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 2025-03-12.

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	11% 10% 4 9% 6% 5% 5% 4 6% 7% 32%	112027
	Night	9% 12% 4 10% 6% 6% 5% 4 6% 7% 31%	115596
Transparency	Day	49% 6% 16% 21% 8% 1	111763
	Night	52% 5% 14% 20% 8% 1	115506
Seeing	Day	16% 12% 29% 26% 13% 4	16461
	Night	14% 10% 29% 31% 13% 1	25059

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	3 14% 5% 12% 9% 6% 8% 5% 6% 7% 25%	2719
	11th to 20th	Day	5% 8% 4 11% 7% 6% 6% 5% 9% 8% 31%	3028
	21st to end	Day	7% 11% 5% 9% 5% 5% 5% 4 7% 7% 35%	4004
February	1st to 10th	Day	7% 13% 4 12% 7% 6% 7% 5% 8% 8% 23%	1600
	11th to 20th	Day	6% 12% 5% 12% 7% 6% 6% 5% 7% 7% 29%	1595
	21st to end	Day	3 13% 4 14% 8% 5% 7% 5% 7% 7% 27%	1650
March	1st to 10th	Day	3 9% 6% 14% 8% 7% 5% 4 6% 9% 29%	3238
	11th to 20th	Day	7% 11% 3 7% 5% 4 5% 3 7% 8% 41%	3314
	21st to end	Day	7% 15% 7% 17% 6% 5% 5% 4 6% 7% 23%	4072
April	1st to 10th	Day	7% 13% 5% 11% 8% 6% 6% 5% 6% 9% 24%	2283
	11th to 20th	Day	11% 16% 4 9% 6% 4 5% 5% 7% 6% 27%	2440
	21st to end	Day	10% 14% 3 10% 7% 5% 5% 4 6% 7% 28%	2566
May	1st to 10th	Day	14% 12% 4 8% 6% 6% 5% 4 6% 6% 28%	4481
	11th to 20th	Day	14% 11% 4 9% 7% 6% 6% 5% 6% 7% 26%	4694
	21st to end	Day	16% 9% 3 10% 8% 6% 6% 4 6% 7% 23%	5161
June	1st to 10th	Day	19% 8% 2 9% 5% 4 6% 5% 7% 7% 28%	3008
	11th to 20th	Day	20% 9% 4 9% 7% 6% 6% 5% 6% 7% 21%	3040
	21st to end	Day	13% 7% 2 9% 6% 6% 6% 5% 8% 9% 29%	3040
July	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 8% 41%	5060
	11th to 20th	Day	8% 4 2 6% 5% 5% 6% 5% 6% 8% 44%	4966
	21st to end	Day	12% 5% 2 6% 5% 5% 6% 5% 8% 9% 38%	5028
August	1st to 10th	Day	16% 5% 2 6% 4 4 4 4 5% 6% 44%	4401
	11th to 20th	Day	11% 7% 3 7% 4 5% 5% 5% 6% 8% 40%	4313
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 6% 7% 38%	4521
September	1st to 10th	Day	13% 7% 2 7% 4 5% 5% 4 6% 7% 39%	2299
	11th to 20th	Day	14% 8% 2 5% 5% 3 4 4 6% 9% 41%	2171
	21st to end	Day	10% 9% 3 8% 5% 5% 5% 4 6% 8% 37%	2090
October	1st to 10th	Day	9% 11% 3 8% 5% 4 4 4 5% 7% 41%	3289
	11th to 20th	Day	11% 12% 4 8% 6% 5% 5% 3 6% 8% 32%	2842
	21st to end	Day	8% 12% 5% 9% 5% 6% 5% 3 5% 7% 36%	3101
November	1st to 10th	Day	10% 17% 5% 10% 6% 5% 4 5% 7% 7% 24%	1570
	11th to 20th	Day	6% 14% 5% 11% 6% 5% 6% 3 6% 6% 31%	1400
	21st to end	Day	7% 16% 6% 13% 7% 6% 5% 4 5% 7% 25%	1400
December	1st to 10th	Day	10% 15% 5% 11% 6% 6% 7% 5% 6% 8% 22%	2290
	11th to 20th	Day	10% 12% 3 11% 8% 7% 6% 5% 6% 8% 24%	2361
	21st to end	Day	3 10% 4 10% 6% 5% 5% 4 7% 7% 40%	2992
January	1st to 10th	Night	5% 14% 6% 16% 9% 6% 5% 3 5% 5% 25%	7226
	11th to 20th	Night	4 11% 5% 12% 6% 6% 6% 5% 7% 7% 32%	6895
	21st to end	Night	7% 14% 5% 9% 6% 5% 5% 4 6% 7% 33%	6955
February	1st to 10th	Night	6% 15% 5% 12% 8% 6% 6% 4 7% 7% 24%	2800
	11th to 20th	Night	5% 14% 5% 11% 8% 7% 7% 4 6% 7% 28%	2688
	21st to end	Night	4 13% 5% 13% 8% 5% 6% 4 6% 6% 30%	1980
March	1st to 10th	Night	3 9% 5% 14% 9% 8% 6% 5% 6% 8% 26%	3856
	11th to 20th	Night	5% 11% 3 7% 5% 5% 5% 5% 8% 8% 37%	3693
	21st to end	Night	7% 16% 7% 15% 5% 5% 5% 4 5% 7% 25%	3566
April	1st to 10th	Night	6% 13% 4 10% 9% 7% 6% 6% 7% 7% 25%	1897
	11th to 20th	Night	11% 14% 5% 10% 5% 5% 5% 4 7% 7% 27%	1691
	21st to end	Night	12% 12% 3 9% 5% 5% 5% 4 7% 9% 30%	1610
May	1st to 10th	Night	16% 14% 4 11% 6% 4 5% 4 5% 6% 26%	2478
	11th to 20th	Night	11% 11% 4 10% 6% 6% 6% 5% 7% 7% 27%	2199
	21st to end	Night	20% 10% 3 8% 4 5% 5% 4 6% 9% 26%	2414
June	1st to 10th	Night	18% 11% 3 8% 5% 4 5% 4 5% 6% 31%	1169
	11th to 20th	Night	21% 7% 3 9% 7% 6% 5% 4 7% 7% 23%	1140
	21st to end	Night	14% 8% 3 8% 6% 5% 5% 6% 8% 8% 28%	1140
July	1st to 10th	Night	14% 7% 3 7% 4 4 4 3 7% 6% 42%	1900
	11th to 20th	Night	9% 5% 3 7% 6% 6% 8% 6% 8% 9% 35%	1991
	21st to end	Night	12% 6% 3 8% 5% 5% 5% 4 7% 8% 38%	2521
August	1st to 10th	Night	16% 6% 3 5% 5% 4 4 4 6% 7% 42%	2529
	11th to 20th	Night	16% 8% 3 7% 5% 5% 5% 4 8% 8% 33%	2515
	21st to end	Night	14% 6% 2 7% 4 6% 5% 4 6% 8% 38%	3146
September	1st to 10th	Night	12% 7% 3 6% 4 6% 5% 4 5% 8% 40%	1878
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 5% 7% 41%	2009
	21st to end	Night	12% 8% 3 6% 4 4 5% 5% 7% 8% 39%	2090
October	1st to 10th	Night	12% 11% 3 9% 6% 6% 6% 3 6% 7% 31%	3686
	11th to 20th	Night	10% 10% 3 8% 5% 5% 6% 4 6% 7% 34%	4086
	21st to end	Night	8% 10% 4 10% 5% 5% 6% 4 7% 9% 32%	4457
November	1st to 10th	Night	12% 17% 6% 9% 6% 4 4 4 6% 6% 27%	2708
	11th to 20th	Night	7% 14% 6% 12% 6% 6% 5% 4 5% 6% 28%	3000
	21st to end	Night	7% 14% 5% 12% 7% 6% 6% 4 6% 7% 26%	3000
December	1st to 10th	Night	9% 16% 5% 11% 7% 6% 5% 4 5% 6% 27%	4890
	11th to 20th	Night	10% 17% 5% 12% 8% 7% 6% 4 5% 6% 20%	5829
	21st to end	Night	3 10% 4 11% 6% 7% 6% 4 6% 6% 36%	7964

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	57% 4 13% 15% 9% 2	2719
	11th to 20th	Day	49% 3 10% 17% 18% 3	3049
	21st to end	Day	48% 5% 20% 19% 7%	4004
February	1st to 10th	Day	56% 6% 13% 13% 11% 1	1600
	11th to 20th	Day	53% 6% 12% 18% 10%	1603
	21st to end	Day	54% 6% 11% 18% 9% 1	1650
March	1st to 10th	Day	51% 5% 17% 18% 10%	3238
	11th to 20th	Day	38% 8% 16% 22% 16% 1	3315
	21st to end	Day	60% 6% 15% 15% 5%	4072
April	1st to 10th	Day	55% 7% 14% 17% 6% 1	2283
	11th to 20th	Day	55% 6% 11% 19% 9% 1	2440
	21st to end	Day	52% 7% 12% 20% 7% 1	2566
May	1st to 10th	Day	55% 5% 10% 19% 10% 1	4481
	11th to 20th	Day	54% 8% 12% 18% 8%	4698
	21st to end	Day	57% 8% 14% 13% 8% 1	5162
June	1st to 10th	Day	51% 8% 16% 18% 7% 1	3008
	11th to 20th	Day	60% 8% 14% 14% 5%	3040
	21st to end	Day	48% 8% 18% 18% 8%	3040
July	1st to 10th	Day	39% 4 12% 25% 14% 5%	4981
	11th to 20th	Day	36% 5% 16% 32% 10% 1	4879
	21st to end	Day	40% 6% 22% 22% 10% 1	4869
August	1st to 10th	Day	41% 5% 17% 34% 3	4384
	11th to 20th	Day	41% 5% 20% 25% 10%	4355
	21st to end	Day	44% 5% 24% 22% 5%	4520
September	1st to 10th	Day	43% 6% 19% 24% 7% 1	2299
	11th to 20th	Day	41% 5% 19% 27% 8%	2171
	21st to end	Day	45% 6% 15% 21% 11% 2	2090
October	1st to 10th	Day	44% 3 24% 23% 5%	3289
	11th to 20th	Day	51% 4 14% 24% 7%	2842
	21st to end	Day	50% 3 15% 26% 5%	3101
November	1st to 10th	Day	57% 6% 15% 17% 6% 1	1570
	11th to 20th	Day	52% 6% 15% 17% 10% 1	1400
	21st to end	Day	57% 7% 15% 13% 6% 2	1400
December	1st to 10th	Day	61% 4 17% 11% 5% 1	2290
	11th to 20th	Day	58% 4 18% 15% 6%	2363
	21st to end	Day	43% 5% 9% 27% 15% 2	2992
January	1st to 10th	Night	61% 4 10% 17% 8% 1	7226
	11th to 20th	Night	51% 4 11% 16% 15% 2	6936
	21st to end	Night	51% 5% 19% 18% 7%	6955
February	1st to 10th	Night	59% 5% 10% 15% 9% 2	2800
	11th to 20th	Night	55% 6% 12% 17% 9% 1	2690
	21st to end	Night	52% 5% 10% 21% 11% 1	1980
March	1st to 10th	Night	52% 7% 14% 19% 8%	3856
	11th to 20th	Night	39% 7% 19% 21% 13%	3693
	21st to end	Night	57% 6% 12% 19% 6%	3566
April	1st to 10th	Night	54% 8% 13% 16% 8% 1	1897
	11th to 20th	Night	53% 7% 11% 19% 9% 2	1691
	21st to end	Night	49% 7% 15% 20% 7% 1	1610
May	1st to 10th	Night	57% 6% 9% 20% 8%	2478
	11th to 20th	Night	50% 10% 13% 20% 7%	2199
	21st to end	Night	53% 8% 17% 15% 7% 1	2414
June	1st to 10th	Night	52% 7% 13% 20% 8% 1	1169
	11th to 20th	Night	58% 7% 15% 17% 3	1140
	21st to end	Night	49% 9% 17% 17% 6% 1	1140
July	1st to 10th	Night	44% 4 14% 22% 15% 1	1870
	11th to 20th	Night	44% 6% 17% 25% 8%	1955
	21st to end	Night	42% 6% 21% 22% 8% 1	2441
August	1st to 10th	Night	42% 5% 19% 31% 3	2521
	11th to 20th	Night	47% 6% 18% 19% 11%	2539
	21st to end	Night	44% 5% 25% 23% 4	3146
September	1st to 10th	Night	41% 7% 19% 24% 8% 2	1878
	11th to 20th	Night	42% 6% 17% 26% 8% 2	2009
	21st to end	Night	40% 6% 16% 25% 11% 1	2090
October	1st to 10th	Night	53% 3 18% 19% 6%	3686
	11th to 20th	Night	49% 3 15% 24% 8%	4086
	21st to end	Night	49% 4 17% 23% 7%	4457
November	1st to 10th	Night	56% 6% 12% 20% 6%	2708
	11th to 20th	Night	55% 6% 12% 17% 8% 1	3000
	21st to end	Night	57% 5% 14% 16% 7% 2	3000
December	1st to 10th	Night	60% 3 13% 16% 6% 1	4890
	11th to 20th	Night	65% 4 13% 13% 4	5826
	21st to end	Night	47% 4 11% 26% 11% 1	7964

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% 29% 15% 6%	200
	11th to 20th	Day	14% 11% 31% 28% 16% 1	200
	21st to end	Day	15% 16% 33% 25% 8% 3	220
February	1st to 10th	Day	16% 13% 33% 26% 11% 2	200
	11th to 20th	Day	14% 11% 35% 30% 10% 1	220
	21st to end	Day	8% 16% 36% 26% 12% 2	414
March	1st to 10th	Day	11% 16% 31% 28% 11% 2	500
	11th to 20th	Day	13% 15% 34% 23% 12% 3	465
	21st to end	Day	18% 16% 30% 23% 12% 1	506
April	1st to 10th	Day	16% 21% 32% 23% 7% 2	460
	11th to 20th	Day	18% 16% 25% 21% 15% 3	452
	21st to end	Day	18% 16% 32% 23% 9% 2	460
May	1st to 10th	Day	19% 16% 28% 24% 10% 2	498
	11th to 20th	Day	16% 11% 26% 26% 18% 3	675
	21st to end	Day	20% 8% 27% 26% 15% 4	734
June	1st to 10th	Day	18% 15% 31% 24% 9% 2	838
	11th to 20th	Day	23% 9% 26% 26% 13% 3	870
	21st to end	Day	16% 9% 26% 27% 16% 6%	870
July	1st to 10th	Day	16% 7% 27% 30% 16% 4	856
	11th to 20th	Day	13% 9% 27% 29% 17% 4	797
	21st to end	Day	13% 8% 22% 33% 19% 6%	678
August	1st to 10th	Day	15% 7% 26% 26% 19% 7%	487
	11th to 20th	Day	11% 9% 27% 35% 13% 4	477
	21st to end	Day	18% 11% 27% 25% 15% 5%	539
September	1st to 10th	Day	19% 9% 28% 24% 15% 4	490
	11th to 20th	Day	18% 9% 27% 29% 13% 3	490
	21st to end	Day	18% 16% 31% 20% 11% 3	490
October	1st to 10th	Day	18% 12% 26% 24% 15% 5%	468
	11th to 20th	Day	18% 13% 29% 27% 9% 4	300
	21st to end	Day	15% 16% 35% 21% 10% 3	330
November	1st to 10th	Day	20% 11% 26% 32% 9% 3	257
	11th to 20th	Day	12% 14% 41% 26% 7% 2	200
	21st to end	Day	11% 16% 35% 27% 7% 5%	200
December	1st to 10th	Day	15% 9% 32% 33% 10% 3	200
	11th to 20th	Day	14% 15% 33% 26% 11% 2	200
	21st to end	Day	11% 7% 30% 30% 17% 5%	220
January	1st to 10th	Night	13% 11% 33% 31% 10% 2	1100
	11th to 20th	Night	14% 14% 33% 28% 10% 1	1033
	21st to end	Night	17% 16% 31% 27% 8%	883
February	1st to 10th	Night	14% 16% 25% 28% 15% 2	800
	11th to 20th	Night	10% 11% 35% 33% 10% 1	784
	21st to end	Night	8% 13% 31% 31% 14% 3	660
March	1st to 10th	Night	12% 10% 33% 30% 13% 2	800
	11th to 20th	Night	9% 10% 35% 33% 12% 2	766
	21st to end	Night	14% 10% 28% 32% 14% 2	836
April	1st to 10th	Night	12% 13% 32% 31% 11% 1	757
	11th to 20th	Night	17% 9% 33% 30% 11% 1	563
	21st to end	Night	17% 11% 30% 30% 10% 1	470
May	1st to 10th	Night	22% 10% 24% 30% 12% 2	380
	11th to 20th	Night	15% 8% 26% 34% 17% 1	374
	21st to end	Night	20% 8% 22% 30% 18% 1	411
June	1st to 10th	Night	24% 8% 27% 25% 15% 1	380
	11th to 20th	Night	22% 4 21% 34% 17% 2	380
	21st to end	Night	19% 6% 23% 32% 18% 3	380
July	1st to 10th	Night	19% 4 16% 41% 20% 1	370
	11th to 20th	Night	14% 5% 24% 33% 23% 1	368
	21st to end	Night	14% 4 19% 36% 24% 3	416
August	1st to 10th	Night	15% 4 18% 28% 32% 4	378
	11th to 20th	Night	12% 5% 18% 39% 25% 2	381
	21st to end	Night	14% 6% 22% 39% 18% 1	627
September	1st to 10th	Night	14% 6% 21% 39% 18% 2	738
	11th to 20th	Night	17% 5% 20% 36% 20% 2	760
	21st to end	Night	13% 8% 31% 31% 14% 2	760
October	1st to 10th	Night	19% 8% 27% 32% 13% 1	760
	11th to 20th	Night	13% 11% 29% 32% 14% 1	760
	21st to end	Night	16% 12% 31% 32% 8% 1	836
November	1st to 10th	Night	21% 10% 28% 29% 11% 1	868
	11th to 20th	Night	13% 14% 37% 27% 8% 1	1000
	21st to end	Night	13% 13% 37% 27% 9% 2	1000
December	1st to 10th	Night	14% 13% 35% 27% 10% 1	1000
	11th to 20th	Night	12% 13% 29% 33% 10% 2	1070
	21st to end	Night	10% 11% 34% 31% 12% 2	1210

Page generated at 2025-03-09 06:08:43. Version ac07

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