Caledon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Caledon clear sky chart from 2005-11-06 to 2026-07-01.

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	14% 10% 4 9% 5% 5% 5% 4 6% 7% 32%	138698
	Night	13% 10% 4 9% 6% 5% 5% 4 6% 7% 33%	133621
Transparency	Day	49% 7% 13% 20% 11% 1	142294
	Night	48% 7% 13% 20% 12% 1	138116
Seeing	Day	20% 18% 32% 19% 8% 3	16874
	Night	19% 16% 32% 23% 9% 1	25906

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% 13% 5% 16% 6% 5% 5% 4 5% 5% 21%	4661
	11th to 20th	Day	9% 19% 8% 18% 9% 8% 5% 4 5% 5% 9%	5165
	21st to end	Day	14% 14% 6% 16% 8% 7% 6% 4 4 6% 15%	5780
February	1st to 10th	Day	12% 16% 5% 14% 8% 5% 5% 4 5% 4 21%	1890
	11th to 20th	Day	12% 13% 6% 14% 9% 5% 4 3 5% 6% 22%	1843
	21st to end	Day	16% 15% 5% 11% 6% 5% 4 4 5% 5% 25%	1623
March	1st to 10th	Day	17% 12% 5% 10% 6% 4 4 3 4 5% 30%	5041
	11th to 20th	Day	11% 13% 4 9% 6% 5% 4 4 6% 8% 30%	5090
	21st to end	Day	16% 12% 4 9% 5% 5% 4 3 4 5% 33%	5586
April	1st to 10th	Day	16% 13% 4 9% 6% 5% 4 4 4 6% 30%	2462
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 3 5% 6% 34%	2605
	21st to end	Day	19% 10% 3 8% 4 4 4 3 5% 6% 34%	2730
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 4 4 5% 7% 34%	7642
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 4 6% 7% 35%	8099
	21st to end	Day	17% 5% 2 6% 4 4 4 3 5% 7% 44%	9060
June	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 5% 6% 8% 39%	2940
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 8% 9% 40%	3007
	21st to end	Day	13% 6% 2 6% 6% 5% 5% 4 7% 8% 39%	3150
July	1st to 10th	Day	9% 5% 2 7% 5% 6% 6% 5% 7% 10% 38%	6664
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 5% 7% 9% 46%	6346
	21st to end	Day	8% 4 2 5% 4 4 6% 4 7% 9% 46%	6424
August	1st to 10th	Day	16% 7% 2 6% 4 5% 6% 4 7% 8% 36%	4234
	11th to 20th	Day	10% 7% 3 8% 6% 6% 6% 4 8% 10% 34%	4174
	21st to end	Day	9% 6% 2 7% 4 6% 6% 4 6% 9% 41%	4524
September	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 5% 6% 8% 40%	2400
	11th to 20th	Day	10% 6% 2 7% 4 4 4 3 6% 9% 45%	2253
	21st to end	Day	15% 7% 3 7% 6% 6% 5% 4 6% 8% 34%	2175
October	1st to 10th	Day	18% 9% 3 7% 4 5% 4 3 5% 7% 35%	2000
	11th to 20th	Day	18% 11% 3 9% 6% 5% 5% 4 6% 6% 28%	2000
	21st to end	Day	23% 13% 3 8% 5% 5% 5% 3 6% 6% 22%	2200
November	1st to 10th	Day	13% 13% 4 7% 5% 4 5% 5% 6% 6% 31%	1776
	11th to 20th	Day	12% 14% 4 10% 6% 5% 6% 4 6% 7% 25%	1680
	21st to end	Day	15% 15% 6% 11% 7% 5% 5% 4 6% 7% 19%	1680
December	1st to 10th	Day	17% 18% 6% 12% 6% 5% 6% 3 6% 7% 14%	2680
	11th to 20th	Day	20% 19% 4 10% 5% 4 4 4 5% 5% 19%	3066
	21st to end	Day	24% 18% 7% 14% 6% 4 4 2 4 4 12%	4048
January	1st to 10th	Night	13% 11% 5% 13% 6% 5% 5% 4 6% 7% 24%	8234
	11th to 20th	Night	9% 16% 7% 14% 12% 7% 6% 4 5% 6% 14%	7717
	21st to end	Night	11% 11% 6% 12% 8% 7% 6% 4 6% 7% 21%	8401
February	1st to 10th	Night	11% 15% 4 11% 7% 4 5% 4 6% 7% 26%	2730
	11th to 20th	Night	11% 11% 5% 12% 8% 6% 5% 4 5% 7% 26%	2663
	21st to end	Night	12% 12% 5% 11% 7% 5% 5% 4 6% 6% 28%	2181
March	1st to 10th	Night	14% 9% 4 9% 5% 5% 5% 4 6% 7% 31%	5018
	11th to 20th	Night	9% 8% 3 8% 5% 5% 6% 5% 7% 9% 36%	5089
	21st to end	Night	18% 8% 3 7% 4 4 4 3 5% 5% 39%	5588
April	1st to 10th	Night	17% 10% 4 8% 5% 5% 4 4 5% 7% 31%	2158
	11th to 20th	Night	14% 9% 2 6% 5% 5% 4 4 5% 6% 38%	1983
	21st to end	Night	14% 9% 3 7% 5% 4 4 4 6% 6% 37%	1890
May	1st to 10th	Night	18% 7% 2 6% 4 4 4 4 5% 6% 38%	5257
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 3 5% 7% 41%	4758
	21st to end	Night	17% 5% 2 5% 3 3 3 3 5% 7% 48%	5114
June	1st to 10th	Night	12% 4 2 5% 5% 4 5% 4 6% 8% 44%	1680
	11th to 20th	Night	8% 4 3 7% 4 4 5% 5% 7% 9% 44%	1603
	21st to end	Night	10% 6% 2 6% 4 4 3 4 6% 7% 48%	1470
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 6% 10% 49%	3290
	11th to 20th	Night	9% 3 2 5% 4 4 4 4 5% 8% 52%	3600
	21st to end	Night	8% 4 1 4 4 4 4 4 6% 8% 53%	4425
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 6% 49%	2915
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 5% 7% 49%	2875
	21st to end	Night	10% 5% 2 6% 4 4 4 3 5% 8% 49%	3340
September	1st to 10th	Night	8% 5% 2 6% 4 4 5% 3 7% 7% 49%	2000
	11th to 20th	Night	10% 4 2 4 4 2 3 4 6% 6% 56%	2143
	21st to end	Night	16% 7% 2 7% 4 4 4 3 4 6% 42%	2223
October	1st to 10th	Night	16% 7% 3 6% 5% 3 5% 3 6% 7% 40%	2400
	11th to 20th	Night	17% 10% 3 7% 6% 4 5% 4 5% 6% 35%	2400
	21st to end	Night	19% 9% 3 8% 6% 4 4 4 5% 7% 29%	2640
November	1st to 10th	Night	15% 8% 3 7% 5% 4 5% 5% 6% 6% 36%	2738
	11th to 20th	Night	14% 12% 4 7% 6% 5% 5% 5% 6% 8% 28%	2940
	21st to end	Night	16% 13% 4 8% 6% 5% 5% 4 6% 8% 24%	2940
December	1st to 10th	Night	16% 15% 6% 11% 6% 5% 6% 5% 6% 7% 17%	4720
	11th to 20th	Night	13% 20% 6% 12% 6% 5% 4 4 5% 6% 20%	5348
	21st to end	Night	22% 19% 7% 13% 5% 4 3 3 4 4 14%	7150

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	61% 8% 12% 12% 8%	4662
	11th to 20th	Day	74% 7% 8% 8% 4	5199
	21st to end	Day	67% 6% 11% 10% 6%	5780
February	1st to 10th	Day	63% 7% 10% 14% 5% 1	1890
	11th to 20th	Day	61% 7% 12% 14% 6% 1	1852
	21st to end	Day	60% 7% 11% 14% 7% 1	1623
March	1st to 10th	Day	55% 5% 14% 14% 11% 1	5044
	11th to 20th	Day	50% 6% 15% 19% 7% 3	5090
	21st to end	Day	53% 5% 10% 18% 13% 2	5586
April	1st to 10th	Day	55% 6% 10% 18% 10% 1	2462
	11th to 20th	Day	49% 6% 9% 21% 14% 1	2605
	21st to end	Day	51% 6% 11% 19% 11% 2	2730
May	1st to 10th	Day	47% 6% 13% 19% 11% 4	7651
	11th to 20th	Day	46% 8% 12% 19% 15% 1	8103
	21st to end	Day	40% 5% 10% 27% 16% 2	9061
June	1st to 10th	Day	40% 8% 12% 22% 16% 1	2940
	11th to 20th	Day	37% 9% 14% 24% 15% 1	3007
	21st to end	Day	40% 8% 15% 23% 14% 1	3150
July	1st to 10th	Day	37% 8% 16% 23% 15% 1	6594
	11th to 20th	Day	30% 8% 13% 33% 16% 1	6271
	21st to end	Day	32% 8% 14% 29% 16% 1	6240
August	1st to 10th	Day	43% 8% 14% 22% 12% 1	4221
	11th to 20th	Day	41% 9% 16% 24% 9%	4213
	21st to end	Day	36% 8% 14% 32% 9% 1	4524
September	1st to 10th	Day	40% 8% 14% 26% 11% 2	2400
	11th to 20th	Day	36% 6% 14% 30% 13%	2253
	21st to end	Day	47% 8% 12% 24% 9%	2175
October	1st to 10th	Day	40% 7% 13% 27% 13% 1	3260
	11th to 20th	Day	40% 7% 16% 22% 15%	3240
	21st to end	Day	54% 7% 13% 19% 6%	3538
November	1st to 10th	Day	49% 9% 14% 18% 9% 1	1776
	11th to 20th	Day	54% 9% 15% 14% 8%	1680
	21st to end	Day	62% 9% 14% 12% 3	1680
December	1st to 10th	Day	68% 8% 14% 8% 2	2680
	11th to 20th	Day	65% 7% 11% 9% 7%	3066
	21st to end	Day	75% 6% 6% 6% 6%	4048
January	1st to 10th	Night	56% 8% 14% 17% 5%	8234
	11th to 20th	Night	69% 8% 9% 10% 4 1	7758
	21st to end	Night	58% 7% 13% 11% 11% 1	8401
February	1st to 10th	Night	55% 8% 12% 19% 6% 1	2730
	11th to 20th	Night	57% 7% 12% 16% 8%	2665
	21st to end	Night	54% 7% 14% 17% 8%	2181
March	1st to 10th	Night	49% 8% 13% 17% 11% 2	5028
	11th to 20th	Night	41% 7% 19% 22% 10% 2	5090
	21st to end	Night	47% 5% 10% 19% 17% 2	5588
April	1st to 10th	Night	52% 6% 10% 18% 12% 1	2158
	11th to 20th	Night	46% 6% 10% 21% 15% 2	1983
	21st to end	Night	44% 7% 13% 19% 16% 2	1890
May	1st to 10th	Night	46% 6% 11% 18% 15% 5%	5264
	11th to 20th	Night	43% 7% 11% 22% 15% 2	4759
	21st to end	Night	37% 5% 11% 27% 18% 2	5115
June	1st to 10th	Night	36% 6% 14% 24% 19% 2	1680
	11th to 20th	Night	34% 7% 12% 25% 19% 1	1603
	21st to end	Night	35% 6% 14% 26% 17% 1	1470
July	1st to 10th	Night	30% 7% 16% 25% 19% 3	3253
	11th to 20th	Night	29% 6% 12% 32% 19% 1	3552
	21st to end	Night	28% 8% 12% 31% 19% 2	4295
August	1st to 10th	Night	34% 6% 14% 29% 15% 2	2904
	11th to 20th	Night	34% 6% 15% 32% 13% 1	2902
	21st to end	Night	33% 7% 14% 31% 14% 1	3340
September	1st to 10th	Night	31% 9% 16% 29% 15% 1	2000
	11th to 20th	Night	28% 6% 12% 34% 18%	2143
	21st to end	Night	43% 6% 13% 27% 10% 1	2223
October	1st to 10th	Night	32% 6% 10% 29% 23% 1	3920
	11th to 20th	Night	41% 6% 13% 25% 15%	3899
	21st to end	Night	42% 7% 17% 23% 10% 1	4252
November	1st to 10th	Night	44% 8% 14% 22% 11% 1	2738
	11th to 20th	Night	51% 9% 14% 17% 9% 1	2940
	21st to end	Night	56% 9% 18% 13% 3	2940
December	1st to 10th	Night	63% 9% 15% 10% 3	4720
	11th to 20th	Night	62% 8% 11% 11% 7%	5348
	21st to end	Night	72% 7% 10% 8% 4	7150

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	23% 30% 30% 14% 3	220
	11th to 20th	Day	25% 29% 30% 12% 3	316
	21st to end	Day	27% 29% 29% 12% 2	363
February	1st to 10th	Day	28% 31% 28% 11% 2	330
	11th to 20th	Day	27% 32% 34% 6% 1	330
	21st to end	Day	36% 30% 29% 5%	273
March	1st to 10th	Day	23% 24% 33% 16% 4	539
	11th to 20th	Day	25% 23% 35% 13% 4	540
	21st to end	Day	30% 22% 31% 12% 4	594
April	1st to 10th	Day	24% 26% 34% 11% 6%	540
	11th to 20th	Day	30% 21% 27% 14% 5% 2	532
	21st to end	Day	26% 21% 33% 14% 5% 1	540
May	1st to 10th	Day	23% 18% 33% 17% 7% 2	543
	11th to 20th	Day	18% 17% 33% 20% 9% 3	567
	21st to end	Day	15% 16% 33% 24% 9% 4	617
June	1st to 10th	Day	12% 18% 36% 24% 8% 2	570
	11th to 20th	Day	14% 16% 34% 24% 10% 2	637
	21st to end	Day	17% 11% 37% 26% 6% 3	780
July	1st to 10th	Day	10% 8% 35% 29% 14% 4	660
	11th to 20th	Day	12% 9% 30% 29% 15% 6%	524
	21st to end	Day	10% 7% 36% 29% 13% 5%	576
August	1st to 10th	Day	10% 9% 27% 31% 17% 7%	526
	11th to 20th	Day	9% 7% 30% 27% 19% 8%	519
	21st to end	Day	13% 10% 30% 27% 15% 6%	583
September	1st to 10th	Day	13% 12% 29% 23% 14% 9%	530
	11th to 20th	Day	8% 9% 26% 24% 21% 12%	530
	21st to end	Day	16% 14% 29% 21% 14% 5%	530
October	1st to 10th	Day	22% 16% 29% 18% 12% 4	530
	11th to 20th	Day	21% 22% 35% 14% 5% 2	530
	21st to end	Day	28% 25% 27% 16% 4	583
November	1st to 10th	Day	25% 27% 28% 16% 3 1	300
	11th to 20th	Day	24% 30% 30% 12% 5%	220
	21st to end	Day	25% 26% 38% 10% 1	220
December	1st to 10th	Day	32% 26% 29% 12% 1	220
	11th to 20th	Day	33% 28% 30% 9% 1	220
	21st to end	Day	31% 29% 29% 9% 2	242
January	1st to 10th	Night	21% 28% 34% 14% 3	840
	11th to 20th	Night	26% 24% 31% 17% 2	840
	21st to end	Night	18% 20% 38% 18% 6%	924
February	1st to 10th	Night	20% 26% 35% 17% 1	840
	11th to 20th	Night	22% 22% 38% 15% 3	823
	21st to end	Night	20% 26% 36% 16% 2	692
March	1st to 10th	Night	20% 23% 35% 19% 3	840
	11th to 20th	Night	21% 24% 32% 18% 5%	840
	21st to end	Night	21% 18% 36% 19% 6%	924
April	1st to 10th	Night	24% 19% 34% 20% 2	840
	11th to 20th	Night	19% 19% 35% 20% 7% 1	739
	21st to end	Night	20% 14% 33% 27% 7%	630
May	1st to 10th	Night	17% 11% 32% 29% 10% 2	630
	11th to 20th	Night	17% 9% 32% 31% 10% 1	457
	21st to end	Night	12% 9% 32% 31% 15%	455
June	1st to 10th	Night	14% 9% 34% 32% 12%	420
	11th to 20th	Night	10% 10% 32% 35% 12%	420
	21st to end	Night	12% 8% 29% 38% 13%	420
July	1st to 10th	Night	6% 5% 27% 43% 18% 1	390
	11th to 20th	Night	10% 6% 28% 36% 19% 1	388
	21st to end	Night	9% 3 29% 39% 19% 1	654
August	1st to 10th	Night	10% 2 23% 39% 25% 1	597
	11th to 20th	Night	8% 4 23% 40% 23% 3	594
	21st to end	Night	13% 5% 30% 27% 22% 2	725
September	1st to 10th	Night	10% 9% 27% 30% 19% 5%	800
	11th to 20th	Night	12% 7% 23% 29% 25% 5%	800
	21st to end	Night	18% 11% 22% 29% 16% 4	800
October	1st to 10th	Night	19% 10% 31% 23% 16% 2	800
	11th to 20th	Night	22% 18% 31% 21% 8% 1	800
	21st to end	Night	24% 19% 32% 21% 4	880
November	1st to 10th	Night	22% 18% 30% 22% 8% 1	820
	11th to 20th	Night	21% 24% 30% 20% 5% 1	840
	21st to end	Night	25% 20% 33% 18% 4	840
December	1st to 10th	Night	27% 22% 32% 15% 3	840
	11th to 20th	Night	23% 25% 35% 14% 2	840
	21st to end	Night	31% 21% 31% 15% 2	924

Page generated at 2026-06-28 02:10:43. Version ac07

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