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 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	9% 12% 4 7% 4 3 4 3 4 6% 45%	112159
	Night	9% 13% 4 7% 4 3 3 3 4 5% 44%	115539
Transparency	Day	38% 7% 10% 19% 17% 9%	111903
	Night	39% 7% 11% 20% 16% 6%	115384
Seeing	Day	16% 18% 30% 23% 11% 2	14698
	Night	16% 8% 22% 34% 18% 2	24372

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% 21% 11% 16% 4 3 3 3 4 5% 23%	3639
	11th to 20th	Day	10% 14% 4 12% 5% 3 3 2 3 5% 38%	3640
	21st to end	Day	11% 20% 5% 5% 2 2 2 3 4 5% 41%	4004
February	1st to 10th	Day	14% 21% 8% 11% 5% 4 3 3 3 5% 25%	1685
	11th to 20th	Day	12% 22% 8% 10% 4 3 3 3 5% 5% 24%	1950
	21st to end	Day	11% 24% 6% 16% 4 3 4 3 4 4 21%	1650
March	1st to 10th	Day	9% 20% 8% 16% 6% 4 4 3 4 5% 23%	3238
	11th to 20th	Day	8% 18% 5% 7% 4 3 3 2 3 4 45%	3369
	21st to end	Day	11% 23% 7% 13% 7% 6% 6% 4 5% 5% 14%	4000
April	1st to 10th	Day	13% 19% 6% 9% 5% 4 5% 3 6% 6% 23%	2280
	11th to 20th	Day	10% 17% 4 8% 4 3 4 3 5% 7% 34%	2318
	21st to end	Day	12% 16% 4 7% 4 4 4 4 6% 7% 32%	2470
May	1st to 10th	Day	8% 15% 5% 8% 5% 4 4 3 5% 6% 36%	4110
	11th to 20th	Day	7% 6% 2 5% 3 4 4 3 6% 8% 52%	4284
	21st to end	Day	9% 14% 4 7% 5% 4 4 3 6% 8% 36%	4813
June	1st to 10th	Day	15% 11% 3 8% 5% 5% 5% 4 6% 8% 30%	2660
	11th to 20th	Day	16% 9% 2 6% 5% 4 4 3 4 7% 41%	2660
	21st to end	Day	7% 5% 2 4 3 2 3 3 4 5% 63%	2660
July	1st to 10th	Day	2 2 1 2 2 2 2 2 4 4 77%	4420
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 4 76%	4420
	21st to end	Day	2 2 1 3 2 3 3 3 4 5% 73%	4790
August	1st to 10th	Day	4 5% 2 5% 3 4 4 3 5% 7% 58%	4287
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 6% 68%	4028
	21st to end	Day	3 3 1 4 2 2 3 2 4 5% 70%	4260
September	1st to 10th	Day	4 3 1 3 2 2 3 3 4 6% 69%	2280
	11th to 20th	Day	8% 6% 2 5% 4 3 3 3 4 6% 56%	2109
	21st to end	Day	8% 5% 2 5% 3 3 4 3 4 6% 57%	2090
October	1st to 10th	Day	8% 6% 2 5% 3 3 2 2 3 5% 61%	3490
	11th to 20th	Day	11% 7% 2 5% 4 4 4 3 4 7% 50%	2985
	21st to end	Day	13% 14% 4 9% 4 4 4 3 3 6% 36%	3101
November	1st to 10th	Day	18% 16% 4 7% 4 3 4 3 5% 7% 30%	1764
	11th to 20th	Day	16% 18% 5% 8% 4 4 4 3 5% 5% 28%	1800
	21st to end	Day	14% 17% 5% 6% 4 4 4 4 5% 6% 33%	1706
December	1st to 10th	Day	9% 12% 6% 8% 4 3 2 2 3 5% 46%	2357
	11th to 20th	Day	15% 29% 8% 10% 4 4 4 3 4 5% 14%	2838
	21st to end	Day	12% 20% 6% 12% 5% 4 4 3 4 5% 25%	4004
January	1st to 10th	Night	11% 20% 7% 12% 5% 4 4 4 4 5% 26%	6306
	11th to 20th	Night	9% 16% 4 13% 4 3 3 2 4 5% 38%	6320
	21st to end	Night	10% 19% 5% 7% 3 3 3 2 3 4 41%	6952
February	1st to 10th	Night	14% 22% 5% 10% 4 4 3 3 4 4 26%	2713
	11th to 20th	Night	12% 20% 6% 9% 3 3 4 3 4 5% 30%	2338
	21st to end	Night	11% 20% 8% 13% 5% 3 3 3 4 4 26%	1980
March	1st to 10th	Night	8% 21% 8% 12% 4 3 2 3 3 5% 31%	3856
	11th to 20th	Night	9% 17% 4 6% 3 3 3 2 4 4 47%	3638
	21st to end	Night	9% 18% 5% 9% 6% 5% 6% 5% 7% 7% 24%	3650
April	1st to 10th	Night	12% 14% 4 6% 5% 4 5% 4 5% 7% 33%	1900
	11th to 20th	Night	13% 13% 4 6% 3 4 4 3 5% 5% 40%	1809
	21st to end	Night	9% 11% 3 6% 5% 4 4 4 5% 7% 43%	1710
May	1st to 10th	Night	8% 13% 3 6% 3 4 4 3 5% 6% 45%	2860
	11th to 20th	Night	5% 5% 2 4 4 3 3 3 5% 6% 60%	2595
	21st to end	Night	11% 10% 2 6% 4 4 3 3 5% 6% 45%	2762
June	1st to 10th	Night	14% 6% 3 6% 4 5% 5% 5% 7% 8% 38%	1520
	11th to 20th	Night	11% 7% 2 5% 3 3 3 4 4 6% 52%	1520
	21st to end	Night	6% 3 1 4 3 3 3 3 6% 6% 63%	1520
July	1st to 10th	Night	1 1 1 2 1 1 2 2 3 5% 80%	2540
	11th to 20th	Night	1 1 1 2 2 1 2 2 4 5% 79%	2540
	21st to end	Night	2 3 1 3 2 2 3 3 5% 6% 71%	2761
August	1st to 10th	Night	3 3 1 4 3 4 3 4 6% 7% 61%	2644
	11th to 20th	Night	1 1 1 2 1 2 3 3 5% 6% 76%	2811
	21st to end	Night	4 4 1 3 2 3 2 2 4 5% 71%	3400
September	1st to 10th	Night	3 3 1 3 2 2 3 2 5% 5% 70%	1900
	11th to 20th	Night	8% 5% 1 3 3 3 3 4 6% 7% 57%	2071
	21st to end	Night	9% 4 2 4 2 2 3 2 4 6% 61%	2090
October	1st to 10th	Night	6% 3 2 5% 3 3 3 2 3 4 66%	3490
	11th to 20th	Night	9% 7% 2 6% 4 3 4 3 5% 7% 51%	3943
	21st to end	Night	10% 12% 2 7% 4 4 4 4 6% 7% 41%	4457
November	1st to 10th	Night	17% 15% 3 6% 3 3 4 3 5% 6% 34%	2535
	11th to 20th	Night	19% 15% 4 6% 4 3 4 3 5% 6% 32%	2600
	21st to end	Night	14% 15% 4 7% 4 3 3 3 4 6% 37%	2690
December	1st to 10th	Night	9% 10% 4 9% 3 3 2 3 4 5% 48%	4780
	11th to 20th	Night	13% 28% 6% 9% 5% 4 3 3 4 4 20%	5386
	21st to end	Night	13% 21% 5% 10% 5% 4 5% 3 5% 6% 24%	6952

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	62% 9% 10% 14% 5%	3639
	11th to 20th	Day	46% 7% 14% 21% 9% 2	3640
	21st to end	Day	45% 7% 11% 17% 14% 6%	4004
February	1st to 10th	Day	61% 8% 10% 16% 3 1	1685
	11th to 20th	Day	60% 8% 11% 13% 7% 1	1960
	21st to end	Day	64% 7% 10% 10% 7% 1	1650
March	1st to 10th	Day	58% 8% 8% 12% 13% 1	3238
	11th to 20th	Day	41% 7% 9% 37% 6%	3369
	21st to end	Day	63% 14% 10% 11% 3 1	4000
April	1st to 10th	Day	57% 9% 14% 14% 4	2280
	11th to 20th	Day	48% 8% 13% 19% 11% 2	2321
	21st to end	Day	49% 10% 13% 20% 8%	2470
May	1st to 10th	Day	44% 9% 11% 22% 13% 1	4110
	11th to 20th	Day	26% 8% 10% 37% 15% 5%	4287
	21st to end	Day	40% 10% 14% 27% 8% 1	4814
June	1st to 10th	Day	49% 10% 12% 20% 8%	2660
	11th to 20th	Day	42% 7% 10% 21% 17% 5%	2660
	21st to end	Day	23% 5% 8% 24% 32% 8%	2660
July	1st to 10th	Day	11% 3 5% 11% 24% 46%	4351
	11th to 20th	Day	12% 2 4 9% 24% 49%	4345
	21st to end	Day	12% 3 5% 13% 35% 32%	4639
August	1st to 10th	Day	23% 4 8% 14% 28% 24%	4271
	11th to 20th	Day	14% 4 7% 20% 38% 17%	4067
	21st to end	Day	16% 4 6% 23% 36% 14%	4259
September	1st to 10th	Day	17% 4 7% 22% 30% 20%	2280
	11th to 20th	Day	29% 6% 9% 22% 24% 10%	2109
	21st to end	Day	27% 5% 9% 30% 23% 6%	2090
October	1st to 10th	Day	26% 5% 6% 26% 32% 4	3490
	11th to 20th	Day	33% 5% 16% 25% 20% 1	2985
	21st to end	Day	45% 9% 8% 24% 14% 1	3101
November	1st to 10th	Day	52% 7% 14% 19% 7% 1	1764
	11th to 20th	Day	55% 8% 14% 16% 7% 1	1800
	21st to end	Day	50% 8% 13% 16% 11% 2	1706
December	1st to 10th	Day	41% 7% 16% 26% 9% 1	2357
	11th to 20th	Day	68% 10% 9% 8% 4	2838
	21st to end	Day	56% 10% 11% 15% 6% 1	4004
January	1st to 10th	Night	58% 8% 11% 16% 7% 1	6306
	11th to 20th	Night	48% 5% 12% 21% 12% 1	6320
	21st to end	Night	47% 7% 8% 17% 12% 9%	6952
February	1st to 10th	Night	60% 8% 11% 15% 4 1	2713
	11th to 20th	Night	55% 8% 12% 14% 8% 2	2339
	21st to end	Night	60% 7% 9% 16% 7% 2	1980
March	1st to 10th	Night	52% 8% 11% 14% 14% 1	3856
	11th to 20th	Night	41% 6% 10% 37% 6%	3638
	21st to end	Night	48% 17% 15% 16% 5%	3650
April	1st to 10th	Night	47% 9% 16% 21% 7% 1	1900
	11th to 20th	Night	43% 8% 13% 21% 12% 2	1809
	21st to end	Night	38% 9% 17% 26% 10%	1710
May	1st to 10th	Night	34% 9% 11% 29% 16% 1	2860
	11th to 20th	Night	22% 8% 12% 36% 23%	2595
	21st to end	Night	37% 8% 15% 31% 8%	2762
June	1st to 10th	Night	40% 10% 16% 26% 8%	1520
	11th to 20th	Night	30% 7% 14% 28% 16% 5%	1520
	21st to end	Night	21% 5% 10% 27% 29% 7%	1520
July	1st to 10th	Night	8% 3 5% 14% 28% 42%	2500
	11th to 20th	Night	8% 2 5% 13% 25% 46%	2492
	21st to end	Night	14% 3 5% 17% 32% 30%	2674
August	1st to 10th	Night	19% 3 7% 16% 37% 18%	2636
	11th to 20th	Night	9% 3 6% 20% 42% 20%	2838
	21st to end	Night	17% 3 5% 24% 32% 19%	3400
September	1st to 10th	Night	16% 3 7% 25% 30% 19%	1900
	11th to 20th	Night	25% 5% 11% 23% 24% 12%	2071
	21st to end	Night	23% 4 10% 31% 23% 8%	2090
October	1st to 10th	Night	21% 6% 7% 20% 37% 8%	3490
	11th to 20th	Night	30% 6% 15% 24% 23% 3	3943
	21st to end	Night	38% 9% 11% 23% 18% 1	4457
November	1st to 10th	Night	47% 9% 13% 20% 10% 2	2535
	11th to 20th	Night	51% 7% 14% 19% 8%	2600
	21st to end	Night	49% 6% 11% 19% 12% 3	2690
December	1st to 10th	Night	37% 6% 18% 26% 11% 1	4780
	11th to 20th	Night	64% 9% 11% 13% 3 1	5386
	21st to end	Night	56% 11% 12% 13% 6% 2	6952

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	21% 17% 29% 21% 11% 1	200
	11th to 20th	Day	23% 17% 26% 19% 11% 7%	200
	21st to end	Day	21% 13% 30% 24% 10% 3	220
February	1st to 10th	Day	24% 24% 30% 15% 6% 1	250
	11th to 20th	Day	20% 25% 30% 19% 6%	495
	21st to end	Day	24% 27% 25% 16% 7%	414
March	1st to 10th	Day	24% 25% 32% 15% 3	500
	11th to 20th	Day	21% 23% 26% 20% 8% 2	465
	21st to end	Day	24% 23% 31% 16% 5%	506
April	1st to 10th	Day	26% 24% 27% 14% 8% 2	460
	11th to 20th	Day	25% 25% 24% 18% 6% 1	452
	21st to end	Day	18% 24% 30% 19% 7% 1	460
May	1st to 10th	Day	13% 19% 31% 25% 11% 1	463
	11th to 20th	Day	21% 17% 28% 19% 11% 3	488
	21st to end	Day	17% 15% 27% 25% 12% 5%	529
June	1st to 10th	Day	17% 18% 28% 22% 13% 2	490
	11th to 20th	Day	22% 24% 28% 18% 7% 1	490
	21st to end	Day	7% 17% 33% 29% 13% 2	490
July	1st to 10th	Day	4 13% 42% 28% 11% 2	486
	11th to 20th	Day	5% 15% 42% 26% 11% 1	484
	21st to end	Day	5% 12% 36% 32% 14% 2	531
August	1st to 10th	Day	6% 10% 38% 31% 14% 2	487
	11th to 20th	Day	3 10% 33% 35% 16% 3	477
	21st to end	Day	7% 13% 35% 29% 13% 3	539
September	1st to 10th	Day	7% 12% 31% 31% 16% 4	490
	11th to 20th	Day	11% 16% 28% 28% 14% 3	490
	21st to end	Day	11% 15% 32% 26% 15% 2	490
October	1st to 10th	Day	15% 16% 30% 23% 14% 1	490
	11th to 20th	Day	17% 18% 24% 22% 14% 5%	359
	21st to end	Day	22% 20% 22% 24% 8% 3	330
November	1st to 10th	Day	27% 16% 21% 25% 11% 1	300
	11th to 20th	Day	20% 21% 21% 25% 10% 2	300
	21st to end	Day	21% 15% 25% 25% 11% 2	253
December	1st to 10th	Day	22% 17% 21% 18% 16% 8%	200
	11th to 20th	Day	30% 24% 21% 15% 10% 2	200
	21st to end	Day	21% 20% 24% 23% 8% 4	220
January	1st to 10th	Night	24% 11% 20% 31% 14% 1	800
	11th to 20th	Night	22% 10% 25% 27% 15% 2	800
	21st to end	Night	19% 9% 26% 28% 16% 3	880
February	1st to 10th	Night	26% 9% 29% 26% 10% 1	800
	11th to 20th	Night	21% 9% 26% 29% 13% 1	784
	21st to end	Night	20% 13% 25% 28% 12% 2	660
March	1st to 10th	Night	20% 14% 27% 27% 12% 1	800
	11th to 20th	Night	19% 11% 24% 30% 15% 1	766
	21st to end	Night	20% 10% 28% 32% 9% 1	836
April	1st to 10th	Night	18% 10% 22% 30% 17% 3	760
	11th to 20th	Night	18% 14% 28% 28% 12% 1	681
	21st to end	Night	14% 8% 26% 36% 15% 1	570
May	1st to 10th	Night	11% 9% 24% 37% 18% 1	570
	11th to 20th	Night	10% 5% 24% 35% 23% 2	427
	21st to end	Night	14% 5% 19% 34% 25% 2	411
June	1st to 10th	Night	17% 5% 18% 38% 21% 2	380
	11th to 20th	Night	13% 4 21% 43% 16% 2	380
	21st to end	Night	5% 3 18% 46% 27% 1	380
July	1st to 10th	Night	2 3 18% 46% 30% 1	370
	11th to 20th	Night	1 1 16% 59% 21% 2	368
	21st to end	Night	2 1 14% 53% 29% 1	416
August	1st to 10th	Night	3 4 15% 46% 29% 2	441
	11th to 20th	Night	1 2 15% 45% 33% 3	564
	21st to end	Night	5% 3 17% 41% 32% 2	777
September	1st to 10th	Night	4 2 15% 44% 33% 1	760
	11th to 20th	Night	9% 3 14% 39% 31% 5%	760
	21st to end	Night	10% 5% 16% 36% 28% 5%	760
October	1st to 10th	Night	11% 5% 20% 38% 25% 2	760
	11th to 20th	Night	14% 8% 17% 35% 21% 4	760
	21st to end	Night	19% 7% 24% 32% 15% 4	836
November	1st to 10th	Night	23% 9% 19% 36% 12% 1	780
	11th to 20th	Night	25% 10% 24% 28% 11% 2	800
	21st to end	Night	20% 10% 23% 30% 16% 3	800
December	1st to 10th	Night	19% 9% 24% 33% 14% 1	929
	11th to 20th	Night	26% 11% 22% 29% 10% 1	926
	21st to end	Night	27% 13% 24% 24% 10% 1	880

Page generated at 2025-03-09 06:08:47. Version ac07

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