Lanphier Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lanphier Observatory clear sky chart from 2005-11-05 to 2024-10-14.

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	14% 11% 5% 9% 5% 4 4 3 5% 6% 34%	100863
	Night	15% 14% 5% 11% 6% 4 4 3 4 5% 29%	97725
Transparency	Day	51% 6% 11% 20% 11% 1	100653
	Night	58% 5% 11% 16% 8% 1	97611
Seeing	Day	18% 13% 29% 26% 12% 3	15748
	Night	21% 13% 27% 27% 11% 1	25742

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% 26% 16% 21% 7% 5% 2 2 2 2 5%	2527
	11th to 20th	Day	13% 19% 10% 25% 14% 9% 3 1 2 2 3	2530
	21st to end	Day	18% 23% 12% 15% 8% 5% 4 2 3 3 7%	2783
February	1st to 10th	Day	10% 20% 7% 18% 16% 7% 3 1 3 4 12%	1614
	11th to 20th	Day	12% 15% 8% 18% 13% 6% 5% 3 3 4 15%	1848
	21st to end	Day	13% 17% 6% 14% 10% 5% 4 3 5% 5% 19%	1570
March	1st to 10th	Day	12% 13% 5% 10% 6% 4 4 3 5% 6% 32%	3120
	11th to 20th	Day	9% 11% 6% 17% 6% 4 4 3 5% 6% 30%	3347
	21st to end	Day	17% 13% 7% 17% 5% 4 3 2 4 4 23%	4005
April	1st to 10th	Day	17% 15% 4 9% 5% 4 4 3 5% 6% 30%	2280
	11th to 20th	Day	19% 13% 4 6% 4 3 3 3 4 6% 35%	2328
	21st to end	Day	16% 10% 3 9% 4 4 4 3 5% 7% 35%	2470
May	1st to 10th	Day	13% 8% 3 6% 4 3 4 3 5% 6% 44%	4082
	11th to 20th	Day	10% 7% 2 6% 4 3 4 3 5% 6% 49%	4293
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 5% 7% 44%	4824
June	1st to 10th	Day	12% 5% 2 6% 4 5% 4 4 5% 7% 45%	2660
	11th to 20th	Day	11% 4 2 6% 4 5% 5% 4 6% 10% 44%	2660
	21st to end	Day	13% 6% 2 5% 4 4 4 3 7% 8% 44%	2660
July	1st to 10th	Day	18% 7% 2 5% 3 3 4 3 6% 8% 41%	4440
	11th to 20th	Day	8% 4 1 4 3 3 4 3 6% 8% 56%	4440
	21st to end	Day	9% 4 2 5% 4 4 3 4 6% 8% 52%	4813
August	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 7% 9% 43%	4300
	11th to 20th	Day	15% 5% 2 4 3 3 3 3 5% 6% 51%	4044
	21st to end	Day	13% 6% 3 6% 4 4 4 3 4 5% 47%	4286
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 6% 7% 44%	2275
	11th to 20th	Day	14% 5% 2 5% 3 3 5% 3 6% 8% 46%	2090
	21st to end	Day	16% 7% 2 7% 4 4 4 4 7% 8% 38%	2090
October	1st to 10th	Day	18% 10% 3 7% 4 4 4 3 4 8% 36%	2090
	11th to 20th	Day	23% 17% 4 9% 6% 4 4 3 4 6% 19%	1725
	21st to end	Day	26% 17% 4 9% 5% 4 4 3 4 5% 17%	1782
November	1st to 10th	Day	18% 20% 4 7% 4 4 4 3 5% 7% 27%	1672
	11th to 20th	Day	14% 27% 8% 11% 5% 4 3 3 5% 4 15%	1710
	21st to end	Day	18% 27% 9% 12% 4 3 3 3 3 4 14%	1630
December	1st to 10th	Day	15% 28% 13% 17% 6% 4 3 1 2 3 8%	1344
	11th to 20th	Day	14% 25% 10% 16% 8% 4 5% 3 4 4 8%	1748
	21st to end	Day	20% 22% 12% 14% 6% 5% 4 2 3 3 8%	2783
January	1st to 10th	Night	13% 27% 10% 22% 7% 3 2 2 2 2 10%	4428
	11th to 20th	Night	12% 18% 9% 22% 16% 8% 3 2 2 2 6%	4440
	21st to end	Night	15% 23% 11% 17% 8% 6% 4 2 3 3 8%	4884
February	1st to 10th	Night	11% 17% 7% 19% 14% 7% 4 3 3 3 13%	2561
	11th to 20th	Night	12% 16% 6% 18% 10% 6% 4 3 4 4 17%	2218
	21st to end	Night	14% 18% 6% 15% 7% 4 3 3 4 6% 20%	1884
March	1st to 10th	Night	16% 11% 5% 7% 4 3 3 3 4 6% 38%	3733
	11th to 20th	Night	8% 15% 6% 10% 5% 4 4 3 5% 7% 34%	3612
	21st to end	Night	15% 13% 6% 12% 5% 5% 4 4 4 5% 26%	3640
April	1st to 10th	Night	18% 14% 3 8% 4 4 5% 3 5% 6% 30%	1900
	11th to 20th	Night	20% 10% 4 6% 4 4 4 4 4 6% 34%	1801
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 6% 36%	1710
May	1st to 10th	Night	16% 8% 2 6% 4 4 5% 3 5% 6% 41%	2813
	11th to 20th	Night	13% 8% 2 7% 4 4 5% 4 6% 7% 41%	2606
	21st to end	Night	18% 6% 2 5% 3 4 3 4 7% 7% 41%	2743
June	1st to 10th	Night	14% 7% 2 6% 5% 4 5% 3 5% 7% 43%	1520
	11th to 20th	Night	13% 6% 2 6% 5% 5% 4 5% 6% 9% 42%	1520
	21st to end	Night	11% 8% 3 6% 4 4 4 4 5% 8% 45%	1520
July	1st to 10th	Night	14% 7% 3 6% 4 4 5% 4 6% 8% 41%	2530
	11th to 20th	Night	7% 5% 2 5% 4 3 4 3 5% 8% 54%	2530
	21st to end	Night	9% 5% 2 7% 4 4 4 4 5% 7% 49%	2750
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 5% 3 4 7% 43%	2633
	11th to 20th	Night	14% 5% 2 4 4 3 3 3 6% 6% 49%	2785
	21st to end	Night	12% 6% 2 6% 5% 4 4 3 5% 7% 47%	3368
September	1st to 10th	Night	13% 6% 3 6% 3 3 3 3 4 7% 49%	1900
	11th to 20th	Night	14% 5% 2 6% 3 4 4 3 5% 7% 48%	2075
	21st to end	Night	17% 7% 3 6% 5% 4 4 3 6% 7% 38%	2090
October	1st to 10th	Night	18% 10% 3 7% 5% 4 3 3 4 5% 37%	2090
	11th to 20th	Night	24% 14% 4 8% 5% 4 4 3 4 6% 24%	2303
	21st to end	Night	24% 18% 5% 9% 6% 4 3 3 3 4 21%	2574
November	1st to 10th	Night	16% 18% 4 7% 5% 5% 4 3 5% 6% 27%	2406
	11th to 20th	Night	14% 24% 7% 14% 5% 4 4 3 3 4 18%	2470
	21st to end	Night	16% 24% 8% 13% 4 4 4 3 4 4 14%	2546
December	1st to 10th	Night	14% 28% 12% 17% 6% 4 3 2 2 3 10%	2831
	11th to 20th	Night	15% 22% 9% 21% 7% 4 3 2 3 4 10%	3427
	21st to end	Night	23% 23% 10% 12% 6% 4 3 2 3 3 11%	4884

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	90% 3 4 2 1	2528
	11th to 20th	Day	92% 3 3 2	2530
	21st to end	Day	85% 4 8% 2 1	2783
February	1st to 10th	Day	80% 3 7% 9% 1	1614
	11th to 20th	Day	73% 6% 9% 9% 3	1858
	21st to end	Day	67% 8% 9% 11% 4 1	1570
March	1st to 10th	Day	51% 7% 12% 19% 10%	3120
	11th to 20th	Day	53% 7% 13% 19% 6% 1	3347
	21st to end	Day	63% 7% 9% 15% 6% 1	4005
April	1st to 10th	Day	55% 6% 10% 19% 10%	2280
	11th to 20th	Day	50% 6% 8% 20% 15% 2	2328
	21st to end	Day	47% 7% 11% 17% 16% 2	2470
May	1st to 10th	Day	39% 7% 10% 25% 18% 2	4120
	11th to 20th	Day	35% 6% 11% 27% 18% 2	4297
	21st to end	Day	36% 9% 11% 23% 19% 2	4837
June	1st to 10th	Day	37% 7% 12% 27% 15% 2	2660
	11th to 20th	Day	35% 7% 13% 24% 19% 1	2660
	21st to end	Day	37% 7% 16% 25% 15% 1	2660
July	1st to 10th	Day	42% 5% 15% 25% 12% 2	4371
	11th to 20th	Day	26% 5% 15% 38% 14% 2	4365
	21st to end	Day	30% 5% 13% 30% 20% 1	4662
August	1st to 10th	Day	36% 5% 16% 30% 12% 1	4285
	11th to 20th	Day	35% 4 13% 33% 14% 1	4083
	21st to end	Day	39% 4 15% 29% 12% 1	4285
September	1st to 10th	Day	39% 8% 13% 26% 14% 1	2275
	11th to 20th	Day	35% 7% 18% 29% 11% 1	2090
	21st to end	Day	43% 7% 15% 26% 9%	2090
October	1st to 10th	Day	47% 6% 12% 25% 9%	2090
	11th to 20th	Day	67% 5% 11% 14% 3	1725
	21st to end	Day	70% 5% 11% 10% 3	1782
November	1st to 10th	Day	59% 6% 10% 17% 7%	1672
	11th to 20th	Day	73% 5% 10% 9% 3	1710
	21st to end	Day	75% 5% 12% 7% 1	1630
December	1st to 10th	Day	85% 3 5% 6% 1	1344
	11th to 20th	Day	82% 6% 8% 3 1	1744
	21st to end	Day	83% 5% 6% 4 1	2783
January	1st to 10th	Night	84% 3 7% 5% 1	4428
	11th to 20th	Night	88% 3 5% 3	4440
	21st to end	Night	84% 6% 8% 3 1	4884
February	1st to 10th	Night	78% 5% 7% 8% 2	2561
	11th to 20th	Night	71% 6% 8% 12% 3	2219
	21st to end	Night	65% 6% 13% 13% 4	1884
March	1st to 10th	Night	48% 5% 16% 22% 8%	3733
	11th to 20th	Night	50% 6% 12% 23% 8% 1	3612
	21st to end	Night	59% 6% 10% 17% 7% 1	3640
April	1st to 10th	Night	55% 6% 10% 19% 10% 1	1900
	11th to 20th	Night	50% 6% 9% 20% 13% 3	1801
	21st to end	Night	48% 6% 10% 20% 13% 3	1710
May	1st to 10th	Night	43% 6% 12% 19% 17% 3	2840
	11th to 20th	Night	41% 6% 10% 27% 15% 1	2607
	21st to end	Night	41% 6% 13% 19% 15% 5%	2751
June	1st to 10th	Night	40% 6% 11% 28% 13% 2	1520
	11th to 20th	Night	39% 6% 12% 23% 17% 3	1520
	21st to end	Night	37% 7% 12% 26% 15% 2	1520
July	1st to 10th	Night	42% 4 14% 23% 13% 4	2490
	11th to 20th	Night	29% 4 15% 31% 18% 2	2482
	21st to end	Night	35% 6% 11% 25% 20% 2	2662
August	1st to 10th	Night	42% 6% 13% 26% 13% 1	2624
	11th to 20th	Night	35% 4 16% 30% 15% 1	2812
	21st to end	Night	38% 5% 15% 23% 18% 1	3368
September	1st to 10th	Night	36% 6% 15% 23% 20% 1	1900
	11th to 20th	Night	38% 5% 15% 28% 13% 1	2075
	21st to end	Night	45% 6% 15% 25% 9%	2090
October	1st to 10th	Night	50% 5% 10% 24% 12% 1	2090
	11th to 20th	Night	62% 5% 11% 16% 5%	2308
	21st to end	Night	68% 5% 10% 13% 4	2574
November	1st to 10th	Night	59% 6% 11% 17% 7% 1	2406
	11th to 20th	Night	73% 4 10% 9% 4	2470
	21st to end	Night	74% 6% 10% 8% 1	2546
December	1st to 10th	Night	83% 4 5% 7% 1	2831
	11th to 20th	Night	81% 6% 8% 4 2	3429
	21st to end	Night	80% 5% 10% 3 1	4884

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% 23% 36% 14% 6% 1	270
	11th to 20th	Day	24% 19% 38% 16% 2	270
	21st to end	Day	23% 15% 36% 22% 3	297
February	1st to 10th	Day	18% 28% 35% 13% 5% 1	270
	11th to 20th	Day	20% 28% 33% 16% 3	270
	21st to end	Day	20% 27% 41% 10% 1	225
March	1st to 10th	Day	18% 24% 40% 15% 3	270
	11th to 20th	Day	19% 20% 33% 20% 8% 1	379
	21st to end	Day	28% 16% 26% 23% 6% 1	506
April	1st to 10th	Day	23% 18% 31% 21% 5% 1	460
	11th to 20th	Day	26% 18% 29% 17% 8% 2	452
	21st to end	Day	18% 17% 30% 24% 8% 2	460
May	1st to 10th	Day	19% 14% 31% 25% 8% 2	463
	11th to 20th	Day	14% 8% 33% 32% 10% 2	608
	21st to end	Day	13% 9% 27% 33% 16% 2	734
June	1st to 10th	Day	14% 8% 31% 30% 15% 3	680
	11th to 20th	Day	14% 8% 30% 34% 12% 3	680
	21st to end	Day	16% 7% 26% 35% 13% 3	680
July	1st to 10th	Day	10% 4 23% 38% 20% 5%	671
	11th to 20th	Day	11% 6% 25% 35% 18% 5%	668
	21st to end	Day	8% 3 26% 41% 18% 4	739
August	1st to 10th	Day	10% 4 23% 34% 23% 5%	605
	11th to 20th	Day	14% 5% 20% 34% 19% 9%	479
	21st to end	Day	17% 7% 24% 30% 19% 3	539
September	1st to 10th	Day	22% 7% 25% 24% 17% 5%	490
	11th to 20th	Day	11% 7% 24% 33% 20% 4	490
	21st to end	Day	19% 11% 23% 27% 16% 4	490
October	1st to 10th	Day	21% 17% 28% 19% 13% 2	490
	11th to 20th	Day	32% 16% 31% 17% 3	321
	21st to end	Day	37% 15% 31% 12% 5%	297
November	1st to 10th	Day	27% 19% 28% 19% 8%	270
	11th to 20th	Day	21% 26% 39% 9% 4	270
	21st to end	Day	24% 27% 33% 14% 2	270
December	1st to 10th	Day	31% 22% 31% 11% 5%	186
	11th to 20th	Day	26% 28% 33% 9% 3	202
	21st to end	Day	28% 26% 33% 9% 2 1	297
January	1st to 10th	Night	22% 21% 33% 19% 5%	950
	11th to 20th	Night	24% 23% 29% 19% 5%	950
	21st to end	Night	22% 15% 34% 23% 5% 1	1045
February	1st to 10th	Night	19% 20% 32% 21% 6% 1	877
	11th to 20th	Night	20% 20% 31% 24% 5%	743
	21st to end	Night	24% 20% 30% 23% 3	628
March	1st to 10th	Night	18% 14% 33% 25% 8% 1	760
	11th to 20th	Night	17% 16% 35% 25% 7% 1	760
	21st to end	Night	21% 12% 29% 29% 7% 1	736
April	1st to 10th	Night	22% 11% 32% 26% 6% 1	570
	11th to 20th	Night	24% 11% 30% 26% 8% 1	563
	21st to end	Night	20% 8% 28% 32% 11% 1	570
May	1st to 10th	Night	19% 7% 28% 34% 11% 1	570
	11th to 20th	Night	17% 7% 27% 35% 12% 2	561
	21st to end	Night	15% 4 26% 34% 20% 2	617
June	1st to 10th	Night	16% 5% 24% 39% 15% 1	570
	11th to 20th	Night	14% 6% 20% 40% 17% 2	570
	21st to end	Night	14% 4 23% 37% 21% 1	570
July	1st to 10th	Night	11% 3 17% 41% 24% 3	555
	11th to 20th	Night	11% 3 20% 35% 28% 3	552
	21st to end	Night	10% 3 21% 38% 25% 2	624
August	1st to 10th	Night	9% 3 21% 37% 28% 2	567
	11th to 20th	Night	11% 4 20% 33% 28% 5%	564
	21st to end	Night	15% 4 20% 41% 19% 2	627
September	1st to 10th	Night	17% 5% 22% 32% 21% 4	570
	11th to 20th	Night	17% 5% 21% 32% 21% 5%	745
	21st to end	Night	22% 8% 20% 28% 18% 4	760
October	1st to 10th	Night	26% 11% 22% 25% 14% 2	760
	11th to 20th	Night	32% 14% 24% 24% 6%	735
	21st to end	Night	35% 13% 23% 22% 6% 1	792
November	1st to 10th	Night	27% 15% 28% 24% 5% 1	740
	11th to 20th	Night	29% 20% 30% 17% 4	760
	21st to end	Night	29% 19% 29% 19% 3	836
December	1st to 10th	Night	29% 23% 29% 16% 3	950
	11th to 20th	Night	26% 21% 33% 15% 4 1	950
	21st to end	Night	31% 19% 33% 15% 1	1045

Page generated at 2024-10-11 10:49:59. Version ac07

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