Leslie C. Peltier Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leslie C. Peltier Observatory clear sky chart from 2005-11-06 to 2024-11-03.

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	17% 7% 2 6% 4 4 4 4 6% 7% 38%	101256
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	97723
Transparency	Day	46% 3 11% 23% 14% 2	101011
	Night	46% 3 11% 23% 15% 2	97588
Seeing	Day	24% 16% 31% 19% 8% 2	14979
	Night	22% 14% 32% 24% 7% 1	24004

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	14% 7% 2 6% 4 4 4 4 5% 5% 45%	2517
	11th to 20th	Day	16% 9% 4 9% 5% 4 5% 4 4 6% 34%	2520
	21st to end	Day	21% 13% 4 7% 4 3 4 3 4 5% 32%	2850
February	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 5% 6% 36%	1756
	11th to 20th	Day	13% 7% 3 6% 5% 5% 5% 4 6% 7% 40%	1848
	21st to end	Day	20% 10% 3 6% 4 4 4 4 4 6% 37%	1570
March	1st to 10th	Day	25% 11% 3 6% 4 3 3 3 3 5% 33%	3116
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 5% 7% 9% 40%	3265
	21st to end	Day	20% 8% 3 7% 4 3 3 3 5% 6% 37%	4166
April	1st to 10th	Day	18% 10% 2 5% 5% 4 4 4 5% 6% 36%	2280
	11th to 20th	Day	18% 6% 2 5% 4 4 5% 4 5% 7% 40%	2254
	21st to end	Day	21% 6% 2 6% 4 4 4 3 5% 7% 39%	2380
May	1st to 10th	Day	27% 8% 3 6% 4 4 3 3 5% 7% 29%	4106
	11th to 20th	Day	22% 7% 2 7% 4 4 4 4 5% 7% 33%	4316
	21st to end	Day	15% 5% 2 5% 4 4 4 4 6% 8% 44%	4837
June	1st to 10th	Day	17% 6% 2 6% 4 5% 5% 5% 7% 9% 35%	2660
	11th to 20th	Day	15% 7% 2 6% 5% 5% 4 5% 7% 9% 36%	2660
	21st to end	Day	14% 6% 3 6% 5% 5% 6% 4 6% 9% 36%	2660
July	1st to 10th	Day	12% 6% 3 6% 6% 6% 6% 5% 7% 8% 36%	4440
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	4440
	21st to end	Day	17% 9% 3 7% 5% 5% 5% 4 6% 7% 32%	4814
August	1st to 10th	Day	20% 6% 3 7% 5% 5% 5% 4 6% 8% 30%	4283
	11th to 20th	Day	12% 6% 3 6% 4 5% 5% 4 6% 9% 39%	3739
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	4180
September	1st to 10th	Day	13% 7% 2 6% 5% 4 5% 4 4 6% 44%	2280
	11th to 20th	Day	13% 6% 2 4 4 4 4 3 4 7% 50%	2157
	21st to end	Day	19% 6% 2 6% 3 4 4 3 5% 6% 41%	2090
October	1st to 10th	Day	22% 7% 2 6% 3 4 4 2 4 5% 40%	2045
	11th to 20th	Day	13% 7% 2 5% 3 4 5% 3 5% 7% 46%	1891
	21st to end	Day	22% 6% 2 5% 4 4 4 3 4 5% 40%	1881
November	1st to 10th	Day	13% 7% 2 5% 5% 3 3 3 5% 6% 49%	1689
	11th to 20th	Day	19% 6% 1 4 3 3 4 3 5% 7% 45%	1710
	21st to end	Day	17% 8% 3 5% 3 4 3 3 5% 6% 43%	1658
December	1st to 10th	Day	18% 7% 2 8% 4 5% 4 5% 5% 5% 37%	1520
	11th to 20th	Day	23% 7% 1 4 3 3 3 4 5% 6% 43%	1906
	21st to end	Day	19% 12% 4 8% 5% 4 4 4 5% 7% 30%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 3 3 3 5% 6% 45%	4429
	11th to 20th	Night	16% 8% 3 7% 4 3 3 3 5% 4 42%	4440
	21st to end	Night	23% 13% 3 6% 4 3 3 3 4 5% 32%	4791
February	1st to 10th	Night	16% 10% 3 6% 4 4 4 3 4 6% 40%	2423
	11th to 20th	Night	14% 8% 3 6% 5% 5% 4 3 6% 6% 40%	2218
	21st to end	Night	19% 8% 1 7% 4 4 4 3 5% 5% 41%	1884
March	1st to 10th	Night	24% 12% 2 6% 3 4 4 3 3 5% 34%	3724
	11th to 20th	Night	11% 7% 3 7% 4 4 4 4 6% 6% 43%	3689
	21st to end	Night	21% 9% 2 5% 4 3 3 3 5% 5% 40%	3466
April	1st to 10th	Night	19% 7% 3 5% 4 5% 4 4 5% 6% 37%	1900
	11th to 20th	Night	19% 6% 2 6% 5% 3 5% 4 5% 6% 40%	1875
	21st to end	Night	20% 7% 2 6% 4 4 3 2 4 6% 41%	1800
May	1st to 10th	Night	25% 9% 3 8% 4 4 3 3 5% 7% 28%	2834
	11th to 20th	Night	22% 9% 3 7% 4 4 4 4 5% 6% 31%	2605
	21st to end	Night	18% 7% 2 5% 3 4 4 3 6% 7% 43%	2738
June	1st to 10th	Night	18% 7% 3 5% 4 4 4 4 4 6% 41%	1520
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 5% 9% 39%	1520
	21st to end	Night	15% 6% 1 6% 5% 3 3 3 7% 9% 41%	1520
July	1st to 10th	Night	13% 6% 2 6% 5% 4 5% 5% 8% 9% 38%	2520
	11th to 20th	Night	16% 6% 2 6% 4 4 3 4 7% 10% 37%	2520
	21st to end	Night	18% 9% 3 7% 5% 5% 4 4 5% 5% 35%	2739
August	1st to 10th	Night	21% 6% 3 7% 5% 5% 5% 3 6% 7% 31%	2602
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 5% 7% 41%	3085
	21st to end	Night	10% 5% 1 4 3 3 4 3 5% 8% 53%	3476
September	1st to 10th	Night	15% 6% 2 6% 4 4 3 3 5% 6% 45%	1900
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	2023
	21st to end	Night	17% 7% 2 5% 4 3 4 4 5% 5% 44%	2090
October	1st to 10th	Night	19% 7% 2 6% 4 3 3 3 4 6% 42%	2133
	11th to 20th	Night	15% 5% 2 6% 3 4 4 3 4 6% 48%	2289
	21st to end	Night	23% 6% 2 4 3 3 4 4 4 6% 41%	2717
November	1st to 10th	Night	14% 6% 2 5% 4 4 3 3 5% 6% 47%	2434
	11th to 20th	Night	18% 7% 3 5% 3 3 4 3 5% 6% 44%	2470
	21st to end	Night	16% 7% 2 4 5% 4 3 3 5% 6% 45%	2517
December	1st to 10th	Night	18% 7% 2 6% 5% 4 3 3 5% 6% 39%	2660
	11th to 20th	Night	20% 8% 2 4 4 3 4 4 5% 6% 40%	3288
	21st to end	Night	22% 11% 3 6% 4 3 3 3 4 5% 35%	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	42% 2 8% 35% 11% 3	2518
	11th to 20th	Day	52% 2 9% 25% 10% 1	2520
	21st to end	Day	56% 2 8% 22% 11% 2	2850
February	1st to 10th	Day	49% 3 12% 21% 14% 2	1756
	11th to 20th	Day	43% 4 9% 25% 16% 3	1857
	21st to end	Day	50% 2 9% 21% 14% 3	1570
March	1st to 10th	Day	56% 2 10% 19% 12% 2	3119
	11th to 20th	Day	39% 2 10% 35% 12% 2	3265
	21st to end	Day	49% 2 5% 18% 21% 6%	4166
April	1st to 10th	Day	48% 4 9% 21% 15% 4	2280
	11th to 20th	Day	44% 4 10% 23% 17% 3	2254
	21st to end	Day	46% 3 9% 21% 17% 4	2380
May	1st to 10th	Day	55% 3 12% 17% 12% 1	4120
	11th to 20th	Day	53% 2 13% 21% 10% 2	4320
	21st to end	Day	38% 3 11% 28% 18% 2	4837
June	1st to 10th	Day	45% 5% 12% 24% 13% 1	2660
	11th to 20th	Day	44% 4 14% 24% 12% 2	2660
	21st to end	Day	43% 5% 13% 24% 14% 1	2660
July	1st to 10th	Day	46% 5% 11% 21% 16% 1	4370
	11th to 20th	Day	42% 4 16% 24% 13% 1	4365
	21st to end	Day	51% 3 12% 18% 15% 1	4661
August	1st to 10th	Day	51% 4 15% 21% 9%	4269
	11th to 20th	Day	41% 3 14% 30% 11% 1	3775
	21st to end	Day	38% 5% 12% 28% 16% 2	4180
September	1st to 10th	Day	41% 5% 9% 24% 19% 2	2280
	11th to 20th	Day	35% 4 9% 25% 24% 3	2157
	21st to end	Day	44% 3 8% 24% 19% 3	2090
October	1st to 10th	Day	47% 3 7% 24% 16% 3	2045
	11th to 20th	Day	38% 3 12% 28% 17% 2	1891
	21st to end	Day	46% 3 10% 22% 16% 3	1881
November	1st to 10th	Day	38% 3 11% 26% 20% 3	1689
	11th to 20th	Day	41% 2 10% 25% 19% 3	1710
	21st to end	Day	43% 2 13% 27% 12% 3	1658
December	1st to 10th	Day	48% 3 14% 19% 15% 1	1520
	11th to 20th	Day	43% 3 15% 20% 16% 2	1906
	21st to end	Day	55% 3 9% 23% 10% 1	2772
January	1st to 10th	Night	42% 2 10% 31% 12% 4	4429
	11th to 20th	Night	46% 2 11% 25% 12% 3	4440
	21st to end	Night	56% 2 8% 21% 12% 2	4791
February	1st to 10th	Night	47% 3 13% 23% 12% 2	2423
	11th to 20th	Night	45% 4 9% 21% 18% 4	2220
	21st to end	Night	46% 3 7% 24% 14% 5%	1884
March	1st to 10th	Night	55% 2 9% 21% 12% 2	3734
	11th to 20th	Night	42% 2 14% 24% 15% 2	3690
	21st to end	Night	48% 2 6% 14% 25% 5%	3466
April	1st to 10th	Night	47% 4 8% 22% 15% 3	1900
	11th to 20th	Night	45% 4 9% 21% 20% 1	1875
	21st to end	Night	46% 2 9% 23% 16% 4	1800
May	1st to 10th	Night	57% 3 11% 16% 10% 2	2840
	11th to 20th	Night	55% 3 13% 17% 10% 2	2606
	21st to end	Night	42% 4 14% 25% 14% 1	2739
June	1st to 10th	Night	45% 4 10% 24% 16% 1	1520
	11th to 20th	Night	43% 3 15% 27% 11% 1	1520
	21st to end	Night	39% 5% 15% 26% 15% 1	1520
July	1st to 10th	Night	42% 5% 17% 20% 15% 1	2480
	11th to 20th	Night	43% 4 16% 24% 12% 1	2472
	21st to end	Night	51% 4 13% 15% 15% 2	2651
August	1st to 10th	Night	53% 5% 13% 18% 9% 1	2592
	11th to 20th	Night	44% 4 13% 30% 9% 1	3115
	21st to end	Night	31% 4 13% 35% 17% 1	3476
September	1st to 10th	Night	41% 3 10% 26% 18% 1	1900
	11th to 20th	Night	35% 3 10% 25% 25% 2	2023
	21st to end	Night	42% 4 8% 24% 20% 2	2090
October	1st to 10th	Night	45% 3 12% 22% 15% 3	2133
	11th to 20th	Night	39% 3 11% 29% 16% 2	2289
	21st to end	Night	46% 3 11% 23% 16% 1	2717
November	1st to 10th	Night	39% 3 11% 22% 21% 4	2434
	11th to 20th	Night	43% 3 10% 23% 19% 3	2470
	21st to end	Night	41% 3 13% 30% 12% 1	2517
December	1st to 10th	Night	47% 3 13% 23% 14% 1	2660
	11th to 20th	Night	45% 3 13% 19% 17% 2	3288
	21st to end	Night	53% 2 9% 24% 12%	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	29% 23% 31% 15% 2	180
	11th to 20th	Day	31% 28% 28% 11% 2	180
	21st to end	Day	23% 30% 34% 8% 4 1	222
February	1st to 10th	Day	32% 24% 32% 10% 1	316
	11th to 20th	Day	29% 25% 34% 11% 1	456
	21st to end	Day	34% 19% 31% 12% 3	382
March	1st to 10th	Day	27% 23% 33% 14% 3	460
	11th to 20th	Day	28% 22% 35% 11% 3 1	460
	21st to end	Day	32% 20% 33% 9% 4 2	506
April	1st to 10th	Day	32% 22% 27% 12% 6% 1	460
	11th to 20th	Day	31% 20% 31% 12% 5% 1	452
	21st to end	Day	31% 19% 32% 12% 5% 1	460
May	1st to 10th	Day	35% 18% 27% 13% 6% 1	463
	11th to 20th	Day	24% 17% 37% 16% 6%	487
	21st to end	Day	22% 12% 31% 23% 9% 2	529
June	1st to 10th	Day	20% 13% 33% 22% 9% 2	490
	11th to 20th	Day	19% 13% 35% 23% 9% 2	490
	21st to end	Day	18% 13% 34% 24% 8% 2	490
July	1st to 10th	Day	17% 7% 31% 27% 14% 3	485
	11th to 20th	Day	14% 8% 32% 29% 15% 2	484
	21st to end	Day	14% 11% 36% 28% 10% 2	532
August	1st to 10th	Day	15% 7% 30% 33% 9% 4	486
	11th to 20th	Day	15% 9% 31% 27% 13% 5%	479
	21st to end	Day	14% 11% 29% 25% 16% 6%	539
September	1st to 10th	Day	19% 13% 25% 22% 15% 6%	490
	11th to 20th	Day	17% 11% 27% 24% 12% 10%	490
	21st to end	Day	23% 13% 32% 20% 8% 5%	490
October	1st to 10th	Day	27% 12% 26% 17% 13% 4	490
	11th to 20th	Day	17% 20% 33% 22% 7% 2	485
	21st to end	Day	29% 17% 25% 20% 7% 1	429
November	1st to 10th	Day	22% 15% 31% 23% 9% 1	371
	11th to 20th	Day	31% 19% 26% 18% 5% 1	370
	21st to end	Day	28% 16% 30% 20% 5% 1	318
December	1st to 10th	Day	25% 23% 33% 13% 6%	180
	11th to 20th	Day	36% 23% 28% 10% 3	180
	21st to end	Day	30% 23% 28% 15% 3 2	198
January	1st to 10th	Night	23% 18% 39% 17% 3	760
	11th to 20th	Night	28% 19% 33% 19% 2	760
	21st to end	Night	22% 20% 36% 20% 2	836
February	1st to 10th	Night	25% 18% 33% 22% 2	760
	11th to 20th	Night	23% 22% 38% 15% 1	743
	21st to end	Night	29% 18% 34% 16% 3	628
March	1st to 10th	Night	25% 20% 35% 18% 3	760
	11th to 20th	Night	22% 21% 36% 18% 3 1	760
	21st to end	Night	26% 20% 32% 17% 4	836
April	1st to 10th	Night	26% 19% 34% 18% 3	760
	11th to 20th	Night	24% 18% 35% 19% 4	751
	21st to end	Night	24% 20% 35% 17% 5%	660
May	1st to 10th	Night	28% 16% 33% 19% 4	570
	11th to 20th	Night	23% 14% 38% 21% 4	445
	21st to end	Night	23% 8% 29% 31% 7% 1	411
June	1st to 10th	Night	20% 9% 31% 30% 9% 1	380
	11th to 20th	Night	20% 6% 33% 30% 10%	380
	21st to end	Night	18% 5% 30% 37% 9%	380
July	1st to 10th	Night	15% 4 27% 35% 18% 1	370
	11th to 20th	Night	15% 4 23% 43% 14% 2	368
	21st to end	Night	15% 5% 29% 38% 13% 1	416
August	1st to 10th	Night	14% 4 28% 40% 13% 1	435
	11th to 20th	Night	15% 5% 25% 36% 17% 1	738
	21st to end	Night	16% 5% 24% 35% 19% 1	836
September	1st to 10th	Night	18% 4 31% 31% 13% 2	760
	11th to 20th	Night	16% 8% 24% 32% 17% 3	760
	21st to end	Night	22% 7% 29% 26% 15% 2	760
October	1st to 10th	Night	23% 9% 28% 25% 11% 3	760
	11th to 20th	Night	20% 13% 31% 27% 9% 1	760
	21st to end	Night	28% 11% 33% 21% 6%	836
November	1st to 10th	Night	18% 15% 33% 25% 8% 1	749
	11th to 20th	Night	24% 15% 34% 20% 6% 1	760
	21st to end	Night	24% 16% 33% 22% 5% 1	760
December	1st to 10th	Night	26% 16% 33% 20% 5% 1	760
	11th to 20th	Night	24% 19% 33% 21% 4	760
	21st to end	Night	29% 18% 33% 19% 2	836

Page generated at 2024-10-31 03:39:22. Version ac07

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