Elkford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elkford clear sky chart from 2005-11-06 to 2026-05-02.

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	6% 10% 4 10% 6% 6% 6% 5% 6% 8% 35%	135520
	Night	3 9% 4 11% 6% 6% 6% 5% 7% 8% 34%	135676
Transparency	Day	46% 8% 15% 20% 10% 1	135234
	Night	46% 9% 16% 19% 8% 1	135541
Seeing	Day	18% 19% 30% 21% 10% 3	17094
	Night	11% 13% 33% 30% 12% 1	26351

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	7% 8% 22% 10% 9% 7% 6% 6% 7% 17%	4125
	11th to 20th	Day	1 9% 3 9% 6% 7% 6% 6% 6% 9% 38%	4518
	21st to end	Day	2 7% 3 9% 6% 6% 7% 6% 8% 9% 36%	5186
February	1st to 10th	Day	1 9% 3 10% 9% 8% 9% 6% 9% 9% 27%	1680
	11th to 20th	Day	1 11% 5% 15% 7% 7% 6% 5% 7% 8% 27%	1843
	21st to end	Day	1 11% 5% 15% 11% 8% 6% 5% 6% 9% 24%	1730
March	1st to 10th	Day	2 11% 5% 12% 7% 7% 5% 4 5% 9% 33%	4618
	11th to 20th	Day	1 14% 6% 13% 7% 7% 6% 4 6% 7% 30%	4989
	21st to end	Day	2 20% 7% 16% 8% 7% 7% 5% 5% 6% 16%	5779
April	1st to 10th	Day	5% 18% 6% 14% 7% 6% 5% 4 6% 7% 23%	2526
	11th to 20th	Day	4 20% 7% 12% 6% 6% 5% 4 6% 7% 24%	2700
	21st to end	Day	9% 17% 5% 11% 5% 6% 5% 4 5% 7% 25%	2730
May	1st to 10th	Day	10% 17% 4 8% 4 3 4 3 5% 6% 37%	6114
	11th to 20th	Day	9% 15% 4 11% 8% 7% 7% 5% 7% 7% 19%	6614
	21st to end	Day	11% 11% 3 10% 6% 5% 5% 4 6% 7% 31%	7405
June	1st to 10th	Day	14% 12% 4 9% 7% 5% 5% 3 6% 7% 28%	3000
	11th to 20th	Day	16% 12% 4 10% 7% 6% 6% 5% 6% 7% 21%	3000
	21st to end	Day	9% 6% 2 9% 7% 6% 6% 5% 7% 9% 34%	3000
July	1st to 10th	Day	6% 4 1 5% 5% 5% 5% 4 6% 8% 51%	6780
	11th to 20th	Day	8% 3 2 6% 4 5% 5% 4 7% 8% 47%	6780
	21st to end	Day	6% 3 2 5% 4 4 4 4 6% 8% 53%	6929
August	1st to 10th	Day	7% 5% 2 7% 6% 5% 6% 5% 7% 8% 42%	4541
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 5% 7% 8% 47%	4218
	21st to end	Day	7% 4 2 5% 5% 5% 5% 4 7% 7% 49%	4664
September	1st to 10th	Day	8% 7% 2 7% 5% 4 4 3 5% 8% 47%	2428
	11th to 20th	Day	9% 8% 2 7% 4 4 5% 4 6% 8% 42%	2210
	21st to end	Day	7% 8% 3 7% 5% 5% 4 4 6% 7% 44%	2200
October	1st to 10th	Day	5% 7% 2 6% 5% 5% 4 4 6% 8% 50%	3520
	11th to 20th	Day	4 6% 2 6% 5% 5% 6% 4 7% 9% 45%	2964
	21st to end	Day	4 8% 3 8% 6% 5% 6% 5% 7% 8% 38%	3200
November	1st to 10th	Day	5% 13% 5% 12% 9% 5% 5% 6% 7% 7% 27%	1811
	11th to 20th	Day	2 10% 3 13% 7% 6% 6% 5% 8% 8% 31%	1601
	21st to end	Day	2 11% 4 11% 7% 6% 6% 4 7% 11% 31%	1470
December	1st to 10th	Day	1 7% 4 12% 7% 7% 8% 6% 9% 9% 30%	2360
	11th to 20th	Day	1 8% 4 15% 12% 10% 9% 6% 7% 8% 20%	2712
	21st to end	Day	1 10% 4 15% 9% 6% 7% 5% 7% 8% 27%	3575
January	1st to 10th	Night	1 8% 9% 22% 10% 8% 9% 7% 6% 6% 15%	8768
	11th to 20th	Night	6% 3 9% 8% 8% 9% 8% 8% 8% 33%	8425
	21st to end	Night	2 10% 4 11% 8% 7% 8% 8% 11% 9% 23%	8994
February	1st to 10th	Night	1 8% 5% 13% 10% 9% 8% 5% 7% 9% 24%	2940
	11th to 20th	Night	1 9% 5% 14% 8% 7% 7% 5% 6% 9% 30%	2659
	21st to end	Night	1 9% 3 14% 9% 7% 6% 6% 7% 9% 29%	2076
March	1st to 10th	Night	1 10% 6% 12% 7% 7% 8% 6% 7% 10% 26%	5496
	11th to 20th	Night	2 14% 4 9% 5% 5% 5% 5% 7% 10% 33%	5230
	21st to end	Night	2 19% 8% 13% 7% 6% 6% 5% 6% 7% 21%	5436
April	1st to 10th	Night	4 13% 4 8% 6% 5% 6% 5% 7% 9% 33%	2093
	11th to 20th	Night	3 13% 5% 10% 5% 5% 5% 4 6% 9% 35%	1871
	21st to end	Night	5% 13% 6% 11% 5% 6% 5% 4 5% 7% 34%	1890
May	1st to 10th	Night	6% 15% 4 7% 4 3 4 4 5% 5% 43%	3864
	11th to 20th	Night	8% 10% 4 10% 5% 6% 6% 5% 7% 8% 30%	3279
	21st to end	Night	9% 11% 3 7% 4 4 4 4 5% 7% 42%	3470
June	1st to 10th	Night	10% 9% 3 7% 6% 3 6% 5% 8% 8% 35%	1400
	11th to 20th	Night	16% 9% 3 8% 5% 5% 6% 5% 6% 7% 31%	1400
	21st to end	Night	7% 5% 2 6% 4 5% 5% 5% 8% 7% 47%	1400
July	1st to 10th	Night	6% 3 1 4 4 4 4 3 4 7% 60%	3180
	11th to 20th	Night	6% 3 2 5% 3 4 4 3 5% 7% 57%	3180
	21st to end	Night	8% 5% 2 4 3 3 3 3 4 6% 60%	3912
August	1st to 10th	Night	7% 6% 2 6% 4 4 5% 3 5% 7% 51%	2609
	11th to 20th	Night	5% 4 1 6% 4 5% 5% 4 6% 10% 50%	2839
	21st to end	Night	6% 4 2 4 3 4 5% 4 6% 9% 54%	3245
September	1st to 10th	Night	6% 4 2 5% 3 3 4 3 5% 9% 57%	1970
	11th to 20th	Night	8% 6% 2 6% 3 3 5% 4 5% 9% 50%	2190
	21st to end	Night	7% 6% 2 6% 4 4 5% 3 6% 9% 48%	2200
October	1st to 10th	Night	4 6% 2 5% 4 3 4 3 6% 10% 53%	3664
	11th to 20th	Night	3 6% 2 6% 4 4 4 4 6% 9% 52%	4182
	21st to end	Night	3 8% 3 9% 4 5% 6% 5% 8% 9% 40%	4600
November	1st to 10th	Night	4 12% 4 11% 8% 6% 6% 5% 8% 9% 26%	2686
	11th to 20th	Night	2 9% 5% 10% 8% 7% 8% 6% 7% 10% 28%	3015
	21st to end	Night	1 10% 4 11% 10% 7% 7% 6% 7% 9% 27%	3150
December	1st to 10th	Night	1 6% 4 13% 9% 8% 11% 8% 8% 8% 24%	5040
	11th to 20th	Night	1 8% 6% 19% 9% 9% 11% 6% 7% 6% 17%	5700
	21st to end	Night	1 9% 6% 16% 9% 9% 8% 6% 8% 9% 20%	7623

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	64% 10% 11% 10% 4 1	4125
	11th to 20th	Day	44% 9% 17% 16% 11% 3	4542
	21st to end	Day	43% 10% 20% 19% 8%	5187
February	1st to 10th	Day	51% 10% 16% 13% 8% 3	1680
	11th to 20th	Day	54% 9% 15% 13% 7% 1	1852
	21st to end	Day	57% 7% 14% 14% 7% 1	1730
March	1st to 10th	Day	49% 8% 15% 15% 13% 1	4618
	11th to 20th	Day	54% 6% 17% 17% 5%	4990
	21st to end	Day	66% 8% 11% 9% 6%	5779
April	1st to 10th	Day	61% 6% 16% 13% 3	2526
	11th to 20th	Day	60% 5% 15% 14% 5%	2700
	21st to end	Day	59% 6% 15% 17% 2 1	2730
May	1st to 10th	Day	49% 4 11% 25% 11%	6114
	11th to 20th	Day	60% 8% 14% 16% 2	6618
	21st to end	Day	50% 9% 17% 20% 5%	7406
June	1st to 10th	Day	56% 6% 14% 17% 7%	3000
	11th to 20th	Day	61% 6% 11% 14% 7% 1	3000
	21st to end	Day	44% 7% 17% 21% 10% 1	3000
July	1st to 10th	Day	29% 6% 11% 24% 26% 3	6706
	11th to 20th	Day	31% 8% 13% 27% 19% 2	6699
	21st to end	Day	28% 5% 13% 28% 18% 7%	6734
August	1st to 10th	Day	36% 8% 14% 25% 14% 3	4524
	11th to 20th	Day	32% 8% 20% 29% 11%	4258
	21st to end	Day	30% 6% 19% 32% 11% 1	4663
September	1st to 10th	Day	35% 6% 16% 25% 16% 2	2428
	11th to 20th	Day	40% 6% 15% 27% 12% 1	2210
	21st to end	Day	40% 6% 19% 24% 9% 1	2200
October	1st to 10th	Day	33% 7% 19% 33% 7%	3520
	11th to 20th	Day	36% 8% 20% 22% 12% 1	2964
	21st to end	Day	41% 10% 21% 20% 8%	3200
November	1st to 10th	Day	58% 10% 14% 13% 5% 1	1811
	11th to 20th	Day	50% 10% 20% 13% 6% 1	1601
	21st to end	Day	49% 11% 17% 14% 7% 1	1470
December	1st to 10th	Day	49% 11% 18% 15% 5% 1	2360
	11th to 20th	Day	59% 14% 15% 9% 3	2714
	21st to end	Day	50% 11% 12% 15% 10% 2	3575
January	1st to 10th	Night	67% 10% 11% 9% 3 1	8769
	11th to 20th	Night	47% 9% 16% 14% 10% 5%	8463
	21st to end	Night	50% 14% 14% 15% 7%	8994
February	1st to 10th	Night	56% 8% 11% 14% 8% 2	2940
	11th to 20th	Night	53% 8% 14% 16% 9%	2660
	21st to end	Night	50% 8% 14% 19% 8% 1	2076
March	1st to 10th	Night	49% 13% 15% 12% 11%	5496
	11th to 20th	Night	45% 8% 19% 21% 5%	5230
	21st to end	Night	58% 10% 16% 12% 4	5436
April	1st to 10th	Night	48% 9% 22% 15% 6%	2093
	11th to 20th	Night	47% 8% 19% 22% 5%	1871
	21st to end	Night	50% 6% 15% 24% 4 1	1890
May	1st to 10th	Night	43% 5% 15% 29% 9%	3861
	11th to 20th	Night	47% 9% 16% 23% 4	3279
	21st to end	Night	42% 8% 19% 24% 8%	3470
June	1st to 10th	Night	45% 8% 20% 20% 7% 1	1400
	11th to 20th	Night	49% 8% 18% 17% 8% 1	1400
	21st to end	Night	33% 8% 20% 27% 10% 1	1400
July	1st to 10th	Night	24% 6% 17% 24% 26% 3	3145
	11th to 20th	Night	25% 7% 18% 28% 19% 3	3138
	21st to end	Night	25% 6% 18% 25% 19% 9%	3802
August	1st to 10th	Night	30% 8% 16% 27% 16% 3	2601
	11th to 20th	Night	29% 7% 26% 26% 11% 1	2865
	21st to end	Night	26% 6% 23% 33% 12% 1	3245
September	1st to 10th	Night	26% 5% 20% 33% 14% 3	1970
	11th to 20th	Night	34% 8% 16% 31% 11% 1	2190
	21st to end	Night	34% 7% 23% 23% 12% 1	2200
October	1st to 10th	Night	28% 8% 19% 33% 11%	3664
	11th to 20th	Night	30% 9% 19% 31% 11% 1	4182
	21st to end	Night	39% 11% 19% 25% 6%	4600
November	1st to 10th	Night	56% 10% 15% 13% 5% 1	2686
	11th to 20th	Night	53% 10% 14% 16% 6%	3015
	21st to end	Night	54% 10% 14% 14% 7% 1	3150
December	1st to 10th	Night	58% 11% 14% 12% 5% 1	5040
	11th to 20th	Night	65% 11% 10% 10% 4	5697
	21st to end	Night	57% 10% 13% 11% 7% 1	7623

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	15% 16% 38% 20% 8% 4	220
	11th to 20th	Day	11% 15% 40% 28% 4 2	220
	21st to end	Day	10% 17% 49% 19% 4 2	242
February	1st to 10th	Day	20% 15% 43% 15% 6% 1	220
	11th to 20th	Day	10% 16% 37% 28% 8% 1	340
	21st to end	Day	17% 24% 35% 20% 4	446
March	1st to 10th	Day	22% 25% 29% 15% 6% 1	540
	11th to 20th	Day	21% 24% 29% 18% 5% 2	540
	21st to end	Day	20% 26% 30% 17% 5% 2	594
April	1st to 10th	Day	20% 24% 30% 19% 6% 1	540
	11th to 20th	Day	21% 23% 32% 15% 7% 2	532
	21st to end	Day	22% 23% 30% 15% 8% 3	540
May	1st to 10th	Day	20% 21% 27% 18% 10% 3	508
	11th to 20th	Day	20% 13% 27% 22% 14% 4	670
	21st to end	Day	23% 15% 20% 25% 15% 3	789
June	1st to 10th	Day	21% 19% 27% 20% 11% 2	730
	11th to 20th	Day	24% 18% 26% 20% 9% 2	730
	21st to end	Day	14% 15% 28% 26% 14% 4	730
July	1st to 10th	Day	13% 15% 25% 26% 17% 3	721
	11th to 20th	Day	15% 17% 24% 27% 15% 3	718
	21st to end	Day	9% 18% 32% 24% 14% 4	604
August	1st to 10th	Day	12% 14% 32% 26% 12% 4	527
	11th to 20th	Day	9% 19% 30% 29% 9% 3	517
	21st to end	Day	13% 17% 32% 24% 11% 4	583
September	1st to 10th	Day	16% 20% 29% 20% 11% 5%	530
	11th to 20th	Day	17% 17% 31% 22% 10% 3	530
	21st to end	Day	23% 26% 30% 16% 5% 1	530
October	1st to 10th	Day	18% 20% 30% 21% 8% 3	489
	11th to 20th	Day	22% 19% 29% 18% 11% 2	330
	21st to end	Day	23% 20% 30% 20% 5% 2	363
November	1st to 10th	Day	19% 23% 33% 19% 5% 1	330
	11th to 20th	Day	20% 22% 38% 16% 3 1	289
	21st to end	Day	16% 16% 37% 16% 9% 5%	220
December	1st to 10th	Day	14% 20% 35% 20% 7% 4	220
	11th to 20th	Day	15% 21% 39% 19% 5% 1	220
	21st to end	Day	8% 13% 45% 23% 9% 2	242
January	1st to 10th	Night	12% 16% 44% 22% 6% 1	1050
	11th to 20th	Night	9% 14% 47% 25% 4 1	927
	21st to end	Night	7% 16% 41% 29% 5% 1	924
February	1st to 10th	Night	10% 13% 42% 26% 8% 2	840
	11th to 20th	Night	10% 11% 40% 31% 7%	824
	21st to end	Night	9% 14% 37% 29% 9% 2	692
March	1st to 10th	Night	8% 16% 39% 26% 10% 1	840
	11th to 20th	Night	12% 19% 30% 29% 8% 1	840
	21st to end	Night	11% 13% 33% 31% 10% 2	924
April	1st to 10th	Night	13% 14% 28% 33% 10% 2	833
	11th to 20th	Night	11% 18% 33% 28% 9% 2	623
	21st to end	Night	13% 15% 30% 30% 11% 1	630
May	1st to 10th	Night	14% 10% 27% 33% 16% 1	501
	11th to 20th	Night	12% 9% 19% 34% 23% 4	394
	21st to end	Night	21% 9% 18% 28% 23% 2	433
June	1st to 10th	Night	17% 8% 26% 33% 16% 2	400
	11th to 20th	Night	20% 9% 25% 30% 15% 1	400
	21st to end	Night	11% 10% 19% 37% 22% 2	400
July	1st to 10th	Night	8% 5% 18% 44% 25% 1	390
	11th to 20th	Night	7% 6% 22% 43% 22%	388
	21st to end	Night	5% 7% 16% 47% 24% 1	438
August	1st to 10th	Night	8% 5% 13% 41% 31% 2	398
	11th to 20th	Night	8% 6% 20% 40% 24% 2	556
	21st to end	Night	11% 10% 21% 37% 19% 2	660
September	1st to 10th	Night	10% 9% 21% 31% 24% 5%	770
	11th to 20th	Night	12% 7% 19% 35% 22% 5%	800
	21st to end	Night	15% 11% 32% 28% 12% 3	800
October	1st to 10th	Night	13% 12% 25% 36% 14% 2	800
	11th to 20th	Night	11% 16% 29% 32% 11% 1	800
	21st to end	Night	13% 16% 33% 30% 7% 1	880
November	1st to 10th	Night	17% 15% 37% 25% 5%	841
	11th to 20th	Night	16% 19% 37% 22% 4 1	1050
	21st to end	Night	11% 16% 40% 25% 7% 1	1050
December	1st to 10th	Night	10% 16% 39% 28% 6% 1	1050
	11th to 20th	Night	10% 17% 44% 23% 5% 1	1050
	21st to end	Night	8% 14% 46% 25% 7%	1155

Page generated at 2026-04-29 00:21:46. Version ac07

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