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 2026-07-16.

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	13% 11% 5% 10% 5% 4 4 3 4 6% 33%	137323
	Night	14% 14% 6% 13% 7% 5% 4 3 4 5% 27%	135593
Transparency	Day	52% 5% 11% 21% 11% 1	140809
	Night	60% 4 10% 16% 8% 1	140170
Seeing	Day	19% 14% 29% 25% 11% 2	18117
	Night	22% 13% 27% 26% 10% 1	28163

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	13% 22% 13% 31% 6% 3 2 1 2 2 4	4691
	11th to 20th	Day	9% 18% 11% 30% 12% 10% 3 1 2 1 2	4710
	21st to end	Day	10% 15% 9% 19% 12% 11% 7% 2 3 3 9%	5156
February	1st to 10th	Day	10% 19% 7% 20% 16% 7% 3 2 3 4 11%	1785
	11th to 20th	Day	12% 15% 8% 18% 13% 6% 4 2 3 4 15%	2048
	21st to end	Day	13% 18% 6% 15% 10% 5% 4 2 4 5% 18%	1730
March	1st to 10th	Day	12% 11% 4 13% 7% 4 4 3 5% 5% 32%	4580
	11th to 20th	Day	11% 10% 5% 14% 6% 5% 5% 3 5% 7% 29%	4897
	21st to end	Day	22% 12% 7% 16% 5% 3 3 2 4 4 23%	5864
April	1st to 10th	Day	17% 15% 4 9% 5% 4 4 3 4 6% 29%	2520
	11th to 20th	Day	19% 13% 4 6% 4 3 3 3 4 6% 35%	2576
	21st to end	Day	15% 10% 4 9% 4 4 4 4 5% 7% 35%	2730
May	1st to 10th	Day	11% 8% 3 5% 4 3 4 3 5% 7% 47%	7616
	11th to 20th	Day	13% 9% 3 7% 4 4 4 3 5% 5% 43%	8020
	21st to end	Day	12% 7% 2 6% 4 4 3 3 4 6% 49%	9047
June	1st to 10th	Day	12% 5% 2 6% 4 5% 4 4 6% 7% 45%	2940
	11th to 20th	Day	12% 4 2 6% 4 5% 5% 4 6% 10% 43%	2940
	21st to end	Day	13% 6% 2 5% 4 3 4 3 6% 8% 44%	2940
July	1st to 10th	Day	16% 6% 2 4 3 3 4 3 6% 9% 45%	6500
	11th to 20th	Day	10% 4 2 4 3 3 4 3 5% 8% 54%	6431
	21st to end	Day	9% 5% 2 5% 4 3 4 3 6% 9% 51%	6924
August	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 7% 9% 43%	4436
	11th to 20th	Day	15% 5% 2 4 3 3 3 3 5% 6% 50%	4174
	21st to end	Day	13% 6% 3 6% 4 4 4 3 4 6% 47%	4421
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 6% 7% 43%	2395
	11th to 20th	Day	13% 5% 2 5% 3 3 5% 3 6% 8% 46%	2200
	21st to end	Day	16% 7% 2 7% 4 4 4 4 6% 7% 38%	2200
October	1st to 10th	Day	17% 10% 3 7% 4 4 4 3 4 8% 36%	2200
	11th to 20th	Day	23% 16% 4 9% 6% 4 4 3 4 5% 21%	1882
	21st to end	Day	24% 16% 4 10% 6% 5% 4 3 4 5% 19%	1980
November	1st to 10th	Day	18% 20% 4 7% 4 4 4 3 4 7% 26%	1852
	11th to 20th	Day	14% 26% 7% 11% 6% 4 3 3 5% 4 16%	1890
	21st to end	Day	18% 26% 10% 12% 4 3 3 3 3 4 14%	1801
December	1st to 10th	Day	11% 34% 13% 17% 7% 4 3 1 1 2 6%	2364
	11th to 20th	Day	11% 27% 14% 19% 8% 4 4 2 2 3 5%	2813
	21st to end	Day	21% 23% 12% 16% 6% 4 4 2 2 3 7%	4070
January	1st to 10th	Night	13% 23% 10% 31% 8% 3 2 1 2 2 7%	8232
	11th to 20th	Night	9% 20% 10% 24% 16% 8% 3 2 2 2 4	8280
	21st to end	Night	9% 16% 9% 20% 13% 9% 7% 3 3 3 9%	9058
February	1st to 10th	Night	10% 18% 7% 19% 15% 6% 4 3 3 3 12%	2829
	11th to 20th	Night	11% 16% 6% 18% 10% 6% 5% 3 4 4 18%	2458
	21st to end	Night	14% 18% 6% 15% 7% 4 3 3 4 6% 20%	2076
March	1st to 10th	Night	16% 10% 4 11% 5% 3 3 3 4 6% 34%	5493
	11th to 20th	Night	11% 12% 5% 10% 5% 4 5% 4 5% 8% 32%	5282
	21st to end	Night	20% 13% 5% 11% 5% 4 3 3 4 5% 27%	5336
April	1st to 10th	Night	18% 14% 3 9% 4 4 5% 3 5% 6% 29%	2100
	11th to 20th	Night	21% 10% 4 6% 5% 3 3 3 4 6% 34%	1993
	21st to end	Night	16% 10% 3 7% 4 5% 4 3 5% 6% 36%	1890
May	1st to 10th	Night	13% 7% 2 6% 4 4 5% 3 6% 7% 42%	5237
	11th to 20th	Night	12% 8% 2 7% 5% 4 4 4 6% 7% 40%	4846
	21st to end	Night	15% 6% 2 6% 4 3 3 3 6% 6% 45%	5139
June	1st to 10th	Night	14% 7% 2 5% 5% 4 4 3 5% 7% 44%	1680
	11th to 20th	Night	14% 6% 2 6% 5% 5% 4 4 6% 8% 40%	1680
	21st to end	Night	12% 8% 3 6% 4 4 4 4 5% 8% 44%	1680
July	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 8% 43%	3698
	11th to 20th	Night	9% 5% 2 5% 4 3 4 3 4 7% 54%	3657
	21st to end	Night	8% 5% 2 6% 4 4 4 4 6% 7% 51%	3947
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 5% 3 4 7% 43%	2717
	11th to 20th	Night	15% 5% 2 4 4 3 4 3 5% 6% 49%	2875
	21st to end	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 47%	3475
September	1st to 10th	Night	13% 6% 3 6% 3 4 3 3 5% 7% 48%	2000
	11th to 20th	Night	13% 5% 2 6% 3 4 4 3 4 7% 48%	2184
	21st to end	Night	17% 8% 3 6% 5% 4 4 3 6% 7% 38%	2200
October	1st to 10th	Night	18% 9% 3 7% 5% 4 3 3 4 6% 38%	2200
	11th to 20th	Night	23% 14% 4 8% 5% 4 4 3 4 5% 25%	2513
	21st to end	Night	23% 17% 4 9% 5% 4 3 2 4 5% 23%	2860
November	1st to 10th	Night	16% 18% 4 8% 5% 4 4 3 5% 6% 27%	2666
	11th to 20th	Night	15% 23% 7% 14% 5% 4 4 3 3 4 19%	2730
	21st to end	Night	16% 25% 9% 12% 4 4 4 3 4 4 13%	2814
December	1st to 10th	Night	11% 26% 16% 17% 6% 4 3 2 3 3 8%	5026
	11th to 20th	Night	13% 24% 10% 21% 9% 4 3 2 3 3 8%	5592
	21st to end	Night	22% 21% 10% 15% 6% 4 3 2 3 3 12%	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	92% 2 4 2	4692
	11th to 20th	Day	93% 2 2 2	4710
	21st to end	Day	84% 3 7% 5% 1	5156
February	1st to 10th	Day	80% 3 7% 9% 1	1785
	11th to 20th	Day	73% 6% 9% 10% 3	2058
	21st to end	Day	68% 7% 9% 11% 4 1	1730
March	1st to 10th	Day	53% 5% 15% 16% 10% 1	4580
	11th to 20th	Day	53% 5% 14% 19% 8% 1	4897
	21st to end	Day	65% 5% 9% 14% 7%	5866
April	1st to 10th	Day	55% 5% 10% 20% 10%	2520
	11th to 20th	Day	50% 6% 8% 21% 14% 2	2576
	21st to end	Day	48% 6% 11% 17% 15% 2	2730
May	1st to 10th	Day	37% 4 10% 29% 18% 2	7651
	11th to 20th	Day	43% 4 9% 25% 17% 1	8024
	21st to end	Day	36% 5% 8% 25% 22% 3	9061
June	1st to 10th	Day	36% 6% 12% 26% 16% 2	2940
	11th to 20th	Day	37% 7% 13% 25% 17% 1	2940
	21st to end	Day	37% 6% 16% 26% 14% 1	2940
July	1st to 10th	Day	37% 4 15% 30% 12% 1	6431
	11th to 20th	Day	29% 4 15% 38% 14% 1	6356
	21st to end	Day	31% 4 14% 31% 18% 1	6728
August	1st to 10th	Day	36% 5% 16% 30% 12% 1	4421
	11th to 20th	Day	35% 4 13% 32% 14% 1	4213
	21st to end	Day	39% 4 15% 30% 11% 1	4420
September	1st to 10th	Day	39% 7% 14% 25% 13% 1	2395
	11th to 20th	Day	35% 7% 17% 29% 11% 1	2200
	21st to end	Day	43% 7% 14% 26% 10%	2200
October	1st to 10th	Day	33% 4 10% 34% 18% 1	3590
	11th to 20th	Day	57% 3 11% 20% 9%	3033
	21st to end	Day	62% 4 14% 16% 4	3180
November	1st to 10th	Day	60% 6% 10% 17% 7%	1852
	11th to 20th	Day	72% 5% 10% 10% 3	1890
	21st to end	Day	76% 5% 11% 7% 1	1801
December	1st to 10th	Day	90% 2 3 4 1	2364
	11th to 20th	Day	88% 4 5% 2 1	2809
	21st to end	Day	83% 5% 5% 5% 1	4070
January	1st to 10th	Night	88% 2 6% 3	8233
	11th to 20th	Night	90% 3 4 2	8280
	21st to end	Night	83% 5% 6% 6% 1	9058
February	1st to 10th	Night	78% 4 7% 8% 2	2829
	11th to 20th	Night	70% 6% 8% 13% 3	2459
	21st to end	Night	65% 5% 13% 13% 3	2076
March	1st to 10th	Night	53% 4 17% 19% 7%	5493
	11th to 20th	Night	51% 4 18% 19% 8% 1	5282
	21st to end	Night	59% 5% 11% 17% 7%	5336
April	1st to 10th	Night	55% 6% 9% 19% 10% 1	2100
	11th to 20th	Night	51% 6% 8% 20% 12% 3	1993
	21st to end	Night	48% 5% 11% 20% 13% 3	1890
May	1st to 10th	Night	41% 4 11% 26% 16% 3	5264
	11th to 20th	Night	42% 5% 9% 27% 17% 1	4847
	21st to end	Night	40% 4 11% 23% 17% 6%	5149
June	1st to 10th	Night	39% 6% 11% 27% 15% 2	1680
	11th to 20th	Night	41% 6% 12% 23% 16% 2	1680
	21st to end	Night	38% 7% 12% 26% 15% 2	1680
July	1st to 10th	Night	40% 4 13% 26% 14% 3	3660
	11th to 20th	Night	32% 3 13% 31% 19% 2	3612
	21st to end	Night	32% 5% 14% 28% 19% 2	3832
August	1st to 10th	Night	41% 6% 13% 26% 13% 1	2708
	11th to 20th	Night	35% 4 16% 30% 14% 1	2902
	21st to end	Night	37% 5% 15% 24% 18% 1	3475
September	1st to 10th	Night	36% 5% 16% 23% 19% 1	2000
	11th to 20th	Night	38% 5% 15% 29% 13% 1	2184
	21st to end	Night	45% 5% 15% 24% 10%	2200
October	1st to 10th	Night	42% 3 9% 33% 11% 1	3590
	11th to 20th	Night	54% 3 10% 22% 11%	4088
	21st to end	Night	56% 3 13% 21% 6%	4610
November	1st to 10th	Night	59% 6% 11% 17% 7% 1	2666
	11th to 20th	Night	72% 4 10% 9% 5% 1	2730
	21st to end	Night	76% 5% 10% 8% 1	2814
December	1st to 10th	Night	85% 4 5% 6% 1	5026
	11th to 20th	Night	84% 4 6% 4 1	5594
	21st to end	Night	79% 5% 9% 5% 3	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% 24% 36% 13% 5% 1	330
	11th to 20th	Day	26% 22% 36% 14% 2	330
	21st to end	Day	24% 19% 36% 18% 3	363
February	1st to 10th	Day	21% 30% 31% 14% 4 1	330
	11th to 20th	Day	22% 28% 33% 15% 3	330
	21st to end	Day	25% 26% 38% 9% 1	273
March	1st to 10th	Day	23% 24% 39% 12% 2	330
	11th to 20th	Day	22% 21% 32% 18% 6% 1	451
	21st to end	Day	31% 17% 25% 20% 5% 1	594
April	1st to 10th	Day	25% 20% 30% 19% 4 1	540
	11th to 20th	Day	27% 17% 30% 16% 8% 2	532
	21st to end	Day	19% 16% 31% 23% 9% 2	540
May	1st to 10th	Day	18% 16% 32% 24% 8% 1	543
	11th to 20th	Day	16% 11% 31% 29% 10% 2	701
	21st to end	Day	14% 10% 30% 30% 14% 2	844
June	1st to 10th	Day	14% 8% 33% 29% 14% 2	780
	11th to 20th	Day	15% 9% 32% 31% 10% 2	780
	21st to end	Day	17% 7% 29% 32% 12% 3	780
July	1st to 10th	Day	11% 5% 25% 38% 18% 4	771
	11th to 20th	Day	11% 6% 28% 34% 17% 4	744
	21st to end	Day	8% 4 28% 40% 17% 3	794
August	1st to 10th	Day	9% 4 24% 34% 23% 6%	651
	11th to 20th	Day	14% 5% 21% 34% 18% 8%	519
	21st to end	Day	16% 8% 24% 31% 18% 4	583
September	1st to 10th	Day	22% 7% 25% 24% 17% 5%	530
	11th to 20th	Day	11% 6% 23% 34% 21% 5%	530
	21st to end	Day	19% 11% 22% 28% 15% 4	530
October	1st to 10th	Day	20% 17% 27% 21% 12% 2	530
	11th to 20th	Day	31% 15% 34% 17% 3	374
	21st to end	Day	35% 15% 31% 13% 5%	363
November	1st to 10th	Day	31% 19% 28% 15% 6%	330
	11th to 20th	Day	27% 23% 36% 10% 3	330
	21st to end	Day	27% 25% 33% 12% 2	330
December	1st to 10th	Day	34% 21% 30% 11% 4	226
	11th to 20th	Day	31% 27% 30% 9% 3	248
	21st to end	Day	32% 25% 31% 9% 2 1	363
January	1st to 10th	Night	23% 21% 34% 17% 4	1050
	11th to 20th	Night	24% 24% 30% 17% 5%	1050
	21st to end	Night	23% 16% 34% 21% 5% 1	1155
February	1st to 10th	Night	20% 20% 33% 20% 6% 1	969
	11th to 20th	Night	21% 21% 30% 24% 4	823
	21st to end	Night	25% 20% 30% 22% 3	692
March	1st to 10th	Night	19% 15% 33% 25% 7% 1	840
	11th to 20th	Night	19% 17% 34% 23% 7%	840
	21st to end	Night	23% 13% 29% 28% 7% 1	814
April	1st to 10th	Night	25% 12% 31% 25% 6% 1	630
	11th to 20th	Night	25% 11% 29% 25% 9% 1	623
	21st to end	Night	20% 9% 28% 32% 10% 1	630
May	1st to 10th	Night	18% 8% 28% 34% 11%	630
	11th to 20th	Night	19% 7% 27% 33% 12% 2	621
	21st to end	Night	16% 5% 27% 33% 18% 1	683
June	1st to 10th	Night	16% 5% 26% 38% 14% 1	630
	11th to 20th	Night	16% 7% 20% 39% 16% 2	630
	21st to end	Night	15% 4 24% 37% 20% 1	630
July	1st to 10th	Night	12% 3 17% 41% 23% 3	615
	11th to 20th	Night	11% 3 21% 35% 28% 3	597
	21st to end	Night	10% 3 23% 38% 24% 2	657
August	1st to 10th	Night	9% 3 21% 38% 27% 2	597
	11th to 20th	Night	11% 4 21% 32% 27% 5%	594
	21st to end	Night	15% 4 20% 40% 19% 2	660
September	1st to 10th	Night	17% 5% 22% 31% 21% 5%	600
	11th to 20th	Night	16% 5% 20% 32% 22% 5%	784
	21st to end	Night	21% 8% 20% 29% 18% 4	800
October	1st to 10th	Night	25% 10% 23% 26% 14% 2	800
	11th to 20th	Night	32% 14% 24% 24% 5%	800
	21st to end	Night	34% 13% 24% 22% 6% 1	880
November	1st to 10th	Night	29% 15% 28% 24% 4	820
	11th to 20th	Night	30% 20% 30% 16% 4	840
	21st to end	Night	31% 19% 30% 18% 3	924
December	1st to 10th	Night	29% 24% 30% 15% 3	1050
	11th to 20th	Night	27% 22% 32% 14% 4 1	1050
	21st to end	Night	32% 19% 32% 15% 1	1155

Page generated at 2026-07-13 03:14:51. Version ac07

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