Twin Lakes Preserve Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Lakes Preserve Observatory clear sky chart from 2005-11-06 to 2024-11-06.

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	16% 8% 3 7% 5% 4 5% 4 6% 7% 36%	101420
	Night	17% 8% 3 6% 4 4 4 4 5% 7% 39%	97659
Transparency	Day	46% 3 11% 23% 14% 2	104927
	Night	44% 3 12% 24% 15% 2	102228
Seeing	Day	24% 17% 28% 19% 9% 3	14889
	Night	22% 15% 28% 24% 9% 1	24059

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	13% 10% 4 7% 5% 4 4 4 5% 6% 38%	2517
	11th to 20th	Day	13% 12% 5% 11% 6% 5% 5% 4 5% 5% 30%	2520
	21st to end	Day	19% 12% 5% 8% 5% 5% 4 3 5% 6% 29%	3063
February	1st to 10th	Day	16% 10% 2 8% 7% 5% 4 5% 6% 6% 32%	1710
	11th to 20th	Day	13% 10% 3 7% 6% 4 5% 4 5% 7% 36%	1792
	21st to end	Day	19% 10% 2 7% 6% 4 5% 3 5% 6% 32%	1570
March	1st to 10th	Day	23% 10% 3 8% 5% 3 3 3 4 4 32%	3116
	11th to 20th	Day	9% 9% 4 8% 5% 4 5% 5% 7% 7% 37%	3434
	21st to end	Day	20% 10% 2 5% 4 3 3 3 4 6% 39%	4070
April	1st to 10th	Day	16% 11% 3 6% 5% 4 5% 4 5% 6% 36%	2280
	11th to 20th	Day	17% 9% 3 6% 4 4 4 3 5% 6% 39%	2254
	21st to end	Day	18% 6% 2 7% 5% 6% 4 4 5% 6% 37%	2280
May	1st to 10th	Day	27% 8% 2 6% 4 4 4 3 4 7% 31%	4214
	11th to 20th	Day	22% 9% 3 7% 5% 5% 5% 4 5% 6% 29%	4398
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 7% 10% 41%	4837
June	1st to 10th	Day	15% 6% 2 8% 6% 5% 5% 4 6% 10% 34%	2660
	11th to 20th	Day	15% 8% 2 6% 5% 5% 5% 5% 6% 9% 34%	2660
	21st to end	Day	13% 7% 2 7% 6% 4 5% 5% 6% 10% 36%	2660
July	1st to 10th	Day	9% 5% 3 8% 6% 6% 6% 4 8% 10% 35%	4440
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 8% 10% 38%	4440
	21st to end	Day	14% 8% 2 8% 5% 5% 5% 5% 7% 8% 33%	4814
August	1st to 10th	Day	21% 5% 2 8% 5% 5% 6% 5% 6% 7% 30%	4178
	11th to 20th	Day	13% 5% 2 7% 4 5% 5% 5% 6% 9% 38%	3762
	21st to end	Day	16% 5% 2 5% 3 3 4 4 6% 10% 43%	4180
September	1st to 10th	Day	15% 6% 2 6% 5% 4 5% 3 5% 8% 40%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 6% 8% 49%	2237
	21st to end	Day	18% 6% 3 7% 5% 4 4 4 5% 7% 38%	2090
October	1st to 10th	Day	19% 7% 2 5% 4 4 4 3 5% 7% 39%	1918
	11th to 20th	Day	14% 8% 2 6% 5% 4 5% 4 6% 7% 41%	1900
	21st to end	Day	21% 7% 2 6% 4 4 5% 4 5% 6% 35%	1972
November	1st to 10th	Day	13% 7% 2 5% 4 4 3 2 4 7% 48%	1717
	11th to 20th	Day	17% 8% 2 6% 4 3 4 4 5% 7% 39%	1710
	21st to end	Day	17% 7% 3 6% 5% 5% 5% 3 5% 6% 37%	1549
December	1st to 10th	Day	17% 10% 4 8% 6% 5% 4 4 6% 6% 31%	1520
	11th to 20th	Day	20% 9% 3 8% 5% 4 4 3 5% 6% 34%	1906
	21st to end	Day	18% 14% 5% 11% 6% 5% 5% 3 5% 5% 23%	2772
January	1st to 10th	Night	14% 7% 3 7% 5% 4 4 4 5% 7% 39%	4429
	11th to 20th	Night	13% 10% 4 10% 6% 5% 4 3 5% 6% 34%	4440
	21st to end	Night	21% 12% 3 6% 6% 4 4 4 5% 6% 29%	4592
February	1st to 10th	Night	15% 9% 3 6% 5% 4 4 4 6% 7% 37%	2470
	11th to 20th	Night	14% 7% 2 8% 6% 4 5% 5% 7% 7% 36%	2273
	21st to end	Night	18% 8% 3 6% 4 5% 4 4 5% 6% 37%	1884
March	1st to 10th	Night	22% 11% 3 6% 4 3 3 3 5% 5% 34%	3724
	11th to 20th	Night	11% 8% 4 7% 5% 4 4 4 7% 7% 40%	3522
	21st to end	Night	15% 10% 3 7% 4 4 3 3 4 6% 40%	3562
April	1st to 10th	Night	16% 9% 3 8% 6% 4 4 3 6% 6% 34%	1900
	11th to 20th	Night	18% 7% 2 6% 4 4 5% 4 4 7% 38%	1875
	21st to end	Night	20% 6% 3 6% 5% 4 4 3 5% 6% 40%	1900
May	1st to 10th	Night	28% 8% 3 6% 4 3 4 3 5% 6% 31%	2753
	11th to 20th	Night	23% 11% 3 7% 4 4 3 3 5% 6% 32%	2495
	21st to end	Night	13% 7% 2 6% 5% 4 5% 4 7% 8% 40%	2738
June	1st to 10th	Night	16% 7% 2 4 4 5% 4 4 5% 8% 41%	1520
	11th to 20th	Night	13% 6% 2 5% 4 5% 4 4 5% 10% 42%	1520
	21st to end	Night	11% 4 2 5% 3 4 5% 5% 7% 9% 45%	1520
July	1st to 10th	Night	10% 6% 2 7% 4 5% 6% 4 6% 9% 41%	2520
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 7% 9% 41%	2520
	21st to end	Night	16% 7% 2 5% 4 4 4 4 6% 8% 40%	2739
August	1st to 10th	Night	21% 5% 2 6% 4 4 4 4 7% 8% 34%	2748
	11th to 20th	Night	15% 6% 2 7% 5% 4 4 3 5% 6% 43%	3033
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 7% 50%	3476
September	1st to 10th	Night	15% 6% 2 5% 3 3 4 3 6% 7% 46%	1900
	11th to 20th	Night	14% 4 2 6% 3 3 3 2 5% 6% 53%	1943
	21st to end	Night	17% 6% 2 5% 4 4 4 4 5% 6% 43%	2090
October	1st to 10th	Night	21% 6% 2 5% 3 4 3 3 4 6% 42%	2258
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 5% 6% 47%	2280
	21st to end	Night	21% 7% 2 5% 3 3 3 3 5% 8% 40%	2624
November	1st to 10th	Night	12% 7% 2 5% 3 4 4 4 5% 6% 48%	2483
	11th to 20th	Night	18% 7% 2 5% 4 3 4 3 5% 6% 43%	2470
	21st to end	Night	14% 7% 2 6% 5% 4 4 3 6% 7% 41%	2626
December	1st to 10th	Night	18% 9% 3 7% 5% 4 4 4 7% 7% 33%	2660
	11th to 20th	Night	17% 9% 2 7% 4 5% 5% 4 5% 6% 35%	3288
	21st to end	Night	21% 11% 4 7% 5% 4 4 3 5% 7% 29%	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	46% 2 9% 32% 8% 3	2518
	11th to 20th	Day	56% 2 10% 20% 10% 2	2520
	21st to end	Day	55% 2 10% 21% 10% 1	3063
February	1st to 10th	Day	51% 3 12% 20% 13% 1	1710
	11th to 20th	Day	47% 3 8% 23% 17% 2	1801
	21st to end	Day	51% 2 8% 23% 13% 3	1570
March	1st to 10th	Day	56% 1 8% 23% 10% 2	3119
	11th to 20th	Day	44% 2 10% 30% 11% 2	3434
	21st to end	Day	48% 2 7% 15% 24% 5%	4070
April	1st to 10th	Day	49% 3 8% 21% 15% 4	2280
	11th to 20th	Day	46% 2 10% 21% 17% 3	2254
	21st to end	Day	47% 3 8% 22% 15% 4	2280
May	1st to 10th	Day	55% 2 11% 18% 12% 2	4228
	11th to 20th	Day	57% 2 10% 20% 9% 1	4402
	21st to end	Day	39% 3 11% 27% 17% 3	4837
June	1st to 10th	Day	46% 5% 11% 23% 15% 1	2660
	11th to 20th	Day	45% 5% 12% 25% 11% 2	2660
	21st to end	Day	43% 4 12% 26% 14%	2660
July	1st to 10th	Day	43% 7% 12% 23% 14% 1	4370
	11th to 20th	Day	39% 6% 17% 24% 13% 1	4365
	21st to end	Day	49% 5% 11% 19% 15% 2	4661
August	1st to 10th	Day	51% 5% 13% 20% 10%	4164
	11th to 20th	Day	41% 5% 14% 28% 11% 1	3799
	21st to end	Day	36% 4 11% 33% 15% 2	4180
September	1st to 10th	Day	41% 5% 11% 24% 18% 2	2280
	11th to 20th	Day	36% 2 9% 25% 25% 3	2237
	21st to end	Day	46% 3 9% 20% 20% 2	2090
October	1st to 10th	Day	41% 4 7% 20% 23% 4	3178
	11th to 20th	Day	33% 3 8% 29% 23% 3	3140
	21st to end	Day	31% 3 16% 27% 21% 3	3223
November	1st to 10th	Day	37% 3 12% 26% 19% 3	1717
	11th to 20th	Day	42% 2 10% 25% 18% 3	1710
	21st to end	Day	44% 5% 13% 27% 10% 2	1549
December	1st to 10th	Day	52% 3 15% 17% 12% 2	1520
	11th to 20th	Day	49% 3 15% 22% 9% 1	1906
	21st to end	Day	62% 3 9% 18% 8%	2772
January	1st to 10th	Night	45% 2 10% 30% 10% 3	4429
	11th to 20th	Night	52% 2 10% 23% 11% 2	4440
	21st to end	Night	55% 2 9% 23% 10% 1	4592
February	1st to 10th	Night	46% 3 14% 24% 12% 1	2470
	11th to 20th	Night	45% 3 9% 22% 17% 4	2275
	21st to end	Night	47% 2 7% 25% 15% 3	1884
March	1st to 10th	Night	53% 1 9% 23% 12% 2	3734
	11th to 20th	Night	41% 2 14% 27% 15% 2	3523
	21st to end	Night	47% 2 6% 18% 21% 5%	3562
April	1st to 10th	Night	50% 3 9% 20% 15% 3	1900
	11th to 20th	Night	47% 3 10% 20% 19% 1	1875
	21st to end	Night	45% 3 9% 23% 17% 4	1900
May	1st to 10th	Night	55% 2 9% 22% 10% 1	2759
	11th to 20th	Night	55% 2 14% 18% 10% 1	2496
	21st to end	Night	41% 4 14% 25% 14% 2	2739
June	1st to 10th	Night	42% 4 11% 25% 19% 1	1520
	11th to 20th	Night	39% 4 16% 28% 11% 1	1520
	21st to end	Night	35% 4 16% 30% 14% 1	1520
July	1st to 10th	Night	39% 7% 16% 20% 16% 2	2480
	11th to 20th	Night	39% 7% 14% 26% 13% 1	2472
	21st to end	Night	43% 6% 14% 18% 18% 1	2651
August	1st to 10th	Night	49% 6% 16% 20% 9% 1	2738
	11th to 20th	Night	43% 4 14% 28% 10%	3062
	21st to end	Night	33% 4 11% 34% 17% 1	3476
September	1st to 10th	Night	38% 4 12% 27% 19% 1	1900
	11th to 20th	Night	34% 3 9% 26% 25% 2	1943
	21st to end	Night	42% 3 8% 24% 22% 1	2090
October	1st to 10th	Night	42% 4 10% 24% 19% 1	3765
	11th to 20th	Night	31% 2 10% 28% 26% 3	3779
	21st to end	Night	32% 3 15% 30% 18% 1	4323
November	1st to 10th	Night	36% 3 12% 24% 21% 2	2483
	11th to 20th	Night	43% 2 10% 23% 19% 3	2470
	21st to end	Night	40% 2 14% 30% 12% 1	2626
December	1st to 10th	Night	49% 3 12% 24% 12% 1	2660
	11th to 20th	Night	50% 3 12% 19% 14% 2	3288
	21st to end	Night	56% 2 11% 22% 8%	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	34% 23% 28% 13% 2 1	180
	11th to 20th	Day	42% 22% 27% 8% 1	180
	21st to end	Day	27% 29% 31% 7% 4 1	281
February	1st to 10th	Day	32% 29% 31% 7% 1	270
	11th to 20th	Day	36% 27% 29% 8% 1	400
	21st to end	Day	33% 23% 30% 12% 2	382
March	1st to 10th	Day	29% 23% 30% 15% 3	460
	11th to 20th	Day	30% 27% 27% 12% 2 1	460
	21st to end	Day	31% 25% 28% 10% 4 2	506
April	1st to 10th	Day	31% 26% 25% 13% 5%	460
	11th to 20th	Day	30% 22% 25% 13% 8% 2	452
	21st to end	Day	30% 20% 31% 13% 4 2	460
May	1st to 10th	Day	35% 18% 24% 13% 8% 2	463
	11th to 20th	Day	22% 19% 29% 18% 9% 2	487
	21st to end	Day	19% 12% 28% 25% 13% 3	529
June	1st to 10th	Day	17% 16% 30% 24% 10% 2	490
	11th to 20th	Day	21% 13% 24% 26% 14% 2	490
	21st to end	Day	17% 13% 32% 26% 10% 2	490
July	1st to 10th	Day	13% 7% 32% 27% 15% 6%	485
	11th to 20th	Day	13% 6% 28% 30% 20% 3	484
	21st to end	Day	14% 11% 32% 27% 11% 4	532
August	1st to 10th	Day	14% 9% 26% 29% 17% 6%	486
	11th to 20th	Day	16% 7% 26% 26% 18% 6%	479
	21st to end	Day	13% 11% 29% 24% 15% 8%	539
September	1st to 10th	Day	22% 10% 24% 21% 15% 8%	490
	11th to 20th	Day	14% 9% 25% 24% 15% 12%	490
	21st to end	Day	22% 11% 28% 22% 12% 5%	490
October	1st to 10th	Day	27% 11% 23% 20% 16% 4	490
	11th to 20th	Day	21% 17% 29% 22% 9% 2	490
	21st to end	Day	29% 15% 29% 19% 8%	476
November	1st to 10th	Day	21% 17% 26% 25% 10% 2	381
	11th to 20th	Day	28% 21% 27% 19% 4 1	370
	21st to end	Day	27% 22% 32% 16% 4	209
December	1st to 10th	Day	33% 24% 27% 11% 5% 1	180
	11th to 20th	Day	38% 22% 29% 9% 2	180
	21st to end	Day	31% 23% 27% 15% 5%	198
January	1st to 10th	Night	23% 25% 35% 15% 2	760
	11th to 20th	Night	29% 18% 31% 19% 3	760
	21st to end	Night	23% 23% 36% 16% 2	836
February	1st to 10th	Night	26% 20% 34% 19% 2	760
	11th to 20th	Night	25% 27% 35% 12% 1	743
	21st to end	Night	31% 21% 30% 15% 3	628
March	1st to 10th	Night	27% 21% 34% 15% 3	760
	11th to 20th	Night	26% 22% 30% 18% 4	760
	21st to end	Night	23% 23% 33% 17% 5%	836
April	1st to 10th	Night	23% 22% 33% 19% 3	760
	11th to 20th	Night	24% 19% 31% 20% 6%	751
	21st to end	Night	25% 17% 30% 22% 6%	760
May	1st to 10th	Night	30% 13% 27% 23% 6% 1	528
	11th to 20th	Night	22% 10% 34% 24% 9% 1	374
	21st to end	Night	17% 7% 23% 39% 14%	411
June	1st to 10th	Night	17% 7% 25% 37% 14%	380
	11th to 20th	Night	17% 6% 27% 36% 14%	380
	21st to end	Night	12% 4 27% 44% 13% 1	380
July	1st to 10th	Night	14% 5% 21% 41% 18% 2	370
	11th to 20th	Night	13% 3 23% 42% 18% 1	368
	21st to end	Night	15% 5% 20% 41% 18% 1	416
August	1st to 10th	Night	13% 4 20% 40% 22% 2	516
	11th to 20th	Night	15% 4 18% 36% 24% 2	710
	21st to end	Night	16% 4 21% 34% 23% 2	836
September	1st to 10th	Night	17% 5% 27% 30% 18% 3	760
	11th to 20th	Night	16% 7% 23% 29% 21% 5%	760
	21st to end	Night	19% 9% 23% 30% 17% 2	760
October	1st to 10th	Night	26% 9% 23% 25% 16% 1	760
	11th to 20th	Night	22% 13% 27% 28% 8%	760
	21st to end	Night	26% 16% 30% 21% 7%	836
November	1st to 10th	Night	19% 17% 28% 26% 9% 1	764
	11th to 20th	Night	26% 18% 26% 22% 7% 1	760
	21st to end	Night	21% 20% 32% 21% 6% 1	760
December	1st to 10th	Night	27% 19% 30% 19% 4	760
	11th to 20th	Night	25% 22% 29% 20% 3	760
	21st to end	Night	27% 21% 32% 18% 2	836

Page generated at 2024-11-03 13:19:01. Version ac07

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