Jordan Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jordan Lake clear sky chart from 2003-08-01 to 2005-11-07.

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	21% 5% 5% 5% 6% 34%	8685
	Night	20% 5% 5% 6% 5% 6% 35%	8485
Cloud Cover	Day	20% 5% 5% 6% 5% 6% 34%	8684
	Night	19% 5% 6% 6% 6% 35%	8487
Transparency	Day	17% 14% 32% 28% 6%	4431
	Night	16% 12% 32% 30% 7%	4404
Seeing	Day	10% 24% 27% 25% 10%	526
	Night	13% 30% 31% 22%	2599

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% 7% 7% 37%	551
	Night	17% 5% 5% 6% 45%	802
February	Day	28% 5% 36%	547
	Night	25% 6% 5% 5% 34%	705
March	Day	20% 6% 5% 5% 40%	682
	Night	18% 5% 5% 6% 40%	682
April	Day	19% 5% 5% 5% 5% 41%	712
	Night	19% 5% 5% 7% 41%	608
May	Day	17% 6% 6% 6% 7% 36%	800
	Night	17% 8% 5% 7% 5% 7% 7% 27%	554
June	Day	25% 8% 7% 5% 6% 7% 5% 5% 5% 20%	780
	Night	22% 6% 5% 8% 5% 10% 6% 7% 7% 17%	536
July	Day	16% 5% 7% 6% 5% 8% 6% 5% 10% 23%	804
	Night	17% 8% 8% 5% 6% 10% 6% 8% 20%	558
August	Day	23% 5% 5% 5% 5% 6% 6% 9% 25%	1164
	Night	24% 5% 7% 5% 9% 5% 6% 6% 22%	875
September	Day	23% 6% 5% 5% 38%	1004
	Night	19% 6% 5% 5% 5% 8% 35%	940
October	Day	22% 5% 5% 6% 38%	618
	Night	24% 5% 5% 6% 36%	744
November	Day	20% 45%	501
	Night	19% 5% 44%	665
December	Day	16% 5% 51%	522
	Night	16% 6% 5% 47%	816

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% 7% 6% 38%	551
	Night	17% 5% 5% 6% 44%	802
February	Day	28% 5% 5% 36%	547
	Night	24% 7% 5% 35%	705
March	Day	19% 7% 5% 5% 40%	682
	Night	17% 6% 6% 40%	682
April	Day	18% 5% 5% 5% 5% 41%	712
	Night	17% 6% 6% 41%	608
May	Day	16% 5% 5% 5% 6% 5% 5% 8% 34%	800
	Night	16% 9% 5% 7% 6% 7% 8% 26%	554
June	Day	25% 8% 6% 6% 5% 7% 5% 5% 6% 18%	780
	Night	22% 7% 5% 7% 5% 8% 6% 8% 6% 17%	537
July	Day	15% 7% 6% 8% 10% 5% 5% 9% 23%	801
	Night	17% 7% 7% 5% 6% 5% 8% 5% 6% 8% 20%	558
August	Day	21% 6% 5% 5% 6% 5% 5% 9% 25%	1165
	Night	23% 5% 7% 5% 5% 9% 6% 5% 6% 22%	875
September	Day	21% 7% 5% 5% 37%	1004
	Night	18% 6% 5% 5% 8% 35%	941
October	Day	21% 6% 7% 37%	618
	Night	23% 5% 5% 5% 37%	744
November	Day	20% 45%	502
	Night	20% 5% 44%	665
December	Day	16% 51%	522
	Night	16% 6% 5% 47%	816

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	15% 15% 38% 28%	276
	Night	19% 12% 39% 23%	453
February	Day	11% 15% 28% 37% 7%	261
	Night	11% 12% 37% 33% 5%	308
March	Day	19% 11% 37% 23% 8%	356
	Night	15% 11% 37% 31%	360
April	Day	12% 7% 32% 35% 12%	396
	Night	13% 29% 42% 9%	314
May	Day	22% 16% 33% 22%	413
	Night	26% 17% 38% 17%	233
June	Day	32% 22% 29% 14%	227
	Night	38% 19% 30% 11%	182
July	Day	35% 18% 30% 15%	317
	Night	34% 19% 29% 16%	201
August	Day	26% 20% 37% 15%	488
	Night	24% 22% 36% 16%	336
September	Day	10% 11% 31% 37% 9%	532
	Night	16% 13% 29% 30% 10%	516
October	Day	9% 13% 35% 31% 10%	482
	Night	10% 13% 33% 32% 9%	560
November	Day	13% 20% 20% 38% 7%	353
	Night	12% 8% 26% 39% 12%	465
December	Day	6% 6% 33% 39% 13%	330
	Night	7% 6% 27% 43% 14%	476

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	17% 47% 26% 7%	210
February	Day	55% 22% 22%	9
	Night	16% 47% 30% 5%	171
March	Day	16% 41% 33% 7%	53
	Night	20% 47% 29%	214
April	Day	22% 30% 32% 11%	53
	Night	15% 41% 29% 13%	206
May	Day	7% 28% 17% 42%	52
	Night	10% 26% 39% 22%	169
June	Day	6% 25% 31% 33%	48
	Night	10% 21% 37% 28%	156
July	Day	7% 11% 24% 32% 24%	53
	Night	6% 15% 32% 42%	166
August	Day	8% 12% 16% 29% 33%	72
	Night	7% 13% 22% 46% 9%	263
September	Day	16% 17% 30% 25% 10%	75
	Night	5% 27% 34% 30%	311
October	Day	6% 28% 36% 25%	76
	Night	13% 26% 37% 23%	302
November	Day	5% 31% 25% 25% 11%	35
	Night	15% 22% 29% 28%	219
December	Night	20% 32% 31% 15%	212

Page generated at 2008-05-07 19:23:57. Version ab11