CMOR
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CMOR clear sky chart from 2005-11-06 to 2024-01-17.

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	15% 10% 4 8% 6% 4 5% 5% 5% 7% 30%	75154
	Night	15% 10% 5% 8% 6% 3 5% 5% 5% 7% 32%	74649
Transparency	Day	51% 8% 13% 18% 10% 1	74868
	Night	50% 7% 12% 19% 10% 1	74471
Seeing	Day	18% 12% 29% 23% 13% 5%	13796
	Night	19% 11% 30% 28% 11% 1	22976

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% 16% 6% 12% 8% 5% 4 5% 4 6% 18%	1583
	11th to 20th	Day	15% 17% 8% 15% 8% 4 5% 4 5% 6% 14%	1674
	21st to end	Day	12% 18% 8% 13% 9% 5% 7% 4 4 4 15%	1782
February	1st to 10th	Day	16% 17% 7% 10% 11% 5% 7% 5% 5% 5% 14%	1620
	11th to 20th	Day	13% 13% 8% 12% 8% 4 6% 5% 6% 6% 18%	1573
	21st to end	Day	17% 14% 6% 10% 7% 4 6% 5% 4 6% 22%	1447
March	1st to 10th	Day	14% 13% 6% 9% 7% 4 5% 5% 5% 7% 26%	1942
	11th to 20th	Day	13% 12% 6% 8% 7% 4 5% 4 4 6% 30%	1980
	21st to end	Day	17% 11% 5% 8% 6% 4 4 4 5% 5% 30%	2178
April	1st to 10th	Day	16% 13% 5% 7% 6% 3 4 5% 6% 7% 27%	2068
	11th to 20th	Day	18% 10% 4 6% 6% 3 4 4 5% 7% 34%	2271
	21st to end	Day	21% 9% 4 7% 6% 3 4 4 4 7% 32%	2340
May	1st to 10th	Day	18% 8% 3 6% 6% 3 5% 4 6% 8% 32%	2340
	11th to 20th	Day	16% 8% 3 7% 6% 3 5% 5% 5% 6% 37%	2351
	21st to end	Day	12% 5% 3 5% 6% 3 5% 6% 7% 8% 40%	2725
June	1st to 10th	Day	13% 5% 3 6% 6% 3 5% 6% 7% 8% 38%	2520
	11th to 20th	Day	11% 6% 3 5% 5% 3 6% 7% 6% 9% 39%	2643
	21st to end	Day	13% 5% 2 6% 5% 4 5% 6% 5% 10% 40%	2700
July	1st to 10th	Day	8% 4 3 5% 5% 4 5% 6% 7% 9% 44%	2700
	11th to 20th	Day	10% 6% 3 5% 7% 4 6% 7% 7% 9% 36%	2421
	21st to end	Day	9% 6% 2 6% 6% 4 6% 6% 6% 10% 39%	2547
August	1st to 10th	Day	9% 5% 2 6% 7% 4 6% 6% 8% 11% 37%	2327
	11th to 20th	Day	8% 6% 3 7% 6% 4 7% 7% 6% 9% 37%	2303
	21st to end	Day	12% 7% 3 5% 5% 3 5% 6% 6% 7% 40%	2527
September	1st to 10th	Day	12% 7% 3 6% 6% 4 6% 5% 6% 9% 37%	2145
	11th to 20th	Day	11% 6% 3 5% 5% 3 5% 6% 6% 8% 42%	1980
	21st to end	Day	15% 7% 2 7% 6% 4 5% 5% 6% 8% 35%	1980
October	1st to 10th	Day	17% 9% 4 7% 6% 3 5% 4 5% 7% 34%	1818
	11th to 20th	Day	21% 9% 4 9% 6% 3 4 4 5% 8% 27%	1800
	21st to end	Day	22% 12% 5% 8% 7% 4 5% 5% 5% 7% 21%	1967
November	1st to 10th	Day	13% 11% 4 7% 7% 4 5% 5% 6% 6% 31%	1664
	11th to 20th	Day	14% 14% 5% 8% 7% 4 4 5% 7% 8% 23%	1520
	21st to end	Day	18% 16% 8% 9% 6% 4 5% 4 5% 6% 18%	1520
December	1st to 10th	Day	14% 18% 9% 11% 8% 4 7% 5% 4 5% 15%	1520
	11th to 20th	Day	18% 15% 8% 13% 7% 4 5% 5% 5% 5% 15%	1906
	21st to end	Day	28% 20% 8% 13% 7% 3 3 3 3 4 7%	2772
January	1st to 10th	Night	16% 13% 7% 11% 9% 5% 6% 5% 5% 5% 18%	2578
	11th to 20th	Night	18% 17% 8% 10% 8% 5% 6% 4 4 5% 14%	2430
	21st to end	Night	12% 12% 9% 13% 9% 4 5% 5% 5% 6% 21%	2574
February	1st to 10th	Night	14% 15% 7% 10% 9% 4 6% 5% 4 6% 19%	2340
	11th to 20th	Night	14% 11% 7% 11% 7% 4 7% 5% 5% 7% 22%	2273
	21st to end	Night	17% 12% 5% 11% 9% 4 5% 5% 5% 5% 24%	1808
March	1st to 10th	Night	13% 9% 3 7% 8% 4 6% 5% 4 8% 32%	2003
	11th to 20th	Night	13% 10% 4 8% 6% 4 5% 4 6% 6% 34%	1979
	21st to end	Night	16% 10% 5% 8% 5% 3 5% 3 5% 5% 35%	2178
April	1st to 10th	Night	18% 9% 3 6% 6% 3 5% 4 5% 7% 33%	1890
	11th to 20th	Night	16% 7% 3 7% 5% 3 4 4 5% 7% 37%	1652
	21st to end	Night	14% 10% 4 6% 6% 3 5% 5% 6% 8% 34%	1620
May	1st to 10th	Night	16% 7% 4 7% 5% 2 5% 4 6% 7% 37%	1620
	11th to 20th	Night	13% 7% 4 5% 5% 3 4 6% 5% 7% 42%	1539
	21st to end	Night	9% 4 2 5% 3 2 5% 5% 5% 9% 51%	1550
June	1st to 10th	Night	11% 4 2 6% 5% 3 5% 5% 6% 8% 45%	1440
	11th to 20th	Night	9% 5% 3 5% 5% 4 5% 6% 7% 9% 43%	1311
	21st to end	Night	9% 5% 2 5% 5% 3 5% 6% 5% 7% 46%	1260
July	1st to 10th	Night	5% 3 2 4 4 2 5% 5% 5% 9% 57%	1260
	11th to 20th	Night	8% 5% 2 5% 4 3 4 5% 6% 9% 51%	1532
	21st to end	Night	8% 4 2 5% 5% 3 5% 5% 6% 9% 47%	1771
August	1st to 10th	Night	8% 4 1 6% 4 4 5% 6% 7% 8% 48%	1611
	11th to 20th	Night	7% 4 2 5% 5% 3 3 5% 7% 10% 49%	1598
	21st to end	Night	8% 5% 2 4 5% 4 5% 5% 6% 9% 47%	1809
September	1st to 10th	Night	10% 6% 2 6% 5% 3 5% 4 5% 7% 46%	1812
	11th to 20th	Night	10% 5% 2 4 4 2 4 4 5% 7% 53%	1980
	21st to end	Night	15% 7% 3 6% 5% 3 4 4 5% 6% 42%	1980
October	1st to 10th	Night	15% 9% 3 5% 5% 3 4 5% 5% 6% 40%	2142
	11th to 20th	Night	18% 8% 4 7% 6% 4 4 5% 6% 7% 32%	2160
	21st to end	Night	22% 8% 4 8% 7% 3 5% 5% 6% 6% 27%	2386
November	1st to 10th	Night	14% 9% 3 6% 6% 4 5% 5% 7% 7% 36%	2411
	11th to 20th	Night	15% 12% 5% 9% 6% 4 6% 5% 6% 7% 25%	2660
	21st to end	Night	18% 13% 5% 9% 7% 3 6% 4 5% 7% 22%	2660
December	1st to 10th	Night	17% 17% 7% 11% 7% 5% 5% 5% 4 5% 17%	2660
	11th to 20th	Night	13% 18% 7% 11% 7% 4 4 5% 5% 6% 19%	3288
	21st to end	Night	26% 19% 8% 10% 7% 3 4 4 4 4 10%	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% 7% 11% 11% 5%	1584
	11th to 20th	Day	71% 7% 10% 7% 4 1	1674
	21st to end	Day	70% 6% 8% 9% 5% 1	1782
February	1st to 10th	Day	69% 7% 11% 10% 3	1620
	11th to 20th	Day	64% 7% 10% 13% 6% 1	1582
	21st to end	Day	64% 6% 10% 13% 7% 1	1447
March	1st to 10th	Day	57% 6% 14% 16% 6% 1	1945
	11th to 20th	Day	55% 7% 9% 17% 10% 2	1980
	21st to end	Day	55% 6% 10% 16% 11% 2	2178
April	1st to 10th	Day	54% 8% 12% 15% 10%	2068
	11th to 20th	Day	49% 6% 12% 19% 12% 1	2271
	21st to end	Day	53% 5% 10% 18% 11% 2	2340
May	1st to 10th	Day	49% 7% 11% 21% 12% 1	2340
	11th to 20th	Day	46% 8% 11% 22% 11% 2	2355
	21st to end	Day	39% 8% 15% 22% 14% 2	2725
June	1st to 10th	Day	41% 8% 13% 23% 14% 2	2520
	11th to 20th	Day	39% 9% 13% 22% 16% 1	2643
	21st to end	Day	39% 8% 13% 25% 15%	2700
July	1st to 10th	Day	33% 9% 14% 24% 17% 2	2626
	11th to 20th	Day	39% 9% 15% 25% 12% 1	2347
	21st to end	Day	38% 9% 15% 24% 13% 2	2405
August	1st to 10th	Day	36% 11% 18% 24% 10% 1	2314
	11th to 20th	Day	39% 11% 17% 22% 10% 1	2303
	21st to end	Day	40% 8% 14% 25% 12% 1	2527
September	1st to 10th	Day	42% 8% 15% 23% 12% 1	2145
	11th to 20th	Day	37% 7% 15% 27% 14%	1980
	21st to end	Day	44% 8% 14% 24% 9% 1	1980
October	1st to 10th	Day	49% 7% 13% 17% 12% 1	1818
	11th to 20th	Day	55% 7% 13% 16% 8% 1	1800
	21st to end	Day	61% 8% 12% 13% 6%	1967
November	1st to 10th	Day	50% 8% 13% 21% 7% 2	1664
	11th to 20th	Day	56% 9% 15% 12% 8% 1	1520
	21st to end	Day	63% 9% 13% 12% 3	1520
December	1st to 10th	Day	68% 9% 11% 8% 4	1520
	11th to 20th	Day	70% 9% 10% 8% 4	1906
	21st to end	Day	80% 7% 8% 5% 1	2772
January	1st to 10th	Night	63% 8% 10% 12% 6%	2578
	11th to 20th	Night	70% 8% 9% 9% 4	2430
	21st to end	Night	62% 7% 10% 13% 6% 1	2574
February	1st to 10th	Night	65% 7% 9% 14% 5%	2340
	11th to 20th	Night	58% 8% 13% 14% 7%	2275
	21st to end	Night	60% 7% 11% 15% 7%	1808
March	1st to 10th	Night	49% 8% 13% 19% 9% 1	2013
	11th to 20th	Night	50% 6% 11% 21% 10% 2	1980
	21st to end	Night	50% 6% 9% 20% 13% 3	2178
April	1st to 10th	Night	50% 5% 11% 19% 13% 1	1890
	11th to 20th	Night	46% 6% 11% 19% 17% 2	1652
	21st to end	Night	47% 7% 10% 19% 15% 3	1620
May	1st to 10th	Night	45% 6% 10% 21% 15% 2	1620
	11th to 20th	Night	41% 6% 13% 24% 12% 4	1540
	21st to end	Night	30% 8% 15% 26% 18% 3	1551
June	1st to 10th	Night	36% 7% 12% 26% 17% 3	1440
	11th to 20th	Night	34% 9% 14% 24% 17% 2	1311
	21st to end	Night	34% 8% 16% 23% 19% 1	1260
July	1st to 10th	Night	24% 8% 13% 28% 24% 4	1225
	11th to 20th	Night	30% 7% 15% 28% 18% 2	1484
	21st to end	Night	32% 9% 15% 25% 16% 3	1672
August	1st to 10th	Night	31% 9% 16% 31% 12% 1	1600
	11th to 20th	Night	29% 8% 16% 31% 14% 2	1598
	21st to end	Night	32% 8% 15% 29% 15% 2	1809
September	1st to 10th	Night	37% 7% 14% 25% 15% 2	1812
	11th to 20th	Night	29% 7% 14% 31% 18% 1	1980
	21st to end	Night	42% 7% 12% 26% 12%	1980
October	1st to 10th	Night	43% 7% 11% 24% 14% 1	2142
	11th to 20th	Night	49% 8% 13% 21% 10% 1	2160
	21st to end	Night	56% 7% 11% 16% 10% 1	2386
November	1st to 10th	Night	44% 8% 14% 21% 12% 1	2411
	11th to 20th	Night	53% 9% 14% 15% 7% 1	2660
	21st to end	Night	60% 7% 17% 12% 4	2660
December	1st to 10th	Night	66% 9% 10% 10% 4	2660
	11th to 20th	Night	63% 8% 14% 12% 3	3288
	21st to end	Night	77% 8% 8% 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	23% 22% 31% 17% 5% 1	211
	11th to 20th	Day	25% 21% 37% 13% 3 1	258
	21st to end	Day	25% 17% 36% 18% 3 1	264
February	1st to 10th	Day	27% 19% 41% 12% 1	240
	11th to 20th	Day	25% 24% 40% 10% 1	240
	21st to end	Day	30% 30% 29% 9% 1	198
March	1st to 10th	Day	24% 15% 38% 17% 5% 1	385
	11th to 20th	Day	22% 15% 37% 20% 5% 1	420
	21st to end	Day	28% 15% 30% 20% 6% 1	462
April	1st to 10th	Day	20% 20% 30% 21% 7% 2	420
	11th to 20th	Day	28% 14% 26% 17% 11% 4	412
	21st to end	Day	26% 12% 31% 20% 8% 2	420
May	1st to 10th	Day	23% 13% 26% 24% 10% 5%	423
	11th to 20th	Day	16% 11% 33% 23% 14% 5%	447
	21st to end	Day	14% 7% 26% 28% 19% 7%	485
June	1st to 10th	Day	14% 11% 31% 28% 12% 4	450
	11th to 20th	Day	13% 9% 28% 31% 16% 4	573
	21st to end	Day	14% 8% 31% 33% 11% 4	630
July	1st to 10th	Day	9% 6% 22% 28% 26% 8%	621
	11th to 20th	Day	13% 5% 25% 26% 20% 11%	453
	21st to end	Day	9% 4 25% 35% 20% 7%	488
August	1st to 10th	Day	9% 4 20% 29% 24% 14%	446
	11th to 20th	Day	10% 5% 21% 26% 23% 15%	439
	21st to end	Day	12% 6% 23% 28% 20% 11%	495
September	1st to 10th	Day	13% 6% 22% 28% 19% 12%	450
	11th to 20th	Day	10% 5% 20% 25% 27% 12%	450
	21st to end	Day	16% 10% 26% 23% 15% 9%	450
October	1st to 10th	Day	21% 11% 25% 21% 15% 7%	450
	11th to 20th	Day	20% 18% 34% 20% 7% 1	450
	21st to end	Day	28% 13% 33% 20% 5% 1	482
November	1st to 10th	Day	22% 23% 28% 18% 7% 2	266
	11th to 20th	Day	25% 20% 33% 13% 7% 2	180
	21st to end	Day	24% 20% 35% 18% 3	180
December	1st to 10th	Day	30% 21% 36% 9% 4 1	180
	11th to 20th	Day	26% 26% 32% 13% 3 1	180
	21st to end	Day	29% 22% 37% 11% 2	198
January	1st to 10th	Night	21% 20% 36% 16% 6% 1	760
	11th to 20th	Night	28% 17% 33% 20% 3	748
	21st to end	Night	18% 12% 40% 25% 6%	792
February	1st to 10th	Night	24% 16% 38% 20% 2	720
	11th to 20th	Night	22% 16% 36% 21% 5%	703
	21st to end	Night	23% 18% 34% 21% 3	592
March	1st to 10th	Night	17% 14% 38% 24% 6%	720
	11th to 20th	Night	20% 14% 36% 23% 6% 1	720
	21st to end	Night	21% 12% 33% 25% 9%	792
April	1st to 10th	Night	21% 15% 33% 27% 5%	720
	11th to 20th	Night	19% 13% 31% 26% 10% 1	588
	21st to end	Night	18% 10% 32% 31% 8%	540
May	1st to 10th	Night	18% 7% 31% 29% 14% 1	540
	11th to 20th	Night	17% 5% 28% 36% 12% 1	478
	21st to end	Night	11% 4 30% 37% 18% 1	389
June	1st to 10th	Night	15% 3 29% 40% 12% 1	360
	11th to 20th	Night	12% 4 29% 43% 12%	360
	21st to end	Night	12% 5% 26% 41% 16%	360
July	1st to 10th	Night	5% 2 22% 48% 21% 2	350
	11th to 20th	Night	8% 4 23% 40% 23% 3	453
	21st to end	Night	9% 3 20% 46% 20% 2	591
August	1st to 10th	Night	8% 2 17% 43% 28% 2	537
	11th to 20th	Night	9% 1 15% 40% 30% 4	534
	21st to end	Night	10% 3 21% 37% 26% 3	621
September	1st to 10th	Night	12% 5% 22% 34% 23% 5%	720
	11th to 20th	Night	13% 3 19% 34% 26% 4	720
	21st to end	Night	17% 7% 22% 31% 19% 5%	720
October	1st to 10th	Night	18% 7% 26% 28% 19% 2	720
	11th to 20th	Night	20% 13% 31% 26% 9% 1	720
	21st to end	Night	27% 10% 32% 27% 4	792
November	1st to 10th	Night	19% 12% 29% 29% 10% 1	740
	11th to 20th	Night	21% 17% 33% 21% 7% 1	760
	21st to end	Night	24% 14% 34% 22% 6%	760
December	1st to 10th	Night	27% 18% 30% 20% 4	760
	11th to 20th	Night	23% 20% 35% 17% 4	760
	21st to end	Night	28% 16% 34% 18% 3	836

Page generated at 2024-01-14 09:55:04. Version ac07

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