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 2024-04-03.

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 5% 5% 3 5% 5% 5% 8% 44%	78978
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 45%	81146
Transparency	Day	38% 7% 12% 20% 18% 4	78700
	Night	38% 7% 11% 19% 20% 5%	80943
Seeing	Day	17% 11% 25% 25% 17% 6%	14519
	Night	16% 8% 26% 31% 17% 2	24861

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 4 2 3 3 3 5% 51%	2836
	11th to 20th	Day	14% 6% 3 4 3 3 3 3 4 5% 53%	2840
	21st to end	Day	19% 10% 3 5% 4 2 4 4 4 5% 42%	3124
February	1st to 10th	Day	14% 6% 3 5% 5% 3 4 4 5% 7% 44%	1710
	11th to 20th	Day	22% 6% 2 4 4 2 3 3 4 4 46%	1666
	21st to end	Day	19% 8% 2 5% 4 3 4 4 4 6% 40%	1727
March	1st to 10th	Day	16% 5% 1 4 3 3 3 4 4 7% 51%	2090
	11th to 20th	Day	15% 6% 2 5% 4 4 3 4 5% 8% 44%	2090
	21st to end	Day	17% 7% 3 5% 6% 3 4 4 5% 6% 41%	2299
April	1st to 10th	Day	11% 4 1 4 3 2 4 4 4 8% 54%	2105
	11th to 20th	Day	11% 5% 2 5% 4 2 5% 4 6% 8% 48%	2134
	21st to end	Day	14% 4 2 5% 5% 3 5% 4 6% 7% 46%	2160
May	1st to 10th	Day	11% 5% 2 5% 6% 3 5% 5% 6% 9% 43%	2325
	11th to 20th	Day	14% 7% 2 5% 5% 3 5% 5% 6% 8% 39%	2301
	21st to end	Day	11% 6% 3 5% 6% 4 5% 6% 6% 9% 39%	2531
June	1st to 10th	Day	10% 5% 2 6% 5% 4 6% 6% 8% 9% 39%	2340
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 6% 7% 10% 42%	2340
	21st to end	Day	8% 5% 2 5% 6% 4 6% 7% 8% 11% 39%	2340
July	1st to 10th	Day	9% 4 2 6% 7% 5% 8% 7% 8% 10% 35%	2340
	11th to 20th	Day	7% 6% 3 5% 7% 4 7% 7% 8% 12% 34%	2340
	21st to end	Day	7% 5% 2 7% 7% 4 7% 8% 8% 11% 35%	2547
August	1st to 10th	Day	11% 6% 3 6% 7% 5% 7% 7% 8% 10% 32%	2327
	11th to 20th	Day	10% 7% 3 7% 7% 4 6% 7% 8% 9% 31%	2241
	21st to end	Day	11% 6% 2 6% 6% 4 5% 5% 7% 10% 37%	2376
September	1st to 10th	Day	10% 3 2 5% 4 3 5% 6% 7% 8% 47%	2160
	11th to 20th	Day	15% 6% 2 6% 5% 3 4 4 5% 7% 44%	2023
	21st to end	Day	20% 6% 2 5% 5% 2 4 4 4 7% 40%	1949
October	1st to 10th	Day	16% 6% 2 5% 3 2 3 3 4 7% 49%	1800
	11th to 20th	Day	12% 4 2 3 4 3 3 3 5% 5% 56%	1800
	21st to end	Day	12% 4 3 5% 4 2 3 3 4 5% 56%	1980
November	1st to 10th	Day	14% 5% 2 4 3 2 3 2 4 6% 55%	1857
	11th to 20th	Day	15% 4 2 4 3 2 4 3 5% 7% 53%	1886
	21st to end	Day	14% 5% 2 4 4 3 4 4 4 6% 50%	1650
December	1st to 10th	Day	19% 6% 2 5% 4 3 4 3 5% 8% 41%	1520
	11th to 20th	Day	16% 5% 1 3 3 2 2 3 4 5% 56%	2100
	21st to end	Day	17% 6% 3 4 5% 3 5% 4 4 8% 42%	3124
January	1st to 10th	Night	15% 6% 2 5% 5% 2 4 4 4 6% 47%	4109
	11th to 20th	Night	13% 7% 3 5% 5% 2 4 4 4 6% 47%	4120
	21st to end	Night	20% 7% 2 5% 4 2 3 4 4 5% 44%	4532
February	1st to 10th	Night	17% 6% 2 5% 4 2 4 4 5% 6% 45%	2470
	11th to 20th	Night	21% 6% 2 4 4 3 4 4 4 5% 44%	2395
	21st to end	Night	16% 5% 2 4 4 3 4 4 6% 6% 45%	1727
March	1st to 10th	Night	15% 5% 2 5% 4 2 4 3 4 6% 50%	2090
	11th to 20th	Night	16% 6% 2 5% 5% 3 4 4 5% 7% 43%	2090
	21st to end	Night	16% 5% 2 5% 4 3 3 4 5% 7% 44%	2299
April	1st to 10th	Night	14% 5% 2 5% 4 3 4 3 4 7% 49%	1900
	11th to 20th	Night	13% 5% 2 5% 5% 2 3 3 5% 6% 51%	1775
	21st to end	Night	12% 4 2 5% 4 3 5% 5% 5% 8% 47%	1800
May	1st to 10th	Night	10% 6% 2 5% 6% 3 5% 5% 6% 8% 44%	1650
	11th to 20th	Night	15% 6% 2 5% 5% 4 5% 5% 5% 9% 40%	1592
	21st to end	Night	11% 6% 2 5% 6% 4 5% 5% 6% 11% 42%	1744
June	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 6% 6% 10% 40%	1620
	11th to 20th	Night	10% 5% 2 7% 6% 3 6% 5% 7% 9% 40%	1620
	21st to end	Night	8% 5% 2 6% 5% 4 5% 6% 7% 12% 40%	1620
July	1st to 10th	Night	7% 5% 3 6% 6% 4 7% 6% 9% 11% 37%	1620
	11th to 20th	Night	7% 5% 2 5% 6% 4 6% 7% 9% 13% 36%	1620
	21st to end	Night	6% 5% 3 6% 6% 5% 7% 6% 7% 12% 37%	1771
August	1st to 10th	Night	11% 5% 3 5% 7% 4 7% 6% 9% 11% 34%	1611
	11th to 20th	Night	11% 6% 3 6% 6% 4 6% 7% 7% 10% 33%	1642
	21st to end	Night	9% 6% 3 6% 6% 3 5% 5% 7% 11% 38%	1980
September	1st to 10th	Night	11% 5% 2 5% 5% 3 5% 5% 6% 8% 47%	1800
	11th to 20th	Night	13% 6% 3 5% 6% 3 4 5% 5% 7% 45%	1933
	21st to end	Night	18% 6% 3 6% 6% 3 4 5% 5% 7% 37%	2011
October	1st to 10th	Night	15% 5% 3 4 5% 2 3 3 4 5% 50%	2160
	11th to 20th	Night	14% 5% 2 5% 4 2 3 3 4 5% 53%	2160
	21st to end	Night	12% 5% 2 4 4 2 3 3 4 6% 54%	2376
November	1st to 10th	Night	14% 5% 2 5% 4 3 3 3 4 5% 53%	2221
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 4 6% 51%	2291
	21st to end	Night	14% 3 2 4 4 3 3 4 5% 7% 51%	2520
December	1st to 10th	Night	19% 7% 3 5% 5% 3 4 4 3 5% 42%	2660
	11th to 20th	Night	17% 6% 2 4 4 2 3 4 5% 5% 49%	3085
	21st to end	Night	18% 6% 2 4 4 2 4 3 4 6% 47%	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	35% 5% 10% 21% 22% 7%	2090
	11th to 20th	Day	39% 6% 10% 20% 18% 8%	2090
	21st to end	Day	44% 6% 10% 18% 18% 4	2299
April	1st to 10th	Day	29% 6% 10% 24% 24% 7%	2105
	11th to 20th	Day	33% 7% 11% 22% 20% 8%	2134
	21st to end	Day	37% 8% 11% 21% 18% 5%	2160
May	1st to 10th	Day	37% 8% 16% 19% 17% 3	2325
	11th to 20th	Day	42% 9% 13% 21% 12% 2	2305
	21st to end	Day	40% 9% 15% 22% 13% 1	2531
June	1st to 10th	Day	37% 11% 16% 21% 14% 1	2340
	11th to 20th	Day	34% 11% 16% 22% 14% 2	2340
	21st to end	Day	36% 12% 16% 20% 15% 1	2340
July	1st to 10th	Day	39% 14% 15% 18% 11% 3	2275
	11th to 20th	Day	38% 13% 21% 18% 8% 2	2271
	21st to end	Day	38% 13% 20% 20% 9% 1	2405
August	1st to 10th	Day	43% 13% 18% 18% 8% 1	2314
	11th to 20th	Day	45% 12% 16% 17% 8% 1	2241
	21st to end	Day	40% 10% 17% 20% 10% 3	2376
September	1st to 10th	Day	32% 10% 15% 19% 18% 5%	2160
	11th to 20th	Day	40% 7% 10% 18% 21% 4	2023
	21st to end	Day	45% 7% 9% 20% 16% 4	1949
October	1st to 10th	Day	36% 5% 10% 22% 23% 4	1800
	11th to 20th	Day	30% 5% 9% 27% 21% 8%	1800
	21st to end	Day	32% 4 7% 22% 25% 9%	1980
November	1st to 10th	Day	32% 4 8% 21% 27% 8%	1857
	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	36% 6% 8% 20% 22% 9%	2090
	11th to 20th	Night	41% 7% 9% 17% 19% 7%	2090
	21st to end	Night	40% 6% 10% 20% 19% 5%	2299
April	1st to 10th	Night	36% 5% 9% 18% 25% 7%	1900
	11th to 20th	Night	34% 5% 10% 21% 21% 8%	1775
	21st to end	Night	35% 7% 12% 24% 18% 5%	1800
May	1st to 10th	Night	35% 8% 15% 21% 17% 4	1650
	11th to 20th	Night	41% 8% 13% 21% 16% 1	1593
	21st to end	Night	36% 10% 16% 23% 14% 1	1745
June	1st to 10th	Night	38% 10% 15% 22% 14% 2	1620
	11th to 20th	Night	38% 9% 17% 18% 15% 2	1620
	21st to end	Night	35% 13% 16% 20% 13% 3	1620
July	1st to 10th	Night	35% 15% 17% 19% 12% 2	1575
	11th to 20th	Night	34% 16% 20% 20% 8% 2	1566
	21st to end	Night	36% 13% 20% 20% 11%	1672
August	1st to 10th	Night	41% 14% 19% 18% 8% 1	1600
	11th to 20th	Night	41% 13% 19% 17% 8% 1	1642
	21st to end	Night	37% 12% 19% 21% 9% 3	1980
September	1st to 10th	Night	34% 10% 14% 21% 15% 5%	1800
	11th to 20th	Night	37% 8% 12% 18% 22% 3	1933
	21st to end	Night	45% 8% 12% 16% 15% 4	2011
October	1st to 10th	Night	37% 5% 9% 22% 23% 5%	2160
	11th to 20th	Night	33% 5% 8% 22% 23% 8%	2160
	21st to end	Night	32% 4 9% 20% 26% 10%	2376
November	1st to 10th	Night	34% 5% 8% 18% 26% 9%	2221
	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% 31% 21% 7% 2	428
	11th to 20th	Day	13% 19% 28% 23% 11% 4	412
	21st to end	Day	19% 12% 28% 27% 12% 1	420
May	1st to 10th	Day	14% 18% 30% 24% 10% 4	423
	11th to 20th	Day	16% 6% 23% 30% 20% 6%	447
	21st to end	Day	19% 7% 17% 26% 24% 8%	485
June	1st to 10th	Day	12% 5% 21% 32% 23% 6%	450
	11th to 20th	Day	10% 6% 22% 26% 26% 9%	450
	21st to end	Day	10% 5% 18% 35% 25% 8%	450
July	1st to 10th	Day	11% 2 9% 31% 35% 13%	445
	11th to 20th	Day	7% 2 10% 29% 39% 14%	444
	21st to end	Day	6% 3 15% 34% 32% 11%	488
August	1st to 10th	Day	13% 3 16% 30% 26% 12%	446
	11th to 20th	Day	11% 2 15% 26% 31% 16%	439
	21st to end	Day	13% 3 12% 27% 26% 19%	495
September	1st to 10th	Day	11% 3 16% 25% 28% 17%	450
	11th to 20th	Day	16% 4 12% 29% 28% 12%	450
	21st to end	Day	24% 6% 20% 29% 16% 4	450
October	1st to 10th	Day	18% 7% 22% 23% 22% 9%	450
	11th to 20th	Day	13% 8% 26% 29% 19% 5%	450
	21st to end	Day	14% 10% 27% 29% 16% 4	495
November	1st to 10th	Day	19% 9% 29% 27% 14% 3	455
	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	19% 14% 34% 26% 7%	729
	11th to 20th	Night	15% 13% 32% 27% 12% 1	711
	21st to end	Night	15% 6% 36% 33% 9%	720
May	1st to 10th	Night	11% 10% 35% 35% 8%	570
	11th to 20th	Night	18% 5% 22% 37% 17% 1	531
	21st to end	Night	15% 1 13% 41% 28% 2	584
June	1st to 10th	Night	12% 4 16% 42% 25% 1	540
	11th to 20th	Night	13% 2 18% 36% 26% 5%	540
	21st to end	Night	8% 2 16% 41% 31% 2	540
July	1st to 10th	Night	8% 2 11% 34% 42% 3	525
	11th to 20th	Night	8% 2 9% 38% 36% 7%	522
	21st to end	Night	7% 1 13% 40% 36% 4	591
August	1st to 10th	Night	12% 2 9% 38% 35% 4	537
	11th to 20th	Night	13% 2 10% 34% 35% 5%	578
	21st to end	Night	12% 2 12% 30% 38% 6%	792
September	1st to 10th	Night	12% 2 12% 33% 35% 6%	720
	11th to 20th	Night	15% 3 14% 31% 33% 4	720
	21st to end	Night	21% 5% 17% 32% 24% 2	720
October	1st to 10th	Night	17% 4 19% 29% 26% 5%	720
	11th to 20th	Night	17% 7% 26% 28% 21% 2	720
	21st to end	Night	15% 8% 27% 31% 19% 1	792
November	1st to 10th	Night	16% 7% 26% 33% 15% 3	740
	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 2024-03-31 06:08:53. Version ac07

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