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 2024-09-29.

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	11% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	101499
	Night	9% 9% 4 9% 6% 5% 5% 4 6% 7% 36%	96849
Transparency	Day	43% 9% 17% 23% 8%	101256
	Night	44% 8% 15% 22% 9% 1	96739
Seeing	Day	14% 9% 30% 29% 14% 3	16116
	Night	14% 7% 32% 34% 12% 1	25997

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	4 16% 7% 16% 7% 6% 5% 5% 9% 9% 16%	2219
	11th to 20th	Day	3 9% 5% 16% 13% 9% 10% 7% 6% 7% 14%	2466
	21st to end	Day	8% 12% 6% 13% 6% 6% 5% 4 6% 7% 27%	2794
February	1st to 10th	Day	9% 13% 6% 14% 7% 6% 5% 4 6% 6% 24%	1520
	11th to 20th	Day	7% 12% 4 10% 9% 7% 8% 6% 6% 8% 24%	1697
	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	15% 6% 2 5% 4 3 3 4 5% 7% 46%	2068
October	1st to 10th	Day	17% 13% 3 6% 4 4 4 3 4 6% 35%	1940
	11th to 20th	Day	13% 10% 3 7% 5% 4 4 2 5% 7% 39%	1630
	21st to end	Day	14% 12% 5% 11% 6% 4 4 4 4 5% 30%	1782
November	1st to 10th	Day	18% 15% 4 10% 5% 4 4 2 5% 5% 28%	1669
	11th to 20th	Day	10% 16% 6% 12% 7% 4 5% 4 6% 6% 27%	1451
	21st to end	Day	10% 14% 5% 10% 7% 5% 5% 5% 5% 6% 29%	1330
December	1st to 10th	Day	7% 13% 6% 16% 8% 8% 6% 5% 5% 5% 22%	1330
	11th to 20th	Day	9% 15% 6% 15% 8% 8% 5% 6% 6% 7% 17%	1679
	21st to end	Day	6% 9% 3 11% 6% 5% 6% 6% 8% 8% 31%	2442
January	1st to 10th	Night	6% 15% 6% 16% 7% 7% 6% 5% 6% 6% 21%	4737
	11th to 20th	Night	5% 10% 4 16% 13% 8% 8% 6% 8% 5% 18%	4424
	21st to end	Night	7% 12% 6% 16% 7% 6% 6% 4 5% 6% 25%	4873
February	1st to 10th	Night	8% 13% 4 11% 7% 7% 5% 4 6% 7% 26%	2660
	11th to 20th	Night	6% 10% 4 10% 7% 6% 7% 5% 6% 6% 33%	2384
	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% 44%	2079
October	1st to 10th	Night	16% 10% 3 7% 4 3 5% 3 5% 5% 41%	2001
	11th to 20th	Night	15% 10% 2 6% 5% 4 5% 3 4 7% 39%	2329
	21st to end	Night	11% 11% 5% 8% 5% 4 5% 4 5% 6% 35%	2574
November	1st to 10th	Night	12% 12% 4 9% 6% 5% 5% 4 5% 6% 32%	2408
	11th to 20th	Night	10% 14% 5% 11% 7% 5% 5% 3 5% 6% 30%	2726
	21st to end	Night	8% 13% 4 10% 7% 5% 5% 4 5% 6% 31%	2850
December	1st to 10th	Night	6% 12% 4 14% 9% 6% 7% 5% 5% 6% 26%	2850
	11th to 20th	Night	9% 17% 6% 14% 7% 6% 5% 4 6% 7% 19%	3518
	21st to end	Night	7% 9% 3 9% 6% 5% 6% 6% 8% 9% 32%	5225

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	57% 13% 14% 12% 3	2219
	11th to 20th	Day	62% 12% 11% 11% 4	2490
	21st to end	Day	54% 7% 11% 22% 5%	2794
February	1st to 10th	Day	58% 6% 13% 17% 5%	1520
	11th to 20th	Day	54% 8% 13% 17% 8%	1706
	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%	2068
October	1st to 10th	Day	51% 6% 13% 23% 7%	1940
	11th to 20th	Day	44% 7% 15% 26% 8%	1630
	21st to end	Day	55% 8% 14% 17% 6% 1	1782
November	1st to 10th	Day	58% 7% 12% 14% 7% 1	1669
	11th to 20th	Day	56% 8% 17% 12% 6% 1	1451
	21st to end	Day	54% 8% 16% 17% 5%	1330
December	1st to 10th	Day	62% 9% 13% 12% 5%	1330
	11th to 20th	Day	62% 10% 12% 13% 3	1680
	21st to end	Day	44% 9% 14% 20% 12% 1	2442
January	1st to 10th	Night	59% 10% 12% 15% 4	4737
	11th to 20th	Night	61% 11% 12% 11% 5%	4462
	21st to end	Night	57% 9% 11% 18% 5%	4873
February	1st to 10th	Night	55% 6% 13% 17% 7% 1	2660
	11th to 20th	Night	46% 10% 13% 18% 12% 1	2385
	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	2079
October	1st to 10th	Night	45% 6% 15% 24% 9% 1	2001
	11th to 20th	Night	44% 7% 12% 26% 11%	2329
	21st to end	Night	48% 8% 15% 22% 7%	2574
November	1st to 10th	Night	51% 7% 14% 18% 7% 2	2408
	11th to 20th	Night	54% 8% 14% 17% 6% 1	2726
	21st to end	Night	51% 9% 16% 17% 6%	2850
December	1st to 10th	Night	56% 8% 16% 15% 6%	2850
	11th to 20th	Night	61% 8% 15% 11% 4 1	3516
	21st to end	Night	42% 9% 16% 18% 13% 1	5225

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	270
	11th to 20th	Day	7% 7% 41% 30% 13% 1	270
	21st to end	Day	14% 9% 36% 26% 12% 3	297
February	1st to 10th	Day	16% 10% 39% 27% 7% 1	270
	11th to 20th	Day	9% 7% 39% 31% 12% 2	270
	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	21% 10% 28% 26% 12% 3	294
October	1st to 10th	Day	24% 14% 25% 21% 14% 3	270
	11th to 20th	Day	15% 10% 34% 28% 10% 3	270
	21st to end	Day	22% 8% 41% 20% 6% 2	297
November	1st to 10th	Day	24% 10% 33% 20% 11% 1	270
	11th to 20th	Day	16% 13% 38% 25% 8%	270
	21st to end	Day	14% 13% 39% 26% 7% 1	270
December	1st to 10th	Day	13% 10% 39% 23% 13% 2	270
	11th to 20th	Day	15% 11% 43% 24% 6% 1	270
	21st to end	Day	11% 7% 37% 29% 15% 1	297
January	1st to 10th	Night	12% 9% 36% 33% 10% 1	950
	11th to 20th	Night	17% 8% 35% 31% 8% 1	950
	21st to end	Night	13% 7% 40% 32% 9%	1045
February	1st to 10th	Night	14% 9% 34% 31% 11% 1	950
	11th to 20th	Night	11% 6% 36% 33% 11% 3	883
	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	567
October	1st to 10th	Night	20% 7% 34% 29% 10%	561
	11th to 20th	Night	21% 9% 28% 32% 10%	889
	21st to end	Night	18% 8% 37% 28% 8% 1	990
November	1st to 10th	Night	17% 11% 35% 28% 8% 1	925
	11th to 20th	Night	16% 9% 37% 27% 9% 1	950
	21st to end	Night	15% 11% 38% 28% 7% 1	950
December	1st to 10th	Night	11% 8% 38% 29% 12% 1	950
	11th to 20th	Night	15% 11% 34% 29% 9% 2	950
	21st to end	Night	16% 5% 34% 32% 11% 2	1045

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