Eagle Plains
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Plains clear sky chart from 2005-11-06 to 2026-01-02.

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% 12% 5% 12% 7% 6% 6% 5% 6% 7% 24%	132821
	Night	6% 13% 6% 13% 7% 7% 6% 5% 8% 9% 19%	127630
Transparency	Day	56% 8% 15% 16% 5%	132401
	Night	56% 7% 11% 15% 9% 1	127629
Seeing	Day	16% 5% 17% 29% 23% 10%	20066
	Night	12% 3 14% 32% 30% 9%	24562

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	2 8% 5% 12% 6% 6% 6% 8% 16% 19% 12%	833
	11th to 20th	Day	2 13% 4 11% 6% 5% 7% 7% 10% 12% 24%	1350
	21st to end	Day	6% 14% 5% 12% 8% 6% 5% 6% 8% 10% 22%	2273
February	1st to 10th	Day	1 9% 4 12% 7% 9% 7% 8% 7% 13% 23%	1121
	11th to 20th	Day	2 8% 4 11% 8% 7% 8% 8% 10% 11% 22%	1369
	21st to end	Day	2 7% 5% 19% 10% 9% 7% 6% 6% 7% 21%	1370
March	1st to 10th	Day	1 7% 6% 18% 8% 7% 6% 5% 7% 8% 28%	4177
	11th to 20th	Day	1 9% 5% 15% 8% 7% 10% 9% 8% 7% 21%	4760
	21st to end	Day	1 11% 6% 17% 9% 7% 6% 5% 7% 8% 24%	5867
April	1st to 10th	Day	3 11% 5% 16% 11% 9% 6% 5% 6% 7% 21%	2623
	11th to 20th	Day	5% 15% 6% 12% 6% 5% 5% 4 7% 7% 28%	2774
	21st to end	Day	3 13% 5% 12% 6% 6% 5% 5% 7% 9% 30%	3155
May	1st to 10th	Day	9% 22% 7% 15% 7% 6% 5% 4 4 5% 17%	7552
	11th to 20th	Day	6% 14% 5% 13% 6% 6% 6% 4 5% 6% 28%	8107
	21st to end	Day	8% 16% 4 9% 6% 6% 5% 5% 6% 8% 26%	9748
June	1st to 10th	Day	13% 8% 3 8% 7% 6% 6% 5% 7% 8% 30%	4180
	11th to 20th	Day	13% 8% 3 8% 5% 4 5% 5% 7% 9% 33%	4560
	21st to end	Day	14% 7% 3 8% 6% 6% 7% 5% 7% 8% 28%	4610
July	1st to 10th	Day	21% 9% 3 9% 6% 5% 5% 5% 6% 8% 23%	9566
	11th to 20th	Day	14% 8% 3 9% 7% 7% 7% 6% 7% 10% 22%	8926
	21st to end	Day	14% 8% 3 9% 6% 7% 6% 5% 7% 8% 28%	9028
August	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	5463
	11th to 20th	Day	19% 11% 3 8% 6% 5% 6% 5% 6% 7% 22%	5030
	21st to end	Day	21% 17% 5% 11% 7% 6% 5% 4 5% 6% 12%	5130
September	1st to 10th	Day	18% 14% 4 8% 5% 5% 5% 5% 6% 7% 24%	2635
	11th to 20th	Day	21% 14% 4 9% 5% 5% 4 4 5% 6% 24%	2400
	21st to end	Day	19% 24% 5% 12% 6% 5% 4 3 4 5% 14%	2114
October	1st to 10th	Day	10% 16% 8% 13% 5% 4 4 3 4 6% 26%	3211
	11th to 20th	Day	8% 17% 8% 16% 8% 6% 5% 4 5% 6% 17%	2639
	21st to end	Day	7% 16% 8% 21% 8% 6% 6% 4 6% 5% 13%	2500
November	1st to 10th	Day	7% 21% 5% 15% 8% 7% 7% 4 7% 4 14%	1181
	11th to 20th	Day	6% 15% 6% 20% 12% 8% 6% 5% 7% 4 11%	887
	21st to end	Day	5% 14% 6% 19% 9% 6% 8% 6% 8% 7% 11%	632
December	1st to 10th	Day	6% 17% 7% 12% 5% 6% 4 4 13% 12% 14%	670
	11th to 20th	Day	6% 20% 7% 9% 8% 8% 9% 12% 10% 7% 5%	126
	21st to end	Day	5% 19% 3 10% 7% 7% 7% 4 6% 11% 20%	254
January	1st to 10th	Night	3 9% 5% 12% 7% 6% 7% 6% 14% 17% 16%	9154
	11th to 20th	Night	3 11% 5% 14% 7% 6% 6% 5% 9% 10% 26%	8567
	21st to end	Night	5% 14% 5% 12% 7% 7% 7% 6% 8% 9% 19%	8728
February	1st to 10th	Night	2 9% 5% 13% 10% 8% 8% 6% 8% 10% 22%	3276
	11th to 20th	Night	2 9% 4 13% 9% 7% 8% 5% 10% 11% 22%	2918
	21st to end	Night	2 10% 4 16% 11% 8% 6% 6% 7% 6% 24%	2260
March	1st to 10th	Night	1 9% 5% 16% 8% 8% 7% 7% 6% 8% 25%	5697
	11th to 20th	Night	2 8% 5% 16% 9% 9% 11% 8% 8% 7% 19%	5194
	21st to end	Night	1 8% 6% 18% 9% 7% 6% 6% 7% 9% 23%	5082
April	1st to 10th	Night	3 14% 6% 14% 9% 9% 5% 5% 7% 7% 21%	1777
	11th to 20th	Night	4 11% 6% 10% 8% 6% 6% 5% 6% 9% 29%	1573
	21st to end	Night	3 9% 5% 14% 7% 6% 5% 4 9% 10% 27%	1245
May	1st to 10th	Night	10% 22% 7% 12% 7% 6% 5% 4 4 4 19%	2408
	11th to 20th	Night	9% 13% 6% 10% 6% 5% 5% 4 7% 8% 28%	1788
	21st to end	Night	8% 11% 3 10% 6% 6% 7% 6% 10% 11% 24%	1144
June	1st to 10th	Night	12% 11% 2 6% 5% 7% 5% 4 5% 11% 33%	219
	July	1st to 10th	Night	29% 9% 4 7% 5% 2 3 4 6% 8% 24%	400
11th to 20th		Night	14% 10% 3 10% 7% 6% 6% 6% 6% 8% 25%	1052
21st to end		Night	15% 7% 3 8% 6% 6% 4 5% 7% 6% 34%	1821
August	1st to 10th	Night	16% 9% 3 8% 6% 5% 4 4 6% 6% 34%	1673
	11th to 20th	Night	14% 10% 4 10% 6% 6% 7% 6% 7% 9% 22%	2018
	21st to end	Night	21% 15% 5% 10% 6% 6% 6% 3 5% 7% 15%	2779
September	1st to 10th	Night	18% 10% 4 7% 6% 5% 6% 5% 7% 9% 24%	1764
	11th to 20th	Night	18% 14% 4 10% 6% 5% 6% 4 5% 6% 24%	2000
	21st to end	Night	19% 22% 5% 11% 6% 4 4 3 5% 6% 16%	2284
October	1st to 10th	Night	9% 18% 7% 14% 5% 4 4 4 5% 6% 22%	3979
	11th to 20th	Night	10% 18% 6% 13% 7% 5% 6% 6% 6% 6% 17%	4506
	21st to end	Night	6% 17% 10% 20% 8% 8% 5% 3 5% 5% 13%	5293
November	1st to 10th	Night	5% 19% 8% 14% 8% 8% 7% 4 5% 6% 15%	3316
	11th to 20th	Night	4 14% 7% 19% 12% 8% 7% 5% 6% 6% 14%	3730
	21st to end	Night	4 14% 6% 17% 9% 8% 7% 6% 8% 9% 13%	3985
December	1st to 10th	Night	6% 17% 6% 11% 6% 6% 7% 6% 11% 13% 11%	6740
	11th to 20th	Night	3 10% 4 11% 7% 7% 7% 8% 11% 17% 14%	8297
	21st to end	Night	3 16% 7% 13% 7% 6% 6% 5% 8% 10% 19%	10963

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	44% 10% 9% 13% 23%	833
	11th to 20th	Day	48% 8% 15% 16% 7% 6%	1359
	21st to end	Day	53% 5% 9% 15% 16% 1	2273
February	1st to 10th	Day	47% 8% 10% 20% 13% 2	1121
	11th to 20th	Day	48% 10% 13% 18% 9% 2	1376
	21st to end	Day	59% 9% 13% 9% 8% 1	1370
March	1st to 10th	Day	51% 6% 7% 23% 11% 4	4177
	11th to 20th	Day	58% 9% 7% 13% 12% 2	4760
	21st to end	Day	56% 7% 14% 13% 11%	5867
April	1st to 10th	Day	61% 8% 13% 11% 6% 1	2623
	11th to 20th	Day	54% 8% 16% 17% 6%	2774
	21st to end	Day	50% 8% 18% 18% 5%	3155
May	1st to 10th	Day	69% 7% 10% 11% 4	7552
	11th to 20th	Day	55% 8% 13% 20% 4	8111
	21st to end	Day	53% 8% 13% 20% 5%	9749
June	1st to 10th	Day	50% 8% 15% 21% 6%	4180
	11th to 20th	Day	46% 7% 16% 26% 4	4560
	21st to end	Day	51% 9% 18% 18% 4	4610
July	1st to 10th	Day	58% 9% 16% 15% 2	9463
	11th to 20th	Day	53% 11% 23% 12% 1	8815
	21st to end	Day	50% 10% 21% 17% 2	8775
August	1st to 10th	Day	50% 9% 15% 19% 8%	5442
	11th to 20th	Day	58% 10% 17% 15% 1	5078
	21st to end	Day	71% 8% 14% 7%	5129
September	1st to 10th	Day	60% 7% 20% 12% 1	2635
	11th to 20th	Day	61% 8% 17% 13% 2	2400
	21st to end	Day	74% 6% 11% 9% 1	2114
October	1st to 10th	Day	60% 5% 13% 17% 4	3211
	11th to 20th	Day	66% 7% 11% 12% 4	2639
	21st to end	Day	70% 6% 13% 10% 1	2500
November	1st to 10th	Day	70% 6% 12% 9% 2	1181
	11th to 20th	Day	72% 6% 9% 9% 4	887
	21st to end	Day	65% 8% 7% 15% 5%	632
December	1st to 10th	Day	56% 10% 9% 12% 13%	670
	11th to 20th	Day	63% 19% 8% 6% 5%	126
	21st to end	Day	58% 7% 5% 15% 10% 6%	254
January	1st to 10th	Night	46% 9% 7% 15% 23%	9154
	11th to 20th	Night	49% 6% 12% 16% 8% 8%	8620
	21st to end	Night	55% 6% 9% 12% 18% 1	8728
February	1st to 10th	Night	52% 7% 8% 18% 13% 2	3276
	11th to 20th	Night	50% 8% 10% 19% 12% 1	2922
	21st to end	Night	58% 6% 12% 11% 12% 1	2260
March	1st to 10th	Night	53% 5% 8% 22% 9% 3	5697
	11th to 20th	Night	60% 8% 6% 14% 10% 2	5196
	21st to end	Night	53% 8% 14% 14% 10% 1	5082
April	1st to 10th	Night	60% 9% 13% 12% 5% 2	1777
	11th to 20th	Night	53% 8% 13% 19% 8%	1573
	21st to end	Night	51% 9% 15% 20% 5% 1	1245
May	1st to 10th	Night	66% 9% 9% 14% 3	2405
	11th to 20th	Night	51% 10% 15% 20% 4	1788
	21st to end	Night	48% 12% 16% 19% 5%	1144
June	1st to 10th	Night	46% 10% 18% 23% 3	219
	July	1st to 10th	Night	57% 9% 16% 14% 3	394
11th to 20th		Night	55% 9% 22% 12% 2	1040
21st to end		Night	44% 10% 26% 18% 2	1769
August	1st to 10th	Night	49% 8% 19% 15% 8%	1669
	11th to 20th	Night	55% 9% 19% 15% 1	2036
	21st to end	Night	65% 10% 19% 6%	2779
September	1st to 10th	Night	56% 9% 23% 12% 1	1764
	11th to 20th	Night	62% 7% 16% 13% 2	2000
	21st to end	Night	70% 6% 12% 11% 1	2284
October	1st to 10th	Night	61% 8% 12% 17% 1	3979
	11th to 20th	Night	61% 8% 14% 14% 2	4506
	21st to end	Night	71% 6% 11% 11% 1	5293
November	1st to 10th	Night	68% 7% 12% 11% 2	3316
	11th to 20th	Night	68% 5% 11% 11% 4	3730
	21st to end	Night	62% 8% 8% 15% 6%	3985
December	1st to 10th	Night	59% 7% 11% 14% 9%	6740
	11th to 20th	Night	50% 8% 10% 17% 15%	8296
	21st to end	Night	57% 7% 8% 15% 13% 1	10963

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	7% 2 9% 42% 30% 11%	101
	11th to 20th	Day	7% 4 16% 39% 24% 10%	100
	21st to end	Day	5% 5% 17% 41% 23% 8%	110
February	1st to 10th	Day	2 2 9% 45% 27% 14%	163
	11th to 20th	Day	5% 3 11% 38% 30% 13%	395
	21st to end	Day	5% 4 17% 31% 26% 16%	331
March	1st to 10th	Day	4 3 13% 33% 28% 19%	400
	11th to 20th	Day	5% 5% 19% 31% 27% 14%	400
	21st to end	Day	4 6% 18% 26% 29% 16%	526
April	1st to 10th	Day	7% 5% 18% 34% 26% 10%	660
	11th to 20th	Day	8% 6% 20% 30% 25% 12%	690
	21st to end	Day	7% 5% 18% 34% 25% 11%	700
May	1st to 10th	Day	14% 6% 23% 31% 20% 7%	753
	11th to 20th	Day	13% 5% 19% 29% 25% 9%	922
	21st to end	Day	16% 7% 17% 33% 22% 5%	1199
June	1st to 10th	Day	17% 7% 21% 32% 19% 5%	1130
	11th to 20th	Day	15% 5% 17% 30% 25% 8%	1210
	21st to end	Day	17% 3 14% 29% 26% 11%	1235
July	1st to 10th	Day	19% 6% 16% 26% 26% 8%	1111
	11th to 20th	Day	20% 4 15% 24% 25% 11%	1106
	21st to end	Day	20% 5% 15% 23% 26% 11%	1084
August	1st to 10th	Day	23% 7% 11% 28% 20% 12%	745
	11th to 20th	Day	27% 6% 18% 26% 16% 7%	715
	21st to end	Day	29% 7% 22% 24% 14% 4	803
September	1st to 10th	Day	24% 8% 19% 21% 18% 11%	680
	11th to 20th	Day	28% 4 16% 26% 19% 6%	530
	21st to end	Day	29% 8% 17% 19% 18% 8%	450
October	1st to 10th	Day	21% 7% 23% 28% 14% 7%	420
	11th to 20th	Day	19% 5% 16% 25% 21% 13%	420
	21st to end	Day	17% 4 14% 27% 25% 13%	317
November	1st to 10th	Day	10% 5% 12% 30% 28% 15%	220
	11th to 20th	Day	8% 4 10% 21% 35% 22%	135
	21st to end	Day	9% 1 18% 27% 29% 15%	110
December	1st to 10th	Day	12% 5% 16% 35% 22% 10%	110
	11th to 20th	Day	15% 8% 15% 23% 31% 8%	26
	21st to end	Day	7% 5% 15% 29% 29% 15%	59
January	1st to 10th	Night	10% 3 10% 32% 32% 13%	1208
	11th to 20th	Night	9% 4 15% 35% 28% 10%	1193
	21st to end	Night	9% 4 15% 35% 29% 8%	1105
February	1st to 10th	Night	6% 2 10% 38% 33% 13%	900
	11th to 20th	Night	6% 2 13% 37% 33% 10%	884
	21st to end	Night	6% 5% 15% 35% 30% 9%	743
March	1st to 10th	Night	5% 2 13% 39% 30% 10%	870
	11th to 20th	Night	6% 2 11% 34% 39% 8%	699
	21st to end	Night	4 3 14% 37% 31% 12%	660
April	1st to 10th	Night	10% 3 15% 30% 33% 9%	600
	11th to 20th	Night	9% 2 14% 34% 34% 7%	593
	21st to end	Night	7% 3 16% 38% 31% 6%	445
May	1st to 10th	Night	12% 5% 17% 36% 28% 2	320
	11th to 20th	Night	12% 4 14% 29% 38% 4	197
	21st to end	Night	12% 6% 15% 36% 31% 1	217
June	1st to 10th	Night	15% 5% 19% 36% 25%	135
	July	1st to 10th	Night	16% 5% 16% 30% 30% 4	135
11th to 20th		Night	19% 3 13% 36% 29% 2	194
21st to end		Night	18% 4 13% 27% 34% 4	219
August	1st to 10th	Night	21% 2 15% 35% 26% 1	241
	11th to 20th	Night	23% 5% 14% 28% 28% 2	446
	21st to end	Night	26% 5% 15% 24% 23% 7%	660
September	1st to 10th	Night	22% 6% 15% 25% 26% 7%	600
	11th to 20th	Night	25% 4 16% 31% 20% 4	600
	21st to end	Night	28% 3 17% 25% 22% 5%	743
October	1st to 10th	Night	24% 5% 18% 28% 20% 5%	800
	11th to 20th	Night	23% 3 14% 23% 28% 9%	897
	21st to end	Night	17% 4 14% 27% 27% 11%	1001
November	1st to 10th	Night	11% 3 14% 28% 33% 10%	964
	11th to 20th	Night	9% 3 11% 27% 32% 18%	1160
	21st to end	Night	8% 3 12% 31% 29% 18%	1196
December	1st to 10th	Night	10% 4 17% 38% 23% 7%	1270
	11th to 20th	Night	8% 2 14% 32% 35% 9%	1270
	21st to end	Night	6% 4 12% 31% 33% 13%	1397

Page generated at 2025-12-29 22:14:10. Version ac07

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