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 2025-02-25.

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	14% 10% 4 9% 6% 5% 5% 4 6% 7% 31%	109253
	Night	14% 10% 4 9% 6% 5% 5% 4 5% 7% 33%	109380
Transparency	Day	49% 8% 13% 19% 10% 1	112892
	Night	48% 7% 13% 20% 11% 1	113907
Seeing	Day	19% 18% 31% 19% 9% 3	15066
	Night	19% 16% 32% 23% 9% 1	24273

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	11% 12% 5% 17% 6% 5% 5% 4 5% 6% 23%	3597
	11th to 20th	Day	10% 18% 7% 19% 9% 7% 5% 4 5% 5% 11%	3959
	21st to end	Day	16% 16% 7% 16% 6% 5% 5% 4 4 5% 16%	4466
February	1st to 10th	Day	12% 16% 5% 14% 9% 5% 5% 4 5% 4 21%	1800
	11th to 20th	Day	12% 13% 6% 14% 9% 5% 4 3 6% 7% 22%	1753
	21st to end	Day	16% 15% 5% 11% 6% 5% 4 4 5% 5% 25%	1509
March	1st to 10th	Day	17% 13% 6% 9% 6% 4 4 3 4 4 29%	3431
	11th to 20th	Day	11% 15% 4 10% 7% 5% 4 4 5% 6% 28%	3480
	21st to end	Day	14% 10% 3 8% 6% 5% 4 4 5% 5% 35%	3815
April	1st to 10th	Day	15% 13% 4 8% 6% 5% 4 4 4 7% 30%	2228
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 3 5% 6% 35%	2354
	21st to end	Day	19% 10% 3 8% 4 4 4 3 5% 6% 33%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 4 4 4 5% 8% 35%	4108
	11th to 20th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	4330
	21st to end	Day	11% 5% 2 6% 4 4 4 4 5% 8% 46%	4837
June	1st to 10th	Day	13% 7% 3 6% 5% 4 5% 5% 6% 8% 37%	2660
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	2721
	21st to end	Day	13% 5% 2 6% 6% 5% 5% 4 8% 8% 38%	2850
July	1st to 10th	Day	10% 4 2 6% 5% 5% 6% 5% 7% 10% 38%	4646
	11th to 20th	Day	9% 5% 2 5% 4 5% 6% 5% 7% 9% 44%	4426
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 9% 41%	4466
August	1st to 10th	Day	16% 7% 2 6% 4 5% 6% 4 7% 8% 36%	4104
	11th to 20th	Day	9% 7% 3 8% 6% 6% 6% 4 8% 9% 33%	4044
	21st to end	Day	9% 6% 2 7% 4 6% 6% 4 6% 9% 41%	4386
September	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 5% 6% 8% 39%	2280
	11th to 20th	Day	11% 7% 2 7% 4 4 4 3 6% 9% 43%	2141
	21st to end	Day	15% 7% 3 7% 6% 6% 5% 4 6% 8% 33%	2066
October	1st to 10th	Day	18% 9% 3 7% 5% 5% 5% 4 5% 7% 33%	1900
	11th to 20th	Day	18% 11% 3 9% 6% 5% 5% 4 6% 6% 28%	1900
	21st to end	Day	24% 14% 3 8% 5% 5% 5% 3 5% 6% 21%	2090
November	1st to 10th	Day	12% 13% 4 7% 5% 4 5% 5% 6% 6% 31%	1690
	11th to 20th	Day	13% 13% 4 10% 6% 5% 6% 5% 6% 7% 25%	1600
	21st to end	Day	15% 15% 6% 11% 7% 5% 5% 4 6% 7% 19%	1600
December	1st to 10th	Day	17% 18% 6% 12% 7% 5% 6% 3 6% 7% 14%	2600
	11th to 20th	Day	20% 19% 4 10% 5% 4 4 4 5% 5% 19%	2986
	21st to end	Day	24% 19% 7% 14% 6% 4 4 2 4 4 12%	3960
January	1st to 10th	Night	13% 10% 5% 13% 6% 5% 5% 4 6% 7% 25%	6349
	11th to 20th	Night	11% 13% 6% 15% 11% 7% 6% 4 5% 6% 14%	5923
	21st to end	Night	14% 12% 6% 12% 7% 6% 6% 4 5% 7% 20%	6490
February	1st to 10th	Night	12% 15% 4 11% 7% 4 5% 4 6% 7% 25%	2600
	11th to 20th	Night	11% 11% 5% 11% 8% 6% 5% 4 5% 7% 25%	2533
	21st to end	Night	12% 12% 5% 11% 6% 5% 5% 4 6% 6% 28%	2038
March	1st to 10th	Night	16% 9% 4 10% 6% 5% 4 4 5% 7% 30%	3408
	11th to 20th	Night	11% 10% 4 8% 5% 5% 5% 4 6% 7% 37%	3479
	21st to end	Night	15% 7% 2 6% 5% 4 4 3 4 5% 43%	3817
April	1st to 10th	Night	17% 11% 3 8% 5% 5% 4 4 5% 7% 32%	1952
	11th to 20th	Night	15% 9% 2 6% 5% 5% 4 4 5% 6% 38%	1792
	21st to end	Night	14% 9% 3 7% 5% 5% 4 4 6% 6% 36%	1710
May	1st to 10th	Night	16% 8% 2 7% 4 4 4 4 5% 6% 40%	2833
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 4 5% 8% 38%	2560
	21st to end	Night	9% 4 2 5% 3 3 3 4 6% 9% 52%	2738
June	1st to 10th	Night	12% 5% 2 5% 6% 4 5% 4 6% 8% 42%	1520
	11th to 20th	Night	8% 4 3 7% 4 4 5% 5% 7% 9% 44%	1451
	21st to end	Night	11% 6% 2 6% 4 4 3 4 6% 7% 48%	1330
July	1st to 10th	Night	6% 4 2 5% 3 4 4 4 6% 9% 53%	2301
	11th to 20th	Night	10% 3 2 5% 4 4 4 4 5% 8% 53%	2520
	21st to end	Night	7% 4 1 4 4 4 5% 4 7% 8% 52%	3084
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 6% 6% 49%	2825
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 5% 7% 49%	2785
	21st to end	Night	11% 5% 2 6% 4 4 4 3 5% 8% 49%	3238
September	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 3 7% 7% 49%	1900
	11th to 20th	Night	10% 4 2 4 4 2 3 4 6% 6% 54%	2036
	21st to end	Night	15% 7% 2 7% 4 4 4 3 4 6% 42%	2112
October	1st to 10th	Night	16% 7% 3 6% 5% 4 5% 3 6% 7% 38%	2280
	11th to 20th	Night	17% 10% 3 7% 6% 5% 5% 4 5% 6% 35%	2280
	21st to end	Night	19% 9% 3 8% 7% 4 4 4 5% 7% 28%	2508
November	1st to 10th	Night	15% 8% 3 7% 5% 4 5% 5% 6% 6% 37%	2604
	11th to 20th	Night	14% 12% 4 7% 6% 5% 5% 5% 6% 8% 27%	2800
	21st to end	Night	16% 13% 4 8% 6% 5% 4 4 7% 8% 25%	2800
December	1st to 10th	Night	16% 15% 6% 11% 6% 5% 6% 5% 7% 7% 16%	4580
	11th to 20th	Night	13% 20% 6% 12% 6% 5% 4 4 5% 6% 19%	5208
	21st to end	Night	22% 19% 7% 13% 5% 4 3 3 4 4 14%	6996

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	59% 7% 12% 14% 8%	3598
	11th to 20th	Day	72% 7% 10% 8% 4	3993
	21st to end	Day	69% 6% 11% 8% 5%	4466
February	1st to 10th	Day	65% 8% 10% 13% 4 1	1800
	11th to 20th	Day	60% 7% 12% 13% 6% 1	1762
	21st to end	Day	60% 7% 11% 14% 7% 1	1509
March	1st to 10th	Day	56% 7% 12% 17% 8% 1	3434
	11th to 20th	Day	54% 7% 11% 19% 8% 1	3480
	21st to end	Day	48% 6% 12% 18% 14% 2	3815
April	1st to 10th	Day	54% 6% 11% 18% 10% 1	2228
	11th to 20th	Day	48% 6% 9% 21% 15% 1	2354
	21st to end	Day	51% 6% 11% 18% 12% 2	2470
May	1st to 10th	Day	46% 7% 12% 21% 13% 2	4120
	11th to 20th	Day	48% 9% 14% 20% 8% 1	4334
	21st to end	Day	35% 7% 14% 22% 18% 4	4837
June	1st to 10th	Day	42% 9% 13% 22% 14% 1	2660
	11th to 20th	Day	37% 9% 14% 24% 16% 1	2721
	21st to end	Day	41% 8% 14% 23% 14%	2850
July	1st to 10th	Day	37% 8% 17% 22% 15% 1	4575
	11th to 20th	Day	32% 8% 14% 35% 11% 1	4351
	21st to end	Day	36% 9% 14% 22% 17% 1	4324
August	1st to 10th	Day	43% 8% 14% 22% 12% 1	4091
	11th to 20th	Day	42% 9% 17% 23% 9%	4083
	21st to end	Day	36% 8% 14% 31% 10% 1	4386
September	1st to 10th	Day	41% 8% 14% 25% 11% 2	2280
	11th to 20th	Day	37% 6% 14% 29% 14%	2141
	21st to end	Day	47% 8% 12% 24% 9%	2066
October	1st to 10th	Day	41% 8% 13% 26% 13% 1	3160
	11th to 20th	Day	40% 7% 16% 23% 15%	3140
	21st to end	Day	55% 7% 13% 18% 6%	3428
November	1st to 10th	Day	49% 9% 15% 18% 9% 1	1690
	11th to 20th	Day	55% 9% 15% 14% 8%	1600
	21st to end	Day	62% 10% 14% 12% 3	1600
December	1st to 10th	Day	68% 8% 14% 8% 2	2600
	11th to 20th	Day	66% 7% 11% 9% 7%	2986
	21st to end	Day	75% 6% 6% 6% 6%	3960
January	1st to 10th	Night	55% 9% 14% 18% 5%	6349
	11th to 20th	Night	68% 8% 9% 10% 4	5964
	21st to end	Night	59% 7% 14% 10% 9% 1	6490
February	1st to 10th	Night	56% 8% 12% 18% 6%	2600
	11th to 20th	Night	57% 7% 12% 16% 8%	2535
	21st to end	Night	54% 7% 14% 17% 8%	2038
March	1st to 10th	Night	51% 9% 12% 21% 7% 1	3418
	11th to 20th	Night	43% 7% 15% 22% 11% 2	3480
	21st to end	Night	42% 6% 11% 22% 18% 2	3817
April	1st to 10th	Night	52% 6% 10% 18% 13% 1	1952
	11th to 20th	Night	45% 6% 11% 20% 16% 2	1792
	21st to end	Night	46% 6% 13% 18% 16% 2	1710
May	1st to 10th	Night	43% 7% 12% 19% 16% 4	2840
	11th to 20th	Night	43% 9% 13% 22% 11% 2	2561
	21st to end	Night	29% 8% 14% 24% 22% 3	2739
June	1st to 10th	Night	37% 7% 14% 23% 17% 2	1520
	11th to 20th	Night	34% 7% 12% 24% 20% 1	1451
	21st to end	Night	35% 7% 14% 26% 18% 1	1330
July	1st to 10th	Night	28% 7% 16% 25% 21% 4	2264
	11th to 20th	Night	29% 6% 12% 35% 17% 1	2472
	21st to end	Night	29% 10% 15% 30% 16% 2	2986
August	1st to 10th	Night	34% 7% 13% 29% 15% 2	2814
	11th to 20th	Night	33% 6% 15% 31% 13% 1	2812
	21st to end	Night	33% 7% 13% 31% 15% 1	3238
September	1st to 10th	Night	31% 9% 16% 28% 15% 1	1900
	11th to 20th	Night	29% 6% 12% 33% 19%	2036
	21st to end	Night	43% 7% 13% 27% 10% 1	2112
October	1st to 10th	Night	33% 6% 10% 28% 23% 1	3800
	11th to 20th	Night	41% 6% 13% 25% 14%	3779
	21st to end	Night	42% 7% 17% 23% 10%	4120
November	1st to 10th	Night	44% 8% 14% 22% 11% 1	2604
	11th to 20th	Night	51% 9% 14% 16% 8% 1	2800
	21st to end	Night	55% 9% 19% 13% 3	2800
December	1st to 10th	Night	63% 9% 15% 10% 3	4580
	11th to 20th	Night	63% 8% 11% 11% 7%	5208
	21st to end	Night	72% 7% 10% 8% 4	6996

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	22% 29% 31% 16% 4 1	200
	11th to 20th	Day	24% 29% 30% 13% 3	287
	21st to end	Day	26% 30% 30% 12% 2	330
February	1st to 10th	Day	28% 33% 27% 9% 2	300
	11th to 20th	Day	27% 34% 33% 6% 1	300
	21st to end	Day	36% 32% 27% 5%	237
March	1st to 10th	Day	22% 24% 33% 17% 4	459
	11th to 20th	Day	21% 24% 37% 13% 4	460
	21st to end	Day	28% 21% 33% 13% 5%	506
April	1st to 10th	Day	22% 26% 34% 12% 6%	460
	11th to 20th	Day	31% 21% 27% 13% 6% 3	452
	21st to end	Day	25% 21% 33% 14% 5% 2	460
May	1st to 10th	Day	22% 17% 32% 19% 8% 3	463
	11th to 20th	Day	17% 16% 31% 22% 10% 3	487
	21st to end	Day	13% 14% 32% 26% 10% 5%	529
June	1st to 10th	Day	13% 18% 35% 25% 7% 2	490
	11th to 20th	Day	13% 16% 32% 25% 11% 2	551
	21st to end	Day	16% 12% 37% 26% 6% 3	680
July	1st to 10th	Day	10% 8% 34% 29% 15% 4	612
	11th to 20th	Day	12% 8% 30% 28% 15% 6%	484
	21st to end	Day	11% 7% 35% 29% 13% 5%	532
August	1st to 10th	Day	11% 9% 28% 29% 16% 7%	486
	11th to 20th	Day	9% 7% 31% 26% 19% 8%	479
	21st to end	Day	12% 10% 31% 25% 16% 6%	539
September	1st to 10th	Day	13% 11% 30% 24% 14% 8%	490
	11th to 20th	Day	9% 10% 26% 23% 21% 12%	490
	21st to end	Day	16% 15% 30% 20% 14% 5%	490
October	1st to 10th	Day	23% 17% 29% 16% 11% 4	490
	11th to 20th	Day	21% 23% 34% 14% 6% 2	490
	21st to end	Day	29% 24% 27% 16% 4	539
November	1st to 10th	Day	22% 28% 28% 18% 4 1	274
	11th to 20th	Day	23% 30% 30% 13% 5% 1	200
	21st to end	Day	24% 27% 38% 11% 1	200
December	1st to 10th	Day	32% 28% 29% 11% 1	200
	11th to 20th	Day	32% 30% 29% 9% 1	200
	21st to end	Day	30% 29% 30% 9% 2	220
January	1st to 10th	Night	22% 28% 34% 13% 4	800
	11th to 20th	Night	25% 23% 32% 18% 2	800
	21st to end	Night	19% 19% 38% 18% 6%	880
February	1st to 10th	Night	21% 27% 35% 16% 1	800
	11th to 20th	Night	22% 23% 38% 14% 3	783
	21st to end	Night	20% 26% 36% 16% 2	647
March	1st to 10th	Night	20% 22% 36% 19% 3	760
	11th to 20th	Night	20% 25% 33% 18% 5%	760
	21st to end	Night	20% 18% 36% 20% 6%	836
April	1st to 10th	Night	24% 18% 35% 21% 3	760
	11th to 20th	Night	19% 18% 35% 20% 7% 1	668
	21st to end	Night	20% 14% 34% 25% 7%	570
May	1st to 10th	Night	16% 11% 32% 29% 10% 2	570
	11th to 20th	Night	17% 7% 33% 31% 11% 1	413
	21st to end	Night	10% 9% 32% 33% 16%	411
June	1st to 10th	Night	14% 8% 34% 32% 11% 1	380
	11th to 20th	Night	10% 10% 32% 36% 13%	380
	21st to end	Night	12% 7% 30% 36% 14%	380
July	1st to 10th	Night	6% 5% 27% 42% 19% 1	370
	11th to 20th	Night	10% 6% 29% 35% 19% 1	368
	21st to end	Night	9% 3 29% 39% 19% 1	621
August	1st to 10th	Night	11% 2 24% 38% 23% 1	567
	11th to 20th	Night	8% 4 24% 39% 23% 2	564
	21st to end	Night	14% 5% 30% 27% 23% 2	689
September	1st to 10th	Night	11% 9% 27% 30% 19% 5%	760
	11th to 20th	Night	12% 7% 24% 28% 24% 5%	760
	21st to end	Night	18% 11% 23% 28% 16% 4	760
October	1st to 10th	Night	19% 10% 32% 22% 14% 2	760
	11th to 20th	Night	22% 18% 30% 21% 8% 1	760
	21st to end	Night	25% 20% 31% 21% 4	836
November	1st to 10th	Night	22% 17% 31% 22% 8% 1	780
	11th to 20th	Night	21% 24% 30% 20% 5% 1	800
	21st to end	Night	25% 20% 33% 18% 4	800
December	1st to 10th	Night	27% 23% 33% 15% 3	800
	11th to 20th	Night	22% 25% 36% 15% 3	800
	21st to end	Night	31% 20% 31% 16% 2	880

Page generated at 2025-02-22 06:51:35. Version ac07

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