Writing-on-Stone Provincial Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Writing-on-Stone Provincial Park clear sky chart from 2005-11-06 to 2024-11-02.

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	9% 8% 3 6% 4 4 5% 4 6% 8% 44%	101737
	Night	7% 9% 3 7% 5% 4 5% 4 6% 8% 43%	97377
Transparency	Day	19% 49% 7% 15% 8% 2	101460
	Night	20% 50% 8% 14% 7% 2	97245
Seeing	Day	13% 10% 27% 28% 17% 5%	15471
	Night	12% 10% 33% 32% 13% 1	24673

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	4 16% 5% 9% 7% 5% 4 5% 7% 8% 32%	2219
	11th to 20th	Day	4 10% 4 10% 7% 7% 9% 5% 6% 6% 32%	2229
	21st to end	Day	3 8% 3 7% 5% 5% 5% 3 6% 8% 46%	2794
February	1st to 10th	Day	6% 14% 4 10% 7% 6% 5% 4 5% 8% 30%	1685
	11th to 20th	Day	7% 15% 4 9% 7% 6% 5% 5% 7% 6% 29%	1665
	21st to end	Day	4 11% 5% 12% 8% 5% 5% 3 5% 7% 34%	1458
March	1st to 10th	Day	3 9% 3 9% 5% 5% 4 4 7% 9% 41%	3256
	11th to 20th	Day	6% 7% 2 6% 4 4 5% 4 6% 9% 47%	3490
	21st to end	Day	11% 16% 5% 10% 5% 4 4 4 6% 7% 27%	3825
April	1st to 10th	Day	9% 11% 3 8% 7% 5% 6% 5% 6% 7% 33%	2290
	11th to 20th	Day	11% 14% 4 9% 5% 5% 4 3 5% 8% 32%	2437
	21st to end	Day	13% 8% 3 9% 5% 4 5% 4 6% 8% 36%	2470
May	1st to 10th	Day	21% 13% 3 6% 4 3 4 3 5% 6% 30%	4238
	11th to 20th	Day	10% 7% 2 7% 5% 4 6% 5% 8% 9% 37%	4497
	21st to end	Day	17% 8% 3 7% 5% 5% 6% 4 6% 7% 31%	5161
June	1st to 10th	Day	14% 7% 2 6% 5% 5% 5% 4 7% 7% 39%	2850
	11th to 20th	Day	16% 6% 2 6% 6% 5% 5% 5% 6% 8% 35%	2850
	21st to end	Day	7% 4 1 4 4 4 5% 4 7% 9% 51%	2850
July	1st to 10th	Day	5% 3 1 4 4 3 4 4 6% 8% 58%	4740
	11th to 20th	Day	4 2 1 3 2 3 3 3 5% 9% 65%	4740
	21st to end	Day	2 1 1 2 2 3 3 3 5% 7% 71%	5063
August	1st to 10th	Day	8% 4 2 4 3 4 5% 3 6% 10% 51%	4159
	11th to 20th	Day	5% 3 1 4 3 4 5% 4 6% 9% 55%	4028
	21st to end	Day	7% 3 1 3 3 3 3 3 5% 6% 60%	4521
September	1st to 10th	Day	11% 4 2 4 3 3 3 3 5% 6% 56%	2348
	11th to 20th	Day	12% 5% 2 5% 4 3 5% 3 5% 7% 49%	2090
	21st to end	Day	11% 5% 2 5% 3 3 3 3 5% 7% 53%	2090
October	1st to 10th	Day	11% 9% 2 7% 3 4 4 4 5% 7% 45%	1938
	11th to 20th	Day	7% 9% 3 8% 5% 4 4 4 6% 7% 43%	1900
	21st to end	Day	9% 9% 2 7% 5% 4 5% 4 6% 9% 41%	1886
November	1st to 10th	Day	14% 13% 3 8% 5% 4 4 4 5% 6% 35%	1520
	11th to 20th	Day	5% 10% 3 9% 5% 5% 5% 5% 6% 8% 39%	1520
	21st to end	Day	4 12% 4 8% 6% 5% 5% 3 5% 9% 39%	1473
December	1st to 10th	Day	5% 13% 5% 10% 7% 5% 6% 3 5% 7% 36%	1330
	11th to 20th	Day	5% 10% 4 10% 5% 6% 5% 4 8% 9% 34%	1685
	21st to end	Day	4 8% 2 7% 4 4 5% 4 5% 8% 49%	2442
January	1st to 10th	Night	4 12% 4 9% 5% 4 4 4 7% 9% 36%	4726
	11th to 20th	Night	4 12% 5% 9% 5% 7% 7% 4 6% 7% 34%	4740
	21st to end	Night	4 9% 4 8% 4 4 5% 4 6% 8% 45%	4885
February	1st to 10th	Night	7% 13% 5% 10% 6% 6% 5% 4 5% 7% 33%	2494
	11th to 20th	Night	5% 14% 4 9% 7% 6% 5% 5% 6% 7% 32%	2402
	21st to end	Night	6% 12% 5% 10% 6% 6% 5% 4 5% 7% 34%	1994
March	1st to 10th	Night	3 8% 5% 11% 7% 6% 6% 4 6% 7% 36%	3617
	11th to 20th	Night	4 7% 3 6% 4 4 4 4 7% 8% 48%	3490
	21st to end	Night	13% 18% 6% 12% 5% 4 4 4 5% 7% 24%	3828
April	1st to 10th	Night	9% 12% 4 7% 5% 5% 5% 4 6% 7% 37%	1884
	11th to 20th	Night	10% 12% 3 9% 4 4 4 4 7% 7% 35%	1691
	21st to end	Night	12% 10% 2 6% 6% 4 7% 4 5% 7% 36%	1710
May	1st to 10th	Night	21% 10% 3 6% 5% 4 5% 3 5% 6% 33%	2732
	11th to 20th	Night	9% 5% 2 7% 5% 5% 5% 4 7% 10% 41%	2399
	21st to end	Night	17% 8% 2 7% 5% 6% 5% 5% 5% 7% 32%	2414
June	1st to 10th	Night	11% 6% 2 4 4 5% 5% 5% 7% 10% 41%	1330
	11th to 20th	Night	16% 4 2 5% 5% 5% 5% 4 5% 8% 41%	1330
	21st to end	Night	7% 4 1 3 3 3 4 4 7% 9% 55%	1330
July	1st to 10th	Night	5% 2 1 3 3 4 3 4 7% 9% 59%	2220
	11th to 20th	Night	4 2 1 3 2 2 2 2 5% 8% 68%	2220
	21st to end	Night	2 2 1 3 3 3 3 3 5% 7% 68%	2473
August	1st to 10th	Night	9% 3 1 4 3 3 4 3 6% 8% 55%	2776
	11th to 20th	Night	4 3 1 4 4 4 4 4 8% 12% 50%	2811
	21st to end	Night	10% 4 1 4 3 3 3 3 4 6% 58%	3146
September	1st to 10th	Night	10% 4 2 4 3 4 3 3 6% 7% 54%	1827
	11th to 20th	Night	11% 7% 2 5% 4 3 3 4 6% 6% 51%	2090
	21st to end	Night	9% 6% 2 5% 3 3 3 4 5% 7% 51%	2090
October	1st to 10th	Night	11% 6% 3 6% 3 4 3 3 5% 7% 48%	2241
	11th to 20th	Night	9% 6% 3 7% 4 4 4 4 6% 8% 45%	2280
	21st to end	Night	8% 8% 3 7% 4 6% 5% 4 7% 7% 41%	2711
November	1st to 10th	Night	11% 12% 4 8% 5% 4 4 3 6% 6% 35%	2561
	11th to 20th	Night	5% 9% 3 8% 6% 5% 6% 4 6% 8% 40%	2660
	21st to end	Night	4 12% 4 8% 5% 4 4 4 6% 9% 40%	2705
December	1st to 10th	Night	5% 12% 4 9% 6% 5% 5% 5% 6% 7% 35%	2850
	11th to 20th	Night	4 8% 4 11% 6% 5% 5% 4 7% 9% 38%	3506
	21st to end	Night	4 8% 3 7% 4 5% 5% 4 6% 7% 47%	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	33% 40% 10% 13% 3 1	2219
	11th to 20th	Day	32% 42% 6% 6% 13% 1	2229
	21st to end	Day	17% 42% 16% 22% 3	2794
February	1st to 10th	Day	23% 65% 3 6% 2	1685
	11th to 20th	Day	19% 66% 5% 7% 3	1674
	21st to end	Day	19% 64% 4 7% 4 1	1458
March	1st to 10th	Day	19% 43% 9% 16% 13%	3256
	11th to 20th	Day	16% 44% 15% 18% 7% 1	3490
	21st to end	Day	37% 43% 10% 7% 3	3825
April	1st to 10th	Day	18% 66% 5% 8% 3	2290
	11th to 20th	Day	15% 67% 4 9% 4 1	2440
	21st to end	Day	17% 65% 4 9% 4	2470
May	1st to 10th	Day	36% 41% 5% 15% 2	4238
	11th to 20th	Day	25% 45% 7% 17% 6%	4501
	21st to end	Day	26% 45% 7% 16% 5%	5162
June	1st to 10th	Day	10% 66% 6% 12% 5% 1	2850
	11th to 20th	Day	17% 66% 5% 7% 4 1	2850
	21st to end	Day	13% 65% 5% 12% 4 1	2850
July	1st to 10th	Day	15% 39% 9% 16% 17% 5%	4666
	11th to 20th	Day	8% 37% 7% 23% 17% 7%	4659
	21st to end	Day	6% 36% 5% 14% 21% 18%	4903
August	1st to 10th	Day	19% 39% 6% 19% 15% 2	4143
	11th to 20th	Day	15% 41% 10% 25% 9% 1	4067
	21st to end	Day	15% 38% 6% 26% 14% 2	4520
September	1st to 10th	Day	12% 60% 7% 12% 6% 3	2348
	11th to 20th	Day	17% 61% 5% 11% 4 1	2090
	21st to end	Day	15% 60% 5% 13% 6% 1	2090
October	1st to 10th	Day	17% 61% 7% 9% 5% 1	1938
	11th to 20th	Day	14% 60% 6% 13% 6%	1900
	21st to end	Day	17% 60% 6% 13% 4	1886
November	1st to 10th	Day	25% 59% 5% 8% 2 1	1520
	11th to 20th	Day	15% 62% 8% 11% 4 1	1520
	21st to end	Day	14% 61% 8% 11% 6%	1473
December	1st to 10th	Day	20% 61% 5% 10% 3 1	1330
	11th to 20th	Day	20% 50% 11% 16% 2 1	1684
	21st to end	Day	16% 38% 12% 17% 15% 3	2442
January	1st to 10th	Night	27% 40% 12% 15% 4 1	4726
	11th to 20th	Night	31% 39% 7% 10% 11% 1	4740
	21st to end	Night	18% 43% 14% 21% 4	4885
February	1st to 10th	Night	21% 65% 4 5% 4 1	2494
	11th to 20th	Night	18% 65% 5% 7% 5%	2403
	21st to end	Night	18% 64% 5% 6% 5% 1	1994
March	1st to 10th	Night	27% 42% 9% 16% 6%	3617
	11th to 20th	Night	15% 44% 14% 19% 7%	3490
	21st to end	Night	44% 41% 8% 6% 1	3828
April	1st to 10th	Night	16% 66% 6% 9% 3	1884
	11th to 20th	Night	12% 67% 5% 9% 6% 1	1691
	21st to end	Night	18% 66% 2 9% 4 1	1710
May	1st to 10th	Night	36% 43% 5% 12% 4	2732
	11th to 20th	Night	22% 46% 9% 18% 6%	2400
	21st to end	Night	25% 44% 9% 17% 5%	2414
June	1st to 10th	Night	10% 65% 5% 14% 4	1330
	11th to 20th	Night	15% 67% 4 9% 5% 1	1330
	21st to end	Night	11% 65% 5% 12% 7% 1	1330
July	1st to 10th	Night	13% 39% 9% 19% 16% 4	2185
	11th to 20th	Night	8% 37% 7% 24% 14% 9%	2178
	21st to end	Night	9% 35% 4 15% 21% 15%	2396
August	1st to 10th	Night	17% 39% 6% 19% 14% 6%	2768
	11th to 20th	Night	16% 42% 14% 21% 7% 1	2838
	21st to end	Night	19% 37% 6% 27% 9% 2	3146
September	1st to 10th	Night	13% 60% 6% 12% 6% 3	1827
	11th to 20th	Night	14% 61% 5% 13% 5% 2	2090
	21st to end	Night	16% 60% 6% 10% 8%	2090
October	1st to 10th	Night	18% 61% 6% 8% 6% 2	2241
	11th to 20th	Night	13% 60% 5% 14% 6% 1	2280
	21st to end	Night	18% 60% 5% 12% 5%	2711
November	1st to 10th	Night	22% 60% 6% 9% 3 1	2561
	11th to 20th	Night	16% 61% 7% 9% 6%	2660
	21st to end	Night	15% 60% 7% 10% 7%	2705
December	1st to 10th	Night	18% 61% 5% 11% 5%	2850
	11th to 20th	Night	17% 53% 15% 12% 3 1	3507
	21st to end	Night	17% 38% 7% 18% 13% 6%	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	10% 12% 36% 19% 14% 9%	180
	11th to 20th	Day	10% 12% 33% 31% 11% 3	180
	21st to end	Day	12% 13% 44% 21% 8% 3	198
February	1st to 10th	Day	16% 17% 35% 24% 6% 2	258
	11th to 20th	Day	10% 14% 38% 27% 8% 3	270
	21st to end	Day	12% 13% 33% 27% 13% 2	270
March	1st to 10th	Day	10% 16% 37% 22% 13% 2	460
	11th to 20th	Day	10% 15% 31% 28% 11% 5%	460
	21st to end	Day	14% 13% 34% 24% 13% 2	506
April	1st to 10th	Day	16% 15% 35% 27% 7%	460
	11th to 20th	Day	15% 15% 32% 24% 12% 2	452
	21st to end	Day	18% 13% 23% 26% 18% 2	460
May	1st to 10th	Day	18% 11% 21% 26% 19% 5%	539
	11th to 20th	Day	17% 8% 20% 28% 20% 6%	675
	21st to end	Day	20% 7% 18% 29% 20% 7%	734
June	1st to 10th	Day	15% 13% 24% 26% 17% 5%	680
	11th to 20th	Day	19% 12% 31% 25% 11% 3	680
	21st to end	Day	9% 7% 26% 32% 21% 5%	680
July	1st to 10th	Day	7% 4 19% 33% 28% 7%	671
	11th to 20th	Day	7% 5% 23% 38% 23% 4	668
	21st to end	Day	3 5% 21% 36% 27% 8%	700
August	1st to 10th	Day	7% 6% 19% 34% 28% 6%	487
	11th to 20th	Day	8% 4 16% 34% 27% 11%	477
	21st to end	Day	8% 5% 25% 30% 23% 8%	539
September	1st to 10th	Day	11% 8% 25% 27% 21% 7%	490
	11th to 20th	Day	14% 8% 24% 31% 16% 6%	490
	21st to end	Day	16% 11% 28% 26% 14% 5%	490
October	1st to 10th	Day	14% 8% 28% 27% 17% 7%	338
	11th to 20th	Day	13% 11% 32% 22% 17% 6%	300
	21st to end	Day	18% 14% 32% 23% 11% 2	330
November	1st to 10th	Day	25% 10% 34% 22% 8%	273
	11th to 20th	Day	9% 14% 44% 24% 8% 1	270
	21st to end	Day	9% 17% 38% 22% 9% 4	248
December	1st to 10th	Day	11% 18% 43% 14% 12% 2	180
	11th to 20th	Day	13% 16% 41% 16% 13% 1	180
	21st to end	Day	13% 11% 28% 29% 13% 7%	198
January	1st to 10th	Night	11% 13% 40% 26% 9% 1	950
	11th to 20th	Night	10% 13% 40% 26% 11% 1	950
	21st to end	Night	9% 14% 39% 27% 8% 2	846
February	1st to 10th	Night	13% 14% 32% 28% 11% 2	760
	11th to 20th	Night	12% 14% 35% 28% 11% 1	744
	21st to end	Night	10% 10% 32% 31% 14% 2	628
March	1st to 10th	Night	7% 11% 36% 31% 14% 1	760
	11th to 20th	Night	10% 12% 34% 32% 10% 1	760
	21st to end	Night	14% 12% 33% 29% 12% 1	836
April	1st to 10th	Night	13% 11% 35% 30% 10% 1	644
	11th to 20th	Night	13% 10% 37% 28% 11% 1	563
	21st to end	Night	17% 10% 30% 30% 13%	570
May	1st to 10th	Night	14% 8% 28% 32% 18% 1	570
	11th to 20th	Night	11% 6% 23% 40% 18% 1	496
	21st to end	Night	24% 6% 16% 36% 15% 3	411
June	1st to 10th	Night	15% 8% 28% 33% 15% 1	380
	11th to 20th	Night	17% 11% 33% 28% 11%	380
	21st to end	Night	9% 4 22% 45% 19%	380
July	1st to 10th	Night	7% 4 23% 46% 21% 1	370
	11th to 20th	Night	9% 2 24% 46% 18% 1	368
	21st to end	Night	5% 3 21% 47% 23% 1	416
August	1st to 10th	Night	8% 3 22% 42% 24% 2	521
	11th to 20th	Night	7% 4 21% 43% 24% 1	564
	21st to end	Night	10% 4 24% 42% 20%	627
September	1st to 10th	Night	12% 2 25% 40% 19% 2	571
	11th to 20th	Night	13% 4 22% 37% 22% 1	760
	21st to end	Night	12% 8% 29% 33% 16% 2	760
October	1st to 10th	Night	15% 7% 24% 35% 17% 1	760
	11th to 20th	Night	13% 9% 34% 29% 12% 3	760
	21st to end	Night	11% 13% 37% 29% 9% 1	836
November	1st to 10th	Night	17% 12% 40% 25% 6%	887
	11th to 20th	Night	10% 15% 42% 24% 8% 1	950
	21st to end	Night	9% 11% 42% 29% 8% 1	950
December	1st to 10th	Night	10% 12% 34% 32% 9% 2	950
	11th to 20th	Night	10% 11% 41% 27% 9% 2	950
	21st to end	Night	12% 12% 39% 27% 9% 2	1045

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