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 2024-04-03.

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% 4 8% 7% 4 6% 6% 6% 8% 33%	78151
	Night	8% 9% 4 8% 8% 4 6% 6% 6% 8% 33%	81934
Transparency	Day	46% 10% 18% 20% 6%	77853
	Night	47% 9% 16% 20% 8% 1	81812
Seeing	Day	13% 7% 26% 31% 18% 6%	14599
	Night	12% 6% 28% 36% 16% 2	23871

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% 14% 13% 6% 8% 6% 6% 6% 19%	2219
	11th to 20th	Day	4 9% 4 10% 9% 5% 7% 11% 9% 9% 23%	2199
	21st to end	Day	7% 12% 5% 10% 7% 4 6% 4 5% 7% 32%	2515
February	1st to 10th	Day	8% 12% 7% 11% 11% 6% 5% 5% 7% 8% 21%	1520
	11th to 20th	Day	6% 11% 7% 12% 8% 4 5% 7% 7% 7% 25%	1643
	21st to end	Day	5% 11% 6% 9% 8% 6% 7% 7% 6% 9% 26%	1413
March	1st to 10th	Day	7% 13% 6% 11% 9% 5% 7% 7% 7% 9% 20%	1913
	11th to 20th	Day	7% 12% 6% 9% 7% 2 5% 5% 6% 9% 33%	2089
	21st to end	Day	11% 13% 6% 11% 9% 4 5% 4 5% 7% 26%	2299
April	1st to 10th	Day	8% 13% 5% 7% 7% 5% 5% 5% 5% 7% 32%	2299
	11th to 20th	Day	12% 11% 3 8% 6% 3 5% 5% 6% 8% 31%	2310
	21st to end	Day	12% 10% 4 7% 6% 4 5% 6% 6% 9% 33%	2353
May	1st to 10th	Day	11% 8% 4 7% 8% 4 6% 5% 7% 7% 32%	2636
	11th to 20th	Day	10% 6% 3 5% 6% 4 6% 5% 6% 8% 41%	2654
	21st to end	Day	16% 7% 3 6% 6% 4 5% 5% 6% 8% 36%	2917
June	1st to 10th	Day	14% 8% 3 7% 7% 4 6% 6% 6% 7% 30%	2700
	11th to 20th	Day	19% 9% 4 7% 7% 4 6% 6% 7% 8% 22%	2700
	21st to end	Day	12% 6% 2 4 5% 4 7% 6% 9% 11% 33%	2700
July	1st to 10th	Day	11% 5% 2 6% 6% 4 5% 5% 7% 9% 39%	2700
	11th to 20th	Day	11% 6% 3 5% 6% 3 6% 7% 7% 11% 36%	2700
	21st to end	Day	9% 5% 2 5% 5% 4 6% 5% 6% 10% 44%	2938
August	1st to 10th	Day	11% 5% 2 5% 6% 4 5% 6% 7% 10% 39%	2641
	11th to 20th	Day	9% 5% 2 6% 6% 3 4 6% 6% 10% 43%	2344
	21st to end	Day	10% 6% 2 6% 5% 4 5% 5% 7% 8% 42%	2574
September	1st to 10th	Day	12% 6% 2 6% 5% 4 6% 5% 6% 7% 41%	2300
	11th to 20th	Day	14% 6% 2 6% 5% 4 6% 4 5% 7% 40%	1991
	21st to end	Day	9% 6% 3 6% 6% 3 6% 5% 6% 8% 42%	1980
October	1st to 10th	Day	12% 9% 4 8% 6% 4 5% 5% 5% 7% 35%	1836
	11th to 20th	Day	9% 9% 4 5% 6% 4 4 6% 5% 9% 39%	1688
	21st to end	Day	11% 11% 4 9% 7% 4 6% 6% 4 7% 31%	1710
November	1st to 10th	Day	9% 15% 5% 8% 8% 4 5% 6% 5% 7% 27%	1488
	11th to 20th	Day	8% 11% 5% 10% 8% 4 7% 7% 7% 8% 26%	1398
	21st to end	Day	4 11% 5% 13% 9% 4 7% 5% 5% 7% 30%	1330
December	1st to 10th	Day	7% 11% 5% 9% 11% 7% 7% 6% 6% 8% 24%	1330
	11th to 20th	Day	9% 9% 4 11% 7% 5% 7% 7% 7% 9% 24%	1682
	21st to end	Day	4 7% 4 8% 7% 4 6% 4 6% 9% 41%	2442
January	1st to 10th	Night	5% 10% 6% 15% 12% 6% 8% 7% 7% 6% 20%	4726
	11th to 20th	Night	3 8% 5% 8% 9% 6% 7% 8% 6% 7% 33%	4699
	21st to end	Night	7% 12% 5% 9% 8% 4 6% 6% 6% 8% 29%	5170
February	1st to 10th	Night	7% 12% 5% 10% 9% 5% 7% 6% 6% 9% 25%	2660
	11th to 20th	Night	6% 10% 5% 9% 9% 5% 6% 7% 7% 6% 30%	2423
	21st to end	Night	3 8% 5% 9% 8% 6% 7% 7% 6% 9% 30%	2040
March	1st to 10th	Night	6% 10% 5% 10% 9% 5% 6% 6% 7% 8% 29%	2266
	11th to 20th	Night	8% 10% 5% 8% 7% 4 6% 6% 7% 8% 33%	2090
	21st to end	Night	9% 12% 6% 10% 7% 3 5% 6% 7% 9% 27%	2299
April	1st to 10th	Night	8% 8% 4 7% 6% 4 6% 6% 7% 8% 34%	1703
	11th to 20th	Night	10% 9% 5% 9% 7% 5% 7% 5% 6% 7% 31%	1601
	21st to end	Night	12% 10% 5% 6% 5% 4 6% 4 6% 8% 36%	1606
May	1st to 10th	Night	13% 6% 3 7% 7% 5% 6% 7% 7% 8% 33%	1321
	11th to 20th	Night	11% 7% 3 5% 6% 5% 5% 5% 6% 8% 40%	1239
	21st to end	Night	17% 9% 3 6% 6% 5% 5% 5% 6% 6% 32%	1358
June	1st to 10th	Night	16% 7% 4 7% 7% 3 7% 6% 5% 7% 32%	1260
	11th to 20th	Night	19% 8% 3 7% 7% 4 6% 6% 7% 8% 26%	1260
	21st to end	Night	8% 6% 3 6% 5% 4 5% 5% 7% 9% 41%	1260
July	1st to 10th	Night	10% 6% 3 5% 6% 3 6% 5% 7% 10% 40%	1260
	11th to 20th	Night	10% 5% 3 6% 5% 3 5% 6% 8% 9% 39%	1260
	21st to end	Night	7% 5% 2 5% 4 3 4 6% 8% 9% 47%	1379
August	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 7% 8% 10% 41%	1296
	11th to 20th	Night	10% 4 1 5% 5% 4 6% 6% 7% 10% 42%	1555
	21st to end	Night	10% 6% 2 6% 6% 4 4 5% 6% 7% 43%	1782
September	1st to 10th	Night	13% 5% 3 6% 6% 4 5% 5% 4 7% 44%	1660
	11th to 20th	Night	12% 6% 2 4 5% 3 5% 5% 4 8% 47%	1966
	21st to end	Night	8% 6% 2 5% 5% 4 5% 5% 6% 7% 46%	1980
October	1st to 10th	Night	10% 9% 3 7% 6% 3 4 6% 6% 7% 39%	2124
	11th to 20th	Night	9% 10% 4 6% 6% 4 5% 5% 6% 7% 39%	2271
	21st to end	Night	9% 10% 5% 9% 7% 4 5% 5% 6% 7% 33%	2628
November	1st to 10th	Night	13% 14% 6% 9% 7% 4 5% 4 6% 6% 27%	2590
	11th to 20th	Night	8% 12% 5% 12% 9% 5% 6% 6% 6% 8% 24%	2778
	21st to end	Night	5% 11% 7% 11% 9% 4 5% 5% 7% 9% 28%	2850
December	1st to 10th	Night	8% 12% 6% 10% 9% 5% 6% 4 6% 8% 28%	2850
	11th to 20th	Night	7% 12% 7% 14% 10% 5% 6% 6% 6% 6% 23%	3510
	21st to end	Night	4 7% 3 7% 6% 5% 6% 6% 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	57% 10% 17% 13% 3	1913
	11th to 20th	Day	47% 8% 16% 19% 9%	2090
	21st to end	Day	58% 8% 14% 17% 3	2299
April	1st to 10th	Day	50% 9% 16% 17% 7% 1	2299
	11th to 20th	Day	48% 9% 15% 20% 7% 1	2310
	21st to end	Day	46% 9% 15% 22% 7% 1	2353
May	1st to 10th	Day	48% 9% 15% 19% 9%	2636
	11th to 20th	Day	39% 7% 14% 27% 12% 1	2658
	21st to end	Day	45% 8% 14% 22% 10% 1	2918
June	1st to 10th	Day	49% 10% 16% 18% 8%	2700
	11th to 20th	Day	56% 10% 15% 15% 3	2700
	21st to end	Day	40% 13% 21% 21% 5% 1	2700
July	1st to 10th	Day	39% 10% 23% 24% 4 1	2626
	11th to 20th	Day	40% 13% 27% 19% 2	2619
	21st to end	Day	34% 11% 27% 26% 2	2775
August	1st to 10th	Day	37% 13% 26% 21% 3	2623
	11th to 20th	Day	35% 10% 26% 24% 5%	2344
	21st to end	Day	37% 10% 23% 25% 5% 1	2574
September	1st to 10th	Day	40% 9% 18% 24% 6% 2	2300
	11th to 20th	Day	41% 10% 18% 26% 6%	1991
	21st to end	Day	38% 10% 17% 26% 9% 2	1980
October	1st to 10th	Day	47% 8% 19% 19% 7%	1836
	11th to 20th	Day	41% 9% 17% 25% 8%	1688
	21st to end	Day	51% 10% 12% 21% 5%	1710
November	1st to 10th	Day	54% 9% 16% 15% 6% 1	1488
	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	50% 9% 16% 20% 6%	2266
	11th to 20th	Night	46% 8% 13% 21% 10% 1	2090
	21st to end	Night	51% 9% 15% 16% 7% 1	2299
April	1st to 10th	Night	43% 9% 16% 20% 12% 1	1703
	11th to 20th	Night	49% 8% 14% 17% 11% 2	1601
	21st to end	Night	45% 8% 13% 21% 10% 2	1606
May	1st to 10th	Night	45% 9% 13% 22% 10% 1	1321
	11th to 20th	Night	41% 7% 12% 26% 13% 2	1239
	21st to end	Night	50% 7% 12% 19% 10% 1	1358
June	1st to 10th	Night	49% 8% 13% 20% 8% 2	1260
	11th to 20th	Night	53% 11% 15% 16% 5%	1260
	21st to end	Night	38% 11% 22% 23% 5% 1	1260
July	1st to 10th	Night	37% 11% 20% 24% 7% 1	1225
	11th to 20th	Night	37% 12% 25% 23% 4	1218
	21st to end	Night	28% 11% 27% 29% 5%	1302
August	1st to 10th	Night	34% 12% 25% 26% 3	1289
	11th to 20th	Night	35% 11% 22% 26% 6%	1555
	21st to end	Night	37% 9% 16% 29% 9%	1782
September	1st to 10th	Night	38% 8% 20% 23% 8% 2	1660
	11th to 20th	Night	35% 8% 18% 28% 10% 1	1966
	21st to end	Night	36% 8% 15% 26% 13% 2	1980
October	1st to 10th	Night	41% 8% 16% 23% 11% 1	2124
	11th to 20th	Night	42% 7% 16% 26% 8% 1	2271
	21st to end	Night	48% 9% 13% 22% 7% 1	2628
November	1st to 10th	Night	56% 7% 12% 19% 6%	2590
	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	7% 9% 34% 35% 12% 3	429
	11th to 20th	Day	15% 8% 26% 32% 15% 4	412
	21st to end	Day	17% 8% 28% 29% 15% 3	433
May	1st to 10th	Day	12% 10% 25% 32% 15% 6%	603
	11th to 20th	Day	11% 7% 24% 32% 19% 8%	625
	21st to end	Day	17% 6% 22% 30% 19% 6%	679
June	1st to 10th	Day	16% 8% 27% 33% 13% 3	630
	11th to 20th	Day	20% 9% 24% 24% 17% 6%	630
	21st to end	Day	12% 6% 18% 30% 24% 10%	630
July	1st to 10th	Day	12% 4 19% 32% 24% 8%	621
	11th to 20th	Day	11% 6% 20% 34% 23% 6%	618
	21st to end	Day	9% 5% 21% 31% 25% 10%	684
August	1st to 10th	Day	13% 4 18% 31% 23% 11%	581
	11th to 20th	Day	8% 6% 27% 32% 22% 6%	437
	21st to end	Day	10% 8% 22% 33% 18% 9%	495
September	1st to 10th	Day	14% 8% 31% 24% 18% 5%	450
	11th to 20th	Day	16% 9% 25% 32% 16% 2	450
	21st to end	Day	12% 12% 32% 25% 17% 3	450
October	1st to 10th	Day	14% 10% 25% 27% 20% 3	306
	11th to 20th	Day	17% 4 34% 31% 13% 1	270
	21st to end	Day	19% 12% 33% 20% 12% 3	297
November	1st to 10th	Day	14% 8% 29% 34% 13% 2	270
	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% 37% 17% 3	836
April	1st to 10th	Night	10% 6% 26% 38% 18% 4	599
	11th to 20th	Night	14% 4 30% 34% 16% 2	533
	21st to end	Night	16% 6% 24% 38% 15% 1	540
May	1st to 10th	Night	15% 7% 22% 33% 20% 4	421
	11th to 20th	Night	14% 7% 20% 39% 18% 3	354
	21st to end	Night	20% 5% 20% 34% 20% 2	389
June	1st to 10th	Night	16% 8% 20% 41% 14% 1	360
	11th to 20th	Night	22% 6% 20% 29% 21% 2	360
	21st to end	Night	13% 3 17% 36% 27% 4	360
July	1st to 10th	Night	12% 2 19% 41% 26%	350
	11th to 20th	Night	11% 4 19% 43% 21% 1	348
	21st to end	Night	8% 4 16% 42% 25% 5%	394
August	1st to 10th	Night	10% 4 15% 37% 30% 4	358
	11th to 20th	Night	11% 5% 20% 38% 25% 2	487
	21st to end	Night	12% 3 23% 38% 24% 1	594
September	1st to 10th	Night	14% 4 22% 37% 22% 2	540
	11th to 20th	Night	13% 5% 21% 41% 19% 1	706
	21st to end	Night	12% 5% 29% 37% 16% 1	720
October	1st to 10th	Night	15% 4 28% 35% 16% 1	720
	11th to 20th	Night	15% 5% 29% 37% 13% 2	720
	21st to end	Night	14% 8% 32% 33% 13% 1	846
November	1st to 10th	Night	18% 6% 30% 34% 10% 2	925
	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 2024-03-31 04:08:54. Version ac07

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