Claresholm
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Claresholm clear sky chart from 2005-11-06 to 2024-02-05.

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 6% 6% 3 5% 5% 6% 8% 41%	77723
	Night	6% 8% 4 7% 6% 3 5% 5% 6% 8% 42%	81089
Transparency	Day	39% 9% 16% 22% 12% 2	77431
	Night	38% 9% 16% 22% 12% 2	80961
Seeing	Day	13% 14% 27% 27% 15% 4	14242
	Night	11% 12% 32% 31% 13% 2	23602

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	2 8% 6% 11% 6% 4 5% 5% 6% 10% 37%	2219
	11th to 20th	Day	3 8% 5% 9% 9% 6% 5% 7% 7% 7% 35%	2299
	21st to end	Day	2 7% 4 8% 6% 4 5% 6% 7% 10% 40%	2794
February	1st to 10th	Day	5% 10% 4 9% 8% 6% 7% 5% 7% 8% 32%	1508
	11th to 20th	Day	4 12% 5% 7% 8% 4 6% 7% 7% 9% 31%	1575
	21st to end	Day	4 12% 6% 9% 9% 3 4 6% 5% 7% 34%	1444
March	1st to 10th	Day	3 11% 5% 8% 8% 4 6% 6% 6% 9% 36%	1800
	11th to 20th	Day	6% 8% 4 7% 6% 4 6% 6% 6% 8% 39%	1970
	21st to end	Day	8% 12% 4 8% 7% 4 6% 6% 5% 9% 31%	2182
April	1st to 10th	Day	8% 13% 5% 8% 8% 4 6% 5% 6% 8% 29%	2210
	11th to 20th	Day	11% 13% 4 7% 5% 3 5% 5% 7% 8% 32%	2310
	21st to end	Day	11% 10% 4 6% 6% 3 6% 5% 6% 8% 34%	2340
May	1st to 10th	Day	12% 11% 4 7% 6% 4 6% 6% 6% 7% 32%	2377
	11th to 20th	Day	13% 6% 3 6% 7% 4 5% 6% 6% 9% 36%	2654
	21st to end	Day	21% 7% 3 5% 6% 3 6% 5% 5% 7% 31%	2917
June	1st to 10th	Day	14% 8% 2 6% 6% 3 7% 6% 6% 8% 33%	2700
	11th to 20th	Day	18% 7% 3 6% 6% 4 6% 6% 6% 8% 30%	2700
	21st to end	Day	8% 3 2 5% 4 3 5% 6% 7% 8% 48%	2700
July	1st to 10th	Day	7% 4 2 4 5% 3 5% 5% 7% 10% 48%	2700
	11th to 20th	Day	7% 3 1 3 4 3 5% 6% 8% 8% 51%	2700
	21st to end	Day	4 2 1 4 4 2 4 5% 6% 8% 60%	2840
August	1st to 10th	Day	8% 3 1 3 4 3 5% 5% 6% 9% 53%	2490
	11th to 20th	Day	8% 3 2 3 4 2 4 5% 6% 9% 53%	2299
	21st to end	Day	10% 3 1 4 4 2 4 5% 6% 8% 53%	2574
September	1st to 10th	Day	11% 6% 2 5% 3 3 4 3 5% 6% 53%	2214
	11th to 20th	Day	13% 5% 2 4 4 3 4 4 5% 8% 49%	1980
	21st to end	Day	10% 6% 2 4 5% 3 4 5% 5% 8% 49%	1980
October	1st to 10th	Day	12% 9% 2 7% 5% 3 4 5% 5% 7% 42%	1900
	11th to 20th	Day	8% 8% 3 6% 5% 3 5% 5% 6% 8% 42%	1697
	21st to end	Day	6% 10% 3 6% 5% 3 5% 7% 7% 10% 37%	1782
November	1st to 10th	Day	10% 11% 5% 8% 5% 3 4 5% 5% 8% 36%	1570
	11th to 20th	Day	5% 9% 3 8% 5% 4 6% 3 6% 8% 43%	1514
	21st to end	Day	4 8% 6% 7% 5% 2 4 6% 6% 11% 39%	1330
December	1st to 10th	Day	2 9% 4 9% 6% 4 5% 5% 6% 10% 40%	1330
	11th to 20th	Day	4 10% 5% 11% 8% 4 6% 6% 7% 7% 32%	1682
	21st to end	Day	4 9% 3 6% 6% 3 4 5% 5% 8% 47%	2442
January	1st to 10th	Night	3 12% 5% 8% 7% 4 7% 6% 6% 9% 33%	4726
	11th to 20th	Night	3 8% 5% 11% 8% 4 6% 7% 6% 7% 34%	4631
	21st to end	Night	3 9% 4 8% 6% 3 6% 6% 6% 8% 40%	4862
February	1st to 10th	Night	5% 9% 4 11% 7% 4 6% 6% 7% 8% 35%	2546
	11th to 20th	Night	5% 13% 6% 9% 7% 4 6% 6% 6% 8% 31%	2272
	21st to end	Night	4 10% 6% 9% 9% 5% 5% 5% 5% 6% 35%	1811
March	1st to 10th	Night	4 9% 6% 10% 9% 4 5% 4 6% 9% 34%	2160
	11th to 20th	Night	5% 9% 3 7% 6% 4 6% 6% 7% 10% 38%	1988
	21st to end	Night	5% 10% 4 8% 7% 3 5% 6% 7% 9% 35%	2171
April	1st to 10th	Night	8% 11% 5% 7% 6% 3 4 5% 5% 7% 38%	1749
	11th to 20th	Night	10% 10% 4 9% 6% 4 5% 5% 7% 6% 34%	1601
	21st to end	Night	11% 9% 4 8% 6% 3 5% 5% 5% 5% 39%	1620
May	1st to 10th	Night	11% 10% 5% 7% 6% 3 5% 4 5% 9% 36%	1578
	11th to 20th	Night	10% 7% 3 5% 5% 3 4 5% 5% 7% 46%	1239
	21st to end	Night	19% 6% 2 6% 6% 3 4 5% 5% 8% 35%	1358
June	1st to 10th	Night	13% 6% 2 5% 5% 3 5% 6% 6% 8% 40%	1260
	11th to 20th	Night	19% 5% 2 6% 5% 3 5% 5% 6% 8% 36%	1260
	21st to end	Night	6% 3 2 4 4 4 6% 6% 7% 7% 52%	1260
July	1st to 10th	Night	5% 4 2 4 3 4 5% 5% 5% 10% 51%	1260
	11th to 20th	Night	6% 3 2 4 4 2 5% 5% 6% 8% 55%	1260
	21st to end	Night	4 3 1 3 3 1 2 5% 5% 7% 66%	1473
August	1st to 10th	Night	8% 2 1 4 4 3 5% 5% 5% 7% 57%	1449
	11th to 20th	Night	6% 4 2 3 3 2 3 6% 6% 9% 56%	1602
	21st to end	Night	7% 3 1 4 3 3 3 4 7% 7% 58%	1782
September	1st to 10th	Night	9% 3 1 5% 4 3 4 4 5% 7% 54%	1742
	11th to 20th	Night	11% 6% 2 4 3 2 3 3 4 7% 55%	1980
	21st to end	Night	11% 6% 2 4 3 2 3 4 6% 7% 51%	1980
October	1st to 10th	Night	11% 7% 2 6% 4 3 4 5% 5% 7% 46%	2060
	11th to 20th	Night	7% 7% 2 5% 5% 3 4 5% 6% 9% 47%	2258
	21st to end	Night	8% 9% 3 6% 5% 3 5% 5% 7% 8% 41%	2574
November	1st to 10th	Night	9% 12% 3 7% 5% 3 5% 5% 6% 8% 38%	2489
	11th to 20th	Night	3 8% 3 6% 6% 3 6% 6% 7% 10% 43%	2664
	21st to end	Night	4 10% 5% 6% 5% 3 4 5% 7% 10% 42%	2850
December	1st to 10th	Night	4 9% 4 7% 7% 4 6% 5% 7% 9% 38%	2850
	11th to 20th	Night	3 8% 4 9% 7% 5% 6% 6% 7% 9% 37%	3510
	21st to end	Night	4 9% 4 7% 7% 3 5% 6% 5% 7% 44%	5214

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	39% 12% 16% 23% 8% 2	2219
	11th to 20th	Day	46% 9% 12% 15% 15% 3	2320
	21st to end	Day	34% 13% 18% 28% 7% 1	2794
February	1st to 10th	Day	49% 9% 16% 17% 8% 2	1508
	11th to 20th	Day	46% 10% 17% 19% 7% 2	1584
	21st to end	Day	50% 7% 13% 16% 12% 1	1444
March	1st to 10th	Day	43% 10% 16% 20% 10% 1	1800
	11th to 20th	Day	38% 11% 17% 22% 11% 1	1971
	21st to end	Day	48% 9% 18% 18% 6% 1	2182
April	1st to 10th	Day	50% 9% 15% 19% 6% 1	2210
	11th to 20th	Day	48% 8% 15% 19% 8% 2	2310
	21st to end	Day	46% 8% 15% 20% 9% 1	2340
May	1st to 10th	Day	47% 9% 15% 21% 8%	2377
	11th to 20th	Day	41% 9% 17% 21% 10% 1	2658
	21st to end	Day	50% 8% 17% 17% 8%	2918
June	1st to 10th	Day	45% 9% 17% 19% 9% 2	2700
	11th to 20th	Day	48% 10% 15% 17% 9% 1	2700
	21st to end	Day	29% 9% 20% 27% 12% 3	2700
July	1st to 10th	Day	27% 10% 18% 29% 14% 3	2626
	11th to 20th	Day	26% 9% 17% 26% 17% 4	2619
	21st to end	Day	21% 7% 15% 28% 24% 5%	2682
August	1st to 10th	Day	26% 8% 18% 29% 15% 4	2473
	11th to 20th	Day	25% 8% 19% 32% 12% 4	2299
	21st to end	Day	27% 7% 15% 28% 19% 4	2574
September	1st to 10th	Day	31% 6% 14% 24% 17% 7%	2214
	11th to 20th	Day	33% 8% 13% 27% 15% 4	1980
	21st to end	Day	33% 7% 14% 30% 13% 3	1980
October	1st to 10th	Day	41% 9% 16% 22% 10% 2	1900
	11th to 20th	Day	38% 8% 17% 22% 12% 2	1697
	21st to end	Day	40% 10% 15% 22% 11% 2	1782
November	1st to 10th	Day	47% 8% 13% 22% 11%	1570
	11th to 20th	Day	38% 8% 20% 22% 11% 1	1514
	21st to end	Day	38% 9% 20% 20% 10% 3	1330
December	1st to 10th	Day	41% 10% 17% 18% 11% 4	1330
	11th to 20th	Day	48% 9% 17% 20% 6% 1	1684
	21st to end	Day	33% 9% 14% 22% 20% 2	2442
January	1st to 10th	Night	45% 11% 16% 19% 7% 2	4726
	11th to 20th	Night	47% 8% 13% 14% 15% 2	4672
	21st to end	Night	37% 11% 18% 23% 9% 1	4862
February	1st to 10th	Night	46% 9% 14% 17% 12% 2	2546
	11th to 20th	Night	49% 9% 13% 21% 8%	2273
	21st to end	Night	49% 7% 12% 20% 10% 3	1811
March	1st to 10th	Night	45% 8% 16% 21% 8% 1	2160
	11th to 20th	Night	39% 11% 17% 21% 12% 1	1988
	21st to end	Night	44% 10% 20% 19% 7% 1	2171
April	1st to 10th	Night	44% 9% 14% 22% 11% 1	1749
	11th to 20th	Night	47% 9% 13% 21% 9% 1	1601
	21st to end	Night	44% 9% 14% 23% 9% 2	1620
May	1st to 10th	Night	44% 7% 17% 23% 8% 1	1578
	11th to 20th	Night	35% 10% 13% 29% 11% 2	1239
	21st to end	Night	47% 10% 15% 19% 8% 1	1358
June	1st to 10th	Night	40% 8% 18% 22% 11% 1	1260
	11th to 20th	Night	44% 8% 17% 20% 10% 1	1260
	21st to end	Night	27% 10% 19% 26% 16% 2	1260
July	1st to 10th	Night	27% 8% 20% 29% 13% 3	1225
	11th to 20th	Night	24% 9% 16% 25% 19% 6%	1218
	21st to end	Night	18% 6% 15% 27% 26% 7%	1391
August	1st to 10th	Night	25% 8% 17% 28% 18% 5%	1441
	11th to 20th	Night	23% 7% 17% 30% 18% 4	1602
	21st to end	Night	23% 7% 12% 29% 23% 5%	1782
September	1st to 10th	Night	28% 6% 16% 28% 17% 5%	1742
	11th to 20th	Night	30% 6% 13% 27% 18% 5%	1980
	21st to end	Night	31% 7% 16% 27% 15% 4	1980
October	1st to 10th	Night	36% 8% 16% 23% 15% 2	2060
	11th to 20th	Night	33% 8% 17% 24% 15% 3	2258
	21st to end	Night	39% 8% 16% 24% 11% 1	2574
November	1st to 10th	Night	43% 9% 15% 21% 10% 1	2489
	11th to 20th	Night	35% 10% 18% 20% 16% 1	2664
	21st to end	Night	37% 8% 20% 20% 11% 4	2850
December	1st to 10th	Night	43% 10% 16% 18% 10% 3	2850
	11th to 20th	Night	40% 12% 22% 20% 6% 1	3507
	21st to end	Night	35% 10% 15% 23% 13% 5%	5214

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	7% 15% 31% 30% 9% 8%	180
	11th to 20th	Day	10% 17% 29% 25% 13% 5%	180
	21st to end	Day	7% 22% 36% 24% 9% 3	198
February	1st to 10th	Day	13% 23% 34% 21% 6% 3	184
	11th to 20th	Day	12% 17% 35% 25% 10% 2	240
	21st to end	Day	12% 18% 30% 28% 11% 1	310
March	1st to 10th	Day	10% 24% 34% 21% 8% 4	420
	11th to 20th	Day	10% 20% 30% 26% 12% 3	420
	21st to end	Day	12% 19% 35% 21% 10% 3	462
April	1st to 10th	Day	14% 22% 31% 23% 10%	420
	11th to 20th	Day	17% 15% 29% 21% 15% 3	412
	21st to end	Day	16% 20% 28% 22% 10% 3	420
May	1st to 10th	Day	17% 11% 25% 28% 14% 5%	437
	11th to 20th	Day	18% 8% 22% 28% 20% 5%	625
	21st to end	Day	21% 9% 17% 27% 20% 6%	679
June	1st to 10th	Day	14% 14% 25% 28% 15% 3	630
	11th to 20th	Day	19% 14% 24% 28% 13% 3	630
	21st to end	Day	10% 6% 25% 30% 22% 7%	630
July	1st to 10th	Day	9% 5% 23% 34% 24% 5%	621
	11th to 20th	Day	7% 9% 24% 35% 21% 5%	618
	21st to end	Day	4 8% 25% 37% 20% 6%	586
August	1st to 10th	Day	10% 8% 21% 34% 21% 6%	447
	11th to 20th	Day	6% 7% 26% 30% 23% 8%	437
	21st to end	Day	9% 10% 27% 28% 18% 7%	495
September	1st to 10th	Day	13% 12% 30% 27% 15% 3	450
	11th to 20th	Day	14% 11% 26% 29% 14% 6%	450
	21st to end	Day	17% 19% 25% 26% 10% 4	450
October	1st to 10th	Day	16% 11% 22% 25% 20% 6%	370
	11th to 20th	Day	13% 18% 28% 20% 15% 6%	270
	21st to end	Day	17% 20% 26% 25% 10% 3	297
November	1st to 10th	Day	20% 21% 29% 19% 10% 1	270
	11th to 20th	Day	13% 19% 33% 26% 9%	266
	21st to end	Day	7% 24% 27% 26% 8% 8%	180
December	1st to 10th	Day	8% 20% 28% 27% 13% 4	180
	11th to 20th	Day	10% 19% 38% 21% 8% 3	180
	21st to end	Day	12% 13% 28% 29% 14% 5%	198
January	1st to 10th	Night	11% 22% 31% 27% 8% 1	950
	11th to 20th	Night	10% 15% 34% 30% 9% 1	908
	21st to end	Night	10% 15% 36% 29% 9% 1	836
February	1st to 10th	Night	9% 18% 32% 26% 13% 3	738
	11th to 20th	Night	10% 11% 37% 31% 9% 2	704
	21st to end	Night	10% 10% 32% 30% 17% 2	592
March	1st to 10th	Night	9% 13% 35% 31% 10% 2	720
	11th to 20th	Night	9% 14% 34% 30% 10% 2	720
	21st to end	Night	11% 12% 32% 31% 11% 3	792
April	1st to 10th	Night	12% 12% 35% 29% 10% 1	669
	11th to 20th	Night	17% 10% 35% 29% 10% 1	533
	21st to end	Night	15% 11% 30% 34% 11% 1	540
May	1st to 10th	Night	13% 10% 28% 32% 16%	514
	11th to 20th	Night	13% 6% 23% 35% 23% 1	354
	21st to end	Night	20% 6% 23% 30% 20% 1	389
June	1st to 10th	Night	14% 8% 28% 34% 15% 2	360
	11th to 20th	Night	20% 8% 29% 29% 14%	360
	21st to end	Night	7% 5% 26% 40% 22% 1	360
July	1st to 10th	Night	8% 3 19% 42% 26% 1	350
	11th to 20th	Night	7% 2 25% 45% 20% 1	348
	21st to end	Night	4 3 24% 44% 23% 2	394
August	1st to 10th	Night	9% 2 17% 42% 28% 2	375
	11th to 20th	Night	8% 2 20% 43% 24% 2	534
	21st to end	Night	8% 5% 24% 43% 19% 1	594
September	1st to 10th	Night	11% 5% 26% 35% 21% 2	627
	11th to 20th	Night	14% 5% 25% 33% 21% 2	720
	21st to end	Night	13% 8% 34% 28% 13% 4	720
October	1st to 10th	Night	15% 8% 25% 32% 18% 2	720
	11th to 20th	Night	12% 10% 32% 28% 15% 3	720
	21st to end	Night	12% 14% 34% 28% 10% 1	792
November	1st to 10th	Night	18% 15% 38% 22% 8%	824
	11th to 20th	Night	11% 20% 39% 23% 5% 1	950
	21st to end	Night	10% 17% 39% 24% 8% 2	950
December	1st to 10th	Night	10% 13% 35% 29% 12% 2	950
	11th to 20th	Night	8% 17% 38% 29% 8% 1	950
	21st to end	Night	11% 16% 33% 28% 10% 2	1045

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