Jordan Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jordan Lake clear sky chart from 2005-11-06 to 2024-11-04.

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	13% 6% 2 6% 4 4 4 4 6% 8% 42%	100845
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	98125
Transparency	Day	38% 7% 12% 20% 18% 5%	104495
	Night	38% 6% 11% 19% 19% 6%	102614
Seeing	Day	16% 11% 25% 25% 17% 6%	15379
	Night	16% 8% 26% 31% 17% 2	25615

By Month

Percentage Cloud Cover SE (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	18% 5% 2 4 3 3 3 2 3 5% 51%	2836
	11th to 20th	Day	14% 7% 3 5% 3 3 3 3 4 5% 53%	2840
	21st to end	Day	19% 10% 3 5% 4 3 3 3 4 5% 42%	3124
February	1st to 10th	Day	14% 6% 3 5% 4 4 4 4 5% 7% 44%	1710
	11th to 20th	Day	22% 6% 2 4 3 3 2 2 4 4 46%	1666
	21st to end	Day	19% 8% 2 6% 4 4 3 3 5% 6% 40%	1727
March	1st to 10th	Day	23% 7% 2 6% 3 4 4 4 5% 7% 37%	3435
	11th to 20th	Day	10% 5% 1 5% 3 4 3 3 4 7% 55%	3480
	21st to end	Day	20% 7% 2 6% 4 3 4 3 4 5% 43%	3815
April	1st to 10th	Day	11% 4 1 4 3 3 3 4 4 7% 54%	2199
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 6% 7% 48%	2254
	21st to end	Day	14% 5% 2 5% 4 5% 4 4 5% 6% 46%	2280
May	1st to 10th	Day	10% 7% 3 8% 6% 5% 6% 4 7% 10% 34%	4067
	11th to 20th	Day	17% 8% 2 7% 5% 4 5% 4 6% 8% 34%	4081
	21st to end	Day	7% 4 2 5% 4 5% 5% 5% 6% 9% 48%	4476
June	1st to 10th	Day	9% 5% 2 7% 4 6% 5% 5% 8% 9% 39%	2470
	11th to 20th	Day	8% 6% 2 5% 5% 5% 5% 5% 7% 10% 43%	2470
	21st to end	Day	7% 5% 2 5% 5% 5% 5% 6% 9% 11% 39%	2470
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 7% 6% 8% 9% 36%	4120
	11th to 20th	Day	10% 7% 3 7% 6% 6% 6% 5% 8% 12% 31%	4120
	21st to end	Day	11% 8% 3 9% 6% 7% 6% 6% 8% 10% 27%	4466
August	1st to 10th	Day	20% 8% 3 8% 6% 6% 6% 5% 8% 9% 22%	4104
	11th to 20th	Day	9% 6% 2 8% 5% 5% 6% 5% 8% 10% 36%	3926
	21st to end	Day	7% 4 2 5% 4 4 4 3 6% 10% 51%	4180
September	1st to 10th	Day	9% 4 1 6% 4 5% 5% 5% 7% 8% 47%	2280
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 5% 7% 42%	2135
	21st to end	Day	21% 7% 2 6% 4 3 4 3 5% 7% 39%	2057
October	1st to 10th	Day	15% 6% 2 6% 3 3 3 2 4 7% 49%	1900
	11th to 20th	Day	12% 4 1 4 3 3 3 3 5% 5% 57%	1900
	21st to end	Day	11% 4 2 6% 3 3 3 2 4 5% 57%	2090
November	1st to 10th	Day	14% 6% 2 4 3 2 3 2 4 6% 54%	1887
	11th to 20th	Day	15% 4 2 4 3 3 3 2 5% 6% 53%	1886
	21st to end	Day	14% 6% 2 5% 3 4 4 3 5% 6% 50%	1650
December	1st to 10th	Day	19% 7% 2 5% 4 4 3 3 5% 7% 41%	1520
	11th to 20th	Day	16% 5% 1 4 2 2 2 2 4 5% 56%	2100
	21st to end	Day	17% 6% 2 5% 4 4 5% 3 4 8% 42%	3124
January	1st to 10th	Night	15% 6% 2 5% 4 3 4 3 4 6% 47%	4109
	11th to 20th	Night	13% 8% 3 6% 4 3 4 3 4 5% 47%	4120
	21st to end	Night	19% 7% 2 5% 4 3 4 3 4 5% 44%	4532
February	1st to 10th	Night	17% 6% 2 6% 3 3 4 3 5% 6% 45%	2470
	11th to 20th	Night	21% 6% 2 5% 4 4 3 3 4 5% 43%	2395
	21st to end	Night	16% 5% 2 5% 4 4 4 3 6% 6% 45%	1727
March	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 4 5% 34%	3418
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	3480
	21st to end	Night	18% 5% 2 5% 3 3 3 3 4 6% 48%	3817
April	1st to 10th	Night	14% 6% 1 6% 3 4 3 3 4 7% 49%	1981
	11th to 20th	Night	13% 5% 2 6% 4 2 4 3 4 6% 51%	1875
	21st to end	Night	12% 4 1 5% 4 4 5% 4 6% 8% 47%	1900
May	1st to 10th	Night	13% 8% 2 7% 5% 4 4 4 6% 7% 39%	2857
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 4 6% 37%	2812
	21st to end	Night	8% 5% 2 5% 4 4 5% 4 6% 11% 45%	3079
June	1st to 10th	Night	11% 6% 2 7% 4 5% 5% 5% 6% 10% 39%	1710
	11th to 20th	Night	10% 6% 2 8% 5% 5% 5% 4 7% 9% 41%	1710
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 11% 40%	1710
July	1st to 10th	Night	9% 6% 3 8% 6% 6% 6% 5% 9% 10% 33%	2840
	11th to 20th	Night	15% 7% 2 6% 5% 5% 5% 5% 8% 11% 31%	2840
	21st to end	Night	15% 10% 4 9% 5% 6% 5% 5% 6% 8% 28%	3087
August	1st to 10th	Night	23% 6% 3 7% 6% 5% 5% 4 8% 9% 23%	2825
	11th to 20th	Night	9% 6% 2 7% 5% 5% 7% 6% 8% 11% 35%	2871
	21st to end	Night	6% 4 2 6% 4 4 4 4 7% 10% 49%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 4 4 4 6% 8% 46%	1900
	11th to 20th	Night	14% 6% 2 6% 5% 3 5% 3 5% 7% 43%	2041
	21st to end	Night	19% 7% 3 7% 5% 4 4 4 5% 7% 37%	2123
October	1st to 10th	Night	15% 6% 3 5% 4 3 3 3 4 5% 50%	2280
	11th to 20th	Night	13% 5% 1 5% 4 2 3 3 4 5% 54%	2280
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 6% 55%	2508
November	1st to 10th	Night	14% 5% 2 5% 3 3 3 3 4 5% 53%	2264
	11th to 20th	Night	13% 5% 2 5% 4 4 3 3 5% 5% 51%	2291
	21st to end	Night	14% 4 2 5% 3 4 3 3 6% 6% 50%	2520
December	1st to 10th	Night	18% 7% 2 6% 4 4 4 3 3 5% 42%	2660
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 5% 5% 49%	3085
	21st to end	Night	18% 6% 2 5% 4 3 3 3 4 6% 46%	4532

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	37% 4 5% 26% 23% 6%	2837
	11th to 20th	Day	35% 4 6% 17% 32% 6%	2840
	21st to end	Day	44% 5% 6% 17% 21% 6%	3124
February	1st to 10th	Day	40% 4 11% 20% 19% 5%	1710
	11th to 20th	Day	42% 4 6% 18% 23% 7%	1675
	21st to end	Day	45% 5% 9% 16% 19% 6%	1727
March	1st to 10th	Day	46% 6% 9% 17% 14% 8%	3435
	11th to 20th	Day	29% 6% 9% 18% 25% 13%	3480
	21st to end	Day	44% 5% 8% 20% 19% 4	3815
April	1st to 10th	Day	29% 6% 10% 24% 24% 7%	2199
	11th to 20th	Day	33% 7% 11% 21% 20% 8%	2254
	21st to end	Day	37% 8% 11% 22% 18% 5%	2280
May	1st to 10th	Day	42% 11% 16% 17% 12% 2	4105
	11th to 20th	Day	45% 10% 12% 21% 12% 1	4085
	21st to end	Day	28% 10% 16% 22% 20% 4	4489
June	1st to 10th	Day	36% 11% 16% 21% 14% 1	2470
	11th to 20th	Day	34% 11% 16% 23% 15% 2	2470
	21st to end	Day	35% 12% 16% 21% 15% 1	2470
July	1st to 10th	Day	41% 9% 17% 17% 13% 3	4055
	11th to 20th	Day	44% 9% 24% 17% 4 1	4051
	21st to end	Day	50% 10% 15% 15% 10%	4324
August	1st to 10th	Day	56% 7% 18% 13% 5%	4091
	11th to 20th	Day	42% 7% 20% 22% 8% 1	3965
	21st to end	Day	29% 6% 14% 33% 16% 2	4180
September	1st to 10th	Day	33% 10% 15% 19% 19% 5%	2280
	11th to 20th	Day	41% 7% 10% 18% 20% 4	2135
	21st to end	Day	45% 6% 9% 19% 15% 5%	2057
October	1st to 10th	Day	35% 3 7% 20% 26% 9%	3160
	11th to 20th	Day	19% 3 5% 20% 26% 26%	3140
	21st to end	Day	26% 2 6% 25% 24% 17%	3428
November	1st to 10th	Day	32% 4 8% 21% 27% 8%	1887
	11th to 20th	Day	32% 5% 9% 20% 27% 7%	1886
	21st to end	Day	35% 4 9% 22% 24% 7%	1650
December	1st to 10th	Day	43% 5% 10% 21% 18% 4	1520
	11th to 20th	Day	32% 3 7% 25% 24% 9%	2097
	21st to end	Day	40% 6% 10% 22% 20% 2	3124
January	1st to 10th	Night	37% 5% 8% 20% 25% 5%	4109
	11th to 20th	Night	38% 5% 8% 16% 26% 6%	4120
	21st to end	Night	42% 5% 6% 17% 22% 7%	4532
February	1st to 10th	Night	40% 4 9% 21% 20% 6%	2470
	11th to 20th	Night	44% 4 8% 15% 21% 8%	2397
	21st to end	Night	37% 6% 9% 20% 20% 8%	1727
March	1st to 10th	Night	51% 8% 7% 13% 15% 6%	3418
	11th to 20th	Night	34% 6% 7% 13% 24% 17%	3480
	21st to end	Night	37% 5% 8% 21% 22% 6%	3817
April	1st to 10th	Night	36% 5% 10% 17% 25% 8%	1981
	11th to 20th	Night	34% 6% 10% 21% 21% 8%	1875
	21st to end	Night	34% 8% 13% 24% 17% 5%	1900
May	1st to 10th	Night	41% 9% 16% 20% 12% 2	2884
	11th to 20th	Night	46% 9% 11% 18% 16% 1	2813
	21st to end	Night	28% 11% 17% 24% 18% 2	3087
June	1st to 10th	Night	38% 11% 15% 21% 14% 2	1710
	11th to 20th	Night	37% 9% 16% 20% 16% 2	1710
	21st to end	Night	35% 12% 16% 21% 13% 3	1710
July	1st to 10th	Night	42% 12% 18% 16% 11% 2	2795
	11th to 20th	Night	44% 12% 23% 16% 4 1	2786
	21st to end	Night	53% 9% 13% 15% 10%	2988
August	1st to 10th	Night	55% 8% 18% 13% 5%	2814
	11th to 20th	Night	41% 8% 21% 23% 7% 1	2898
	21st to end	Night	29% 7% 12% 28% 21% 3	3476
September	1st to 10th	Night	34% 9% 14% 21% 17% 5%	1900
	11th to 20th	Night	39% 8% 11% 17% 21% 3	2041
	21st to end	Night	46% 8% 12% 15% 15% 4	2123
October	1st to 10th	Night	38% 3 7% 21% 25% 6%	3800
	11th to 20th	Night	25% 3 6% 18% 28% 21%	3779
	21st to end	Night	25% 2 7% 25% 24% 16%	4120
November	1st to 10th	Night	34% 5% 8% 18% 26% 9%	2264
	11th to 20th	Night	35% 5% 9% 16% 24% 12%	2291
	21st to end	Night	33% 5% 7% 22% 25% 7%	2520
December	1st to 10th	Night	45% 6% 7% 19% 19% 4	2660
	11th to 20th	Night	38% 4 8% 19% 23% 8%	3087
	21st to end	Night	38% 4 8% 24% 23% 3	4532

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	24% 23% 35% 16% 3	270
	11th to 20th	Day	26% 23% 35% 13% 4	270
	21st to end	Day	20% 23% 40% 14% 3	297
February	1st to 10th	Day	20% 19% 40% 17% 4	270
	11th to 20th	Day	36% 20% 34% 9% 1	273
	21st to end	Day	25% 19% 34% 18% 3	382
March	1st to 10th	Day	23% 17% 34% 20% 7%	460
	11th to 20th	Day	19% 22% 39% 14% 5% 1	460
	21st to end	Day	21% 22% 33% 18% 6% 1	506
April	1st to 10th	Day	21% 18% 33% 20% 7% 2	460
	11th to 20th	Day	14% 19% 29% 23% 11% 4	452
	21st to end	Day	18% 12% 29% 28% 12% 1	460
May	1st to 10th	Day	14% 19% 30% 24% 11% 4	463
	11th to 20th	Day	16% 7% 23% 31% 19% 5%	487
	21st to end	Day	17% 7% 19% 26% 23% 8%	529
June	1st to 10th	Day	11% 5% 23% 32% 22% 6%	490
	11th to 20th	Day	10% 5% 21% 29% 26% 9%	490
	21st to end	Day	10% 4 18% 35% 25% 8%	490
July	1st to 10th	Day	10% 1 9% 31% 35% 13%	485
	11th to 20th	Day	7% 1 9% 31% 38% 13%	484
	21st to end	Day	7% 2 16% 34% 30% 11%	532
August	1st to 10th	Day	14% 3 17% 30% 25% 11%	486
	11th to 20th	Day	10% 2 15% 29% 29% 15%	479
	21st to end	Day	12% 3 12% 29% 27% 19%	539
September	1st to 10th	Day	11% 3 17% 25% 27% 16%	490
	11th to 20th	Day	18% 4 12% 28% 27% 11%	490
	21st to end	Day	26% 6% 20% 30% 15% 4	490
October	1st to 10th	Day	17% 7% 22% 23% 22% 9%	490
	11th to 20th	Day	12% 9% 26% 29% 19% 5%	490
	21st to end	Day	13% 10% 27% 28% 17% 6%	539
November	1st to 10th	Day	18% 9% 30% 27% 13% 3	467
	11th to 20th	Day	17% 15% 28% 28% 11% 1	446
	21st to end	Day	12% 18% 30% 24% 15% 1	241
December	1st to 10th	Day	23% 14% 39% 15% 8%	180
	11th to 20th	Day	22% 15% 34% 20% 8% 1	245
	21st to end	Day	25% 15% 31% 18% 9% 1	297
January	1st to 10th	Night	21% 14% 34% 26% 6% 1	760
	11th to 20th	Night	19% 13% 34% 28% 6%	760
	21st to end	Night	20% 11% 38% 27% 3	836
February	1st to 10th	Night	19% 12% 38% 29% 3	760
	11th to 20th	Night	24% 16% 38% 21% 1	743
	21st to end	Night	18% 18% 35% 25% 5%	628
March	1st to 10th	Night	17% 14% 35% 29% 5%	760
	11th to 20th	Night	20% 14% 34% 23% 9%	760
	21st to end	Night	17% 13% 39% 26% 5%	836
April	1st to 10th	Night	18% 15% 34% 26% 7%	760
	11th to 20th	Night	15% 13% 32% 28% 11% 1	751
	21st to end	Night	14% 7% 36% 33% 9%	760
May	1st to 10th	Night	11% 10% 35% 35% 8%	601
	11th to 20th	Night	18% 6% 22% 36% 16% 1	561
	21st to end	Night	14% 1 15% 41% 27% 2	617
June	1st to 10th	Night	12% 4 16% 42% 24% 1	570
	11th to 20th	Night	12% 2 18% 36% 26% 5%	570
	21st to end	Night	8% 2 16% 40% 31% 2	570
July	1st to 10th	Night	8% 2 12% 35% 40% 3	555
	11th to 20th	Night	9% 2 9% 38% 36% 7%	552
	21st to end	Night	8% 1 13% 41% 34% 3	624
August	1st to 10th	Night	14% 2 9% 37% 34% 4	567
	11th to 20th	Night	12% 2 11% 36% 34% 5%	611
	21st to end	Night	12% 2 11% 31% 39% 6%	836
September	1st to 10th	Night	12% 2 13% 33% 34% 6%	760
	11th to 20th	Night	16% 3 13% 30% 33% 4	760
	21st to end	Night	21% 5% 17% 33% 23% 1	760
October	1st to 10th	Night	17% 3 19% 29% 27% 5%	760
	11th to 20th	Night	16% 7% 26% 29% 20% 2	760
	21st to end	Night	14% 7% 26% 31% 21% 1	836
November	1st to 10th	Night	16% 7% 26% 33% 15% 3	755
	11th to 20th	Night	15% 11% 28% 34% 11%	760
	21st to end	Night	15% 9% 30% 32% 14% 1	760
December	1st to 10th	Night	21% 10% 31% 30% 6%	760
	11th to 20th	Night	19% 9% 31% 34% 8%	760
	21st to end	Night	21% 11% 29% 30% 8%	836

Page generated at 2024-11-01 22:47:41. Version ac07

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