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 2026-07-31.

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% 10% 6% 4 4 3 5% 6% 30%	138184
	Night	14% 14% 6% 13% 7% 5% 4 3 4 5% 25%	134864
Transparency	Day	53% 6% 11% 19% 10% 1	141747
	Night	59% 6% 10% 16% 9% 1	139390
Seeing	Day	20% 12% 30% 23% 11% 4	17432
	Night	21% 12% 28% 27% 10% 1	26617

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	12% 19% 11% 24% 12% 5% 4 2 2 3 6%	4256
	11th to 20th	Day	7% 21% 13% 28% 14% 7% 3 1 2 1 3	4863
	21st to end	Day	10% 17% 8% 21% 12% 9% 6% 4 3 3 6%	5780
February	1st to 10th	Day	13% 20% 8% 18% 11% 6% 4 2 4 3 13%	1890
	11th to 20th	Day	13% 15% 9% 21% 10% 5% 5% 3 4 3 12%	1843
	21st to end	Day	14% 18% 6% 14% 8% 5% 4 2 4 5% 18%	1709
March	1st to 10th	Day	14% 14% 6% 16% 7% 3 3 3 4 5% 25%	4877
	11th to 20th	Day	11% 15% 8% 12% 5% 4 4 4 6% 7% 25%	5090
	21st to end	Day	17% 16% 7% 12% 5% 3 3 3 4 6% 24%	5586
April	1st to 10th	Day	17% 15% 5% 9% 5% 4 3 3 5% 5% 28%	2410
	11th to 20th	Day	18% 12% 2 6% 4 4 3 4 4 6% 35%	2702
	21st to end	Day	18% 10% 4 7% 5% 4 4 3 5% 7% 33%	2730
May	1st to 10th	Day	14% 8% 3 7% 5% 4 5% 4 6% 7% 37%	7642
	11th to 20th	Day	13% 11% 3 7% 5% 4 4 3 5% 7% 37%	7823
	21st to end	Day	17% 9% 2 5% 3 3 3 3 5% 6% 44%	9060
June	1st to 10th	Day	13% 8% 2 6% 4 4 4 4 6% 8% 40%	3071
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 7% 9% 42%	3150
	21st to end	Day	15% 6% 2 6% 4 4 5% 4 5% 8% 41%	3150
July	1st to 10th	Day	12% 7% 3 6% 4 4 5% 4 7% 9% 40%	6969
	11th to 20th	Day	11% 5% 2 5% 3 4 4 3 5% 8% 51%	6671
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 9% 50%	6554
August	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 8% 39%	4234
	11th to 20th	Day	14% 7% 2 6% 5% 5% 5% 4 6% 9% 38%	4174
	21st to end	Day	10% 6% 2 5% 4 4 4 4 7% 9% 44%	4650
September	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 6% 8% 39%	2352
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 6% 7% 46%	2200
	21st to end	Day	16% 9% 3 7% 6% 4 5% 4 5% 7% 35%	2200
October	1st to 10th	Day	19% 8% 4 7% 4 5% 4 4 5% 7% 35%	2040
	11th to 20th	Day	23% 13% 4 9% 5% 4 4 4 5% 7% 21%	2000
	21st to end	Day	26% 18% 5% 9% 6% 4 4 3 4 5% 18%	2120
November	1st to 10th	Day	16% 21% 4 10% 6% 5% 4 4 4 5% 23%	1842
	11th to 20th	Day	15% 19% 5% 14% 6% 5% 5% 4 5% 5% 16%	1680
	21st to end	Day	17% 24% 9% 14% 6% 5% 4 3 4 5% 10%	1680
December	1st to 10th	Day	14% 31% 14% 17% 7% 4 4 2 2 2 4	2680
	11th to 20th	Day	18% 24% 8% 20% 6% 4 3 2 3 4 7%	2953
	21st to end	Day	23% 24% 7% 14% 5% 5% 4 3 4 4 8%	3553
January	1st to 10th	Night	12% 18% 11% 28% 11% 6% 4 2 2 2 4	8651
	11th to 20th	Night	9% 20% 10% 27% 13% 7% 4 2 2 2 3	8025
	21st to end	Night	10% 14% 8% 21% 11% 9% 6% 4 5% 4 8%	8401
February	1st to 10th	Night	12% 20% 7% 18% 12% 6% 4 3 4 3 13%	2730
	11th to 20th	Night	13% 16% 8% 18% 8% 5% 4 3 4 5% 15%	2663
	21st to end	Night	14% 15% 6% 14% 7% 5% 5% 4 5% 6% 20%	2094
March	1st to 10th	Night	12% 14% 5% 12% 8% 5% 4 3 5% 5% 27%	5183
	11th to 20th	Night	8% 13% 6% 11% 5% 5% 5% 4 5% 7% 29%	5089
	21st to end	Night	18% 12% 6% 13% 5% 4 4 3 4 4 27%	5588
April	1st to 10th	Night	18% 14% 5% 8% 5% 4 4 4 5% 6% 29%	2225
	11th to 20th	Night	18% 9% 3 7% 4 4 5% 3 4 6% 36%	1869
	21st to end	Night	17% 10% 3 8% 5% 5% 4 4 5% 5% 32%	1890
May	1st to 10th	Night	15% 8% 3 8% 4 4 4 4 5% 7% 38%	5257
	11th to 20th	Night	16% 8% 3 7% 4 4 4 3 4 6% 41%	5021
	21st to end	Night	18% 6% 2 4 3 4 3 3 5% 7% 45%	5114
June	1st to 10th	Night	13% 8% 2 7% 4 5% 3 3 5% 9% 42%	1544
	11th to 20th	Night	12% 5% 2 7% 4 4 6% 5% 7% 9% 40%	1470
	21st to end	Night	12% 8% 2 6% 5% 5% 4 4 5% 8% 41%	1470
July	1st to 10th	Night	9% 8% 3 7% 4 4 3 3 5% 7% 44%	3230
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 5% 8% 48%	3509
	21st to end	Night	9% 6% 2 6% 3 4 4 4 5% 8% 49%	4518
August	1st to 10th	Night	11% 6% 3 7% 5% 4 4 4 5% 7% 45%	2915
	11th to 20th	Night	13% 8% 3 6% 5% 4 4 4 5% 8% 41%	2875
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 6% 48%	3223
September	1st to 10th	Night	11% 5% 3 6% 4 4 5% 3 6% 7% 46%	2035
	11th to 20th	Night	11% 5% 2 5% 4 4 3 3 6% 7% 51%	2200
	21st to end	Night	15% 8% 3 8% 5% 4 5% 4 5% 6% 37%	2200
October	1st to 10th	Night	17% 8% 3 7% 5% 4 4 4 5% 6% 38%	2360
	11th to 20th	Night	23% 12% 3 9% 5% 5% 4 3 5% 7% 24%	2400
	21st to end	Night	23% 16% 4 10% 5% 5% 4 3 4 5% 21%	2715
November	1st to 10th	Night	16% 17% 4 9% 6% 6% 4 3 5% 6% 26%	2673
	11th to 20th	Night	16% 21% 5% 11% 6% 5% 5% 4 5% 5% 17%	2940
	21st to end	Night	19% 23% 8% 13% 6% 5% 4 2 4 5% 12%	2940
December	1st to 10th	Night	13% 27% 9% 20% 7% 5% 5% 3 3 3 5%	4720
	11th to 20th	Night	11% 23% 9% 19% 8% 6% 4 3 4 3 10%	5460
	21st to end	Night	20% 21% 9% 16% 6% 4 4 3 3 4 9%	7667

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	83% 5% 7% 3 1	4257
	11th to 20th	Day	91% 4 3 2 1	4895
	21st to end	Day	80% 7% 7% 3 2	5780
February	1st to 10th	Day	77% 5% 7% 10% 2	1890
	11th to 20th	Day	77% 5% 7% 8% 3	1852
	21st to end	Day	68% 5% 8% 13% 5%	1709
March	1st to 10th	Day	63% 4 14% 13% 6%	4880
	11th to 20th	Day	57% 5% 13% 18% 6% 2	5090
	21st to end	Day	62% 5% 10% 15% 8% 1	5586
April	1st to 10th	Day	57% 5% 10% 17% 10%	2410
	11th to 20th	Day	50% 5% 9% 22% 14% 1	2702
	21st to end	Day	49% 6% 11% 21% 11% 2	2730
May	1st to 10th	Day	43% 6% 12% 21% 14% 4	7651
	11th to 20th	Day	45% 6% 11% 23% 15% 1	7827
	21st to end	Day	41% 4 9% 26% 17% 4	9061
June	1st to 10th	Day	40% 7% 11% 24% 16% 1	3071
	11th to 20th	Day	37% 7% 12% 27% 17% 1	3150
	21st to end	Day	41% 5% 12% 26% 13% 1	3150
July	1st to 10th	Day	38% 6% 15% 22% 17% 1	6896
	11th to 20th	Day	31% 5% 12% 35% 16% 1	6591
	21st to end	Day	30% 6% 14% 32% 17% 2	6370
August	1st to 10th	Day	39% 8% 13% 25% 14% 1	4221
	11th to 20th	Day	42% 7% 16% 25% 10%	4213
	21st to end	Day	34% 6% 16% 31% 12% 1	4650
September	1st to 10th	Day	41% 7% 13% 25% 11% 2	2352
	11th to 20th	Day	36% 7% 14% 29% 14%	2200
	21st to end	Day	47% 7% 13% 23% 9% 1	2200
October	1st to 10th	Day	43% 7% 13% 25% 10% 1	3326
	11th to 20th	Day	51% 7% 12% 21% 9%	3240
	21st to end	Day	62% 6% 12% 16% 5%	3409
November	1st to 10th	Day	64% 5% 9% 16% 7%	1842
	11th to 20th	Day	67% 8% 10% 8% 6% 1	1680
	21st to end	Day	79% 5% 7% 7% 1	1680
December	1st to 10th	Day	88% 5% 4 3 1	2680
	11th to 20th	Day	82% 5% 6% 6% 1	2953
	21st to end	Day	79% 6% 8% 5% 2	3553
January	1st to 10th	Night	85% 6% 5% 3 1	8651
	11th to 20th	Night	87% 6% 4 2 1	8068
	21st to end	Night	76% 7% 8% 5% 4	8401
February	1st to 10th	Night	77% 5% 7% 9% 2	2730
	11th to 20th	Night	71% 5% 10% 10% 3	2665
	21st to end	Night	65% 6% 11% 12% 6%	2094
March	1st to 10th	Night	58% 5% 13% 16% 7% 1	5193
	11th to 20th	Night	52% 5% 16% 18% 8% 1	5090
	21st to end	Night	61% 4 9% 15% 10% 1	5588
April	1st to 10th	Night	56% 6% 10% 17% 11% 1	2225
	11th to 20th	Night	49% 5% 8% 20% 16% 1	1869
	21st to end	Night	52% 5% 10% 17% 15% 2	1890
May	1st to 10th	Night	45% 6% 9% 21% 14% 6%	5264
	11th to 20th	Night	43% 7% 9% 23% 17% 1	5022
	21st to end	Night	40% 5% 8% 27% 19% 2	5115
June	1st to 10th	Night	40% 6% 9% 23% 19% 3	1544
	11th to 20th	Night	38% 6% 13% 24% 17% 2	1470
	21st to end	Night	41% 6% 10% 25% 17% 2	1470
July	1st to 10th	Night	39% 5% 12% 23% 18% 4	3195
	11th to 20th	Night	33% 6% 11% 29% 19% 2	3466
	21st to end	Night	32% 6% 12% 29% 20% 2	4387
August	1st to 10th	Night	38% 6% 10% 29% 15% 1	2904
	11th to 20th	Night	40% 7% 15% 23% 14% 1	2902
	21st to end	Night	36% 6% 12% 32% 13% 1	3223
September	1st to 10th	Night	35% 7% 12% 29% 14% 2	2035
	11th to 20th	Night	33% 6% 14% 30% 17% 1	2200
	21st to end	Night	47% 7% 11% 24% 10% 1	2200
October	1st to 10th	Night	37% 7% 11% 27% 17% 1	3854
	11th to 20th	Night	49% 6% 15% 18% 12%	3899
	21st to end	Night	54% 6% 15% 18% 7%	4376
November	1st to 10th	Night	59% 7% 10% 18% 6%	2673
	11th to 20th	Night	68% 7% 9% 11% 4 1	2940
	21st to end	Night	76% 5% 10% 7% 1	2940
December	1st to 10th	Night	84% 6% 6% 4 1	4720
	11th to 20th	Night	78% 6% 8% 6% 2	5460
	21st to end	Night	78% 5% 8% 6% 2	7667

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	20% 24% 36% 14% 6% 1	250
	11th to 20th	Day	22% 24% 36% 12% 6% 1	330
	21st to end	Day	25% 18% 30% 22% 5%	363
February	1st to 10th	Day	22% 25% 33% 14% 5%	330
	11th to 20th	Day	26% 20% 38% 14% 2	330
	21st to end	Day	22% 32% 32% 12% 3	273
March	1st to 10th	Day	23% 19% 37% 15% 5%	461
	11th to 20th	Day	25% 19% 29% 21% 6% 1	540
	21st to end	Day	30% 13% 32% 19% 5% 1	594
April	1st to 10th	Day	26% 17% 31% 18% 7%	540
	11th to 20th	Day	29% 15% 27% 16% 8% 5%	532
	21st to end	Day	25% 11% 30% 23% 8% 2	540
May	1st to 10th	Day	21% 11% 34% 22% 10% 2	543
	11th to 20th	Day	20% 10% 29% 23% 14% 5%	567
	21st to end	Day	19% 8% 29% 24% 13% 5%	617
June	1st to 10th	Day	14% 10% 33% 28% 14% 1	701
	11th to 20th	Day	14% 11% 31% 29% 12% 3	780
	21st to end	Day	17% 7% 37% 27% 10% 2	780
July	1st to 10th	Day	11% 6% 30% 30% 19% 5%	771
	11th to 20th	Day	13% 7% 32% 28% 14% 6%	747
	21st to end	Day	11% 6% 29% 31% 17% 7%	616
August	1st to 10th	Day	11% 3 24% 32% 18% 11%	526
	11th to 20th	Day	14% 3 20% 30% 20% 12%	519
	21st to end	Day	15% 5% 23% 31% 19% 7%	583
September	1st to 10th	Day	12% 9% 23% 29% 18% 8%	530
	11th to 20th	Day	11% 5% 18% 27% 24% 14%	530
	21st to end	Day	17% 9% 25% 27% 16% 6%	530
October	1st to 10th	Day	22% 9% 26% 23% 14% 5%	530
	11th to 20th	Day	25% 17% 31% 20% 5% 1	530
	21st to end	Day	33% 16% 31% 16% 4	503
November	1st to 10th	Day	28% 19% 30% 16% 6% 1	324
	11th to 20th	Day	26% 23% 29% 15% 5% 2	220
	21st to end	Day	27% 24% 34% 14% 1	220
December	1st to 10th	Day	29% 20% 34% 14% 1 1	220
	11th to 20th	Day	33% 22% 28% 13% 4	220
	21st to end	Day	36% 20% 29% 11% 3	242
January	1st to 10th	Night	23% 19% 34% 18% 6% 1	1050
	11th to 20th	Night	25% 19% 32% 20% 4 1	981
	21st to end	Night	20% 14% 36% 24% 6% 1	924
February	1st to 10th	Night	21% 17% 35% 23% 4	840
	11th to 20th	Night	22% 16% 35% 22% 5%	823
	21st to end	Night	22% 20% 33% 22% 3	692
March	1st to 10th	Night	19% 17% 35% 23% 5%	840
	11th to 20th	Night	19% 17% 35% 24% 5% 1	840
	21st to end	Night	23% 13% 29% 25% 9% 1	924
April	1st to 10th	Night	24% 13% 33% 24% 6%	840
	11th to 20th	Night	21% 15% 26% 26% 10% 1	625
	21st to end	Night	24% 11% 24% 30% 10%	630
May	1st to 10th	Night	18% 6% 30% 34% 12% 1	630
	11th to 20th	Night	19% 6% 26% 36% 13% 1	551
	21st to end	Night	15% 3 26% 40% 15% 1	455
June	1st to 10th	Night	16% 6% 25% 38% 13% 1	420
	11th to 20th	Night	14% 7% 29% 39% 11%	420
	21st to end	Night	16% 4 25% 41% 13% 1	420
July	1st to 10th	Night	8% 3 20% 50% 18% 1	410
	11th to 20th	Night	8% 5% 24% 39% 23% 2	512
	21st to end	Night	11% 2 20% 44% 22% 1	687
August	1st to 10th	Night	10% 4 16% 40% 28% 1	597
	11th to 20th	Night	10% 4 16% 39% 27% 4	594
	21st to end	Night	13% 3 20% 34% 27% 2	660
September	1st to 10th	Night	12% 4 22% 36% 20% 6%	790
	11th to 20th	Night	13% 4 18% 37% 25% 4	800
	21st to end	Night	17% 8% 22% 31% 18% 4	800
October	1st to 10th	Night	21% 7% 27% 30% 15% 1	800
	11th to 20th	Night	28% 12% 24% 27% 8% 1	800
	21st to end	Night	32% 12% 29% 23% 4	880
November	1st to 10th	Night	28% 14% 26% 23% 7% 1	820
	11th to 20th	Night	25% 21% 29% 18% 6%	840
	21st to end	Night	30% 17% 30% 20% 3	840
December	1st to 10th	Night	30% 16% 32% 17% 4	840
	11th to 20th	Night	23% 19% 39% 16% 3 1	887
	21st to end	Night	32% 14% 33% 18% 3	1155

Page generated at 2026-07-28 03:25:26. Version ac07

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