27% 30% 10% 5% 1	460
	21st to end	Day	26% 24% 33% 12% 4 1	506
April	1st to 10th	Day	27% 23% 34% 10% 5% 1	460
	11th to 20th	Day	22% 22% 30% 18% 6% 2	452
	21st to end	Day	24% 20% 36% 13% 6%	460
May	1st to 10th	Day	32% 16% 29% 16% 6% 1	463
	11th to 20th	Day	21% 15% 34% 20% 9% 1	487
	21st to end	Day	19% 11% 26% 25% 16% 4	529
June	1st to 10th	Day	13% 13% 33% 24% 15% 3	490
	11th to 20th	Day	15% 10% 30% 28% 13% 4	490
	21st to end	Day	13% 9% 32% 31% 11% 4	490
July	1st to 10th	Day	13% 5% 23% 33% 18% 8%	485
	11th to 20th	Day	7% 2 24% 37% 23% 6%	484
	21st to end	Day	13% 5% 25% 34% 20% 3	532
August	1st to 10th	Day	14% 3 22% 35% 19% 7%	486
	11th to 20th	Day	12% 5% 19% 35% 20% 9%	479
	21st to end	Day	12% 5% 28% 29% 18% 9%	539
September	1st to 10th	Day	18% 9% 21% 26% 18% 8%	490
	11th to 20th	Day	14% 6% 26% 30% 17% 8%	490
	21st to end	Day	27% 9% 25% 27% 10% 2	490
October	1st to 10th	Day	21% 8% 28% 22% 15% 6%	490
	11th to 20th	Day	17% 16% 28% 24% 13% 2	490
	21st to end	Day	19% 15% 35% 20% 9% 2	527
November	1st to 10th	Day	15% 18% 33% 21% 11% 2	371
	11th to 20th	Day	21% 23% 28% 21% 6% 1	370
	21st to end	Day	21% 23% 30% 22% 5%	218
December	1st to 10th	Day	26% 26% 29% 14% 4	180
	11th to 20th	Day	34% 21% 29% 13% 3	180
	21st to end	Day	23% 23% 30% 17% 6% 1	198
January	1st to 10th	Night	21% 22% 36% 18% 3	760
	11th to 20th	Night	26% 18% 31% 21% 3	760
	21st to end	Night	19% 22% 38% 20% 2	836
February	1st to 10th	Night	21% 19% 35% 22% 2	760
	11th to 20th	Night	25% 26% 33% 15% 1	743
	21st to end	Night	23% 23% 34% 17% 3	628
March	1st to 10th	Night	20% 21% 35% 20% 4	760
	11th to 20th	Night	22% 21% 33% 18% 5% 1	760
	21st to end	Night	22% 14% 39% 19% 5%	836
April	1st to 10th	Night	22% 21% 34% 18% 5%	760
	11th to 20th	Night	19% 15% 34% 26% 6%	751
	21st to end	Night	24% 14% 31% 23% 8%	760
May	1st to 10th	Night	21% 11% 34% 27% 5% 1	637
	11th to 20th	Night	22% 10% 31% 28% 9%	374
	21st to end	Night	18% 6% 22% 38% 16% 1	411
June	1st to 10th	Night	16% 5% 28% 34% 16%	380
	11th to 20th	Night	13% 5% 27% 43% 12% 1	380
	21st to end	Night	10% 3 28% 43% 16% 1	380
July	1st to 10th	Night	12% 5% 22% 40% 19% 2	370
	11th to 20th	Night	6% 5% 16% 45% 26% 2	368
	21st to end	Night	11% 4 17% 42% 24% 2	527
August	1st to 10th	Night	11% 2 17% 42% 25% 2	567
	11th to 20th	Night	14% 4 15% 39% 25% 3	701
	21st to end	Night	14% 4 19% 36% 24% 3	836
September	1st to 10th	Night	16% 5% 22% 34% 20% 3	760
	11th to 20th	Night	13% 4 19% 35% 25% 4	760
	21st to end	Night	23% 4 24% 28% 18% 2	760
October	1st to 10th	Night	23% 6% 24% 25% 17% 4	760
	11th to 20th	Night	18% 11% 28% 31% 12% 1	760
	21st to end	Night	20% 13% 31% 24% 10% 1	836
November	1st to 10th	Night	14% 12% 35% 26% 11% 1	749
	11th to 20th	Night	20% 18% 29% 26% 7% 1	760
	21st to end	Night	16% 19% 31% 25% 8%	760
December	1st to 10th	Night	23% 18% 33% 18% 6% 1	760
	11th to 20th	Night	19% 19% 37% 21% 5%	760
	21st to end	Night	21% 18% 32% 26% 3	836

Page generated at 2024-10-31 03:39:22. Version ac07

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