Edson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edson clear sky chart from 2005-11-06 to 2026-07-16.

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	10% 10% 4 9% 6% 5% 6% 4 6% 8% 32%	142330
	Night	9% 12% 4 10% 6% 6% 5% 4 6% 7% 31%	139039
Transparency	Day	49% 4 15% 21% 9% 1	142022
	Night	52% 4 14% 20% 9% 1	138930
Seeing	Day	16% 12% 29% 27% 13% 4	18425
	Night	14% 10% 29% 31% 13% 1	26690

By Month

Percentage Cloud Cover NW (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	5% 15% 5% 12% 8% 6% 7% 5% 6% 7% 24%	3527
	11th to 20th	Day	4 7% 4 10% 6% 5% 6% 5% 8% 8% 38%	3960
	21st to end	Day	8% 12% 5% 9% 5% 5% 5% 4 7% 7% 32%	5186
February	1st to 10th	Day	7% 13% 4 11% 7% 7% 7% 5% 8% 8% 23%	1680
	11th to 20th	Day	5% 12% 5% 12% 7% 6% 6% 5% 7% 6% 28%	1677
	21st to end	Day	3 14% 4 14% 8% 5% 7% 5% 6% 7% 26%	1730
March	1st to 10th	Day	3 9% 5% 12% 8% 7% 6% 4 7% 9% 30%	4618
	11th to 20th	Day	7% 14% 4 9% 5% 4 5% 3 6% 8% 36%	4839
	21st to end	Day	10% 16% 6% 15% 6% 5% 5% 4 5% 6% 22%	5966
April	1st to 10th	Day	8% 13% 5% 11% 7% 6% 6% 5% 6% 9% 24%	2523
	11th to 20th	Day	10% 16% 4 9% 6% 4 5% 5% 7% 7% 27%	2700
	21st to end	Day	10% 14% 3 9% 7% 5% 5% 4 7% 7% 29%	2836
May	1st to 10th	Day	9% 10% 4 9% 6% 5% 5% 4 6% 8% 33%	8310
	11th to 20th	Day	12% 10% 4 10% 6% 6% 6% 5% 7% 8% 25%	8755
	21st to end	Day	12% 8% 3 9% 7% 6% 6% 4 7% 9% 28%	9649
June	1st to 10th	Day	19% 9% 3 8% 5% 5% 6% 5% 7% 7% 28%	3325
	11th to 20th	Day	20% 9% 4 9% 7% 6% 6% 5% 6% 7% 21%	3360
	21st to end	Day	13% 7% 3 9% 6% 6% 6% 5% 8% 9% 29%	3360
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 5% 8% 10% 39%	7400
	11th to 20th	Day	11% 5% 3 7% 6% 6% 6% 5% 6% 8% 38%	7185
	21st to end	Day	12% 6% 2 7% 5% 5% 6% 5% 7% 9% 36%	7224
August	1st to 10th	Day	16% 5% 2 6% 4 4 4 4 5% 7% 43%	4541
	11th to 20th	Day	12% 7% 3 7% 4 5% 5% 5% 6% 8% 39%	4453
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 6% 7% 39%	4664
September	1st to 10th	Day	13% 7% 2 7% 4 5% 5% 4 6% 7% 40%	2420
	11th to 20th	Day	14% 8% 2 5% 4 3 4 4 5% 9% 42%	2285
	21st to end	Day	11% 9% 3 8% 5% 5% 5% 3 6% 8% 37%	2200
October	1st to 10th	Day	9% 11% 3 9% 5% 4 4 4 5% 7% 41%	3393
	11th to 20th	Day	11% 12% 4 8% 6% 5% 5% 3 6% 8% 32%	2932
	21st to end	Day	8% 11% 5% 9% 5% 6% 5% 3 5% 7% 36%	3200
November	1st to 10th	Day	9% 16% 5% 10% 7% 5% 4 5% 7% 8% 25%	1650
	11th to 20th	Day	6% 14% 5% 11% 6% 5% 6% 3 6% 6% 31%	1470
	21st to end	Day	7% 15% 6% 13% 6% 6% 5% 4 6% 7% 25%	1470
December	1st to 10th	Day	10% 15% 5% 11% 6% 6% 7% 5% 6% 8% 22%	2360
	11th to 20th	Day	10% 13% 4 11% 8% 7% 6% 5% 6% 7% 23%	2424
	21st to end	Day	4 10% 4 10% 6% 5% 5% 4 7% 6% 40%	3058
January	1st to 10th	Night	6% 16% 6% 15% 8% 6% 6% 3 5% 5% 23%	9366
	11th to 20th	Night	3 10% 5% 10% 5% 6% 6% 5% 7% 7% 36%	8977
	21st to end	Night	7% 13% 5% 10% 6% 6% 5% 4 6% 8% 30%	8997
February	1st to 10th	Night	6% 15% 5% 12% 7% 6% 6% 4 7% 6% 25%	2940
	11th to 20th	Night	5% 14% 5% 11% 8% 7% 7% 4 5% 7% 28%	2825
	21st to end	Night	3 13% 5% 13% 8% 6% 6% 4 6% 6% 29%	2076
March	1st to 10th	Night	3 9% 5% 12% 8% 7% 6% 5% 7% 9% 30%	5496
	11th to 20th	Night	4 14% 5% 10% 7% 6% 6% 5% 8% 7% 28%	5380
	21st to end	Night	12% 16% 6% 14% 5% 4 5% 3 4 6% 24%	5236
April	1st to 10th	Night	5% 14% 4 10% 9% 7% 6% 6% 7% 7% 26%	2097
	11th to 20th	Night	10% 14% 5% 10% 6% 5% 5% 4 7% 7% 27%	1871
	21st to end	Night	11% 12% 3 9% 5% 5% 5% 4 7% 9% 31%	1780
May	1st to 10th	Night	13% 11% 3 8% 5% 4 4 4 6% 8% 33%	4608
	11th to 20th	Night	11% 11% 5% 11% 7% 6% 5% 5% 7% 7% 25%	4105
	21st to end	Night	13% 8% 2 8% 5% 5% 5% 4 6% 9% 35%	4522
June	1st to 10th	Night	19% 11% 3 8% 5% 4 5% 4 5% 6% 30%	1292
	11th to 20th	Night	21% 8% 3 9% 7% 7% 5% 3 7% 7% 22%	1260
	21st to end	Night	15% 8% 3 8% 6% 5% 5% 6% 8% 8% 28%	1260
July	1st to 10th	Night	12% 7% 2 7% 5% 4 4 4 7% 8% 38%	2780
	11th to 20th	Night	13% 6% 3 8% 5% 5% 7% 5% 8% 9% 30%	2883
	21st to end	Night	13% 7% 3 7% 5% 4 4 4 6% 8% 38%	3616
August	1st to 10th	Night	16% 6% 3 5% 4 4 4 4 6% 7% 41%	2609
	11th to 20th	Night	16% 8% 3 7% 5% 5% 5% 4 8% 8% 33%	2595
	21st to end	Night	13% 6% 2 7% 4 5% 4 4 6% 8% 39%	3245
September	1st to 10th	Night	12% 7% 3 6% 4 5% 5% 4 6% 8% 41%	1977
	11th to 20th	Night	14% 7% 3 7% 4 4 4 3 5% 8% 42%	2115
	21st to end	Night	12% 7% 3 6% 4 4 5% 5% 7% 8% 39%	2200
October	1st to 10th	Night	12% 10% 3 9% 6% 6% 6% 3 6% 7% 31%	3802
	11th to 20th	Night	10% 10% 3 8% 5% 5% 6% 4 6% 7% 34%	4216
	21st to end	Night	8% 10% 4 10% 5% 5% 6% 4 7% 9% 33%	4600
November	1st to 10th	Night	11% 17% 5% 9% 6% 4 4 4 5% 6% 28%	2847
	11th to 20th	Night	7% 14% 5% 12% 6% 6% 5% 4 5% 6% 29%	3150
	21st to end	Night	7% 14% 5% 12% 7% 6% 6% 4 6% 6% 26%	3150
December	1st to 10th	Night	9% 17% 5% 11% 7% 6% 5% 4 5% 6% 26%	5040
	11th to 20th	Night	10% 17% 5% 12% 8% 7% 6% 4 5% 6% 19%	5986
	21st to end	Night	3 10% 4 11% 7% 7% 6% 4 6% 6% 36%	8140

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	59% 3 11% 13% 13% 1	3527
	11th to 20th	Day	43% 2 14% 20% 18% 3	3981
	21st to end	Day	51% 4 18% 21% 6%	5187
February	1st to 10th	Day	56% 5% 13% 14% 11% 1	1680
	11th to 20th	Day	53% 6% 12% 18% 10%	1685
	21st to end	Day	55% 6% 11% 18% 9% 1	1730
March	1st to 10th	Day	50% 3 15% 16% 15% 1	4618
	11th to 20th	Day	45% 6% 12% 22% 16% 1	4840
	21st to end	Day	63% 4 11% 14% 8%	5966
April	1st to 10th	Day	55% 7% 14% 17% 6% 1	2523
	11th to 20th	Day	54% 5% 11% 19% 9%	2700
	21st to end	Day	52% 7% 12% 21% 8% 1	2836
May	1st to 10th	Day	49% 3 10% 23% 13% 1	8310
	11th to 20th	Day	54% 4 12% 21% 8% 1	8759
	21st to end	Day	51% 5% 16% 21% 7% 1	9650
June	1st to 10th	Day	51% 7% 15% 18% 8% 1	3325
	11th to 20th	Day	61% 7% 14% 14% 4	3360
	21st to end	Day	49% 7% 17% 19% 7%	3360
July	1st to 10th	Day	39% 3 17% 25% 11% 4	7321
	11th to 20th	Day	44% 4 15% 29% 8% 1	7098
	21st to end	Day	42% 4 22% 24% 8%	7020
August	1st to 10th	Day	42% 5% 17% 33% 2	4524
	11th to 20th	Day	42% 4 20% 25% 10%	4495
	21st to end	Day	43% 5% 23% 24% 5%	4663
September	1st to 10th	Day	41% 6% 19% 26% 6% 1	2420
	11th to 20th	Day	39% 5% 19% 28% 8%	2285
	21st to end	Day	45% 6% 15% 21% 11% 2	2200
October	1st to 10th	Day	44% 3 23% 24% 5%	3393
	11th to 20th	Day	51% 4 13% 24% 7%	2932
	21st to end	Day	49% 3 15% 26% 6%	3200
November	1st to 10th	Day	56% 5% 15% 17% 6% 1	1650
	11th to 20th	Day	51% 6% 15% 17% 10% 1	1470
	21st to end	Day	56% 6% 15% 14% 7% 2	1470
December	1st to 10th	Day	62% 4 17% 11% 5% 1	2360
	11th to 20th	Day	58% 4 17% 15% 6%	2426
	21st to end	Day	43% 5% 9% 27% 15% 2	3058
January	1st to 10th	Night	64% 3 9% 14% 10% 1	9367
	11th to 20th	Night	47% 3 14% 18% 15% 2	9018
	21st to end	Night	52% 4 20% 17% 6%	8997
February	1st to 10th	Night	58% 5% 10% 15% 10% 2	2940
	11th to 20th	Night	55% 6% 11% 17% 10% 1	2827
	21st to end	Night	54% 5% 9% 21% 10% 1	2076
March	1st to 10th	Night	49% 5% 16% 20% 11%	5496
	11th to 20th	Night	51% 5% 13% 19% 11%	5380
	21st to end	Night	60% 4 8% 18% 9%	5236
April	1st to 10th	Night	54% 7% 13% 16% 8% 1	2097
	11th to 20th	Night	53% 6% 11% 19% 9% 1	1871
	21st to end	Night	49% 6% 14% 22% 8% 1	1780
May	1st to 10th	Night	49% 3 9% 28% 10% 1	4605
	11th to 20th	Night	56% 5% 12% 20% 7%	4105
	21st to end	Night	45% 4 19% 25% 6% 1	4526
June	1st to 10th	Night	52% 6% 13% 20% 9% 1	1292
	11th to 20th	Night	60% 7% 15% 16% 3	1260
	21st to end	Night	49% 8% 17% 19% 6% 1	1260
July	1st to 10th	Night	45% 3 19% 19% 14% 1	2750
	11th to 20th	Night	49% 4 17% 23% 7%	2847
	21st to end	Night	42% 4 25% 23% 6% 1	3515
August	1st to 10th	Night	43% 5% 19% 30% 2	2601
	11th to 20th	Night	47% 5% 18% 19% 10%	2619
	21st to end	Night	43% 5% 24% 24% 5%	3245
September	1st to 10th	Night	39% 6% 19% 25% 7% 2	1977
	11th to 20th	Night	41% 5% 17% 27% 8% 2	2115
	21st to end	Night	40% 6% 17% 25% 10% 2	2200
October	1st to 10th	Night	53% 3 18% 20% 6%	3802
	11th to 20th	Night	49% 3 15% 24% 9%	4216
	21st to end	Night	49% 4 17% 23% 7%	4600
November	1st to 10th	Night	56% 5% 11% 20% 7% 1	2847
	11th to 20th	Night	55% 6% 13% 17% 9% 1	3150
	21st to end	Night	57% 5% 13% 16% 7% 2	3150
December	1st to 10th	Night	61% 3 13% 16% 6% 1	5040
	11th to 20th	Night	66% 4 13% 14% 4	5983
	21st to end	Night	47% 4 11% 26% 11% 1	8140

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	10% 10% 32% 30% 13% 5%	220
	11th to 20th	Day	14% 12% 32% 27% 14% 1	220
	21st to end	Day	15% 17% 32% 26% 7% 3	242
February	1st to 10th	Day	15% 12% 35% 26% 10% 1	220
	11th to 20th	Day	14% 10% 34% 30% 11% 1	242
	21st to end	Day	9% 16% 36% 26% 12% 2	446
March	1st to 10th	Day	12% 16% 32% 27% 11% 2	540
	11th to 20th	Day	13% 15% 34% 24% 11% 3	540
	21st to end	Day	18% 15% 31% 23% 12% 2	594
April	1st to 10th	Day	16% 19% 31% 24% 8% 2	540
	11th to 20th	Day	19% 16% 25% 21% 15% 3	532
	21st to end	Day	18% 16% 31% 22% 11% 2	540
May	1st to 10th	Day	18% 17% 28% 24% 11% 2	582
	11th to 20th	Day	16% 11% 26% 27% 17% 3	775
	21st to end	Day	19% 8% 27% 27% 15% 4	844
June	1st to 10th	Day	19% 15% 30% 24% 9% 2	955
	11th to 20th	Day	23% 10% 24% 26% 13% 3	990
	21st to end	Day	16% 8% 25% 27% 17% 7%	990
July	1st to 10th	Day	15% 7% 27% 31% 17% 4	976
	11th to 20th	Day	15% 8% 27% 29% 16% 4	885
	21st to end	Day	14% 8% 21% 32% 19% 6%	730
August	1st to 10th	Day	15% 7% 25% 26% 20% 7%	527
	11th to 20th	Day	12% 9% 27% 34% 13% 4	517
	21st to end	Day	17% 10% 26% 24% 16% 7%	583
September	1st to 10th	Day	18% 8% 27% 24% 17% 5%	530
	11th to 20th	Day	18% 8% 25% 30% 15% 5%	530
	21st to end	Day	19% 15% 32% 21% 11% 2	530
October	1st to 10th	Day	18% 12% 26% 25% 15% 5%	507
	11th to 20th	Day	18% 12% 31% 27% 8% 3	330
	21st to end	Day	15% 15% 37% 21% 9% 3	363
November	1st to 10th	Day	18% 11% 28% 32% 8% 2	283
	11th to 20th	Day	11% 13% 40% 26% 7% 2	220
	21st to end	Day	11% 15% 33% 27% 8% 6%	220
December	1st to 10th	Day	15% 9% 34% 31% 9% 2	220
	11th to 20th	Day	13% 15% 35% 26% 10% 2	220
	21st to end	Day	14% 7% 30% 29% 16% 5%	242
January	1st to 10th	Night	14% 11% 34% 30% 10% 2	1160
	11th to 20th	Night	13% 14% 35% 27% 10% 1	1086
	21st to end	Night	17% 16% 31% 28% 8%	927
February	1st to 10th	Night	14% 15% 25% 29% 14% 2	840
	11th to 20th	Night	10% 11% 35% 33% 10% 1	824
	21st to end	Night	9% 13% 32% 30% 13% 3	692
March	1st to 10th	Night	12% 9% 34% 30% 13% 2	840
	11th to 20th	Night	10% 9% 34% 34% 11% 2	840
	21st to end	Night	15% 10% 28% 32% 13% 2	924
April	1st to 10th	Night	13% 12% 32% 32% 11% 1	837
	11th to 20th	Night	17% 9% 33% 30% 10% 1	623
	21st to end	Night	16% 11% 30% 32% 10% 1	520
May	1st to 10th	Night	20% 9% 27% 30% 12% 1	420
	11th to 20th	Night	14% 8% 25% 35% 17%	414
	21st to end	Night	19% 7% 22% 31% 19% 1	455
June	1st to 10th	Night	25% 9% 26% 26% 14% 1	420
	11th to 20th	Night	22% 5% 21% 33% 17% 2	420
	21st to end	Night	19% 5% 21% 34% 19% 2	420
July	1st to 10th	Night	18% 4 16% 42% 20% 1	410
	11th to 20th	Night	15% 5% 25% 32% 22% 1	398
	21st to end	Night	14% 4 18% 36% 25% 3	438
August	1st to 10th	Night	15% 4 17% 27% 32% 4	398
	11th to 20th	Night	12% 5% 18% 39% 24% 1	401
	21st to end	Night	13% 6% 21% 39% 20% 1	660
September	1st to 10th	Night	14% 6% 20% 39% 20% 2	777
	11th to 20th	Night	16% 5% 19% 36% 22% 2	800
	21st to end	Night	13% 8% 32% 31% 14% 2	800
October	1st to 10th	Night	18% 8% 28% 33% 13% 1	800
	11th to 20th	Night	13% 11% 29% 33% 14% 1	800
	21st to end	Night	16% 11% 33% 31% 8% 1	880
November	1st to 10th	Night	21% 10% 29% 29% 10% 1	913
	11th to 20th	Night	13% 13% 37% 27% 8% 1	1050
	21st to end	Night	13% 12% 36% 27% 9% 2	1050
December	1st to 10th	Night	14% 13% 35% 27% 10% 1	1050
	11th to 20th	Night	12% 13% 29% 34% 10% 2	1127
	21st to end	Night	11% 11% 34% 31% 12% 1	1276

Page generated at 2026-07-13 01:14:54. Version ac07

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