Worth Mountain WMA
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Worth Mountain WMA clear sky chart from 2005-11-06 to 2025-10-04.

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% 6% 2 6% 4 4 5% 4 6% 8% 43%	126451
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 44%	122945
Transparency	Day	38% 7% 12% 20% 18% 6%	130123
	Night	38% 7% 10% 18% 21% 7%	127342
Seeing	Day	17% 9% 24% 24% 18% 8%	16452
	Night	16% 8% 23% 30% 19% 3	26488

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% 5% 2 5% 3 2 3 2 4 5% 55%	4056
	11th to 20th	Day	12% 6% 2 4 3 3 2 2 3 3 59%	4060
	21st to end	Day	19% 7% 2 6% 4 3 4 3 3 5% 44%	4466
February	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 5% 7% 43%	1821
	11th to 20th	Day	23% 6% 2 4 3 3 4 3 4 4 45%	1948
	21st to end	Day	19% 7% 2 6% 5% 3 4 4 3 5% 42%	1671
March	1st to 10th	Day	20% 7% 2 6% 4 4 3 3 4 5% 42%	4935
	11th to 20th	Day	10% 5% 2 5% 3 3 4 3 5% 6% 54%	4980
	21st to end	Day	18% 6% 2 6% 3 3 3 3 4 5% 46%	5465
April	1st to 10th	Day	12% 5% 2 4 3 3 4 4 5% 8% 49%	2200
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 6% 6% 48%	2334
	21st to end	Day	11% 5% 2 7% 4 3 4 4 5% 6% 49%	2595
May	1st to 10th	Day	11% 6% 3 7% 4 5% 5% 5% 8% 11% 35%	5862
	11th to 20th	Day	18% 7% 3 8% 5% 5% 5% 4 7% 8% 31%	5861
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 8% 42%	6433
June	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 11% 37%	2600
	11th to 20th	Day	7% 4 2 5% 6% 4 6% 5% 8% 10% 43%	2600
	21st to end	Day	7% 4 2 6% 4 5% 6% 5% 8% 11% 42%	2600
July	1st to 10th	Day	9% 5% 3 7% 5% 6% 7% 5% 8% 10% 36%	5900
	11th to 20th	Day	6% 5% 2 7% 5% 6% 7% 6% 9% 13% 34%	5900
	21st to end	Day	10% 7% 3 8% 6% 7% 7% 6% 9% 10% 29%	6424
August	1st to 10th	Day	21% 7% 3 7% 5% 5% 6% 5% 8% 10% 25%	4234
	11th to 20th	Day	11% 5% 2 7% 5% 5% 6% 6% 8% 11% 35%	4174
	21st to end	Day	6% 4 1 5% 4 4 4 4 6% 10% 51%	4361
September	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	2200
	11th to 20th	Day	13% 7% 3 6% 4 4 5% 4 6% 8% 41%	2200
	21st to end	Day	17% 5% 3 6% 5% 4 5% 4 5% 5% 41%	2200
October	1st to 10th	Day	15% 4 2 4 3 2 3 2 4 5% 56%	2037
	11th to 20th	Day	13% 5% 1 4 3 3 2 2 4 4 60%	1900
	21st to end	Day	14% 5% 2 3 3 3 2 2 3 5% 57%	2090
November	1st to 10th	Day	14% 5% 2 4 4 2 3 3 4 5% 54%	1957
	11th to 20th	Day	14% 5% 1 3 3 3 4 2 5% 7% 53%	1818
	21st to end	Day	16% 5% 2 4 4 4 3 3 4 6% 50%	1800
December	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 3 5% 53%	2930
	11th to 20th	Day	19% 7% 3 7% 3 3 4 3 5% 5% 40%	3373
	21st to end	Day	22% 6% 2 4 2 3 3 3 4 6% 46%	4466
January	1st to 10th	Night	14% 4 1 4 3 3 3 2 3 4 59%	5889
	11th to 20th	Night	12% 6% 2 4 3 3 3 2 4 4 56%	5900
	21st to end	Night	19% 8% 2 5% 3 3 3 2 3 6% 48%	6490
February	1st to 10th	Night	15% 6% 2 6% 5% 3 4 3 4 5% 48%	2575
	11th to 20th	Night	21% 7% 2 5% 4 4 3 3 4 5% 43%	2338
	21st to end	Night	16% 7% 2 6% 4 4 4 3 4 6% 44%	1957
March	1st to 10th	Night	20% 7% 2 5% 4 3 4 3 4 5% 44%	4918
	11th to 20th	Night	10% 3 2 4 3 3 4 3 6% 8% 54%	4980
	21st to end	Night	16% 5% 2 5% 4 4 4 3 4 6% 47%	5467
April	1st to 10th	Night	13% 5% 2 4 4 3 4 3 5% 8% 49%	2200
	11th to 20th	Night	12% 5% 2 4 4 3 3 3 5% 7% 51%	2015
	21st to end	Night	11% 5% 1 6% 4 3 4 3 5% 6% 50%	1820
May	1st to 10th	Night	12% 7% 3 7% 4 4 4 4 6% 10% 39%	4033
	11th to 20th	Night	20% 7% 3 7% 5% 4 5% 4 6% 9% 31%	4032
	21st to end	Night	14% 5% 2 6% 4 4 5% 4 7% 9% 39%	4421
June	1st to 10th	Night	10% 5% 2 7% 6% 5% 6% 6% 7% 11% 34%	1800
	11th to 20th	Night	10% 5% 2 6% 5% 6% 5% 6% 7% 11% 37%	1800
	21st to end	Night	8% 5% 2 7% 7% 5% 7% 5% 9% 11% 35%	1800
July	1st to 10th	Night	11% 7% 3 9% 6% 5% 6% 5% 8% 10% 28%	4058
	11th to 20th	Night	8% 6% 3 8% 6% 6% 6% 6% 11% 14% 27%	4057
	21st to end	Night	12% 8% 4 10% 7% 6% 7% 5% 7% 10% 23%	4427
August	1st to 10th	Night	20% 10% 3 8% 5% 5% 5% 4 7% 9% 23%	2915
	11th to 20th	Night	13% 7% 2 8% 6% 7% 6% 5% 8% 9% 29%	2875
	21st to end	Night	6% 4 2 6% 5% 5% 6% 5% 7% 9% 46%	3499
September	1st to 10th	Night	11% 5% 2 7% 5% 4 5% 4 6% 9% 44%	2200
	11th to 20th	Night	14% 7% 2 7% 4 5% 6% 4 5% 8% 37%	2200
	21st to end	Night	17% 6% 2 6% 4 4 4 4 5% 7% 41%	2200
October	1st to 10th	Night	15% 4 2 5% 4 3 3 2 4 6% 52%	2209
	11th to 20th	Night	14% 5% 1 5% 3 3 3 2 5% 6% 54%	2280
	21st to end	Night	13% 4 2 5% 2 2 3 2 3 4 58%	2508
November	1st to 10th	Night	15% 5% 2 5% 3 3 3 2 4 5% 54%	2341
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 4 6% 52%	2579
	21st to end	Night	15% 4 2 4 3 4 5% 4 5% 6% 50%	2600
December	1st to 10th	Night	16% 6% 1 4 2 3 3 3 4 5% 53%	4250
	11th to 20th	Night	20% 7% 2 6% 3 3 3 3 4 5% 43%	4822
	21st to end	Night	21% 5% 2 4 3 4 3 3 4 6% 45%	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	33% 3 5% 21% 31% 8%	4057
	11th to 20th	Day	32% 3 4 15% 37% 10%	4060
	21st to end	Day	43% 3 4 16% 23% 10%	4466
February	1st to 10th	Day	40% 5% 9% 22% 19% 5%	1821
	11th to 20th	Day	43% 5% 7% 17% 23% 6%	1958
	21st to end	Day	45% 5% 6% 14% 23% 7%	1671
March	1st to 10th	Day	45% 4 6% 15% 19% 12%	4935
	11th to 20th	Day	32% 5% 6% 14% 25% 19%	4980
	21st to end	Day	41% 5% 6% 21% 22% 6%	5465
April	1st to 10th	Day	33% 6% 9% 21% 25% 6%	2200
	11th to 20th	Day	35% 6% 8% 20% 21% 9%	2334
	21st to end	Day	35% 6% 12% 24% 19% 4	2595
May	1st to 10th	Day	39% 10% 18% 20% 12% 1	5897
	11th to 20th	Day	49% 8% 13% 18% 11% 1	5865
	21st to end	Day	37% 9% 13% 21% 17% 3	6447
June	1st to 10th	Day	38% 9% 15% 26% 10% 1	2600
	11th to 20th	Day	33% 10% 20% 22% 14% 1	2600
	21st to end	Day	33% 11% 17% 23% 14% 2	2600
July	1st to 10th	Day	38% 11% 17% 23% 10% 1	5835
	11th to 20th	Day	35% 15% 30% 16% 4 1	5831
	21st to end	Day	44% 13% 16% 21% 6% 1	6240
August	1st to 10th	Day	50% 10% 17% 18% 5%	4221
	11th to 20th	Day	39% 12% 18% 18% 12% 2	4213
	21st to end	Day	27% 8% 16% 30% 16% 3	4361
September	1st to 10th	Day	36% 9% 14% 19% 19% 4	2200
	11th to 20th	Day	39% 8% 13% 17% 20% 3	2200
	21st to end	Day	45% 6% 10% 18% 15% 5%	2200
October	1st to 10th	Day	28% 4 7% 20% 31% 10%	3362
	11th to 20th	Day	19% 3 6% 18% 29% 25%	3140
	21st to end	Day	26% 3 5% 25% 25% 16%	3428
November	1st to 10th	Day	34% 5% 7% 18% 28% 9%	1957
	11th to 20th	Day	33% 4 7% 21% 26% 8%	1818
	21st to end	Day	37% 4 8% 21% 24% 7%	1800
December	1st to 10th	Day	36% 3 6% 18% 27% 9%	2930
	11th to 20th	Day	45% 4 7% 17% 19% 7%	3370
	21st to end	Day	40% 4 8% 26% 20% 2	4466
January	1st to 10th	Night	31% 3 5% 17% 36% 8%	5889
	11th to 20th	Night	32% 4 6% 15% 36% 8%	5900
	21st to end	Night	40% 3 4 17% 27% 8%	6490
February	1st to 10th	Night	39% 5% 9% 20% 21% 6%	2575
	11th to 20th	Night	45% 4 7% 16% 22% 7%	2339
	21st to end	Night	41% 5% 8% 16% 23% 7%	1957
March	1st to 10th	Night	41% 6% 7% 12% 26% 7%	4918
	11th to 20th	Night	27% 4 8% 14% 29% 18%	4980
	21st to end	Night	38% 4 6% 21% 21% 8%	5467
April	1st to 10th	Night	34% 6% 9% 19% 25% 7%	2200
	11th to 20th	Night	31% 5% 9% 22% 23% 9%	2015
	21st to end	Night	34% 6% 11% 25% 21% 4	1820
May	1st to 10th	Night	40% 8% 15% 21% 15% 1	4060
	11th to 20th	Night	48% 8% 14% 18% 11%	4033
	21st to end	Night	37% 8% 14% 23% 15% 3	4429
June	1st to 10th	Night	40% 11% 16% 19% 12% 2	1800
	11th to 20th	Night	38% 11% 17% 22% 11% 2	1800
	21st to end	Night	39% 12% 16% 16% 13% 4	1800
July	1st to 10th	Night	46% 12% 17% 15% 8% 1	4015
	11th to 20th	Night	42% 16% 25% 14% 2 1	4006
	21st to end	Night	53% 12% 15% 15% 5%	4297
August	1st to 10th	Night	55% 10% 18% 13% 4	2904
	11th to 20th	Night	44% 13% 20% 14% 8%	2902
	21st to end	Night	29% 10% 15% 25% 19% 2	3499
September	1st to 10th	Night	35% 10% 14% 19% 17% 5%	2200
	11th to 20th	Night	42% 8% 14% 15% 19% 2	2200
	21st to end	Night	41% 8% 13% 17% 17% 5%	2200
October	1st to 10th	Night	33% 6% 9% 19% 27% 7%	3664
	11th to 20th	Night	23% 3 5% 19% 26% 24%	3779
	21st to end	Night	28% 3 5% 20% 27% 17%	4120
November	1st to 10th	Night	34% 5% 7% 18% 26% 11%	2341
	11th to 20th	Night	34% 5% 6% 17% 26% 12%	2579
	21st to end	Night	34% 5% 6% 21% 27% 7%	2600
December	1st to 10th	Night	35% 4 6% 20% 28% 8%	4250
	11th to 20th	Night	44% 5% 9% 15% 18% 9%	4824
	21st to end	Night	40% 4 10% 23% 21% 2	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	22% 19% 40% 16% 2	300
	11th to 20th	Day	29% 18% 31% 18% 4	300
	21st to end	Day	24% 22% 37% 14% 4	330
February	1st to 10th	Day	20% 22% 36% 15% 6%	300
	11th to 20th	Day	39% 16% 34% 10% 1	300
	21st to end	Day	25% 22% 37% 13% 3	270
March	1st to 10th	Day	25% 15% 30% 22% 7% 1	500
	11th to 20th	Day	22% 15% 37% 20% 5% 1	500
	21st to end	Day	21% 19% 35% 19% 5% 1	550
April	1st to 10th	Day	20% 16% 32% 21% 10% 1	500
	11th to 20th	Day	14% 15% 33% 23% 13% 2	492
	21st to end	Day	15% 10% 27% 27% 15% 5%	500
May	1st to 10th	Day	11% 14% 33% 25% 13% 5%	503
	11th to 20th	Day	18% 6% 23% 24% 20% 9%	527
	21st to end	Day	17% 5% 18% 23% 24% 12%	573
June	1st to 10th	Day	12% 5% 16% 32% 23% 11%	530
	11th to 20th	Day	7% 5% 17% 29% 27% 14%	530
	21st to end	Day	9% 3 15% 31% 29% 14%	530
July	1st to 10th	Day	10% 2 10% 25% 32% 21%	525
	11th to 20th	Day	8% 1 9% 28% 36% 18%	524
	21st to end	Day	8% 1 11% 33% 32% 15%	576
August	1st to 10th	Day	21% 4 12% 24% 25% 14%	526
	11th to 20th	Day	13% 4 10% 27% 29% 17%	519
	21st to end	Day	11% 3 12% 28% 28% 19%	583
September	1st to 10th	Day	12% 1 14% 30% 28% 15%	530
	11th to 20th	Day	16% 4 15% 23% 27% 15%	530
	21st to end	Day	20% 5% 21% 25% 24% 6%	530
October	1st to 10th	Day	17% 4 23% 26% 22% 8%	502
	11th to 20th	Day	13% 8% 21% 30% 22% 6%	490
	21st to end	Day	18% 8% 19% 29% 22% 5%	539
November	1st to 10th	Day	22% 8% 24% 27% 16% 3	495
	11th to 20th	Day	18% 14% 37% 22% 6% 2	318
	21st to end	Day	14% 13% 31% 30% 10% 2	300
December	1st to 10th	Day	24% 15% 39% 16% 7%	300
	11th to 20th	Day	25% 11% 35% 20% 8% 1	300
	21st to end	Day	29% 15% 32% 15% 8% 2	330
January	1st to 10th	Night	20% 17% 30% 26% 6%	800
	11th to 20th	Night	20% 15% 30% 30% 5%	800
	21st to end	Night	19% 14% 36% 28% 3	880
February	1st to 10th	Night	18% 13% 35% 30% 4	800
	11th to 20th	Night	26% 14% 38% 20% 2	783
	21st to end	Night	20% 14% 38% 25% 3	660
March	1st to 10th	Night	19% 13% 31% 32% 5%	800
	11th to 20th	Night	18% 14% 34% 26% 8% 1	800
	21st to end	Night	19% 13% 34% 27% 6%	880
April	1st to 10th	Night	17% 14% 33% 27% 8%	800
	11th to 20th	Night	15% 12% 29% 30% 13% 1	791
	21st to end	Night	13% 6% 27% 37% 17% 1	620
May	1st to 10th	Night	10% 9% 28% 38% 16%	600
	11th to 20th	Night	15% 4 24% 35% 21% 2	591
	21st to end	Night	15% 3 14% 31% 35% 2	650
June	1st to 10th	Night	13% 3 15% 38% 29% 4	600
	11th to 20th	Night	12% 2 15% 31% 32% 8%	600
	21st to end	Night	8% 3 11% 35% 38% 5%	600
July	1st to 10th	Night	10% 3 8% 31% 39% 9%	585
	11th to 20th	Night	10% 2 6% 29% 41% 12%	582
	21st to end	Night	9% 2 10% 29% 43% 7%	657
August	1st to 10th	Night	17% 3 8% 29% 37% 7%	597
	11th to 20th	Night	13% 3 9% 30% 38% 7%	594
	21st to end	Night	12% 3 9% 27% 42% 7%	789
September	1st to 10th	Night	10% 3 12% 30% 38% 7%	800
	11th to 20th	Night	15% 3 14% 27% 35% 6%	800
	21st to end	Night	19% 4 16% 31% 28% 3	800
October	1st to 10th	Night	17% 4 17% 30% 27% 6%	773
	11th to 20th	Night	16% 6% 24% 30% 22% 2	760
	21st to end	Night	15% 8% 22% 34% 19% 3	836
November	1st to 10th	Night	16% 7% 24% 32% 19% 2	780
	11th to 20th	Night	15% 11% 29% 33% 12% 1	800
	21st to end	Night	15% 9% 28% 34% 13% 1	800
December	1st to 10th	Night	23% 12% 26% 33% 6%	800
	11th to 20th	Night	21% 8% 26% 34% 11%	800
	21st to end	Night	26% 11% 25% 29% 9%	880

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