Blue River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue River clear sky chart from 2005-11-06 to 2025-02-06.

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	14% 15% 4 10% 6% 5% 5% 4 5% 6% 26%	111564
	Night	15% 19% 5% 10% 6% 5% 5% 4 5% 5% 21%	115341
Transparency	Day	58% 8% 13% 15% 6% 1	111307
	Night	64% 7% 11% 12% 5% 1	115244
Seeing	Day	22% 12% 25% 25% 13% 3	16204
	Night	26% 8% 24% 28% 13% 1	24688

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	8% 31% 9% 17% 9% 7% 5% 3 2 3 6%	2829
	11th to 20th	Day	12% 16% 4 12% 4 3 4 5% 7% 7% 27%	3266
	21st to end	Day	15% 32% 4 10% 4 4 4 3 3 4 17%	4004
February	1st to 10th	Day	14% 27% 7% 10% 5% 5% 4 3 4 3 18%	1560
	11th to 20th	Day	12% 19% 7% 13% 7% 5% 4 3 5% 4 21%	1629
	21st to end	Day	8% 22% 6% 14% 7% 6% 4 3 4 4 22%	1522
March	1st to 10th	Day	11% 21% 6% 13% 6% 6% 5% 4 5% 5% 19%	3138
	11th to 20th	Day	8% 20% 5% 8% 5% 5% 4 3 5% 5% 32%	3294
	21st to end	Day	7% 21% 5% 11% 6% 5% 5% 4 6% 7% 23%	4150
April	1st to 10th	Day	11% 22% 6% 12% 9% 6% 5% 4 5% 5% 15%	2280
	11th to 20th	Day	12% 21% 4 9% 7% 5% 5% 3 6% 7% 22%	2321
	21st to end	Day	14% 16% 4 10% 6% 6% 6% 4 5% 7% 21%	2650
May	1st to 10th	Day	10% 14% 3 9% 5% 6% 5% 4 6% 7% 29%	4420
	11th to 20th	Day	11% 12% 4 10% 6% 6% 6% 5% 6% 7% 25%	4399
	21st to end	Day	22% 14% 4 9% 6% 6% 4 4 5% 6% 19%	5215
June	1st to 10th	Day	24% 12% 4 10% 6% 6% 5% 4 4 5% 22%	3040
	11th to 20th	Day	25% 13% 5% 11% 7% 6% 6% 4 6% 4 14%	3040
	21st to end	Day	19% 10% 4 10% 7% 6% 5% 4 6% 5% 25%	3040
July	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 3 5% 6% 45%	5060
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 6% 7% 53%	4882
	21st to end	Day	15% 7% 2 8% 5% 5% 5% 4 6% 8% 35%	4803
August	1st to 10th	Day	8% 4 2 5% 4 3 4 4 6% 8% 52%	4401
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 5% 8% 11% 35%	4330
	21st to end	Day	20% 7% 2 7% 4 5% 5% 4 6% 7% 34%	4386
September	1st to 10th	Day	17% 9% 3 8% 5% 4 5% 3 5% 6% 36%	2280
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 4 5% 6% 34%	2256
	21st to end	Day	23% 11% 3 8% 4 5% 4 3 5% 5% 26%	2072
October	1st to 10th	Day	21% 15% 5% 10% 6% 6% 5% 4 4 4 20%	3180
	11th to 20th	Day	27% 17% 4 8% 5% 3 4 3 4 5% 22%	2984
	21st to end	Day	16% 20% 6% 13% 5% 4 4 4 5% 6% 17%	3101
November	1st to 10th	Day	23% 23% 6% 13% 6% 5% 4 2 4 3 12%	1608
	11th to 20th	Day	19% 25% 7% 11% 5% 4 4 3 4 4 14%	1500
	21st to end	Day	15% 29% 6% 12% 6% 4 4 3 4 4 15%	1400
December	1st to 10th	Day	16% 18% 5% 17% 8% 7% 4 3 4 4 14%	2270
	11th to 20th	Day	15% 31% 8% 14% 6% 4 3 2 3 4 10%	2262
	21st to end	Day	12% 30% 8% 13% 7% 4 4 3 5% 4 11%	2992
January	1st to 10th	Night	11% 31% 11% 19% 7% 5% 4 2 2 3 6%	7157
	11th to 20th	Night	12% 15% 5% 12% 7% 6% 6% 5% 7% 5% 20%	6629
	21st to end	Night	18% 29% 5% 8% 5% 5% 4 3 3 5% 15%	6952
February	1st to 10th	Night	15% 26% 7% 11% 7% 4 4 3 4 5% 14%	2730
	11th to 20th	Night	12% 24% 7% 11% 5% 5% 3 3 5% 5% 19%	2436
	21st to end	Night	7% 24% 5% 11% 7% 5% 5% 4 5% 6% 20%	1931
March	1st to 10th	Night	9% 22% 6% 10% 6% 4 5% 4 5% 6% 21%	3736
	11th to 20th	Night	9% 21% 5% 7% 4 4 5% 4 6% 7% 28%	3684
	21st to end	Night	8% 22% 5% 9% 5% 5% 5% 5% 6% 7% 25%	3502
April	1st to 10th	Night	11% 23% 5% 9% 6% 4 5% 4 5% 6% 22%	1900
	11th to 20th	Night	11% 18% 3 9% 6% 6% 5% 4 6% 6% 26%	1810
	21st to end	Night	12% 16% 4 10% 6% 6% 5% 4 5% 5% 28%	1528
May	1st to 10th	Night	13% 10% 3 7% 6% 6% 5% 4 5% 8% 32%	2540
	11th to 20th	Night	13% 10% 4 8% 5% 5% 6% 5% 6% 8% 30%	2494
	21st to end	Night	21% 16% 4 9% 6% 5% 3 3 5% 5% 23%	2356
June	1st to 10th	Night	22% 9% 3 7% 6% 6% 4 3 6% 7% 26%	1140
	11th to 20th	Night	23% 13% 5% 9% 4 7% 6% 4 5% 7% 17%	1140
	21st to end	Night	15% 7% 3 7% 6% 6% 7% 4 7% 8% 31%	1140
July	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 5% 5% 52%	1900
	11th to 20th	Night	7% 4 2 4 3 3 4 3 5% 6% 60%	2076
	21st to end	Night	15% 8% 3 6% 5% 4 4 4 5% 7% 38%	2748
August	1st to 10th	Night	6% 5% 2 6% 4 4 5% 4 7% 8% 50%	2529
	11th to 20th	Night	10% 5% 2 7% 4 5% 5% 4 8% 10% 39%	2497
	21st to end	Night	19% 7% 2 7% 5% 5% 5% 4 7% 8% 32%	3285
September	1st to 10th	Night	16% 7% 3 6% 5% 3 4 3 5% 6% 41%	1900
	11th to 20th	Night	21% 8% 2 6% 3 4 4 3 5% 7% 38%	1924
	21st to end	Night	22% 11% 3 6% 4 4 4 4 5% 6% 30%	2104
October	1st to 10th	Night	21% 14% 4 11% 7% 7% 5% 3 5% 4 20%	3800
	11th to 20th	Night	22% 13% 3 8% 6% 5% 5% 4 6% 7% 22%	3947
	21st to end	Night	18% 20% 5% 11% 5% 5% 5% 3 5% 6% 18%	4457
November	1st to 10th	Night	27% 23% 5% 10% 5% 4 5% 3 3 4 11%	2687
	11th to 20th	Night	20% 26% 5% 11% 5% 5% 4 3 3 3 16%	2880
	21st to end	Night	16% 26% 7% 13% 6% 6% 4 3 4 4 11%	3000
December	1st to 10th	Night	13% 20% 6% 16% 9% 7% 5% 4 5% 4 12%	4908
	11th to 20th	Night	15% 33% 9% 14% 7% 5% 4 3 3 3 6%	5930
	21st to end	Night	15% 29% 7% 13% 6% 5% 4 3 5% 4 8%	7964

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	85% 4 5% 4 1	2829
	11th to 20th	Day	55% 9% 12% 13% 7% 4	3287
	21st to end	Day	72% 4 14% 7% 2	4004
February	1st to 10th	Day	72% 5% 8% 8% 7% 1	1560
	11th to 20th	Day	68% 8% 11% 7% 5% 1	1638
	21st to end	Day	66% 6% 11% 10% 6% 1	1522
March	1st to 10th	Day	67% 6% 11% 9% 6%	3138
	11th to 20th	Day	55% 8% 14% 21% 2	3294
	21st to end	Day	59% 9% 13% 12% 7%	4150
April	1st to 10th	Day	73% 7% 11% 8% 2	2280
	11th to 20th	Day	62% 7% 15% 13% 3	2321
	21st to end	Day	62% 8% 13% 14% 3	2650
May	1st to 10th	Day	51% 9% 17% 19% 4	4420
	11th to 20th	Day	52% 11% 16% 17% 4	4402
	21st to end	Day	62% 10% 13% 13% 2	5216
June	1st to 10th	Day	64% 8% 9% 10% 7% 2	3040
	11th to 20th	Day	71% 8% 10% 10% 2	3040
	21st to end	Day	59% 10% 12% 14% 5% 1	3040
July	1st to 10th	Day	39% 6% 9% 24% 21% 1	4981
	11th to 20th	Day	29% 7% 14% 34% 15% 1	4796
	21st to end	Day	46% 7% 14% 20% 11% 1	4651
August	1st to 10th	Day	30% 7% 14% 39% 10%	4384
	11th to 20th	Day	38% 11% 24% 21% 6%	4372
	21st to end	Day	49% 9% 22% 17% 3	4385
September	1st to 10th	Day	50% 8% 16% 19% 7% 1	2280
	11th to 20th	Day	50% 9% 13% 19% 7% 1	2256
	21st to end	Day	59% 10% 12% 12% 7% 1	2072
October	1st to 10th	Day	65% 10% 13% 10% 2	3180
	11th to 20th	Day	68% 5% 17% 9% 1	2984
	21st to end	Day	68% 7% 16% 6% 3	3101
November	1st to 10th	Day	79% 5% 5% 6% 3	1608
	11th to 20th	Day	77% 6% 8% 6% 3 1	1500
	21st to end	Day	74% 7% 7% 4 7% 1	1400
December	1st to 10th	Day	73% 8% 10% 6% 2	2270
	11th to 20th	Day	80% 4 7% 6% 3	2264
	21st to end	Day	74% 7% 9% 7% 2	2992
January	1st to 10th	Night	85% 5% 5% 3 1	7157
	11th to 20th	Night	63% 8% 7% 11% 6% 4	6670
	21st to end	Night	75% 4 11% 8% 2	6952
February	1st to 10th	Night	73% 5% 8% 7% 6% 1	2730
	11th to 20th	Night	68% 6% 10% 9% 6% 1	2438
	21st to end	Night	63% 8% 11% 12% 5% 2	1931
March	1st to 10th	Night	60% 7% 12% 13% 7% 1	3736
	11th to 20th	Night	54% 10% 17% 16% 3	3685
	21st to end	Night	57% 8% 14% 12% 7% 1	3502
April	1st to 10th	Night	65% 7% 13% 12% 3	1900
	11th to 20th	Night	57% 8% 14% 14% 7%	1810
	21st to end	Night	58% 8% 10% 18% 6%	1528
May	1st to 10th	Night	48% 11% 17% 17% 7%	2540
	11th to 20th	Night	49% 12% 16% 17% 6%	2494
	21st to end	Night	62% 8% 10% 15% 3	2356
June	1st to 10th	Night	56% 10% 13% 14% 5% 2	1140
	11th to 20th	Night	65% 10% 11% 11% 2	1140
	21st to end	Night	50% 11% 16% 16% 7%	1140
July	1st to 10th	Night	34% 7% 8% 23% 28% 1	1870
	11th to 20th	Night	27% 6% 11% 38% 17% 1	2039
	21st to end	Night	46% 7% 12% 21% 13% 1	2661
August	1st to 10th	Night	30% 9% 13% 40% 7%	2521
	11th to 20th	Night	37% 8% 26% 23% 6% 1	2521
	21st to end	Night	49% 9% 27% 11% 4	3285
September	1st to 10th	Night	44% 9% 15% 23% 8% 1	1900
	11th to 20th	Night	47% 7% 13% 22% 9% 1	1924
	21st to end	Night	55% 9% 14% 14% 8% 1	2104
October	1st to 10th	Night	65% 9% 12% 11% 3	3800
	11th to 20th	Night	63% 6% 17% 13% 1	3947
	21st to end	Night	70% 6% 14% 8% 3	4457
November	1st to 10th	Night	77% 6% 7% 7% 2	2687
	11th to 20th	Night	75% 6% 7% 6% 5% 1	2880
	21st to end	Night	78% 5% 7% 4 5% 1	3000
December	1st to 10th	Night	73% 9% 9% 7% 3	4908
	11th to 20th	Night	85% 4 4 4 2	5927
	21st to end	Night	77% 9% 7% 5% 2	7964

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	20% 11% 30% 28% 10% 3	200
	11th to 20th	Day	28% 11% 25% 24% 12% 2	200
	21st to end	Day	24% 12% 30% 26% 7% 1	220
February	1st to 10th	Day	22% 16% 37% 17% 8% 1	190
	11th to 20th	Day	19% 17% 33% 22% 8% 2	329
	21st to end	Day	16% 21% 30% 22% 9% 1	359
March	1st to 10th	Day	23% 18% 28% 20% 10% 1	460
	11th to 20th	Day	23% 19% 27% 18% 12% 1	460
	21st to end	Day	25% 20% 25% 15% 13% 2	506
April	1st to 10th	Day	24% 20% 29% 18% 7% 1	460
	11th to 20th	Day	22% 16% 26% 23% 10% 3	452
	21st to end	Day	22% 18% 26% 19% 13% 3	460
May	1st to 10th	Day	20% 13% 29% 24% 12% 2	463
	11th to 20th	Day	18% 9% 20% 27% 20% 5%	497
	21st to end	Day	20% 8% 21% 27% 18% 5%	762
June	1st to 10th	Day	26% 10% 26% 26% 10% 1	870
	11th to 20th	Day	28% 10% 21% 26% 12% 2	870
	21st to end	Day	22% 6% 23% 28% 18% 3	870
July	1st to 10th	Day	19% 6% 20% 33% 18% 3	856
	11th to 20th	Day	15% 8% 25% 31% 17% 3	753
	21st to end	Day	13% 7% 22% 34% 20% 4	544
August	1st to 10th	Day	10% 5% 22% 37% 21% 5%	487
	11th to 20th	Day	11% 10% 26% 32% 18% 3	477
	21st to end	Day	18% 10% 27% 29% 14% 3	539
September	1st to 10th	Day	21% 10% 29% 24% 12% 3	490
	11th to 20th	Day	24% 9% 24% 25% 16% 2	490
	21st to end	Day	31% 14% 22% 21% 11% 2	490
October	1st to 10th	Day	32% 10% 22% 20% 12% 4	490
	11th to 20th	Day	33% 14% 21% 19% 12% 2	390
	21st to end	Day	32% 12% 28% 21% 6% 1	330
November	1st to 10th	Day	33% 17% 27% 16% 5% 1	220
	11th to 20th	Day	36% 13% 21% 22% 7% 3	200
	21st to end	Day	30% 17% 22% 18% 10% 5%	200
December	1st to 10th	Day	22% 10% 20% 26% 20% 3	200
	11th to 20th	Day	24% 14% 27% 26% 10% 1	200
	21st to end	Day	21% 7% 35% 24% 12% 1	220
January	1st to 10th	Night	33% 13% 24% 22% 7% 1	1070
	11th to 20th	Night	30% 9% 29% 25% 7%	877
	21st to end	Night	28% 9% 30% 26% 7%	880
February	1st to 10th	Night	29% 9% 31% 21% 9%	780
	11th to 20th	Night	25% 8% 31% 29% 8%	744
	21st to end	Night	17% 9% 26% 31% 16% 1	628
March	1st to 10th	Night	23% 10% 29% 28% 11%	760
	11th to 20th	Night	24% 12% 25% 28% 11%	760
	21st to end	Night	23% 9% 24% 26% 15% 3	836
April	1st to 10th	Night	20% 9% 26% 28% 15% 2	760
	11th to 20th	Night	19% 9% 24% 30% 18%	682
	21st to end	Night	20% 7% 21% 30% 20% 2	388
May	1st to 10th	Night	17% 6% 21% 36% 21% 1	380
	11th to 20th	Night	17% 4 21% 36% 21% 2	374
	21st to end	Night	23% 4 17% 31% 22% 3	411
June	1st to 10th	Night	23% 7% 23% 31% 14% 2	380
	11th to 20th	Night	28% 6% 24% 24% 16% 2	380
	21st to end	Night	19% 4 20% 31% 22% 5%	380
July	1st to 10th	Night	19% 4 18% 32% 25% 2	370
	11th to 20th	Night	14% 6% 18% 35% 25% 2	368
	21st to end	Night	13% 5% 11% 38% 29% 3	416
August	1st to 10th	Night	11% 3 15% 33% 35% 3	378
	11th to 20th	Night	13% 2 16% 39% 27% 3	376
	21st to end	Night	20% 3 17% 37% 20% 1	701
September	1st to 10th	Night	20% 4 18% 34% 21% 3	760
	11th to 20th	Night	23% 4 17% 30% 23% 4	760
	21st to end	Night	29% 9% 17% 29% 14% 2	760
October	1st to 10th	Night	28% 5% 19% 30% 14% 2	760
	11th to 20th	Night	33% 6% 20% 29% 10% 1	760
	21st to end	Night	36% 9% 23% 23% 8% 1	836
November	1st to 10th	Night	39% 9% 25% 21% 5%	780
	11th to 20th	Night	36% 12% 25% 19% 7%	880
	21st to end	Night	31% 11% 27% 23% 6% 2	1000
December	1st to 10th	Night	29% 6% 30% 26% 8%	1003
	11th to 20th	Night	33% 10% 29% 22% 6%	1100
	21st to end	Night	29% 9% 31% 24% 7% 1	1210

Page generated at 2025-02-03 00:05:50. Version ac07

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