Jordan Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jordan Lake clear sky chart from 2005-11-05 to 2012-03-25.

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	13% 5% 5% 5% 7% 44%	25377
	Night	13% 5% 7% 45%	25601
Cloud Cover	Day	13% 5% 5% 5% 7% 44%	24842
	Night	13% 5% 7% 45%	24793
Transparency	Day	7% 12% 22% 21% 5%	22376
	Night	6% 12% 21% 23% 6%	22650
Seeing	Day	21% 23% 24% 12%	1625
	Night	8% 27% 31% 18%	8350

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	18% 5% 5% 47%	1944
	Night	16% 5% 6% 46%	2808
February	Day	15% 5% 6% 49%	1844
	Night	14% 5% 6% 49%	2385
March	Day	15% 6% 5% 6% 46%	2310
	Night	15% 7% 45%	2309
April	Day	11% 5% 7% 49%	2126
	Night	13% 7% 47%	1822
May	Day	12% 5% 5% 6% 5% 5% 8% 41%	2339
	Night	11% 5% 5% 5% 5% 6% 8% 41%	1639
June	Day	8% 5% 6% 6% 7% 10% 39%	2340
	Night	8% 5% 6% 6% 6% 6% 6% 8% 39%	1620
July	Day	7% 6% 7% 8% 6% 7% 9% 35%	2413
	Night	6% 5% 5% 6% 6% 8% 12% 38%	1667
August	Day	9% 7% 6% 7% 7% 9% 10% 30%	2332
	Night	7% 6% 6% 6% 8% 12% 38%	1754
September	Day	17% 5% 6% 43%	2045
	Night	17% 5% 7% 44%	1914
October	Day	15% 5% 52%	1860
	Night	14% 5% 52%	2232
November	Day	14% 5% 54%	1961
	Night	15% 6% 50%	2544
December	Day	15% 6% 6% 46%	1863
	Night	17% 5% 6% 45%	2907

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	18% 5% 5% 47%	1665
	Night	17% 6% 46%	2405
February	Day	15% 5% 6% 49%	1844
	Night	14% 5% 6% 49%	2378
March	Day	15% 6% 5% 5% 46%	2320
	Night	15% 6% 45%	2321
April	Day	11% 5% 5% 7% 49%	2126
	Night	13% 7% 47%	1822
May	Day	12% 5% 5% 6% 5% 5% 8% 40%	2339
	Night	11% 5% 5% 5% 5% 6% 8% 41%	1638
June	Day	8% 5% 6% 6% 7% 10% 39%	2340
	Night	8% 6% 6% 6% 6% 6% 8% 39%	1620
July	Day	7% 6% 7% 7% 6% 7% 10% 35%	2413
	Night	7% 5% 5% 6% 6% 7% 12% 38%	1667
August	Day	9% 6% 6% 7% 7% 9% 10% 30%	2332
	Night	8% 6% 6% 5% 8% 12% 38%	1754
September	Day	17% 5% 6% 43%	2045
	Night	17% 5% 7% 44%	1914
October	Day	15% 5% 52%	1860
	Night	14% 5% 53%	2232
November	Day	14% 5% 53%	1961
	Night	15% 5% 6% 50%	2551
December	Day	15% 6% 6% 47%	1597
	Night	17% 5% 6% 47%	2491

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	8% 25% 25%	1668
	Night	10% 22% 27% 6%	2416
February	Day	11% 26% 24%	1662
	Night	11% 24% 25% 6%	2126
March	Day	6% 12% 24% 19%	2053
	Night	7% 11% 23% 21% 5%	2060
April	Day	6% 9% 23% 23% 11%	1874
	Night	5% 8% 24% 21% 12%	1587
May	Day	9% 15% 24% 16%	2077
	Night	8% 15% 24% 17%	1451
June	Day	11% 18% 25% 17%	1961
	Night	11% 17% 22% 17%	1337
July	Day	12% 15% 20% 14%	1885
	Night	11% 17% 20% 17% 5%	1319
August	Day	11% 15% 19% 12%	2125
	Night	10% 20% 21% 13%	1616
September	Day	6% 10% 17% 21% 7%	1893
	Night	6% 12% 15% 23% 6%	1783
October	Day	6% 21% 30% 7%	1744
	Night	7% 17% 30% 11%	2087
November	Day	10% 21% 29% 8%	1761
	Night	5% 10% 18% 29% 10%	2258
December	Day	12% 24% 21%	1673
	Night	9% 23% 22% 5%	2610

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	14% 37% 28% 5%	818
February	Day	10% 46% 23%	56
	Night	16% 38% 29%	742
March	Day	8% 37% 23% 15%	206
	Night	12% 34% 27% 10%	827
April	Day	7% 32% 21% 17% 7%	176
	Night	11% 37% 27% 12%	694
May	Day	6% 21% 25% 21% 10%	176
	Night	5% 25% 39% 17%	547
June	Day	14% 26% 36% 10%	173
	Night	16% 41% 29%	525
July	Day	10% 21% 37% 21%	171
	Night	12% 35% 40%	513
August	Day	9% 18% 28% 31%	180
	Night	8% 36% 39% 6%	631
September	Day	9% 22% 29% 14%	175
	Night	14% 33% 30%	702
October	Day	22% 25% 21% 7%	185
	Night	5% 29% 26% 21%	731
November	Day	7% 25% 31% 16% 5%	127
	Night	8% 29% 31% 15%	789
December	Night	10% 31% 33% 8%	831

Page generated at 2012-03-28 10:40:47. Version ac01