Greasy Ridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greasy Ridge clear sky chart from 2005-11-06 to 2025-04-11.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	113980
	Night	14% 10% 3 8% 5% 4 4 3 5% 7% 36%	114309
Transparency	Day	46% 5% 10% 23% 14% 2	117709
	Night	46% 5% 10% 22% 15% 3	118719
Seeing	Day	21% 12% 26% 22% 13% 6%	15474
	Night	20% 9% 24% 29% 15% 2	25654

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	15% 18% 7% 13% 7% 4 4 3 4 5% 21%	4056
	11th to 20th	Day	14% 18% 8% 12% 6% 5% 3 2 3 4 25%	4060
	21st to end	Day	19% 14% 5% 9% 6% 5% 4 3 5% 5% 26%	4466
February	1st to 10th	Day	22% 12% 5% 9% 5% 3 4 3 3 5% 30%	1800
	11th to 20th	Day	21% 12% 5% 9% 5% 4 3 3 5% 5% 27%	1920
	21st to end	Day	20% 15% 3 8% 4 3 3 3 4 5% 32%	1650
March	1st to 10th	Day	17% 13% 3 9% 5% 4 4 3 5% 5% 31%	4796
	11th to 20th	Day	12% 7% 3 7% 4 4 4 4 6% 8% 42%	4980
	21st to end	Day	17% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	5465
April	1st to 10th	Day	15% 10% 3 7% 5% 4 4 4 5% 6% 36%	2200
	11th to 20th	Day	16% 8% 3 6% 5% 4 4 3 5% 6% 40%	2378
	21st to end	Day	17% 8% 3 6% 5% 5% 5% 3 5% 6% 36%	2470
May	1st to 10th	Day	18% 11% 3 9% 5% 5% 5% 4 5% 6% 28%	4082
	11th to 20th	Day	18% 9% 4 8% 5% 4 4 4 6% 7% 33%	4081
	21st to end	Day	9% 6% 2 7% 6% 6% 6% 5% 8% 9% 36%	4476
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	2470
	11th to 20th	Day	8% 6% 2 7% 5% 5% 6% 6% 7% 8% 40%	2470
	21st to end	Day	10% 5% 1 6% 5% 5% 6% 5% 8% 10% 39%	2470
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 6% 9% 42%	4120
	11th to 20th	Day	8% 5% 3 6% 5% 5% 6% 5% 7% 10% 41%	4120
	21st to end	Day	13% 9% 4 9% 6% 6% 6% 4 6% 8% 29%	4466
August	1st to 10th	Day	7% 6% 3 7% 5% 6% 6% 5% 8% 11% 35%	4104
	11th to 20th	Day	8% 6% 3 7% 5% 6% 5% 5% 7% 11% 38%	4044
	21st to end	Day	5% 4 1 5% 4 4 5% 4 6% 9% 54%	4404
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 7% 47%	2090
	11th to 20th	Day	10% 7% 2 6% 5% 4 4 4 4 8% 47%	2090
	21st to end	Day	17% 8% 2 7% 4 3 5% 3 5% 5% 41%	2090
October	1st to 10th	Day	11% 6% 3 6% 3 3 3 3 6% 8% 48%	2015
	11th to 20th	Day	14% 7% 2 5% 3 4 4 3 4 6% 46%	1900
	21st to end	Day	19% 7% 2 7% 4 4 3 3 4 6% 41%	2090
November	1st to 10th	Day	12% 6% 2 6% 3 3 4 4 5% 5% 50%	1788
	11th to 20th	Day	15% 12% 3 6% 5% 4 4 3 5% 6% 38%	1800
	21st to end	Day	16% 12% 3 6% 5% 4 4 4 4 6% 37%	1800
December	1st to 10th	Day	19% 12% 4 9% 5% 4 4 3 4 5% 31%	2930
	11th to 20th	Day	23% 14% 5% 8% 4 4 4 3 5% 5% 26%	3373
	21st to end	Day	17% 16% 5% 12% 6% 5% 5% 4 5% 6% 21%	4466
January	1st to 10th	Night	15% 16% 6% 16% 6% 5% 4 3 4 5% 20%	5889
	11th to 20th	Night	19% 14% 5% 13% 5% 5% 4 3 4 5% 24%	5900
	21st to end	Night	20% 11% 4 8% 5% 5% 4 3 4 5% 31%	6490
February	1st to 10th	Night	20% 14% 4 8% 4 4 4 3 4 5% 30%	2600
	11th to 20th	Night	22% 12% 4 9% 5% 4 3 3 4 6% 28%	2363
	21st to end	Night	21% 14% 4 7% 5% 4 4 3 5% 5% 29%	1980
March	1st to 10th	Night	18% 11% 3 6% 4 4 4 3 4 6% 38%	5056
	11th to 20th	Night	11% 9% 3 6% 3 3 4 3 6% 9% 43%	4980
	21st to end	Night	14% 10% 4 9% 6% 5% 5% 4 5% 6% 33%	5467
April	1st to 10th	Night	15% 10% 2 7% 5% 4 4 3 5% 7% 38%	2200
	11th to 20th	Night	14% 8% 3 6% 5% 4 4 4 6% 8% 40%	1771
	21st to end	Night	16% 7% 3 7% 4 4 4 4 6% 6% 39%	1710
May	1st to 10th	Night	22% 10% 3 8% 4 5% 5% 4 6% 6% 27%	2813
	11th to 20th	Night	19% 9% 3 6% 3 4 3 3 5% 8% 37%	2812
	21st to end	Night	9% 6% 3 6% 5% 4 5% 4 6% 8% 43%	3079
June	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 4 8% 9% 44%	1710
	11th to 20th	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 11% 43%	1710
	21st to end	Night	8% 6% 2 5% 4 4 4 5% 7% 11% 44%	1710
July	1st to 10th	Night	7% 5% 2 7% 5% 4 5% 4 8% 10% 43%	2840
	11th to 20th	Night	7% 6% 2 7% 5% 5% 4 4 6% 9% 45%	2840
	21st to end	Night	11% 9% 3 8% 5% 5% 6% 3 6% 9% 35%	3087
August	1st to 10th	Night	8% 7% 3 8% 5% 5% 5% 5% 7% 9% 37%	2825
	11th to 20th	Night	9% 7% 3 7% 5% 4 5% 4 6% 9% 42%	2785
	21st to end	Night	5% 3 1 4 4 4 5% 4 6% 10% 55%	3202
September	1st to 10th	Night	12% 4 2 5% 4 4 4 4 5% 7% 49%	2090
	11th to 20th	Night	9% 4 2 6% 4 3 3 4 5% 6% 54%	2090
	21st to end	Night	14% 7% 2 5% 4 4 4 3 5% 7% 44%	2090
October	1st to 10th	Night	10% 4 2 7% 4 4 3 3 4 6% 51%	2163
	11th to 20th	Night	14% 7% 2 5% 4 4 3 3 5% 7% 46%	2280
	21st to end	Night	19% 7% 3 6% 4 3 4 3 4 5% 43%	2508
November	1st to 10th	Night	11% 7% 3 6% 4 4 4 3 4 6% 50%	2507
	11th to 20th	Night	16% 9% 3 6% 5% 4 4 3 5% 7% 39%	2600
	21st to end	Night	18% 11% 3 7% 5% 4 4 3 4 5% 38%	2600
December	1st to 10th	Night	16% 11% 4 10% 5% 4 4 3 4 5% 33%	4250
	11th to 20th	Night	17% 14% 6% 10% 5% 5% 3 2 4 6% 28%	4822
	21st to end	Night	17% 16% 4 11% 6% 5% 5% 4 4 6% 21%	6490

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	67% 5% 8% 14% 5%	4057
	11th to 20th	Day	65% 2 6% 16% 10% 1	4060
	21st to end	Day	59% 4 7% 21% 7% 1	4466
February	1st to 10th	Day	59% 4 9% 17% 10% 1	1800
	11th to 20th	Day	60% 4 7% 18% 10% 1	1930
	21st to end	Day	55% 4 8% 21% 10% 2	1650
March	1st to 10th	Day	54% 4 7% 20% 11% 4	4796
	11th to 20th	Day	40% 4 8% 26% 20% 3	4980
	21st to end	Day	49% 5% 9% 22% 14% 2	5465
April	1st to 10th	Day	48% 5% 10% 21% 13% 4	2200
	11th to 20th	Day	43% 5% 9% 22% 17% 4	2378
	21st to end	Day	47% 6% 11% 21% 11% 3	2470
May	1st to 10th	Day	54% 6% 10% 19% 10% 1	4120
	11th to 20th	Day	49% 7% 10% 21% 12% 1	4085
	21st to end	Day	39% 9% 14% 19% 16% 4	4489
June	1st to 10th	Day	37% 9% 13% 24% 16% 1	2470
	11th to 20th	Day	37% 8% 14% 22% 16% 2	2470
	21st to end	Day	38% 8% 14% 23% 14% 3	2470
July	1st to 10th	Day	36% 8% 13% 26% 15% 2	4055
	11th to 20th	Day	35% 7% 12% 31% 14% 1	4051
	21st to end	Day	52% 6% 10% 16% 15% 2	4324
August	1st to 10th	Day	38% 9% 14% 28% 11%	4091
	11th to 20th	Day	38% 7% 10% 30% 16% 1	4083
	21st to end	Day	25% 6% 14% 32% 21% 2	4404
September	1st to 10th	Day	36% 6% 9% 21% 21% 6%	2090
	11th to 20th	Day	36% 5% 10% 26% 22% 2	2090
	21st to end	Day	44% 5% 9% 22% 19% 2	2090
October	1st to 10th	Day	27% 3 8% 26% 33% 2	3353
	11th to 20th	Day	28% 3 10% 29% 24% 5%	3140
	21st to end	Day	32% 3 10% 29% 22% 3	3428
November	1st to 10th	Day	35% 4 9% 28% 21% 3	1788
	11th to 20th	Day	47% 3 6% 22% 18% 3	1800
	21st to end	Day	49% 3 9% 22% 16% 1	1800
December	1st to 10th	Day	56% 3 7% 24% 9%	2930
	11th to 20th	Day	61% 4 9% 17% 9%	3370
	21st to end	Day	64% 5% 10% 16% 5%	4466
January	1st to 10th	Night	66% 4 9% 15% 6% 1	5889
	11th to 20th	Night	61% 5% 7% 16% 8% 3	5900
	21st to end	Night	55% 3 9% 22% 9% 1	6490
February	1st to 10th	Night	58% 4 8% 18% 11% 1	2600
	11th to 20th	Night	59% 3 8% 18% 12% 1	2364
	21st to end	Night	58% 3 10% 15% 10% 3	1980
March	1st to 10th	Night	48% 3 6% 25% 15% 3	5056
	11th to 20th	Night	37% 5% 8% 27% 21% 2	4980
	21st to end	Night	51% 4 7% 21% 14% 2	5467
April	1st to 10th	Night	47% 5% 8% 21% 17% 3	2200
	11th to 20th	Night	41% 6% 10% 22% 16% 7%	1771
	21st to end	Night	44% 6% 10% 19% 18% 2	1710
May	1st to 10th	Night	55% 8% 10% 16% 10% 2	2840
	11th to 20th	Night	46% 8% 11% 21% 12% 2	2813
	21st to end	Night	35% 9% 14% 23% 14% 4	3087
June	1st to 10th	Night	35% 7% 13% 25% 17% 4	1710
	11th to 20th	Night	33% 9% 15% 18% 22% 3	1710
	21st to end	Night	32% 9% 16% 23% 17% 3	1710
July	1st to 10th	Night	35% 8% 13% 22% 18% 4	2795
	11th to 20th	Night	34% 7% 13% 28% 16% 2	2786
	21st to end	Night	46% 7% 11% 20% 12% 4	2988
August	1st to 10th	Night	41% 8% 13% 25% 11% 1	2814
	11th to 20th	Night	39% 7% 10% 24% 20% 1	2812
	21st to end	Night	24% 6% 13% 32% 23% 3	3202
September	1st to 10th	Night	32% 6% 13% 22% 19% 8%	2090
	11th to 20th	Night	31% 5% 11% 24% 25% 4	2090
	21st to end	Night	40% 5% 10% 20% 22% 2	2090
October	1st to 10th	Night	28% 4 7% 24% 32% 4	3605
	11th to 20th	Night	29% 4 9% 25% 25% 10%	3779
	21st to end	Night	32% 3 6% 26% 27% 6%	4120
November	1st to 10th	Night	36% 4 9% 24% 23% 5%	2507
	11th to 20th	Night	44% 4 8% 20% 20% 4	2600
	21st to end	Night	49% 4 8% 23% 15% 2	2600
December	1st to 10th	Night	54% 4 11% 22% 9% 1	4250
	11th to 20th	Night	58% 3 11% 20% 7% 1	4824
	21st to end	Night	63% 5% 9% 17% 6%	6490

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	30% 21% 35% 10% 4 1	300
	11th to 20th	Day	37% 23% 28% 9% 2	300
	21st to end	Day	32% 25% 28% 11% 4	330
February	1st to 10th	Day	32% 22% 31% 11% 4	300
	11th to 20th	Day	48% 19% 27% 4 2 1	300
	21st to end	Day	38% 21% 33% 8%	249
March	1st to 10th	Day	30% 19% 30% 15% 5% 1	434
	11th to 20th	Day	28% 22% 30% 14% 5% 1	500
	21st to end	Day	29% 18% 33% 16% 4	550
April	1st to 10th	Day	27% 18% 29% 18% 7% 1	500
	11th to 20th	Day	23% 16% 32% 18% 9% 3	452
	21st to end	Day	25% 15% 33% 19% 6% 2	460
May	1st to 10th	Day	26% 14% 31% 18% 8% 3	463
	11th to 20th	Day	20% 10% 29% 23% 13% 6%	487
	21st to end	Day	14% 7% 24% 29% 18% 8%	529
June	1st to 10th	Day	13% 7% 26% 26% 20% 7%	490
	11th to 20th	Day	12% 7% 26% 27% 20% 8%	490
	21st to end	Day	12% 6% 31% 25% 16% 10%	490
July	1st to 10th	Day	13% 4 20% 24% 19% 19%	485
	11th to 20th	Day	9% 4 22% 32% 22% 12%	484
	21st to end	Day	14% 5% 20% 28% 23% 10%	532
August	1st to 10th	Day	13% 4 17% 33% 23% 10%	486
	11th to 20th	Day	14% 5% 16% 31% 23% 10%	479
	21st to end	Day	9% 4 15% 33% 26% 13%	539
September	1st to 10th	Day	14% 3 15% 29% 26% 12%	490
	11th to 20th	Day	13% 2 14% 29% 29% 13%	490
	21st to end	Day	24% 7% 19% 26% 18% 6%	490
October	1st to 10th	Day	14% 6% 24% 27% 22% 6%	490
	11th to 20th	Day	17% 12% 30% 23% 13% 4	490
	21st to end	Day	24% 12% 29% 23% 11% 1	539
November	1st to 10th	Day	21% 13% 33% 23% 8% 3	326
	11th to 20th	Day	27% 14% 33% 17% 7% 1	300
	21st to end	Day	26% 17% 32% 20% 4 1	300
December	1st to 10th	Day	31% 19% 31% 12% 5% 1	300
	11th to 20th	Day	27% 20% 31% 17% 3 1	300
	21st to end	Day	33% 17% 32% 14% 4 1	330
January	1st to 10th	Night	28% 16% 31% 21% 5%	800
	11th to 20th	Night	32% 15% 30% 20% 3	800
	21st to end	Night	28% 16% 32% 21% 4	880
February	1st to 10th	Night	28% 13% 31% 27% 2	800
	11th to 20th	Night	33% 18% 30% 17% 2	783
	21st to end	Night	31% 16% 32% 20% 1	660
March	1st to 10th	Night	26% 14% 28% 27% 5%	800
	11th to 20th	Night	24% 17% 29% 22% 7% 1	800
	21st to end	Night	22% 15% 32% 25% 5%	880
April	1st to 10th	Night	23% 14% 32% 25% 7%	800
	11th to 20th	Night	16% 13% 29% 29% 12% 1	614
	21st to end	Night	20% 7% 36% 28% 8% 1	570
May	1st to 10th	Night	18% 8% 29% 30% 14% 1	570
	11th to 20th	Night	19% 8% 25% 31% 15% 2	561
	21st to end	Night	12% 4 20% 33% 28% 3	617
June	1st to 10th	Night	11% 4 19% 38% 26% 2	570
	11th to 20th	Night	9% 2 18% 38% 26% 5%	570
	21st to end	Night	11% 3 18% 38% 28% 2	570
July	1st to 10th	Night	11% 2 13% 33% 33% 8%	555
	11th to 20th	Night	7% 2 15% 37% 36% 3	552
	21st to end	Night	12% 1 14% 37% 32% 5%	624
August	1st to 10th	Night	13% 1 11% 37% 34% 3	567
	11th to 20th	Night	12% 3 10% 33% 35% 7%	564
	21st to end	Night	11% 2 11% 33% 35% 8%	651
September	1st to 10th	Night	14% 2 12% 33% 34% 6%	760
	11th to 20th	Night	12% 2 13% 34% 33% 6%	760
	21st to end	Night	17% 6% 19% 31% 24% 3	760
October	1st to 10th	Night	14% 4 20% 32% 26% 4	760
	11th to 20th	Night	17% 8% 26% 30% 16% 2	760
	21st to end	Night	23% 8% 23% 31% 13% 1	836
November	1st to 10th	Night	16% 8% 26% 32% 17% 1	780
	11th to 20th	Night	23% 13% 27% 27% 11%	800
	21st to end	Night	24% 10% 24% 34% 7% 1	800
December	1st to 10th	Night	31% 13% 26% 25% 5%	800
	11th to 20th	Night	26% 13% 29% 27% 5%	800
	21st to end	Night	29% 15% 25% 27% 3	880

Page generated at 2025-04-08 09:17:27. Version ac07

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