Economy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Economy clear sky chart from 2005-11-06 to 2026-04-02.

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	19% 11% 4 9% 5% 5% 5% 4 5% 6% 28%	132595
	Night	20% 11% 4 9% 5% 4 4 3 5% 6% 28%	129386
Transparency	Day	35% 39% 8% 12% 6% 1	136169
	Night	36% 38% 7% 12% 6% 1	133899
Seeing	Day	25% 19% 30% 19% 6% 1	19271
	Night	25% 17% 30% 22% 5%	26627

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% 17% 6% 14% 8% 7% 5% 3 5% 5% 18%	4690
	11th to 20th	Day	18% 17% 8% 16% 7% 4 4 2 4 4 14%	4774
	21st to end	Day	12% 10% 4 11% 6% 5% 7% 5% 9% 7% 25%	5781
February	1st to 10th	Day	18% 14% 5% 11% 8% 6% 4 3 4 6% 21%	1890
	11th to 20th	Day	16% 13% 4 13% 7% 6% 4 3 5% 4 25%	1843
	21st to end	Day	13% 12% 5% 10% 8% 4 4 3 5% 7% 31%	1581
March	1st to 10th	Day	20% 13% 5% 12% 7% 5% 4 3 4 4 23%	4995
	11th to 20th	Day	14% 16% 6% 9% 5% 5% 4 4 5% 6% 26%	5090
	21st to end	Day	26% 15% 4 10% 5% 4 4 3 4 4 19%	5587
April	1st to 10th	Day	24% 12% 4 7% 6% 4 4 3 4 5% 25%	2409
	11th to 20th	Day	20% 10% 3 8% 5% 5% 4 3 5% 7% 30%	2453
	21st to end	Day	22% 10% 3 8% 5% 5% 4 4 4 7% 29%	2600
May	1st to 10th	Day	28% 12% 4 8% 5% 4 4 4 5% 5% 20%	6087
	11th to 20th	Day	19% 10% 3 9% 6% 5% 5% 4 5% 6% 29%	6318
	21st to end	Day	20% 10% 3 8% 5% 4 5% 4 5% 8% 29%	6948
June	1st to 10th	Day	23% 10% 4 8% 5% 5% 5% 4 5% 7% 25%	2800
	11th to 20th	Day	20% 8% 2 7% 5% 4 5% 4 5% 7% 33%	2975
	21st to end	Day	28% 9% 3 7% 5% 4 5% 3 4 6% 28%	3000
July	1st to 10th	Day	21% 9% 3 7% 5% 5% 5% 4 6% 7% 28%	6784
	11th to 20th	Day	19% 9% 3 7% 4 4 4 3 5% 7% 36%	6360
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	6797
August	1st to 10th	Day	19% 10% 3 8% 5% 4 5% 4 6% 6% 29%	4235
	11th to 20th	Day	14% 8% 3 8% 5% 5% 5% 4 6% 7% 35%	4175
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 8% 47%	4492
September	1st to 10th	Day	16% 6% 2 6% 4 4 5% 4 5% 7% 41%	2400
	11th to 20th	Day	17% 7% 3 6% 4 4 4 2 5% 6% 42%	2330
	21st to end	Day	19% 6% 2 6% 3 4 3 3 5% 7% 42%	2130
October	1st to 10th	Day	17% 6% 3 8% 5% 4 4 3 6% 7% 39%	2000
	11th to 20th	Day	20% 10% 2 6% 4 5% 5% 4 6% 6% 31%	2000
	21st to end	Day	20% 10% 4 8% 5% 4 4 4 4 6% 30%	2200
November	1st to 10th	Day	23% 13% 3 7% 5% 3 4 3 4 5% 29%	1675
	11th to 20th	Day	22% 16% 4 6% 4 4 4 4 4 5% 27%	1680
	21st to end	Day	19% 14% 6% 9% 6% 5% 4 4 5% 5% 23%	1680
December	1st to 10th	Day	20% 14% 5% 8% 5% 4 4 4 5% 5% 24%	2690
	11th to 20th	Day	28% 12% 5% 8% 5% 3 4 3 3 3 25%	3076
	21st to end	Day	20% 15% 4 12% 5% 5% 4 3 4 4 23%	4070
January	1st to 10th	Night	14% 16% 6% 11% 7% 5% 5% 4 6% 6% 21%	8234
	11th to 20th	Night	21% 14% 6% 14% 5% 5% 4 3 5% 5% 17%	8132
	21st to end	Night	11% 11% 5% 11% 6% 5% 6% 4 7% 7% 26%	8400
February	1st to 10th	Night	19% 13% 5% 12% 7% 5% 4 3 5% 6% 20%	2730
	11th to 20th	Night	17% 13% 4 10% 6% 5% 4 4 5% 6% 26%	2663
	21st to end	Night	13% 13% 5% 9% 6% 5% 5% 4 5% 5% 30%	2223
March	1st to 10th	Night	24% 13% 4 11% 7% 5% 4 3 3 4 23%	5051
	11th to 20th	Night	18% 14% 6% 10% 5% 4 4 3 5% 5% 26%	5089
	21st to end	Night	29% 13% 6% 8% 5% 4 3 2 3 4 24%	5587
April	1st to 10th	Night	24% 14% 2 8% 4 4 4 4 4 5% 27%	2013
	11th to 20th	Night	22% 10% 3 7% 5% 3 4 3 5% 7% 31%	1893
	21st to end	Night	26% 9% 3 7% 5% 3 4 3 4 6% 30%	1800
May	1st to 10th	Night	30% 12% 3 8% 5% 5% 4 3 5% 5% 21%	3861
	11th to 20th	Night	24% 8% 3 7% 4 4 5% 4 5% 7% 30%	3596
	21st to end	Night	19% 10% 4 9% 6% 5% 4 3 5% 5% 29%	3948
June	1st to 10th	Night	26% 10% 3 7% 5% 4 4 3 5% 8% 27%	1600
	11th to 20th	Night	20% 8% 2 6% 4 4 4 4 6% 7% 36%	1438
	21st to end	Night	24% 10% 3 8% 5% 4 5% 5% 5% 6% 26%	1400
July	1st to 10th	Night	20% 11% 3 9% 5% 6% 5% 5% 6% 8% 21%	3160
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 6% 7% 34%	3592
	21st to end	Night	17% 7% 3 7% 4 5% 5% 4 6% 7% 36%	4068
August	1st to 10th	Night	23% 9% 3 6% 4 4 4 4 6% 6% 32%	2915
	11th to 20th	Night	17% 7% 3 6% 5% 4 5% 4 7% 8% 35%	2872
	21st to end	Night	14% 6% 2 5% 4 4 4 4 5% 7% 46%	3405
September	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	2000
	11th to 20th	Night	18% 7% 2 5% 5% 3 3 3 5% 6% 43%	2065
	21st to end	Night	19% 6% 2 5% 3 4 5% 4 5% 7% 40%	2269
October	1st to 10th	Night	18% 6% 2 6% 4 4 5% 4 5% 7% 40%	2400
	11th to 20th	Night	19% 9% 3 6% 4 5% 5% 4 5% 6% 35%	2400
	21st to end	Night	26% 10% 2 7% 4 4 3 3 4 6% 31%	2640
November	1st to 10th	Night	23% 9% 3 7% 4 5% 5% 3 5% 6% 31%	2839
	11th to 20th	Night	21% 12% 4 8% 6% 4 5% 4 5% 6% 25%	2940
	21st to end	Night	22% 14% 4 8% 5% 4 5% 3 5% 5% 25%	2940
December	1st to 10th	Night	17% 13% 4 9% 5% 5% 4 4 6% 7% 25%	4720
	11th to 20th	Night	27% 13% 3 7% 4 3 3 2 3 5% 29%	5353
	21st to end	Night	24% 14% 4 10% 4 4 4 3 4 4 26%	7150

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	49% 28% 10% 9% 5%	4691
	11th to 20th	Day	56% 27% 7% 8% 2	4803
	21st to end	Day	38% 27% 9% 12% 11% 4	5781
February	1st to 10th	Day	27% 60% 3 5% 4 1	1890
	11th to 20th	Day	24% 60% 4 8% 4	1851
	21st to end	Day	22% 59% 4 8% 6% 1	1581
March	1st to 10th	Day	45% 31% 8% 9% 6% 2	4999
	11th to 20th	Day	41% 34% 10% 11% 3	5090
	21st to end	Day	52% 29% 3 10% 4	5587
April	1st to 10th	Day	24% 62% 3 4 4 1	2409
	11th to 20th	Day	21% 64% 4 9% 2	2453
	21st to end	Day	22% 63% 4 6% 5% 1	2600
May	1st to 10th	Day	46% 33% 7% 10% 4	6098
	11th to 20th	Day	39% 34% 10% 15% 2	6322
	21st to end	Day	36% 34% 11% 14% 6%	6948
June	1st to 10th	Day	21% 63% 5% 8% 3 1	2800
	11th to 20th	Day	18% 63% 6% 9% 4	2975
	21st to end	Day	22% 61% 4 7% 6%	3000
July	1st to 10th	Day	42% 28% 10% 11% 7% 1	6709
	11th to 20th	Day	35% 28% 9% 21% 6%	6284
	21st to end	Day	31% 30% 13% 20% 6%	6602
August	1st to 10th	Day	37% 38% 6% 13% 5%	4222
	11th to 20th	Day	29% 40% 8% 15% 8%	4214
	21st to end	Day	21% 40% 8% 20% 11%	4492
September	1st to 10th	Day	16% 58% 7% 12% 6% 1	2400
	11th to 20th	Day	21% 58% 6% 10% 5%	2330
	21st to end	Day	16% 58% 5% 14% 7%	2130
October	1st to 10th	Day	30% 39% 7% 16% 8%	3260
	11th to 20th	Day	30% 38% 5% 20% 7%	3240
	21st to end	Day	28% 37% 10% 14% 10%	3538
November	1st to 10th	Day	29% 55% 5% 8% 2	1675
	11th to 20th	Day	30% 56% 5% 6% 3	1680
	21st to end	Day	28% 57% 6% 6% 3	1680
December	1st to 10th	Day	36% 36% 8% 16% 3	2690
	11th to 20th	Day	44% 33% 5% 10% 8%	3075
	21st to end	Day	48% 30% 7% 10% 5%	4070
January	1st to 10th	Night	45% 27% 10% 15% 3	8234
	11th to 20th	Night	53% 27% 7% 9% 4	8178
	21st to end	Night	40% 25% 7% 13% 12% 2	8400
February	1st to 10th	Night	28% 60% 3 5% 3 1	2730
	11th to 20th	Night	23% 59% 4 9% 4	2666
	21st to end	Night	21% 60% 3 9% 6% 1	2223
March	1st to 10th	Night	50% 29% 3 8% 9% 2	5060
	11th to 20th	Night	44% 31% 10% 8% 6%	5090
	21st to end	Night	52% 29% 3 10% 7%	5587
April	1st to 10th	Night	23% 63% 3 6% 4 2	2013
	11th to 20th	Night	21% 63% 3 9% 4 1	1893
	21st to end	Night	23% 62% 4 6% 4 1	1800
May	1st to 10th	Night	49% 31% 6% 9% 4	3867
	11th to 20th	Night	38% 32% 10% 16% 3 1	3597
	21st to end	Night	39% 34% 11% 12% 4	3949
June	1st to 10th	Night	20% 64% 5% 8% 4	1600
	11th to 20th	Night	16% 62% 6% 11% 3 1	1438
	21st to end	Night	20% 62% 5% 8% 4 1	1400
July	1st to 10th	Night	45% 29% 9% 11% 5% 1	3125
	11th to 20th	Night	35% 29% 13% 16% 7%	3545
	21st to end	Night	31% 29% 13% 19% 8%	3949
August	1st to 10th	Night	35% 39% 9% 14% 3	2903
	11th to 20th	Night	27% 41% 11% 14% 6%	2899
	21st to end	Night	21% 38% 12% 18% 11%	3404
September	1st to 10th	Night	14% 59% 6% 14% 7% 1	2000
	11th to 20th	Night	19% 58% 6% 12% 5%	2065
	21st to end	Night	15% 58% 6% 14% 5%	2269
October	1st to 10th	Night	32% 38% 7% 17% 6%	3920
	11th to 20th	Night	23% 38% 8% 21% 11%	3899
	21st to end	Night	25% 38% 11% 17% 10%	4252
November	1st to 10th	Night	26% 56% 7% 8% 3	2839
	11th to 20th	Night	28% 57% 5% 7% 3	2940
	21st to end	Night	28% 57% 6% 7% 3	2940
December	1st to 10th	Night	33% 38% 7% 17% 6%	4720
	11th to 20th	Night	40% 32% 6% 11% 8% 2	5355
	21st to end	Night	44% 29% 8% 12% 6%	7150

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	28% 24% 30% 16% 1	430
	11th to 20th	Day	34% 23% 26% 13% 4	430
	21st to end	Day	22% 23% 36% 17% 2	473
February	1st to 10th	Day	26% 24% 31% 16% 3	430
	11th to 20th	Day	26% 29% 28% 14% 3	426
	21st to end	Day	21% 25% 33% 17% 3 1	355
March	1st to 10th	Day	21% 29% 34% 13% 3	529
	11th to 20th	Day	23% 27% 32% 13% 5%	540
	21st to end	Day	30% 25% 31% 10% 3	594
April	1st to 10th	Day	33% 30% 25% 10% 2	504
	11th to 20th	Day	26% 28% 28% 13% 4	492
	21st to end	Day	26% 20% 32% 16% 5%	500
May	1st to 10th	Day	33% 19% 29% 13% 5% 1	587
	11th to 20th	Day	22% 18% 31% 20% 7% 1	724
	21st to end	Day	27% 15% 32% 21% 4 1	790
June	1st to 10th	Day	29% 15% 30% 20% 6%	730
	11th to 20th	Day	22% 16% 33% 23% 5% 1	730
	21st to end	Day	31% 11% 27% 23% 7% 1	730
July	1st to 10th	Day	24% 8% 34% 27% 7% 1	720
	11th to 20th	Day	21% 9% 30% 29% 11%	718
	21st to end	Day	21% 8% 33% 27% 10%	740
August	1st to 10th	Day	15% 7% 33% 35% 10% 1	526
	11th to 20th	Day	18% 10% 29% 29% 12% 2	519
	21st to end	Day	16% 12% 31% 26% 12% 2	583
September	1st to 10th	Day	17% 12% 32% 28% 9% 1	530
	11th to 20th	Day	21% 13% 30% 26% 8% 2	530
	21st to end	Day	18% 15% 34% 19% 13% 2	491
October	1st to 10th	Day	20% 13% 30% 24% 11% 2	420
	11th to 20th	Day	23% 22% 27% 18% 9%	420
	21st to end	Day	24% 23% 29% 17% 6% 1	462
November	1st to 10th	Day	29% 21% 30% 14% 5% 1	425
	11th to 20th	Day	31% 26% 26% 13% 4 1	430
	21st to end	Day	30% 25% 30% 11% 3	430
December	1st to 10th	Day	32% 22% 30% 13% 1	430
	11th to 20th	Day	34% 27% 26% 10% 2	430
	21st to end	Day	27% 26% 28% 15% 3	473
January	1st to 10th	Night	27% 25% 30% 16% 3	950
	11th to 20th	Night	29% 21% 30% 16% 4	931
	21st to end	Night	21% 26% 33% 17% 3	924
February	1st to 10th	Night	25% 23% 32% 18% 3	840
	11th to 20th	Night	25% 27% 31% 15% 2	823
	21st to end	Night	20% 20% 35% 21% 4	692
March	1st to 10th	Night	23% 23% 34% 18% 2	840
	11th to 20th	Night	22% 20% 32% 21% 5%	840
	21st to end	Night	25% 20% 30% 19% 5%	924
April	1st to 10th	Night	31% 19% 30% 18% 3	606
	11th to 20th	Night	27% 17% 32% 19% 5%	594
	21st to end	Night	29% 15% 31% 20% 6% 1	600
May	1st to 10th	Night	31% 15% 30% 19% 5%	600
	11th to 20th	Night	26% 13% 29% 27% 6%	592
	21st to end	Night	20% 15% 39% 22% 3	649
June	1st to 10th	Night	29% 12% 31% 24% 5%	600
	11th to 20th	Night	22% 10% 32% 29% 6%	438
	21st to end	Night	28% 6% 28% 31% 8%	400
July	1st to 10th	Night	24% 6% 29% 34% 6%	390
	11th to 20th	Night	18% 9% 29% 35% 8%	568
	21st to end	Night	20% 6% 29% 35% 9%	656
August	1st to 10th	Night	17% 6% 28% 38% 10% 1	598
	11th to 20th	Night	19% 6% 29% 35% 10% 1	592
	21st to end	Night	17% 7% 27% 37% 12% 1	660
September	1st to 10th	Night	17% 9% 33% 31% 10% 1	600
	11th to 20th	Night	20% 12% 25% 32% 10% 1	665
	21st to end	Night	22% 12% 31% 26% 8% 1	800
October	1st to 10th	Night	22% 12% 27% 30% 9% 1	800
	11th to 20th	Night	24% 15% 34% 17% 9% 1	800
	21st to end	Night	32% 19% 26% 19% 4	880
November	1st to 10th	Night	28% 20% 29% 18% 5% 1	930
	11th to 20th	Night	27% 23% 28% 18% 4 1	950
	21st to end	Night	30% 24% 25% 18% 2 1	950
December	1st to 10th	Night	33% 18% 30% 17% 2	950
	11th to 20th	Night	33% 26% 28% 11% 2	950
	21st to end	Night	27% 25% 28% 17% 2 1	1045

Page generated at 2026-03-30 03:18:39. Version ac07

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