Weyburn
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Weyburn clear sky chart from 2005-11-06 to 2025-03-27.

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% 8% 3 8% 6% 5% 5% 4 6% 8% 38%	112887
	Night	7% 9% 4 9% 6% 5% 5% 4 6% 8% 37%	115229
Transparency	Day	43% 7% 15% 25% 9% 1	112631
	Night	44% 6% 16% 23% 10% 1	115076
Seeing	Day	12% 9% 30% 30% 16% 3	16645
	Night	12% 8% 32% 35% 12% 1	26447

By Month

Percentage Cloud Cover SW (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% 6% 17% 9% 8% 8% 5% 6% 6% 16%	3638
	11th to 20th	Day	4 8% 4 13% 9% 9% 9% 10% 12% 7% 16%	3640
	21st to end	Day	6% 10% 6% 14% 7% 6% 5% 3 4 7% 33%	4004
February	1st to 10th	Day	9% 13% 5% 12% 9% 6% 8% 5% 6% 5% 21%	1632
	11th to 20th	Day	7% 11% 6% 11% 8% 8% 8% 6% 6% 7% 23%	1768
	21st to end	Day	5% 11% 5% 12% 9% 7% 6% 6% 7% 8% 24%	1650
March	1st to 10th	Day	8% 14% 6% 13% 7% 5% 6% 4 5% 6% 25%	3230
	11th to 20th	Day	5% 12% 5% 14% 7% 5% 5% 4 6% 7% 30%	3360
	21st to end	Day	7% 13% 6% 15% 7% 6% 5% 4 6% 8% 23%	4234
April	1st to 10th	Day	7% 8% 2 7% 6% 5% 5% 4 7% 8% 40%	2280
	11th to 20th	Day	13% 14% 3 9% 5% 5% 5% 4 6% 7% 28%	2293
	21st to end	Day	13% 10% 2 7% 5% 5% 4 4 5% 8% 37%	2559
May	1st to 10th	Day	17% 10% 3 7% 4 4 4 4 6% 8% 34%	4430
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 5% 7% 9% 36%	4388
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 5% 6% 8% 37%	4939
June	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 7% 9% 40%	2850
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 8% 35%	2935
	21st to end	Day	10% 5% 2 5% 5% 4 5% 5% 8% 9% 44%	3040
July	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 5% 8% 10% 46%	4738
	11th to 20th	Day	4 3 1 4 3 4 5% 4 7% 9% 56%	4430
	21st to end	Day	4 3 1 4 3 4 4 4 7% 8% 58%	4802
August	1st to 10th	Day	9% 4 2 5% 4 4 4 4 6% 8% 49%	4411
	11th to 20th	Day	6% 4 1 5% 4 5% 5% 4 6% 9% 51%	4343
	21st to end	Day	9% 4 2 5% 4 4 4 3 4 8% 54%	4218
September	1st to 10th	Day	11% 5% 2 5% 3 3 4 4 5% 8% 50%	2280
	11th to 20th	Day	13% 7% 3 6% 4 3 4 3 5% 7% 45%	2235
	21st to end	Day	12% 6% 2 6% 3 4 3 3 5% 8% 49%	2090
October	1st to 10th	Day	9% 7% 2 5% 3 4 4 3 5% 6% 51%	3202
	11th to 20th	Day	7% 6% 2 5% 4 3 3 3 6% 10% 50%	2974
	21st to end	Day	7% 10% 3 9% 5% 4 4 3 6% 8% 40%	3091
November	1st to 10th	Day	12% 14% 4 9% 6% 5% 5% 4 5% 6% 31%	1712
	11th to 20th	Day	7% 13% 4 12% 8% 6% 5% 4 5% 6% 29%	1600
	21st to end	Day	7% 15% 6% 11% 7% 6% 6% 4 5% 6% 27%	1432
December	1st to 10th	Day	5% 13% 5% 14% 8% 6% 7% 5% 6% 8% 22%	2290
	11th to 20th	Day	8% 17% 5% 12% 9% 8% 7% 4 5% 6% 18%	2643
	21st to end	Day	5% 8% 4 12% 7% 5% 5% 5% 6% 7% 36%	3526
January	1st to 10th	Night	3 12% 5% 13% 11% 7% 8% 5% 7% 6% 22%	6327
	11th to 20th	Night	4 8% 4 12% 9% 10% 10% 7% 9% 6% 20%	6340
	21st to end	Night	4 11% 6% 12% 8% 5% 5% 4 6% 8% 30%	6974
February	1st to 10th	Night	7% 13% 5% 11% 8% 7% 7% 6% 7% 8% 22%	2785
	11th to 20th	Night	5% 11% 4 11% 8% 7% 6% 5% 7% 7% 28%	2518
	21st to end	Night	4 9% 4 11% 7% 6% 6% 4 6% 8% 35%	1980
March	1st to 10th	Night	6% 11% 5% 12% 7% 5% 4 4 7% 9% 30%	3854
	11th to 20th	Night	5% 9% 4 9% 6% 5% 6% 4 7% 9% 36%	3829
	21st to end	Night	7% 13% 7% 14% 6% 5% 4 3 5% 7% 30%	3545
April	1st to 10th	Night	6% 9% 3 7% 4 4 4 4 6% 8% 45%	1900
	11th to 20th	Night	13% 12% 4 9% 5% 4 4 4 7% 6% 32%	1835
	21st to end	Night	12% 9% 3 8% 5% 4 4 5% 6% 7% 38%	1619
May	1st to 10th	Night	18% 10% 3 7% 3 4 4 2 5% 6% 38%	2540
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 4 6% 8% 42%	2517
	21st to end	Night	14% 6% 2 6% 5% 5% 5% 5% 6% 9% 38%	2647
June	1st to 10th	Night	12% 4 2 5% 4 4 4 3 6% 8% 47%	1330
	11th to 20th	Night	13% 6% 2 6% 5% 3 3 4 5% 10% 44%	1237
	21st to end	Night	9% 4 2 6% 4 3 3 5% 7% 9% 47%	1140
July	1st to 10th	Night	5% 3 1 5% 4 4 4 4 8% 13% 48%	2204
	11th to 20th	Night	6% 3 1 5% 3 3 5% 4 6% 7% 56%	2540
	21st to end	Night	3 2 1 4 3 3 3 3 4 7% 67%	2761
August	1st to 10th	Night	8% 4 2 5% 4 5% 4 3 5% 8% 53%	2528
	11th to 20th	Night	5% 3 1 4 3 3 4 3 6% 9% 57%	2496
	21st to end	Night	6% 3 2 4 3 3 3 4 6% 9% 56%	3446
September	1st to 10th	Night	9% 4 2 5% 3 3 4 3 5% 7% 55%	1900
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 7% 50%	1944
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 7% 47%	2090
October	1st to 10th	Night	9% 6% 3 7% 4 4 3 3 5% 6% 51%	3763
	11th to 20th	Night	6% 6% 2 5% 4 4 5% 4 7% 10% 48%	3923
	21st to end	Night	7% 8% 3 8% 5% 5% 5% 4 6% 8% 43%	4467
November	1st to 10th	Night	12% 14% 3 10% 6% 4 4 3 5% 6% 34%	2585
	11th to 20th	Night	8% 12% 4 11% 7% 7% 5% 4 7% 7% 29%	2800
	21st to end	Night	8% 12% 5% 11% 6% 5% 5% 4 5% 7% 31%	2965
December	1st to 10th	Night	7% 14% 6% 14% 7% 9% 6% 4 6% 7% 21%	4900
	11th to 20th	Night	7% 14% 6% 13% 10% 7% 7% 4 5% 6% 21%	5564
	21st to end	Night	4 8% 4 13% 7% 6% 6% 5% 6% 7% 36%	7436

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	66% 6% 11% 12% 4	3639
	11th to 20th	Day	58% 6% 14% 12% 9%	3640
	21st to end	Day	52% 6% 19% 20% 3	4004
February	1st to 10th	Day	63% 5% 11% 15% 7%	1632
	11th to 20th	Day	58% 6% 11% 13% 11%	1777
	21st to end	Day	55% 7% 14% 16% 8% 1	1650
March	1st to 10th	Day	58% 7% 16% 16% 3	3230
	11th to 20th	Day	51% 9% 17% 18% 5%	3360
	21st to end	Day	54% 10% 14% 16% 6%	4234
April	1st to 10th	Day	39% 8% 16% 26% 10% 1	2280
	11th to 20th	Day	53% 7% 14% 18% 8% 1	2296
	21st to end	Day	45% 7% 17% 23% 8% 1	2559
May	1st to 10th	Day	45% 8% 15% 23% 8% 1	4430
	11th to 20th	Day	40% 10% 13% 23% 14%	4392
	21st to end	Day	40% 11% 14% 28% 8% 1	4939
June	1st to 10th	Day	39% 8% 16% 26% 9% 2	2850
	11th to 20th	Day	44% 9% 16% 19% 10% 1	2935
	21st to end	Day	34% 9% 19% 28% 9% 1	3040
July	1st to 10th	Day	30% 10% 23% 29% 7% 1	4668
	11th to 20th	Day	22% 7% 16% 39% 15% 1	4355
	21st to end	Day	21% 7% 14% 38% 16% 5%	4651
August	1st to 10th	Day	31% 7% 17% 25% 18% 1	4396
	11th to 20th	Day	28% 7% 19% 36% 9% 1	4385
	21st to end	Day	29% 6% 14% 40% 10% 1	4217
September	1st to 10th	Day	31% 6% 15% 29% 16% 3	2280
	11th to 20th	Day	39% 5% 14% 27% 11% 3	2235
	21st to end	Day	35% 5% 12% 31% 15% 2	2090
October	1st to 10th	Day	34% 4 13% 34% 13% 1	3202
	11th to 20th	Day	30% 4 17% 36% 12% 1	2974
	21st to end	Day	42% 5% 16% 30% 7%	3091
November	1st to 10th	Day	54% 5% 14% 19% 6% 1	1712
	11th to 20th	Day	55% 7% 15% 15% 7% 1	1600
	21st to end	Day	58% 7% 16% 14% 5%	1432
December	1st to 10th	Day	60% 7% 17% 12% 4	2290
	11th to 20th	Day	66% 5% 17% 9% 2	2640
	21st to end	Day	46% 5% 10% 25% 13% 2	3526
January	1st to 10th	Night	59% 6% 14% 16% 5%	6327
	11th to 20th	Night	57% 7% 15% 14% 7%	6340
	21st to end	Night	51% 7% 22% 17% 3	6974
February	1st to 10th	Night	57% 7% 12% 17% 7%	2785
	11th to 20th	Night	53% 6% 13% 17% 11% 1	2519
	21st to end	Night	46% 6% 16% 22% 10%	1980
March	1st to 10th	Night	48% 7% 19% 21% 4	3854
	11th to 20th	Night	41% 9% 24% 21% 5%	3829
	21st to end	Night	52% 8% 14% 19% 8%	3545
April	1st to 10th	Night	36% 6% 15% 24% 18% 1	1900
	11th to 20th	Night	50% 5% 12% 21% 11% 2	1835
	21st to end	Night	42% 7% 13% 25% 11% 1	1619
May	1st to 10th	Night	45% 6% 13% 22% 12% 1	2540
	11th to 20th	Night	37% 9% 14% 21% 17% 2	2518
	21st to end	Night	38% 10% 13% 27% 11% 1	2647
June	1st to 10th	Night	33% 7% 18% 27% 13% 3	1330
	11th to 20th	Night	36% 9% 19% 20% 14% 3	1237
	21st to end	Night	31% 9% 18% 32% 9%	1140
July	1st to 10th	Night	26% 10% 27% 29% 7% 1	2166
	11th to 20th	Night	25% 7% 14% 38% 15% 2	2492
	21st to end	Night	18% 4 16% 36% 18% 8%	2674
August	1st to 10th	Night	30% 6% 15% 31% 16% 1	2520
	11th to 20th	Night	23% 5% 19% 39% 13% 1	2520
	21st to end	Night	24% 5% 19% 34% 16% 2	3446
September	1st to 10th	Night	27% 6% 11% 30% 23% 3	1900
	11th to 20th	Night	33% 6% 14% 26% 18% 2	1944
	21st to end	Night	36% 5% 12% 29% 15% 2	2090
October	1st to 10th	Night	35% 4 13% 33% 12% 3	3763
	11th to 20th	Night	31% 4 14% 37% 12% 2	3923
	21st to end	Night	40% 4 12% 34% 10% 1	4467
November	1st to 10th	Night	51% 5% 14% 19% 8% 2	2585
	11th to 20th	Night	52% 8% 16% 17% 6% 1	2800
	21st to end	Night	52% 7% 18% 18% 5%	2965
December	1st to 10th	Night	62% 7% 17% 11% 3	4900
	11th to 20th	Night	63% 6% 17% 10% 4	5566
	21st to end	Night	45% 6% 11% 22% 13% 3	7436

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	9% 7% 36% 30% 14% 3	300
	11th to 20th	Day	9% 11% 33% 34% 12% 1	300
	21st to end	Day	11% 11% 35% 33% 9% 1	330
February	1st to 10th	Day	16% 10% 35% 30% 9%	300
	11th to 20th	Day	7% 7% 37% 31% 14% 4	300
	21st to end	Day	4 8% 32% 35% 19% 2	249
March	1st to 10th	Day	15% 7% 36% 28% 12% 2	300
	11th to 20th	Day	13% 12% 34% 27% 11% 3	351
	21st to end	Day	11% 13% 34% 26% 14% 2	531
April	1st to 10th	Day	11% 14% 40% 27% 7% 1	460
	11th to 20th	Day	20% 14% 29% 28% 8% 1	494
	21st to end	Day	15% 10% 31% 28% 15% 1	650
May	1st to 10th	Day	13% 9% 27% 32% 16% 3	653
	11th to 20th	Day	13% 10% 27% 26% 17% 7%	675
	21st to end	Day	16% 9% 27% 25% 19% 4	734
June	1st to 10th	Day	12% 11% 31% 26% 17% 4	680
	11th to 20th	Day	17% 10% 32% 26% 13% 2	680
	21st to end	Day	10% 9% 24% 33% 20% 5%	680
July	1st to 10th	Day	8% 4 23% 37% 24% 5%	671
	11th to 20th	Day	6% 6% 29% 34% 21% 5%	668
	21st to end	Day	4 5% 29% 34% 20% 9%	739
August	1st to 10th	Day	9% 6% 22% 37% 20% 7%	676
	11th to 20th	Day	9% 5% 21% 33% 24% 7%	665
	21st to end	Day	9% 7% 25% 35% 20% 5%	564
September	1st to 10th	Day	12% 9% 30% 31% 14% 4	490
	11th to 20th	Day	18% 11% 26% 27% 17% 1	445
	21st to end	Day	17% 8% 29% 28% 16% 1	300
October	1st to 10th	Day	20% 8% 29% 23% 18% 3	300
	11th to 20th	Day	11% 11% 35% 25% 16% 3	300
	21st to end	Day	17% 12% 35% 28% 7% 1	330
November	1st to 10th	Day	21% 9% 31% 23% 14% 2	300
	11th to 20th	Day	14% 12% 34% 30% 8% 1	300
	21st to end	Day	9% 12% 35% 33% 10% 1	300
December	1st to 10th	Day	13% 10% 33% 29% 11% 3	300
	11th to 20th	Day	11% 16% 38% 28% 6% 1	300
	21st to end	Day	10% 6% 30% 37% 14% 3	330
January	1st to 10th	Night	8% 10% 37% 32% 12% 1	1000
	11th to 20th	Night	13% 12% 35% 32% 8%	1000
	21st to end	Night	11% 11% 38% 31% 8% 1	1100
February	1st to 10th	Night	14% 9% 33% 32% 12% 1	985
	11th to 20th	Night	10% 7% 35% 36% 10% 2	784
	21st to end	Night	5% 8% 28% 38% 18% 3	660
March	1st to 10th	Night	11% 8% 33% 35% 12% 2	800
	11th to 20th	Night	10% 8% 35% 33% 13% 2	800
	21st to end	Night	14% 7% 29% 35% 14% 1	650
April	1st to 10th	Night	8% 10% 36% 36% 11%	570
	11th to 20th	Night	18% 8% 36% 31% 6% 1	563
	21st to end	Night	16% 9% 34% 31% 9% 1	570
May	1st to 10th	Night	16% 5% 26% 40% 13% 1	570
	11th to 20th	Night	14% 4 30% 36% 14% 1	561
	21st to end	Night	17% 8% 25% 32% 17% 1	617
June	1st to 10th	Night	15% 6% 28% 35% 16%	570
	11th to 20th	Night	15% 4 35% 31% 14%	477
	21st to end	Night	10% 4 28% 42% 16% 1	380
July	1st to 10th	Night	6% 4 23% 47% 19% 1	449
	11th to 20th	Night	6% 4 29% 46% 14% 1	552
	21st to end	Night	4 3 28% 46% 17% 2	624
August	1st to 10th	Night	7% 3 24% 48% 16% 2	567
	11th to 20th	Night	8% 3 23% 42% 22% 2	564
	21st to end	Night	7% 5% 26% 43% 18% 1	627
September	1st to 10th	Night	11% 6% 25% 39% 18% 1	570
	11th to 20th	Night	12% 4 31% 36% 16% 1	570
	21st to end	Night	14% 6% 31% 38% 10% 1	570
October	1st to 10th	Night	16% 8% 27% 35% 13% 1	736
	11th to 20th	Night	13% 8% 29% 37% 12% 1	841
	21st to end	Night	14% 9% 33% 35% 7% 1	1045
November	1st to 10th	Night	18% 10% 33% 31% 7% 1	975
	11th to 20th	Night	13% 10% 37% 30% 9% 2	1000
	21st to end	Night	13% 10% 37% 32% 8%	1000
December	1st to 10th	Night	12% 8% 34% 32% 12% 2	1000
	11th to 20th	Night	13% 10% 36% 31% 9% 1	1000
	21st to end	Night	13% 6% 33% 33% 12% 2	1100

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