Edmonds Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edmonds Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	18% 8% 3 6% 4 4 4 3 5% 7% 39%	101201
	Night	18% 9% 3 6% 4 4 4 3 5% 6% 38%	97957
Transparency	Day	25% 47% 7% 12% 8% 1	104768
	Night	25% 47% 6% 12% 8% 1	102467
Seeing	Day	20% 15% 32% 22% 9% 2	15205
	Night	21% 14% 31% 25% 8% 1	24072

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	16% 9% 3 5% 3 3 3 3 5% 6% 45%	2517
	11th to 20th	Day	20% 9% 2 5% 3 3 4 3 5% 4 40%	2520
	21st to end	Day	20% 13% 4 7% 4 4 4 3 4 5% 33%	2800
February	1st to 10th	Day	19% 9% 3 7% 4 4 4 4 5% 6% 36%	1814
	11th to 20th	Day	15% 7% 3 6% 4 4 4 4 5% 6% 43%	1848
	21st to end	Day	20% 9% 3 6% 4 3 4 4 4 5% 38%	1570
March	1st to 10th	Day	25% 16% 3 7% 3 3 2 2 3 4 31%	3116
	11th to 20th	Day	11% 6% 3 6% 4 4 4 3 6% 8% 45%	3379
	21st to end	Day	23% 10% 3 7% 4 4 4 3 3 5% 35%	3960
April	1st to 10th	Day	20% 10% 3 5% 3 3 4 3 4 6% 39%	2280
	11th to 20th	Day	18% 8% 3 6% 4 4 4 3 5% 6% 40%	2282
	21st to end	Day	21% 7% 3 5% 3 4 4 3 5% 7% 38%	2470
May	1st to 10th	Day	27% 12% 4 7% 4 3 3 3 4 6% 27%	4106
	11th to 20th	Day	23% 11% 3 6% 4 3 4 3 4 7% 31%	4081
	21st to end	Day	16% 6% 2 5% 4 4 4 3 6% 8% 42%	4764
June	1st to 10th	Day	20% 6% 2 5% 5% 4 4 4 6% 8% 35%	2660
	11th to 20th	Day	17% 6% 2 5% 5% 4 5% 4 6% 8% 39%	2660
	21st to end	Day	15% 7% 3 5% 4 4 4 4 6% 8% 39%	2660
July	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 5% 6% 8% 36%	4440
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 4 6% 10% 37%	4440
	21st to end	Day	19% 8% 3 7% 4 4 4 5% 6% 8% 34%	4752
August	1st to 10th	Day	17% 7% 3 8% 5% 4 5% 4 6% 8% 33%	4105
	11th to 20th	Day	13% 6% 3 6% 5% 5% 5% 5% 7% 8% 39%	4023
	21st to end	Day	8% 4 2 5% 4 4 4 4 6% 9% 49%	4180
September	1st to 10th	Day	14% 7% 2 5% 4 4 4 3 4 6% 47%	2247
	11th to 20th	Day	14% 6% 2 6% 3 3 3 2 5% 7% 50%	2090
	21st to end	Day	21% 6% 2 5% 3 4 3 3 5% 5% 42%	2090
October	1st to 10th	Day	22% 5% 2 5% 3 3 3 3 5% 6% 42%	2090
	11th to 20th	Day	16% 5% 2 4 3 3 3 3 4 8% 48%	1887
	21st to end	Day	18% 6% 1 6% 4 3 3 3 5% 5% 45%	1881
November	1st to 10th	Day	17% 7% 2 5% 4 3 3 3 4 6% 45%	1752
	11th to 20th	Day	17% 7% 2 5% 4 3 3 3 5% 7% 44%	1710
	21st to end	Day	17% 7% 2 5% 4 4 4 3 5% 5% 44%	1710
December	1st to 10th	Day	20% 8% 2 6% 4 4 4 3 4 6% 40%	1639
	11th to 20th	Day	21% 7% 2 7% 3 3 3 3 3 5% 43%	1906
	21st to end	Day	21% 11% 3 8% 4 4 3 3 5% 5% 34%	2772
January	1st to 10th	Night	17% 8% 2 5% 3 3 3 3 4 5% 48%	4429
	11th to 20th	Night	16% 11% 4 7% 4 3 3 2 4 5% 40%	4440
	21st to end	Night	23% 12% 4 9% 5% 4 4 3 4 4 29%	4853
February	1st to 10th	Night	17% 9% 3 8% 5% 4 3 3 5% 5% 40%	2362
	11th to 20th	Night	18% 9% 3 6% 4 4 4 3 4 5% 40%	2218
	21st to end	Night	17% 9% 2 7% 5% 4 3 3 4 5% 42%	1884
March	1st to 10th	Night	30% 12% 2 4 3 3 2 3 4 5% 32%	3724
	11th to 20th	Night	11% 9% 4 7% 5% 5% 4 4 6% 6% 40%	3580
	21st to end	Night	24% 10% 2 7% 5% 4 5% 3 4 4 32%	3668
April	1st to 10th	Night	18% 9% 3 7% 5% 5% 4 3 4 5% 38%	1900
	11th to 20th	Night	19% 9% 2 5% 4 4 4 3 5% 6% 38%	1847
	21st to end	Night	20% 7% 2 6% 5% 3 4 2 5% 7% 37%	1710
May	1st to 10th	Night	25% 11% 4 9% 5% 4 4 4 5% 6% 24%	2834
	11th to 20th	Night	24% 12% 3 8% 5% 4 5% 4 6% 6% 24%	2813
	21st to end	Night	17% 8% 3 7% 5% 4 5% 5% 6% 8% 33%	2837
June	1st to 10th	Night	17% 8% 3 7% 6% 4 4 3 5% 8% 34%	1520
	11th to 20th	Night	18% 8% 2 6% 4 4 5% 3 4 7% 39%	1520
	21st to end	Night	18% 8% 3 5% 4 3 4 4 7% 9% 35%	1520
July	1st to 10th	Night	19% 13% 3 6% 4 4 4 3 6% 8% 31%	2520
	11th to 20th	Night	19% 7% 2 5% 4 4 5% 4 7% 8% 34%	2520
	21st to end	Night	18% 9% 3 8% 5% 5% 5% 4 5% 7% 31%	2768
August	1st to 10th	Night	24% 7% 3 7% 4 5% 5% 4 6% 7% 29%	2825
	11th to 20th	Night	10% 8% 3 7% 5% 6% 5% 5% 7% 8% 37%	2800
	21st to end	Night	9% 4 2 5% 4 3 3 4 6% 7% 54%	3476
September	1st to 10th	Night	14% 6% 3 6% 5% 4 4 3 5% 6% 45%	1933
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 5% 6% 50%	2090
	21st to end	Night	20% 6% 3 5% 4 4 4 4 5% 5% 40%	2090
October	1st to 10th	Night	21% 7% 2 6% 3 4 4 3 4 6% 39%	2090
	11th to 20th	Night	15% 5% 2 5% 4 3 4 3 5% 6% 48%	2289
	21st to end	Night	19% 8% 3 6% 3 4 4 4 4 6% 40%	2717
November	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 6% 6% 45%	2531
	11th to 20th	Night	17% 8% 2 5% 4 3 4 3 4 5% 44%	2470
	21st to end	Night	16% 5% 2 5% 4 3 4 4 4 7% 45%	2470
December	1st to 10th	Night	21% 8% 2 7% 4 4 3 3 4 5% 39%	2537
	11th to 20th	Night	19% 8% 2 5% 4 4 4 3 4 6% 41%	3288
	21st to end	Night	19% 12% 4 7% 3 3 4 3 4 5% 36%	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	26% 37% 6% 19% 11% 2	2518
	11th to 20th	Day	28% 39% 6% 18% 8% 2	2520
	21st to end	Day	40% 40% 5% 11% 4 1	2800
February	1st to 10th	Day	19% 66% 5% 6% 4 1	1814
	11th to 20th	Day	17% 64% 2 8% 7% 1	1857
	21st to end	Day	17% 65% 5% 8% 4 2	1570
March	1st to 10th	Day	42% 40% 7% 5% 5% 1	3119
	11th to 20th	Day	16% 43% 12% 18% 10% 1	3379
	21st to end	Day	36% 41% 3 8% 7% 5%	3960
April	1st to 10th	Day	19% 65% 3 6% 6% 1	2280
	11th to 20th	Day	14% 66% 4 9% 7%	2282
	21st to end	Day	17% 66% 3 6% 6% 1	2470
May	1st to 10th	Day	38% 44% 8% 6% 4	4120
	11th to 20th	Day	36% 41% 11% 9% 3	4085
	21st to end	Day	24% 43% 7% 13% 13%	4764
June	1st to 10th	Day	16% 66% 4 8% 6%	2660
	11th to 20th	Day	15% 65% 5% 9% 6% 1	2660
	21st to end	Day	14% 64% 5% 10% 7%	2660
July	1st to 10th	Day	34% 39% 7% 10% 10% 1	4370
	11th to 20th	Day	28% 38% 11% 14% 8%	4365
	21st to end	Day	35% 37% 8% 11% 8% 1	4601
August	1st to 10th	Day	34% 39% 11% 12% 4	4092
	11th to 20th	Day	26% 40% 12% 19% 3	4062
	21st to end	Day	15% 39% 11% 22% 12%	4180
September	1st to 10th	Day	15% 60% 4 13% 7%	2247
	11th to 20th	Day	15% 61% 5% 10% 9% 2	2090
	21st to end	Day	21% 60% 3 8% 7%	2090
October	1st to 10th	Day	23% 38% 7% 19% 10% 3	3480
	11th to 20th	Day	17% 37% 3 19% 20% 3	3103
	21st to end	Day	16% 37% 10% 24% 12% 1	3081
November	1st to 10th	Day	19% 57% 6% 9% 8% 1	1752
	11th to 20th	Day	17% 60% 4 8% 9% 2	1710
	21st to end	Day	15% 59% 5% 13% 6% 2	1710
December	1st to 10th	Day	21% 60% 5% 6% 8%	1639
	11th to 20th	Day	23% 49% 7% 8% 10% 4	1906
	21st to end	Day	34% 37% 9% 13% 6%	2772
January	1st to 10th	Night	24% 36% 6% 23% 8% 3	4429
	11th to 20th	Night	29% 37% 7% 16% 9% 2	4440
	21st to end	Night	42% 41% 3 8% 5% 1	4853
February	1st to 10th	Night	18% 65% 5% 7% 4 1	2362
	11th to 20th	Night	17% 64% 2 6% 10% 2	2220
	21st to end	Night	16% 65% 4 7% 6% 2	1884
March	1st to 10th	Night	40% 41% 5% 8% 5% 2	3734
	11th to 20th	Night	22% 44% 9% 12% 12% 1	3581
	21st to end	Night	38% 41% 3 4 10% 4	3668
April	1st to 10th	Night	20% 65% 3 6% 5% 1	1900
	11th to 20th	Night	15% 66% 4 6% 7% 1	1847
	21st to end	Night	18% 65% 3 7% 6% 1	1710
May	1st to 10th	Night	38% 43% 9% 7% 2	2840
	11th to 20th	Night	40% 43% 8% 7% 2	2814
	21st to end	Night	27% 45% 9% 13% 7%	2838
June	1st to 10th	Night	16% 65% 4 9% 6%	1520
	11th to 20th	Night	14% 65% 4 11% 6% 1	1520
	21st to end	Night	15% 65% 4 10% 7% 1	1520
July	1st to 10th	Night	38% 36% 4 9% 12%	2480
	11th to 20th	Night	30% 39% 10% 14% 6%	2472
	21st to end	Night	36% 36% 9% 9% 8% 1	2680
August	1st to 10th	Night	38% 40% 7% 9% 5% 1	2813
	11th to 20th	Night	26% 41% 10% 19% 4	2827
	21st to end	Night	13% 39% 12% 20% 16%	3476
September	1st to 10th	Night	15% 61% 5% 11% 7% 1	1933
	11th to 20th	Night	17% 60% 3 9% 10% 1	2090
	21st to end	Night	21% 61% 4 8% 6% 1	2090
October	1st to 10th	Night	26% 38% 7% 19% 9% 2	3480
	11th to 20th	Night	11% 37% 4 17% 28% 3	3799
	21st to end	Night	17% 37% 7% 21% 17% 1	4467
November	1st to 10th	Night	19% 57% 5% 9% 8% 1	2531
	11th to 20th	Night	17% 59% 4 8% 9% 3	2470
	21st to end	Night	15% 60% 5% 13% 5% 2	2470
December	1st to 10th	Night	21% 60% 5% 7% 6%	2537
	11th to 20th	Night	22% 49% 7% 9% 11% 2	3288
	21st to end	Night	34% 38% 7% 15% 5%	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% 24% 32% 18% 3	180
	11th to 20th	Day	23% 28% 35% 10% 4	180
	21st to end	Day	19% 23% 39% 13% 6% 1	213
February	1st to 10th	Day	25% 21% 36% 16% 2	419
	11th to 20th	Day	24% 26% 38% 12% 1	456
	21st to end	Day	24% 24% 35% 14% 4	382
March	1st to 10th	Day	25% 21% 33% 17% 3	460
	11th to 20th	Day	19% 28% 32% 17% 3	460
	21st to end	Day	22% 23% 34% 15% 5% 2	506
April	1st to 10th	Day	25% 20% 35% 15% 4 1	460
	11th to 20th	Day	24% 20% 36% 17% 3	452
	21st to end	Day	25% 16% 34% 18% 6% 2	460
May	1st to 10th	Day	30% 17% 31% 17% 5%	463
	11th to 20th	Day	22% 12% 41% 17% 6% 1	487
	21st to end	Day	21% 10% 31% 28% 9% 2	529
June	1st to 10th	Day	19% 10% 31% 29% 10% 1	490
	11th to 20th	Day	16% 9% 37% 29% 9% 1	490
	21st to end	Day	14% 10% 35% 29% 10% 1	490
July	1st to 10th	Day	16% 7% 27% 33% 16% 2	485
	11th to 20th	Day	11% 6% 29% 33% 17% 4	484
	21st to end	Day	15% 6% 33% 32% 13% 2	532
August	1st to 10th	Day	12% 7% 30% 35% 14% 2	486
	11th to 20th	Day	14% 8% 24% 33% 17% 4	479
	21st to end	Day	14% 5% 28% 31% 15% 6%	539
September	1st to 10th	Day	18% 6% 28% 28% 15% 5%	490
	11th to 20th	Day	16% 9% 29% 24% 15% 7%	490
	21st to end	Day	25% 10% 29% 23% 9% 4	490
October	1st to 10th	Day	23% 11% 26% 23% 12% 5%	490
	11th to 20th	Day	18% 12% 35% 20% 12% 2	425
	21st to end	Day	23% 16% 29% 21% 9% 3	429
November	1st to 10th	Day	15% 16% 36% 21% 10% 2	392
	11th to 20th	Day	22% 22% 31% 19% 5%	370
	21st to end	Day	20% 24% 29% 18% 8% 1	370
December	1st to 10th	Day	21% 17% 38% 19% 4	299
	11th to 20th	Day	26% 28% 32% 11% 3	180
	21st to end	Day	26% 19% 38% 9% 5% 2	198
January	1st to 10th	Night	22% 18% 39% 17% 4	760
	11th to 20th	Night	28% 20% 35% 15% 2	760
	21st to end	Night	21% 22% 35% 18% 4	836
February	1st to 10th	Night	22% 18% 37% 22% 2	760
	11th to 20th	Night	24% 21% 40% 14% 1	743
	21st to end	Night	22% 23% 34% 18% 3	628
March	1st to 10th	Night	23% 17% 37% 20% 4	760
	11th to 20th	Night	21% 16% 39% 20% 4	760
	21st to end	Night	23% 17% 33% 21% 6%	836
April	1st to 10th	Night	22% 15% 34% 24% 4	760
	11th to 20th	Night	22% 16% 35% 23% 4	723
	21st to end	Night	22% 14% 32% 25% 6%	570
May	1st to 10th	Night	28% 12% 30% 24% 7%	570
	11th to 20th	Night	23% 12% 38% 22% 4 1	562
	21st to end	Night	23% 7% 23% 38% 9% 1	471
June	1st to 10th	Night	22% 5% 28% 32% 12%	380
	11th to 20th	Night	22% 5% 23% 39% 10% 1	380
	21st to end	Night	23% 5% 22% 40% 10%	380
July	1st to 10th	Night	19% 6% 24% 36% 14% 1	370
	11th to 20th	Night	16% 4 22% 41% 16% 1	368
	21st to end	Night	17% 4 23% 43% 12% 1	433
August	1st to 10th	Night	13% 5% 24% 45% 13% 1	568
	11th to 20th	Night	13% 5% 22% 43% 16% 1	567
	21st to end	Night	16% 4 19% 37% 20% 3	836
September	1st to 10th	Night	17% 3 26% 34% 18% 2	760
	11th to 20th	Night	18% 5% 25% 27% 20% 4	760
	21st to end	Night	24% 6% 23% 30% 14% 2	760
October	1st to 10th	Night	25% 10% 22% 27% 14% 3	760
	11th to 20th	Night	18% 14% 30% 25% 12% 2	760
	21st to end	Night	23% 14% 32% 21% 9%	836
November	1st to 10th	Night	20% 12% 32% 25% 11% 1	779
	11th to 20th	Night	20% 22% 31% 19% 7% 1	760
	21st to end	Night	17% 22% 33% 21% 6% 1	760
December	1st to 10th	Night	25% 19% 34% 17% 5% 1	760
	11th to 20th	Night	24% 23% 32% 17% 3 1	760
	21st to end	Night	25% 19% 38% 16% 3	836

Page generated at 2024-11-07 06:55:48. Version ac07

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