Lac Boswell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Boswell clear sky chart from 2005-11-06 to 2024-11-25.

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	18% 12% 4 9% 6% 5% 5% 4 5% 6% 26%	101580
	Night	18% 13% 4 9% 6% 5% 5% 4 5% 6% 26%	97908
Transparency	Day	57% 6% 11% 18% 8% 1	105029
	Night	57% 6% 12% 18% 7% 1	102549
Seeing	Day	27% 18% 30% 17% 7% 1	14996
	Night	26% 14% 30% 23% 7% 1	23667

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% 19% 7% 17% 10% 5% 4 3 4 5% 13%	2517
	11th to 20th	Day	13% 15% 7% 18% 9% 6% 3 3 3 4 19%	2520
	21st to end	Day	11% 14% 7% 12% 7% 6% 6% 4 6% 7% 19%	2772
February	1st to 10th	Day	10% 16% 6% 13% 10% 7% 5% 4 4 5% 19%	1551
	11th to 20th	Day	12% 19% 7% 12% 6% 6% 6% 3 4 6% 19%	1784
	21st to end	Day	14% 16% 6% 12% 7% 5% 5% 3 4 4 23%	1570
March	1st to 10th	Day	16% 16% 5% 11% 6% 5% 4 3 3 5% 27%	3116
	11th to 20th	Day	15% 19% 6% 13% 6% 5% 4 3 4 4 22%	3247
	21st to end	Day	12% 16% 4 10% 6% 4 3 3 4 5% 33%	4158
April	1st to 10th	Day	21% 17% 5% 9% 4 5% 4 2 3 4 25%	2280
	11th to 20th	Day	21% 12% 3 8% 4 3 4 3 3 6% 32%	2305
	21st to end	Day	21% 13% 4 9% 5% 4 4 3 5% 6% 27%	2470
May	1st to 10th	Day	21% 10% 3 9% 5% 4 4 4 5% 6% 27%	4345
	11th to 20th	Day	17% 8% 3 7% 6% 5% 5% 4 6% 8% 31%	4398
	21st to end	Day	18% 8% 3 8% 6% 5% 5% 5% 7% 7% 29%	4837
June	1st to 10th	Day	22% 9% 3 7% 6% 5% 5% 4 6% 7% 25%	2779
	11th to 20th	Day	21% 7% 3 7% 5% 4 5% 4 6% 8% 30%	2850
	21st to end	Day	24% 9% 3 8% 5% 6% 5% 3 6% 6% 25%	2788
July	1st to 10th	Day	16% 8% 3 9% 6% 5% 6% 4 7% 8% 28%	4440
	11th to 20th	Day	17% 8% 3 8% 6% 6% 6% 4 7% 8% 27%	4440
	21st to end	Day	14% 7% 2 6% 5% 5% 6% 4 7% 8% 35%	4814
August	1st to 10th	Day	16% 8% 3 8% 6% 6% 6% 5% 7% 9% 26%	4423
	11th to 20th	Day	22% 7% 3 8% 5% 5% 5% 4 7% 8% 26%	4119
	21st to end	Day	20% 7% 3 8% 5% 5% 5% 4 5% 7% 31%	4246
September	1st to 10th	Day	18% 7% 3 7% 5% 5% 5% 4 5% 7% 35%	2280
	11th to 20th	Day	18% 8% 3 7% 4 4 3 3 4 6% 40%	2156
	21st to end	Day	24% 8% 2 7% 5% 4 4 4 4 6% 33%	2090
October	1st to 10th	Day	24% 9% 3 8% 5% 5% 4 3 6% 6% 28%	2022
	11th to 20th	Day	25% 15% 3 10% 6% 5% 4 3 6% 5% 20%	1778
	21st to end	Day	28% 15% 4 8% 4 3 4 3 5% 5% 21%	1881
November	1st to 10th	Day	21% 17% 5% 8% 4 5% 4 2 4 5% 26%	1761
	11th to 20th	Day	20% 19% 6% 10% 6% 4 3 3 3 4 21%	1725
	21st to end	Day	20% 23% 5% 11% 6% 5% 4 3 4 5% 14%	1476
December	1st to 10th	Day	22% 19% 6% 11% 6% 4 4 3 4 5% 16%	1330
	11th to 20th	Day	22% 17% 5% 11% 6% 4 3 3 3 4 22%	1668
	21st to end	Day	21% 20% 6% 10% 7% 5% 4 3 4 4 15%	2644
January	1st to 10th	Night	14% 19% 8% 14% 7% 6% 6% 4 4 4 14%	4429
	11th to 20th	Night	12% 15% 6% 15% 9% 8% 6% 3 4 5% 17%	4440
	21st to end	Night	10% 14% 7% 12% 8% 8% 5% 5% 6% 7% 19%	4884
February	1st to 10th	Night	11% 15% 5% 10% 8% 7% 5% 4 5% 7% 24%	2627
	11th to 20th	Night	12% 17% 6% 12% 7% 7% 5% 4 4 5% 21%	2281
	21st to end	Night	15% 15% 5% 10% 6% 6% 5% 4 4 5% 26%	1884
March	1st to 10th	Night	21% 15% 4 9% 5% 4 6% 3 4 5% 24%	3724
	11th to 20th	Night	16% 18% 6% 11% 5% 5% 5% 4 4 5% 22%	3711
	21st to end	Night	13% 13% 5% 10% 5% 5% 5% 4 5% 6% 30%	3471
April	1st to 10th	Night	21% 16% 5% 8% 5% 5% 4 3 5% 4 26%	1900
	11th to 20th	Night	21% 10% 3 7% 4 4 4 3 6% 6% 32%	1822
	21st to end	Night	21% 12% 3 7% 4 4 3 3 4 6% 32%	1710
May	1st to 10th	Night	21% 10% 4 9% 6% 5% 3 3 4 6% 30%	2624
	11th to 20th	Night	20% 7% 2 7% 4 4 5% 4 5% 8% 34%	2495
	21st to end	Night	20% 7% 3 7% 5% 5% 5% 4 6% 7% 30%	2738
June	1st to 10th	Night	21% 8% 3 7% 5% 5% 5% 4 6% 7% 30%	1397
	11th to 20th	Night	18% 7% 2 7% 5% 4 5% 3 6% 7% 35%	1330
	21st to end	Night	22% 8% 2 8% 5% 5% 4 4 6% 7% 28%	1385
July	1st to 10th	Night	16% 7% 3 8% 6% 6% 6% 4 7% 9% 29%	2520
	11th to 20th	Night	16% 7% 3 7% 5% 6% 5% 4 7% 7% 34%	2520
	21st to end	Night	13% 5% 2 6% 4 4 5% 4 6% 7% 45%	2739
August	1st to 10th	Night	15% 8% 3 7% 5% 6% 5% 5% 6% 7% 33%	2506
	11th to 20th	Night	18% 8% 3 7% 4 5% 5% 5% 6% 7% 30%	2678
	21st to end	Night	18% 8% 3 7% 5% 5% 4 4 6% 7% 34%	3407
September	1st to 10th	Night	19% 8% 3 6% 3 4 4 3 4 6% 41%	1900
	11th to 20th	Night	19% 6% 2 6% 4 4 4 4 5% 7% 40%	2023
	21st to end	Night	20% 7% 2 7% 4 4 5% 3 4 5% 40%	2090
October	1st to 10th	Night	19% 9% 3 7% 4 4 4 3 5% 6% 35%	2156
	11th to 20th	Night	25% 11% 3 8% 4 4 4 3 4 6% 27%	2401
	21st to end	Night	27% 13% 3 8% 4 4 5% 3 5% 5% 23%	2717
November	1st to 10th	Night	20% 15% 5% 9% 4 4 4 3 4 6% 26%	2537
	11th to 20th	Night	21% 13% 5% 10% 5% 4 5% 3 5% 5% 24%	2674
	21st to end	Night	22% 18% 5% 11% 6% 4 4 3 4 5% 18%	2796
December	1st to 10th	Night	21% 19% 6% 12% 6% 4 4 3 4 4 16%	2850
	11th to 20th	Night	20% 17% 5% 14% 7% 4 4 3 3 4 18%	3531
	21st to end	Night	19% 22% 7% 11% 6% 5% 3 3 3 3 17%	5011

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	72% 6% 9% 11% 3	2518
	11th to 20th	Day	68% 4 6% 17% 5%	2520
	21st to end	Day	61% 6% 6% 18% 9% 1	2772
February	1st to 10th	Day	67% 4 7% 12% 8% 1	1551
	11th to 20th	Day	65% 4 9% 12% 9% 1	1793
	21st to end	Day	65% 4 6% 15% 7% 3	1570
March	1st to 10th	Day	62% 3 9% 14% 10% 2	3119
	11th to 20th	Day	65% 5% 7% 15% 7%	3247
	21st to end	Day	53% 4 6% 18% 14% 4	4158
April	1st to 10th	Day	64% 3 9% 12% 10% 2	2280
	11th to 20th	Day	54% 4 8% 20% 12% 2	2305
	21st to end	Day	59% 3 8% 15% 13% 2	2470
May	1st to 10th	Day	54% 7% 9% 15% 13% 1	4359
	11th to 20th	Day	47% 8% 15% 20% 9% 1	4402
	21st to end	Day	51% 7% 9% 16% 15% 2	4837
June	1st to 10th	Day	57% 6% 9% 18% 8% 2	2779
	11th to 20th	Day	50% 6% 13% 19% 10% 2	2850
	21st to end	Day	59% 6% 11% 14% 10%	2788
July	1st to 10th	Day	52% 6% 13% 24% 5%	4370
	11th to 20th	Day	52% 7% 18% 19% 4	4365
	21st to end	Day	46% 6% 18% 23% 6%	4661
August	1st to 10th	Day	52% 7% 17% 19% 4	4409
	11th to 20th	Day	53% 7% 20% 17% 4	4160
	21st to end	Day	52% 6% 13% 17% 12%	4246
September	1st to 10th	Day	47% 6% 15% 23% 9% 1	2280
	11th to 20th	Day	45% 5% 16% 24% 9%	2156
	21st to end	Day	52% 5% 13% 22% 8%	2090
October	1st to 10th	Day	57% 5% 11% 22% 5%	3360
	11th to 20th	Day	62% 4 13% 19% 1	2929
	21st to end	Day	58% 5% 17% 16% 3	3081
November	1st to 10th	Day	61% 6% 9% 18% 5% 1	1761
	11th to 20th	Day	67% 4 9% 14% 6%	1725
	21st to end	Day	72% 6% 9% 11% 2	1476
December	1st to 10th	Day	71% 4 9% 13% 3	1330
	11th to 20th	Day	66% 5% 6% 17% 6%	1668
	21st to end	Day	70% 6% 6% 12% 5%	2644
January	1st to 10th	Night	70% 7% 9% 11% 4	4429
	11th to 20th	Night	66% 7% 8% 15% 4 1	4440
	21st to end	Night	63% 5% 10% 13% 9%	4884
February	1st to 10th	Night	59% 6% 8% 17% 9% 1	2627
	11th to 20th	Night	64% 5% 9% 13% 7% 1	2283
	21st to end	Night	60% 5% 7% 16% 11% 1	1884
March	1st to 10th	Night	64% 5% 9% 14% 8% 1	3734
	11th to 20th	Night	64% 5% 7% 15% 8% 1	3712
	21st to end	Night	55% 4 9% 20% 9% 3	3471
April	1st to 10th	Night	61% 4 7% 14% 12% 2	1900
	11th to 20th	Night	51% 6% 7% 22% 12% 2	1822
	21st to end	Night	54% 4 7% 20% 13% 2	1710
May	1st to 10th	Night	54% 6% 10% 19% 9% 1	2630
	11th to 20th	Night	44% 9% 14% 22% 10% 1	2496
	21st to end	Night	50% 7% 10% 19% 13% 1	2739
June	1st to 10th	Night	51% 7% 11% 21% 9% 1	1397
	11th to 20th	Night	47% 5% 14% 19% 12% 3	1330
	21st to end	Night	54% 7% 12% 17% 11%	1385
July	1st to 10th	Night	49% 7% 18% 20% 5%	2480
	11th to 20th	Night	48% 6% 21% 21% 4	2472
	21st to end	Night	37% 6% 23% 25% 8%	2651
August	1st to 10th	Night	47% 7% 19% 19% 7%	2496
	11th to 20th	Night	50% 7% 21% 17% 4	2703
	21st to end	Night	48% 6% 13% 24% 9%	3407
September	1st to 10th	Night	44% 6% 15% 25% 10% 1	1900
	11th to 20th	Night	43% 6% 15% 28% 6%	2023
	21st to end	Night	47% 5% 13% 28% 8%	2090
October	1st to 10th	Night	53% 4 13% 22% 7%	3598
	11th to 20th	Night	55% 4 15% 22% 4	3989
	21st to end	Night	56% 4 16% 15% 7%	4467
November	1st to 10th	Night	59% 5% 12% 17% 6% 1	2537
	11th to 20th	Night	59% 7% 9% 18% 7%	2674
	21st to end	Night	69% 5% 10% 13% 4	2796
December	1st to 10th	Night	72% 4 10% 12% 4	2850
	11th to 20th	Night	69% 5% 6% 15% 6%	3532
	21st to end	Night	71% 5% 6% 14% 4	5011

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	27% 20% 41% 12% 1	180
	11th to 20th	Day	26% 17% 39% 14% 3	180
	21st to end	Day	20% 16% 40% 16% 7% 1	198
February	1st to 10th	Day	24% 31% 35% 8% 1 1	195
	11th to 20th	Day	27% 27% 34% 10% 2	392
	21st to end	Day	27% 30% 29% 10% 4	382
March	1st to 10th	Day	24% 24% 33% 14% 5%	460
	11th to 20th	Day	27% 22% 32% 13% 4 1	460
	21st to end	Day	28% 25% 28% 13% 5% 1	506
April	1st to 10th	Day	31% 19% 32% 13% 4 1	460
	11th to 20th	Day	33% 21% 25% 13% 5% 3	452
	21st to end	Day	31% 23% 30% 10% 4 1	460
May	1st to 10th	Day	33% 17% 31% 13% 6% 1	463
	11th to 20th	Day	25% 18% 31% 20% 5% 1	487
	21st to end	Day	28% 24% 27% 16% 5%	529
June	1st to 10th	Day	24% 18% 33% 18% 6%	609
	11th to 20th	Day	24% 17% 29% 20% 9% 1	680
	21st to end	Day	27% 14% 28% 22% 8% 1	618
July	1st to 10th	Day	19% 13% 38% 21% 8% 1	485
	11th to 20th	Day	19% 14% 36% 23% 7% 2	484
	21st to end	Day	20% 11% 31% 26% 10% 1	532
August	1st to 10th	Day	22% 12% 31% 23% 10% 2	486
	11th to 20th	Day	20% 8% 32% 25% 11% 4	479
	21st to end	Day	24% 14% 27% 18% 13% 5%	539
September	1st to 10th	Day	23% 15% 30% 19% 9% 3	490
	11th to 20th	Day	19% 14% 27% 23% 13% 4	490
	21st to end	Day	26% 16% 27% 15% 12% 5%	490
October	1st to 10th	Day	26% 19% 25% 18% 10% 1	490
	11th to 20th	Day	31% 23% 26% 10% 8% 2	425
	21st to end	Day	39% 16% 25% 15% 5%	429
November	1st to 10th	Day	35% 19% 28% 13% 4 1	395
	11th to 20th	Day	33% 18% 28% 16% 4	325
	21st to end	Day	32% 24% 30% 13% 1	188
December	1st to 10th	Day	33% 16% 31% 15% 4	180
	11th to 20th	Day	32% 22% 34% 7% 4 1	180
	21st to end	Day	37% 21% 28% 8% 6% 1	198
January	1st to 10th	Night	27% 17% 34% 17% 4	760
	11th to 20th	Night	25% 17% 35% 18% 5%	760
	21st to end	Night	17% 15% 36% 25% 6%	836
February	1st to 10th	Night	18% 21% 35% 20% 5%	760
	11th to 20th	Night	23% 19% 35% 18% 4	743
	21st to end	Night	23% 19% 32% 21% 4	628
March	1st to 10th	Night	24% 16% 37% 19% 4	760
	11th to 20th	Night	26% 17% 33% 17% 6% 1	760
	21st to end	Night	24% 19% 31% 19% 7%	836
April	1st to 10th	Night	31% 15% 27% 21% 5% 1	760
	11th to 20th	Night	28% 15% 29% 22% 5% 1	698
	21st to end	Night	29% 20% 29% 17% 5%	570
May	1st to 10th	Night	27% 16% 28% 22% 6%	451
	11th to 20th	Night	24% 11% 32% 25% 8%	374
	21st to end	Night	26% 12% 33% 24% 5%	411
June	1st to 10th	Night	23% 10% 32% 28% 7%	380
	11th to 20th	Night	18% 11% 29% 33% 9%	380
	21st to end	Night	24% 8% 27% 31% 9% 1	380
July	1st to 10th	Night	17% 8% 30% 34% 12%	370
	11th to 20th	Night	17% 4 27% 35% 16% 1	368
	21st to end	Night	17% 6% 26% 38% 13% 1	416
August	1st to 10th	Night	16% 5% 24% 41% 14%	378
	11th to 20th	Night	17% 7% 26% 32% 16% 1	494
	21st to end	Night	22% 10% 25% 28% 14% 2	793
September	1st to 10th	Night	23% 8% 27% 32% 9% 1	760
	11th to 20th	Night	24% 6% 25% 28% 15% 2	760
	21st to end	Night	23% 11% 27% 25% 13% 1	760
October	1st to 10th	Night	24% 13% 26% 27% 9% 1	760
	11th to 20th	Night	33% 12% 26% 21% 8% 1	760
	21st to end	Night	35% 13% 29% 18% 5%	836
November	1st to 10th	Night	31% 14% 28% 20% 5% 1	780
	11th to 20th	Night	29% 16% 31% 16% 7% 2	800
	21st to end	Night	35% 17% 25% 18% 3	814
December	1st to 10th	Night	31% 16% 28% 19% 5%	850
	11th to 20th	Night	29% 18% 31% 17% 4 1	850
	21st to end	Night	33% 15% 32% 16% 3	871

Page generated at 2024-11-22 08:02:25. Version ac07

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