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 2024-02-05.

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 8% 7% 4 5% 5% 6% 7% 31%	78563
	Night	14% 10% 4 7% 7% 4 5% 5% 5% 7% 32%	80275
Transparency	Day	51% 8% 13% 18% 10% 1	78279
	Night	50% 8% 13% 19% 10% 1	80096
Seeing	Day	19% 18% 32% 19% 9% 3	13709
	Night	19% 16% 32% 23% 9% 1	22932

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% 15% 6% 10% 7% 4 4 5% 4 5% 24%	2517
	11th to 20th	Day	11% 18% 8% 15% 10% 5% 5% 5% 5% 5% 12%	2787
	21st to end	Day	20% 18% 8% 11% 7% 3 5% 4 3 4 16%	3124
February	1st to 10th	Day	13% 15% 6% 11% 10% 4 6% 5% 4 5% 20%	1656
	11th to 20th	Day	12% 12% 5% 12% 9% 4 5% 4 6% 7% 24%	1573
	21st to end	Day	17% 14% 6% 10% 6% 3 5% 3 5% 5% 25%	1388
March	1st to 10th	Day	12% 11% 5% 9% 9% 4 5% 4 5% 6% 30%	1976
	11th to 20th	Day	13% 11% 4 9% 8% 3 5% 5% 5% 5% 32%	1980
	21st to end	Day	16% 11% 4 7% 7% 3 5% 4 5% 5% 32%	2178
April	1st to 10th	Day	15% 11% 5% 8% 7% 4 5% 4 5% 7% 29%	2110
	11th to 20th	Day	17% 10% 3 6% 6% 4 4 4 5% 7% 36%	2228
	21st to end	Day	20% 9% 4 7% 6% 3 4 4 5% 6% 33%	2340
May	1st to 10th	Day	16% 8% 3 7% 7% 4 5% 5% 5% 6% 34%	2340
	11th to 20th	Day	15% 6% 3 7% 6% 3 5% 4 5% 7% 39%	2438
	21st to end	Day	11% 4 3 6% 6% 4 5% 6% 5% 8% 42%	2725
June	1st to 10th	Day	13% 6% 3 5% 6% 3 5% 6% 6% 8% 39%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 6% 7% 9% 41%	2577
	21st to end	Day	13% 5% 2 5% 6% 3 6% 5% 7% 9% 40%	2700
July	1st to 10th	Day	8% 4 2 5% 6% 4 6% 6% 6% 9% 44%	2642
	11th to 20th	Day	11% 6% 2 5% 5% 4 6% 6% 7% 10% 38%	2520
	21st to end	Day	10% 5% 3 6% 6% 3 7% 6% 7% 10% 35%	2547
August	1st to 10th	Day	9% 5% 2 6% 6% 4 7% 6% 8% 10% 38%	2327
	11th to 20th	Day	8% 6% 3 7% 7% 5% 7% 6% 7% 10% 35%	2303
	21st to end	Day	11% 6% 2 6% 6% 4 6% 7% 6% 9% 37%	2498
September	1st to 10th	Day	13% 6% 3 6% 6% 4 5% 6% 6% 8% 38%	2160
	11th to 20th	Day	11% 6% 3 7% 5% 3 4 4 6% 9% 42%	2029
	21st to end	Day	14% 7% 3 7% 7% 4 6% 5% 6% 8% 34%	1958
October	1st to 10th	Day	19% 9% 3 6% 5% 4 5% 5% 5% 7% 32%	1800
	11th to 20th	Day	19% 11% 3 8% 7% 3 5% 5% 6% 6% 26%	1800
	21st to end	Day	25% 13% 4 7% 6% 4 5% 4 5% 6% 21%	1980
November	1st to 10th	Day	13% 12% 5% 6% 6% 3 5% 6% 6% 7% 32%	1604
	11th to 20th	Day	13% 11% 5% 8% 8% 3 7% 6% 6% 8% 25%	1520
	21st to end	Day	16% 13% 7% 10% 7% 4 6% 5% 6% 7% 20%	1520
December	1st to 10th	Day	14% 17% 7% 13% 8% 4 5% 4 5% 7% 16%	1520
	11th to 20th	Day	17% 15% 5% 11% 7% 4 5% 5% 6% 5% 19%	1906
	21st to end	Day	26% 18% 7% 12% 8% 3 4 3 4 3 10%	2772
January	1st to 10th	Night	17% 13% 7% 12% 7% 4 5% 5% 5% 6% 20%	4429
	11th to 20th	Night	13% 12% 7% 11% 13% 6% 8% 6% 5% 6% 12%	4170
	21st to end	Night	19% 12% 7% 10% 8% 5% 5% 5% 5% 6% 17%	4532
February	1st to 10th	Night	13% 14% 5% 9% 9% 3 5% 6% 5% 7% 25%	2399
	11th to 20th	Night	12% 11% 5% 10% 8% 5% 6% 5% 5% 7% 26%	2273
	21st to end	Night	13% 12% 5% 9% 7% 4 5% 5% 6% 6% 29%	1866
March	1st to 10th	Night	12% 8% 4 8% 7% 4 6% 5% 5% 7% 34%	1970
	11th to 20th	Night	13% 10% 4 8% 6% 3 5% 4 5% 7% 35%	1979
	21st to end	Night	15% 8% 3 6% 7% 3 5% 4 4 5% 39%	2178
April	1st to 10th	Night	17% 10% 4 7% 5% 4 4 5% 5% 7% 32%	1850
	11th to 20th	Night	14% 8% 3 6% 6% 3 5% 5% 6% 6% 39%	1697
	21st to end	Night	15% 9% 4 6% 6% 4 4 5% 6% 6% 36%	1620
May	1st to 10th	Night	15% 7% 2 5% 6% 3 5% 5% 5% 7% 39%	1620
	11th to 20th	Night	14% 5% 3 4 4 2 4 5% 4 8% 46%	1452
	21st to end	Night	10% 3 2 5% 4 2 3 5% 5% 9% 52%	1550
June	1st to 10th	Night	12% 4 2 4 6% 3 5% 5% 6% 9% 43%	1440
	11th to 20th	Night	9% 4 3 6% 5% 3 5% 6% 6% 9% 45%	1375
	21st to end	Night	11% 5% 2 4 5% 3 3 5% 6% 7% 49%	1260
July	1st to 10th	Night	5% 4 2 4 3 3 4 5% 4 8% 59%	1312
	11th to 20th	Night	9% 2 2 5% 6% 3 5% 5% 5% 8% 50%	1440
	21st to end	Night	7% 4 2 4 5% 3 5% 4 6% 9% 52%	1768
August	1st to 10th	Night	7% 5% 2 5% 5% 3 4 5% 7% 7% 51%	1611
	11th to 20th	Night	6% 4 3 4 5% 3 5% 5% 6% 8% 51%	1598
	21st to end	Night	11% 4 2 5% 5% 3 5% 4 5% 8% 48%	1840
September	1st to 10th	Night	8% 5% 2 5% 6% 3 5% 4 7% 8% 48%	1800
	11th to 20th	Night	11% 4 2 4 4 2 3 5% 6% 6% 53%	1928
	21st to end	Night	15% 7% 3 6% 6% 3 4 4 5% 7% 43%	2000
October	1st to 10th	Night	17% 7% 3 5% 6% 3 5% 4 6% 7% 37%	2160
	11th to 20th	Night	18% 9% 3 6% 7% 3 5% 5% 5% 6% 34%	2160
	21st to end	Night	20% 9% 3 8% 8% 3 4 5% 5% 7% 27%	2376
November	1st to 10th	Night	15% 7% 4 5% 6% 3 5% 6% 6% 6% 37%	2470
	11th to 20th	Night	15% 10% 4 7% 7% 4 5% 6% 6% 9% 27%	2660
	21st to end	Night	16% 12% 4 7% 7% 4 5% 5% 6% 8% 26%	2660
December	1st to 10th	Night	19% 13% 6% 8% 7% 4 6% 4 6% 7% 21%	2660
	11th to 20th	Night	13% 17% 6% 9% 8% 3 5% 5% 6% 6% 19%	3288
	21st to end	Night	26% 19% 7% 11% 7% 4 4 4 4 4 12%	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	59% 9% 13% 13% 6%	2518
	11th to 20th	Day	71% 7% 10% 8% 3	2787
	21st to end	Day	71% 7% 10% 8% 4 1	3124
February	1st to 10th	Day	65% 8% 10% 13% 4 1	1656
	11th to 20th	Day	59% 7% 13% 14% 7% 1	1582
	21st to end	Day	61% 6% 10% 14% 7% 1	1388
March	1st to 10th	Day	54% 7% 13% 16% 9% 1	1979
	11th to 20th	Day	53% 7% 10% 17% 11% 2	1980
	21st to end	Day	54% 5% 10% 16% 13% 2	2178
April	1st to 10th	Day	55% 6% 11% 17% 10% 1	2110
	11th to 20th	Day	48% 6% 10% 21% 15% 1	2228
	21st to end	Day	51% 6% 11% 18% 11% 2	2340
May	1st to 10th	Day	49% 7% 10% 21% 13% 1	2340
	11th to 20th	Day	43% 7% 12% 24% 13% 1	2442
	21st to end	Day	38% 9% 16% 23% 14% 1	2725
June	1st to 10th	Day	41% 9% 13% 22% 15% 1	2520
	11th to 20th	Day	37% 9% 14% 24% 16% 1	2577
	21st to end	Day	40% 8% 15% 23% 14%	2700
July	1st to 10th	Day	34% 8% 14% 23% 18% 2	2571
	11th to 20th	Day	38% 9% 14% 28% 11% 1	2445
	21st to end	Day	40% 9% 16% 20% 13% 1	2405
August	1st to 10th	Day	37% 11% 17% 22% 11% 2	2314
	11th to 20th	Day	39% 11% 16% 23% 11%	2303
	21st to end	Day	39% 10% 15% 24% 11% 1	2498
September	1st to 10th	Day	41% 8% 14% 24% 10% 2	2160
	11th to 20th	Day	38% 6% 14% 28% 13%	2029
	21st to end	Day	47% 8% 12% 24% 8%	1958
October	1st to 10th	Day	51% 8% 13% 18% 10% 1	1800
	11th to 20th	Day	54% 8% 14% 17% 7% 1	1800
	21st to end	Day	62% 8% 12% 13% 5%	1980
November	1st to 10th	Day	49% 9% 15% 18% 9% 1	1604
	11th to 20th	Day	54% 9% 15% 13% 8%	1520
	21st to end	Day	61% 10% 14% 12% 3	1520
December	1st to 10th	Day	67% 9% 13% 9% 2	1520
	11th to 20th	Day	64% 9% 12% 11% 4	1906
	21st to end	Day	77% 7% 8% 6% 1	2772
January	1st to 10th	Night	61% 8% 14% 12% 4	4429
	11th to 20th	Night	70% 9% 9% 8% 3 1	4170
	21st to end	Night	65% 8% 14% 9% 4 1	4532
February	1st to 10th	Night	57% 8% 11% 18% 5% 1	2399
	11th to 20th	Night	58% 7% 11% 15% 8%	2275
	21st to end	Night	54% 7% 13% 17% 8%	1866
March	1st to 10th	Night	48% 7% 14% 19% 10% 1	1980
	11th to 20th	Night	49% 7% 11% 20% 11% 2	1980
	21st to end	Night	47% 5% 10% 20% 15% 2	2178
April	1st to 10th	Night	52% 6% 10% 18% 13% 1	1850
	11th to 20th	Night	44% 6% 11% 20% 16% 2	1697
	21st to end	Night	46% 6% 12% 18% 15% 2	1620
May	1st to 10th	Night	43% 7% 9% 22% 16% 2	1620
	11th to 20th	Night	38% 6% 10% 26% 17% 4	1453
	21st to end	Night	30% 7% 16% 26% 17% 4	1551
June	1st to 10th	Night	36% 6% 15% 23% 18% 2	1440
	11th to 20th	Night	35% 7% 11% 25% 20% 1	1375
	21st to end	Night	34% 7% 14% 26% 18% 1	1260
July	1st to 10th	Night	24% 7% 12% 27% 25% 4	1275
	11th to 20th	Night	31% 6% 12% 32% 17% 2	1392
	21st to end	Night	29% 9% 15% 30% 16% 3	1670
August	1st to 10th	Night	30% 8% 17% 31% 13% 2	1600
	11th to 20th	Night	29% 8% 14% 34% 14% 2	1598
	21st to end	Night	34% 8% 12% 28% 16% 1	1840
September	1st to 10th	Night	32% 9% 17% 27% 15% 1	1800
	11th to 20th	Night	30% 6% 13% 33% 18% 1	1928
	21st to end	Night	42% 7% 13% 28% 10% 1	2000
October	1st to 10th	Night	45% 8% 12% 21% 14% 1	2160
	11th to 20th	Night	49% 8% 14% 22% 7%	2160
	21st to end	Night	55% 8% 13% 15% 9%	2376
November	1st to 10th	Night	44% 8% 14% 21% 11% 1	2470
	11th to 20th	Night	51% 9% 14% 16% 8% 1	2660
	21st to end	Night	55% 9% 19% 13% 3	2660
December	1st to 10th	Night	61% 8% 15% 13% 3	2660
	11th to 20th	Night	62% 9% 14% 12% 3	3288
	21st to end	Night	74% 8% 10% 6% 2	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	22% 27% 31% 16% 4 1	180
	11th to 20th	Day	24% 29% 30% 12% 3	258
	21st to end	Day	26% 28% 30% 13% 2	297
February	1st to 10th	Day	28% 33% 29% 8% 3	252
	11th to 20th	Day	24% 37% 34% 4 1	240
	21st to end	Day	36% 35% 25% 4	198
March	1st to 10th	Day	21% 25% 33% 16% 4	419
	11th to 20th	Day	20% 23% 39% 13% 5%	420
	21st to end	Day	28% 21% 32% 13% 5%	462
April	1st to 10th	Day	20% 27% 33% 13% 7%	420
	11th to 20th	Day	28% 21% 28% 14% 6% 3	412
	21st to end	Day	24% 22% 33% 14% 5% 2	420
May	1st to 10th	Day	22% 17% 33% 17% 8% 3	423
	11th to 20th	Day	18% 17% 32% 21% 9% 4	447
	21st to end	Day	13% 14% 31% 27% 10% 5%	485
June	1st to 10th	Day	12% 18% 36% 25% 8% 2	450
	11th to 20th	Day	14% 16% 30% 26% 12% 2	507
	21st to end	Day	16% 10% 37% 27% 7% 3	630
July	1st to 10th	Day	8% 8% 34% 30% 16% 4	566
	11th to 20th	Day	12% 8% 29% 28% 16% 7%	444
	21st to end	Day	11% 7% 36% 29% 12% 5%	488
August	1st to 10th	Day	9% 8% 27% 31% 17% 8%	446
	11th to 20th	Day	9% 6% 30% 27% 20% 8%	439
	21st to end	Day	13% 10% 31% 25% 15% 6%	495
September	1st to 10th	Day	13% 10% 31% 24% 14% 8%	450
	11th to 20th	Day	9% 10% 28% 23% 18% 10%	450
	21st to end	Day	15% 15% 30% 20% 14% 5%	450
October	1st to 10th	Day	24% 16% 28% 16% 12% 4	450
	11th to 20th	Day	22% 24% 35% 13% 5% 1	450
	21st to end	Day	30% 24% 26% 15% 4	495
November	1st to 10th	Day	22% 27% 29% 18% 3 1	248
	11th to 20th	Day	21% 29% 32% 13% 5% 1	180
	21st to end	Day	24% 25% 39% 11% 1	180
December	1st to 10th	Day	31% 28% 29% 11% 1	180
	11th to 20th	Day	29% 30% 31% 9% 1	180
	21st to end	Day	29% 30% 31% 8% 2	198
January	1st to 10th	Night	22% 27% 33% 14% 4	760
	11th to 20th	Night	25% 23% 31% 18% 2	760
	21st to end	Night	18% 19% 38% 19% 6%	836
February	1st to 10th	Night	20% 28% 36% 15% 1	739
	11th to 20th	Night	21% 23% 39% 13% 3	703
	21st to end	Night	20% 26% 37% 15% 2	592
March	1st to 10th	Night	20% 22% 36% 18% 3	720
	11th to 20th	Night	20% 24% 33% 18% 5%	720
	21st to end	Night	20% 17% 35% 21% 6%	792
April	1st to 10th	Night	23% 18% 35% 21% 3	720
	11th to 20th	Night	18% 18% 35% 21% 7% 1	633
	21st to end	Night	20% 14% 34% 25% 7%	540
May	1st to 10th	Night	17% 10% 32% 28% 11% 2	540
	11th to 20th	Night	17% 7% 34% 31% 9% 1	391
	21st to end	Night	10% 9% 32% 33% 16%	389
June	1st to 10th	Night	13% 8% 35% 32% 12% 1	360
	11th to 20th	Night	10% 10% 32% 35% 13%	360
	21st to end	Night	12% 7% 29% 37% 15%	360
July	1st to 10th	Night	6% 5% 25% 42% 20% 1	350
	11th to 20th	Night	10% 6% 29% 34% 19% 1	348
	21st to end	Night	9% 3 30% 38% 19% 1	588
August	1st to 10th	Night	10% 2 25% 38% 24% 1	537
	11th to 20th	Night	7% 4 23% 40% 23% 2	534
	21st to end	Night	14% 5% 30% 27% 22% 2	652
September	1st to 10th	Night	11% 8% 27% 30% 19% 5%	720
	11th to 20th	Night	13% 7% 25% 29% 21% 5%	720
	21st to end	Night	17% 11% 23% 28% 16% 4	720
October	1st to 10th	Night	20% 10% 32% 21% 15% 2	720
	11th to 20th	Night	23% 17% 32% 20% 7% 1	720
	21st to end	Night	26% 20% 31% 20% 3	792
November	1st to 10th	Night	21% 17% 31% 22% 8% 1	740
	11th to 20th	Night	21% 23% 30% 19% 5% 1	760
	21st to end	Night	24% 20% 33% 19% 4	760
December	1st to 10th	Night	28% 23% 33% 14% 3	760
	11th to 20th	Night	22% 25% 35% 15% 3	760
	21st to end	Night	31% 21% 31% 15% 2	836

Page generated at 2024-02-02 05:20:29. Version ac07

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