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 2024-02-05.

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	17% 16% 5% 8% 7% 4 5% 5% 5% 6% 24%	77543
	Night	17% 19% 5% 9% 6% 3 5% 4 4 5% 21%	81260
Transparency	Day	62% 8% 12% 13% 5% 1	77244
	Night	65% 7% 10% 11% 5% 1	81139
Seeing	Day	22% 11% 25% 25% 14% 3	14864
	Night	26% 8% 24% 27% 13% 1	23384

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	12% 31% 10% 12% 10% 5% 5% 4 2 2 8%	1967
	11th to 20th	Day	15% 20% 5% 10% 4 2 2 5% 5% 5% 26%	2264
	21st to end	Day	20% 37% 5% 9% 5% 3 3 3 3 3 10%	2794
February	1st to 10th	Day	15% 26% 8% 9% 6% 3 4 4 4 3 18%	1472
	11th to 20th	Day	13% 18% 8% 12% 8% 4 5% 4 4 5% 19%	1541
	21st to end	Day	8% 17% 8% 13% 8% 5% 5% 3 4 5% 23%	1435
March	1st to 10th	Day	12% 21% 7% 12% 8% 4 5% 4 5% 5% 18%	1800
	11th to 20th	Day	12% 24% 7% 7% 7% 4 4 4 4 5% 21%	1862
	21st to end	Day	13% 23% 7% 11% 6% 4 6% 5% 5% 5% 17%	2361
April	1st to 10th	Day	12% 21% 8% 11% 10% 4 6% 5% 5% 4 15%	2160
	11th to 20th	Day	13% 20% 5% 8% 7% 3 6% 4 6% 7% 21%	2197
	21st to end	Day	15% 15% 4 9% 7% 4 6% 6% 5% 7% 22%	2510
May	1st to 10th	Day	15% 16% 5% 7% 6% 4 6% 5% 5% 5% 26%	2520
	11th to 20th	Day	16% 11% 4 8% 7% 3 5% 6% 5% 7% 28%	2485
	21st to end	Day	19% 10% 4 7% 7% 4 6% 5% 5% 7% 25%	2943
June	1st to 10th	Day	24% 10% 4 8% 8% 4 6% 5% 4 5% 22%	2880
	11th to 20th	Day	27% 12% 6% 9% 8% 5% 6% 5% 5% 4 13%	2880
	21st to end	Day	20% 9% 4 8% 8% 4 6% 5% 6% 5% 25%	2880
July	1st to 10th	Day	17% 7% 4 6% 7% 4 5% 5% 6% 8% 31%	2880
	11th to 20th	Day	13% 7% 3 7% 7% 4 6% 6% 7% 8% 32%	2786
	21st to end	Day	11% 5% 3 6% 6% 4 6% 5% 6% 7% 41%	2754
August	1st to 10th	Day	11% 6% 3 6% 7% 3 6% 6% 6% 8% 39%	2507
	11th to 20th	Day	10% 5% 3 6% 6% 3 5% 5% 6% 9% 41%	2475
	21st to end	Day	19% 8% 3 7% 7% 3 6% 4 5% 7% 30%	2504
September	1st to 10th	Day	17% 9% 4 7% 6% 3 5% 4 5% 6% 34%	2160
	11th to 20th	Day	17% 9% 3 6% 6% 4 4 5% 5% 6% 35%	2138
	21st to end	Day	23% 11% 3 7% 5% 3 4 4 5% 6% 28%	1963
October	1st to 10th	Day	21% 13% 3 7% 6% 3 4 5% 5% 5% 30%	1800
	11th to 20th	Day	23% 15% 4 8% 7% 4 5% 5% 4 5% 20%	1706
	21st to end	Day	22% 20% 3 8% 6% 3 3 4 4 6% 21%	1782
November	1st to 10th	Day	23% 23% 6% 11% 7% 4 4 3 4 3 13%	1526
	11th to 20th	Day	20% 23% 7% 10% 6% 3 4 4 4 4 15%	1425
	21st to end	Day	16% 26% 7% 10% 6% 3 4 3 4 4 16%	1330
December	1st to 10th	Day	16% 19% 6% 13% 9% 4 4 4 4 4 16%	1324
	11th to 20th	Day	20% 27% 7% 12% 6% 4 4 3 3 3 11%	1442
	21st to end	Day	14% 29% 6% 8% 7% 3 5% 5% 4 4 14%	2090
January	1st to 10th	Night	13% 32% 10% 14% 9% 3 4 3 2 3 8%	5005
	11th to 20th	Night	14% 16% 7% 9% 7% 4 6% 6% 7% 5% 19%	4631
	21st to end	Night	26% 35% 7% 7% 5% 2 4 3 2 3 7%	4862
February	1st to 10th	Night	16% 25% 7% 10% 8% 3 3 4 4 5% 15%	2582
	11th to 20th	Night	13% 23% 7% 11% 6% 4 4 4 5% 5% 18%	2304
	21st to end	Night	7% 20% 7% 10% 8% 4 5% 5% 5% 7% 21%	1820
March	1st to 10th	Night	11% 23% 7% 10% 7% 3 5% 5% 4 5% 21%	2160
	11th to 20th	Night	14% 23% 7% 7% 6% 3 4 5% 5% 5% 22%	2096
	21st to end	Night	12% 21% 5% 9% 6% 5% 5% 5% 5% 6% 21%	1994
April	1st to 10th	Night	11% 21% 6% 8% 6% 4 5% 5% 5% 7% 23%	1800
	11th to 20th	Night	12% 17% 4 8% 7% 4 6% 5% 5% 6% 26%	1714
	21st to end	Night	12% 14% 4 8% 7% 5% 6% 5% 5% 6% 29%	1448
May	1st to 10th	Night	15% 11% 4 6% 7% 5% 5% 5% 4 8% 31%	1440
	11th to 20th	Night	14% 8% 3 7% 7% 3 6% 7% 6% 8% 31%	1408
	21st to end	Night	17% 9% 3 7% 6% 4 5% 5% 6% 7% 29%	1328
June	1st to 10th	Night	21% 9% 4 6% 7% 4 5% 5% 5% 8% 26%	1080
	11th to 20th	Night	23% 13% 5% 9% 5% 5% 6% 6% 5% 7% 17%	1080
	21st to end	Night	15% 7% 3 5% 8% 5% 8% 4 6% 8% 31%	1080
July	1st to 10th	Night	17% 6% 3 6% 5% 3 6% 5% 7% 7% 36%	1080
	11th to 20th	Night	11% 7% 3 7% 5% 4 5% 5% 5% 8% 39%	1172
	21st to end	Night	12% 5% 2 5% 5% 3 4 5% 6% 8% 45%	1562
August	1st to 10th	Night	10% 5% 2 4 6% 4 5% 6% 6% 8% 44%	1432
	11th to 20th	Night	10% 5% 1 5% 4 3 4 4 5% 8% 49%	1424
	21st to end	Night	14% 8% 2 5% 6% 4 5% 6% 7% 9% 35%	1851
September	1st to 10th	Night	17% 7% 3 5% 7% 3 4 4 5% 7% 39%	1800
	11th to 20th	Night	21% 8% 2 5% 4 3 4 4 5% 7% 38%	1822
	21st to end	Night	22% 11% 3 5% 5% 3 5% 5% 5% 6% 31%	1993
October	1st to 10th	Night	21% 10% 3 5% 5% 4 4 3 5% 6% 34%	2160
	11th to 20th	Night	23% 14% 5% 8% 6% 4 4 4 5% 6% 22%	2253
	21st to end	Night	23% 20% 4 8% 4 3 4 4 4 6% 19%	2574
November	1st to 10th	Night	28% 22% 5% 9% 6% 3 5% 4 3 4 11%	2549
	11th to 20th	Night	21% 24% 6% 10% 6% 3 5% 4 3 3 16%	2736
	21st to end	Night	17% 24% 8% 11% 7% 4 6% 4 4 5% 11%	2850
December	1st to 10th	Night	16% 21% 7% 12% 9% 4 4 4 3 5% 16%	2854
	11th to 20th	Night	20% 30% 8% 11% 7% 3 4 3 2 3 8%	3750
	21st to end	Night	17% 25% 6% 9% 7% 4 5% 5% 5% 6% 10%	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	85% 4 4 5% 1 1	1967
	11th to 20th	Day	60% 8% 9% 11% 6% 6%	2285
	21st to end	Day	83% 5% 5% 4 3	2794
February	1st to 10th	Day	72% 5% 9% 7% 6% 1	1472
	11th to 20th	Day	70% 8% 11% 7% 3 1	1550
	21st to end	Day	65% 6% 11% 11% 6% 2	1435
March	1st to 10th	Day	70% 7% 10% 7% 5% 1	1800
	11th to 20th	Day	68% 6% 11% 11% 3 1	1862
	21st to end	Day	71% 8% 12% 7% 2	2361
April	1st to 10th	Day	73% 7% 10% 8% 2	2160
	11th to 20th	Day	63% 7% 15% 12% 3	2197
	21st to end	Day	62% 8% 13% 14% 3	2510
May	1st to 10th	Day	60% 9% 13% 15% 3	2520
	11th to 20th	Day	55% 9% 14% 16% 5%	2488
	21st to end	Day	57% 9% 14% 15% 4	2944
June	1st to 10th	Day	65% 8% 9% 10% 6% 2	2880
	11th to 20th	Day	73% 8% 9% 8% 1	2880
	21st to end	Day	58% 10% 12% 14% 5% 1	2880
July	1st to 10th	Day	51% 9% 13% 18% 9%	2801
	11th to 20th	Day	49% 10% 14% 18% 8% 1	2700
	21st to end	Day	40% 9% 15% 25% 9% 1	2601
August	1st to 10th	Day	42% 10% 17% 22% 8%	2490
	11th to 20th	Day	39% 11% 19% 21% 11% 1	2475
	21st to end	Day	54% 9% 14% 18% 5%	2504
September	1st to 10th	Day	51% 8% 15% 19% 6% 1	2160
	11th to 20th	Day	50% 9% 13% 20% 8% 1	2138
	21st to end	Day	58% 10% 12% 12% 7% 1	1963
October	1st to 10th	Day	58% 8% 16% 15% 3	1800
	11th to 20th	Day	67% 8% 12% 11% 1	1706
	21st to end	Day	67% 8% 12% 9% 5%	1782
November	1st to 10th	Day	78% 6% 6% 6% 4	1526
	11th to 20th	Day	76% 6% 8% 6% 3 1	1425
	21st to end	Day	74% 7% 7% 4 7% 1	1330
December	1st to 10th	Day	73% 6% 6% 10% 4 1	1324
	11th to 20th	Day	81% 5% 5% 6% 3	1444
	21st to end	Day	71% 8% 8% 9% 3	2090
January	1st to 10th	Night	85% 4 5% 4 2 1	5005
	11th to 20th	Night	65% 7% 7% 9% 7% 6%	4672
	21st to end	Night	84% 5% 4 4 2	4862
February	1st to 10th	Night	74% 4 8% 7% 6% 1	2582
	11th to 20th	Night	70% 6% 11% 9% 4	2306
	21st to end	Night	62% 7% 12% 12% 5% 2	1820
March	1st to 10th	Night	66% 6% 11% 9% 6% 1	2160
	11th to 20th	Night	65% 6% 12% 11% 5%	2097
	21st to end	Night	65% 8% 15% 9% 4	1994
April	1st to 10th	Night	64% 7% 13% 12% 3	1800
	11th to 20th	Night	57% 8% 14% 13% 7%	1714
	21st to end	Night	57% 8% 11% 18% 6%	1448
May	1st to 10th	Night	52% 11% 16% 17% 4	1440
	11th to 20th	Night	51% 11% 13% 18% 7%	1408
	21st to end	Night	53% 10% 15% 17% 5%	1328
June	1st to 10th	Night	56% 10% 13% 14% 5% 2	1080
	11th to 20th	Night	66% 10% 12% 9% 2	1080
	21st to end	Night	50% 12% 16% 16% 6%	1080
July	1st to 10th	Night	46% 10% 13% 19% 10% 1	1050
	11th to 20th	Night	44% 10% 17% 21% 8%	1135
	21st to end	Night	36% 9% 16% 26% 12% 1	1475
August	1st to 10th	Night	38% 11% 19% 23% 9%	1424
	11th to 20th	Night	33% 7% 19% 29% 10% 1	1424
	21st to end	Night	45% 11% 18% 18% 8%	1851
September	1st to 10th	Night	46% 9% 15% 21% 7% 1	1800
	11th to 20th	Night	47% 7% 13% 22% 10% 1	1822
	21st to end	Night	55% 8% 14% 14% 8% 1	1993
October	1st to 10th	Night	53% 7% 16% 20% 4	2160
	11th to 20th	Night	64% 8% 13% 13% 2	2253
	21st to end	Night	68% 7% 11% 10% 5%	2574
November	1st to 10th	Night	78% 6% 6% 7% 2	2549
	11th to 20th	Night	75% 7% 7% 5% 5% 1	2736
	21st to end	Night	77% 5% 7% 5% 5% 1	2850
December	1st to 10th	Night	73% 5% 7% 10% 5%	2854
	11th to 20th	Night	85% 4 4 4 3	3747
	21st to end	Night	71% 12% 9% 6% 2	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	21% 11% 30% 26% 10% 3	180
	11th to 20th	Day	30% 11% 24% 22% 11% 2	180
	21st to end	Day	26% 13% 30% 24% 7% 1	198
February	1st to 10th	Day	24% 17% 35% 15% 7% 1	168
	11th to 20th	Day	20% 18% 34% 21% 6% 1	301
	21st to end	Day	15% 20% 32% 22% 10% 1	326
March	1st to 10th	Day	23% 19% 28% 19% 10% 1	420
	11th to 20th	Day	25% 18% 28% 17% 11% 1	420
	21st to end	Day	27% 19% 24% 14% 13% 2	462
April	1st to 10th	Day	24% 21% 28% 19% 7% 1	420
	11th to 20th	Day	23% 17% 25% 21% 10% 3	412
	21st to end	Day	22% 17% 27% 18% 13% 3	420
May	1st to 10th	Day	21% 13% 28% 25% 12% 2	423
	11th to 20th	Day	19% 8% 19% 28% 21% 5%	456
	21st to end	Day	20% 7% 20% 28% 20% 6%	705
June	1st to 10th	Day	26% 9% 26% 27% 11% 1	810
	11th to 20th	Day	28% 10% 21% 26% 12% 2	810
	21st to end	Day	22% 5% 22% 29% 19% 4	810
July	1st to 10th	Day	20% 6% 19% 33% 19% 3	796
	11th to 20th	Day	16% 8% 23% 30% 18% 4	699
	21st to end	Day	10% 6% 22% 35% 21% 4	500
August	1st to 10th	Day	11% 5% 21% 38% 21% 4	447
	11th to 20th	Day	11% 10% 27% 31% 18% 3	437
	21st to end	Day	17% 10% 27% 29% 15% 3	495
September	1st to 10th	Day	22% 11% 29% 23% 12% 3	450
	11th to 20th	Day	25% 9% 24% 25% 16% 1	450
	21st to end	Day	29% 13% 23% 22% 12% 2	450
October	1st to 10th	Day	30% 11% 22% 20% 13% 4	450
	11th to 20th	Day	32% 14% 22% 19% 12% 2	356
	21st to end	Day	32% 12% 29% 19% 7% 1	297
November	1st to 10th	Day	30% 18% 28% 17% 6% 2	198
	11th to 20th	Day	34% 12% 22% 24% 7% 2	180
	21st to end	Day	31% 18% 21% 17% 10% 4	180
December	1st to 10th	Day	22% 10% 21% 26% 19% 3	180
	11th to 20th	Day	23% 13% 27% 26% 10% 1	180
	21st to end	Day	19% 7% 37% 25% 12% 1	198
January	1st to 10th	Night	34% 12% 25% 21% 6% 1	1012
	11th to 20th	Night	31% 9% 29% 24% 7%	830
	21st to end	Night	29% 9% 31% 24% 7%	836
February	1st to 10th	Night	30% 9% 30% 21% 9%	738
	11th to 20th	Night	26% 8% 31% 28% 7%	704
	21st to end	Night	17% 7% 27% 31% 16% 1	592
March	1st to 10th	Night	23% 10% 29% 27% 10%	720
	11th to 20th	Night	25% 12% 25% 27% 11%	720
	21st to end	Night	24% 8% 24% 26% 15% 3	792
April	1st to 10th	Night	20% 8% 25% 28% 16% 3	720
	11th to 20th	Night	20% 9% 23% 30% 18%	646
	21st to end	Night	20% 7% 21% 30% 20% 2	368
May	1st to 10th	Night	17% 6% 21% 35% 21% 1	360
	11th to 20th	Night	17% 4 19% 37% 21% 2	354
	21st to end	Night	23% 3 16% 32% 23% 3	389
June	1st to 10th	Night	24% 6% 22% 32% 15% 2	360
	11th to 20th	Night	28% 5% 24% 24% 16% 2	360
	21st to end	Night	19% 4 18% 32% 23% 5%	360
July	1st to 10th	Night	20% 3 17% 31% 27% 2	350
	11th to 20th	Night	15% 6% 17% 33% 27% 2	348
	21st to end	Night	12% 5% 10% 39% 30% 3	394
August	1st to 10th	Night	11% 2 14% 33% 37% 3	358
	11th to 20th	Night	13% 2 15% 37% 29% 3	356
	21st to end	Night	19% 3 17% 38% 22% 2	663
September	1st to 10th	Night	21% 5% 17% 33% 22% 3	720
	11th to 20th	Night	23% 4 16% 30% 23% 4	720
	21st to end	Night	28% 8% 16% 30% 15% 2	720
October	1st to 10th	Night	28% 5% 19% 31% 15% 3	720
	11th to 20th	Night	34% 6% 20% 29% 11% 1	720
	21st to end	Night	36% 8% 24% 23% 8% 1	792
November	1st to 10th	Night	39% 9% 25% 21% 6%	740
	11th to 20th	Night	36% 12% 26% 19% 7%	836
	21st to end	Night	32% 11% 28% 21% 6% 2	950
December	1st to 10th	Night	30% 7% 31% 25% 8% 1	952
	11th to 20th	Night	33% 10% 29% 22% 5%	1040
	21st to end	Night	28% 9% 32% 24% 6%	1144

Page generated at 2024-02-02 02:20:33. Version ac07

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