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 2026-08-30.

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% 34%	143688
	Night	14% 10% 3 8% 5% 4 4 4 5% 7% 35%	138530
Transparency	Day	46% 5% 10% 22% 14% 2	147373
	Night	47% 5% 10% 21% 15% 2	142917
Seeing	Day	21% 12% 26% 22% 13% 5%	17376
	Night	20% 9% 24% 29% 15% 2	27397

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	16% 17% 6% 12% 7% 4 4 3 4 5% 21%	5258
	11th to 20th	Day	13% 16% 7% 13% 6% 5% 4 3 3 4 28%	5280
	21st to end	Day	17% 13% 5% 11% 8% 5% 5% 4 5% 5% 22%	5780
February	1st to 10th	Day	21% 12% 5% 9% 5% 3 4 3 3 5% 30%	1890
	11th to 20th	Day	21% 12% 5% 9% 5% 5% 3 3 5% 5% 27%	2019
	21st to end	Day	20% 15% 4 8% 4 3 3 3 4 5% 32%	1730
March	1st to 10th	Day	18% 13% 3 9% 5% 4 4 3 5% 5% 31%	4903
	11th to 20th	Day	12% 7% 3 7% 4 4 4 4 6% 8% 41%	5090
	21st to end	Day	16% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	5586
April	1st to 10th	Day	14% 10% 3 7% 5% 4 4 4 5% 6% 37%	2310
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 4 5% 7% 40%	2632
	21st to end	Day	17% 8% 3 6% 5% 5% 5% 4 6% 6% 36%	2730
May	1st to 10th	Day	15% 9% 3 8% 5% 5% 5% 5% 7% 8% 29%	7616
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 4 7% 8% 33%	7626
	21st to end	Day	18% 8% 3 8% 5% 5% 5% 4 6% 8% 30%	8391
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	2730
	11th to 20th	Day	8% 6% 3 7% 5% 5% 6% 6% 7% 9% 39%	2730
	21st to end	Day	10% 5% 1 6% 5% 5% 5% 5% 8% 10% 40%	2730
July	1st to 10th	Day	8% 6% 3 7% 5% 5% 5% 4 6% 8% 42%	7680
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 5% 7% 10% 34%	7680
	21st to end	Day	10% 8% 3 9% 6% 6% 6% 4 8% 9% 31%	8340
August	1st to 10th	Day	7% 6% 3 8% 5% 6% 6% 5% 8% 11% 35%	4364
	11th to 20th	Day	8% 6% 3 7% 5% 6% 5% 5% 7% 11% 38%	4304
	21st to end	Day	5% 4 1 5% 4 4 5% 4 6% 9% 54%	4661
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 47%	2200
	11th to 20th	Day	9% 6% 2 6% 5% 4 4 4 5% 8% 48%	2200
	21st to end	Day	17% 8% 2 7% 4 3 5% 3 5% 5% 41%	2200
October	1st to 10th	Day	11% 6% 3 6% 3 3 3 3 6% 8% 49%	2121
	11th to 20th	Day	14% 7% 2 5% 3 4 4 3 4 6% 47%	2000
	21st to end	Day	19% 7% 2 7% 4 4 3 3 5% 6% 41%	2200
November	1st to 10th	Day	12% 7% 2 6% 3 3 4 4 5% 5% 49%	1879
	11th to 20th	Day	15% 12% 3 6% 5% 4 3 3 5% 6% 38%	1890
	21st to end	Day	17% 12% 3 6% 5% 4 4 4 4 6% 36%	1890
December	1st to 10th	Day	19% 12% 4 9% 5% 4 4 3 4 5% 30%	3020
	11th to 20th	Day	22% 13% 5% 8% 4 4 4 3 5% 5% 26%	3463
	21st to end	Day	17% 16% 5% 12% 6% 5% 5% 4 5% 6% 20%	4565
January	1st to 10th	Night	15% 15% 6% 14% 6% 5% 5% 4 5% 5% 21%	7635
	11th to 20th	Night	17% 13% 5% 14% 6% 5% 4 3 4 5% 24%	7680
	21st to end	Night	18% 11% 4 10% 6% 5% 4 3 4 5% 30%	8401
February	1st to 10th	Night	19% 14% 4 8% 5% 4 4 3 4 5% 30%	2730
	11th to 20th	Night	21% 12% 4 9% 5% 4 3 3 4 6% 28%	2484
	21st to end	Night	20% 14% 4 7% 5% 4 4 3 5% 5% 29%	2076
March	1st to 10th	Night	18% 11% 3 6% 4 4 4 3 4 6% 37%	5169
	11th to 20th	Night	11% 9% 3 6% 3 3 4 3 6% 9% 43%	5090
	21st to end	Night	14% 10% 4 10% 6% 5% 5% 4 5% 6% 33%	5588
April	1st to 10th	Night	15% 10% 2 7% 5% 4 4 3 5% 7% 38%	2310
	11th to 20th	Night	13% 8% 3 7% 4 4 4 5% 6% 8% 39%	1952
	21st to end	Night	15% 8% 2 7% 4 4 4 4 7% 7% 39%	1890
May	1st to 10th	Night	17% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	5237
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 4 7% 9% 36%	5234
	21st to end	Night	18% 10% 4 7% 5% 4 5% 4 6% 7% 31%	5761
June	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 4 8% 9% 44%	1890
	11th to 20th	Night	7% 6% 3 6% 5% 4 5% 4 7% 10% 42%	1890
	21st to end	Night	8% 6% 2 5% 4 4 4 5% 7% 11% 44%	1890
July	1st to 10th	Night	7% 7% 2 8% 5% 5% 5% 4 7% 9% 41%	5278
	11th to 20th	Night	10% 8% 3 8% 5% 5% 5% 4 7% 9% 37%	5277
	21st to end	Night	9% 8% 3 8% 5% 5% 6% 4 6% 9% 36%	5736
August	1st to 10th	Night	8% 8% 3 8% 5% 5% 5% 5% 7% 9% 36%	3005
	11th to 20th	Night	9% 7% 3 7% 5% 4 5% 4 6% 9% 41%	2965
	21st to end	Night	5% 3 1 4 4 4 5% 4 6% 10% 55%	3384
September	1st to 10th	Night	11% 4 2 5% 4 4 4 4 6% 7% 50%	2200
	11th to 20th	Night	9% 4 2 6% 4 3 4 4 5% 6% 54%	2200
	21st to end	Night	14% 8% 2 5% 4 4 5% 3 5% 7% 44%	2200
October	1st to 10th	Night	10% 4 2 7% 4 4 3 3 4 6% 52%	2277
	11th to 20th	Night	13% 6% 2 5% 4 4 3 4 5% 7% 47%	2400
	21st to end	Night	19% 7% 3 6% 4 3 4 3 4 5% 43%	2640
November	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 4 6% 50%	2636
	11th to 20th	Night	16% 9% 3 6% 4 4 4 3 5% 7% 39%	2730
	21st to end	Night	18% 11% 3 7% 5% 4 4 3 4 5% 37%	2730
December	1st to 10th	Night	16% 11% 4 11% 5% 4 4 3 4 5% 32%	4380
	11th to 20th	Night	17% 14% 6% 10% 5% 5% 3 2 4 6% 28%	4952
	21st to end	Night	17% 16% 4 11% 6% 5% 5% 4 4 6% 21%	6633

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	66% 4 10% 15% 5%	5259
	11th to 20th	Day	61% 3 6% 17% 11% 2	5280
	21st to end	Day	63% 4 7% 20% 6% 1	5780
February	1st to 10th	Day	59% 3 9% 18% 10% 1	1890
	11th to 20th	Day	59% 4 7% 18% 10% 1	2029
	21st to end	Day	55% 4 8% 21% 10% 2	1730
March	1st to 10th	Day	54% 4 7% 20% 11% 4	4903
	11th to 20th	Day	41% 4 8% 25% 20% 3	5090
	21st to end	Day	48% 5% 9% 22% 14% 2	5586
April	1st to 10th	Day	46% 5% 10% 22% 13% 4	2310
	11th to 20th	Day	43% 5% 9% 22% 17% 4	2632
	21st to end	Day	47% 5% 11% 22% 12% 3	2730
May	1st to 10th	Day	49% 6% 12% 21% 10% 1	7651
	11th to 20th	Day	47% 6% 11% 24% 11% 1	7630
	21st to end	Day	49% 6% 11% 16% 13% 4	8405
June	1st to 10th	Day	37% 8% 13% 23% 17% 1	2730
	11th to 20th	Day	38% 8% 14% 22% 16% 2	2730
	21st to end	Day	37% 8% 15% 24% 14% 3	2730
July	1st to 10th	Day	39% 7% 12% 26% 15% 1	7615
	11th to 20th	Day	42% 8% 12% 27% 10% 1	7611
	21st to end	Day	46% 6% 11% 19% 15% 1	8156
August	1st to 10th	Day	38% 9% 14% 28% 10%	4351
	11th to 20th	Day	38% 7% 10% 29% 15% 1	4343
	21st to end	Day	25% 6% 14% 32% 22% 2	4661
September	1st to 10th	Day	36% 6% 9% 21% 22% 6%	2200
	11th to 20th	Day	35% 5% 10% 26% 22% 2	2200
	21st to end	Day	44% 5% 9% 21% 18% 2	2200
October	1st to 10th	Day	26% 3 8% 26% 34% 2	3459
	11th to 20th	Day	28% 3 10% 29% 24% 5%	3240
	21st to end	Day	33% 3 10% 28% 23% 3	3538
November	1st to 10th	Day	36% 4 9% 27% 20% 3	1879
	11th to 20th	Day	47% 3 7% 23% 18% 3	1890
	21st to end	Day	50% 3 9% 22% 15% 1	1890
December	1st to 10th	Day	57% 3 7% 24% 9%	3020
	11th to 20th	Day	61% 4 9% 17% 8%	3460
	21st to end	Day	64% 5% 9% 16% 5%	4565
January	1st to 10th	Night	64% 4 10% 17% 5%	7636
	11th to 20th	Night	60% 5% 7% 16% 11% 2	7680
	21st to end	Night	57% 3 10% 20% 9% 1	8401
February	1st to 10th	Night	58% 4 8% 19% 11% 1	2730
	11th to 20th	Night	59% 3 8% 19% 11% 1	2485
	21st to end	Night	58% 3 10% 16% 10% 3	2076
March	1st to 10th	Night	49% 3 6% 25% 15% 2	5169
	11th to 20th	Night	38% 5% 8% 27% 21% 2	5090
	21st to end	Night	51% 5% 7% 21% 14% 2	5588
April	1st to 10th	Night	46% 4 9% 21% 17% 3	2310
	11th to 20th	Night	41% 6% 10% 23% 15% 6%	1952
	21st to end	Night	43% 6% 10% 21% 18% 2	1890
May	1st to 10th	Night	50% 7% 11% 19% 12% 2	5264
	11th to 20th	Night	44% 8% 14% 20% 14% 1	5235
	21st to end	Night	51% 7% 11% 16% 11% 4	5771
June	1st to 10th	Night	35% 7% 12% 24% 18% 4	1890
	11th to 20th	Night	35% 8% 14% 18% 21% 3	1890
	21st to end	Night	33% 9% 16% 22% 18% 3	1890
July	1st to 10th	Night	39% 8% 10% 24% 17% 2	5235
	11th to 20th	Night	42% 8% 14% 24% 11% 1	5226
	21st to end	Night	43% 8% 12% 21% 14% 3	5606
August	1st to 10th	Night	41% 8% 13% 25% 11% 1	2994
	11th to 20th	Night	39% 6% 10% 24% 20% 1	2992
	21st to end	Night	24% 6% 13% 32% 23% 3	3384
September	1st to 10th	Night	32% 6% 13% 22% 19% 8%	2200
	11th to 20th	Night	31% 4 11% 24% 26% 4	2200
	21st to end	Night	41% 5% 10% 20% 22% 2	2200
October	1st to 10th	Night	28% 4 7% 24% 32% 4	3719
	11th to 20th	Night	28% 4 9% 25% 25% 9%	3899
	21st to end	Night	32% 3 6% 25% 27% 6%	4252
November	1st to 10th	Night	36% 4 9% 24% 23% 4	2636
	11th to 20th	Night	44% 4 8% 21% 19% 4	2730
	21st to end	Night	50% 4 8% 22% 14% 2	2730
December	1st to 10th	Night	54% 4 11% 21% 9% 1	4380
	11th to 20th	Night	58% 3 11% 20% 7% 1	4954
	21st to end	Night	63% 5% 10% 16% 6%	6633

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	31% 19% 35% 10% 4 1	330
	11th to 20th	Day	37% 26% 27% 8% 2	330
	21st to end	Day	33% 26% 28% 10% 4	363
February	1st to 10th	Day	31% 22% 31% 13% 4	330
	11th to 20th	Day	47% 18% 27% 5% 2 1	330
	21st to end	Day	37% 21% 32% 9%	273
March	1st to 10th	Day	30% 19% 30% 15% 5% 1	471
	11th to 20th	Day	29% 21% 30% 14% 5% 1	540
	21st to end	Day	28% 18% 33% 16% 4	594
April	1st to 10th	Day	26% 18% 30% 19% 6% 1	540
	11th to 20th	Day	23% 17% 33% 17% 8% 2	532
	21st to end	Day	24% 15% 32% 20% 6% 2	540
May	1st to 10th	Day	25% 17% 30% 17% 7% 3	543
	11th to 20th	Day	20% 12% 29% 22% 12% 5%	567
	21st to end	Day	18% 8% 24% 27% 17% 7%	617
June	1st to 10th	Day	13% 7% 26% 27% 20% 7%	570
	11th to 20th	Day	11% 9% 27% 26% 19% 8%	570
	21st to end	Day	12% 6% 28% 26% 18% 10%	570
July	1st to 10th	Day	13% 4 19% 24% 21% 19%	565
	11th to 20th	Day	10% 4 21% 32% 22% 11%	564
	21st to end	Day	15% 5% 21% 28% 22% 10%	620
August	1st to 10th	Day	13% 5% 19% 32% 22% 9%	566
	11th to 20th	Day	13% 5% 17% 31% 24% 10%	559
	21st to end	Day	8% 4 17% 34% 25% 12%	619
September	1st to 10th	Day	14% 4 15% 29% 26% 12%	530
	11th to 20th	Day	12% 2 13% 28% 30% 14%	530
	21st to end	Day	23% 7% 21% 26% 17% 6%	530
October	1st to 10th	Day	14% 6% 23% 27% 23% 6%	530
	11th to 20th	Day	16% 12% 31% 24% 14% 4	530
	21st to end	Day	25% 12% 29% 22% 10% 1	583
November	1st to 10th	Day	21% 15% 32% 22% 7% 3	357
	11th to 20th	Day	30% 13% 33% 16% 7% 1	330
	21st to end	Day	28% 17% 32% 18% 3 1	330
December	1st to 10th	Day	31% 19% 33% 12% 5% 1	330
	11th to 20th	Day	27% 20% 33% 16% 3 1	330
	21st to end	Day	34% 17% 31% 14% 3 1	363
January	1st to 10th	Night	28% 16% 31% 21% 4	840
	11th to 20th	Night	32% 16% 30% 19% 3	840
	21st to end	Night	28% 16% 32% 21% 3	924
February	1st to 10th	Night	27% 13% 31% 27% 2	840
	11th to 20th	Night	32% 18% 30% 18% 2	823
	21st to end	Night	30% 16% 32% 21% 1	692
March	1st to 10th	Night	27% 14% 28% 27% 4	840
	11th to 20th	Night	25% 17% 30% 22% 7% 1	840
	21st to end	Night	22% 15% 32% 25% 5%	924
April	1st to 10th	Night	23% 14% 32% 25% 7%	840
	11th to 20th	Night	16% 13% 30% 29% 11% 1	676
	21st to end	Night	20% 7% 37% 28% 8% 1	630
May	1st to 10th	Night	18% 8% 29% 30% 13% 1	630
	11th to 20th	Night	18% 9% 25% 31% 14% 2	621
	21st to end	Night	14% 4 20% 33% 25% 3	683
June	1st to 10th	Night	11% 4 19% 39% 25% 2	630
	11th to 20th	Night	10% 3 19% 38% 25% 4	630
	21st to end	Night	12% 3 17% 36% 29% 3	630
July	1st to 10th	Night	11% 2 13% 32% 34% 8%	615
	11th to 20th	Night	8% 2 15% 36% 35% 4	612
	21st to end	Night	12% 2 14% 36% 31% 5%	690
August	1st to 10th	Night	13% 1 13% 38% 32% 3	627
	11th to 20th	Night	12% 3 10% 34% 34% 7%	624
	21st to end	Night	10% 2 12% 34% 35% 7%	712
September	1st to 10th	Night	13% 2 12% 33% 34% 6%	800
	11th to 20th	Night	11% 2 13% 34% 33% 7%	800
	21st to end	Night	17% 6% 19% 31% 23% 3	800
October	1st to 10th	Night	14% 4 20% 32% 28% 4	800
	11th to 20th	Night	17% 9% 26% 31% 16% 2	800
	21st to end	Night	24% 9% 23% 31% 12% 1	880
November	1st to 10th	Night	16% 8% 27% 33% 16% 1	820
	11th to 20th	Night	23% 14% 26% 26% 10%	840
	21st to end	Night	25% 10% 23% 33% 7% 1	840
December	1st to 10th	Night	30% 13% 26% 26% 5%	840
	11th to 20th	Night	26% 13% 29% 27% 5%	840
	21st to end	Night	30% 15% 26% 27% 3	924

Page generated at 2026-08-27 04:07:12. Version ac07

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