Highvale
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highvale clear sky chart from 2005-11-06 to 2025-02-25.

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	10% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	112858
	Night	9% 11% 4 10% 6% 6% 5% 4 6% 7% 32%	114445
Transparency	Day	45% 7% 17% 22% 8% 1	112597
	Night	49% 6% 15% 20% 8% 1	114352
Seeing	Day	13% 7% 24% 31% 19% 7%	16185
	Night	14% 6% 27% 35% 16% 2	24846

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	5% 12% 6% 12% 8% 5% 5% 3 5% 8% 31%	3179
	11th to 20th	Day	6% 9% 3 10% 7% 6% 5% 6% 8% 8% 32%	3159
	21st to end	Day	7% 13% 3 8% 6% 5% 4 4 6% 7% 36%	3866
February	1st to 10th	Day	8% 13% 5% 13% 7% 8% 6% 4 7% 7% 22%	1600
	11th to 20th	Day	5% 13% 6% 12% 7% 4 6% 5% 6% 7% 29%	1664
	21st to end	Day	4 14% 5% 12% 7% 8% 7% 5% 6% 7% 25%	1541
March	1st to 10th	Day	4 12% 6% 14% 9% 6% 5% 3 6% 7% 28%	3138
	11th to 20th	Day	6% 10% 3 7% 4 4 4 4 7% 9% 41%	3412
	21st to end	Day	7% 15% 6% 14% 7% 6% 5% 4 6% 7% 24%	3944
April	1st to 10th	Day	7% 13% 4 9% 6% 5% 6% 6% 7% 7% 29%	2342
	11th to 20th	Day	11% 11% 4 8% 6% 5% 5% 5% 7% 7% 31%	2440
	21st to end	Day	11% 9% 4 9% 6% 5% 6% 5% 6% 9% 31%	2481
May	1st to 10th	Day	15% 11% 4 8% 5% 5% 5% 4 5% 8% 30%	4606
	11th to 20th	Day	10% 11% 4 9% 6% 6% 5% 5% 7% 8% 30%	4694
	21st to end	Day	12% 8% 3 8% 6% 6% 6% 5% 8% 9% 28%	5161
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 7% 8% 32%	2850
	11th to 20th	Day	18% 8% 3 8% 7% 6% 6% 4 7% 7% 24%	3032
	21st to end	Day	10% 5% 2 6% 6% 5% 6% 5% 8% 9% 39%	3040
July	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 50%	5010
	11th to 20th	Day	8% 4 2 6% 4 4 5% 4 6% 9% 48%	4740
	21st to end	Day	11% 6% 2 5% 4 5% 4 4 6% 9% 43%	5138
August	1st to 10th	Day	13% 5% 2 6% 4 5% 5% 4 7% 9% 41%	4437
	11th to 20th	Day	10% 6% 2 5% 4 5% 4 4 7% 10% 42%	4209
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 9% 39%	4521
September	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 6% 8% 43%	2380
	11th to 20th	Day	15% 7% 2 6% 3 4 5% 3 5% 8% 42%	2110
	21st to end	Day	9% 8% 3 8% 5% 4 5% 3 6% 8% 40%	2090
October	1st to 10th	Day	9% 9% 4 8% 5% 4 5% 3 5% 7% 41%	3320
	11th to 20th	Day	11% 12% 4 7% 4 4 6% 4 6% 8% 34%	2842
	21st to end	Day	7% 12% 3 10% 6% 6% 5% 4 5% 7% 35%	3101
November	1st to 10th	Day	10% 18% 4 10% 7% 5% 4 4 5% 6% 26%	1581
	11th to 20th	Day	7% 14% 5% 12% 6% 5% 4 2 7% 6% 33%	1400
	21st to end	Day	7% 11% 6% 13% 6% 7% 6% 5% 6% 6% 27%	1400
December	1st to 10th	Day	10% 15% 6% 13% 6% 6% 6% 4 6% 7% 21%	2290
	11th to 20th	Day	9% 13% 5% 14% 9% 5% 5% 3 6% 7% 24%	2642
	21st to end	Day	4 8% 3 10% 5% 5% 5% 4 6% 8% 42%	3498
January	1st to 10th	Night	5% 12% 5% 15% 8% 7% 5% 4 5% 6% 28%	6766
	11th to 20th	Night	4 9% 4 12% 8% 7% 6% 5% 7% 6% 33%	6739
	21st to end	Night	8% 14% 4 9% 5% 5% 5% 4 6% 7% 33%	7122
February	1st to 10th	Night	6% 14% 5% 12% 8% 7% 6% 4 5% 6% 27%	2800
	11th to 20th	Night	5% 12% 6% 11% 8% 6% 6% 5% 6% 6% 28%	2622
	21st to end	Night	5% 14% 5% 10% 8% 6% 6% 4 6% 7% 29%	2002
March	1st to 10th	Night	3 10% 5% 14% 8% 8% 6% 4 7% 9% 26%	3736
	11th to 20th	Night	5% 9% 3 8% 6% 5% 6% 5% 7% 9% 36%	3567
	21st to end	Night	7% 15% 8% 15% 7% 6% 5% 4 6% 6% 22%	3705
April	1st to 10th	Night	9% 10% 4 11% 7% 6% 6% 5% 7% 7% 27%	1838
	11th to 20th	Night	10% 12% 4 10% 7% 6% 6% 5% 7% 6% 28%	1691
	21st to end	Night	10% 12% 3 8% 4 4 5% 4 7% 9% 33%	1696
May	1st to 10th	Night	21% 10% 4 9% 5% 4 6% 4 5% 5% 27%	2353
	11th to 20th	Night	10% 10% 4 9% 6% 6% 6% 5% 8% 8% 28%	2199
	21st to end	Night	15% 10% 3 9% 7% 6% 6% 5% 7% 8% 25%	2414
June	1st to 10th	Night	17% 10% 3 9% 5% 5% 5% 4 6% 7% 28%	1330
	11th to 20th	Night	17% 8% 4 9% 7% 6% 7% 5% 8% 8% 21%	1143
	21st to end	Night	11% 6% 3 8% 5% 6% 6% 5% 8% 9% 32%	1140
July	1st to 10th	Night	10% 5% 3 6% 5% 4 5% 4 6% 8% 44%	1948
	11th to 20th	Night	8% 5% 2 8% 6% 6% 6% 4 8% 10% 35%	2220
	21st to end	Night	14% 6% 2 6% 5% 4 5% 4 7% 8% 41%	2414
August	1st to 10th	Night	15% 7% 2 6% 5% 5% 5% 4 5% 8% 38%	2490
	11th to 20th	Night	14% 8% 3 7% 5% 5% 4 5% 6% 9% 37%	2621
	21st to end	Night	14% 5% 2 6% 4 4 5% 3 7% 8% 41%	3146
September	1st to 10th	Night	12% 6% 3 6% 4 5% 5% 4 6% 7% 44%	1796
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 4 6% 8% 42%	2069
	21st to end	Night	11% 8% 2 7% 4 4 5% 4 6% 7% 42%	2090
October	1st to 10th	Night	10% 9% 3 8% 5% 5% 6% 4 6% 6% 38%	3652
	11th to 20th	Night	10% 9% 3 8% 5% 5% 5% 5% 6% 8% 36%	4086
	21st to end	Night	7% 10% 4 8% 6% 6% 5% 5% 7% 8% 34%	4457
November	1st to 10th	Night	14% 14% 5% 10% 6% 5% 5% 3 5% 6% 27%	2695
	11th to 20th	Night	8% 15% 6% 11% 6% 6% 5% 4 6% 7% 28%	3000
	21st to end	Night	7% 13% 5% 11% 8% 6% 4 4 6% 8% 28%	3000
December	1st to 10th	Night	10% 17% 5% 10% 6% 5% 4 4 5% 6% 25%	4890
	11th to 20th	Night	9% 16% 6% 13% 6% 6% 5% 4 6% 7% 22%	5550
	21st to end	Night	3 9% 4 10% 6% 5% 5% 4 5% 7% 41%	7458

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	51% 4 15% 18% 11% 1	3179
	11th to 20th	Day	47% 6% 11% 13% 21% 2	3180
	21st to end	Day	45% 6% 21% 22% 6%	3866
February	1st to 10th	Day	59% 6% 13% 13% 9% 1	1600
	11th to 20th	Day	52% 8% 13% 17% 9%	1672
	21st to end	Day	54% 8% 12% 18% 8% 1	1541
March	1st to 10th	Day	54% 7% 14% 18% 7%	3138
	11th to 20th	Day	37% 8% 18% 21% 15% 1	3413
	21st to end	Day	56% 7% 13% 18% 5%	3944
April	1st to 10th	Day	48% 10% 15% 19% 7% 1	2342
	11th to 20th	Day	49% 7% 15% 21% 8% 1	2440
	21st to end	Day	47% 8% 16% 21% 7% 2	2481
May	1st to 10th	Day	51% 7% 10% 22% 9%	4606
	11th to 20th	Day	47% 9% 13% 23% 8%	4698
	21st to end	Day	47% 9% 19% 17% 8% 1	5162
June	1st to 10th	Day	47% 7% 18% 21% 6% 1	2850
	11th to 20th	Day	56% 8% 16% 15% 6%	3032
	21st to end	Day	38% 10% 22% 24% 6% 1	3040
July	1st to 10th	Day	32% 6% 16% 32% 13% 1	4932
	11th to 20th	Day	33% 7% 18% 31% 12%	4659
	21st to end	Day	36% 6% 23% 21% 13% 1	4976
August	1st to 10th	Day	38% 7% 20% 33% 2	4419
	11th to 20th	Day	36% 7% 22% 29% 6%	4251
	21st to end	Day	40% 6% 27% 23% 4	4520
September	1st to 10th	Day	39% 7% 20% 26% 6% 2	2380
	11th to 20th	Day	40% 6% 20% 27% 7%	2110
	21st to end	Day	40% 8% 16% 25% 9% 2	2090
October	1st to 10th	Day	44% 4 23% 24% 5%	3320
	11th to 20th	Day	47% 5% 14% 25% 9%	2842
	21st to end	Day	48% 4 18% 25% 4	3101
November	1st to 10th	Day	57% 6% 15% 16% 5% 1	1581
	11th to 20th	Day	51% 7% 16% 18% 8%	1400
	21st to end	Day	55% 7% 15% 16% 6% 1	1400
December	1st to 10th	Day	61% 5% 17% 11% 5% 1	2290
	11th to 20th	Day	59% 5% 17% 14% 5%	2644
	21st to end	Day	38% 5% 13% 27% 15% 2	3498
January	1st to 10th	Night	56% 5% 13% 16% 9% 1	6766
	11th to 20th	Night	49% 5% 13% 15% 16% 2	6780
	21st to end	Night	50% 5% 19% 18% 7%	7122
February	1st to 10th	Night	57% 5% 12% 17% 8% 1	2800
	11th to 20th	Night	53% 7% 12% 16% 10% 1	2624
	21st to end	Night	52% 5% 11% 20% 10% 1	2002
March	1st to 10th	Night	52% 7% 15% 19% 7%	3736
	11th to 20th	Night	40% 9% 19% 19% 13% 1	3567
	21st to end	Night	58% 8% 13% 16% 4	3705
April	1st to 10th	Night	52% 9% 13% 17% 9% 1	1838
	11th to 20th	Night	52% 7% 11% 18% 9% 2	1691
	21st to end	Night	45% 8% 14% 22% 10% 1	1696
May	1st to 10th	Night	56% 6% 8% 19% 10%	2353
	11th to 20th	Night	47% 10% 14% 21% 9%	2199
	21st to end	Night	53% 8% 16% 13% 9% 1	2414
June	1st to 10th	Night	52% 9% 14% 18% 7% 1	1330
	11th to 20th	Night	56% 11% 16% 14% 3	1143
	21st to end	Night	44% 12% 19% 21% 4 1	1140
July	1st to 10th	Night	37% 7% 15% 24% 16%	1917
	11th to 20th	Night	41% 9% 16% 26% 8%	2178
	21st to end	Night	40% 8% 19% 24% 8% 1	2337
August	1st to 10th	Night	44% 7% 19% 28% 2	2483
	11th to 20th	Night	43% 7% 20% 22% 8%	2645
	21st to end	Night	39% 5% 24% 27% 5%	3146
September	1st to 10th	Night	36% 8% 19% 25% 10% 2	1796
	11th to 20th	Night	40% 7% 15% 28% 8% 2	2069
	21st to end	Night	39% 8% 15% 24% 13% 2	2090
October	1st to 10th	Night	45% 4 19% 25% 6%	3652
	11th to 20th	Night	45% 5% 13% 30% 7%	4086
	21st to end	Night	46% 6% 19% 23% 6%	4457
November	1st to 10th	Night	57% 5% 12% 19% 7%	2695
	11th to 20th	Night	55% 7% 13% 18% 7% 1	3000
	21st to end	Night	53% 6% 16% 18% 5% 1	3000
December	1st to 10th	Night	59% 6% 14% 15% 5% 1	4890
	11th to 20th	Night	61% 5% 16% 13% 5%	5547
	21st to end	Night	41% 5% 13% 27% 14% 2	7458

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	9% 6% 26% 33% 20% 8%	200
	11th to 20th	Day	12% 5% 29% 35% 15% 5%	200
	21st to end	Day	11% 11% 25% 32% 15% 5%	220
February	1st to 10th	Day	14% 10% 27% 37% 10% 4	200
	11th to 20th	Day	11% 5% 36% 30% 15% 3	253
	21st to end	Day	7% 9% 31% 33% 15% 6%	329
March	1st to 10th	Day	12% 9% 29% 31% 16% 3	460
	11th to 20th	Day	10% 5% 34% 30% 16% 6%	460
	21st to end	Day	15% 6% 27% 30% 17% 5%	506
April	1st to 10th	Day	11% 13% 32% 29% 12% 3	460
	11th to 20th	Day	14% 6% 24% 31% 17% 7%	452
	21st to end	Day	14% 10% 26% 30% 14% 6%	460
May	1st to 10th	Day	16% 9% 22% 29% 19% 5%	571
	11th to 20th	Day	10% 8% 20% 36% 20% 6%	675
	21st to end	Day	17% 4 20% 28% 22% 8%	734
June	1st to 10th	Day	17% 7% 24% 32% 15% 4	680
	11th to 20th	Day	20% 6% 19% 28% 21% 6%	862
	21st to end	Day	13% 3 20% 28% 27% 9%	870
July	1st to 10th	Day	11% 3 18% 34% 24% 8%	833
	11th to 20th	Day	13% 4 17% 32% 25% 9%	668
	21st to end	Day	11% 6% 17% 26% 28% 12%	739
August	1st to 10th	Day	9% 5% 17% 27% 26% 15%	510
	11th to 20th	Day	8% 5% 23% 29% 26% 8%	477
	21st to end	Day	15% 6% 17% 30% 24% 9%	539
September	1st to 10th	Day	15% 5% 27% 25% 21% 7%	490
	11th to 20th	Day	17% 5% 21% 32% 18% 7%	490
	21st to end	Day	11% 11% 29% 29% 14% 6%	490
October	1st to 10th	Day	15% 6% 25% 33% 15% 6%	409
	11th to 20th	Day	13% 11% 26% 30% 16% 5%	300
	21st to end	Day	13% 12% 33% 28% 11% 3	330
November	1st to 10th	Day	21% 6% 28% 30% 13% 2	298
	11th to 20th	Day	13% 5% 34% 34% 13% 2	200
	21st to end	Day	8% 8% 30% 38% 12% 5%	200
December	1st to 10th	Day	11% 6% 27% 39% 14% 5%	200
	11th to 20th	Day	12% 10% 31% 30% 15% 4	200
	21st to end	Day	8% 3 23% 35% 23% 7%	220
January	1st to 10th	Night	12% 5% 32% 34% 15% 2	1000
	11th to 20th	Night	12% 10% 29% 35% 13% 2	1000
	21st to end	Night	14% 11% 32% 30% 11% 1	959
February	1st to 10th	Night	9% 10% 25% 35% 18% 3	800
	11th to 20th	Night	10% 7% 31% 36% 15% 1	784
	21st to end	Night	10% 6% 26% 36% 18% 4	646
March	1st to 10th	Night	10% 5% 31% 34% 17% 2	760
	11th to 20th	Night	11% 4 29% 39% 14% 2	760
	21st to end	Night	15% 5% 25% 38% 14% 3	836
April	1st to 10th	Night	12% 7% 28% 36% 15% 2	698
	11th to 20th	Night	15% 5% 30% 34% 15% 1	563
	21st to end	Night	16% 6% 26% 36% 15% 1	556
May	1st to 10th	Night	15% 6% 24% 38% 13% 3	380
	11th to 20th	Night	14% 5% 26% 36% 19% 1	374
	21st to end	Night	21% 5% 19% 37% 17% 1	411
June	1st to 10th	Night	20% 8% 22% 34% 14% 2	380
	11th to 20th	Night	20% 4 19% 36% 19% 2	380
	21st to end	Night	12% 3 19% 36% 25% 4	380
July	1st to 10th	Night	15% 3 14% 46% 22% 1	370
	11th to 20th	Night	14% 2 19% 39% 24% 2	368
	21st to end	Night	12% 4 16% 38% 29% 2	416
August	1st to 10th	Night	12% 3 17% 33% 30% 5%	378
	11th to 20th	Night	14% 2 17% 36% 28% 3	448
	21st to end	Night	15% 3 19% 40% 23%	627
September	1st to 10th	Night	14% 2 20% 39% 23% 2	656
	11th to 20th	Night	16% 3 20% 39% 21% 1	760
	21st to end	Night	15% 4 29% 35% 16% 2	760
October	1st to 10th	Night	17% 4 25% 37% 15% 1	760
	11th to 20th	Night	14% 7% 30% 33% 15% 1	760
	21st to end	Night	14% 6% 31% 34% 14% 1	836
November	1st to 10th	Night	20% 6% 29% 33% 10% 1	940
	11th to 20th	Night	12% 8% 36% 32% 10% 2	1000
	21st to end	Night	14% 5% 36% 33% 11% 2	1000
December	1st to 10th	Night	15% 8% 31% 32% 12% 2	1000
	11th to 20th	Night	13% 6% 33% 32% 14% 2	1000
	21st to end	Night	12% 4 30% 34% 17% 2	1100

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