Hiddenwell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hiddenwell Observatory clear sky chart from 2005-11-06 to 2025-03-27.

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% 12% 5% 11% 6% 4 4 3 5% 6% 29%	108880
	Night	14% 14% 6% 13% 6% 5% 4 3 4 5% 25%	110481
Transparency	Day	54% 6% 11% 18% 10% 1	112486
	Night	59% 6% 10% 15% 9% 1	115039
Seeing	Day	20% 12% 29% 23% 12% 4	15565
	Night	21% 12% 28% 27% 11% 1	25000

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	11% 19% 10% 25% 13% 5% 4 2 2 3 6%	3278
	11th to 20th	Day	8% 20% 12% 28% 14% 6% 3 2 2 1 4	3734
	21st to end	Day	13% 19% 10% 24% 9% 6% 5% 3 3 3 6%	4466
February	1st to 10th	Day	13% 20% 8% 18% 10% 5% 4 2 4 3 12%	1800
	11th to 20th	Day	13% 15% 9% 21% 10% 5% 5% 3 4 3 12%	1753
	21st to end	Day	15% 18% 6% 14% 8% 5% 4 2 4 5% 19%	1630
March	1st to 10th	Day	15% 16% 6% 12% 6% 3 3 3 3 5% 27%	3433
	11th to 20th	Day	11% 16% 9% 13% 5% 4 4 4 5% 5% 25%	3590
	21st to end	Day	15% 13% 6% 11% 5% 4 4 3 5% 6% 27%	3881
April	1st to 10th	Day	17% 15% 5% 9% 5% 4 3 4 5% 5% 28%	2180
	11th to 20th	Day	18% 12% 2 7% 4 4 3 4 4 6% 36%	2442
	21st to end	Day	19% 9% 4 7% 5% 4 4 3 5% 7% 34%	2470
May	1st to 10th	Day	17% 8% 3 6% 5% 4 4 4 6% 7% 37%	4108
	11th to 20th	Day	16% 9% 3 7% 4 4 3 3 5% 8% 38%	4194
	21st to end	Day	14% 5% 2 5% 4 4 4 3 5% 7% 47%	4837
June	1st to 10th	Day	13% 8% 2 7% 5% 4 4 4 6% 7% 39%	2779
	11th to 20th	Day	10% 5% 2 6% 6% 4 5% 4 7% 8% 43%	2850
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 5% 8% 42%	2850
July	1st to 10th	Day	12% 6% 2 6% 4 4 6% 5% 8% 9% 38%	4760
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 9% 47%	4551
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 9% 46%	4466
August	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 8% 39%	4104
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 5% 6% 9% 37%	4044
	21st to end	Day	10% 6% 2 5% 4 4 4 4 7% 9% 44%	4508
September	1st to 10th	Day	12% 7% 2 8% 5% 4 5% 4 6% 8% 39%	2235
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 3 6% 7% 45%	2090
	21st to end	Day	16% 9% 3 7% 6% 4 5% 4 5% 8% 34%	2090
October	1st to 10th	Day	19% 8% 4 8% 4 5% 3 4 5% 7% 33%	1938
	11th to 20th	Day	24% 14% 4 9% 6% 4 4 4 5% 6% 20%	1900
	21st to end	Day	27% 18% 5% 9% 6% 4 4 3 5% 5% 16%	2014
November	1st to 10th	Day	15% 20% 4 10% 6% 5% 4 4 4 5% 23%	1753
	11th to 20th	Day	15% 20% 5% 14% 6% 5% 5% 4 5% 5% 17%	1600
	21st to end	Day	18% 24% 9% 14% 6% 5% 4 3 4 5% 10%	1600
December	1st to 10th	Day	14% 31% 14% 17% 7% 4 4 2 2 2 4	2600
	11th to 20th	Day	18% 25% 8% 20% 6% 4 3 3 4 4 7%	2876
	21st to end	Day	23% 24% 7% 13% 5% 5% 4 3 4 4 8%	3476
January	1st to 10th	Night	12% 18% 9% 27% 11% 6% 4 3 2 3 4	6670
	11th to 20th	Night	10% 17% 10% 27% 13% 7% 4 2 2 2 4	6161
	21st to end	Night	12% 17% 10% 22% 8% 5% 5% 3 5% 5% 9%	6490
February	1st to 10th	Night	12% 21% 7% 17% 11% 6% 4 3 4 3 12%	2600
	11th to 20th	Night	13% 17% 8% 18% 8% 5% 5% 3 4 5% 15%	2533
	21st to end	Night	14% 15% 6% 14% 7% 5% 5% 4 5% 6% 20%	1997
March	1st to 10th	Night	12% 14% 5% 11% 5% 4 4 3 4 6% 32%	3627
	11th to 20th	Night	9% 15% 6% 12% 5% 4 4 3 5% 6% 31%	3589
	21st to end	Night	15% 10% 6% 12% 6% 5% 5% 3 4 5% 30%	3890
April	1st to 10th	Night	18% 15% 5% 7% 5% 4 4 4 5% 5% 30%	2013
	11th to 20th	Night	19% 10% 3 6% 4 4 5% 3 4 6% 37%	1689
	21st to end	Night	18% 11% 3 8% 5% 5% 4 4 5% 5% 31%	1710
May	1st to 10th	Night	15% 8% 3 8% 4 4 4 4 5% 7% 39%	2833
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 3 5% 7% 40%	2697
	21st to end	Night	11% 6% 2 5% 4 5% 4 3 5% 7% 48%	2738
June	1st to 10th	Night	13% 8% 2 7% 5% 5% 3 3 5% 9% 40%	1397
	11th to 20th	Night	12% 5% 2 7% 4 4 5% 4 7% 9% 41%	1330
	21st to end	Night	14% 7% 2 5% 5% 5% 4 4 6% 7% 41%	1330
July	1st to 10th	Night	8% 7% 3 8% 4 4 3 3 5% 8% 47%	2210
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 8% 50%	2400
	21st to end	Night	7% 7% 2 6% 3 4 5% 5% 6% 8% 48%	3087
August	1st to 10th	Night	11% 6% 3 7% 5% 4 4 4 5% 7% 45%	2825
	11th to 20th	Night	12% 8% 3 6% 5% 4 4 4 5% 8% 41%	2785
	21st to end	Night	11% 6% 2 6% 4 4 4 3 5% 7% 48%	3124
September	1st to 10th	Night	11% 5% 3 6% 4 4 5% 3 6% 7% 46%	1933
	11th to 20th	Night	11% 5% 2 6% 4 4 3 3 6% 7% 50%	2090
	21st to end	Night	16% 7% 3 8% 5% 4 5% 4 5% 6% 37%	2090
October	1st to 10th	Night	18% 8% 3 7% 5% 4 4 4 5% 5% 37%	2242
	11th to 20th	Night	23% 12% 3 9% 5% 5% 4 3 5% 7% 24%	2280
	21st to end	Night	24% 16% 4 10% 5% 5% 4 3 4 5% 20%	2579
November	1st to 10th	Night	17% 16% 3 9% 5% 6% 4 3 5% 6% 26%	2542
	11th to 20th	Night	17% 20% 5% 11% 6% 5% 5% 4 5% 4 17%	2800
	21st to end	Night	20% 22% 8% 13% 6% 5% 4 2 4 5% 13%	2800
December	1st to 10th	Night	13% 27% 9% 20% 7% 5% 5% 2 3 3 5%	4580
	11th to 20th	Night	11% 23% 9% 19% 7% 6% 4 3 4 4 10%	5318
	21st to end	Night	20% 22% 9% 15% 6% 4 4 3 3 4 9%	7502

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	84% 5% 6% 3 2	3279
	11th to 20th	Day	90% 4 3 2 1	3766
	21st to end	Day	82% 6% 7% 3 2	4466
February	1st to 10th	Day	77% 5% 7% 10% 1	1800
	11th to 20th	Day	77% 5% 7% 8% 3	1762
	21st to end	Day	68% 5% 8% 13% 5%	1630
March	1st to 10th	Day	61% 4 11% 15% 8%	3436
	11th to 20th	Day	60% 5% 11% 17% 6% 1	3590
	21st to end	Day	57% 6% 11% 15% 10% 1	3881
April	1st to 10th	Day	57% 6% 11% 17% 9%	2180
	11th to 20th	Day	49% 5% 9% 22% 14% 1	2442
	21st to end	Day	50% 6% 11% 19% 11% 2	2470
May	1st to 10th	Day	44% 6% 11% 20% 17% 2	4120
	11th to 20th	Day	43% 7% 14% 26% 9% 1	4198
	21st to end	Day	37% 5% 11% 22% 20% 5%	4837
June	1st to 10th	Day	41% 7% 11% 24% 15% 1	2779
	11th to 20th	Day	36% 7% 12% 26% 18% 1	2850
	21st to end	Day	41% 6% 12% 26% 14% 1	2850
July	1st to 10th	Day	40% 7% 16% 20% 16% 2	4686
	11th to 20th	Day	32% 6% 13% 35% 13% 1	4471
	21st to end	Day	33% 7% 13% 27% 18% 2	4324
August	1st to 10th	Day	39% 8% 13% 24% 14% 1	4091
	11th to 20th	Day	42% 7% 16% 25% 10%	4083
	21st to end	Day	35% 6% 16% 31% 12% 1	4508
September	1st to 10th	Day	42% 7% 13% 25% 11% 2	2235
	11th to 20th	Day	37% 7% 14% 28% 14%	2090
	21st to end	Day	47% 7% 13% 23% 8% 1	2090
October	1st to 10th	Day	44% 7% 13% 24% 10% 1	3224
	11th to 20th	Day	51% 7% 12% 21% 9%	3140
	21st to end	Day	62% 6% 12% 16% 4	3303
November	1st to 10th	Day	63% 5% 9% 16% 7%	1753
	11th to 20th	Day	67% 8% 11% 8% 6% 1	1600
	21st to end	Day	78% 5% 8% 7% 1	1600
December	1st to 10th	Day	88% 5% 4 2 1	2600
	11th to 20th	Day	82% 5% 6% 6% 1	2876
	21st to end	Day	79% 6% 8% 6% 2	3476
January	1st to 10th	Night	84% 6% 5% 4 1	6670
	11th to 20th	Night	86% 6% 5% 2 1	6204
	21st to end	Night	76% 6% 9% 5% 3	6490
February	1st to 10th	Night	78% 5% 7% 9% 2	2600
	11th to 20th	Night	72% 5% 10% 10% 3	2535
	21st to end	Night	64% 6% 11% 12% 7%	1997
March	1st to 10th	Night	53% 5% 15% 20% 7%	3637
	11th to 20th	Night	53% 6% 14% 18% 9% 1	3590
	21st to end	Night	56% 5% 10% 18% 9% 1	3890
April	1st to 10th	Night	55% 6% 9% 18% 11% 1	2013
	11th to 20th	Night	48% 5% 8% 20% 17% 2	1689
	21st to end	Night	53% 5% 9% 16% 15% 2	1710
May	1st to 10th	Night	43% 7% 11% 20% 16% 4	2840
	11th to 20th	Night	43% 7% 10% 23% 15% 2	2698
	21st to end	Night	35% 6% 11% 23% 21% 3	2739
June	1st to 10th	Night	42% 6% 10% 23% 17% 2	1397
	11th to 20th	Night	38% 6% 13% 24% 17% 2	1330
	21st to end	Night	41% 6% 10% 24% 17% 2	1330
July	1st to 10th	Night	35% 5% 12% 25% 17% 6%	2175
	11th to 20th	Night	31% 7% 12% 34% 16% 1	2357
	21st to end	Night	32% 7% 14% 25% 20% 2	2988
August	1st to 10th	Night	39% 6% 10% 29% 15% 1	2814
	11th to 20th	Night	40% 7% 15% 22% 14% 1	2812
	21st to end	Night	36% 6% 12% 32% 14% 1	3124
September	1st to 10th	Night	35% 7% 12% 29% 15% 2	1933
	11th to 20th	Night	34% 6% 14% 29% 17% 1	2090
	21st to end	Night	47% 7% 12% 24% 10%	2090
October	1st to 10th	Night	38% 7% 11% 26% 17% 1	3736
	11th to 20th	Night	49% 6% 16% 18% 12%	3779
	21st to end	Night	54% 6% 15% 18% 6%	4240
November	1st to 10th	Night	59% 6% 10% 18% 6%	2542
	11th to 20th	Night	68% 7% 9% 11% 4 1	2800
	21st to end	Night	76% 5% 10% 7% 1	2800
December	1st to 10th	Night	84% 6% 6% 3 1	4580
	11th to 20th	Night	78% 6% 8% 6% 2	5318
	21st to end	Night	78% 6% 8% 6% 2	7502

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	18% 22% 37% 15% 6% 1	227
	11th to 20th	Day	21% 21% 38% 13% 6% 1	300
	21st to end	Day	25% 17% 30% 22% 5%	330
February	1st to 10th	Day	23% 26% 34% 14% 4	300
	11th to 20th	Day	25% 21% 39% 12% 2	300
	21st to end	Day	22% 32% 32% 12% 2	249
March	1st to 10th	Day	22% 19% 38% 16% 5%	425
	11th to 20th	Day	23% 18% 31% 22% 6% 1	500
	21st to end	Day	26% 12% 33% 21% 6% 1	530
April	1st to 10th	Day	23% 17% 33% 20% 8%	460
	11th to 20th	Day	27% 16% 28% 16% 8% 5%	452
	21st to end	Day	27% 11% 28% 24% 9% 2	460
May	1st to 10th	Day	24% 9% 30% 23% 12% 3	463
	11th to 20th	Day	21% 8% 28% 24% 15% 5%	487
	21st to end	Day	17% 7% 27% 27% 15% 6%	529
June	1st to 10th	Day	15% 9% 31% 29% 15% 1	609
	11th to 20th	Day	13% 10% 29% 30% 14% 3	680
	21st to end	Day	17% 7% 35% 27% 11% 2	680
July	1st to 10th	Day	11% 6% 28% 30% 20% 5%	671
	11th to 20th	Day	13% 6% 32% 28% 15% 7%	649
	21st to end	Day	11% 5% 26% 32% 18% 8%	532
August	1st to 10th	Day	12% 4 25% 30% 18% 11%	486
	11th to 20th	Day	14% 4 20% 29% 21% 12%	479
	21st to end	Day	15% 5% 22% 31% 20% 7%	539
September	1st to 10th	Day	12% 9% 23% 30% 17% 8%	490
	11th to 20th	Day	11% 6% 20% 27% 24% 12%	490
	21st to end	Day	17% 9% 25% 27% 16% 7%	490
October	1st to 10th	Day	23% 10% 26% 22% 13% 6%	490
	11th to 20th	Day	26% 17% 30% 20% 6% 1	490
	21st to end	Day	35% 15% 30% 15% 5%	463
November	1st to 10th	Day	26% 18% 32% 16% 7% 1	295
	11th to 20th	Day	26% 24% 28% 17% 4 3	200
	21st to end	Day	26% 25% 34% 15% 1	200
December	1st to 10th	Day	29% 21% 34% 15% 2 1	200
	11th to 20th	Day	31% 23% 29% 14% 4 1	200
	21st to end	Day	35% 19% 31% 11% 4	220
January	1st to 10th	Night	23% 18% 34% 18% 6% 1	1000
	11th to 20th	Night	24% 18% 32% 20% 4 1	935
	21st to end	Night	20% 13% 36% 24% 7% 1	880
February	1st to 10th	Night	22% 17% 36% 22% 4	800
	11th to 20th	Night	22% 15% 35% 22% 5% 1	783
	21st to end	Night	21% 20% 33% 23% 3	660
March	1st to 10th	Night	19% 17% 35% 23% 6% 1	800
	11th to 20th	Night	17% 17% 36% 24% 5% 1	800
	21st to end	Night	23% 12% 29% 26% 10% 1	863
April	1st to 10th	Night	24% 12% 33% 25% 6%	760
	11th to 20th	Night	22% 14% 26% 27% 10% 1	565
	21st to end	Night	25% 10% 24% 29% 11% 1	570
May	1st to 10th	Night	19% 5% 29% 33% 12% 1	570
	11th to 20th	Night	19% 5% 25% 37% 13% 1	498
	21st to end	Night	13% 3 26% 40% 17% 1	411
June	1st to 10th	Night	17% 6% 24% 39% 13% 1	380
	11th to 20th	Night	14% 6% 28% 39% 12%	380
	21st to end	Night	17% 4 23% 41% 14% 1	380
July	1st to 10th	Night	8% 4 19% 49% 19% 1	370
	11th to 20th	Night	9% 5% 23% 38% 24% 2	462
	21st to end	Night	11% 2 19% 43% 24% 1	624
August	1st to 10th	Night	11% 4 16% 39% 28% 1	567
	11th to 20th	Night	10% 3 16% 39% 27% 4	564
	21st to end	Night	13% 4 20% 33% 28% 2	627
September	1st to 10th	Night	12% 4 22% 36% 19% 6%	750
	11th to 20th	Night	13% 4 19% 37% 23% 4	760
	21st to end	Night	17% 8% 23% 31% 18% 4	760
October	1st to 10th	Night	22% 7% 27% 28% 14% 1	760
	11th to 20th	Night	28% 12% 24% 27% 8% 1	760
	21st to end	Night	32% 12% 29% 23% 4	836
November	1st to 10th	Night	28% 14% 26% 23% 7% 1	780
	11th to 20th	Night	26% 21% 29% 18% 6%	800
	21st to end	Night	30% 16% 30% 20% 3	800
December	1st to 10th	Night	32% 16% 31% 17% 4	800
	11th to 20th	Night	23% 18% 39% 16% 3 1	845
	21st to end	Night	32% 14% 32% 19% 3	1100

Page generated at 2025-03-24 09:04:30. Version ac07

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