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 2026-07-16.

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	7% 10% 4 10% 7% 6% 6% 5% 7% 8% 30%	141922
	Night	7% 11% 4 10% 6% 6% 6% 5% 6% 7% 31%	139433
Transparency	Day	46% 7% 16% 21% 9% 1	141615
	Night	48% 7% 15% 20% 8% 1	139323
Seeing	Day	15% 13% 28% 26% 15% 3	18701
	Night	15% 11% 28% 29% 16% 2	26444

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% 13% 6% 16% 8% 7% 6% 4 7% 7% 21%	3929
	11th to 20th	Day	3 10% 4 8% 6% 5% 7% 5% 6% 7% 39%	4119
	21st to end	Day	5% 13% 5% 14% 8% 7% 5% 4 5% 7% 28%	4529
February	1st to 10th	Day	9% 14% 4 10% 8% 5% 6% 4 6% 7% 28%	1692
	11th to 20th	Day	7% 9% 5% 12% 7% 6% 6% 5% 7% 9% 27%	1845
	21st to end	Day	4 13% 5% 12% 8% 7% 4 5% 6% 7% 29%	1557
March	1st to 10th	Day	4 11% 5% 13% 10% 7% 7% 5% 7% 6% 26%	4597
	11th to 20th	Day	3 12% 4 10% 7% 8% 8% 7% 10% 10% 23%	5110
	21st to end	Day	5% 13% 5% 10% 6% 5% 6% 4 6% 7% 33%	5783
April	1st to 10th	Day	6% 13% 5% 14% 8% 7% 7% 5% 7% 6% 23%	2530
	11th to 20th	Day	6% 14% 5% 12% 9% 7% 6% 4 5% 6% 24%	2698
	21st to end	Day	9% 13% 4 10% 7% 6% 6% 4 7% 7% 28%	2908
May	1st to 10th	Day	4 9% 4 9% 6% 5% 6% 4 6% 8% 37%	8195
	11th to 20th	Day	7% 10% 4 12% 8% 7% 8% 5% 7% 8% 24%	8613
	21st to end	Day	10% 9% 4 11% 8% 8% 8% 6% 7% 8% 22%	10008
June	1st to 10th	Day	10% 10% 4 10% 7% 7% 6% 5% 6% 7% 28%	3360
	11th to 20th	Day	13% 10% 3 11% 8% 7% 6% 5% 7% 8% 23%	3360
	21st to end	Day	10% 8% 4 11% 8% 7% 6% 5% 7% 8% 27%	3360
July	1st to 10th	Day	8% 7% 3 7% 5% 5% 5% 4 7% 7% 41%	7365
	11th to 20th	Day	6% 6% 3 7% 5% 6% 6% 5% 7% 8% 41%	6856
	21st to end	Day	6% 5% 2 8% 6% 7% 7% 5% 8% 9% 37%	7375
August	1st to 10th	Day	4 4 2 5% 4 4 5% 4 7% 10% 52%	4683
	11th to 20th	Day	8% 8% 3 8% 5% 6% 6% 5% 7% 8% 36%	4358
	21st to end	Day	9% 9% 3 8% 5% 6% 5% 4 7% 7% 36%	4664
September	1st to 10th	Day	9% 6% 3 9% 6% 6% 5% 4 7% 9% 36%	2420
	11th to 20th	Day	9% 9% 3 8% 7% 6% 6% 5% 6% 8% 34%	2395
	21st to end	Day	15% 11% 4 9% 6% 6% 5% 5% 7% 7% 26%	2107
October	1st to 10th	Day	10% 13% 4 11% 7% 6% 7% 5% 7% 8% 23%	3280
	11th to 20th	Day	13% 11% 4 9% 6% 6% 5% 4 7% 7% 27%	3261
	21st to end	Day	8% 10% 3 9% 6% 5% 6% 5% 7% 8% 32%	2916
November	1st to 10th	Day	12% 14% 5% 10% 7% 6% 6% 3 5% 7% 24%	1648
	11th to 20th	Day	8% 14% 6% 11% 8% 8% 6% 6% 6% 7% 20%	1680
	21st to end	Day	8% 15% 5% 13% 9% 8% 6% 5% 5% 7% 21%	1321
December	1st to 10th	Day	9% 16% 6% 14% 7% 6% 4 4 7% 7% 20%	2020
	11th to 20th	Day	8% 14% 6% 16% 10% 7% 6% 4 5% 6% 18%	2322
	21st to end	Day	4 13% 6% 14% 8% 6% 7% 4 6% 8% 25%	3058
January	1st to 10th	Night	4 15% 6% 15% 8% 6% 6% 5% 6% 8% 20%	9009
	11th to 20th	Night	4 8% 4 10% 6% 6% 6% 4 6% 7% 41%	8779
	21st to end	Night	7% 14% 5% 11% 6% 6% 6% 4 6% 7% 28%	9651
February	1st to 10th	Night	8% 15% 5% 11% 7% 7% 6% 4 5% 5% 25%	2924
	11th to 20th	Night	6% 11% 4 13% 7% 6% 5% 5% 6% 8% 29%	2662
	21st to end	Night	5% 10% 5% 13% 8% 5% 6% 5% 6% 8% 30%	2249
March	1st to 10th	Night	3 11% 5% 14% 8% 7% 6% 4 7% 7% 29%	5509
	11th to 20th	Night	5% 10% 4 10% 7% 6% 7% 6% 8% 9% 29%	5109
	21st to end	Night	5% 11% 3 8% 5% 5% 6% 5% 6% 6% 40%	5434
April	1st to 10th	Night	5% 11% 4 11% 7% 7% 7% 5% 6% 7% 29%	2086
	11th to 20th	Night	6% 11% 4 9% 8% 6% 7% 5% 7% 8% 29%	1871
	21st to end	Night	6% 9% 4 9% 6% 6% 6% 4 5% 8% 37%	1712
May	1st to 10th	Night	7% 7% 3 8% 6% 5% 6% 5% 8% 8% 37%	4724
	11th to 20th	Night	6% 9% 4 9% 7% 7% 8% 6% 8% 9% 28%	4247
	21st to end	Night	10% 11% 4 11% 7% 6% 6% 5% 6% 7% 27%	4147
June	1st to 10th	Night	13% 8% 3 8% 6% 7% 7% 4 6% 8% 31%	1260
	11th to 20th	Night	11% 9% 5% 8% 7% 6% 5% 4 7% 8% 30%	1260
	21st to end	Night	7% 9% 3 9% 6% 7% 7% 6% 8% 9% 29%	1260
July	1st to 10th	Night	5% 5% 2 6% 5% 4 4 4 6% 7% 51%	2798
	11th to 20th	Night	6% 5% 2 6% 4 4 4 3 7% 7% 49%	3215
	21st to end	Night	7% 5% 2 5% 4 5% 6% 5% 7% 10% 45%	3468
August	1st to 10th	Night	3 3 2 3 2 2 3 2 4 6% 69%	2466
	11th to 20th	Night	7% 5% 2 4 5% 4 5% 5% 5% 9% 50%	2690
	21st to end	Night	12% 9% 3 8% 5% 5% 4 4 5% 8% 35%	3245
September	1st to 10th	Night	9% 8% 3 7% 5% 5% 4 4 7% 8% 40%	1980
	11th to 20th	Night	8% 7% 2 6% 6% 5% 5% 5% 6% 6% 43%	2003
	21st to end	Night	13% 10% 4 9% 6% 5% 5% 4 6% 8% 31%	2293
October	1st to 10th	Night	10% 13% 5% 12% 7% 7% 6% 5% 5% 6% 25%	3920
	11th to 20th	Night	9% 9% 3 9% 7% 7% 7% 5% 8% 9% 28%	3897
	21st to end	Night	9% 12% 3 8% 6% 6% 7% 4 7% 7% 31%	4872
November	1st to 10th	Night	12% 12% 4 11% 8% 6% 7% 5% 7% 6% 23%	2870
	11th to 20th	Night	8% 13% 5% 11% 8% 6% 7% 5% 6% 6% 24%	2940
	21st to end	Night	8% 14% 5% 13% 9% 7% 5% 5% 7% 8% 21%	3273
December	1st to 10th	Night	7% 13% 5% 13% 7% 6% 6% 4 6% 7% 25%	5380
	11th to 20th	Night	7% 19% 6% 12% 7% 6% 6% 5% 6% 7% 19%	6090
	21st to end	Night	4 12% 6% 16% 8% 7% 6% 5% 6% 7% 23%	8140

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% 10% 10% 16% 5%	3929
	11th to 20th	Day	39% 9% 21% 17% 11% 3	4140
	21st to end	Day	53% 10% 15% 16% 4	4530
February	1st to 10th	Day	55% 7% 12% 13% 12% 1	1692
	11th to 20th	Day	54% 8% 16% 17% 6%	1854
	21st to end	Day	53% 6% 15% 17% 7% 2	1557
March	1st to 10th	Day	53% 6% 11% 19% 10% 1	4597
	11th to 20th	Day	45% 8% 15% 21% 11% 1	5110
	21st to end	Day	47% 5% 12% 22% 13% 1	5783
April	1st to 10th	Day	55% 7% 13% 19% 6% 1	2530
	11th to 20th	Day	55% 5% 13% 19% 8%	2698
	21st to end	Day	50% 5% 14% 21% 9%	2908
May	1st to 10th	Day	40% 6% 15% 26% 11% 2	8195
	11th to 20th	Day	50% 9% 10% 21% 10%	8616
	21st to end	Day	50% 8% 14% 20% 6% 1	10009
June	1st to 10th	Day	49% 6% 13% 20% 11% 1	3360
	11th to 20th	Day	52% 7% 14% 20% 6%	3360
	21st to end	Day	48% 7% 17% 20% 7%	3360
July	1st to 10th	Day	36% 6% 12% 23% 21% 2	7286
	11th to 20th	Day	34% 7% 19% 30% 10%	6775
	21st to end	Day	34% 8% 21% 28% 9%	7168
August	1st to 10th	Day	24% 5% 17% 39% 14%	4665
	11th to 20th	Day	37% 7% 21% 28% 7%	4400
	21st to end	Day	42% 7% 25% 21% 5%	4663
September	1st to 10th	Day	38% 7% 26% 22% 6%	2420
	11th to 20th	Day	42% 8% 21% 24% 6%	2395
	21st to end	Day	52% 9% 16% 17% 5% 1	2107
October	1st to 10th	Day	53% 8% 19% 14% 5% 1	3280
	11th to 20th	Day	50% 7% 20% 19% 4	3261
	21st to end	Day	43% 9% 25% 19% 5%	2916
November	1st to 10th	Day	58% 8% 13% 15% 6%	1648
	11th to 20th	Day	59% 9% 14% 12% 6%	1680
	21st to end	Day	61% 9% 11% 14% 4 1	1321
December	1st to 10th	Day	62% 9% 15% 11% 3	2020
	11th to 20th	Day	67% 8% 12% 9% 4	2324
	21st to end	Day	56% 10% 13% 16% 5%	3058
January	1st to 10th	Night	59% 8% 10% 14% 7%	9010
	11th to 20th	Night	41% 7% 20% 18% 10% 4	8820
	21st to end	Night	56% 9% 15% 16% 4	9651
February	1st to 10th	Night	59% 7% 11% 12% 11% 1	2924
	11th to 20th	Night	52% 7% 16% 18% 8%	2664
	21st to end	Night	50% 6% 13% 19% 9% 2	2249
March	1st to 10th	Night	50% 8% 9% 21% 12% 1	5509
	11th to 20th	Night	46% 7% 11% 22% 14%	5110
	21st to end	Night	40% 6% 11% 25% 17%	5434
April	1st to 10th	Night	49% 6% 13% 22% 9% 1	2086
	11th to 20th	Night	49% 6% 13% 23% 9% 1	1871
	21st to end	Night	44% 6% 12% 25% 12% 1	1712
May	1st to 10th	Night	38% 6% 17% 29% 10% 1	4721
	11th to 20th	Night	46% 8% 12% 28% 7%	4247
	21st to end	Night	52% 6% 10% 22% 9% 1	4151
June	1st to 10th	Night	47% 8% 12% 21% 12% 1	1260
	11th to 20th	Night	50% 6% 15% 22% 7%	1260
	21st to end	Night	45% 9% 18% 23% 5%	1260
July	1st to 10th	Night	31% 6% 13% 27% 23% 1	2768
	11th to 20th	Night	31% 5% 18% 37% 9%	3173
	21st to end	Night	30% 8% 25% 26% 11% 1	3370
August	1st to 10th	Night	18% 5% 15% 42% 20%	2459
	11th to 20th	Night	29% 6% 19% 36% 9%	2714
	21st to end	Night	45% 7% 22% 20% 5%	3245
September	1st to 10th	Night	38% 7% 19% 28% 7% 1	1980
	11th to 20th	Night	37% 7% 15% 32% 9%	2003
	21st to end	Night	48% 9% 14% 20% 9%	2293
October	1st to 10th	Night	54% 8% 16% 17% 5%	3920
	11th to 20th	Night	46% 7% 21% 20% 6%	3897
	21st to end	Night	46% 8% 18% 23% 5%	4872
November	1st to 10th	Night	56% 8% 15% 15% 6%	2870
	11th to 20th	Night	56% 10% 14% 14% 6%	2940
	21st to end	Night	58% 7% 16% 14% 5%	3273
December	1st to 10th	Night	57% 8% 15% 15% 3	5380
	11th to 20th	Night	64% 10% 13% 10% 4	6087
	21st to end	Night	57% 9% 15% 14% 5%	8140

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% 13% 31% 23% 15% 5%	220
	11th to 20th	Day	13% 17% 30% 20% 16% 3	220
	21st to end	Day	18% 16% 28% 22% 14% 3	242
February	1st to 10th	Day	16% 18% 34% 21% 10% 2	291
	11th to 20th	Day	14% 12% 37% 23% 13% 1	425
	21st to end	Day	16% 20% 31% 20% 9% 3	355
March	1st to 10th	Day	12% 19% 29% 25% 13% 2	513
	11th to 20th	Day	15% 16% 32% 25% 12% 1	540
	21st to end	Day	15% 21% 26% 22% 12% 4	594
April	1st to 10th	Day	13% 19% 32% 24% 9% 2	540
	11th to 20th	Day	14% 18% 30% 21% 12% 4	532
	21st to end	Day	14% 17% 33% 25% 9% 3	540
May	1st to 10th	Day	13% 18% 32% 22% 13% 2	543
	11th to 20th	Day	14% 12% 26% 29% 16% 3	720
	21st to end	Day	16% 12% 28% 24% 19% 2	970
June	1st to 10th	Day	15% 13% 29% 27% 13% 2	990
	11th to 20th	Day	17% 9% 26% 30% 13% 3	990
	21st to end	Day	12% 8% 28% 29% 19% 4	990
July	1st to 10th	Day	14% 9% 24% 29% 21% 3	967
	11th to 20th	Day	13% 10% 25% 27% 21% 4	744
	21st to end	Day	10% 8% 22% 33% 23% 4	794
August	1st to 10th	Day	9% 6% 21% 33% 25% 5%	618
	11th to 20th	Day	9% 11% 28% 29% 16% 7%	517
	21st to end	Day	14% 10% 27% 28% 15% 6%	583
September	1st to 10th	Day	13% 10% 28% 28% 16% 4	530
	11th to 20th	Day	14% 10% 27% 27% 17% 5%	530
	21st to end	Day	22% 16% 34% 16% 9% 1	530
October	1st to 10th	Day	22% 15% 24% 25% 12% 3	530
	11th to 20th	Day	19% 16% 32% 21% 11%	530
	21st to end	Day	22% 14% 29% 22% 10% 3	271
November	1st to 10th	Day	22% 20% 28% 18% 9% 3	220
	11th to 20th	Day	18% 16% 27% 21% 12% 5%	220
	21st to end	Day	14% 13% 33% 26% 9% 5%	220
December	1st to 10th	Day	17% 12% 23% 29% 17% 3	220
	11th to 20th	Day	9% 12% 32% 31% 14% 3	220
	21st to end	Day	14% 12% 29% 26% 14% 5%	242
January	1st to 10th	Night	16% 14% 31% 27% 10% 2	1037
	11th to 20th	Night	15% 12% 34% 26% 13% 1	950
	21st to end	Night	16% 14% 30% 28% 12% 1	1045
February	1st to 10th	Night	15% 16% 26% 27% 14% 3	870
	11th to 20th	Night	13% 11% 31% 30% 13% 1	824
	21st to end	Night	14% 12% 28% 29% 14% 2	692
March	1st to 10th	Night	11% 15% 28% 27% 15% 3	840
	11th to 20th	Night	13% 13% 31% 29% 13% 1	840
	21st to end	Night	11% 11% 25% 27% 22% 4	924
April	1st to 10th	Night	13% 11% 24% 33% 17% 3	826
	11th to 20th	Night	14% 9% 26% 30% 17% 4	623
	21st to end	Night	11% 10% 32% 31% 15% 1	452
May	1st to 10th	Night	14% 11% 29% 30% 15% 2	420
	11th to 20th	Night	14% 7% 23% 35% 20% 2	414
	21st to end	Night	17% 11% 25% 26% 20% 2	455
June	1st to 10th	Night	17% 7% 29% 30% 16% 1	420
	11th to 20th	Night	14% 8% 29% 29% 19% 2	420
	21st to end	Night	10% 7% 25% 37% 20% 2	420
July	1st to 10th	Night	14% 5% 24% 36% 20% 1	410
	11th to 20th	Night	12% 6% 24% 35% 21% 2	398
	21st to end	Night	10% 4 20% 38% 21% 5%	438
August	1st to 10th	Night	6% 5% 22% 33% 29% 6%	398
	11th to 20th	Night	9% 5% 22% 34% 27% 4	457
	21st to end	Night	15% 5% 22% 34% 22% 3	660
September	1st to 10th	Night	14% 4 23% 32% 25% 2	780
	11th to 20th	Night	12% 7% 19% 32% 26% 6%	800
	21st to end	Night	19% 11% 29% 25% 15% 1	800
October	1st to 10th	Night	17% 9% 26% 30% 16% 3	800
	11th to 20th	Night	19% 10% 28% 27% 15% 2	800
	21st to end	Night	21% 12% 31% 26% 10% 1	880
November	1st to 10th	Night	21% 12% 31% 25% 10% 1	820
	11th to 20th	Night	16% 14% 33% 26% 10% 1	840
	21st to end	Night	15% 14% 33% 26% 9% 2	1095
December	1st to 10th	Night	16% 10% 27% 32% 13% 2	1160
	11th to 20th	Night	17% 11% 31% 27% 12% 1	1160
	21st to end	Night	12% 12% 33% 29% 12% 1	1276

Page generated at 2026-07-13 00:14:47. Version ac07

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