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 2024-11-12.

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% 12% 5% 12% 7% 6% 6% 5% 6% 7% 23%	107938
	Night	6% 13% 6% 14% 8% 7% 6% 5% 7% 8% 20%	100143
Transparency	Day	57% 8% 15% 15% 4	107572
	Night	58% 8% 11% 14% 8% 1	100157
Seeing	Day	16% 5% 17% 29% 23% 9%	18636
	Night	12% 3 14% 32% 29% 10%	22911

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% 4 13% 7% 7% 6% 8% 14% 18% 14%	575
	11th to 20th	Day	2 15% 5% 15% 6% 6% 6% 5% 11% 10% 18%	927
	21st to end	Day	4 13% 5% 11% 8% 6% 5% 7% 8% 13% 22%	1581
February	1st to 10th	Day	1 8% 4 12% 8% 9% 8% 8% 8% 13% 22%	1064
	11th to 20th	Day	2 8% 4 11% 8% 7% 8% 8% 10% 10% 22%	1298
	21st to end	Day	2 7% 4 18% 10% 9% 7% 6% 6% 7% 21%	1303
March	1st to 10th	Day	1 9% 8% 24% 10% 7% 6% 4 7% 7% 18%	2905
	11th to 20th	Day	2 13% 7% 22% 10% 7% 8% 6% 6% 5% 15%	3325
	21st to end	Day	2 12% 6% 14% 7% 6% 6% 6% 7% 8% 26%	4091
April	1st to 10th	Day	3 11% 5% 17% 11% 9% 6% 5% 5% 7% 21%	2492
	11th to 20th	Day	4 14% 6% 13% 6% 6% 5% 4 7% 7% 28%	2633
	21st to end	Day	3 12% 5% 12% 6% 6% 5% 5% 7% 9% 31%	2997
May	1st to 10th	Day	7% 18% 6% 15% 8% 6% 5% 4 5% 6% 21%	5274
	11th to 20th	Day	6% 11% 4 11% 6% 7% 7% 5% 6% 6% 30%	5647
	21st to end	Day	9% 14% 4 8% 6% 5% 5% 4 6% 8% 30%	6790
June	1st to 10th	Day	13% 8% 3 8% 7% 5% 6% 5% 7% 8% 31%	3971
	11th to 20th	Day	14% 8% 3 8% 5% 4 6% 5% 7% 9% 31%	4332
	21st to end	Day	15% 8% 3 8% 6% 6% 7% 6% 7% 8% 27%	4380
July	1st to 10th	Day	24% 10% 4 11% 7% 6% 6% 5% 6% 6% 16%	6680
	11th to 20th	Day	18% 9% 3 9% 7% 6% 7% 5% 7% 8% 21%	6228
	21st to end	Day	15% 9% 3 9% 6% 6% 6% 5% 7% 8% 27%	6289
August	1st to 10th	Day	17% 9% 3 7% 5% 5% 5% 4 5% 7% 33%	5294
	11th to 20th	Day	19% 11% 3 8% 6% 6% 6% 5% 6% 7% 22%	4873
	21st to end	Day	22% 17% 5% 11% 7% 6% 5% 4 5% 6% 12%	4973
September	1st to 10th	Day	18% 14% 4 8% 5% 5% 5% 5% 6% 7% 24%	2504
	11th to 20th	Day	20% 14% 3 9% 5% 5% 4 4 5% 6% 25%	2280
	21st to end	Day	19% 23% 5% 12% 6% 4 4 3 4 4 14%	2008
October	1st to 10th	Day	10% 16% 8% 14% 5% 4 4 3 4 6% 27%	3113
	11th to 20th	Day	8% 17% 8% 16% 8% 6% 5% 4 5% 6% 17%	2558
	21st to end	Day	6% 16% 8% 21% 8% 6% 6% 4 6% 5% 13%	2422
November	1st to 10th	Day	6% 21% 4 15% 9% 7% 7% 4 7% 4 15%	1124
	11th to 20th	Day	6% 15% 6% 19% 12% 8% 6% 5% 7% 4 12%	808
	21st to end	Day	6% 14% 5% 17% 10% 7% 9% 7% 9% 6% 11%	574
December	1st to 10th	Day	4 14% 7% 17% 8% 7% 6% 4 8% 5% 18%	380
	11th to 20th	Day	7% 17% 9% 14% 11% 11% 5% 2 7% 11% 5%	81
	21st to end	Day	8% 20% 2 9% 5% 7% 6% 2 9% 11% 20%	164
January	1st to 10th	Night	3 9% 5% 12% 8% 7% 7% 7% 12% 16% 15%	6379
	11th to 20th	Night	3 13% 7% 17% 8% 6% 5% 4 7% 9% 23%	5981
	21st to end	Night	5% 13% 5% 12% 7% 7% 7% 7% 8% 10% 19%	6106
February	1st to 10th	Night	2 9% 4 13% 10% 8% 8% 6% 9% 10% 21%	3113
	11th to 20th	Night	2 9% 4 14% 9% 7% 8% 5% 10% 11% 22%	2769
	21st to end	Night	2 9% 4 16% 11% 8% 6% 6% 7% 6% 25%	2151
March	1st to 10th	Night	1 11% 7% 20% 9% 7% 7% 6% 6% 6% 20%	3959
	11th to 20th	Night	3 10% 7% 20% 10% 9% 9% 6% 5% 5% 16%	3624
	21st to end	Night	2 10% 6% 13% 7% 6% 6% 6% 9% 8% 27%	3549
April	1st to 10th	Night	3 14% 5% 14% 10% 9% 5% 5% 7% 7% 21%	1688
	11th to 20th	Night	4 11% 5% 9% 8% 6% 6% 5% 7% 9% 30%	1494
	21st to end	Night	3 9% 5% 14% 7% 6% 5% 4 9% 10% 28%	1183
May	1st to 10th	Night	8% 18% 8% 13% 8% 6% 4 4 4 4 22%	1686
	11th to 20th	Night	7% 10% 3 11% 6% 6% 6% 5% 8% 9% 29%	1248
	21st to end	Night	10% 11% 3 8% 5% 5% 7% 5% 9% 9% 29%	792
June	1st to 10th	Night	13% 11% 2 6% 5% 7% 4 4 5% 11% 34%	208
	July	1st to 10th	Night	24% 11% 5% 9% 7% 3 4 3 7% 9% 18%	276
11th to 20th		Night	17% 9% 3 8% 7% 4 6% 6% 6% 7% 27%	740
21st to end		Night	16% 7% 3 8% 6% 6% 4 5% 7% 6% 32%	1266
August	1st to 10th	Night	16% 9% 3 8% 6% 5% 4 4 6% 6% 34%	1622
	11th to 20th	Night	14% 10% 4 10% 6% 6% 7% 6% 7% 9% 22%	1955
	21st to end	Night	21% 15% 5% 10% 6% 6% 6% 4 5% 7% 15%	2694
September	1st to 10th	Night	19% 11% 4 7% 6% 5% 6% 5% 7% 8% 23%	1675
	11th to 20th	Night	18% 13% 4 9% 6% 5% 6% 4 5% 6% 24%	1900
	21st to end	Night	18% 22% 5% 11% 6% 4 4 3 5% 5% 16%	2170
October	1st to 10th	Night	9% 18% 7% 14% 5% 4 4 4 5% 6% 23%	3857
	11th to 20th	Night	10% 17% 6% 13% 7% 5% 6% 6% 6% 6% 18%	4367
	21st to end	Night	6% 17% 10% 20% 8% 7% 5% 3 5% 5% 13%	5129
November	1st to 10th	Night	5% 18% 7% 14% 9% 8% 7% 5% 5% 6% 16%	3154
	11th to 20th	Night	4 14% 6% 18% 12% 8% 7% 5% 6% 6% 14%	3392
	21st to end	Night	4 14% 6% 16% 9% 8% 7% 6% 9% 7% 13%	3604
December	1st to 10th	Night	5% 15% 6% 13% 8% 8% 7% 5% 8% 8% 17%	3800
	11th to 20th	Night	3 12% 6% 16% 10% 8% 6% 6% 10% 10% 13%	5112
	21st to end	Night	4 15% 5% 11% 7% 6% 7% 5% 9% 10% 21%	7500

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	45% 11% 7% 12% 25%	575
	11th to 20th	Day	55% 7% 6% 15% 8% 9%	936
	21st to end	Day	50% 6% 7% 12% 23% 2	1581
February	1st to 10th	Day	47% 9% 11% 19% 13% 2	1064
	11th to 20th	Day	48% 11% 13% 19% 8% 2	1305
	21st to end	Day	58% 9% 14% 9% 8% 1	1303
March	1st to 10th	Day	61% 5% 6% 21% 6%	2905
	11th to 20th	Day	68% 7% 8% 12% 4	3325
	21st to end	Day	51% 9% 19% 17% 4	4091
April	1st to 10th	Day	62% 8% 13% 10% 6% 1	2492
	11th to 20th	Day	53% 8% 16% 17% 6%	2633
	21st to end	Day	48% 8% 19% 19% 5% 1	2997
May	1st to 10th	Day	64% 6% 12% 12% 5%	5274
	11th to 20th	Day	52% 8% 16% 22% 2	5651
	21st to end	Day	51% 8% 16% 20% 6%	6791
June	1st to 10th	Day	49% 7% 15% 22% 6%	3971
	11th to 20th	Day	48% 7% 16% 24% 4	4332
	21st to end	Day	51% 9% 18% 18% 4	4380
July	1st to 10th	Day	67% 9% 14% 9% 1	6577
	11th to 20th	Day	57% 9% 20% 12% 2	6117
	21st to end	Day	51% 9% 20% 17% 3	6090
August	1st to 10th	Day	49% 9% 16% 19% 8%	5273
	11th to 20th	Day	58% 10% 17% 15% 1	4921
	21st to end	Day	72% 8% 13% 6%	4972
September	1st to 10th	Day	60% 7% 20% 12% 1	2504
	11th to 20th	Day	60% 8% 17% 13% 2	2280
	21st to end	Day	74% 5% 10% 9% 1	2008
October	1st to 10th	Day	60% 5% 13% 17% 4	3113
	11th to 20th	Day	66% 7% 11% 11% 4	2558
	21st to end	Day	69% 6% 14% 10% 1	2422
November	1st to 10th	Day	69% 6% 13% 10% 2	1124
	11th to 20th	Day	71% 7% 10% 10% 3	808
	21st to end	Day	65% 9% 6% 14% 5% 1	574
December	1st to 10th	Day	63% 8% 9% 13% 7%	380
	11th to 20th	Day	77% 5% 5% 9% 5%	81
	21st to end	Day	55% 10% 5% 14% 9% 7%	164
January	1st to 10th	Night	48% 10% 7% 14% 21%	6379
	11th to 20th	Night	56% 5% 5% 13% 9% 12%	6034
	21st to end	Night	54% 6% 6% 9% 24% 1	6106
February	1st to 10th	Night	52% 7% 9% 19% 12% 2	3113
	11th to 20th	Night	51% 8% 10% 19% 11% 1	2773
	21st to end	Night	57% 6% 13% 12% 12% 1	2151
March	1st to 10th	Night	61% 5% 6% 20% 7%	3959
	11th to 20th	Night	66% 8% 6% 13% 6%	3626
	21st to end	Night	50% 10% 18% 17% 5% 1	3549
April	1st to 10th	Night	60% 9% 13% 12% 5% 2	1688
	11th to 20th	Night	52% 8% 13% 19% 8%	1494
	21st to end	Night	50% 9% 15% 20% 5% 1	1183
May	1st to 10th	Night	63% 9% 11% 13% 4	1686
	11th to 20th	Night	46% 12% 20% 20% 1	1248
	21st to end	Night	48% 7% 16% 24% 5%	792
June	1st to 10th	Night	46% 11% 17% 23% 3	208
	July	1st to 10th	Night	61% 12% 17% 10% 1	270
11th to 20th		Night	54% 9% 23% 12% 3	728
21st to end		Night	48% 9% 23% 19% 2	1226
August	1st to 10th	Night	49% 8% 20% 15% 8%	1618
	11th to 20th	Night	55% 9% 20% 15% 1	1973
	21st to end	Night	66% 10% 18% 6%	2694
September	1st to 10th	Night	57% 8% 22% 12% 1	1675
	11th to 20th	Night	61% 7% 17% 13% 2	1900
	21st to end	Night	70% 7% 12% 11% 1	2170
October	1st to 10th	Night	61% 8% 13% 17% 1	3857
	11th to 20th	Night	61% 8% 15% 14% 2	4367
	21st to end	Night	71% 6% 11% 11% 1	5129
November	1st to 10th	Night	67% 7% 13% 11% 2	3154
	11th to 20th	Night	68% 5% 12% 11% 4	3392
	21st to end	Night	62% 8% 9% 14% 6%	3604
December	1st to 10th	Night	61% 7% 12% 14% 6%	3800
	11th to 20th	Night	60% 8% 9% 13% 10%	5111
	21st to end	Night	52% 8% 7% 17% 16% 1	7500

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	8% 1 8% 44% 27% 12%	90
	11th to 20th	Day	7% 3 13% 40% 26% 11%	90
	21st to end	Day	5% 5% 16% 42% 22% 9%	99
February	1st to 10th	Day	3 1 10% 45% 26% 15%	146
	11th to 20th	Day	5% 3 12% 37% 29% 13%	365
	21st to end	Day	5% 5% 18% 30% 25% 17%	307
March	1st to 10th	Day	4 3 14% 35% 25% 19%	370
	11th to 20th	Day	5% 5% 20% 31% 26% 12%	370
	21st to end	Day	5% 6% 19% 27% 27% 16%	484
April	1st to 10th	Day	8% 4 17% 34% 27% 10%	612
	11th to 20th	Day	8% 4 20% 31% 26% 13%	640
	21st to end	Day	7% 5% 17% 34% 27% 11%	650
May	1st to 10th	Day	13% 5% 23% 33% 20% 6%	700
	11th to 20th	Day	13% 5% 18% 29% 26% 9%	862
	21st to end	Day	16% 7% 17% 34% 22% 5%	1123
June	1st to 10th	Day	16% 6% 21% 33% 20% 5%	1060
	11th to 20th	Day	16% 5% 17% 31% 24% 7%	1136
	21st to end	Day	18% 3 14% 30% 26% 9%	1160
July	1st to 10th	Day	19% 6% 16% 26% 26% 8%	1041
	11th to 20th	Day	21% 4 15% 23% 25% 11%	1036
	21st to end	Day	20% 5% 15% 22% 27% 11%	1015
August	1st to 10th	Day	23% 7% 11% 28% 19% 11%	694
	11th to 20th	Day	27% 6% 19% 26% 15% 7%	665
	21st to end	Day	30% 7% 21% 23% 14% 5%	748
September	1st to 10th	Day	24% 8% 18% 20% 19% 11%	633
	11th to 20th	Day	27% 3 16% 27% 20% 6%	490
	21st to end	Day	29% 8% 17% 19% 18% 8%	417
October	1st to 10th	Day	21% 6% 23% 28% 14% 8%	390
	11th to 20th	Day	19% 5% 16% 25% 22% 13%	390
	21st to end	Day	18% 3 14% 28% 25% 11%	291
November	1st to 10th	Day	9% 6% 13% 30% 28% 15%	200
	11th to 20th	Day	10% 3 11% 25% 34% 19%	113
	21st to end	Day	11% 1 20% 28% 27% 13%	90
December	1st to 10th	Day	13% 3 17% 33% 24% 9%	90
	11th to 20th	Day	14% 5% 18% 27% 27% 9%	22
	21st to end	Day	9% 6% 15% 30% 23% 17%	47
January	1st to 10th	Night	10% 3 10% 32% 30% 14%	1130
	11th to 20th	Night	9% 3 13% 36% 29% 10%	1124
	21st to end	Night	9% 4 14% 36% 29% 9%	1045
February	1st to 10th	Night	6% 2 9% 36% 33% 14%	850
	11th to 20th	Night	6% 2 13% 36% 33% 10%	834
	21st to end	Night	6% 4 16% 35% 29% 9%	703
March	1st to 10th	Night	5% 2 13% 39% 30% 10%	823
	11th to 20th	Night	6% 2 11% 35% 38% 8%	664
	21st to end	Night	4 3 14% 36% 31% 12%	627
April	1st to 10th	Night	10% 3 14% 29% 34% 9%	570
	11th to 20th	Night	8% 2 14% 33% 35% 8%	563
	21st to end	Night	6% 3 16% 38% 30% 6%	423
May	1st to 10th	Night	12% 4 17% 37% 29% 2	304
	11th to 20th	Night	11% 4 14% 28% 39% 3	187
	21st to end	Night	12% 6% 15% 37% 30%	206
June	1st to 10th	Night	15% 5% 19% 36% 26%	128
	July	1st to 10th	Night	16% 5% 17% 30% 28% 4	128
11th to 20th		Night	20% 3 13% 34% 29% 2	184
21st to end		Night	19% 3 13% 27% 35% 2	208
August	1st to 10th	Night	21% 2 14% 35% 25% 1	229
	11th to 20th	Night	23% 5% 14% 29% 27% 2	423
	21st to end	Night	26% 5% 15% 22% 24% 8%	627
September	1st to 10th	Night	22% 6% 14% 23% 27% 7%	570
	11th to 20th	Night	25% 4 16% 31% 21% 4	570
	21st to end	Night	27% 3 17% 25% 22% 5%	706
October	1st to 10th	Night	24% 4 17% 29% 21% 6%	760
	11th to 20th	Night	23% 2 14% 23% 28% 9%	848
	21st to end	Night	17% 4 14% 27% 27% 11%	946
November	1st to 10th	Night	11% 3 14% 28% 33% 11%	912
	11th to 20th	Night	10% 4 11% 29% 32% 15%	1047
	21st to end	Night	9% 3 13% 30% 28% 18%	1069
December	1st to 10th	Night	11% 4 17% 38% 23% 7%	1130
	11th to 20th	Night	9% 2 14% 32% 34% 10%	1130
	21st to end	Night	6% 4 13% 30% 33% 14%	1243

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