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 2024-11-25.

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	11% 9% 3 9% 6% 5% 5% 4 6% 7% 34%	106005
	Night	10% 11% 4 10% 6% 5% 5% 4 6% 7% 32%	102038
Transparency	Day	46% 8% 16% 22% 7%	105738
	Night	49% 8% 15% 20% 8%	101952
Seeing	Day	15% 10% 29% 28% 15% 4	16180
	Night	16% 7% 29% 32% 14% 2	25591

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	6% 14% 8% 21% 10% 7% 5% 5% 7% 4 12%	1899
	11th to 20th	Day	4 10% 5% 25% 12% 9% 7% 4 6% 4 13%	2076
	21st to end	Day	8% 18% 7% 13% 5% 6% 7% 5% 7% 7% 18%	2742
February	1st to 10th	Day	7% 10% 4 14% 6% 7% 8% 7% 7% 8% 22%	1520
	11th to 20th	Day	6% 11% 4 9% 7% 6% 7% 6% 9% 7% 28%	1516
	21st to end	Day	4 9% 4 13% 9% 8% 8% 5% 7% 7% 28%	1567
March	1st to 10th	Day	8% 10% 4 9% 7% 6% 6% 4 6% 9% 32%	3130
	11th to 20th	Day	7% 10% 5% 13% 7% 4 5% 4 5% 6% 34%	3317
	21st to end	Day	5% 9% 4 6% 4 4 4 4 5% 7% 50%	4037
April	1st to 10th	Day	8% 10% 3 7% 6% 6% 5% 5% 6% 6% 40%	2303
	11th to 20th	Day	11% 10% 4 9% 6% 5% 4 3 4 6% 37%	2442
	21st to end	Day	9% 7% 3 7% 5% 5% 6% 5% 6% 8% 39%	2558
May	1st to 10th	Day	15% 10% 3 8% 5% 5% 4 4 6% 7% 32%	4553
	11th to 20th	Day	18% 9% 3 6% 4 4 4 4 5% 6% 37%	4705
	21st to end	Day	19% 12% 4 7% 4 4 4 3 6% 6% 31%	5173
June	1st to 10th	Day	17% 10% 3 7% 5% 5% 5% 4 6% 7% 33%	3014
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 5% 5% 8% 31%	3040
	21st to end	Day	14% 7% 3 7% 4 5% 6% 5% 6% 7% 36%	3040
July	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	5060
	11th to 20th	Day	8% 4 1 4 3 4 4 4 6% 10% 51%	4974
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 8% 11% 41%	5122
August	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 4 5% 8% 45%	4412
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 7% 10% 44%	4322
	21st to end	Day	14% 6% 2 7% 4 4 5% 4 7% 8% 38%	4532
September	1st to 10th	Day	14% 6% 3 7% 5% 6% 5% 4 5% 9% 38%	2328
	11th to 20th	Day	18% 8% 3 6% 4 4 5% 4 6% 8% 33%	2159
	21st to end	Day	13% 9% 3 6% 5% 5% 5% 3 5% 9% 39%	2090
October	1st to 10th	Day	15% 11% 2 7% 4 4 5% 4 6% 8% 32%	3245
	11th to 20th	Day	10% 13% 4 9% 6% 5% 5% 4 6% 8% 30%	2832
	21st to end	Day	14% 17% 6% 11% 6% 6% 4 4 5% 6% 22%	3091
November	1st to 10th	Day	15% 20% 6% 13% 8% 6% 3 3 4 5% 16%	1542
	11th to 20th	Day	14% 14% 6% 16% 10% 5% 4 4 4 4 19%	1400
	21st to end	Day	8% 16% 8% 13% 10% 7% 5% 5% 5% 5% 17%	1358
December	1st to 10th	Day	5% 13% 5% 16% 11% 9% 8% 5% 7% 5% 16%	1330
	11th to 20th	Day	11% 16% 6% 12% 9% 6% 5% 4 4 6% 21%	1486
	21st to end	Day	6% 8% 3 11% 8% 7% 6% 4 6% 7% 36%	2090
January	1st to 10th	Night	5% 13% 6% 16% 11% 8% 7% 6% 6% 6% 17%	5046
	11th to 20th	Night	5% 11% 6% 25% 11% 7% 7% 5% 7% 5% 12%	4825
	21st to end	Night	9% 17% 6% 13% 7% 6% 6% 5% 6% 5% 21%	4923
February	1st to 10th	Night	7% 11% 4 11% 7% 8% 8% 5% 7% 6% 25%	2660
	11th to 20th	Night	5% 9% 5% 11% 9% 7% 6% 6% 6% 6% 29%	2550
	21st to end	Night	5% 9% 4 10% 8% 6% 5% 4 6% 8% 34%	1903
March	1st to 10th	Night	8% 13% 4 9% 5% 4 5% 3 5% 7% 39%	3734
	11th to 20th	Night	7% 9% 4 12% 7% 5% 5% 3 6% 7% 35%	3645
	21st to end	Night	5% 8% 3 5% 4 4 4 3 5% 6% 53%	3586
April	1st to 10th	Night	10% 10% 2 7% 5% 4 4 4 6% 7% 41%	1876
	11th to 20th	Night	12% 11% 3 7% 5% 5% 5% 3 6% 6% 38%	1689
	21st to end	Night	9% 9% 4 7% 5% 5% 4 4 5% 5% 43%	1620
May	1st to 10th	Night	16% 9% 3 7% 5% 4 5% 3 6% 7% 35%	2417
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 6% 7% 33%	2201
	21st to end	Night	19% 11% 3 8% 5% 3 4 4 4 5% 35%	2414
June	1st to 10th	Night	16% 8% 2 5% 4 4 6% 4 5% 7% 39%	1163
	11th to 20th	Night	16% 8% 2 6% 6% 5% 3 5% 6% 9% 35%	1140
	21st to end	Night	14% 6% 2 6% 4 4 5% 5% 7% 7% 39%	1140
July	1st to 10th	Night	9% 7% 2 6% 6% 5% 5% 5% 8% 9% 39%	1900
	11th to 20th	Night	6% 4 1 4 4 4 5% 4 6% 9% 53%	1986
	21st to end	Night	8% 4 2 5% 4 4 5% 5% 8% 11% 45%	2439
August	1st to 10th	Night	8% 5% 1 4 3 3 4 3 5% 9% 54%	2528
	11th to 20th	Night	10% 4 2 5% 5% 4 4 3 7% 10% 46%	2517
	21st to end	Night	15% 6% 2 6% 4 4 4 3 6% 8% 43%	3135
September	1st to 10th	Night	13% 5% 2 5% 3 4 4 4 6% 9% 44%	1849
	11th to 20th	Night	16% 9% 2 7% 5% 4 4 4 5% 6% 38%	2021
	21st to end	Night	14% 6% 2 6% 4 5% 5% 4 5% 7% 41%	2090
October	1st to 10th	Night	12% 9% 3 7% 4 4 4 3 6% 7% 41%	3685
	11th to 20th	Night	10% 12% 3 8% 5% 5% 5% 4 6% 8% 35%	4097
	21st to end	Night	16% 15% 5% 11% 6% 5% 4 4 4 6% 24%	4467
November	1st to 10th	Night	16% 20% 6% 12% 8% 5% 4 3 4 4 17%	2755
	11th to 20th	Night	12% 15% 5% 15% 11% 7% 4 3 4 6% 19%	3000
	21st to end	Night	9% 18% 6% 14% 9% 7% 5% 4 5% 5% 18%	2917
December	1st to 10th	Night	7% 14% 6% 14% 10% 9% 7% 5% 6% 5% 16%	2850
	11th to 20th	Night	8% 15% 6% 13% 8% 6% 5% 5% 6% 6% 23%	3704
	21st to end	Night	7% 11% 3 9% 8% 6% 5% 4 6% 6% 36%	5566

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	70% 9% 10% 9% 2	1899
	11th to 20th	Day	72% 6% 8% 12% 2	2097
	21st to end	Day	61% 10% 14% 11% 3	2742
February	1st to 10th	Day	56% 7% 14% 16% 7% 1	1520
	11th to 20th	Day	51% 8% 14% 18% 9%	1524
	21st to end	Day	53% 8% 13% 18% 8%	1567
March	1st to 10th	Day	47% 8% 16% 21% 7% 1	3130
	11th to 20th	Day	48% 8% 16% 17% 11%	3319
	21st to end	Day	33% 7% 13% 26% 20% 1	4037
April	1st to 10th	Day	42% 7% 15% 21% 14% 1	2303
	11th to 20th	Day	48% 6% 11% 19% 15% 1	2442
	21st to end	Day	41% 8% 14% 24% 13%	2558
May	1st to 10th	Day	47% 9% 12% 25% 7% 1	4553
	11th to 20th	Day	45% 7% 14% 22% 10% 2	4709
	21st to end	Day	51% 9% 12% 21% 8%	5173
June	1st to 10th	Day	48% 9% 13% 18% 12%	3014
	11th to 20th	Day	49% 9% 14% 17% 10% 1	3040
	21st to end	Day	45% 9% 15% 24% 7%	3040
July	1st to 10th	Day	38% 9% 20% 26% 6%	4981
	11th to 20th	Day	27% 8% 21% 37% 7%	4887
	21st to end	Day	34% 11% 25% 26% 4	4960
August	1st to 10th	Day	36% 8% 21% 30% 5%	4396
	11th to 20th	Day	33% 9% 22% 32% 4	4364
	21st to end	Day	40% 9% 22% 23% 6%	4531
September	1st to 10th	Day	41% 10% 20% 21% 8% 1	2328
	11th to 20th	Day	48% 8% 20% 21% 3	2159
	21st to end	Day	43% 8% 17% 26% 6%	2090
October	1st to 10th	Day	46% 8% 19% 23% 4	3245
	11th to 20th	Day	50% 6% 15% 21% 7%	2832
	21st to end	Day	62% 7% 17% 12% 2	3091
November	1st to 10th	Day	71% 6% 12% 7% 4	1542
	11th to 20th	Day	68% 7% 12% 11% 2	1400
	21st to end	Day	67% 7% 13% 11% 2	1358
December	1st to 10th	Day	65% 10% 14% 8% 4	1330
	11th to 20th	Day	63% 8% 15% 9% 4	1487
	21st to end	Day	45% 8% 14% 20% 12% 2	2090
January	1st to 10th	Night	63% 9% 14% 12% 2	5046
	11th to 20th	Night	70% 6% 9% 11% 3	4866
	21st to end	Night	60% 9% 14% 12% 4	4923
February	1st to 10th	Night	56% 6% 13% 16% 8% 1	2660
	11th to 20th	Night	51% 7% 14% 21% 8%	2552
	21st to end	Night	45% 7% 16% 21% 10%	1903
March	1st to 10th	Night	44% 6% 15% 25% 9% 1	3734
	11th to 20th	Night	44% 9% 14% 23% 10%	3645
	21st to end	Night	30% 7% 12% 26% 24% 1	3586
April	1st to 10th	Night	40% 7% 12% 22% 15% 3	1876
	11th to 20th	Night	46% 5% 11% 19% 18% 1	1689
	21st to end	Night	40% 7% 10% 24% 17% 1	1620
May	1st to 10th	Night	44% 9% 14% 22% 10% 1	2417
	11th to 20th	Night	46% 9% 12% 18% 11% 3	2201
	21st to end	Night	50% 8% 15% 18% 9%	2414
June	1st to 10th	Night	44% 8% 12% 22% 14%	1163
	11th to 20th	Night	45% 8% 15% 19% 12% 1	1140
	21st to end	Night	39% 11% 17% 21% 12%	1140
July	1st to 10th	Night	38% 8% 23% 24% 8% 1	1870
	11th to 20th	Night	25% 8% 21% 37% 8%	1950
	21st to end	Night	29% 11% 26% 30% 5%	2362
August	1st to 10th	Night	26% 8% 21% 38% 7%	2520
	11th to 20th	Night	31% 7% 22% 32% 6%	2541
	21st to end	Night	37% 9% 20% 28% 6%	3135
September	1st to 10th	Night	35% 9% 18% 27% 10% 1	1849
	11th to 20th	Night	44% 9% 15% 27% 5%	2021
	21st to end	Night	41% 8% 13% 26% 11% 1	2090
October	1st to 10th	Night	41% 7% 16% 30% 7%	3685
	11th to 20th	Night	45% 6% 17% 25% 7%	4097
	21st to end	Night	59% 8% 13% 17% 3	4467
November	1st to 10th	Night	68% 7% 11% 9% 3	2755
	11th to 20th	Night	66% 7% 14% 11% 2	3000
	21st to end	Night	67% 7% 12% 11% 2	2917
December	1st to 10th	Night	65% 9% 12% 11% 3	2850
	11th to 20th	Night	60% 7% 15% 12% 6%	3702
	21st to end	Night	47% 6% 13% 21% 13%	5566

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	12% 6% 39% 31% 11% 1	180
	11th to 20th	Day	7% 5% 36% 37% 14% 2	237
	21st to end	Day	20% 6% 25% 33% 15% 1	297
February	1st to 10th	Day	11% 7% 33% 31% 15% 3	270
	11th to 20th	Day	8% 9% 31% 34% 15% 4	270
	21st to end	Day	4 8% 35% 32% 18% 3	225
March	1st to 10th	Day	13% 5% 33% 33% 13% 3	270
	11th to 20th	Day	7% 9% 32% 34% 15% 3	270
	21st to end	Day	11% 11% 31% 27% 16% 3	430
April	1st to 10th	Day	13% 12% 31% 29% 13% 4	483
	11th to 20th	Day	15% 11% 28% 30% 13% 3	640
	21st to end	Day	10% 11% 30% 33% 14% 2	650
May	1st to 10th	Day	17% 9% 30% 27% 15% 1	653
	11th to 20th	Day	12% 13% 31% 25% 15% 4	675
	21st to end	Day	22% 7% 25% 28% 14% 3	734
June	1st to 10th	Day	21% 11% 26% 22% 16% 4	680
	11th to 20th	Day	19% 13% 26% 25% 13% 4	680
	21st to end	Day	18% 9% 25% 27% 16% 6%	680
July	1st to 10th	Day	13% 10% 25% 28% 18% 6%	671
	11th to 20th	Day	15% 7% 25% 29% 17% 7%	668
	21st to end	Day	11% 7% 25% 30% 20% 7%	739
August	1st to 10th	Day	11% 10% 25% 27% 22% 5%	676
	11th to 20th	Day	13% 8% 25% 27% 20% 8%	665
	21st to end	Day	20% 8% 26% 27% 16% 2	748
September	1st to 10th	Day	19% 11% 33% 26% 10% 1	538
	11th to 20th	Day	22% 10% 27% 29% 9% 3	369
	21st to end	Day	14% 16% 30% 27% 13% 1	300
October	1st to 10th	Day	24% 11% 30% 21% 12% 1	300
	11th to 20th	Day	21% 17% 38% 14% 8% 2	300
	21st to end	Day	23% 12% 30% 25% 8% 2	330
November	1st to 10th	Day	18% 12% 31% 27% 10% 2	300
	11th to 20th	Day	21% 10% 32% 29% 6% 1	300
	21st to end	Day	16% 11% 41% 24% 6% 1	282
December	1st to 10th	Day	10% 7% 31% 34% 14% 4	270
	11th to 20th	Day	13% 9% 37% 34% 8%	202
	21st to end	Day	7% 6% 24% 40% 19% 4	198
January	1st to 10th	Night	14% 5% 34% 33% 12% 2	950
	11th to 20th	Night	13% 8% 32% 36% 9% 2	950
	21st to end	Night	19% 7% 34% 29% 10% 1	1045
February	1st to 10th	Night	12% 7% 33% 34% 14% 1	950
	11th to 20th	Night	9% 5% 33% 34% 16% 3	929
	21st to end	Night	7% 6% 31% 35% 19% 2	647
March	1st to 10th	Night	13% 8% 25% 35% 18% 2	760
	11th to 20th	Night	13% 9% 33% 31% 14% 1	670
	21st to end	Night	12% 5% 29% 34% 16% 4	627
April	1st to 10th	Night	13% 5% 26% 34% 19% 2	570
	11th to 20th	Night	16% 5% 29% 31% 17% 2	563
	21st to end	Night	11% 7% 33% 38% 10% 1	570
May	1st to 10th	Night	19% 6% 29% 32% 14% 1	570
	11th to 20th	Night	15% 9% 29% 33% 13% 1	561
	21st to end	Night	20% 6% 27% 34% 12% 1	617
June	1st to 10th	Night	20% 4 26% 30% 18% 1	403
	11th to 20th	Night	19% 8% 22% 36% 14% 2	380
	21st to end	Night	18% 6% 20% 38% 16% 1	380
July	1st to 10th	Night	11% 6% 24% 38% 19% 2	370
	11th to 20th	Night	11% 3 25% 38% 20% 2	415
	21st to end	Night	13% 5% 21% 34% 23% 4	624
August	1st to 10th	Night	8% 6% 24% 36% 22% 3	567
	11th to 20th	Night	13% 5% 21% 30% 27% 3	564
	21st to end	Night	19% 5% 25% 35% 16% 1	627
September	1st to 10th	Night	15% 7% 28% 32% 18% 1	570
	11th to 20th	Night	20% 6% 27% 35% 10% 1	570
	21st to end	Night	18% 6% 30% 36% 10% 1	570
October	1st to 10th	Night	23% 7% 27% 32% 11% 1	684
	11th to 20th	Night	22% 10% 27% 30% 10% 1	950
	21st to end	Night	26% 11% 29% 22% 11% 1	1045
November	1st to 10th	Night	22% 9% 32% 27% 9% 1	975
	11th to 20th	Night	20% 10% 34% 26% 10% 1	1000
	21st to end	Night	17% 12% 33% 29% 8% 1	973
December	1st to 10th	Night	14% 6% 34% 30% 13% 3	950
	11th to 20th	Night	17% 9% 32% 27% 12% 2	950
	21st to end	Night	16% 4 27% 32% 18% 3	1045

Page generated at 2024-11-22 07:02:26. Version ac07

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