Souris
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Souris clear sky chart from 2005-11-06 to 2025-02-21.

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	10% 8% 3 9% 6% 5% 5% 4 6% 8% 36%	112140
	Night	8% 9% 4 10% 6% 5% 5% 4 6% 7% 34%	115161
Transparency	Day	44% 8% 16% 23% 8%	111897
	Night	46% 8% 15% 22% 9% 1	115051
Seeing	Day	14% 9% 31% 29% 14% 3	16551
	Night	14% 7% 32% 34% 12% 1	26694

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	3 13% 7% 16% 10% 8% 6% 5% 8% 10% 13%	3179
	11th to 20th	Day	3 9% 4 13% 12% 8% 10% 9% 8% 9% 14%	3552
	21st to end	Day	6% 12% 7% 14% 7% 7% 5% 4 6% 6% 27%	4004
February	1st to 10th	Day	9% 12% 6% 14% 7% 6% 5% 4 6% 7% 23%	1600
	11th to 20th	Day	6% 12% 4 10% 9% 7% 8% 5% 6% 8% 25%	1790
	21st to end	Day	7% 11% 4 12% 8% 7% 8% 5% 6% 7% 26%	1570
March	1st to 10th	Day	10% 13% 4 11% 9% 7% 6% 4 7% 9% 22%	3130
	11th to 20th	Day	6% 11% 6% 13% 9% 7% 6% 4 6% 7% 25%	3375
	21st to end	Day	9% 10% 4 12% 7% 6% 6% 4 6% 9% 28%	3961
April	1st to 10th	Day	10% 10% 3 8% 5% 5% 5% 4 5% 8% 38%	2280
	11th to 20th	Day	14% 12% 5% 9% 5% 4 5% 4 5% 6% 31%	2428
	21st to end	Day	15% 9% 4 8% 6% 4 4 3 6% 7% 34%	2470
May	1st to 10th	Day	19% 10% 3 6% 4 4 4 3 5% 8% 35%	4275
	11th to 20th	Day	20% 8% 3 7% 5% 5% 5% 4 5% 6% 32%	4561
	21st to end	Day	18% 7% 2 5% 4 4 4 4 5% 8% 38%	5173
June	1st to 10th	Day	13% 7% 2 7% 5% 5% 4 4 7% 8% 38%	2850
	11th to 20th	Day	15% 8% 2 8% 6% 5% 4 5% 6% 7% 35%	2850
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	2850
July	1st to 10th	Day	8% 4 2 5% 4 4 5% 5% 8% 11% 45%	4750
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 7% 9% 50%	4718
	21st to end	Day	4 3 1 4 4 4 5% 5% 7% 11% 51%	4802
August	1st to 10th	Day	8% 6% 2 6% 4 4 5% 4 6% 10% 45%	4412
	11th to 20th	Day	10% 5% 2 5% 3 3 4 3 6% 9% 49%	4104
	21st to end	Day	9% 5% 2 5% 3 3 4 4 6% 9% 49%	4532
September	1st to 10th	Day	10% 6% 2 6% 3 4 3 3 5% 7% 52%	2282
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 3 5% 6% 45%	2109
	21st to end	Day	14% 5% 2 6% 4 3 4 4 5% 7% 46%	2090
October	1st to 10th	Day	11% 9% 3 6% 4 4 4 3 5% 6% 45%	3398
	11th to 20th	Day	8% 7% 2 7% 4 4 4 3 6% 9% 48%	2842
	21st to end	Day	12% 11% 5% 9% 5% 3 3 4 4 7% 37%	3091
November	1st to 10th	Day	17% 15% 4 10% 5% 4 4 3 5% 6% 28%	1758
	11th to 20th	Day	10% 16% 5% 12% 7% 4 4 4 5% 6% 27%	1527
	21st to end	Day	9% 14% 5% 10% 7% 6% 5% 5% 5% 6% 28%	1400
December	1st to 10th	Day	6% 13% 7% 18% 9% 11% 8% 4 4 4 16%	2290
	11th to 20th	Day	9% 12% 5% 13% 8% 8% 5% 5% 7% 9% 20%	2639
	21st to end	Day	4 8% 4 16% 7% 6% 7% 5% 6% 7% 29%	3498
January	1st to 10th	Night	4 11% 5% 17% 10% 9% 7% 5% 5% 8% 17%	6787
	11th to 20th	Night	5% 9% 4 13% 10% 8% 8% 8% 10% 7% 17%	6348
	21st to end	Night	6% 14% 7% 16% 7% 6% 6% 4 6% 6% 23%	6974
February	1st to 10th	Night	8% 13% 4 12% 7% 7% 6% 5% 6% 6% 26%	2800
	11th to 20th	Night	5% 9% 4 9% 7% 6% 7% 5% 6% 7% 33%	2512
	21st to end	Night	7% 10% 5% 10% 7% 5% 6% 4 6% 7% 34%	1884
March	1st to 10th	Night	8% 12% 5% 10% 7% 5% 5% 4 6% 8% 29%	3734
	11th to 20th	Night	7% 10% 4 8% 6% 4 5% 4 6% 9% 39%	3586
	21st to end	Night	7% 10% 5% 13% 8% 5% 4 4 5% 7% 32%	3673
April	1st to 10th	Night	5% 8% 3 8% 5% 4 6% 4 7% 8% 42%	1900
	11th to 20th	Night	14% 12% 4 7% 5% 4 5% 4 7% 8% 31%	1702
	21st to end	Night	14% 8% 3 7% 6% 5% 5% 3 6% 7% 36%	1710
May	1st to 10th	Night	18% 9% 3 7% 4 4 5% 4 5% 6% 35%	2680
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 4 6% 6% 41%	2343
	21st to end	Night	17% 7% 3 6% 4 4 3 3 5% 6% 42%	2414
June	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 7% 8% 45%	1330
	11th to 20th	Night	13% 5% 3 6% 4 5% 5% 3 6% 9% 41%	1330
	21st to end	Night	10% 4 2 6% 3 4 4 5% 7% 9% 46%	1330
July	1st to 10th	Night	7% 4 2 4 4 3 5% 5% 9% 11% 46%	2220
	11th to 20th	Night	7% 3 1 4 3 4 4 3 5% 9% 58%	2249
	21st to end	Night	4 4 1 4 4 4 4 4 6% 9% 56%	2762
August	1st to 10th	Night	6% 4 2 5% 4 3 4 3 5% 9% 54%	2528
	11th to 20th	Night	5% 3 1 5% 4 5% 5% 4 7% 9% 50%	2735
	21st to end	Night	8% 4 2 6% 3 4 4 3 6% 8% 52%	3135
September	1st to 10th	Night	9% 4 1 5% 3 3 3 3 5% 8% 54%	1895
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 8% 48%	2071
	21st to end	Night	15% 7% 2 6% 4 4 4 4 4 7% 43%	2090
October	1st to 10th	Night	12% 8% 2 6% 3 3 4 3 5% 6% 48%	3529
	11th to 20th	Night	10% 7% 2 5% 5% 5% 5% 5% 6% 8% 44%	4086
	21st to end	Night	8% 9% 4 7% 5% 4 4 4 6% 7% 43%	4467
November	1st to 10th	Night	12% 12% 4 9% 5% 5% 5% 4 5% 6% 32%	2539
	11th to 20th	Night	10% 15% 5% 11% 7% 5% 5% 3 5% 6% 29%	2870
	21st to end	Night	8% 13% 4 11% 7% 6% 5% 4 6% 6% 30%	3000
December	1st to 10th	Night	6% 14% 5% 15% 10% 8% 8% 6% 5% 5% 18%	4900
	11th to 20th	Night	9% 15% 5% 12% 8% 6% 6% 4 6% 8% 21%	5568
	21st to end	Night	5% 8% 3 13% 8% 7% 7% 6% 8% 9% 27%	7480

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% 10% 10% 14% 4	3179
	11th to 20th	Day	57% 10% 10% 15% 7%	3576
	21st to end	Day	55% 7% 15% 20% 4	4004
February	1st to 10th	Day	58% 6% 12% 17% 6% 1	1600
	11th to 20th	Day	52% 8% 13% 18% 9%	1799
	21st to end	Day	54% 8% 15% 16% 7%	1570
March	1st to 10th	Day	53% 10% 17% 15% 5%	3130
	11th to 20th	Day	52% 12% 15% 15% 5%	3377
	21st to end	Day	47% 10% 17% 18% 8%	3961
April	1st to 10th	Day	43% 8% 16% 23% 10%	2280
	11th to 20th	Day	52% 7% 12% 17% 11% 1	2428
	21st to end	Day	47% 8% 15% 21% 8% 1	2470
May	1st to 10th	Day	45% 8% 17% 20% 8% 1	4275
	11th to 20th	Day	48% 9% 13% 18% 12% 1	4565
	21st to end	Day	42% 10% 14% 26% 8%	5173
June	1st to 10th	Day	42% 9% 19% 20% 10% 1	2850
	11th to 20th	Day	46% 9% 15% 20% 9% 1	2850
	21st to end	Day	39% 10% 20% 24% 6% 1	2850
July	1st to 10th	Day	30% 11% 27% 26% 5%	4676
	11th to 20th	Day	28% 9% 19% 37% 7%	4637
	21st to end	Day	24% 9% 25% 32% 10% 1	4651
August	1st to 10th	Day	33% 8% 19% 29% 11%	4396
	11th to 20th	Day	31% 7% 21% 33% 7%	4144
	21st to end	Day	30% 7% 21% 33% 9%	4531
September	1st to 10th	Day	32% 7% 15% 32% 12% 1	2282
	11th to 20th	Day	39% 7% 17% 26% 10% 1	2109
	21st to end	Day	38% 7% 14% 29% 12%	2090
October	1st to 10th	Day	40% 4 13% 35% 8%	3398
	11th to 20th	Day	34% 5% 14% 37% 10%	2842
	21st to end	Day	48% 5% 10% 28% 9%	3091
November	1st to 10th	Day	57% 7% 12% 15% 7% 1	1758
	11th to 20th	Day	56% 8% 17% 13% 6% 1	1527
	21st to end	Day	55% 8% 16% 16% 5%	1400
December	1st to 10th	Day	70% 8% 12% 8% 3	2290
	11th to 20th	Day	57% 9% 16% 16% 3	2640
	21st to end	Day	50% 8% 11% 20% 10% 1	3498
January	1st to 10th	Night	62% 8% 10% 16% 4	6787
	11th to 20th	Night	57% 10% 11% 15% 7%	6386
	21st to end	Night	60% 8% 12% 16% 4	6974
February	1st to 10th	Night	56% 6% 13% 17% 8% 1	2800
	11th to 20th	Night	45% 9% 13% 20% 13%	2513
	21st to end	Night	47% 7% 14% 22% 10%	1884
March	1st to 10th	Night	48% 9% 17% 20% 5%	3734
	11th to 20th	Night	37% 10% 20% 23% 8% 1	3586
	21st to end	Night	49% 9% 13% 23% 6%	3673
April	1st to 10th	Night	37% 7% 13% 25% 15% 2	1900
	11th to 20th	Night	49% 6% 13% 19% 12% 1	1702
	21st to end	Night	45% 7% 15% 21% 10% 2	1710
May	1st to 10th	Night	45% 9% 12% 22% 12%	2680
	11th to 20th	Night	41% 9% 13% 23% 11% 3	2343
	21st to end	Night	41% 8% 14% 28% 10%	2414
June	1st to 10th	Night	35% 8% 20% 24% 12% 2	1330
	11th to 20th	Night	38% 9% 16% 22% 12% 2	1330
	21st to end	Night	33% 10% 20% 30% 6% 1	1330
July	1st to 10th	Night	28% 13% 25% 26% 8% 1	2185
	11th to 20th	Night	23% 7% 18% 40% 10% 1	2207
	21st to end	Night	23% 7% 22% 33% 14% 1	2674
August	1st to 10th	Night	26% 8% 18% 32% 14% 2	2520
	11th to 20th	Night	28% 9% 18% 35% 9% 1	2761
	21st to end	Night	29% 6% 19% 33% 11% 1	3135
September	1st to 10th	Night	27% 7% 14% 33% 17% 2	1895
	11th to 20th	Night	33% 8% 18% 28% 13% 1	2071
	21st to end	Night	40% 6% 13% 29% 11% 2	2090
October	1st to 10th	Night	38% 4 12% 30% 13% 3	3529
	11th to 20th	Night	37% 6% 12% 32% 12% 1	4086
	21st to end	Night	40% 6% 13% 32% 9%	4467
November	1st to 10th	Night	50% 7% 14% 19% 7% 2	2539
	11th to 20th	Night	55% 8% 14% 17% 6% 1	2870
	21st to end	Night	52% 9% 16% 17% 6%	3000
December	1st to 10th	Night	63% 8% 15% 10% 4	4900
	11th to 20th	Night	58% 7% 15% 16% 3	5566
	21st to end	Night	49% 9% 14% 18% 10% 1	7480

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	10% 7% 40% 27% 14% 2	300
	11th to 20th	Day	8% 8% 39% 31% 13% 1	300
	21st to end	Day	14% 9% 38% 25% 11% 2	330
February	1st to 10th	Day	15% 13% 38% 27% 6% 1	300
	11th to 20th	Day	8% 6% 39% 32% 13% 2	300
	21st to end	Day	4 6% 38% 33% 16% 2	225
March	1st to 10th	Day	12% 13% 33% 29% 11% 2	270
	11th to 20th	Day	10% 13% 26% 33% 15% 2	270
	21st to end	Day	14% 10% 32% 30% 12% 3	380
April	1st to 10th	Day	14% 13% 34% 29% 9% 2	460
	11th to 20th	Day	20% 12% 31% 25% 12% 1	626
	21st to end	Day	18% 9% 31% 31% 11% 1	650
May	1st to 10th	Day	16% 10% 28% 30% 15% 1	653
	11th to 20th	Day	19% 8% 29% 27% 15% 2	675
	21st to end	Day	20% 10% 23% 30% 16% 1	734
June	1st to 10th	Day	14% 11% 30% 28% 12% 5%	680
	11th to 20th	Day	16% 9% 34% 27% 11% 3	680
	21st to end	Day	12% 9% 26% 34% 15% 4	680
July	1st to 10th	Day	9% 4 26% 33% 19% 8%	671
	11th to 20th	Day	10% 7% 30% 27% 20% 7%	668
	21st to end	Day	6% 6% 25% 34% 23% 8%	739
August	1st to 10th	Day	11% 6% 24% 34% 19% 7%	676
	11th to 20th	Day	10% 7% 22% 30% 23% 8%	665
	21st to end	Day	12% 7% 25% 33% 19% 4	748
September	1st to 10th	Day	11% 10% 34% 26% 15% 4	492
	11th to 20th	Day	16% 10% 29% 33% 10% 2	319
	21st to end	Day	22% 10% 29% 25% 12% 3	300
October	1st to 10th	Day	23% 15% 25% 21% 13% 3	300
	11th to 20th	Day	14% 11% 35% 28% 9% 3	300
	21st to end	Day	20% 8% 41% 21% 8% 2	330
November	1st to 10th	Day	23% 10% 33% 22% 11% 1	300
	11th to 20th	Day	18% 12% 36% 26% 7% 1	300
	21st to end	Day	13% 13% 40% 25% 8% 1	300
December	1st to 10th	Day	14% 10% 39% 23% 12% 2	300
	11th to 20th	Day	15% 10% 41% 27% 6% 1	300
	21st to end	Day	10% 7% 36% 30% 15% 2	330
January	1st to 10th	Night	12% 9% 36% 33% 10% 2	1000
	11th to 20th	Night	17% 8% 36% 31% 8% 1	1000
	21st to end	Night	12% 8% 41% 31% 8%	1100
February	1st to 10th	Night	14% 9% 34% 31% 10% 1	1000
	11th to 20th	Night	10% 6% 35% 34% 11% 3	930
	21st to end	Night	11% 6% 31% 35% 15% 2	628
March	1st to 10th	Night	14% 8% 28% 36% 11% 3	760
	11th to 20th	Night	8% 8% 35% 35% 12% 2	637
	21st to end	Night	15% 6% 28% 36% 13% 2	627
April	1st to 10th	Night	9% 6% 36% 38% 10% 1	570
	11th to 20th	Night	18% 7% 32% 33% 9%	563
	21st to end	Night	17% 5% 34% 33% 10% 1	570
May	1st to 10th	Night	18% 6% 30% 33% 12%	570
	11th to 20th	Night	17% 6% 31% 32% 14%	561
	21st to end	Night	22% 6% 24% 35% 12%	617
June	1st to 10th	Night	15% 5% 35% 29% 15% 1	570
	11th to 20th	Night	15% 6% 35% 34% 10% 1	570
	21st to end	Night	11% 5% 27% 40% 16%	570
July	1st to 10th	Night	8% 3 23% 42% 23% 1	555
	11th to 20th	Night	8% 3 28% 41% 19% 1	552
	21st to end	Night	7% 3 22% 48% 18% 3	624
August	1st to 10th	Night	8% 3 25% 45% 19% 1	567
	11th to 20th	Night	8% 4 23% 39% 24% 2	564
	21st to end	Night	14% 4 26% 40% 16% 1	627
September	1st to 10th	Night	11% 4 29% 36% 19% 2	570
	11th to 20th	Night	15% 8% 28% 39% 9%	570
	21st to end	Night	18% 8% 28% 34% 11% 1	570
October	1st to 10th	Night	20% 7% 34% 29% 10%	593
	11th to 20th	Night	20% 9% 29% 32% 10%	939
	21st to end	Night	17% 8% 38% 28% 8%	1045
November	1st to 10th	Night	17% 10% 34% 29% 9% 1	975
	11th to 20th	Night	16% 9% 37% 27% 9% 1	1000
	21st to end	Night	16% 11% 39% 28% 7% 1	1000
December	1st to 10th	Night	11% 8% 38% 29% 12% 1	1000
	11th to 20th	Night	15% 11% 34% 29% 9% 2	1000
	21st to end	Night	15% 5% 34% 33% 12% 2	1100

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