Isle Pierre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Isle Pierre clear sky chart from 2005-11-06 to 2025-03-12.

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	8% 10% 4 10% 7% 6% 6% 5% 7% 7% 30%	111650
	Night	7% 11% 4 10% 7% 6% 6% 4 6% 7% 31%	115975
Transparency	Day	47% 8% 16% 20% 8% 1	111387
	Night	50% 8% 15% 19% 8% 1	115884
Seeing	Day	14% 12% 28% 26% 16% 3	16740
	Night	15% 10% 27% 29% 16% 2	24810

By Month

Percentage Cloud Cover NW (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	5% 12% 5% 16% 9% 8% 6% 4 7% 6% 23%	3023
	11th to 20th	Day	4 13% 4 9% 6% 6% 8% 5% 6% 6% 32%	3159
	21st to end	Day	5% 15% 6% 15% 8% 6% 4 3 5% 6% 26%	3498
February	1st to 10th	Day	9% 14% 4 10% 8% 5% 5% 3 5% 7% 28%	1611
	11th to 20th	Day	7% 10% 5% 12% 7% 5% 6% 5% 7% 9% 27%	1755
	21st to end	Day	4 13% 5% 11% 8% 7% 4 5% 6% 7% 30%	1485
March	1st to 10th	Day	4 10% 5% 13% 10% 7% 6% 5% 7% 7% 26%	3220
	11th to 20th	Day	4 13% 4 9% 7% 7% 7% 6% 9% 9% 25%	3503
	21st to end	Day	4 10% 4 9% 7% 5% 6% 4 7% 7% 36%	3945
April	1st to 10th	Day	6% 13% 5% 14% 9% 7% 6% 5% 6% 6% 22%	2289
	11th to 20th	Day	7% 15% 5% 12% 10% 7% 6% 4 4 6% 24%	2438
	21st to end	Day	10% 13% 5% 10% 7% 6% 6% 4 7% 6% 26%	2631
May	1st to 10th	Day	5% 11% 4 10% 7% 6% 6% 5% 7% 8% 31%	4420
	11th to 20th	Day	8% 12% 4 11% 8% 7% 7% 4 7% 7% 26%	4620
	21st to end	Day	11% 13% 5% 12% 7% 6% 6% 5% 6% 7% 22%	5352
June	1st to 10th	Day	11% 10% 4 11% 7% 7% 5% 5% 6% 7% 26%	3040
	11th to 20th	Day	13% 11% 4 11% 8% 7% 6% 5% 6% 7% 23%	3040
	21st to end	Day	10% 9% 4 11% 8% 7% 6% 5% 7% 7% 27%	3040
July	1st to 10th	Day	7% 6% 2 6% 4 4 4 4 6% 7% 48%	5039
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 49%	4740
	21st to end	Day	7% 6% 3 8% 7% 7% 8% 6% 9% 9% 31%	5138
August	1st to 10th	Day	4 4 2 5% 4 4 4 3 7% 9% 54%	4539
	11th to 20th	Day	8% 7% 3 8% 5% 6% 6% 5% 7% 8% 37%	4221
	21st to end	Day	9% 9% 4 9% 5% 6% 5% 4 7% 7% 35%	4521
September	1st to 10th	Day	9% 6% 3 10% 6% 6% 6% 4 7% 8% 36%	2299
	11th to 20th	Day	9% 9% 3 8% 7% 6% 6% 5% 6% 8% 34%	2275
	21st to end	Day	14% 10% 4 9% 6% 6% 5% 5% 7% 7% 26%	2002
October	1st to 10th	Day	10% 13% 4 11% 7% 7% 7% 5% 7% 7% 22%	3180
	11th to 20th	Day	13% 11% 4 9% 6% 6% 5% 4 7% 7% 26%	3161
	21st to end	Day	7% 10% 3 9% 6% 5% 6% 5% 7% 9% 32%	2826
November	1st to 10th	Day	13% 15% 5% 10% 7% 6% 6% 3 5% 6% 25%	1568
	11th to 20th	Day	8% 14% 6% 11% 9% 8% 6% 6% 6% 7% 20%	1600
	21st to end	Day	8% 15% 5% 13% 9% 8% 6% 5% 5% 6% 20%	1258
December	1st to 10th	Day	9% 16% 6% 14% 7% 6% 4 4 7% 7% 20%	1960
	11th to 20th	Day	8% 15% 6% 16% 10% 7% 6% 4 5% 6% 18%	2262
	21st to end	Day	4 13% 6% 14% 8% 6% 7% 4 6% 8% 25%	2992
January	1st to 10th	Night	5% 14% 6% 14% 8% 7% 6% 5% 6% 7% 22%	6953
	11th to 20th	Night	5% 9% 4 11% 7% 7% 6% 4 6% 7% 34%	6739
	21st to end	Night	8% 17% 6% 12% 6% 6% 6% 4 5% 6% 25%	7458
February	1st to 10th	Night	8% 15% 5% 11% 7% 7% 6% 4 5% 5% 26%	2785
	11th to 20th	Night	6% 12% 4 12% 7% 6% 5% 5% 6% 8% 29%	2532
	21st to end	Night	5% 11% 5% 12% 7% 5% 6% 5% 6% 8% 31%	2145
March	1st to 10th	Night	4 13% 5% 12% 8% 6% 5% 4 6% 7% 30%	3868
	11th to 20th	Night	6% 11% 4 11% 7% 6% 7% 5% 7% 8% 29%	3504
	21st to end	Night	3 9% 3 7% 5% 5% 5% 5% 6% 7% 45%	3708
April	1st to 10th	Night	5% 12% 5% 11% 7% 6% 7% 5% 6% 7% 29%	1888
	11th to 20th	Night	6% 12% 4 9% 8% 6% 7% 5% 7% 8% 28%	1691
	21st to end	Night	7% 10% 5% 10% 6% 6% 6% 4 5% 7% 36%	1549
May	1st to 10th	Night	8% 10% 4 9% 6% 5% 6% 5% 8% 7% 32%	2540
	11th to 20th	Night	8% 11% 5% 9% 7% 7% 7% 6% 7% 8% 27%	2273
	21st to end	Night	12% 14% 5% 10% 6% 5% 5% 4 5% 6% 26%	2207
June	1st to 10th	Night	14% 9% 3 8% 6% 7% 7% 4 6% 9% 29%	1140
	11th to 20th	Night	11% 9% 5% 9% 7% 6% 5% 5% 8% 7% 28%	1140
	21st to end	Night	7% 8% 3 9% 6% 7% 7% 6% 8% 9% 30%	1140
July	1st to 10th	Night	6% 5% 2 5% 4 3 4 3 6% 7% 55%	1918
	11th to 20th	Night	5% 4 1 5% 4 4 3 4 7% 8% 55%	2220
	21st to end	Night	10% 7% 3 5% 4 4 4 4 7% 9% 43%	2414
August	1st to 10th	Night	3 3 2 2 2 2 3 2 4 6% 70%	2390
	11th to 20th	Night	7% 5% 2 4 5% 4 5% 5% 5% 9% 50%	2607
	21st to end	Night	12% 9% 3 9% 6% 5% 5% 5% 5% 8% 34%	3146
September	1st to 10th	Night	9% 8% 3 7% 5% 5% 4 4 7% 8% 38%	1881
	11th to 20th	Night	8% 7% 3 7% 6% 5% 5% 4 6% 6% 43%	1903
	21st to end	Night	13% 10% 4 9% 5% 5% 5% 4 6% 7% 32%	2178
October	1st to 10th	Night	10% 13% 5% 12% 7% 7% 6% 5% 5% 6% 24%	3800
	11th to 20th	Night	9% 9% 3 10% 7% 7% 7% 5% 8% 9% 27%	3777
	21st to end	Night	9% 12% 3 8% 6% 6% 7% 5% 7% 7% 31%	4720
November	1st to 10th	Night	12% 12% 4 11% 8% 6% 7% 4 6% 6% 23%	2730
	11th to 20th	Night	8% 13% 5% 12% 8% 6% 7% 5% 6% 6% 24%	2800
	21st to end	Night	8% 14% 5% 13% 9% 7% 5% 5% 7% 8% 20%	3117
December	1st to 10th	Night	7% 13% 5% 13% 7% 6% 6% 4 6% 7% 25%	5220
	11th to 20th	Night	7% 19% 6% 12% 7% 6% 6% 5% 6% 7% 20%	5930
	21st to end	Night	4 13% 6% 15% 8% 7% 6% 5% 6% 7% 23%	7964

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	59% 11% 10% 15% 5%	3023
	11th to 20th	Day	46% 10% 16% 14% 11% 3	3180
	21st to end	Day	56% 10% 14% 14% 5%	3498
February	1st to 10th	Day	56% 6% 12% 13% 12% 1	1611
	11th to 20th	Day	53% 8% 16% 17% 5%	1764
	21st to end	Day	52% 5% 16% 17% 7% 2	1485
March	1st to 10th	Day	53% 6% 11% 20% 10% 1	3220
	11th to 20th	Day	46% 10% 17% 21% 6%	3503
	21st to end	Day	43% 6% 16% 22% 12% 1	3945
April	1st to 10th	Day	57% 7% 12% 17% 6% 1	2289
	11th to 20th	Day	57% 5% 11% 19% 7%	2438
	21st to end	Day	53% 6% 14% 18% 9%	2631
May	1st to 10th	Day	44% 7% 17% 22% 8% 2	4420
	11th to 20th	Day	51% 11% 10% 17% 10% 1	4623
	21st to end	Day	55% 7% 12% 20% 5% 1	5353
June	1st to 10th	Day	51% 6% 14% 19% 9% 1	3040
	11th to 20th	Day	53% 7% 14% 20% 6%	3040
	21st to end	Day	48% 8% 16% 20% 8%	3040
July	1st to 10th	Day	31% 5% 11% 26% 25% 2	4960
	11th to 20th	Day	28% 5% 20% 34% 13%	4659
	21st to end	Day	39% 9% 18% 23% 12% 1	4976
August	1st to 10th	Day	23% 5% 17% 40% 15%	4521
	11th to 20th	Day	37% 7% 21% 28% 7%	4263
	21st to end	Day	44% 7% 26% 20% 3	4520
September	1st to 10th	Day	40% 7% 26% 21% 6%	2299
	11th to 20th	Day	42% 8% 20% 24% 6%	2275
	21st to end	Day	51% 9% 17% 17% 5% 1	2002
October	1st to 10th	Day	53% 8% 19% 14% 5% 1	3180
	11th to 20th	Day	51% 7% 20% 19% 3	3161
	21st to end	Day	42% 8% 25% 19% 6%	2826
November	1st to 10th	Day	59% 7% 13% 14% 6%	1568
	11th to 20th	Day	60% 9% 14% 13% 5%	1600
	21st to end	Day	62% 9% 11% 14% 4	1258
December	1st to 10th	Day	63% 9% 15% 11% 3	1960
	11th to 20th	Day	67% 8% 12% 9% 4	2264
	21st to end	Day	56% 10% 13% 16% 5%	2992
January	1st to 10th	Night	57% 9% 12% 15% 6%	6953
	11th to 20th	Night	48% 7% 15% 14% 11% 5%	6780
	21st to end	Night	60% 8% 16% 12% 4	7458
February	1st to 10th	Night	59% 7% 10% 12% 11% 1	2785
	11th to 20th	Night	53% 7% 16% 18% 7%	2534
	21st to end	Night	50% 6% 13% 20% 10% 2	2145
March	1st to 10th	Night	49% 9% 10% 21% 10% 1	3868
	11th to 20th	Night	48% 8% 13% 22% 9%	3505
	21st to end	Night	36% 7% 13% 26% 19%	3708
April	1st to 10th	Night	50% 7% 12% 21% 9% 1	1888
	11th to 20th	Night	51% 6% 11% 23% 9%	1691
	21st to end	Night	47% 6% 11% 23% 12% 1	1549
May	1st to 10th	Night	44% 8% 14% 25% 9%	2540
	11th to 20th	Night	49% 9% 13% 21% 7%	2273
	21st to end	Night	54% 8% 11% 22% 5%	2207
June	1st to 10th	Night	49% 8% 13% 19% 11% 1	1140
	11th to 20th	Night	51% 6% 15% 22% 7%	1140
	21st to end	Night	44% 9% 18% 22% 6%	1140
July	1st to 10th	Night	28% 6% 11% 28% 26% 1	1888
	11th to 20th	Night	25% 5% 18% 41% 10%	2178
	21st to end	Night	33% 8% 25% 19% 14% 1	2337
August	1st to 10th	Night	17% 5% 14% 43% 21%	2383
	11th to 20th	Night	29% 6% 19% 36% 9%	2631
	21st to end	Night	46% 8% 23% 20% 3	3146
September	1st to 10th	Night	39% 7% 20% 27% 7% 1	1881
	11th to 20th	Night	37% 7% 14% 32% 9%	1903
	21st to end	Night	47% 9% 14% 20% 9%	2178
October	1st to 10th	Night	55% 7% 15% 17% 5%	3800
	11th to 20th	Night	47% 7% 21% 20% 6%	3777
	21st to end	Night	46% 8% 18% 23% 5%	4720
November	1st to 10th	Night	57% 8% 15% 14% 6%	2730
	11th to 20th	Night	56% 10% 14% 14% 6%	2800
	21st to end	Night	58% 7% 16% 13% 5%	3117
December	1st to 10th	Night	58% 9% 16% 15% 3	5220
	11th to 20th	Night	64% 10% 13% 10% 3	5927
	21st to end	Night	57% 9% 15% 14% 5%	7964

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	14% 12% 31% 24% 16% 6%	200
	11th to 20th	Day	14% 18% 29% 20% 17% 4	200
	21st to end	Day	19% 17% 27% 21% 13% 3	220
February	1st to 10th	Day	16% 18% 33% 20% 10% 2	267
	11th to 20th	Day	13% 12% 36% 23% 13% 2	395
	21st to end	Day	15% 20% 31% 21% 9% 4	331
March	1st to 10th	Day	12% 17% 29% 26% 14% 2	476
	11th to 20th	Day	13% 15% 33% 26% 13% 1	465
	21st to end	Day	16% 20% 25% 22% 13% 4	506
April	1st to 10th	Day	14% 17% 32% 24% 10% 2	460
	11th to 20th	Day	13% 17% 29% 23% 13% 4	452
	21st to end	Day	13% 16% 33% 25% 10% 3	460
May	1st to 10th	Day	13% 14% 32% 24% 14% 2	463
	11th to 20th	Day	14% 11% 25% 31% 17% 3	625
	21st to end	Day	14% 11% 27% 26% 21% 3	848
June	1st to 10th	Day	15% 11% 28% 29% 14% 2	870
	11th to 20th	Day	16% 9% 26% 31% 15% 3	870
	21st to end	Day	13% 7% 28% 29% 19% 4	870
July	1st to 10th	Day	14% 7% 22% 30% 23% 4	848
	11th to 20th	Day	13% 9% 25% 27% 23% 4	668
	21st to end	Day	10% 8% 23% 33% 22% 4	739
August	1st to 10th	Day	7% 7% 20% 33% 27% 6%	574
	11th to 20th	Day	8% 10% 27% 30% 17% 7%	477
	21st to end	Day	15% 11% 28% 27% 14% 5%	539
September	1st to 10th	Day	14% 11% 30% 28% 14% 3	490
	11th to 20th	Day	13% 11% 27% 27% 18% 5%	490
	21st to end	Day	21% 15% 34% 18% 10% 1	490
October	1st to 10th	Day	22% 14% 24% 24% 12% 3	490
	11th to 20th	Day	18% 16% 33% 21% 12%	490
	21st to end	Day	20% 14% 29% 23% 10% 3	247
November	1st to 10th	Day	22% 20% 27% 19% 10% 4	200
	11th to 20th	Day	19% 16% 27% 21% 13% 6%	200
	21st to end	Day	14% 14% 34% 25% 9% 5%	200
December	1st to 10th	Day	15% 9% 23% 32% 19% 4	200
	11th to 20th	Day	9% 11% 31% 32% 15% 3	200
	21st to end	Day	15% 11% 29% 25% 15% 5%	220
January	1st to 10th	Night	16% 13% 30% 28% 11% 2	983
	11th to 20th	Night	15% 13% 33% 26% 13% 1	900
	21st to end	Night	16% 15% 30% 26% 12% 1	990
February	1st to 10th	Night	15% 16% 25% 26% 15% 3	827
	11th to 20th	Night	14% 11% 30% 31% 13% 1	784
	21st to end	Night	12% 12% 28% 30% 15% 2	660
March	1st to 10th	Night	11% 16% 27% 27% 16% 3	800
	11th to 20th	Night	12% 13% 30% 31% 14% 1	766
	21st to end	Night	11% 11% 23% 28% 23% 4	836
April	1st to 10th	Night	13% 11% 23% 32% 18% 3	748
	11th to 20th	Night	14% 7% 26% 31% 18% 4	563
	21st to end	Night	11% 9% 31% 32% 15% 1	409
May	1st to 10th	Night	14% 11% 26% 31% 16% 2	380
	11th to 20th	Night	14% 5% 22% 36% 21% 2	374
	21st to end	Night	17% 9% 22% 27% 22% 2	411
June	1st to 10th	Night	17% 6% 28% 31% 17% 2	380
	11th to 20th	Night	13% 7% 29% 28% 20% 2	380
	21st to end	Night	10% 6% 23% 37% 22% 2	380
July	1st to 10th	Night	14% 4 22% 36% 23% 1	370
	11th to 20th	Night	11% 5% 23% 36% 23% 2	368
	21st to end	Night	10% 4 20% 39% 21% 6%	416
August	1st to 10th	Night	6% 4 20% 33% 30% 6%	378
	11th to 20th	Night	9% 5% 21% 34% 29% 4	434
	21st to end	Night	16% 5% 22% 33% 21% 3	627
September	1st to 10th	Night	14% 4 24% 31% 24% 2	741
	11th to 20th	Night	12% 7% 18% 30% 27% 6%	760
	21st to end	Night	19% 11% 28% 26% 16% 1	760
October	1st to 10th	Night	17% 9% 24% 30% 17% 3	760
	11th to 20th	Night	19% 10% 28% 27% 15% 2	760
	21st to end	Night	20% 12% 30% 27% 11% 1	836
November	1st to 10th	Night	21% 12% 31% 25% 10% 2	780
	11th to 20th	Night	16% 15% 32% 26% 10% 1	800
	21st to end	Night	16% 14% 33% 26% 9% 2	1039
December	1st to 10th	Night	15% 10% 26% 34% 14% 2	1100
	11th to 20th	Night	17% 11% 31% 28% 13% 1	1100
	21st to end	Night	13% 12% 32% 29% 13% 1	1210

Page generated at 2025-03-09 05:08:47. Version ac07

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