Cap-Chat
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cap-Chat clear sky chart from 2005-11-06 to 2024-02-10.

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% 5% 8% 7% 4 5% 5% 5% 6% 27%	77722
	Night	17% 14% 6% 10% 9% 4 5% 4 4 5% 21%	81280
Transparency	Day	40% 39% 8% 10% 4	77407
	Night	44% 37% 7% 8% 3	81131
Seeing	Day	24% 16% 27% 22% 9% 2	15131
	Night	24% 16% 24% 24% 10% 1	23055

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	13% 17% 9% 16% 15% 10% 9% 3 3 2 4	2207
	11th to 20th	Day	11% 15% 10% 16% 21% 4 6% 4 4 4 6%	2219
	21st to end	Day	5% 10% 7% 12% 14% 9% 10% 6% 6% 6% 16%	2772
February	1st to 10th	Day	8% 14% 7% 10% 12% 6% 7% 6% 6% 5% 19%	1668
	11th to 20th	Day	12% 15% 7% 12% 8% 5% 7% 7% 5% 5% 17%	1573
	21st to end	Day	9% 11% 8% 8% 8% 5% 6% 8% 7% 8% 23%	1393
March	1st to 10th	Day	12% 15% 6% 9% 7% 3 7% 5% 6% 5% 26%	1858
	11th to 20th	Day	16% 15% 5% 9% 8% 4 6% 4 5% 5% 24%	1980
	21st to end	Day	14% 17% 5% 7% 7% 3 4 4 4 5% 31%	2178
April	1st to 10th	Day	18% 15% 5% 10% 7% 3 5% 4 5% 5% 24%	2185
	11th to 20th	Day	14% 12% 4 7% 6% 3 4 5% 5% 7% 34%	2312
	21st to end	Day	21% 10% 4 6% 4 3 4 4 5% 6% 33%	2340
May	1st to 10th	Day	24% 10% 4 6% 5% 3 4 4 4 5% 30%	2407
	11th to 20th	Day	22% 7% 3 5% 4 3 5% 4 5% 6% 35%	2556
	21st to end	Day	23% 7% 3 5% 5% 3 4 4 5% 7% 34%	2919
June	1st to 10th	Day	22% 8% 3 6% 5% 3 5% 5% 6% 6% 30%	2700
	11th to 20th	Day	20% 6% 2 6% 4 3 5% 5% 5% 8% 36%	2700
	21st to end	Day	21% 7% 3 6% 5% 3 5% 5% 6% 9% 31%	2700
July	1st to 10th	Day	17% 7% 3 6% 6% 3 5% 5% 7% 8% 33%	2700
	11th to 20th	Day	15% 6% 3 5% 5% 3 5% 5% 6% 9% 38%	2700
	21st to end	Day	14% 7% 3 5% 5% 3 6% 6% 6% 7% 36%	2904
August	1st to 10th	Day	15% 6% 3 5% 6% 3 5% 6% 7% 8% 37%	2359
	11th to 20th	Day	15% 7% 2 5% 5% 3 5% 5% 6% 9% 38%	2304
	21st to end	Day	18% 5% 3 6% 5% 4 5% 6% 5% 8% 35%	2574
September	1st to 10th	Day	21% 7% 3 5% 5% 2 3 4 4 6% 39%	2213
	11th to 20th	Day	24% 8% 2 4 4 2 3 3 4 5% 41%	1980
	21st to end	Day	19% 8% 2 6% 5% 3 4 4 5% 6% 36%	1980
October	1st to 10th	Day	20% 8% 3 6% 6% 3 3 5% 5% 7% 34%	1824
	11th to 20th	Day	24% 12% 3 7% 5% 4 4 4 5% 6% 27%	1800
	21st to end	Day	26% 15% 5% 6% 5% 3 4 4 5% 6% 21%	1785
November	1st to 10th	Day	21% 15% 7% 7% 7% 4 4 5% 6% 5% 21%	1513
	11th to 20th	Day	21% 15% 8% 13% 7% 4 4 3 4 5% 16%	1520
	21st to end	Day	20% 18% 9% 14% 8% 3 4 3 5% 4 11%	1470
December	1st to 10th	Day	18% 16% 8% 16% 14% 3 5% 4 4 4 7%	1330
	11th to 20th	Day	15% 15% 7% 19% 14% 6% 7% 5% 3 3 7%	1668
	21st to end	Day	12% 17% 7% 15% 14% 6% 5% 4 4 5% 10%	2431
January	1st to 10th	Night	10% 21% 9% 16% 20% 7% 5% 3 3 2 4	4748
	11th to 20th	Night	11% 18% 8% 18% 17% 5% 6% 3 3 3 8%	4750
	21st to end	Night	6% 14% 8% 14% 11% 8% 9% 6% 5% 6% 16%	4884
February	1st to 10th	Night	9% 13% 7% 12% 11% 7% 7% 5% 5% 5% 20%	2495
	11th to 20th	Night	15% 16% 6% 10% 10% 7% 7% 5% 4 5% 15%	2273
	21st to end	Night	10% 14% 8% 10% 9% 5% 7% 5% 4 5% 23%	1862
March	1st to 10th	Night	12% 15% 6% 11% 8% 4 6% 4 5% 5% 25%	2089
	11th to 20th	Night	16% 16% 7% 10% 8% 3 5% 3 3 4 24%	1979
	21st to end	Night	16% 18% 5% 8% 6% 4 4 4 4 5% 27%	2178
April	1st to 10th	Night	21% 13% 5% 10% 8% 4 4 4 5% 5% 21%	1772
	11th to 20th	Night	18% 11% 3 5% 6% 3 5% 5% 5% 5% 33%	1598
	21st to end	Night	24% 9% 5% 5% 4 3 4 3 4 6% 33%	1620
May	1st to 10th	Night	28% 10% 2 7% 6% 2 4 4 4 6% 26%	1553
	11th to 20th	Night	19% 11% 3 6% 6% 4 4 4 6% 6% 31%	1353
	21st to end	Night	24% 6% 3 6% 7% 4 4 5% 6% 8% 29%	1356
June	1st to 10th	Night	24% 8% 3 6% 6% 4 5% 4 5% 8% 26%	1260
	11th to 20th	Night	22% 7% 3 6% 6% 3 4 5% 5% 7% 34%	1260
	21st to end	Night	22% 7% 3 9% 6% 4 5% 5% 5% 6% 28%	1260
July	1st to 10th	Night	20% 7% 3 6% 6% 3 6% 6% 5% 7% 30%	1260
	11th to 20th	Night	13% 7% 3 5% 6% 3 8% 6% 7% 8% 34%	1260
	21st to end	Night	16% 7% 2 6% 5% 4 5% 6% 8% 8% 33%	1412
August	1st to 10th	Night	16% 8% 2 6% 7% 4 5% 6% 5% 8% 32%	1562
	11th to 20th	Night	15% 6% 4 7% 7% 4 5% 5% 7% 7% 33%	1596
	21st to end	Night	18% 7% 3 6% 4 3 5% 5% 5% 8% 35%	1782
September	1st to 10th	Night	21% 6% 2 5% 6% 4 4 5% 6% 6% 36%	1745
	11th to 20th	Night	23% 8% 3 6% 5% 2 3 4 4 6% 37%	1980
	21st to end	Night	20% 7% 2 6% 5% 3 4 4 4 5% 41%	1980
October	1st to 10th	Night	20% 9% 3 5% 5% 3 4 4 6% 6% 35%	2135
	11th to 20th	Night	28% 11% 4 6% 6% 3 4 4 4 5% 26%	2160
	21st to end	Night	25% 14% 3 6% 5% 4 4 4 5% 6% 24%	2569
November	1st to 10th	Night	22% 17% 5% 8% 7% 3 4 4 5% 5% 18%	2565
	11th to 20th	Night	21% 20% 7% 10% 6% 3 5% 3 4 5% 18%	2660
	21st to end	Night	19% 19% 9% 14% 7% 4 4 4 4 4 13%	2707
December	1st to 10th	Night	17% 18% 9% 18% 12% 4 4 3 4 2 9%	2850
	11th to 20th	Night	15% 18% 7% 15% 15% 5% 5% 3 4 4 8%	3531
	21st to end	Night	13% 19% 8% 14% 13% 5% 5% 4 4 5% 11%	5236

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	62% 35% 2	2208
	11th to 20th	Day	65% 27% 4 3 1	2219
	21st to end	Day	47% 32% 9% 9% 3	2772
February	1st to 10th	Day	45% 36% 7% 9% 3	1668
	11th to 20th	Day	49% 39% 5% 5% 2	1581
	21st to end	Day	39% 41% 7% 10% 3	1393
March	1st to 10th	Day	44% 37% 7% 9% 2	1862
	11th to 20th	Day	42% 39% 7% 8% 4	1980
	21st to end	Day	39% 38% 7% 10% 6%	2178
April	1st to 10th	Day	43% 40% 6% 8% 4	2185
	11th to 20th	Day	36% 39% 7% 12% 6%	2312
	21st to end	Day	33% 39% 6% 12% 8% 1	2340
May	1st to 10th	Day	39% 38% 6% 10% 7% 1	2407
	11th to 20th	Day	32% 39% 9% 13% 7%	2560
	21st to end	Day	34% 40% 7% 11% 8%	2919
June	1st to 10th	Day	36% 40% 6% 10% 6% 1	2700
	11th to 20th	Day	30% 40% 10% 12% 8% 1	2700
	21st to end	Day	37% 41% 7% 9% 5%	2700
July	1st to 10th	Day	31% 42% 12% 11% 4	2625
	11th to 20th	Day	31% 42% 9% 13% 5%	2619
	21st to end	Day	33% 42% 10% 12% 3	2742
August	1st to 10th	Day	32% 42% 10% 13% 3	2345
	11th to 20th	Day	30% 40% 14% 14% 2	2304
	21st to end	Day	34% 40% 11% 13% 2	2574
September	1st to 10th	Day	34% 40% 10% 13% 3	2213
	11th to 20th	Day	30% 38% 11% 16% 5%	1980
	21st to end	Day	35% 40% 8% 14% 4	1980
October	1st to 10th	Day	38% 39% 12% 9% 2	1824
	11th to 20th	Day	42% 39% 9% 8% 3	1800
	21st to end	Day	44% 40% 5% 8% 2 1	1785
November	1st to 10th	Day	39% 44% 9% 7% 2	1513
	11th to 20th	Day	44% 43% 7% 5% 1	1520
	21st to end	Day	49% 42% 6% 3 1	1470
December	1st to 10th	Day	53% 41% 3 2	1330
	11th to 20th	Day	55% 36% 4 4 1	1668
	21st to end	Day	53% 34% 7% 6% 1	2431
January	1st to 10th	Night	64% 32% 3 1	4748
	11th to 20th	Night	60% 29% 4 4 2	4750
	21st to end	Night	52% 28% 6% 7% 4 1	4884
February	1st to 10th	Night	45% 36% 7% 7% 3	2495
	11th to 20th	Night	50% 38% 5% 5% 2	2276
	21st to end	Night	44% 39% 6% 9% 2	1862
March	1st to 10th	Night	43% 38% 6% 11% 2	2098
	11th to 20th	Night	42% 38% 5% 11% 4	1980
	21st to end	Night	41% 38% 6% 9% 6%	2178
April	1st to 10th	Night	44% 40% 6% 5% 5%	1772
	11th to 20th	Night	32% 38% 7% 13% 8% 1	1598
	21st to end	Night	33% 37% 7% 13% 9% 1	1620
May	1st to 10th	Night	39% 37% 6% 11% 6% 1	1553
	11th to 20th	Night	33% 38% 7% 14% 7%	1354
	21st to end	Night	36% 40% 7% 10% 6%	1357
June	1st to 10th	Night	38% 37% 8% 10% 5% 1	1260
	11th to 20th	Night	32% 39% 9% 12% 8% 1	1260
	21st to end	Night	39% 40% 6% 9% 6%	1260
July	1st to 10th	Night	33% 40% 10% 12% 4	1225
	11th to 20th	Night	30% 43% 11% 11% 4	1218
	21st to end	Night	30% 43% 11% 13% 3	1334
August	1st to 10th	Night	33% 39% 11% 14% 3	1552
	11th to 20th	Night	32% 41% 13% 11% 3	1596
	21st to end	Night	32% 40% 8% 17% 3	1782
September	1st to 10th	Night	32% 39% 10% 15% 4	1745
	11th to 20th	Night	31% 38% 11% 14% 5%	1980
	21st to end	Night	31% 39% 9% 14% 7%	1980
October	1st to 10th	Night	34% 39% 11% 11% 4 1	2135
	11th to 20th	Night	42% 38% 9% 8% 3	2160
	21st to end	Night	41% 40% 8% 8% 3 1	2569
November	1st to 10th	Night	39% 44% 9% 5% 2	2565
	11th to 20th	Night	43% 42% 7% 6% 1	2660
	21st to end	Night	47% 43% 5% 3 1	2707
December	1st to 10th	Night	53% 42% 3 2	2850
	11th to 20th	Night	55% 38% 3 3	3532
	21st to end	Night	55% 33% 7% 4 1	5236

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% 30% 21% 4 1	180
	11th to 20th	Day	27% 26% 29% 12% 6% 1	180
	21st to end	Day	19% 28% 26% 21% 5% 2	198
February	1st to 10th	Day	20% 22% 33% 20% 4 1	334
	11th to 20th	Day	18% 29% 29% 18% 5%	336
	21st to end	Day	16% 25% 32% 17% 8% 1	308
March	1st to 10th	Day	20% 20% 33% 20% 6% 1	420
	11th to 20th	Day	25% 20% 24% 21% 9% 1	420
	21st to end	Day	23% 26% 28% 16% 5% 2	462
April	1st to 10th	Day	24% 25% 28% 16% 6% 1	420
	11th to 20th	Day	21% 19% 31% 20% 7% 2	412
	21st to end	Day	26% 15% 30% 18% 8% 3	420
May	1st to 10th	Day	28% 12% 28% 22% 8% 1	490
	11th to 20th	Day	25% 11% 27% 25% 10% 2	624
	21st to end	Day	28% 16% 28% 21% 7% 1	680
June	1st to 10th	Day	26% 10% 30% 22% 12% 1	630
	11th to 20th	Day	25% 12% 25% 23% 14% 1	630
	21st to end	Day	23% 8% 25% 32% 10% 2	630
July	1st to 10th	Day	20% 12% 27% 27% 11% 2	620
	11th to 20th	Day	19% 10% 25% 32% 13% 2	618
	21st to end	Day	17% 7% 26% 33% 14% 2	648
August	1st to 10th	Day	20% 8% 28% 28% 14% 3	446
	11th to 20th	Day	16% 10% 24% 34% 13% 3	439
	21st to end	Day	19% 10% 25% 28% 14% 3	495
September	1st to 10th	Day	23% 14% 25% 27% 10% 2	450
	11th to 20th	Day	29% 14% 24% 23% 8% 3	450
	21st to end	Day	24% 19% 30% 18% 8% 2	450
October	1st to 10th	Day	23% 20% 28% 20% 7% 2	372
	11th to 20th	Day	34% 17% 21% 19% 7% 2	360
	21st to end	Day	33% 23% 20% 13% 9% 1	396
November	1st to 10th	Day	31% 24% 24% 17% 3 1	365
	11th to 20th	Day	30% 23% 25% 14% 7% 1	370
	21st to end	Day	32% 24% 27% 13% 3 1	320
December	1st to 10th	Day	23% 19% 32% 17% 7% 2	180
	11th to 20th	Day	25% 31% 27% 14% 3	180
	21st to end	Day	24% 27% 29% 17% 3 1	198
January	1st to 10th	Night	25% 21% 29% 19% 6% 1	850
	11th to 20th	Night	21% 24% 31% 18% 5%	845
	21st to end	Night	16% 23% 28% 23% 8% 1	836
February	1st to 10th	Night	15% 22% 33% 22% 7% 1	759
	11th to 20th	Night	24% 17% 27% 23% 7% 1	703
	21st to end	Night	16% 16% 29% 26% 11% 2	592
March	1st to 10th	Night	16% 19% 29% 25% 10% 1	720
	11th to 20th	Night	24% 19% 24% 23% 8% 1	720
	21st to end	Night	23% 16% 24% 25% 10% 1	792
April	1st to 10th	Night	28% 15% 26% 21% 9% 1	615
	11th to 20th	Night	24% 14% 23% 25% 12% 2	534
	21st to end	Night	29% 12% 20% 26% 11% 3	540
May	1st to 10th	Night	29% 10% 20% 28% 11% 2	540
	11th to 20th	Night	23% 9% 22% 30% 14% 2	469
	21st to end	Night	25% 9% 24% 31% 9% 1	389
June	1st to 10th	Night	25% 6% 19% 36% 14% 1	360
	11th to 20th	Night	25% 5% 16% 34% 19% 1	360
	21st to end	Night	23% 7% 20% 34% 15% 1	360
July	1st to 10th	Night	19% 6% 22% 38% 12% 3	350
	11th to 20th	Night	13% 5% 26% 36% 19% 1	348
	21st to end	Night	18% 6% 19% 32% 23% 3	394
August	1st to 10th	Night	19% 6% 19% 34% 19% 3	488
	11th to 20th	Night	15% 7% 17% 37% 23% 2	532
	21st to end	Night	19% 7% 22% 32% 18% 3	594
September	1st to 10th	Night	22% 11% 23% 28% 15% 1	542
	11th to 20th	Night	26% 11% 20% 28% 13% 2	720
	21st to end	Night	24% 12% 27% 28% 9%	720
October	1st to 10th	Night	26% 16% 22% 26% 8% 1	720
	11th to 20th	Night	35% 15% 17% 22% 10% 1	720
	21st to end	Night	34% 17% 21% 19% 8% 1	792
November	1st to 10th	Night	34% 22% 23% 16% 3 1	816
	11th to 20th	Night	31% 22% 22% 17% 6% 2	850
	21st to end	Night	29% 23% 25% 17% 6%	850
December	1st to 10th	Night	27% 22% 28% 16% 7% 1	850
	11th to 20th	Night	27% 27% 25% 15% 5% 1	850
	21st to end	Night	27% 23% 23% 20% 5% 2	935

Page generated at 2024-02-07 06:11:58. Version ac07

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