Ashern
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashern clear sky chart from 2005-11-06 to 2024-11-11.

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	11% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	105690
	Night	9% 9% 4 9% 6% 5% 5% 4 6% 8% 35%	102087
Transparency	Day	43% 8% 17% 24% 7%	105433
	Night	45% 8% 15% 23% 8% 1	101991
Seeing	Day	14% 9% 30% 28% 15% 3	16326
	Night	14% 7% 31% 34% 13% 1	26258

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% 16% 6% 12% 6% 8% 9% 6% 6% 7% 19%	2219
	11th to 20th	Day	5% 9% 6% 19% 11% 9% 8% 5% 9% 7% 12%	2199
	21st to end	Day	6% 14% 7% 14% 7% 6% 6% 5% 5% 7% 24%	2775
February	1st to 10th	Day	8% 14% 5% 12% 9% 6% 6% 6% 7% 6% 22%	1532
	11th to 20th	Day	6% 11% 4 8% 7% 7% 7% 6% 7% 7% 30%	1664
	21st to end	Day	7% 10% 4 10% 8% 6% 6% 6% 6% 7% 30%	1517
March	1st to 10th	Day	10% 10% 5% 10% 8% 6% 5% 4 6% 8% 29%	3130
	11th to 20th	Day	7% 11% 4 13% 8% 6% 6% 5% 7% 7% 27%	3473
	21st to end	Day	6% 9% 3 9% 6% 5% 6% 4 6% 7% 39%	3831
April	1st to 10th	Day	9% 10% 3 8% 5% 6% 5% 4 5% 8% 38%	2355
	11th to 20th	Day	12% 11% 4 7% 5% 6% 4 4 5% 6% 37%	2442
	21st to end	Day	13% 7% 3 8% 4 5% 5% 4 6% 8% 38%	2470
May	1st to 10th	Day	16% 9% 2 6% 4 4 4 4 6% 7% 39%	4353
	11th to 20th	Day	19% 9% 3 7% 4 4 4 4 5% 6% 37%	4705
	21st to end	Day	18% 7% 2 6% 5% 5% 4 4 5% 7% 36%	5173
June	1st to 10th	Day	15% 8% 3 7% 5% 4 4 4 6% 8% 37%	2850
	11th to 20th	Day	14% 7% 2 7% 6% 5% 5% 4 5% 7% 39%	2850
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 6% 7% 9% 37%	2850
July	1st to 10th	Day	11% 5% 2 5% 4 4 5% 5% 7% 10% 43%	4750
	11th to 20th	Day	7% 4 1 5% 3 4 4 4 7% 9% 51%	4750
	21st to end	Day	6% 3 2 5% 4 4 5% 4 6% 9% 52%	5098
August	1st to 10th	Day	7% 4 2 6% 5% 6% 6% 4 8% 10% 43%	4412
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 6% 8% 45%	4050
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 8% 43%	4532
September	1st to 10th	Day	11% 6% 2 6% 4 3 5% 4 7% 8% 46%	2371
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 4 6% 7% 37%	2090
	21st to end	Day	12% 7% 2 7% 4 5% 4 4 7% 9% 38%	2090
October	1st to 10th	Day	13% 8% 2 7% 5% 5% 4 4 6% 8% 39%	3268
	11th to 20th	Day	9% 10% 3 7% 5% 5% 5% 4 6% 10% 36%	2941
	21st to end	Day	12% 13% 6% 9% 5% 5% 5% 5% 6% 7% 28%	3091
November	1st to 10th	Day	17% 16% 5% 11% 7% 4 3 4 4 5% 25%	1605
	11th to 20th	Day	9% 13% 5% 15% 8% 6% 5% 3 5% 8% 23%	1473
	21st to end	Day	12% 15% 4 11% 7% 6% 5% 3 5% 7% 25%	1330
December	1st to 10th	Day	6% 14% 6% 14% 10% 8% 6% 6% 6% 7% 19%	1330
	11th to 20th	Day	7% 16% 5% 13% 8% 6% 5% 4 8% 8% 20%	1679
	21st to end	Day	6% 9% 4 10% 6% 5% 7% 5% 6% 7% 35%	2442
January	1st to 10th	Night	5% 12% 6% 12% 7% 8% 8% 5% 7% 8% 21%	4737
	11th to 20th	Night	5% 11% 6% 18% 11% 9% 8% 5% 7% 6% 13%	4709
	21st to end	Night	7% 13% 7% 16% 7% 7% 6% 5% 6% 7% 19%	4891
February	1st to 10th	Night	8% 12% 5% 12% 6% 5% 5% 6% 7% 8% 27%	2647
	11th to 20th	Night	4 10% 4 8% 6% 6% 7% 5% 8% 8% 34%	2403
	21st to end	Night	6% 9% 4 11% 7% 5% 6% 4 5% 7% 36%	1955
March	1st to 10th	Night	10% 12% 3 9% 7% 4 5% 4 6% 9% 31%	3734
	11th to 20th	Night	5% 8% 4 8% 7% 6% 5% 5% 7% 7% 38%	3485
	21st to end	Night	7% 10% 4 8% 6% 5% 6% 4 6% 7% 38%	3801
April	1st to 10th	Night	8% 8% 3 6% 6% 5% 5% 6% 7% 7% 40%	1825
	11th to 20th	Night	13% 8% 3 8% 6% 6% 5% 5% 5% 7% 34%	1689
	21st to end	Night	10% 8% 4 9% 5% 4 5% 3 6% 8% 38%	1710
May	1st to 10th	Night	17% 11% 3 7% 4 4 5% 4 5% 7% 35%	2612
	11th to 20th	Night	16% 8% 3 8% 5% 3 4 3 5% 7% 38%	2201
	21st to end	Night	14% 6% 1 7% 5% 5% 5% 4 6% 7% 40%	2414
June	1st to 10th	Night	14% 7% 3 7% 4 4 5% 5% 7% 7% 36%	1330
	11th to 20th	Night	15% 4 2 5% 6% 4 4 3 7% 10% 39%	1330
	21st to end	Night	11% 5% 2 6% 4 5% 7% 5% 8% 7% 40%	1330
July	1st to 10th	Night	8% 3 2 4 4 3 4 3 6% 9% 53%	2220
	11th to 20th	Night	6% 4 2 5% 3 4 4 3 6% 10% 53%	2220
	21st to end	Night	4 3 2 5% 4 4 5% 4 7% 8% 54%	2464
August	1st to 10th	Night	9% 4 2 5% 4 5% 5% 4 7% 8% 47%	2528
	11th to 20th	Night	8% 4 2 4 4 3 4 4 7% 10% 51%	2789
	21st to end	Night	12% 5% 2 6% 3 4 3 4 6% 7% 48%	3135
September	1st to 10th	Night	9% 5% 1 5% 4 3 4 4 6% 11% 49%	1806
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 3 6% 7% 43%	2090
	21st to end	Night	12% 6% 2 5% 5% 5% 4 4 5% 8% 43%	2090
October	1st to 10th	Night	11% 7% 3 7% 4 4 4 3 6% 8% 43%	3659
	11th to 20th	Night	8% 7% 3 8% 5% 5% 5% 5% 7% 9% 39%	3969
	21st to end	Night	9% 10% 3 9% 5% 5% 5% 4 6% 8% 35%	4467
November	1st to 10th	Night	13% 14% 4 11% 6% 6% 5% 4 5% 6% 25%	2692
	11th to 20th	Night	9% 15% 5% 13% 6% 6% 5% 4 6% 6% 25%	2712
	21st to end	Night	11% 14% 5% 11% 8% 6% 6% 4 6% 6% 23%	2850
December	1st to 10th	Night	6% 12% 5% 12% 9% 7% 8% 6% 5% 7% 23%	2850
	11th to 20th	Night	7% 14% 6% 13% 6% 6% 5% 5% 6% 7% 24%	3518
	21st to end	Night	6% 9% 4 10% 7% 5% 5% 4 7% 8% 35%	5225

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	60% 10% 15% 14% 2	2219
	11th to 20th	Day	66% 9% 9% 13% 3	2220
	21st to end	Day	58% 9% 13% 16% 5%	2775
February	1st to 10th	Day	58% 8% 12% 14% 6% 1	1532
	11th to 20th	Day	48% 9% 16% 19% 8%	1673
	21st to end	Day	49% 7% 13% 22% 9%	1517
March	1st to 10th	Day	51% 9% 14% 21% 5%	3130
	11th to 20th	Day	48% 13% 13% 19% 6%	3475
	21st to end	Day	40% 9% 14% 26% 10%	3831
April	1st to 10th	Day	44% 7% 13% 23% 12% 1	2355
	11th to 20th	Day	46% 7% 11% 20% 14% 1	2442
	21st to end	Day	42% 7% 15% 26% 7% 2	2470
May	1st to 10th	Day	41% 7% 12% 29% 10% 1	4353
	11th to 20th	Day	46% 9% 10% 23% 11% 2	4709
	21st to end	Day	43% 10% 12% 25% 10%	5173
June	1st to 10th	Day	44% 8% 15% 23% 9% 1	2850
	11th to 20th	Day	44% 8% 15% 22% 10% 1	2850
	21st to end	Day	41% 10% 20% 23% 6%	2850
July	1st to 10th	Day	35% 9% 25% 24% 6%	4676
	11th to 20th	Day	27% 8% 23% 37% 5%	4669
	21st to end	Day	27% 8% 25% 31% 8%	4937
August	1st to 10th	Day	32% 9% 21% 30% 7%	4396
	11th to 20th	Day	35% 7% 24% 30% 4	4089
	21st to end	Day	36% 8% 25% 26% 4	4531
September	1st to 10th	Day	34% 9% 20% 29% 8% 1	2371
	11th to 20th	Day	44% 9% 19% 23% 4	2090
	21st to end	Day	41% 9% 19% 24% 8%	2090
October	1st to 10th	Day	42% 7% 17% 30% 4	3268
	11th to 20th	Day	42% 7% 16% 28% 6%	2941
	21st to end	Day	54% 7% 18% 17% 4	3091
November	1st to 10th	Day	61% 7% 12% 15% 4 1	1605
	11th to 20th	Day	59% 11% 14% 11% 4	1473
	21st to end	Day	58% 8% 16% 14% 4	1330
December	1st to 10th	Day	63% 7% 14% 11% 4	1330
	11th to 20th	Day	58% 9% 16% 14% 4	1680
	21st to end	Day	44% 9% 15% 17% 14% 1	2442
January	1st to 10th	Night	54% 11% 14% 17% 5%	4737
	11th to 20th	Night	68% 8% 9% 12% 3	4750
	21st to end	Night	60% 10% 12% 14% 5%	4891
February	1st to 10th	Night	53% 7% 14% 17% 9%	2647
	11th to 20th	Night	42% 9% 17% 22% 9%	2404
	21st to end	Night	46% 6% 12% 27% 9%	1955
March	1st to 10th	Night	48% 8% 12% 25% 7%	3734
	11th to 20th	Night	36% 13% 16% 23% 11% 1	3485
	21st to end	Night	42% 8% 12% 27% 11% 1	3801
April	1st to 10th	Night	38% 6% 13% 23% 17% 3	1825
	11th to 20th	Night	47% 6% 9% 18% 16% 3	1689
	21st to end	Night	42% 7% 13% 24% 11% 2	1710
May	1st to 10th	Night	46% 8% 13% 23% 9% 1	2612
	11th to 20th	Night	45% 7% 13% 24% 10% 2	2201
	21st to end	Night	38% 11% 14% 25% 10% 1	2414
June	1st to 10th	Night	43% 9% 15% 23% 10% 1	1330
	11th to 20th	Night	40% 8% 17% 22% 11% 3	1330
	21st to end	Night	37% 12% 19% 25% 6% 1	1330
July	1st to 10th	Night	27% 8% 27% 30% 7%	2185
	11th to 20th	Night	24% 8% 24% 37% 7% 1	2178
	21st to end	Night	25% 8% 23% 31% 13% 1	2386
August	1st to 10th	Night	32% 9% 16% 31% 12%	2520
	11th to 20th	Night	27% 7% 25% 33% 7%	2816
	21st to end	Night	34% 7% 20% 31% 7%	3135
September	1st to 10th	Night	28% 7% 20% 31% 13% 1	1806
	11th to 20th	Night	37% 10% 18% 26% 8% 1	2090
	21st to end	Night	38% 8% 15% 29% 9% 1	2090
October	1st to 10th	Night	38% 6% 15% 29% 12%	3659
	11th to 20th	Night	39% 7% 15% 28% 10% 1	3969
	21st to end	Night	45% 8% 17% 26% 4	4467
November	1st to 10th	Night	58% 9% 15% 13% 5% 1	2692
	11th to 20th	Night	58% 10% 15% 12% 4	2712
	21st to end	Night	60% 9% 14% 13% 4	2850
December	1st to 10th	Night	58% 9% 16% 13% 5%	2850
	11th to 20th	Night	56% 8% 15% 14% 7%	3516
	21st to end	Night	46% 8% 12% 19% 14% 1	5225

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% 9% 36% 34% 9% 3	270
	11th to 20th	Day	8% 9% 37% 32% 13% 1	270
	21st to end	Day	14% 9% 30% 30% 15% 2	297
February	1st to 10th	Day	13% 8% 36% 33% 8% 2	270
	11th to 20th	Day	13% 8% 34% 30% 11% 4	270
	21st to end	Day	5% 12% 34% 29% 18% 1	225
March	1st to 10th	Day	15% 9% 34% 26% 14% 1	270
	11th to 20th	Day	12% 14% 36% 25% 10% 3	270
	21st to end	Day	13% 10% 31% 30% 15% 1	302
April	1st to 10th	Day	14% 10% 32% 31% 10% 2	535
	11th to 20th	Day	18% 9% 30% 30% 11% 1	640
	21st to end	Day	14% 10% 33% 31% 11% 1	650
May	1st to 10th	Day	14% 11% 32% 29% 13% 2	653
	11th to 20th	Day	18% 9% 27% 28% 14% 3	675
	21st to end	Day	19% 11% 25% 25% 18% 2	734
June	1st to 10th	Day	16% 11% 29% 25% 14% 5%	680
	11th to 20th	Day	16% 10% 31% 26% 13% 3	680
	21st to end	Day	14% 6% 24% 33% 19% 4	680
July	1st to 10th	Day	10% 6% 27% 30% 21% 6%	671
	11th to 20th	Day	11% 6% 29% 31% 17% 6%	668
	21st to end	Day	9% 7% 26% 29% 21% 8%	739
August	1st to 10th	Day	7% 7% 29% 29% 20% 6%	676
	11th to 20th	Day	12% 7% 22% 27% 23% 9%	665
	21st to end	Day	15% 9% 26% 28% 20% 3	748
September	1st to 10th	Day	12% 9% 31% 33% 13% 2	581
	11th to 20th	Day	20% 9% 36% 22% 13% 1	300
	21st to end	Day	20% 9% 35% 27% 8% 2	300
October	1st to 10th	Day	22% 13% 26% 25% 12% 3	300
	11th to 20th	Day	19% 12% 36% 23% 8% 1	300
	21st to end	Day	22% 14% 34% 21% 8% 2	330
November	1st to 10th	Day	23% 11% 32% 22% 11% 1	300
	11th to 20th	Day	14% 13% 38% 24% 9% 2	270
	21st to end	Day	20% 11% 37% 25% 5% 1	270
December	1st to 10th	Day	13% 9% 37% 23% 15% 3	270
	11th to 20th	Day	15% 11% 37% 27% 8% 2	270
	21st to end	Day	9% 6% 36% 29% 17% 3	297
January	1st to 10th	Night	11% 7% 34% 34% 12% 2	950
	11th to 20th	Night	14% 7% 33% 33% 11% 1	950
	21st to end	Night	15% 8% 32% 34% 11% 1	1045
February	1st to 10th	Night	13% 8% 30% 36% 12% 1	950
	11th to 20th	Night	9% 6% 32% 34% 17% 2	929
	21st to end	Night	9% 5% 31% 36% 16% 1	699
March	1st to 10th	Night	15% 7% 26% 34% 16% 2	760
	11th to 20th	Night	11% 8% 37% 33% 11% 1	575
	21st to end	Night	17% 7% 30% 31% 13% 3	627
April	1st to 10th	Night	10% 6% 35% 36% 12% 1	570
	11th to 20th	Night	17% 5% 30% 35% 12% 1	563
	21st to end	Night	12% 7% 35% 36% 9% 1	570
May	1st to 10th	Night	19% 7% 29% 34% 11% 1	570
	11th to 20th	Night	17% 8% 27% 34% 13% 2	561
	21st to end	Night	18% 8% 24% 35% 14%	617
June	1st to 10th	Night	17% 6% 27% 32% 18% 1	570
	11th to 20th	Night	17% 5% 26% 36% 14% 1	570
	21st to end	Night	13% 7% 18% 41% 20% 1	570
July	1st to 10th	Night	7% 3 24% 43% 22% 2	555
	11th to 20th	Night	9% 5% 27% 38% 19% 3	552
	21st to end	Night	7% 4 27% 33% 25% 4	624
August	1st to 10th	Night	8% 5% 22% 41% 22% 2	567
	11th to 20th	Night	10% 4 24% 38% 21% 5%	564
	21st to end	Night	15% 4 25% 36% 19% 2	627
September	1st to 10th	Night	10% 5% 30% 36% 17% 2	570
	11th to 20th	Night	13% 8% 27% 40% 11% 1	570
	21st to end	Night	14% 6% 33% 34% 12% 1	570
October	1st to 10th	Night	19% 9% 31% 32% 8%	671
	11th to 20th	Night	18% 7% 32% 31% 11% 1	874
	21st to end	Night	20% 11% 31% 29% 7% 1	1045
November	1st to 10th	Night	17% 11% 34% 26% 11% 2	975
	11th to 20th	Night	15% 12% 35% 26% 8% 3	953
	21st to end	Night	16% 11% 39% 27% 6% 1	950
December	1st to 10th	Night	10% 8% 31% 36% 13% 2	950
	11th to 20th	Night	14% 9% 37% 30% 9% 1	950
	21st to end	Night	15% 6% 33% 30% 14% 2	1045

Page generated at 2024-11-08 05:44:47. Version ac07

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