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 2024-03-18.

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% 3 5% 5% 3 5% 5% 5% 7% 41%	78648
	Night	16% 6% 2 5% 5% 3 4 4 5% 7% 43%	81126
Transparency	Day	40% 6% 11% 23% 16% 3	78360
	Night	41% 5% 11% 24% 16% 3	80949
Seeing	Day	20% 15% 29% 22% 11% 3	14070
	Night	19% 13% 29% 27% 10% 1	23566

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% 3 4 4 4 5% 46%	2517
	11th to 20th	Day	14% 10% 3 9% 7% 3 4 4 4 5% 37%	2684
	21st to end	Day	21% 8% 3 6% 5% 3 5% 4 5% 6% 36%	3124
February	1st to 10th	Day	16% 7% 3 6% 5% 3 5% 4 6% 7% 40%	1710
	11th to 20th	Day	16% 7% 3 6% 5% 3 4 5% 5% 6% 40%	1775
	21st to end	Day	19% 11% 3 5% 5% 2 3 3 4 5% 39%	1570
March	1st to 10th	Day	14% 6% 2 5% 5% 2 4 4 4 6% 47%	1944
	11th to 20th	Day	16% 7% 3 5% 6% 4 4 4 5% 6% 41%	2058
	21st to end	Day	20% 6% 3 5% 6% 3 4 4 4 5% 39%	2275
April	1st to 10th	Day	14% 7% 3 5% 5% 3 4 5% 4 7% 42%	2160
	11th to 20th	Day	14% 5% 2 5% 5% 3 5% 5% 5% 7% 44%	2134
	21st to end	Day	17% 4 2 5% 5% 3 5% 6% 5% 8% 39%	2160
May	1st to 10th	Day	17% 7% 3 5% 6% 3 5% 5% 6% 7% 37%	2286
	11th to 20th	Day	19% 6% 3 6% 5% 4 5% 4 6% 8% 35%	2478
	21st to end	Day	14% 5% 2 4 5% 2 5% 5% 6% 8% 42%	2725
June	1st to 10th	Day	12% 5% 3 5% 5% 4 5% 6% 6% 10% 39%	2520
	11th to 20th	Day	12% 6% 3 6% 6% 3 5% 6% 7% 9% 37%	2520
	21st to end	Day	11% 5% 2 5% 5% 4 5% 6% 6% 10% 43%	2520
July	1st to 10th	Day	10% 4 3 5% 6% 4 6% 6% 8% 9% 40%	2520
	11th to 20th	Day	6% 3 2 5% 6% 4 6% 7% 8% 11% 43%	2520
	21st to end	Day	10% 6% 3 6% 7% 4 6% 6% 8% 9% 36%	2635
August	1st to 10th	Day	9% 6% 2 6% 6% 4 6% 6% 7% 9% 38%	2327
	11th to 20th	Day	10% 5% 2 5% 6% 4 6% 6% 7% 10% 39%	2155
	21st to end	Day	11% 6% 3 5% 4 3 5% 5% 7% 9% 41%	2376
September	1st to 10th	Day	15% 6% 2 5% 6% 3 4 5% 6% 6% 43%	2160
	11th to 20th	Day	13% 4 2 5% 4 2 4 4 4 7% 51%	2158
	21st to end	Day	17% 7% 3 6% 5% 3 3 5% 4 7% 39%	1939
October	1st to 10th	Day	17% 7% 2 5% 5% 2 4 5% 4 7% 43%	1800
	11th to 20th	Day	16% 6% 2 4 5% 2 4 4 4 6% 47%	1800
	21st to end	Day	18% 6% 2 5% 5% 2 4 4 4 5% 45%	1961
November	1st to 10th	Day	14% 6% 2 4 3 2 3 4 4 6% 52%	1671
	11th to 20th	Day	16% 5% 2 4 4 3 3 4 5% 7% 48%	1710
	21st to end	Day	15% 5% 3 5% 5% 2 5% 5% 5% 6% 46%	1558
December	1st to 10th	Day	19% 6% 3 5% 6% 3 4 4 6% 7% 39%	1520
	11th to 20th	Day	19% 7% 3 4 4 3 4 4 5% 6% 42%	1906
	21st to end	Day	16% 6% 3 6% 6% 4 5% 6% 6% 7% 35%	2772
January	1st to 10th	Night	17% 7% 2 4 5% 3 4 4 5% 6% 44%	4429
	11th to 20th	Night	19% 7% 3 4 4 2 4 3 4 5% 43%	4274
	21st to end	Night	22% 8% 2 6% 5% 3 4 4 4 5% 39%	4532
February	1st to 10th	Night	16% 8% 3 5% 5% 3 4 4 5% 6% 40%	2470
	11th to 20th	Night	18% 7% 3 5% 4 3 4 4 5% 5% 42%	2289
	21st to end	Night	18% 6% 2 5% 5% 3 4 5% 5% 7% 41%	1884
March	1st to 10th	Night	15% 4 2 4 5% 2 4 4 5% 8% 47%	2220
	11th to 20th	Night	16% 6% 3 5% 5% 2 4 4 4 6% 44%	2067
	21st to end	Night	17% 6% 3 5% 5% 3 5% 3 4 6% 43%	2080
April	1st to 10th	Night	16% 7% 2 7% 5% 2 4 4 5% 7% 41%	1800
	11th to 20th	Night	15% 5% 3 5% 4 4 3 4 6% 7% 44%	1775
	21st to end	Night	19% 6% 2 4 5% 2 5% 3 4 6% 43%	1800
May	1st to 10th	Night	17% 8% 3 6% 6% 3 4 4 5% 7% 37%	1684
	11th to 20th	Night	19% 7% 3 5% 4 4 4 7% 5% 7% 37%	1415
	21st to end	Night	16% 6% 2 6% 5% 3 3 4 6% 8% 40%	1550
June	1st to 10th	Night	13% 6% 2 4 5% 3 4 4 6% 8% 45%	1440
	11th to 20th	Night	11% 6% 3 6% 6% 3 6% 5% 6% 9% 39%	1440
	21st to end	Night	10% 4 2 5% 6% 3 5% 6% 6% 11% 42%	1440
July	1st to 10th	Night	10% 6% 3 6% 6% 4 6% 6% 7% 10% 37%	1440
	11th to 20th	Night	6% 5% 2 5% 5% 3 7% 7% 7% 10% 43%	1440
	21st to end	Night	10% 4 3 6% 6% 4 6% 5% 8% 9% 41%	1679
August	1st to 10th	Night	9% 4 2 6% 5% 4 6% 6% 8% 9% 42%	1611
	11th to 20th	Night	12% 6% 2 5% 7% 4 5% 5% 6% 9% 39%	1727
	21st to end	Night	13% 5% 2 4 5% 3 4 5% 5% 8% 45%	1980
September	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 5% 6% 46%	1800
	11th to 20th	Night	13% 5% 2 3 4 2 3 3 5% 7% 54%	1801
	21st to end	Night	17% 5% 2 5% 5% 2 4 5% 5% 7% 41%	2019
October	1st to 10th	Night	19% 6% 3 6% 5% 2 4 3 4 5% 43%	2160
	11th to 20th	Night	17% 4 2 4 4 2 4 4 5% 6% 49%	2160
	21st to end	Night	18% 5% 2 4 4 2 3 3 4 5% 48%	2394
November	1st to 10th	Night	11% 5% 2 5% 3 2 3 4 5% 6% 53%	2407
	11th to 20th	Night	16% 6% 2 5% 4 2 3 4 4 6% 47%	2470
	21st to end	Night	14% 4 1 5% 4 3 5% 5% 5% 7% 46%	2617
December	1st to 10th	Night	19% 7% 2 5% 5% 3 4 4 5% 6% 39%	2660
	11th to 20th	Night	18% 5% 2 5% 5% 3 5% 4 6% 7% 42%	3288
	21st to end	Night	16% 7% 3 5% 5% 3 5% 5% 6% 8% 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	39% 3 11% 27% 17% 2	1947
	11th to 20th	Day	42% 6% 9% 20% 17% 5%	2058
	21st to end	Day	47% 4 8% 20% 18% 4	2275
April	1st to 10th	Day	41% 5% 11% 20% 17% 6%	2160
	11th to 20th	Day	38% 6% 11% 22% 17% 5%	2134
	21st to end	Day	41% 6% 11% 19% 19% 4	2160
May	1st to 10th	Day	45% 6% 10% 20% 16% 4	2286
	11th to 20th	Day	45% 5% 13% 20% 13% 3	2482
	21st to end	Day	39% 7% 14% 23% 13% 2	2725
June	1st to 10th	Day	38% 7% 13% 25% 15% 2	2520
	11th to 20th	Day	41% 7% 13% 24% 13% 3	2520
	21st to end	Day	33% 9% 14% 24% 18% 1	2520
July	1st to 10th	Day	37% 9% 12% 24% 15% 3	2450
	11th to 20th	Day	31% 8% 15% 28% 15% 3	2445
	21st to end	Day	39% 9% 12% 23% 16% 2	2488
August	1st to 10th	Day	39% 8% 14% 24% 14% 1	2314
	11th to 20th	Day	35% 9% 14% 23% 16% 2	2155
	21st to end	Day	36% 7% 13% 24% 16% 4	2376
September	1st to 10th	Day	40% 5% 12% 21% 19% 4	2160
	11th to 20th	Day	33% 5% 9% 26% 23% 4	2158
	21st to end	Day	45% 5% 8% 19% 21% 2	1939
October	1st to 10th	Day	40% 6% 9% 24% 18% 2	1800
	11th to 20th	Day	37% 5% 11% 22% 23% 2	1800
	21st to end	Day	41% 4 7% 27% 18% 2	1961
November	1st to 10th	Day	34% 3 13% 25% 20% 4	1671
	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	37% 4 11% 26% 19% 3	2230
	11th to 20th	Night	41% 4 11% 24% 17% 4	2068
	21st to end	Night	44% 4 9% 19% 18% 6%	2080
April	1st to 10th	Night	43% 4 10% 19% 20% 5%	1800
	11th to 20th	Night	39% 5% 11% 21% 19% 5%	1775
	21st to end	Night	41% 5% 10% 20% 18% 6%	1800
May	1st to 10th	Night	46% 6% 10% 18% 17% 3	1684
	11th to 20th	Night	46% 7% 11% 16% 18% 3	1416
	21st to end	Night	41% 8% 16% 19% 13% 3	1551
June	1st to 10th	Night	38% 7% 11% 24% 18% 2	1440
	11th to 20th	Night	40% 7% 13% 22% 16% 2	1440
	21st to end	Night	34% 7% 14% 26% 16% 2	1440
July	1st to 10th	Night	42% 8% 15% 19% 13% 3	1400
	11th to 20th	Night	33% 8% 17% 25% 15% 3	1392
	21st to end	Night	35% 9% 16% 22% 17% 2	1586
August	1st to 10th	Night	35% 11% 15% 22% 16% 1	1600
	11th to 20th	Night	40% 8% 15% 19% 15% 2	1727
	21st to end	Night	36% 7% 14% 22% 17% 3	1980
September	1st to 10th	Night	39% 5% 11% 22% 19% 4	1800
	11th to 20th	Night	31% 5% 9% 24% 25% 5%	1801
	21st to end	Night	42% 5% 8% 22% 20% 3	2019
October	1st to 10th	Night	44% 4 10% 22% 17% 2	2160
	11th to 20th	Night	36% 4 10% 28% 18% 3	2160
	21st to end	Night	38% 5% 9% 27% 19% 3	2394
November	1st to 10th	Night	33% 5% 10% 27% 19% 6%	2407
	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% 26% 31% 10% 5% 1	449
	21st to end	Day	26% 24% 33% 12% 4 1	462
April	1st to 10th	Day	25% 24% 35% 10% 5% 1	420
	11th to 20th	Day	22% 23% 28% 19% 7% 2	412
	21st to end	Day	25% 21% 36% 12% 5%	420
May	1st to 10th	Day	31% 16% 29% 17% 6%	423
	11th to 20th	Day	20% 16% 34% 20% 8% 1	447
	21st to end	Day	20% 10% 25% 25% 17% 4	485
June	1st to 10th	Day	12% 12% 33% 25% 15% 3	450
	11th to 20th	Day	16% 11% 30% 27% 12% 4	450
	21st to end	Day	12% 9% 30% 32% 12% 5%	450
July	1st to 10th	Day	13% 5% 23% 30% 20% 9%	445
	11th to 20th	Day	6% 2 24% 38% 23% 6%	444
	21st to end	Day	12% 5% 24% 34% 21% 4	488
August	1st to 10th	Day	12% 3 21% 36% 20% 7%	446
	11th to 20th	Day	11% 4 18% 36% 21% 10%	439
	21st to end	Day	12% 5% 27% 29% 18% 10%	495
September	1st to 10th	Day	19% 8% 21% 25% 19% 9%	450
	11th to 20th	Day	14% 6% 26% 27% 17% 9%	450
	21st to end	Day	23% 10% 25% 28% 11% 2	450
October	1st to 10th	Day	22% 6% 28% 23% 15% 6%	450
	11th to 20th	Day	17% 16% 28% 24% 13% 1	450
	21st to end	Day	20% 15% 36% 19% 8% 2	485
November	1st to 10th	Day	15% 18% 33% 21% 11% 2	365
	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	752
	21st to end	Night	21% 14% 40% 19% 6%	792
April	1st to 10th	Night	22% 21% 34% 18% 5%	720
	11th to 20th	Night	18% 15% 34% 26% 7%	711
	21st to end	Night	24% 14% 31% 23% 7%	720
May	1st to 10th	Night	21% 11% 34% 28% 5% 1	604
	11th to 20th	Night	22% 10% 31% 27% 9%	354
	21st to end	Night	19% 6% 21% 38% 16% 1	389
June	1st to 10th	Night	16% 4 28% 34% 17%	360
	11th to 20th	Night	13% 5% 27% 42% 12% 1	360
	21st to end	Night	10% 3 26% 44% 16% 1	360
July	1st to 10th	Night	13% 4 22% 39% 20% 2	350
	11th to 20th	Night	6% 5% 16% 45% 27% 2	348
	21st to end	Night	10% 4 18% 41% 25% 2	499
August	1st to 10th	Night	10% 2 17% 43% 26% 3	537
	11th to 20th	Night	14% 3 15% 38% 26% 3	663
	21st to end	Night	14% 4 20% 36% 23% 4	792
September	1st to 10th	Night	17% 5% 21% 33% 20% 4	720
	11th to 20th	Night	13% 4 20% 35% 25% 4	720
	21st to end	Night	21% 5% 25% 29% 19% 2	720
October	1st to 10th	Night	23% 7% 24% 25% 17% 5%	720
	11th to 20th	Night	19% 10% 28% 32% 11%	720
	21st to end	Night	21% 14% 31% 23% 9% 1	792
November	1st to 10th	Night	14% 12% 35% 26% 11% 1	740
	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 2024-03-15 14:01:39. Version ac07

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