Gold Mountain Observing Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gold Mountain Observing Center clear sky chart from 2005-11-06 to 2024-03-23.

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	18% 9% 4 7% 7% 4 5% 5% 5% 7% 29%	78565
	Night	19% 10% 4 7% 6% 4 5% 5% 5% 6% 30%	81272
Transparency	Day	53% 8% 14% 17% 7% 1	78281
	Night	54% 8% 14% 16% 7% 1	81136
Seeing	Day	22% 12% 20% 24% 17% 5%	14274
	Night	23% 10% 15% 28% 21% 3	22848

By Month

Percentage Cloud Cover NW (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	31% 13% 4 8% 7% 5% 5% 5% 5% 5% 13%	2219
	11th to 20th	Day	25% 9% 5% 9% 6% 3 4 4 5% 6% 23%	2456
	21st to end	Day	37% 13% 5% 9% 6% 3 4 4 4 4 10%	2922
February	1st to 10th	Day	22% 13% 4 8% 8% 4 6% 6% 6% 6% 17%	1710
	11th to 20th	Day	22% 14% 5% 8% 7% 3 4 5% 4 6% 22%	1665
	21st to end	Day	18% 13% 4 9% 7% 4 6% 5% 5% 6% 23%	1458
March	1st to 10th	Day	20% 12% 5% 8% 7% 5% 6% 5% 6% 7% 21%	1968
	11th to 20th	Day	23% 12% 4 7% 7% 4 5% 5% 5% 6% 21%	2090
	21st to end	Day	22% 10% 5% 9% 8% 5% 6% 6% 5% 7% 17%	2255
April	1st to 10th	Day	22% 10% 4 7% 8% 4 5% 6% 6% 7% 21%	2160
	11th to 20th	Day	20% 10% 4 8% 7% 4 6% 5% 6% 6% 24%	2174
	21st to end	Day	17% 10% 4 8% 7% 4 6% 6% 5% 7% 25%	2358
May	1st to 10th	Day	14% 8% 3 8% 6% 4 7% 5% 6% 8% 31%	2520
	11th to 20th	Day	17% 8% 3 7% 6% 4 6% 6% 6% 7% 29%	2477
	21st to end	Day	20% 10% 4 7% 7% 4 6% 4 6% 6% 25%	2723
June	1st to 10th	Day	17% 9% 4 8% 6% 4 6% 5% 6% 8% 26%	2596
	11th to 20th	Day	17% 11% 5% 9% 8% 5% 6% 6% 7% 7% 19%	2700
	21st to end	Day	13% 7% 3 7% 6% 3 5% 6% 6% 7% 38%	2700
July	1st to 10th	Day	10% 7% 3 6% 6% 3 4 4 5% 6% 46%	2700
	11th to 20th	Day	7% 5% 3 6% 4 3 5% 6% 7% 9% 46%	2620
	21st to end	Day	8% 5% 2 4 4 2 3 4 4 7% 57%	2741
August	1st to 10th	Day	8% 6% 3 5% 5% 3 4 3 5% 7% 50%	2436
	11th to 20th	Day	7% 5% 2 5% 5% 2 4 4 5% 8% 54%	2298
	21st to end	Day	10% 7% 3 6% 5% 3 5% 5% 5% 7% 43%	2484
September	1st to 10th	Day	9% 6% 2 6% 5% 2 4 4 4 8% 49%	2160
	11th to 20th	Day	11% 7% 3 7% 6% 3 5% 5% 5% 7% 41%	2160
	21st to end	Day	15% 7% 3 7% 6% 3 4 5% 5% 7% 39%	1896
October	1st to 10th	Day	17% 9% 4 6% 6% 2 4 5% 6% 9% 32%	1800
	11th to 20th	Day	20% 9% 4 8% 6% 3 5% 5% 6% 8% 28%	1800
	21st to end	Day	25% 10% 3 7% 6% 3 4 4 6% 5% 26%	1893
November	1st to 10th	Day	27% 12% 3 8% 6% 3 5% 6% 5% 6% 19%	1508
	11th to 20th	Day	27% 10% 4 7% 7% 4 5% 3 4 5% 23%	1520
	21st to end	Day	25% 11% 4 7% 8% 4 4 4 5% 7% 21%	1520
December	1st to 10th	Day	24% 10% 4 8% 7% 3 5% 5% 5% 7% 22%	1520
	11th to 20th	Day	29% 11% 4 12% 10% 4 6% 4 5% 5% 10%	1916
	21st to end	Day	24% 14% 6% 10% 9% 5% 7% 5% 5% 5% 11%	2442
January	1st to 10th	Night	30% 14% 4 8% 7% 5% 5% 5% 5% 4 13%	4726
	11th to 20th	Night	24% 10% 4 7% 5% 3 4 4 5% 8% 26%	4439
	21st to end	Night	33% 14% 4 9% 7% 3 4 4 4 5% 12%	4737
February	1st to 10th	Night	21% 14% 4 8% 7% 4 4 5% 5% 7% 20%	2470
	11th to 20th	Night	19% 14% 4 7% 7% 4 5% 4 4 6% 26%	2402
	21st to end	Night	18% 12% 4 7% 8% 5% 5% 6% 5% 7% 24%	1995
March	1st to 10th	Night	20% 11% 5% 7% 7% 4 5% 4 6% 7% 25%	2209
	11th to 20th	Night	21% 10% 3 6% 6% 4 5% 5% 5% 8% 27%	2089
	21st to end	Night	21% 12% 4 9% 7% 4 6% 5% 5% 6% 21%	2146
April	1st to 10th	Night	18% 10% 4 7% 7% 3 6% 6% 6% 7% 25%	1800
	11th to 20th	Night	16% 9% 3 7% 7% 3 5% 5% 7% 7% 30%	1735
	21st to end	Night	15% 8% 4 8% 6% 4 5% 5% 6% 7% 31%	1602
May	1st to 10th	Night	13% 7% 4 6% 6% 3 6% 5% 5% 6% 39%	1440
	11th to 20th	Night	11% 7% 2 6% 7% 5% 5% 6% 8% 7% 35%	1416
	21st to end	Night	11% 8% 4 7% 7% 5% 6% 6% 6% 7% 33%	1552
June	1st to 10th	Night	14% 5% 4 7% 5% 4 6% 5% 7% 8% 35%	1360
	11th to 20th	Night	13% 8% 3 7% 7% 5% 6% 5% 7% 9% 29%	1260
	21st to end	Night	7% 6% 3 5% 6% 3 5% 5% 5% 7% 49%	1260
July	1st to 10th	Night	7% 5% 3 4 4 2 5% 4 5% 6% 55%	1260
	11th to 20th	Night	5% 4 2 3 4 2 4 4 4 6% 63%	1338
	21st to end	Night	5% 3 1 3 3 1 2 3 5% 7% 68%	1576
August	1st to 10th	Night	4 3 1 4 4 2 3 5% 4 7% 62%	1499
	11th to 20th	Night	4 3 1 3 3 2 3 3 5% 8% 65%	1602
	21st to end	Night	7% 5% 2 4 5% 3 5% 5% 5% 7% 52%	1872
September	1st to 10th	Night	6% 4 1 4 4 2 4 4 6% 6% 59%	1800
	11th to 20th	Night	11% 7% 2 6% 6% 3 4 5% 4 7% 45%	1800
	21st to end	Night	14% 7% 3 5% 5% 3 4 5% 4 7% 42%	2060
October	1st to 10th	Night	16% 7% 3 6% 5% 3 4 5% 4 7% 40%	2160
	11th to 20th	Night	20% 8% 3 6% 6% 4 4 5% 5% 6% 33%	2160
	21st to end	Night	21% 9% 3 6% 6% 3 4 4 5% 6% 32%	2462
November	1st to 10th	Night	28% 10% 3 6% 5% 4 5% 5% 4 5% 24%	2567
	11th to 20th	Night	25% 9% 4 8% 7% 4 5% 4 4 5% 26%	2660
	21st to end	Night	23% 10% 3 8% 8% 4 5% 5% 5% 6% 23%	2660
December	1st to 10th	Night	23% 11% 5% 7% 6% 3 4 4 5% 5% 25%	2660
	11th to 20th	Night	26% 12% 4 10% 10% 5% 5% 4 4 6% 14%	3284
	21st to end	Night	27% 14% 7% 10% 8% 4 5% 4 4 4 14%	5214

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	72% 7% 10% 9% 2	2219
	11th to 20th	Day	61% 7% 14% 14% 3 1	2480
	21st to end	Day	77% 6% 9% 6% 2	2922
February	1st to 10th	Day	68% 7% 13% 7% 5%	1710
	11th to 20th	Day	64% 7% 11% 11% 6% 1	1674
	21st to end	Day	60% 8% 12% 14% 5% 1	1458
March	1st to 10th	Day	60% 9% 14% 14% 3 1	1968
	11th to 20th	Day	63% 6% 11% 16% 3 1	2090
	21st to end	Day	65% 9% 12% 13% 2	2255
April	1st to 10th	Day	61% 8% 17% 12% 2	2160
	11th to 20th	Day	57% 8% 11% 16% 5% 1	2174
	21st to end	Day	56% 8% 15% 13% 6% 1	2358
May	1st to 10th	Day	49% 8% 19% 16% 7%	2520
	11th to 20th	Day	51% 9% 19% 17% 5% 1	2480
	21st to end	Day	58% 9% 16% 15% 3	2724
June	1st to 10th	Day	53% 9% 19% 13% 5% 1	2596
	11th to 20th	Day	60% 10% 16% 11% 2	2700
	21st to end	Day	43% 9% 20% 18% 8% 2	2700
July	1st to 10th	Day	37% 8% 14% 26% 12% 2	2626
	11th to 20th	Day	31% 10% 16% 29% 14% 1	2539
	21st to end	Day	25% 7% 13% 37% 16% 3	2589
August	1st to 10th	Day	33% 8% 16% 28% 14% 2	2419
	11th to 20th	Day	28% 8% 20% 28% 13% 3	2298
	21st to end	Day	38% 8% 15% 29% 10% 1	2484
September	1st to 10th	Day	34% 7% 17% 24% 14% 5%	2160
	11th to 20th	Day	41% 8% 15% 17% 15% 3	2160
	21st to end	Day	44% 8% 16% 18% 11% 2	1896
October	1st to 10th	Day	48% 7% 16% 20% 9%	1800
	11th to 20th	Day	53% 9% 17% 16% 5% 1	1800
	21st to end	Day	59% 7% 12% 13% 8%	1893
November	1st to 10th	Day	65% 7% 12% 11% 5% 1	1508
	11th to 20th	Day	65% 7% 9% 12% 6% 1	1520
	21st to end	Day	64% 6% 11% 13% 7%	1520
December	1st to 10th	Day	63% 6% 11% 13% 7%	1520
	11th to 20th	Day	75% 9% 7% 7% 2 1	1919
	21st to end	Day	72% 10% 9% 7% 2	2442
January	1st to 10th	Night	73% 8% 10% 7% 2 1	4726
	11th to 20th	Night	57% 6% 14% 17% 5% 1	4477
	21st to end	Night	75% 6% 8% 8% 2	4737
February	1st to 10th	Night	63% 9% 12% 11% 5%	2470
	11th to 20th	Night	59% 9% 12% 12% 7% 1	2404
	21st to end	Night	58% 8% 12% 15% 6% 1	1995
March	1st to 10th	Night	58% 7% 13% 16% 5%	2209
	11th to 20th	Night	55% 8% 13% 18% 5% 1	2090
	21st to end	Night	63% 8% 16% 12% 1	2146
April	1st to 10th	Night	56% 9% 17% 16% 3	1800
	11th to 20th	Night	49% 10% 16% 15% 8% 1	1735
	21st to end	Night	52% 8% 16% 16% 7% 1	1602
May	1st to 10th	Night	44% 9% 18% 18% 10% 1	1440
	11th to 20th	Night	44% 9% 20% 19% 6% 2	1416
	21st to end	Night	47% 11% 20% 18% 4	1552
June	1st to 10th	Night	44% 7% 22% 21% 5% 1	1360
	11th to 20th	Night	48% 11% 22% 16% 3	1260
	21st to end	Night	34% 8% 26% 21% 8% 4	1260
July	1st to 10th	Night	29% 7% 18% 29% 12% 5%	1225
	11th to 20th	Night	22% 7% 19% 34% 15% 2	1296
	21st to end	Night	15% 6% 16% 37% 21% 5%	1488
August	1st to 10th	Night	23% 6% 20% 29% 18% 3	1491
	11th to 20th	Night	18% 6% 23% 30% 18% 4	1602
	21st to end	Night	31% 8% 16% 29% 14% 2	1872
September	1st to 10th	Night	26% 6% 19% 28% 16% 5%	1800
	11th to 20th	Night	39% 8% 14% 17% 16% 5%	1800
	21st to end	Night	43% 7% 12% 22% 13% 2	2060
October	1st to 10th	Night	44% 7% 15% 24% 11%	2160
	11th to 20th	Night	51% 8% 14% 19% 8%	2160
	21st to end	Night	52% 6% 13% 17% 11%	2462
November	1st to 10th	Night	61% 7% 14% 14% 4 1	2567
	11th to 20th	Night	61% 7% 12% 11% 7% 2	2660
	21st to end	Night	60% 8% 13% 11% 7% 2	2660
December	1st to 10th	Night	62% 7% 10% 13% 7% 1	2660
	11th to 20th	Night	70% 9% 12% 6% 3	3280
	21st to end	Night	71% 10% 8% 9% 3	5214

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	36% 16% 17% 14% 12% 5%	180
	11th to 20th	Day	39% 12% 13% 16% 17% 3	180
	21st to end	Day	34% 16% 19% 18% 11% 2	274
February	1st to 10th	Day	34% 16% 18% 21% 10% 2	370
	11th to 20th	Day	34% 19% 20% 19% 7% 1	365
	21st to end	Day	28% 19% 25% 19% 8% 1	330
March	1st to 10th	Day	27% 19% 26% 19% 8% 1	460
	11th to 20th	Day	26% 18% 22% 17% 11% 6%	460
	21st to end	Day	28% 19% 24% 18% 9% 3	471
April	1st to 10th	Day	31% 15% 21% 19% 9% 4	420
	11th to 20th	Day	25% 17% 26% 16% 10% 6%	412
	21st to end	Day	22% 14% 27% 26% 8% 2	420
May	1st to 10th	Day	16% 12% 24% 30% 15% 3	423
	11th to 20th	Day	24% 8% 20% 23% 17% 7%	448
	21st to end	Day	21% 7% 20% 26% 20% 7%	485
June	1st to 10th	Day	20% 13% 25% 22% 16% 5%	526
	11th to 20th	Day	22% 13% 22% 27% 13% 3	630
	21st to end	Day	15% 8% 21% 29% 21% 5%	630
July	1st to 10th	Day	13% 7% 17% 32% 25% 7%	621
	11th to 20th	Day	5% 4 19% 35% 28% 9%	538
	21st to end	Day	8% 3 11% 26% 38% 14%	487
August	1st to 10th	Day	9% 7% 15% 24% 33% 13%	447
	11th to 20th	Day	7% 3 12% 32% 34% 11%	437
	21st to end	Day	13% 9% 18% 31% 22% 8%	495
September	1st to 10th	Day	14% 7% 23% 33% 18% 5%	450
	11th to 20th	Day	16% 9% 18% 31% 19% 7%	450
	21st to end	Day	16% 13% 22% 29% 16% 4	450
October	1st to 10th	Day	22% 10% 22% 21% 19% 6%	450
	11th to 20th	Day	25% 11% 18% 25% 16% 5%	450
	21st to end	Day	32% 16% 18% 19% 12% 3	408
November	1st to 10th	Day	31% 18% 20% 20% 10% 2	189
	11th to 20th	Day	34% 16% 18% 17% 12% 4	180
	21st to end	Day	32% 14% 18% 14% 15% 7%	180
December	1st to 10th	Day	36% 17% 11% 18% 14% 4	180
	11th to 20th	Day	33% 21% 19% 16% 11% 1	180
	21st to end	Day	35% 16% 19% 19% 10% 2	198
January	1st to 10th	Night	40% 13% 13% 19% 13% 2	850
	11th to 20th	Night	33% 11% 13% 24% 16% 2	774
	21st to end	Night	29% 11% 15% 26% 16% 3	836
February	1st to 10th	Night	30% 15% 15% 25% 12% 3	760
	11th to 20th	Night	26% 13% 17% 26% 15% 2	744
	21st to end	Night	26% 13% 21% 25% 12% 2	628
March	1st to 10th	Night	26% 13% 20% 27% 13% 1	760
	11th to 20th	Night	24% 15% 20% 25% 13% 3	760
	21st to end	Night	26% 16% 18% 26% 12% 2	800
April	1st to 10th	Night	24% 12% 20% 25% 16% 3	720
	11th to 20th	Night	18% 12% 21% 31% 15% 2	667
	21st to end	Night	20% 9% 17% 34% 17% 2	522
May	1st to 10th	Night	16% 11% 16% 36% 19% 2	360
	11th to 20th	Night	14% 6% 14% 34% 29% 3	354
	21st to end	Night	13% 5% 12% 38% 26% 5%	389
June	1st to 10th	Night	17% 9% 15% 31% 25% 3	360
	11th to 20th	Night	15% 9% 20% 32% 22% 2	360
	21st to end	Night	11% 7% 14% 37% 29% 3	360
July	1st to 10th	Night	8% 3 11% 34% 41% 4	350
	11th to 20th	Night	7% 3 10% 37% 39% 4	348
	21st to end	Night	4 3 7% 34% 46% 7%	394
August	1st to 10th	Night	5% 2 8% 27% 44% 14%	425
	11th to 20th	Night	6% 2 6% 26% 48% 11%	534
	21st to end	Night	10% 4 10% 35% 36% 5%	684
September	1st to 10th	Night	8% 4 14% 37% 31% 5%	720
	11th to 20th	Night	14% 4 13% 27% 35% 6%	720
	21st to end	Night	18% 7% 15% 34% 23% 3	720
October	1st to 10th	Night	18% 7% 15% 29% 26% 5%	720
	11th to 20th	Night	23% 9% 14% 28% 23% 4	720
	21st to end	Night	28% 10% 14% 28% 18% 2	792
November	1st to 10th	Night	33% 11% 16% 28% 12% 1	740
	11th to 20th	Night	30% 13% 18% 23% 14% 1	760
	21st to end	Night	27% 11% 19% 25% 15% 3	760
December	1st to 10th	Night	28% 9% 14% 30% 16% 2	760
	11th to 20th	Night	36% 13% 15% 22% 12% 2	762
	21st to end	Night	37% 13% 17% 23% 9% 1	935

Page generated at 2024-03-19 20:31:06. Version ac07

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