Clearwater Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clearwater Lake clear sky chart from 2005-11-06 to 2026-01-17.

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	10% 9% 4 9% 6% 5% 5% 4 6% 7% 35%	131754
	Night	9% 11% 4 11% 6% 5% 5% 4 6% 7% 31%	128657
Transparency	Day	46% 8% 15% 22% 8%	131442
	Night	50% 7% 14% 20% 8%	128550
Seeing	Day	15% 10% 29% 28% 14% 3	17689
	Night	16% 7% 30% 32% 14% 2	27199

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	5% 14% 7% 23% 10% 6% 5% 5% 8% 4 13%	2779
	11th to 20th	Day	4 9% 5% 20% 10% 9% 7% 7% 10% 4 15%	3033
	21st to end	Day	6% 16% 7% 14% 7% 6% 7% 5% 7% 7% 17%	3938
February	1st to 10th	Day	7% 11% 5% 14% 6% 7% 8% 7% 7% 8% 22%	1600
	11th to 20th	Day	6% 11% 4 9% 7% 6% 8% 6% 9% 7% 29%	1598
	21st to end	Day	5% 9% 4 12% 8% 8% 8% 5% 7% 7% 27%	1647
March	1st to 10th	Day	6% 10% 5% 14% 8% 7% 7% 4 6% 8% 27%	4500
	11th to 20th	Day	7% 9% 5% 13% 8% 7% 5% 4 6% 7% 29%	4752
	21st to end	Day	4 9% 4 8% 5% 6% 5% 4 6% 7% 42%	5785
April	1st to 10th	Day	8% 10% 3 7% 6% 6% 5% 5% 6% 6% 40%	2424
	11th to 20th	Day	11% 10% 4 9% 6% 5% 5% 3 4 6% 37%	2572
	21st to end	Day	9% 7% 3 7% 5% 5% 6% 5% 6% 8% 39%	2693
May	1st to 10th	Day	13% 10% 3 7% 5% 4 4 4 5% 7% 40%	6519
	11th to 20th	Day	17% 9% 3 8% 4 4 5% 4 5% 8% 33%	6755
	21st to end	Day	13% 9% 3 6% 3 3 4 3 5% 6% 45%	7428
June	1st to 10th	Day	17% 10% 3 7% 5% 5% 5% 4 6% 7% 33%	3173
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 5% 5% 8% 32%	3200
	21st to end	Day	15% 7% 3 7% 4 5% 6% 5% 6% 7% 35%	3200
July	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 49%	7240
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 7% 9% 50%	7115
	21st to end	Day	8% 5% 2 6% 4 4 6% 5% 8% 10% 44%	7358
August	1st to 10th	Day	11% 6% 2 6% 4 5% 4 4 6% 8% 45%	4552
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 7% 10% 43%	4461
	21st to end	Day	14% 6% 2 7% 4 4 5% 4 7% 8% 39%	4675
September	1st to 10th	Day	14% 6% 3 7% 5% 6% 5% 4 5% 9% 37%	2450
	11th to 20th	Day	17% 8% 3 7% 4 5% 5% 4 6% 8% 33%	2272
	21st to end	Day	13% 9% 3 6% 4 5% 4 3 5% 9% 40%	2200
October	1st to 10th	Day	15% 11% 2 7% 4 5% 5% 4 7% 9% 32%	3348
	11th to 20th	Day	11% 13% 4 9% 6% 5% 5% 4 6% 8% 30%	2922
	21st to end	Day	14% 17% 6% 11% 6% 6% 4 4 5% 6% 22%	3190
November	1st to 10th	Day	15% 20% 6% 13% 9% 6% 3 3 4 5% 17%	1621
	11th to 20th	Day	14% 13% 6% 15% 9% 5% 4 4 4 4 20%	1470
	21st to end	Day	8% 16% 8% 15% 10% 7% 5% 4 5% 5% 17%	1470
December	1st to 10th	Day	9% 16% 6% 16% 11% 10% 7% 4 5% 4 13%	2360
	11th to 20th	Day	8% 13% 6% 11% 7% 7% 8% 5% 6% 8% 22%	2396
	21st to end	Day	6% 13% 5% 13% 8% 6% 6% 4 5% 6% 28%	3058
January	1st to 10th	Night	4 13% 7% 18% 10% 8% 6% 6% 5% 6% 18%	7386
	11th to 20th	Night	5% 11% 6% 19% 9% 8% 8% 8% 10% 5% 11%	7008
	21st to end	Night	7% 17% 7% 14% 7% 7% 6% 5% 6% 5% 20%	7038
February	1st to 10th	Night	7% 11% 5% 11% 7% 8% 8% 5% 6% 6% 25%	2800
	11th to 20th	Night	5% 9% 5% 11% 8% 7% 7% 7% 6% 6% 30%	2688
	21st to end	Night	4 10% 4 11% 8% 6% 5% 4 6% 8% 33%	2000
March	1st to 10th	Night	6% 13% 4 11% 6% 4 5% 3 5% 6% 37%	5374
	11th to 20th	Night	8% 10% 4 12% 8% 5% 5% 3 5% 6% 33%	5215
	21st to end	Night	4 8% 3 7% 4 5% 5% 4 6% 7% 47%	5145
April	1st to 10th	Night	10% 10% 2 7% 5% 4 4 4 6% 7% 41%	1975
	11th to 20th	Night	12% 11% 3 7% 5% 5% 5% 3 6% 6% 38%	1779
	21st to end	Night	8% 8% 3 7% 5% 5% 5% 4 5% 6% 43%	1705
May	1st to 10th	Night	12% 7% 3 7% 5% 4 5% 3 6% 7% 41%	3461
	11th to 20th	Night	16% 8% 3 8% 5% 4 5% 5% 7% 8% 31%	3161
	21st to end	Night	13% 9% 2 7% 4 3 4 3 4 6% 45%	3470
June	1st to 10th	Night	16% 7% 2 5% 4 4 6% 4 5% 7% 39%	1224
	11th to 20th	Night	16% 8% 2 6% 6% 5% 4 5% 6% 8% 35%	1200
	21st to end	Night	15% 6% 2 6% 4 4 5% 5% 7% 8% 38%	1200
July	1st to 10th	Night	6% 5% 2 5% 4 4 4 4 8% 10% 47%	2720
	11th to 20th	Night	5% 5% 1 5% 5% 4 5% 4 6% 9% 52%	2848
	21st to end	Night	8% 4 2 5% 4 4 5% 5% 8% 10% 46%	3505
August	1st to 10th	Night	8% 4 1 4 4 3 4 3 5% 9% 54%	2608
	11th to 20th	Night	10% 5% 2 5% 5% 4 4 3 7% 10% 45%	2598
	21st to end	Night	14% 6% 2 6% 4 4 4 3 6% 8% 43%	3234
September	1st to 10th	Night	13% 5% 2 5% 3 5% 4 4 7% 9% 43%	1947
	11th to 20th	Night	16% 9% 2 7% 5% 4 4 4 5% 6% 37%	2128
	21st to end	Night	14% 6% 2 6% 4 5% 5% 4 5% 7% 43%	2200
October	1st to 10th	Night	11% 9% 3 7% 4 4 4 3 6% 7% 41%	3801
	11th to 20th	Night	10% 12% 3 8% 5% 5% 5% 4 6% 8% 36%	4227
	21st to end	Night	16% 15% 5% 11% 6% 5% 4 4 4 6% 24%	4610
November	1st to 10th	Night	16% 19% 6% 12% 8% 5% 4 3 4 4 19%	2896
	11th to 20th	Night	12% 15% 5% 14% 10% 6% 4 3 4 5% 20%	3150
	21st to end	Night	8% 18% 6% 15% 9% 6% 5% 4 5% 5% 18%	3150
December	1st to 10th	Night	10% 17% 6% 15% 10% 10% 6% 4 5% 4 11%	5050
	11th to 20th	Night	7% 13% 5% 12% 7% 6% 8% 8% 6% 6% 22%	6016
	21st to end	Night	6% 13% 6% 14% 8% 6% 5% 3 5% 5% 28%	8140

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	68% 7% 8% 14% 3	2779
	11th to 20th	Day	65% 6% 7% 19% 4	3054
	21st to end	Day	62% 10% 13% 12% 4	3938
February	1st to 10th	Day	57% 6% 14% 15% 7% 1	1600
	11th to 20th	Day	50% 8% 15% 19% 9%	1606
	21st to end	Day	54% 8% 13% 18% 8%	1647
March	1st to 10th	Day	53% 8% 13% 17% 8% 1	4500
	11th to 20th	Day	51% 8% 15% 16% 11%	4754
	21st to end	Day	38% 7% 11% 25% 17% 1	5785
April	1st to 10th	Day	42% 7% 15% 21% 14% 1	2424
	11th to 20th	Day	48% 6% 12% 19% 15% 1	2572
	21st to end	Day	40% 8% 14% 24% 13%	2693
May	1st to 10th	Day	43% 7% 11% 26% 12% 1	6519
	11th to 20th	Day	48% 7% 15% 22% 7% 1	6759
	21st to end	Day	39% 7% 10% 20% 23% 2	7428
June	1st to 10th	Day	48% 9% 13% 18% 12%	3173
	11th to 20th	Day	48% 10% 14% 18% 9% 1	3200
	21st to end	Day	45% 9% 15% 23% 7%	3200
July	1st to 10th	Day	31% 8% 20% 34% 7%	7161
	11th to 20th	Day	27% 8% 18% 40% 6%	7028
	21st to end	Day	32% 10% 23% 28% 8%	7151
August	1st to 10th	Day	36% 8% 21% 30% 5%	4536
	11th to 20th	Day	34% 9% 22% 32% 3	4503
	21st to end	Day	40% 9% 22% 23% 5%	4674
September	1st to 10th	Day	41% 10% 20% 20% 8% 1	2450
	11th to 20th	Day	48% 8% 20% 21% 3	2272
	21st to end	Day	41% 8% 18% 27% 6%	2200
October	1st to 10th	Day	45% 8% 20% 23% 4	3348
	11th to 20th	Day	51% 6% 15% 21% 7%	2922
	21st to end	Day	62% 7% 17% 12% 2	3190
November	1st to 10th	Day	70% 6% 12% 8% 4	1621
	11th to 20th	Day	66% 7% 12% 12% 2	1470
	21st to end	Day	67% 7% 12% 12% 2	1470
December	1st to 10th	Day	73% 7% 9% 5% 5%	2360
	11th to 20th	Day	58% 8% 14% 16% 4	2397
	21st to end	Day	55% 7% 11% 18% 8% 1	3058
January	1st to 10th	Night	64% 8% 11% 14% 4	7386
	11th to 20th	Night	67% 7% 8% 15% 4	7049
	21st to end	Night	64% 8% 11% 12% 5%	7038
February	1st to 10th	Night	56% 6% 13% 16% 8% 1	2800
	11th to 20th	Night	50% 7% 14% 21% 8%	2690
	21st to end	Night	47% 7% 16% 21% 10%	2000
March	1st to 10th	Night	47% 6% 13% 20% 12% 2	5374
	11th to 20th	Night	48% 7% 11% 22% 11%	5215
	21st to end	Night	33% 6% 11% 30% 20% 1	5145
April	1st to 10th	Night	40% 7% 13% 22% 16% 3	1975
	11th to 20th	Night	46% 5% 11% 19% 17% 1	1779
	21st to end	Night	40% 7% 10% 25% 17% 1	1705
May	1st to 10th	Night	39% 8% 16% 25% 12% 1	3461
	11th to 20th	Night	46% 9% 14% 20% 8% 2	3161
	21st to end	Night	41% 6% 11% 18% 21% 3	3470
June	1st to 10th	Night	43% 8% 12% 23% 14%	1224
	11th to 20th	Night	44% 8% 15% 21% 11% 1	1200
	21st to end	Night	40% 11% 17% 21% 11%	1200
July	1st to 10th	Night	29% 7% 21% 35% 8%	2690
	11th to 20th	Night	26% 8% 19% 40% 6%	2812
	21st to end	Night	29% 10% 25% 30% 6%	3407
August	1st to 10th	Night	26% 8% 21% 38% 7%	2600
	11th to 20th	Night	33% 7% 22% 31% 6%	2622
	21st to end	Night	37% 9% 20% 28% 6%	3234
September	1st to 10th	Night	35% 9% 20% 26% 10% 1	1947
	11th to 20th	Night	45% 8% 15% 27% 5%	2128
	21st to end	Night	40% 8% 13% 28% 11% 1	2200
October	1st to 10th	Night	40% 7% 17% 29% 7%	3801
	11th to 20th	Night	45% 6% 16% 25% 8%	4227
	21st to end	Night	59% 8% 13% 17% 3	4610
November	1st to 10th	Night	67% 7% 11% 10% 4	2896
	11th to 20th	Night	65% 7% 13% 11% 3	3150
	21st to end	Night	67% 7% 12% 11% 3	3150
December	1st to 10th	Night	75% 7% 9% 8% 2	5050
	11th to 20th	Night	59% 7% 14% 13% 7%	6014
	21st to end	Night	57% 6% 11% 18% 9%	8140

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	11% 10% 36% 32% 10% 1	220
	11th to 20th	Day	10% 6% 36% 34% 12% 2	279
	21st to end	Day	19% 7% 26% 33% 13% 1	330
February	1st to 10th	Day	11% 8% 33% 31% 15% 2	300
	11th to 20th	Day	7% 8% 30% 36% 15% 4	300
	21st to end	Day	6% 8% 36% 31% 16% 3	249
March	1st to 10th	Day	11% 6% 33% 33% 13% 3	300
	11th to 20th	Day	7% 9% 34% 32% 14% 3	300
	21st to end	Day	10% 11% 31% 29% 16% 3	470
April	1st to 10th	Day	12% 11% 32% 30% 12% 4	524
	11th to 20th	Day	14% 11% 30% 30% 12% 3	690
	21st to end	Day	9% 11% 30% 33% 14% 3	700
May	1st to 10th	Day	17% 10% 31% 27% 14% 1	703
	11th to 20th	Day	13% 13% 31% 24% 15% 4	725
	21st to end	Day	21% 7% 25% 29% 14% 4	789
June	1st to 10th	Day	22% 12% 26% 21% 16% 3	730
	11th to 20th	Day	19% 13% 26% 26% 13% 4	730
	21st to end	Day	18% 8% 25% 27% 16% 6%	730
July	1st to 10th	Day	12% 10% 25% 29% 18% 7%	721
	11th to 20th	Day	14% 7% 25% 29% 18% 7%	718
	21st to end	Day	11% 7% 27% 30% 19% 6%	794
August	1st to 10th	Day	12% 10% 24% 28% 22% 5%	726
	11th to 20th	Day	14% 8% 26% 26% 19% 7%	715
	21st to end	Day	19% 8% 26% 27% 18% 3	803
September	1st to 10th	Day	19% 11% 33% 26% 10% 1	580
	11th to 20th	Day	22% 10% 26% 28% 11% 3	402
	21st to end	Day	13% 15% 32% 28% 12% 1	330
October	1st to 10th	Day	23% 12% 31% 21% 12% 1	330
	11th to 20th	Day	22% 16% 38% 14% 8% 2	330
	21st to end	Day	22% 12% 31% 25% 8% 1	363
November	1st to 10th	Day	17% 14% 32% 26% 9% 2	330
	11th to 20th	Day	21% 12% 32% 28% 6% 1	330
	21st to end	Day	15% 13% 40% 25% 6% 1	330
December	1st to 10th	Day	12% 9% 31% 32% 13% 3	330
	11th to 20th	Day	13% 11% 36% 31% 9%	246
	21st to end	Day	10% 8% 26% 36% 17% 4	242
January	1st to 10th	Night	14% 6% 33% 33% 12% 2	1050
	11th to 20th	Night	13% 9% 33% 35% 8% 2	1031
	21st to end	Night	19% 8% 34% 28% 10% 1	1100
February	1st to 10th	Night	12% 7% 33% 34% 14% 1	1000
	11th to 20th	Night	8% 5% 32% 36% 16% 3	979
	21st to end	Night	7% 7% 31% 35% 18% 2	680
March	1st to 10th	Night	12% 8% 26% 35% 17% 2	800
	11th to 20th	Night	13% 9% 32% 31% 14% 1	705
	21st to end	Night	11% 5% 29% 34% 17% 4	660
April	1st to 10th	Night	13% 5% 26% 35% 19% 2	600
	11th to 20th	Night	16% 5% 29% 32% 16% 2	593
	21st to end	Night	10% 7% 34% 38% 10% 1	600
May	1st to 10th	Night	18% 6% 30% 32% 13% 1	600
	11th to 20th	Night	15% 9% 30% 32% 13% 1	591
	21st to end	Night	20% 6% 26% 35% 13% 1	650
June	1st to 10th	Night	20% 5% 26% 31% 17% 1	424
	11th to 20th	Night	19% 7% 22% 36% 14% 2	400
	21st to end	Night	19% 6% 20% 37% 17% 2	400
July	1st to 10th	Night	10% 6% 25% 38% 19% 2	390
	11th to 20th	Night	11% 3 26% 38% 20% 2	438
	21st to end	Night	12% 4 22% 35% 22% 4	657
August	1st to 10th	Night	9% 6% 24% 36% 22% 3	597
	11th to 20th	Night	14% 6% 21% 30% 26% 3	594
	21st to end	Night	18% 5% 24% 35% 17% 1	660
September	1st to 10th	Night	14% 8% 28% 32% 17% 1	600
	11th to 20th	Night	21% 6% 27% 35% 11% 1	600
	21st to end	Night	17% 6% 30% 36% 10% 1	600
October	1st to 10th	Night	22% 7% 28% 32% 10% 1	720
	11th to 20th	Night	23% 10% 28% 29% 10% 1	1000
	21st to end	Night	26% 11% 30% 22% 10% 1	1100
November	1st to 10th	Night	21% 9% 34% 26% 9% 1	1025
	11th to 20th	Night	19% 11% 34% 25% 10% 1	1050
	21st to end	Night	16% 12% 34% 29% 8% 1	1050
December	1st to 10th	Night	14% 7% 35% 29% 12% 3	1050
	11th to 20th	Night	16% 10% 34% 27% 11% 2	1050
	21st to end	Night	16% 5% 27% 32% 17% 3	1155

Page generated at 2026-01-14 00:14:26. Version ac07

Copyright © 2026 Attilla Danko.