Loon Call Observatory
Clear Sky Chart
History

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

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% 12% 4 9% 5% 4 4 3 5% 6% 31%	89206
	Night	16% 12% 4 9% 5% 4 4 3 5% 6% 30%	89304
Transparency	Day	53% 6% 10% 19% 11% 1	88925
	Night	53% 6% 11% 18% 10% 1	89138
Seeing	Day	24% 16% 31% 18% 8% 3	13812
	Night	23% 13% 31% 23% 9% 1	23155

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	15% 21% 6% 14% 6% 3 3 2 3 3 23%	2517
	11th to 20th	Day	12% 18% 9% 17% 7% 6% 5% 3 3 4 15%	2520
	21st to end	Day	20% 20% 7% 15% 5% 4 3 2 3 3 17%	3105
February	1st to 10th	Day	13% 17% 5% 15% 7% 5% 4 4 5% 4 20%	1710
	11th to 20th	Day	13% 16% 6% 13% 6% 4 4 3 4 5% 27%	1663
	21st to end	Day	17% 17% 5% 9% 6% 5% 4 3 4 5% 24%	1491
March	1st to 10th	Day	19% 15% 4 9% 5% 4 4 2 4 6% 27%	3326
	11th to 20th	Day	11% 18% 6% 10% 5% 5% 4 3 5% 6% 27%	3480
	21st to end	Day	13% 10% 3 7% 4 3 3 3 4 5% 44%	3892
April	1st to 10th	Day	20% 15% 4 7% 5% 4 4 3 4 5% 29%	2280
	11th to 20th	Day	22% 11% 2 6% 5% 4 3 2 4 5% 36%	2254
	21st to end	Day	22% 11% 3 8% 5% 4 4 3 4 5% 32%	2469
May	1st to 10th	Day	20% 8% 3 7% 5% 5% 4 3 5% 6% 33%	4319
	11th to 20th	Day	17% 10% 3 8% 4 5% 4 4 5% 8% 31%	4398
	21st to end	Day	15% 7% 3 6% 4 4 4 4 5% 7% 41%	4797
June	1st to 10th	Day	21% 9% 2 7% 5% 5% 4 3 5% 7% 31%	2548
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 4 6% 9% 36%	2520
	21st to end	Day	17% 8% 2 6% 5% 5% 5% 4 6% 8% 35%	2520
July	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 3 7% 8% 40%	2520
	11th to 20th	Day	12% 7% 2 7% 5% 5% 5% 5% 6% 9% 38%	2520
	21st to end	Day	12% 7% 2 7% 5% 5% 6% 5% 7% 10% 34%	2740
August	1st to 10th	Day	12% 6% 3 8% 6% 5% 5% 5% 7% 9% 35%	2327
	11th to 20th	Day	13% 7% 3 7% 5% 5% 6% 4 6% 8% 36%	2303
	21st to end	Day	14% 7% 2 7% 4 5% 5% 4 7% 8% 36%	2426
September	1st to 10th	Day	15% 7% 3 6% 5% 4 4 4 6% 8% 38%	2160
	11th to 20th	Day	13% 6% 2 7% 5% 4 3 4 5% 7% 45%	2160
	21st to end	Day	17% 6% 2 7% 5% 5% 4 4 6% 7% 36%	1877
October	1st to 10th	Day	22% 9% 3 7% 5% 4 4 3 4 7% 33%	1800
	11th to 20th	Day	25% 11% 2 9% 6% 4 4 3 6% 6% 24%	1800
	21st to end	Day	28% 13% 3 8% 5% 4 4 3 3 6% 22%	1940
November	1st to 10th	Day	17% 10% 4 7% 5% 4 5% 3 5% 7% 32%	1586
	11th to 20th	Day	17% 15% 4 9% 6% 4 4 4 6% 6% 26%	1520
	21st to end	Day	21% 17% 7% 10% 5% 4 5% 3 5% 4 19%	1520
December	1st to 10th	Day	20% 22% 7% 11% 6% 5% 4 3 4 5% 15%	1520
	11th to 20th	Day	17% 19% 5% 11% 5% 4 3 4 4 5% 25%	1906
	21st to end	Day	25% 22% 5% 12% 5% 3 2 2 3 4 17%	2772
January	1st to 10th	Night	18% 18% 9% 13% 5% 4 4 3 4 5% 17%	4429
	11th to 20th	Night	13% 15% 6% 15% 10% 6% 6% 4 4 5% 15%	4440
	21st to end	Night	18% 16% 8% 12% 6% 6% 5% 3 5% 5% 17%	4550
February	1st to 10th	Night	12% 17% 5% 11% 7% 5% 5% 4 6% 7% 21%	2470
	11th to 20th	Night	12% 15% 6% 10% 6% 5% 5% 3 5% 4 29%	2403
	21st to end	Night	14% 16% 4 9% 6% 4 4 4 5% 7% 27%	1962
March	1st to 10th	Night	18% 13% 4 10% 5% 4 3 3 4 5% 30%	3513
	11th to 20th	Night	13% 17% 6% 10% 5% 4 4 3 5% 6% 27%	3479
	21st to end	Night	15% 8% 3 8% 5% 4 4 4 5% 7% 37%	3739
April	1st to 10th	Night	19% 12% 3 8% 5% 3 4 3 4 6% 32%	1900
	11th to 20th	Night	18% 9% 3 8% 5% 3 4 3 4 6% 37%	1875
	21st to end	Night	19% 9% 3 7% 5% 5% 5% 4 6% 6% 32%	1727
May	1st to 10th	Night	20% 8% 2 6% 5% 4 5% 3 5% 7% 35%	2620
	11th to 20th	Night	17% 8% 2 6% 5% 4 4 4 5% 7% 35%	2495
	21st to end	Night	12% 7% 2 6% 5% 5% 4 3 5% 7% 45%	2732
June	1st to 10th	Night	16% 7% 3 8% 4 4 5% 5% 6% 7% 37%	1462
	11th to 20th	Night	12% 6% 2 4 5% 5% 4 4 6% 8% 43%	1440
	21st to end	Night	14% 7% 2 6% 6% 5% 5% 3 5% 8% 38%	1440
July	1st to 10th	Night	7% 6% 1 7% 5% 4 6% 4 5% 7% 48%	1440
	11th to 20th	Night	12% 6% 3 5% 5% 4 4 4 6% 8% 46%	1440
	21st to end	Night	10% 6% 1 5% 4 4 3 5% 6% 9% 47%	1575
August	1st to 10th	Night	9% 5% 2 6% 3 4 5% 5% 7% 8% 46%	1611
	11th to 20th	Night	9% 6% 3 5% 4 4 6% 4 5% 8% 46%	1598
	21st to end	Night	11% 6% 2 6% 4 5% 4 3 6% 9% 44%	1912
September	1st to 10th	Night	11% 6% 2 6% 4 4 3 4 6% 9% 45%	1800
	11th to 20th	Night	13% 4 2 5% 3 4 4 4 5% 7% 49%	1800
	21st to end	Night	19% 6% 2 6% 4 3 4 3 5% 5% 42%	2077
October	1st to 10th	Night	19% 7% 3 7% 4 4 4 3 5% 7% 36%	2160
	11th to 20th	Night	22% 11% 3 8% 6% 4 5% 3 5% 5% 29%	2160
	21st to end	Night	22% 13% 3 7% 5% 5% 4 4 6% 6% 24%	2416
November	1st to 10th	Night	18% 11% 3 7% 5% 4 4 3 5% 6% 34%	2487
	11th to 20th	Night	18% 13% 4 9% 5% 4 4 3 5% 6% 29%	2660
	21st to end	Night	19% 15% 4 9% 6% 5% 4 4 5% 6% 21%	2660
December	1st to 10th	Night	20% 20% 6% 10% 6% 4 4 4 5% 6% 16%	2660
	11th to 20th	Night	17% 19% 5% 12% 5% 4 3 2 3 5% 24%	3288
	21st to end	Night	27% 19% 6% 12% 5% 4 3 3 3 4 14%	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	66% 5% 10% 11% 7% 1	2518
	11th to 20th	Day	71% 6% 9% 8% 6% 1	2520
	21st to end	Day	72% 4 7% 10% 6% 1	3105
February	1st to 10th	Day	65% 6% 9% 14% 5% 1	1710
	11th to 20th	Day	60% 5% 9% 13% 11% 1	1672
	21st to end	Day	62% 5% 9% 12% 11% 1	1491
March	1st to 10th	Day	58% 4 13% 13% 11% 1	3329
	11th to 20th	Day	56% 5% 12% 16% 9% 2	3480
	21st to end	Day	42% 5% 8% 24% 17% 4	3892
April	1st to 10th	Day	57% 4 7% 18% 11% 3	2280
	11th to 20th	Day	51% 4 7% 21% 15% 1	2254
	21st to end	Day	55% 5% 7% 18% 12% 3	2469
May	1st to 10th	Day	49% 5% 9% 23% 11% 2	4332
	11th to 20th	Day	49% 8% 10% 21% 10% 1	4402
	21st to end	Day	41% 7% 13% 21% 15% 3	4797
June	1st to 10th	Day	52% 6% 10% 19% 13% 1	2548
	11th to 20th	Day	44% 8% 10% 23% 13% 2	2520
	21st to end	Day	45% 8% 14% 20% 12% 1	2520
July	1st to 10th	Day	39% 7% 11% 26% 15% 2	2450
	11th to 20th	Day	41% 9% 13% 27% 10%	2445
	21st to end	Day	43% 10% 13% 24% 10% 1	2587
August	1st to 10th	Day	44% 9% 13% 23% 11% 1	2314
	11th to 20th	Day	45% 8% 14% 24% 9% 1	2303
	21st to end	Day	43% 7% 12% 26% 11% 1	2426
September	1st to 10th	Day	42% 7% 12% 27% 12% 1	2160
	11th to 20th	Day	38% 7% 11% 29% 15% 1	2160
	21st to end	Day	46% 7% 12% 24% 10%	1877
October	1st to 10th	Day	52% 5% 11% 19% 12% 1	1800
	11th to 20th	Day	59% 8% 11% 15% 7% 1	1800
	21st to end	Day	65% 5% 8% 14% 7%	1940
November	1st to 10th	Day	51% 6% 14% 20% 8% 1	1586
	11th to 20th	Day	57% 6% 12% 14% 9% 2	1520
	21st to end	Day	67% 6% 9% 10% 7% 1	1520
December	1st to 10th	Day	73% 5% 8% 9% 5%	1520
	11th to 20th	Day	63% 8% 10% 11% 9%	1906
	21st to end	Day	73% 3 6% 13% 5%	2772
January	1st to 10th	Night	69% 5% 9% 12% 5%	4429
	11th to 20th	Night	68% 8% 9% 9% 5% 1	4440
	21st to end	Night	68% 6% 10% 9% 7%	4550
February	1st to 10th	Night	62% 5% 11% 14% 7% 1	2470
	11th to 20th	Night	57% 4 11% 18% 9%	2405
	21st to end	Night	55% 6% 10% 18% 10% 1	1962
March	1st to 10th	Night	56% 4 9% 19% 10% 1	3523
	11th to 20th	Night	56% 6% 14% 16% 7% 1	3480
	21st to end	Night	43% 6% 12% 21% 16% 2	3739
April	1st to 10th	Night	54% 4 7% 20% 13% 2	1900
	11th to 20th	Night	48% 6% 8% 22% 15% 2	1875
	21st to end	Night	50% 7% 10% 16% 16% 2	1727
May	1st to 10th	Night	47% 6% 11% 19% 14% 2	2626
	11th to 20th	Night	44% 9% 12% 22% 11% 2	2496
	21st to end	Night	38% 7% 11% 23% 19% 2	2733
June	1st to 10th	Night	44% 8% 12% 22% 13% 1	1462
	11th to 20th	Night	38% 7% 11% 24% 19% 2	1440
	21st to end	Night	42% 8% 14% 23% 12% 2	1440
July	1st to 10th	Night	32% 9% 12% 26% 19% 3	1400
	11th to 20th	Night	36% 7% 12% 31% 13%	1392
	21st to end	Night	31% 9% 16% 31% 12% 1	1487
August	1st to 10th	Night	34% 8% 17% 28% 13% 1	1600
	11th to 20th	Night	35% 9% 16% 26% 13% 1	1598
	21st to end	Night	37% 8% 12% 29% 13% 1	1912
September	1st to 10th	Night	36% 9% 16% 25% 14% 1	1800
	11th to 20th	Night	33% 6% 16% 32% 12% 1	1800
	21st to end	Night	43% 7% 10% 29% 11%	2077
October	1st to 10th	Night	48% 7% 10% 21% 14% 1	2160
	11th to 20th	Night	55% 6% 12% 19% 7%	2160
	21st to end	Night	59% 7% 10% 13% 10%	2416
November	1st to 10th	Night	49% 6% 13% 22% 10%	2487
	11th to 20th	Night	54% 7% 12% 17% 9% 1	2660
	21st to end	Night	61% 6% 13% 14% 5%	2660
December	1st to 10th	Night	68% 7% 9% 12% 4	2660
	11th to 20th	Night	65% 4 9% 14% 7% 1	3288
	21st to end	Night	75% 5% 6% 10% 4	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	24% 23% 29% 18% 4 1	180
	11th to 20th	Day	31% 18% 33% 15% 3 1	180
	21st to end	Day	30% 18% 34% 15% 3	294
February	1st to 10th	Day	31% 23% 34% 9% 2	270
	11th to 20th	Day	31% 27% 36% 6% 1	270
	21st to end	Day	36% 19% 34% 10% 1	303
March	1st to 10th	Day	25% 20% 37% 15% 3	460
	11th to 20th	Day	27% 19% 35% 14% 4 1	460
	21st to end	Day	33% 19% 29% 13% 5% 1	506
April	1st to 10th	Day	28% 20% 34% 12% 6%	460
	11th to 20th	Day	34% 21% 23% 12% 8% 2	452
	21st to end	Day	30% 20% 30% 14% 5% 1	460
May	1st to 10th	Day	28% 15% 30% 18% 5% 5%	463
	11th to 20th	Day	23% 15% 34% 18% 7% 3	487
	21st to end	Day	19% 17% 32% 19% 10% 3	529
June	1st to 10th	Day	23% 13% 34% 21% 8% 1	458
	11th to 20th	Day	19% 12% 34% 22% 10% 2	450
	21st to end	Day	23% 10% 34% 20% 10% 2	450
July	1st to 10th	Day	13% 9% 31% 29% 15% 3	445
	11th to 20th	Day	14% 14% 30% 23% 16% 4	444
	21st to end	Day	14% 12% 33% 27% 11% 3	488
August	1st to 10th	Day	14% 8% 31% 29% 13% 5%	446
	11th to 20th	Day	14% 7% 26% 33% 14% 7%	439
	21st to end	Day	16% 11% 31% 22% 13% 7%	495
September	1st to 10th	Day	15% 11% 33% 20% 14% 7%	450
	11th to 20th	Day	12% 13% 28% 19% 18% 9%	450
	21st to end	Day	19% 14% 25% 23% 12% 6%	450
October	1st to 10th	Day	28% 14% 23% 18% 13% 3	450
	11th to 20th	Day	29% 21% 29% 14% 5% 2	450
	21st to end	Day	35% 18% 27% 16% 3 1	475
November	1st to 10th	Day	28% 16% 31% 18% 7%	280
	11th to 20th	Day	32% 22% 30% 11% 4 2	180
	21st to end	Day	30% 21% 37% 8% 4 1	180
December	1st to 10th	Day	31% 22% 29% 16% 2	180
	11th to 20th	Day	36% 24% 26% 11% 2 1	180
	21st to end	Day	36% 21% 28% 12% 3 1	198
January	1st to 10th	Night	29% 19% 30% 17% 4	760
	11th to 20th	Night	30% 16% 30% 19% 5%	760
	21st to end	Night	21% 16% 34% 23% 6% 1	836
February	1st to 10th	Night	24% 20% 34% 20% 2	760
	11th to 20th	Night	23% 19% 37% 18% 3	743
	21st to end	Night	25% 20% 34% 18% 4	628
March	1st to 10th	Night	25% 18% 35% 19% 4	760
	11th to 20th	Night	24% 19% 31% 20% 5% 1	760
	21st to end	Night	22% 15% 34% 21% 8% 1	836
April	1st to 10th	Night	26% 14% 32% 22% 5%	760
	11th to 20th	Night	25% 18% 29% 19% 8% 1	751
	21st to end	Night	24% 11% 31% 23% 11%	587
May	1st to 10th	Night	23% 10% 28% 26% 12% 1	447
	11th to 20th	Night	16% 12% 32% 30% 9%	374
	21st to end	Night	14% 8% 36% 29% 13% 1	411
June	1st to 10th	Night	18% 8% 33% 30% 11%	366
	11th to 20th	Night	14% 12% 28% 33% 12% 1	360
	21st to end	Night	16% 8% 28% 36% 12%	360
July	1st to 10th	Night	7% 6% 31% 41% 15% 1	350
	11th to 20th	Night	11% 5% 30% 36% 16% 1	348
	21st to end	Night	12% 4 31% 38% 14% 1	395
August	1st to 10th	Night	12% 4 23% 34% 25% 2	537
	11th to 20th	Night	12% 4 21% 34% 25% 4	534
	21st to end	Night	13% 6% 29% 30% 19% 3	724
September	1st to 10th	Night	13% 8% 31% 28% 17% 3	720
	11th to 20th	Night	14% 6% 27% 29% 21% 4	720
	21st to end	Night	22% 10% 22% 25% 17% 4	720
October	1st to 10th	Night	23% 11% 29% 22% 14% 2	720
	11th to 20th	Night	28% 14% 29% 20% 8% 1	720
	21st to end	Night	31% 15% 29% 20% 5%	792
November	1st to 10th	Night	24% 12% 31% 24% 9% 1	740
	11th to 20th	Night	26% 17% 32% 17% 8% 1	760
	21st to end	Night	30% 16% 28% 20% 5% 1	760
December	1st to 10th	Night	31% 19% 31% 15% 4	760
	11th to 20th	Night	27% 19% 33% 16% 3 1	760
	21st to end	Night	34% 14% 32% 16% 2	836

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