Due West
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Due West clear sky chart from 2005-11-06 to 2024-04-10.

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	14% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	83536
	Night	14% 6% 2 5% 5% 3 4 5% 5% 7% 44%	85248
Transparency	Day	38% 6% 11% 20% 19% 5%	83259
	Night	38% 6% 10% 19% 21% 7%	85044
Seeing	Day	17% 9% 23% 24% 19% 9%	14294
	Night	16% 8% 22% 30% 20% 4	24467

By Month

Percentage Cloud Cover SE (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	17% 4 2 4 5% 3 4 4 5% 8% 46%	2836
	11th to 20th	Day	14% 5% 2 3 4 2 4 4 3 6% 53%	2840
	21st to end	Day	24% 7% 2 3 3 2 3 3 3 5% 45%	3124
February	1st to 10th	Day	15% 6% 2 5% 6% 2 5% 5% 6% 7% 42%	1819
	11th to 20th	Day	21% 5% 2 5% 4 2 4 3 4 5% 44%	1848
	21st to end	Day	20% 6% 2 5% 5% 3 4 3 5% 5% 42%	1570
March	1st to 10th	Day	23% 8% 3 5% 4 2 4 3 4 5% 39%	3395
	11th to 20th	Day	11% 5% 2 4 4 3 4 5% 5% 6% 52%	3480
	21st to end	Day	20% 6% 2 6% 4 3 4 4 4 5% 42%	3815
April	1st to 10th	Day	11% 4 2 5% 5% 3 4 5% 6% 7% 49%	2080
	11th to 20th	Day	12% 4 2 5% 5% 3 4 4 5% 7% 48%	2094
	21st to end	Day	10% 4 2 4 4 2 4 4 6% 8% 52%	2340
May	1st to 10th	Day	8% 4 3 5% 5% 3 4 6% 6% 8% 48%	2340
	11th to 20th	Day	12% 5% 2 5% 6% 4 5% 5% 6% 9% 41%	2301
	21st to end	Day	11% 6% 2 5% 5% 3 5% 5% 8% 9% 41%	2531
June	1st to 10th	Day	9% 6% 2 6% 6% 4 6% 6% 9% 11% 36%	2340
	11th to 20th	Day	6% 4 2 5% 6% 4 6% 7% 8% 10% 43%	2340
	21st to end	Day	5% 4 2 5% 7% 5% 7% 6% 8% 12% 38%	2340
July	1st to 10th	Day	8% 6% 3 5% 8% 4 6% 7% 8% 11% 33%	2340
	11th to 20th	Day	7% 6% 2 6% 6% 4 7% 8% 9% 13% 33%	2340
	21st to end	Day	6% 4 3 6% 7% 5% 6% 7% 9% 12% 35%	2547
August	1st to 10th	Day	9% 6% 3 7% 7% 5% 8% 7% 8% 11% 29%	2327
	11th to 20th	Day	13% 5% 2 5% 7% 5% 6% 7% 7% 11% 32%	2303
	21st to end	Day	11% 6% 3 7% 8% 4 7% 7% 7% 10% 30%	2342
September	1st to 10th	Day	8% 5% 3 6% 6% 4 6% 6% 8% 10% 40%	1980
	11th to 20th	Day	12% 7% 2 5% 5% 3 4 6% 6% 9% 41%	1980
	21st to end	Day	15% 6% 2 4 5% 3 5% 5% 5% 6% 44%	1980
October	1st to 10th	Day	14% 5% 2 4 3 2 4 3 4 6% 55%	1953
	11th to 20th	Day	12% 5% 2 3 4 1 3 3 5% 6% 56%	1800
	21st to end	Day	11% 4 2 4 4 3 3 3 3 4 58%	1980
November	1st to 10th	Day	13% 5% 2 4 3 2 3 2 4 5% 55%	1824
	11th to 20th	Day	14% 5% 2 4 4 2 4 4 4 7% 52%	1710
	21st to end	Day	14% 5% 2 4 4 3 3 4 5% 6% 50%	1710
December	1st to 10th	Day	20% 8% 3 4 5% 2 4 4 4 6% 40%	1710
	11th to 20th	Day	18% 5% 2 5% 3 2 3 4 5% 5% 48%	2153
	21st to end	Day	22% 6% 2 4 4 3 3 4 5% 6% 41%	3124
January	1st to 10th	Night	18% 5% 2 4 4 3 4 4 4 6% 47%	4109
	11th to 20th	Night	11% 6% 2 5% 5% 3 5% 5% 5% 6% 47%	4120
	21st to end	Night	22% 8% 2 5% 4 2 3 3 3 4 45%	4532
February	1st to 10th	Night	16% 6% 2 4 5% 3 5% 4 4 6% 46%	2356
	11th to 20th	Night	19% 6% 2 5% 4 2 4 4 3 5% 45%	2218
	21st to end	Night	17% 6% 2 5% 4 3 4 4 5% 7% 44%	1884
March	1st to 10th	Night	22% 7% 3 5% 4 2 4 4 5% 7% 37%	3456
	11th to 20th	Night	12% 4 2 3 3 3 4 5% 5% 8% 51%	3480
	21st to end	Night	19% 5% 2 5% 5% 3 4 4 4 6% 42%	3817
April	1st to 10th	Night	11% 4 2 4 4 3 4 4 5% 7% 49%	2090
	11th to 20th	Night	11% 5% 2 5% 4 3 3 3 4 6% 53%	1827
	21st to end	Night	9% 4 2 5% 4 2 4 5% 5% 6% 53%	1620
May	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 4 6% 8% 48%	1620
	11th to 20th	Night	10% 5% 3 6% 7% 5% 6% 6% 7% 8% 38%	1592
	21st to end	Night	11% 4 2 6% 8% 3 5% 5% 8% 9% 39%	1744
June	1st to 10th	Night	11% 5% 2 5% 6% 4 6% 5% 10% 11% 35%	1620
	11th to 20th	Night	7% 5% 2 5% 6% 4 4 6% 8% 13% 40%	1620
	21st to end	Night	9% 5% 2 6% 6% 3 6% 8% 9% 11% 37%	1620
July	1st to 10th	Night	8% 6% 3 7% 7% 5% 8% 7% 9% 13% 27%	1620
	11th to 20th	Night	6% 5% 3 7% 5% 4 7% 8% 9% 13% 32%	1620
	21st to end	Night	6% 5% 3 6% 7% 5% 6% 8% 8% 13% 33%	1771
August	1st to 10th	Night	10% 5% 3 6% 7% 4 6% 8% 10% 13% 28%	1611
	11th to 20th	Night	10% 5% 4 7% 7% 5% 5% 6% 8% 10% 34%	1598
	21st to end	Night	10% 6% 3 6% 6% 6% 6% 7% 8% 10% 32%	1988
September	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 6% 6% 10% 42%	1980
	11th to 20th	Night	13% 7% 3 6% 5% 4 4 6% 7% 9% 38%	1980
	21st to end	Night	12% 6% 2 6% 5% 3 4 4 5% 7% 46%	1980
October	1st to 10th	Night	11% 5% 2 5% 4 2 3 4 4 5% 54%	2006
	11th to 20th	Night	12% 5% 2 4 4 2 4 4 4 5% 54%	2160
	21st to end	Night	12% 4 2 4 4 2 4 3 4 5% 57%	2376
November	1st to 10th	Night	12% 6% 2 4 4 2 3 3 4 5% 57%	2249
	11th to 20th	Night	15% 5% 2 3 4 2 3 4 4 5% 53%	2470
	21st to end	Night	16% 4 2 4 4 2 4 5% 5% 6% 48%	2470
December	1st to 10th	Night	17% 7% 3 5% 5% 3 4 4 5% 6% 43%	2470
	11th to 20th	Night	17% 6% 2 4 3 2 2 3 3 5% 52%	3042
	21st to end	Night	20% 7% 2 5% 5% 3 5% 4 5% 7% 38%	4532

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	38% 3 6% 23% 22% 7%	2837
	11th to 20th	Day	34% 3 6% 20% 29% 8%	2840
	21st to end	Day	43% 3 3 18% 26% 7%	3124
February	1st to 10th	Day	41% 4 9% 20% 20% 6%	1819
	11th to 20th	Day	42% 4 5% 19% 23% 6%	1858
	21st to end	Day	45% 3 8% 15% 21% 8%	1570
March	1st to 10th	Day	49% 4 7% 16% 14% 11%	3395
	11th to 20th	Day	33% 5% 7% 16% 28% 11%	3480
	21st to end	Day	45% 4 6% 19% 21% 4	3815
April	1st to 10th	Day	35% 4 11% 19% 26% 5%	2080
	11th to 20th	Day	36% 4 9% 20% 20% 10%	2094
	21st to end	Day	30% 5% 11% 29% 21% 4	2340
May	1st to 10th	Day	31% 7% 14% 23% 20% 5%	2340
	11th to 20th	Day	39% 7% 16% 22% 15% 1	2305
	21st to end	Day	37% 7% 14% 25% 15% 2	2531
June	1st to 10th	Day	38% 9% 17% 25% 10% 2	2340
	11th to 20th	Day	32% 9% 19% 26% 13% 1	2340
	21st to end	Day	35% 11% 18% 20% 13% 3	2340
July	1st to 10th	Day	41% 9% 19% 19% 10% 2	2275
	11th to 20th	Day	37% 13% 21% 19% 8% 2	2271
	21st to end	Day	35% 12% 21% 21% 10% 1	2405
August	1st to 10th	Day	45% 10% 17% 20% 8%	2314
	11th to 20th	Day	44% 9% 17% 18% 10% 2	2303
	21st to end	Day	45% 11% 16% 17% 9% 3	2342
September	1st to 10th	Day	37% 9% 14% 19% 19% 3	1980
	11th to 20th	Day	39% 7% 11% 18% 22% 2	1980
	21st to end	Day	39% 5% 10% 21% 18% 6%	1980
October	1st to 10th	Day	32% 4 9% 22% 27% 7%	1953
	11th to 20th	Day	31% 3 9% 25% 24% 9%	1800
	21st to end	Day	32% 4 4 20% 30% 10%	1980
November	1st to 10th	Day	34% 3 7% 18% 29% 10%	1824
	11th to 20th	Day	34% 3 6% 22% 25% 10%	1710
	21st to end	Day	35% 4 8% 22% 24% 7%	1710
December	1st to 10th	Day	46% 4 7% 20% 17% 6%	1710
	11th to 20th	Day	38% 3 7% 20% 20% 12%	2150
	21st to end	Day	44% 3 6% 21% 23% 3	3124
January	1st to 10th	Night	38% 4 6% 18% 27% 7%	4109
	11th to 20th	Night	37% 4 6% 18% 26% 8%	4120
	21st to end	Night	45% 3 4 16% 25% 7%	4532
February	1st to 10th	Night	41% 4 8% 20% 21% 7%	2356
	11th to 20th	Night	43% 4 5% 18% 23% 8%	2219
	21st to end	Night	40% 5% 7% 18% 20% 10%	1884
March	1st to 10th	Night	46% 5% 10% 15% 16% 8%	3456
	11th to 20th	Night	31% 4 8% 14% 28% 14%	3480
	21st to end	Night	43% 4 6% 18% 19% 9%	3817
April	1st to 10th	Night	34% 5% 9% 19% 25% 8%	2090
	11th to 20th	Night	33% 4 6% 23% 24% 10%	1827
	21st to end	Night	31% 5% 10% 27% 22% 5%	1620
May	1st to 10th	Night	34% 6% 15% 22% 20% 4	1620
	11th to 20th	Night	40% 8% 15% 20% 16% 1	1593
	21st to end	Night	38% 9% 12% 24% 15% 2	1745
June	1st to 10th	Night	39% 9% 19% 20% 11% 2	1620
	11th to 20th	Night	34% 8% 19% 24% 12% 2	1620
	21st to end	Night	36% 13% 17% 18% 12% 4	1620
July	1st to 10th	Night	43% 13% 21% 12% 9% 2	1575
	11th to 20th	Night	37% 12% 25% 17% 7% 2	1566
	21st to end	Night	36% 12% 23% 20% 7% 1	1672
August	1st to 10th	Night	42% 13% 19% 20% 6%	1600
	11th to 20th	Night	42% 10% 18% 17% 12% 1	1598
	21st to end	Night	43% 10% 19% 16% 9% 2	1988
September	1st to 10th	Night	36% 9% 17% 16% 18% 5%	1980
	11th to 20th	Night	40% 7% 13% 17% 20% 3	1980
	21st to end	Night	38% 5% 11% 19% 20% 6%	1980
October	1st to 10th	Night	33% 4 9% 19% 29% 6%	2006
	11th to 20th	Night	33% 4 9% 22% 24% 10%	2160
	21st to end	Night	30% 3 5% 20% 29% 13%	2376
November	1st to 10th	Night	32% 3 7% 19% 27% 12%	2249
	11th to 20th	Night	34% 4 5% 18% 27% 12%	2470
	21st to end	Night	37% 4 6% 20% 26% 8%	2470
December	1st to 10th	Night	43% 5% 6% 21% 19% 6%	2470
	11th to 20th	Night	36% 3 7% 17% 27% 10%	3044
	21st to end	Night	46% 4 7% 19% 20% 4	4532

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	20% 19% 40% 18% 3	270
	11th to 20th	Day	26% 20% 33% 18% 4	270
	21st to end	Day	22% 24% 38% 12% 3 1	297
February	1st to 10th	Day	19% 19% 42% 17% 2	270
	11th to 20th	Day	35% 16% 35% 13% 1	270
	21st to end	Day	31% 21% 37% 11% 1	225
March	1st to 10th	Day	23% 13% 31% 26% 7%	431
	11th to 20th	Day	18% 16% 41% 18% 6% 1	460
	21st to end	Day	21% 14% 36% 20% 8%	506
April	1st to 10th	Day	19% 17% 30% 23% 10% 2	457
	11th to 20th	Day	15% 12% 31% 25% 14% 2	412
	21st to end	Day	15% 10% 27% 26% 15% 5%	420
May	1st to 10th	Day	12% 11% 34% 24% 14% 6%	423
	11th to 20th	Day	17% 6% 17% 27% 24% 10%	447
	21st to end	Day	17% 4 15% 25% 25% 14%	485
June	1st to 10th	Day	12% 4 13% 31% 28% 11%	450
	11th to 20th	Day	8% 2 16% 29% 27% 18%	450
	21st to end	Day	10% 3 15% 33% 24% 15%	450
July	1st to 10th	Day	10% 2 9% 24% 31% 23%	445
	11th to 20th	Day	9% 2 7% 25% 38% 19%	444
	21st to end	Day	5% 1 8% 29% 38% 18%	488
August	1st to 10th	Day	15% 4 9% 26% 27% 19%	446
	11th to 20th	Day	14% 2 8% 26% 32% 17%	439
	21st to end	Day	15% 4 12% 23% 29% 18%	495
September	1st to 10th	Day	9% 2 8% 30% 34% 16%	450
	11th to 20th	Day	17% 2 10% 23% 32% 15%	450
	21st to end	Day	19% 4 16% 26% 26% 8%	450
October	1st to 10th	Day	17% 5% 22% 28% 16% 12%	450
	11th to 20th	Day	12% 7% 24% 30% 22% 6%	450
	21st to end	Day	15% 7% 26% 28% 20% 3	495
November	1st to 10th	Day	19% 9% 24% 27% 15% 5%	422
	11th to 20th	Day	19% 9% 40% 23% 8% 1	270
	21st to end	Day	13% 13% 35% 26% 10% 2	270
December	1st to 10th	Day	29% 14% 30% 22% 4	270
	11th to 20th	Day	24% 11% 34% 24% 6% 1	270
	21st to end	Day	29% 17% 29% 16% 6% 3	297
January	1st to 10th	Night	23% 17% 27% 27% 7%	760
	11th to 20th	Night	20% 15% 31% 27% 6%	760
	21st to end	Night	21% 15% 33% 27% 3	836
February	1st to 10th	Night	19% 13% 32% 31% 6%	760
	11th to 20th	Night	24% 13% 36% 24% 2	743
	21st to end	Night	21% 15% 33% 28% 3	628
March	1st to 10th	Night	19% 11% 32% 32% 6%	760
	11th to 20th	Night	16% 13% 34% 26% 9% 1	760
	21st to end	Night	17% 12% 35% 27% 10%	836
April	1st to 10th	Night	13% 16% 31% 30% 10%	760
	11th to 20th	Night	15% 12% 26% 31% 15% 1	666
	21st to end	Night	13% 6% 28% 33% 19% 1	540
May	1st to 10th	Night	11% 8% 26% 36% 19% 1	540
	11th to 20th	Night	14% 3 22% 35% 24% 3	531
	21st to end	Night	14% 2 11% 33% 35% 6%	584
June	1st to 10th	Night	14% 2 13% 34% 31% 6%	540
	11th to 20th	Night	9% 2 16% 28% 34% 11%	540
	21st to end	Night	10% 3 10% 34% 35% 8%	540
July	1st to 10th	Night	10% 3 7% 29% 40% 12%	525
	11th to 20th	Night	9% 2 6% 29% 44% 11%	522
	21st to end	Night	8% 2 7% 28% 46% 8%	591
August	1st to 10th	Night	13% 3 5% 28% 41% 10%	537
	11th to 20th	Night	14% 3 5% 29% 41% 8%	534
	21st to end	Night	12% 4 8% 25% 40% 11%	666
September	1st to 10th	Night	10% 3 8% 30% 40% 10%	720
	11th to 20th	Night	17% 2 9% 26% 40% 7%	720
	21st to end	Night	15% 3 16% 31% 31% 5%	720
October	1st to 10th	Night	14% 4 18% 29% 29% 6%	720
	11th to 20th	Night	14% 6% 22% 33% 20% 5%	720
	21st to end	Night	15% 8% 21% 32% 21% 3	792
November	1st to 10th	Night	15% 5% 23% 32% 21% 3	740
	11th to 20th	Night	18% 9% 28% 31% 13% 1	760
	21st to end	Night	17% 9% 25% 34% 14% 1	760
December	1st to 10th	Night	21% 13% 26% 32% 9% 1	760
	11th to 20th	Night	19% 11% 25% 33% 11% 1	760
	21st to end	Night	28% 12% 23% 30% 7%	836

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