Hobbs Observatory
Clear Sky Chart
History

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

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% 8% 3 8% 5% 4 4 4 5% 7% 38%	127327
	Night	13% 9% 4 9% 5% 4 4 3 5% 6% 37%	123014
Transparency	Day	46% 3 12% 26% 12% 1	130826
	Night	48% 3 11% 24% 13% 1	127588
Seeing	Day	17% 10% 29% 26% 14% 4	17407
	Night	18% 8% 31% 31% 11% 1	27223

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	8% 14% 6% 18% 7% 6% 4 2 4 4 27%	3617
	11th to 20th	Day	8% 11% 7% 13% 6% 7% 7% 9% 7% 5% 20%	3620
	21st to end	Day	10% 15% 7% 11% 5% 4 4 3 4 6% 31%	4276
February	1st to 10th	Day	9% 11% 6% 10% 6% 5% 6% 4 6% 6% 31%	1800
	11th to 20th	Day	10% 10% 4 8% 6% 5% 4 4 6% 7% 35%	1754
	21st to end	Day	13% 11% 4 11% 6% 5% 4 4 4 7% 31%	1644
March	1st to 10th	Day	15% 7% 2 4 3 3 4 2 4 7% 48%	4562
	11th to 20th	Day	12% 8% 2 8% 4 5% 5% 4 6% 7% 40%	4980
	21st to end	Day	23% 10% 3 10% 4 4 4 3 5% 6% 28%	5727
April	1st to 10th	Day	17% 12% 3 8% 5% 4 4 3 5% 6% 33%	2400
	11th to 20th	Day	22% 11% 4 7% 6% 4 4 3 5% 5% 31%	2374
	21st to end	Day	21% 11% 3 7% 6% 4 4 3 4 5% 30%	2494
May	1st to 10th	Day	14% 6% 2 6% 3 3 3 3 4 6% 49%	6319
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 5% 7% 41%	6319
	21st to end	Day	19% 7% 2 6% 5% 4 4 3 5% 6% 40%	6935
June	1st to 10th	Day	14% 5% 2 6% 4 3 4 4 6% 8% 43%	2800
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 4 5% 9% 35%	2800
	21st to end	Day	13% 5% 2 6% 5% 5% 5% 5% 7% 9% 39%	2800
July	1st to 10th	Day	11% 4 2 5% 4 4 5% 4 7% 8% 46%	6360
	11th to 20th	Day	9% 3 1 5% 3 3 4 3 5% 9% 54%	6360
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 5% 8% 46%	6924
August	1st to 10th	Day	14% 6% 2 6% 4 5% 4 4 6% 8% 42%	4402
	11th to 20th	Day	13% 5% 2 5% 4 4 4 3 6% 8% 46%	4171
	21st to end	Day	13% 6% 2 6% 4 5% 4 4 6% 8% 42%	4312
September	1st to 10th	Day	13% 6% 2 5% 4 3 3 4 5% 7% 47%	2400
	11th to 20th	Day	12% 5% 3 6% 5% 4 4 4 5% 8% 45%	2400
	21st to end	Day	15% 6% 3 5% 3 4 4 4 5% 7% 44%	2124
October	1st to 10th	Day	15% 6% 3 6% 4 4 4 3 5% 6% 44%	2000
	11th to 20th	Day	17% 12% 3 7% 4 5% 5% 4 4 6% 35%	2000
	21st to end	Day	21% 12% 3 6% 4 3 3 2 4 5% 37%	2073
November	1st to 10th	Day	14% 9% 3 7% 5% 4 3 3 4 7% 39%	1780
	11th to 20th	Day	16% 13% 5% 10% 5% 5% 4 3 5% 5% 28%	1600
	21st to end	Day	14% 13% 4 7% 7% 3 4 3 5% 5% 35%	1600
December	1st to 10th	Day	7% 10% 5% 18% 11% 7% 6% 4 4 5% 23%	2610
	11th to 20th	Day	13% 17% 6% 10% 7% 4 4 3 4 4 28%	3008
	21st to end	Day	21% 20% 8% 15% 5% 4 3 2 3 3 15%	3982
January	1st to 10th	Night	7% 13% 6% 15% 8% 4 3 3 4 5% 32%	6348
	11th to 20th	Night	8% 12% 6% 14% 6% 6% 8% 8% 7% 4 21%	6360
	21st to end	Night	10% 17% 7% 11% 6% 4 4 3 5% 4 29%	6699
February	1st to 10th	Night	8% 12% 6% 11% 7% 6% 4 4 5% 5% 33%	2600
	11th to 20th	Night	8% 10% 4 10% 5% 5% 6% 4 5% 7% 38%	2533
	21st to end	Night	13% 11% 3 8% 7% 5% 4 3 5% 6% 34%	1985
March	1st to 10th	Night	11% 7% 3 6% 4 4 4 3 6% 7% 46%	5332
	11th to 20th	Night	10% 8% 3 9% 5% 5% 5% 4 6% 8% 37%	4980
	21st to end	Night	25% 11% 4 10% 4 3 3 2 3 5% 29%	5202
April	1st to 10th	Night	19% 11% 3 5% 4 3 4 4 5% 5% 36%	2000
	11th to 20th	Night	22% 9% 3 7% 4 3 4 3 4 5% 36%	1975
	21st to end	Night	21% 9% 2 6% 4 3 3 3 5% 6% 37%	1903
May	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 4 5% 45%	3596
	11th to 20th	Night	13% 5% 2 6% 3 3 3 2 4 7% 51%	3596
	21st to end	Night	17% 7% 3 7% 4 3 4 3 5% 6% 40%	3942
June	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 6% 8% 45%	1600
	11th to 20th	Night	14% 5% 2 5% 4 4 5% 4 6% 7% 43%	1600
	21st to end	Night	11% 4 3 5% 4 4 4 4 7% 8% 46%	1600
July	1st to 10th	Night	11% 4 1 5% 4 4 4 4 6% 8% 49%	3618
	11th to 20th	Night	9% 3 2 4 4 3 4 3 5% 8% 55%	3617
	21st to end	Night	9% 3 1 5% 4 4 5% 3 5% 8% 51%	3947
August	1st to 10th	Night	13% 5% 2 6% 4 4 4 4 6% 7% 46%	2755
	11th to 20th	Night	14% 5% 2 6% 4 4 4 3 5% 6% 49%	2888
	21st to end	Night	15% 5% 2 6% 4 4 4 3 4 6% 47%	3585
September	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 5% 6% 53%	2000
	11th to 20th	Night	12% 5% 2 4 4 4 3 3 5% 7% 51%	2000
	21st to end	Night	14% 4 2 6% 4 3 4 2 5% 7% 50%	2253
October	1st to 10th	Night	15% 5% 2 5% 3 4 3 3 5% 6% 50%	2400
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 5% 7% 40%	2400
	21st to end	Night	18% 12% 3 6% 4 4 4 3 4 5% 36%	2766
November	1st to 10th	Night	14% 11% 4 6% 3 3 3 4 5% 7% 39%	2563
	11th to 20th	Night	15% 11% 5% 9% 5% 4 4 3 4 6% 33%	2796
	21st to end	Night	15% 12% 4 9% 5% 4 3 3 5% 5% 35%	2800
December	1st to 10th	Night	8% 10% 5% 13% 7% 6% 5% 4 6% 7% 29%	4580
	11th to 20th	Night	13% 18% 7% 14% 6% 4 4 4 4 4 23%	5199
	21st to end	Night	23% 16% 6% 14% 5% 4 3 2 3 4 19%	6996

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	62% 2 10% 18% 7%	3618
	11th to 20th	Day	63% 2 6% 17% 12% 1	3620
	21st to end	Day	55% 2 14% 20% 8%	4276
February	1st to 10th	Day	53% 3 12% 19% 11% 1	1800
	11th to 20th	Day	47% 4 12% 26% 10% 1	1763
	21st to end	Day	53% 3 10% 23% 9% 2	1644
March	1st to 10th	Day	39% 2 14% 26% 15% 4	4562
	11th to 20th	Day	43% 2 13% 27% 13% 2	4980
	21st to end	Day	59% 2 8% 18% 12% 1	5729
April	1st to 10th	Day	53% 3 9% 20% 13% 1	2400
	11th to 20th	Day	57% 2 9% 19% 12% 2	2374
	21st to end	Day	57% 3 11% 19% 10% 1	2494
May	1st to 10th	Day	39% 2 9% 31% 18% 1	6357
	11th to 20th	Day	44% 3 10% 27% 14% 2	6323
	21st to end	Day	47% 3 8% 28% 13% 1	6949
June	1st to 10th	Day	38% 3 13% 31% 13% 2	2800
	11th to 20th	Day	45% 4 13% 24% 13% 1	2800
	21st to end	Day	40% 5% 16% 27% 11% 1	2800
July	1st to 10th	Day	33% 5% 16% 36% 8% 1	6291
	11th to 20th	Day	28% 4 14% 37% 15% 1	6285
	21st to end	Day	36% 5% 14% 28% 17% 1	6728
August	1st to 10th	Day	40% 5% 13% 27% 14% 1	4387
	11th to 20th	Day	37% 4 12% 36% 11%	4210
	21st to end	Day	40% 4 13% 30% 12% 1	4311
September	1st to 10th	Day	37% 4 13% 31% 15%	2400
	11th to 20th	Day	38% 4 17% 32% 8% 1	2400
	21st to end	Day	40% 3 12% 33% 11%	2124
October	1st to 10th	Day	29% 2 9% 39% 21%	3260
	11th to 20th	Day	42% 3 10% 25% 17% 2	3240
	21st to end	Day	45% 2 14% 30% 9%	3324
November	1st to 10th	Day	47% 3 12% 22% 14% 2	1780
	11th to 20th	Day	57% 3 11% 19% 8% 1	1600
	21st to end	Day	52% 3 16% 21% 7% 1	1600
December	1st to 10th	Day	64% 4 10% 17% 5%	2610
	11th to 20th	Day	61% 2 10% 19% 8% 1	3005
	21st to end	Day	77% 2 6% 11% 5%	3982
January	1st to 10th	Night	57% 2 9% 22% 10%	6348
	11th to 20th	Night	64% 2 8% 14% 12%	6360
	21st to end	Night	59% 3 10% 19% 9%	6699
February	1st to 10th	Night	54% 3 10% 22% 11% 2	2600
	11th to 20th	Night	46% 4 11% 28% 10% 1	2534
	21st to end	Night	52% 2 13% 20% 11% 2	1985
March	1st to 10th	Night	39% 2 14% 28% 13% 5%	5332
	11th to 20th	Night	47% 2 13% 25% 12% 2	4980
	21st to end	Night	61% 2 8% 16% 12% 1	5202
April	1st to 10th	Night	50% 4 8% 19% 18% 2	2000
	11th to 20th	Night	52% 2 8% 20% 16% 2	1975
	21st to end	Night	49% 2 8% 23% 16% 2	1903
May	1st to 10th	Night	43% 2 9% 23% 21% 1	3620
	11th to 20th	Night	36% 2 10% 26% 21% 5%	3597
	21st to end	Night	47% 2 9% 26% 14% 1	3950
June	1st to 10th	Night	37% 5% 10% 29% 17% 1	1600
	11th to 20th	Night	38% 5% 13% 24% 18% 2	1600
	21st to end	Night	35% 4 14% 31% 14% 3	1600
July	1st to 10th	Night	33% 5% 16% 33% 11% 1	3580
	11th to 20th	Night	28% 4 14% 37% 16% 1	3572
	21st to end	Night	31% 5% 16% 28% 18% 2	3832
August	1st to 10th	Night	37% 5% 12% 28% 16% 2	2746
	11th to 20th	Night	35% 5% 14% 29% 15% 1	2915
	21st to end	Night	38% 4 15% 27% 14% 2	3585
September	1st to 10th	Night	33% 3 12% 33% 18% 1	2000
	11th to 20th	Night	34% 3 15% 34% 14%	2000
	21st to end	Night	35% 3 12% 34% 15% 1	2253
October	1st to 10th	Night	27% 2 6% 37% 25% 4	3920
	11th to 20th	Night	35% 3 10% 30% 21% 1	3899
	21st to end	Night	49% 3 9% 25% 14%	4465
November	1st to 10th	Night	45% 3 11% 26% 14% 1	2563
	11th to 20th	Night	53% 3 13% 18% 12% 1	2796
	21st to end	Night	52% 3 15% 23% 7% 1	2800
December	1st to 10th	Night	53% 6% 17% 19% 4	4580
	11th to 20th	Night	66% 3 9% 15% 7%	5201
	21st to end	Night	72% 2 6% 13% 7%	6996

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	14% 13% 33% 26% 11% 3	300
	11th to 20th	Day	17% 13% 39% 23% 7% 2	300
	21st to end	Day	20% 11% 35% 25% 8% 2	330
February	1st to 10th	Day	18% 13% 44% 17% 6% 2	300
	11th to 20th	Day	15% 19% 37% 22% 7%	300
	21st to end	Day	18% 14% 42% 24% 2	249
March	1st to 10th	Day	18% 14% 39% 19% 8% 1	300
	11th to 20th	Day	20% 12% 38% 19% 9% 2	300
	21st to end	Day	24% 12% 31% 21% 8% 3	440
April	1st to 10th	Day	26% 13% 34% 20% 5% 1	500
	11th to 20th	Day	28% 15% 26% 22% 8% 1	492
	21st to end	Day	27% 14% 26% 22% 9% 2	579
May	1st to 10th	Day	21% 10% 31% 25% 11% 2	703
	11th to 20th	Day	21% 11% 26% 25% 14% 3	725
	21st to end	Day	20% 9% 25% 28% 14% 4	789
June	1st to 10th	Day	13% 8% 25% 33% 17% 4	730
	11th to 20th	Day	18% 7% 34% 26% 12% 3	730
	21st to end	Day	16% 8% 28% 28% 14% 7%	730
July	1st to 10th	Day	10% 4 21% 29% 25% 11%	721
	11th to 20th	Day	11% 6% 24% 30% 21% 9%	718
	21st to end	Day	6% 4 24% 37% 21% 9%	794
August	1st to 10th	Day	11% 5% 22% 30% 24% 8%	726
	11th to 20th	Day	13% 5% 19% 29% 27% 8%	715
	21st to end	Day	14% 6% 22% 28% 23% 6%	583
September	1st to 10th	Day	15% 7% 25% 28% 19% 5%	530
	11th to 20th	Day	12% 5% 27% 32% 21% 4	530
	21st to end	Day	16% 8% 27% 27% 18% 5%	434
October	1st to 10th	Day	16% 12% 28% 25% 14% 5%	330
	11th to 20th	Day	23% 15% 35% 20% 6% 1	330
	21st to end	Day	25% 14% 34% 19% 6% 2	363
November	1st to 10th	Day	19% 11% 37% 23% 8% 2	306
	11th to 20th	Day	19% 19% 35% 22% 5%	300
	21st to end	Day	23% 12% 41% 17% 7%	300
December	1st to 10th	Day	14% 14% 38% 26% 6% 1	300
	11th to 20th	Day	19% 15% 39% 19% 7%	300
	21st to end	Day	27% 14% 38% 18% 4 1	330
January	1st to 10th	Night	14% 11% 35% 29% 9% 1	1000
	11th to 20th	Night	18% 9% 37% 28% 7% 1	1000
	21st to end	Night	20% 10% 33% 30% 7% 1	1100
February	1st to 10th	Night	14% 13% 37% 29% 7% 1	1000
	11th to 20th	Night	12% 13% 40% 27% 7% 1	979
	21st to end	Night	19% 12% 35% 29% 5%	665
March	1st to 10th	Night	16% 11% 37% 27% 7% 1	785
	11th to 20th	Night	16% 12% 34% 31% 7% 1	600
	21st to end	Night	23% 8% 30% 27% 10% 2	660
April	1st to 10th	Night	25% 9% 35% 24% 6% 1	600
	11th to 20th	Night	26% 8% 28% 30% 7%	593
	21st to end	Night	23% 8% 32% 27% 9% 1	600
May	1st to 10th	Night	23% 6% 33% 31% 6% 1	600
	11th to 20th	Night	19% 6% 31% 33% 9% 2	591
	21st to end	Night	16% 7% 24% 38% 15% 1	650
June	1st to 10th	Night	13% 6% 28% 41% 12%	600
	11th to 20th	Night	14% 6% 29% 40% 10% 1	600
	21st to end	Night	13% 4 25% 43% 14% 2	600
July	1st to 10th	Night	8% 3 21% 41% 25% 3	585
	11th to 20th	Night	8% 4 23% 39% 23% 3	582
	21st to end	Night	6% 2 20% 47% 22% 3	657
August	1st to 10th	Night	9% 2 16% 47% 25% 1	597
	11th to 20th	Night	13% 4 17% 37% 27% 2	594
	21st to end	Night	14% 2 22% 37% 23% 2	660
September	1st to 10th	Night	12% 5% 22% 40% 18% 4	600
	11th to 20th	Night	13% 4 25% 37% 18% 3	600
	21st to end	Night	14% 7% 27% 33% 17% 2	760
October	1st to 10th	Night	17% 7% 27% 32% 15% 1	800
	11th to 20th	Night	19% 10% 34% 28% 8% 1	800
	21st to end	Night	24% 9% 30% 29% 9%	880
November	1st to 10th	Night	20% 10% 34% 29% 7% 1	789
	11th to 20th	Night	21% 12% 36% 24% 7%	996
	21st to end	Night	21% 13% 36% 23% 7%	1000
December	1st to 10th	Night	19% 10% 36% 27% 8% 1	1000
	11th to 20th	Night	23% 10% 35% 24% 7% 1	1000
	21st to end	Night	28% 10% 31% 25% 6%	1100

Page generated at 2025-10-31 01:02:41. Version ac07

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