Four Winds Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Four Winds Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	14% 11% 4 9% 5% 4 4 3 5% 6% 34%	101292
	Night	15% 14% 5% 11% 6% 4 4 3 4 5% 29%	98510
Transparency	Day	49% 7% 12% 20% 11% 1	104789
	Night	56% 7% 11% 17% 8% 1	103101
Seeing	Day	17% 9% 26% 27% 16% 4	15871
	Night	20% 10% 26% 29% 13% 2	25878

By Month

Percentage Cloud Cover NE (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	12% 25% 15% 21% 7% 5% 2 1 3 2 5%	2527
	11th to 20th	Day	14% 17% 9% 26% 15% 8% 2 2 2 2 3	2530
	21st to end	Day	18% 23% 11% 16% 8% 5% 4 2 3 3 7%	2783
February	1st to 10th	Day	9% 20% 6% 17% 15% 7% 3 2 4 4 12%	1614
	11th to 20th	Day	12% 14% 7% 18% 12% 6% 5% 3 3 4 16%	1848
	21st to end	Day	13% 17% 7% 12% 8% 6% 5% 3 5% 4 20%	1570
March	1st to 10th	Day	13% 13% 4 10% 5% 4 3 3 5% 6% 33%	3118
	11th to 20th	Day	8% 11% 6% 17% 6% 4 4 3 5% 6% 30%	3369
	21st to end	Day	17% 12% 8% 15% 5% 4 3 3 4 4 23%	3995
April	1st to 10th	Day	18% 14% 4 8% 5% 4 4 3 6% 6% 30%	2280
	11th to 20th	Day	19% 12% 4 6% 3 4 3 3 4 6% 35%	2337
	21st to end	Day	16% 9% 3 9% 4 4 4 4 6% 6% 35%	2470
May	1st to 10th	Day	13% 8% 2 6% 4 4 4 3 5% 6% 44%	4108
	11th to 20th	Day	10% 7% 2 6% 4 4 4 3 5% 5% 50%	4271
	21st to end	Day	12% 6% 2 6% 4 5% 4 4 5% 8% 44%	4837
June	1st to 10th	Day	13% 4 2 7% 4 4 4 3 6% 8% 45%	2660
	11th to 20th	Day	11% 5% 2 5% 4 5% 4 5% 6% 9% 45%	2666
	21st to end	Day	13% 6% 2 5% 3 3 5% 4 5% 7% 45%	2660
July	1st to 10th	Day	18% 6% 2 5% 4 3 4 4 6% 8% 42%	4440
	11th to 20th	Day	8% 4 1 4 3 3 4 3 6% 8% 56%	4440
	21st to end	Day	9% 4 2 5% 3 3 3 4 6% 8% 53%	4814
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 5% 4 7% 9% 44%	4279
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 4 6% 51%	4044
	21st to end	Day	13% 5% 3 7% 4 4 4 3 4 6% 47%	4310
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 6% 45%	2271
	11th to 20th	Day	14% 4 2 6% 4 3 4 4 5% 9% 46%	2090
	21st to end	Day	17% 6% 2 6% 5% 4 5% 4 7% 8% 38%	2090
October	1st to 10th	Day	19% 8% 3 7% 4 4 4 3 5% 7% 36%	2090
	11th to 20th	Day	24% 16% 3 9% 5% 5% 5% 3 4 5% 21%	1791
	21st to end	Day	25% 16% 4 10% 6% 4 5% 3 4 5% 18%	1881
November	1st to 10th	Day	19% 19% 4 6% 4 4 4 3 5% 7% 26%	1762
	11th to 20th	Day	15% 23% 7% 12% 6% 5% 4 3 5% 4 15%	1800
	21st to end	Day	17% 27% 9% 12% 5% 3 4 2 3 4 13%	1698
December	1st to 10th	Day	16% 30% 13% 17% 4 4 3 2 2 2 8%	1386
	11th to 20th	Day	16% 24% 9% 17% 9% 4 4 3 3 4 8%	1680
	21st to end	Day	21% 21% 11% 14% 6% 4 4 2 3 3 9%	2783
January	1st to 10th	Night	13% 27% 10% 21% 8% 4 2 2 2 2 10%	4428
	11th to 20th	Night	12% 18% 9% 22% 17% 7% 3 2 2 2 6%	4440
	21st to end	Night	16% 23% 10% 17% 8% 6% 4 2 3 3 8%	4884
February	1st to 10th	Night	11% 18% 6% 18% 14% 7% 4 3 3 3 13%	2564
	11th to 20th	Night	12% 15% 7% 17% 11% 5% 4 3 3 4 18%	2218
	21st to end	Night	16% 17% 5% 14% 7% 4 4 3 4 7% 21%	1884
March	1st to 10th	Night	15% 11% 3 7% 4 4 3 3 5% 6% 39%	3722
	11th to 20th	Night	8% 15% 6% 10% 5% 4 4 3 4 6% 34%	3589
	21st to end	Night	15% 13% 6% 13% 6% 4 4 3 4 6% 26%	3665
April	1st to 10th	Night	18% 13% 3 9% 5% 4 4 4 5% 6% 30%	1900
	11th to 20th	Night	20% 10% 3 7% 4 4 4 4 5% 5% 34%	1792
	21st to end	Night	17% 9% 3 8% 5% 4 4 4 4 6% 36%	1710
May	1st to 10th	Night	16% 7% 3 6% 4 5% 4 3 5% 6% 41%	2833
	11th to 20th	Night	13% 7% 2 7% 5% 4 5% 4 6% 5% 42%	2614
	21st to end	Night	18% 6% 2 5% 4 3 4 3 6% 7% 43%	2750
June	1st to 10th	Night	13% 7% 2 6% 4 5% 4 3 5% 6% 43%	1520
	11th to 20th	Night	12% 6% 2 5% 5% 5% 4 4 6% 8% 43%	1420
	21st to end	Night	12% 6% 2 7% 4 4 4 4 5% 7% 45%	1520
July	1st to 10th	Night	14% 7% 3 6% 4 4 4 4 6% 7% 42%	2530
	11th to 20th	Night	7% 4 1 6% 3 3 4 3 5% 7% 55%	2530
	21st to end	Night	10% 4 2 7% 4 3 5% 4 5% 7% 49%	2750
August	1st to 10th	Night	12% 6% 2 7% 5% 5% 4 3 5% 6% 43%	2653
	11th to 20th	Night	15% 4 2 5% 4 3 3 3 5% 7% 49%	2785
	21st to end	Night	14% 5% 2 5% 4 4 4 3 5% 6% 48%	3343
September	1st to 10th	Night	12% 6% 3 6% 3 4 4 3 5% 7% 49%	1900
	11th to 20th	Night	14% 5% 2 5% 3 4 4 4 5% 7% 47%	2080
	21st to end	Night	18% 6% 2 7% 5% 4 4 3 6% 7% 38%	2090
October	1st to 10th	Night	19% 8% 3 7% 5% 4 4 2 4 6% 37%	2090
	11th to 20th	Night	25% 13% 3 8% 4 4 4 4 4 6% 25%	2388
	21st to end	Night	25% 15% 3 8% 6% 5% 4 3 4 5% 22%	2717
November	1st to 10th	Night	17% 17% 4 8% 5% 5% 4 3 4 6% 27%	2536
	11th to 20th	Night	16% 24% 7% 11% 6% 5% 4 3 3 4 18%	2600
	21st to end	Night	18% 24% 8% 12% 6% 5% 3 3 4 4 14%	2692
December	1st to 10th	Night	15% 27% 11% 17% 7% 4 3 2 3 3 9%	2977
	11th to 20th	Night	15% 22% 9% 20% 8% 4 4 2 3 3 10%	3512
	21st to end	Night	24% 23% 9% 13% 5% 3 3 2 3 4 10%	4884

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	88% 5% 4 3	2528
	11th to 20th	Day	91% 4 3 2	2530
	21st to end	Day	83% 7% 7% 3 1	2783
February	1st to 10th	Day	77% 5% 7% 9% 1	1614
	11th to 20th	Day	73% 7% 8% 9% 3	1858
	21st to end	Day	67% 7% 9% 13% 3 1	1570
March	1st to 10th	Day	51% 7% 13% 19% 9%	3120
	11th to 20th	Day	53% 8% 14% 18% 5% 1	3369
	21st to end	Day	62% 8% 10% 15% 5% 1	3995
April	1st to 10th	Day	55% 6% 10% 19% 10%	2280
	11th to 20th	Day	49% 6% 11% 19% 13% 2	2337
	21st to end	Day	47% 7% 12% 16% 16% 3	2470
May	1st to 10th	Day	39% 8% 11% 23% 18% 2	4120
	11th to 20th	Day	34% 7% 11% 28% 17% 2	4275
	21st to end	Day	35% 9% 13% 22% 19% 2	4837
June	1st to 10th	Day	36% 8% 13% 26% 16% 2	2660
	11th to 20th	Day	35% 8% 13% 24% 18% 2	2666
	21st to end	Day	37% 7% 16% 25% 14% 1	2660
July	1st to 10th	Day	41% 5% 15% 24% 13% 2	4371
	11th to 20th	Day	25% 6% 16% 37% 14% 1	4365
	21st to end	Day	28% 7% 14% 30% 19% 1	4662
August	1st to 10th	Day	34% 7% 17% 29% 12% 1	4264
	11th to 20th	Day	35% 6% 14% 31% 14% 1	4083
	21st to end	Day	39% 6% 14% 29% 11% 1	4309
September	1st to 10th	Day	38% 7% 14% 25% 14% 1	2271
	11th to 20th	Day	33% 10% 16% 29% 11% 1	2090
	21st to end	Day	43% 8% 15% 24% 9%	2090
October	1st to 10th	Day	33% 5% 9% 32% 19% 1	3480
	11th to 20th	Day	56% 6% 10% 19% 10%	2942
	21st to end	Day	63% 6% 13% 16% 3	3081
November	1st to 10th	Day	58% 7% 11% 17% 7%	1762
	11th to 20th	Day	70% 7% 10% 9% 4	1800
	21st to end	Day	75% 6% 11% 6% 1	1698
December	1st to 10th	Day	86% 4 4 5% 1	1386
	11th to 20th	Day	80% 9% 6% 4 1	1680
	21st to end	Day	80% 9% 7% 3 1	2783
January	1st to 10th	Night	82% 6% 6% 5% 1	4428
	11th to 20th	Night	86% 6% 4 3 1	4440
	21st to end	Night	82% 8% 7% 3	4884
February	1st to 10th	Night	77% 6% 7% 8% 2	2564
	11th to 20th	Night	69% 8% 9% 12% 3	2219
	21st to end	Night	64% 7% 12% 14% 3	1884
March	1st to 10th	Night	46% 7% 17% 22% 8%	3733
	11th to 20th	Night	48% 9% 12% 23% 8% 1	3590
	21st to end	Night	56% 11% 11% 16% 6% 1	3665
April	1st to 10th	Night	53% 8% 9% 19% 10% 1	1900
	11th to 20th	Night	50% 6% 10% 18% 13% 3	1792
	21st to end	Night	48% 7% 9% 20% 13% 3	1710
May	1st to 10th	Night	41% 9% 11% 19% 16% 3	2840
	11th to 20th	Night	39% 9% 10% 26% 15% 1	2615
	21st to end	Night	39% 8% 14% 19% 15% 5%	2751
June	1st to 10th	Night	38% 9% 11% 27% 14% 1	1520
	11th to 20th	Night	37% 8% 14% 23% 17% 3	1420
	21st to end	Night	37% 8% 11% 27% 15% 2	1520
July	1st to 10th	Night	39% 6% 15% 24% 13% 4	2490
	11th to 20th	Night	27% 7% 16% 31% 18% 1	2482
	21st to end	Night	34% 7% 13% 25% 20% 1	2662
August	1st to 10th	Night	39% 7% 15% 26% 12% 1	2644
	11th to 20th	Night	34% 6% 15% 29% 15% 1	2812
	21st to end	Night	36% 6% 14% 24% 19% 1	3343
September	1st to 10th	Night	35% 7% 14% 23% 20% 1	1900
	11th to 20th	Night	36% 7% 17% 27% 13%	2080
	21st to end	Night	44% 8% 15% 23% 9% 1	2090
October	1st to 10th	Night	41% 6% 9% 32% 12% 1	3480
	11th to 20th	Night	51% 6% 10% 22% 11%	3976
	21st to end	Night	55% 6% 13% 21% 5%	4467
November	1st to 10th	Night	57% 8% 12% 17% 6% 1	2536
	11th to 20th	Night	70% 7% 9% 9% 5% 1	2600
	21st to end	Night	74% 8% 10% 7% 1	2692
December	1st to 10th	Night	82% 6% 5% 6% 1	2977
	11th to 20th	Night	78% 8% 8% 3 2	3511
	21st to end	Night	78% 9% 9% 3 1	4884

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	18% 16% 37% 21% 7% 2	270
	11th to 20th	Day	23% 13% 37% 22% 4 1	270
	21st to end	Day	23% 13% 32% 26% 6% 1	297
February	1st to 10th	Day	21% 19% 37% 16% 6% 1	270
	11th to 20th	Day	17% 19% 39% 18% 6%	270
	21st to end	Day	17% 25% 41% 15% 2	225
March	1st to 10th	Day	20% 16% 40% 20% 5%	270
	11th to 20th	Day	19% 14% 29% 26% 11% 2	388
	21st to end	Day	24% 12% 29% 24% 10% 1	506
April	1st to 10th	Day	23% 12% 30% 26% 8% 1	460
	11th to 20th	Day	25% 13% 28% 19% 11% 3	452
	21st to end	Day	18% 10% 29% 27% 14% 3	460
May	1st to 10th	Day	17% 10% 30% 27% 12% 4	463
	11th to 20th	Day	15% 5% 28% 34% 14% 4	599
	21st to end	Day	13% 7% 22% 30% 23% 5%	734
June	1st to 10th	Day	13% 5% 25% 32% 20% 4	680
	11th to 20th	Day	13% 4 25% 33% 20% 5%	680
	21st to end	Day	15% 5% 20% 34% 21% 5%	680
July	1st to 10th	Day	10% 2 17% 36% 27% 8%	671
	11th to 20th	Day	9% 4 22% 33% 24% 8%	668
	21st to end	Day	8% 3 19% 35% 29% 6%	739
August	1st to 10th	Day	9% 4 18% 33% 27% 9%	597
	11th to 20th	Day	12% 3 17% 30% 28% 10%	479
	21st to end	Day	16% 4 19% 29% 25% 7%	539
September	1st to 10th	Day	17% 7% 22% 24% 22% 8%	490
	11th to 20th	Day	11% 4 22% 26% 26% 10%	490
	21st to end	Day	19% 8% 17% 30% 21% 6%	490
October	1st to 10th	Day	20% 12% 25% 24% 15% 4	490
	11th to 20th	Day	28% 14% 29% 23% 6% 1	352
	21st to end	Day	30% 15% 27% 22% 5% 1	330
November	1st to 10th	Day	29% 15% 27% 18% 11% 1	300
	11th to 20th	Day	19% 20% 40% 17% 4	300
	21st to end	Day	28% 20% 32% 17% 3	285
December	1st to 10th	Day	31% 16% 32% 13% 7% 1	196
	11th to 20th	Day	27% 22% 33% 16% 3 1	184
	21st to end	Day	27% 20% 36% 13% 3 1	297
January	1st to 10th	Night	20% 15% 37% 22% 6% 1	950
	11th to 20th	Night	25% 15% 31% 21% 7% 1	950
	21st to end	Night	20% 11% 33% 26% 8% 1	1045
February	1st to 10th	Night	17% 15% 34% 26% 7% 1	870
	11th to 20th	Night	20% 13% 35% 24% 8%	743
	21st to end	Night	23% 15% 30% 27% 5%	628
March	1st to 10th	Night	17% 10% 30% 31% 11% 1	760
	11th to 20th	Night	15% 11% 35% 29% 9% 1	760
	21st to end	Night	21% 8% 26% 34% 10% 1	748
April	1st to 10th	Night	23% 9% 29% 31% 8% 1	570
	11th to 20th	Night	23% 9% 25% 31% 11% 1	563
	21st to end	Night	18% 6% 28% 34% 12% 1	570
May	1st to 10th	Night	17% 5% 26% 35% 16% 1	570
	11th to 20th	Night	18% 3 22% 39% 17% 1	561
	21st to end	Night	13% 4 21% 34% 25% 3	617
June	1st to 10th	Night	16% 3 21% 37% 21% 1	570
	11th to 20th	Night	13% 4 19% 39% 23% 2	470
	21st to end	Night	14% 2 18% 38% 26% 2	570
July	1st to 10th	Night	11% 2 13% 43% 28% 5%	555
	11th to 20th	Night	11% 1 17% 37% 29% 5%	552
	21st to end	Night	9% 3 17% 37% 31% 4	624
August	1st to 10th	Night	11% 1 15% 42% 28% 3	567
	11th to 20th	Night	11% 4 15% 32% 32% 6%	564
	21st to end	Night	15% 3 15% 38% 27% 2	627
September	1st to 10th	Night	15% 3 20% 32% 27% 4	570
	11th to 20th	Night	16% 4 18% 32% 25% 5%	750
	21st to end	Night	19% 7% 19% 30% 19% 5%	760
October	1st to 10th	Night	23% 9% 21% 29% 16% 2	760
	11th to 20th	Night	29% 11% 25% 26% 8% 1	760
	21st to end	Night	32% 11% 27% 23% 7% 1	836
November	1st to 10th	Night	27% 14% 24% 28% 6% 1	780
	11th to 20th	Night	29% 16% 31% 19% 4	800
	21st to end	Night	28% 16% 30% 21% 4	870
December	1st to 10th	Night	26% 20% 31% 19% 4	993
	11th to 20th	Night	25% 15% 35% 18% 5% 1	950
	21st to end	Night	30% 13% 35% 20% 2	1045

Page generated at 2024-12-06 03:54:52. Version ac07

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