Stavely
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stavely clear sky chart from 2005-11-06 to 2024-01-14.

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% 6% 3 5% 5% 6% 8% 40%	74633
	Night	6% 8% 4 7% 6% 3 5% 5% 6% 8% 41%	75135
Transparency	Day	39% 8% 16% 23% 11% 2	74320
	Night	39% 8% 15% 23% 12% 2	74966
Seeing	Day	13% 15% 30% 26% 13% 3	14199
	Night	11% 12% 33% 30% 13% 2	23501

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 8% 5% 9% 6% 4 4 6% 7% 9% 38%	1329
	11th to 20th	Day	3 8% 5% 7% 8% 4 7% 5% 6% 9% 36%	1335
	21st to end	Day	4 7% 4 9% 8% 4 7% 6% 6% 11% 33%	1584
February	1st to 10th	Day	4 10% 4 9% 7% 5% 7% 6% 7% 9% 31%	1468
	11th to 20th	Day	4 12% 5% 8% 7% 4 6% 6% 8% 8% 30%	1575
	21st to end	Day	4 11% 5% 9% 9% 4 6% 5% 6% 7% 33%	1444
March	1st to 10th	Day	3 11% 5% 8% 8% 4 6% 5% 7% 10% 35%	1800
	11th to 20th	Day	6% 7% 4 8% 5% 4 6% 6% 7% 10% 39%	1969
	21st to end	Day	8% 11% 4 8% 7% 4 8% 5% 6% 8% 31%	2186
April	1st to 10th	Day	8% 12% 6% 9% 7% 4 5% 6% 6% 7% 30%	2209
	11th to 20th	Day	11% 12% 4 8% 6% 3 5% 6% 6% 8% 32%	2310
	21st to end	Day	11% 9% 4 7% 7% 3 5% 6% 7% 9% 33%	2340
May	1st to 10th	Day	13% 9% 4 7% 6% 4 7% 6% 6% 7% 31%	2390
	11th to 20th	Day	12% 6% 3 7% 7% 4 5% 5% 7% 8% 36%	2654
	21st to end	Day	20% 7% 3 7% 5% 3 5% 6% 5% 8% 30%	2917
June	1st to 10th	Day	15% 7% 3 6% 7% 4 6% 6% 7% 8% 32%	2700
	11th to 20th	Day	18% 7% 3 6% 6% 4 6% 6% 7% 9% 28%	2700
	21st to end	Day	8% 4 2 4 5% 3 5% 6% 8% 9% 46%	2700
July	1st to 10th	Day	7% 4 2 5% 5% 4 5% 5% 7% 9% 48%	2700
	11th to 20th	Day	7% 4 2 3 4 3 5% 6% 7% 9% 51%	2700
	21st to end	Day	4 3 1 4 3 3 4 4 6% 9% 59%	2844
August	1st to 10th	Day	8% 4 2 4 4 3 4 5% 6% 8% 52%	2497
	11th to 20th	Day	7% 4 2 4 4 2 4 5% 6% 9% 53%	2299
	21st to end	Day	9% 4 2 4 4 3 4 4 6% 8% 53%	2574
September	1st to 10th	Day	11% 5% 2 5% 4 3 3 4 5% 6% 53%	2219
	11th to 20th	Day	12% 7% 1 4 4 3 4 5% 6% 7% 48%	1980
	21st to end	Day	9% 7% 2 5% 5% 3 4 4 5% 8% 49%	1980
October	1st to 10th	Day	12% 8% 3 6% 5% 3 4 6% 4 7% 42%	1900
	11th to 20th	Day	7% 9% 3 6% 5% 3 5% 5% 5% 9% 41%	1692
	21st to end	Day	6% 10% 3 7% 5% 4 5% 6% 7% 10% 37%	1782
November	1st to 10th	Day	10% 12% 4 7% 6% 4 4 5% 5% 7% 36%	1568
	11th to 20th	Day	4 9% 4 7% 5% 4 5% 4 6% 9% 43%	1504
	21st to end	Day	4 8% 6% 8% 5% 2 5% 5% 6% 12% 38%	1330
December	1st to 10th	Day	3 8% 5% 9% 7% 5% 6% 4 6% 9% 39%	1330
	11th to 20th	Day	3 10% 5% 11% 9% 4 8% 5% 6% 7% 32%	1682
	21st to end	Day	3 9% 3 7% 5% 3 5% 6% 5% 9% 46%	2442
January	1st to 10th	Night	3 11% 6% 8% 7% 4 7% 6% 8% 9% 32%	2836
	11th to 20th	Night	4 9% 5% 9% 8% 4 6% 6% 6% 8% 36%	2721
	21st to end	Night	3 9% 4 7% 6% 4 6% 7% 8% 9% 37%	2772
February	1st to 10th	Night	4 9% 4 10% 7% 5% 6% 6% 5% 9% 34%	2490
	11th to 20th	Night	5% 13% 6% 8% 7% 4 6% 7% 6% 7% 31%	2272
	21st to end	Night	4 9% 6% 11% 9% 5% 5% 5% 5% 6% 34%	1812
March	1st to 10th	Night	3 9% 5% 11% 9% 4 6% 6% 6% 9% 33%	2160
	11th to 20th	Night	5% 9% 4 7% 7% 4 6% 6% 7% 10% 37%	1990
	21st to end	Night	6% 11% 5% 8% 7% 4 5% 5% 6% 9% 34%	2168
April	1st to 10th	Night	7% 12% 5% 8% 6% 3 5% 4 6% 7% 36%	1750
	11th to 20th	Night	10% 11% 4 8% 6% 3 6% 6% 6% 6% 33%	1601
	21st to end	Night	11% 9% 4 7% 6% 3 5% 6% 5% 7% 36%	1620
May	1st to 10th	Night	11% 10% 4 7% 5% 3 6% 5% 5% 8% 36%	1566
	11th to 20th	Night	11% 5% 2 7% 5% 4 4 6% 4 6% 46%	1239
	21st to end	Night	19% 6% 3 5% 5% 4 6% 5% 5% 8% 34%	1358
June	1st to 10th	Night	13% 5% 2 6% 5% 4 5% 4 6% 8% 40%	1260
	11th to 20th	Night	17% 7% 3 5% 6% 2 6% 4 5% 10% 35%	1260
	21st to end	Night	6% 4 2 3 5% 3 4 6% 7% 9% 50%	1260
July	1st to 10th	Night	5% 4 2 4 5% 3 5% 5% 7% 9% 50%	1260
	11th to 20th	Night	6% 3 2 4 4 3 4 6% 7% 8% 54%	1260
	21st to end	Night	4 3 1 2 4 2 3 5% 5% 8% 64%	1469
August	1st to 10th	Night	8% 4 1 4 4 2 4 4 6% 7% 55%	1441
	11th to 20th	Night	5% 5% 1 3 3 2 4 4 7% 10% 55%	1602
	21st to end	Night	7% 4 1 3 4 2 3 5% 5% 8% 58%	1782
September	1st to 10th	Night	9% 4 2 5% 4 3 4 4 6% 7% 53%	1740
	11th to 20th	Night	12% 7% 1 4 3 2 3 3 5% 6% 54%	1980
	21st to end	Night	10% 6% 2 4 4 2 4 4 6% 7% 50%	1980
October	1st to 10th	Night	12% 7% 2 5% 4 3 4 5% 5% 8% 45%	2060
	11th to 20th	Night	8% 6% 2 5% 5% 3 4 5% 7% 9% 46%	2264
	21st to end	Night	7% 9% 4 5% 6% 3 6% 5% 7% 9% 41%	2574
November	1st to 10th	Night	8% 12% 4 7% 5% 4 5% 6% 6% 8% 37%	2490
	11th to 20th	Night	3 8% 3 7% 5% 3 5% 5% 7% 9% 44%	2674
	21st to end	Night	4 9% 6% 6% 5% 3 4 5% 7% 10% 41%	2850
December	1st to 10th	Night	4 9% 4 9% 7% 4 7% 6% 7% 8% 37%	2850
	11th to 20th	Night	2 8% 4 9% 7% 4 6% 6% 7% 10% 36%	3510
	21st to end	Night	4 8% 4 8% 6% 3 5% 6% 6% 8% 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	41% 10% 16% 22% 8% 4	1329
	11th to 20th	Day	43% 10% 14% 23% 8% 3	1335
	21st to end	Day	43% 9% 17% 18% 11% 2	1584
February	1st to 10th	Day	50% 8% 14% 18% 8% 2	1468
	11th to 20th	Day	47% 8% 17% 19% 8% 1	1584
	21st to end	Day	49% 8% 12% 17% 12% 2	1444
March	1st to 10th	Day	44% 9% 16% 19% 10% 1	1800
	11th to 20th	Day	39% 9% 17% 22% 12% 1	1970
	21st to end	Day	50% 8% 17% 18% 6% 1	2186
April	1st to 10th	Day	50% 9% 15% 19% 7% 1	2209
	11th to 20th	Day	48% 7% 14% 20% 9% 2	2310
	21st to end	Day	45% 8% 16% 21% 9% 1	2340
May	1st to 10th	Day	48% 9% 15% 21% 8%	2390
	11th to 20th	Day	42% 8% 17% 22% 10% 1	2658
	21st to end	Day	51% 8% 15% 18% 8%	2918
June	1st to 10th	Day	46% 8% 17% 18% 9% 1	2700
	11th to 20th	Day	49% 9% 16% 18% 8% 1	2700
	21st to end	Day	30% 9% 20% 27% 12% 3	2700
July	1st to 10th	Day	29% 9% 18% 28% 13% 3	2626
	11th to 20th	Day	28% 8% 18% 27% 16% 4	2619
	21st to end	Day	21% 7% 16% 29% 22% 5%	2686
August	1st to 10th	Day	27% 9% 19% 28% 14% 4	2480
	11th to 20th	Day	26% 8% 20% 31% 12% 3	2299
	21st to end	Day	27% 7% 15% 29% 18% 4	2574
September	1st to 10th	Day	31% 5% 15% 25% 17% 7%	2219
	11th to 20th	Day	35% 6% 14% 28% 14% 3	1980
	21st to end	Day	34% 6% 14% 29% 13% 3	1980
October	1st to 10th	Day	41% 9% 15% 23% 11% 2	1900
	11th to 20th	Day	38% 7% 18% 23% 12% 2	1692
	21st to end	Day	40% 10% 15% 23% 11% 2	1782
November	1st to 10th	Day	48% 7% 13% 21% 11%	1568
	11th to 20th	Day	38% 8% 18% 24% 10% 1	1504
	21st to end	Day	38% 8% 21% 20% 10% 3	1330
December	1st to 10th	Day	43% 8% 16% 18% 11% 4	1330
	11th to 20th	Day	49% 9% 16% 20% 6% 1	1684
	21st to end	Day	33% 8% 14% 23% 20% 2	2442
January	1st to 10th	Night	46% 10% 15% 17% 10% 3	2836
	11th to 20th	Night	44% 9% 16% 20% 9% 2	2721
	21st to end	Night	39% 10% 15% 20% 14% 2	2772
February	1st to 10th	Night	46% 9% 13% 18% 12% 2	2490
	11th to 20th	Night	48% 8% 14% 20% 9%	2273
	21st to end	Night	50% 5% 13% 19% 10% 2	1812
March	1st to 10th	Night	46% 8% 16% 21% 8% 1	2160
	11th to 20th	Night	40% 10% 16% 23% 11% 1	1990
	21st to end	Night	46% 9% 18% 20% 7% 1	2168
April	1st to 10th	Night	45% 8% 13% 21% 12% 1	1750
	11th to 20th	Night	48% 8% 13% 21% 9% 1	1601
	21st to end	Night	45% 8% 13% 23% 8% 2	1620
May	1st to 10th	Night	44% 8% 14% 24% 9% 1	1566
	11th to 20th	Night	37% 8% 13% 29% 10% 2	1239
	21st to end	Night	48% 9% 14% 20% 8% 1	1358
June	1st to 10th	Night	42% 9% 15% 24% 10% 1	1260
	11th to 20th	Night	45% 8% 16% 22% 8% 2	1260
	21st to end	Night	27% 9% 21% 26% 15% 2	1260
July	1st to 10th	Night	26% 9% 20% 28% 13% 3	1225
	11th to 20th	Night	25% 10% 15% 26% 18% 6%	1218
	21st to end	Night	18% 7% 15% 29% 24% 7%	1387
August	1st to 10th	Night	27% 7% 16% 29% 16% 5%	1433
	11th to 20th	Night	23% 9% 16% 31% 17% 4	1602
	21st to end	Night	24% 6% 12% 31% 22% 5%	1782
September	1st to 10th	Night	30% 5% 15% 26% 18% 5%	1740
	11th to 20th	Night	31% 6% 13% 27% 18% 5%	1980
	21st to end	Night	32% 7% 16% 26% 15% 4	1980
October	1st to 10th	Night	37% 7% 15% 24% 15% 2	2060
	11th to 20th	Night	34% 8% 17% 24% 14% 3	2264
	21st to end	Night	38% 8% 16% 25% 12% 1	2574
November	1st to 10th	Night	44% 8% 14% 21% 10% 1	2490
	11th to 20th	Night	36% 9% 17% 21% 15% 1	2674
	21st to end	Night	37% 8% 19% 20% 12% 4	2850
December	1st to 10th	Night	42% 9% 16% 19% 10% 3	2850
	11th to 20th	Night	41% 10% 21% 21% 6% 1	3507
	21st to end	Night	36% 9% 13% 24% 13% 4	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% 33% 25% 12% 8%	180
	11th to 20th	Day	10% 16% 34% 22% 14% 4	166
	21st to end	Day	8% 20% 32% 28% 9% 3	176
February	1st to 10th	Day	14% 23% 39% 17% 5% 3	173
	11th to 20th	Day	11% 17% 37% 23% 10% 1	240
	21st to end	Day	11% 17% 35% 25% 11%	310
March	1st to 10th	Day	10% 26% 35% 20% 7% 3	420
	11th to 20th	Day	9% 22% 30% 26% 11% 3	420
	21st to end	Day	11% 22% 36% 19% 9% 3	462
April	1st to 10th	Day	14% 23% 34% 22% 5% 1	420
	11th to 20th	Day	17% 17% 32% 21% 12% 1	412
	21st to end	Day	17% 22% 28% 22% 9% 2	420
May	1st to 10th	Day	16% 13% 28% 27% 11% 5%	441
	11th to 20th	Day	19% 11% 23% 25% 18% 4	625
	21st to end	Day	20% 10% 20% 27% 19% 4	679
June	1st to 10th	Day	15% 13% 30% 27% 12% 3	630
	11th to 20th	Day	20% 15% 28% 25% 10% 2	630
	21st to end	Day	11% 8% 25% 31% 20% 5%	630
July	1st to 10th	Day	9% 6% 29% 33% 20% 3	621
	11th to 20th	Day	8% 10% 30% 31% 17% 4	618
	21st to end	Day	5% 8% 31% 35% 18% 4	590
August	1st to 10th	Day	10% 8% 28% 35% 15% 4	447
	11th to 20th	Day	7% 11% 26% 32% 19% 5%	437
	21st to end	Day	8% 12% 33% 26% 15% 6%	495
September	1st to 10th	Day	12% 15% 31% 28% 11% 3	450
	11th to 20th	Day	15% 14% 27% 26% 14% 4	450
	21st to end	Day	16% 21% 28% 25% 8% 2	450
October	1st to 10th	Day	15% 15% 25% 25% 18% 2	370
	11th to 20th	Day	12% 17% 32% 18% 15% 6%	270
	21st to end	Day	16% 21% 30% 23% 8% 2	297
November	1st to 10th	Day	19% 18% 32% 22% 7% 2	270
	11th to 20th	Day	13% 20% 38% 21% 8% 1	262
	21st to end	Day	8% 23% 31% 21% 9% 8%	180
December	1st to 10th	Day	7% 20% 31% 27% 12% 4	180
	11th to 20th	Day	7% 25% 38% 18% 9% 3	180
	21st to end	Day	10% 13% 27% 31% 16% 4	198
January	1st to 10th	Night	8% 20% 35% 26% 9% 1	950
	11th to 20th	Night	8% 15% 40% 28% 9% 1	883
	21st to end	Night	8% 15% 39% 28% 9% 1	792
February	1st to 10th	Night	9% 17% 33% 27% 12% 3	720
	11th to 20th	Night	10% 12% 39% 28% 11% 1	704
	21st to end	Night	8% 10% 35% 29% 16% 2	592
March	1st to 10th	Night	8% 13% 36% 29% 11% 2	720
	11th to 20th	Night	8% 16% 35% 30% 9% 2	720
	21st to end	Night	11% 11% 34% 31% 10% 3	792
April	1st to 10th	Night	12% 15% 33% 28% 11% 1	670
	11th to 20th	Night	16% 11% 32% 29% 10% 1	533
	21st to end	Night	18% 11% 28% 33% 10% 1	540
May	1st to 10th	Night	15% 11% 27% 32% 15%	504
	11th to 20th	Night	13% 7% 23% 35% 22% 1	354
	21st to end	Night	19% 7% 24% 30% 19% 1	389
June	1st to 10th	Night	15% 8% 26% 33% 15% 2	360
	11th to 20th	Night	22% 9% 29% 27% 14%	360
	21st to end	Night	9% 4 24% 38% 24% 1	360
July	1st to 10th	Night	7% 6% 17% 43% 26% 1	350
	11th to 20th	Night	7% 3 26% 43% 19% 1	348
	21st to end	Night	5% 4 24% 43% 21% 3	394
August	1st to 10th	Night	8% 4 17% 41% 29% 1	367
	11th to 20th	Night	8% 3 23% 43% 21% 2	534
	21st to end	Night	9% 6% 26% 39% 19% 1	594
September	1st to 10th	Night	11% 5% 27% 35% 19% 3	629
	11th to 20th	Night	17% 4 24% 32% 20% 3	720
	21st to end	Night	13% 8% 32% 30% 13% 4	720
October	1st to 10th	Night	16% 8% 26% 33% 15% 3	720
	11th to 20th	Night	12% 10% 33% 27% 16% 2	720
	21st to end	Night	11% 14% 36% 29% 10% 1	792
November	1st to 10th	Night	14% 17% 39% 22% 8%	825
	11th to 20th	Night	10% 20% 40% 23% 5% 1	950
	21st to end	Night	9% 17% 39% 25% 9% 2	950
December	1st to 10th	Night	8% 14% 37% 29% 11% 2	950
	11th to 20th	Night	7% 16% 38% 31% 7% 1	950
	21st to end	Night	10% 13% 37% 29% 10% 2	1045

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