Lanphier Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lanphier Observatory clear sky chart from 2005-11-06 to 2026-09-14.

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	12% 8% 3 7% 5% 4 5% 4 6% 8% 39%	149194
	Night	13% 8% 3 7% 4 4 4 3 5% 7% 41%	142218
Transparency	Day	41% 6% 12% 24% 15% 2	152730
	Night	41% 5% 11% 24% 16% 2	146761
Seeing	Day	16% 11% 28% 26% 15% 5%	18290
	Night	17% 10% 30% 29% 13% 1	28008

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	12% 10% 5% 14% 6% 5% 4 3 5% 7% 29%	4691
	11th to 20th	Day	8% 10% 5% 10% 8% 7% 7% 4 5% 6% 30%	4807
	21st to end	Day	14% 15% 7% 10% 5% 4 3 3 4 5% 30%	5812
February	1st to 10th	Day	14% 12% 5% 9% 6% 4 4 3 5% 7% 30%	1890
	11th to 20th	Day	13% 11% 4 8% 6% 5% 5% 3 5% 7% 33%	2030
	21st to end	Day	14% 11% 4 10% 5% 4 3 3 4 6% 35%	1730
March	1st to 10th	Day	17% 13% 3 6% 3 3 3 2 3 4 43%	4580
	11th to 20th	Day	7% 8% 3 5% 4 4 3 4 7% 8% 47%	5038
	21st to end	Day	16% 10% 4 8% 5% 5% 5% 4 6% 7% 31%	5954
April	1st to 10th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	2520
	11th to 20th	Day	15% 9% 3 7% 4 4 5% 3 5% 6% 39%	2494
	21st to end	Day	18% 7% 3 6% 6% 5% 5% 3 5% 7% 36%	2520
May	1st to 10th	Day	16% 8% 3 7% 4 5% 4 4 6% 9% 33%	7438
	11th to 20th	Day	13% 8% 2 7% 5% 4 5% 3 5% 7% 41%	8177
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 5% 6% 8% 34%	9047
June	1st to 10th	Day	9% 4 2 5% 4 4 5% 5% 6% 9% 46%	2940
	11th to 20th	Day	9% 4 2 5% 4 5% 5% 4 6% 8% 48%	2940
	21st to end	Day	7% 6% 2 6% 6% 5% 5% 5% 7% 9% 42%	2940
July	1st to 10th	Day	9% 5% 3 5% 4 3 5% 4 7% 10% 45%	8280
	11th to 20th	Day	7% 6% 2 7% 5% 4 5% 4 6% 10% 44%	8280
	21st to end	Day	11% 5% 2 6% 5% 4 6% 4 8% 11% 37%	8897
August	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 44%	5996
	11th to 20th	Day	10% 7% 2 7% 5% 5% 5% 4 7% 9% 38%	5486
	21st to end	Day	4 3 1 4 4 3 5% 4 7% 11% 54%	6080
September	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 5% 7% 51%	2520
	11th to 20th	Day	8% 6% 2 6% 3 4 4 3 5% 6% 52%	2386
	21st to end	Day	8% 6% 2 6% 4 3 4 4 6% 7% 50%	2200
October	1st to 10th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 52%	2030
	11th to 20th	Day	14% 7% 2 6% 4 4 3 3 4 6% 47%	2000
	21st to end	Day	17% 9% 3 7% 4 4 2 3 5% 6% 41%	2111
November	1st to 10th	Day	10% 8% 3 5% 4 4 4 3 4 7% 50%	1852
	11th to 20th	Day	14% 10% 3 7% 3 3 3 3 5% 6% 42%	1890
	21st to end	Day	16% 11% 4 8% 4 4 3 4 3 5% 37%	1790
December	1st to 10th	Day	8% 8% 4 7% 4 3 4 3 5% 6% 48%	2690
	11th to 20th	Day	14% 12% 6% 9% 5% 4 4 4 5% 7% 30%	3088
	21st to end	Day	25% 18% 6% 12% 4 4 4 3 3 4 17%	4070
January	1st to 10th	Night	12% 12% 6% 10% 4 4 4 3 4 5% 35%	8232
	11th to 20th	Night	9% 12% 5% 11% 6% 5% 6% 4 5% 5% 32%	8178
	21st to end	Night	15% 12% 5% 11% 5% 3 4 3 4 5% 33%	8402
February	1st to 10th	Night	16% 12% 5% 9% 5% 4 4 3 5% 6% 33%	2730
	11th to 20th	Night	14% 10% 3 9% 6% 3 4 3 5% 6% 38%	2474
	21st to end	Night	14% 10% 3 8% 4 4 4 3 4 5% 40%	2076
March	1st to 10th	Night	20% 11% 3 6% 3 3 3 2 3 5% 40%	5493
	11th to 20th	Night	11% 7% 2 5% 4 3 3 3 5% 6% 50%	5184
	21st to end	Night	18% 10% 3 7% 5% 5% 4 4 5% 6% 32%	5215
April	1st to 10th	Night	13% 8% 3 6% 4 5% 5% 4 5% 6% 41%	2100
	11th to 20th	Night	14% 6% 3 6% 4 4 4 3 5% 7% 44%	2075
	21st to end	Night	19% 8% 3 6% 4 4 4 5% 3 5% 40%	2100
May	1st to 10th	Night	17% 8% 3 7% 5% 4 5% 4 6% 7% 35%	5402
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 7% 9% 42%	4709
	21st to end	Night	14% 7% 3 7% 4 4 5% 4 6% 9% 37%	5139
June	1st to 10th	Night	8% 6% 1 5% 3 3 4 4 6% 9% 51%	1680
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 6% 9% 49%	1680
	21st to end	Night	7% 4 2 6% 4 5% 4 4 6% 9% 48%	1680
July	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	4708
	11th to 20th	Night	7% 4 2 5% 4 5% 5% 4 7% 9% 48%	4707
	21st to end	Night	8% 5% 2 6% 4 5% 5% 4 7% 10% 43%	5193
August	1st to 10th	Night	10% 4 2 5% 3 3 4 4 6% 9% 51%	4173
	11th to 20th	Night	8% 4 2 6% 4 5% 6% 3 6% 9% 48%	4560
	21st to end	Night	4 2 1 4 3 4 4 4 7% 10% 58%	5046
September	1st to 10th	Night	10% 4 2 5% 3 3 3 3 5% 8% 56%	2100
	11th to 20th	Night	7% 5% 2 6% 3 3 3 3 5% 8% 54%	2060
	21st to end	Night	9% 5% 2 5% 4 4 4 3 5% 7% 53%	2200
October	1st to 10th	Night	9% 4 1 5% 4 3 4 3 5% 6% 56%	2365
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 5% 7% 51%	2400
	21st to end	Night	18% 8% 2 6% 4 3 4 2 5% 5% 43%	2727
November	1st to 10th	Night	10% 7% 2 5% 4 3 3 2 4 6% 53%	2666
	11th to 20th	Night	12% 7% 3 6% 4 3 3 3 4 6% 48%	2730
	21st to end	Night	17% 11% 3 7% 4 3 4 3 4 5% 40%	2825
December	1st to 10th	Night	11% 10% 3 7% 5% 3 4 3 4 6% 45%	4720
	11th to 20th	Night	15% 9% 4 10% 4 4 4 4 5% 6% 36%	5339
	21st to end	Night	24% 18% 5% 10% 5% 4 4 3 4 4 18%	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	56% 4 11% 20% 9% 1	4692
	11th to 20th	Day	55% 4 11% 17% 11% 2	4807
	21st to end	Day	57% 4 10% 20% 8% 1	5812
February	1st to 10th	Day	55% 5% 12% 19% 8% 1	1890
	11th to 20th	Day	51% 5% 10% 20% 12% 2	2040
	21st to end	Day	52% 3 10% 22% 11% 2	1730
March	1st to 10th	Day	46% 3 7% 22% 19% 2	4580
	11th to 20th	Day	34% 5% 11% 30% 19% 1	5038
	21st to end	Day	51% 6% 15% 21% 6% 1	5956
April	1st to 10th	Day	46% 6% 12% 22% 13%	2520
	11th to 20th	Day	46% 5% 9% 24% 14% 2	2494
	21st to end	Day	47% 7% 12% 21% 12% 1	2520
May	1st to 10th	Day	45% 7% 13% 22% 12% 1	7474
	11th to 20th	Day	42% 7% 11% 24% 15% 2	8181
	21st to end	Day	45% 8% 11% 20% 15% 1	9061
June	1st to 10th	Day	32% 9% 13% 26% 16% 3	2940
	11th to 20th	Day	33% 7% 11% 25% 23% 2	2940
	21st to end	Day	35% 9% 14% 21% 17% 3	2940
July	1st to 10th	Day	33% 7% 15% 28% 16% 1	8211
	11th to 20th	Day	34% 8% 15% 25% 17% 1	8205
	21st to end	Day	37% 8% 18% 27% 8% 1	8702
August	1st to 10th	Day	32% 8% 17% 29% 13% 1	5982
	11th to 20th	Day	41% 8% 16% 25% 10%	5522
	21st to end	Day	23% 7% 15% 33% 19% 3	6079
September	1st to 10th	Day	32% 6% 11% 26% 20% 6%	2520
	11th to 20th	Day	32% 5% 9% 25% 24% 5%	2386
	21st to end	Day	32% 6% 9% 27% 24% 2	2200
October	1st to 10th	Day	23% 4 7% 17% 45% 4	3303
	11th to 20th	Day	27% 3 8% 22% 34% 5%	3240
	21st to end	Day	40% 4 7% 26% 21% 2	3388
November	1st to 10th	Day	36% 4 13% 25% 19% 4	1852
	11th to 20th	Day	42% 4 11% 24% 15% 3	1890
	21st to end	Day	50% 5% 10% 23% 11%	1790
December	1st to 10th	Day	37% 4 16% 31% 11%	2690
	11th to 20th	Day	52% 5% 11% 22% 8% 2	3085
	21st to end	Day	72% 3 10% 10% 4	4070
January	1st to 10th	Night	52% 4 14% 22% 7%	8233
	11th to 20th	Night	54% 4 9% 18% 13% 2	8178
	21st to end	Night	55% 3 10% 20% 10% 1	8402
February	1st to 10th	Night	53% 4 11% 19% 11% 2	2730
	11th to 20th	Night	48% 3 11% 23% 14% 2	2475
	21st to end	Night	46% 4 11% 23% 14% 3	2076
March	1st to 10th	Night	48% 4 6% 23% 17% 2	5493
	11th to 20th	Night	35% 5% 8% 29% 19% 4	5184
	21st to end	Night	51% 6% 10% 23% 8% 1	5215
April	1st to 10th	Night	42% 5% 11% 23% 15% 3	2100
	11th to 20th	Night	39% 4 11% 24% 17% 3	2075
	21st to end	Night	46% 5% 10% 21% 15% 3	2100
May	1st to 10th	Night	47% 7% 12% 22% 10% 2	5430
	11th to 20th	Night	37% 7% 13% 24% 16% 3	4710
	21st to end	Night	42% 7% 12% 19% 18% 2	5149
June	1st to 10th	Night	28% 7% 15% 28% 18% 5%	1680
	11th to 20th	Night	31% 7% 11% 23% 24% 5%	1680
	21st to end	Night	31% 7% 15% 24% 19% 4	1680
July	1st to 10th	Night	33% 6% 12% 29% 18% 1	4670
	11th to 20th	Night	28% 10% 14% 27% 19% 1	4662
	21st to end	Night	33% 9% 18% 26% 12% 1	5077
August	1st to 10th	Night	28% 6% 16% 32% 17% 1	4163
	11th to 20th	Night	33% 8% 17% 28% 13% 1	4590
	21st to end	Night	20% 7% 16% 37% 18% 3	5046
September	1st to 10th	Night	28% 5% 10% 27% 23% 7%	2100
	11th to 20th	Night	28% 5% 9% 25% 27% 5%	2060
	21st to end	Night	32% 5% 9% 24% 26% 5%	2200
October	1st to 10th	Night	21% 3 7% 21% 44% 4	3872
	11th to 20th	Night	24% 4 9% 23% 36% 5%	3899
	21st to end	Night	35% 4 10% 23% 24% 4	4400
November	1st to 10th	Night	33% 4 11% 26% 20% 5%	2666
	11th to 20th	Night	38% 4 9% 27% 20% 2	2730
	21st to end	Night	48% 3 10% 23% 15% 1	2825
December	1st to 10th	Night	42% 3 11% 30% 13% 1	4720
	11th to 20th	Night	49% 5% 12% 22% 11% 1	5341
	21st to end	Night	69% 5% 9% 11% 4	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	22% 20% 34% 18% 6%	330
	11th to 20th	Day	25% 19% 40% 14% 2	330
	21st to end	Day	19% 17% 40% 20% 4	363
February	1st to 10th	Day	25% 15% 40% 15% 5%	330
	11th to 20th	Day	25% 18% 35% 18% 4	330
	21st to end	Day	23% 16% 47% 13% 1	273
March	1st to 10th	Day	23% 22% 39% 14% 2	330
	11th to 20th	Day	26% 18% 35% 16% 4	330
	21st to end	Day	28% 17% 35% 16% 4	527
April	1st to 10th	Day	22% 17% 32% 23% 5% 1	540
	11th to 20th	Day	21% 20% 31% 19% 9% 1	532
	21st to end	Day	21% 16% 36% 20% 7% 1	540
May	1st to 10th	Day	20% 13% 34% 24% 8% 2	543
	11th to 20th	Day	17% 13% 28% 26% 13% 3	755
	21st to end	Day	13% 8% 33% 26% 13% 7%	844
June	1st to 10th	Day	10% 7% 24% 31% 22% 6%	780
	11th to 20th	Day	11% 7% 23% 35% 20% 5%	780
	21st to end	Day	9% 6% 29% 34% 18% 4	780
July	1st to 10th	Day	10% 3 14% 32% 27% 13%	771
	11th to 20th	Day	7% 4 20% 34% 25% 10%	768
	21st to end	Day	10% 3 18% 32% 30% 7%	849
August	1st to 10th	Day	8% 3 16% 38% 25% 9%	771
	11th to 20th	Day	8% 5% 20% 28% 26% 13%	559
	21st to end	Day	7% 2 17% 33% 32% 10%	627
September	1st to 10th	Day	12% 4 18% 30% 28% 8%	570
	11th to 20th	Day	9% 2 13% 32% 31% 13%	542
	21st to end	Day	10% 11% 21% 25% 23% 10%	530
October	1st to 10th	Day	12% 8% 25% 32% 18% 5%	360
	11th to 20th	Day	16% 18% 31% 25% 9% 1	330
	21st to end	Day	30% 13% 34% 18% 4	363
November	1st to 10th	Day	12% 18% 35% 22% 9% 4	330
	11th to 20th	Day	22% 17% 34% 17% 8% 2	330
	21st to end	Day	25% 14% 35% 19% 7%	330
December	1st to 10th	Day	14% 23% 38% 17% 5% 3	330
	11th to 20th	Day	21% 19% 37% 18% 4	330
	21st to end	Day	29% 20% 35% 14% 2	363
January	1st to 10th	Night	19% 14% 39% 23% 5%	1050
	11th to 20th	Night	20% 17% 38% 21% 4	1050
	21st to end	Night	21% 15% 36% 25% 3	1155
February	1st to 10th	Night	22% 14% 37% 24% 3	1050
	11th to 20th	Night	21% 15% 35% 26% 2	839
	21st to end	Night	21% 16% 38% 22% 3	692
March	1st to 10th	Night	23% 16% 36% 22% 3	840
	11th to 20th	Night	20% 13% 34% 27% 6%	672
	21st to end	Night	27% 11% 34% 23% 5%	693
April	1st to 10th	Night	18% 16% 37% 25% 4	630
	11th to 20th	Night	17% 13% 35% 26% 8%	623
	21st to end	Night	21% 10% 37% 26% 6%	630
May	1st to 10th	Night	18% 6% 39% 28% 8% 1	630
	11th to 20th	Night	17% 6% 28% 35% 12% 1	621
	21st to end	Night	12% 5% 27% 33% 20% 2	683
June	1st to 10th	Night	10% 4 22% 45% 20%	630
	11th to 20th	Night	10% 4 22% 44% 18% 2	630
	21st to end	Night	9% 3 27% 42% 19% 1	630
July	1st to 10th	Night	10% 2 11% 37% 35% 5%	615
	11th to 20th	Night	5% 2 18% 40% 32% 2	612
	21st to end	Night	7% 1 14% 45% 31% 1	690
August	1st to 10th	Night	8% 3 13% 43% 29% 4	627
	11th to 20th	Night	7% 2 14% 39% 32% 5%	624
	21st to end	Night	5% 1 12% 40% 39% 2	693
September	1st to 10th	Night	11% 3 16% 38% 28% 3	630
	11th to 20th	Night	8% 1 16% 39% 31% 4	639
	21st to end	Night	10% 8% 22% 32% 24% 4	800
October	1st to 10th	Night	11% 4 30% 32% 22% 2	800
	11th to 20th	Night	16% 11% 31% 30% 12% 1	800
	21st to end	Night	23% 13% 34% 24% 6%	880
November	1st to 10th	Night	13% 10% 41% 27% 9%	820
	11th to 20th	Night	18% 14% 38% 24% 5% 1	840
	21st to end	Night	23% 14% 34% 24% 5%	935
December	1st to 10th	Night	21% 12% 39% 23% 5%	1050
	11th to 20th	Night	22% 12% 35% 25% 6%	1050
	21st to end	Night	26% 17% 33% 22% 2	1155

Page generated at 2026-09-11 03:11:53. Version ac07

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