The Islands Provincial Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Islands Provincial Park clear sky chart from 2005-11-06 to 2024-04-03.

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	22% 10% 4 7% 5% 3 4 4 5% 6% 31%	79320
	Night	21% 10% 4 7% 5% 3 4 4 5% 6% 29%	80811
Transparency	Day	54% 3 11% 20% 11% 1	79030
	Night	56% 3 10% 21% 10% 1	80636
Seeing	Day	28% 16% 32% 18% 6% 1	16244
	Night	27% 14% 29% 22% 7% 1	23990

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	20% 13% 5% 9% 7% 3 5% 5% 5% 6% 21%	2533
	11th to 20th	Day	20% 14% 6% 15% 7% 4 5% 4 5% 5% 17%	2840
	21st to end	Day	22% 11% 5% 10% 7% 4 5% 4 4 6% 22%	3124
February	1st to 10th	Day	21% 15% 6% 9% 7% 4 6% 4 4 5% 18%	1710
	11th to 20th	Day	19% 11% 5% 10% 9% 4 5% 4 5% 6% 21%	1663
	21st to end	Day	15% 13% 5% 8% 6% 3 5% 4 5% 8% 27%	1498
March	1st to 10th	Day	20% 13% 4 9% 6% 2 4 5% 4 5% 26%	2063
	11th to 20th	Day	20% 12% 5% 6% 6% 3 4 3 4 6% 31%	2090
	21st to end	Day	20% 12% 5% 8% 6% 3 4 3 3 5% 31%	2299
April	1st to 10th	Day	25% 14% 4 6% 5% 3 4 3 4 5% 27%	2110
	11th to 20th	Day	22% 9% 3 5% 5% 3 5% 4 4 6% 35%	2253
	21st to end	Day	26% 9% 3 6% 4 2 4 4 5% 6% 33%	2340
May	1st to 10th	Day	27% 11% 3 6% 6% 3 4 4 4 5% 28%	2340
	11th to 20th	Day	24% 8% 3 5% 4 2 3 4 5% 6% 35%	2405
	21st to end	Day	24% 8% 3 5% 4 3 4 4 5% 7% 32%	2724
June	1st to 10th	Day	27% 8% 3 5% 4 2 4 4 4 6% 32%	2520
	11th to 20th	Day	22% 8% 3 5% 5% 2 4 3 5% 6% 37%	2664
	21st to end	Day	26% 7% 3 5% 5% 3 5% 4 5% 8% 29%	2700
July	1st to 10th	Day	22% 6% 3 6% 4 2 4 5% 6% 7% 36%	2692
	11th to 20th	Day	21% 8% 3 5% 5% 3 5% 6% 5% 9% 31%	2480
	21st to end	Day	22% 9% 3 5% 4 3 5% 4 6% 7% 32%	2548
August	1st to 10th	Day	18% 7% 2 5% 5% 3 5% 4 6% 7% 38%	2327
	11th to 20th	Day	19% 7% 3 6% 5% 3 4 4 6% 8% 36%	2304
	21st to end	Day	19% 6% 1 5% 4 2 4 4 5% 7% 42%	2516
September	1st to 10th	Day	16% 7% 2 5% 4 2 4 4 5% 7% 44%	2160
	11th to 20th	Day	19% 6% 3 5% 4 3 3 3 5% 5% 43%	1998
	21st to end	Day	21% 8% 2 4 4 3 3 3 3 6% 42%	1979
October	1st to 10th	Day	20% 7% 2 4 5% 3 4 4 4 7% 39%	1800
	11th to 20th	Day	21% 7% 2 6% 4 4 4 5% 4 7% 35%	1800
	21st to end	Day	22% 8% 3 7% 6% 4 5% 3 5% 6% 31%	1977
November	1st to 10th	Day	21% 9% 3 5% 5% 2 5% 4 5% 6% 34%	1614
	11th to 20th	Day	21% 12% 4 7% 6% 3 4 4 4 8% 27%	1520
	21st to end	Day	20% 13% 4 8% 7% 4 5% 5% 5% 5% 24%	1520
December	1st to 10th	Day	25% 13% 4 8% 6% 4 4 4 5% 6% 21%	1520
	11th to 20th	Day	31% 12% 4 8% 5% 3 5% 4 4 5% 19%	1906
	21st to end	Day	23% 13% 7% 7% 5% 3 5% 4 5% 5% 24%	2783
January	1st to 10th	Night	17% 12% 6% 13% 7% 4 5% 5% 5% 5% 20%	4420
	11th to 20th	Night	18% 15% 6% 13% 7% 3 5% 5% 5% 6% 18%	4120
	21st to end	Night	20% 14% 5% 11% 6% 3 5% 5% 5% 6% 20%	4532
February	1st to 10th	Night	20% 12% 6% 9% 8% 4 5% 5% 5% 5% 21%	2470
	11th to 20th	Night	18% 11% 4 8% 8% 5% 6% 5% 6% 7% 21%	2403
	21st to end	Night	14% 11% 4 7% 7% 4 6% 5% 5% 8% 29%	1951
March	1st to 10th	Night	19% 11% 4 6% 6% 4 7% 5% 4 6% 28%	2103
	11th to 20th	Night	18% 11% 4 6% 8% 3 4 6% 4 6% 29%	2089
	21st to end	Night	20% 9% 4 7% 5% 3 4 3 4 6% 35%	2299
April	1st to 10th	Night	24% 12% 3 6% 5% 2 3 4 5% 6% 30%	1893
	11th to 20th	Night	24% 10% 3 4 4 3 4 4 4 7% 34%	1652
	21st to end	Night	26% 9% 3 5% 5% 3 4 5% 4 7% 32%	1620
May	1st to 10th	Night	24% 10% 4 6% 4 3 4 5% 5% 6% 28%	1620
	11th to 20th	Night	26% 8% 3 6% 5% 3 3 4 4 6% 33%	1488
	21st to end	Night	23% 10% 2 7% 5% 2 4 4 6% 6% 31%	1550
June	1st to 10th	Night	26% 8% 4 7% 4 3 3 4 5% 8% 29%	1440
	11th to 20th	Night	22% 9% 3 6% 5% 3 4 4 4 6% 34%	1309
	21st to end	Night	28% 9% 4 5% 5% 3 4 3 5% 6% 27%	1260
July	1st to 10th	Night	23% 9% 3 5% 5% 2 3 4 6% 9% 31%	1260
	11th to 20th	Night	22% 9% 4 6% 6% 4 5% 5% 6% 8% 26%	1462
	21st to end	Night	25% 9% 3 5% 5% 3 5% 5% 4 7% 31%	1770
August	1st to 10th	Night	18% 9% 3 5% 5% 2 4 3 3 8% 38%	1612
	11th to 20th	Night	20% 10% 3 6% 6% 2 4 3 6% 7% 33%	1596
	21st to end	Night	19% 7% 2 4 4 3 4 4 5% 8% 39%	1840
September	1st to 10th	Night	17% 7% 3 5% 5% 3 5% 4 5% 7% 41%	1800
	11th to 20th	Night	21% 7% 2 4 3 2 4 4 5% 6% 44%	1957
	21st to end	Night	21% 8% 3 5% 3 2 3 3 5% 6% 39%	1980
October	1st to 10th	Night	21% 7% 3 4 5% 3 4 4 4 7% 39%	2160
	11th to 20th	Night	20% 7% 2 5% 4 3 3 4 5% 6% 41%	2160
	21st to end	Night	24% 8% 3 5% 4 2 4 4 4 7% 34%	2376
November	1st to 10th	Night	19% 7% 4 5% 5% 3 4 4 5% 6% 37%	2462
	11th to 20th	Night	20% 9% 3 6% 6% 4 6% 5% 5% 7% 28%	2660
	21st to end	Night	20% 12% 4 7% 5% 3 5% 5% 6% 6% 28%	2660
December	1st to 10th	Night	24% 12% 4 8% 7% 4 5% 4 5% 7% 21%	2660
	11th to 20th	Night	29% 12% 4 6% 5% 3 4 5% 5% 6% 21%	3293
	21st to end	Night	25% 11% 5% 8% 5% 3 5% 4 4 5% 25%	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	61% 2 13% 19% 5%	2534
	11th to 20th	Day	68% 3 10% 14% 5%	2840
	21st to end	Day	62% 2 8% 19% 8%	3124
February	1st to 10th	Day	65% 3 11% 13% 8% 1	1710
	11th to 20th	Day	61% 3 10% 17% 8% 1	1671
	21st to end	Day	54% 3 11% 20% 9% 3	1498
March	1st to 10th	Day	58% 2 9% 18% 10% 2	2067
	11th to 20th	Day	52% 3 11% 18% 14% 2	2090
	21st to end	Day	57% 3 7% 19% 12% 3	2299
April	1st to 10th	Day	59% 2 8% 15% 14% 1	2110
	11th to 20th	Day	50% 4 10% 22% 14% 1	2253
	21st to end	Day	52% 3 10% 20% 13% 2	2340
May	1st to 10th	Day	61% 3 8% 18% 10% 1	2340
	11th to 20th	Day	50% 3 8% 23% 14% 2	2409
	21st to end	Day	53% 4 13% 19% 10% 1	2724
June	1st to 10th	Day	54% 3 8% 23% 11% 1	2520
	11th to 20th	Day	50% 2 11% 20% 14% 3	2664
	21st to end	Day	55% 4 13% 17% 10% 1	2700
July	1st to 10th	Day	48% 3 15% 21% 11% 2	2617
	11th to 20th	Day	51% 3 13% 24% 8% 1	2404
	21st to end	Day	51% 4 13% 23% 8% 1	2406
August	1st to 10th	Day	46% 4 14% 23% 13% 1	2314
	11th to 20th	Day	47% 3 15% 23% 11% 1	2304
	21st to end	Day	42% 3 11% 26% 17% 1	2516
September	1st to 10th	Day	41% 3 12% 25% 18% 2	2160
	11th to 20th	Day	43% 3 9% 25% 17% 3	1998
	21st to end	Day	45% 3 7% 24% 19% 2	1979
October	1st to 10th	Day	45% 4 10% 26% 13% 2	1800
	11th to 20th	Day	49% 3 12% 25% 11% 1	1800
	21st to end	Day	55% 3 10% 20% 12% 1	1977
November	1st to 10th	Day	51% 3 12% 22% 11% 1	1614
	11th to 20th	Day	55% 4 11% 20% 9%	1520
	21st to end	Day	58% 4 12% 20% 5% 1	1520
December	1st to 10th	Day	64% 3 11% 16% 6%	1520
	11th to 20th	Day	67% 3 8% 14% 7%	1905
	21st to end	Day	61% 2 14% 15% 7% 1	2783
January	1st to 10th	Night	63% 2 10% 20% 5% 1	4420
	11th to 20th	Night	65% 3 10% 15% 6%	4120
	21st to end	Night	64% 2 11% 16% 6%	4532
February	1st to 10th	Night	64% 3 11% 15% 7%	2470
	11th to 20th	Night	59% 3 10% 19% 8% 1	2406
	21st to end	Night	52% 3 11% 21% 11% 1	1951
March	1st to 10th	Night	57% 4 9% 18% 11% 2	2112
	11th to 20th	Night	56% 3 12% 15% 13% 2	2090
	21st to end	Night	51% 2 8% 22% 14% 2	2299
April	1st to 10th	Night	57% 2 9% 16% 13% 4	1893
	11th to 20th	Night	50% 3 8% 24% 13% 1	1652
	21st to end	Night	53% 4 10% 20% 11% 2	1620
May	1st to 10th	Night	57% 3 8% 22% 10% 1	1620
	11th to 20th	Night	53% 3 7% 24% 13% 1	1489
	21st to end	Night	56% 3 12% 21% 8% 1	1551
June	1st to 10th	Night	56% 2 7% 25% 9% 1	1440
	11th to 20th	Night	52% 3 11% 20% 13% 1	1309
	21st to end	Night	60% 4 9% 15% 11% 1	1260
July	1st to 10th	Night	52% 3 14% 22% 9%	1225
	11th to 20th	Night	58% 4 10% 20% 8% 1	1415
	21st to end	Night	55% 3 11% 22% 7% 2	1672
August	1st to 10th	Night	50% 2 11% 25% 12%	1600
	11th to 20th	Night	52% 3 13% 22% 9% 1	1596
	21st to end	Night	46% 3 10% 26% 14% 1	1840
September	1st to 10th	Night	44% 3 8% 28% 15% 3	1800
	11th to 20th	Night	43% 3 8% 27% 18% 2	1957
	21st to end	Night	48% 2 6% 26% 17% 1	1980
October	1st to 10th	Night	45% 4 10% 24% 15% 2	2160
	11th to 20th	Night	44% 3 11% 29% 12% 1	2160
	21st to end	Night	51% 2 11% 23% 13% 1	2376
November	1st to 10th	Night	48% 2 14% 24% 11%	2462
	11th to 20th	Night	53% 3 12% 21% 10%	2660
	21st to end	Night	53% 5% 15% 19% 7%	2660
December	1st to 10th	Night	63% 2 12% 17% 6%	2660
	11th to 20th	Night	63% 3 9% 17% 6% 1	3295
	21st to end	Night	61% 2 11% 20% 5% 1	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	30% 25% 28% 14% 4	370
	11th to 20th	Day	31% 21% 31% 14% 3	370
	21st to end	Day	21% 27% 32% 16% 3	407
February	1st to 10th	Day	32% 22% 30% 14% 3	370
	11th to 20th	Day	30% 26% 28% 13% 3	366
	21st to end	Day	29% 22% 32% 15% 3	348
March	1st to 10th	Day	33% 20% 33% 11% 3	460
	11th to 20th	Day	31% 22% 31% 10% 4 1	460
	21st to end	Day	29% 23% 31% 10% 5% 1	506
April	1st to 10th	Day	34% 24% 29% 11% 2	428
	11th to 20th	Day	28% 21% 37% 12% 2	412
	21st to end	Day	31% 17% 32% 13% 5% 1	420
May	1st to 10th	Day	30% 22% 31% 12% 3 1	423
	11th to 20th	Day	26% 19% 32% 17% 5% 1	551
	21st to end	Day	32% 11% 32% 18% 7% 1	680
June	1st to 10th	Day	32% 10% 33% 20% 5%	630
	11th to 20th	Day	26% 11% 34% 21% 8% 1	630
	21st to end	Day	32% 9% 31% 22% 5% 1	630
July	1st to 10th	Day	28% 7% 28% 26% 9% 1	620
	11th to 20th	Day	28% 5% 33% 24% 10% 1	578
	21st to end	Day	25% 7% 33% 27% 8% 1	488
August	1st to 10th	Day	18% 8% 38% 25% 9% 2	446
	11th to 20th	Day	26% 8% 33% 20% 11% 2	439
	21st to end	Day	23% 8% 32% 22% 11% 2	495
September	1st to 10th	Day	19% 10% 34% 28% 8% 2	450
	11th to 20th	Day	25% 11% 32% 19% 8% 4	450
	21st to end	Day	22% 11% 36% 20% 7% 3	449
October	1st to 10th	Day	23% 10% 35% 20% 11% 2	360
	11th to 20th	Day	20% 18% 32% 21% 7% 2	360
	21st to end	Day	26% 16% 33% 17% 7% 1	396
November	1st to 10th	Day	23% 20% 31% 17% 8% 1	365
	11th to 20th	Day	29% 24% 27% 13% 6%	370
	21st to end	Day	30% 22% 29% 16% 3 1	370
December	1st to 10th	Day	37% 17% 29% 14% 3	370
	11th to 20th	Day	39% 24% 23% 11% 3	370
	21st to end	Day	31% 24% 28% 13% 3 1	407
January	1st to 10th	Night	28% 22% 29% 17% 4	846
	11th to 20th	Night	29% 17% 29% 21% 3	760
	21st to end	Night	24% 22% 32% 18% 4	836
February	1st to 10th	Night	29% 22% 28% 19% 2	760
	11th to 20th	Night	26% 24% 32% 15% 2	743
	21st to end	Night	23% 17% 35% 19% 6%	628
March	1st to 10th	Night	28% 19% 34% 17% 3	760
	11th to 20th	Night	24% 18% 33% 19% 6%	760
	21st to end	Night	26% 19% 32% 18% 6%	836
April	1st to 10th	Night	30% 14% 34% 19% 3	619
	11th to 20th	Night	29% 13% 38% 16% 3 1	534
	21st to end	Night	31% 10% 29% 21% 8% 1	540
May	1st to 10th	Night	31% 10% 34% 19% 5% 1	540
	11th to 20th	Night	29% 10% 32% 23% 5% 1	532
	21st to end	Night	30% 7% 30% 24% 7% 1	583
June	1st to 10th	Night	29% 7% 34% 25% 5%	540
	11th to 20th	Night	25% 7% 31% 30% 7%	409
	21st to end	Night	34% 2 27% 28% 8% 1	360
July	1st to 10th	Night	29% 2 27% 32% 9%	350
	11th to 20th	Night	26% 3 29% 31% 11%	509
	21st to end	Night	29% 4 27% 32% 7%	590
August	1st to 10th	Night	21% 4 30% 35% 10% 1	538
	11th to 20th	Night	23% 6% 23% 34% 13% 1	532
	21st to end	Night	24% 4 25% 29% 16% 2	594
September	1st to 10th	Night	20% 6% 30% 32% 11% 2	540
	11th to 20th	Night	24% 6% 26% 26% 15% 3	697
	21st to end	Night	26% 8% 26% 25% 14% 2	720
October	1st to 10th	Night	26% 7% 29% 27% 11% 1	720
	11th to 20th	Night	23% 15% 26% 24% 9% 2	720
	21st to end	Night	29% 15% 27% 23% 6%	792
November	1st to 10th	Night	25% 14% 27% 25% 9% 1	767
	11th to 20th	Night	25% 19% 29% 21% 6%	850
	21st to end	Night	27% 21% 27% 18% 6%	850
December	1st to 10th	Night	31% 17% 29% 18% 5%	850
	11th to 20th	Night	32% 23% 28% 14% 2	850
	21st to end	Night	30% 22% 26% 18% 4	935

Page generated at 2024-03-31 07:08:55. Version ac07

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