Cape Race
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cape Race clear sky chart from 2005-11-06 to 2024-09-29.

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	26% 14% 5% 10% 6% 5% 4 3 4 5% 18%	101181
	Night	25% 15% 5% 10% 5% 4 4 3 4 5% 19%	97194
Transparency	Day	63% 9% 11% 12% 5%	100927
	Night	64% 8% 10% 12% 5% 1	97068
Seeing	Day	29% 13% 27% 22% 8% 1	18022
	Night	30% 13% 28% 21% 7% 1	24505

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	19% 12% 7% 11% 6% 5% 5% 4 3 4 23%	2247
	11th to 20th	Day	25% 14% 5% 15% 7% 5% 4 3 4 4 15%	2530
	21st to end	Day	19% 14% 8% 14% 7% 5% 4 4 4 4 17%	2783
February	1st to 10th	Day	22% 12% 8% 13% 9% 7% 6% 4 5% 4 10%	1695
	11th to 20th	Day	22% 16% 6% 13% 8% 5% 3 3 4 6% 14%	1682
	21st to end	Day	15% 14% 6% 14% 8% 6% 5% 4 5% 5% 17%	1570
March	1st to 10th	Day	25% 13% 5% 12% 6% 5% 5% 3 4 4 18%	3167
	11th to 20th	Day	21% 13% 6% 16% 8% 5% 5% 3 5% 5% 13%	3480
	21st to end	Day	26% 14% 5% 14% 8% 5% 4 3 4 5% 11%	3817
April	1st to 10th	Day	26% 15% 5% 11% 6% 5% 4 3 4 4 17%	2270
	11th to 20th	Day	25% 13% 4 9% 6% 5% 4 3 4 5% 21%	2441
	21st to end	Day	26% 14% 5% 11% 5% 5% 3 3 4 5% 20%	2470
May	1st to 10th	Day	21% 19% 5% 12% 6% 4 4 3 5% 6% 17%	4105
	11th to 20th	Day	31% 18% 4 8% 5% 4 4 3 4 5% 15%	4279
	21st to end	Day	24% 15% 5% 13% 6% 5% 4 3 4 4 17%	5173
June	1st to 10th	Day	36% 16% 4 8% 4 4 3 2 4 5% 13%	2850
	11th to 20th	Day	27% 15% 4 8% 5% 4 4 4 5% 6% 18%	2850
	21st to end	Day	32% 15% 4 8% 5% 4 4 3 4 6% 14%	2850
July	1st to 10th	Day	38% 13% 4 8% 4 4 3 3 4 5% 14%	4750
	11th to 20th	Day	32% 18% 4 9% 5% 5% 4 3 3 5% 14%	4640
	21st to end	Day	24% 12% 3 9% 5% 5% 5% 4 5% 6% 23%	4815
August	1st to 10th	Day	33% 13% 3 7% 4 4 3 3 4 6% 19%	4113
	11th to 20th	Day	25% 13% 4 10% 6% 4 5% 3 5% 5% 20%	4046
	21st to end	Day	24% 9% 3 8% 4 4 4 3 5% 7% 29%	4532
September	1st to 10th	Day	23% 10% 3 8% 4 4 4 4 6% 7% 26%	2252
	11th to 20th	Day	23% 9% 3 9% 6% 5% 4 3 5% 6% 28%	2090
	21st to end	Day	20% 8% 3 6% 5% 5% 5% 4 7% 6% 31%	2071
October	1st to 10th	Day	21% 10% 3 9% 5% 6% 5% 4 5% 8% 25%	1888
	11th to 20th	Day	25% 12% 4 11% 6% 4 5% 4 4 6% 21%	1786
	21st to end	Day	25% 13% 4 9% 5% 4 4 3 5% 7% 21%	1782
November	1st to 10th	Day	24% 12% 3 10% 5% 4 4 4 4 6% 24%	1669
	11th to 20th	Day	24% 12% 4 10% 6% 6% 3 4 5% 7% 18%	1520
	21st to end	Day	25% 14% 4 10% 5% 5% 4 4 5% 6% 19%	1520
December	1st to 10th	Day	27% 15% 3 10% 5% 5% 5% 4 5% 6% 15%	1338
	11th to 20th	Day	18% 16% 5% 11% 7% 5% 4 3 6% 7% 17%	1668
	21st to end	Day	20% 20% 6% 11% 5% 5% 5% 4 4 5% 14%	2442
January	1st to 10th	Night	18% 14% 7% 11% 6% 5% 5% 3 5% 6% 21%	4706
	11th to 20th	Night	21% 13% 7% 16% 7% 5% 4 3 5% 5% 14%	4440
	21st to end	Night	17% 14% 9% 15% 7% 5% 5% 3 4 5% 16%	4884
February	1st to 10th	Night	23% 14% 6% 13% 7% 6% 5% 3 4 5% 13%	2483
	11th to 20th	Night	24% 14% 5% 12% 6% 5% 4 3 5% 5% 15%	2380
	21st to end	Night	16% 12% 6% 13% 8% 5% 5% 4 5% 6% 20%	1884
March	1st to 10th	Night	25% 13% 6% 10% 5% 4 3 3 4 6% 22%	3673
	11th to 20th	Night	17% 13% 8% 17% 7% 4 4 4 5% 5% 17%	3479
	21st to end	Night	29% 15% 5% 10% 5% 4 4 3 5% 4 16%	3815
April	1st to 10th	Night	27% 17% 5% 9% 5% 5% 4 2 3 5% 19%	1905
	11th to 20th	Night	26% 14% 4 9% 5% 4 3 3 5% 5% 22%	1688
	21st to end	Night	28% 18% 5% 8% 5% 4 4 3 3 4 19%	1710
May	1st to 10th	Night	24% 19% 5% 10% 6% 3 3 3 3 5% 18%	2845
	11th to 20th	Night	35% 17% 4 8% 5% 3 3 3 3 5% 14%	2620
	21st to end	Night	26% 17% 5% 12% 5% 4 4 3 4 5% 16%	2412
June	1st to 10th	Night	38% 16% 4 6% 4 3 3 2 4 5% 14%	1330
	11th to 20th	Night	30% 17% 5% 8% 5% 3 4 3 4 5% 16%	1330
	21st to end	Night	33% 17% 4 9% 5% 4 3 3 3 4 14%	1330
July	1st to 10th	Night	47% 14% 4 9% 4 3 2 2 3 4 9%	2220
	11th to 20th	Night	34% 25% 6% 10% 4 3 3 2 2 3 8%	2327
	21st to end	Night	26% 17% 4 9% 6% 4 3 3 3 3 21%	2750
August	1st to 10th	Night	29% 21% 4 8% 4 3 3 3 4 4 17%	2825
	11th to 20th	Night	29% 17% 5% 8% 4 4 4 3 5% 5% 17%	2791
	21st to end	Night	30% 10% 3 7% 4 3 3 3 4 6% 27%	3135
September	1st to 10th	Night	26% 11% 3 8% 4 3 4 3 5% 7% 27%	1924
	11th to 20th	Night	27% 11% 3 7% 5% 5% 4 3 5% 4 25%	2090
	21st to end	Night	22% 7% 3 6% 5% 5% 4 4 6% 6% 32%	2077
October	1st to 10th	Night	23% 10% 3 8% 5% 4 4 4 5% 7% 28%	2071
	11th to 20th	Night	24% 12% 4 8% 5% 4 4 4 5% 6% 22%	2172
	21st to end	Night	25% 13% 4 9% 6% 4 4 3 5% 5% 20%	2574
November	1st to 10th	Night	25% 13% 4 8% 5% 5% 4 3 5% 6% 23%	2408
	11th to 20th	Night	23% 14% 4 8% 5% 5% 5% 4 5% 6% 22%	2660
	21st to end	Night	22% 12% 3 9% 5% 5% 5% 4 6% 7% 21%	2660
December	1st to 10th	Night	24% 17% 5% 10% 5% 4 4 3 5% 6% 16%	2840
	11th to 20th	Night	22% 16% 5% 11% 6% 5% 5% 4 5% 5% 15%	3531
	21st to end	Night	21% 15% 5% 11% 5% 5% 4 3 5% 6% 20%	5225

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	58% 11% 10% 12% 8% 1	2248
	11th to 20th	Day	68% 7% 10% 7% 7% 1	2530
	21st to end	Day	66% 7% 8% 13% 6%	2783
February	1st to 10th	Day	72% 10% 8% 6% 4 1	1695
	11th to 20th	Day	67% 8% 12% 10% 3 1	1689
	21st to end	Day	65% 8% 9% 8% 8% 2	1570
March	1st to 10th	Day	65% 6% 9% 12% 6% 1	3172
	11th to 20th	Day	67% 8% 12% 9% 4	3480
	21st to end	Day	70% 5% 10% 10% 3 1	3817
April	1st to 10th	Day	65% 6% 12% 11% 6% 1	2270
	11th to 20th	Day	61% 8% 11% 11% 8% 1	2441
	21st to end	Day	65% 7% 8% 11% 8% 1	2470
May	1st to 10th	Day	68% 8% 9% 11% 4	4120
	11th to 20th	Day	72% 8% 7% 9% 4	4283
	21st to end	Day	63% 11% 9% 12% 3	5173
June	1st to 10th	Day	74% 6% 8% 9% 3	2850
	11th to 20th	Day	65% 9% 10% 11% 4	2850
	21st to end	Day	68% 11% 7% 11% 3	2850
July	1st to 10th	Day	70% 8% 9% 9% 3	4675
	11th to 20th	Day	65% 12% 10% 8% 5%	4558
	21st to end	Day	51% 14% 15% 13% 7%	4662
August	1st to 10th	Day	61% 10% 12% 14% 3	4099
	11th to 20th	Day	59% 11% 13% 14% 3	4085
	21st to end	Day	50% 9% 14% 24% 3	4532
September	1st to 10th	Day	53% 8% 12% 19% 7%	2252
	11th to 20th	Day	54% 8% 11% 16% 10%	2090
	21st to end	Day	49% 8% 15% 19% 8% 1	2071
October	1st to 10th	Day	55% 9% 13% 16% 6% 1	1888
	11th to 20th	Day	62% 7% 10% 15% 5%	1786
	21st to end	Day	59% 8% 12% 14% 5% 1	1782
November	1st to 10th	Day	57% 8% 16% 13% 5%	1669
	11th to 20th	Day	61% 8% 12% 13% 6% 1	1520
	21st to end	Day	64% 8% 12% 12% 5%	1520
December	1st to 10th	Day	65% 11% 9% 10% 6%	1338
	11th to 20th	Day	61% 8% 15% 11% 4 1	1667
	21st to end	Day	70% 8% 8% 11% 3	2442
January	1st to 10th	Night	60% 10% 9% 10% 7% 4	4706
	11th to 20th	Night	69% 8% 10% 8% 5%	4440
	21st to end	Night	67% 7% 12% 9% 5% 1	4884
February	1st to 10th	Night	71% 8% 8% 8% 4 1	2483
	11th to 20th	Night	67% 10% 10% 9% 4	2384
	21st to end	Night	62% 9% 11% 11% 6% 1	1884
March	1st to 10th	Night	64% 6% 10% 15% 5%	3681
	11th to 20th	Night	66% 9% 10% 10% 4	3480
	21st to end	Night	69% 5% 10% 11% 5%	3815
April	1st to 10th	Night	66% 6% 8% 12% 7% 1	1905
	11th to 20th	Night	62% 6% 9% 12% 9% 1	1688
	21st to end	Night	70% 4 7% 11% 7% 1	1710
May	1st to 10th	Night	66% 8% 9% 12% 4	2850
	11th to 20th	Night	73% 5% 7% 10% 4	2621
	21st to end	Night	67% 7% 9% 13% 4	2413
June	1st to 10th	Night	75% 5% 7% 9% 3	1330
	11th to 20th	Night	68% 8% 8% 11% 4	1330
	21st to end	Night	72% 9% 8% 7% 4 1	1330
July	1st to 10th	Night	77% 7% 6% 6% 3	2186
	11th to 20th	Night	71% 15% 6% 6% 2	2285
	21st to end	Night	56% 13% 12% 16% 4	2663
August	1st to 10th	Night	64% 11% 11% 12% 3	2814
	11th to 20th	Night	61% 12% 12% 11% 3	2818
	21st to end	Night	56% 7% 12% 22% 3	3134
September	1st to 10th	Night	55% 9% 10% 19% 6% 1	1924
	11th to 20th	Night	59% 8% 11% 12% 9%	2090
	21st to end	Night	51% 8% 14% 19% 8%	2077
October	1st to 10th	Night	55% 8% 11% 19% 7%	2071
	11th to 20th	Night	60% 9% 11% 14% 6%	2172
	21st to end	Night	63% 8% 11% 11% 6% 1	2574
November	1st to 10th	Night	60% 7% 14% 13% 5% 1	2408
	11th to 20th	Night	61% 8% 12% 13% 4 1	2660
	21st to end	Night	59% 8% 14% 12% 6% 1	2660
December	1st to 10th	Night	68% 9% 9% 10% 4	2840
	11th to 20th	Night	66% 10% 11% 8% 5%	3533
	21st to end	Night	63% 8% 12% 13% 4	5225

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	28% 18% 35% 14% 5%	370
	11th to 20th	Day	28% 18% 34% 16% 5% 1	370
	21st to end	Day	30% 16% 31% 20% 3	407
February	1st to 10th	Day	31% 18% 30% 16% 4 1	370
	11th to 20th	Day	28% 21% 36% 11% 3	366
	21st to end	Day	22% 21% 31% 22% 5%	307
March	1st to 10th	Day	23% 27% 32% 15% 3	370
	11th to 20th	Day	23% 15% 31% 24% 8% 1	370
	21st to end	Day	27% 20% 29% 16% 6% 1	407
April	1st to 10th	Day	32% 16% 30% 18% 4 1	473
	11th to 20th	Day	30% 15% 27% 19% 8% 1	639
	21st to end	Day	30% 14% 30% 19% 6% 1	650
May	1st to 10th	Day	29% 13% 29% 21% 7% 2	653
	11th to 20th	Day	28% 9% 28% 25% 8% 1	674
	21st to end	Day	29% 12% 26% 24% 8%	735
June	1st to 10th	Day	43% 9% 21% 19% 7% 1	680
	11th to 20th	Day	33% 7% 26% 27% 7% 1	680
	21st to end	Day	33% 9% 24% 24% 9% 1	680
July	1st to 10th	Day	33% 10% 25% 25% 8% 1	670
	11th to 20th	Day	32% 9% 19% 28% 11% 1	668
	21st to end	Day	32% 8% 22% 26% 11% 1	740
August	1st to 10th	Day	29% 8% 22% 29% 11% 1	675
	11th to 20th	Day	30% 7% 19% 27% 16% 1	667
	21st to end	Day	25% 6% 25% 28% 15% 1	748
September	1st to 10th	Day	25% 9% 23% 25% 16% 2	510
	11th to 20th	Day	28% 11% 27% 24% 9% 1	390
	21st to end	Day	24% 9% 30% 26% 10% 1	385
October	1st to 10th	Day	23% 12% 32% 26% 8%	360
	11th to 20th	Day	29% 8% 32% 19% 10% 2	360
	21st to end	Day	29% 18% 27% 20% 5% 1	396
November	1st to 10th	Day	24% 20% 27% 21% 7%	365
	11th to 20th	Day	30% 17% 29% 18% 6% 1	370
	21st to end	Day	32% 16% 29% 15% 6% 1	370
December	1st to 10th	Day	30% 18% 29% 15% 7%	370
	11th to 20th	Day	28% 25% 29% 14% 3	370
	21st to end	Day	26% 18% 32% 19% 5%	407
January	1st to 10th	Night	28% 21% 35% 13% 3	850
	11th to 20th	Night	32% 17% 30% 16% 4	850
	21st to end	Night	27% 19% 30% 20% 3	935
February	1st to 10th	Night	27% 22% 35% 14% 2	850
	11th to 20th	Night	30% 18% 37% 12% 3	822
	21st to end	Night	21% 16% 36% 21% 6%	628
March	1st to 10th	Night	28% 18% 34% 16% 3	732
	11th to 20th	Night	22% 14% 31% 22% 9% 1	570
	21st to end	Night	33% 15% 27% 20% 4 1	627
April	1st to 10th	Night	34% 14% 27% 17% 7% 1	570
	11th to 20th	Night	34% 13% 25% 21% 7%	564
	21st to end	Night	34% 11% 26% 20% 8% 1	570
May	1st to 10th	Night	33% 9% 23% 24% 9% 1	570
	11th to 20th	Night	33% 5% 26% 25% 10% 1	562
	21st to end	Night	32% 9% 26% 26% 7% 1	616
June	1st to 10th	Night	44% 6% 20% 23% 6% 1	570
	11th to 20th	Night	36% 8% 25% 21% 9% 1	570
	21st to end	Night	36% 7% 22% 24% 9% 1	570
July	1st to 10th	Night	36% 8% 21% 26% 8% 1	556
	11th to 20th	Night	32% 8% 24% 27% 9%	552
	21st to end	Night	34% 8% 20% 27% 10% 1	623
August	1st to 10th	Night	32% 5% 23% 27% 11% 2	568
	11th to 20th	Night	34% 4 20% 29% 13% 1	562
	21st to end	Night	28% 5% 23% 31% 12%	627
September	1st to 10th	Night	27% 5% 27% 27% 13% 1	570
	11th to 20th	Night	30% 8% 27% 25% 9% 1	570
	21st to end	Night	26% 7% 29% 27% 10% 1	567
October	1st to 10th	Night	26% 10% 30% 26% 8% 1	586
	11th to 20th	Night	29% 9% 33% 19% 8% 1	642
	21st to end	Night	31% 15% 28% 20% 6% 1	891
November	1st to 10th	Night	30% 15% 29% 19% 6%	830
	11th to 20th	Night	28% 15% 31% 19% 7% 1	850
	21st to end	Night	30% 17% 33% 16% 4	850
December	1st to 10th	Night	31% 17% 29% 18% 5%	850
	11th to 20th	Night	31% 25% 28% 13% 3	850
	21st to end	Night	24% 17% 33% 20% 6%	935

Page generated at 2024-09-26 10:52:24. Version ac07

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