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 2025-02-25.

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% 7% 35%	112157
	Night	8% 9% 4 10% 6% 6% 5% 4 6% 7% 34%	115294
Transparency	Day	46% 7% 15% 24% 8%	111885
	Night	48% 6% 14% 23% 9% 1	115156
Seeing	Day	15% 11% 33% 27% 12% 3	16552
	Night	14% 9% 34% 31% 11% 1	26684

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 14% 6% 12% 11% 10% 8% 6% 7% 7% 15%	3178
	11th to 20th	Day	4 7% 4 12% 11% 10% 11% 11% 12% 6% 12%	3474
	21st to end	Day	5% 11% 6% 16% 7% 6% 8% 4 5% 6% 25%	4004
February	1st to 10th	Day	9% 13% 5% 13% 8% 8% 6% 6% 8% 6% 20%	1649
	11th to 20th	Day	5% 11% 3 10% 9% 7% 8% 7% 9% 8% 23%	1764
	21st to end	Day	5% 12% 7% 12% 7% 6% 8% 5% 6% 7% 25%	1610
March	1st to 10th	Day	10% 13% 4 9% 8% 7% 5% 5% 6% 7% 27%	3130
	11th to 20th	Day	7% 12% 5% 11% 12% 6% 5% 4 7% 8% 24%	3466
	21st to end	Day	9% 12% 7% 13% 9% 5% 5% 3 6% 7% 25%	3838
April	1st to 10th	Day	9% 13% 5% 8% 5% 5% 5% 4 6% 8% 33%	2313
	11th to 20th	Day	13% 12% 4 9% 6% 5% 5% 4 6% 7% 30%	2439
	21st to end	Day	16% 9% 4 8% 6% 5% 4 4 6% 6% 34%	2470
May	1st to 10th	Day	19% 11% 3 7% 4 4 3 3 6% 7% 33%	4137
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 7% 32%	4641
	21st to end	Day	17% 9% 2 8% 5% 4 5% 4 5% 7% 35%	5173
June	1st to 10th	Day	13% 7% 2 6% 5% 4 6% 4 7% 8% 37%	2850
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 36%	2850
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 5% 8% 8% 37%	2850
July	1st to 10th	Day	9% 4 2 5% 5% 5% 6% 5% 8% 11% 41%	4750
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 9% 50%	4750
	21st to end	Day	5% 4 2 5% 4 4 4 4 7% 10% 51%	4868
August	1st to 10th	Day	9% 6% 2 6% 5% 4 4 4 6% 9% 45%	4357
	11th to 20th	Day	12% 5% 2 5% 3 3 4 3 6% 9% 48%	4041
	21st to end	Day	10% 6% 2 6% 4 3 4 3 5% 8% 49%	4532
September	1st to 10th	Day	12% 5% 2 5% 4 4 3 3 5% 6% 52%	2314
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 4 7% 43%	2090
	21st to end	Day	14% 7% 2 5% 4 3 4 4 6% 7% 43%	2090
October	1st to 10th	Day	10% 8% 3 5% 4 3 4 3 5% 5% 49%	3328
	11th to 20th	Day	10% 10% 2 6% 5% 4 4 4 6% 8% 42%	2961
	21st to end	Day	13% 12% 3 8% 4 4 5% 3 5% 8% 34%	3091
November	1st to 10th	Day	14% 15% 4 12% 5% 4 3 4 5% 5% 29%	1701
	11th to 20th	Day	8% 14% 7% 15% 8% 4 5% 4 4 5% 26%	1600
	21st to end	Day	9% 15% 4 12% 9% 6% 4 4 5% 5% 26%	1417
December	1st to 10th	Day	7% 13% 7% 16% 11% 9% 8% 5% 5% 6% 14%	2290
	11th to 20th	Day	9% 11% 6% 14% 9% 8% 7% 4 7% 7% 19%	2643
	21st to end	Day	6% 10% 4 16% 9% 5% 5% 5% 6% 6% 28%	3498
January	1st to 10th	Night	4 11% 6% 16% 10% 9% 7% 5% 6% 8% 18%	6787
	11th to 20th	Night	4 10% 5% 13% 8% 8% 10% 9% 9% 7% 16%	6506
	21st to end	Night	6% 13% 8% 16% 8% 5% 5% 4 6% 6% 22%	6974
February	1st to 10th	Night	8% 12% 5% 11% 8% 6% 8% 7% 7% 6% 22%	2750
	11th to 20th	Night	6% 9% 3 9% 7% 6% 7% 6% 8% 8% 31%	2533
	21st to end	Night	6% 10% 4 10% 8% 6% 7% 3 7% 8% 31%	1945
March	1st to 10th	Night	8% 10% 4 10% 9% 7% 5% 3 6% 7% 30%	3734
	11th to 20th	Night	6% 11% 4 9% 6% 4 5% 3 6% 7% 38%	3494
	21st to end	Night	7% 10% 5% 14% 8% 6% 4 3 5% 5% 31%	3792
April	1st to 10th	Night	7% 8% 3 7% 6% 4 5% 5% 7% 8% 41%	1867
	11th to 20th	Night	13% 12% 4 8% 5% 4 6% 5% 5% 7% 33%	1689
	21st to end	Night	13% 8% 3 7% 4 5% 5% 4 6% 7% 36%	1710
May	1st to 10th	Night	20% 9% 3 7% 4 4 4 4 5% 6% 35%	2829
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 5% 6% 41%	2249
	21st to end	Night	17% 7% 3 5% 4 3 3 3 5% 6% 43%	2414
June	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 4 5% 9% 45%	1330
	11th to 20th	Night	12% 6% 2 6% 4 5% 4 3 7% 6% 43%	1330
	21st to end	Night	10% 4 2 5% 3 4 4 4 6% 12% 45%	1330
July	1st to 10th	Night	9% 3 1 4 3 3 4 4 6% 10% 53%	2220
	11th to 20th	Night	6% 3 1 4 3 4 3 4 5% 8% 59%	2220
	21st to end	Night	3 5% 1 4 3 5% 5% 5% 8% 10% 51%	2691
August	1st to 10th	Night	6% 4 2 6% 4 4 4 3 6% 7% 54%	2581
	11th to 20th	Night	7% 4 1 5% 4 4 4 4 6% 10% 51%	2798
	21st to end	Night	10% 5% 2 6% 3 3 4 4 4 7% 53%	3135
September	1st to 10th	Night	9% 5% 1 5% 3 3 4 3 5% 8% 54%	1862
	11th to 20th	Night	12% 5% 2 5% 3 3 3 4 6% 7% 49%	2090
	21st to end	Night	14% 7% 3 6% 5% 4 4 3 5% 6% 45%	2090
October	1st to 10th	Night	10% 8% 3 6% 3 4 3 3 5% 7% 47%	3599
	11th to 20th	Night	10% 8% 3 6% 3 4 4 4 6% 9% 43%	3959
	21st to end	Night	7% 10% 3 8% 5% 5% 4 3 5% 7% 42%	4467
November	1st to 10th	Night	11% 12% 4 9% 5% 5% 5% 4 6% 7% 32%	2595
	11th to 20th	Night	9% 15% 6% 13% 6% 5% 4 4 5% 6% 27%	2800
	21st to end	Night	9% 14% 4 12% 7% 6% 6% 3 6% 6% 28%	2980
December	1st to 10th	Night	7% 12% 6% 15% 10% 10% 8% 5% 6% 6% 17%	4900
	11th to 20th	Night	8% 13% 5% 16% 10% 7% 6% 4 5% 6% 20%	5564
	21st to end	Night	7% 10% 4 14% 9% 8% 6% 4 6% 6% 26%	7480

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	63% 6% 11% 16% 5%	3179
	11th to 20th	Day	60% 7% 10% 15% 8%	3474
	21st to end	Day	58% 5% 14% 18% 4	4004
February	1st to 10th	Day	60% 6% 9% 17% 7% 1	1649
	11th to 20th	Day	52% 7% 11% 20% 9% 1	1773
	21st to end	Day	56% 7% 12% 17% 8%	1610
March	1st to 10th	Day	54% 7% 14% 18% 8%	3130
	11th to 20th	Day	54% 9% 14% 17% 5%	3466
	21st to end	Day	56% 7% 12% 19% 6%	3838
April	1st to 10th	Day	47% 6% 14% 24% 8% 1	2313
	11th to 20th	Day	52% 7% 13% 18% 10% 1	2442
	21st to end	Day	50% 6% 16% 19% 7% 1	2470
May	1st to 10th	Day	48% 5% 15% 21% 9% 1	4137
	11th to 20th	Day	49% 7% 12% 23% 8% 1	4645
	21st to end	Day	47% 7% 12% 24% 8%	5173
June	1st to 10th	Day	41% 9% 18% 22% 10% 1	2850
	11th to 20th	Day	45% 9% 14% 22% 9% 1	2850
	21st to end	Day	41% 9% 20% 24% 6% 1	2850
July	1st to 10th	Day	33% 11% 25% 25% 5%	4676
	11th to 20th	Day	28% 8% 21% 36% 7%	4669
	21st to end	Day	26% 9% 24% 32% 8%	4714
August	1st to 10th	Day	35% 8% 18% 26% 12% 1	4342
	11th to 20th	Day	31% 7% 19% 34% 8%	4080
	21st to end	Day	33% 6% 20% 32% 9%	4531
September	1st to 10th	Day	32% 6% 18% 31% 12% 1	2314
	11th to 20th	Day	41% 6% 18% 25% 10% 1	2090
	21st to end	Day	39% 7% 15% 30% 9%	2090
October	1st to 10th	Day	37% 5% 11% 37% 10% 1	3328
	11th to 20th	Day	39% 5% 11% 32% 12%	2961
	21st to end	Day	49% 5% 12% 25% 9%	3091
November	1st to 10th	Day	56% 6% 11% 18% 8% 1	1701
	11th to 20th	Day	59% 6% 15% 14% 6% 1	1600
	21st to end	Day	60% 7% 11% 16% 6%	1417
December	1st to 10th	Day	70% 6% 11% 10% 3	2290
	11th to 20th	Day	62% 5% 11% 14% 7%	2640
	21st to end	Day	54% 5% 10% 18% 13%	3498
January	1st to 10th	Night	62% 7% 10% 17% 5%	6787
	11th to 20th	Night	60% 7% 10% 16% 6%	6506
	21st to end	Night	61% 5% 11% 19% 5%	6974
February	1st to 10th	Night	56% 6% 12% 16% 10% 1	2750
	11th to 20th	Night	46% 7% 14% 20% 13% 1	2534
	21st to end	Night	49% 6% 13% 21% 10% 1	1945
March	1st to 10th	Night	51% 7% 14% 20% 8%	3734
	11th to 20th	Night	43% 6% 17% 23% 11% 1	3494
	21st to end	Night	53% 7% 11% 21% 8%	3792
April	1st to 10th	Night	39% 6% 13% 24% 16% 2	1867
	11th to 20th	Night	50% 7% 11% 18% 13% 1	1689
	21st to end	Night	45% 8% 14% 21% 11% 1	1710
May	1st to 10th	Night	47% 6% 12% 25% 10% 1	2829
	11th to 20th	Night	41% 8% 14% 24% 10% 3	2250
	21st to end	Night	40% 6% 13% 31% 9%	2414
June	1st to 10th	Night	35% 8% 19% 28% 9% 2	1330
	11th to 20th	Night	38% 7% 16% 25% 12% 1	1330
	21st to end	Night	32% 8% 21% 32% 6% 1	1330
July	1st to 10th	Night	25% 10% 28% 28% 7% 1	2185
	11th to 20th	Night	23% 7% 18% 41% 11% 1	2178
	21st to end	Night	24% 7% 24% 33% 10% 1	2607
August	1st to 10th	Night	28% 6% 17% 33% 15% 1	2573
	11th to 20th	Night	27% 8% 21% 33% 11% 1	2825
	21st to end	Night	31% 6% 17% 34% 11% 1	3135
September	1st to 10th	Night	28% 6% 15% 35% 15% 2	1862
	11th to 20th	Night	33% 7% 18% 29% 13% 1	2090
	21st to end	Night	40% 5% 12% 30% 11% 1	2090
October	1st to 10th	Night	37% 5% 12% 29% 15% 1	3599
	11th to 20th	Night	38% 5% 12% 29% 16%	3959
	21st to end	Night	42% 5% 13% 32% 8%	4467
November	1st to 10th	Night	50% 7% 14% 19% 8% 2	2595
	11th to 20th	Night	57% 6% 13% 15% 7% 1	2800
	21st to end	Night	55% 7% 14% 18% 6%	2980
December	1st to 10th	Night	66% 7% 13% 10% 4	4900
	11th to 20th	Night	63% 5% 11% 16% 4 1	5566
	21st to end	Night	56% 6% 9% 18% 10% 1	7480

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	9% 11% 36% 32% 11% 3	300
	11th to 20th	Day	11% 12% 42% 24% 10% 1	300
	21st to end	Day	15% 11% 42% 21% 9% 2	330
February	1st to 10th	Day	14% 14% 40% 25% 6% 1	300
	11th to 20th	Day	8% 14% 38% 33% 7% 1	300
	21st to end	Day	6% 10% 43% 30% 9% 1	237
March	1st to 10th	Day	14% 15% 34% 30% 5% 1	270
	11th to 20th	Day	14% 15% 30% 29% 10% 2	270
	21st to end	Day	16% 10% 33% 26% 12% 3	309
April	1st to 10th	Day	14% 17% 34% 25% 9% 1	493
	11th to 20th	Day	20% 13% 33% 23% 10% 1	640
	21st to end	Day	18% 12% 36% 22% 11% 1	650
May	1st to 10th	Day	16% 14% 29% 27% 12% 2	653
	11th to 20th	Day	20% 8% 34% 23% 12% 3	675
	21st to end	Day	19% 10% 26% 30% 13% 2	734
June	1st to 10th	Day	15% 11% 31% 24% 13% 5%	680
	11th to 20th	Day	14% 13% 36% 24% 11% 3	680
	21st to end	Day	13% 8% 30% 32% 14% 3	680
July	1st to 10th	Day	8% 6% 28% 30% 20% 7%	671
	11th to 20th	Day	13% 7% 30% 27% 18% 5%	668
	21st to end	Day	5% 6% 27% 36% 19% 7%	739
August	1st to 10th	Day	9% 7% 26% 33% 19% 7%	676
	11th to 20th	Day	14% 5% 24% 30% 19% 8%	665
	21st to end	Day	14% 6% 27% 31% 19% 3	748
September	1st to 10th	Day	13% 8% 37% 26% 13% 3	524
	11th to 20th	Day	20% 9% 31% 31% 9% 1	300
	21st to end	Day	21% 11% 34% 24% 10% 1	300
October	1st to 10th	Day	20% 16% 27% 24% 12% 1	300
	11th to 20th	Day	18% 11% 40% 23% 5% 2	300
	21st to end	Day	23% 12% 37% 19% 7% 2	330
November	1st to 10th	Day	23% 13% 35% 21% 8%	300
	11th to 20th	Day	14% 18% 37% 24% 6%	300
	21st to end	Day	15% 17% 42% 21% 5%	300
December	1st to 10th	Day	14% 12% 38% 26% 8% 2	300
	11th to 20th	Day	16% 16% 40% 24% 3 1	300
	21st to end	Day	13% 9% 41% 25% 8% 4	330
January	1st to 10th	Night	11% 11% 38% 29% 10% 1	1000
	11th to 20th	Night	14% 11% 40% 27% 7%	1000
	21st to end	Night	13% 13% 39% 27% 7% 1	1100
February	1st to 10th	Night	13% 12% 36% 30% 8% 1	1000
	11th to 20th	Night	9% 10% 37% 33% 10% 2	979
	21st to end	Night	11% 9% 37% 31% 11% 2	653
March	1st to 10th	Night	14% 10% 33% 27% 12% 3	760
	11th to 20th	Night	11% 9% 40% 28% 11% 1	584
	21st to end	Night	15% 9% 31% 30% 12% 2	627
April	1st to 10th	Night	10% 9% 36% 34% 9% 2	570
	11th to 20th	Night	19% 8% 31% 33% 8% 1	563
	21st to end	Night	15% 9% 30% 32% 11% 1	570
May	1st to 10th	Night	17% 8% 31% 31% 12% 1	570
	11th to 20th	Night	16% 9% 28% 33% 13% 1	561
	21st to end	Night	18% 7% 30% 33% 12%	617
June	1st to 10th	Night	14% 7% 31% 35% 12% 2	570
	11th to 20th	Night	14% 7% 35% 30% 14% 1	570
	21st to end	Night	11% 5% 27% 40% 16% 1	570
July	1st to 10th	Night	6% 3 26% 42% 21% 1	555
	11th to 20th	Night	7% 5% 28% 41% 18% 1	552
	21st to end	Night	5% 4 25% 46% 17% 3	624
August	1st to 10th	Night	8% 2 23% 46% 19% 1	567
	11th to 20th	Night	9% 6% 23% 39% 20% 3	564
	21st to end	Night	11% 4 29% 37% 17% 1	627
September	1st to 10th	Night	11% 4 32% 35% 16% 3	570
	11th to 20th	Night	14% 7% 30% 37% 11%	570
	21st to end	Night	17% 9% 33% 30% 11% 1	570
October	1st to 10th	Night	19% 10% 32% 29% 9%	637
	11th to 20th	Night	19% 11% 30% 30% 9%	864
	21st to end	Night	16% 12% 37% 25% 8% 1	1045
November	1st to 10th	Night	17% 12% 38% 25% 8% 1	975
	11th to 20th	Night	16% 13% 39% 23% 9% 2	1000
	21st to end	Night	16% 15% 39% 23% 5% 1	1000
December	1st to 10th	Night	11% 11% 39% 29% 8% 2	1000
	11th to 20th	Night	16% 12% 37% 27% 7% 2	1000
	21st to end	Night	18% 7% 36% 28% 9% 1	1100

Page generated at 2025-02-22 05:51:40. Version ac07

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