Cavendish
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cavendish clear sky chart from 2005-11-06 to 2024-12-24.

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% 11% 4 9% 5% 5% 4 3 5% 7% 30%	102339
	Night	18% 12% 4 11% 6% 4 4 3 5% 6% 26%	97825
Transparency	Day	52% 7% 13% 19% 8% 1	105893
	Night	56% 8% 12% 16% 7% 1	102363
Seeing	Day	22% 10% 27% 28% 12% 2	17373
	Night	24% 11% 29% 27% 9% 1	24743

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% 8% 25% 7% 5% 5% 2 3 4 11%	2244
	11th to 20th	Day	12% 12% 6% 14% 8% 6% 5% 4 4 5% 24%	2530
	21st to end	Day	12% 10% 5% 16% 6% 5% 4 3 5% 6% 26%	3040
February	1st to 10th	Day	17% 13% 4 9% 6% 5% 5% 4 5% 5% 26%	1710
	11th to 20th	Day	15% 15% 4 8% 6% 6% 6% 4 5% 6% 25%	1663
	21st to end	Day	9% 13% 4 9% 7% 6% 5% 4 5% 7% 32%	1443
March	1st to 10th	Day	21% 13% 5% 8% 4 6% 3 2 4 5% 29%	3333
	11th to 20th	Day	12% 18% 6% 12% 7% 5% 5% 4 4 6% 21%	3480
	21st to end	Day	22% 16% 4 11% 5% 4 4 3 5% 5% 21%	3866
April	1st to 10th	Day	17% 12% 4 8% 6% 4 4 3 5% 6% 31%	2280
	11th to 20th	Day	19% 10% 3 6% 4 4 4 3 5% 8% 34%	2323
	21st to end	Day	19% 12% 4 7% 4 4 4 4 6% 7% 30%	2470
May	1st to 10th	Day	24% 13% 3 6% 3 3 4 3 5% 6% 31%	4353
	11th to 20th	Day	16% 7% 3 7% 5% 4 4 4 5% 7% 38%	4398
	21st to end	Day	17% 9% 3 7% 6% 5% 5% 4 6% 8% 31%	4836
June	1st to 10th	Day	23% 11% 3 7% 6% 4 5% 3 5% 6% 25%	2707
	11th to 20th	Day	18% 9% 3 8% 5% 4 4 4 5% 6% 35%	2850
	21st to end	Day	22% 9% 3 8% 5% 4 4 3 5% 7% 30%	2850
July	1st to 10th	Day	13% 8% 3 8% 5% 5% 6% 4 7% 8% 33%	4760
	11th to 20th	Day	13% 6% 3 6% 4 5% 5% 4 7% 9% 38%	4518
	21st to end	Day	11% 6% 3 7% 4 4 5% 4 7% 9% 40%	4815
August	1st to 10th	Day	14% 10% 3 8% 5% 5% 5% 4 6% 7% 33%	4154
	11th to 20th	Day	13% 6% 3 7% 4 5% 5% 4 6% 8% 39%	4045
	21st to end	Day	14% 5% 2 6% 4 4 4 4 6% 8% 44%	4350
September	1st to 10th	Day	15% 6% 2 6% 4 3 4 4 7% 8% 40%	2280
	11th to 20th	Day	18% 9% 2 7% 4 4 5% 3 5% 6% 40%	2252
	21st to end	Day	18% 8% 2 6% 4 4 4 3 4 7% 39%	2001
October	1st to 10th	Day	19% 8% 3 6% 4 5% 5% 4 5% 8% 34%	1900
	11th to 20th	Day	20% 12% 4 9% 5% 5% 5% 3 5% 7% 25%	1900
	21st to end	Day	19% 15% 4 9% 5% 5% 4 3 4 8% 23%	2033
November	1st to 10th	Day	20% 18% 4 8% 6% 3 5% 3 5% 5% 23%	1590
	11th to 20th	Day	21% 21% 7% 10% 5% 4 4 3 5% 5% 15%	1600
	21st to end	Day	19% 17% 8% 14% 7% 4 4 3 6% 5% 13%	1600
December	1st to 10th	Day	23% 20% 7% 15% 6% 4 4 3 4 3 12%	1600
	11th to 20th	Day	18% 20% 7% 17% 9% 5% 4 2 2 3 12%	1986
	21st to end	Day	19% 16% 10% 16% 6% 5% 3 2 3 4 17%	2579
January	1st to 10th	Night	13% 13% 6% 22% 8% 5% 5% 3 5% 4 16%	4704
	11th to 20th	Night	14% 13% 5% 13% 7% 6% 5% 4 5% 4 23%	4440
	21st to end	Night	11% 14% 5% 18% 11% 4 5% 3 5% 6% 19%	4614
February	1st to 10th	Night	17% 14% 4 9% 5% 4 4 3 6% 6% 27%	2470
	11th to 20th	Night	16% 15% 5% 9% 6% 6% 5% 3 5% 6% 23%	2403
	21st to end	Night	12% 12% 5% 9% 6% 5% 6% 3 6% 6% 31%	2010
March	1st to 10th	Night	21% 13% 4 11% 6% 5% 4 2 5% 4 26%	3505
	11th to 20th	Night	20% 16% 6% 12% 6% 5% 4 3 4 5% 19%	3479
	21st to end	Night	24% 13% 4 10% 5% 4 5% 4 5% 4 22%	3765
April	1st to 10th	Night	21% 12% 4 8% 6% 4 4 4 5% 6% 26%	1900
	11th to 20th	Night	19% 13% 3 6% 5% 5% 4 3 4 6% 32%	1802
	21st to end	Night	21% 13% 5% 8% 5% 3 3 3 4 5% 30%	1710
May	1st to 10th	Night	27% 14% 3 8% 5% 5% 4 2 4 4 24%	2593
	11th to 20th	Night	15% 8% 3 7% 4 5% 4 3 6% 6% 40%	2506
	21st to end	Night	14% 9% 3 8% 7% 6% 6% 4 6% 8% 28%	2749
June	1st to 10th	Night	26% 12% 3 7% 4 5% 3 3 4 6% 27%	1486
	11th to 20th	Night	17% 7% 4 5% 5% 5% 4 3 5% 7% 38%	1330
	21st to end	Night	22% 10% 4 8% 5% 4 5% 4 6% 5% 28%	1330
July	1st to 10th	Night	13% 8% 3 9% 6% 6% 6% 5% 6% 7% 30%	2210
	11th to 20th	Night	12% 6% 2 8% 6% 5% 7% 6% 8% 9% 32%	2419
	21st to end	Night	12% 7% 3 6% 4 4 4 4 6% 8% 44%	2750
August	1st to 10th	Night	16% 8% 3 9% 5% 6% 6% 4 7% 7% 29%	2762
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 4 6% 8% 39%	2782
	21st to end	Night	12% 7% 2 6% 4 4 5% 4 6% 8% 42%	3305
September	1st to 10th	Night	16% 6% 2 7% 4 5% 3 3 5% 7% 42%	1900
	11th to 20th	Night	17% 7% 3 6% 3 4 5% 3 5% 6% 42%	1924
	21st to end	Night	18% 7% 3 6% 3 4 4 3 5% 8% 40%	2178
October	1st to 10th	Night	20% 8% 3 6% 4 3 5% 3 4 7% 37%	2280
	11th to 20th	Night	18% 12% 4 9% 5% 4 4 4 5% 6% 30%	2280
	21st to end	Night	25% 13% 3 8% 5% 5% 4 3 5% 5% 23%	2563
November	1st to 10th	Night	21% 17% 4 7% 5% 4 4 3 5% 5% 25%	2704
	11th to 20th	Night	22% 18% 6% 10% 6% 4 4 3 4 6% 17%	2800
	21st to end	Night	25% 19% 5% 12% 6% 4 4 3 4 5% 14%	2800
December	1st to 10th	Night	21% 19% 7% 15% 6% 4 4 3 4 5% 12%	2800
	11th to 20th	Night	19% 20% 7% 16% 7% 5% 3 3 3 3 14%	3433
	21st to end	Night	25% 15% 6% 17% 5% 4 3 2 3 4 16%	5139

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	73% 11% 8% 5% 3	2245
	11th to 20th	Day	55% 12% 10% 14% 7% 1	2530
	21st to end	Day	56% 10% 12% 12% 10% 1	3040
February	1st to 10th	Day	58% 5% 12% 15% 9% 1	1710
	11th to 20th	Day	59% 6% 11% 16% 7% 1	1671
	21st to end	Day	50% 6% 13% 18% 11% 2	1443
March	1st to 10th	Day	57% 5% 10% 22% 6% 1	3337
	11th to 20th	Day	63% 7% 10% 15% 5% 1	3480
	21st to end	Day	63% 5% 10% 14% 6% 1	3866
April	1st to 10th	Day	55% 5% 11% 17% 11% 3	2280
	11th to 20th	Day	48% 5% 11% 22% 13% 1	2323
	21st to end	Day	52% 6% 12% 16% 12% 2	2470
May	1st to 10th	Day	54% 6% 15% 17% 7% 1	4368
	11th to 20th	Day	45% 8% 14% 26% 7%	4402
	21st to end	Day	48% 10% 14% 19% 8%	4836
June	1st to 10th	Day	58% 7% 11% 18% 5%	2707
	11th to 20th	Day	50% 6% 12% 23% 9% 1	2850
	21st to end	Day	55% 5% 12% 18% 9% 1	2850
July	1st to 10th	Day	46% 8% 18% 18% 9% 1	4685
	11th to 20th	Day	42% 8% 17% 26% 7%	4439
	21st to end	Day	39% 9% 21% 24% 6%	4662
August	1st to 10th	Day	50% 8% 13% 24% 5%	4140
	11th to 20th	Day	41% 8% 15% 25% 11%	4084
	21st to end	Day	37% 7% 16% 28% 12%	4350
September	1st to 10th	Day	40% 7% 17% 26% 10%	2280
	11th to 20th	Day	46% 5% 13% 25% 11%	2252
	21st to end	Day	45% 6% 11% 25% 12% 1	2001
October	1st to 10th	Day	48% 8% 14% 24% 6%	3160
	11th to 20th	Day	53% 7% 11% 23% 6%	3140
	21st to end	Day	51% 7% 19% 18% 5%	3338
November	1st to 10th	Day	62% 7% 10% 16% 5%	1590
	11th to 20th	Day	69% 8% 11% 9% 4	1600
	21st to end	Day	68% 11% 12% 7% 2	1600
December	1st to 10th	Day	74% 9% 8% 7% 2	1600
	11th to 20th	Day	76% 7% 7% 6% 4 1	1985
	21st to end	Day	72% 6% 11% 7% 4	2579
January	1st to 10th	Night	60% 15% 12% 10% 2	4704
	11th to 20th	Night	56% 13% 10% 15% 7%	4440
	21st to end	Night	58% 14% 10% 12% 5% 1	4614
February	1st to 10th	Night	56% 5% 12% 14% 11% 2	2470
	11th to 20th	Night	61% 5% 9% 15% 8% 1	2406
	21st to end	Night	52% 5% 12% 18% 10% 2	2010
March	1st to 10th	Night	60% 5% 8% 17% 8% 2	3514
	11th to 20th	Night	66% 8% 8% 12% 5% 1	3480
	21st to end	Night	64% 4 8% 14% 8% 1	3765
April	1st to 10th	Night	58% 5% 10% 14% 11% 2	1900
	11th to 20th	Night	53% 4 9% 21% 11% 2	1802
	21st to end	Night	57% 4 8% 15% 13% 2	1710
May	1st to 10th	Night	63% 6% 9% 15% 7% 1	2598
	11th to 20th	Night	42% 8% 16% 25% 9% 1	2507
	21st to end	Night	49% 11% 17% 16% 6%	2750
June	1st to 10th	Night	58% 6% 13% 16% 7%	1486
	11th to 20th	Night	46% 6% 12% 24% 11%	1330
	21st to end	Night	56% 7% 12% 15% 9%	1330
July	1st to 10th	Night	49% 8% 15% 19% 8% 1	2175
	11th to 20th	Night	44% 10% 20% 20% 6%	2375
	21st to end	Night	37% 9% 22% 21% 11%	2663
August	1st to 10th	Night	52% 8% 14% 20% 5%	2751
	11th to 20th	Night	41% 9% 17% 22% 10% 1	2809
	21st to end	Night	38% 8% 17% 26% 12%	3304
September	1st to 10th	Night	41% 6% 12% 30% 11%	1900
	11th to 20th	Night	42% 6% 12% 27% 12%	1924
	21st to end	Night	42% 7% 13% 27% 11% 1	2178
October	1st to 10th	Night	50% 6% 15% 22% 7%	3800
	11th to 20th	Night	46% 8% 14% 23% 9%	3779
	21st to end	Night	52% 8% 14% 17% 9%	4211
November	1st to 10th	Night	61% 6% 12% 14% 6% 1	2704
	11th to 20th	Night	64% 10% 10% 11% 4	2800
	21st to end	Night	69% 10% 11% 8% 3	2800
December	1st to 10th	Night	73% 7% 8% 8% 3	2800
	11th to 20th	Night	72% 9% 6% 9% 3	3435
	21st to end	Night	72% 6% 11% 9% 3	5139

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% 18% 34% 19% 5%	204
	11th to 20th	Day	25% 18% 31% 19% 7% 1	370
	21st to end	Day	17% 11% 38% 30% 4	407
February	1st to 10th	Day	28% 13% 32% 21% 4 3	370
	11th to 20th	Day	21% 13% 39% 22% 5%	366
	21st to end	Day	14% 13% 35% 28% 9% 1	307
March	1st to 10th	Day	22% 13% 32% 25% 8%	431
	11th to 20th	Day	17% 14% 32% 26% 10% 1	460
	21st to end	Day	27% 11% 27% 26% 8% 1	506
April	1st to 10th	Day	26% 14% 32% 22% 6%	460
	11th to 20th	Day	22% 10% 32% 26% 9% 2	452
	21st to end	Day	22% 8% 26% 30% 12% 2	460
May	1st to 10th	Day	31% 6% 27% 24% 9% 2	607
	11th to 20th	Day	21% 6% 24% 29% 17% 3	674
	21st to end	Day	21% 7% 27% 32% 12% 1	735
June	1st to 10th	Day	30% 6% 22% 29% 12% 2	680
	11th to 20th	Day	20% 6% 24% 34% 13% 3	680
	21st to end	Day	25% 3 20% 33% 15% 4	680
July	1st to 10th	Day	19% 3 25% 33% 17% 4	670
	11th to 20th	Day	14% 3 23% 36% 21% 4	668
	21st to end	Day	18% 4 17% 39% 20% 2	740
August	1st to 10th	Day	14% 3 18% 37% 24% 5%	522
	11th to 20th	Day	17% 4 20% 32% 20% 8%	479
	21st to end	Day	17% 7% 19% 32% 21% 5%	539
September	1st to 10th	Day	15% 6% 28% 33% 15% 3	490
	11th to 20th	Day	22% 8% 23% 30% 16% 2	490
	21st to end	Day	20% 10% 26% 27% 13% 4	443
October	1st to 10th	Day	21% 11% 22% 27% 16% 4	390
	11th to 20th	Day	24% 13% 27% 23% 11% 2	390
	21st to end	Day	25% 16% 31% 20% 7% 2	429
November	1st to 10th	Day	24% 18% 31% 22% 6% 1	395
	11th to 20th	Day	34% 17% 27% 17% 5% 1	400
	21st to end	Day	29% 17% 31% 20% 3	400
December	1st to 10th	Day	31% 16% 32% 17% 4	400
	11th to 20th	Day	29% 22% 33% 14% 3	400
	21st to end	Day	22% 21% 35% 18% 4 1	279
January	1st to 10th	Night	26% 14% 34% 21% 5%	850
	11th to 20th	Night	24% 15% 34% 22% 5%	850
	21st to end	Night	17% 16% 35% 24% 7% 1	857
February	1st to 10th	Night	25% 13% 34% 23% 6% 1	760
	11th to 20th	Night	25% 13% 36% 23% 3 1	743
	21st to end	Night	18% 12% 32% 28% 9% 1	628
March	1st to 10th	Night	23% 11% 33% 30% 3	760
	11th to 20th	Night	20% 13% 31% 27% 9% 1	760
	21st to end	Night	27% 12% 27% 24% 9% 1	810
April	1st to 10th	Night	27% 9% 30% 26% 7%	570
	11th to 20th	Night	26% 7% 29% 27% 10% 1	564
	21st to end	Night	26% 8% 26% 28% 10% 1	570
May	1st to 10th	Night	30% 6% 24% 24% 12% 3	570
	11th to 20th	Night	23% 4 23% 32% 14% 2	562
	21st to end	Night	19% 6% 33% 36% 6% 1	616
June	1st to 10th	Night	29% 5% 23% 34% 7% 1	536
	11th to 20th	Night	20% 4 25% 37% 13% 1	380
	21st to end	Night	26% 4 21% 36% 12% 2	380
July	1st to 10th	Night	18% 5% 25% 36% 13% 2	370
	11th to 20th	Night	15% 3 25% 43% 13% 1	484
	21st to end	Night	18% 4 22% 40% 16% 1	623
August	1st to 10th	Night	16% 3 26% 37% 18% 1	568
	11th to 20th	Night	15% 5% 22% 38% 19% 1	562
	21st to end	Night	16% 5% 19% 37% 22% 2	627
September	1st to 10th	Night	17% 6% 31% 33% 12% 1	570
	11th to 20th	Night	18% 9% 21% 36% 14% 2	594
	21st to end	Night	20% 9% 29% 29% 11% 1	760
October	1st to 10th	Night	22% 9% 26% 30% 12% 1	760
	11th to 20th	Night	22% 13% 27% 26% 11% 1	760
	21st to end	Night	30% 16% 27% 22% 5%	866
November	1st to 10th	Night	30% 16% 29% 20% 5%	880
	11th to 20th	Night	31% 17% 27% 19% 5% 1	900
	21st to end	Night	34% 16% 29% 18% 3	900
December	1st to 10th	Night	29% 16% 32% 19% 4	900
	11th to 20th	Night	27% 21% 32% 17% 3 1	900
	21st to end	Night	29% 17% 30% 19% 4 1	953

Page generated at 2024-12-21 05:13:49. Version ac07

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