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 2024-01-14.

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	20% 11% 4 8% 7% 4 5% 5% 5% 6% 26%	74557
	Night	19% 12% 5% 8% 6% 4 5% 4 5% 6% 27%	75192
Transparency	Day	58% 5% 10% 17% 8% 1	74262
	Night	58% 5% 10% 18% 8% 1	75022
Seeing	Day	27% 18% 30% 17% 7% 1	13818
	Night	26% 14% 30% 23% 7% 1	22633

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	17% 17% 8% 14% 10% 4 6% 4 4 4 13%	1517
	11th to 20th	Day	17% 16% 7% 9% 7% 5% 6% 4 4 6% 19%	1464
	21st to end	Day	11% 12% 7% 11% 10% 4 5% 5% 6% 7% 22%	1584
February	1st to 10th	Day	10% 16% 6% 12% 11% 7% 6% 6% 3 5% 19%	1470
	11th to 20th	Day	13% 19% 7% 10% 7% 3 6% 4 4 7% 20%	1688
	21st to end	Day	14% 15% 7% 12% 9% 4 6% 4 4 5% 23%	1480
March	1st to 10th	Day	14% 13% 6% 11% 8% 4 5% 4 3 5% 27%	1797
	11th to 20th	Day	17% 14% 6% 8% 7% 3 5% 4 4 5% 27%	1845
	21st to end	Day	16% 12% 5% 9% 8% 4 4 4 4 5% 28%	2368
April	1st to 10th	Day	22% 15% 6% 8% 5% 4 5% 3 3 4 24%	2160
	11th to 20th	Day	21% 10% 4 7% 5% 2 5% 3 3 6% 34%	2182
	21st to end	Day	21% 13% 4 8% 6% 2 5% 3 4 6% 28%	2340
May	1st to 10th	Day	22% 10% 3 7% 5% 3 3 4 4 6% 32%	2467
	11th to 20th	Day	19% 9% 3 5% 7% 4 5% 4 5% 7% 33%	2478
	21st to end	Day	22% 7% 3 7% 6% 3 5% 5% 5% 7% 29%	2725
June	1st to 10th	Day	22% 9% 3 7% 7% 4 5% 5% 6% 7% 25%	2632
	11th to 20th	Day	22% 7% 3 6% 6% 3 5% 5% 6% 8% 30%	2700
	21st to end	Day	24% 8% 4 7% 6% 4 5% 4 5% 6% 26%	2642
July	1st to 10th	Day	18% 7% 3 7% 7% 4 6% 5% 6% 9% 28%	2520
	11th to 20th	Day	16% 8% 3 7% 7% 4 6% 6% 6% 9% 27%	2520
	21st to end	Day	15% 9% 4 7% 7% 4 7% 6% 6% 7% 28%	2744
August	1st to 10th	Day	18% 9% 4 8% 7% 5% 7% 6% 6% 8% 23%	2506
	11th to 20th	Day	18% 7% 3 7% 7% 4 6% 5% 6% 8% 29%	2352
	21st to end	Day	16% 7% 3 7% 7% 5% 6% 5% 6% 7% 30%	2414
September	1st to 10th	Day	19% 7% 3 6% 5% 4 5% 5% 4 7% 35%	2160
	11th to 20th	Day	19% 8% 3 6% 5% 3 4 4 4 6% 38%	2043
	21st to end	Day	24% 8% 2 6% 5% 3 3 6% 4 6% 34%	1980
October	1st to 10th	Day	25% 9% 3 7% 5% 4 4 4 6% 6% 28%	1916
	11th to 20th	Day	26% 14% 4 9% 7% 3 4 4 6% 5% 19%	1685
	21st to end	Day	30% 15% 4 6% 5% 2 4 4 5% 5% 20%	1782
November	1st to 10th	Day	20% 16% 6% 7% 6% 3 4 3 3 5% 26%	1671
	11th to 20th	Day	21% 18% 7% 9% 7% 3 3 4 3 5% 20%	1639
	21st to end	Day	20% 20% 7% 11% 7% 4 4 4 4 5% 15%	1444
December	1st to 10th	Day	23% 18% 6% 9% 7% 4 4 3 4 5% 16%	1330
	11th to 20th	Day	22% 16% 6% 10% 7% 3 4 3 3 4 22%	1668
	21st to end	Day	22% 20% 6% 9% 8% 4 4 4 4 5% 15%	2644
January	1st to 10th	Night	17% 19% 8% 12% 9% 4 5% 5% 5% 4 12%	2649
	11th to 20th	Night	17% 16% 7% 11% 7% 4 6% 4 5% 5% 19%	2574
	21st to end	Night	10% 13% 6% 10% 8% 5% 6% 5% 6% 7% 24%	2772
February	1st to 10th	Night	12% 14% 6% 9% 8% 5% 6% 5% 5% 7% 23%	2488
	11th to 20th	Night	13% 17% 7% 10% 7% 5% 6% 5% 4 5% 22%	2157
	21st to end	Night	15% 14% 5% 10% 7% 5% 5% 5% 4 5% 26%	1776
March	1st to 10th	Night	15% 13% 6% 9% 8% 4 6% 4 4 5% 25%	2150
	11th to 20th	Night	17% 15% 5% 7% 7% 3 6% 5% 4 5% 25%	2113
	21st to end	Night	15% 12% 5% 8% 6% 3 6% 4 5% 6% 32%	1985
April	1st to 10th	Night	22% 14% 6% 8% 6% 3 5% 4 5% 4 24%	1800
	11th to 20th	Night	20% 9% 3 6% 5% 3 5% 4 5% 6% 33%	1725
	21st to end	Night	22% 11% 4 6% 5% 3 4 4 3 7% 32%	1620
May	1st to 10th	Night	23% 9% 4 6% 6% 3 3 4 4 5% 33%	1508
	11th to 20th	Night	20% 8% 2 7% 5% 3 4 4 4 7% 35%	1415
	21st to end	Night	23% 7% 3 6% 5% 3 4 3 4 6% 36%	1550
June	1st to 10th	Night	22% 7% 3 6% 5% 3 5% 5% 6% 7% 30%	1324
	11th to 20th	Night	19% 7% 2 6% 5% 3 4 4 6% 8% 35%	1260
	21st to end	Night	21% 7% 3 7% 6% 4 5% 5% 6% 7% 29%	1312
July	1st to 10th	Night	17% 6% 3 6% 5% 3 6% 6% 7% 8% 33%	1440
	11th to 20th	Night	14% 6% 3 7% 6% 4 7% 5% 6% 8% 34%	1440
	21st to end	Night	15% 6% 3 7% 6% 3 6% 5% 6% 8% 35%	1574
August	1st to 10th	Night	14% 6% 2 5% 5% 4 5% 6% 8% 8% 36%	1432
	11th to 20th	Night	17% 7% 3 5% 6% 4 6% 5% 7% 8% 33%	1531
	21st to end	Night	18% 7% 3 5% 6% 3 4 5% 6% 7% 37%	1939
September	1st to 10th	Night	18% 7% 3 5% 5% 3 4 4 4 6% 41%	1800
	11th to 20th	Night	19% 6% 2 5% 5% 3 4 5% 5% 6% 39%	1916
	21st to end	Night	20% 6% 2 5% 5% 3 4 4 4 6% 41%	1980
October	1st to 10th	Night	20% 9% 3 6% 5% 3 4 3 4 6% 36%	2042
	11th to 20th	Night	26% 11% 3 7% 5% 3 4 4 4 6% 27%	2274
	21st to end	Night	27% 13% 4 7% 5% 3 5% 4 5% 5% 22%	2574
November	1st to 10th	Night	20% 14% 5% 8% 6% 3 4 4 4 6% 26%	2407
	11th to 20th	Night	22% 12% 5% 9% 6% 3 5% 4 5% 5% 24%	2540
	21st to end	Night	23% 16% 6% 10% 7% 3 4 4 4 5% 18%	2733
December	1st to 10th	Night	21% 18% 7% 12% 7% 3 4 4 4 4 16%	2850
	11th to 20th	Night	21% 16% 5% 13% 9% 3 4 4 3 4 18%	3531
	21st to end	Night	20% 22% 7% 9% 8% 4 4 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	73% 4 6% 11% 5%	1518
	11th to 20th	Day	66% 4 8% 15% 6% 1	1464
	21st to end	Day	60% 5% 6% 17% 12% 1	1584
February	1st to 10th	Day	68% 4 7% 12% 7% 1	1470
	11th to 20th	Day	65% 4 9% 12% 10% 1	1697
	21st to end	Day	65% 4 6% 16% 8% 2	1480
March	1st to 10th	Day	61% 4 7% 16% 11% 2	1800
	11th to 20th	Day	60% 4 8% 16% 11% 1	1845
	21st to end	Day	58% 5% 7% 16% 12% 2	2368
April	1st to 10th	Day	65% 3 9% 11% 9% 3	2160
	11th to 20th	Day	53% 4 9% 20% 12% 3	2182
	21st to end	Day	59% 3 8% 15% 13% 2	2340
May	1st to 10th	Day	54% 3 8% 18% 14% 3	2467
	11th to 20th	Day	51% 5% 9% 19% 14% 1	2482
	21st to end	Day	54% 6% 8% 17% 13% 2	2725
June	1st to 10th	Day	57% 6% 10% 17% 9% 2	2632
	11th to 20th	Day	51% 6% 12% 19% 10% 2	2700
	21st to end	Day	58% 6% 11% 14% 10%	2642
July	1st to 10th	Day	50% 7% 15% 21% 6%	2450
	11th to 20th	Day	51% 8% 14% 19% 7%	2445
	21st to end	Day	54% 9% 14% 18% 5%	2591
August	1st to 10th	Day	57% 8% 15% 17% 3	2492
	11th to 20th	Day	50% 8% 16% 20% 7%	2352
	21st to end	Day	52% 6% 13% 22% 7%	2414
September	1st to 10th	Day	47% 6% 15% 22% 9% 1	2160
	11th to 20th	Day	47% 4 16% 23% 9%	2043
	21st to end	Day	51% 6% 13% 22% 7%	1980
October	1st to 10th	Day	56% 4 12% 19% 8%	1916
	11th to 20th	Day	66% 5% 12% 16% 1	1685
	21st to end	Day	65% 5% 11% 14% 4 1	1782
November	1st to 10th	Day	61% 6% 10% 17% 6% 1	1671
	11th to 20th	Day	68% 4 9% 13% 5%	1639
	21st to end	Day	71% 6% 9% 11% 2	1444
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	73% 6% 6% 10% 4	2649
	11th to 20th	Night	66% 4 8% 14% 6% 1	2574
	21st to end	Night	58% 4 9% 17% 12%	2772
February	1st to 10th	Night	60% 5% 8% 17% 9% 1	2488
	11th to 20th	Night	65% 4 9% 13% 8% 1	2159
	21st to end	Night	60% 5% 7% 16% 12% 1	1776
March	1st to 10th	Night	62% 4 8% 16% 9% 1	2160
	11th to 20th	Night	59% 5% 8% 14% 13% 1	2114
	21st to end	Night	53% 5% 8% 20% 11% 3	1985
April	1st to 10th	Night	63% 4 7% 14% 11% 2	1800
	11th to 20th	Night	50% 7% 8% 22% 13% 2	1725
	21st to end	Night	54% 4 7% 20% 12% 2	1620
May	1st to 10th	Night	53% 4 9% 17% 14% 2	1508
	11th to 20th	Night	49% 5% 11% 20% 13% 2	1416
	21st to end	Night	50% 5% 10% 20% 13% 2	1551
June	1st to 10th	Night	52% 7% 12% 20% 9% 1	1324
	11th to 20th	Night	47% 5% 13% 20% 12% 3	1260
	21st to end	Night	53% 7% 12% 17% 11%	1312
July	1st to 10th	Night	45% 8% 18% 21% 8%	1400
	11th to 20th	Night	45% 6% 17% 23% 7% 1	1392
	21st to end	Night	46% 8% 16% 24% 7%	1486
August	1st to 10th	Night	42% 9% 20% 24% 5%	1422
	11th to 20th	Night	46% 8% 21% 20% 5%	1531
	21st to end	Night	45% 6% 16% 27% 7%	1939
September	1st to 10th	Night	44% 6% 15% 26% 9% 1	1800
	11th to 20th	Night	45% 6% 15% 27% 6%	1916
	21st to end	Night	46% 5% 13% 28% 8%	1980
October	1st to 10th	Night	50% 4 12% 22% 11% 1	2042
	11th to 20th	Night	59% 5% 13% 18% 5%	2274
	21st to end	Night	62% 5% 11% 15% 5% 1	2574
November	1st to 10th	Night	59% 5% 12% 17% 6% 1	2407
	11th to 20th	Night	60% 7% 9% 17% 7% 1	2540
	21st to end	Night	68% 5% 10% 14% 4	2733
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	27% 13% 42% 14% 4	166
	21st to end	Day	21% 15% 40% 16% 7% 1	176
February	1st to 10th	Day	24% 32% 34% 7% 1 1	174
	11th to 20th	Day	29% 27% 32% 10% 3	356
	21st to end	Day	26% 30% 29% 11% 5%	346
March	1st to 10th	Day	23% 25% 32% 15% 5%	420
	11th to 20th	Day	29% 21% 31% 14% 4 1	420
	21st to end	Day	28% 23% 28% 14% 5% 1	462
April	1st to 10th	Day	31% 19% 31% 14% 4 1	420
	11th to 20th	Day	34% 19% 25% 13% 5% 3	412
	21st to end	Day	32% 22% 30% 11% 4 1	420
May	1st to 10th	Day	33% 17% 31% 13% 6%	423
	11th to 20th	Day	26% 18% 32% 18% 5% 1	447
	21st to end	Day	28% 24% 26% 16% 5%	485
June	1st to 10th	Day	25% 18% 34% 17% 6%	562
	11th to 20th	Day	25% 17% 28% 19% 9% 1	630
	21st to end	Day	26% 13% 28% 23% 8% 1	572
July	1st to 10th	Day	19% 12% 38% 22% 8% 1	445
	11th to 20th	Day	19% 13% 36% 23% 7% 2	444
	21st to end	Day	21% 11% 31% 26% 10% 1	488
August	1st to 10th	Day	23% 10% 31% 24% 10% 2	446
	11th to 20th	Day	20% 8% 33% 24% 11% 4	439
	21st to end	Day	23% 15% 27% 17% 12% 5%	495
September	1st to 10th	Day	23% 14% 30% 18% 10% 4	450
	11th to 20th	Day	21% 15% 29% 20% 11% 3	450
	21st to end	Day	26% 16% 27% 14% 12% 5%	450
October	1st to 10th	Day	27% 19% 25% 17% 10% 2	450
	11th to 20th	Day	32% 22% 26% 10% 7% 3	392
	21st to end	Day	40% 16% 25% 15% 5%	396
November	1st to 10th	Day	34% 20% 27% 14% 4 1	365
	11th to 20th	Day	33% 19% 29% 15% 4	299
	21st to end	Day	32% 24% 30% 13% 1	180
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	26% 17% 34% 19% 5%	736
	21st to end	Night	18% 15% 35% 25% 6% 1	792
February	1st to 10th	Night	18% 21% 35% 20% 5%	720
	11th to 20th	Night	24% 19% 34% 18% 4	703
	21st to end	Night	23% 19% 33% 21% 4 1	592
March	1st to 10th	Night	24% 15% 37% 19% 5%	720
	11th to 20th	Night	27% 17% 33% 16% 6% 1	720
	21st to end	Night	23% 19% 30% 20% 7% 1	792
April	1st to 10th	Night	31% 15% 27% 22% 5% 1	720
	11th to 20th	Night	27% 15% 29% 23% 6% 1	661
	21st to end	Night	28% 20% 29% 17% 5%	540
May	1st to 10th	Night	28% 16% 28% 22% 6%	428
	11th to 20th	Night	24% 11% 31% 25% 8%	354
	21st to end	Night	26% 12% 32% 24% 5% 1	389
June	1st to 10th	Night	24% 10% 32% 28% 6%	360
	11th to 20th	Night	19% 11% 28% 33% 9%	360
	21st to end	Night	23% 8% 27% 32% 10% 1	360
July	1st to 10th	Night	17% 8% 31% 33% 12%	350
	11th to 20th	Night	18% 4 27% 34% 16% 1	348
	21st to end	Night	17% 6% 26% 37% 13% 1	394
August	1st to 10th	Night	16% 5% 24% 41% 14%	358
	11th to 20th	Night	17% 7% 27% 32% 15% 1	467
	21st to end	Night	22% 10% 25% 28% 14% 2	751
September	1st to 10th	Night	23% 8% 27% 32% 10% 1	720
	11th to 20th	Night	25% 6% 26% 27% 13% 2	720
	21st to end	Night	24% 12% 27% 24% 12% 1	720
October	1st to 10th	Night	24% 13% 26% 28% 8% 1	720
	11th to 20th	Night	33% 12% 26% 20% 8% 1	720
	21st to end	Night	35% 13% 28% 18% 6%	792
November	1st to 10th	Night	30% 15% 29% 20% 5% 1	740
	11th to 20th	Night	29% 16% 30% 16% 7% 2	760
	21st to end	Night	34% 17% 26% 19% 4	795
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 2024-01-11 13:32:00. Version ac07

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