Northwest River Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northwest River Park clear sky chart from 2005-11-06 to 2024-04-03.

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	13% 6% 3 5% 5% 3 5% 5% 6% 8% 42%	78931
	Night	14% 6% 3 5% 5% 3 4 5% 5% 7% 44%	81199
Transparency	Day	41% 4 12% 23% 17% 3	78644
	Night	41% 4 11% 23% 18% 4	81005
Seeing	Day	17% 10% 25% 26% 17% 6%	14469
	Night	17% 8% 26% 31% 16% 2	24184

By Month

Percentage Cloud Cover SE (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	17% 6% 2 4 3 2 3 4 4 6% 49%	2677
	11th to 20th	Day	12% 5% 3 6% 5% 3 3 5% 5% 6% 47%	2840
	21st to end	Day	14% 11% 4 7% 5% 3 4 4 5% 4 41%	3124
February	1st to 10th	Day	13% 8% 3 5% 5% 3 4 5% 5% 8% 40%	1710
	11th to 20th	Day	20% 6% 2 5% 5% 3 4 4 3 6% 43%	1835
	21st to end	Day	17% 6% 3 6% 5% 2 4 4 6% 8% 40%	1570
March	1st to 10th	Day	15% 6% 3 4 4 2 4 3 4 6% 50%	2004
	11th to 20th	Day	17% 6% 2 4 5% 2 4 4 4 6% 44%	2090
	21st to end	Day	16% 6% 2 6% 5% 4 5% 4 5% 7% 41%	2375
April	1st to 10th	Day	13% 6% 2 4 3 3 4 3 4 7% 51%	2184
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 3 4 7% 51%	2134
	21st to end	Day	12% 6% 2 5% 5% 3 4 5% 5% 8% 45%	2160
May	1st to 10th	Day	14% 5% 3 5% 4 3 5% 5% 5% 8% 42%	2160
	11th to 20th	Day	17% 6% 3 6% 5% 3 4 5% 5% 7% 38%	2334
	21st to end	Day	13% 6% 2 5% 5% 3 4 5% 7% 9% 40%	2725
June	1st to 10th	Day	11% 5% 2 4 5% 3 7% 7% 8% 11% 38%	2520
	11th to 20th	Day	11% 5% 3 5% 5% 3 7% 6% 7% 11% 38%	2520
	21st to end	Day	8% 5% 2 5% 6% 3 7% 6% 8% 11% 38%	2520
July	1st to 10th	Day	8% 5% 1 5% 6% 4 6% 7% 8% 11% 38%	2520
	11th to 20th	Day	8% 5% 3 6% 6% 5% 7% 7% 8% 11% 34%	2387
	21st to end	Day	7% 4 3 6% 7% 5% 7% 7% 9% 11% 35%	2547
August	1st to 10th	Day	12% 5% 3 7% 6% 4 7% 7% 8% 10% 32%	2288
	11th to 20th	Day	11% 7% 3 7% 6% 5% 6% 6% 8% 10% 31%	2126
	21st to end	Day	12% 6% 3 5% 6% 4 7% 5% 7% 10% 34%	2376
September	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 5% 7% 9% 38%	2160
	11th to 20th	Day	14% 6% 3 6% 7% 4 5% 5% 6% 8% 38%	2160
	21st to end	Day	21% 6% 3 5% 6% 4 4 4 5% 7% 35%	1938
October	1st to 10th	Day	17% 6% 2 4 4 3 5% 4 4 5% 45%	1800
	11th to 20th	Day	14% 6% 3 6% 4 3 4 5% 4 6% 47%	1800
	21st to end	Day	12% 6% 2 5% 5% 2 4 5% 5% 5% 50%	1980
November	1st to 10th	Day	16% 5% 3 5% 4 2 3 4 4 6% 48%	1765
	11th to 20th	Day	16% 6% 3 4 4 3 2 4 4 7% 48%	1710
	21st to end	Day	14% 4 2 4 5% 3 4 4 5% 7% 49%	1690
December	1st to 10th	Day	17% 6% 3 5% 5% 3 4 4 5% 6% 43%	1520
	11th to 20th	Day	15% 6% 2 4 4 2 3 4 4 5% 51%	1910
	21st to end	Day	16% 6% 3 5% 4 3 4 4 5% 7% 45%	2772
January	1st to 10th	Night	14% 6% 3 5% 4 2 4 4 5% 6% 46%	4265
	11th to 20th	Night	16% 8% 3 5% 5% 2 4 4 5% 6% 42%	4120
	21st to end	Night	17% 7% 3 5% 5% 3 4 4 4 6% 42%	4532
February	1st to 10th	Night	18% 7% 2 4 4 2 4 4 5% 7% 42%	2470
	11th to 20th	Night	19% 8% 2 5% 4 3 4 4 4 6% 41%	2229
	21st to end	Night	15% 8% 2 5% 4 3 4 4 4 6% 45%	1884
March	1st to 10th	Night	15% 5% 2 4 5% 3 4 4 4 6% 49%	2174
	11th to 20th	Night	17% 7% 3 5% 5% 3 4 5% 5% 7% 40%	2090
	21st to end	Night	17% 5% 3 5% 5% 3 4 4 5% 6% 44%	2222
April	1st to 10th	Night	14% 6% 2 5% 4 3 4 4 5% 6% 45%	1821
	11th to 20th	Night	13% 5% 3 5% 4 2 4 4 4 7% 49%	1775
	21st to end	Night	14% 6% 3 4 5% 3 3 5% 4 7% 48%	1800
May	1st to 10th	Night	14% 6% 3 5% 5% 3 5% 5% 5% 9% 42%	1800
	11th to 20th	Night	15% 5% 3 5% 5% 2 5% 5% 5% 9% 40%	1571
	21st to end	Night	12% 6% 3 4 5% 3 4 5% 6% 9% 44%	1550
June	1st to 10th	Night	10% 5% 2 5% 5% 3 5% 5% 7% 10% 42%	1440
	11th to 20th	Night	7% 4 4 7% 6% 4 6% 5% 7% 11% 39%	1440
	21st to end	Night	8% 5% 2 4 6% 3 5% 7% 7% 10% 44%	1440
July	1st to 10th	Night	7% 6% 3 5% 5% 4 5% 6% 7% 12% 40%	1440
	11th to 20th	Night	8% 4 2 4 5% 4 6% 7% 8% 10% 42%	1568
	21st to end	Night	9% 4 3 5% 7% 4 5% 8% 8% 11% 37%	1771
August	1st to 10th	Night	9% 6% 3 6% 6% 4 5% 6% 7% 8% 38%	1632
	11th to 20th	Night	9% 6% 3 7% 6% 4 6% 6% 7% 10% 37%	1774
	21st to end	Night	12% 6% 2 7% 6% 3 5% 4 7% 10% 38%	1980
September	1st to 10th	Night	10% 6% 3 5% 4 3 5% 4 6% 10% 43%	1800
	11th to 20th	Night	13% 7% 3 5% 5% 2 4 4 5% 8% 45%	1800
	21st to end	Night	18% 7% 3 6% 5% 4 4 5% 5% 8% 36%	2017
October	1st to 10th	Night	13% 6% 2 4 4 3 5% 4 5% 6% 48%	2160
	11th to 20th	Night	14% 7% 2 4 4 2 3 3 4 6% 49%	2160
	21st to end	Night	12% 5% 2 4 5% 3 3 4 4 6% 51%	2376
November	1st to 10th	Night	16% 6% 2 5% 4 2 4 4 4 7% 47%	2311
	11th to 20th	Night	15% 7% 2 5% 4 2 4 5% 4 6% 47%	2470
	21st to end	Night	14% 4 2 4 4 3 4 4 5% 7% 50%	2488
December	1st to 10th	Night	16% 7% 4 7% 6% 3 4 4 4 6% 40%	2660
	11th to 20th	Night	17% 5% 2 5% 4 3 4 4 4 6% 46%	3285
	21st to end	Night	14% 6% 2 5% 4 3 4 5% 5% 6% 46%	4884

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% 2 6% 31% 20% 3	2678
	11th to 20th	Day	40% 2 6% 18% 28% 5%	2840
	21st to end	Day	48% 2 8% 20% 18% 4	3124
February	1st to 10th	Day	43% 3 11% 25% 15% 3	1710
	11th to 20th	Day	45% 3 8% 19% 20% 6%	1844
	21st to end	Day	43% 3 12% 19% 16% 6%	1570
March	1st to 10th	Day	38% 3 10% 24% 21% 4	2004
	11th to 20th	Day	42% 2 10% 21% 18% 6%	2090
	21st to end	Day	44% 3 12% 19% 19% 3	2375
April	1st to 10th	Day	36% 2 13% 22% 22% 5%	2184
	11th to 20th	Day	35% 3 10% 26% 21% 5%	2134
	21st to end	Day	38% 4 12% 23% 18% 5%	2160
May	1st to 10th	Day	40% 4 15% 22% 15% 3	2160
	11th to 20th	Day	45% 4 13% 25% 11% 2	2338
	21st to end	Day	39% 6% 16% 26% 12% 1	2725
June	1st to 10th	Day	38% 6% 16% 25% 13% 2	2520
	11th to 20th	Day	39% 6% 17% 23% 13% 1	2520
	21st to end	Day	38% 7% 16% 25% 13% 1	2520
July	1st to 10th	Day	37% 7% 17% 24% 13% 2	2450
	11th to 20th	Day	39% 8% 18% 25% 9% 1	2315
	21st to end	Day	39% 7% 17% 26% 11% 1	2405
August	1st to 10th	Day	44% 8% 17% 23% 8%	2275
	11th to 20th	Day	45% 7% 15% 23% 10% 1	2126
	21st to end	Day	43% 5% 17% 20% 12% 3	2376
September	1st to 10th	Day	41% 7% 16% 18% 15% 3	2160
	11th to 20th	Day	44% 5% 10% 21% 18% 2	2160
	21st to end	Day	50% 5% 8% 20% 15% 2	1938
October	1st to 10th	Day	41% 4 7% 23% 22% 3	1800
	11th to 20th	Day	40% 4 6% 26% 21% 4	1800
	21st to end	Day	37% 3 6% 24% 25% 6%	1980
November	1st to 10th	Day	41% 2 8% 25% 20% 4	1765
	11th to 20th	Day	39% 2 11% 21% 21% 6%	1710
	21st to end	Day	38% 2 8% 27% 20% 4	1690
December	1st to 10th	Day	43% 3 12% 23% 15% 3	1520
	11th to 20th	Day	38% 2 8% 28% 17% 7%	1906
	21st to end	Day	41% 2 9% 29% 18% 2	2772
January	1st to 10th	Night	40% 2 6% 26% 21% 5%	4265
	11th to 20th	Night	46% 2 6% 21% 21% 3	4120
	21st to end	Night	46% 3 6% 19% 19% 6%	4532
February	1st to 10th	Night	43% 3 8% 25% 18% 3	2470
	11th to 20th	Night	46% 3 7% 21% 18% 6%	2231
	21st to end	Night	43% 2 8% 22% 19% 7%	1884
March	1st to 10th	Night	39% 2 11% 24% 20% 4	2174
	11th to 20th	Night	46% 4 10% 20% 16% 5%	2090
	21st to end	Night	43% 3 9% 24% 17% 4	2222
April	1st to 10th	Night	40% 3 12% 17% 23% 5%	1821
	11th to 20th	Night	37% 2 10% 26% 20% 6%	1775
	21st to end	Night	38% 3 10% 26% 19% 3	1800
May	1st to 10th	Night	41% 5% 14% 25% 14% 3	1800
	11th to 20th	Night	42% 5% 15% 24% 12% 3	1572
	21st to end	Night	37% 7% 17% 26% 12% 2	1551
June	1st to 10th	Night	37% 6% 15% 28% 13% 1	1440
	11th to 20th	Night	39% 6% 18% 22% 13% 1	1440
	21st to end	Night	35% 8% 17% 26% 13% 2	1440
July	1st to 10th	Night	37% 8% 17% 23% 12% 3	1400
	11th to 20th	Night	33% 7% 22% 26% 11% 1	1517
	21st to end	Night	38% 8% 17% 27% 9% 1	1672
August	1st to 10th	Night	42% 7% 22% 22% 8%	1621
	11th to 20th	Night	43% 5% 18% 23% 10%	1774
	21st to end	Night	42% 5% 16% 23% 11% 3	1980
September	1st to 10th	Night	38% 6% 19% 21% 14% 3	1800
	11th to 20th	Night	41% 5% 10% 23% 19% 2	1800
	21st to end	Night	49% 4 10% 20% 16% 2	2017
October	1st to 10th	Night	38% 4 7% 24% 23% 4	2160
	11th to 20th	Night	37% 3 9% 23% 23% 4	2160
	21st to end	Night	35% 2 7% 24% 25% 6%	2376
November	1st to 10th	Night	40% 3 7% 23% 24% 4	2311
	11th to 20th	Night	41% 2 9% 20% 20% 7%	2470
	21st to end	Night	35% 3 9% 26% 22% 5%	2488
December	1st to 10th	Night	47% 2 10% 21% 16% 3	2660
	11th to 20th	Night	41% 2 10% 21% 20% 6%	3288
	21st to end	Night	40% 2 12% 25% 19% 2	4884

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	19% 20% 41% 16% 4	225
	11th to 20th	Day	17% 24% 41% 16% 2	270
	21st to end	Day	19% 18% 41% 17% 3 1	297
February	1st to 10th	Day	17% 19% 41% 18% 5%	270
	11th to 20th	Day	27% 19% 37% 14% 3	443
	21st to end	Day	21% 19% 35% 20% 4 1	382
March	1st to 10th	Day	21% 18% 35% 19% 6%	460
	11th to 20th	Day	19% 20% 35% 19% 5% 2	460
	21st to end	Day	17% 17% 37% 21% 7% 1	506
April	1st to 10th	Day	17% 17% 38% 19% 7% 2	428
	11th to 20th	Day	12% 14% 31% 28% 12% 3	412
	21st to end	Day	16% 10% 35% 24% 12% 3	420
May	1st to 10th	Day	17% 14% 31% 25% 9% 3	423
	11th to 20th	Day	19% 7% 24% 30% 15% 5%	447
	21st to end	Day	19% 3 19% 30% 20% 8%	485
June	1st to 10th	Day	13% 4 18% 32% 26% 6%	450
	11th to 20th	Day	14% 5% 20% 27% 26% 9%	450
	21st to end	Day	8% 4 20% 35% 24% 8%	450
July	1st to 10th	Day	12% 2 8% 34% 33% 11%	445
	11th to 20th	Day	10% 2 7% 30% 38% 14%	444
	21st to end	Day	10% 2 14% 35% 30% 9%	488
August	1st to 10th	Day	13% 2 12% 35% 28% 10%	446
	11th to 20th	Day	11% 3 9% 28% 34% 15%	439
	21st to end	Day	15% 3 11% 31% 26% 15%	495
September	1st to 10th	Day	14% 3 17% 28% 21% 17%	450
	11th to 20th	Day	17% 4 14% 30% 24% 11%	450
	21st to end	Day	25% 8% 17% 24% 21% 6%	450
October	1st to 10th	Day	21% 5% 19% 28% 19% 9%	450
	11th to 20th	Day	17% 9% 23% 29% 17% 5%	450
	21st to end	Day	15% 11% 28% 25% 16% 4	495
November	1st to 10th	Day	20% 9% 27% 27% 14% 4	411
	11th to 20th	Day	18% 14% 28% 27% 10% 2	370
	21st to end	Day	15% 16% 27% 22% 17% 3	350
December	1st to 10th	Day	21% 18% 34% 17% 7% 2	180
	11th to 20th	Day	17% 17% 36% 20% 9% 1	180
	21st to end	Day	23% 13% 31% 23% 9% 2	198
January	1st to 10th	Night	20% 16% 34% 25% 5%	760
	11th to 20th	Night	21% 16% 30% 27% 6%	760
	21st to end	Night	18% 14% 39% 26% 3	836
February	1st to 10th	Night	22% 11% 35% 28% 4	760
	11th to 20th	Night	23% 17% 38% 19% 2	743
	21st to end	Night	21% 16% 35% 22% 6%	628
March	1st to 10th	Night	19% 13% 36% 26% 6%	760
	11th to 20th	Night	21% 11% 38% 23% 7% 1	760
	21st to end	Night	20% 11% 37% 26% 6%	836
April	1st to 10th	Night	18% 12% 38% 27% 6%	729
	11th to 20th	Night	14% 9% 35% 30% 11%	711
	21st to end	Night	17% 7% 32% 36% 8% 1	720
May	1st to 10th	Night	17% 9% 30% 33% 10% 1	720
	11th to 20th	Night	18% 5% 25% 36% 16% 1	510
	21st to end	Night	15% 3 13% 42% 23% 4	389
June	1st to 10th	Night	12% 3 16% 44% 23% 2	360
	11th to 20th	Night	8% 3 16% 42% 27% 4	360
	21st to end	Night	9% 2 14% 46% 28% 1	360
July	1st to 10th	Night	9% 3 11% 42% 31% 4	350
	11th to 20th	Night	7% 3 4 40% 40% 7%	473
	21st to end	Night	9% 2 11% 41% 31% 5%	591
August	1st to 10th	Night	11% 3 8% 42% 31% 5%	558
	11th to 20th	Night	11% 2 8% 38% 34% 6%	710
	21st to end	Night	13% 3 8% 31% 39% 7%	792
September	1st to 10th	Night	13% 2 10% 35% 31% 9%	720
	11th to 20th	Night	16% 4 11% 34% 30% 4	720
	21st to end	Night	23% 4 15% 31% 24% 2	720
October	1st to 10th	Night	16% 3 17% 33% 25% 6%	720
	11th to 20th	Night	18% 6% 22% 33% 19% 2	720
	21st to end	Night	15% 9% 24% 32% 17% 4	792
November	1st to 10th	Night	19% 7% 25% 31% 16% 4	740
	11th to 20th	Night	19% 9% 32% 28% 12% 1	760
	21st to end	Night	14% 9% 29% 33% 13% 1	760
December	1st to 10th	Night	19% 11% 33% 28% 9% 1	760
	11th to 20th	Night	17% 9% 36% 29% 8%	760
	21st to end	Night	19% 10% 30% 33% 8%	836

Page generated at 2024-03-31 06:08:52. Version ac07

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