McCall
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McCall 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	8% 11% 4 7% 4 4 4 3 4 6% 47%	146197
	Night	8% 12% 4 7% 3 3 3 3 5% 6% 46%	143781
Transparency	Day	36% 7% 10% 21% 18% 8%	140922
	Night	38% 7% 11% 22% 17% 6%	140060
Seeing	Day	16% 18% 30% 23% 10% 2	16470
	Night	16% 8% 22% 34% 18% 2	25980

By Month

Percentage Cloud Cover SW (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	9% 25% 9% 16% 5% 3 3 3 4 5% 19%	4722
	11th to 20th	Day	8% 11% 3 10% 4 3 3 2 4 6% 48%	4740
	21st to end	Day	8% 18% 5% 7% 3 3 3 3 4 5% 42%	5187
February	1st to 10th	Day	14% 20% 7% 11% 5% 4 3 3 4 5% 26%	1770
	11th to 20th	Day	11% 22% 8% 11% 4 3 3 3 5% 6% 24%	2050
	21st to end	Day	10% 24% 6% 15% 4 3 4 3 4 4 23%	1730
March	1st to 10th	Day	6% 16% 7% 14% 6% 5% 4 3 5% 6% 27%	4618
	11th to 20th	Day	8% 20% 7% 10% 4 3 3 3 3 4 35%	4922
	21st to end	Day	9% 24% 7% 12% 6% 6% 5% 4 5% 6% 16%	5865
April	1st to 10th	Day	12% 18% 6% 9% 5% 4 5% 3 6% 6% 25%	2520
	11th to 20th	Day	9% 17% 4 8% 4 4 4 4 5% 7% 34%	2566
	21st to end	Day	12% 15% 3 7% 5% 4 4 3 6% 7% 32%	2730
May	1st to 10th	Day	5% 9% 3 5% 4 4 4 3 5% 6% 52%	7626
	11th to 20th	Day	6% 8% 3 7% 4 5% 5% 4 6% 9% 44%	7991
	21st to end	Day	6% 9% 3 6% 4 4 4 3 5% 7% 48%	8992
June	1st to 10th	Day	13% 11% 4 7% 5% 6% 5% 4 6% 8% 32%	2940
	11th to 20th	Day	15% 9% 2 6% 5% 4 4 3 4 6% 43%	2940
	21st to end	Day	7% 5% 2 4 3 2 3 3 4 5% 61%	2940
July	1st to 10th	Day	3 2 1 2 2 2 2 2 4 4 76%	6459
	11th to 20th	Day	1 2 1 3 2 2 2 2 3 3 79%	6391
	21st to end	Day	2 3 1 3 2 3 4 4 5% 6% 68%	6880
August	1st to 10th	Day	3 4 2 5% 4 4 5% 4 6% 8% 55%	6049
	11th to 20th	Day	2 2 1 2 3 2 3 3 4 5% 72%	5798
	21st to end	Day	6% 4 2 4 3 3 3 2 4 5% 64%	6103
September	1st to 10th	Day	4 3 1 3 2 2 3 3 5% 6% 68%	2400
	11th to 20th	Day	8% 6% 2 5% 4 4 3 3 4 6% 55%	2220
	21st to end	Day	8% 5% 2 5% 3 3 4 3 4 6% 58%	2200
October	1st to 10th	Day	8% 6% 2 5% 3 3 2 2 3 5% 61%	3600
	11th to 20th	Day	11% 7% 2 5% 4 4 4 3 4 7% 50%	3080
	21st to end	Day	13% 14% 4 9% 4 4 4 3 3 6% 37%	3200
November	1st to 10th	Day	17% 16% 4 7% 4 3 4 3 5% 7% 30%	1854
	11th to 20th	Day	16% 18% 5% 8% 4 4 4 3 5% 5% 28%	1890
	21st to end	Day	13% 17% 5% 6% 4 4 4 4 5% 6% 32%	1791
December	1st to 10th	Day	10% 12% 6% 9% 4 3 2 2 3 5% 45%	2429
	11th to 20th	Day	15% 29% 7% 10% 4 4 4 3 4 5% 15%	2912
	21st to end	Day	12% 20% 6% 12% 5% 4 4 3 4 5% 25%	4092
January	1st to 10th	Night	10% 24% 7% 13% 5% 4 3 3 4 5% 23%	8172
	11th to 20th	Night	7% 12% 3 10% 3 2 3 2 4 6% 48%	8220
	21st to end	Night	8% 16% 5% 7% 3 4 4 3 4 4 43%	8994
February	1st to 10th	Night	14% 22% 5% 10% 4 4 3 3 4 4 27%	2848
	11th to 20th	Night	12% 20% 6% 10% 3 3 4 3 4 5% 30%	2458
	21st to end	Night	11% 20% 7% 12% 5% 3 3 3 4 4 27%	2076
March	1st to 10th	Night	6% 17% 7% 12% 4 4 3 3 4 7% 34%	5496
	11th to 20th	Night	10% 21% 5% 7% 3 3 3 2 4 3 38%	5297
	21st to end	Night	8% 20% 5% 8% 5% 4 5% 5% 6% 7% 27%	5348
April	1st to 10th	Night	12% 14% 4 6% 5% 4 5% 4 6% 7% 34%	2100
	11th to 20th	Night	12% 13% 4 6% 3 4 4 3 5% 5% 41%	2001
	21st to end	Night	9% 11% 3 7% 5% 4 4 4 5% 7% 43%	1890
May	1st to 10th	Night	6% 7% 2 4 2 3 4 3 5% 7% 57%	5321
	11th to 20th	Night	5% 6% 2 6% 4 4 5% 4 5% 7% 51%	4861
	21st to end	Night	6% 7% 2 5% 4 4 3 3 5% 6% 55%	5181
June	1st to 10th	Night	13% 6% 3 5% 4 4 5% 4 6% 7% 42%	1680
	11th to 20th	Night	10% 6% 2 5% 3 3 3 4 4 6% 53%	1680
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 5% 62%	1680
July	1st to 10th	Night	1 2 1 2 2 2 2 3 4 6% 77%	3720
	11th to 20th	Night	1 1 1 1 1 2 2 3 4 83%	3680
	21st to end	Night	2 3 1 2 2 2 3 3 6% 8% 68%	3970
August	1st to 10th	Night	3 3 1 4 3 4 3 3 6% 7% 63%	3749
	11th to 20th	Night	1 1 1 2 1 2 2 2 4 5% 77%	4051
	21st to end	Night	6% 5% 2 4 2 3 3 2 4 5% 64%	4875
September	1st to 10th	Night	3 3 1 3 2 2 3 3 5% 6% 69%	2000
	11th to 20th	Night	8% 5% 1 3 3 3 3 4 6% 7% 58%	2180
	21st to end	Night	9% 4 2 4 2 2 3 2 4 6% 62%	2200
October	1st to 10th	Night	6% 3 2 5% 3 3 3 2 3 4 66%	3600
	11th to 20th	Night	9% 7% 2 6% 4 3 4 3 5% 6% 51%	4068
	21st to end	Night	10% 12% 3 7% 4 4 4 4 6% 7% 41%	4600
November	1st to 10th	Night	17% 14% 4 6% 3 3 4 3 5% 6% 34%	2665
	11th to 20th	Night	19% 14% 4 7% 4 3 4 3 5% 6% 31%	2730
	21st to end	Night	14% 15% 4 7% 4 3 3 3 4 6% 37%	2825
December	1st to 10th	Night	9% 10% 4 9% 3 3 2 3 4 5% 47%	4927
	11th to 20th	Night	13% 27% 6% 9% 5% 4 3 3 4 5% 20%	5532
	21st to end	Night	13% 21% 5% 10% 5% 4 5% 3 5% 6% 24%	7106

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% 9% 12% 4	4723
	11th to 20th	Day	36% 6% 13% 26% 15% 5%	4740
	21st to end	Day	43% 7% 11% 17% 17% 5%	5187
February	1st to 10th	Day	60% 8% 11% 16% 4 1	1770
	11th to 20th	Day	60% 8% 11% 13% 7% 1	2060
	21st to end	Day	62% 7% 10% 11% 8% 1	1730
March	1st to 10th	Day	53% 8% 10% 14% 12% 4	4618
	11th to 20th	Day	48% 7% 10% 29% 5%	4922
	21st to end	Day	61% 13% 10% 13% 3 1	5865
April	1st to 10th	Day	54% 9% 15% 17% 5%	2520
	11th to 20th	Day	48% 8% 13% 19% 10% 2	2569
	21st to end	Day	48% 10% 13% 20% 9%	2730
May	1st to 10th	Day	28% 6% 10% 30% 24% 1	7626
	11th to 20th	Day	30% 8% 11% 31% 17% 3	7994
	21st to end	Day	31% 8% 11% 30% 19% 2	8994
June	1st to 10th	Day	47% 9% 12% 21% 11% 1	2940
	11th to 20th	Day	39% 6% 9% 21% 19% 5%	2940
	21st to end	Day	24% 5% 8% 23% 31% 8%	2940
July	1st to 10th	Day	11% 3 4 16% 27% 38%	6391
	11th to 20th	Day	11% 2 3 9% 31% 44%	6316
	21st to end	Day	15% 4 5% 22% 33% 22%	6681
August	1st to 10th	Day	22% 4 8% 15% 28% 23%	4407
	11th to 20th	Day	14% 4 7% 20% 38% 17%	4197
	21st to end	Day	17% 4 6% 23% 35% 14%	4394
September	1st to 10th	Day	17% 4 7% 22% 30% 19%	2400
	11th to 20th	Day	29% 6% 9% 22% 25% 9%	2220
	21st to end	Day	27% 5% 9% 29% 24% 6%	2200
October	1st to 10th	Day	26% 5% 6% 27% 32% 4	3600
	11th to 20th	Day	33% 5% 16% 25% 20% 1	3080
	21st to end	Day	44% 9% 9% 24% 14% 1	3200
November	1st to 10th	Day	51% 8% 14% 19% 7% 1	1854
	11th to 20th	Day	55% 9% 14% 15% 7% 1	1890
	21st to end	Day	50% 9% 13% 16% 10% 2	1791
December	1st to 10th	Day	42% 7% 16% 26% 8% 1	2429
	11th to 20th	Day	68% 10% 10% 8% 4	2912
	21st to end	Day	56% 10% 11% 15% 5% 1	4092
January	1st to 10th	Night	60% 10% 12% 13% 5%	8172
	11th to 20th	Night	38% 5% 13% 25% 17% 4	8220
	21st to end	Night	43% 8% 9% 17% 14% 9%	8994
February	1st to 10th	Night	59% 8% 12% 16% 4 1	2848
	11th to 20th	Night	55% 9% 12% 15% 8% 2	2459
	21st to end	Night	59% 7% 9% 16% 7% 2	2076
March	1st to 10th	Night	46% 8% 10% 17% 12% 6%	5496
	11th to 20th	Night	48% 7% 8% 29% 8%	5297
	21st to end	Night	48% 15% 14% 18% 5%	5348
April	1st to 10th	Night	45% 9% 16% 23% 7% 1	2100
	11th to 20th	Night	42% 8% 13% 23% 12% 2	2001
	21st to end	Night	38% 9% 16% 26% 12%	1890
May	1st to 10th	Night	23% 7% 9% 34% 26% 1	5319
	11th to 20th	Night	25% 8% 13% 31% 23%	4861
	21st to end	Night	29% 7% 13% 36% 15% 1	5182
June	1st to 10th	Night	37% 10% 15% 28% 11%	1680
	11th to 20th	Night	30% 7% 13% 27% 19% 5%	1680
	21st to end	Night	22% 6% 9% 27% 29% 7%	1680
July	1st to 10th	Night	10% 3 4 19% 27% 37%	3680
	11th to 20th	Night	6% 2 5% 15% 35% 37%	3632
	21st to end	Night	13% 3 4 29% 30% 21%	3857
August	1st to 10th	Night	19% 3 7% 17% 36% 17%	2720
	11th to 20th	Night	9% 3 6% 20% 42% 19%	2928
	21st to end	Night	18% 3 5% 24% 31% 19%	3507
September	1st to 10th	Night	16% 4 7% 25% 30% 18%	2000
	11th to 20th	Night	25% 5% 10% 24% 24% 11%	2180
	21st to end	Night	23% 4 9% 30% 25% 8%	2200
October	1st to 10th	Night	21% 6% 7% 21% 37% 8%	3600
	11th to 20th	Night	30% 6% 15% 23% 23% 3	4068
	21st to end	Night	37% 9% 11% 24% 18% 1	4600
November	1st to 10th	Night	47% 9% 13% 20% 10% 2	2665
	11th to 20th	Night	51% 8% 15% 19% 7%	2730
	21st to end	Night	48% 6% 11% 19% 12% 3	2825
December	1st to 10th	Night	38% 7% 18% 26% 11% 1	4927
	11th to 20th	Night	64% 9% 11% 13% 3 1	5532
	21st to end	Night	56% 11% 13% 13% 6% 2	7106

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	22% 19% 28% 20% 10% 1	220
	11th to 20th	Day	20% 15% 27% 20% 11% 6%	220
	21st to end	Day	19% 12% 30% 26% 10% 2	242
February	1st to 10th	Day	23% 23% 30% 16% 6% 2	275
	11th to 20th	Day	20% 25% 30% 19% 6%	535
	21st to end	Day	24% 27% 26% 16% 7%	446
March	1st to 10th	Day	24% 26% 33% 14% 3	540
	11th to 20th	Day	23% 25% 26% 18% 7% 1	540
	21st to end	Day	25% 24% 31% 15% 5%	594
April	1st to 10th	Day	24% 22% 26% 17% 9% 2	540
	11th to 20th	Day	24% 26% 25% 17% 7% 1	532
	21st to end	Day	17% 24% 30% 19% 8% 1	540
May	1st to 10th	Day	12% 19% 32% 25% 11% 1	543
	11th to 20th	Day	21% 21% 27% 18% 10% 3	568
	21st to end	Day	15% 15% 29% 25% 11% 4	617
June	1st to 10th	Day	17% 18% 28% 22% 12% 3	570
	11th to 20th	Day	20% 25% 30% 18% 6% 1	570
	21st to end	Day	8% 17% 34% 27% 12% 2	570
July	1st to 10th	Day	5% 12% 42% 29% 11% 2	566
	11th to 20th	Day	6% 15% 41% 26% 11% 1	545
	21st to end	Day	5% 11% 36% 32% 14% 2	575
August	1st to 10th	Day	6% 11% 36% 31% 14% 2	527
	11th to 20th	Day	3 10% 35% 34% 16% 3	517
	21st to end	Day	7% 12% 34% 31% 13% 3	583
September	1st to 10th	Day	6% 11% 30% 32% 17% 4	530
	11th to 20th	Day	11% 15% 26% 29% 15% 3	530
	21st to end	Day	10% 15% 31% 27% 16% 2	530
October	1st to 10th	Day	15% 16% 31% 23% 13% 2	530
	11th to 20th	Day	17% 18% 24% 22% 13% 5%	392
	21st to end	Day	21% 20% 23% 26% 8% 3	363
November	1st to 10th	Day	25% 18% 21% 24% 10% 2	330
	11th to 20th	Day	21% 20% 23% 25% 9% 2	330
	21st to end	Day	19% 17% 25% 26% 11% 2	278
December	1st to 10th	Day	24% 17% 20% 18% 14% 7%	220
	11th to 20th	Day	30% 25% 21% 14% 9% 1	220
	21st to end	Day	23% 21% 22% 22% 8% 3	242
January	1st to 10th	Night	24% 11% 20% 31% 13% 1	840
	11th to 20th	Night	21% 9% 25% 28% 14% 2	840
	21st to end	Night	18% 9% 27% 28% 15% 3	924
February	1st to 10th	Night	25% 8% 28% 27% 10% 1	840
	11th to 20th	Night	20% 10% 27% 29% 13% 1	824
	21st to end	Night	20% 13% 25% 28% 12% 2	692
March	1st to 10th	Night	19% 14% 28% 26% 11% 1	840
	11th to 20th	Night	20% 12% 26% 28% 14% 1	840
	21st to end	Night	19% 12% 29% 31% 8% 1	924
April	1st to 10th	Night	17% 10% 23% 31% 17% 2	840
	11th to 20th	Night	17% 14% 28% 28% 11% 1	753
	21st to end	Night	13% 8% 26% 37% 14% 1	630
May	1st to 10th	Night	11% 9% 24% 39% 17% 1	630
	11th to 20th	Night	10% 6% 25% 36% 21% 2	473
	21st to end	Night	13% 5% 20% 36% 23% 2	455
June	1st to 10th	Night	16% 5% 19% 38% 20% 1	420
	11th to 20th	Night	12% 5% 24% 42% 15% 2	420
	21st to end	Night	6% 3 20% 45% 25% 1	420
July	1st to 10th	Night	2 3 19% 47% 28% 1	410
	11th to 20th	Night	2 1 17% 58% 20% 2	398
	21st to end	Night	2 1 15% 53% 28% 1	438
August	1st to 10th	Night	3 4 16% 46% 28% 2	465
	11th to 20th	Night	1 3 16% 46% 31% 3	594
	21st to end	Night	6% 3 17% 41% 31% 2	818
September	1st to 10th	Night	4 2 15% 46% 32% 1	800
	11th to 20th	Night	9% 3 14% 39% 31% 5%	800
	21st to end	Night	10% 5% 17% 36% 28% 4	800
October	1st to 10th	Night	11% 6% 21% 37% 24% 2	800
	11th to 20th	Night	14% 8% 19% 35% 20% 4	800
	21st to end	Night	19% 8% 24% 32% 14% 3	880
November	1st to 10th	Night	23% 9% 19% 35% 12% 1	820
	11th to 20th	Night	25% 10% 24% 29% 11% 2	840
	21st to end	Night	19% 10% 23% 30% 16% 3	840
December	1st to 10th	Night	20% 9% 25% 32% 13% 1	976
	11th to 20th	Night	26% 11% 23% 29% 10% 1	972
	21st to end	Night	28% 13% 24% 24% 10% 1	924

Page generated at 2026-07-13 01:14:50. Version ac07

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