Isle Pierre
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Isle Pierre clear sky chart from 2005-11-05 to 2024-10-14.

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% 31%	101788
	Night	8% 11% 4 10% 6% 6% 6% 4 6% 7% 31%	96806
Transparency	Day	47% 8% 16% 21% 8% 1	101525
	Night	50% 8% 14% 19% 8% 1	96715
Seeing	Day	14% 12% 28% 27% 16% 3	16384
	Night	15% 10% 27% 29% 16% 2	24098

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	6% 14% 5% 13% 7% 8% 6% 4 7% 6% 22%	2105
	11th to 20th	Day	5% 17% 6% 10% 6% 5% 7% 4 5% 6% 30%	2199
	21st to end	Day	7% 18% 8% 15% 8% 6% 5% 4 5% 6% 17%	2442
February	1st to 10th	Day	10% 15% 4 11% 8% 5% 5% 3 5% 6% 28%	1529
	11th to 20th	Day	7% 10% 5% 12% 7% 5% 6% 5% 7% 9% 27%	1665
	21st to end	Day	4 13% 5% 11% 8% 7% 4 5% 5% 7% 30%	1413
March	1st to 10th	Day	4 10% 5% 12% 10% 7% 6% 5% 7% 7% 26%	3120
	11th to 20th	Day	4 13% 4 9% 7% 7% 7% 6% 9% 9% 25%	3490
	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	13% 12% 3 9% 5% 6% 6% 5% 7% 8% 27%	1900
	11th to 20th	Day	12% 10% 5% 10% 7% 6% 6% 5% 6% 7% 27%	1831
	21st to end	Day	12% 11% 4 11% 5% 5% 5% 5% 6% 7% 30%	1629
November	1st to 10th	Day	13% 15% 5% 10% 7% 6% 6% 3 5% 6% 25%	1488
	11th to 20th	Day	8% 14% 6% 11% 9% 8% 6% 6% 6% 7% 19%	1520
	21st to end	Day	8% 16% 5% 13% 9% 8% 6% 5% 5% 6% 20%	1196
December	1st to 10th	Day	11% 9% 4 13% 7% 7% 5% 4 8% 7% 25%	1140
	11th to 20th	Day	10% 15% 6% 14% 8% 6% 5% 4 5% 7% 20%	1442
	21st to end	Day	5% 13% 5% 11% 7% 7% 7% 4 6% 8% 27%	2090
January	1st to 10th	Night	6% 15% 6% 13% 8% 7% 6% 5% 6% 7% 20%	4857
	11th to 20th	Night	7% 12% 5% 12% 8% 7% 5% 3 5% 5% 30%	4699
	21st to end	Night	11% 20% 7% 12% 7% 6% 6% 4 6% 6% 15%	5214
February	1st to 10th	Night	9% 16% 6% 12% 7% 6% 6% 4 5% 5% 25%	2647
	11th to 20th	Night	6% 12% 4 13% 7% 6% 5% 4 6% 8% 28%	2402
	21st to end	Night	5% 11% 5% 12% 7% 5% 6% 5% 6% 7% 32%	2041
March	1st to 10th	Night	5% 13% 5% 11% 8% 6% 5% 4 6% 7% 30%	3748
	11th to 20th	Night	6% 11% 4 11% 7% 6% 7% 5% 7% 8% 29%	3489
	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% 10% 5% 10% 6% 6% 6% 5% 6% 7% 30%	2280
	11th to 20th	Night	13% 11% 3 10% 6% 6% 6% 4 6% 7% 27%	2207
	21st to end	Night	12% 13% 4 8% 5% 5% 6% 4 7% 6% 29%	2723
November	1st to 10th	Night	13% 13% 4 11% 8% 6% 7% 4 6% 6% 23%	2590
	11th to 20th	Night	8% 13% 5% 12% 8% 6% 7% 5% 6% 6% 24%	2660
	21st to end	Night	8% 14% 5% 13% 9% 6% 5% 5% 7% 8% 20%	2960
December	1st to 10th	Night	9% 10% 4 11% 7% 6% 6% 4 7% 8% 28%	3040
	11th to 20th	Night	8% 17% 6% 12% 7% 7% 6% 5% 6% 6% 21%	3750
	21st to end	Night	5% 13% 5% 14% 9% 7% 6% 5% 7% 8% 24%	5566

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% 12% 10% 16% 3	2105
	11th to 20th	Day	52% 10% 15% 7% 11% 5%	2220
	21st to end	Day	64% 11% 10% 10% 3	2442
February	1st to 10th	Day	56% 7% 12% 13% 11% 1	1529
	11th to 20th	Day	54% 8% 16% 17% 6%	1674
	21st to end	Day	52% 5% 16% 17% 7% 2	1413
March	1st to 10th	Day	52% 6% 11% 20% 10% 1	3120
	11th to 20th	Day	47% 10% 17% 21% 6%	3490
	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	50% 9% 20% 17% 4	1900
	11th to 20th	Day	52% 8% 18% 19% 3	1831
	21st to end	Day	50% 8% 18% 19% 5%	1629
November	1st to 10th	Day	60% 7% 13% 14% 6%	1488
	11th to 20th	Day	60% 9% 15% 12% 5%	1520
	21st to end	Day	63% 10% 11% 13% 4	1196
December	1st to 10th	Day	57% 9% 14% 15% 5%	1140
	11th to 20th	Day	64% 9% 11% 11% 5%	1444
	21st to end	Day	54% 11% 13% 15% 6% 1	2090
January	1st to 10th	Night	60% 10% 12% 15% 3	4857
	11th to 20th	Night	56% 6% 12% 8% 12% 6%	4740
	21st to end	Night	69% 10% 9% 8% 4	5214
February	1st to 10th	Night	60% 7% 11% 12% 9% 1	2647
	11th to 20th	Night	54% 7% 15% 17% 7%	2404
	21st to end	Night	50% 6% 13% 20% 10% 2	2041
March	1st to 10th	Night	49% 9% 10% 21% 10% 1	3748
	11th to 20th	Night	48% 8% 13% 22% 9%	3490
	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	49% 8% 19% 19% 5%	2280
	11th to 20th	Night	52% 8% 19% 18% 4	2207
	21st to end	Night	51% 8% 15% 20% 6%	2723
November	1st to 10th	Night	58% 8% 15% 14% 6%	2590
	11th to 20th	Night	57% 10% 14% 14% 6%	2660
	21st to end	Night	58% 7% 16% 13% 5%	2960
December	1st to 10th	Night	54% 10% 14% 17% 5%	3040
	11th to 20th	Night	64% 10% 12% 10% 5%	3747
	21st to end	Night	55% 11% 14% 13% 7% 1	5566

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	12% 12% 32% 24% 14% 6%	180
	11th to 20th	Day	13% 17% 28% 20% 18% 4	180
	21st to end	Day	18% 18% 26% 22% 13% 4	198
February	1st to 10th	Day	18% 19% 33% 20% 9% 2	243
	11th to 20th	Day	14% 13% 36% 23% 13% 2	365
	21st to end	Day	12% 19% 32% 22% 10% 4	307
March	1st to 10th	Day	12% 16% 29% 26% 14% 3	438
	11th to 20th	Day	13% 15% 33% 25% 13% 1	460
	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	17% 14% 35% 21% 13%	463
	21st to end	Day	19% 15% 30% 23% 10% 3	223
November	1st to 10th	Day	21% 20% 27% 19% 10% 3	180
	11th to 20th	Day	18% 15% 26% 21% 13% 7%	180
	21st to end	Day	16% 13% 32% 26% 8% 5%	180
December	1st to 10th	Day	13% 9% 22% 32% 20% 4	180
	11th to 20th	Day	9% 12% 29% 32% 16% 3	180
	21st to end	Day	15% 12% 29% 25% 15% 5%	198
January	1st to 10th	Night	17% 14% 30% 27% 10% 2	929
	11th to 20th	Night	15% 12% 32% 26% 13% 1	850
	21st to end	Night	16% 15% 30% 27% 12% 1	935
February	1st to 10th	Night	16% 17% 24% 26% 14% 3	785
	11th to 20th	Night	15% 12% 29% 30% 13% 1	744
	21st to end	Night	12% 12% 27% 31% 15% 2	628
March	1st to 10th	Night	11% 16% 26% 27% 17% 3	760
	11th to 20th	Night	13% 13% 29% 31% 14% 1	760
	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% 9% 27% 27% 16% 2	734
	21st to end	Night	21% 12% 29% 27% 11% 1	792
November	1st to 10th	Night	21% 13% 30% 25% 10% 2	740
	11th to 20th	Night	16% 15% 32% 26% 10% 1	760
	21st to end	Night	16% 15% 32% 26% 9% 2	982
December	1st to 10th	Night	14% 10% 25% 33% 15% 2	1040
	11th to 20th	Night	16% 12% 30% 28% 13% 1	1040
	21st to end	Night	13% 12% 32% 29% 13% 1	1144

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