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 2024-11-04.

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% 7% 2 6% 4 4 5% 4 6% 8% 40%	100944
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 42%	98019
Transparency	Day	41% 5% 12% 23% 16% 3	104580
	Night	41% 4 11% 23% 18% 4	102522
Seeing	Day	16% 10% 25% 26% 17% 6%	15329
	Night	17% 8% 26% 32% 16% 2	24901

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	16% 6% 2 4 3 3 3 3 4 6% 48%	2677
	11th to 20th	Day	12% 6% 3 7% 4 4 4 4 5% 6% 47%	2840
	21st to end	Day	14% 11% 3 8% 4 4 4 3 5% 4 41%	3124
February	1st to 10th	Day	13% 8% 3 6% 4 4 4 4 5% 8% 40%	1710
	11th to 20th	Day	19% 7% 2 5% 4 4 4 3 4 5% 43%	1835
	21st to end	Day	17% 7% 2 6% 4 3 4 3 7% 8% 39%	1570
March	1st to 10th	Day	24% 9% 2 5% 3 3 4 3 4 6% 37%	3301
	11th to 20th	Day	12% 5% 2 5% 3 2 3 3 4 6% 54%	3480
	21st to end	Day	17% 7% 2 5% 4 4 4 3 4 6% 44%	3942
April	1st to 10th	Day	12% 7% 1 4 4 4 3 3 4 7% 51%	2280
	11th to 20th	Day	10% 5% 2 5% 4 5% 4 3 4 7% 51%	2254
	21st to end	Day	12% 7% 2 6% 4 4 4 4 6% 7% 44%	2280
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 5% 8% 35%	3765
	11th to 20th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 7% 30%	4156
	21st to end	Day	9% 5% 2 6% 4 5% 4 4 7% 10% 44%	4823
June	1st to 10th	Day	10% 5% 2 5% 4 5% 7% 6% 7% 10% 38%	2660
	11th to 20th	Day	10% 5% 2 5% 4 5% 6% 5% 7% 11% 39%	2660
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 38%	2660
July	1st to 10th	Day	8% 5% 1 7% 4 5% 6% 6% 9% 13% 35%	4440
	11th to 20th	Day	11% 7% 3 8% 6% 6% 6% 5% 7% 9% 31%	4195
	21st to end	Day	9% 7% 3 9% 7% 7% 6% 6% 8% 9% 30%	4466
August	1st to 10th	Day	17% 8% 3 9% 6% 6% 6% 5% 8% 9% 21%	4024
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 4 8% 11% 34%	3730
	21st to end	Day	9% 5% 2 6% 5% 6% 6% 4 8% 11% 39%	4180
September	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 4 7% 9% 38%	2280
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 7% 36%	2280
	21st to end	Day	21% 7% 3 6% 5% 4 4 3 5% 7% 34%	2045
October	1st to 10th	Day	17% 6% 2 5% 3 4 5% 3 4 6% 45%	1900
	11th to 20th	Day	13% 6% 2 6% 3 3 4 4 4 5% 49%	1900
	21st to end	Day	11% 6% 2 5% 4 4 4 3 5% 6% 51%	2090
November	1st to 10th	Day	16% 5% 3 5% 4 3 3 3 5% 6% 47%	1795
	11th to 20th	Day	16% 7% 2 5% 3 4 3 3 4 7% 48%	1710
	21st to end	Day	14% 4 2 4 5% 4 3 3 5% 6% 48%	1690
December	1st to 10th	Day	17% 7% 3 6% 5% 4 4 3 5% 6% 42%	1520
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 4 5% 50%	1910
	21st to end	Day	16% 6% 2 6% 3 3 4 3 5% 7% 45%	2772
January	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 5% 6% 46%	4265
	11th to 20th	Night	16% 8% 3 6% 4 3 4 4 5% 5% 42%	4120
	21st to end	Night	16% 8% 3 6% 4 4 4 3 4 6% 42%	4532
February	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 6% 6% 42%	2470
	11th to 20th	Night	19% 8% 2 5% 4 4 3 3 4 5% 41%	2229
	21st to end	Night	15% 9% 2 6% 3 4 4 3 4 5% 45%	1884
March	1st to 10th	Night	25% 9% 3 6% 5% 4 4 3 4 5% 33%	3550
	11th to 20th	Night	15% 6% 2 6% 3 3 3 3 4 6% 50%	3480
	21st to end	Night	19% 9% 3 4 3 2 3 2 3 4 47%	3676
April	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 6% 45%	1900
	11th to 20th	Night	12% 6% 3 5% 4 3 3 3 5% 7% 49%	1875
	21st to end	Night	14% 6% 2 5% 4 3 4 3 4 6% 47%	1900
May	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 4 5% 7% 36%	3130
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 4 5% 8% 35%	2763
	21st to end	Night	10% 7% 3 7% 4 4 5% 4 6% 9% 41%	2732
June	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 5% 7% 10% 41%	1520
	11th to 20th	Night	6% 5% 3 8% 4 5% 5% 4 7% 11% 40%	1520
	21st to end	Night	8% 6% 2 5% 5% 4 5% 5% 7% 9% 45%	1520
July	1st to 10th	Night	7% 6% 3 6% 4 6% 6% 5% 8% 12% 37%	2520
	11th to 20th	Night	9% 7% 2 7% 6% 5% 6% 5% 7% 10% 35%	2760
	21st to end	Night	14% 8% 3 9% 6% 5% 6% 5% 6% 8% 30%	3087
August	1st to 10th	Night	17% 8% 4 8% 5% 5% 5% 4 7% 8% 29%	2874
	11th to 20th	Night	9% 7% 3 8% 5% 5% 6% 4 6% 9% 38%	3097
	21st to end	Night	9% 5% 2 6% 4 4 5% 5% 7% 9% 43%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 5% 5% 3 6% 10% 44%	1900
	11th to 20th	Night	13% 7% 3 6% 4 3 4 3 5% 8% 43%	1900
	21st to end	Night	18% 8% 2 7% 4 4 4 3 5% 8% 36%	2130
October	1st to 10th	Night	13% 7% 2 5% 4 4 5% 4 5% 5% 48%	2280
	11th to 20th	Night	14% 7% 2 5% 4 2 3 3 4 6% 51%	2280
	21st to end	Night	11% 5% 2 5% 4 3 3 3 4 6% 53%	2508
November	1st to 10th	Night	16% 6% 2 6% 3 3 3 3 4 7% 47%	2354
	11th to 20th	Night	15% 7% 2 5% 4 3 4 4 4 6% 47%	2470
	21st to end	Night	13% 5% 2 5% 4 4 4 3 5% 7% 50%	2488
December	1st to 10th	Night	16% 7% 3 8% 5% 4 3 4 5% 6% 40%	2660
	11th to 20th	Night	17% 6% 2 5% 4 3 4 3 4 6% 46%	3285
	21st to end	Night	14% 6% 2 5% 4 4 4 4 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	51% 2 9% 18% 14% 6%	3301
	11th to 20th	Day	33% 1 8% 22% 25% 11%	3480
	21st to end	Day	44% 2 14% 18% 18% 4	3942
April	1st to 10th	Day	36% 2 12% 22% 23% 6%	2280
	11th to 20th	Day	35% 3 10% 26% 21% 6%	2254
	21st to end	Day	38% 4 12% 23% 18% 5%	2280
May	1st to 10th	Day	48% 4 16% 21% 9% 2	3800
	11th to 20th	Day	54% 3 12% 22% 8% 1	4160
	21st to end	Day	36% 3 15% 29% 14% 3	4837
June	1st to 10th	Day	38% 6% 15% 25% 14% 2	2660
	11th to 20th	Day	38% 6% 17% 25% 14% 1	2660
	21st to end	Day	37% 7% 16% 26% 13% 1	2660
July	1st to 10th	Day	35% 11% 20% 22% 10% 1	4370
	11th to 20th	Day	46% 9% 22% 18% 5% 1	4123
	21st to end	Day	47% 9% 13% 19% 11% 1	4324
August	1st to 10th	Day	54% 8% 17% 16% 5%	4011
	11th to 20th	Day	40% 8% 16% 24% 11%	3766
	21st to end	Day	35% 6% 15% 28% 14% 2	4180
September	1st to 10th	Day	41% 7% 16% 17% 17% 3	2280
	11th to 20th	Day	45% 5% 10% 20% 18% 2	2280
	21st to end	Day	50% 5% 8% 20% 15% 2	2045
October	1st to 10th	Day	32% 6% 8% 25% 26% 3	3160
	11th to 20th	Day	27% 4 6% 21% 32% 10%	3140
	21st to end	Day	23% 3 9% 28% 29% 8%	3428
November	1st to 10th	Day	41% 2 8% 25% 20% 4	1795
	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	56% 1 8% 18% 13% 3	3550
	11th to 20th	Night	38% 2 8% 18% 23% 10%	3480
	21st to end	Night	43% 2 6% 28% 16% 4	3676
April	1st to 10th	Night	40% 3 12% 16% 24% 4	1900
	11th to 20th	Night	37% 2 9% 26% 20% 6%	1875
	21st to end	Night	38% 3 10% 26% 19% 3	1900
May	1st to 10th	Night	48% 4 16% 22% 9% 2	3160
	11th to 20th	Night	50% 4 11% 26% 7% 1	2764
	21st to end	Night	41% 4 16% 24% 13% 1	2739
June	1st to 10th	Night	38% 6% 15% 27% 13% 1	1520
	11th to 20th	Night	38% 6% 18% 24% 14% 1	1520
	21st to end	Night	34% 8% 16% 27% 13% 2	1520
July	1st to 10th	Night	38% 12% 18% 21% 10% 2	2480
	11th to 20th	Night	40% 10% 25% 18% 6% 1	2709
	21st to end	Night	51% 8% 12% 18% 11%	2988
August	1st to 10th	Night	50% 7% 20% 18% 4	2863
	11th to 20th	Night	42% 7% 15% 24% 12%	3127
	21st to end	Night	35% 6% 13% 28% 17% 2	3476
September	1st to 10th	Night	37% 6% 19% 20% 15% 3	1900
	11th to 20th	Night	42% 5% 10% 22% 19% 2	1900
	21st to end	Night	49% 4 10% 20% 15% 2	2130
October	1st to 10th	Night	38% 5% 7% 24% 24% 3	3800
	11th to 20th	Night	28% 3 6% 19% 33% 12%	3779
	21st to end	Night	21% 2 7% 31% 28% 11%	4120
November	1st to 10th	Night	39% 3 7% 23% 24% 4	2354
	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% 18% 39% 18% 6% 2	460
	11th to 20th	Day	12% 15% 31% 27% 11% 3	452
	21st to end	Day	16% 12% 33% 26% 11% 2	460
May	1st to 10th	Day	17% 13% 32% 26% 9% 3	463
	11th to 20th	Day	19% 9% 25% 29% 14% 5%	487
	21st to end	Day	18% 4 22% 29% 20% 7%	529
June	1st to 10th	Day	12% 4 19% 33% 26% 6%	490
	11th to 20th	Day	13% 5% 19% 29% 26% 8%	490
	21st to end	Day	8% 4 20% 36% 24% 8%	490
July	1st to 10th	Day	12% 2 8% 34% 33% 11%	485
	11th to 20th	Day	10% 2 7% 30% 37% 13%	484
	21st to end	Day	10% 2 14% 35% 29% 8%	532
August	1st to 10th	Day	14% 3 12% 35% 27% 9%	486
	11th to 20th	Day	11% 3 10% 30% 32% 14%	479
	21st to end	Day	14% 3 11% 32% 26% 15%	539
September	1st to 10th	Day	14% 3 18% 29% 21% 16%	490
	11th to 20th	Day	19% 5% 14% 30% 23% 10%	490
	21st to end	Day	25% 8% 19% 23% 20% 6%	490
October	1st to 10th	Day	21% 5% 19% 28% 19% 9%	490
	11th to 20th	Day	16% 10% 23% 29% 17% 5%	490
	21st to end	Day	14% 11% 27% 26% 17% 6%	539
November	1st to 10th	Day	19% 9% 27% 26% 14% 4	423
	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	17% 13% 38% 26% 6%	760
	11th to 20th	Night	14% 10% 35% 30% 11%	751
	21st to end	Night	17% 7% 32% 36% 7% 1	760
May	1st to 10th	Night	17% 9% 31% 33% 10% 1	760
	11th to 20th	Night	18% 5% 25% 36% 15% 1	538
	21st to end	Night	14% 4 14% 41% 24% 4	411
June	1st to 10th	Night	12% 4 16% 44% 23% 2	380
	11th to 20th	Night	8% 3 16% 42% 28% 4	380
	21st to end	Night	9% 2 14% 46% 29% 1	380
July	1st to 10th	Night	9% 3 11% 42% 32% 4	370
	11th to 20th	Night	7% 3 4 41% 38% 7%	501
	21st to end	Night	10% 3 11% 42% 30% 5%	624
August	1st to 10th	Night	12% 4 8% 42% 30% 5%	590
	11th to 20th	Night	11% 3 9% 39% 33% 6%	750
	21st to end	Night	12% 3 8% 32% 39% 7%	836
September	1st to 10th	Night	12% 3 11% 35% 30% 9%	760
	11th to 20th	Night	16% 4 12% 33% 30% 4	760
	21st to end	Night	24% 4 16% 31% 24% 2	760
October	1st to 10th	Night	16% 4 17% 33% 24% 6%	760
	11th to 20th	Night	18% 6% 23% 33% 19% 2	760
	21st to end	Night	14% 8% 23% 32% 18% 5%	836
November	1st to 10th	Night	19% 7% 25% 31% 16% 4	755
	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

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