Andrew
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Andrew 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	10% 9% 3 9% 6% 5% 5% 4 6% 8% 34%	105681
	Night	8% 9% 4 9% 6% 6% 5% 5% 7% 8% 33%	101906
Transparency	Day	45% 8% 18% 22% 7%	105423
	Night	46% 8% 17% 21% 8% 1	101810
Seeing	Day	13% 7% 26% 31% 18% 6%	15526
	Night	12% 6% 28% 36% 16% 2	24479

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	4 12% 5% 16% 11% 7% 8% 5% 6% 6% 19%	2219
	11th to 20th	Day	4 9% 3 12% 8% 6% 9% 8% 9% 9% 23%	2199
	21st to end	Day	7% 13% 4 11% 6% 5% 5% 3 5% 7% 32%	2515
February	1st to 10th	Day	8% 13% 6% 13% 9% 7% 4 4 7% 8% 21%	1520
	11th to 20th	Day	6% 12% 6% 14% 7% 6% 6% 5% 7% 7% 25%	1643
	21st to end	Day	5% 14% 4 10% 8% 8% 6% 6% 6% 9% 26%	1413
March	1st to 10th	Day	4 11% 5% 12% 8% 5% 7% 5% 7% 9% 26%	3163
	11th to 20th	Day	4 10% 4 14% 6% 4 4 3 6% 10% 35%	3489
	21st to end	Day	9% 13% 5% 15% 7% 5% 5% 3 6% 8% 24%	3825
April	1st to 10th	Day	8% 14% 4 9% 7% 6% 5% 4 5% 7% 31%	2402
	11th to 20th	Day	11% 11% 3 9% 5% 5% 5% 4 7% 8% 31%	2440
	21st to end	Day	13% 10% 3 8% 4 5% 5% 4 7% 8% 32%	2484
May	1st to 10th	Day	16% 9% 4 9% 6% 5% 5% 4 6% 6% 30%	4637
	11th to 20th	Day	14% 11% 3 7% 5% 5% 6% 4 6% 8% 30%	4694
	21st to end	Day	11% 9% 4 10% 7% 6% 6% 4 7% 9% 28%	5161
June	1st to 10th	Day	14% 9% 3 8% 6% 6% 6% 5% 7% 7% 30%	2850
	11th to 20th	Day	19% 10% 4 8% 7% 5% 6% 4 7% 8% 23%	2850
	21st to end	Day	12% 6% 2 5% 5% 6% 6% 5% 9% 10% 34%	2850
July	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 4 6% 9% 47%	4740
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 46%	4740
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 8% 44%	5138
August	1st to 10th	Day	12% 7% 3 6% 4 4 5% 4 5% 8% 44%	4633
	11th to 20th	Day	8% 5% 3 6% 4 5% 5% 4 7% 10% 43%	4097
	21st to end	Day	10% 4 2 5% 5% 4 5% 4 7% 9% 44%	4521
September	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 4 6% 7% 43%	2427
	11th to 20th	Day	13% 6% 2 7% 5% 5% 6% 3 5% 7% 40%	2101
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 4 6% 8% 42%	2090
October	1st to 10th	Day	10% 8% 3 8% 5% 5% 5% 5% 6% 8% 37%	3234
	11th to 20th	Day	10% 9% 3 7% 5% 5% 4 4 5% 9% 38%	2949
	21st to end	Day	7% 12% 4 9% 5% 6% 5% 5% 5% 7% 36%	2963
November	1st to 10th	Day	9% 16% 4 10% 7% 5% 6% 4 5% 7% 27%	1512
	11th to 20th	Day	7% 12% 5% 13% 6% 6% 6% 5% 7% 8% 26%	1398
	21st to end	Day	4 12% 4 14% 7% 5% 7% 3 5% 7% 30%	1330
December	1st to 10th	Day	6% 12% 4 10% 10% 9% 6% 5% 6% 8% 24%	1330
	11th to 20th	Day	9% 10% 4 12% 7% 7% 7% 4 7% 9% 24%	1682
	21st to end	Day	4 8% 3 9% 6% 6% 5% 3 6% 9% 40%	2442
January	1st to 10th	Night	4 11% 5% 18% 9% 8% 7% 5% 7% 6% 20%	4726
	11th to 20th	Night	3 9% 4 9% 9% 7% 7% 7% 6% 7% 33%	4699
	21st to end	Night	7% 13% 5% 11% 7% 5% 5% 5% 6% 8% 29%	5170
February	1st to 10th	Night	6% 13% 5% 11% 8% 7% 7% 4 6% 8% 25%	2660
	11th to 20th	Night	6% 11% 5% 11% 7% 7% 5% 6% 7% 6% 30%	2423
	21st to end	Night	3 10% 5% 10% 8% 8% 7% 5% 7% 9% 30%	2040
March	1st to 10th	Night	4 11% 5% 11% 7% 6% 6% 6% 8% 9% 26%	3710
	11th to 20th	Night	4 8% 4 10% 6% 6% 6% 4 7% 9% 36%	3490
	21st to end	Night	7% 11% 6% 14% 8% 6% 5% 5% 7% 8% 22%	3828
April	1st to 10th	Night	8% 9% 3 8% 6% 6% 7% 5% 7% 8% 33%	1775
	11th to 20th	Night	10% 9% 5% 10% 6% 6% 7% 4 7% 6% 30%	1691
	21st to end	Night	12% 11% 4 7% 5% 5% 5% 4 6% 7% 36%	1695
May	1st to 10th	Night	21% 8% 3 8% 5% 6% 5% 4 5% 6% 30%	2323
	11th to 20th	Night	14% 10% 3 8% 5% 5% 5% 4 7% 8% 31%	2199
	21st to end	Night	13% 10% 3 9% 5% 5% 6% 4 7% 9% 29%	2414
June	1st to 10th	Night	15% 7% 4 9% 5% 5% 7% 5% 5% 7% 31%	1330
	11th to 20th	Night	18% 8% 3 8% 7% 5% 6% 5% 7% 8% 26%	1330
	21st to end	Night	8% 7% 3 7% 4 5% 5% 4 7% 9% 40%	1330
July	1st to 10th	Night	8% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	2220
	11th to 20th	Night	7% 5% 2 5% 5% 4 5% 4 8% 10% 45%	2220
	21st to end	Night	14% 6% 2 5% 3 3 3 5% 6% 8% 45%	2414
August	1st to 10th	Night	12% 6% 2 7% 5% 4 4 4 6% 7% 42%	2295
	11th to 20th	Night	10% 6% 2 7% 5% 6% 5% 5% 7% 9% 39%	2738
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 8% 46%	3146
September	1st to 10th	Night	12% 5% 3 7% 4 5% 5% 3 5% 7% 45%	1753
	11th to 20th	Night	12% 6% 2 5% 4 4 5% 4 4 8% 46%	2076
	21st to end	Night	9% 6% 2 6% 5% 4 5% 4 6% 8% 45%	2090
October	1st to 10th	Night	7% 8% 2 8% 5% 5% 5% 4 7% 9% 40%	3738
	11th to 20th	Night	10% 8% 2 6% 5% 4 5% 4 7% 8% 40%	3978
	21st to end	Night	8% 10% 4 9% 5% 4 5% 4 7% 9% 34%	4564
November	1st to 10th	Night	13% 15% 5% 9% 6% 5% 4 4 6% 6% 27%	2639
	11th to 20th	Night	8% 13% 5% 13% 8% 6% 5% 4 7% 8% 24%	2778
	21st to end	Night	5% 12% 5% 13% 8% 5% 5% 4 7% 8% 28%	2850
December	1st to 10th	Night	7% 14% 4 11% 8% 5% 5% 4 6% 7% 28%	2850
	11th to 20th	Night	7% 12% 6% 15% 8% 7% 5% 5% 6% 6% 22%	3510
	21st to end	Night	4 8% 3 8% 5% 6% 6% 5% 7% 7% 42%	5214

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	58% 11% 11% 15% 4	2219
	11th to 20th	Day	50% 9% 14% 15% 11% 1	2220
	21st to end	Day	49% 9% 17% 18% 6%	2515
February	1st to 10th	Day	59% 7% 15% 13% 7%	1520
	11th to 20th	Day	54% 8% 16% 15% 7%	1652
	21st to end	Day	52% 8% 15% 18% 7%	1413
March	1st to 10th	Day	50% 10% 17% 18% 5%	3163
	11th to 20th	Day	43% 8% 23% 19% 7%	3490
	21st to end	Day	54% 10% 14% 19% 3	3825
April	1st to 10th	Day	50% 9% 16% 17% 7% 1	2402
	11th to 20th	Day	48% 9% 15% 21% 8% 1	2440
	21st to end	Day	46% 9% 15% 22% 7% 1	2484
May	1st to 10th	Day	51% 8% 13% 22% 6%	4637
	11th to 20th	Day	47% 9% 12% 22% 9% 1	4698
	21st to end	Day	45% 12% 18% 17% 8%	5162
June	1st to 10th	Day	48% 10% 16% 18% 8% 1	2850
	11th to 20th	Day	56% 10% 15% 16% 4	2850
	21st to end	Day	40% 13% 20% 21% 6% 1	2850
July	1st to 10th	Day	35% 6% 23% 28% 8%	4666
	11th to 20th	Day	34% 7% 18% 28% 12%	4659
	21st to end	Day	38% 7% 22% 26% 7%	4976
August	1st to 10th	Day	39% 7% 19% 32% 3	4615
	11th to 20th	Day	36% 6% 25% 25% 8%	4137
	21st to end	Day	36% 6% 28% 27% 3	4520
September	1st to 10th	Day	39% 9% 18% 26% 7% 2	2427
	11th to 20th	Day	41% 9% 18% 27% 6%	2101
	21st to end	Day	37% 10% 17% 25% 9% 2	2090
October	1st to 10th	Day	45% 4 22% 24% 4	3234
	11th to 20th	Day	43% 5% 16% 28% 8%	2949
	21st to end	Day	47% 6% 17% 26% 3	2963
November	1st to 10th	Day	54% 9% 16% 15% 6% 1	1512
	11th to 20th	Day	53% 9% 19% 16% 3	1398
	21st to end	Day	50% 10% 17% 17% 5% 1	1330
December	1st to 10th	Day	56% 9% 13% 14% 7% 1	1330
	11th to 20th	Day	52% 10% 16% 16% 6%	1684
	21st to end	Day	39% 7% 13% 29% 11% 1	2442
January	1st to 10th	Night	58% 11% 11% 13% 5% 1	4726
	11th to 20th	Night	47% 7% 14% 19% 11% 1	4740
	21st to end	Night	50% 9% 20% 16% 6%	5170
February	1st to 10th	Night	54% 8% 14% 16% 7% 1	2660
	11th to 20th	Night	50% 10% 13% 16% 10%	2424
	21st to end	Night	47% 9% 13% 21% 9% 1	2040
March	1st to 10th	Night	48% 9% 17% 20% 6%	3710
	11th to 20th	Night	39% 10% 20% 21% 9% 1	3490
	21st to end	Night	51% 13% 14% 16% 5%	3828
April	1st to 10th	Night	44% 9% 15% 20% 12% 1	1775
	11th to 20th	Night	49% 8% 14% 17% 11% 2	1691
	21st to end	Night	45% 8% 13% 21% 11% 2	1695
May	1st to 10th	Night	52% 7% 10% 23% 7% 1	2323
	11th to 20th	Night	46% 10% 13% 22% 9% 1	2199
	21st to end	Night	45% 12% 17% 18% 7% 1	2414
June	1st to 10th	Night	49% 8% 13% 20% 8% 2	1330
	11th to 20th	Night	52% 11% 15% 17% 5%	1330
	21st to end	Night	39% 10% 21% 23% 6% 1	1330
July	1st to 10th	Night	37% 8% 19% 20% 15% 1	2185
	11th to 20th	Night	33% 6% 18% 32% 9% 1	2178
	21st to end	Night	36% 6% 23% 27% 7%	2337
August	1st to 10th	Night	40% 7% 19% 32% 2	2288
	11th to 20th	Night	40% 7% 21% 24% 8%	2764
	21st to end	Night	35% 5% 25% 29% 6%	3146
September	1st to 10th	Night	37% 8% 19% 25% 10% 2	1753
	11th to 20th	Night	36% 8% 17% 28% 10% 1	2076
	21st to end	Night	37% 8% 15% 25% 13% 2	2090
October	1st to 10th	Night	40% 4 22% 27% 7%	3738
	11th to 20th	Night	40% 4 15% 34% 7%	3978
	21st to end	Night	45% 5% 22% 22% 4	4564
November	1st to 10th	Night	56% 7% 12% 19% 6%	2639
	11th to 20th	Night	56% 9% 14% 16% 5%	2778
	21st to end	Night	52% 9% 18% 16% 4	2850
December	1st to 10th	Night	54% 7% 13% 17% 8% 1	2850
	11th to 20th	Night	58% 10% 14% 12% 6%	3507
	21st to end	Night	37% 8% 16% 20% 16% 2	5214

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% 5% 27% 36% 19% 4	180
	11th to 20th	Day	10% 11% 23% 37% 14% 6%	180
	21st to end	Day	9% 6% 39% 29% 13% 5%	198
February	1st to 10th	Day	10% 11% 23% 39% 14% 3	180
	11th to 20th	Day	8% 6% 30% 35% 17% 4	260
	21st to end	Day	9% 4 32% 29% 18% 8%	225
March	1st to 10th	Day	10% 7% 30% 34% 16% 2	460
	11th to 20th	Day	10% 6% 33% 31% 14% 6%	460
	21st to end	Day	15% 5% 29% 31% 17% 3	506
April	1st to 10th	Day	8% 10% 33% 34% 11% 3	460
	11th to 20th	Day	14% 9% 27% 32% 14% 4	452
	21st to end	Day	18% 8% 27% 29% 14% 3	474
May	1st to 10th	Day	13% 10% 25% 31% 15% 6%	653
	11th to 20th	Day	12% 8% 25% 31% 17% 7%	675
	21st to end	Day	16% 7% 22% 29% 19% 7%	734
June	1st to 10th	Day	16% 10% 27% 31% 12% 3	680
	11th to 20th	Day	19% 9% 24% 24% 17% 7%	680
	21st to end	Day	12% 5% 18% 31% 23% 10%	680
July	1st to 10th	Day	11% 4 18% 33% 25% 9%	671
	11th to 20th	Day	11% 6% 19% 33% 24% 7%	668
	21st to end	Day	10% 4 21% 30% 24% 10%	739
August	1st to 10th	Day	13% 4 18% 30% 24% 11%	628
	11th to 20th	Day	7% 6% 26% 31% 22% 7%	477
	21st to end	Day	10% 8% 23% 34% 17% 9%	539
September	1st to 10th	Day	13% 8% 29% 24% 19% 6%	490
	11th to 20th	Day	16% 9% 25% 31% 17% 2	490
	21st to end	Day	12% 12% 33% 25% 16% 3	490
October	1st to 10th	Day	14% 9% 27% 27% 19% 3	338
	11th to 20th	Day	17% 5% 33% 32% 11% 1	300
	21st to end	Day	17% 13% 35% 21% 11% 4	330
November	1st to 10th	Day	13% 8% 29% 33% 14% 2	279
	11th to 20th	Day	10% 8% 32% 37% 12% 1	212
	21st to end	Day	4 8% 39% 29% 11% 8%	180
December	1st to 10th	Day	8% 7% 38% 28% 14% 4	180
	11th to 20th	Day	11% 7% 31% 32% 17% 2	180
	21st to end	Day	10% 4 26% 37% 16% 7%	198
January	1st to 10th	Night	11% 7% 32% 36% 12% 2	950
	11th to 20th	Night	9% 8% 31% 38% 13% 2	950
	21st to end	Night	12% 10% 31% 33% 12% 2	1014
February	1st to 10th	Night	11% 7% 28% 35% 17% 3	760
	11th to 20th	Night	9% 5% 32% 36% 16% 2	744
	21st to end	Night	7% 4 26% 41% 18% 5%	628
March	1st to 10th	Night	10% 5% 26% 43% 14% 2	760
	11th to 20th	Night	11% 6% 29% 36% 15% 3	760
	21st to end	Night	12% 6% 26% 36% 17% 3	836
April	1st to 10th	Night	10% 6% 26% 38% 17% 3	623
	11th to 20th	Night	14% 5% 29% 34% 16% 2	563
	21st to end	Night	16% 6% 25% 38% 15% 1	570
May	1st to 10th	Night	16% 7% 22% 33% 19% 3	444
	11th to 20th	Night	14% 7% 21% 39% 17% 2	374
	21st to end	Night	18% 5% 20% 34% 20% 2	411
June	1st to 10th	Night	16% 8% 21% 39% 14% 1	380
	11th to 20th	Night	22% 6% 20% 29% 21% 2	380
	21st to end	Night	13% 3 18% 35% 27% 4	380
July	1st to 10th	Night	12% 2 19% 41% 26%	370
	11th to 20th	Night	11% 4 18% 43% 22% 2	368
	21st to end	Night	9% 4 16% 41% 25% 5%	416
August	1st to 10th	Night	10% 4 15% 37% 31% 4	378
	11th to 20th	Night	11% 4 19% 39% 25% 2	515
	21st to end	Night	11% 3 24% 38% 23% 1	627
September	1st to 10th	Night	13% 5% 22% 37% 22% 2	570
	11th to 20th	Night	13% 5% 21% 41% 19% 1	746
	21st to end	Night	12% 5% 31% 36% 15% 1	760
October	1st to 10th	Night	15% 4 29% 36% 16% 1	760
	11th to 20th	Night	15% 5% 29% 37% 12% 2	760
	21st to end	Night	14% 8% 32% 33% 13% 1	894
November	1st to 10th	Night	19% 6% 30% 34% 10% 2	943
	11th to 20th	Night	13% 7% 33% 32% 12% 3	950
	21st to end	Night	7% 7% 39% 34% 11% 2	950
December	1st to 10th	Night	13% 6% 33% 31% 14% 3	950
	11th to 20th	Night	11% 7% 34% 34% 12% 2	950
	21st to end	Night	11% 3 30% 36% 16% 4	1045

Page generated at 2024-11-01 20:47:51. Version ac07

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