Welsh Mountain Community Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Welsh Mountain Community Center 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	15% 7% 2 7% 4 4 5% 4 6% 7% 39%	131497
	Night	14% 7% 3 6% 4 4 4 4 5% 7% 41%	130329
Transparency	Day	41% 6% 11% 23% 16% 3	135058
	Night	40% 6% 11% 23% 17% 3	134841
Seeing	Day	21% 16% 28% 22% 10% 3	16683
	Night	18% 14% 31% 26% 10% 1	26140

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	13% 7% 3 9% 5% 5% 4 3 4 6% 41%	4661
	11th to 20th	Day	14% 10% 3 9% 4 4 3 3 5% 6% 40%	4948
	21st to end	Day	14% 6% 3 8% 6% 5% 6% 4 5% 6% 36%	5780
February	1st to 10th	Day	14% 9% 4 6% 5% 4 4 4 7% 7% 38%	1890
	11th to 20th	Day	16% 10% 3 7% 5% 3 4 3 5% 7% 37%	1952
	21st to end	Day	17% 11% 2 8% 4 3 4 2 4 6% 38%	1730
March	1st to 10th	Day	20% 6% 2 5% 4 4 4 3 4 6% 43%	4714
	11th to 20th	Day	11% 7% 3 7% 5% 4 5% 4 5% 7% 42%	5090
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 6% 42%	5834
April	1st to 10th	Day	16% 8% 3 6% 5% 4 4 4 6% 7% 38%	2412
	11th to 20th	Day	14% 7% 2 7% 4 4 5% 4 5% 7% 42%	2374
	21st to end	Day	16% 6% 3 6% 4 5% 5% 4 6% 7% 40%	2400
May	1st to 10th	Day	24% 8% 2 7% 4 4 4 4 5% 8% 29%	5846
	11th to 20th	Day	23% 8% 3 7% 4 4 4 3 6% 8% 31%	6318
	21st to end	Day	17% 6% 2 6% 4 4 5% 4 6% 8% 37%	6949
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2800
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	2800
	21st to end	Day	11% 5% 2 5% 4 5% 5% 3 7% 10% 42%	2800
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 11% 39%	6360
	11th to 20th	Day	10% 7% 3 8% 6% 6% 6% 5% 8% 10% 31%	6360
	21st to end	Day	10% 7% 3 6% 4 5% 6% 4 7% 9% 39%	6656
August	1st to 10th	Day	17% 7% 3 7% 5% 5% 6% 4 6% 7% 34%	4234
	11th to 20th	Day	13% 6% 2 7% 4 4 5% 4 7% 8% 40%	3923
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 8% 48%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 5% 5% 46%	2400
	11th to 20th	Day	11% 5% 2 5% 4 4 3 3 5% 8% 49%	2400
	21st to end	Day	17% 9% 3 7% 4 5% 4 4 5% 6% 37%	2144
October	1st to 10th	Day	15% 7% 2 6% 3 4 3 4 6% 6% 45%	2000
	11th to 20th	Day	15% 7% 3 5% 4 3 4 3 4 7% 47%	2000
	21st to end	Day	16% 6% 2 4 3 3 4 3 5% 6% 46%	2179
November	1st to 10th	Day	11% 7% 3 5% 3 2 3 3 4 8% 51%	1851
	11th to 20th	Day	13% 7% 2 5% 4 4 4 4 6% 6% 45%	1890
	21st to end	Day	15% 7% 2 6% 4 4 4 4 5% 7% 42%	1696
December	1st to 10th	Day	13% 7% 3 8% 5% 4 4 3 5% 5% 43%	2680
	11th to 20th	Day	19% 10% 2 5% 4 3 3 3 5% 6% 41%	3066
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 5% 7% 36%	4048
January	1st to 10th	Night	11% 8% 3 8% 5% 5% 4 4 5% 7% 39%	8234
	11th to 20th	Night	14% 8% 2 6% 4 4 4 3 5% 6% 45%	7921
	21st to end	Night	14% 7% 2 7% 4 3 4 3 5% 6% 44%	8401
February	1st to 10th	Night	16% 8% 3 6% 5% 4 4 4 5% 6% 39%	2730
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 3 6% 5% 39%	2553
	21st to end	Night	15% 9% 3 7% 5% 4 4 4 6% 6% 39%	2076
March	1st to 10th	Night	17% 9% 2 6% 4 3 3 3 4 5% 43%	5343
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 5% 6% 50%	5089
	21st to end	Night	14% 8% 2 7% 4 4 4 3 5% 5% 43%	5339
April	1st to 10th	Night	17% 8% 3 6% 5% 4 4 3 7% 7% 38%	2011
	11th to 20th	Night	14% 6% 3 6% 4 4 4 4 5% 8% 41%	1975
	21st to end	Night	15% 6% 3 6% 4 3 4 3 6% 7% 44%	2000
May	1st to 10th	Night	22% 8% 3 7% 5% 5% 5% 3 6% 8% 28%	4123
	11th to 20th	Night	21% 9% 3 7% 4 4 4 3 5% 8% 30%	3575
	21st to end	Night	20% 7% 3 6% 3 4 4 3 5% 8% 37%	3926
June	1st to 10th	Night	13% 6% 2 6% 5% 4 4 5% 6% 7% 42%	1600
	11th to 20th	Night	12% 6% 2 5% 4 5% 5% 4 7% 9% 39%	1600
	21st to end	Night	10% 6% 2 5% 3 4 5% 4 8% 10% 43%	1600
July	1st to 10th	Night	8% 6% 3 7% 5% 6% 6% 5% 7% 9% 39%	3600
	11th to 20th	Night	10% 8% 3 9% 6% 6% 5% 5% 8% 10% 29%	3600
	21st to end	Night	10% 7% 2 6% 4 4 5% 4 6% 9% 42%	4192
August	1st to 10th	Night	17% 8% 3 6% 5% 4 5% 4 6% 7% 35%	2915
	11th to 20th	Night	12% 8% 3 7% 5% 4 4 4 5% 7% 41%	3091
	21st to end	Night	10% 5% 2 5% 3 4 4 4 6% 7% 48%	3586
September	1st to 10th	Night	13% 5% 3 7% 3 4 4 3 5% 6% 48%	2000
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 5% 7% 52%	2000
	21st to end	Night	18% 7% 3 7% 4 4 4 4 5% 6% 39%	2253
October	1st to 10th	Night	18% 8% 3 6% 3 3 4 2 4 6% 44%	2400
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 5% 6% 50%	2400
	21st to end	Night	16% 5% 2 5% 3 3 3 3 5% 7% 48%	2660
November	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 5% 6% 53%	2667
	11th to 20th	Night	14% 8% 2 6% 3 3 4 3 5% 6% 45%	2730
	21st to end	Night	13% 6% 2 6% 5% 4 5% 4 6% 6% 44%	2921
December	1st to 10th	Night	12% 8% 3 6% 5% 4 4 3 5% 7% 44%	4720
	11th to 20th	Night	21% 7% 2 6% 3 3 3 3 4 6% 40%	5348
	21st to end	Night	18% 8% 3 7% 4 4 4 4 5% 6% 36%	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	42% 5% 11% 26% 15% 2	4662
	11th to 20th	Day	44% 4 8% 21% 17% 6%	4980
	21st to end	Day	44% 6% 12% 24% 13% 1	5780
February	1st to 10th	Day	44% 5% 14% 24% 12% 2	1890
	11th to 20th	Day	47% 5% 9% 24% 14% 2	1961
	21st to end	Day	47% 4 10% 22% 13% 4	1730
March	1st to 10th	Day	41% 4 9% 24% 15% 6%	4717
	11th to 20th	Day	39% 5% 12% 27% 13% 5%	5090
	21st to end	Day	43% 5% 9% 17% 21% 4	5834
April	1st to 10th	Day	44% 6% 11% 19% 15% 5%	2412
	11th to 20th	Day	41% 6% 11% 21% 17% 4	2374
	21st to end	Day	41% 6% 11% 20% 18% 4	2400
May	1st to 10th	Day	51% 7% 12% 18% 10% 2	5855
	11th to 20th	Day	51% 6% 9% 23% 10% 1	6322
	21st to end	Day	43% 7% 12% 23% 14% 1	6949
June	1st to 10th	Day	39% 8% 12% 24% 15% 2	2800
	11th to 20th	Day	41% 8% 13% 24% 12% 3	2800
	21st to end	Day	36% 9% 14% 25% 16% 1	2800
July	1st to 10th	Day	37% 10% 14% 21% 15% 2	6290
	11th to 20th	Day	44% 10% 16% 20% 9% 1	6285
	21st to end	Day	39% 8% 10% 21% 21% 1	6465
August	1st to 10th	Day	47% 8% 12% 22% 10%	4221
	11th to 20th	Day	39% 7% 11% 29% 13% 1	3961
	21st to end	Day	33% 7% 11% 28% 19% 2	4312
September	1st to 10th	Day	39% 6% 11% 20% 20% 4	2400
	11th to 20th	Day	33% 5% 9% 27% 23% 3	2400
	21st to end	Day	48% 5% 9% 17% 19% 2	2144
October	1st to 10th	Day	36% 4 8% 19% 28% 5%	3260
	11th to 20th	Day	27% 5% 12% 26% 23% 8%	3240
	21st to end	Day	25% 4 12% 27% 28% 4	3493
November	1st to 10th	Day	33% 4 13% 25% 21% 4	1851
	11th to 20th	Day	37% 5% 10% 25% 20% 2	1890
	21st to end	Day	40% 6% 11% 29% 11% 2	1696
December	1st to 10th	Day	42% 4 16% 25% 11% 2	2680
	11th to 20th	Day	44% 3 13% 29% 9% 1	3066
	21st to end	Day	45% 6% 14% 20% 14% 1	4048
January	1st to 10th	Night	41% 5% 13% 24% 14% 3	8234
	11th to 20th	Night	38% 4 11% 22% 18% 6%	7963
	21st to end	Night	39% 4 9% 27% 19% 2	8401
February	1st to 10th	Night	44% 5% 12% 25% 12% 2	2730
	11th to 20th	Night	46% 5% 9% 20% 18% 3	2555
	21st to end	Night	44% 5% 10% 21% 16% 4	2076
March	1st to 10th	Night	42% 5% 9% 24% 13% 8%	5353
	11th to 20th	Night	34% 5% 14% 28% 14% 5%	5090
	21st to end	Night	42% 5% 7% 17% 25% 4	5339
April	1st to 10th	Night	44% 5% 11% 19% 17% 4	2011
	11th to 20th	Night	39% 7% 11% 20% 19% 3	1975
	21st to end	Night	40% 5% 10% 22% 19% 5%	2000
May	1st to 10th	Night	53% 7% 10% 16% 11% 3	4130
	11th to 20th	Night	51% 8% 11% 19% 11% 1	3576
	21st to end	Night	45% 6% 11% 22% 13% 2	3927
June	1st to 10th	Night	39% 7% 11% 23% 19% 1	1600
	11th to 20th	Night	39% 8% 13% 24% 14% 1	1600
	21st to end	Night	33% 8% 16% 25% 16% 2	1600
July	1st to 10th	Night	40% 10% 14% 19% 14% 3	3560
	11th to 20th	Night	46% 10% 17% 17% 9% 1	3552
	21st to end	Night	36% 8% 12% 23% 21% 1	4068
August	1st to 10th	Night	46% 8% 17% 19% 9% 1	2904
	11th to 20th	Night	41% 7% 11% 25% 14% 1	3119
	21st to end	Night	32% 6% 12% 30% 18% 1	3586
September	1st to 10th	Night	38% 6% 10% 22% 21% 4	2000
	11th to 20th	Night	33% 5% 10% 24% 25% 4	2000
	21st to end	Night	45% 6% 8% 19% 20% 2	2253
October	1st to 10th	Night	43% 4 9% 20% 22% 2	3920
	11th to 20th	Night	25% 4 10% 28% 27% 5%	3899
	21st to end	Night	25% 4 11% 32% 23% 4	4284
November	1st to 10th	Night	32% 4 12% 26% 21% 5%	2667
	11th to 20th	Night	39% 5% 9% 22% 20% 5%	2730
	21st to end	Night	38% 5% 12% 27% 16% 2	2921
December	1st to 10th	Night	39% 5% 13% 30% 13% 1	4720
	11th to 20th	Night	45% 4 12% 24% 13% 3	5348
	21st to end	Night	46% 6% 11% 19% 17% 1	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	30% 29% 27% 12% 2	220
	11th to 20th	Day	31% 30% 29% 8% 1	275
	21st to end	Day	25% 33% 29% 11% 2 1	363
February	1st to 10th	Day	25% 30% 34% 9% 2 1	330
	11th to 20th	Day	34% 24% 34% 7% 1	439
	21st to end	Day	32% 23% 30% 12% 2	446
March	1st to 10th	Day	27% 25% 31% 14% 3	540
	11th to 20th	Day	29% 24% 31% 11% 3 1	540
	21st to end	Day	28% 22% 33% 13% 3 1	594
April	1st to 10th	Day	28% 23% 31% 13% 4 1	504
	11th to 20th	Day	24% 23% 28% 17% 6% 2	492
	21st to end	Day	26% 17% 34% 16% 6% 1	500
May	1st to 10th	Day	26% 21% 25% 20% 6% 1	503
	11th to 20th	Day	21% 16% 31% 21% 8% 2	527
	21st to end	Day	19% 11% 26% 23% 18% 3	573
June	1st to 10th	Day	13% 14% 29% 25% 15% 3	530
	11th to 20th	Day	18% 11% 28% 27% 13% 2	530
	21st to end	Day	14% 8% 28% 31% 14% 5%	530
July	1st to 10th	Day	13% 5% 20% 33% 21% 8%	525
	11th to 20th	Day	7% 4 24% 36% 23% 6%	524
	21st to end	Day	12% 7% 28% 32% 18% 4	576
August	1st to 10th	Day	13% 5% 26% 28% 20% 7%	526
	11th to 20th	Day	12% 8% 18% 35% 19% 8%	519
	21st to end	Day	13% 6% 22% 32% 19% 8%	583
September	1st to 10th	Day	17% 9% 21% 27% 17% 8%	530
	11th to 20th	Day	14% 6% 24% 29% 17% 10%	530
	21st to end	Day	24% 13% 23% 23% 13% 4	530
October	1st to 10th	Day	21% 8% 26% 24% 16% 5%	530
	11th to 20th	Day	19% 15% 31% 21% 12% 2	530
	21st to end	Day	17% 17% 37% 20% 7% 2	571
November	1st to 10th	Day	17% 17% 31% 23% 9% 3	425
	11th to 20th	Day	20% 22% 32% 20% 5%	430
	21st to end	Day	27% 22% 31% 16% 4	236
December	1st to 10th	Day	23% 28% 33% 13% 2 1	220
	11th to 20th	Day	30% 26% 30% 11% 3	220
	21st to end	Day	27% 22% 31% 15% 5%	242
January	1st to 10th	Night	18% 24% 40% 16% 3	840
	11th to 20th	Night	25% 20% 33% 20% 3	840
	21st to end	Night	18% 22% 40% 18% 2	924
February	1st to 10th	Night	21% 20% 38% 19% 2	840
	11th to 20th	Night	26% 25% 35% 13% 1	823
	21st to end	Night	23% 22% 39% 15% 2	692
March	1st to 10th	Night	21% 21% 35% 19% 4	840
	11th to 20th	Night	23% 21% 34% 17% 5%	840
	21st to end	Night	21% 16% 40% 18% 5%	924
April	1st to 10th	Night	22% 19% 38% 17% 3	805
	11th to 20th	Night	19% 16% 35% 24% 6%	791
	21st to end	Night	20% 16% 33% 25% 7%	800
May	1st to 10th	Night	21% 13% 32% 28% 6%	644
	11th to 20th	Night	18% 11% 34% 29% 8%	394
	21st to end	Night	15% 6% 28% 37% 12% 1	433
June	1st to 10th	Night	14% 5% 28% 41% 12%	400
	11th to 20th	Night	13% 6% 26% 44% 11%	400
	21st to end	Night	11% 4 26% 47% 13%	400
July	1st to 10th	Night	11% 3 22% 42% 21% 1	390
	11th to 20th	Night	8% 4 18% 44% 25% 1	388
	21st to end	Night	11% 3 20% 42% 22% 2	551
August	1st to 10th	Night	11% 3 15% 45% 24% 2	597
	11th to 20th	Night	13% 5% 14% 41% 25% 2	720
	21st to end	Night	13% 3 19% 39% 23% 3	880
September	1st to 10th	Night	15% 4 26% 33% 20% 3	800
	11th to 20th	Night	12% 5% 19% 37% 24% 3	800
	21st to end	Night	20% 7% 22% 32% 18% 2	800
October	1st to 10th	Night	22% 8% 23% 29% 15% 4	800
	11th to 20th	Night	18% 12% 30% 28% 11% 1	800
	21st to end	Night	19% 13% 33% 26% 9%	880
November	1st to 10th	Night	14% 13% 34% 28% 10% 1	820
	11th to 20th	Night	18% 20% 30% 25% 6% 1	840
	21st to end	Night	17% 21% 35% 21% 6%	840
December	1st to 10th	Night	22% 19% 35% 18% 5%	840
	11th to 20th	Night	20% 19% 37% 21% 4	840
	21st to end	Night	21% 19% 35% 23% 2	924

Page generated at 2026-03-30 02:18:45. Version ac07

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