Pilot Mound
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pilot Mound clear sky chart from 2005-11-06 to 2026-07-01.

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	10% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	147082
	Night	8% 9% 4 10% 6% 6% 5% 4 6% 7% 34%	142682
Transparency	Day	45% 7% 15% 24% 9% 1	141642
	Night	47% 6% 13% 23% 10% 1	139132
Seeing	Day	14% 11% 33% 27% 12% 3	18511
	Night	14% 10% 34% 31% 11% 1	28455

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	4 13% 5% 12% 11% 11% 8% 5% 7% 6% 17%	4123
	11th to 20th	Day	3 9% 4 13% 10% 9% 12% 10% 11% 6% 12%	4518
	21st to end	Day	4 9% 5% 13% 7% 6% 8% 4 7% 10% 27%	5188
February	1st to 10th	Day	9% 13% 5% 14% 8% 8% 6% 5% 8% 5% 20%	1732
	11th to 20th	Day	5% 12% 3 10% 9% 7% 8% 6% 8% 8% 23%	1855
	21st to end	Day	5% 11% 7% 12% 8% 8% 8% 5% 7% 7% 23%	1730
March	1st to 10th	Day	8% 12% 4 11% 7% 6% 5% 5% 7% 8% 27%	4600
	11th to 20th	Day	7% 12% 6% 12% 11% 6% 5% 4 6% 8% 21%	5062
	21st to end	Day	9% 13% 6% 14% 8% 7% 6% 4 6% 6% 21%	5624
April	1st to 10th	Day	9% 13% 5% 8% 5% 5% 5% 4 6% 8% 33%	2557
	11th to 20th	Day	13% 12% 4 10% 6% 5% 5% 4 6% 7% 30%	2699
	21st to end	Day	15% 9% 5% 8% 6% 5% 4 4 6% 6% 33%	2730
May	1st to 10th	Day	11% 8% 3 6% 3 3 3 3 6% 7% 45%	7685
	11th to 20th	Day	19% 10% 3 7% 5% 5% 4 4 5% 8% 31%	8668
	21st to end	Day	11% 7% 2 6% 4 4 4 3 5% 7% 46%	9682
June	1st to 10th	Day	12% 7% 2 6% 5% 4 6% 4 7% 9% 38%	3150
	11th to 20th	Day	14% 6% 3 8% 5% 5% 6% 4 7% 8% 36%	3150
	21st to end	Day	12% 7% 2 6% 5% 5% 6% 5% 8% 8% 36%	3150
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 11% 41%	6800
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 6% 9% 44%	6800
	21st to end	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	6997
August	1st to 10th	Day	10% 7% 3 7% 5% 4 4 4 6% 9% 41%	6154
	11th to 20th	Day	12% 6% 2 5% 4 3 4 4 6% 9% 47%	5821
	21st to end	Day	8% 5% 2 5% 3 3 4 4 6% 9% 52%	6490
September	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 5% 6% 51%	2435
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 4 7% 41%	2200
	21st to end	Day	13% 6% 2 5% 4 3 4 4 6% 7% 44%	2200
October	1st to 10th	Day	10% 8% 3 5% 4 3 4 3 5% 5% 49%	3433
	11th to 20th	Day	10% 10% 2 7% 5% 4 4 4 6% 7% 41%	3055
	21st to end	Day	13% 12% 3 8% 4 4 5% 3 6% 8% 34%	3190
November	1st to 10th	Day	14% 15% 4 12% 5% 4 3 4 5% 5% 30%	1788
	11th to 20th	Day	8% 13% 7% 15% 8% 4 5% 4 4 5% 28%	1680
	21st to end	Day	9% 15% 5% 13% 9% 6% 4 4 5% 5% 27%	1488
December	1st to 10th	Day	7% 13% 6% 16% 11% 9% 8% 5% 5% 6% 14%	2360
	11th to 20th	Day	9% 11% 6% 14% 9% 8% 7% 4 7% 7% 19%	2713
	21st to end	Day	6% 10% 4 16% 9% 5% 5% 5% 6% 6% 28%	3575
January	1st to 10th	Night	4 11% 6% 17% 10% 8% 7% 5% 6% 7% 19%	8799
	11th to 20th	Night	4 11% 5% 13% 8% 8% 11% 8% 8% 7% 17%	8458
	21st to end	Night	5% 10% 6% 13% 7% 5% 6% 5% 7% 9% 27%	9026
February	1st to 10th	Night	8% 12% 5% 12% 8% 6% 7% 6% 7% 7% 22%	2887
	11th to 20th	Night	6% 9% 3 9% 7% 6% 7% 5% 8% 8% 30%	2663
	21st to end	Night	6% 10% 4 10% 8% 6% 8% 4 7% 8% 31%	2083
March	1st to 10th	Night	7% 10% 4 10% 8% 6% 5% 5% 7% 8% 30%	5494
	11th to 20th	Night	7% 11% 4 11% 7% 5% 5% 3 6% 7% 33%	5119
	21st to end	Night	8% 13% 6% 15% 7% 5% 4 3 5% 5% 28%	5549
April	1st to 10th	Night	8% 8% 3 8% 6% 4 5% 4 6% 7% 41%	2063
	11th to 20th	Night	12% 12% 4 9% 5% 4 6% 5% 5% 6% 33%	1869
	21st to end	Night	13% 9% 4 8% 4 5% 5% 4 6% 7% 36%	1890
May	1st to 10th	Night	12% 8% 3 8% 4 5% 4 4 6% 6% 40%	5258
	11th to 20th	Night	16% 10% 2 6% 4 4 4 4 6% 8% 37%	4209
	21st to end	Night	12% 6% 2 5% 3 3 3 3 5% 7% 51%	4526
June	1st to 10th	Night	10% 5% 2 5% 5% 4 5% 4 5% 9% 45%	1470
	11th to 20th	Night	12% 6% 2 6% 5% 5% 5% 3 7% 7% 42%	1470
	21st to end	Night	12% 5% 2 6% 4 4 4 4 5% 11% 44%	1470
July	1st to 10th	Night	7% 3 1 4 4 3 4 4 6% 11% 52%	3180
	11th to 20th	Night	7% 4 1 5% 4 4 3 4 6% 8% 54%	3180
	21st to end	Night	4 6% 2 6% 4 5% 5% 5% 7% 9% 48%	3872
August	1st to 10th	Night	8% 6% 2 7% 4 4 4 3 6% 7% 50%	3657
	11th to 20th	Night	8% 5% 1 5% 3 4 4 4 6% 10% 51%	4028
	21st to end	Night	7% 4 2 5% 3 4 4 4 6% 8% 54%	4487
September	1st to 10th	Night	8% 6% 2 5% 3 3 4 3 5% 8% 53%	1961
	11th to 20th	Night	13% 5% 2 6% 4 3 3 4 6% 7% 48%	2200
	21st to end	Night	13% 6% 3 6% 5% 4 3 3 5% 6% 47%	2200
October	1st to 10th	Night	10% 8% 3 6% 3 4 3 3 5% 7% 47%	3713
	11th to 20th	Night	10% 9% 3 7% 3 4 4 4 6% 8% 42%	4085
	21st to end	Night	7% 10% 3 8% 5% 5% 4 3 5% 7% 41%	4610
November	1st to 10th	Night	11% 12% 4 9% 5% 5% 5% 4 6% 8% 32%	2728
	11th to 20th	Night	9% 15% 6% 13% 6% 5% 4 4 5% 6% 28%	2940
	21st to end	Night	9% 13% 4 12% 7% 6% 5% 3 5% 6% 28%	3129
December	1st to 10th	Night	6% 11% 6% 15% 10% 10% 8% 5% 6% 6% 17%	5050
	11th to 20th	Night	8% 13% 5% 15% 9% 7% 6% 4 5% 6% 20%	5714
	21st to end	Night	7% 10% 4 14% 9% 8% 6% 4 6% 6% 26%	7645

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% 5% 9% 15% 6%	4125
	11th to 20th	Day	62% 6% 10% 14% 7%	4518
	21st to end	Day	51% 5% 12% 21% 10%	5188
February	1st to 10th	Day	60% 6% 10% 16% 7% 1	1732
	11th to 20th	Day	54% 7% 11% 20% 9% 1	1864
	21st to end	Day	57% 7% 11% 16% 8%	1730
March	1st to 10th	Day	51% 7% 17% 16% 9%	4600
	11th to 20th	Day	58% 8% 14% 16% 5%	5062
	21st to end	Day	61% 7% 11% 17% 5%	5624
April	1st to 10th	Day	47% 6% 14% 23% 9% 1	2557
	11th to 20th	Day	52% 7% 12% 18% 10% 1	2702
	21st to end	Day	50% 6% 15% 19% 8% 1	2730
May	1st to 10th	Day	36% 5% 14% 31% 14% 1	7685
	11th to 20th	Day	50% 6% 9% 24% 8% 2	8672
	21st to end	Day	36% 6% 10% 27% 20% 1	9683
June	1st to 10th	Day	40% 9% 18% 23% 10% 1	3150
	11th to 20th	Day	44% 9% 15% 23% 9% 1	3150
	21st to end	Day	42% 10% 19% 23% 6% 1	3150
July	1st to 10th	Day	33% 10% 26% 27% 4	6727
	11th to 20th	Day	35% 8% 21% 31% 5%	6719
	21st to end	Day	33% 10% 22% 27% 8%	6796
August	1st to 10th	Day	35% 8% 18% 26% 12% 1	4480
	11th to 20th	Day	32% 7% 20% 34% 7%	4210
	21st to end	Day	32% 6% 20% 33% 9%	4674
September	1st to 10th	Day	33% 6% 18% 31% 12% 1	2435
	11th to 20th	Day	43% 6% 18% 24% 9% 1	2200
	21st to end	Day	37% 7% 16% 31% 10%	2200
October	1st to 10th	Day	36% 5% 11% 37% 11% 1	3433
	11th to 20th	Day	40% 5% 11% 32% 12%	3055
	21st to end	Day	48% 5% 12% 25% 9%	3190
November	1st to 10th	Day	56% 6% 10% 18% 8% 1	1788
	11th to 20th	Day	58% 6% 15% 14% 6% 1	1680
	21st to end	Day	60% 7% 11% 16% 6%	1488
December	1st to 10th	Day	69% 6% 11% 10% 3	2360
	11th to 20th	Day	63% 5% 11% 14% 7% 1	2710
	21st to end	Day	54% 5% 10% 18% 13%	3575
January	1st to 10th	Night	63% 6% 10% 15% 6%	8800
	11th to 20th	Night	60% 7% 10% 18% 6%	8458
	21st to end	Night	52% 5% 11% 23% 9%	9026
February	1st to 10th	Night	57% 6% 12% 15% 9% 1	2887
	11th to 20th	Night	46% 7% 13% 21% 12% 1	2664
	21st to end	Night	49% 6% 13% 21% 10% 1	2083
March	1st to 10th	Night	48% 7% 17% 18% 10% 1	5494
	11th to 20th	Night	49% 5% 13% 20% 12% 1	5119
	21st to end	Night	57% 6% 10% 20% 7%	5549
April	1st to 10th	Night	41% 6% 13% 24% 15% 2	2063
	11th to 20th	Night	50% 7% 11% 18% 12% 1	1869
	21st to end	Night	46% 7% 13% 21% 12% 1	1890
May	1st to 10th	Night	41% 6% 11% 27% 15%	5259
	11th to 20th	Night	42% 6% 12% 26% 12% 2	4210
	21st to end	Night	33% 5% 10% 27% 24% 2	4526
June	1st to 10th	Night	34% 8% 18% 28% 9% 2	1470
	11th to 20th	Night	38% 8% 16% 24% 12% 1	1470
	21st to end	Night	34% 8% 21% 30% 6% 1	1470
July	1st to 10th	Night	25% 10% 28% 30% 6% 1	3145
	11th to 20th	Night	28% 7% 19% 39% 8%	3138
	21st to end	Night	29% 9% 24% 30% 8% 1	3761
August	1st to 10th	Night	28% 6% 17% 32% 15% 1	2655
	11th to 20th	Night	28% 8% 21% 32% 10% 1	2915
	21st to end	Night	31% 6% 17% 34% 11% 1	3234
September	1st to 10th	Night	29% 6% 15% 35% 14% 1	1961
	11th to 20th	Night	35% 7% 18% 27% 12% 1	2200
	21st to end	Night	38% 5% 12% 31% 12% 1	2200
October	1st to 10th	Night	36% 5% 12% 30% 15% 1	3713
	11th to 20th	Night	39% 5% 12% 28% 16%	4085
	21st to end	Night	42% 5% 13% 31% 8%	4610
November	1st to 10th	Night	49% 7% 14% 19% 9% 2	2728
	11th to 20th	Night	56% 6% 14% 16% 7% 1	2940
	21st to end	Night	55% 7% 14% 18% 6%	3129
December	1st to 10th	Night	65% 7% 13% 11% 4	5050
	11th to 20th	Night	63% 5% 11% 16% 5% 1	5716
	21st to end	Night	57% 6% 9% 18% 10% 1	7645

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% 12% 37% 31% 10% 2	330
	11th to 20th	Day	11% 14% 42% 24% 9% 1	330
	21st to end	Day	14% 12% 41% 22% 9% 2	363
February	1st to 10th	Day	14% 15% 39% 25% 6% 1	330
	11th to 20th	Day	9% 14% 37% 31% 8% 1	330
	21st to end	Day	7% 12% 41% 30% 9% 1	273
March	1st to 10th	Day	13% 14% 36% 30% 5% 2	330
	11th to 20th	Day	16% 13% 32% 28% 8% 2	330
	21st to end	Day	16% 12% 34% 25% 10% 2	377
April	1st to 10th	Day	13% 18% 34% 26% 9% 1	577
	11th to 20th	Day	19% 13% 34% 24% 10% 1	740
	21st to end	Day	17% 13% 35% 22% 11% 1	750
May	1st to 10th	Day	15% 14% 30% 28% 12% 2	753
	11th to 20th	Day	21% 9% 34% 23% 11% 2	775
	21st to end	Day	17% 10% 25% 30% 16% 3	844
June	1st to 10th	Day	15% 12% 31% 24% 13% 5%	780
	11th to 20th	Day	14% 12% 35% 25% 11% 2	780
	21st to end	Day	14% 9% 31% 30% 13% 3	780
July	1st to 10th	Day	8% 6% 28% 30% 20% 7%	722
	11th to 20th	Day	13% 7% 31% 27% 18% 4	718
	21st to end	Day	6% 6% 26% 36% 20% 6%	794
August	1st to 10th	Day	9% 7% 26% 33% 19% 6%	726
	11th to 20th	Day	13% 5% 25% 30% 18% 8%	715
	21st to end	Day	13% 6% 27% 31% 19% 4	803
September	1st to 10th	Day	12% 9% 36% 26% 13% 3	565
	11th to 20th	Day	22% 8% 30% 31% 8% 1	330
	21st to end	Day	19% 11% 34% 24% 11% 2	330
October	1st to 10th	Day	19% 15% 28% 25% 12% 1	330
	11th to 20th	Day	20% 12% 39% 22% 5% 2	330
	21st to end	Day	23% 13% 37% 20% 7% 1	363
November	1st to 10th	Day	24% 14% 35% 20% 7%	330
	11th to 20th	Day	14% 19% 37% 24% 6%	330
	21st to end	Day	14% 17% 42% 22% 6%	330
December	1st to 10th	Day	14% 12% 40% 25% 8% 2	330
	11th to 20th	Day	17% 18% 38% 22% 3 1	330
	21st to end	Day	13% 10% 40% 25% 7% 4	363
January	1st to 10th	Night	10% 11% 39% 29% 10% 1	1050
	11th to 20th	Night	14% 12% 40% 26% 7%	1050
	21st to end	Night	12% 14% 39% 27% 7% 1	1155
February	1st to 10th	Night	12% 13% 36% 29% 8% 1	1050
	11th to 20th	Night	10% 10% 36% 33% 10% 2	1029
	21st to end	Night	10% 10% 37% 31% 10% 2	699
March	1st to 10th	Night	14% 10% 34% 27% 11% 3	840
	11th to 20th	Night	10% 10% 41% 28% 11% 1	646
	21st to end	Night	15% 9% 32% 30% 11% 2	693
April	1st to 10th	Night	11% 9% 36% 35% 8% 2	630
	11th to 20th	Night	18% 9% 32% 33% 8%	623
	21st to end	Night	15% 10% 30% 32% 11% 1	630
May	1st to 10th	Night	16% 8% 32% 31% 12% 1	630
	11th to 20th	Night	17% 10% 29% 32% 12%	621
	21st to end	Night	18% 7% 29% 34% 12%	683
June	1st to 10th	Night	13% 8% 30% 36% 11% 2	630
	11th to 20th	Night	13% 7% 34% 33% 13% 1	630
	21st to end	Night	12% 5% 27% 39% 15% 1	630
July	1st to 10th	Night	6% 3 26% 42% 21% 1	585
	11th to 20th	Night	7% 5% 27% 42% 17% 1	582
	21st to end	Night	5% 4 24% 47% 17% 3	657
August	1st to 10th	Night	8% 3 24% 45% 20% 1	597
	11th to 20th	Night	9% 6% 24% 39% 20% 3	594
	21st to end	Night	11% 5% 28% 38% 17% 1	660
September	1st to 10th	Night	10% 4 32% 35% 16% 3	600
	11th to 20th	Night	15% 8% 30% 36% 11%	600
	21st to end	Night	16% 9% 32% 31% 12% 1	600
October	1st to 10th	Night	19% 10% 33% 30% 8%	671
	11th to 20th	Night	20% 12% 30% 30% 8%	910
	21st to end	Night	17% 12% 37% 25% 8% 1	1100
November	1st to 10th	Night	17% 12% 38% 25% 8% 1	1025
	11th to 20th	Night	15% 13% 39% 23% 9% 1	1050
	21st to end	Night	16% 15% 40% 23% 5% 1	1050
December	1st to 10th	Night	11% 11% 40% 29% 8% 1	1050
	11th to 20th	Night	16% 13% 36% 26% 7% 2	1050
	21st to end	Night	18% 8% 36% 28% 9% 1	1155

Page generated at 2026-06-28 01:10:48. Version ac07

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